Investigation of flame emission and absorption ... · Master of Science Thesis by Susan Lindecrantz...

Master of Science Thesis by Susan Lindecrantz Division of Combustion Physics Lund University

May 2010

Investigation of flame emission and absorption spectroscopy using the HITRAN/HITEMP database and simulations for concentration and temperature determination in combustion environments

2 Abstract

Susan Lindecrantz | LTH

© Lindecrantz, Susan

Investigation of flame emission and absorption spectroscopy using

the HITRAN/HITEMP database and simulations for concentration

and temperature determination in combustion environments.

Master of Science Thesis - May, 2010

Lund Report on Combustion Physics, LRCP-140

ISRN LUTFD2/TFC -- 140 -- SE

ISSN 1102-8718

Susan Lindecrantz

Division of Combustion Physics,

Department of Physics

Faculty of Engineering, LTH

Lund University

P.O. Box 118

S-221 00 Lund

Sweden

Master of Science Thesis 3

LTH | Susan Lindecrantz

Abstract

In this thesis the possibility of using the HITRAN/HITEMP database for

spectroscopic studies in combustion applications was investigated. The database was

used for radiative gas emission and absorption simulations. From the relation of the

radiative transfer for absorption (Beer-Lambert law) and emission, the spectra from

a methane/air premixed flame was measured and studied. A model for temperature

and species concentrations was suggested for combustion applications.

A Fourier Transform Infrared Spectrometer was used to record high resolution

spectra from specific height-positions around the visible flame zone, above a

premixed laminar burner. The recorded spectrum was used to study the flame

characteristics and compared with simulated emission spectra based on the

HITRAN/HITEMP database. The goal was to study the flame spectra and identify

its species and also to develop the simulation program.

The second application was to perform simulation just before combustion in a

spark assisted HCCI, i.e. homogeneous charge compression ignition, engine with a

spark-plug added in the combustion chamber. A simulation procedure was

formulated to be able to determine important parameters of the investigated gas

mixture, such as temperature and concentration. With this information the internal

exhaust gas recirculation (EGR) ratio just before combustion in the engine can be

determined with cycle-to-cycle resolution. For this investigation the concentration of

carbon dioxide was in focus to find the EGR with known temperature. An estimation

of the temperature would come from emission measurement on optically thick bands

originating from the in-cylinder gas just before combustion. An alternative method

to extract the temperature from two line absorption was investigated. With known

temperature the concentration can also be determined. A setup with an LED or a

diode laser was suggested for absorption measurements to find the concentration, in

which Beer-Lambert’s law is applied.

4 Content


Content

Abstract ............................................................................................................................ 3

Content ............................................................................................................................. 4

Chapter 1 – Introduction ................................................................................................ 6

1.1 Objectives .................................................................................................................. 6

1.2 Scope .......................................................................................................................... 7

1.3 Outline ....................................................................................................................... 7

Chapter 2 – Background and Motivation ..................................................................... 8

2.1 The study of light and matter interaction .............................................................. 8

2.1.1 Atomic and molecular spectra ................................................................................ 8

2.1.2 Broadening of spectral lines ................................................................................. 10

2.2 The equation of radiative transfer ........................................................................ 11

2.2.1 Absorption ............................................................................................................ 12

2.2.2 Emission ............................................................................................................... 13

2.3 Line-by-line gas radiation simulation ................................................................... 14

2.3.1 HITRAN/HITEMP database ................................................................................ 14

2.3.2 Applications of HITRAN database ...................................................................... 15

2.4 Briefly about combustion ....................................................................................... 18

2.5 Internal combustion engine ................................................................................... 19

Chapter 3 - Experimental equipment and considerations ........................................ 21

3.1 Measurements with FTIR Spectrometer on a flame ........................................... 21

3.1.1 Experimental setup ............................................................................................... 21

3.1.2 Burner .................................................................................................................. 21

3.1.3 Slit ........................................................................................................................ 23

3.1.4 Fourier Transform Infrared Spectrometer .......................................................... 23

3.2 Engine experiment proposal .................................................................................. 25

3.2.1 Experimental setup ............................................................................................... 25

3.2.2 Possible light sources ........................................................................................... 26

3.2.3 Filters ................................................................................................................... 27

3.2.4 Engine .................................................................................................................. 28

3.2.5 Detectors .............................................................................................................. 29

Chapter 4 - Measurement and Simulations ................................................................ 31

4.1 Introduction ............................................................................................................ 31

4.2 Investigation and modelling infrared spectra in a flat flame ............................. 31

4.2.1 Experiment setup ................................................................................................. 31

4.2.2 Construction and simulation of flame spectra ..................................................... 32

4.2.3 Discussion of the flame investigation and simulation ......................................... 35

4.3 Temperature and Concentration simulations in the combustion chamber ...... 43

4.3.1 Implementation and simulation of engine spectra ............................................... 43

4.3.2 Suggestion of experiment setup ........................................................................... 48

4.3.3 Discussion of the engine simulations .................................................................. 49



Chapter 5 – Conclusion and outlook ........................................................................... 60

5.1 Conclusion ............................................................................................................... 60

5.2 Outlook .................................................................................................................... 62

Acknowledgement ......................................................................................................... 64

Bibliography .................................................................................................................. 65

List of figures ................................................................................................................. 67

List of tables ................................................................................................................... 70

Appendix A: Code for flame investigation ................................................................. 71

A.1 CallProcessFTIRSpectra ........................................................................................ 71

A.2 CallOpticalDepthFunc ............................................................................................ 73

A.3 CallEmissionFunc .................................................................................................. 75

A.4 FlameEmissionSimulations .................................................................................... 78

Appendix B: Code for engine investigation ................................................................ 80

B.1 EngineOpticalDepthAndEmissionSimulations ...................................................... 80

B.2 EngineTemperatureSimulations ............................................................................. 82

B.3 EngineConcentrationSimulations ........................................................................... 85

B.4 CallTwoLineMethodAbsorptionTemperatureSimulation ...................................... 88

B.5 EngineConcentrationLEDSimulations ................................................................... 90

B.6 EngineConcentrationDiodeLaserSimulations ........................................................ 92

Appendix C: Comparison between measured and simulated spectra ..................... 94

C.1 Comparison for 3 mm below the flame zone ......................................................... 94

C.2 Comparison for 1 mm below the flame zone ......................................................... 94

C.3 Comparison at the flame zone ................................................................................ 95

C.4 Comparison for 1 mm above the flame zone ......................................................... 95

C.5 Comparison for 3 mm above the flame zone ......................................................... 96

Appendix D: Populärvetenskapling sammanfattning ............................................... 97

6 Chapter 1 – Introduction


Chapter 1 – Introduction

1.1 Objectives

In today’s society, combustion is a large part of the everyday life; more than

90% of the energy used in the world is related to combustion [1]. The combustion of

fossil fuels leads to environmental problems, e.g. air pollutants and global warming,

requires a better understanding of the processes taking place in combustion.

Combustion also plays a big role in many industrial devices like engines and requires

industries to think about efficiency and environmentally friendly combustion to be

able to compete on an international market [2]. Many different non-intrusive optical

techniques for spectroscopic diagnostics have been developed for measurements of

species concentrations and temperatures.

Within the field of flame spectroscopic studies the infrared regions are of high

interest because important fuels like methane and combustion products like CO2, CO

and H2O are detectable in the infrared region. Detection of species, within the

infrared region, for concentration measurements can give an opportunity to better

understand the processes in an engine or a flame.

In previous master’s projects [3] it has been stated that spectroscopic

diagnostic techniques, e.g. LIF (Laser-Induced Fluorescence) and Rayleigh

scattering, are mostly conduced in the ultraviolet and visible region, in which

molecules undergo electronic transitions and thus have broad and structure less

distribution. Therefore the UV and visible regions are not always optimal for

spectroscopic diagnostics since these species do not have accessible transitions in

those regions. In the field of engine measurements, these methods require not only

optical access for observation and also an additional opening for introduction of

excitation signal to the combustion chamber.

However, in the infrared regions it can appear with strong rotational or

vibrational transitions, forming bands and band-heads. The spectra from a flame or a

combustion chamber may be recorded with line-of-sight absorption or thermal

emission spectroscopy. The main difficulties with diagnostics in this region are line

overlapping and spectral interference [3].

Combustion based engines will remain indispensable for many years, despite

efforts in introducing new energy sources; and thus urgently need to be improved

with regard to fuel efficiency and pollutant emission. One promising approach to

reduce pollution emission is to dilute the air with recirculated gases from the

preceding ignition cycle, so called internal exhaust gas recirculation (EGR). But, in

order to control and optimize this complicated process, new high-speed diagnostic

techniques are needed to determine the amount of recirculated gas in the engine,

especially near the spark plug, during intake and compression cycle by monitoring

water vapor or carbon dioxide. If one can, with line-of-sight measurements determine

the concentration of the carbon dioxide just before the ignition; it can be used to

estimate the amount of internal EGR.



1.2 Scope

In this thesis the objective was to investigate the infrared radiation properties

from a flame or a gas flow theoretically with help of the HITRAN/HITEMP database

and compare with experimental measurements.

The main focus in this study was molecular species such as CO2, H2O, CO and

hydrocarbon fuels. The ambition was to be able to simulate or describe the detailed

spectroscopy of the infrared emission and absorption of hot gases mixtures. Based on

the simulations, valuable information likes temperature; species concentrations are to

be extracted from either emission or absorption spectroscopy.

A high resolution FTIR emission spectrum from laminar methane/air premixed

flame has been recorded, which will be used as a validation of the developed code for

hot gas emission simulation. A model for temperature and carbon dioxide

concentration measurement in an HCCI engine to obtain real time EGR ratio inform-

ation is going to be proposed.

1.3 Outline

The outline of the report is as follows: The following chapter contains a brief

review of the background theory applied in this work. A theory involving emission

and absorption is discussed as well as a brief description of combustion applications

such as premixed flames and the type of engine proposed for application of testing

the simulations. The concept of the HITRAN/HITEMP is described together with

line-to-line modelling used for simulations of the spectra. The following chapter

describes the experimental setup and its components used or suggested for the flame

and the engine part respectively. Thereafter, the creation and implementation of the

simulations is described, as are methods for the experiments. The result and the

objective of the project are presented together with the discussion, as well as

conclusions. In the appendix the written simulations programs and the spectra

obtained from the FTIR measurement and simulations are listed.

8 Chapter 2 – Background and Motivation


Chapter 2 – Background and Motivation

The main physical phenomenon encountered in this work is infrared emission

and absorption spectroscopy, arising from the theory of radiative transfer and its

associated relation to optical depth. In the following sections, this theory has been

discussed. Important subjects such as line broadening effects, molecular and atomic

transitions have also been touched upon briefly. Afterwards constructions of the

different experiments and simulations are presented.

2.1 The study of light and matter interaction

In short, spectroscopy is the study of light and matter interaction and is used

important and useful in many various fields, e.g., astrophysics, lasers and

combustions studies; in which the different transition processes between various

energy states of the molecules are the atoms are studied. The aim of this work was to

extract valuable information from the studied system, such as species concentration

and temperature. For this purpose, different theories and models are used together

with experimentally determined energy levels and transition probabilities, found in

databases; to obtain a better understanding of the behavior of the system investigated

[4].

2.1.1 Atomic and molecular spectra

Matter consists of atoms and molecules, and the vast theory of matter will not

be discussed in detail in this work, for more information it is recommended to read

reference [4]. Simply put an atom contains a cloud of negatively charged electrons

surrounding a dense, positively charged nucleus containing protons and neutrons.

The electrons are attached to the nucleus of the atom by electromagnetic forces. A

transition in an atom between two levels gives rise to a single spectralline with finite

width. A molecule is a little more complicated than an atom, and contains a group of

atoms, held together by strong chemical bonds. The molecules can both vibrate and

rotate around a center axis, which also generates other types of transitions than the

usual electronic transitions. These transitions are called vibration and rotational

transitions, and form the so called ‘molecular bands’, a series of equally spaced lines

forming a band structure [4]. The spectra from molecular band from diatomic

molecules can be written as Eq. (2.1) with m = 1, 2, 3… = J+1, represent trans-

missions from the R-branch and m = -1, -2. -3, …, = -J for the P-branch.

2'''''')()( mBBmBBhvE vvvv −+++=∆ (2.1)

The constants B’v and B

’’v are rotational constant for the higher and the lower

rotational state respectively. This stems from the selection rules for the allowed

molecular transmissions of diatomic molecules. For anharmonic oscillator, the

vibrational quantum number changes with ∆vi = ±1, and the rotational quantum

number J only changes with one unit or none, ∆J = ±1 and 0. If a more complicated

model than the harmonic oscillator is used, the selection rules allows the following

vibrational transmissions: ∆vi = ±2, ±3… where the ∆vi = ±1, is called the



fundamental and the ∆vi = ±2 is called the second harmonic and so on [5].

Combination or difference bands arise from anharmonic oscillators, when addition or

subtraction of two or more fundamental frequencies or overtones is allowed

respectively. Example of such bands are, vi+1+vi, 2vi+1+vi or vi+1-vi [6]. Sometimes

one can observe a so called ‘band head’ and it is at this point in which the branch

separation decreases to zero. This can be seen as an inversion of the branch. If B’v<

B’’

v then the band is shaded towards the red, for the other case the band is shaded

towards the violet [4].

Fig. 2.1 Illustrates the molecular energy structure, showing the electronic, vibrational and rotational

energy levels. The size of the energy difference between two electronic states is around a few eV,

two vibrational states a few 0.1 eV and two rotational states a few 0.001 eV.

Pure rotational lines are typically found in the microwave region, revibrational

lines in the infrared region, electronic transitions in the ultraviolet and visible range

of electromagnetic radiation. This division of the transitions comes from the

electronic and the molecular structures see Fig. 2.1 [7]. Light interactions between

two bound energy levels can occur through three possible radiative processes. The

atom or molecule can experience a spontaneous transition (also called emission)

given by the Einstein coefficient, A21, stating the probability of an atom to deexcite

back to a lower energy state. In the presence of an electromagnetic photon with the

appropriate wavenumber for a transition between two energy levels, the atom or

molecule can undergo an absorption transition. The third process takes place when

the atom is in its excited state and, in the presence of an electromagnetic photon, it

undergoes stimulated emission. Fig. 2.2 illustrates these three processes [8].

Fig. 2.2 Illustrating the three possible radiative processes for a two-level atom or molecule;

a) emission, b) absorption and c) stimulated emission.



For gases at very high temperatures, the absorption of a photon may cause a so

called bound-free transition, in which the electron may break loose from the molecule

or even break the whole molecules apart due to strong vibrations. This is also called

ionization. The same process, but reversed, may occur with emission. Ionization

results in a continuous radiation, usually found in the ultraviolet and visible region.

The electrons in ionized gas may also interact by collisions with the electric fields of

the ions locations in a free-free transition, causing Bremsstrahlung radiation and

giving rise to continuous spectra [5]. For combustion applications bound-bound

transitions only will only considered.

Other none-radiative transitions may also occur, such as quenching when the

molecule or atom is deexcited without release of photons or through collision

between atoms or molecules.

2.1.2 Broadening of spectral lines

The radiation propagating through a gas is transformed by the absorption and

emission processes mentioned in the previous section. Emission and absorption lines

may occur at the same frequencies but have different intensity distribution. This

radiation is characterized by a spectrum of spectral lines with a certain molecular or

atomic configuration.

Spectral lines have a finite width; they may be broadened by different

processes. One of these is natural broadening because the excited state has a finite

lifetime and will eventually relax to lower state by spontaneous emission. As

consequence of Heisenberg’s uncertainty principle, when the atom relaxes back to its

original state, the energy release is slightly different. This small difference generates

a photon distribution around the differences of the two theoretical energy states of the

two-level system, which has a finite width called the natural line width [9]. The line

profile given by such broadening effect is a Lorentzian function.

Another broadening effect is the Doppler broadening. It arises from the

different thermal movements of the emitting atoms or molecules, creating spread of

Doppler shifts in the direction of the observer. The line profile representing this

spread is given by the Gaussian line profile.

Pressure broadening, also referred to as collision broadening, is another type of

broadening, and arises from interaction between the emitting or absorbing atom and

molecules in the gas. The effects arise from different types of perturbations, such as

charged or neutral particles. These perturbations will not be discussed in detail here

[8]. Pressure broadening gives rise to a Lorentzian line profile.

Sometimes these broadening effects occur simultaneously and are in the same

order. In such cases the Gaussian and the Lorentzian broadening profiles are

convoluted, creating a new line profile called the Voigt profile. The wings of a Voigt

profile often represent the Lorentzian and the center the Gaussian profile [10]. Fig.

2.3 illustrates the different line profiles.



Fig. 2.3 Shows the three line profiles comparison with normalized intensity and the same width. [11].

2.2 The equation of radiative transfer

To relate the measured signal from a system with a variable of interest, such

as species concentration or temperature in a volume of gas, the equation of radiative

transfer may be used [10]. Fig. 2.4 shows an illustration of the optical system for

radiative transfer. A radiative emitter transmits in various or all angles depending on

the frequency of the light. One differs between irradiance Iv: [W/(cm2 cm

-1)] and

radiance Jv: [W/(cm2 sr cm

-1)][10].

Fig. 2.4 Illustration of the optical system for the radiative transfer.

The radiative transfer can be expressed in terms of the emission coefficient εv

and the absorption coefficient, kv, given by Eq. (2.2) [10]. The source function, Sv, is

defined as Eq. (2.3) and the total optical depth, τv, is defined as Eq. (2.4) with the

optical path length l.

vvvv Jzkz

dz

dJ)()( −= ε (2.2)



v

vv

kS

ε≡ (2.3)

∫=l

vv dzzkl0

')'()(τ (2.4)

With these definitions, the radiative transfer equation can be re-written into Eq.

(2.5). If scattering is considered, the radiative transfer equation becomes much more

complicated and can only be solved numerically [12]. Hence if the extinction is

described by absorption and scattering, the radiative equation looks something like

Eq. (2.6). Where a(v) is the single scattering albedo which is the ratio of scattering

coefficient to the total extinction coefficient. The general solution of the equation of

radiative transfer, with no scattering, is given by Eq. (2.7) [10].

vv

v

v SJd

dJ=+

τ (2.5)

[ ] ∫ ΩΩ+−+−=+ π

νννν ω

πν

νττ

4

)ˆ,'ˆ('4

)()()(1

)(Jpd

aTSaj

d

dJ

absorptionscattering

(2.6)

∫−− +=)(

)0(

)()()()()()0()(

l

v

l

v

ll

vv

v

v

vvv zdezSeeJlJ

τ

τ

τττ τ (2.7)

In a combustion system the investigated medium is not always homogeneous,

but a path-averaged result is obtained in line-of-sight measurements. By assuming

homogeneity, one can simplify the radiative transfer equation further. In such

scenario the optical depth Eq. (2.4) and source function Eq. (2.3) is no longer

dependent of the optical path length z. The Eq. (2.7) is then simplified to Eq. (2.8)

and represents the light registered as a function of path length, as a result of the

absorption and the emission in the investigated system [10].

[ ]lk

v

lk

vvvv eSeJlJ

−− −+= 1)0()( (2.8)

The first term represents the absorption and the second term represents the

emission. As the photon reaches the gas cloud it may interact with the molecules and

atom by either being absorbed, emitted or scattered, however scattering of photons by

molecules is negligible for heat of transfer applications [5].

2.2.1 Absorption

In the case of a gas which is not emitting very strongly, the emissivity and

source functions can be approximated to zero. The solution to the equation of

radiative transfer, Eq. (2.8), then becomes the Beer-Lambert law, see Eq. (2.9). This

law describes the absorption of the radiation as a function of the distance through the

absorbers [10].



lk

vvveJlJ

−= )0()( (2.9)

Here Jv(l ) describes the intensity transmitted and Jv(0) is the intensity before it

enters the absorbing medium. This equation can be used to obtain a linear relation

between the absorption intensity and the concentration. According to reference [13],

there might be some deviation from this linearity; for example, if there is scattering

of light due to particles, fluorescence or phosphorescence in the sample.

2.2.2 Emission

In the case of a very strong emitting gas, with no external light source,

J(0) = 0, and neglecting line-of-sight absorption, then Eq. (2.7) can be simplified to

only describe the emission. The emission is given by Eq. (2.10). This relation is not

dependent on the optical depth.

[ ]lk

vvveBlJ

−−= 1)( (2.10)

If the gas is optically thin, then τv(l) << 1 and a linear relation can exists

between the intensity and the number density of the emitting molecules or atoms. As

optical depth increases, the emission departs from linearity, and reaches a limiting

value when the emission equals the source function, i.e., when the emission starts to

acts as a blackbody. The gas is in this optically thick stage when τv(l) > 1. One can

then describe the emission by Eq. (2.11) where the radiation constants c1 is 1.191·e-12

[W cm2 sr

-1] and c2 is 1.438 [K cm] [10]. Equation (2.11) describes a true blackbody,

scaled with the emissivity. By assuming local thermal equilibrium (LTE), the

emission and absorption coefficient are functions of temperature and density only,

and the source function Sv is equal to the Planck function Bv due to the Kirchhoff law.

Then the source function in Eq. (2.3) becomes the blackbody. A black body is an

object that absorbs all electromagnetic radiation that it is in contact with and emits a

blackbody radiation in return and is only temperature dependent. For an object that is

not an ideal blackbody one mention the objects emissivity. The emissivity describes

an object’s ability to emit radiation. A true blackbody has emissivity equal to unity,

ε = 1, while a real object has emissivity less than one, ε < 1. It should be mentioned

that the gas will never act as a true blackbody radiator, not even the Sun is a true

blackbody.

[ ]1

11

/

3

1

/

3

1

22 −⋅−=

−⋅=⋅= −

−− Tvc

lk

Tvcvve

vce

e

vcBJ vεε (2.11)

Hence, if one has a blackbody emitter, the emission is only dependent on the

temperature of the gas and the light frequency. Otherwise, it is also dependent upon

the absorption coefficient and the optical path length. The emissivity is given by Eq.

(2.12) where the transmittance arises from the Beer-Lambert’s law.

( )lkJ

lJv

v

v −−=−= exp1)0(

)(1ε (2.12)

When considering measurements practical one has to consider the spectral

response of the measurement setup (includes the response from the lenses, the



window of the engine allowing in-situ measurements, the filter and other objects used

in the measurement setup).

2.3 Line-by-line gas radiation simulation

To be able to predict the thermal emission and absorption spectra a line-by-line

program was created in MATLAB based upon the HITRAN database. In the

following chapters the HITRAN and HITEMP database and its applications are

described. Afterwards the line-by-line models are used for the simulations in the

presented methods.

2.3.1 HITRAN/HITEMP database

HITRAN stands for high-resolution transmission molecular absorption

database. It is a compilation of spectroscopic parameters to be used to predict and

simulate the transmission and emission of light from a gas column. The database

stems from a long-running project started by the Air Force Cambridge Research

Laboratories in the late 1960's in response to the need for detailed knowledge of the

infrared properties of the atmosphere. In addition to HITRAN, which only covers the

line transitions accurately at temperature range below 1000K, there is another similar

database named HITEMP (high-temperature spectroscopic absorption parameters)

that covers temperatures in the range above 1000K. Both databases are being

constantly developed at the Atomic and Molecular Physics Division at Harvard-

Smithsonian Center for Astrophysics under the direction of Dr. Laurence S.

Rothman. The HITRAN database is recognized by many researches and used in

many different applications such as transmission simulations, fundamental laboratory

spectroscopy studies and combustion physics [14].

The latest edition, 2008 v13.0, of the HITRAN molecular spectroscopic

database is available on the website for the Smithsonian Astrophysical Observatory

in Cambridge, USA. The database contains line-by-line parameters which can be

compiled in the written software named JavaHAWKS which then can be processed in

MATLAB. The latest edition of the HITEMP database was in 1995; however,

according to Dr. Rothman a new version, will come out soon in the same format as

the current HITRAN [15]. Since flame’s temperatures often are above 1000K,

HITEMP can be useful in the research field of combustion physics, but the current

version of HITEMP is missing valuable data, such as the statistical weights and

Einstein coefficient. In addition HITEMP is only available for certain molecules like

CO2, CO and H2O.

It should also be noted that the newer version of the HITRAN is not completely

functional with JavaHAWKS, which was built for the 2004 version of HITRAN. This

is probably because the new HITRAN not only includes more precision for line-to-

line transitions, but also, additional isotopes of some species, which makes the

current software freeze for these isotopes when processing the new data. It is possible

to create one’s own JavaHAWKS version to work with the 2009 version, but that is

beyond this project. For this reason, the 2004 version of HITRAN and, whenever

possible, the 2009 version of HITRAN were used in the simulations.

The spectroscopic constants in the HITRAN databases are from different

sources and all have their own uncertainties stated in the database by different codes,



see Table 1. The uncertainties are wavelength positions, half-widths and line intensity

strengths. These uncertainties have not been utilized in this report but should be

considered for further investigations.

Table 1 Illustrates the uncertainties of the HITRAN database. [15]

The 2004 edition of HITRAN contains line data for 39 molecules [14],

including their isotopes and the 2008 edition of HITRAN contains line data for 42

molecules [16]. Although primarily intended for atmospheric studies, important

combustion species are also included such as H2O, CO2, NO, NO2, OH and fuels

such as CH4 and C2H2.

2.3.2 Applications of HITRAN database

The following section will describe the different parameters and how HITRAN

is used for the line-to-line modelling [17]. The database contains the line strength,

S(T), which can be calculated from Eq. (2.13). The line strength values at

temperatures T can be corrected from the line strengths at the reference temperature,

296K, by using the relationship in Eq. (2.14).

( ) )/exp()/exp(1)(3

8),( 12

2

reflowerref

refref

ref kTEkThcvTTQ

P

hck

vvTS −−−ℜ=

π (2.13)

−−

−−

−

−=

)exp(1

)exp(1

)exp(

)exp(

)(

)(),(),(

2

2

2

2

refref

lower

lower

refref

ref

T

vc

T

vc

T

EcT

Ec

TQ

TQ

T

TvTSvTS (2.14)

S(Tref) is the spectral line intensity or line strength at reference temperature

[cm-1

/molecules cm-2

], c2 is the second radiant constant, v is the transition

wavenumber [cm-1

], Elower is the lower state energy [cm-1

], T is the temperature [K]

of the gas, Tref is the reference temperature at 296K, k is the Boltzmann’s constant, h

is the Planck constant, P is the pressure of the gas volume and Q(T) is the total

Line position and air pressure-

induced line shift (cm-1)

Intensity, half-width (air- and self-)

and temperature-dependence

Code

Uncertainty range

Code

Uncertainty range

0

> 1.0 or unreported

0

Unreported or unavailable

1 > 0.1 and < 1.0 1 Default or constant

2 > 0.01 and < 0.1 2 Average or estimate

3 > 0.001 and < 0.01 3 > 20%

4 > 0.0001 and < 0.001 4 > 10% and < 20%

5 > 0.00001 and < 0.0001 5 > 5% and < 10%

6 < 0.00001 6 > 2% and < 5%

7 > 1% and < 2%

8 > 1%



internal partition sum given by the parasum.dat from HITRAN’s homepage. The line

strengths are tabulated in HITRAN with the unit [cm-1

/molecules cm-2

] and can be

converted into [cm-2

/atm] in Eq. (2.15) at reference point. The Eq. (2.14) may then be

used to correct the line strength for the temperature.

TcmmoleculescmSatmcmS

296102.68676)/()/( 19212 ⋅⋅⋅= −−− (2.15)

The value 2.68676 1019

[molecules/cm3 atm] is the Loschmidt number at STP

(standard conditions for temperature and pressure). The following procedure was

used for the conversion; all line strengths at reference point 296K where converted

and then this value was temperature corrected using (2.14). Pressure shift of the

transition wavenumber may occur, and is corrected by (2.16).

ppvv refcorr )(δ+= (2.16)

Where the δ(pref) is the air-broadened pressure shift [cm-1

/atm] and is given in

the HITRAN database. The HITRAN/HITEMP database provides air-broadening and

self-broadening half-widths for all lines listed in the database at the reference

temperature of 296K. The total coalitional broadening half width at half maximum

(HWHM) can be corrected for a given temperature and pressure with help of Eq.

(2.17).

srefrefselfsrefrefair

n

ref

L pTpppTpT

TTp ),())(,(),( γγγ +−

= (2.17)

The p is the total pressure of the gas [atm], temperature T [K] and partial

pressure ps [atm] of the gas. In this equation γair [cm-1

/atm] is the air-broadened

halfwidth at half maximum at Tref =296 K and pref at 1 atm, γself [cm-1

/atm] is the self-

broadened halfwidth at half maximum and n is the coefficient of temperature

dependence of the air-broadened halfwidth. In the engine cylinder there exists

elevated pressure changes during the combustion cycle and thereby should give rise

to collision-broadened spectral lines. This broadening is represented by the

Lorentzian (2.18).

22 )(

1

corrL

L

Lvv

f−+

=γ

γπ

(2.18)

In the engine’s cylinder the temperature is also elevated with every combustion

cycle giving cause for Doppler broadening, see in Eq. (2.19). This broadening is

represented by the Gaussian lineshape with a Doppler HWHM given by (2.20) with

molecular weight, M [a.m.u] at temperature, T.

−−=

2

2))(2ln(exp

2ln

D

o

D

D

vvf

γγπ (2.19)

MTvD /10581.3 0

7−×=γ (2.20)



The Lorentz and Gaussian lineshapes can be combined in the Voigt line shape.

The Voigt profile is given by the following equations (2.21) [18].

∫∞

∞− −+

−==

=

dttxy

tyyxKA

yxAKf

D

v

22

2

)(

)exp(),(;

2ln1

);,(

ππγ

2ln;2ln)( 0

D

L

D

yvv

xγγ

γ=

−= (2.21)

Where γD and γL is the Doppler and pressure broadening half-widths at half-

maximum, v0 the transition wavenumber. The transmitted intensity, It, through a gas

can be related to the incident intensity at a certain wavenumber, Io, by Beer’s Law as

stated from the radiative transfer for the case of pure absorption. This can be

simulated using the HITRAN database where the Beer’s law is given by Eq. (2.9)

where the optical depth is given by,

LfvTSPxLk vvspeciesvv 0),( −==τ (2.22)

Here the kv [cm-1

] is the spectral absorption coefficient, L is the optical path

length of the absorbing medium, xspecies is the mole fraction of the absorbing species,

P is the total pressure of the gas mixture, S(T,v) is the line strength [cm-2

/ atm] at the

temperature T [K] and fv-v0 [cm] is the normalized lineshape function. Table 2 lists the

spectroscopic parameters and its units listed in the HITRAN database.

Table 2 Contains the spectroscopic parameters and units used in HITRAN 2004

and 2008 [16,15].



2.4 Briefly about combustion

Combustion is a chemical processes between fuel and its oxidant which results

in heat and the conversion of chemical species. The release of heat in the conversions

results in what we know as a flame. Combustion takes place in a Bunsen burner and

in a spark-ignition engine. What characterize a flame is its high heat release reaching

over 2000K in combustion and the creation of soot particles [19].

There are two types of flames, the premixed flame and the diffusion flame. In

the premixed flame the fuel and the oxidant are mixed before combustion occurs. In

the diffusion flame the oxidant and the fuel are separated and do not mix until the

moment of the combustion. In fundamental research a flame without turbulence is

often required, the laminar flame. A premixed flame can be divided into the follow-

ing zones; unburned gas zone, preheat zone, reaction zone, and product zone. This is

illustrated in Fig. 2.5.

Fig. 2.5 Displaying the different zones in one dimensional premixed adiabatic flame along with the

concentrations and temperature profiles of the flame [20].

For a premixed flame in the preheated zone, the gas mixture is heated by heat

conduction from the reaction zone and only a small amount of heat is released by

chemical reactions. The separation of the preheat zone and the reaction zone is often

defined as the position at which there is an inflexion point in the temperature profile,

or the location of creation of intermediates. In the reaction zone there is a fast release

of energy which leads to a very steep temperature gradient. A visible flame front lies

within this reaction zone and it is therefore a good distinction of where the reaction

zone is located in a premixed laminar burner. It is in this region most reactions take

place. The location of the visible flame front depends on the pressure, flux speed and

composition of the mixture. Directly after the flame front, the products zone emerges

in which most reactions have already occurred and the products of the combustion

exist [20]. It is difficult to draw a distinct line between preheat and reaction zones but

it can be thought of as the point at which exothermic reactions become significant

and where the temperature profile is the steepest [21].



For these projects, two different types of flames are considered, a lean and a

rich flame. The equivalence ratio, defined as Eq. (2.23), describes the flames

composition.

λ

ϕ1

_/#_#

_/#_#

_

_ ==mixturetricstoichiome

mixturereal

oxygenmolesfuelmoles

oxygenmolesfuelmoles (2.23)

Stoichiometric mixture represents an ideal combustion in which the fuel is

completely burned. Lean flames have excess of oxygen and their equivalence ratio is

less than one, φ < 1, while rich flames do not have enough oxygen to allow complete

combustion. Its equivalence ratio is greater than one, φ > 1. Another term often used

is the air-fuel-ratio, λ, and is defined as the inverse of the equivalence ratio. In this

project both lean and rich flame’s spectra are to be studied. Reaction formulas for

combustion of any fuel can be rather complicated since many subreactants may occur

before it reaches the stable end product. It is for this reason that reaction formulas are

not described in detail.

The global reaction of combustion of isooctane is shown as Eq. (2.24) [22].

Based upon this relation the reaction formula for methane and air is described as

(2.25).

222222188 16.47)1(5.1298)773.3(5.12 NOOHCONOHC +−++⇒++ λλ (2.24)

2222224 16.47)1(5.1221)773.3(5.12 NOOHCONOCH +−++⇒++ λλ (2.25)

λ is a measure of the mass ratio of air and fuel during the fresh charged inducted

through the intake [22].

2.5 Internal combustion engine

There are two main types of internal combustion engines commonly used, the spark

ignition (SI) and the compression ignition (IC) engine. For the spark ignition engine

the fuel is ignited by a spark and the timing of the combustion can easily be

controlled. In the compression ignition engine, the temperature and pressure rise

during compression to the point that it will induce an ignition of the fuel [23]. In this

project an engine with combination of the two was considered for the engine

simulation. This engine is called an HCCI (Homogeneous Charge Compression

Ignition) engine, which includes a spark plug to be able to control the ignition timing.

An HCCI engine is in general based on the four-stroke Otto cycle. The cycle

contains four reciprocating motions [24]. The first step is called the intake stroke,

where the piston moves down and air and fuel are pulled into the combustion

chamber. It is followed by the compression stroke, where the piston moves up and

the air and fuel is mixed and compressed. The next step is called the power stroke

and the fuel/air mixture is ignited and the piston is forced down. The cycle ends with

an exhaust stroke where the piston moves back up and get rid of the exhaust gases,

making way for a new intake stroke. See Fig. 2.6 for illustration of the process.



Fig. 2.6 Illustrating the four stroke engine cycle presented in

Internal EGR (Exhaust Gas Recirculation) is when residual gas from the

previous cycle is trapped and mixed with fresh inducted charge. For an HCCI engine,

the mixing of the fresh charge and the reinducted products during the induction step

for lean or Stoichiometric

introducing the EGR [22].

2188

2188

)(5.12

773.3(5.12

OHC

NOHC

−−+

++

λααλ

λ

α = Negr / Nfresh is the ratio of the moles of

moles of the inducted fresh charge. Thus the

considered can be obtained from the following relationships [22],

60

188

188 +==

αλχ

total

CC

CCN

N

460

2

2 +==

αλχ

total

OH

OHN

N

Background and Motivation

Illustrating the four stroke engine cycle presented in the text [25].




toichiometric, isooctane can be rewritten from Eq. (2.24) to (2.26)

[22].

2222

22222

)1(16.4798

16.47)1(5.1298)

NOHCO

NOOHCON

++++

⇒+−+++

αλαα

λα

is the ratio of the moles of reinducted product Negr

fresh charge. Thus the mole fractions with the internal EGR

considered can be obtained from the following relationships [22],

1605.4

1

+++ λα

1605.4

9

++ λαα




Eq. (2.24) to (2.26) when

⇒ (2.26)

and Nfresh is the

s with the internal EGR

(2.27)

(2.28)



Chapter 3 - Experimental equipment and considerations

This chapter describes the experimental setup behind the two different types of

investigations that were made for simulations in emission and absorption

spectroscopy. The first part involved a high resolution investigation of the spectra

properties of a laminar flame. The second part involved the usage of absorption and

emission simulations. In the following sections the setup of such possible

experiments is discussed.

3.1 Measurements with FTIR Spectrometer on a flame

In order to study the relationship between the emission and the concentrations

of a gas an experiment was arranged in which the emission of a premixed laminar

burner was captured and measured with a Fourier Transform Infrared Spectrometer

(FTIR Spectrometer). The data collected during these measurements is then used to

create simulation programs and to study the relation between concentration,

absorption and emission. Each spectral line is identified with help of the HITRAN or

HITEMP database.

3.1.1 Experimental setup

The experimental setup for this experiment is shown in Fig. 3.1; each part is

discussed in detail in the following chapters. He-Ne laser is used for alignment

between the burner, the slit and the aperture before the measurement. It was turned

off when the spectrometer recorded the flame emission.

Fig. 3.1 The experimental setup of the Fourier Transform Infrared Spectroscopy for the

flame measurement.

3.1.2 Burner

For the experiment, a premixed laminar burner was used to create lean and rich

premixed flame from the mix of the gases methane, nitrogen and oxygen. The

22 Chapter 3 - Experimental equipment and considerations


respective flow velocities of the components are listed in table 3. The premixed

laminar burner is assumed to have a flat flame, meaning that the concentration of the

molecular and atoms occupying the area of the burners opening are relative uniform

at a particular height.

Table 3 The gas mixture of the flame with their respective gas flows in liter per min.

Fuel of the flame

[Liter per min]

Rich flame

[φ = 1.6]

Lean flame

[φ = 0.8]

Methane 3,115 1,558

Oxygen 3,896 3,896

Nitrogen 15,440 20,000

Co-flow 10,500 10,500

From the center of the burner, premixed gases of methane, oxygen and nitrogen

flow out and combustion takes place when the gas reaches the reaction zone. Around

the center a flow of nitrogen emerges. This co-flow protects the flame from any

disturbances like wind and combustion of surrounding air.

Fig. 3.2 The premixed laminar burner with a flame stabilizer on top and a tube ventilation system which

carries most of the burned gases outdoors. The red spot is the laser beam used for alignment into the

spectrometer.

Fig. 3.2 shows the premixed laminar burner used in the setup together with a

stabilizer which can prevent turbulence arises in the flame. A tube which leads

outside is placed on top of the flame so its exhaust fumes will not accumulate and

cause danger to the lab participants. The height of the burner was aligned with help

of a laser beam to place the burner at a height that the light emerging from the

measurement position of the flame comes through to the aperture of the instrument.

The burner was placed on an adjustable mounting, so it could move in the vertical

direction to the different measurements positions. A ruler was used to determine the

different heights from the flame zone. The burner was placed at twice the focal

length of the first mirror, 2f = 50 cm, which leads the light into the second mirror and

focusing it into spectrometers aperture. The diameter of the burner was 70 mm,



which is assumed to be the optical path length of the gas investigated with no

scattering effects taking into account.

3.1.3 Slit

A slit was used to block most of the thermal light from the stabilizer and

surrounding metal surface near the flame and to block light from other regions of the

flame. A rectangle was cut away from a piece of metal, see Fig. 3.3. Five locations in

the flame were measured, one in the reaction zone, two locations below and two

locations above the reactions zone. A laser beam was used to align the measurement

location and the slit at the new height, enabling the spectrometer to collect the light

from the set flame height. In order to align the burner to the wanted positions the

burner was moved in correlation with the slit and the rest of the setup. The slit was

placed 5 cm from the burner and has a minimum of 2 mm aperture.

Fig. 3.3 Image showing the

design of the slit used in the

FTIR Spectrometer experiment

with an minimum aperture of

2 mm.

3.1.4 Fourier Transform Infrared Spectrometer

A spectrometer split the light into the different wavelengths components it

contains and the light intensity (number of photons) is measured as a function of the

wavelength. In the experiment, FTIR Spectrometer was used so the flames spectral

distribution in the infrared region could be recorded with a high resolution of 0.05

cm-1

. This data was later used to evaluate the emission simulation. The FTIR

Spectrometer is a Michelson interferometer with a movable mirror, see Fig. 3.4.

Light merging from the entrance aperture is split into two beams by a beam splitter;

one beam is reflected onto a fixed mirror and the other beam onto a moving mirror

which introduces a time delay in one of the beams [8].

Fig. 3.4 The figure shows principle of the Michelson interferometer.



The detector registers the combined signal from the fixed and movable mirror

as a function of the path differences between the two beams, which is called an

interferogram; this is the Fourier transform of the spectrum. The spectrum can then

be obtained by taking the inverse Fourier transform of the signal [8]. For this

experiment the spectra is recorded with the FTIR Spectrometer of model type IFS

125 HR by Bruker Optics, see Fig. 3.5.

Fig. 3.5 The figure shows the Fourier Transform Infrared Spectrometer used in the space experiment

from the Atomic Astrophysics department in Lund University.

A program called OPUS was used to process the recorded signal and Fourier

transform the interferogram into a spectrum. Fig. 3.6 displays the interior layout of

the spectrometer in which one can recognize the Michelson interferometer from Fig.

3.4. The detector used inside the spectrometer is made of InSb and the beam splitters

of CaF2.

Fig. 3.6 The figure shows layout of the spectrometer used in the experiment.



Two external mirrors outside the spectrometer opening are used to direct the

light source into the aperture of the spectrometer, so the signal can be processed and

recorded. Since light with different wavenumber responds differently to the optical

components within the spectrometer one has to consider the spectrometer’s response

function when analyzing the spectrum. For this experiment the aperture to the

spectrometer was set to 1.5 mm. For the blackbody measurement the opening was set

to 0.5 mm since a bigger aperture proved to give a saturated spectrum. For each

measurement, 20 a scans were made, to obtain an average value of the intensity.

3.2 Engine experiment proposal

Without a spectrometer, the integrated emission intensity can be collected with

an ordinary detector. This intensity can then be compared with the simulations of the

integrated intensity dependent on either the concentration or temperature. The

spreading of the spectral lines according to their line profile often results in overlaps

between the multiple lines. The same goes if an overlap exists between spectral lines

of different species located at the same wavenumbers. With no spectrometer, the

spectral lines cannot be resolved for emission spectroscopy. In absorption

spectroscopy a light source is used to determine the transmission from the

experiment. If the light source is monochromatic and tunable, the transmission as a

function of wavelength can be obtained.

3.2.1 Experimental setup

The suggested experimental setup for this experiment is shown in Fig. 3.7,

each part is discussed in detail in the following chapters; Fig. 3.7a) and 3.7b) consists

of a setup for the absorption measurements using a diode laser and LED respectively.

Fig. 3.7c) consists of a setup for thermal emission measurements.

a) b)



Fig. 3.7 A simple illustration of the three possible measurements setup with the engine.

Image a) represents the absorption measurement using diode laser and b) using an LED with the same

setup. Image c) represents the thermal emission measurement.

3.2.2 Possible light sources

The engine part of this report deals with two different tasks, one part is to

estimate the temperature and the second part is then to determine the concentration.

The information about the temperature can be extracted with help of the radiative

transfer relation applied for two optical thick bands. The bands investigated for this

purpose are the CO2 band around 2250-2450 cm-1

and the CO2 band around 3450-

3915 cm-1

. The band at 3450-3915 cm-1

also included water lines which have been

accounted for in the simulations.

Two detectors are placed in front of each filter and a collimator, to focus the

thermal light into the detector and register only the spectral region which is

transmitted through the filter. The task is to determine the concentration of CO2 with

help of absorption or emission. The band investigated for this purpose is the CO2

band around 4840-4925 cm-1

. These regions have been chosen with respect to

available filters.

Measurement of the transmission gives the concentration of the investigated

species with help of Beer’s law. For this purpose the choice of the light source and

wavelength of the investigated region is important. The absorption must take place at

the wavelength in which transitions exist; otherwise there will be no absorption.

One of the light sources for the absorption measurement considered in this

thesis is a light emitting diode (LED). The main function of any diode is to direct

current in one direction. A diode is essentially a semiconductor and contains an

anode and cathode. When an electron moves from the n-type side to the p-type side,

the energy difference of these two levels is the energy that is emitted in form of a

photon with a certain frequency. By using different atoms to dope the material in the

semiconductor, different energy level differences can be obtained and thus different

colors of the LED can be generated [26].

In these simulations the LED chosen is called LED20, which is designed for

emitting at a spectral range around 2050 nm. From the HITRAN database it has been

verified that within this region there exists an optically thin band of CO2, clear from

water lines, especially at low temperatures. The LED emits a broadband light, see

Fig. 3.8. The LED is said to have stable output power and lifetime over 10000 hours

[27].

c)



Fig. 3.8 The figure shows the typical line profile at different temperatures for the LED investigated. [27].

Another light source that can be considered is the diode laser, emitting

monochromatic light. For this experiment a mid IR-laser tunable diode was

considered. According to ‘Roithner Laser Technique’, one of many diode laser

providers, custom wavelengths from 1.8-2.6 µm are available on request [28].

3.2.3 Filters

A narrow band pass filter is placed in front of the detector in order to only

register intensities from the spectral region within the band regions of interest. A

filter was chosen for each band region under investigation. An ideal filter includes no

absorption from CO2 and H2O in the surrounding air during the measurement of

desired wavenumbers. This is however difficult to achieve, for example, the

fundamental band of CO2 showed apparent absorption lines from the air (see chapter

5.1). The selection was based on the possibility of measuring CO2 at best without

H2O interference and the locations of the CO2 bands and availability from the

manufacture. At the location of the main fundamental band a filter called NB-4235-

082 was chosen. This filter has a center wavelength (CWL) of 2361 cm-1

and a half

width at half maximum (HWHM) of 46.7 cm-1

, see Fig. 3.9 c), and the peak

transmission is 90.22%. For the first combination band of CO2 a filter called

NB-2690-050 was chosen. This filter has a center wavelength of 3691.8 cm-1

and a

HFHM of 69.1 cm-1

, sees in Fig. 3.9 a) and the peak transmission is 89.99%. For the

second combination band of CO2 a filter called NB-2050-012 was chosen. This filter

has a center wavelength of 4881.8 cm-1

and HFHM of 27.1 cm-1

, see Fig. 3.9 b) and

the peak transmission is 79.86%.



Fig. 3.9 The figure illustrates the three filters transmittance profile. Figure a) displays an transmitt-

ance curve around 3600-3800 cm-1

, b) an transmittance curve around 4840-4949 cm-1

and c) an

transmittance curve around 2300-2450 cm-1

.

3.2.4 Engine

The engine intended for this project was based on a Volvo D5 diesel engine

operating on one cylinder, see Fig. 3.10. The engine has been modified to operate

with SACI combustion, an HCCI engine with a spark plug. The fuel considered for

these simulations is isooctane. The combustion chamber of the engine contains two

sapphire windows on opposite sides, enabling line-of-sight access through the engine

chamber, near the spark plug. With this engine it is possible to measure cycle to cycle

variations of the intensity. In the measurements, the hot spark plug might be a source

of interference since it is in the field of view. To avoid the spark plug acting as a

main emitter it can be physically blocked from view in the line-of-sight measurement

and thus minimize its interference with the surrounding gas in the chamber. This is a

rather big engine, and when using a fiber to collect the intensity to the detector, the

problems arising such as the fiber falling off due to the engine turbulence when

running should be negligible. For the simulations, the engine is expected to be

running on a lean fuel mixture, air-fuel-ratio between 1.2 and 1.6 with no EGR

accounted for. The changes of the λ due to the internal EGR are stated according to

Eq. (2.26). Two optical windows at opposite sides are required for the concentration

measurement.

4840 4860 4880 4900 4920 49400

20

40

60

80

100Transmission curve for filter NB-2050-012

Wavenumber [ cm-1 ]

Transmission [ %

]

3400 3500 3600 3700 3800 3900 40000

10

20

30

40

50

60

70

80

90


Wavenumber [ cm-1 ]

Transmission [ %

]

2250 2300 2350 2400 2450 25000

20

40

60

80


Wavenumber [ cm-1 ]

Transmission [ %

]

a) b)

c)

Fig. 3.10 The figure illustrates the engine considered for this

between a collimator and the engine

been placed in front of the detector to only detect light at a certain wavelength band.

3.2.5 Detectors

Fig. 3.11 shows the different types of materials for

According to [29] certain criteria need

must be registering at the wavenumber of interest, sensitive enough to register the

signal and fulfilling other

Fig. 3.11 The figure shows the sensitivities of the different types of detector materials in function of

the wave length [30].

A detector consisting of

since it has a high sensitivit

Master of Science Thesis

LTH |

The figure illustrates the engine considered for this project. A paper tube has been

een a collimator and the engine opening to minimize light interference from the room. A filter has


Fig. 3.11 shows the different types of materials for the photodiode detector.

g to [29] certain criteria need to be considered when choosing a detector; it


signal and fulfilling other requirements such as pricing and availability.

The figure shows the sensitivities of the different types of detector materials in function of

A detector consisting of Indium antimonite (Insb) is suggested for the purpose

since it has a high sensitivity of the range of interest and is available. For the thermal


| Susan Lindecrantz

project. A paper tube has been placed

opening to minimize light interference from the room. A filter has


the photodiode detector.

to be considered when choosing a detector; it


availability.

The figure shows the sensitivities of the different types of detector materials in function of

is suggested for the purpose

y of the range of interest and is available. For the thermal

30


emission measurement two detectors are needed, where the line-of-slight intensity

splits onto two detectors by a beamsplitter. Each detector is equipped with a

collimator that transmits IR light and focuses the light onto the detector. For the line-

of-sight measurement of the intensity, two filters are placed in front of the detector.

For the second part, the signal from an LED and diode laser is registered with a

detector before and after the light is sent through the chamber.



Chapter 4 - Measurement and Simulations

4.1 Introduction

In this chapter the code for emission simulations in MATLAB (MATrix

LABoratory) was created and compared with measurements [31]. The data required

for the calculation of the ‘synthetic’ spectra such as line positions, line strength

intensities and line broadening coefficients, can be taken from the spectral database

HITRAN or HITEMP depending on the temperature ranges used. The setup of such

an experiment is discussed, as well as the construction and implementation of the

simulation programs.

The first application is the emission of a flame from a porous-plug burner. The

light is collected into an Infrared Fourier Transform Spectrometer at Lund

Observatory, and its spectrum is recorded at different locations around the visible

flame zone located in the reaction zone. This spectrum is compared with the

simulated emission using the database.

The second application will use the simulation of the emission or absorption to

extract the temperature and, if possible, the CO2 concentration just before the fuel in

the engine is ignited. The ultimate goal is to find a method to determine how much

CO2 is recycled within the engine per ignition cycle. Comparisons between the

measured and calculated spectra can be made when possible.

4.2 Investigation and modelling infrared spectra in a flat

flame

In order to study the spectra from a flame and the relationship between the

emission, the concentration and the temperature of a gas, an experiment was

arranged. The emission of a premixed laminar burner was recorded with an FTIR

Spectrometer.

4.2.1 Experiment setup

After arranging the setup as described in the previous chapter, five height

positions above the burner were measured, see Fig. 4.1. Their positions were located

in the visible flame zone, above and below, 1 mm and 3 mm from the visible flame

zone respectively. The premixed flame is assumed to have a temperature between

300K and 2000K based on the chemistry modelling. These five measurements are

repeated for a lean flame with φ = 0.8 and for a rich flame with φ = 1.6. One

measurement was also done for a blackbody radiator at the temperature of 1473.15K

chosen arbitrarily.

32 Chapter 4 - Measurement and Simulations


Fig. 4.1 Shows the setup for the flame measurement.

The aperture of the instrument was set to 1.5 mm for the two different flame

types and 0.5 mm for the measurement of the blackbody due to saturation of the

signal. In each measurement, 20 scans with the movable mirror in the FTIR

Spectrometer were made. The computer program later took an average of these scans

to produce the measured spectra of the flame emission.

4.2.2 Construction and simulation of flame spectra

In the following section a short description of the construction and

implementation of the simulations is presented. To simulate the emission, the theory

of the radiative transfer is used with the simplification of assuming scattering effects

negligible. Rayleight-scattering is much stronger than Raman, but can also be

considered insignificant in the infrared region since the intensity of scattered light is

inversely proportional to the fourth power of the wavelength, and linearly dependent

on the number density. If particles exist in the system the Mie scattering have to be

taken into account, which is considerable stronger than the Raman and the Rayleight

scattering. In the case of the premixed laminar burner, no particles enter the burner,

since the gas is filtered. Although particles can be formed during combustion, in form

of soot, this if often only the case for rich diffusions flames. In the engine combustion

chamber there might be a smaller amount of particles, but since the engine is running

on a very lean fuel, this effect is ignored in this initial investigation. In the case of the

engine, the amount of particles could be minimized further by filtering out the

particles during induction stage. In the flame the Raman- and Rayleight scattering

always exists. Since the Raman scattering often is very weak, on the order of 1000

times weaker than Rayleight scattering, this effect is considered small in combustion.

For these reasons the scattering has been assumed to be negligible for this initial

investigation of the radiative transfer. In addition the gas is also assumed to be in

local thermal equilibrium (LTE) and homogenous.



The spectra recorded with the FTIR spectrometer are saved into files

containing two columns, the wavenumber and the intensity from the measurement.

The instruments used in the spectrometer give rise to a response function. It is the

collected response from the instruments inside the spectrometer which is determined

from measuring the spectra of the thermal lamp, approximately a blackbody source.

This spectrum is compared with the calculated Planck function with known

temperature. A thermometer measured the temperature of the blackbody source to be

1473.15 K. The response function can be determined in Eq. (4.1) and divided from

the measured flame spectra in Eq. (4.2).

BlackbodyCalculated

ackbodyMeasuredBl

FunctionsponseI

II =Re

(4.1)

Functionsponse

ectraMeasuredSp

spectraI

II

Re

= (4.2)

A Matlab program was created to process the data, named

CallProcessFTIRSpectraFunc.m, see Appendix A.1, in which the data from the

measurements was uploaded into vectors, and the response function removed from

the spectra as described above. The light from the flame also travels in the air

between the flame and the spectrometer. Due to this, the spectra obtained are

expected to contain absorption lines. This has been eliminated by fitting the

curvature of the measured blackbody.

The possibility of using a Voigt profile was also studied since the line profile is

often used in combustion applications. Due to the difficulty to evaluate the Voigt

formula, see Eq. (2.21), many approximations of the Voigt profile have been

suggested. One of them is given by Whitting [32] and another one is given by Yuyan

Liu [33]. Both of these Voigt approximations were investigated. A Lorentzian line

profile has been used for the spectral simulations since the Voigt line profile could

not be verified due to inaccessibility of available data for a true Voigt line profile.

Two different functions were created to simulate emission using Eq. (2.10)

valid for both optical thick and thin mediums. A function, called

CallOpticalDepthFunc.m, calculates the optical depth of the investigated species

according to Eq. (2.22). This result is used in the second function called

CallEmissionFunc.m, which uploads the HITRAN or HITEMP file created in

JavaHAWKS into vectors. The HWHM is calculated with Eq. (2.17) and calls

CallOpticalDepthFunc.m, which returns the optical depth of the spectral region for

the investigated species. The emissivity accordingly to Eq. (2.12) is determined and

multiplied with the Planck function to produce the emission spectra. The emission

function in the end returns the optical depth, the emissivity and the emission. See

Appendix A.2, A.3 and A.4 for the written programs.

The resolution of the spectra has been set to 0.02 cm-1

and is calculated

between the region 1500 cm-1

and 6000 cm-1

at the atmospheric pressure. For these

simulations the partial pressures and the temperature are assumed to be known.

These parameters were calculated by a modelling program named CHEMKIN, a

software tool for solving complex chemical kinetics problems. Table 4 shows the

result from the mole fraction and temperature simulation for the species investigated



for this flame. The species chosen for investigation are the main species expected in

the IR region for the flame, such as CO2, CO, H2O and CH4. Once the visible flame

zone was identified in the CHEMKIN simulation, the other measurement locations

were also identified from this position.

Table 4 Illustrate the calculated mole fractions and temperatures for the respective

investigated species versus the flame coordinates using CHEMKIN.

Position from the

visible flame zone

[mm]

- 3 mm - 1 mm 0 mm + 1 mm + 3 mm

Flame coordinates in

plot [mm] -1.3 0.7071 2.32 3.33 5.25

Estimated

temperature [K] 300 398 1597 1669 1693

Φ = 0,8

CH4 0.061 0.0556 3.73E-06 6.61E-12 1.03E-18

O2 0.1525 0.1455 0.035 0.032 0.031

CO 8.71E-05 0.00133 0.0061 0.0013 0.00033

CO2 4.21E-05 0.0012 0.054 0.059 0.06

H2O 0.001 0.0122 0.1168 0.12 0.1216

N2 0.7848 0.7819 0.7828 0.7848 0.7855

SUM 0.9994292 0.99773 0.994707 0.9971 0.99843

Flame coordinates in

plot [mm] 0.5051 2.525 3.53 4.545 6.566

Estimated

temperature [K] 358 1353 1752 1794 1799

Φ = 1.6

CH4 0.1294 0.0446 0.0088 0.00572 0.004604

O2 0.1645 0.05887 0.0056 0.000778 5.75E-05

CO 0.0023 0.0513 0.0754 0.0753 0.074

CO2 0.000331 0.0154 0.03 0.0348 0.0379

H2O 0.009795 0.1271 0.1715 0.1723 0.1695

N2 0.6699 0.6388 0.6347 0.6347 0.6347

SUM 0.976226 0.93607 0.926 0.923598 0.9207615

Adding the partial mole fractions of each species at a certain measurement

location should equal one. It can be noted that, for the lean flame, the sum of the

species listed is almost equal to one but for the rich flame there is at most 8 %

difference from total concentration, indicating there might be species that are not

considered in this investigation. After further investigation this minor contribution

comes from species like CH2O, C2H2, CH3 that are created during or after the

reaction zone. For the lean flame these species are not of importance.

With help of a ray tracing program [34] the light path to setup was

investigated. The setup in the ray tracing simulation was simplified with a lens with

the same diameter and focal length as the mirrors used in the setup. The result gave

the same amount in number of photons in the spectrometer aperture as sent out from

the modelled light source. Different placements of the light source in the location

within the burner diameter did not change the results, for line-of-sight measurements.



This indicates that the aperture is big enough to let through all photons released from

the gas column in the burner. The investigation didn’t tell anything more about the

actual optical length for the flame measurement, but with no scattering considered,

the optical path length has been assumed for light-in-sight measurement to be the full

length of the gas column in of the burner, which is 7 cm.

4.2.3 Discussion of the flame investigation and simulation

Fig. 4.2 below illustrates the flame front above the premixed laminar burner

during measurement. The flame front consists of a stable layer of light blue color.

This is the visible flame zone and exists within the reaction zone. The flame does

not show any yellow light, indicating that no soot or very little soot is created during

this combustion. If soot existed the flame zone would be yellow in color.

Fig. 4.2 Illustrates the visible flame zone during the measurements, in which the positions of the

measurements locations was derived from.

The spectra from the premixed flame was recorded and processed to obtain the

‘true’ spectra without the response function. The same setup was used to measure

blackbody emission at 1473.15 K, its spectra is displayed in Fig. 4.3.



Fig. 4.3 Shows the measured spectra, fitted curve of the measured spectra and the calculated

blackbody spectra for T = 1473.15 K. The calculated Planck function was corrected to fit the

measured curve with an arbitrary value.

Fig. 4.4 Displaying the effect of the sensitivity drop-off from the detector on the blackbody spectra

from Fig. 4.3 (zoomed).

This spectrum contains H2O and CO2 absorption lines, which arise when the

light from the flame passed the cold air layer between the spectrometer and the

lightsource. There is a dip between 2900-3500 cm-1

which is not saturated like the

other absorption lines despite being very deep. For this reason this structure has been

assumed to be part of the response function of the instrument and not due to

absorption. The blackbody spectrum was to remove these absorption lines and then

expanded at lower wavenumbers since the spectrometers sensitivity falls off in this

area. Fig. 4.4 shows this drop-off in which the sensitivity seems to fall off rapidly

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

measured blackbody curve

curve fitting of the measured blackbody

calculated Planck function with T = 1473.15 K

1650 1700 1750 1800 1850 1900 1950 2000 2050 2100

0

0.05

0.1

0.15

0.2

0.25

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

measured blackbody curve

curve fitting of the measured blackbody

calculated Planck function with T = 1473.15 K



around 1850 cm-1

. This is consistent with the detector’s material sensitivity curve for

InSb. In Fig. 3.11 the InSb curve falls off drastically after 5µm (2000 cm-1

). For this

reason the spectra in this region are not very reliable, this is clearly shown in

Appendix C when the simulated and the measured spectra are compared.

Fig. 4.5 displays the resulting response function after using Eq. (4.1) for the

measured (red dotted line in Fig. 4.3) and the calculated blackbody spectrum (green

line in Fig. 4.3).

Fig. 4.5 Shows the resulting response function from Eq. (4.1).

Using the response function from Fig. 4.5 the true spectra for the premixed

methane/air flame is obtained with Eq. (4.2). The resulting spectra for the two flames

are displayed in Fig. 4.6. There are notable differences between the lean and the rich

flame. The spectra for lean flame below the visible flame zone shows less emission

and contains more static noise than the other spectral points for the same flame. This

apparent spectral noise could be explained by lower temperatures are thus less

emission and the existence of fluid gas before the reaction zone. For the spectra at

the visible flame zone, the CO2 band becomes more apparent and there is a CO band

just becoming visible. The spectra above the visible flame zone show very strong

water lines and CO2 band while the CO band is no longer clearly visible in

comparison, as shown in Fig. 4.6. This is expected for the lean flame since according

to the CHEMKIN, the CO is created near the visible flame zone and then disappears

afterwards as it is transformed into CO2. In the fundamental band of CO2 there are

very strong absorption lines, this is the same for all spectra. There is a band structure

from the CH4 that has been identified around 3000 cm-1

. The CH4 band seems to only

exist at the visible flame zone for the lean flame. There is no indication that this band

exist before the visible flame zone, possibly since the CH4 exists here as fluid gas

and has not been heated enough to produce emission bands. After the visible flame

zone this structure seems to have disappeared again. Since, in a lean flame, there

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 650040

60

80

100

120

140

160

180

Wavenumber [ cm-1 ]

Response function [ - ]



exists an excess of oxygen, indicating that all fuel will have been transferred into

products after the visible flame zone.

Fig. 4.6 Shows the comparison between the different measured locations of the flame spectra with φ = 0.8 and φ = 1.6.

The rich flame shows apparent emission spectra for all measurements heights

except 3 mm below the visible flame zone, indicating that the rich flame is much

hotter than the lean flame. It is also possible that it has a much larger reaction zone or

is located closer to the burner surface than the lean flame. In the rich flame, the CO

band emission is very strong and stays strong even above the visible flame zone,

indicating that CO has survived into the product zone. The CH4 band show a very

2000 2500 3000 3500 4000 4500 5000 5500

0

1

2

3

4

5

6

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

Measured spectra from a flame with phi =0.8

2000 2500 3000 3500 4000 4500 5000 5500

0

2

4

6

8

10

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

3 mm above the visible flamezone


at the visible flamezone


1 mm below the visible flamezone


H2O + CO

2

H2O

H2O

CO

CO2

CO2

H2O + CO

2

H2O + CO

2

H2O + CO

2

CH4

CH4

CO

2000 2500 3000 3500 4000 4500 5000 5500

0

2

4

6

8

10

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

Measured spectra from a flame with phi = 1.6

2000 2500 3000 3500 4000 4500 5000 5500

0

2

4

6

8

10

12

14

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


1 mm below visible flamezone


3 mm above visible flamezone



CH4 H

2O + CO

2

H2O + CO

2CH

4

H2O + CO

2

H2O + CO

2

CO

CO

CO2

CO2

CO

H2O

CO

H2O



clear band structure for the lean flame at 1 mm below the visible flame zone and

shows a less clear band structure at the visible flame zone in comparison, indicating a

decrease of the concentration of CH4.

For the plots for 3 mm below the reaction zone, the two different flame spectra

show little emission. Because of this, the noise level of the signal is very apparent

and lays around 10-5

to 10-6

a.u, shown in Fig. 4.7. This noise level of the signal

exists in all spectra. The only difference is that it is more prominent here due to the

lower emission levels. For the rich flame, the CO band emerges around 2140 cm-1

from the cold flame structure, indicating that CO is already formed here from the

heat of the reaction zone. Very few water lines are shown.

Fig. 4.7 Shows the comparison between the flame spectra for 1 mm and 3 mm below the visible

flame zone for φ = 0.8 and φ = 1.6.

From the plots 1 mm below, the lean flame shows similar spectra as for the

previous spectra while the rich flame shows strong emission lines for CO2, H2O and

CO. The rich flame also indicates a structure from the CH4 band at 3000 cm-1

, see

Fig. 4.6. This CH4 structure appears very strong for the rich flame at this location. As

previous stated only the rich flame at 1 mm below the visible flame zone shows this

structure. This is due to that there is more fluid gas as actual emission of the CH4

molecules. The CH4 molecules must be heated enough to be excited to higher

excitation states and thus no photons emitted to be registered by the spectrometer of

this band. The rich flame shows a relative strong CO band around 2140 cm-1

but

there are also some CO band heads around 4350 cm-1

and 4300 cm-1

.

At the visible flame zone for the lean flame a CO structure is emerging, but the

CO band head is still not visible compared to the rich flame. Both flames show the

CH4 structure indicating that there is still some fuel in this region, even if it is much

weaker than previous measurement locations.

For plots 1 mm above, the lean flame is missing the CO band at 2140 cm-1

; see

Fig. 4.6, indicating that the CO radical have already been consumed in the product

zone. At this point the fuel lines have disappeared from the structure for both flames.

2000 2500 3000 3500 4000 4500 5000 5500

0

1

2

3

4

5

6

7x 10

-5

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


2000 2500 3000 3500 4000 4500 5000 5500

0

1

2

3

4

5

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]








For plots 3 mm above, around 1850 cm-1

there are some water lines. These

lines are very apparent for the lean flame because the CO band at that region is

missing, while for the rich flame, some CO has survived. Both flames contain strong

band structures from H2O, although it is slightly stronger for the rich flame.

The two bands around 2000 cm-1

show a certain shift of the baseline. This is of

course due to the many lines in the area being added together; however, this structure

is very strong even at the lower wavenumber for the CO band. This feature is either

showing the beginning of the formation of a blackbody radiative curve or is due to

the large number of lines in the region. However, this structure is even shown for

spectra below the visible flame zone, where no or little emission exists.

The investigated species within this region in the previous plots have been

identified from the simulations; Fig. 4.8 shows an example of the identification. The

CO band around 3000 cm-1

and the CO2 around 5000 cm-1

is not visible in this plot

because they are too weak in the simulation to be displayed.

Fig. 4.8 Shows an example of a study of the investigated species locations for the flame with φ = 1.6.

Fig. 4.9 shows some examples of the comparison between the measured and

the simulated spectra. The comparison between the simulated and the measured

spectra for all locations can be found in Appendix C. It should be noted that no

corrections have been made between the simulated and the measured spectra.

2000 2500 3000 3500 4000 4500 5000 5500

0

2

4

6

8

10

x 10-4 Spectra for phi = 1.6 flame at visible reactionzone - Identification of the species

Intensity [ cm-1 ]

Wavenumber [ cm-1 ]

2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3

Wavenumber [ cm-1 ]

Intensity [ cm-1 ]

measured spectra

H2O

measured spectra

CO2

CO

CH4



Fig. 4.9 Shows the two examples of features in comparison between the flame spectra for 1 mm

above the visible flame zone for φ = 0.8 and φ = 1.6. The upper image shows the band head of the

fundamental CO2 (to the right) and the CO2 absorption lines (to the left). The lower image shows part

of the combination band of H2O.

It can be noticed that in terms of line position, the simulated spectra fit well to

the measured, however the line strengths are sometimes much greater or smaller for

the simulation for some species and flame locations. Uncertainties in the

spectroscopic database might be a source for the spectra’s fit not being perfect. This

could be that the CHEMKIN models a flame that is perfect laminar and adiabatic.

However in reality, the flame is not perfectly adiabatic since there will always be

heat loss to the environment. The burner has a stabilizer above the flame which

deviate the flame from perfect laminar. This is especially true at the edges of the

visible flame zone, seen in Fig. 4.2. For example in the plot 1 mm above, for the rich

flame, the CO band seems to be missing in the simulation. In the same plot the H2O

lines seem to be much bigger; however, this could be a result of partial or full

absorption in the band, see Fig. 4.10 and Appendix C. The possible reason why some

of the lines seem to fit well while some are partial or completely absorbed, is that the

absorbing medium is cold and thus can only excite certain populations in the

molecules: the ground state transitions. As given from the Boltzmann distribution,

when the temperature increases, higher populations are occupied. This phenomenon

is also seen for the fundamental band of CO2.

2380 2381 2382 2383 2384 2385 2386 2387 2388 2389

0

0.5

1

1.5

2

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

Example of comparison between measured and simulated spectra for phi = 0.8 at 1 mm above the visible flamezone

3475 3480 3485 34900

0.5

1

1.5

2

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


simulated spectra

measured spectra

simulated spectra

measured spectra



Fig. 4.10 Shows the two examples of features in comparison between the flame spectra for 1 mm

above the visible flame zone for φ = 0.8 and φ = 1.6. The upper image shows the combination band

of H2O in which some lines have been absorbed. The lower image shows part of the combination band

of H2O.

The simulated spectra of 3 mm below the visible flame zone, in both flames,

shows very little agreement with the simulated spectra. This is because we do not

have much emission in this region due to low temperature and concentrations in the

simulations. For the plots in the visible flame zone, the CO seems to be

underestimated for both lean and rich flame. The only plot that has visible CO band

in the simulation is the 1mm below the visible flame zone for the rich flame, and it is

seem to be bigger than the measured CO band. This is an indication that the either

the temperature or the concentration is not accurate with the measurement for some

species like CO. The simulation was based upon the given mole fractions and the

temperature calculated from the program CHEMKIN. It is clear from the

measurement and the simulated emission that some lines should be more prominent,

but is in the simulation too weak to be comparable with the CO2 band and water

lines, especially for higher temperatures. A possibility is that the CHEMKIN was

provided with too low concentrations or incorrect temperatures to give a perfect fit.

Another possibility is that since the simulations with over 1000K have been

simulated with HITEMP95 lines can be missing in the database for CO, CO2 and

H2O. Most of the H2O and the CO2 lines in the measured spectra seem to be weaker

since there is absorption. It is difficult to determine if it is a good fit or not, due to the

large amount of absorption in the fundamental band of the CO2 and the combination

band of H2O. The species of N2 and O2 are too small in comparison with the other

features, and they do not appear together with the other species.

3670 3672 3674 3676 3678 3680 3682 3684 3686 3688

0

2

4

6

8

10

12

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


3500 3505 3510 3515

0

5

10

15

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

simulated spectra

measured spectra

simulated spectra

measured spectra


Absorption lines



4.3 Temperature and Concentration simulations in the combustion chamber

With the knowledge from the flame measurements, the goal is to investigate

different methods to determine the temperature and the concentration of investigated

species just before combustion.

4.3.1 Implementation and simulation of engine spectra

During a cycle of the engine, the gas in the cylinder is exposed to temperature

and pressure variations before, during and after combustion. Fig. 4.10 shows the

pressure and the temperature changes in function of the crank angle degree (CAD).

The CAD is a unit to measure the pistons position when the engine is running. As a

reference point, when the piston is located at its highest point, top dead center, the

CAD is equal to zero. The pressure variations have been measured during the cycle

of the engine. The temperature variation has been simulated (based on the pressure

trace) and is therefore subject to a greater uncertainty.

Fig. 4.11 Shows the temperature and measured pressure changes in the engine.

-400 -300 -200 -100 0 100 200 300 4000

10

20

30

40

50

60

X: -9.25

Y: 35.05

CAD / degrees

Pressure / Bar

X: -37.35

Y: 10.07

X: -55.4

Y: 5.024

X: -94

Y: 2.01

-400 -300 -200 -100 0 100 200 300 400400

600

800

1000

1200

1400

1600

1800

X: -9.25

Y: 1008

CAD / degrees

Temperature / K

X: -37.35

Y: 780.2

X: -55.4

Y: 656.2

X: -94

Y: 527.9



The temperature varies between about 400–1800 K and the pressure about

1-60 Bar. The ignition point can be identified in Fig. 4.11 on both the temperature

and the pressure plots, just before top dead center where the temperature and

pressure curves get much steeper. Four different points, before combustion have been

chosen for investigation; these points have been marked in Fig. 4.11. To find the

optimal point for measurements, these simulations were performed with temperatures

and pressures listed in table 5.

Table 5 Lists the possible measurements points for the engine experiment.

Measurement

points

CAD

[ Degrees ]

Pressure

[ Bar ]

Estimated

temperature [ K ]

P1 -9.25 35.05 1008

P2 -37.5 20.07 780

P3 -65.4 5.02 656

P4 -94.0 2.01 528

The simulation of the emission, created in the previous chapter, requires that

there is some first estimation of the mole fraction of CO2 in the combustion chamber,

to give an approximation of the half-widths of the lines and the partial number

density. This is mainly used for the optical depth simulation. For this purpose Eq.

(2.24) is used to estimate the mole fractions of H2O and CO2 at intake when the

engine is running on a lean fuel. From this equation the air-fuel-ratio of 1.2 gives a

mole fraction of 10.51% CO2 and 11.83% H2O after combustion and for air-fuel-

ratio of 1.6 gives a mole fraction of 8.00% CO2 and 9.00% H2O. It should be noticed

that these concentrations come from combustion and a large fraction is removed in

the exhaust stoke. Only a small fraction is remaining for the new cycle during intake

of new air and fuel. Despite this the concentration has been used as a first estimation.

For the simulations the air-fuel-ratio of 1.2 has been considered since the change

between the two is minimal with one being slightly bigger, see Fig. 4.12.



Fig. 4.12 Shows the comparison between spectra simulated for CO2 with air-fuel-ratio of 1.2 and 1.6.

The first step in this investigation is to determine the optical depth and the

emission for the four measurement points in the engine chamber. Studying the

spectra of the flame gave a hint of what kind of species lay within the investigated

spectral regions of interest for CO2. A program was created, EngineOptical-

DepthAndEmissionSimulation.m, calculating the optical depth and the emission,

based on the previous program, using HITRAN for the three different spectral

regions of interest. With Eq. (2.22) the optical depth as a function of wavenumber,

can be calculated.

The first region is the fundamental band of CO2, located approximately

between the regions of 2250–2450 cm-1

and is the region of the chosen filter. The

second band is the combination band of CO2, located approximately between the

regions of 3450–3915 cm-1

. For this band there is interference from water lines even

at lower temperatures. For optical thick measurements this is not an issue, since the

blackbody is only dependent of the temperature of the investigated gas and not the

species. The third band for the second combination band of CO2, located

approximately between the regions of 4840–5100 cm-1

, is a weaker band of CO2 in

the infrared region and should therefore be a valid choice for concentration

measurement since it is not optically thick. For higher temperatures interference from

the water lines may arise in this region, especially above 5000 cm-1

. The pressure and

temperature is set to the points derived from Fig. 4.10 and listed in table 5. The path

length of the investigated gas column is 8.1cm. In the other case when the gas cloud

is not a true blackbody the emissivity in Eq. (4.3) is described by Eq. (2.12) and the

optical depth is determined with help of Eq. (2.22). To be able to estimate the

emissivity, an initial assumption of the mole fractions for CO2 and H2O of 10.51%

and 11.83% respectively, given from the global reaction formula have been used. It

should be noticed that if there is internal EGR, this relation might be slightly changed

according to Eq. (2.26). This program can be found in Appendix B.1.

2220 2221 2222 2223 2224 2225 2226 2227

0

0.5

1

1.5

2

2.5

3

x 10-6

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

10.51% CO2

9% CO2



The next program, EngineTemperatureSimulations.m, is calculates the

temperature using the radiative transfer for optically thick case. For a true blackbody,

the intensity is only dependent on the temperature. Since this is not always the case,

the emissivity to the Planck function is also determined. Two filters for each spectral

region are used to transmit only the wavenumber within the regions that are to be

studied and block all other wavenumbers. By ratio measurement of the emission

between two bands, it is possible to get rid of the solid angle dependence of the

intensity for the setup. The idea is to use two optically thick bands to determine the

temperature. With no possibility of resolving the spectra from the engine are function

of wavelength, as obtained with a spectrometer, line-of-sight path-averaged

measurements are conducted with the infrared detector. The ratio between two

blackbody radiating bands, and a known emissivity, one obtains a function of

temperature,

∑

∑

∑∑

−−

−−==

1)/exp(

1

1)/exp(

1

)(

2

3

122

2

3

111

2

1

Tvcvcr

Tvcvcr

I

ITf

i

ibib

i

ibib

thickbi

thickbi

ε

ε (4.3)

Here r represents the spectral response of the setup and is set to one in these

simulations. ε is the emissivity of the gas in the engine for the spectral region, c1 and

c2 as the radiative constants and v is the wavenumber. The emissivity for a true

blackbody is equal to one. The initial assumption of 10.51% CO2 and 11.83% H2O

has been used here as well. Each emission band is multiplied with the filter’s

transmission curve for each region. The general idea is to investigate if the two bands

can be estimated as blackbody without the concentration dependence. This program

can be found in Appendix B.2.

Another possibility to determine the temperature is to use the transmission, and

thus the absorbance, to obtain the temperature for the combustion. One could use

H2O lines to obtain the temperature since they are more abundant and relatively free

from disturbances. The absorption coefficient depends on intensity of the line

strength component; therefore the temperature should be able to be estimated by

comparing the absorbance of different peaks for the same species. This method is

often called two-line technique. The Eq. (4.4) shows the absorbance at a specific

wavenumber, which is dependent on the absorption coefficient, the path length, the

total pressure and mole fraction of the investigated species. Dividing the absorbance

for two lines at specific wavenumber for the same species gives the relation stated

above, where the pressure, path length and mole fraction are cancelled out. Thus the

ratio of two absorption lines of the same species is a function of the temperature, see

Eq. (4.5). The temperature is determined using a tunable diode laser [35]. A line-pair

is scanned and its integrated intensity will give the temperature by taking the ratio of

the two lines.

LfvTSPxIIvTA vvspeciesvotv ),()/ln(),( =−= (4.4)



(4.5)

S1(Tref, v1) and S2(Tref,v2) are given by Eq. (2.14) are the line strengths for the

line transitions 1 and 2 at a reference temperature Tref. The A(T,v1) and A(T,v2) is the

peak or integrated absorbance for each transition line. The selection of lines is based

upon that certain criteria must be fulfilled. The line should be free from interference

from other species; the absorption line should be strong enough to be registered by

the detector but small enough to avoid optical thickness. The transitions with large

lower state energies absorb at higher temperatures and not so much at lower

temperatures (room temperatures). Thus, for temperatures between 500-1000 K,

transitions with smaller lower state energies should be is considered. If one calculates

the integrated absorbance instead of the peak absorbance for the two-line method the

lines must also be accessed while scanning the diode laser; but, at the same time the

lines cannot be too close for overlapping at higher pressures. For this reason, this

method for integration at high pressures is not easily applicable since the broadening

of the lines makes it difficult to distinguish distinct lines. Another criterion is that the

lines should have well-separated lower state energies to obtain temperature

sensitivity. From reference [36] two line-pairs are selected for this investigation of

the temperature determination using this method, the H2O lines at 3982.06cm-1

and

3982.75cm-1

respectively 3966.77cm-1

and 3967.39cm-1

, see table 6. This simulation

can be found in CallTwoLineMethodAbsorptionTemperatureSimulation.m

where the absorbance ratio in Eq (4.5) is calculated is function of the temperature for

the given lines and their atomic parameters given in HITRAN. The program can be

found in appendix B.4.

Table 6 Shows candidate H2O line pairs for measurements of temperature and

water concentration near 2.5 µm based on HITRAN database [36].

Line

pair

Wavenumber

(cm-1

)

Wavelengh

(cm)

S@296 K

(cm-2

atm-1

)

E’’

(cm-1

)

∆E’’

(cm-1

)

Line

spacing

(cm-1

)

A 3982.06 2511.26 8.84x10-3

1581.33 2072.71 0.69

3982.75 2510.83 7.54x10-7

3654.04

B 3966.77 2520.94 4.61x10-5

2522.26 868.86 0.62

3967.39 2520.55 2.81x10-6

3391.12

With a known temperature, the concentrations can also be estimated from

emission using Eq. (4.3). For the temperature determination, the mole fraction of the

two major species H2O and CO2 is assumed to be known from the global reaction.

However, if there is internal EGR, these concentrations are changed according to Eq.

(2.26). A simulation was made to calculate the emission ratio between 3450–3915

cm-1

and 4840–5100 cm-1

. Since both H2O and CO2 exist in the band regions, an

−−−=

====∫∫

refref

ref

vspecies

vspecies

TTEE

k

hc

vTS

vTS

vTS

vTS

LdvfvTSPx

LdvfvTSPx

A

ATf

11)(exp

),(

),(

...),(

),(

),(

),()(

''

1

''

2

1

2

1

2

1

2

1

2



assumption is made that for every mole of CO2, there is 1.2 times more H2O for

λ = 1.2, given from Eq. (2.24) . Each emission band is multiplied with the filter’s

transmission curve for each region. This simulation, EngineConcentration-

Simulation.m, can be found in Appendix B.3.

The next program, EngineConcentrationDiodeLaserSimulation.m, is

calculates the concentration of the investigated species using absorption

measurements with a known light source, such as a diode laser. The diode laser,

being monochromatic, makes it possible to only excite one wavelength and to avoid

interference from nearby lines that might come from other molecules. Some lasers

have the ability to tune the laser to desire wavelength, example of a tuning range is in

order of 1 cm-1

. The transmission is determined with Eq. (4.6) at the wavenumber of

the investigated spectral line and species of interest. The optical depth simulations

are used to determine the appropriate line in terms of interference of other species

such as H2O, absorbance and spacing between spectrallines. This program can be

found in Appendix B.6.

LfvTSPxt

ontransmissi

vvspecieseI

IT 0

),(

0

−−== (4.6)

In the next program, EngineConcentrationLEDSimulation.m, the same

investigation is made but with an LED light source. An LED’s line profile is much

wider, but it is a much cheaper option. The concentration can be obtained from a

modified version of the Beer-Lambert law, given by Eq. (4.6), in which the LED’s

line profile, Φ∆v, is used to calculate the transmittance for all wavenumbers i within

the LED’s band region. The center intensity of the LED’s profile is canceled out in

the ratio relation, thus one has a relation that is only dependent on the line profile of

the LED and the optical depth at each wavenumber within the LED band. The LED

line profile is multiplied with the filter’s transmission curve for the region. In the

measurement, the integrated intensity is measured and for this reason the modified

Beer’s law is summed with the band region of the LED. The modified relation is

given by Eq. (4.7). This program can be found in Appendix B.5.

∑∑

∑∑

∑∑

=

=

−

=

=

−

=

=

−

∆

−

====2

1

2

1

),(

2

1

2

1

2

1 0

2

1 0

0

0

v

vi i

v

vi

LfvTSPx

i

v

vi i

center

o

v

vi

L

i

center

o

v

vi

v

vi

L

v

t

ontransmissi

vvspeciesii e

I

eI

I

eI

I

IT

φ

φ

φ

φ κκ

(4.7)

4.3.2 Suggestion of experiment setup

The first step is to determine the temperature from optically thick thermal

emission measurement, directly from the gas within the cylinder of the engine while

it is running. The detector is timed with the engine cycle and registers the intensity

only when the engine comes to a pre-decided CAD value. Multiple measurements are

made to obtain an average. This data is then compared with the simulation of the

temperature, showing the band intensity ratio as a function of the temperature. The

simple illustration of the setup can be seen in Fig. 3.7c. The same setup can be used

to determine the concentration from emission measurement, as described above.

The next part is to estimate the concentration as a known temperature. Since

the temperature has not been experimentally determined, four different values were

chosen from pressure and temperature plots listed in table 5. Simulations of the



optical depth for these values give, not only an idea of the optical depth, but also the

line positions of the different species. In the region of the second combination band,

only CO2 and H2O are of interest. With the experimentally determined temperature

and the given pressure, the concentration simulation provides a plot with the

transmission as a function of the concentration. The setup is displayed in Fig. 3.7a-b.

The light source intensity is measured before and after it enters the engine chamber.

The ratio between these two intensities gives the transmission.

4.3.3 Discussion of the engine simulations

The optical depth for three bands using HITRAN was evaluated for the three

different band regions of interest. The first one is the fundamental band of CO2,

located between the regions of 2250–2450 cm-1

, Fig. 4.13 displays the result. The

simulation showed that the fundamental band is optically thick for both the low

pressure and high pressures used for the simulation.

2250 2300 2350 2400 2450 25000

20

40

60

80

100

120

Wavenumber [ cm-1 ]

P = 2.01 Bar; T = 528 K

Optical depth [ - ]

2250 2300 2350 2400 2450 25000

10

20

30

40

50

60

70P = 5.02 Bar; T = 656 K

Wavenumber [ cm-1 ]

Optical depth [ - ]

2250 2300 2350 2400 2450 25000

20

40

60

80

100P = 20.07 Bar; T = 780 K

Optical depth [ - ]

Wavenumber [ cm-1 ]

2250 2300 2350 2400 2450 25000

10

20

30

40

50

60

70P = 35.05 Bar; T = 1008 K

Optical depth [ - ]

Wavenumber [ cm-1 ]

a)



Fig. 4.13 Shows the optical depth a) and the corresponding emission simulations b) for the

fundamental band for the investigated points, P1-P4.

The fundamental band of the CO2 is clearly optically thick, especially at the

center of the band structure. This can also been seen in the emission plot for the same

band. In Fig. 4.13 b) the center of the band has merged to the Planck curve for all

investigated points. As a line becomes optically thick, the wing of the line grows and

at some point reaches the continuum, where it becomes a blackbody radiator. The

second band is the combination bands of CO2 and H2O, located approximately

between the regions of 3450 – 3915 cm-1

, Fig. 4.14 displays the result.

2250 2300 2350 2400 2450

0

0.5

1

1.5

2

2.5

x 10-5 P = 2.01 Bar; T = 528 K

Intensity [ a.u. ]

Wavenumber [ cm-1 ]

2250 2300 2350 2400 2450 2500

0

2

4

6

8

x 10-5 P = 5.02 Bar; T = 656 K

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

2250 2300 2350 2400 2450

0

0.5

1

1.5

2

2.5

3

3.5

x 10-4

Wavenumber [ cm-1 ]

Intensity [ cm-1 ]

P = 20.07 Bar; T = 780 K

2300 2350 2400 24500

1

2

3

4

5

x 10-4 P = 35.05 Bar; T = 1008 K

Intensity [ a.u. ]

Wavenumber [ cm-1 ]Planck curve simulated emission

3450 3500 3550 3600 3650 3700 3750 3800 3850 3900 39500

1

2

3

4

5P = 35.05 Bar; T = 1008 K

Wavenumber [ cm-1 ]

Optical depth [ - ]

3450 3500 3550 3600 3650 3700 3750 3800 3850 3900 39500

1

2

3

4

5

6P = 20.07 Bar; T = 780 K

Wavenumber [ cm-1 ]

Optical depth [ - ]

3450 3500 3550 3600 3650 3700 3750 3800 3850 3900 39500

1

2

3

4

5

6P = 5.02 Bar; T = 656 K

Wavenumber [ cm-1 ]

Optical depth [ - ]

3450 3500 3550 3600 3650 3700 3750 3800 3850 3900 39500

1

2

3

4

5

6

7P = 2.01 Bar; T = 528 K

Wavenumber [ cm-1 ]

Optical depth [ - ]

b)

a)




combination band around 3700 cm-1

for the investigated points, P1-P4.

The third band for the combination band of CO2, located approximately

between the region of 4840 – 5100 cm-1

, Fig. 4.15 displays the result. This is the

weakest among the chosen bands of CO2, in the infrared region for investigation and

should therefore be a candidate for optically thin measurements. The simulation

showed that the band is optically thin for all four measurement points. The emission

lines are well under the Planck function for all measurement points.

3500 3550 3600 3650 3700 3750 3800 3850 3900

0

1

2

3

4

x 10-6

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

P = 2.01 Bar; T = 528 K

3500 3550 3600 3650 3700 3750 3800 3850 3900

0

0.5

1

1.5

2

2.5

x 10-5 P = 5.02 Bar; T = 656 K

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

3500 3550 3600 3650 3700 3750 3800 3850 3900

0

2

4

6

8

x 10-5 P = 20.07 Bar; T = 780 K

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

3500 3550 3600 3650 3700 3750 3800 3850 3900

0.5

1

1.5

2

2.5

3

3.5

x 10-4

Wavenumber [ cm-1 ]Intensity [ a.u. ]

P = 35.05 Bar; T = 1008 K

simulated emission Planck function

b)




combination band around 4900 cm-1

for the investigated points, P1-P4. The Planck function is not

visible in figure.

Overall the line strength for CO2 decreases with increasing pressure as the lines

become wider, and it is more difficult to distinguish separate the line profiles. At

higher temperature, higher energy levels are populated and thus the molecular bands

expand to higher rotational and vibrational quantum numbers. This is seen as a

widening of the band structure.

The fundamental band is classified as optically thick for all considered

measurements points for the engine measurement. The simulation showed that the

fundamental band is optically thick for both the low pressure and high pressures used

4750 4800 4850 4900 4950 5000 50500

0.01

0.02

0.03

0.04

0.05

Wavenumber [ cm-1 ]

Optical Depth [ - ]

P = 2.01 Bar; T = 528 K

4750 4800 4850 4900 4950 5000 50500

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Wavenumber [ cm-1 ]

Optical Depth [ - ]

P = 5.02 Bar; T = 656 K

4750 4800 4850 4900 4950 5000 50500

0.02

0.04

0.06

0.08

0.1

Optical Depth [ - ]

Wavenumber [ cm-1 ]

P = 20.07 Bar; T = 780 K

4750 4800 4850 4900 4950 5000 50500

0.02

0.04

0.06

0.08

0.1

0.12P = 35.05 Bar; T = 1008 K

Wavenumber [ cm-1 ]Optical Depth [ - ]

4750 4800 4850 4900 4950 5000 50500

1

2

3

4

5

6

7

8x 10

-9 P = 2.01 Bar; T = 528 K

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

4750 4800 4850 4900 4950 5000 50500

0.5

1

1.5

2x 10

-7 P = 5.02 Bar; T = 656 K

Intensity [ a.u. ]

Wavenumber [ cm-1 ]

4800 4850 4900 4950 5000

2

4

6

8

10

12

x 10-7 P = 20.07 Bar; T = 780 K

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

4750 4800 4850 4900 4950 5000 50500

0.2

0.4

0.6

0.8

1

1.2

1.4x 10

-5 P = 35.05 Bar; T = 1008 K

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

a)

b)



for the simulation. The optical depth of the combination band at 3500 cm-1

is more

difficult to decide since the optical depth is less than one for the lines between the

stronger H2O lines and in the centerlines it never reaches the blackbody continuum in

the emission spectra. This is perhaps something to consider for the temperature

determination of a true blackbody radiator. For the CO2 the optical depth seems to be

more or less below one, indicating that for a pressure of 2 bars, in the band region, it

is not always optically thick. Only around 3750 cm-1

is the optical depth larger than

one for CO2 in the two limiting cases. For the combination band at 4900 cm-1

the

optical depth is clearly optically thin since it is below one and the emission spectra is

well under the blackbody curve.

The temperature can be estimated for optical thick bands accordingly to Eq.

4.3. The temperature simulation was conducted for the case of a true blackbody, and

the case where the emission is dependent on the blackbody times the emissivity for

the four measurements point’s pressures during the engine cycle before ignition, the

result are displayed in Fig. 4.16.

Fig. 4.16 Shows the temperature simulations for the four different points with pressures as constant

using HITRAN from table 5. Each plot displays also the band ratio for a true blackbody radiation

when the emissivity is equal to one.

For P4 and P3, at lower temperatures the ratio of the emission from the bands

does not act like the ratio between the bands of a true blackbody emitter. When the

pressure increases, for P2 and P1, the similarities are apparent for the lower

temperatures. In these simulations, the first combination band has been divided with

the fundamental band of CO2. The first combination band contains both the

possibility of emission from H2O and CO2. As seen in the flame measurements, H2O

lines grow with higher temperatures. It follows that, for lower temperatures, the

fundamental band is much stronger than the first combination band; thus, the

emission ratio is less sensitive to temperature. This deviation could be due to the first

combination band no longer being optically thick. However, as shown in previous

plots, as temperature and pressure grow, so that the first combination band (mostly



due to H2O lines), and the fundamental band has merged to the continuum. This is

true at least for the lower temperature ranges. A certain decrease in the temperature

plot is noted for temperatures higher than 1000 K. This is probably due to the fact

that one or both bands are optically thin for the given conditions. Another reason

could be that HITRAN database is less accurate for these higher temperatures, and is

missing many of the hot bands that can be found in HITEMP95. For P1 the

HITEMP95 was used for temperature simulation, the result is displayed in Fig. 4.17.

The same simulation was made, but with lower concentrations to see if there was a

difference. The previous used concentration has been estimated from the products of

the global reaction formula and hence the concentration has been for a situation with

100% EGR to the next cycle. In reality most of the exhaust gas will have left the

chamber as the new cycle begins and only a small percentage is left behind in the

chamber as it is filled with new fuel and air. The result is also displayed in Fig. 4.17.

Fig. 4.17 Shows the temperature simulations for point 1 (P = 35.05 Bar and T = 1008K) using

HITEMP (purple curve). The same simulation was made with lower concentrations with 5% CO2 and

6% H2O (light blue curve).

The result was that at higher temperature, the curve simulated with HITEMP is

closer, however, still not equal to the ratio of the Planck curves. The HITEMP was

last updated in 1995 so some lines may be not accounted for. Another explanation for

this deviation is that the first combination band might not be optically thick for the

combination of high pressure and high temperatures. Further investigation showed

that the band was optically thin. It appears that the optical depth for the first

combination band is optically thin for P = 35.05 Bar and T = 1008K and might be the

reason the temperature simulations fail here. The same investigation was made for

lower concentrations of water and CO2; the figure showed less agreement to the ratio

of Planck curves. The explanation could be that the first combination is optically thin

at this pressure and temperature. In other words, not only the temperature, but also

the concentration has impact on the optical depth of the band for the same optical

path length.

Temperature determination by absorption method is also studied. A method

called the two-line method has been reported, that uses the absorbances of two lines

200 400 600 800 1000 1200 1400 1600 1800 20000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Temperature [ K ]

Sum(Iv(3450-3915)/I v(2250-2450)) [ - ]

P1: P = 35.05 Bar

Planck function

Simulated curve - HITRAN - 10.51 % CO2 + 11.83 % H

2O

Simulated curve - HITEMP - 10.51 % CO2 + 11.83 % H

2O

Simulated curve - HITEMP - 5.0 % CO2 + 6.0 % H

2O



of the same species. The temperature then becomes a function of the ratio between

the line strengths and temperature, see Fig. 4.18 and Fig. 4.19 for the result. Two

line-pairs where studied at 3982.06 cm-1

and 3982.75 cm-1

respectively 3966.77 cm-1

and 3967.39 cm-1

based on certain criteria for high temperature relations,

recommended by Farooq et. al. [36]. These lines were chosen for high temperature

measurements at atmospheric pressures, like combustion in a flame.

However, in the engine chamber the pressure variations are between 2-35 bars.

As the pressure increases so does the broadening of the line displayed in the two

figures. To obtain the integrated absorbance of the two lines with a tunable diode

laser the line profile has to be distinguishable, this proves to be difficult for higher

pressures. For this reason, the absorbance peaks are used here in Eq. (4.5) with the

assumption of the same line profiles for the lines. Fig. 4.19 shows a temperature

curve that is more sensitive to the absorbance ratio. It should be noticed that the

figures also can be used for integrated intensities. This could be because the lines

have lower energy difference than the lines in Fig. 4.18.

Fig. 4.18 Upper image shows the simulation of the ratio of the peak absorbance’s for two water lines

at 3982.06 cm-1

and 3982.75 cm-1

as function of temperature. The lower images show the two lines

influences of temperature and concentration. Image to the right has been rued with T = 528 K and the

image to the left with T = 1008 K.

400 600 800 1000 1200 1400 1600 1800 20000

0.1

0.2

0.3

0.4

0.5

Temperature [ K ]

f(T) = A(T,v2)/A(T,v1)

3980 3980.5 3981 3981.5 3982 3982.5 3983 3983.5 3984 3984.5 39850

0.2

0.4

0.6

0.8

1

1.2

1.4x 10

-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

T = 1008 K

3980 3980.5 3981 3981.5 3982 3982.5 3983 3983.5 3984 3984.5 39850

0.2

0.4

0.6

0.8

1x 10

-6

Wavenumber [ cm-11 ]

Intensity [ a.u. ]

T = 528 K

P = 35.05 Bar P = 20.07 Bar P = 5.02 Bar P = 2.01 Bar 3982.75 cm-1 3982.06 cm-1



Fig. 4.19 The upper image shows the simulation of the ratio of the peak absorbance’s for two water

lines at 3966.77 cm-1

and 3967.39 cm-1

as function of temperature. The lower images show the two

lines influences of temperature and concentration. Image to the right has been rued with T = 528 K

and the image to the left with T = 1008 K.

The concentration simulation from the ratio of two emission bands with known

temperature can be found in Fig. 4.20. The results seem to implicate that the

concentration is more sensitive for the measurement points with lower temperatures,

in which the intensity between the two bands differs a lot. As the temperature

increases, the intensity for the first combination band seems to decrease to such

extent that the second combination band gets stronger in comparison. It should be

noted that these simulations assumes that the relation between the H2O and the CO2

stays the same, which might not be the case in the reality during the engine cycle.

Although the two band regions had been specially chosen to be ‘water free’, the first

combination band contains water lines. The trouble with emission measurement is

the interference of water lines for both bands for optically thin measurements. The

optimal case would be to investigate band regions that are free from H2O

interference.

400 600 800 1000 1200 1400 1600 1800 20000

0.5

1

1.5

2

2.5

Temperature [ K]

f(T) = A(T,v 2)/A(T,v1)

3964 3965 3966 3967 3968 3969 39700

1

2

3

4x 10

-7

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

3964 3965 3966 3967 3968 3969 39700

0.5

1

1.5x 10

-4

Intensity [ a.u. ]

P = 2.01 Bar P = 5.02 Bar P = 20.07 Bar 35.05 Bar 3966.77 cm-1 3967.39 cm-1



Fig. 4.20 Shows the simulation of the ratio of band emission of CO2 as function of concentration.

The assumption of for every mole CO2 there exists 1.2 times more H2O. Each bandintensity is

multiplied with the filter transmission curve.

The optical depth plots were used to find possible line positions of CO2 that

were not compromised by strong water lines and could be used for concentration

measurement with a diode laser as a light source. The chosen line positions for this

investigation are displayed in table 5. The result of the simulation using these

wavenumbers is displayed in Fig. 4.21.

Table 7 Lists the possible measurements points for concentration measurement

using a laser diode at the same wavelength.

Measurement

points

Line position

[cm-1

]

Optical Depth

[ - ]

P1 4991.26 0.07035

P2 4991.25 0.0226

P3 4991.23 0.0188

P3 4945.10 0.01847

P4 4945.10 0.02165

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

5

10

15

20

25Concentration Simulation between Two Optical Thick Bands (combustion of lambda = 1.2)

Concentration / -

Sum(Iv(3450-3915)/I v(4752-5027)) [ a.u ]

P3: T = 656K; P = 5.02 Bar

P4: T = 528K; P = 2.01 Bar

P1: T = 1008K; P = 35.05 Bar

P2: T = 780K; P = 20.07 Bar



Fig. 4.21 Shows the simulation of the absorbance in function of the mole fraction of CO2 when the

laser diode has been used as a light source for a T = 528K.

According to this simulation, the absorbance changes very little for small

concentration changes. For the lines investigated, only about 20% of the CO2 is

absorbed for a concentration of 100%. For about 10% CO2 there is about 2-4%

absorption. If it is possible to measure small absorbances in the engine setup, this

could be an alternative method since water interference should be minimal for the

diode laser due to its monochromatic feature.

The concentration simulation, using an LED as light source, can be found in

Fig. 4.22. All four points have been used, and is distinguished by different colors in

the figure. The LED line profile is very broad, to narrow it down a filter was

incorporated into the simulation, preventing unwanted water lines at higher

wavenumbers.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Concentration [ - ]

Absorbance [ - ]

Concentration simulation with an laser diode for different lines

P1 - 4991.26 cm-1

P2 - 4991.25 cm-1

P4 - 4945.10 cm-1

P4 - 4945.10 cm-1

P2 - 4991.23 cm-1



Fig. 4.22 Shows the simulation of the absorbance in function of the mole fraction of the combined

CO2 and H2O when the LED has been used as a light source. The filter around 4840-4949 is used to

narrow the LED line profile.

The figure shows that the absorbance increases almost linearly with the

concentration for the LED. The absorbance is much stronger than for the laser diode

simulation. This is since the absorbances from all lines within the LED region (or

filter) contribute and is much stronger than the single lines. If this region is free from

water lines, this could be a method to determine the concentration of CO2.

The biggest difficulties are to find appropriate lines for the CO2 concentration

measurements without interference of H2O lines. As the pressure increases, so does

the broadening of the spectral lines and the lines get more smeared out? From Eq.

(4.4) the absorbance is linear to the mole fraction of the investigated species, this

relation is hinted at a previous absorption concentrations simulations. With known

concentration the EGR can be estimated with help of Eq. (2.27) and (2.28).

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Concentration [ - ]

Absorbance [ - ]

Concentration simulation with an LED for the different measurement points

P1 - LED

P2 - LED

P3 - LED

P4 - LED

60 Chapter 5 – Conclusion and outlook


Chapter 5 – Conclusion and outlook

5.1 Conclusion

In this investigation high resolution spectra of a premixed laminar burner for a

lean and a rich flame at different locations above the burner are studied. With help of

these spectra a simulation code for generating emission was created. The different

approaches were studied in order to obtain information about the temperature or

concentration from a gas in an engine just before combustion, with the aim of finding

ways to be able to estimate the internal EGR by the CO2 concentration.

From the CHEMKIN simulation, six species were chosen to be studied since

they are assumed to be the main contributors of the combustion of CH4 and C8H18.

From the flame investigation, it is clear that the HITRAN and HITEMP database

provides with important spectroscopic data for the infrared region. It has shown to be

easy to use and a good tool to for simulating spectra in MATLAB, in terms of line

identification and simulation, provided that there is no absorption from the

surrounding.

Absorption from air is a huge factor when measuring emission, since it absorbs

at the regions of interest; the fundamental band of CO2 and the first combination

band of H2O. To simulate the intensity it is essential to know the temperature and the

mole fractions of the investigated species. This creates a problem since the two are

often not known. In this study, an initial estimation of the mole fraction from the

reaction formulas was made to give an initial estimation in the engine simulations.

Different methods have been studied to extract this information with either emission

or absorption methods.

Using the emission from two optically thick bands to obtain the temperature has

proved to be dependent on the optical thickness of the first combination band, which

proved to be optically thick at the central line of most lines, and optically thin in the

wings. From the emission plots it is seen that the combination band never really

reaches the continuum at the center of the lines, but is very close. Despite this it

seems to be acting almost like a blackbody for high pressures in the temperature

simulation, where the ratio of emission of the two bands was very closes the other

curve using emissivity equal to one at lower temperatures.

At higher temperatures and thus higher pressures, this deviation increases,

probably due to the fact that HITRAN is less accurate above 1000K and that the first

combination band is less optically thick, especially for the water lines. When

HITEMP was used for higher temperatures, the band ratio increased but not enough

to agree with the curve of two blackbody curves. This is probably due to missing

lines in the HITEMP database, which last was updated in 1995, or due to the first

combination band being optically thin. It was shown that the concentration affects the

optical depth of the bands. For the concentration simulation, the following

assumption has been made, that for every mole of CO2 there is 1.2 times more H2O

given from the reaction formula of C8H18. This assumption is not ideal, especially if

the relation does not agree with the reality. For this reason, it would be desirable to

get rid of the concentration dependence in the emission by using blackbody



measurements. Thus, with the knowledge of the concentration and temperature the

emissivity can be estimated and hence the emission.

Another method to investigate the temperature with absorbance, hence

transmittance, is to take the ratio of integrated absorbance from two lines. For the

same species this gives a relationship that is temperature dependent only. The line

used for this investigation was chosen from reference [36], which was aimed for

combustion of a flame in the range of 1000-2000K. If temperatures below this range

are considered, then lines with lower low energy states should be considered, since

they absorb at lower temperatures.

This method is attended to be used for the integrated absorbance instead of the

peak absorbance. The problem with integrated absorbance measurement is to find

lines that are easily distinguishable in the line profile, especially at higher pressures,

since the lines get broadened with increasing pressure. In the engine there is high

pressures, this method is then not optimal for the measurement points near the

combustion point. It might be possible to use this method for P4 and P3 since the

lines are less broadened, but in the same time, it was noticed that for the chosen lines

the intensity was weaker.

A simplified solution would be to consider the peak absorbance instead. With

the peak absorbance, the line profile at the center of the lines from the absorption

coefficient relation cannot be cancelled out. As the line profile changes with the

HWHM, even at the centerline, knowledge of the partial pressures due to the

Lorentzian broadening. However, in this investigation, Lorentzian is assumed to be

the same for both lines for simplification. Peak absorbances are easier to obtain

where there is rapid change in temperature and pressure as the engine goes thru its

cycle. It is not clear if it is possible to tune the laser fast enough to obtain the needed

information during one measurement at the given CAD position or to tune the laser

with every new cycle for obtaining the integrated intensity in sum of the cycles. The

integrated intensity would provide a better option, because no assumption is made,

and it is not dependent on the concentration to estimate the line profile as with the

peak absorbance. This is because the integrated line profile is normalized to be equal

to one for the whole line. In conclusion, this two line method works best for low

pressures and high temperature, something obtained in a flame but perhaps not in an

engine.

With the knowledge of the temperature, the concentration can be determined.

Using the Beer’s law for the peak transmission of two lines from the same species,

the concentration can be obtained. The line can’t be too weak in intensity, since it

gives less sensitivity, but it can’t be optically thick, since then the emission is only

dependent on the temperature. Two light sources were investigated, the LED and the

laser diode. The LED gave higher concentration sensitivity, since the absorbance for

each line within the LED line profile (or in this case; the filter) are added together.

Water lines might interfere here since these lines gets stronger with increasing

temperature and concentration. The chosen filters are used to narrow down the LED

region to a region with little interference of water lines. Even so, this is not a perfect

solution to minimize the interference from water. The downside is that the CO2 lines

are very weak in the second combination band region compared to the other stronger

combination bands. The CO2 is stronger around 5000 cm-1

but since the water

interference is too great in this region, the CO2 around 4881.8 cm-1

was chosen for

this study. The diode laser can be tuned into a region free of water lines; however, the

absorption changes very little with the concentrations since these lines are not great

62 Chapter 5 – Conclusion and outlook


absorbers. The diode laser is a suitable choice since it is simple to use, provides in-

situ measurement and an optimal choice of line the light source provides with an

interference free measurement due to the monochromatic characteristic. On the other

hand, the LED is a much cheaper choice and simple to use. In this study the LED was

very broadband and it is difficult to avoid interferences from other species like water.

Accordingly, with Beer’s law, the summed effect can be obtained and thus the

concentration from the contributors.

5.2 Outlook

In this initial investigation certain assumptions have been made. The scattering

effect is assumed to be negligible. In further investigation, the scattering effect

should be more closely investigated, especially if there are particles in the system.

Then the radiative transfer becomes dependent on the extinction from absorption and

scattering, see Eq. (2.6).

To determine the temperature from emission measurement, an estimation of the

concentration from the reaction formulas has been used for optically thin emission.

The optimal case would be to find another band that is optically thick like the

fundamental band of CO2. Then the ratio of emission can be expressed as a function

of temperature and wavenumber and not the concentration. For temperature

determination with the two-line method, a further investigation of lines fitting the

preferences of the combustion engine situation can be made. The lines chosen in this

investigation were optimal for low pressure and high temperature measurement. It

might be possible to obtain a line of CO2 or H2O that is well-defined for relatively

high pressure (but still not too wide to be undistinguishable from the neighboring

lines) and high temperature for integrating absorbance measurement. If the HWHM

is known for the line peak, absorbance’s can be used instead of the integrated

absorbances.

Instead of using CO2 concentration to estimate the EGR, the water lines in the

second combination band are a possible alternative for the diode laser simulation,

since it might give higher absorbance sensitivity for the concentration determinations

and is not as sensitive of CO2 interference since its dominant feature for higher

temperatures in the region.

Another assumption would be that if the temperature and the air-to-fuel ratio

are known, the EGR can be determined indirectly using (2.26) in which the

concentration is obtained from the reaction formula. Then the emission ratio can be

calculated as function of the EGR and compared with measurement. Another way

would to use the new concentration at certain assumption of EGR to fit the scanned

absorbance spectra of a diode laser with the simulated spectra.

For the emission measurement, air absorption can be avoided by using fibers

between the window of the engine chamber and the detector. For the engine

measurement, one might have to consider the radiative emission from the walls of the

combustion chamber and the spark plug. The emission from the heated walls and

spark plug might also be captured by the detector and be a source of error. If it is

large enough, compared to the spectral features of interest, it needs either to be

subtracted or accounted for in the simulation. If it’s small enough, it can be

neglected. The temperature of the walls in the engine should be much lower than the



actual gas inside the chamber. If that is the case then the wall should give rise to a

lower blackbody radiation curve contribution. However since this engine has two

opposite windows this effect can be assumed to be reliable. The spark plug has been

blocked in the line-of-sight measurement. Due to this these contributions have been

assumed in this initial study to be insignificant.

If the emission spectra could be obtained from a FTIR spectrometer, emission

simulations could be made to obtain a best fit of the simulated and measured spectra.

By study of these spectra, the information about the temperature and then the

concentration can be made. The next step would then be to use the emission ratio of

two single lines of the same species to obtain the concentration. As stated before the

emission depends linearly on the concentration for optically thin lines, hence the Eq.

(2.10) which simplifies to the Planck function times the optical depth.

Using a FTIR spectrometer might prove to be difficult if one want to obtain

high resolution spectra since it takes time of scanning the movable mirror if high

resolution is desired. This is a problem if you are to measure the intensity at a certain

CAD position since there is not time for the FTIR spectrometer to complete its

measurement as the engine is running.

With the upcoming new release of the HITEMP database, more precise and

extended simulations can be made for high temperature spectra. The next step could

be to create a program which can simulate the emission, the optical depth and hence

the transmission and absorbance with a simple click. This could be very useful for

students and researchers alike.

Experiments to test the possibility of determining the temperature and the

concentration from the simulations were not conducted in this work, but can be

considered for future investigations.

64 Acknowledgement


Acknowledgement

The author wishes to thank the division of Combustion Physics at Lund

University, Faculty of Engineering for giving me the opportunity to perform this

master thesis. I also would like to thank my two supervisors, Zhongshan Li and

Mattias Richter for taking their time to answer my questions. Also many thanks to

Sven-Göran Pettersson for his kind help.

Secondly I would like to thank my mother for always standing beside me and

encouraging me to go on. I would also like to thank my little Star for always cheering

me up when I most needed it.

Further I am very grateful to the division of Astronomy and Astrophysics for

letting us use their excellent FTIR spectrometer for the flame measurement, and for

the kind help from Hampus Nilsson and Henrik Hartman.

Finally many thanks to Dainis Dravins, Larry Rothman, Mark Linne, Bo Li,

Sun Zhiwei for helping me with my questions.



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66 Bibliography


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List of figures

Fig. 2.1 Illustrating the molecular energy structure, showing the electronic, vibrational

and rotational energy levels. The size of the energy difference between two

electronic states is around a few eV, two vibrational states a few 0.1 eV and

two rotational states a few 0.001 eV.

Fig. 2.2 Illustrating the three possible radiative processes for a two-level atom or molecule;

a) emission, b) absorption and c) stimulated emission.

Fig. 2.3 Shows comparison of three line profiles with the normalized intensity and the same

width.

Fig. 2.4 Illustration of the optical system for radiative transfer.

Fig. 2.5 Displaying the different zones in one dimensional premixed adiabatic flame along

with the concentrations and temperature profiles of the flame.

Fig. 2.6 Illustrating the four stroke engine cycle presented in the text.

Fig. 3.1 The experimental setup for the Fourier Transform Infrared Spectroscopy of the

flame.

Fig. 3.2 The premixed laminar burner with a flame stabilizer on top and a tube ventilation

system which carries most of the burned gases outdoors. The red spot is the laser

beam used for alignment into the spectrometer.

Fig. 3.3 Image showing the design of the slit used in the FTIR Spectrometer experiment

with a minimum aperture of 2 mm.

Fig. 3.4 The figure shows principle of the Michelson interferometer.

Fig. 3.5 The figure show the Fourier Transform Infrared Spectrometer used in the

experiment from the Atomic Astrophysics department in Lund University.

Fig. 3.6 The figure show layout of the spectrometer used in the experiment.

Fig. 3.7 A very simple illustration of the three possible measurements setup with the engine.

Image a) represents the absorption measurement using and diode laser and b) using

an LED with the same setup. Image c) represents the thermal emission

measurement.

Fig. 3.8 The figure shows the typical line profile at different temperatures for the LED

investigated.

Fig. 3.9 The figure illustrates the three filters transmittance profile. Figure a) displays an

transmittance curve around 3600-3800 cm-1

, b) an transmittance curve around

4840-4949 cm-1

and c) an transmittance curve around 2300-2450 cm-1

.

Fig. 3.10 The figure illustrates the engine considered for this project. A paper tube has been

placed between a collimator and the engine opening to minimize light interference

from the room. A filter has been placed in front of the detector to only detect light

at a certain wavelength band.

68 List of figures


Fig. 3.11 The figure shows the sensitivities of the different types of detector materials in

functions of wavelength.

Fig. 4.1 Shows the setup for the flame measurement.

Fig. 4.2 Illustrates the visible flame zone during measurements which the positions of the

measurements locations was derived from.

Fig. 4.3 Shows the measured spectra, fitted curve of the measured spectra and the

calculated blackbody spectra for T = 1473.15 K. The calculated Planck function

was corrected to fit the measured curve with an arbitrary value.

Fig. 4.4 Displaying the effect of the sensitivity drop-off from the detector on the blackbody

spectra from Fig. 4.3 (zoomed).

Fig 4.5 Shows the resulting response function from Eq. (4.1).

Fig. 4.6 Shows the comparison between the different measured locations of the flame

spectra with φ = 0.8 and φ = 1.6.

Fig. 4.7 Shows the comparison between the flame spectra for 1 mm and 3 mm below

the visible flame zone for φ = 0.8 and φ = 1.6

Fig. 4.8 Shows an example of a study of the investigated species locations for the

flame with φ = 1.6.

Fig. 4.9 Shows the two examples of features in comparison between the flame spectra

for 1 mm above the visible flame zone for φ = 0.8 and φ = 1.6. The upper

image shows the band head of the fundamental CO2 (to the right) and the CO2

absorption lines (to the left). The lower image shows part of the combination

band of H2O.

Fig. 4.10 Shows the two examples of features in comparison between the flame spectra

for 1 mm above the visible flame zone for φ = 0.8 and φ = 1.6. The upper

image shows the combination band of H2O in which some lines have been

absorbed. The lower image shows part of the combination band of H2O.

Fig. 4.11 Shows the temperature and measured pressure changes in the engine.

Fig. 4.12 Shows the comparison between spectra simulated for CO2 with air-fuel-ratio

of 1.2 and 1.6.

Fig. 4.13 Shows the optical depth a) and the corresponding emission simulations b) for

the fundamental band for the investigated points, P1-P4.


the combination band around 3700 cm-1



the combination band around 4900 cm-1


The Planck function is not visible in figure.

Fig. 4.16 Shows the temperature simulations for the four different points with pressures

as constant using HITRAN from table 5. Each plot displays also the band ratio

for a true blackbody radiation when the emissivity is equal to one.



Fig. 4.17 Shows the temperature simulations for point 1 (P = 35.05 Bar and T = 1008K)

using HITEMP. The first plot displays the temperature simulation. The second

and third plot shows the emissivity and the filter used for each band region,

the fundamental (band 1) and the first combination band (band 2). The filter

plot shows the filter for band 2.

Fig. 4.18 The upper image shows the simulation of the ratio of the peak absorbances for

two water lines at 3982.06 cm-1

and 3982.75 cm-1

as function of temperature.

The lower images show the two lines influences of temperature and

concentration.

Fig. 4.19 The upper image shows the simulation of the ratio of the peak absorbances for

two water lines at 3966.77 cm-1

and 3967.39 cm-1

as function of temperature.

The lower images show the two lines influences of temperature and

concentration. Image to the right has been runed with T = 528 K and the

image to the left with T = 1008 K.

Fig. 4.20 Shows the simulation of concentration of CO2 as function of temperature. The

assumption of for every mole CO2 there exists 1.2 times more H2O. Each

intensity of the band is multiplied with the filter transmission curve.

Fig. 4.21 Shows the simulation of the absorbance in function of the mole fraction of

CO2 when the laser diode has been used as a light source for a T = 528K.

Fig. 4.22 Shows the simulation of the absorbance in function of the mole fraction of the

combined CO2 and H2O when the LED has been used as a light source. The

filter around 4840-4949 is used to narrow the LED line profile.

70 List of tables


List of tables

Table 1 Illustrates the uncertainties of the HITRAN database.

Table 2 Contains the spectroscopic parameters and units used in HITRAN

2004 and 2008.

Table 3 The gas mixture of the flame with their respective gas flows.

Table 4 Illustrates the calculated mole fractions and temperatures for the

respective investigated species versus the flame coordinates using

CHEMKIN.

Table 5 Lists the possible measurements points for the engine experiment.

Table 6 Shows candidate H2O line pairs for measurements of temperature

and water concentration near 2.5 µm based on HITRAN database.

Table 7 Lists the possible measurements points for concentration

measurement using a laser diode at the same wavelength.



Appendix A: Code for flame investigation

A.1 CallProcessFTIRSpectraFunc

Example of code processing the measured spectra data in

MATLAB for one measurement point

function [plotWavenumber,measuredSpectra]= CallProcessFTIRSpectraFunc

% disp('. ')

% disp('. This program has been created by Susan Lindecrantz ')

% disp('. Contact: [email protected] ') % disp('. Master Thesis 2009/2010 ')

% disp('. ')

% Program: CallProcessFTIRSpectraFunc m

% last modified: 12-05-02

% 2009/2010 (c) Susan Lindecrantz, % Lund University - Faculty of Engineering

% About: % ---------------------------------------------------------------------

% Determines the ‘true’ spectra from the measurement. The function

% calculates and plot the Planck curve and use it to determine the % true spectra from the FTIR data measured by the spectrometer by

% eliminating the instrumental response function. The rows used in the files

% is already set below, cannot be set by values called with the func. %

% Note:

% This is an example for point at reaction zone, phi = 1.6 %

% Variables:

% --------------------------------------------------------------------- % measuredSpectra – measured spectra without the response of the setup

% RawDataFile – file containing the vector Data [ .DPT ] or [ .txt ]

% Data = [ plotWavenumber intensity ] – vector containing % plotWavenumber [ cm-1 ] measured wavenumber region from flame

% intensity [ a.u. ] measured intensity from flame

% Temp – temperature in [ K ] % FittedMesuredBBFile – file containing the fitted data from the vector BBData

% BBData = [ wavenumber BBintensity ] – vector containing

% BBintensity [ a.u. ] fitted measured blackbody intensity % wavenumber [cm-1] fitted measured blackbody wavenumber region

% FittedMesuredBBFile – file containing the fitted data from the vector BBData

% BBrowmax – maximum value of the row position for max wavenumber in % FittedMeasuredBBFile; set here to BBrowmax = 96 for fittedBB_expanded.txt

% BBrowmin – minimum value for the row position for min wavenumber in

% FittedMeasuredBBFile; set here to BBrowmax = 1 for fittedBB_expanded.txt % BBcolmax – maximum value of the col position for max wavenumber in

% FittedMeasuredBBFile; set here to BBrowmax = 2 for fittedBB_expanded.txt

% BBcolmin – minimum value for the col position for min wavenumber in % FittedMeasuredBBFile; set here to BBrowmax = 1 for fittedBB_expanded.txt

% MesuredBBFile – file containing the measured BB data, vector MBBData

% MBBData = [plotWavenumber measuredInt ] % rowmax – maximum value of the row position for max wavenumber in

% FittedMeasuredBBFile and RawDataFile; set here to

% rowmax = 398245 for the .DAT files from measurement (for the region) % rowmin – minimum value for the row position for min wavenumber in

% FittedMeasuredBBFile and RawDataFile; set here to

% rowmax = 99562 for the .DAT files from measurement (for the region) % colmax – maximum value of the col position for max wavenumber in

% FittedMeasuredBBFile and RawDataFile; set here to % rowmax = 2 for the .DAT files from measurement (for the region)

% colmin – minimum value for the col position for min wavenumber in

% FittedMeasuredBBFile and RawDataFile; set here to % rowmax = 1 for the .DAT files from measurement (for the region)

% PlanckCurve – calculated Planck curve for temperature Temp

% responseFTIR – the response functions curve % ---------------------------------------------------------------------

72 Appendix A: Code for flame investigation


Temp = 1475.15;

PlanckNormValue = 190;

% =/\= Uploading the measured BB curve into vector MBBData

% =/\= Enter filename, row and column positions of the investigated region of the BB data.

MRawDataBB = load('Burner09042812.DPT');

MBBData = MRawDataBB(99562:398245,1:2);

% = /\= Uploading the fitted measured BB curve into vector BBData

% =/\= Enter filename, row and column positions of the investigated region.

RawDataBB = load('fittedBB_expanded.txt');

BBData = RawDataBB(1:96,1:2);

% =/\= Setting the wavelength region into vector plotWavenumber plotWavenumber = MBBData(:,1);

% =/\= Interpolate the fitted measured BB curve so it covers the whole region of plotWavenumber.

BBintensity = interp1(BBData(:,1),BBData(:,2),plotWavenumber,'linear');

% =/\= Uploading the RawDataFile into vectors Data

% =/\= Enter filename, row and column positions of the investigated region. RawData = load('Burner0904282.DPT');

Data = RawData(99562:398245,1:2);

% =/\= Calculating Planck curve for temperature

fradiationconst = 1.191062e-12; % First Radiation Constant [W cm^2 /sr]

sradiationconst = 1.438786; % Second Radiation Constant [K cm]

PlanckCurve = Planck_func(plotWavenumber,Temp);

% =/\= Calculating the true ‘spectra’ curve, using equations (4.1) and (4.2) in report.

% =/\= Calculating the Response function – Eq. (4.1)

ResponseFTIR = (BBintensity./PlanckCurve);

% =/\= Calculates the the ‘true’ spectra curve without response curve

measuredSpectra = (Data(:,2)./ResponseFTIR);

function [LPlanck] = Planck_func(v,T)

% =/\= Constants fradiationconst = 1.191062e-12; % [W cm^2 /sr]

sradiationconst = 1.438786; % [K cm]

% =/\= The Calculation of Planck's function

dominator = fradiationconst*(v.^3); expvalues = (sradiationconst/T).*v;

nominator = exp(expvalues)-1;

LPlanck = dominator./nominator;

% end of Planck_func func

end

% end of CallProcessFTIRSpectra func

end



A.2 CallOpticalDepthFunc

Example of code for calling the function CallOpticalDepthFunc for calculating optical

depth in MATLAB

function [tauSpectra]=CallOpticalDepthFunc(v0, v, HWHM_L, SInt0, Temp, Elow, QTfunc,...

QTfunc_ref, ISOVALUE, ISONR, p, ps,opticallength)

% disp('. ')

% disp('. This program has been created by Susan Lindecrantz ') % disp('. Contact: [email protected] ')

% disp('. Master Thesis 2009/2010 ')

% disp('. ') %

% Program: CallOpticalDepthFunc m

% last modified: 12-05-02 % 2009/2010 (c) Susan Lindecrantz,

% Lund University - Faculty of Engineering

% % About:

% ---------------------------------------------------------------------

% Caculates the optical depth of the spectra called with the function. % The definition of optical thick gas is tau >> 1 and for optical thin gas, tau <= 1

% The function can only calculate the optical depth spectra for one species at the time.

% The data from the HITRAN file [.txt] must have been upoaded in previous code % before one calls this func.

%

% Variables: % ---------------------------------------------------------------------

% tauSpectra – the optical depth of the spectra

% v [ cm-1 ] – vector containing the region of the spectral range under investigation % v0 [ cm-1 ] – vectr containing the center wavenumber of the spectral lines with range of vector v

% Temp – temperature in [ K ]

% HWHM_L [ cm-1 ] – The Lorienztain half-with at half-maximum of the spectral line % Elow [ cm-1 ] – Lower energy level of the two level atom/molecule

% QTfunc [-] – The total partition function value for the molecule and isoptope for Temp % QTfunc_ref [-] – The total partition function value for the molecule and isoptope at

% reference temperature of 296K.

% ISOVALUE – The isotopic value for the molecule accordingly to HITRAN % ISONR – The isotopic number according the numbering system of HITRAN

% p [ atm ] – total pressure

% ps [ atm ] – partial pressure for the species investigated % opticalpath length [ cm ] – the optical path length estimated for gas column investigated.

% ---------------------------------------------------------------------

% Constants NL = 2.68676e19; % [ molecules cm^-3 atm^-1] Lochsmidths' number

% Definition of empty vectors tauSpectra = zeros(length(v),1);

count = 0;

% =/\= Calculating the absorption coefficient =/\=

% For Each Spectral Line the optical depth is calculated for the whole line for line = 1:length(v0)

% Get values of the partition functions and abundance QT = QTfunc(ISONR(line));

QTref = QTfunc_ref(ISONR(line));

% Transform the SInt (cm/molecules) to SInt (cm^-2 atm^-1) SInt = SInt0(line)*NL*(296/Temp);

% Obtaining the temperature corrected line intensity

% Unit (cm^-2 atm^-1) [ SIntT ] = SintensityTempConversion(SInt,Temp,Elow(line),...

QT,QTref,v0(line));

% Sets the Lorentzian Line profile [ line profile ] = Lorentzian( v0(line), v, HWHM_L(line) );

% Calculate the optical depth line for wavenumber(i)



tauspectraline = SIntT*line profile*opticallength*ps;

% Summing overlapping lines to the total optical depth of the spectra tauSpectra = tauSpectra + (tauspectraline)';

% Printing out calculation progress as its being runned!

steps = round(length(v0)*0.05);

if count == steps

percent = (line)/(length(v0))*100;

D = ['--> Processing Optical Depth... ',num2str(fix(percent)),'%']; disp(D)

count = 0;

else count = count +1;

% end if

end

% end for

end

function [ SIntT ] = SintensityTempConversion(SInt0,T,lowE,...

QT,QTref,v0)

% =/\= Constants =/\=

fradiationconst = 1.191062e-12; % [W cm^2 /sr]


% =/\= Calculating the Temp Conversion =/\= SIntT = SInt0*((297*QTref*exp(-sradiationconst*lowE/T)*...

(1-exp(-sradiationconst*v0/T)))/...

(T*QT*exp(-sradiationconst*lowE/296)*... (1-exp(-sradiationconst*v0/296))));

% end of SintensityTempConversion func

end

function [ line profile ] = Lorentzian( v0, v, HWHM )

% =/\= Determine the line profile =/\= line profile = (((1/pi)*HWHM)./(HWHM^2 + ((v-v0).^2) ));

% end of Lorentzian func

end

% end of optical depth function

end



A.3 CallEmissionFunc

Example of code calling the function CallEmissionFunc for emission simulation in MATLAB

function [plotWavenumber, emissionSpectra, emittanceSpectra, tauSpectra]=...

CallEmissionFunc(minWaveNr, maxWaveNr, resolution,Temp, p, ps,...

opticallength, hiType,RawDataFile, parasumFile, colmin, colmax, ISOVALUE)

% disp('. ')

% disp('. This simulation has been created by Susan Lindecrantz ') % disp('. Contact: [email protected] ')

% disp('. Master Thesis 2009/2010 ')

% disp('. ')

% Program: CallEmissionFunc m



% About:

% ---------------------------------------------------------------------

% Calculating the emission, the emittance and the optical depth spectra for the investigated region % and species. The emission here is not dependent on the gas to be either optical thick or thin.

% Assumes the medium is 'hot' (i.e. emission is strong) and No external light source + neglecting

% line-of-sight absorption and scattering. % Assuming homogenity, line-of-sight measurement.

% Note! Function uploadHITRAN needs to be edited for CH4 where uploads fails for the current.

% Variables: % ---------------------------------------------------------------------

% emissionSpectra – the result; simulated emission spectra for the investigated region

% emittanceSpectra – the result; the emittance spectra for the investigated region % tauSpectra – the result; optical depth spectra for the investigated region

% plotWavenumber [ cm-1 ] – the investigated region % maxWaveNr – maximum value of the investigated region

% minWaveNr – minimum value of the investigated region

% resolution – resolution of the investigated region % Temp – temperature in [ K ]

% wavenumber [ cm-1 ] – a vector containing the wavenumbers of the uploaded spectral lines

% wavenumbershift [ cm-1 ] – a vector containing the shifted wavenumbers due to air-broadening % ISOVALUE – A vector of all isotopic values for the molecule accordingly to HITRAN

% ISONR – A vector for the uploaded isotopic number according the numbering system of HITRAN for vector wavenumber

% S0Intensity [cm-2 atm-1] – vector of the uploaded line strengths at 296K. % AirHWHM [ cm-1] – vector of the uploaded air-broadening for each line at 296K

% SelfHWHM [ cm-1] - vector of the uploaded self-broadening for each line at 296K

% Elow [ cm-1] – vector of the uploaded lower energy state of the spectral lines. % nT – temperature dependent exponent of AirHWHM.

% deltaP – air-pressure induced shift.

% p [ atm ] – total pressure % ps [ atm ] – partial pressure for the species investigated, ps = x*p where x is the species mole fraction.

% opticalpath length [ cm ] – the optical path length estimated for gas column investigated.

% RawDataFile [ .txt ] – file containing the vector of data from HITRAN or HITEMP generated by JavaHAWK. % parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in HITRAN’s

% ‘parasum.dat’ file. This file needs to be downloaded and first row removed to be able to be processed.

% colmax – maximum value of the col position in parasumFile % colmin – minimum value for the col position in parasumFile

% hiTYPE - can obtain values ‘HITRAN’ or ‘HITEMP95’ depending

% on what kind of file is uploaded. New HITEMP2010 is in the same format as HITRAN. % Note! Sometimes HITEMP95 don’t work – something with g-values.

% Partialfunc_ref – Partition func values at 296K

% Partialfunc – Partition func values at Temp % ---------------------------------------------------------------------

% =/\= Setting the wavenumber region for the bands

plotWavenumber = minWaveNr:resolution:maxWaveNr;

if strcmp(hiType,'HITRAN')



% =/\= Uploading HITRAN data [ISONR,wavenumber,S0Intensity, AirHWHM,SelfHWHM,...

Elow, nT,deltaP] = uploadHITRAN (RawDataFile);

elseif strcmp(hiType,'HITEMP95')

% =/\= Uploading HITEMP data

[ISONR,wavenumber,S0Intensity, AirHWHM,SelfHWHM,...

Elow, nT,deltaP] = uploadHITEMPOld(RawDataFile);

else

disp('Wrong! Check your inputs.') end

% = /\= Loading partition func

parsumdat = load(parasumFile);

trow = Temp-69; % Temperature begins with 70 K in file. Partialfunc_ref = parsumdat(296-69, colmin:colmax);

Partialfunc = parsumdat(trow, colmin:colmax);

% =/\= Sets the Air Pressure induced Shifts

wavenumbershift = wavenumber + deltaP*p;

% =/\= Sets the Lorentzian HWHM HWHM_L = (((296/Temp)).^(nT)).*((AirHWHM.*(p-ps))+(SelfHWHM.*ps));

% -------- =/\= The simulation =/\= -------------------------------------

% =/\= Calculating the optical depth for the bands per species [tauSpectra]=CallOpticalDepthFunc(wavenumbershift, plotWavenumber, HWHM_L, S0Intensity, Temp,

Elow, Partialfunc,Partialfunc_ref, ISOVALUE, ISONR, p, ps,opticallength);

% .... =/\= The Calculation of the emittance and the emission spectra.

emittanceSpectra = (1 - exp(-tauSpectra)); emissionSpectra = emittanceSpectra '.Planck_func(plotWavenumber,Temp);

% Saving data disp('... saving! ')

disp(' ') save('OpticalDepthSimulation');

function [ISO,wavenumber,Sintensity,AirHWHM,SelfHWHM,lowerE,...

nT,deltaP,gUpper,glower] = uploadHITRAN( filename )

% -------- =/\= Upload data =/\= -------------------------------- fid = fopen(filename);

HITRANdata = textscan(fid,...

'%s %f %f %f %f %f %f %f %f %f %78c %f %f'); % '%s %f %f %f %f %f %f %f %f %f %79c %f %f'); % This is needed for some species like CH4

fclose(fid);

% -------- =/\= Upload data =/\= --------------------------------

ISO = HITRANdata1,2; wavenumber = HITRANdata1,3;

Sintensity = HITRANdata1,4;

% Acoeff = HITRANdata1,5; AirHWHM = HITRANdata1,6;

SelfHWHM = HITRANdata1,7;

lowerE = HITRANdata1,8; nT = HITRANdata1,9;

deltaP = HITRANdata1,10;

gUpper = HITRANdata1,12;



glower = HITRANdata1,13;

end

function [ISO,wavenumber,Sintensity,AirHWHM,SelfHWHM,lowerE,...

nT,deltaP] = uploadHITEMPOld( filename )

% -------- =/\= Upload data =/\= --------------------------------

mid = fopen(filename);

HITRANdata = textscan(mid,... '%s %u %f %f %f %f %f %f %f %f %48c');

fclose(mid);

% -------- =/\= Upload data =/\= --------------------------------

ISO = HITRANdata1,2; wavenumber = HITRANdata1,3;

Sintensity = HITRANdata1,4;

% Rcoeff = HITRANdata1,5; AirHWHM = HITRANdata1,6;

SelfHWHM = HITRANdata1,7;

lowerE = HITRANdata1,8; nT = HITRANdata1,9;

deltaP = HITRANdata1,10;

end


% .... =/\= Constants ..... fradiationconst = 1.191062e-12; % [W cm^2 /sr]


% .... =/\= The Calculation of Planck's function .....





end

% end CallEmissionFunc func end



A.4 FlameEmissionSimulations

Extraction of an example of the main code for simulating the flame emission in MATLAB

Extraction of the code:

% Program: FlameEmissionSimulations.m



% About:

% ---------------------------------------------------------------------

% Main program caling the function CallEmissionSpectra.m to calculating the % emission of each species under investigation for the investigated region.

% The emission is not dependent on the gas to be either optical thick or thin.

% For the flame experiment the partial pressures (species mole fractions) and % the temperature has been estimated by CHEMKIN simulation of the flame.

% Assumes the medium is 'hot' (i.e. emission is strong) and

% No external light source + neglecting line-of-sight absorption and no scattering % Assuming homogenity, line-of-sight measurement.

% % Variables:

% ---------------------------------------------------------------------

% emissionSpectra_species_point]_[flame – the result; simulated emission spectra for the investigated region % emittanceSpectra_species_point]_[flame – the result; the emittance spectra for the investigated region

% tauSpectra_species_point]_[flame – the result; optical depth spectra for the investigated region

% plotWavenumber_species_point]_[flame [ cm-1 ] – the investigated region % maxWaveNr – maximum value of the investigated region

% minWaveNr – minimum value of the investigated region

% resolution – resolution of the investigated region % Temp – temperature in [ K ]

% ISOVALUE_species – A vector of all isotopic values for the molecule accordingly to HITRAN % p [ atm ] – total pressure

% ps_species [ atm ] – partial pressure for the species investigated, ps = x*p where x is the species mole fraction.

% opticalpath length [ cm ] – the optical path length estimated for gas column investigated. % RawDataFile_species [ .txt ] – file containing the vector of data from HITRAN or HITEMP generated by JavaHAWK.

% parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in HITRAN’s

% ‘parasum.dat’ file. This file needs to be downloaded and first row removed to be able to be processed. % colmax_species – maximum value of the col position in parasumFile

% colmin_species – minimum value for the col position in parasumFile

% hiTYPE - can obtain values ‘HITRAN’ or ‘HITEMP95’ depending % on what kind of file is uploaded. New HITEMP2010 is in the same format as HITRAN.

% Note! Sometimes HITEMP95 don’t work – something with g-values.

% ---------------------------------------------------------------------

% Calling the CallEmissionSpectra.m for each measurement point, Species: CO2

% Reaction zone, phi = 1.6 [plotWavenumber, emissionSpectra_CO2_R_phi16, emittanceSpectra_CO2_R_phi16,

tauSpectra_CO2_R_phi16]=CallEmissionFunc(1500,6000, 0.02,1752,1, (1*0.03),7, 'HITEMP95',

'296_C02_hitemp1000k_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Reaction zone + 1mm, phi = 1.6

[plotWavenumber, emissionSpectra_CO2_Rp1_phi16, emittanceSpectra_CO2_Rp1_phi16, tauSpectra_CO2_Rp1_phi16]=CallEmissionFunc(1500, 6000, 0.02,1794,1, (1*0.0348),7,

'HITEMP95','296_C02_hitemp1000k_1500_6000_readable.txt', 'parsumData.txt', 8, 17, [0.9842 1.106e-2 3.947e-3 7.339e-4

4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

….

etc.



% Saving all data

save('Result_SimulatedSpectrasC02);

….

etc.

80 Appendix B: Code for engine investigation


Appendix B: Code for engine investigation

B.1 EngineOpticalDepthAndEmissionSimulations

Example of the main code for determining the optical depth and emission for the engine simulation data in MATLAB

% Program: EngineOpticalDepthAndEmissionSimulations.m



% About:

% --------------------------------------------------------------------- % Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to

% calculating the emission and the optical depth for the investigated region and the two extreme measurements

% points P1 and P4. Only two species is under investigation for the three considered band regions. %

% Variables:

% --------------------------------------------------------------------- %

% emissionSpectra_species_band)_[CADpoint – simulated emission spectra for given species

% at given band region and species, for the measurement point % emittanceSpectra_species_band_[CADpoint – simulated emittance spectra for given species

% at given band region and species, for the measurement point

% tauSpectra_species_band_[CADpoint – the optical depth of the spectra spectra for given % species at given band region and species, for the measurement point

% plotWavenumber_band [ cm-1 ] - investigated region for the given band region.

% RawDataFile_species [ .txt ] – file containing the line positions and the hitran data for each species generated by JavaHAWK.

% maxWaveNr_band – maximum value of the investigated region

% minWaveNr_band – minimum value of the investigated region % resolution – resolution of the investigated region

% Temp – temperature in [ K ]

% p [ atm ] – total pressure % ps_species_CADpoint [ atm ] – partial pressure for the species investigated, ps = x*p where x is the species

% mole fraction, for the measurement point

% opticalpath length [ cm ] – the optical path length estimated for gas column investigated. % parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in HITRAN's

% 'parasum.dat' file. This file needs to be downloaded and first row removed to be able to be processed.

% colmax_species – maximum value of the col position in parasumFile % colmin_species – minimum value for the col position in parasumFile

% ISOVALUE_species – A vector of all isotopic values for the molecule accordingly to HITRAN

% ---------------------------------------------------------------------

% Measuring Point P1: P = 35.05*0.98692 Atm, T = 1008 K

% Calling the CallEmissionSpectra.m for each measurement point, Species: CO2, X_CO2 = 0.1051

% Band 1 – Region: 2250 -2498 cm-1

[plotWavenumber_Band1, emissionSpectra_CO2_Band1_P1, emittanceSpectra_CO2_Band1_P1,

tauSpectra_CO2_Band1_P1]=CallEmissionFunc(2250,2498, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1051),8.1, 'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6

3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Band 2 – Region: 3450 -3915 cm-1

[plotWavenumber_Band2, emissionSpectra_CO2_Band2_P1, emittanceSpectra_CO2_Band2_P1, tauSpectra_CO2_Band2_P1]=CallEmissionFunc(3450,3915, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1051),8.1,

'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Band 3 – Region: 4840-5125 cm-1



3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Calling the CallEmissionSpectra.m for each measurement point, Species: H20, X_H20 = 0.1183



% Band 1 – Region: 2250 -2498 cm-1 [plotWavenumber_Band1, emissionSpectra_H20_Band1_P1, emittanceSpectra_H20_Band1_P1,

tauSpectra_H20_Band1_P1]=CallEmissionFunc(2250,2498, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1183),8.1, 'HITRAN',

'296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);



'296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7, [ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);

% Band 3 – Region: 4840-5125 cm-1

[plotWavenumber_Band3, emissionSpectra_H20_Band3_P1, emittanceSpectra_H20_Band3_P1,

tauSpectra_H20_Band3_P1]=CallEmissionFunc(4840,5125, 0.02,1008,(35.05*0.98692), (35.05*0.98692*0.1183),8.1, 'HITRAN','296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7

1.158e-7]);

% Measuring Point P4: P = 2.01*0.98692 Atm, T = 528K


% Band 1 – Region: 2250 -2498 cm-1 [plotWavenumber_Band1, emissionSpectra_CO2_Band1_P4, emittanceSpectra_CO2_Band1_P4,

tauSpectra_CO2_Band1_P4]=CallEmissionFunc(2250,2498, 0.02,528,(2.01*0.98692), (2.01*0.98692*0.1051),8.1,

'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Band 2 – Region: 3450 -3915 cm-1



3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Band 3 – Region: 4840-5125 cm-1

[plotWavenumber_Band3, emissionSpectra_CO2_Band3_P4, emittanceSpectra_CO2_Band3_P4, tauSpectra_CO2_Band3_P4]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692*0.1051),8.1,

'HITRAN','296_C02_hi04_1500_6000_readable.txt', 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6

3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Calling the CallEmissionSpectra.m for each measurement point, Species: H20, X_H20 = 0.1183



'296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);



'296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7, [ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);

% Band 3 – Region: 4840-5125 cm-1 [plotWavenumber_Band3, emissionSpectra_H20_Band3_P4, emittanceSpectra_H20_Band3_P4,

tauSpectra_H20_Band3_P4]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692*0.1183),8.1,

'HITRAN','296_H20_hitran09_1500_6000_readable.txt', 'parsumData.txt', 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);

% save all data

save('Result_EngineSimulationOpticalDepthVSEmission');



B.2 EngineTemperatureSimulations

Extraction of an example of the main code for calculating the temperature with emission

for the engine simulation data in MATLAB

% Program: EngineTemperatureSimulations.m



% About:

% ---------------------------------------------------------------------

% Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to % calculating the temperature from the ratio of emission bands for true blackbody emissitivity = 1and for

% emissitivity < 1. For this the emissitivity and hence the emission for the investigated region and the

% measurements is to determined and the blackbody curve. %

% The following band is considered; Band 1 at 2250 -2498 cm-1 and Band 2 at 3450 -3915 cm-1.

% All 4 measuring points in table (4.2) are caulcated; The concentration is assumed to be 10.51% C02 and % 11.83% H20 as given in the induction stagte by Eq. (2.24) for lambda = 1.2

%

% Variables: % ---------------------------------------------------------------------

%

% emissionBBRatio_CADPoint – the result, the band ratio vector as function of Temperature, % emissitivity = 1

% emissionHITRANRatio_CADPoint – the result, the band ratio vector as function of Temperature, emissitivity < 1

% opticalDepth_band - containing the summed optical depth for the different species for band region % emittance_band – calculated emittance using opticalDepth_bandfor each band region

% emission_band – the emission of the summed effect of the different species from emittance_band

% emissionSpectra_species_band)_[CADpoint – simulated emission spectra for given species at % given band region and species, for the measurement point

% emittanceSpectra_species_band_[CADpoint – simulated emittance spectra for given species at

% given band region and species, for the measurement point % tauSpectra_species_band_[CADpoint – the optical depth of the spectra spectra for given species at

% given band region and species, for the measurement point % plotWavenumber_band [ cm-1 ] - investigated region for the given band region.

% RawDataFile_species [ .txt ] – file containing the line positions and the hitran data for each species generated by

JavaHAWK. % maxWaveNr_band – maximum value of the investigated region

% minWaveNr_band – minimum value of the investigated region

% resolution – resolution of the investigated region % TempVector – vector containg the temperature range in [ K ]


% ps_species_[CADpoint [ atm ] – partial pressure for the species investigated, ps = x*p where is the species % mole fraction, for the measurement point


% parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in % HITRAN’s ‘parasum.dat’ file. This file needs to be downloaded and first row removed to be able to be processed.

% colmax_species – maximum value of the col position in parasumFile

% colmin_species – minimum value for the col position in parasumFile % ISOVALUE_species – A vector of all isotopic values for the molecule accordingly to HITRAN

% filterFile [.txt] – This file contains the filer data used for the simulation per band region.

% calibration_band - Response of the setup instruments for the band region, to be measured. Here set to 1; % ---------------------------------------------------------------------

% =/\= Setting the wavenumber region for the bands

plotWavenumber_B1 = maxWaveNr_B1:resolution: maxWaveNr_B1;

plotWavenumber_B2 = maxWaveNr_B2:resolution: maxWaveNr_B2;

% Simulation Temperature Determination for


% Comment; Calculating the emission and multipying with filter, then summing the

% intensity before dividing it between the two bands.

% For Each Temperature the Emission is…

for T = 1:length(TempVector)

% obtaining the Planck function for each band region



Planck_B1 = Planck_func(plotWavenumberB1,TempVector(T));

Planck_B2 = Planck_func(plotWavenumberB2,TempVector(T));

% Taking the filter into account Planckfilter_B1 = PlanckB1.* uploadFilter(plotWavenumber_B1,filterFile_B1);

Planckfilter_B2 = PlanckB2.* uploadFilter(plotWavenumber_B1,filterFile_B1);

% Calibration of the setup (including spectral response of setup) calibrationRatio = calibration_B2./calibration_B1;


% Band 1 – Region: 2250 -2498 cm-1


tauSpectra_CO2_Band1_P1]=CallEmissionFunc(2250,2498, 0.02, TempVector(T),(35.05*0.98692), (35.05*0.98692*0.1051),8.1, ‘HITRAN’,’296_C02_hi04_1500_6000_readable.txt’, ‘parsumData.txt’, 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-

6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Band 2 – Region: 3450 -3915 cm-1

[plotWavenumber_Band2, emissionSpectra_CO2_Band2_P1, emittanceSpectra_CO2_Band2_P1, tauSpectra_CO2_Band2_P1]=CallEmissionFunc(3450,3915, 0.02, TempVector(T),(35.05*0.98692), (35.05*0.98692*0.1051),8.1,

‘HITRAN’,’296_C02_hi04_1500_6000_readable.txt’, ‘parsumData.txt’, 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Calling the CallEmissionSpectra.m for each measurement point, Species: H20, X_H20 = 1.2*X_C02 = 0.1183


tauSpectra_H20_Band1_P1]=CallEmissionFunc(2250,2498, 0.02, TempVector(T),(35.05*0.98692), (35.05*0.98692*0.1183),8.1,

‘HITRAN’, ‘296_H20_hitran09_1500_6000_readable.txt’, ‘parsumData.txt’, 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);

% Band 2 – Region: 3450 -3915 cm-1


tauSpectra_H20_Band2_P1]=CallEmissionFunc(3450,3915, 0.02, TempVector(T),(35.05*0.98692), (35.05*0.98692*0.1183),8.1, ‘HITRAN’, ‘296_H20_hitran09_1500_6000_readable.txt’, ‘parsumData.txt’, 2, 7, [ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7

1.158e-7]);

% Summing the optical depth for the different species; water and CO2; and band regions

opticalDepth_B1 = tauSpectra_H20_Band1_P1 + tauSpectra_CO2_Band1_P1; opticalDepth _B2 = tauSpectra_H20_Band2_P1 + tauSpectra_CO2_Band2_P1;

% Calculating the emittance for the different species; water and CO2; and band regions

emittance_B1 = 1-exp(-opticalDepth_B1);


% .... =/\= The Calculation of the emittance spectra .....

% + taking the filter into account emission_B1 = (Planckfilter_B1.*emittance_B1');

emission_B2 = (Planckfilter_B2.*emittance_B2');

% Simulation result True BB: The ratio of the summed band intensities. emissionBBRatio(T) = calibrationRatio.* (sum(Planckfilter_B2)/sum(Planckfilter_B1));

% Simulation result emission with emissitivity less than 1: The ratio of the summed band intensities. emissionHITRANRatio(T) = calibrationRatio.* (sum(emission_B2)/sum(emission_B1));

% Printing out calculation progress if count == 5

percent = (T)/(length(tempertureVector))*100; D = ['--> Processing temperature ... ',num2str(fix(percent)),'%'];

disp(D)

count = 0; else

count = count +1;

end

end



% save all data Save(‘Result_EngineTemperatureSimulation_P1’);

…

etc

function [filter] = uploadFilter(plotWavenumber,filterFile)

% =/\= Loading filter data for given band region and interpolating data

% within the region to fit plotWavenumber

fid = fopen( filterFile); filterData = textscan(fid,'%f %f');

fclose(fid);

filterDataVector(:,1) = filterData 1,1; filterDataVector (:,2) = filterData 1,2;

filter = interp1(filterDataVector (:,1), filterDataVector (:,2),plotWavenumber,'cubic');

end


% .... =/\= Constants ..... fradiationconst = 1.191062e-12; % [W cm^2 /sr]


% .... =/\= The Calculation of Planck's function .....





end



B.3 EngineConcentrationSimulations

Extraction of an example of the main code for calculating the concentration with emission for the engine simulation data in MATLAB

% Program: EngineConcentrationSimulations.m

% last modified: 12-05-02

% 2009/2010 (c) Susan Lindecrantz, % Lund University - Faculty of Engineering

% About: % ---------------------------------------------------------------------

% Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to

% calculating the concentration from the ratio of emission bands for emissitivity < 1. % The temperature is KNOWN factor!

%

% The following band is considered; Band 2 at 3450 -3915 cm-1 cm-1 and Band 3 at 4840-5125 cm-1. % All 4 measuring points in table (4.2) are caulcated; The relation between water and C02 is assumed to be

% the same. times 9moels/8moles = 1.2 H20 on each mole fraction of C02.

% % Variables:

% ---------------------------------------------------------------------

% % emissionBBRatio_CADPoint – the result, the band ratio vector as function of Temperature, emissitivity = 1

% emissionHITRANRatio_CADPoint – the result, the band ratio vector as function of Temperature, emissitivity < 1

% opticalDepth_band - containing the summed optical depth for the different species for band region % emittance_band – calculated emittance using opticalDepth_bandfor each band region

% emission_band – the emission of the summed effect of the different species from emittance_band

% emissionSpectra_species_band)_[CADpoint – simulated emission spectra for given species at % given band region and species, for the measurement point

% emittanceSpectra_species_band_[CADpoint – simulated emittance spectra for given species at

% given band region and species, for the measurement point % tauSpectra_species_band_[CADpoint – the optical depth of the spectra spectra for given species at

% given band region and species, for the measurement point

% plotWavenumber_band [ cm-1 ] - investigated region for the given band region. % RawDataFile_species [ .txt ] – file containing the line positions and the hitran data for each species generated by

JavaHAWK. % maxWaveNr_band – maximum value of the investigated region

% minWaveNr_band – minimum value of the investigated region

% resolution – resolution of the investigated region % ConcVector – vector containg the mole fractions range for CO2 in [ K ]


% ps_species_[CADpoint [ atm ] – partial pressure for the species investigated, ps = x*p where x is the % species mole fraction, for the measurement point


% parasumFile [ .txt ]– file containing the partition function values as function of temperature, values given in HITRAN’s % ‘parasum.dat’ file. This file needs to be downloaded and first row removed to be able to be processed.

% colmax_species – maximum value of the col position in parasumFile

% colmin_species – minimum value for the col position in parasumFile % ISOVALUE_species – A vector of all isotopic values for the molecule accordingly to HITRAN

% filterFile [.txt] – This file contains the filer data used for the simulation per band region.

% calibration_band - Response of the setup instruments for the band region, to be measured. Here set to 1; % ---------------------------------------------------------------------

% Simulation Temperature Determination for


% Calculating the emission and multipying with filter, then summing the

% intensity before dividing it between the two bands. ConcVector = (0.1051:0.10:1)';

filterFile_B3 = 'filter[NB-2050-012 nm]CWL4881.txt';

filterFile_B2 = 'filter[NB-2690-050 nm]CWL3692.txt'; calibration_B3 = 1;

calibration_B2 = 1;

count = 0;

% Simulation Concentration Determination for


% Calculating the emission and multipying with filter, then summing the

% intensity before dividing it between the two bands.



% For Each Concentration Step the Emission is… for ConcNr = 1:length(ConcVector)

% Concentration in mole fraction of total, with (moleH20/moleC02) = 9/8 mole fractionC02 = ConcVector(ConcNr); mole fractionH20 = (9/8)*mole fractionC02;


% Band 2 – Region: 3450 -3915 cm-1 [~, emissionSpectra_CO2_Band2_P1, emittanceSpectra_CO2_Band2_P1,

tauSpectra_CO2_Band2_P1]=CallEmissionFunc(3450,3915,...

0.02,1008,(35.05*0.98692), (35.05*0.98692* mole fractionC02),8.1, 'HITRAN','296_C02_hi04_1500_6000_readable.txt', ... 'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Band 3 – Region: 4840-5125 cm-1

[~, emissionSpectra_CO2_Band3_P1, emittanceSpectra_CO2_Band3_P1,

tauSpectra_CO2_Band3_P1]=CallEmissionFunc(4840,5125,... 0.02,1008,(35.05*0.98692), (35.05*0.98692* mole fractionC02),8.1, 'HITRAN','296_C02_hi04_1500_6000_readable.txt', ...

'parsumData.txt', 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Calling the CallEmissionSpectra.m for each measurement point, Species: H20, X_H20 = 1.2*X_C02 = 0.1183

% Band 2 – Region: 3450 -3915 cm-1


tauSpectra_H20_Band2_P1]=CallEmissionFunc(3450,3915,... 0.02,1008,(35.05*0.98692), (35.05*0.98692* mole fractionH20),8.1, 'HITRAN', '296_H20_hitran09_1500_6000_readable.txt', ...

'parsumData.txt', 2, 7, [ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);

% Band 3 – Region: 4840-5125 cm-1

[plotWavenumber_Band3, emissionSpectra_H20_Band3_P1, emittanceSpectra_H20_Band3_P1, tauSpectra_H20_Band3_P1]=CallEmissionFunc(4840,5125,...

0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionH20),8.1, 'HITRAN','296_H20_hitran09_1500_6000_readable.txt',

'parsumData.txt', ... 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);

% Summing the optical depth for the different species; water and CO2; and band regions

opticalDepth_B3 = tauSpectra_H20_Band1_P1 + tauSpectra_CO2_Band1_P1;

opticalDepth_B2 = tauSpectra_H20_Band2_P1 + tauSpectra_CO2_Band2_P1;

% Calculating the emittance for the different species; water and CO2; and band regions emittance_B3 = 1-exp(-opticalDepth_B3);


% obtaining the Planck function for each band region Planck_B3 = Planck_func(plotWavenumber_Band1,ConcVector(ConcNr)); Planck_B2 = Planck_func(plotWavenumber_Band2,ConcVector(ConcNr));

% Taking the filter into account Planckfilter_B3 = Planck_B3.* uploadFilter(plotWavenumber_Band1,filterFile_B3);

Planckfilter_B2 = Planck_B2.* uploadFilter(plotWavenumber_Band2,filterFile_B2);

% Calibration of the setup (including spectral response of setup) calibrationRatio = calibration_B2./calibration_B3;

% .... =/\= The Calculation of the emittance spectra .....

% + taking the filter into account emission_B3 = emittance_B3.*Planckfilter_B3';

emission_B2 = emittance_B2.*Planckfilter_B2';

% Simulation result emission with emissitivity less than 1: The ratio of the summed band intensities.

emissionHITRANRatio(ConcNr) = calibrationRatio.* (sum(emission_B2)/sum(emission_B3));

% Printing out calculation progress if count == 2

percent = (ConcNr)/(length(ConcVector))*100;



D = ['--> Processing concentration ... ',num2str(fix(percent)),'%'];

disp(D)

count = 0; else

count = count +1;

end

end

% save all data

save('Result_EngineConcentrationSimulation_P1.mat');

% …

% etc



B.4 CallTwoLineMethodAbsorptionTemperatureSimulation.m Example of the code for calculating the temperature dependence of the ratio of absorpance from two chosen lines for the engine simulation data in MATLAB

function [ratioAbs] = CallTwoLineMethodAbsorptionTemperatureSimulationFunc (v0_L1, v0_L2,S0Line1,S0Line2,EuppLine1,

ElowLine1,EuppLine2, ElowLine2, QTfunc, QTfunc_ref, ISONR_L1, ISONR_L2, T)

% Program: CallTwoLineMethodAbsorptionTemperatureSimulation.m % last modified: 12-05-02

% 2009/2010 (c) Susan Lindecrantz,


% About:

% --------------------------------------------------------------------- % The function calculates the ratio between absorpbance for two lines accordingkly

% to Eq. (4.5) as functiuon of temperature.

% The absorpbance can be obtained from the measuring the transmission at wavelength v. % This is to be compared with the measured ratio of the two integrated absorbance

% to obtain the temperature.

% The partition functions values need to be uploaded a prior. %

% Variables:

% --------------------------------------------------------------------- % parasumFile = file from HITRAN called parasumData.txt

% minParasum = first column value in the liting of parasumData.txt for species

% maxParasum = last column value in the liting of parasumData.txt for species % Tmax = maximum temperature

% Tmin = minimum temperature

% Resolution = resolution of spectra % v0_L1 = wavenumber for line 1

% S0_L1 = line strengthfor line 1 at 296K

% Elow_L1 = lower energy state for line 1 % Eupp_L1 = upper energy state for line 1

% ISONR_L1 = isotopic number for line 1 % v0_L2 = wavenumber for line 2

% S0_L2 = line strengthfor line 2 at 296K

% Elow_L2 = lower energy state for line 2 % Eupp_L2 = upper energy state for line 2

% ISONR_L2 = isotopic number for line 2

% ratio = the ratio from Eq. (4.5) as function of Temperature % ---------------------------------------------------------------------

% =/\= Constants =/\=

fradiationconst = 1.191062e-12; % [W cm^2 /sr] sradiationconst = 1.438786; % [K cm]

NL = 2.68676e19; % [ molecules cm^-3 atm^-1] Lochsmidths' number

% For Each Spectral Line for temp = 1:length(T)

% Get values of the partition functions and abundance QT_L1 = QTfunc(temp,ISONR_L1);

QTref_L1 = QTfunc_ref(ISONR_L1); QT_L2 = QTfunc(temp,ISONR_L2);

QTref_L2 = QTfunc_ref(ISONR_L2);

% .... =/\= The Calculation of the temperature .....

% Transform the SInt (cm/molecules) to SInt (cm^-2 atm^-1) SInt0_L1 = S0Line1*NL*(296/T(temp));

SInt0_L2 = S0Line2*NL*(296/T(temp));

% Obtaining the temperature corrected line intensity

% Unit (cm^-2 atm^-1) [ SIntT_L1 ] = SintensityTempConversion(S0Line1,T(temp),Elow_L1,... QT_L1,QTref_L1,v0_L1);

[ SIntT_L2 ] = SintensityTempConversion(S0Line2,T(temp),Elow_L2,...

QT_L2,QTref_L2,v0_L2);



% Ratio of R(T) = S(T,v01)/S(T,v02) ratioAbs(temp) = SIntT_L2/SIntT_L1;

% Printing out calculation progress steps = round(length(T)*0.1);

if count == steps percent = (temp)/(length(T))*100;

D = ['--> Processing ... ',num2str(fix(percent)),'%'];

disp(D) count = 0;

else

count = count +1; end

end

end

% end CallTwoLineMethodAbsorptionTemperatureSimulationFunc

end



B.5 EngineConcentrationLEDSimulations

Extraction of an example of the main code for calculating the concentration with absorption with LED light source for the engine simulation data in MATLAB

% Program: EngineConcentrationLEDSimulations.m % last modified: 12-05-02

% 2009/2010 (c) Susan Lindecrantz,


% About:

% --------------------------------------------------------------------- % Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to

% calculating the transmittance in function of concentration from given wavenumber! Light Source: LED

% % The following band is considered; Band 3 at 4840-5125 cm-1.

% All 4 measuring points in table (4.2) are caulcated; The relation between water and C02 is assumed to be

% the same. H20 times 9/8 moles = 1.2 H20 on each mole fraction of C02.

…

etc

% For Each Concentration Step the Emission is…

for ConcNr = 1:length(ConcVector)

% Concentration in mole fraction of total, with (moleH20/moleC02) = 9/8 mole fractionC02 = concVector(ConcNr);

mole fractionH20 = (9/8)*mole fractionC02;

…

etc



% =/\= Calculating the emissivity for the bands per species

% Band 3 – Region: 4840-5125 cm-1 C02

[plotWavenumber_Band3, emissionSpectra_CO2_Band3_P4(n) , emittanceSpectra_CO2_Band3_P4(n) , tauSpectra_CO2_Band3_P4(n) ]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionC02),8.1,

‘HITRAN’,’296_C02_hi04_1500_6000_readable.txt’, ‘parsumData.txt’, 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-

6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Band 3 – Region: 4840-5125 cm-1 H20 [plotWavenumber_Band3, emissionSpectra_H20_Band3_P4(n) , emittanceSpectra_H20_Band3_P4(n) ,

tauSpectra_H20_Band3_P4(n) ]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionH20),8.1,

‘HITRAN’,’296_H20_hitran09_1500_6000_readable.txt’, ‘parsumData.txt’, 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7 1.158e-7]);

% =/\= Loading The LED BandWidth + Uploading the expanded LED profile

fid = fopen(LEDfile);

LEDdata = textscan(fid,'%f %f'); fclose(fid);

LEDvector(:,1) = LEDdata1,1;

LEDvector(:,2) = LEDdata1,2;

xi = plotWavenumber ;

yi = interp1(LEDvector(:,1),...

LEDvector(:,2),xi,'cubic');

LEDwavenumber = xi;

LEDprofile = yi;

% =/\= Calculating the transmission using Beer's law



% Calculaing Beers law - broadband version

upperBeerlaw=LEDprofile.*exp(-(tauSpectra_H20_Band3_P4(n)+ tauSpectra_CO2_Band3_P4 (n)) ;) lowerBeerlaw = LEDprofile;

transmittance(n)= sum(upperBeerlaw)/sum(lowerBeerlaw);

…

etc



B.6 EngineConcentrationDiodeLaserSimulations

Extraction of an example of the main code for calculating the concentration with

absorption and an Diode Laser source for the engine simulation data in MATLAB

% Program: EngineConcentrationDiodeLaserSimulations.m



% About:

% ---------------------------------------------------------------------

% Main program caling the function CallEmissionSpectra.m and indirectly CallOpticalDepthFunc m to % calculating the concentration from given wavenumber! Source: Diode Laser

%

% The following band is considered; Band 3 at 4840-5125 cm-1. % All 4 measuring points in table (4.2) are caulcated; The relation between water and C02 is assumed to be

% the same. times 9moels/8moles = 1.2 H20 on each mole fraction of C02.

…

etc

diodeWavenumber = 4884.0; % 2.045 um

…

etc

% =/\= Finding the diode-wavenumber's position in plotWavenumber diodeWavenumberNR = find(plotWavenumber == diodeWavenumber)

if isempty(diodeWavenumberNR) == true

disp('Error - diode wavenumber couldn´t be found');

else

diodeWavenumber = plotWavenumber(diodeWavenumberNR)

disp('Diode wavenumber found!');

…

etc

% For Each Concentration Step the Emission is… for ConcNr = 1:length(ConcVector)

% Concentration in mole fraction of total, with (moleH20/moleC02) = 9/8 mole fractionC02 = concVector(ConcNr); mole fractionH20 = (9/8)*mole fractionC02;

…

etc



% =/\= Calculating the emissivity for the bands per species

% Band 3 – Region: 4840-5125 cm-1 C02

[plotWavenumber_Band3, emissionSpectra_CO2_Band3_P4(n) , emittanceSpectra_CO2_Band3_P4(n) ,

tauSpectra_CO2_Band3_P4(n) ]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionC02),8.1, ‘HITRAN’,’296_C02_hi04_1500_6000_readable.txt’, ‘parsumData.txt’, 8, 17,[0.9842 1.106e-2 3.947e-3 7.339e-4 4.434e-5 8.246e-

6 3.957e-6 1.472e-6 4.446e-8 1.654e-8]);

% Band 3 – Region: 4840-5125 cm-1 H20



[plotWavenumber_Band3, emissionSpectra_H20_Band3_P4(n) , emittanceSpectra_H20_Band3_P4(n) ,

tauSpectra_H20_Band3_P4(n) ]=CallEmissionFunc(4840,5125, 0.02,528,(2.01*0.98692), (2.01*0.98692* mole fractionH20),8.1, ‘HITRAN’,’296_H20_hitran09_1500_6000_readable.txt’, ‘parsumData.txt’, 2, 7,[ 0.997317 1.999e-3 3.718e-4 3.107e-4 6.23e-7

1.158e-7]);

% =/\= Calculating the transmission using Beer's law

transmittance(n) = exp(-(tauSpectra_H20_Band3_P4(n,diodeWavenumberNR)+ tauSpectra_CO2_Band3_P4 (n,diodeWavenumberNR) ) );

…

etc

94 Appendix C: Comparison between measured and simulated spectra


Appendix C: Comparison between measured and simulated spectra

C.1 Comparison for 3 mm below the flame zone

C.2 Comparison for 1 mm below the flame zone

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-1

0

1

2

3

4

5

6x 10

-5

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

Comparison between measured and simulated spectra for phi = 0.8 at 3 mm below the visible flamezone

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-4

-2

0

2

4

6

8

10x 10

-5

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


measured spectra

simulated spectra

measured spectra

simulated spectra

CO

H2O

H2O

H2O

H2O

CO2

CO2

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-2

0

2

4

6

8x 10

-5

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


measured spectra

simulated spectra

simulated spectra

measured spectra

H2O

CO

CO

CO

CO2

CO2

H2O

H2O

H2O

H2O

CH4

H2O + CO

2



C.3 Comparison at the flame zone

C.4 Comparison for 1 mm above the flame zone

2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3 Comparison between measured and simulated spectra for phi = 1.6 at visible flamezone

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

2000 2500 3000 3500 4000 4500 5000 5500

0

5

10

15

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

Comparison between measured and simulated spectra for phi = 0.8 at visible flamezone

simulated spectra

measured spectra

simulated spectra

measured spectra

H2O + CO

2

H2O + CO

2

H2O + CO

2

H2O + CO

2

H2O

H2O CO

2

CO

CH4

CH4

CO2

CO2

CO

CO

2000 2500 3000 3500 4000 4500 5000 5500 6000

0

5

10

15

20

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

Comparison between measured and simulated spectra for phi = 0.8 at 1 mm above the visible flamezone

2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


simulated spectra

measured spectra

simulated spectra

measured spectra

H2O + CO

2

H2O + CO

2

H2O + CO

2

H2O + CO

2CO2

CO2

H2O

H2O

CO

CO

96 Appendix C: Comparison between measured and simulated spectra


C.5 Comparison for 3 mm above the flame zone

2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


simulated spectra

measured spectra

simulated spectra

measured spectraCO

2

CO2

H2O

H2O

H2O + CO

2

H2O + CO

2

H2O + CO

2

H2O + CO

2

CO

CO



Appendix D: Populärvetenskapling sammanfattning

This section contains the summary of the work in form of a scientific paper (Swedish:

Populärvetenskapling sammanfattning). It only includes the part concerning the flame

measurement.

98 Appendix D: Populärvetenskapling sammanfattning


Investigation of flame emission and absorption spectroscopy using the

HITRAN/HITEMP database and simulations for concentration and

temperature determination in combustion environments Susan Lindecrantz @ May 2010 Lund University, Faculty of Engineering (LTH)

Division of Combustion Physics

Sweden

The aim of this work was to investigate the spectral infrared radiation properties from a flame or gas flow theoretically with help

of HITRAN/HITEMP database and compare with experimental measurements. The main focus in this study was molecular

species such as CO2, H2O, CO and hydrocarbon fuels. The ambition was to be able to simulate or describe the detailed spectroscopy of the infrared emission and absorption of hot gases mixtures. Based on the simulations, valuable information like

temperature, species concentrations can be extracted from either emission or absorption spectroscopy. A high resolution FTIR

emission spectrum from laminar methane/air premixed flame has been recorded, which will be used as a validation of the developed code for hot gas emission simulation.

1 Introduction

In today’s society, combustion is a large part of

the everyday life; more than 90% of the energy used

in the world is related to combustion [1]. The

combustion of fossil fuels leads to environmental

problems, e.g. air pollutants and global warming,

requires a better understanding of the processes

taking place in combustion. Combustion also plays a

big role in many industrial devices like engines and

requires industries to think about efficiency and

environmentally friendly combustion to be able to

compete on an international market. Many different

non-intrusive optical techniques for spectroscopic

diagnostics have been developed for measurements

of species concentrations and temperatures.

Within the field of flame spectroscopic studies

the infrared regions are of high interest because

important fuels like methane and combustion

products like CO2, CO and H2O are detectable in the

infrared region. Detection of species, within the

infrared region, for concentration measurements can

give an opportunity to better understand the

processes in an engine or a flame.

In previous master’s projects [2] it has been

stated that spectroscopic diagnostic techniques, e.g.

LIF (Laser-Induced Fluorescence) and Rayleigh

scattering, are mostly conduced in the ultraviolet and

visible region, in which molecules undergo

electronic transitions and thus have broad and

structure less distribution. Therefore the UV and

visible regions are not always optimal for

spectroscopic diagnostics since these species do not

have accessible transitions in those regions. In the

field of engine measurements, these methods require

not only optical access for observation and also an

additional opening for introduction of excitation

signal to the combustion chamber.

However, in the infrared regions can appear

with strong rotational or vibrational transitions,

forming bands and band-heads. The spectra from a

flame or a combustion chamber may be recorded

with line-of-sight absorption or thermal emission

spectroscopy. The main difficulties with diagnostics

in this region are line overlapping and spectral

interference [2].

Combustion based engines will remain

indispensable for many years, despite efforts in

introducing new energy sources; and thus urgently

need to be improved with regard to fuel efficiency

and pollutant emission. One promising approach to

reduce pollution emission is to dilute the air with

recirculated gases from the preceding ignition cycle,

so called internal exhaust gas recirculation (EGR).

But, in order to control and optimize this

complicated process, new high-speed diagnostic

techniques are needed to determine the amount of

recirculated gas in the engine, especially near the

spark plug, during intake and compression cycle by

monitoring water vapor or carbon dioxide. If one

can, with line-of-sight measurements determine the

concentration of the carbon dioxide just before the

ignition; it can be used to estimate the amount of

internal EGR.

2 Investigation and modelling of infra-red spectra in a flat flame The spectra from the premixed laminar burner were

reordered with a Fourier transform infrared

spectrometer. Fig. 1 illustrates the setup of the flame

measurement.

Fig. 1: Experimental setup for the flame experiment for

measurement on a methane/air laminar premixed flame.



With help of a database containing molecular

parameters called HITRAN (T<1000K) and

HITEMP (T>1000K) a line-by-line radiation model

was created. With the assumption of no scattering

and homogeneous medium the radiative transfer is

simplified to Eq. (1). The solution of the question of

radiative transfer can then be obtained from Eq. (2)

used to calculate the absorption or emission.

vv

v

v SJd

dJ=+

τ (1)

[ ]vv eSeJlJ vvv

ττ −− −+= 1)0()( (2)

Assuming LTE the source function Sv is equal

to the Planck function Bv due to the Kirchhoff’s law.

The transmitted intensity at certain wavenumber,

Jv(l), be through a gas can be related to the incident

intensity, Jv(0), by the Beer-Lambert’s Law as stated

from the radiative transfer for the case of pure

absorption. This can be simulated using the

HITRAN or HITEMP database where the Beer’s law

given in Eq. (3) and the optical depth can be

calculated as Eq. (4).

veJ

lJ

v

v τ−=)0(

)( (3)

LfTSPxLk vvspeciesvv 0)( −==τ (4)

Here the kv [cm-1

] is the spectral absorption

coefficient, L is the optical path length of the

absorbing medium, xspecies is the mole fraction of the

absorbing species, P is the total pressure of the gas

mixture, S(T) is the line strength [cm-2

/atm] at the

temperature T [K] The line strengths are tabulated in

HITRAN with the unit [cm-1

/ molecules cm-2

] and

can be converted into [cm-2

/atm] in Eq. (5) at

reference point. Eq. (6) may then be used to correct

the line strength for the temperature. The line

strength has been transferred with help of Loschmidt

number at STP.

−−

−−

−

−=

)exp(1

)exp(1

)exp(

)exp(

)(

)()()(

2

2

2

2

refref

lower

lower

refref

ref

T

vc

T

vc

T

Ec

T

Ec

TQ

TQ

T

TTSTS

(5)

TcmmoleculescmSatmcmS

296102.68676)/()/( 19212 ⋅⋅⋅= −−−

(6) (2.15)

The fv-v0 [cm] is the normalized lineshape

function. Pressure changes and other perturbations

give rise to collision-broadened spectral lines. This

broadening is represented by the Lorentzian Eq. (6)

and has been used in these simulations. Although

different methods for giving approximations for the

Voigt line profile by Whitting [4] and another one is

given by Yuyan Liu [5], representing a combination

of Gaussian and Lorentzian, it was never verified.

The half-width-at-half-maximum has been calcul-

ated by Eq. (8).

22 )(

1

corrL

LL

vvf

−+=

γγ

π (7)

srefrefselfsrefrefair

n

ref

L pTpppTpT

TTp ),())(,(),( γγγ +−

= (8)

The p is the total pressure of the gas [atm],

temperature T [K] and partial pressure ps [atm] of

the gas. In this equation γair [cm-1

/atm] is the air-

broadened halfwidth at half maximum at Tref = 296

K and pref at 1 atm, γself [cm-1

/atm] is the self-

broadened halfwidth at half maximum and n is the

coefficient of temperature dependence of the air-

broadened halfwidth.

The spectra from the premixed flame was

recorded and processed to obtain the ‘true’ spectra

without the response function. The same setup was

used to measure a blackbody at temperature 1473.15

K.

Using the obtained response function the true

spectra for the premixed methane/air flame can be

determined. The resulting spectra for the two flames

are displayed in Fig. 2. The blackbody spectrum was

fitted to get rid of these absorption lines and then

expanded at lower wavenumbers since the

spectrometers sensitivity falls off in this area.

Fig. 3 shows this drop-off in which the sensi-

tivity seems to fall off rapidly around 1850 cm-1

.

This is consistent with the detector’s material

sensitivity curve for Insb which falls off drastically

after 5µm (2000 cm-1

).

Fig. 2: Shows the comparison between the different measured

locations of the flame spectra with φ = 0.8 and φ = 1.6.

2000 2500 3000 3500 4000 4500 5000 5500

0

1

2

3

4

5

6

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

Measured spectra from a flame with phi =0.8

2000 2500 3000 3500 4000 4500 5000 5500

0

2

4

6

8

10

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]







H2O + CO

2

H2O

H2O

CO

CO2

CO2

H2O + CO

2

H2O + CO

2

H2O + CO

2

CH4

CH4

CO

2000 2500 3000 3500 4000 4500 5000 5500

0

2

4

6

8

10

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


2000 2500 3000 3500 4000 4500 5000 5500

0

2

4

6

8

10

12

14

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]







CH4 H

2O + CO

2

H2O + CO

2CH

4

H2O + CO

2

H2O + CO

2

CO

CO

CO2

CO2

CO

H2O

CO

H2O



Fig. 3 shows some comparison between the

measured and the simulated spectra. The simulated

spectra have been simulated with the concentration

and temperature taken from the CHEMKIN

estimations for methane/air flame. There are notable

differences between the lean and the rich flame.

Fig. 3: Shows the comparison between the simulated spectra and

the measured spectra for the different locations above the flame

with φ = 0.8 and φ = 1.6.

The spectra for lean flame below the visible

flame zone shows less emission and contains more

static noise than the other spectra points for the same

flame. This apparent spectra noise could be

explained by the lower temperatures thus less

emission and the existence of fluid gas before the

reaction zone. For the spectra at the visible flame

zone the CO2 band becomes more apparent and there

is a CO band just becoming visible. The spectra

above the visible flame zone show very strong water

lines and CO2 band while the CO band no longer is

clearly visible in comparison, as shown in Fig. 3.

This is expected for the lean flame since according

to the CHEMKIN the CO is created near the visible

flame zone and then disappears afterwards as it is

transformed into CO2.

At the fundamental band of CO2 one can see

very strong absorption lines; this is the same for all

spectra.

There is a band structure from the CH4 that

has been identified around 3000 cm-1

. The CH4 band

seems to only exist at the visible flame zone for the

lean flame. There is no indication that this band exist

before the visible flame zone, possibly since the CH4

exists here as fluid gas and has not been heated

enough to produce emission bands. After the visible

flame zone this structure seems to have disappeared

again. Since in a lean flame there exists an excess of

oxygen, indicating that all fuel will have been

transferred into products after the visible flame zone.

The rich flame shows apparent emission

spectra for all measurements point except 3 mm

below the visible flame zone, indicating that the rich

flame is much hotter than the lean flame. It is also

possible that it has a much larger reaction zone or is

located earlier above the burner than the lean flame.

In the rich flame the CO bands emission are

very strong and stay strong even above the visible

flame zone, indicating that CO has survived into the

product zone. The CH4 band show a very clear band

structure for the lean flame at 1 mm below the

visible flame zone and shows a less clear band

structure at the visible flame zone in comparison,

indicating a decrease of the concentration of CH4.

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-1

0

1

2

3

4

5

6x 10

-5

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-4

-2

0

2

4

6

8

10x 10

-5

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


measured spectra

simulated spectra

measured spectra

simulated spectra

CO

H2O

H2O

H2O

H2O

CO2

CO2

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500-2

0

2

4

6

8x 10

-5

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


measured spectra

simulated spectra

simulated spectra

measured spectra

H2O

CO

CO

CO

CO2

CO2

H2O

H2O

H2O

H2O

CH4

H2O + CO

2

2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3 Comparison between measured and simulated spectra for phi = 1.6 at visible flamezone

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

2000 2500 3000 3500 4000 4500 5000 5500

0

5

10

15

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

Comparison between measured and simulated spectra for phi = 0.8 at visible flamezone

simulated spectra

measured spectra

simulated spectra

measured spectra

H2O + CO

2

H2O + CO

2

H2O + CO

2

H2O + CO

2

H2O

H2O CO

2

CO

CH4

CH4

CO2

CO2

CO

CO

2000 2500 3000 3500 4000 4500 5000 5500 6000

0

5

10

15

20

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


simulated spectra

measured spectra

simulated spectra

measured spectra

H2O + CO

2

H2O + CO

2

H2O + CO

2

H2O + CO

2CO2

CO2

H2O

H2O

CO

CO

2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


2000 2500 3000 3500 4000 4500 5000 5500

0

0.5

1

1.5

2

2.5

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


simulated spectra

measured spectra

simulated spectra

measured spectraCO

2

CO2

H2O

H2O

H2O + CO

2

H2O + CO

2

H2O + CO

2

H2O + CO

2

CO

CO



For the plots for 3 mm below the reaction zone

the two different flame spectra’s shows little

emission. Because of this the noise level of the

signal is very apparent and lays around 10-5

to 10-6

a.u. This noise level of the signal exists in all

spectra. The only difference is that it is more

prominent here due to the lower emission levels. For

the rich flame the CO band emerges around 2140

cm-1

from the cold flame structure, indicating that

CO is already formed here from the heat of the

reaction zone. Very little water lines are shown.

It can be noticed that in terms of line position

the simulated spectra fits overall well to the

measured, however the line strengths are sometimes

much bigger or smaller for the simulation for some

species and flame locations, see Fig. 4 for some

examples.

Uncertainties in the spectroscopic database

might be a source for the spectra’s fit not being

perfect. Uncertainty could be that the CHEMKIN

models a flame that is perfect laminar and adiabatic.

However in reality, the flame is not perfect adiabatic

since there will always be heat losses to the

environment. The burner has a stabilizer above the

flame which deviate the flame from perfect laminar.

This is especially true at the edges of the visible

flame zone, seen in Fig. 1. For example in the plot 1

mm above, for the rich flame, the CO band seem to

be missing in the simulation, while for the rich flame

this band is not seen in the measured nor the

simulated as expected. In the same plot the H2O

lines seem to be much bigger, however this could be

a result from partially absorption existing in the

band, see Fig. 4. The possible reason why some of

the lines seem to fit somewhat well and some are

partially or completely absorbed is because the

absorbing medium is cold and thus can only excite

certain populations in the molecules, the ground

state transitions. As given from the Boltzmann

distribution when the temperature increases higher

populations is occupied. This phenomenon is also

seen for the fundamental band of CO2.

Fig. 4: Shows the four examples of features in comparison

between the flame spectra for 1 mm above the visible flame zone

for φ = 0.8 and φ = 1.6. In the first upper image shows the combination band of H2O in which some lines have been

absorbed. The lower image shows part of the combination band of

H2O. The second upper image shows the band head of the fundamental CO2 (to the right) and the CO2 absorption lines (to

the left). The lower image shows part of the combination band of

H2O.

For the simulated spectra of 3 mm below the

visible flame zone in both flames shows very little

agreement with the simulated spectra. This is

because we do not have much emission in this

region and very low measured temperature and

concentrations in the simulations. For the plots in the

visible flame zone the CO seem to be

underestimated for both lean and rich flame. The

only plot that has visible CO band in the simulation

is the 1 mm below the visible flame zone for the rich

flame, and it is seem to be bigger than the measured

CO band. This is an indication that the either the

temperature or the concentration is not accurate with

the measurement for some species like CO.

The simulation was based upon the given

mole fractions and the temperature calculated from

the program CHEMKIN. It is clear from the

measurement and the simulated emission that some

lines should been more prominent but is in the

simulation too weak to be comparable with the CO2

band and water lines, especially true for higher

temperatures. A possibility is that the CHEMKIN

was provided with too low concentrations or

incorrect temperatures to give a perfect fit. Another

possibility is that since the simulations with over

1000K has been simulated with HITEMP95 lines

can be missing in the database for CO, CO2 and

H2O. Most of the H2O and the CO2 lines seem to be

weaker since there is absorption. It is difficult to

determine if it is a good fit or not, due to the large

amount of absorption in the fundamental band of the

CO2 and the combination band of H2O. The species

of N2 and O2 is too small in comparison with the

other features that they do not appear together with

the other species.

3 Conclusion and outlook In this investigation high resolution spectra

of a premixed laminar burner for a lean and a rich

flame at different locations above the burner are

studied. With help of these spectra a simulation code

3670 3672 3674 3676 3678 3680 3682 3684 3686 3688

0

2

4

6

8

10

12

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


3500 3505 3510 3515

0

5

10

15

x 10-4

Wavenumber [ cm-1 ]

Intensity [ a.u. ]

simulated spectra

measured spectra

simulated spectra

measured spectra


2380 2381 2382 2383 2384 2385 2386 2387 2388 2389

0

0.5

1

1.5

2

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


3475 3480 3485 34900

0.5

1

1.5

2

x 10-3

Wavenumber [ cm-1 ]

Intensity [ a.u. ]


simulated spectra

measured spectra

simulated spectra

measured spectra



for generating emission was created. The different

approaches were studied in order to obtain

information about the temperature or concentration

from a gas in an engine just before combustion, with

the aim of finding ways to be able to estimate the

internal EGR by the CO2 concentration.

From the CHEMKIN simulation, six species

were chosen to be studied since they are assumed to

be the main contributors of the combustion of CH4

and C8H18. From the flame investigation, it is clear

that the HITRAN and HITEMP database provides

with important spectroscopic data for the infrared

region. It has shown to be easy to use and a good

tool to for simulating spectra in MATLAB, in terms

of line identification and simulation, provided that

there is no absorption from the surrounding.

Absorption from air is a huge factor when

measuring emission, since it absorbs at the regions

of interest; the fundamental band of CO2 and the

first combination band of H2O. To simulate the

intensity it is essential to know the temperature and

the mole fractions of the investigated species. This

creates a problem since the two are often not known.

In this study, an initial estimation of the mole

fraction from the reaction formulas was made to

give an initial estimation in the engine simulations.

Different methods have been studied to extract this

information with either emission or absorption

methods.

In this initial investigation certain

assumptions have been made. The scattering effect

is assumed to be negligible. In further investigation,

the scattering effect should be more closely

investigated, especially if there are particles in the

system. Then the radiative transfer becomes

dependent on the extinction from absorption and

scattering, see Eq. (9).

For the emission measurement, air absorp-

tion can be avoided by using fibers between the

window of the engine chamber and the detector. For

the engine measurement, one might have to consider

the radiative emission from the walls of the

combustion chamber and the spark plug. The

emission from the heated walls and spark plug might

also be captured by the detector and be a source of

error. If it is large enough, compared to the spectral

features of interest, it needs either to be subtracted or

accounted for in the simulation. If it’s small enough,

it can be neglected. The temperature of the walls in

the engine should be much lower than the actual gas

inside the chamber. If that is the case then the wall

should give rise to a lower blackbody radiation

curve contribution. However since this engine has

two opposite windows this effect can be assumed to

be reliable. The spark plug has been blocked in the

line-of-sight measurement. Due to this these

contributions have been assumed in this initial study

to be insignificant.

If the emission spectra could be obtained

from a FTIR spectrometer, emission simulations

could be made to obtain a best fit of the simulated

and measured spectra. By study of these spectra, the

information about the temperature and then the

concentration can be made. The next step would

then be to use the emission ratio of two single lines

of the same species to obtain the concentration. As

stated before the emission depends linearly on the

concentration for optically thin lines, hence the Eq. Eq. (10) then simplifies to the Planck function times

the optical depth,

[ ] vvvv BeBlJ v ττ =−= −1)(

With the upcoming new release of the

HITEMP database, more precise and extended

simulations can be made for high temperature

spectra. The next step could be to create a program

which can simulate the emission, the optical depth

and hence the transmission and absorbance with a

simple click. This could be very useful for students

and researchers alike.

Experiments to test the possibility of deter-

mining the temperature and the concentration from

the simulations were not conducted in this work, but

can be considered for future investigations.

4 Reference [1]

Bood, J. (2009) Introduction to combustion, Lecture material

in Laser-based combustion diagnostics.

[2] Pettersson, A. (2004) Investigation of infrared chemiluminescence emission from laboratory flames, Master of Science

Thesis LTH, Division of Combustion, Lund University, p7.

[3] Zhou, X. et. al. (2005) Development

of a fast temperature sensor for combustion gases using a

single tunable diode laser, Appl. Phys. B 82, pp711-722.

[4] Witting, E. (1968) Quant. Spectrosc. Radiat. Transfer 8, p1379

[5] Liu, Y et. al. (2001) Simple empirical analytical approximati-

on to the Voight profile, Optical Society of America, pp711-722

[6] Farooq, A. et. al. (2008) In situ combustion measurements of

H2O and temperature near 2.5µm using tunable diode laser absorption, IOP publishing,, Meas Sci. Technol. 19, pp1-11

Investigation of flame emission and absorption ... · Master of Science Thesis by Susan Lindecrantz...

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