Research ArticleThe Effects of Air Preheating and FuelAir Inlet Diameter onthe Characteristics of Vortex Flame

Mostafa Khaleghi1 S E Hosseini1 M A Wahid1 and H A Mohammed2

1High-Speed Reacting Flow Laboratory Faculty of Mechanical Engineering Universiti Teknologi Malaysia (UTM)81310 Skudai Johor Malaysia2Department of Environmental Engineering College of Engineering Komar University of Science and Technology (KUST)King Mahmud Circle Sulaymaniyah Kurdistan Iraq

Correspondence should be addressed to Mostafa Khaleghi mostafa26 kyahoocom

Received 28 September 2014 Revised 8 April 2015 Accepted 26 April 2015

Academic Editor David Kubicka

Copyright copy 2015 Mostafa Khaleghi et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

The effects of fuelair inlet diameter as well as air preheating on the flame stability temperature distribution pollutant formationand combustion characteristics of a lab-scaled asymmetric vortex flame have been investigated A three-dimensional steady-statefinite volume solver has been used to solve the governing and energy equations The solver uses a first-order upwind scheme todiscretize the governing equations in the spaceThe semi-implicit method for pressure linked equations has been applied to couplethe pressure to the velocity terms Several turbulence models were applied to predict the flame temperature and it was found thatK-120576 RNG has given the best results in accordance with the experimental results The results reveal that the inlet air diameter canenhance the thermal properties and reduce the NO

119909emission while the inlet fuel diameter has less significant impact Increasing

diameters are accompanied with a pressure drop It was found that preheating the air and fuel would significantly affect the flametemperature and NO

119909emission with constant mass flow rate

1 Introduction

Emissions of nitrogen oxides (NO119909) are allied with a range of

environmental anxieties that include increasing ground levelozone acidification of aquatic systems forest damage andformation of fine particles in the atmosphere [1ndash3] Theseanxieties have resulted in a need to reduce emissions invarious combustion systems Vortex combustion has beenknown for its ability to improve flame stability and decreaseNO119909formation [4 5] Vortex combustion is widely employed

in furnaces and gas turbine combustors Due to the wideindustrial applications of vortex combustion there has beena considerable amount of research on such flames both pre-mixed and nonpremixedThe first discussion of vortex flameswas reported in 1998 byGabler [6]The turbulent vortex flamewas described for the first time in such work by both exper-imental and computational methods The major objective of

Gablerrsquos work was to identify the possible reduction in pollu-tant formation from vortex flames A concise description ofthe flame anatomy was presented and some of the basic fea-tures of vortex flames were reported These features includethe enhanced stability near the lean flammability limit of thefuel and some primary temperature profiling In previousstudies a description of the flame anatomy was presentedand some of the basic features of vortex flames were reportedThese features include the enhanced stability near the leanflammability limit of the fuel and some primary temperatureprofiling [7 8] Recent issues in the vortex combustion couldbe found in modern gas turbines which rely on premixedcombustion to reduce NO

119909emissions but are more sensitive

to resonant coupling leading to instability [9ndash11] Gas turbinecombustion dynamics have been considered in a series ofarticles edited by Lieuwen and Yang [12] Effect of the oxygenconcentration preheating pressure and equivalence ratio

Hindawi Publishing CorporationJournal of EnergyVolume 2015 Article ID 397219 10 pageshttpdxdoiorg1011552015397219

2 Journal of Energy

on the vortex flame characteristics of oxy-fuel flames at anatmospheric pressure showed that the percentage ofO

2in the

oxidizer plays a crucial role in the flame stabilization Flameswith lower O

2concentrations were seen to be more sensitive

to stoichiometry and preheating temperatures [13] Vortexinteractions play a key role in many practical combustionapplications by enhanced mixing organize the flame regionand improve the flame stabilization process [14] Around thelower stagnation point for partially premixed swirl flamewiththe lean blowout the flame root is inherently unstable nearlean blowout due to the presence of high strain rates featuringfrequent extinction and reigniting [15] The lack of a strongrecirculation zone and the shorter residence time withinthe low-swirl injector is a promising solution for attainingultralow emissions in gas turbines [16] Vortex flame is stabledby using cavity as flame holder which is essential for the betterperformance of the engine andmore efficiency of combustion[17 18] The interplay of a vortex pair with a premixedflame provides an important model for premixed turbulentcombustion Investigation of this behavior has proven that thevortex not only stretches and strains the flame but also scoursmaterial from the preheating region in front of the flame andat early times replaces it with inlet gases [19]

In the previous studies of vortex flows the role of the airfuel inlet as well as swirl number is underlined Conditionsgiving increase to the central recirculation zone (CRZ) havebeen surveyed by Beer [20] and Gupta and Lilley [21] whofound that this area is formed when the swirl number (119878

119899)

exceeds a certain threshold with a value of 119878119899ge 06 given

tentatively Choi et al [22] indicated that the CRZ resultedfrom a swirling flow instability that depends on the levelof swirl tube length end conditions and flow exothermi-city The precessing vortex core (PVC) rotates in the flowdirection and its frequency increases linearly with the flowvelocity but does not necessarily coincide with the flowrotation rate [23] The PVC modifies conditions of flameanchoring and under similar aerodynamic conditions flamestabilization is improved by effectively enhancing hot gasrecirculation [24 25] Saqr et al [26] analyzed a low-emissioncombustion process based on the vortex flame concept bycomputational and experimental investigations of a turbulentasymmetric vortex flame The three-dimensional reactingflow fields were described using a computational method-ology where the 119877120576119896-120576 turbulence model and the Eddy-dissipation combustionmodel were implementedThe resultshave shown uniform trend for modified 119896-120576 and standard 119896-120576and it is evident that the vortex flames for a nonpremixedcombustion exhibit the characteristics of premixed flames interms of color and temperature

The major motivation of the present study is to discoversome of the main characteristics of the reactive flow fieldof the asymmetric vortex flames such as effects of airfuelinlet diameter and preheating airfuel on the flame stabilitytemperature distribution and pollutant formationThe paperhas been motivated by two major concernsThe first concernis the recent growing global trends to reduce nitrogen emis-sion from the industrial and power generation sectors Thesecond concern is the absence of complete understanding ofthe aerodynamic stability mechanism of vortex flames Such

absence significantly impedes their practical utilization indifferent applications

2 The Asymmetric Vortex Combustor

Based on the schematic of the combustor presented inFigure 1 the vortex combustor was designed to enhance theaerodynamics of vortex flames and create a strong vortex fieldfor the flame stabilization This concept has two inlets for airand two inlets for fuel The allocation of each pair of air andfuel inlets was designed to allow the mixing between fuel andair to occur in the vicinity of a strong forced vortex field Suchvortex is created by the introduction of the air with a fulltangential velocity component to the asymmetric combustorThe fuel and air inlet nozzles were circular in cross sectionwith a diameter of 2mm and 5mm respectively The equiva-lence ratio was controlled by varying the inlet mass flow rateof air and fuel Methane has been utilized as a fuel Air andfuel flow rates were measured by columnar flowmeters andthe values were corrected to account for the inlet conditionsof both pressure and gas density Air was supplied at 2-barpressure from a compressor equipped with a damping tankFuel was supplied from a pressurized tank at 2 bars

3 Experimental Setup

The experimental stage was settled to allow direct photog-raphy from one plane and intrusive access of gas analyzerfor emission and temperature measurements A schematicof the experimental platform is shown in Figure 2 Air wasdelivered at 2 bars from a gush tank connected to a singlestage reciprocating compressor equipped with a pressuregauge and regulator Methane was supplied at 2 bars from apressurized cylinder Two columnar flowmeters with flow-regulating screw fromCole-Palmer were used to measure theflow rate of fuel and air Stretchy plastic plumbingwas appliedto connect the combustor chamber to the fuel-air supplysystem A Sony 300 FPS digital camera was installed perpen-dicular to the outlet plane of the combustor to execute directphotographs for the flame A TELEGAN Tempest-100 gasanalyzer with a stainless steel probe was used to measure theemissions and temperature inside the combustor To enablethe axial movement of the probe a traverse system was set

4 Mathematical Model

41 Governing Equations The three-dimensional steady-state Favre-averaged governing equations for mass momen-tum species transport and energy in Cartesian coordinatesare given as [27]

120597120588119895

120597119909119895

= 0

120597120588119894119895

120597119909119895

= minus

120597119875

120597119909119894

+

120597

120597119909119895

[(120583 + 120583119905) (

120597119894

120597119909119895

+

120597119895

120597119909119894

)]

Journal of Energy 3

400

Air AirFuel

Fuel

(a)

110 Air inlet

Air inlet

10

20 Fuelinlets

(b)

Figure 1 Schematic diagram of the asymmetric combustor (a) isometric view and (b) top view all dimensions are in mm

(1) Air compressor(2) Settling tank(3) Pressurized fuel tank(4) Air flowmeter(5) Fuel flowmeter(6) Asymmetric vortex combustor(7) Thermocouple

(8) TELEGAN gas analyzer probe(9) TELEGAN gas analyzer logger(10) DAQ(11) Traverse system(12) Sony 300 fps video camera(13) PC(14) Support structure

12

3

4

5

6

7

8

9

10

11

1213

14

F

F

middot middot middotmiddot middot middot

middot middot middotmiddot middot middot

Figure 2 Schematic of the experimental setup of the asymmetric vortex combustor

4 Journal of Energy

120597120588119894119899

120597119909119895

=

120597

120597119909119895

[(120588119863119899+

120583119905

119878119862119905

)(

120597119899

120597119909119895

)] + 119899

120597120588119895

120597119909119895

=

120597

120597119909119895

[120582

120597119879

120597119909119895

+

120583119905

Pr119905

120597ℎ

120597119909119895

+

119873

sum

119899=1

120588119863119899ℎ119899

120597119899

120597119909119895

]

minus

119873

sum

119899=1

ℎ119891

119899119899

(1)

where 120588 is the density 119906119894119895

is the velocity vector components119875 is the pressure 120582 is the thermal conductivity Pr

119905is the

turbulent Prandtl number119863119899is themass diffusivity of species

(119899) which was assumed to be constant for each species 119884119899is

the mass fraction of species (119899) 119899is the chemical reaction

rate 120583 is the dynamic viscosity and 120583119905is the turbulent

viscosity sim denotes the Favre averaging [28]

42 Numerical Procedures A three-dimensional (3D) finitevolume solver has been used to discretize the flow domainthrough a second-order upwind scheme Several tetrahedrongrids have been generated for ensuring that the solution isgrid independentThe SIMPLE algorithmhas been employedto achieve the mass conservation between the pressureand velocity terms in the discretized momentum equationChemical reaction has considered volumetric and Eddy-dissipation (ED) algorithm has been selected for turbulence-chemistry interactions The ED reaction model ignores che-mical kinetics (ie the Arrhenius rate) and uses only theparameters in reaction flow The operating pressure andtemperature were set to 101 bars and 300K respectively Thepartial-equilibrium model is utilized to predict the O radicalconcentration required for thermal NO

119909prediction In all the

simulations a steady-state pressure based solver was used tosolve the governing equations by CFD code ANSYS Fluent140 [29]

The solution is considered to be converged when theresiduals of each governing equation at consecutive iterationsbecame less than 1 times 10

minus3 except for energy equation andchemical reactions equation which are converged at quanti-ties less than 1 times 10

minus6 At such condition the flow field vari-ables reached stable local values with respect to any numberof iterations Also monitor for parameters of NO

119909and

temperature converged separately as well This convergencecriterion was applied on reacting flow cases The equivalenceratio air mass flow rate and fuel mass flow rate in all casesare constant and equal to 120593 = 097 00011 kgs and 645 times

10minus5 kgs respectively The dimensions of the computational

domain were similar to the full-scale actual dimensions ofthe asymmetric vortex combustor illustrated in Figure 3

43 Grid Testing and Model Validation

431 Grid Independence Test A grid independence test wasperformed to evaluate the effects of grid sizes on the results asshown in Figure 4 Four sets of meshes were generated usingtetrahedron elements with 211606 nodes 375534 nodes

Figure 3 Schematic diagram of the computational domain of asym-metric vortex chamber

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

1415488 nodes898306 nodes

375534 nodes 211606 nodes

Tem

pera

ture

(K)

Figure 4Grid independence test on the central temperature profile

898306 nodes and 1415488 nodes Laminar flowwith coun-terflow configuration was considered for the fueloxidizerinlets at this test where the inlet air and fuel temperaturewere set at 300K It was observed that the 375534 nodesand 898306 nodes produce almost identical results along thechamber with a percentage error of less than 2 Hence adomain with 375534 nodes was chosen to reduce the com-puting time

432 Code Validation Themodel validation was done basedon the geometry and boundary conditions which were usedby Wu et al [7] Air flows with a full tangential velocitycomponent to the asymmetric combustor (300K) and fuelflows coaxially with the center line (300K) The mass flowrate for the air inlet was set to 00011 kgs and the reacting casewas performed at equivalence ratios of 120593 = 0974 Six trialswere performed with different turbulencemodels to comparewith the experimental results As can be seen in Figure 5the central temperature profile is in good agreement with theexperimental results when 119896-120576 RNG was chosen as turbu-lence model The code was further validated by comparingthe other turbulence modelsrsquo results with the experimentalcorrelation developed by Saqr and Khaleghi [30 31] FromFigure 5 it can be seen that the temperature values fallbetween the accepted ranges for 119896-120576 turbulence model

Journal of Energy 5

Position (m)003 004 005 006 007 008 009 010 011

200

400

600

800

1000

1200

1400

1600

1800

Tem

pera

ture

(K)

K-120596K-120576 realizableReynolds-stressK-120576 RNG

Spalart-AllmarasK-120576 standardExperimental

Figure 5 Comparison of the present results of central temperatureprofile along the chamber with the experimental result

This figure clearly shows that Spalart-Allmaras could notestimate the vortex flame and also resulted in a fixed axis tem-perature of 300K It could be observed that 119896-120576 turbulencemodel deviates significantly from the experimental resultsTurbulence model of 119896-120596 except for region near the end ofchamber was not acceptable compared to the experimentalresults while the error of Reynolds-stress model is low It isnoticed that 119870-120576 realizable turbulence model had little errorand 119896-120576 RNG has good adjustment with the experimentalresults

5 NO119909

Formation Mechanisms

51 Thermal and Prompt NO119909 Oxygen and nitrogen in ext-

remely high temperature can react inside the combustionfurnace according to the following reactions which are calledZeldivich formulation [32]

O + N2

1198701

999445999468

119870minus1

NO +N (2)

N +O2

1198702

999445999468

119870minus2

NO +O (3)

N +OH1198703

999445999468

119870minus3

NO +H (4)

where11987011198702 and119870

3are forward rate constant and119870

minus1119870minus2

and 119870minus3

are the reverse rate constants according to Table 1[33] Thermal NO

119909formation is accelerated exponentially

according to formula (5) at temperatures more than 1500∘C[34 35]

119870119894= 119860119894119879119861119894 exp(

minus119862119894

119879

) (5)

Table 1 Thermal NO119909reaction rate constants [m3gmol s]

1198701

(18 times 108

) 119890minus38370119879

119870minus1

(38 times 107

) 119890minus425119879

1198702

(18 times 104

) 1198791198904680119879

119870minus2

(38 times 103

) 119879119890minus20820119879

1198703

(71 times 107

) 119890minus450119879

119870minus3

(17 times 108

) 119890minus24560119879

The rate of NO formation is achieved by formula (6) when thenitrogen radical (N) is assumed in steady-state conditions

119889 [NO]119889119905

=

1

1 + 119870minus1[NO] (119870

2[O2] + 1198703[OH]) + 2119870

1[O] [N

2]

times [minus

2119870minus1

1198702[O2] + 1198703[OH]

times (119870minus2[O] [NO])

+ 119870minus3[H] [NO]]

(6)

where 119879 is temperature (K) and the reaction constants 119860119894

119861119894 and 119862

119894were taken from Fernando et al [33] As there are

back-and-forth reactions it can be seen that when the rateof reaction decreases NO

119909formation declines because com-

bustion takes place in limited time in the furnace MoreoverNO119909constitution mitigates in low temperatures

Prompt NO119909formation mechanism was introduced by

Fenimore in 1971 Prompt or FenimoreNO119909formation occurs

in fuel rich conditions (equivalence ratio greater than 12)[36] The rate of prompt NO

119909constitution augments near

equivalence ratio of 14 [37]

52 N2O Intermediate NO Formation Malte and Pratt [38]

introduced N2O intermediate NO formation mechanism

which occurred in lean fuel moderate temperatures and lowpressure combustion conditions In these circumstances N

2O

is converted to NO via the following formulas [39]

N2+O +119872 larrrarr N

2O +119872 (7)

N2O +O larrrarr N

2+O2

(8)

N2O +O larrrarr NO +NO (9)

According to Bedat and Cheng the presence of H2O impuri-

ties conspicuously affects the N2O decomposition [40]

H2O +O larrrarr OH +OH (10)

N2O +OH larrrarr N

2+H2O (11)

In (7) 119872 is general third body N2O which was constituted

in (7) decomposes by (8) and (10) Equation (12) shows thechemical kinetics law for the rate of NO

119909formation via N

2O

intermediate mechanism119889 [NO]119889119905

= 1198701015840

5[N2O] [O] minus 119870

1015840

6[NO]2 (12)

6 Journal of Energy

00 01 02 03 04

Position (m)

200

400

600

800

1000

1200

1400

1600

1800

5mm6mm

7mm8mm

Tem

pera

ture

(K)

(a)

200e+03

190e+03

180e+03

170e+03

160e+03

150e+03

140e+03

130e+03

120e+03

110e+03

100e+03

900e+02

800e+02

700e+02

600e+02

500e+02

400e+02

300e+02

200e+02

100e+02

000e+00

5mm

6mm

7mm

8mm

(b)

Figure 6 Effect of variations of air diameter on central temperature (K) profile (a) line type and (b) contour type

The reaction rate constants are calculated by

1198701015840

119894= 1198700119879120573 exp(minus

119864119886

119877119879

) (13)

If 119889[N2O]119889119905 = 0 then (13) can be written as

[N2O]

=

[1198701015840

1[N2] [O] [119872] + 119870

1015840

4[N2] [O2] + 1198701015840

6[NO]2 + 119870

1015840

8[N2] [OH]]

1198701015840

2[119872] + (119870

1015840

3+ 1198701015840

5) [O] + 119870

1015840

7[H]

(14)

The concentration of radicals like O OH and H affects theconcentration rates and NO constitution [41] N

2O interme-

diate NO formation increases in low oxygen concentrationconditions [42]

53 Fuel-Bond NO119909Formation Mechanism Fuel-bond NO

119909

formation mechanism occurs when the molecular structuresof the fuel are constituted by nitrogen species In the com-bustion of these fuels the nitrogen atoms are decomposed tointermediate products form which can react with NO

119909[43]

6 Results and Discussion

61The Influence of Inlet Air Diameter on the Characteristics ofVortex Combustion The effect of inlet air diameter changingon the performance of vortex combustion is analyzed whilethe mass flow of fuel and air is kept constant Therefore theequivalence ratio was constant and equal to 0974 Figure 6(a)depicts the effect of inlet diameter changing on the statictemperature along the centerline with respect to the constantmass flow rate The temperature increases along the centralaxis due to the heat released by reactions For larger inletair diameter the temperature first sharply increases and thendecreases along the axial direction Figure 6(b) demonstratesthe temperature contours in two various surfaces There are

Position (m)000 005 010 015 020 025 030 035

40

60

80

100

120

140

5mm6mm

7mm8mm

NOx

(ppm

)

Figure 7 Effect of air diameter variation on the central NO119909profile

obvious differences in these contours From this figure itcan be interpreted that increasing in inlet air diameter withconstant mass flow rate (decreasing inlet velocity) leads toincrease in residence time The decrease of speed of vortexflame and diffusion of flame to the center of chamber are thetwo original reasons of these changes

The effect of diameter variation on the flame structureshowed that the NO

119909value on the centerline of the chamber

increased when the inlet air diameter increased as shownin Figure 7 It should be noted that the NO

119909concentration

increased with the increase of air inlet diameter due toincrease of the excess air and flame high temperature asshown in Figure 8 and Table 2 It is concluded that NO

119909for-

mation (Based on Zeldovich equations) is mainly controlledby temperature of combustion

Journal of Energy 7

Table 2 Average outlet quantity of chamber

Inlet air diameter Average NO119909outlet Average temperature

outlet5 72 4706 82 5007 95 5358 98 568

5mm

6mm

7mm

8mm

270e+02

257e+02

243e+02

230e+02

189e+02

176e+02

162e+02

140e+02

135e+02

122e+02

108e+02

945e+02

810e+01

675e+01

540e+01

405e+01

270e+01

135e+01

000e+00

(a)

(b)

(c)

(d)

Figure 8 NO119909emissions (ppm) contour for different air diameters

(a) 119889 = 5mm (b) 119889 = 6mm (c) 119889 = 7mm and (d) 119889 = 8mm

62 The Effect of Inlet Fuel Diameter on the Characteristics ofVortex Combustion Figure 9 illustrates the trend of NO

119909for-

mation and temperature distribution along with the chamberlength with respect to the various fuel diameters (2 25 3 35and 4mm) From this figure it can be construed that the sizeof the fuel inlet has insignificant effect on the NO

119909formation

and static temperature This shows that temperature flameas well as NO

119909emission in the chamber has more effect on

inlet air compared to inlet fuel in other words the inletfuel velocity has negligible contribution to vortex flamescompared to air inlet velocity

63 Preheating Air Effects Figure 10 shows temperature dis-tribution and NO

119909emissions formation when oxidizer is

applied in four different air temperatures (119879 = 300K 400K500K and 600K) while the diameter of the air and fuel inletthe mass flow rate of air and fuel inlet and equivalence ratioare kept constant at 5mm 2mm 00011 kgs 645 times 10minus5 kgsand 097 respectively All of the predictions are performedat the same central axis location with the above discussedconditions It was found that increasing the preheating airtemperature and decreasing the air viscosity could limit themaximum flame temperature and improve the temperature

Position (m)005 010 015 020 025 030 035

40

50

60

70

80

90

100

110

2mm25mm

3mm35mm

NOx

(ppm

)

(a)

Position (m)00 01 02 03 04

200

400

600

800

1200

1000

2mm25mm

3mm35mm

Tem

pera

ture

(K)

(b)

Figure 9 Effect of variations of fuel diameter on central (a) NO119909

profile and (b) temperature profile

uniformity in the furnace The data shows that with increas-ing preheating air at a constant mass flow rate the flamelocationmoves toward the air inlet because themomentumofthe air stream decreases Because the flame tends to approachthewall the temperature along the central axis decreases withincrease of air inlet temperature As a result the NO

119909emiss-

ion decreases when the flame temperature decreases

64 Preheating Fuel Effects Figures 11 and 12 show a min-imum effect of preheating fuel on the flame characteristicssuch as static temperature and NO

119909emissions The tempera-

ture and oxygen mole fraction of air kept constant and equalto 300K and 20 respectively It can be seen that the temper-ature along the central axis of the combustion chamber has nosignificant change with increasing of the fuel temperature In

8 Journal of Energy

Position (m)000 005 010 015 020 025 030 035

0

20

40

60

80

100

120

140

NOx

(ppm

)

300K400K

500K600K

(a)

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

Tem

pera

ture

(K)

300K400K

500K600K

(b)

Figure 10 Effect of preheating air on the central (a) NO119909profile and (b) temperature profile

Position (m)00 01 02 03 04

400

600

800

1000

1200

1400

300K350K

400K450K

Tem

pera

ture

(K)

Figure 11 The effect of preheating fuel on the central temperatureprofile

addition the results show that at all fuel temperatures thetemperature decreases along the combustion chamber dueto recession of flame and design of exhaust chamber Themaximum temperature is found in the vicinity of the bottomwall where the fuel enters the combustion chamber Theresults reveal that preheating inlet fuel has insignificant effecton the maximum flame temperature

Figure 12 shows that the NO119909emission rises as the max-

imum flame temperature increases With the increase ofthe fuel temperature at a fixed air flow rate there is a hightemperature mixing in the flame zone so there will be morethermal NO

119909products with the fuel and increases in the

temperatureThe increasedNO119909 caused by fuel preheating is

consistent with the hypothesis that preheating levels of 300K500K and 700K enhance fuel pyrolysis rates

Position (m)00 01 02 03 04

20

40

60

80

100

120

140

NOx

(ppm

)

300K350K

400K450K

Figure 12 The effect of preheating fuel on the central NO119909profile

7 Conclusions

A computational study on the performance of asymmetricvortex flame for various inlet flow diameters (air and fuel)and effect of preheating air and fuel was analyzedThe resultsshowed that increasing the inlet fuel diameter has negligibleeffect on the flame compared to effect of increasing inlet airto flame temperature and NO

119909emission The thermal field

results show that the effect of preheating can attain low-emission NO

119909as compared to fuel It is found that increasing

the preheated air temperature and fuel temperature coulddecrease the flame temperature and the combustion intensityandNO

119909emission when the airmass flow rate fuelmass flow

rate and equivalence ratio were considered constant for allsimulations Increasing the air velocity due to preheated air

Journal of Energy 9

in constant mass flow rate and equivalence ratio is found tobe an effective way to control the NO

119909emission because of

the decrease of the flame temperature

Nomenclature

119889 Chamber diameter (mm)

119863119899 Mass diffusivity (m2s)

119871 Length of chamber (mm)

119898 Air and fuel mass flow rate (kgs)119901 Pressure (pa)Pr119905 Prandtl number

Re Reynolds number (Re = 120588119906119889120583)119879 Temperature (K)119906119894119895 Velocity vector component (ms)

119884119899 Mass fraction of species 119899

Greek Symbols

120582 Thermal conductivity (W(msdotK))120583 Dynamic viscosity (kgmsdots)120583119905 Turbulent viscosity (kgmsdots)

120588 Density (kgm3)120593 Equivalence ratio119899 Chemical reaction rate

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] S EHosseiniMAWahid andAAAAbuelnuor ldquoHigh tem-perature air combustion sustainable technology to low NOxformationrdquo International Review ofMechanical Engineering vol6 no 5 pp 947ndash953 2012

[2] R K Srivastava R E Hall S Khan K Culligan and B WLani ldquoNitrogen oxides emission control options for coal-firedelectric utility boilersrdquo Journal of theAir andWasteManagementAssociation vol 55 no 9 pp 1367ndash1388 2005

[3] R K Srivastava W Neuffer D Grano S Khan J E Staudtand W Jozewicz ldquoControlling NO

119909emission from industrial

sourcesrdquo Environmental Progress vol 24 no 2 pp 181ndash1972005

[4] M Khaleghi S E Hosseini and M Abdul Wahid ldquoInvestiga-tions of asymmetric non-premixed meso-scale vortex combus-tionrdquo Applied Thermal Engineering vol 81 pp 140ndash153 2015

[5] D Feikema R H Chen and J F Driscoll ldquoEnhancement offlame blowout limits by the use of swirlrdquoCombustion and Flamevol 80 no 2 pp 183ndash195 1990

[6] H Gabler An Experimental and Numerical Investigation ofAsymmetrically-Fueled Whirl Flames Princeton University1998

[7] M-H Wu Y Wang V Yang and R A Yetter ldquoCombustionin meso-scale vortex chambersrdquo Proceedings of the CombustionInstitute vol 31 pp 3235ndash3242 2007

[8] M Khaleghi M A Wahid M M Seis and A Saat ldquoInves-tigation of vortex reacting flows in asymmetric Meso scale

combustorrdquoAppliedMechanics andMaterials vol 388 pp 246ndash250 2013

[9] K R McManus T Poinsot and S M Candel ldquoA review ofactive control of combustion instabilitiesrdquo Progress in Energyand Combustion Science vol 19 no 1 pp 1ndash29 1993

[10] S Candel ldquoCombustion dynamics and control progress andchallengesrdquo Proceedings of the Combustion Institute vol 29 no1 pp 1ndash28 2002

[11] Y Huang and V Yang ldquoDynamics and stability of lean-premixed swirl-stabilized combustionrdquo Progress in Energy andCombustion Science vol 35 no 4 pp 293ndash364 2009

[12] T C Lieuwen and V Yang Combustion Instabilities in GasTurbine Engines (Operational Experience Fundamental Mech-anisms and Modeling) Progress in Astronautics and Aeronau-tics American Institute of Aeronautics and Astronautics 2005

[13] B Kapadia and P Kutne ldquoCombustion behavior of swirl sta-bilised oxyfuel flames at elevated pressurerdquo in Proceedings of the9th AIAA Annual International Energy Conversion EngineeringConference (IECEC rsquo11) AIAA-5593 San Diego Calif USAJuly-August 2011

[14] P-H Renard DThevenin J C Rolon and S Candel ldquoDynam-ics of flamevortex interactionsrdquo Progress in Energy and Com-bustion Science vol 26 no 3 pp 225ndash282 2000

[15] M Stohr I Boxx C Carter and W Meier ldquoDynamics oflean blowout of a swirl-stabilized flame in a gas turbine modelcombustorrdquo Proceedings of the Combustion Institute vol 33 no2 pp 2953ndash2960 2011

[16] M R Johnson D Littlejohn W A Nazeer K O Smith andR K Cheng ldquoA comparison of the flowfields and emissions ofhigh-swirl injectors and low-swirl injectors for lean premixedgas turbinesrdquo Proceedings of the Combustion Institute vol 30pp 2867ndash2874 2005

[17] P K Ezhil Kumar and D P Mishra ldquoNumerical investigation ofthe flow and flame structure in an axisymmetric trapped vortexcombustorrdquo Fuel vol 102 pp 78ndash84 2012

[18] J Yuan and INaruse ldquoEffects of air dilution onhighly preheatedair combustion in a regenerative furnacerdquo Energy amp Fuels vol13 no 1 pp 99ndash104 1999

[19] J B Bell N J Brown M S Day M Frenklach J F Grcarand S R Tonse ldquoThe dependence of chemistry on the inletequivalence ratio in vortex-flame interactionsrdquo Proceedings ofthe Combustion Institute vol 28 no 2 pp 1933ndash1939 2000

[20] J Beer Combustion Aerodynumics Combustion TechnologySome Modern Developments 2012

[21] AKGupta andDG LilleyFlowfieldModeling andDiagnosticsTaylor amp Francis London UK 1985

[22] J J Choi Z Rusak and A K Kapila ldquoNumerical simulationof premixed chemical reactions with swirlrdquo CombustionTheoryand Modelling vol 11 no 6 pp 863ndash887 2007

[23] N Syred ldquoA review of oscillation mechanisms and the role ofthe precessing vortex core (PVC) in swirl combustion systemsrdquoProgress in Energy and Combustion Science vol 32 no 2 pp93ndash161 2006

[24] M Stohr I Boxx C D Carter and W Meier ldquoExperimentalstudy of vortex-flame interaction in a gas turbine modelcombustorrdquo Combustion and Flame vol 159 no 8 pp 2636ndash2649 2012

[25] M Stohr R Sadanandan and W Meier ldquoPhase-resolved char-acterization of vortex-flame interaction in a turbulent swirlflamerdquo Experiments in Fluids vol 51 no 4 pp 1153ndash1167 2011

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

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FuelsJournal of

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Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

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RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

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High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

2 Journal of Energy

on the vortex flame characteristics of oxy-fuel flames at anatmospheric pressure showed that the percentage ofO

2in the

oxidizer plays a crucial role in the flame stabilization Flameswith lower O

2concentrations were seen to be more sensitive

to stoichiometry and preheating temperatures [13] Vortexinteractions play a key role in many practical combustionapplications by enhanced mixing organize the flame regionand improve the flame stabilization process [14] Around thelower stagnation point for partially premixed swirl flamewiththe lean blowout the flame root is inherently unstable nearlean blowout due to the presence of high strain rates featuringfrequent extinction and reigniting [15] The lack of a strongrecirculation zone and the shorter residence time withinthe low-swirl injector is a promising solution for attainingultralow emissions in gas turbines [16] Vortex flame is stabledby using cavity as flame holder which is essential for the betterperformance of the engine andmore efficiency of combustion[17 18] The interplay of a vortex pair with a premixedflame provides an important model for premixed turbulentcombustion Investigation of this behavior has proven that thevortex not only stretches and strains the flame but also scoursmaterial from the preheating region in front of the flame andat early times replaces it with inlet gases [19]

In the previous studies of vortex flows the role of the airfuel inlet as well as swirl number is underlined Conditionsgiving increase to the central recirculation zone (CRZ) havebeen surveyed by Beer [20] and Gupta and Lilley [21] whofound that this area is formed when the swirl number (119878

119899)

exceeds a certain threshold with a value of 119878119899ge 06 given

tentatively Choi et al [22] indicated that the CRZ resultedfrom a swirling flow instability that depends on the levelof swirl tube length end conditions and flow exothermi-city The precessing vortex core (PVC) rotates in the flowdirection and its frequency increases linearly with the flowvelocity but does not necessarily coincide with the flowrotation rate [23] The PVC modifies conditions of flameanchoring and under similar aerodynamic conditions flamestabilization is improved by effectively enhancing hot gasrecirculation [24 25] Saqr et al [26] analyzed a low-emissioncombustion process based on the vortex flame concept bycomputational and experimental investigations of a turbulentasymmetric vortex flame The three-dimensional reactingflow fields were described using a computational method-ology where the 119877120576119896-120576 turbulence model and the Eddy-dissipation combustionmodel were implementedThe resultshave shown uniform trend for modified 119896-120576 and standard 119896-120576and it is evident that the vortex flames for a nonpremixedcombustion exhibit the characteristics of premixed flames interms of color and temperature

The major motivation of the present study is to discoversome of the main characteristics of the reactive flow fieldof the asymmetric vortex flames such as effects of airfuelinlet diameter and preheating airfuel on the flame stabilitytemperature distribution and pollutant formationThe paperhas been motivated by two major concernsThe first concernis the recent growing global trends to reduce nitrogen emis-sion from the industrial and power generation sectors Thesecond concern is the absence of complete understanding ofthe aerodynamic stability mechanism of vortex flames Such

absence significantly impedes their practical utilization indifferent applications

2 The Asymmetric Vortex Combustor

Based on the schematic of the combustor presented inFigure 1 the vortex combustor was designed to enhance theaerodynamics of vortex flames and create a strong vortex fieldfor the flame stabilization This concept has two inlets for airand two inlets for fuel The allocation of each pair of air andfuel inlets was designed to allow the mixing between fuel andair to occur in the vicinity of a strong forced vortex field Suchvortex is created by the introduction of the air with a fulltangential velocity component to the asymmetric combustorThe fuel and air inlet nozzles were circular in cross sectionwith a diameter of 2mm and 5mm respectively The equiva-lence ratio was controlled by varying the inlet mass flow rateof air and fuel Methane has been utilized as a fuel Air andfuel flow rates were measured by columnar flowmeters andthe values were corrected to account for the inlet conditionsof both pressure and gas density Air was supplied at 2-barpressure from a compressor equipped with a damping tankFuel was supplied from a pressurized tank at 2 bars

3 Experimental Setup

The experimental stage was settled to allow direct photog-raphy from one plane and intrusive access of gas analyzerfor emission and temperature measurements A schematicof the experimental platform is shown in Figure 2 Air wasdelivered at 2 bars from a gush tank connected to a singlestage reciprocating compressor equipped with a pressuregauge and regulator Methane was supplied at 2 bars from apressurized cylinder Two columnar flowmeters with flow-regulating screw fromCole-Palmer were used to measure theflow rate of fuel and air Stretchy plastic plumbingwas appliedto connect the combustor chamber to the fuel-air supplysystem A Sony 300 FPS digital camera was installed perpen-dicular to the outlet plane of the combustor to execute directphotographs for the flame A TELEGAN Tempest-100 gasanalyzer with a stainless steel probe was used to measure theemissions and temperature inside the combustor To enablethe axial movement of the probe a traverse system was set

4 Mathematical Model

41 Governing Equations The three-dimensional steady-state Favre-averaged governing equations for mass momen-tum species transport and energy in Cartesian coordinatesare given as [27]

120597120588119895

120597119909119895

= 0

120597120588119894119895

120597119909119895

= minus

120597119875

120597119909119894

+

120597

120597119909119895

[(120583 + 120583119905) (

120597119894

120597119909119895

+

120597119895

120597119909119894

)]

Journal of Energy 3

400

Air AirFuel

Fuel

(a)

110 Air inlet

Air inlet

10

20 Fuelinlets

(b)

Figure 1 Schematic diagram of the asymmetric combustor (a) isometric view and (b) top view all dimensions are in mm

(1) Air compressor(2) Settling tank(3) Pressurized fuel tank(4) Air flowmeter(5) Fuel flowmeter(6) Asymmetric vortex combustor(7) Thermocouple

(8) TELEGAN gas analyzer probe(9) TELEGAN gas analyzer logger(10) DAQ(11) Traverse system(12) Sony 300 fps video camera(13) PC(14) Support structure

12

3

4

5

6

7

8

9

10

11

1213

14

F

F

middot middot middotmiddot middot middot

middot middot middotmiddot middot middot

Figure 2 Schematic of the experimental setup of the asymmetric vortex combustor

4 Journal of Energy

120597120588119894119899

120597119909119895

=

120597

120597119909119895

[(120588119863119899+

120583119905

119878119862119905

)(

120597119899

120597119909119895

)] + 119899

120597120588119895

120597119909119895

=

120597

120597119909119895

[120582

120597119879

120597119909119895

+

120583119905

Pr119905

120597ℎ

120597119909119895

+

119873

sum

119899=1

120588119863119899ℎ119899

120597119899

120597119909119895

]

minus

119873

sum

119899=1

ℎ119891

119899119899

(1)

where 120588 is the density 119906119894119895

is the velocity vector components119875 is the pressure 120582 is the thermal conductivity Pr

119905is the

turbulent Prandtl number119863119899is themass diffusivity of species

(119899) which was assumed to be constant for each species 119884119899is

the mass fraction of species (119899) 119899is the chemical reaction

rate 120583 is the dynamic viscosity and 120583119905is the turbulent

viscosity sim denotes the Favre averaging [28]

42 Numerical Procedures A three-dimensional (3D) finitevolume solver has been used to discretize the flow domainthrough a second-order upwind scheme Several tetrahedrongrids have been generated for ensuring that the solution isgrid independentThe SIMPLE algorithmhas been employedto achieve the mass conservation between the pressureand velocity terms in the discretized momentum equationChemical reaction has considered volumetric and Eddy-dissipation (ED) algorithm has been selected for turbulence-chemistry interactions The ED reaction model ignores che-mical kinetics (ie the Arrhenius rate) and uses only theparameters in reaction flow The operating pressure andtemperature were set to 101 bars and 300K respectively Thepartial-equilibrium model is utilized to predict the O radicalconcentration required for thermal NO

119909prediction In all the

simulations a steady-state pressure based solver was used tosolve the governing equations by CFD code ANSYS Fluent140 [29]

The solution is considered to be converged when theresiduals of each governing equation at consecutive iterationsbecame less than 1 times 10

minus3 except for energy equation andchemical reactions equation which are converged at quanti-ties less than 1 times 10

minus6 At such condition the flow field vari-ables reached stable local values with respect to any numberof iterations Also monitor for parameters of NO

119909and

temperature converged separately as well This convergencecriterion was applied on reacting flow cases The equivalenceratio air mass flow rate and fuel mass flow rate in all casesare constant and equal to 120593 = 097 00011 kgs and 645 times

10minus5 kgs respectively The dimensions of the computational

domain were similar to the full-scale actual dimensions ofthe asymmetric vortex combustor illustrated in Figure 3

43 Grid Testing and Model Validation

431 Grid Independence Test A grid independence test wasperformed to evaluate the effects of grid sizes on the results asshown in Figure 4 Four sets of meshes were generated usingtetrahedron elements with 211606 nodes 375534 nodes

Figure 3 Schematic diagram of the computational domain of asym-metric vortex chamber

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

1415488 nodes898306 nodes

375534 nodes 211606 nodes

Tem

pera

ture

(K)

Figure 4Grid independence test on the central temperature profile

898306 nodes and 1415488 nodes Laminar flowwith coun-terflow configuration was considered for the fueloxidizerinlets at this test where the inlet air and fuel temperaturewere set at 300K It was observed that the 375534 nodesand 898306 nodes produce almost identical results along thechamber with a percentage error of less than 2 Hence adomain with 375534 nodes was chosen to reduce the com-puting time

432 Code Validation Themodel validation was done basedon the geometry and boundary conditions which were usedby Wu et al [7] Air flows with a full tangential velocitycomponent to the asymmetric combustor (300K) and fuelflows coaxially with the center line (300K) The mass flowrate for the air inlet was set to 00011 kgs and the reacting casewas performed at equivalence ratios of 120593 = 0974 Six trialswere performed with different turbulencemodels to comparewith the experimental results As can be seen in Figure 5the central temperature profile is in good agreement with theexperimental results when 119896-120576 RNG was chosen as turbu-lence model The code was further validated by comparingthe other turbulence modelsrsquo results with the experimentalcorrelation developed by Saqr and Khaleghi [30 31] FromFigure 5 it can be seen that the temperature values fallbetween the accepted ranges for 119896-120576 turbulence model

Journal of Energy 5

Position (m)003 004 005 006 007 008 009 010 011

200

400

600

800

1000

1200

1400

1600

1800

Tem

pera

ture

(K)

K-120596K-120576 realizableReynolds-stressK-120576 RNG

Spalart-AllmarasK-120576 standardExperimental

Figure 5 Comparison of the present results of central temperatureprofile along the chamber with the experimental result

This figure clearly shows that Spalart-Allmaras could notestimate the vortex flame and also resulted in a fixed axis tem-perature of 300K It could be observed that 119896-120576 turbulencemodel deviates significantly from the experimental resultsTurbulence model of 119896-120596 except for region near the end ofchamber was not acceptable compared to the experimentalresults while the error of Reynolds-stress model is low It isnoticed that 119870-120576 realizable turbulence model had little errorand 119896-120576 RNG has good adjustment with the experimentalresults

5 NO119909

Formation Mechanisms

51 Thermal and Prompt NO119909 Oxygen and nitrogen in ext-

remely high temperature can react inside the combustionfurnace according to the following reactions which are calledZeldivich formulation [32]

O + N2

1198701

999445999468

119870minus1

NO +N (2)

N +O2

1198702

999445999468

119870minus2

NO +O (3)

N +OH1198703

999445999468

119870minus3

NO +H (4)

where11987011198702 and119870

3are forward rate constant and119870

minus1119870minus2

and 119870minus3

are the reverse rate constants according to Table 1[33] Thermal NO

119909formation is accelerated exponentially

according to formula (5) at temperatures more than 1500∘C[34 35]

119870119894= 119860119894119879119861119894 exp(

minus119862119894

119879

) (5)

Table 1 Thermal NO119909reaction rate constants [m3gmol s]

1198701

(18 times 108

) 119890minus38370119879

119870minus1

(38 times 107

) 119890minus425119879

1198702

(18 times 104

) 1198791198904680119879

119870minus2

(38 times 103

) 119879119890minus20820119879

1198703

(71 times 107

) 119890minus450119879

119870minus3

(17 times 108

) 119890minus24560119879

The rate of NO formation is achieved by formula (6) when thenitrogen radical (N) is assumed in steady-state conditions

119889 [NO]119889119905

=

1

1 + 119870minus1[NO] (119870

2[O2] + 1198703[OH]) + 2119870

1[O] [N

2]

times [minus

2119870minus1

1198702[O2] + 1198703[OH]

times (119870minus2[O] [NO])

+ 119870minus3[H] [NO]]

(6)

where 119879 is temperature (K) and the reaction constants 119860119894

119861119894 and 119862

119894were taken from Fernando et al [33] As there are

back-and-forth reactions it can be seen that when the rateof reaction decreases NO

119909formation declines because com-

bustion takes place in limited time in the furnace MoreoverNO119909constitution mitigates in low temperatures

Prompt NO119909formation mechanism was introduced by

Fenimore in 1971 Prompt or FenimoreNO119909formation occurs

in fuel rich conditions (equivalence ratio greater than 12)[36] The rate of prompt NO

119909constitution augments near

equivalence ratio of 14 [37]

52 N2O Intermediate NO Formation Malte and Pratt [38]

introduced N2O intermediate NO formation mechanism

which occurred in lean fuel moderate temperatures and lowpressure combustion conditions In these circumstances N

2O

is converted to NO via the following formulas [39]

N2+O +119872 larrrarr N

2O +119872 (7)

N2O +O larrrarr N

2+O2

(8)

N2O +O larrrarr NO +NO (9)

According to Bedat and Cheng the presence of H2O impuri-

ties conspicuously affects the N2O decomposition [40]

H2O +O larrrarr OH +OH (10)

N2O +OH larrrarr N

2+H2O (11)

In (7) 119872 is general third body N2O which was constituted

in (7) decomposes by (8) and (10) Equation (12) shows thechemical kinetics law for the rate of NO

119909formation via N

2O

intermediate mechanism119889 [NO]119889119905

= 1198701015840

5[N2O] [O] minus 119870

1015840

6[NO]2 (12)

6 Journal of Energy

00 01 02 03 04

Position (m)

200

400

600

800

1000

1200

1400

1600

1800

5mm6mm

7mm8mm

Tem

pera

ture

(K)

(a)

200e+03

190e+03

180e+03

170e+03

160e+03

150e+03

140e+03

130e+03

120e+03

110e+03

100e+03

900e+02

800e+02

700e+02

600e+02

500e+02

400e+02

300e+02

200e+02

100e+02

000e+00

5mm

6mm

7mm

8mm

(b)

Figure 6 Effect of variations of air diameter on central temperature (K) profile (a) line type and (b) contour type

The reaction rate constants are calculated by

1198701015840

119894= 1198700119879120573 exp(minus

119864119886

119877119879

) (13)

If 119889[N2O]119889119905 = 0 then (13) can be written as

[N2O]

=

[1198701015840

1[N2] [O] [119872] + 119870

1015840

4[N2] [O2] + 1198701015840

6[NO]2 + 119870

1015840

8[N2] [OH]]

1198701015840

2[119872] + (119870

1015840

3+ 1198701015840

5) [O] + 119870

1015840

7[H]

(14)

The concentration of radicals like O OH and H affects theconcentration rates and NO constitution [41] N

2O interme-

diate NO formation increases in low oxygen concentrationconditions [42]

53 Fuel-Bond NO119909Formation Mechanism Fuel-bond NO

119909

formation mechanism occurs when the molecular structuresof the fuel are constituted by nitrogen species In the com-bustion of these fuels the nitrogen atoms are decomposed tointermediate products form which can react with NO

119909[43]

6 Results and Discussion

61The Influence of Inlet Air Diameter on the Characteristics ofVortex Combustion The effect of inlet air diameter changingon the performance of vortex combustion is analyzed whilethe mass flow of fuel and air is kept constant Therefore theequivalence ratio was constant and equal to 0974 Figure 6(a)depicts the effect of inlet diameter changing on the statictemperature along the centerline with respect to the constantmass flow rate The temperature increases along the centralaxis due to the heat released by reactions For larger inletair diameter the temperature first sharply increases and thendecreases along the axial direction Figure 6(b) demonstratesthe temperature contours in two various surfaces There are

Position (m)000 005 010 015 020 025 030 035

40

60

80

100

120

140

5mm6mm

7mm8mm

NOx

(ppm

)

Figure 7 Effect of air diameter variation on the central NO119909profile

obvious differences in these contours From this figure itcan be interpreted that increasing in inlet air diameter withconstant mass flow rate (decreasing inlet velocity) leads toincrease in residence time The decrease of speed of vortexflame and diffusion of flame to the center of chamber are thetwo original reasons of these changes

The effect of diameter variation on the flame structureshowed that the NO

119909value on the centerline of the chamber

increased when the inlet air diameter increased as shownin Figure 7 It should be noted that the NO

119909concentration

increased with the increase of air inlet diameter due toincrease of the excess air and flame high temperature asshown in Figure 8 and Table 2 It is concluded that NO

119909for-

mation (Based on Zeldovich equations) is mainly controlledby temperature of combustion

Journal of Energy 7

Table 2 Average outlet quantity of chamber

Inlet air diameter Average NO119909outlet Average temperature

outlet5 72 4706 82 5007 95 5358 98 568

5mm

6mm

7mm

8mm

270e+02

257e+02

243e+02

230e+02

189e+02

176e+02

162e+02

140e+02

135e+02

122e+02

108e+02

945e+02

810e+01

675e+01

540e+01

405e+01

270e+01

135e+01

000e+00

(a)

(b)

(c)

(d)

Figure 8 NO119909emissions (ppm) contour for different air diameters

(a) 119889 = 5mm (b) 119889 = 6mm (c) 119889 = 7mm and (d) 119889 = 8mm

62 The Effect of Inlet Fuel Diameter on the Characteristics ofVortex Combustion Figure 9 illustrates the trend of NO

119909for-

mation and temperature distribution along with the chamberlength with respect to the various fuel diameters (2 25 3 35and 4mm) From this figure it can be construed that the sizeof the fuel inlet has insignificant effect on the NO

119909formation

and static temperature This shows that temperature flameas well as NO

119909emission in the chamber has more effect on

inlet air compared to inlet fuel in other words the inletfuel velocity has negligible contribution to vortex flamescompared to air inlet velocity

63 Preheating Air Effects Figure 10 shows temperature dis-tribution and NO

119909emissions formation when oxidizer is

applied in four different air temperatures (119879 = 300K 400K500K and 600K) while the diameter of the air and fuel inletthe mass flow rate of air and fuel inlet and equivalence ratioare kept constant at 5mm 2mm 00011 kgs 645 times 10minus5 kgsand 097 respectively All of the predictions are performedat the same central axis location with the above discussedconditions It was found that increasing the preheating airtemperature and decreasing the air viscosity could limit themaximum flame temperature and improve the temperature

Position (m)005 010 015 020 025 030 035

40

50

60

70

80

90

100

110

2mm25mm

3mm35mm

NOx

(ppm

)

(a)

Position (m)00 01 02 03 04

200

400

600

800

1200

1000

2mm25mm

3mm35mm

Tem

pera

ture

(K)

(b)

Figure 9 Effect of variations of fuel diameter on central (a) NO119909

profile and (b) temperature profile

uniformity in the furnace The data shows that with increas-ing preheating air at a constant mass flow rate the flamelocationmoves toward the air inlet because themomentumofthe air stream decreases Because the flame tends to approachthewall the temperature along the central axis decreases withincrease of air inlet temperature As a result the NO

119909emiss-

ion decreases when the flame temperature decreases

64 Preheating Fuel Effects Figures 11 and 12 show a min-imum effect of preheating fuel on the flame characteristicssuch as static temperature and NO

119909emissions The tempera-

ture and oxygen mole fraction of air kept constant and equalto 300K and 20 respectively It can be seen that the temper-ature along the central axis of the combustion chamber has nosignificant change with increasing of the fuel temperature In

8 Journal of Energy

Position (m)000 005 010 015 020 025 030 035

0

20

40

60

80

100

120

140

NOx

(ppm

)

300K400K

500K600K

(a)

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

Tem

pera

ture

(K)

300K400K

500K600K

(b)

Figure 10 Effect of preheating air on the central (a) NO119909profile and (b) temperature profile

Position (m)00 01 02 03 04

400

600

800

1000

1200

1400

300K350K

400K450K

Tem

pera

ture

(K)

Figure 11 The effect of preheating fuel on the central temperatureprofile

addition the results show that at all fuel temperatures thetemperature decreases along the combustion chamber dueto recession of flame and design of exhaust chamber Themaximum temperature is found in the vicinity of the bottomwall where the fuel enters the combustion chamber Theresults reveal that preheating inlet fuel has insignificant effecton the maximum flame temperature

Figure 12 shows that the NO119909emission rises as the max-

imum flame temperature increases With the increase ofthe fuel temperature at a fixed air flow rate there is a hightemperature mixing in the flame zone so there will be morethermal NO

119909products with the fuel and increases in the

temperatureThe increasedNO119909 caused by fuel preheating is

consistent with the hypothesis that preheating levels of 300K500K and 700K enhance fuel pyrolysis rates

Position (m)00 01 02 03 04

20

40

60

80

100

120

140

NOx

(ppm

)

300K350K

400K450K

Figure 12 The effect of preheating fuel on the central NO119909profile

7 Conclusions

A computational study on the performance of asymmetricvortex flame for various inlet flow diameters (air and fuel)and effect of preheating air and fuel was analyzedThe resultsshowed that increasing the inlet fuel diameter has negligibleeffect on the flame compared to effect of increasing inlet airto flame temperature and NO

119909emission The thermal field

results show that the effect of preheating can attain low-emission NO

119909as compared to fuel It is found that increasing

the preheated air temperature and fuel temperature coulddecrease the flame temperature and the combustion intensityandNO

119909emission when the airmass flow rate fuelmass flow

rate and equivalence ratio were considered constant for allsimulations Increasing the air velocity due to preheated air

Journal of Energy 9

in constant mass flow rate and equivalence ratio is found tobe an effective way to control the NO

119909emission because of

the decrease of the flame temperature

Nomenclature

119889 Chamber diameter (mm)

119863119899 Mass diffusivity (m2s)

119871 Length of chamber (mm)

119898 Air and fuel mass flow rate (kgs)119901 Pressure (pa)Pr119905 Prandtl number

Re Reynolds number (Re = 120588119906119889120583)119879 Temperature (K)119906119894119895 Velocity vector component (ms)

119884119899 Mass fraction of species 119899

Greek Symbols

120582 Thermal conductivity (W(msdotK))120583 Dynamic viscosity (kgmsdots)120583119905 Turbulent viscosity (kgmsdots)

120588 Density (kgm3)120593 Equivalence ratio119899 Chemical reaction rate

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] S EHosseiniMAWahid andAAAAbuelnuor ldquoHigh tem-perature air combustion sustainable technology to low NOxformationrdquo International Review ofMechanical Engineering vol6 no 5 pp 947ndash953 2012

[2] R K Srivastava R E Hall S Khan K Culligan and B WLani ldquoNitrogen oxides emission control options for coal-firedelectric utility boilersrdquo Journal of theAir andWasteManagementAssociation vol 55 no 9 pp 1367ndash1388 2005

[3] R K Srivastava W Neuffer D Grano S Khan J E Staudtand W Jozewicz ldquoControlling NO

119909emission from industrial

sourcesrdquo Environmental Progress vol 24 no 2 pp 181ndash1972005

[4] M Khaleghi S E Hosseini and M Abdul Wahid ldquoInvestiga-tions of asymmetric non-premixed meso-scale vortex combus-tionrdquo Applied Thermal Engineering vol 81 pp 140ndash153 2015

[5] D Feikema R H Chen and J F Driscoll ldquoEnhancement offlame blowout limits by the use of swirlrdquoCombustion and Flamevol 80 no 2 pp 183ndash195 1990

[6] H Gabler An Experimental and Numerical Investigation ofAsymmetrically-Fueled Whirl Flames Princeton University1998

[7] M-H Wu Y Wang V Yang and R A Yetter ldquoCombustionin meso-scale vortex chambersrdquo Proceedings of the CombustionInstitute vol 31 pp 3235ndash3242 2007

[8] M Khaleghi M A Wahid M M Seis and A Saat ldquoInves-tigation of vortex reacting flows in asymmetric Meso scale

combustorrdquoAppliedMechanics andMaterials vol 388 pp 246ndash250 2013

[9] K R McManus T Poinsot and S M Candel ldquoA review ofactive control of combustion instabilitiesrdquo Progress in Energyand Combustion Science vol 19 no 1 pp 1ndash29 1993

[10] S Candel ldquoCombustion dynamics and control progress andchallengesrdquo Proceedings of the Combustion Institute vol 29 no1 pp 1ndash28 2002

[11] Y Huang and V Yang ldquoDynamics and stability of lean-premixed swirl-stabilized combustionrdquo Progress in Energy andCombustion Science vol 35 no 4 pp 293ndash364 2009

[12] T C Lieuwen and V Yang Combustion Instabilities in GasTurbine Engines (Operational Experience Fundamental Mech-anisms and Modeling) Progress in Astronautics and Aeronau-tics American Institute of Aeronautics and Astronautics 2005

[13] B Kapadia and P Kutne ldquoCombustion behavior of swirl sta-bilised oxyfuel flames at elevated pressurerdquo in Proceedings of the9th AIAA Annual International Energy Conversion EngineeringConference (IECEC rsquo11) AIAA-5593 San Diego Calif USAJuly-August 2011

[14] P-H Renard DThevenin J C Rolon and S Candel ldquoDynam-ics of flamevortex interactionsrdquo Progress in Energy and Com-bustion Science vol 26 no 3 pp 225ndash282 2000

[15] M Stohr I Boxx C Carter and W Meier ldquoDynamics oflean blowout of a swirl-stabilized flame in a gas turbine modelcombustorrdquo Proceedings of the Combustion Institute vol 33 no2 pp 2953ndash2960 2011

[16] M R Johnson D Littlejohn W A Nazeer K O Smith andR K Cheng ldquoA comparison of the flowfields and emissions ofhigh-swirl injectors and low-swirl injectors for lean premixedgas turbinesrdquo Proceedings of the Combustion Institute vol 30pp 2867ndash2874 2005

[17] P K Ezhil Kumar and D P Mishra ldquoNumerical investigation ofthe flow and flame structure in an axisymmetric trapped vortexcombustorrdquo Fuel vol 102 pp 78ndash84 2012

[18] J Yuan and INaruse ldquoEffects of air dilution onhighly preheatedair combustion in a regenerative furnacerdquo Energy amp Fuels vol13 no 1 pp 99ndash104 1999

[19] J B Bell N J Brown M S Day M Frenklach J F Grcarand S R Tonse ldquoThe dependence of chemistry on the inletequivalence ratio in vortex-flame interactionsrdquo Proceedings ofthe Combustion Institute vol 28 no 2 pp 1933ndash1939 2000

[20] J Beer Combustion Aerodynumics Combustion TechnologySome Modern Developments 2012

[21] AKGupta andDG LilleyFlowfieldModeling andDiagnosticsTaylor amp Francis London UK 1985

[22] J J Choi Z Rusak and A K Kapila ldquoNumerical simulationof premixed chemical reactions with swirlrdquo CombustionTheoryand Modelling vol 11 no 6 pp 863ndash887 2007

[23] N Syred ldquoA review of oscillation mechanisms and the role ofthe precessing vortex core (PVC) in swirl combustion systemsrdquoProgress in Energy and Combustion Science vol 32 no 2 pp93ndash161 2006

[24] M Stohr I Boxx C D Carter and W Meier ldquoExperimentalstudy of vortex-flame interaction in a gas turbine modelcombustorrdquo Combustion and Flame vol 159 no 8 pp 2636ndash2649 2012

[25] M Stohr R Sadanandan and W Meier ldquoPhase-resolved char-acterization of vortex-flame interaction in a turbulent swirlflamerdquo Experiments in Fluids vol 51 no 4 pp 1153ndash1167 2011

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of Energy 3

400

Air AirFuel

Fuel

(a)

110 Air inlet

Air inlet

10

20 Fuelinlets

(b)

Figure 1 Schematic diagram of the asymmetric combustor (a) isometric view and (b) top view all dimensions are in mm

(1) Air compressor(2) Settling tank(3) Pressurized fuel tank(4) Air flowmeter(5) Fuel flowmeter(6) Asymmetric vortex combustor(7) Thermocouple

(8) TELEGAN gas analyzer probe(9) TELEGAN gas analyzer logger(10) DAQ(11) Traverse system(12) Sony 300 fps video camera(13) PC(14) Support structure

12

3

4

5

6

7

8

9

10

11

1213

14

F

F

middot middot middotmiddot middot middot

middot middot middotmiddot middot middot

Figure 2 Schematic of the experimental setup of the asymmetric vortex combustor

4 Journal of Energy

120597120588119894119899

120597119909119895

=

120597

120597119909119895

[(120588119863119899+

120583119905

119878119862119905

)(

120597119899

120597119909119895

)] + 119899

120597120588119895

120597119909119895

=

120597

120597119909119895

[120582

120597119879

120597119909119895

+

120583119905

Pr119905

120597ℎ

120597119909119895

+

119873

sum

119899=1

120588119863119899ℎ119899

120597119899

120597119909119895

]

minus

119873

sum

119899=1

ℎ119891

119899119899

(1)

where 120588 is the density 119906119894119895

is the velocity vector components119875 is the pressure 120582 is the thermal conductivity Pr

119905is the

turbulent Prandtl number119863119899is themass diffusivity of species

(119899) which was assumed to be constant for each species 119884119899is

the mass fraction of species (119899) 119899is the chemical reaction

rate 120583 is the dynamic viscosity and 120583119905is the turbulent

viscosity sim denotes the Favre averaging [28]

42 Numerical Procedures A three-dimensional (3D) finitevolume solver has been used to discretize the flow domainthrough a second-order upwind scheme Several tetrahedrongrids have been generated for ensuring that the solution isgrid independentThe SIMPLE algorithmhas been employedto achieve the mass conservation between the pressureand velocity terms in the discretized momentum equationChemical reaction has considered volumetric and Eddy-dissipation (ED) algorithm has been selected for turbulence-chemistry interactions The ED reaction model ignores che-mical kinetics (ie the Arrhenius rate) and uses only theparameters in reaction flow The operating pressure andtemperature were set to 101 bars and 300K respectively Thepartial-equilibrium model is utilized to predict the O radicalconcentration required for thermal NO

119909prediction In all the

simulations a steady-state pressure based solver was used tosolve the governing equations by CFD code ANSYS Fluent140 [29]

The solution is considered to be converged when theresiduals of each governing equation at consecutive iterationsbecame less than 1 times 10

minus3 except for energy equation andchemical reactions equation which are converged at quanti-ties less than 1 times 10

minus6 At such condition the flow field vari-ables reached stable local values with respect to any numberof iterations Also monitor for parameters of NO

119909and

temperature converged separately as well This convergencecriterion was applied on reacting flow cases The equivalenceratio air mass flow rate and fuel mass flow rate in all casesare constant and equal to 120593 = 097 00011 kgs and 645 times

10minus5 kgs respectively The dimensions of the computational

domain were similar to the full-scale actual dimensions ofthe asymmetric vortex combustor illustrated in Figure 3

43 Grid Testing and Model Validation

431 Grid Independence Test A grid independence test wasperformed to evaluate the effects of grid sizes on the results asshown in Figure 4 Four sets of meshes were generated usingtetrahedron elements with 211606 nodes 375534 nodes

Figure 3 Schematic diagram of the computational domain of asym-metric vortex chamber

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

1415488 nodes898306 nodes

375534 nodes 211606 nodes

Tem

pera

ture

(K)

Figure 4Grid independence test on the central temperature profile

898306 nodes and 1415488 nodes Laminar flowwith coun-terflow configuration was considered for the fueloxidizerinlets at this test where the inlet air and fuel temperaturewere set at 300K It was observed that the 375534 nodesand 898306 nodes produce almost identical results along thechamber with a percentage error of less than 2 Hence adomain with 375534 nodes was chosen to reduce the com-puting time

432 Code Validation Themodel validation was done basedon the geometry and boundary conditions which were usedby Wu et al [7] Air flows with a full tangential velocitycomponent to the asymmetric combustor (300K) and fuelflows coaxially with the center line (300K) The mass flowrate for the air inlet was set to 00011 kgs and the reacting casewas performed at equivalence ratios of 120593 = 0974 Six trialswere performed with different turbulencemodels to comparewith the experimental results As can be seen in Figure 5the central temperature profile is in good agreement with theexperimental results when 119896-120576 RNG was chosen as turbu-lence model The code was further validated by comparingthe other turbulence modelsrsquo results with the experimentalcorrelation developed by Saqr and Khaleghi [30 31] FromFigure 5 it can be seen that the temperature values fallbetween the accepted ranges for 119896-120576 turbulence model

Journal of Energy 5

Position (m)003 004 005 006 007 008 009 010 011

200

400

600

800

1000

1200

1400

1600

1800

Tem

pera

ture

(K)

K-120596K-120576 realizableReynolds-stressK-120576 RNG

Spalart-AllmarasK-120576 standardExperimental

Figure 5 Comparison of the present results of central temperatureprofile along the chamber with the experimental result

This figure clearly shows that Spalart-Allmaras could notestimate the vortex flame and also resulted in a fixed axis tem-perature of 300K It could be observed that 119896-120576 turbulencemodel deviates significantly from the experimental resultsTurbulence model of 119896-120596 except for region near the end ofchamber was not acceptable compared to the experimentalresults while the error of Reynolds-stress model is low It isnoticed that 119870-120576 realizable turbulence model had little errorand 119896-120576 RNG has good adjustment with the experimentalresults

5 NO119909

Formation Mechanisms

51 Thermal and Prompt NO119909 Oxygen and nitrogen in ext-

remely high temperature can react inside the combustionfurnace according to the following reactions which are calledZeldivich formulation [32]

O + N2

1198701

999445999468

119870minus1

NO +N (2)

N +O2

1198702

999445999468

119870minus2

NO +O (3)

N +OH1198703

999445999468

119870minus3

NO +H (4)

where11987011198702 and119870

3are forward rate constant and119870

minus1119870minus2

and 119870minus3

are the reverse rate constants according to Table 1[33] Thermal NO

119909formation is accelerated exponentially

according to formula (5) at temperatures more than 1500∘C[34 35]

119870119894= 119860119894119879119861119894 exp(

minus119862119894

119879

) (5)

Table 1 Thermal NO119909reaction rate constants [m3gmol s]

1198701

(18 times 108

) 119890minus38370119879

119870minus1

(38 times 107

) 119890minus425119879

1198702

(18 times 104

) 1198791198904680119879

119870minus2

(38 times 103

) 119879119890minus20820119879

1198703

(71 times 107

) 119890minus450119879

119870minus3

(17 times 108

) 119890minus24560119879

The rate of NO formation is achieved by formula (6) when thenitrogen radical (N) is assumed in steady-state conditions

119889 [NO]119889119905

=

1

1 + 119870minus1[NO] (119870

2[O2] + 1198703[OH]) + 2119870

1[O] [N

2]

times [minus

2119870minus1

1198702[O2] + 1198703[OH]

times (119870minus2[O] [NO])

+ 119870minus3[H] [NO]]

(6)

where 119879 is temperature (K) and the reaction constants 119860119894

119861119894 and 119862

119894were taken from Fernando et al [33] As there are

back-and-forth reactions it can be seen that when the rateof reaction decreases NO

119909formation declines because com-

bustion takes place in limited time in the furnace MoreoverNO119909constitution mitigates in low temperatures

Prompt NO119909formation mechanism was introduced by

Fenimore in 1971 Prompt or FenimoreNO119909formation occurs

in fuel rich conditions (equivalence ratio greater than 12)[36] The rate of prompt NO

119909constitution augments near

equivalence ratio of 14 [37]

52 N2O Intermediate NO Formation Malte and Pratt [38]

introduced N2O intermediate NO formation mechanism

which occurred in lean fuel moderate temperatures and lowpressure combustion conditions In these circumstances N

2O

is converted to NO via the following formulas [39]

N2+O +119872 larrrarr N

2O +119872 (7)

N2O +O larrrarr N

2+O2

(8)

N2O +O larrrarr NO +NO (9)

According to Bedat and Cheng the presence of H2O impuri-

ties conspicuously affects the N2O decomposition [40]

H2O +O larrrarr OH +OH (10)

N2O +OH larrrarr N

2+H2O (11)

In (7) 119872 is general third body N2O which was constituted

in (7) decomposes by (8) and (10) Equation (12) shows thechemical kinetics law for the rate of NO

119909formation via N

2O

intermediate mechanism119889 [NO]119889119905

= 1198701015840

5[N2O] [O] minus 119870

1015840

6[NO]2 (12)

6 Journal of Energy

00 01 02 03 04

Position (m)

200

400

600

800

1000

1200

1400

1600

1800

5mm6mm

7mm8mm

Tem

pera

ture

(K)

(a)

200e+03

190e+03

180e+03

170e+03

160e+03

150e+03

140e+03

130e+03

120e+03

110e+03

100e+03

900e+02

800e+02

700e+02

600e+02

500e+02

400e+02

300e+02

200e+02

100e+02

000e+00

5mm

6mm

7mm

8mm

(b)

Figure 6 Effect of variations of air diameter on central temperature (K) profile (a) line type and (b) contour type

The reaction rate constants are calculated by

1198701015840

119894= 1198700119879120573 exp(minus

119864119886

119877119879

) (13)

If 119889[N2O]119889119905 = 0 then (13) can be written as

[N2O]

=

[1198701015840

1[N2] [O] [119872] + 119870

1015840

4[N2] [O2] + 1198701015840

6[NO]2 + 119870

1015840

8[N2] [OH]]

1198701015840

2[119872] + (119870

1015840

3+ 1198701015840

5) [O] + 119870

1015840

7[H]

(14)

The concentration of radicals like O OH and H affects theconcentration rates and NO constitution [41] N

2O interme-

diate NO formation increases in low oxygen concentrationconditions [42]

53 Fuel-Bond NO119909Formation Mechanism Fuel-bond NO

119909

formation mechanism occurs when the molecular structuresof the fuel are constituted by nitrogen species In the com-bustion of these fuels the nitrogen atoms are decomposed tointermediate products form which can react with NO

119909[43]

6 Results and Discussion

61The Influence of Inlet Air Diameter on the Characteristics ofVortex Combustion The effect of inlet air diameter changingon the performance of vortex combustion is analyzed whilethe mass flow of fuel and air is kept constant Therefore theequivalence ratio was constant and equal to 0974 Figure 6(a)depicts the effect of inlet diameter changing on the statictemperature along the centerline with respect to the constantmass flow rate The temperature increases along the centralaxis due to the heat released by reactions For larger inletair diameter the temperature first sharply increases and thendecreases along the axial direction Figure 6(b) demonstratesthe temperature contours in two various surfaces There are

Position (m)000 005 010 015 020 025 030 035

40

60

80

100

120

140

5mm6mm

7mm8mm

NOx

(ppm

)

Figure 7 Effect of air diameter variation on the central NO119909profile

obvious differences in these contours From this figure itcan be interpreted that increasing in inlet air diameter withconstant mass flow rate (decreasing inlet velocity) leads toincrease in residence time The decrease of speed of vortexflame and diffusion of flame to the center of chamber are thetwo original reasons of these changes

The effect of diameter variation on the flame structureshowed that the NO

119909value on the centerline of the chamber

increased when the inlet air diameter increased as shownin Figure 7 It should be noted that the NO

119909concentration

increased with the increase of air inlet diameter due toincrease of the excess air and flame high temperature asshown in Figure 8 and Table 2 It is concluded that NO

119909for-

mation (Based on Zeldovich equations) is mainly controlledby temperature of combustion

Journal of Energy 7

Table 2 Average outlet quantity of chamber

Inlet air diameter Average NO119909outlet Average temperature

outlet5 72 4706 82 5007 95 5358 98 568

5mm

6mm

7mm

8mm

270e+02

257e+02

243e+02

230e+02

189e+02

176e+02

162e+02

140e+02

135e+02

122e+02

108e+02

945e+02

810e+01

675e+01

540e+01

405e+01

270e+01

135e+01

000e+00

(a)

(b)

(c)

(d)

Figure 8 NO119909emissions (ppm) contour for different air diameters

(a) 119889 = 5mm (b) 119889 = 6mm (c) 119889 = 7mm and (d) 119889 = 8mm

62 The Effect of Inlet Fuel Diameter on the Characteristics ofVortex Combustion Figure 9 illustrates the trend of NO

119909for-

mation and temperature distribution along with the chamberlength with respect to the various fuel diameters (2 25 3 35and 4mm) From this figure it can be construed that the sizeof the fuel inlet has insignificant effect on the NO

119909formation

and static temperature This shows that temperature flameas well as NO

119909emission in the chamber has more effect on

inlet air compared to inlet fuel in other words the inletfuel velocity has negligible contribution to vortex flamescompared to air inlet velocity

63 Preheating Air Effects Figure 10 shows temperature dis-tribution and NO

119909emissions formation when oxidizer is

applied in four different air temperatures (119879 = 300K 400K500K and 600K) while the diameter of the air and fuel inletthe mass flow rate of air and fuel inlet and equivalence ratioare kept constant at 5mm 2mm 00011 kgs 645 times 10minus5 kgsand 097 respectively All of the predictions are performedat the same central axis location with the above discussedconditions It was found that increasing the preheating airtemperature and decreasing the air viscosity could limit themaximum flame temperature and improve the temperature

Position (m)005 010 015 020 025 030 035

40

50

60

70

80

90

100

110

2mm25mm

3mm35mm

NOx

(ppm

)

(a)

Position (m)00 01 02 03 04

200

400

600

800

1200

1000

2mm25mm

3mm35mm

Tem

pera

ture

(K)

(b)

Figure 9 Effect of variations of fuel diameter on central (a) NO119909

profile and (b) temperature profile

uniformity in the furnace The data shows that with increas-ing preheating air at a constant mass flow rate the flamelocationmoves toward the air inlet because themomentumofthe air stream decreases Because the flame tends to approachthewall the temperature along the central axis decreases withincrease of air inlet temperature As a result the NO

119909emiss-

ion decreases when the flame temperature decreases

64 Preheating Fuel Effects Figures 11 and 12 show a min-imum effect of preheating fuel on the flame characteristicssuch as static temperature and NO

119909emissions The tempera-

ture and oxygen mole fraction of air kept constant and equalto 300K and 20 respectively It can be seen that the temper-ature along the central axis of the combustion chamber has nosignificant change with increasing of the fuel temperature In

8 Journal of Energy

Position (m)000 005 010 015 020 025 030 035

0

20

40

60

80

100

120

140

NOx

(ppm

)

300K400K

500K600K

(a)

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

Tem

pera

ture

(K)

300K400K

500K600K

(b)

Figure 10 Effect of preheating air on the central (a) NO119909profile and (b) temperature profile

Position (m)00 01 02 03 04

400

600

800

1000

1200

1400

300K350K

400K450K

Tem

pera

ture

(K)

Figure 11 The effect of preheating fuel on the central temperatureprofile

addition the results show that at all fuel temperatures thetemperature decreases along the combustion chamber dueto recession of flame and design of exhaust chamber Themaximum temperature is found in the vicinity of the bottomwall where the fuel enters the combustion chamber Theresults reveal that preheating inlet fuel has insignificant effecton the maximum flame temperature

Figure 12 shows that the NO119909emission rises as the max-

imum flame temperature increases With the increase ofthe fuel temperature at a fixed air flow rate there is a hightemperature mixing in the flame zone so there will be morethermal NO

119909products with the fuel and increases in the

temperatureThe increasedNO119909 caused by fuel preheating is

consistent with the hypothesis that preheating levels of 300K500K and 700K enhance fuel pyrolysis rates

Position (m)00 01 02 03 04

20

40

60

80

100

120

140

NOx

(ppm

)

300K350K

400K450K

Figure 12 The effect of preheating fuel on the central NO119909profile

7 Conclusions

A computational study on the performance of asymmetricvortex flame for various inlet flow diameters (air and fuel)and effect of preheating air and fuel was analyzedThe resultsshowed that increasing the inlet fuel diameter has negligibleeffect on the flame compared to effect of increasing inlet airto flame temperature and NO

119909emission The thermal field

results show that the effect of preheating can attain low-emission NO

119909as compared to fuel It is found that increasing

the preheated air temperature and fuel temperature coulddecrease the flame temperature and the combustion intensityandNO

119909emission when the airmass flow rate fuelmass flow

rate and equivalence ratio were considered constant for allsimulations Increasing the air velocity due to preheated air

Journal of Energy 9

in constant mass flow rate and equivalence ratio is found tobe an effective way to control the NO

119909emission because of

the decrease of the flame temperature

Nomenclature

119889 Chamber diameter (mm)

119863119899 Mass diffusivity (m2s)

119871 Length of chamber (mm)

119898 Air and fuel mass flow rate (kgs)119901 Pressure (pa)Pr119905 Prandtl number

Re Reynolds number (Re = 120588119906119889120583)119879 Temperature (K)119906119894119895 Velocity vector component (ms)

119884119899 Mass fraction of species 119899

Greek Symbols

120582 Thermal conductivity (W(msdotK))120583 Dynamic viscosity (kgmsdots)120583119905 Turbulent viscosity (kgmsdots)

120588 Density (kgm3)120593 Equivalence ratio119899 Chemical reaction rate

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] S EHosseiniMAWahid andAAAAbuelnuor ldquoHigh tem-perature air combustion sustainable technology to low NOxformationrdquo International Review ofMechanical Engineering vol6 no 5 pp 947ndash953 2012

[2] R K Srivastava R E Hall S Khan K Culligan and B WLani ldquoNitrogen oxides emission control options for coal-firedelectric utility boilersrdquo Journal of theAir andWasteManagementAssociation vol 55 no 9 pp 1367ndash1388 2005

[3] R K Srivastava W Neuffer D Grano S Khan J E Staudtand W Jozewicz ldquoControlling NO

119909emission from industrial

sourcesrdquo Environmental Progress vol 24 no 2 pp 181ndash1972005

[4] M Khaleghi S E Hosseini and M Abdul Wahid ldquoInvestiga-tions of asymmetric non-premixed meso-scale vortex combus-tionrdquo Applied Thermal Engineering vol 81 pp 140ndash153 2015

[5] D Feikema R H Chen and J F Driscoll ldquoEnhancement offlame blowout limits by the use of swirlrdquoCombustion and Flamevol 80 no 2 pp 183ndash195 1990

[6] H Gabler An Experimental and Numerical Investigation ofAsymmetrically-Fueled Whirl Flames Princeton University1998

[7] M-H Wu Y Wang V Yang and R A Yetter ldquoCombustionin meso-scale vortex chambersrdquo Proceedings of the CombustionInstitute vol 31 pp 3235ndash3242 2007

[8] M Khaleghi M A Wahid M M Seis and A Saat ldquoInves-tigation of vortex reacting flows in asymmetric Meso scale

combustorrdquoAppliedMechanics andMaterials vol 388 pp 246ndash250 2013

[9] K R McManus T Poinsot and S M Candel ldquoA review ofactive control of combustion instabilitiesrdquo Progress in Energyand Combustion Science vol 19 no 1 pp 1ndash29 1993

[10] S Candel ldquoCombustion dynamics and control progress andchallengesrdquo Proceedings of the Combustion Institute vol 29 no1 pp 1ndash28 2002

[11] Y Huang and V Yang ldquoDynamics and stability of lean-premixed swirl-stabilized combustionrdquo Progress in Energy andCombustion Science vol 35 no 4 pp 293ndash364 2009

[12] T C Lieuwen and V Yang Combustion Instabilities in GasTurbine Engines (Operational Experience Fundamental Mech-anisms and Modeling) Progress in Astronautics and Aeronau-tics American Institute of Aeronautics and Astronautics 2005

[13] B Kapadia and P Kutne ldquoCombustion behavior of swirl sta-bilised oxyfuel flames at elevated pressurerdquo in Proceedings of the9th AIAA Annual International Energy Conversion EngineeringConference (IECEC rsquo11) AIAA-5593 San Diego Calif USAJuly-August 2011

[14] P-H Renard DThevenin J C Rolon and S Candel ldquoDynam-ics of flamevortex interactionsrdquo Progress in Energy and Com-bustion Science vol 26 no 3 pp 225ndash282 2000

[15] M Stohr I Boxx C Carter and W Meier ldquoDynamics oflean blowout of a swirl-stabilized flame in a gas turbine modelcombustorrdquo Proceedings of the Combustion Institute vol 33 no2 pp 2953ndash2960 2011

[16] M R Johnson D Littlejohn W A Nazeer K O Smith andR K Cheng ldquoA comparison of the flowfields and emissions ofhigh-swirl injectors and low-swirl injectors for lean premixedgas turbinesrdquo Proceedings of the Combustion Institute vol 30pp 2867ndash2874 2005

[17] P K Ezhil Kumar and D P Mishra ldquoNumerical investigation ofthe flow and flame structure in an axisymmetric trapped vortexcombustorrdquo Fuel vol 102 pp 78ndash84 2012

[18] J Yuan and INaruse ldquoEffects of air dilution onhighly preheatedair combustion in a regenerative furnacerdquo Energy amp Fuels vol13 no 1 pp 99ndash104 1999

[19] J B Bell N J Brown M S Day M Frenklach J F Grcarand S R Tonse ldquoThe dependence of chemistry on the inletequivalence ratio in vortex-flame interactionsrdquo Proceedings ofthe Combustion Institute vol 28 no 2 pp 1933ndash1939 2000

[20] J Beer Combustion Aerodynumics Combustion TechnologySome Modern Developments 2012

[21] AKGupta andDG LilleyFlowfieldModeling andDiagnosticsTaylor amp Francis London UK 1985

[22] J J Choi Z Rusak and A K Kapila ldquoNumerical simulationof premixed chemical reactions with swirlrdquo CombustionTheoryand Modelling vol 11 no 6 pp 863ndash887 2007

[23] N Syred ldquoA review of oscillation mechanisms and the role ofthe precessing vortex core (PVC) in swirl combustion systemsrdquoProgress in Energy and Combustion Science vol 32 no 2 pp93ndash161 2006

[24] M Stohr I Boxx C D Carter and W Meier ldquoExperimentalstudy of vortex-flame interaction in a gas turbine modelcombustorrdquo Combustion and Flame vol 159 no 8 pp 2636ndash2649 2012

[25] M Stohr R Sadanandan and W Meier ldquoPhase-resolved char-acterization of vortex-flame interaction in a turbulent swirlflamerdquo Experiments in Fluids vol 51 no 4 pp 1153ndash1167 2011

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

4 Journal of Energy

120597120588119894119899

120597119909119895

=

120597

120597119909119895

[(120588119863119899+

120583119905

119878119862119905

)(

120597119899

120597119909119895

)] + 119899

120597120588119895

120597119909119895

=

120597

120597119909119895

[120582

120597119879

120597119909119895

+

120583119905

Pr119905

120597ℎ

120597119909119895

+

119873

sum

119899=1

120588119863119899ℎ119899

120597119899

120597119909119895

]

minus

119873

sum

119899=1

ℎ119891

119899119899

(1)

where 120588 is the density 119906119894119895

is the velocity vector components119875 is the pressure 120582 is the thermal conductivity Pr

119905is the

turbulent Prandtl number119863119899is themass diffusivity of species

(119899) which was assumed to be constant for each species 119884119899is

the mass fraction of species (119899) 119899is the chemical reaction

rate 120583 is the dynamic viscosity and 120583119905is the turbulent

viscosity sim denotes the Favre averaging [28]

42 Numerical Procedures A three-dimensional (3D) finitevolume solver has been used to discretize the flow domainthrough a second-order upwind scheme Several tetrahedrongrids have been generated for ensuring that the solution isgrid independentThe SIMPLE algorithmhas been employedto achieve the mass conservation between the pressureand velocity terms in the discretized momentum equationChemical reaction has considered volumetric and Eddy-dissipation (ED) algorithm has been selected for turbulence-chemistry interactions The ED reaction model ignores che-mical kinetics (ie the Arrhenius rate) and uses only theparameters in reaction flow The operating pressure andtemperature were set to 101 bars and 300K respectively Thepartial-equilibrium model is utilized to predict the O radicalconcentration required for thermal NO

119909prediction In all the

simulations a steady-state pressure based solver was used tosolve the governing equations by CFD code ANSYS Fluent140 [29]

The solution is considered to be converged when theresiduals of each governing equation at consecutive iterationsbecame less than 1 times 10

minus3 except for energy equation andchemical reactions equation which are converged at quanti-ties less than 1 times 10

minus6 At such condition the flow field vari-ables reached stable local values with respect to any numberof iterations Also monitor for parameters of NO

119909and

temperature converged separately as well This convergencecriterion was applied on reacting flow cases The equivalenceratio air mass flow rate and fuel mass flow rate in all casesare constant and equal to 120593 = 097 00011 kgs and 645 times

10minus5 kgs respectively The dimensions of the computational

domain were similar to the full-scale actual dimensions ofthe asymmetric vortex combustor illustrated in Figure 3

43 Grid Testing and Model Validation

431 Grid Independence Test A grid independence test wasperformed to evaluate the effects of grid sizes on the results asshown in Figure 4 Four sets of meshes were generated usingtetrahedron elements with 211606 nodes 375534 nodes

Figure 3 Schematic diagram of the computational domain of asym-metric vortex chamber

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

1415488 nodes898306 nodes

375534 nodes 211606 nodes

Tem

pera

ture

(K)

Figure 4Grid independence test on the central temperature profile

898306 nodes and 1415488 nodes Laminar flowwith coun-terflow configuration was considered for the fueloxidizerinlets at this test where the inlet air and fuel temperaturewere set at 300K It was observed that the 375534 nodesand 898306 nodes produce almost identical results along thechamber with a percentage error of less than 2 Hence adomain with 375534 nodes was chosen to reduce the com-puting time

432 Code Validation Themodel validation was done basedon the geometry and boundary conditions which were usedby Wu et al [7] Air flows with a full tangential velocitycomponent to the asymmetric combustor (300K) and fuelflows coaxially with the center line (300K) The mass flowrate for the air inlet was set to 00011 kgs and the reacting casewas performed at equivalence ratios of 120593 = 0974 Six trialswere performed with different turbulencemodels to comparewith the experimental results As can be seen in Figure 5the central temperature profile is in good agreement with theexperimental results when 119896-120576 RNG was chosen as turbu-lence model The code was further validated by comparingthe other turbulence modelsrsquo results with the experimentalcorrelation developed by Saqr and Khaleghi [30 31] FromFigure 5 it can be seen that the temperature values fallbetween the accepted ranges for 119896-120576 turbulence model

Journal of Energy 5

Position (m)003 004 005 006 007 008 009 010 011

200

400

600

800

1000

1200

1400

1600

1800

Tem

pera

ture

(K)

K-120596K-120576 realizableReynolds-stressK-120576 RNG

Spalart-AllmarasK-120576 standardExperimental

Figure 5 Comparison of the present results of central temperatureprofile along the chamber with the experimental result

This figure clearly shows that Spalart-Allmaras could notestimate the vortex flame and also resulted in a fixed axis tem-perature of 300K It could be observed that 119896-120576 turbulencemodel deviates significantly from the experimental resultsTurbulence model of 119896-120596 except for region near the end ofchamber was not acceptable compared to the experimentalresults while the error of Reynolds-stress model is low It isnoticed that 119870-120576 realizable turbulence model had little errorand 119896-120576 RNG has good adjustment with the experimentalresults

5 NO119909

Formation Mechanisms

51 Thermal and Prompt NO119909 Oxygen and nitrogen in ext-

remely high temperature can react inside the combustionfurnace according to the following reactions which are calledZeldivich formulation [32]

O + N2

1198701

999445999468

119870minus1

NO +N (2)

N +O2

1198702

999445999468

119870minus2

NO +O (3)

N +OH1198703

999445999468

119870minus3

NO +H (4)

where11987011198702 and119870

3are forward rate constant and119870

minus1119870minus2

and 119870minus3

are the reverse rate constants according to Table 1[33] Thermal NO

119909formation is accelerated exponentially

according to formula (5) at temperatures more than 1500∘C[34 35]

119870119894= 119860119894119879119861119894 exp(

minus119862119894

119879

) (5)

Table 1 Thermal NO119909reaction rate constants [m3gmol s]

1198701

(18 times 108

) 119890minus38370119879

119870minus1

(38 times 107

) 119890minus425119879

1198702

(18 times 104

) 1198791198904680119879

119870minus2

(38 times 103

) 119879119890minus20820119879

1198703

(71 times 107

) 119890minus450119879

119870minus3

(17 times 108

) 119890minus24560119879

The rate of NO formation is achieved by formula (6) when thenitrogen radical (N) is assumed in steady-state conditions

119889 [NO]119889119905

=

1

1 + 119870minus1[NO] (119870

2[O2] + 1198703[OH]) + 2119870

1[O] [N

2]

times [minus

2119870minus1

1198702[O2] + 1198703[OH]

times (119870minus2[O] [NO])

+ 119870minus3[H] [NO]]

(6)

where 119879 is temperature (K) and the reaction constants 119860119894

119861119894 and 119862

119894were taken from Fernando et al [33] As there are

back-and-forth reactions it can be seen that when the rateof reaction decreases NO

119909formation declines because com-

bustion takes place in limited time in the furnace MoreoverNO119909constitution mitigates in low temperatures

Prompt NO119909formation mechanism was introduced by

Fenimore in 1971 Prompt or FenimoreNO119909formation occurs

in fuel rich conditions (equivalence ratio greater than 12)[36] The rate of prompt NO

119909constitution augments near

equivalence ratio of 14 [37]

52 N2O Intermediate NO Formation Malte and Pratt [38]

introduced N2O intermediate NO formation mechanism

which occurred in lean fuel moderate temperatures and lowpressure combustion conditions In these circumstances N

2O

is converted to NO via the following formulas [39]

N2+O +119872 larrrarr N

2O +119872 (7)

N2O +O larrrarr N

2+O2

(8)

N2O +O larrrarr NO +NO (9)

According to Bedat and Cheng the presence of H2O impuri-

ties conspicuously affects the N2O decomposition [40]

H2O +O larrrarr OH +OH (10)

N2O +OH larrrarr N

2+H2O (11)

In (7) 119872 is general third body N2O which was constituted

in (7) decomposes by (8) and (10) Equation (12) shows thechemical kinetics law for the rate of NO

119909formation via N

2O

intermediate mechanism119889 [NO]119889119905

= 1198701015840

5[N2O] [O] minus 119870

1015840

6[NO]2 (12)

6 Journal of Energy

00 01 02 03 04

Position (m)

200

400

600

800

1000

1200

1400

1600

1800

5mm6mm

7mm8mm

Tem

pera

ture

(K)

(a)

200e+03

190e+03

180e+03

170e+03

160e+03

150e+03

140e+03

130e+03

120e+03

110e+03

100e+03

900e+02

800e+02

700e+02

600e+02

500e+02

400e+02

300e+02

200e+02

100e+02

000e+00

5mm

6mm

7mm

8mm

(b)

Figure 6 Effect of variations of air diameter on central temperature (K) profile (a) line type and (b) contour type

The reaction rate constants are calculated by

1198701015840

119894= 1198700119879120573 exp(minus

119864119886

119877119879

) (13)

If 119889[N2O]119889119905 = 0 then (13) can be written as

[N2O]

=

[1198701015840

1[N2] [O] [119872] + 119870

1015840

4[N2] [O2] + 1198701015840

6[NO]2 + 119870

1015840

8[N2] [OH]]

1198701015840

2[119872] + (119870

1015840

3+ 1198701015840

5) [O] + 119870

1015840

7[H]

(14)

The concentration of radicals like O OH and H affects theconcentration rates and NO constitution [41] N

2O interme-

diate NO formation increases in low oxygen concentrationconditions [42]

53 Fuel-Bond NO119909Formation Mechanism Fuel-bond NO

119909

formation mechanism occurs when the molecular structuresof the fuel are constituted by nitrogen species In the com-bustion of these fuels the nitrogen atoms are decomposed tointermediate products form which can react with NO

119909[43]

6 Results and Discussion

61The Influence of Inlet Air Diameter on the Characteristics ofVortex Combustion The effect of inlet air diameter changingon the performance of vortex combustion is analyzed whilethe mass flow of fuel and air is kept constant Therefore theequivalence ratio was constant and equal to 0974 Figure 6(a)depicts the effect of inlet diameter changing on the statictemperature along the centerline with respect to the constantmass flow rate The temperature increases along the centralaxis due to the heat released by reactions For larger inletair diameter the temperature first sharply increases and thendecreases along the axial direction Figure 6(b) demonstratesthe temperature contours in two various surfaces There are

Position (m)000 005 010 015 020 025 030 035

40

60

80

100

120

140

5mm6mm

7mm8mm

NOx

(ppm

)

Figure 7 Effect of air diameter variation on the central NO119909profile

obvious differences in these contours From this figure itcan be interpreted that increasing in inlet air diameter withconstant mass flow rate (decreasing inlet velocity) leads toincrease in residence time The decrease of speed of vortexflame and diffusion of flame to the center of chamber are thetwo original reasons of these changes

The effect of diameter variation on the flame structureshowed that the NO

119909value on the centerline of the chamber

increased when the inlet air diameter increased as shownin Figure 7 It should be noted that the NO

119909concentration

increased with the increase of air inlet diameter due toincrease of the excess air and flame high temperature asshown in Figure 8 and Table 2 It is concluded that NO

119909for-

mation (Based on Zeldovich equations) is mainly controlledby temperature of combustion

Journal of Energy 7

Table 2 Average outlet quantity of chamber

Inlet air diameter Average NO119909outlet Average temperature

outlet5 72 4706 82 5007 95 5358 98 568

5mm

6mm

7mm

8mm

270e+02

257e+02

243e+02

230e+02

189e+02

176e+02

162e+02

140e+02

135e+02

122e+02

108e+02

945e+02

810e+01

675e+01

540e+01

405e+01

270e+01

135e+01

000e+00

(a)

(b)

(c)

(d)

Figure 8 NO119909emissions (ppm) contour for different air diameters

(a) 119889 = 5mm (b) 119889 = 6mm (c) 119889 = 7mm and (d) 119889 = 8mm

62 The Effect of Inlet Fuel Diameter on the Characteristics ofVortex Combustion Figure 9 illustrates the trend of NO

119909for-

mation and temperature distribution along with the chamberlength with respect to the various fuel diameters (2 25 3 35and 4mm) From this figure it can be construed that the sizeof the fuel inlet has insignificant effect on the NO

119909formation

and static temperature This shows that temperature flameas well as NO

119909emission in the chamber has more effect on

inlet air compared to inlet fuel in other words the inletfuel velocity has negligible contribution to vortex flamescompared to air inlet velocity

63 Preheating Air Effects Figure 10 shows temperature dis-tribution and NO

119909emissions formation when oxidizer is

applied in four different air temperatures (119879 = 300K 400K500K and 600K) while the diameter of the air and fuel inletthe mass flow rate of air and fuel inlet and equivalence ratioare kept constant at 5mm 2mm 00011 kgs 645 times 10minus5 kgsand 097 respectively All of the predictions are performedat the same central axis location with the above discussedconditions It was found that increasing the preheating airtemperature and decreasing the air viscosity could limit themaximum flame temperature and improve the temperature

Position (m)005 010 015 020 025 030 035

40

50

60

70

80

90

100

110

2mm25mm

3mm35mm

NOx

(ppm

)

(a)

Position (m)00 01 02 03 04

200

400

600

800

1200

1000

2mm25mm

3mm35mm

Tem

pera

ture

(K)

(b)

Figure 9 Effect of variations of fuel diameter on central (a) NO119909

profile and (b) temperature profile

uniformity in the furnace The data shows that with increas-ing preheating air at a constant mass flow rate the flamelocationmoves toward the air inlet because themomentumofthe air stream decreases Because the flame tends to approachthewall the temperature along the central axis decreases withincrease of air inlet temperature As a result the NO

119909emiss-

ion decreases when the flame temperature decreases

64 Preheating Fuel Effects Figures 11 and 12 show a min-imum effect of preheating fuel on the flame characteristicssuch as static temperature and NO

119909emissions The tempera-

ture and oxygen mole fraction of air kept constant and equalto 300K and 20 respectively It can be seen that the temper-ature along the central axis of the combustion chamber has nosignificant change with increasing of the fuel temperature In

8 Journal of Energy

Position (m)000 005 010 015 020 025 030 035

0

20

40

60

80

100

120

140

NOx

(ppm

)

300K400K

500K600K

(a)

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

Tem

pera

ture

(K)

300K400K

500K600K

(b)

Figure 10 Effect of preheating air on the central (a) NO119909profile and (b) temperature profile

Position (m)00 01 02 03 04

400

600

800

1000

1200

1400

300K350K

400K450K

Tem

pera

ture

(K)

Figure 11 The effect of preheating fuel on the central temperatureprofile

addition the results show that at all fuel temperatures thetemperature decreases along the combustion chamber dueto recession of flame and design of exhaust chamber Themaximum temperature is found in the vicinity of the bottomwall where the fuel enters the combustion chamber Theresults reveal that preheating inlet fuel has insignificant effecton the maximum flame temperature

Figure 12 shows that the NO119909emission rises as the max-

imum flame temperature increases With the increase ofthe fuel temperature at a fixed air flow rate there is a hightemperature mixing in the flame zone so there will be morethermal NO

119909products with the fuel and increases in the

temperatureThe increasedNO119909 caused by fuel preheating is

consistent with the hypothesis that preheating levels of 300K500K and 700K enhance fuel pyrolysis rates

Position (m)00 01 02 03 04

20

40

60

80

100

120

140

NOx

(ppm

)

300K350K

400K450K

Figure 12 The effect of preheating fuel on the central NO119909profile

7 Conclusions

A computational study on the performance of asymmetricvortex flame for various inlet flow diameters (air and fuel)and effect of preheating air and fuel was analyzedThe resultsshowed that increasing the inlet fuel diameter has negligibleeffect on the flame compared to effect of increasing inlet airto flame temperature and NO

119909emission The thermal field

results show that the effect of preheating can attain low-emission NO

119909as compared to fuel It is found that increasing

the preheated air temperature and fuel temperature coulddecrease the flame temperature and the combustion intensityandNO

119909emission when the airmass flow rate fuelmass flow

rate and equivalence ratio were considered constant for allsimulations Increasing the air velocity due to preheated air

Journal of Energy 9

in constant mass flow rate and equivalence ratio is found tobe an effective way to control the NO

119909emission because of

the decrease of the flame temperature

Nomenclature

119889 Chamber diameter (mm)

119863119899 Mass diffusivity (m2s)

119871 Length of chamber (mm)

119898 Air and fuel mass flow rate (kgs)119901 Pressure (pa)Pr119905 Prandtl number

Re Reynolds number (Re = 120588119906119889120583)119879 Temperature (K)119906119894119895 Velocity vector component (ms)

119884119899 Mass fraction of species 119899

Greek Symbols

120582 Thermal conductivity (W(msdotK))120583 Dynamic viscosity (kgmsdots)120583119905 Turbulent viscosity (kgmsdots)

120588 Density (kgm3)120593 Equivalence ratio119899 Chemical reaction rate

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] S EHosseiniMAWahid andAAAAbuelnuor ldquoHigh tem-perature air combustion sustainable technology to low NOxformationrdquo International Review ofMechanical Engineering vol6 no 5 pp 947ndash953 2012

[2] R K Srivastava R E Hall S Khan K Culligan and B WLani ldquoNitrogen oxides emission control options for coal-firedelectric utility boilersrdquo Journal of theAir andWasteManagementAssociation vol 55 no 9 pp 1367ndash1388 2005

[3] R K Srivastava W Neuffer D Grano S Khan J E Staudtand W Jozewicz ldquoControlling NO

119909emission from industrial

sourcesrdquo Environmental Progress vol 24 no 2 pp 181ndash1972005

[4] M Khaleghi S E Hosseini and M Abdul Wahid ldquoInvestiga-tions of asymmetric non-premixed meso-scale vortex combus-tionrdquo Applied Thermal Engineering vol 81 pp 140ndash153 2015

[5] D Feikema R H Chen and J F Driscoll ldquoEnhancement offlame blowout limits by the use of swirlrdquoCombustion and Flamevol 80 no 2 pp 183ndash195 1990

[6] H Gabler An Experimental and Numerical Investigation ofAsymmetrically-Fueled Whirl Flames Princeton University1998

[7] M-H Wu Y Wang V Yang and R A Yetter ldquoCombustionin meso-scale vortex chambersrdquo Proceedings of the CombustionInstitute vol 31 pp 3235ndash3242 2007

[8] M Khaleghi M A Wahid M M Seis and A Saat ldquoInves-tigation of vortex reacting flows in asymmetric Meso scale

combustorrdquoAppliedMechanics andMaterials vol 388 pp 246ndash250 2013

[9] K R McManus T Poinsot and S M Candel ldquoA review ofactive control of combustion instabilitiesrdquo Progress in Energyand Combustion Science vol 19 no 1 pp 1ndash29 1993

[10] S Candel ldquoCombustion dynamics and control progress andchallengesrdquo Proceedings of the Combustion Institute vol 29 no1 pp 1ndash28 2002

[11] Y Huang and V Yang ldquoDynamics and stability of lean-premixed swirl-stabilized combustionrdquo Progress in Energy andCombustion Science vol 35 no 4 pp 293ndash364 2009

[12] T C Lieuwen and V Yang Combustion Instabilities in GasTurbine Engines (Operational Experience Fundamental Mech-anisms and Modeling) Progress in Astronautics and Aeronau-tics American Institute of Aeronautics and Astronautics 2005

[13] B Kapadia and P Kutne ldquoCombustion behavior of swirl sta-bilised oxyfuel flames at elevated pressurerdquo in Proceedings of the9th AIAA Annual International Energy Conversion EngineeringConference (IECEC rsquo11) AIAA-5593 San Diego Calif USAJuly-August 2011

[14] P-H Renard DThevenin J C Rolon and S Candel ldquoDynam-ics of flamevortex interactionsrdquo Progress in Energy and Com-bustion Science vol 26 no 3 pp 225ndash282 2000

[15] M Stohr I Boxx C Carter and W Meier ldquoDynamics oflean blowout of a swirl-stabilized flame in a gas turbine modelcombustorrdquo Proceedings of the Combustion Institute vol 33 no2 pp 2953ndash2960 2011

[16] M R Johnson D Littlejohn W A Nazeer K O Smith andR K Cheng ldquoA comparison of the flowfields and emissions ofhigh-swirl injectors and low-swirl injectors for lean premixedgas turbinesrdquo Proceedings of the Combustion Institute vol 30pp 2867ndash2874 2005

[17] P K Ezhil Kumar and D P Mishra ldquoNumerical investigation ofthe flow and flame structure in an axisymmetric trapped vortexcombustorrdquo Fuel vol 102 pp 78ndash84 2012

[18] J Yuan and INaruse ldquoEffects of air dilution onhighly preheatedair combustion in a regenerative furnacerdquo Energy amp Fuels vol13 no 1 pp 99ndash104 1999

[19] J B Bell N J Brown M S Day M Frenklach J F Grcarand S R Tonse ldquoThe dependence of chemistry on the inletequivalence ratio in vortex-flame interactionsrdquo Proceedings ofthe Combustion Institute vol 28 no 2 pp 1933ndash1939 2000

[20] J Beer Combustion Aerodynumics Combustion TechnologySome Modern Developments 2012

[21] AKGupta andDG LilleyFlowfieldModeling andDiagnosticsTaylor amp Francis London UK 1985

[22] J J Choi Z Rusak and A K Kapila ldquoNumerical simulationof premixed chemical reactions with swirlrdquo CombustionTheoryand Modelling vol 11 no 6 pp 863ndash887 2007

[23] N Syred ldquoA review of oscillation mechanisms and the role ofthe precessing vortex core (PVC) in swirl combustion systemsrdquoProgress in Energy and Combustion Science vol 32 no 2 pp93ndash161 2006

[24] M Stohr I Boxx C D Carter and W Meier ldquoExperimentalstudy of vortex-flame interaction in a gas turbine modelcombustorrdquo Combustion and Flame vol 159 no 8 pp 2636ndash2649 2012

[25] M Stohr R Sadanandan and W Meier ldquoPhase-resolved char-acterization of vortex-flame interaction in a turbulent swirlflamerdquo Experiments in Fluids vol 51 no 4 pp 1153ndash1167 2011

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of Energy 5

Position (m)003 004 005 006 007 008 009 010 011

200

400

600

800

1000

1200

1400

1600

1800

Tem

pera

ture

(K)

K-120596K-120576 realizableReynolds-stressK-120576 RNG

Spalart-AllmarasK-120576 standardExperimental

Figure 5 Comparison of the present results of central temperatureprofile along the chamber with the experimental result

This figure clearly shows that Spalart-Allmaras could notestimate the vortex flame and also resulted in a fixed axis tem-perature of 300K It could be observed that 119896-120576 turbulencemodel deviates significantly from the experimental resultsTurbulence model of 119896-120596 except for region near the end ofchamber was not acceptable compared to the experimentalresults while the error of Reynolds-stress model is low It isnoticed that 119870-120576 realizable turbulence model had little errorand 119896-120576 RNG has good adjustment with the experimentalresults

5 NO119909

Formation Mechanisms

51 Thermal and Prompt NO119909 Oxygen and nitrogen in ext-

remely high temperature can react inside the combustionfurnace according to the following reactions which are calledZeldivich formulation [32]

O + N2

1198701

999445999468

119870minus1

NO +N (2)

N +O2

1198702

999445999468

119870minus2

NO +O (3)

N +OH1198703

999445999468

119870minus3

NO +H (4)

where11987011198702 and119870

3are forward rate constant and119870

minus1119870minus2

and 119870minus3

are the reverse rate constants according to Table 1[33] Thermal NO

119909formation is accelerated exponentially

according to formula (5) at temperatures more than 1500∘C[34 35]

119870119894= 119860119894119879119861119894 exp(

minus119862119894

119879

) (5)

Table 1 Thermal NO119909reaction rate constants [m3gmol s]

1198701

(18 times 108

) 119890minus38370119879

119870minus1

(38 times 107

) 119890minus425119879

1198702

(18 times 104

) 1198791198904680119879

119870minus2

(38 times 103

) 119879119890minus20820119879

1198703

(71 times 107

) 119890minus450119879

119870minus3

(17 times 108

) 119890minus24560119879

The rate of NO formation is achieved by formula (6) when thenitrogen radical (N) is assumed in steady-state conditions

119889 [NO]119889119905

=

1

1 + 119870minus1[NO] (119870

2[O2] + 1198703[OH]) + 2119870

1[O] [N

2]

times [minus

2119870minus1

1198702[O2] + 1198703[OH]

times (119870minus2[O] [NO])

+ 119870minus3[H] [NO]]

(6)

where 119879 is temperature (K) and the reaction constants 119860119894

119861119894 and 119862

119894were taken from Fernando et al [33] As there are

back-and-forth reactions it can be seen that when the rateof reaction decreases NO

119909formation declines because com-

bustion takes place in limited time in the furnace MoreoverNO119909constitution mitigates in low temperatures

Prompt NO119909formation mechanism was introduced by

Fenimore in 1971 Prompt or FenimoreNO119909formation occurs

in fuel rich conditions (equivalence ratio greater than 12)[36] The rate of prompt NO

119909constitution augments near

equivalence ratio of 14 [37]

52 N2O Intermediate NO Formation Malte and Pratt [38]

introduced N2O intermediate NO formation mechanism

which occurred in lean fuel moderate temperatures and lowpressure combustion conditions In these circumstances N

2O

is converted to NO via the following formulas [39]

N2+O +119872 larrrarr N

2O +119872 (7)

N2O +O larrrarr N

2+O2

(8)

N2O +O larrrarr NO +NO (9)

According to Bedat and Cheng the presence of H2O impuri-

ties conspicuously affects the N2O decomposition [40]

H2O +O larrrarr OH +OH (10)

N2O +OH larrrarr N

2+H2O (11)

In (7) 119872 is general third body N2O which was constituted

in (7) decomposes by (8) and (10) Equation (12) shows thechemical kinetics law for the rate of NO

119909formation via N

2O

intermediate mechanism119889 [NO]119889119905

= 1198701015840

5[N2O] [O] minus 119870

1015840

6[NO]2 (12)

6 Journal of Energy

00 01 02 03 04

Position (m)

200

400

600

800

1000

1200

1400

1600

1800

5mm6mm

7mm8mm

Tem

pera

ture

(K)

(a)

200e+03

190e+03

180e+03

170e+03

160e+03

150e+03

140e+03

130e+03

120e+03

110e+03

100e+03

900e+02

800e+02

700e+02

600e+02

500e+02

400e+02

300e+02

200e+02

100e+02

000e+00

5mm

6mm

7mm

8mm

(b)

Figure 6 Effect of variations of air diameter on central temperature (K) profile (a) line type and (b) contour type

The reaction rate constants are calculated by

1198701015840

119894= 1198700119879120573 exp(minus

119864119886

119877119879

) (13)

If 119889[N2O]119889119905 = 0 then (13) can be written as

[N2O]

=

[1198701015840

1[N2] [O] [119872] + 119870

1015840

4[N2] [O2] + 1198701015840

6[NO]2 + 119870

1015840

8[N2] [OH]]

1198701015840

2[119872] + (119870

1015840

3+ 1198701015840

5) [O] + 119870

1015840

7[H]

(14)

The concentration of radicals like O OH and H affects theconcentration rates and NO constitution [41] N

2O interme-

diate NO formation increases in low oxygen concentrationconditions [42]

53 Fuel-Bond NO119909Formation Mechanism Fuel-bond NO

119909

formation mechanism occurs when the molecular structuresof the fuel are constituted by nitrogen species In the com-bustion of these fuels the nitrogen atoms are decomposed tointermediate products form which can react with NO

119909[43]

6 Results and Discussion

61The Influence of Inlet Air Diameter on the Characteristics ofVortex Combustion The effect of inlet air diameter changingon the performance of vortex combustion is analyzed whilethe mass flow of fuel and air is kept constant Therefore theequivalence ratio was constant and equal to 0974 Figure 6(a)depicts the effect of inlet diameter changing on the statictemperature along the centerline with respect to the constantmass flow rate The temperature increases along the centralaxis due to the heat released by reactions For larger inletair diameter the temperature first sharply increases and thendecreases along the axial direction Figure 6(b) demonstratesthe temperature contours in two various surfaces There are

Position (m)000 005 010 015 020 025 030 035

40

60

80

100

120

140

5mm6mm

7mm8mm

NOx

(ppm

)

Figure 7 Effect of air diameter variation on the central NO119909profile

obvious differences in these contours From this figure itcan be interpreted that increasing in inlet air diameter withconstant mass flow rate (decreasing inlet velocity) leads toincrease in residence time The decrease of speed of vortexflame and diffusion of flame to the center of chamber are thetwo original reasons of these changes

The effect of diameter variation on the flame structureshowed that the NO

119909value on the centerline of the chamber

increased when the inlet air diameter increased as shownin Figure 7 It should be noted that the NO

119909concentration

increased with the increase of air inlet diameter due toincrease of the excess air and flame high temperature asshown in Figure 8 and Table 2 It is concluded that NO

119909for-

mation (Based on Zeldovich equations) is mainly controlledby temperature of combustion

Journal of Energy 7

Table 2 Average outlet quantity of chamber

Inlet air diameter Average NO119909outlet Average temperature

outlet5 72 4706 82 5007 95 5358 98 568

5mm

6mm

7mm

8mm

270e+02

257e+02

243e+02

230e+02

189e+02

176e+02

162e+02

140e+02

135e+02

122e+02

108e+02

945e+02

810e+01

675e+01

540e+01

405e+01

270e+01

135e+01

000e+00

(a)

(b)

(c)

(d)

Figure 8 NO119909emissions (ppm) contour for different air diameters

(a) 119889 = 5mm (b) 119889 = 6mm (c) 119889 = 7mm and (d) 119889 = 8mm

62 The Effect of Inlet Fuel Diameter on the Characteristics ofVortex Combustion Figure 9 illustrates the trend of NO

119909for-

mation and temperature distribution along with the chamberlength with respect to the various fuel diameters (2 25 3 35and 4mm) From this figure it can be construed that the sizeof the fuel inlet has insignificant effect on the NO

119909formation

and static temperature This shows that temperature flameas well as NO

119909emission in the chamber has more effect on

inlet air compared to inlet fuel in other words the inletfuel velocity has negligible contribution to vortex flamescompared to air inlet velocity

63 Preheating Air Effects Figure 10 shows temperature dis-tribution and NO

119909emissions formation when oxidizer is

applied in four different air temperatures (119879 = 300K 400K500K and 600K) while the diameter of the air and fuel inletthe mass flow rate of air and fuel inlet and equivalence ratioare kept constant at 5mm 2mm 00011 kgs 645 times 10minus5 kgsand 097 respectively All of the predictions are performedat the same central axis location with the above discussedconditions It was found that increasing the preheating airtemperature and decreasing the air viscosity could limit themaximum flame temperature and improve the temperature

Position (m)005 010 015 020 025 030 035

40

50

60

70

80

90

100

110

2mm25mm

3mm35mm

NOx

(ppm

)

(a)

Position (m)00 01 02 03 04

200

400

600

800

1200

1000

2mm25mm

3mm35mm

Tem

pera

ture

(K)

(b)

Figure 9 Effect of variations of fuel diameter on central (a) NO119909

profile and (b) temperature profile

uniformity in the furnace The data shows that with increas-ing preheating air at a constant mass flow rate the flamelocationmoves toward the air inlet because themomentumofthe air stream decreases Because the flame tends to approachthewall the temperature along the central axis decreases withincrease of air inlet temperature As a result the NO

119909emiss-

ion decreases when the flame temperature decreases

64 Preheating Fuel Effects Figures 11 and 12 show a min-imum effect of preheating fuel on the flame characteristicssuch as static temperature and NO

119909emissions The tempera-

ture and oxygen mole fraction of air kept constant and equalto 300K and 20 respectively It can be seen that the temper-ature along the central axis of the combustion chamber has nosignificant change with increasing of the fuel temperature In

8 Journal of Energy

Position (m)000 005 010 015 020 025 030 035

0

20

40

60

80

100

120

140

NOx

(ppm

)

300K400K

500K600K

(a)

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

Tem

pera

ture

(K)

300K400K

500K600K

(b)

Figure 10 Effect of preheating air on the central (a) NO119909profile and (b) temperature profile

Position (m)00 01 02 03 04

400

600

800

1000

1200

1400

300K350K

400K450K

Tem

pera

ture

(K)

Figure 11 The effect of preheating fuel on the central temperatureprofile

addition the results show that at all fuel temperatures thetemperature decreases along the combustion chamber dueto recession of flame and design of exhaust chamber Themaximum temperature is found in the vicinity of the bottomwall where the fuel enters the combustion chamber Theresults reveal that preheating inlet fuel has insignificant effecton the maximum flame temperature

Figure 12 shows that the NO119909emission rises as the max-

imum flame temperature increases With the increase ofthe fuel temperature at a fixed air flow rate there is a hightemperature mixing in the flame zone so there will be morethermal NO

119909products with the fuel and increases in the

temperatureThe increasedNO119909 caused by fuel preheating is

consistent with the hypothesis that preheating levels of 300K500K and 700K enhance fuel pyrolysis rates

Position (m)00 01 02 03 04

20

40

60

80

100

120

140

NOx

(ppm

)

300K350K

400K450K

Figure 12 The effect of preheating fuel on the central NO119909profile

7 Conclusions

A computational study on the performance of asymmetricvortex flame for various inlet flow diameters (air and fuel)and effect of preheating air and fuel was analyzedThe resultsshowed that increasing the inlet fuel diameter has negligibleeffect on the flame compared to effect of increasing inlet airto flame temperature and NO

119909emission The thermal field

results show that the effect of preheating can attain low-emission NO

119909as compared to fuel It is found that increasing

the preheated air temperature and fuel temperature coulddecrease the flame temperature and the combustion intensityandNO

119909emission when the airmass flow rate fuelmass flow

rate and equivalence ratio were considered constant for allsimulations Increasing the air velocity due to preheated air

Journal of Energy 9

in constant mass flow rate and equivalence ratio is found tobe an effective way to control the NO

119909emission because of

the decrease of the flame temperature

Nomenclature

119889 Chamber diameter (mm)

119863119899 Mass diffusivity (m2s)

119871 Length of chamber (mm)

119898 Air and fuel mass flow rate (kgs)119901 Pressure (pa)Pr119905 Prandtl number

Re Reynolds number (Re = 120588119906119889120583)119879 Temperature (K)119906119894119895 Velocity vector component (ms)

119884119899 Mass fraction of species 119899

Greek Symbols

120582 Thermal conductivity (W(msdotK))120583 Dynamic viscosity (kgmsdots)120583119905 Turbulent viscosity (kgmsdots)

120588 Density (kgm3)120593 Equivalence ratio119899 Chemical reaction rate

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] S EHosseiniMAWahid andAAAAbuelnuor ldquoHigh tem-perature air combustion sustainable technology to low NOxformationrdquo International Review ofMechanical Engineering vol6 no 5 pp 947ndash953 2012

[2] R K Srivastava R E Hall S Khan K Culligan and B WLani ldquoNitrogen oxides emission control options for coal-firedelectric utility boilersrdquo Journal of theAir andWasteManagementAssociation vol 55 no 9 pp 1367ndash1388 2005

[3] R K Srivastava W Neuffer D Grano S Khan J E Staudtand W Jozewicz ldquoControlling NO

119909emission from industrial

sourcesrdquo Environmental Progress vol 24 no 2 pp 181ndash1972005

[4] M Khaleghi S E Hosseini and M Abdul Wahid ldquoInvestiga-tions of asymmetric non-premixed meso-scale vortex combus-tionrdquo Applied Thermal Engineering vol 81 pp 140ndash153 2015

[5] D Feikema R H Chen and J F Driscoll ldquoEnhancement offlame blowout limits by the use of swirlrdquoCombustion and Flamevol 80 no 2 pp 183ndash195 1990

[6] H Gabler An Experimental and Numerical Investigation ofAsymmetrically-Fueled Whirl Flames Princeton University1998

[7] M-H Wu Y Wang V Yang and R A Yetter ldquoCombustionin meso-scale vortex chambersrdquo Proceedings of the CombustionInstitute vol 31 pp 3235ndash3242 2007

[8] M Khaleghi M A Wahid M M Seis and A Saat ldquoInves-tigation of vortex reacting flows in asymmetric Meso scale

combustorrdquoAppliedMechanics andMaterials vol 388 pp 246ndash250 2013

[9] K R McManus T Poinsot and S M Candel ldquoA review ofactive control of combustion instabilitiesrdquo Progress in Energyand Combustion Science vol 19 no 1 pp 1ndash29 1993

[10] S Candel ldquoCombustion dynamics and control progress andchallengesrdquo Proceedings of the Combustion Institute vol 29 no1 pp 1ndash28 2002

[11] Y Huang and V Yang ldquoDynamics and stability of lean-premixed swirl-stabilized combustionrdquo Progress in Energy andCombustion Science vol 35 no 4 pp 293ndash364 2009

[12] T C Lieuwen and V Yang Combustion Instabilities in GasTurbine Engines (Operational Experience Fundamental Mech-anisms and Modeling) Progress in Astronautics and Aeronau-tics American Institute of Aeronautics and Astronautics 2005

[13] B Kapadia and P Kutne ldquoCombustion behavior of swirl sta-bilised oxyfuel flames at elevated pressurerdquo in Proceedings of the9th AIAA Annual International Energy Conversion EngineeringConference (IECEC rsquo11) AIAA-5593 San Diego Calif USAJuly-August 2011

[14] P-H Renard DThevenin J C Rolon and S Candel ldquoDynam-ics of flamevortex interactionsrdquo Progress in Energy and Com-bustion Science vol 26 no 3 pp 225ndash282 2000

[15] M Stohr I Boxx C Carter and W Meier ldquoDynamics oflean blowout of a swirl-stabilized flame in a gas turbine modelcombustorrdquo Proceedings of the Combustion Institute vol 33 no2 pp 2953ndash2960 2011

[16] M R Johnson D Littlejohn W A Nazeer K O Smith andR K Cheng ldquoA comparison of the flowfields and emissions ofhigh-swirl injectors and low-swirl injectors for lean premixedgas turbinesrdquo Proceedings of the Combustion Institute vol 30pp 2867ndash2874 2005

[17] P K Ezhil Kumar and D P Mishra ldquoNumerical investigation ofthe flow and flame structure in an axisymmetric trapped vortexcombustorrdquo Fuel vol 102 pp 78ndash84 2012

[18] J Yuan and INaruse ldquoEffects of air dilution onhighly preheatedair combustion in a regenerative furnacerdquo Energy amp Fuels vol13 no 1 pp 99ndash104 1999

[19] J B Bell N J Brown M S Day M Frenklach J F Grcarand S R Tonse ldquoThe dependence of chemistry on the inletequivalence ratio in vortex-flame interactionsrdquo Proceedings ofthe Combustion Institute vol 28 no 2 pp 1933ndash1939 2000

[20] J Beer Combustion Aerodynumics Combustion TechnologySome Modern Developments 2012

[21] AKGupta andDG LilleyFlowfieldModeling andDiagnosticsTaylor amp Francis London UK 1985

[22] J J Choi Z Rusak and A K Kapila ldquoNumerical simulationof premixed chemical reactions with swirlrdquo CombustionTheoryand Modelling vol 11 no 6 pp 863ndash887 2007

[23] N Syred ldquoA review of oscillation mechanisms and the role ofthe precessing vortex core (PVC) in swirl combustion systemsrdquoProgress in Energy and Combustion Science vol 32 no 2 pp93ndash161 2006

[24] M Stohr I Boxx C D Carter and W Meier ldquoExperimentalstudy of vortex-flame interaction in a gas turbine modelcombustorrdquo Combustion and Flame vol 159 no 8 pp 2636ndash2649 2012

[25] M Stohr R Sadanandan and W Meier ldquoPhase-resolved char-acterization of vortex-flame interaction in a turbulent swirlflamerdquo Experiments in Fluids vol 51 no 4 pp 1153ndash1167 2011

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

6 Journal of Energy

00 01 02 03 04

Position (m)

200

400

600

800

1000

1200

1400

1600

1800

5mm6mm

7mm8mm

Tem

pera

ture

(K)

(a)

200e+03

190e+03

180e+03

170e+03

160e+03

150e+03

140e+03

130e+03

120e+03

110e+03

100e+03

900e+02

800e+02

700e+02

600e+02

500e+02

400e+02

300e+02

200e+02

100e+02

000e+00

5mm

6mm

7mm

8mm

(b)

Figure 6 Effect of variations of air diameter on central temperature (K) profile (a) line type and (b) contour type

The reaction rate constants are calculated by

1198701015840

119894= 1198700119879120573 exp(minus

119864119886

119877119879

) (13)

If 119889[N2O]119889119905 = 0 then (13) can be written as

[N2O]

=

[1198701015840

1[N2] [O] [119872] + 119870

1015840

4[N2] [O2] + 1198701015840

6[NO]2 + 119870

1015840

8[N2] [OH]]

1198701015840

2[119872] + (119870

1015840

3+ 1198701015840

5) [O] + 119870

1015840

7[H]

(14)

The concentration of radicals like O OH and H affects theconcentration rates and NO constitution [41] N

2O interme-

diate NO formation increases in low oxygen concentrationconditions [42]

53 Fuel-Bond NO119909Formation Mechanism Fuel-bond NO

119909

formation mechanism occurs when the molecular structuresof the fuel are constituted by nitrogen species In the com-bustion of these fuels the nitrogen atoms are decomposed tointermediate products form which can react with NO

119909[43]

6 Results and Discussion

61The Influence of Inlet Air Diameter on the Characteristics ofVortex Combustion The effect of inlet air diameter changingon the performance of vortex combustion is analyzed whilethe mass flow of fuel and air is kept constant Therefore theequivalence ratio was constant and equal to 0974 Figure 6(a)depicts the effect of inlet diameter changing on the statictemperature along the centerline with respect to the constantmass flow rate The temperature increases along the centralaxis due to the heat released by reactions For larger inletair diameter the temperature first sharply increases and thendecreases along the axial direction Figure 6(b) demonstratesthe temperature contours in two various surfaces There are

Position (m)000 005 010 015 020 025 030 035

40

60

80

100

120

140

5mm6mm

7mm8mm

NOx

(ppm

)

Figure 7 Effect of air diameter variation on the central NO119909profile

obvious differences in these contours From this figure itcan be interpreted that increasing in inlet air diameter withconstant mass flow rate (decreasing inlet velocity) leads toincrease in residence time The decrease of speed of vortexflame and diffusion of flame to the center of chamber are thetwo original reasons of these changes

The effect of diameter variation on the flame structureshowed that the NO

119909value on the centerline of the chamber

increased when the inlet air diameter increased as shownin Figure 7 It should be noted that the NO

119909concentration

increased with the increase of air inlet diameter due toincrease of the excess air and flame high temperature asshown in Figure 8 and Table 2 It is concluded that NO

119909for-

mation (Based on Zeldovich equations) is mainly controlledby temperature of combustion

Journal of Energy 7

Table 2 Average outlet quantity of chamber

Inlet air diameter Average NO119909outlet Average temperature

outlet5 72 4706 82 5007 95 5358 98 568

5mm

6mm

7mm

8mm

270e+02

257e+02

243e+02

230e+02

189e+02

176e+02

162e+02

140e+02

135e+02

122e+02

108e+02

945e+02

810e+01

675e+01

540e+01

405e+01

270e+01

135e+01

000e+00

(a)

(b)

(c)

(d)

Figure 8 NO119909emissions (ppm) contour for different air diameters

(a) 119889 = 5mm (b) 119889 = 6mm (c) 119889 = 7mm and (d) 119889 = 8mm

62 The Effect of Inlet Fuel Diameter on the Characteristics ofVortex Combustion Figure 9 illustrates the trend of NO

119909for-

mation and temperature distribution along with the chamberlength with respect to the various fuel diameters (2 25 3 35and 4mm) From this figure it can be construed that the sizeof the fuel inlet has insignificant effect on the NO

119909formation

and static temperature This shows that temperature flameas well as NO

119909emission in the chamber has more effect on

inlet air compared to inlet fuel in other words the inletfuel velocity has negligible contribution to vortex flamescompared to air inlet velocity

63 Preheating Air Effects Figure 10 shows temperature dis-tribution and NO

119909emissions formation when oxidizer is

applied in four different air temperatures (119879 = 300K 400K500K and 600K) while the diameter of the air and fuel inletthe mass flow rate of air and fuel inlet and equivalence ratioare kept constant at 5mm 2mm 00011 kgs 645 times 10minus5 kgsand 097 respectively All of the predictions are performedat the same central axis location with the above discussedconditions It was found that increasing the preheating airtemperature and decreasing the air viscosity could limit themaximum flame temperature and improve the temperature

Position (m)005 010 015 020 025 030 035

40

50

60

70

80

90

100

110

2mm25mm

3mm35mm

NOx

(ppm

)

(a)

Position (m)00 01 02 03 04

200

400

600

800

1200

1000

2mm25mm

3mm35mm

Tem

pera

ture

(K)

(b)

Figure 9 Effect of variations of fuel diameter on central (a) NO119909

profile and (b) temperature profile

uniformity in the furnace The data shows that with increas-ing preheating air at a constant mass flow rate the flamelocationmoves toward the air inlet because themomentumofthe air stream decreases Because the flame tends to approachthewall the temperature along the central axis decreases withincrease of air inlet temperature As a result the NO

119909emiss-

ion decreases when the flame temperature decreases

64 Preheating Fuel Effects Figures 11 and 12 show a min-imum effect of preheating fuel on the flame characteristicssuch as static temperature and NO

119909emissions The tempera-

ture and oxygen mole fraction of air kept constant and equalto 300K and 20 respectively It can be seen that the temper-ature along the central axis of the combustion chamber has nosignificant change with increasing of the fuel temperature In

8 Journal of Energy

Position (m)000 005 010 015 020 025 030 035

0

20

40

60

80

100

120

140

NOx

(ppm

)

300K400K

500K600K

(a)

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

Tem

pera

ture

(K)

300K400K

500K600K

(b)

Figure 10 Effect of preheating air on the central (a) NO119909profile and (b) temperature profile

Position (m)00 01 02 03 04

400

600

800

1000

1200

1400

300K350K

400K450K

Tem

pera

ture

(K)

Figure 11 The effect of preheating fuel on the central temperatureprofile

addition the results show that at all fuel temperatures thetemperature decreases along the combustion chamber dueto recession of flame and design of exhaust chamber Themaximum temperature is found in the vicinity of the bottomwall where the fuel enters the combustion chamber Theresults reveal that preheating inlet fuel has insignificant effecton the maximum flame temperature

Figure 12 shows that the NO119909emission rises as the max-

imum flame temperature increases With the increase ofthe fuel temperature at a fixed air flow rate there is a hightemperature mixing in the flame zone so there will be morethermal NO

119909products with the fuel and increases in the

temperatureThe increasedNO119909 caused by fuel preheating is

consistent with the hypothesis that preheating levels of 300K500K and 700K enhance fuel pyrolysis rates

Position (m)00 01 02 03 04

20

40

60

80

100

120

140

NOx

(ppm

)

300K350K

400K450K

Figure 12 The effect of preheating fuel on the central NO119909profile

7 Conclusions

A computational study on the performance of asymmetricvortex flame for various inlet flow diameters (air and fuel)and effect of preheating air and fuel was analyzedThe resultsshowed that increasing the inlet fuel diameter has negligibleeffect on the flame compared to effect of increasing inlet airto flame temperature and NO

119909emission The thermal field

results show that the effect of preheating can attain low-emission NO

119909as compared to fuel It is found that increasing

the preheated air temperature and fuel temperature coulddecrease the flame temperature and the combustion intensityandNO

119909emission when the airmass flow rate fuelmass flow

rate and equivalence ratio were considered constant for allsimulations Increasing the air velocity due to preheated air

Journal of Energy 9

in constant mass flow rate and equivalence ratio is found tobe an effective way to control the NO

119909emission because of

the decrease of the flame temperature

Nomenclature

119889 Chamber diameter (mm)

119863119899 Mass diffusivity (m2s)

119871 Length of chamber (mm)

119898 Air and fuel mass flow rate (kgs)119901 Pressure (pa)Pr119905 Prandtl number

Re Reynolds number (Re = 120588119906119889120583)119879 Temperature (K)119906119894119895 Velocity vector component (ms)

119884119899 Mass fraction of species 119899

Greek Symbols

120582 Thermal conductivity (W(msdotK))120583 Dynamic viscosity (kgmsdots)120583119905 Turbulent viscosity (kgmsdots)

120588 Density (kgm3)120593 Equivalence ratio119899 Chemical reaction rate

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] S EHosseiniMAWahid andAAAAbuelnuor ldquoHigh tem-perature air combustion sustainable technology to low NOxformationrdquo International Review ofMechanical Engineering vol6 no 5 pp 947ndash953 2012

[2] R K Srivastava R E Hall S Khan K Culligan and B WLani ldquoNitrogen oxides emission control options for coal-firedelectric utility boilersrdquo Journal of theAir andWasteManagementAssociation vol 55 no 9 pp 1367ndash1388 2005

[3] R K Srivastava W Neuffer D Grano S Khan J E Staudtand W Jozewicz ldquoControlling NO

119909emission from industrial

sourcesrdquo Environmental Progress vol 24 no 2 pp 181ndash1972005

[4] M Khaleghi S E Hosseini and M Abdul Wahid ldquoInvestiga-tions of asymmetric non-premixed meso-scale vortex combus-tionrdquo Applied Thermal Engineering vol 81 pp 140ndash153 2015

[5] D Feikema R H Chen and J F Driscoll ldquoEnhancement offlame blowout limits by the use of swirlrdquoCombustion and Flamevol 80 no 2 pp 183ndash195 1990

[6] H Gabler An Experimental and Numerical Investigation ofAsymmetrically-Fueled Whirl Flames Princeton University1998

[7] M-H Wu Y Wang V Yang and R A Yetter ldquoCombustionin meso-scale vortex chambersrdquo Proceedings of the CombustionInstitute vol 31 pp 3235ndash3242 2007

[8] M Khaleghi M A Wahid M M Seis and A Saat ldquoInves-tigation of vortex reacting flows in asymmetric Meso scale

combustorrdquoAppliedMechanics andMaterials vol 388 pp 246ndash250 2013

[9] K R McManus T Poinsot and S M Candel ldquoA review ofactive control of combustion instabilitiesrdquo Progress in Energyand Combustion Science vol 19 no 1 pp 1ndash29 1993

[10] S Candel ldquoCombustion dynamics and control progress andchallengesrdquo Proceedings of the Combustion Institute vol 29 no1 pp 1ndash28 2002

[11] Y Huang and V Yang ldquoDynamics and stability of lean-premixed swirl-stabilized combustionrdquo Progress in Energy andCombustion Science vol 35 no 4 pp 293ndash364 2009

[12] T C Lieuwen and V Yang Combustion Instabilities in GasTurbine Engines (Operational Experience Fundamental Mech-anisms and Modeling) Progress in Astronautics and Aeronau-tics American Institute of Aeronautics and Astronautics 2005

[13] B Kapadia and P Kutne ldquoCombustion behavior of swirl sta-bilised oxyfuel flames at elevated pressurerdquo in Proceedings of the9th AIAA Annual International Energy Conversion EngineeringConference (IECEC rsquo11) AIAA-5593 San Diego Calif USAJuly-August 2011

[14] P-H Renard DThevenin J C Rolon and S Candel ldquoDynam-ics of flamevortex interactionsrdquo Progress in Energy and Com-bustion Science vol 26 no 3 pp 225ndash282 2000

[15] M Stohr I Boxx C Carter and W Meier ldquoDynamics oflean blowout of a swirl-stabilized flame in a gas turbine modelcombustorrdquo Proceedings of the Combustion Institute vol 33 no2 pp 2953ndash2960 2011

[16] M R Johnson D Littlejohn W A Nazeer K O Smith andR K Cheng ldquoA comparison of the flowfields and emissions ofhigh-swirl injectors and low-swirl injectors for lean premixedgas turbinesrdquo Proceedings of the Combustion Institute vol 30pp 2867ndash2874 2005

[17] P K Ezhil Kumar and D P Mishra ldquoNumerical investigation ofthe flow and flame structure in an axisymmetric trapped vortexcombustorrdquo Fuel vol 102 pp 78ndash84 2012

[18] J Yuan and INaruse ldquoEffects of air dilution onhighly preheatedair combustion in a regenerative furnacerdquo Energy amp Fuels vol13 no 1 pp 99ndash104 1999

[19] J B Bell N J Brown M S Day M Frenklach J F Grcarand S R Tonse ldquoThe dependence of chemistry on the inletequivalence ratio in vortex-flame interactionsrdquo Proceedings ofthe Combustion Institute vol 28 no 2 pp 1933ndash1939 2000

[20] J Beer Combustion Aerodynumics Combustion TechnologySome Modern Developments 2012

[21] AKGupta andDG LilleyFlowfieldModeling andDiagnosticsTaylor amp Francis London UK 1985

[22] J J Choi Z Rusak and A K Kapila ldquoNumerical simulationof premixed chemical reactions with swirlrdquo CombustionTheoryand Modelling vol 11 no 6 pp 863ndash887 2007

[23] N Syred ldquoA review of oscillation mechanisms and the role ofthe precessing vortex core (PVC) in swirl combustion systemsrdquoProgress in Energy and Combustion Science vol 32 no 2 pp93ndash161 2006

[24] M Stohr I Boxx C D Carter and W Meier ldquoExperimentalstudy of vortex-flame interaction in a gas turbine modelcombustorrdquo Combustion and Flame vol 159 no 8 pp 2636ndash2649 2012

[25] M Stohr R Sadanandan and W Meier ldquoPhase-resolved char-acterization of vortex-flame interaction in a turbulent swirlflamerdquo Experiments in Fluids vol 51 no 4 pp 1153ndash1167 2011

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of Energy 7

Table 2 Average outlet quantity of chamber

Inlet air diameter Average NO119909outlet Average temperature

outlet5 72 4706 82 5007 95 5358 98 568

5mm

6mm

7mm

8mm

270e+02

257e+02

243e+02

230e+02

189e+02

176e+02

162e+02

140e+02

135e+02

122e+02

108e+02

945e+02

810e+01

675e+01

540e+01

405e+01

270e+01

135e+01

000e+00

(a)

(b)

(c)

(d)

Figure 8 NO119909emissions (ppm) contour for different air diameters

(a) 119889 = 5mm (b) 119889 = 6mm (c) 119889 = 7mm and (d) 119889 = 8mm

62 The Effect of Inlet Fuel Diameter on the Characteristics ofVortex Combustion Figure 9 illustrates the trend of NO

119909for-

mation and temperature distribution along with the chamberlength with respect to the various fuel diameters (2 25 3 35and 4mm) From this figure it can be construed that the sizeof the fuel inlet has insignificant effect on the NO

119909formation

and static temperature This shows that temperature flameas well as NO

119909emission in the chamber has more effect on

inlet air compared to inlet fuel in other words the inletfuel velocity has negligible contribution to vortex flamescompared to air inlet velocity

63 Preheating Air Effects Figure 10 shows temperature dis-tribution and NO

119909emissions formation when oxidizer is

applied in four different air temperatures (119879 = 300K 400K500K and 600K) while the diameter of the air and fuel inletthe mass flow rate of air and fuel inlet and equivalence ratioare kept constant at 5mm 2mm 00011 kgs 645 times 10minus5 kgsand 097 respectively All of the predictions are performedat the same central axis location with the above discussedconditions It was found that increasing the preheating airtemperature and decreasing the air viscosity could limit themaximum flame temperature and improve the temperature

Position (m)005 010 015 020 025 030 035

40

50

60

70

80

90

100

110

2mm25mm

3mm35mm

NOx

(ppm

)

(a)

Position (m)00 01 02 03 04

200

400

600

800

1200

1000

2mm25mm

3mm35mm

Tem

pera

ture

(K)

(b)

Figure 9 Effect of variations of fuel diameter on central (a) NO119909

profile and (b) temperature profile

uniformity in the furnace The data shows that with increas-ing preheating air at a constant mass flow rate the flamelocationmoves toward the air inlet because themomentumofthe air stream decreases Because the flame tends to approachthewall the temperature along the central axis decreases withincrease of air inlet temperature As a result the NO

119909emiss-

ion decreases when the flame temperature decreases

64 Preheating Fuel Effects Figures 11 and 12 show a min-imum effect of preheating fuel on the flame characteristicssuch as static temperature and NO

119909emissions The tempera-

ture and oxygen mole fraction of air kept constant and equalto 300K and 20 respectively It can be seen that the temper-ature along the central axis of the combustion chamber has nosignificant change with increasing of the fuel temperature In

8 Journal of Energy

Position (m)000 005 010 015 020 025 030 035

0

20

40

60

80

100

120

140

NOx

(ppm

)

300K400K

500K600K

(a)

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

Tem

pera

ture

(K)

300K400K

500K600K

(b)

Figure 10 Effect of preheating air on the central (a) NO119909profile and (b) temperature profile

Position (m)00 01 02 03 04

400

600

800

1000

1200

1400

300K350K

400K450K

Tem

pera

ture

(K)

Figure 11 The effect of preheating fuel on the central temperatureprofile

addition the results show that at all fuel temperatures thetemperature decreases along the combustion chamber dueto recession of flame and design of exhaust chamber Themaximum temperature is found in the vicinity of the bottomwall where the fuel enters the combustion chamber Theresults reveal that preheating inlet fuel has insignificant effecton the maximum flame temperature

Figure 12 shows that the NO119909emission rises as the max-

imum flame temperature increases With the increase ofthe fuel temperature at a fixed air flow rate there is a hightemperature mixing in the flame zone so there will be morethermal NO

119909products with the fuel and increases in the

temperatureThe increasedNO119909 caused by fuel preheating is

consistent with the hypothesis that preheating levels of 300K500K and 700K enhance fuel pyrolysis rates

Position (m)00 01 02 03 04

20

40

60

80

100

120

140

NOx

(ppm

)

300K350K

400K450K

Figure 12 The effect of preheating fuel on the central NO119909profile

7 Conclusions

A computational study on the performance of asymmetricvortex flame for various inlet flow diameters (air and fuel)and effect of preheating air and fuel was analyzedThe resultsshowed that increasing the inlet fuel diameter has negligibleeffect on the flame compared to effect of increasing inlet airto flame temperature and NO

119909emission The thermal field

results show that the effect of preheating can attain low-emission NO

119909as compared to fuel It is found that increasing

the preheated air temperature and fuel temperature coulddecrease the flame temperature and the combustion intensityandNO

119909emission when the airmass flow rate fuelmass flow

rate and equivalence ratio were considered constant for allsimulations Increasing the air velocity due to preheated air

Journal of Energy 9

in constant mass flow rate and equivalence ratio is found tobe an effective way to control the NO

119909emission because of

the decrease of the flame temperature

Nomenclature

119889 Chamber diameter (mm)

119863119899 Mass diffusivity (m2s)

119871 Length of chamber (mm)

119898 Air and fuel mass flow rate (kgs)119901 Pressure (pa)Pr119905 Prandtl number

Re Reynolds number (Re = 120588119906119889120583)119879 Temperature (K)119906119894119895 Velocity vector component (ms)

119884119899 Mass fraction of species 119899

Greek Symbols

120582 Thermal conductivity (W(msdotK))120583 Dynamic viscosity (kgmsdots)120583119905 Turbulent viscosity (kgmsdots)

120588 Density (kgm3)120593 Equivalence ratio119899 Chemical reaction rate

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] S EHosseiniMAWahid andAAAAbuelnuor ldquoHigh tem-perature air combustion sustainable technology to low NOxformationrdquo International Review ofMechanical Engineering vol6 no 5 pp 947ndash953 2012

[2] R K Srivastava R E Hall S Khan K Culligan and B WLani ldquoNitrogen oxides emission control options for coal-firedelectric utility boilersrdquo Journal of theAir andWasteManagementAssociation vol 55 no 9 pp 1367ndash1388 2005

[3] R K Srivastava W Neuffer D Grano S Khan J E Staudtand W Jozewicz ldquoControlling NO

119909emission from industrial

sourcesrdquo Environmental Progress vol 24 no 2 pp 181ndash1972005

[4] M Khaleghi S E Hosseini and M Abdul Wahid ldquoInvestiga-tions of asymmetric non-premixed meso-scale vortex combus-tionrdquo Applied Thermal Engineering vol 81 pp 140ndash153 2015

[5] D Feikema R H Chen and J F Driscoll ldquoEnhancement offlame blowout limits by the use of swirlrdquoCombustion and Flamevol 80 no 2 pp 183ndash195 1990

[6] H Gabler An Experimental and Numerical Investigation ofAsymmetrically-Fueled Whirl Flames Princeton University1998

[7] M-H Wu Y Wang V Yang and R A Yetter ldquoCombustionin meso-scale vortex chambersrdquo Proceedings of the CombustionInstitute vol 31 pp 3235ndash3242 2007

[8] M Khaleghi M A Wahid M M Seis and A Saat ldquoInves-tigation of vortex reacting flows in asymmetric Meso scale

combustorrdquoAppliedMechanics andMaterials vol 388 pp 246ndash250 2013

[9] K R McManus T Poinsot and S M Candel ldquoA review ofactive control of combustion instabilitiesrdquo Progress in Energyand Combustion Science vol 19 no 1 pp 1ndash29 1993

[10] S Candel ldquoCombustion dynamics and control progress andchallengesrdquo Proceedings of the Combustion Institute vol 29 no1 pp 1ndash28 2002

[11] Y Huang and V Yang ldquoDynamics and stability of lean-premixed swirl-stabilized combustionrdquo Progress in Energy andCombustion Science vol 35 no 4 pp 293ndash364 2009

[12] T C Lieuwen and V Yang Combustion Instabilities in GasTurbine Engines (Operational Experience Fundamental Mech-anisms and Modeling) Progress in Astronautics and Aeronau-tics American Institute of Aeronautics and Astronautics 2005

[13] B Kapadia and P Kutne ldquoCombustion behavior of swirl sta-bilised oxyfuel flames at elevated pressurerdquo in Proceedings of the9th AIAA Annual International Energy Conversion EngineeringConference (IECEC rsquo11) AIAA-5593 San Diego Calif USAJuly-August 2011

[14] P-H Renard DThevenin J C Rolon and S Candel ldquoDynam-ics of flamevortex interactionsrdquo Progress in Energy and Com-bustion Science vol 26 no 3 pp 225ndash282 2000

[15] M Stohr I Boxx C Carter and W Meier ldquoDynamics oflean blowout of a swirl-stabilized flame in a gas turbine modelcombustorrdquo Proceedings of the Combustion Institute vol 33 no2 pp 2953ndash2960 2011

[16] M R Johnson D Littlejohn W A Nazeer K O Smith andR K Cheng ldquoA comparison of the flowfields and emissions ofhigh-swirl injectors and low-swirl injectors for lean premixedgas turbinesrdquo Proceedings of the Combustion Institute vol 30pp 2867ndash2874 2005

[17] P K Ezhil Kumar and D P Mishra ldquoNumerical investigation ofthe flow and flame structure in an axisymmetric trapped vortexcombustorrdquo Fuel vol 102 pp 78ndash84 2012

[18] J Yuan and INaruse ldquoEffects of air dilution onhighly preheatedair combustion in a regenerative furnacerdquo Energy amp Fuels vol13 no 1 pp 99ndash104 1999

[19] J B Bell N J Brown M S Day M Frenklach J F Grcarand S R Tonse ldquoThe dependence of chemistry on the inletequivalence ratio in vortex-flame interactionsrdquo Proceedings ofthe Combustion Institute vol 28 no 2 pp 1933ndash1939 2000

[20] J Beer Combustion Aerodynumics Combustion TechnologySome Modern Developments 2012

[21] AKGupta andDG LilleyFlowfieldModeling andDiagnosticsTaylor amp Francis London UK 1985

[22] J J Choi Z Rusak and A K Kapila ldquoNumerical simulationof premixed chemical reactions with swirlrdquo CombustionTheoryand Modelling vol 11 no 6 pp 863ndash887 2007

[23] N Syred ldquoA review of oscillation mechanisms and the role ofthe precessing vortex core (PVC) in swirl combustion systemsrdquoProgress in Energy and Combustion Science vol 32 no 2 pp93ndash161 2006

[24] M Stohr I Boxx C D Carter and W Meier ldquoExperimentalstudy of vortex-flame interaction in a gas turbine modelcombustorrdquo Combustion and Flame vol 159 no 8 pp 2636ndash2649 2012

[25] M Stohr R Sadanandan and W Meier ldquoPhase-resolved char-acterization of vortex-flame interaction in a turbulent swirlflamerdquo Experiments in Fluids vol 51 no 4 pp 1153ndash1167 2011

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

8 Journal of Energy

Position (m)000 005 010 015 020 025 030 035

0

20

40

60

80

100

120

140

NOx

(ppm

)

300K400K

500K600K

(a)

Position (m)00 01 02 03 04

200

400

600

800

1000

1200

1400

Tem

pera

ture

(K)

300K400K

500K600K

(b)

Figure 10 Effect of preheating air on the central (a) NO119909profile and (b) temperature profile

Position (m)00 01 02 03 04

400

600

800

1000

1200

1400

300K350K

400K450K

Tem

pera

ture

(K)

Figure 11 The effect of preheating fuel on the central temperatureprofile

addition the results show that at all fuel temperatures thetemperature decreases along the combustion chamber dueto recession of flame and design of exhaust chamber Themaximum temperature is found in the vicinity of the bottomwall where the fuel enters the combustion chamber Theresults reveal that preheating inlet fuel has insignificant effecton the maximum flame temperature

Figure 12 shows that the NO119909emission rises as the max-

imum flame temperature increases With the increase ofthe fuel temperature at a fixed air flow rate there is a hightemperature mixing in the flame zone so there will be morethermal NO

119909products with the fuel and increases in the

temperatureThe increasedNO119909 caused by fuel preheating is

consistent with the hypothesis that preheating levels of 300K500K and 700K enhance fuel pyrolysis rates

Position (m)00 01 02 03 04

20

40

60

80

100

120

140

NOx

(ppm

)

300K350K

400K450K

Figure 12 The effect of preheating fuel on the central NO119909profile

7 Conclusions

A computational study on the performance of asymmetricvortex flame for various inlet flow diameters (air and fuel)and effect of preheating air and fuel was analyzedThe resultsshowed that increasing the inlet fuel diameter has negligibleeffect on the flame compared to effect of increasing inlet airto flame temperature and NO

119909emission The thermal field

results show that the effect of preheating can attain low-emission NO

119909as compared to fuel It is found that increasing

the preheated air temperature and fuel temperature coulddecrease the flame temperature and the combustion intensityandNO

119909emission when the airmass flow rate fuelmass flow

rate and equivalence ratio were considered constant for allsimulations Increasing the air velocity due to preheated air

Journal of Energy 9

in constant mass flow rate and equivalence ratio is found tobe an effective way to control the NO

119909emission because of

the decrease of the flame temperature

Nomenclature

119889 Chamber diameter (mm)

119863119899 Mass diffusivity (m2s)

119871 Length of chamber (mm)

119898 Air and fuel mass flow rate (kgs)119901 Pressure (pa)Pr119905 Prandtl number

Re Reynolds number (Re = 120588119906119889120583)119879 Temperature (K)119906119894119895 Velocity vector component (ms)

119884119899 Mass fraction of species 119899

Greek Symbols

120582 Thermal conductivity (W(msdotK))120583 Dynamic viscosity (kgmsdots)120583119905 Turbulent viscosity (kgmsdots)

120588 Density (kgm3)120593 Equivalence ratio119899 Chemical reaction rate

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] S EHosseiniMAWahid andAAAAbuelnuor ldquoHigh tem-perature air combustion sustainable technology to low NOxformationrdquo International Review ofMechanical Engineering vol6 no 5 pp 947ndash953 2012

[2] R K Srivastava R E Hall S Khan K Culligan and B WLani ldquoNitrogen oxides emission control options for coal-firedelectric utility boilersrdquo Journal of theAir andWasteManagementAssociation vol 55 no 9 pp 1367ndash1388 2005

[3] R K Srivastava W Neuffer D Grano S Khan J E Staudtand W Jozewicz ldquoControlling NO

119909emission from industrial

sourcesrdquo Environmental Progress vol 24 no 2 pp 181ndash1972005

[4] M Khaleghi S E Hosseini and M Abdul Wahid ldquoInvestiga-tions of asymmetric non-premixed meso-scale vortex combus-tionrdquo Applied Thermal Engineering vol 81 pp 140ndash153 2015

[5] D Feikema R H Chen and J F Driscoll ldquoEnhancement offlame blowout limits by the use of swirlrdquoCombustion and Flamevol 80 no 2 pp 183ndash195 1990

[6] H Gabler An Experimental and Numerical Investigation ofAsymmetrically-Fueled Whirl Flames Princeton University1998

[7] M-H Wu Y Wang V Yang and R A Yetter ldquoCombustionin meso-scale vortex chambersrdquo Proceedings of the CombustionInstitute vol 31 pp 3235ndash3242 2007

[8] M Khaleghi M A Wahid M M Seis and A Saat ldquoInves-tigation of vortex reacting flows in asymmetric Meso scale

combustorrdquoAppliedMechanics andMaterials vol 388 pp 246ndash250 2013

[9] K R McManus T Poinsot and S M Candel ldquoA review ofactive control of combustion instabilitiesrdquo Progress in Energyand Combustion Science vol 19 no 1 pp 1ndash29 1993

[10] S Candel ldquoCombustion dynamics and control progress andchallengesrdquo Proceedings of the Combustion Institute vol 29 no1 pp 1ndash28 2002

[11] Y Huang and V Yang ldquoDynamics and stability of lean-premixed swirl-stabilized combustionrdquo Progress in Energy andCombustion Science vol 35 no 4 pp 293ndash364 2009

[12] T C Lieuwen and V Yang Combustion Instabilities in GasTurbine Engines (Operational Experience Fundamental Mech-anisms and Modeling) Progress in Astronautics and Aeronau-tics American Institute of Aeronautics and Astronautics 2005

[13] B Kapadia and P Kutne ldquoCombustion behavior of swirl sta-bilised oxyfuel flames at elevated pressurerdquo in Proceedings of the9th AIAA Annual International Energy Conversion EngineeringConference (IECEC rsquo11) AIAA-5593 San Diego Calif USAJuly-August 2011

[14] P-H Renard DThevenin J C Rolon and S Candel ldquoDynam-ics of flamevortex interactionsrdquo Progress in Energy and Com-bustion Science vol 26 no 3 pp 225ndash282 2000

[15] M Stohr I Boxx C Carter and W Meier ldquoDynamics oflean blowout of a swirl-stabilized flame in a gas turbine modelcombustorrdquo Proceedings of the Combustion Institute vol 33 no2 pp 2953ndash2960 2011

[16] M R Johnson D Littlejohn W A Nazeer K O Smith andR K Cheng ldquoA comparison of the flowfields and emissions ofhigh-swirl injectors and low-swirl injectors for lean premixedgas turbinesrdquo Proceedings of the Combustion Institute vol 30pp 2867ndash2874 2005

[17] P K Ezhil Kumar and D P Mishra ldquoNumerical investigation ofthe flow and flame structure in an axisymmetric trapped vortexcombustorrdquo Fuel vol 102 pp 78ndash84 2012

[18] J Yuan and INaruse ldquoEffects of air dilution onhighly preheatedair combustion in a regenerative furnacerdquo Energy amp Fuels vol13 no 1 pp 99ndash104 1999

[19] J B Bell N J Brown M S Day M Frenklach J F Grcarand S R Tonse ldquoThe dependence of chemistry on the inletequivalence ratio in vortex-flame interactionsrdquo Proceedings ofthe Combustion Institute vol 28 no 2 pp 1933ndash1939 2000

[20] J Beer Combustion Aerodynumics Combustion TechnologySome Modern Developments 2012

[21] AKGupta andDG LilleyFlowfieldModeling andDiagnosticsTaylor amp Francis London UK 1985

[22] J J Choi Z Rusak and A K Kapila ldquoNumerical simulationof premixed chemical reactions with swirlrdquo CombustionTheoryand Modelling vol 11 no 6 pp 863ndash887 2007

[23] N Syred ldquoA review of oscillation mechanisms and the role ofthe precessing vortex core (PVC) in swirl combustion systemsrdquoProgress in Energy and Combustion Science vol 32 no 2 pp93ndash161 2006

[24] M Stohr I Boxx C D Carter and W Meier ldquoExperimentalstudy of vortex-flame interaction in a gas turbine modelcombustorrdquo Combustion and Flame vol 159 no 8 pp 2636ndash2649 2012

[25] M Stohr R Sadanandan and W Meier ldquoPhase-resolved char-acterization of vortex-flame interaction in a turbulent swirlflamerdquo Experiments in Fluids vol 51 no 4 pp 1153ndash1167 2011

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of Energy 9

in constant mass flow rate and equivalence ratio is found tobe an effective way to control the NO

119909emission because of

the decrease of the flame temperature

Nomenclature

119889 Chamber diameter (mm)

119863119899 Mass diffusivity (m2s)

119871 Length of chamber (mm)

119898 Air and fuel mass flow rate (kgs)119901 Pressure (pa)Pr119905 Prandtl number

Re Reynolds number (Re = 120588119906119889120583)119879 Temperature (K)119906119894119895 Velocity vector component (ms)

119884119899 Mass fraction of species 119899

Greek Symbols

120582 Thermal conductivity (W(msdotK))120583 Dynamic viscosity (kgmsdots)120583119905 Turbulent viscosity (kgmsdots)

120588 Density (kgm3)120593 Equivalence ratio119899 Chemical reaction rate

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] S EHosseiniMAWahid andAAAAbuelnuor ldquoHigh tem-perature air combustion sustainable technology to low NOxformationrdquo International Review ofMechanical Engineering vol6 no 5 pp 947ndash953 2012

[2] R K Srivastava R E Hall S Khan K Culligan and B WLani ldquoNitrogen oxides emission control options for coal-firedelectric utility boilersrdquo Journal of theAir andWasteManagementAssociation vol 55 no 9 pp 1367ndash1388 2005

[3] R K Srivastava W Neuffer D Grano S Khan J E Staudtand W Jozewicz ldquoControlling NO

119909emission from industrial

sourcesrdquo Environmental Progress vol 24 no 2 pp 181ndash1972005

[4] M Khaleghi S E Hosseini and M Abdul Wahid ldquoInvestiga-tions of asymmetric non-premixed meso-scale vortex combus-tionrdquo Applied Thermal Engineering vol 81 pp 140ndash153 2015

[5] D Feikema R H Chen and J F Driscoll ldquoEnhancement offlame blowout limits by the use of swirlrdquoCombustion and Flamevol 80 no 2 pp 183ndash195 1990

[6] H Gabler An Experimental and Numerical Investigation ofAsymmetrically-Fueled Whirl Flames Princeton University1998

[7] M-H Wu Y Wang V Yang and R A Yetter ldquoCombustionin meso-scale vortex chambersrdquo Proceedings of the CombustionInstitute vol 31 pp 3235ndash3242 2007

[8] M Khaleghi M A Wahid M M Seis and A Saat ldquoInves-tigation of vortex reacting flows in asymmetric Meso scale

combustorrdquoAppliedMechanics andMaterials vol 388 pp 246ndash250 2013

[9] K R McManus T Poinsot and S M Candel ldquoA review ofactive control of combustion instabilitiesrdquo Progress in Energyand Combustion Science vol 19 no 1 pp 1ndash29 1993

[10] S Candel ldquoCombustion dynamics and control progress andchallengesrdquo Proceedings of the Combustion Institute vol 29 no1 pp 1ndash28 2002

[11] Y Huang and V Yang ldquoDynamics and stability of lean-premixed swirl-stabilized combustionrdquo Progress in Energy andCombustion Science vol 35 no 4 pp 293ndash364 2009

[12] T C Lieuwen and V Yang Combustion Instabilities in GasTurbine Engines (Operational Experience Fundamental Mech-anisms and Modeling) Progress in Astronautics and Aeronau-tics American Institute of Aeronautics and Astronautics 2005

[13] B Kapadia and P Kutne ldquoCombustion behavior of swirl sta-bilised oxyfuel flames at elevated pressurerdquo in Proceedings of the9th AIAA Annual International Energy Conversion EngineeringConference (IECEC rsquo11) AIAA-5593 San Diego Calif USAJuly-August 2011

[14] P-H Renard DThevenin J C Rolon and S Candel ldquoDynam-ics of flamevortex interactionsrdquo Progress in Energy and Com-bustion Science vol 26 no 3 pp 225ndash282 2000

[15] M Stohr I Boxx C Carter and W Meier ldquoDynamics oflean blowout of a swirl-stabilized flame in a gas turbine modelcombustorrdquo Proceedings of the Combustion Institute vol 33 no2 pp 2953ndash2960 2011

[16] M R Johnson D Littlejohn W A Nazeer K O Smith andR K Cheng ldquoA comparison of the flowfields and emissions ofhigh-swirl injectors and low-swirl injectors for lean premixedgas turbinesrdquo Proceedings of the Combustion Institute vol 30pp 2867ndash2874 2005

[17] P K Ezhil Kumar and D P Mishra ldquoNumerical investigation ofthe flow and flame structure in an axisymmetric trapped vortexcombustorrdquo Fuel vol 102 pp 78ndash84 2012

[18] J Yuan and INaruse ldquoEffects of air dilution onhighly preheatedair combustion in a regenerative furnacerdquo Energy amp Fuels vol13 no 1 pp 99ndash104 1999

[19] J B Bell N J Brown M S Day M Frenklach J F Grcarand S R Tonse ldquoThe dependence of chemistry on the inletequivalence ratio in vortex-flame interactionsrdquo Proceedings ofthe Combustion Institute vol 28 no 2 pp 1933ndash1939 2000

[20] J Beer Combustion Aerodynumics Combustion TechnologySome Modern Developments 2012

[21] AKGupta andDG LilleyFlowfieldModeling andDiagnosticsTaylor amp Francis London UK 1985

[22] J J Choi Z Rusak and A K Kapila ldquoNumerical simulationof premixed chemical reactions with swirlrdquo CombustionTheoryand Modelling vol 11 no 6 pp 863ndash887 2007

[23] N Syred ldquoA review of oscillation mechanisms and the role ofthe precessing vortex core (PVC) in swirl combustion systemsrdquoProgress in Energy and Combustion Science vol 32 no 2 pp93ndash161 2006

[24] M Stohr I Boxx C D Carter and W Meier ldquoExperimentalstudy of vortex-flame interaction in a gas turbine modelcombustorrdquo Combustion and Flame vol 159 no 8 pp 2636ndash2649 2012

[25] M Stohr R Sadanandan and W Meier ldquoPhase-resolved char-acterization of vortex-flame interaction in a turbulent swirlflamerdquo Experiments in Fluids vol 51 no 4 pp 1153ndash1167 2011

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

10 Journal of Energy

[26] K M Saqr H S Aly M M Sies and M A Wahid ldquoComputa-tional and experimental investigations of turbulent asymmetricvortex flamesrdquo International Communications in Heat andMassTransfer vol 38 no 3 pp 353ndash362 2011

[27] A Obieglo J Gass and D Poulikakos ldquoComparative study ofmodeling a hydrogen nonpremixed turbulent flamerdquo Combus-tion and Flame vol 122 no 1-2 pp 176ndash194 2000

[28] K M Saqr MM Sies andM AWahid ldquoNumerical investiga-tion of the turbulence-combustion interaction in nonpremixedCH4air flamesrdquo International Journal of Applied Mathematics

and Mechanics vol 5 no 8 pp 69ndash79 2009[29] ANSYS ANSYS FLUENT Userrsquos Guide ANSYS Canonsburg

Pa USA 2011[30] K M Saqr H S Aly M M Sies and M A Wahid ldquoEffect of

free stream turbulence on NOx and soot formation in turbulentdiffusion CH4-air flamesrdquo International Communications inHeat and Mass Transfer vol 37 no 6 pp 611ndash617 2010

[31] M Khaleghi S E Hosseini and M A Wahid ldquoEmission andcombustion characteristics of hydrogen in vortex flamerdquo JurnalTeknologi vol 66 no 2 pp 47ndash51 2014

[32] C T Bowman ldquoKinetics of pollutant formation and destructionin combustionrdquo Progress in Energy and Combustion Science vol1 no 1 pp 33ndash45 1975

[33] S Fernando C Hall and S Jha ldquoNOx reduction from biodieselfuelsrdquo Energy amp Fuels vol 20 no 1 pp 376ndash382 2006

[34] W C Gardiner Ed Gas-Phase Combustion ChemistrySpringer New York NY USA 2000

[35] G Lavoie J Heywood and J Keck ldquoExperimental and theo-retical study of nitric oxide formation in internal combustionenginesrdquo Combustion Science and Technology vol 1 no 4 pp313ndash326 1970

[36] C P Fenimore ldquoFormation of nitric oxide in premixed hydro-carbon flamesrdquo Symposium (International) on Combustion vol13 no 1 pp 373ndash380 1971

[37] L Pillier A El Bakali X Mercier et al ldquoInfluence of C2

and C3compounds of natural gas on NO formation an

experimental study based on LIFCRDS couplingrdquo Proceedingsof the Combustion Institute vol 30 pp 1183ndash1191 2005

[38] P CMalte and D T Pratt ldquoMeasurement of atomic oxygen andnitrogen oxides in jet-stirred combustionrdquo pp 1061ndash1070 1975

[39] G Loffler V J Wargadalam F Winter and H HofbauerldquoDecomposition of nitrous oxide at medium temperaturesrdquoCombustion and Flame vol 120 no 4 pp 427ndash438 2000

[40] B Bedat and R K Cheng ldquoExperimental study of premixedflames in intense isotropic turbulencerdquo Combustion and Flamevol 100 no 3 pp 485ndash494 1995

[41] A Khoshhal M Rahimi and A A Alsairafi ldquoCFD study oninfluence of fuel temperature on NOx emission in a HiTACfurnacerdquo International Communications in Heat and MassTransfer vol 38 no 10 pp 1421ndash1427 2011

[42] W Yang and W Blasiak ldquoMathematical modelling of NOemissions from high-temperature air combustion with nitrousoxidemechanismrdquo Fuel Processing Technology vol 86 no 9 pp943ndash957 2005

[43] I Glassman Combustion Academic Press 1997

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Industrial EngineeringJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Renewable Energy

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

StructuresJournal of

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear InstallationsScience and Technology of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Solar EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Wind EnergyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nuclear EnergyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014