Biodiesel Kinetics and Flame Chemistry · Biodiesel Kinetics and Flame Chemistry Yiguang Ju,...
Transcript of Biodiesel Kinetics and Flame Chemistry · Biodiesel Kinetics and Flame Chemistry Yiguang Ju,...
Biodiesel Kinetics and Flame Chemistry
Yiguang Ju, Princeton University
On behalf of CEFRC: Biodiesel Thrust and Flame Chemistry Working Group
Sept. 17-20, 2012, MACCCR
•Mechanisms of butanols •Automatic mechanism
generation
•Flow reactor experiments •Reactivity and species history •H2, CO, small HC chemistry •DME, small oxygenates
•Shock tube/Laser diagnostics
• Ignition/Species histories •Rate constants
•Flame species by Synchrotron MS
•Burner-stabilized flames •Ab initio methods •Thermochemical kinetics •Ester chemistry
•Potential energy surfaces •Rate constants with
tunneling
•Potential energy surfaces •Reaction rate constants •High pressure theories
W. H. Green
N. Hansen
H. Wang
F. L. Dryer
R. K. Hanson
C. J. Sung
E. A. Carter
D. G. Truhlar
S. J. Klippenstein
Synergistic
2D Research
Structure
Three Thrusts
Unite the Team
Alcohols Biodiesel
Foundation Fuels
•Rapid compression machine
•High-pressure ignition •Thermometry and species
C. K. Law
F. N. Egolfopoulos
S. B. Pope
Y. Ju
J. H. Chen
•Flame chemistry •Biodiesel kinetics •Model reduction & multi-scale modeling
•Laminar flame speeds,
extinction and ignition, pollutants
•DNS of HCCI/SACI combustion •DNS data for model validation •High pressure turbulence/
chemistry interaction
•LES/PDF/ISAT turbulent combustion
•Turbulence/chemistry
•Low-T combustion engines •HCCI and RCCI CFD modeling • Interface with DERC
consortium
R. D. Reitz •Soot •Small HC chemistry •Transport properties •UQ methods
•High-pressure flames •Turbulent flames •Droplet processes
Motivation
Biodiesel:
• Produced from vegetable oils, animal fats, & waste materials
• Energy density much higher than ethanol
• 28 billion gallons of biodiesel produced in 2010 worldwide
• Large molecules: C16-C18 with ester functional group
• Different combustion chemistry/emissions from hydrocarbons
• Large disparities in alkyl chain length and structures
Biodiesel Trans-esterification
O
O
R1
R2
Sooting Propensity of Diesel Surrogate and Large Ester Flames
Diesel surrogate: 70% n-C10H22 + 30% 1-methyl naphthalene Dagaut and coworkers (2010)
Diesel Biodiesel
(Law, Princeton)
Scientific Questions?
How to address the knowledge gaps in
kinetics of large, oxygenated fuel molecules?
How can we use quantum chemistry and
kinetic experiments to provide a better,
predictive model?
How to address the transport and chemistry
interaction in flames?
Research Objectives
Advance the understanding of combustion
kinetics of methyl esters
Develop a validated kinetic methyl ester kinetic
mechanism to model oxidation with quantum
chemistry calculations
Advance understanding of chemistry/transport
interaction
+ =
Methyl Butanoate
(C4+1)
Alkane
(C14) methyl stearate (C18+1)
Decomposition
1. Biodiesel Kinetics: Hypothesis
O
O
O
O
O
O
O
O
O
O
Methyl Formate Methyl Acetate Methyl Popanoate Methyl Butanoate
Methyl Decanoate
Similarity between Small/Large Esters?
Biodesel
Methyl Propanoate
1A. Small Methyl Ester Pyrolysis in Shock Tube Stanford University
0.60 0.65 0.70 0.75 0.800.0
0.2
0.4
0.6
0.8
1.0
C
O2 F
ractional Y
ield
1000/T [K-1]
1428K 1250K
1666K
MA
MB MP
2% Methyl Ester/Argon
1.5 atm, Yield at 1 ms
The reactivity is strongly affected by the alkyl chain length
1B. Comparison of Premixed Flame Speeds
of Small Methyl-Esters/Air (C1-C4: 1 atm)
Egolfopoulos et al. •Methyl formate has the highest reactivity
•Methyl propanoate is the second
0
100
200
300
400
500
0.5 1 1.5 2
Exti
nc
tio
n s
tra
in r
ate
aE
[1/s
]
Transport-Weighted Enthalpy [cal/cm3]
Tf = 500 K, Tox = 298 K
Methyl Formate
Methyl Ethanoate
Methyl Propanoate
Methyl Butanoate
Methyl Pentanoate
Methyl Hexanoate
Methyl Octanoate
Methyl Decanoate
1C. Comparison of Extinction Limits of Methyl Esters (C1-C10)
•Uniqueness of small methyl esters: methyl formate & methyl propanoate
•Similarity of large methyl esters
Extinction limit vs. Transport weighted enthalpy (TWE)
MRSDCI /cc-pV∞Z // B3LYP
CBS-QB3-Isodesmic*
1D: BDEs (D298 ) (kcal/mol) in Biodiesel Methyl Butanoate (MB)
* Osmont et al. J. Phys. Chem. A, 111, 3727 (2007)
• Weakest bonds: dissociated radicals are resonance stabilized.
• C-C bonds are weaker than C-H bonds: alkyl fragments allow more
structural relaxation than H.
C O C C C C
H O H H H
H H H H
H H
98.0
98.9
95.4
93.5
92.9
94.2
96.8
98.7
98.6
101.1
83.1
84.4
85.8
89.1
MB
101.2
101.3
Oyeyemi, V. B.; Pavone, M.; Keith, J. A.; Carter, E. A.
in preparation, (2012).
Seshadri et al. : 80.8 kcal/mol, 2009
C8-C10
MB Extension
C1-C7
H2/O2
C1-C7: n-heptane model Curran et al., 2008, 2010
MB: Ester functional group Dooley et al., 2008
1E. Kinetic Mechanism Development
(Ester-MECH: C2-C11 methyl esters)
H2/O2: PU hydrogen model
Dievart et al., 34th Symposium on Combustion on Comb., 2012
Dievart et al. Combustion and Flame, 2012, Vol.159 , pp. 1795-1803.
1F. Model Validation: Ignition Delay Time
Ignition delays from Hanson’s group (Aerosol Shock
Tube, very lean mixtures, diluted in argon, ~7.5 atm)
Present model in good
agreement (35%), whereas
literature models overestimate
MD oxidation rate (50 to 80%)
Bond dissociation energy
affects strongly fuel
decomposition pathway
Present model, Seshadri et al’s model:
Metathesis reactions: 95% Fuel Decomposition: 5%
Seshadri et al’s model:
Metathesis reactions: 55% Fuel Decomposition: 45%
Model validation: JSR & Flame speeds
methyl decanoate
• high temperature kinetics • speciation profiles, flame speeds
0.6 0.8 1.0 1.2 1.4 1.6
20
30
40
50
60
70
Experimental data
Reduced model (529 species)
Reduced model (228 species)
Seshadri et al.'s model [14]
Luo et al's model [20]
Fla
me
sp
ee
d [
cm
.s-1]
Equivalence Ratio
0
5000
10000
15000
20000
25000
0
500
1000
1500
2000
2500
3000
500 600 700 800 900 1000 1100
CO
and
CO
2M
ole
Fraction
[pp
m]
MD
an
d C
2H
4M
ole
Fra
ctio
n [
pp
m]
Temperature [K]
Jet-Stirred reactor (Glaude et al., C&F 157, 2010)
P = 1atm, τ = 1.5 s Laminar Flame Speeds
(Wang et al., C&F 158, 2011) P = 1atm, T = 403 K
14 Glaude et al., CF, 2010.
Model comparison in diffusion flame: MD
Model validation: Diffusion flame extinction
Methyl formate Methyl ethanoate Methyl propanoate Methyl butanoate
0
100
200
300
400
500
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Extinc
tion
Str
ain r
ate
, aE[s
-1]
Fuel Mole Fraction, Xf
C2-C11 esters
Methyl pentanoate Methyl hexanoate Methyl octanoate Methyl decanoate
Dievart et al., 34th symposium on combustion, 2012
Model validation: Species time history
17
0.0E+00
5.0E-13
1.0E-12
1.5E-12
2.0E-12
2.5E-12
3.0E-12
0.E+00 5.E-04 1.E-03 2.E-03 2.E-03
[H] , [m
ol.c
m-3]
Time [s]
T = 1333 K P = 0.51 atm Xfuel = 239.1 ppm
Methyl formate
H abstraction reactions by OH and H: Methyl Formate
CH3OCHO + OH = CH3OCO + H2O
Large deviations between the rate constants calculated by the Carter’s group (J. Phys. Chem. A, 2012) and the previous estimates or calculations.
CH3OCHO + H = CH3OCO + H2
Good and Francisco, J. Phys. Chem. A, 2002, Vol. 106, pp. 1733-1738 Peukert et al., Combustion and Flame, 2012, Vol. 159, pp. 2312-2323 Akih-Kumgeh and Bergthorson, Comb. Flame, 2011, Vol. 158, pp. 1037-1058 Szilagyi et al., J. Phys. Chem, 2004, Vol. 118, pp. 479-492
1.0E+09
1.0E+10
1.0E+11
1.0E+12
1.0E+13
300 500 700 900 1100 1300 1500 1700 1900
Rate
con
stant
[mol c
m-3.s
-1]
Temperature [K]
Ting Tan (Carter)
Good and Francisco
Current Model
Akih-Kumgeh
Peukert et al. (Argonne)
Peukert et al.1.0E+09
1.0E+10
1.0E+11
1.0E+12
1.0E+13
300 800 1300 1800
Rate
con
stant
[mol c
m-3.s
-1]
Temperature [K]
Ting Tan (Carter)
Good and Francisco
Current Model
Szilagyi et al. (2004)
Decomposition of small methyl ester radicals such as CH3OCO (and C2H5OCO) are key reactions.
Literature: only high pressure limit rate constant with low level PES is available (e.g. BH&HLYP/CC-PVTZ).
Present method: MRACPF/CBS//CASPT2/CC-PVTZ method on PES and VARIFLEX for pressure dependence
L.K. Huynh, A. Violi. J. Org. Chem. 72 (2008) 94-101.
Methyl-Ester Radical Decomposition Reactions (Collaborative work : Carter, Klippenstein and Ju)
1.0E+03
1.0E+05
1.0E+07
1.0E+09
1.0E+11
1.0E+13
0.3 0.8 1.3 1.8
Rate
con
stant
[s-
1]
1000/T [K]
HPL
100 atm
10 atm
1 atm
HPL Huynh and Violi
CH3OCO = CH3 + CO2
Ester-MECH C2-C11 Esters
Carter
• Thermochemistry
H, Cp, S •Rate constants
MF+X , ME+X, MP+X… (OH, H, CH3, HO2)
Yang, Raghu, Ju, Klippenstein
•Rate constants
CH3OCO C2H5OCO
MF, ME, MP… Decomposition
Hanson group
•Rate constants MX+ OH
X=F,A,P,B
•Speciation time history
Egolfopoulos, Ju, Law
•Flame speeds •Flame structure •Extinction •Emissions
Sung and Hanson
•Ignition delay (Shock tube, RCM)
Dryer, Hansen and Ju
•Speciation experiments (Flow tube, flames)
20
Collaborative structure of the Biodiesel
Summary: OH + Methyl Esters Products
• Data agree within 25% with Structure Activity Relationship (SAR) estimated rate constants ( the same rate used in the current model).
21
0.7 0.8 0.9 1.0 1.1 1.2
1E12
1E13
833K909K1000K1111K1250K
MButanoate
MPropanoate
MFormate
MAcetate
Lines: Modified SAR (SAR x 0.75)
kM
eth
yl E
ste
r +
OH [
cm
3 m
ol-1
s-1]
1000/T [1/K]
Methyl Ester + OH = Products
1429K
Methyl Formate Decomposition Kinetics Summary Arrhenius Plot k1: MF → CO + CH3OH
22
Wide T range
Low data scatter
Repeatable
±25%
MBMS/mid-IR with flow reactor/jet stirred reactor
Advanced diagnostics- high pressure reactors
at low and intermediate temperatures
Multipath-IR
Fuel
Pre
he
ate
d a
ir
Hig
h p
res
su
re, h
igh
te
mp
era
ture
ch
am
ber
Mix
ing
JSR
Herriott cell reflections
0
500
1000
1500
2000
2500
0
20
40
60
80
100
120
0 500 1000 1500
Me
asu
red
H2O
[p
pm
]
Me
asu
red
CH
4 [
pp
m]
Calibration mole fraction [ppm]
In air, 60 Torr, 293 KCH4
H2O
500 550 600 650 700 750
0
500
1000
1500
2000
2500
3000
3500
4000
Temperature (K)
H2O
2 c
on
cen
tra
tio
n (
pp
m) MBMS
Modeling
H2O2 Measurements, DME/O2/He
(2 sec, 1 atm (0.02/0.1/0.88)
H2O2
HO2 ?
2. Flame Chemistry: Kinetic &Transport Interaction
•Interaction of Transport and Chemistry on Flame Extinction
•Low Temperature Ignition and New Flame Regimes
50
150
250
350
450
0.05 0.09 0.13 0.17 0.21 0.25 0.29
Exti
nc
tio
n s
tra
in r
ate
aE
[1/s
]
Fuel mole fraction, Xf
Tf = 500 K, Tox = 298 K
Methyl Formate
Methyl Ethanoate
Methyl Propanoate
Methyl Butanoate
Methyl Pentanoate
Methyl Hexanoate
Methyl Octanoate
Methyl Decanoate
2A. Diffusion Flame Extinction Limits: From Methyl Formate to Methyl Decanoate
ΔHcomb (kcal/mol)
MW (g/mol)
MB -651.6 102.14
MD -1533.3 186.29
How to separate chemistry from
transport and fuel heating value?
i
fp
FF
F
e RTTC
QY
MMa *
)(/
1 ,
A generic correlation for extinction limit:
Transport weighted Enthalpy & radical
index Theoretical analysis of Extinction Damkohler
number
Transport Heat release/heat loss
Fuel chemistry
Radical production
rate
32
, 3
2
,
1 2 1( , , ) ( , ) exp
fO aF F F O F F
E F f a f
TY TLe P Le Le L Le
Da e Y T T T T
Extinction Strain Rate
Won et al. CNF 159 (2012)
Transport weighted Enthalpy *Radical index
0
100
200
300
400
500
0.5 1 1.5 2
Exti
nc
tio
n s
tra
in r
ate
aE
[1/s
]
Transport-Weighted Enthalpy [cal/cm3]
Tf = 500 K, Tox = 298 K,
Methyl Formate
Methyl Ethanoate
Methyl Propanoate
Methyl Butanoate
Methyl Pentanoate
Methyl Hexanoate
Methyl Octanoate
Methyl Decanoate
Reactivity Scaling of Small/Large Methyl Esters: From Methyl Formate (C1) to Methyl Decanoate (C10)
•Uniqueness of small methyl ester
•Similarity of large methyl ester
Extinction limit vs. Transport weighted enthalpy (TWE) flux
CH3OH+
CO
CH2O+
HCO
CH3O+
CO
CH3
+CO2
H + CO HO2 + CO
35% 18%
42%
+R/-RH
+R/-RH
62%38%
81%
9%
88% 12%
+M +O2
Impact of alkyl chain length on methyl ester reactivity
Methyl Formate, R0C
Higher reactivity
CH2OCH3OCH2CO CH3CO
CH3 + CO
+ +
-H
+R/-RH +R/-RH
47% 47%
5%
95%
HCCO
CO + CO
+H35%
56%
+OH+O
Methyl Acetate, R1C
Lower reactivity
Diévart et al, 2012
to presented on Monday at 34th
Symposium
H abstraction reactions,
Fuel, CH3OCO, and CH3OC(O)CH2
decomposition reaction rates
Extinction Limit: n-Alkanes, iso-Alkanes, Aromatics
0
100
200
300
400
500
0 0.05 0.1 0.15 0.2
Ex
tin
cti
on
str
ain
ra
te a
E[1
/s]
Fuel mole fraction Xf
n-decane
n-nonane
n-heptane
JETA POSF 4658
Princeton Surrogate
iso-octane
nPB
toluene
124TMB
135TMB
n-alkanes
aromatics
Tf = 500 K and To = 300 K
How to separate chemistry from transport?
What is the ranking high temperature reactivity?
A General Correlation of Hydrocarbon Fuel Extinction vs. TWE and Radical Index
30
R² = 0.97
0
100
200
300
400
500
0.5 1 1.5 2
Ex
tin
cti
on
str
ain
ra
te a
E[1
/s]
Ri[Fuel]Hc(MWfuel/MWnitrogen)-1/2 [cal/cm3]
n-decane
n-nonane
n-heptane
iso-octane
n-propyl benzene
toluene
1,2,4-trimethly benzene
1,3,5-trimethly benzene
Tf = 500 K and To = 300 K
Radical Index for Screening of Alternative Fuels
• Extinction limits of diffusion flames for pure fuel samples have been completely measured and compared by using TWE – Heat of combustion, Hc has been re-estimated based on H/C ratio correlation. – Re-evaluation of Hc might be necessary.
• High temperature reactivity based on Radical index – SPK HRJ camelina HRJ Tallow > JP8 IPK (~iso-octane) – Similar order to DCN measurements, IPK must be heavily isomerized.
Fuel Radical
Index DCN
JP8 POSF 6169 0.78 47.3
SHELL SPK POSF 5729 0.85 58.4
HRJ Camelina POSF 7720 0.82 58.9
HRJ Tallow POSF 6308 0.8 58.1
SASOL IPK POSF 7629 0.76 31.3 50
100
150
200
250
300
350
400
450
0.5 1 1.5 2 2.5
Ex
tin
cti
on
str
ain
ra
te [
s-1
]
Transport-weighted enthalpy [cal/cm3]
[fuel]Hc(MWf/MWn)-0.5
JP8 POSF 6169
SHELL SPK POSF 5729
HRJ Camelina POSF 7720
HRJ Tallow POSF 6308
SASOL IPK POSF 7629
n-alkane
iso-octane
Extinction of diffusion flame in counterflow configuration
Tf = 500 K and Tair = 300 K @ 1 atm
Won et al. CNF 159 (2012)
2B. Effects of Transport on Low Temperature Ignition in
Non-premixed Counterflow Flames
Law’s group
• NTC behavior extensively observed for homogeneous systems
• Corresponding non-monotonic behavior signaling NTC chemistry in steady state strained has not been well studied in flows (e.g. counterflow),
Seshadri et al., CF 2009.
• Reason: Reduced residence time => higher ignition temperature => shifting away from NTC temperature regime
• Explore possible existence of NTC behavior for flows – with low strain rates – at high pressures
Heptane/air
flames
No NTC at 1 atm, 200/s
NTC temp. ↑ as pressure ↑
tNTC > tconv
tNTC ~ tconv ?
Decrease k
Increase P Decrease P
Increase k
n-Heptane vs. Air in Counterflow Ignition
Single
ignition
1st ignition, Low-T
chemistry
2nd ignition,
High-T chemistry
Single ignition
Low-T chemistry
1st ign, low-T
chemistry
2nd ign,
high-T
High-T
Chemistry
Unsteady Flow Perturbation on Low Temperature Ignition in Diffusion Flame
6.17 ms at 74 Hz
Rise
from 72 to
73 Hz
• No effect on initial RO2 formation,
• H2O2 decomposition is delayed by
heat loss at high strain rate. Reaction 2: RO2 = R’O2H
Reaction 3: H2O2 + M = 2OH + M
850 K
30 atm
100 s-1
Shan et al., 2012
0.000 0.005 0.010 0.0150.0
0.2
0.4
0.6
0.8
1.0
Hot ignition
LTI
at wall
Low temperature flame dominated
double flame (decoupled)
Single high temperature
flame front
Lo
ca
tio
n o
f m
axim
um
he
at
rele
ase
(cm
)
Time (s)
High temperature flame
dominated double flame (coupled)
Low temperature ignition
Transition
Multi Flame Regimes in HCCI Ignition n-Heptane: Flame Initiation by a Spark at 40 atm, T=700 K
Sf=15.3 cm/s
Sf=27.5 cm/s Sf=25.6 m/s
Movie
Ju et al., 33rd symposium on Comb., 2011
Combustion properties, species, and kinetic data methyl
esters are experimentally measured by a collective effort.
An updated methyl ester (C2-C11) kinetic mechanism is
developed and partially validated.
Large uncertainties in elementary rate constant and
species time history.
Conclusions
Flame theory to correlate flame extinction with TWE and
radical index. Uniqueness and similarity of high
temperature reactivity of methyl esters are demonstrated.
Significant impacts of low temperature ignition on ignition
and flame propagation are demonstrated. New flame
regimes are identified.
Acknowledgement:
Pascale Dievart
Sanghee Won
Xueliang Yang
Funding support: DOE-BES CEFRC