Hybrid Approach to Chemical Kinetics Model C H R RH CH C H ...
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This work was funded by the US Federal Aviation Administration (FAA) Office of Environment and Energy as a part of ASCENT Project 26 under FAA Award Number: 13-C-AJFE-SU-006 and by the National Aeronautics and Space Administration under agreement number 13-C-AJFE-SU-006, and also by the US Air Force Office of Scientific Research under grant number FA9550-14-1-0235 . Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the FAA or other ASCENT Sponsors. Project 26 Hybrid Approach to Chemical Kinetics Model Development and Evaluation Project manager: Mohan Gupta, FAA Lead investigator: Hai Wang, Stanford University Staff/Students: Rui Xu, Dongping Chen September 27-28, 2016 Results – Fuel Oxidative Pyrolysis Motivation and Objectives Methods and Materials Conclusions and Next Steps Motivations o Next generation of jet engines will operate at pressures far higher than those of current engines for fuel efficiency improvement. o A basic understanding of the combustion chemistry of jet fuels is critical to the design of high- pressure turbine engines. o Alternative fuels are expected to enter into the market in the next decade. Their use in commercial aviation is hindered by the lack of quick and inexpensive fuel certification methods. o Approaches that can quickly and accurately unravel the combustion chemistry of alternative fuels are essential to enable engine design and fuel certification. Assumptions o Early studies [1] suggest that for large hydrocarbon fuels pyrolysis precedes the oxidation of the decomposed fragments in real, liquid fuel combustion. These two reaction processes are decoupled in time scales. o In flames almost all large hydrocarbon fuels undergo oxidation also in two steps. In the preheat zone of the flame the fuel decomposes into about a half dozen of small molecular fragments in an endothermic process, regardless how complex the composition of the initial fuel is. The fragments then enter into the flame zone and to combustion products in the second, exothermic step, which is rate limiting. o The pyrolysis fragments are dominated by ethylene (C 2 H ), propene (C H 6 ), iso-butene (i-C 4 H 8 ), 1-butene (1-C ), methane (CH 4 ), benzene (C 6 H 6 ), toluene (C 7 H ) and hydrogen (H 2 ). HyChem Approach o The kinetic rate of the overall pyrolysis is fast as compared to oxidation, and the distribution of the pyrolysis products has the dominant impact on radical buildup and heat release. o The overall jet fuel reaction kinetics can be dealt with by combining an experimentally constrained, lumped pyrolysis model with a foundational chemistry model for the oxidation process of decomposition products (e.g., USC Mech II [2]). We term the approach as the hy brid chem istry (HyChem) approach. Methodology – HyChem Approach Pyrolysis Model – Reactions o In HyChem, we write the lumped, pyrolysis model in the form of (1) (2) where R = H, CH 3 , OH, O, O 2 and HO 2 Pyrolysis Model – Parameters o The model has 11 stoichiometric parameters: e d , e a , b d ,b a , α, β, γ, χ , λ 3 , λ 4i and λ 4n . Under the condition of complete reaction, elemental balances will eliminate four parameters, which are e d ,e a ,b d and b a . o The 7 independent parameters, α , β, γ, χ, λ 3 , λ 4i and λ 4n , along with 7 reaction rate constants (k i , i = 1,2,…,7) can be directly determined from shock tube and flow reactor experiments. Results – Fuel Pyrolysis Shock tube pyrolysis ethylene/methane yields at 1.0 ms Shock tube pyrolysis species time history profiles Data: Hanson group o The HyChem approach provides a direct path towards real, liquid fuel combustion chemistry modeling. The resulting model is capable of predicting a wide range of combustion behaviors of typical jet fuels. o An automatic code for model derivation and refinement is currently under development. o Fuel X approach is under development. Reference [1] Davidson, D. F., Z. Hong, G. L. Pilla, A. Farooq, R. D. Cook, and R. K. Hanson. "Multi-species time-history measurements during n-dodecane oxidation behind reflected shock waves." Proceedings of the Combustion Institute 33, no. 1 (2011): 151-157. [2] Hai Wang, Xiaoqing You, Ameya V. Joshi, Scott G. Davis, Alexander Laskin, Fokion Egolfopoulos, and Chung K. Law, USC Mech Version II.High-Temperature Combustion Reaction Model of H2/CO/C1-C4 Compounds. http://ignis.usc.edu/USC_Mech_II.htm, May 2007. i n 7 8 CH CH CH -C H 1-C H CH CH H CH m n d d e i b 2 4 3 3 6 4 4 8 4 4 8 6 6 3 1 2 i n 7 8 CH R RH CH CH CH -C H 1-C H CH CH H CH m n a a e i b 4 2 4 3 3 6 4 4 8 4 4 8 6 6 3 1 1 0 0.5 1 1.5 2 2.5 1050 1100 1150 1200 1250 1300 1350 A1 A2 A3 A2 Model Yield @ 1.0 ms Temperature, T (K) 0.73% fuel in Ar p 5 = 12.4 atm C 2 H 4 CH 4 0.000 0.005 0.010 0 500 1000 1500 2000 Mole Fraction Time, t (s) C 2 H 4 CH 4 Run 19 0.70% A2 in Ar T 5 = 1168 K, p 5 = 12.71 atm Flow reactor oxidative pyrolysis species time profiles Data: Bowman group o The 14 unknown parameters, α, β, γ , χ , λ 3 , λ 4i , λ 4n and k i ,(i = 1,2,…,7) may be determined from shock and flow reactor experiments under a wide range of conditions. The left figure shows the ethylene/methane yields at 1.0 ms during shock tube pyrolysis of selected jet fuels over the temperature range of 1050 to 1350 K, along with model predictions. The right figure shows one selected case of shock tube pyrolysis species time histories. The temperature sensitivity (±15 K) is shown with the dashed lines. The fuel oxidative pyrolysis section presents the species time profiles during flow reactor oxidative pyrolysis for a Jet A fuel, along with model predictions. 0 50 100 150 200 250 300 350 0 5 10 15 20 25 30 Mole Fraction (PPM) Time, t (ms) Fuel C 2 H 4 H 2 C 3 H 6 A2 314 PPM, = 1 p = 1 atm, T = 1030 K 0 20 40 60 80 100 0 5 10 15 20 25 30 Mole Fraction (PPM) Time, t (ms) C 6 H 5 CH 3 CH 4 C 6 H 6 A2 314 PPM, = 1 p = 1 atm, T = 1030 K Results – Fuel Oxidation Shock tube ignition delay time 10 1 10 2 10 3 10 4 0.7 0.8 0.9 1.0 A1-4%O 2 -Ar = 1.1 = 0.5 = 2.1 = 1.2, p 5 = 54.4 atm Ignition Delay, s) 1000K/T { p 5 = 13.0 atm 10 2 10 3 10 4 0.7 0.8 0.9 A2 expt. A1 expt. A2 Model Ignition Delay, (s) 1000K/T p 5 = 1.3 atm, = 1.0 A2-4%O 2 -Ar p 5 = 1.1 atm, = 0.9 A2/A1-13.3%O 2 -Ar A2/A1-O 2 -Ar 10 2 10 3 10 4 0.8 0.9 1.0 A2-Air Ignition Delay, s) 1000K/T p 5 = 10.9 atm, = 1.1 Data: Hanson group 20 30 40 50 60 70 0.6 0.8 1 1.2 1.4 1.6 Equivalence Ratio, A2, T 0 = 403 K, p = 1 atm Laminar Flame Speed, S u o (cm/s) 50 100 150 200 250 300 350 400 0.06 0.065 0.07 0.075 0.08 Extinction Strain Rate, K ext (s -1 ) Fuel/N 2 Mass Ratio A2/N 2 versus O 2 T u = 473 K for A2/N 2 T = 300 K for O 2 p = 1 atm Laminar flame speed Non-premixed flame extinction Data: Egolfopoulos group
Transcript of Hybrid Approach to Chemical Kinetics Model C H R RH CH C H ...
This work was funded by the US Federal Aviation Administration (FAA) Office of Environment and Energy as a part of ASCENT Project 26 under FAA Award Number: 13-C-AJFE-SU-006 and by the National Aeronautics and Space Administration under agreement number 13-C-AJFE-SU-006, and also by the US Air Force Office of Scientific Research under grant number FA9550-14-1-0235 . Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the FAA or other ASCENT Sponsors.
Project 26
Hybrid Approach to Chemical Kinetics Model Development and Evaluation
Project manager: Mohan Gupta, FAALead investigator: Hai Wang, Stanford University
Staff/Students: Rui Xu, Dongping Chen
September 27-28, 2016
Results – Fuel Oxidative PyrolysisMotivation and Objectives
Methods and Materials
Conclusions and Next Steps
Motivations
o Next generation of jet engines will operate at pressures far higher than those of currentengines for fuel efficiency improvement.
o A basic understanding of the combustion chemistry of jet fuels is critical to the design of high-pressure turbine engines.
o Alternative fuels are expected to enter into the market in the next decade. Their use incommercial aviation is hindered by the lack of quick and inexpensive fuel certificationmethods.
o Approaches that can quickly and accurately unravel the combustion chemistry of alternativefuels are essential to enable engine design and fuel certification.
Assumptions
o Early studies [1] suggest that for large hydrocarbonfuels pyrolysis precedes the oxidation of thedecomposed fragments in real, liquid fuelcombustion. These two reaction processes aredecoupled in time scales.
o In flames almost all large hydrocarbon fuels undergooxidation also in two steps. In the preheat zone ofthe flame the fuel decomposes into about a halfdozen of small molecular fragments in anendothermic process, regardless how complex thecomposition of the initial fuel is. The fragments thenenter into the flame zone and are oxidized tocombustion products in the second, exothermic step,which is rate limiting.
o The pyrolysis fragments are dominated by ethylene(C2H4), propene (C3H6), iso-butene (i-C4H8), 1-butene(1-C4H8), methane (CH4), benzene (C6H6), toluene(C7H8) and hydrogen (H2).
HyChem Approach
o The kinetic rate of the overall pyrolysis is fast as compared to oxidation, and thedistribution of the pyrolysis products has the dominant impact on radical buildup andheat release.
o The overall jet fuel reaction kinetics can be dealt with by combining an experimentallyconstrained, lumped pyrolysis model with a foundational chemistry model for theoxidation process of decomposition products (e.g., USC Mech II [2]). We term theapproach as the hybrid chemistry (HyChem) approach.
Methodology – HyChem Approach Pyrolysis Model – Reactions
o In HyChem, we write the lumped, pyrolysis model in the form of
(1)
(2)
where R = H, CH3, OH, O, O2 and HO2
Pyrolysis Model – Parameters
o The model has 11 stoichiometric parameters: ed, ea, bd, ba, α, β, γ, χ, λ3, λ4i and λ4n.Under the condition of complete reaction, elemental balances will eliminate fourparameters, which are ed, ea, bd and ba.
o The 7 independent parameters, α, β, γ, χ, λ3, λ4i and λ4n, along with 7 reaction rateconstants (ki, i = 1,2,…,7) can be directly determined from shock tube and flowreactor experiments.
Results – Fuel Pyrolysis
Shock tube pyrolysis ethylene/methane yields at 1.0 ms
Shock tube pyrolysis species time history profiles
Data: Hanson group
o The HyChem approach provides a direct path towards real, liquid fuel combustion chemistrymodeling. The resulting model is capable of predicting a wide range of combustion behaviorsof typical jet fuels.
o An automatic code for model derivation and refinement is currently under development.o Fuel X approach is under development.
Reference[1] Davidson, D. F., Z. Hong, G. L. Pilla, A. Farooq, R. D. Cook, and R. K. Hanson. "Multi-species time-history measurements during n-dodecaneoxidation behind reflected shock waves." Proceedings of the Combustion Institute 33, no. 1 (2011): 151-157.
[2] Hai Wang, Xiaoqing You, Ameya V. Joshi, Scott G. Davis, Alexander Laskin, Fokion Egolfopoulos, and Chung K. Law, USC Mech VersionII.High-Temperature Combustion Reaction Model of H2/CO/C1-C4 Compounds. http://ignis.usc.edu/USC_Mech_II.htm, May 2007.
i n
7 8
C H C H C H -C H 1-C H
C H C H H CH
m n d
d
e i
b
2 4 3 3 6 4 4 8 4 4 8
6 6 31 2
i n
7 8
C H R RH CH C H C H -C H 1-C H
C H C H H CH
m n a
a
e i
b
4 2 4 3 3 6 4 4 8 4 4 8
6 6 31 1
0
0.5
1
1.5
2
2.5
1050 1100 1150 1200 1250 1300 1350
A1 A2 A3 A2 Model
Yie
ld @
1.0
ms
Temperature, T (K)
0.73% fuel in Ar
p5 = 12.4 atm
C2H4
CH4
0.000
0.005
0.010
0 500 1000 1500 2000
Mo
le F
rac
tio
n
Time, t (s)
C2H4
CH4
Run 19
0.70% A2 in Ar
T5 = 1168 K, p5 = 12.71 atm
Flow reactor oxidative pyrolysis species time profiles
Data: Bowman group
o The 14 unknown parameters, α, β, γ, χ, λ3, λ4i, λ4n and ki, (i = 1,2,…,7) may bedetermined from shock and flow reactor experiments under a wide range ofconditions. The left figure shows the ethylene/methane yields at 1.0 ms during shocktube pyrolysis of selected jet fuels over the temperature range of 1050 to 1350 K,along with model predictions. The right figure shows one selected case of shock tubepyrolysis species time histories. The temperature sensitivity (±15 K) is shown withthe dashed lines. The fuel oxidative pyrolysis section presents the species timeprofiles during flow reactor oxidative pyrolysis for a Jet A fuel, along with modelpredictions.
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30
Mo
le F
racti
on
(P
PM
)
Time, t (ms)
Fuel
C2H4
H2
C3H6
A2 314 PPM, = 1
p = 1 atm, T = 1030 K
0
20
40
60
80
100
0 5 10 15 20 25 30
Mo
le F
racti
on
(P
PM
)
Time, t (ms)
C6H5CH3
CH4 C6H6
A2 314 PPM, = 1
p = 1 atm, T = 1030 K
Results – Fuel OxidationShock tube ignition delay time
101
102
103
104
0.7 0.8 0.9 1.0
A1-4%O2-Ar
= 1.1
= 0.5
= 2.1
= 1.2, p5 = 54.4 atm
Ign
itio
n D
ela
y,
s)
1000K/T
{p5 = 13.0 atm
102
103
104
0.7 0.8 0.9
A2 expt.A1 expt.A2 Model
Ign
itio
n D
ela
y,
(s
)
1000K/T
p5 = 1.3 atm, = 1.0
A2-4%O2-Ar
p5 = 1.1 atm, = 0.9
A2/A1-13.3%O2-Ar
A2/A1-O2-Ar
102
103
104
0.8 0.9 1.0
A2-Air
Ign
itio
n D
ela
y,
s)
1000K/T
p5 = 10.9 atm, = 1.1
Data: Hanson group
20
30
40
50
60
70
0.6 0.8 1 1.2 1.4 1.6
Equivalence Ratio,
A2, T0 = 403 K, p = 1 atm
Lam
inar
Fla
me S
peed
, S
u
o(c
m/s
)
50
100
150
200
250
300
350
400
0.06 0.065 0.07 0.075 0.08
Exti
nc
tio
n S
train
Rate
, K
ex
t (s
-1)
Fuel/N2 Mass Ratio
A2/N2 versus O2
Tu = 473 K for A2/N2
T = 300 K for O2
p = 1 atm
Laminar flame speed Non-premixed flame extinction
Data: Egolfopoulos group
![CH3E4 notes: Asymmetric Catalysis, Prof Martin …...PPh 2 Ph 2 P B O P O N C NHCOMe 25 atm H 2 2 mol % [Rh(C) 2]+ 20 oC, ClCH 2 CH Cl. H [Rh(SS-DuPHOS)]+ (R=Et), rt MeOH. 96% ee Ph](https://static.fdocuments.us/doc/165x107/5ebd2e8d22ba8a30017e81f3/ch3e4-notes-asymmetric-catalysis-prof-martin-pph-2-ph-2-p-b-o-p-o-n-c-nhcome.jpg)
