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Massachusetts Institute of Technology Kinetic Modeling of Methyl Formate Oxidation Richard H West, C Franklin Goldsmith, Michael R Harper, William H Green, Laurent Catoire, Nabiha Chaumeix 1a06

2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

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A kinetic model for methyl formate oxidation is generated using our open-source Reaction Mechanism Gen- erator (RMG) software, supplemented with high level quantum calculations and transition state theory (TST). New rate coefficients are calculated for the decomposition pathways of methyl formate, methoxy-formyl (CH3 OC · O), and formyloxy-methyl (C · H2 OCHO), and hydrogen abstractions from methyl formate by H and methyl radicals. We compare the predictions to experimental data including previously unpublished shock tube ignition delays over a wide range of T and P, as well as atmospheric-pressure laminar burning velocities and low-pressure flame species profiles from the literature. Using RMG we investigate the effect of changing the small molecule (C0−C1) “seed mechanism” and show that predictions of all the experiments are sensi- tive to these reactions. Until the small molecule chemistry is resolved it is impossible to have a conclusive mechanism for the fuel molecule oxidation.

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Page 1: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Massachusetts Institute of Technology

Kinetic Modeling of Methyl Formate OxidationRichard H West, C Franklin Goldsmith, Michael R Harper, William H Green, Laurent Catoire, Nabiha Chaumeix

1a06

Page 2: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

We would like to model kinetics of biofuel combustion predictively.

•Automatically built models are more extensible than hand-curated models, and easier to update.

Hand curated models Automatically built models

Interpretation tool Design tool

Specific to validated fuels, T, P Extensible to new fuels, T, P

Chosen sub-models may be inconsistent with new data

Model can be rebuilt with new data, adding all new pathways

Accurate (where validated) Improving...

2

Page 3: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Three steps towards predictive kinetic models of biofuels.

•Develop method to build kinetic models automatically.

•Collect or generate data and rules suitable for biofuels.

•Perform experiments to validate and check understanding.

3

Page 4: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Three steps towards predictive kinetic models of biofuels.

•Develop method to build kinetic models automatically.

•Collect or generate data and rules suitable for biofuels.

•Perform experiments to validate and check understanding.

⇌���facebook.com/rmg.mitr m g . s o u rc e f o r g e . n e t

Reaction Mechanism Generator

•free and open source software

•version 3.3 released last month

3

Page 5: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Methyl Formate is a useful moleculeto study for biofuel modeling.

•Biodiesel consists of methyl esters.

•Methyl formate is the smallest methyl ester.

•Rules that can predict methyl formatecan likely predict other esters.

��

Methyl Formate

Biodiesel

Diesel

4

Page 6: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Overview of this study

•Use RMG to build a kinetic model

5

Page 7: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Overview of this study

•Use RMG to build a kinetic model

•Improve some estimates

•thermochemistry data from quantum calculations

•decomposition kinetics of fuel molecule and radicals

6

Page 8: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Overview of this study

•Use RMG to build a kinetic model

•Improve some estimates

•Use improved RMG to build new kinetic models

•use 3 different ‘seed’ mechanisms from the literature

7

Page 9: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Overview of this study

•Use RMG to build a kinetic model

•Improve some estimates

•Use improved RMG to build new kinetic models

•Compare with experiments

•new dilute shock tube ignition delay times

•flame speed and low-P flame profile from Dooley et al. (Dryer group at Princeton).

8

Page 10: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Overview of this study

•Use RMG to build a kinetic model

•Improve some estimates

•Use improved RMG to build new kinetic models

•Compare with experiments

•Conclude

•choice of small-molecule seed mechanism (C0-C1 sub-model) affects all other conclusions

9

Page 11: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

RMG generates secondary chemistry of byproducts, exploring paths with high flux.

•Reaction family templates generate all possible reactions.

•‘Edge’ species with highest flux are moved to ‘core’.

•Expansion continues until tolerance reached.

AB

CD

E

FG

H

AB

CD

E

F

10

Page 12: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Thermochemistry for ~200 small molecules from high-level QCI//DFT calculations

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• conformer search:CBS-QB3

• geometry and frequencies:B3LYP/6-311++G(d,p)

• scan for hindered rotors:B3LYP/6-31+G(d,p)

• electronic energy:RQCISD(T)/CBS extrapolated from RQCISD(T)/cc-pVTZ and RQCISD(T)/cc-pVQZ

11

Page 13: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Same QM methods used to calculate PES of methylformate & radical decomposition

•High-Pressure rate coefficients calculated with TST:

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Methyl Formate PESFormyloxymethyl and Methyloxyformyl PES

12

kcal/mol

90

60

30

0

-30

O OCO + CH3OH

CH4 + CO2

kcal/mol

30

20

10

0

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40

-20

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OO

OO

OO +

O

OH +

CO + CH3O·

CH3 + CO2

80.8

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67.5

9.60.0

Page 14: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Pressure-dependence calculated in RMG using reservoir state method

•RMG explores additional pathways and solves full Master Equation for chemically activated and fall-off reaction rates

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Methyl Formate PESFormyloxymethyl and Methyloxyformyl PES

13

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Page 15: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

“Seed” mechanism placed in RMG’s core at start of mechanism generation

•Used for trusted rates of small-molecule chemistry.

•Rate expressions used without modification.

•Additional reactions generated by RMG.

AB

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Seed Mechanism 1

Seed Mechanism 2

14

Page 16: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

“GRI”

•GRI-Mech 3.0

•(Methane

oxidation)

•Smith (1999)

Three Seed Mechanisms were taken from published literature.

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“Glarborg”

•Glarborg group’s “Master Mechanism”

•C0-C1 only

•Lopez (2009)

“Dooley”•Dryer group’s mechanism

•Used in methyl formate study

•C0-C1 only•Dooley (2010)

15

Page 17: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

The models are built using a hierarchy of data sources.

16

QCISD(T)//B3LYP database

Semi-empirical PM3

Seed MechanismGRI / Glarborg / Dooley

Methyl-formatecalculations

Glarborg Master Mechanism

Rule-based estimates

Benson group estimates

GRI-Mech

Group-based estimates

Kinetics Thermochemistry Transport

150

10

100

4000

Page 18: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

The models are built using a hierarchy of data sources.

16

QCISD(T)//B3LYP database

Semi-empirical PM3

Seed MechanismGRI / Glarborg / Dooley

Methyl-formatecalculations

Glarborg Master Mechanism

Rule-based estimates

Benson group estimates

GRI-Mech

Group-based estimates

Kinetics Thermochemistry Transport

k(T,P) calculated by Master Equation solution in RMG (+3000)ME

ME

ME

ME

150

10

100

4000

Page 19: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

The models are built using a hierarchy of data sources.

16

QCISD(T)//B3LYP database

Semi-empirical PM3

Seed MechanismGRI / Glarborg / Dooley

Methyl-formatecalculations

Glarborg Master Mechanism

Rule-based estimates

Benson group estimates

GRI-Mech

Group-based estimates

Kinetics Thermochemistry Transport

Radicals calculated by Hydrogen Bond Increment methodHBI

HBI

HBI

k(T,P) calculated by Master Equation solution in RMG (+3000)ME

ME

ME

ME

150

10

100

4000

Page 20: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

The models are built using a hierarchy of data sources.

16

QCISD(T)//B3LYP database

Semi-empirical PM3

Seed MechanismGRI / Glarborg / Dooley

Methyl-formatecalculations

Glarborg Master Mechanism

Rule-based estimates

Benson group estimates

GRI-Mech

Group-based estimates

Kinetics Thermochemistry Transport

Radicals calculated by Hydrogen Bond Increment methodHBI

HBI

HBI

k(T,P) calculated by Master Equation solution in RMG (+3000)ME

ME

ME

ME Constant across all models in this work

150

10

100

4000

Page 21: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Shock tube experiments performed by CNRS in Orleans.

•99% Argon

•Equivalence ratios ɸ = 0.5, 1, 2

•Ignition defined as half of peak OH* emission

•P5 = 151 – 1446 kPa

•T5 = 1268 – 1812 K

High Pressure Low Pressure

P transducers

UV photomultiplier

! "!! #!! $!! %!! &!!!

'()*+, -.

!

!

Pressure

- OH* emission

delay

17

Page 22: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Unscaled ignition delay times (IDT) are hard to interpret plotted vs 1/T

Phi = 10 p scaling

0.908841851 correl0.7425 optimum

0.688625 global optimum2.690715605

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()

*+++),)%)$-)

)*+,-./,01#

Phi = 20 p scaling

0.89880299 correl0.64875 optimum

0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()

*+++),)%)$-)

)*+,-./,01#

Phi = 0.50 p scaling

0.883070764 correl0.689325 optimum0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()

*+++),)%)$-)

)*+,-./,01#

•Each experiment performed at a different P5 pressure.

ɸ=0.5 ɸ=1 ɸ=2

18

Page 23: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Phi = 20 p scaling

0.89880299 correl0.64875 optimum

0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()

*+++),)%)$-)

)**+,-#./0#123,456,78#.+94:*4;#

Phi = 10 p scaling

0.908841851 correl0.7425 optimum

0.688625 global optimum2.690715605

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()

*+++),)%)$-)

)**+,-#./0#123,456,78#.+94:*4;#

Phi = 0.50 p scaling

0.883070764 correl0.689325 optimum0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()

*+++),)%)$-)

)**+,-#./0#123,456,78#.+94:*4;#

ɸ=0.5 ɸ=1 ɸ=2

Unscaled ignition delay times (IDT) are hard to interpret plotted vs 1/T

•Each experiment performed at a different P5 pressure.

•Simulate each experiment with the corresponding T5, P5.

19

Page 24: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Scale ignition delay times by P5α

to improve correlation with 1/T

Phi = 10 p scaling

0.908841851 correl0.7425 optimum

0.688625 global optimum2.690715605

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()

*+++),)%)$-)

)*+,-./,01#

Phi = 20 p scaling

0.89880299 correl0.64875 optimum

0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()

*+++),)%)$-)

)*+,-./,01#

Phi = 0.50 p scaling

0.883070764 correl0.689325 optimum0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()

*+++),)%)$-)

)*+,-./,01#

ɸ=0.5 ɸ=1 ɸ=2

•Each experiment performed at a different P5 pressure.

20

Page 25: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Scale ignition delay times by P50.69

to maximize correlation with 1/T

Phi = 10.688625 p scaling

0.982161783 correl0.7425 optimum

0.688625 global optimum2.946534131

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()!*

+%,-.(/0123

4///353%3$+3

)*+,-./,01#

Phi = 20.688625 p scaling

0.982344879 correl0.64875 optimum

0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()!*

+%,-.(/0123

4///353%3$+3

)*+,-./,01#

Phi = 0.50.688625 p scaling

0.982027468 correl0.689325 optimum0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()!*

+%,-.(/0123

4///353%3$+3

)*+,-./,01#

ɸ=0.5 ɸ=1 ɸ=2

21

Page 26: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Phi = 0.50.688625 p scaling

0.982027468 correl0.689325 optimum0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()!*

+%,-.(/0123

4///353%3$+3

)**+,-#./0#.+123*24##567,289,:;#

Phi = 10.688625 p scaling

0.982161783 correl0.7425 optimum

0.688625 global optimum2.946534131

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()!*

+%,-.(/0123

4///353%3$+3

)**+,-#./0#.+123*24##567,289,:;#

Phi = 20.688625 p scaling

0.982344879 correl0.64875 optimum

0.688625 global optimum

!""#

!"""#

!""""#

"$%"# "$&"# "$'"# "$("#

!"#$%&'()!*

+%,-.(/0123

4///353%3$+3

)**+,-#./0#.+123*24##567,289,:;#

ɸ=0.5 ɸ=1 ɸ=2

•All too fast

•Glarborg seed fastest

•Dooley seed slowest

•Good agreement

•Glarborg seed slowest

•Dooley seed fastest

•All too slow

•Glarborg seed slowest

•GRI-Mech seed fastest

Shock tube ignition delays predicted OK, but vary with ɸ and seed mechanism.

22

Page 27: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

!"#!"$

%&'

(!'

(&'

)!'

)&'

*!'

*&'

!"+' !"#' %' %"(' %"*' %"+'

!"#$%"&'()&%$%*'+,-./$01

'2/#345'

67)$+"-,%/,'8"9.'

,-./01/2'3445',67'3445'811-49'3445':;<4/=>4?@'A811-49B'(!%!C'811-49'A(!%!C'>154-'

Laminar flame speeds all over-predicted, and also vary with seed mechanism.

•Experimental data and model from Dooley et al. (2010) Int. J. Chem. Kinet.

23

Page 28: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Seed mechanism is mostly responsible for over-predicted flame speed.

•For model with GRI seed mechanism, the10 most sensitive reactions are all from the GRI seed.

24

Reac%on Sensi%vityH.0+0O20=0O0+0OH 0.22OH0+0CO0=0H.0+0CO2 0.15H.0+0HO20=0O20+0H2 90.09H.0+0HO20=0OH0+0OH 0.09H.0+0O20+0H2O0=0HO20+0H2O 90.08HC.O0+0H2O0=0H.0+0CO0+0H2O 0.08HC.O0+0m0=0H.0+0CO0+0m 0.07HC.O0+0O20=0HO20+0CO 90.07HO20+0CH30=0OH0+0CH3O. 0.06H.0+0HC.O0=0H20+0CO 90.05

Sensitivity of flame speed with respect to reaction A factor

!"#!"$

%&'

(!'

(&'

)!'

)&'

*!'

*&'

!"+' !"#' %' %"(' %"*' %"+'

!"#$%"&'()&%$%*'+,-./$01

'2/#345'

67)$+"-,%/,'8"9.'

,-.'/001'

2340567089':;<<=0>?'(!%!@'

Page 29: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Minor species profiles poorly predicted in low-pressure flame. Seed has some effect.

•Low pressure (22 torr) stoichiometric (ɸ=1) flame data and temperature profile from Dooley et al. (2010) Comb. Flame.

•Overpredicted C2H4 in model with Glarborg seedis due to missing decomposition pathway.

!"#$

%&'()%($*

('()+((*

&'()%($*

,'()%(-*

,'&)%(-*

"'()%(-*

(* "* $* .* /* ,(*

!"#$%&'()*"

+%

,-./(+)$%&'"0%12'+$'%3%00%

01234536*078*9551:;*)<=:3>?:@A*

!"#

$%&'($')*'&'(+''*%&'($')*,&'($'#*,&%($'#*-&'($'#*-&%($'#*#&'($'#*#&%($'#*)&'($'#*

'* -* )* .* /* ,'*

!"#$%&'()*"

+%

,-./(+)$%&'"0%12'+$'%3%00%

01234536*078*9551:;*(<=:3>?:@A*

CH3 mole fraction C2H4 mole fraction

25

Page 30: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Pressure-dependent ethyl formate reactions important to C2H4 profile

•Replacing high-pressure-limit ethyl formate reactions with chemically activated pressure-dependent network increases prediction of C2H4 and C2H2 concentrations.

C2H2 mole fractionC2H4 mole fraction

26

Page 31: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Acknowledgments

•C Franklin Goldsmith

•Michael R Harper

•William H Green

•Laurent Catoire

•Nabiha Chaumeix

•Stephen Dooley

27

Page 32: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Contributions

•Improved tools to automatically build kinetic models.

•Calculated new data for methyl esters.

•New shock tube ignition delay data for methyl formate.

•Information in hard-to-read fonts is better remembered than easier to read information (Diemand-Yauman et al., Cognition, 2011)

28

Page 33: 2011 US Combustion Meeting - Kinetic Modeling of Methyl Formate Oxidation

Contributions

•Improved tools to automatically build kinetic models.

•Calculated new data for methyl esters.

•New shock tube ignition delay data for methyl formate.

•Choice of C0-C1 kinetic model affects all other conclusions. Hard to “validate” other parts of model when this remains unsure.

29