Studies of kinetics and flame chemistry of methyl-esters and C0-C2 foundation fuels

Yiguang JuPrinceton University

Jeffery Santner, Michael Burke Pascal Dievart, Sanghee WonStephen Dooley, Fredrick L Dryer, Stephen Klippenstein

Collaborators:

Research Thrusts

•High pressure flame chemistry study for C0-C2 foundation

fuels

•Methyl-ester kinetic mechanism development

•A generic correlation between flame chemistry and transport

•Unsteady flow/chemistry interaction on low temperature

ignition

•Development of high pressure jet stirred reactor with

molecular beam mass spectrometry

1. High pressure flame chemistry study for C0-

C2 foundation fuels

High pressure flame experiments

4Few burning rate data are available at high pressure conditions

5

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 5 10 15 20 25 30

Pressure (atm)

Ma

ss

bu

rnin

g r

ate

(g

/cm

^2

s)

Present experiments

Li et al. (2007)

Davis et al. (2005)

Sun et al. (2007)

Konnov (2008)

O'Connaire et al. (2004)

Saxena & Williams (2006)

H2/O2/Ar, φ=2.5

Tf ~1600K

Burning velocity dependence on pressure, rich H2/O2

Experimental data and mechanism validation

6

Experimental data and mechanism validationH2, C1, C2 mixtures

• Model over-predicts flame burning rates for

CO, CH4, C2H4, C2H6M.P. Burke, F.L. Dryer, Y. Ju, Proceedings of the Combustion Institute (2010) in press.

J. Santner, M.P. Burke, F.L. Dryer, Y. Ju, in preparation.

0.00

0.03

0.06

0.09

0.12

0.15

0 5 10 15 20 25 30

Pressure (atm)

Ma

ss

bu

rnin

g r

ate

(g

cm

-2 s

-1)

USC-MECH II

H2/CH4/O2/He,

φ=0.7

Tf ~1600K

H2/CH4 = 100/0

H2/CH4 = 90/10

0

0.05

0.1

0.15

0.2

0 5 10 15 20 25 30

Pressure, atm

Ma

ss

bu

rnin

g r

ate

(g

cm

-2 s

-1)

0

0.02

0.04

0.06

0.08

0.1

0.12

USC-MECH II

H2/add/O2/dil

φ=0.7

Tf ~1600K

H2/CO = 90/10

H2/C2H4 = 90/10

H2/C2H6 = 90/10

7

Effect of pressure on kinetics and model development

H+O2

OH+O (R1)

+Mhigher pressures and lower temperatures

lower pressures and higher temperatures

HO2 (R2)

OH+OHH2+O2

+H +OH

H2O+O2 O2+OH

+O

H2O2+O2

+HO2

H+HO2=OH+OH=H2+O2 OH+HO2=H2O+O2

• R1/R2 competition still controls pressure dependence• New branching and termination reactions becomes important

1. M.P. Burke, M. Chaos, Y. Ju, F.L. Dryer, S.J. Klippenstein, "Comprehensive H2/O2 Kinetic Model for High-Pressure Combustion," Int. J. Chem. Kinet. (2011).

8

A new hydrogen mechanismImprovements for C0-C2 flames

• Updated H2 model improves predictions of CO, CH4, C2H4, and C2H6 flames at high pressure

0

0.05

0.1

0.15

0.2

0 5 10 15 20 25 30

Pressure, atmM

as

s b

urn

ing

ra

te (

g c

m-2

s-1

)

0

0.02

0.04

0.06

0.08

0.1

0.12

USC-MECH II

Updated H2 + USC-MECH II C1-C2

H2/add/O2/dil

φ=0.7

Tf ~1600K

H2/CO = 90/10

H2/C2H4 = 90/10

H2/C2H6 = 90/10

0.00

0.03

0.06

0.09

0.12

0.15

0 5 10 15 20 25 30

Pressure (atm)

Ma

ss

bu

rnin

g r

ate

(g

cm

-2 s

-1)

USC-MECH II

Updated H2 + USC-MECH II C1-C2

H2/CH4/O2/He,

φ=0.7

Tf ~1600K

H2/CH4 = 100/0

H2/CH4 = 90/10

CH4 C2H4/C2H6

2. Methyl-ester kinetic mechanism development

Research Methodology: A Bottom Up Approach for Biodiesel

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 Butanoate(C4+1)

Alkane(C14)methyl stearate (C18+1)

Decomposition

0.60 0.65 0.70 0.75 0.800.0

0.2

0.4

0.6

0.8

1.0

CO

2

Fra

ctio

na

l Y

ield

1000/T [K-1]

1428K 1250K

1666K

MA

MB MP

2% Methyl Ester/Argon

1.5 atm, Yield at 1 ms

Reactivity of Methyl Ester Group:Ester pyrolysis : CO2 yield (Stanford University)

12

Fig. Branching ratio of Methyl Butanoate reactions with H atoms (a) and OH radicals (b), rate constant of the MBMJ

(CH3CH2CH2CO2CH2) radical β-scission reaction (c) and unimolecular methyl butanoate decomposition reaction to CH3O and

C3H7CO radical (d) in the models of Dooley et al. [7] (green), Hakka et al [29] (blue) and Fisher et al. [5] (black)

Branching ratio of Methyl Butanoate reactions with

H atoms (a) and OH radicals (b)

Bond Dissociation Energies (BDEs) (black: C–C bonds; gray, C–H bonds) calculated at 298.15 K for Methyl Decanoate (unit: kcal.mol-1)

Weakest bond

C1

H4

H5

C14 O12 C3

O13

H15

H17

H16

H11C2

H7

H8

C6

H9

H10

98.9

98.0

98.9

92.9

92.9

94.2

97.9

96.8

98.7

99.5

98.6

101.1

83.3

83.1

84.4

94.8

95.4

93.5

86.0

---

89.1

103.1

101.2

101.3

90.1

97.9

87.0

Methyl Butanoate

Bond Dissociation Energy of Methyl Esters

KEY: ExperimentMRSDCI//HF/cc-pVDZMRSDCI//B3LYP/6-311G(2d,p)CBS-QB3 of El-Nahas et al.

Carter et al. 2011 for MB

Seshadri et al. : 80.8 kcal/mol

14

Fig. Consumption pathways of methyl decanoate in a diffusion flame: differences between the present model, Seshadri et al. [14], and Luo et al. [20].

Consumption pathways of methyl decanoate in a diffusion flame

MD subset +C8-C10 linear

MB subset

C6-C7 linear

C0-C5

linear

C0-C7: n-heptane model Curran et al., 2008, 2010

MB: Ester functional groupDooley et al., 2008

MD subset

• Thermo: Benson’s group additivitymethod with updated group contributions

• Kinetics: direct analogy from MB for the methyl ester group atoms

Detailed model was reduced with Chem-RC (PFA, path flux analysis)

Mechanism development and validation

(C4, C10 Methyl esters)

MODEL VALIDATION (1)

The present model has been tested against ignition delays from Hanson’s group (Aerosol Shock Tube, very lean mixtures, highly diluted in argon, ~7.5 atm)

Present model in good agreement (35%), whereas literature models strongly overestimate MD oxidation rate (50 to 80%)

UFD Pressure Dependence can not entirely explained these discrepancies

EXTINCTION LIMITS

Present data are in close agreement with previous results of Seshadri et al.

Present model reproduces satisfactorily the experimental data

Seshadri et al.’s model strongly overestimates extinction limits

MB data, 500 K, Uddi et al.◆ MD data, 500 K▲ MD data, 468 K, Seshadri et al.

−−− MB computations, 500 K−−− MD computations, 500 K−−− MD computations, 468 K− − MD computations, 500K, Seshadri et al.

3. A generic correlation for diffusion flame extinction:

Extraction of kinetic information from global flame

properties

Diffusion flame extinction experiments:

ΔHcomb

(kcal/mol)MW

(g/mol)

MB -651.6 102.14

MD -1533.3 186.29

How to decouple chemistry from transport and

fuel heating value?

Methyl butanoate vs. methyl decanoate

i

fp

FF

F

e RTTC

QY

MMa *

)(/

1 ,

A generic correlation for extinction limit:Chemistry and Transport

Theory of counterflow flame extinction ( Won et al. 2011)

Transport Heat release/heat lossFuel chemistryRadical productionrate

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 Damkohler number

Extinction Strain Rate

21

Extinction limit vs. Transport-weighted enthalpy flux

MB and MD have the same high temperature kinetics!Dievart et al. 2011

Radical index and reactivity scaling of

Methyl butanoate (C4) vs. methyl decanoate (C10)

4. Low temperature flow/chemistry interaction in

unsteady counterflow flow flames

X [C7H16] = 0.1

X [He] = 0.9

X [O2 ] = 0.21

X [He] = 0.79

a = 20/100 s-1

vu

r

OxidizerFuel x

L = 2cm

Flame

Stagnation plane

p = 30 atm

2

2 exp sin 2

2

xPerturbation A f t

Unsteady counterflow diffusion flame ignition

IntroducingStrain

Φ = 1,

p = 30 atm

Impact of H2O2 addition on Low temperature ignition

a = 100 s-1

Tfuel = Toxidizer = 850 K

σ = 0.05/0.1/0.15/0.2 cm,

f = 15 ~ 2000 Hz

Impact of flow oscillation on ignition

5. Development of high pressure jet stirred reactor with

molecular beam mass spectrometry for low temperature

chemistry study

10 20 30 40 50 60 70 80 90 100

0

500

1000

1500

2000

Re

l. Io

n In

ten

sity

m/z

mass=4 He

mass=18 H2O

mass=32 O2

mass=34 H2O2

x 20

32 34

18

4

MBMS setup

JSR setup

Conclusions

• High pressure flame speeds are obtained for C0-C2 and a

validated high pressure hydrogen kinetic mechanism is

developed.

• An updated low temperature methyl decanoate mechanism

is developed.

• A generic correlation using radical index and transport

weighted enthalpy is obtained for diffusion flame extinction.

• Unsteady low temperature ignition is modeled and strong

flow chemistry coupling is demonstrated.

• A high pressure jet stirred reactor with molecular beam

mass spectrometry is developed.