Sub-mechanism Advancements for Surrogate Fuel Modelling

Sub-mechanism Advancements for Surrogate Fuel Modelling

MULTI AGENCY COORDINATION COMMITTEE FOR COMBUSTION RESEARCH MULTI AGENCY COORDINATION COMMITTEE FOR COMBUSTION RESEARCH (MACCCR) FUELS RESEARCH REVIEW(MACCCR) FUELS RESEARCH REVIEW

Princeton, NJ 20Princeton, NJ 20--22 September 201022 September 2010

Dr. Henry CurranCombustion Chemistry Centre

NUI Galway, Irelandhttp://c3.nuigalway.ie/

Visiting Researcher, Princeton University

Motivation

Alkanes and iso-alkanes are a very large fraction of petroleum derived and alternative (Fischer Tropsch) gas

turbine fuels

Alkenes are primary products formed by the decomposition of higher

hydrocarbons

Alkenes also result from R + O2chemistry at higher temperatures

Limited studies are available for the oxidation of higher alkenes

Discuss C5 – C7 but higher alkenes still need further study

Gas Turbine Fuel Functional Class Distribution

(POSF-4658)

Cycloalkanes

Napthalenes

Aromatic(alkyl benenes)

iso-alkanes

25.53%

29.55%

3.32%

38.59%3.02%

n-alkanes

Flow reactor oxidation data for conditions of 12.5 atm, 0.3% carbon, φ= 1.0 and t =1.8s, for POSF-4658 (symbols), POSF-4658 surrogate (solid lines) and model simulation of POSF-4658 surrogate (dashed lines), Inset;DT. from Dooley et al. doi:10.1016/j.combustflame.2010.07.001

500 600 700 800 900 1000

POSF 4658 Surrogate ModelCO CO2 O2 H2O

Spe

cies

con

cent

ratio

n / p

pm x

103

Temperature / K

1

2

3

4

5

500 600 700 800 900 10000

10

20

30

40

50POSF 4658 Δ TSurrogateModel

Δ T

/ K

Temperature / K

•1st generation surrogate model predictions generally in line with actual real fuel and surrogate experimental behaviours!Modeling shows that n-decane is principally active in radical generation=> exclusively so at lowest temperatures.•Excellent emulation of POSF 4658 at low Ts indicates quantity of n-alkyl fragments are approximately. correctly prescribed in surrogate.•Aromatic/iso-alkanes mainly compete for radicals generated by n-decane oxidation, while having little or no radical production, slowing overall reaction.•Iso-octane/toluene start to contribute some radical generation above ~800 and ~900K respectively.•These and other data suggest that there may be deficiencies in n-decane model kinetic at conditions above the hot ignition, but where β-scission remains slow relative to reaction with molecular oxygen..

3

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40

10

20

30

40

50

60

70

80

90

100

110

120

Spec

ies

conc

entra

tion

/ ppm

Time / seconds0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0

20

40

60

80

100

120

140

160

ΔT /

K

Time / seconds

n‐Decane Oxidation Time‐History Princeton Variable Pressure Flow Reactor

4

Model predictions; Westbrook C.K., Pitz W.J., Herbinet O., Curran H.J, and Silke E.J., Combust. Flame 156 2009 181 ⎯199.

Data Copyright, Princeton University 9/20/2010

Data Copyright, Princeton University 9/20/2010

Model predictions show that 1-olefins are derived from QOOH+O2, R+O2, and R beta-scission channels at the present conditions.

Experimental data (symbols) versus simulation (lines) for n‐decane oxidation.

1-olefin species Profiles

Previous Studies 1

Experiments:• 1971 Tipper and Titehard: Effect of olefin addition to n-heptane cool

flames

• 1973 Hughes and Prodhan: Cool flames from 1- and 2-pentene

• 1980 Baldwin et al.: H2/O2 system plus 1- and 2-pentene (low T)

• 1996 Prabhu et al.: Flow reactor data for 1-pentene

• 1999 Minetti et al.: RCM data for 1-pentene

• 2005 Vanhove et al.: RCM data (low T) for the three isomers of hexene

• 2006 Yahyaoui et al.: Shock Tube and JSR study of 1-hexene

Previous Studies 2

Modeling Studies:• S. Touchard et al., Proc. Combust. Inst. 30 (1) (2005) 1073-1081

(1-pentene, 1-hexene low T)

• M. Mehl et al., 29th Meeting on Combustion, Pisa – Italy 2006 (1-pentene, high and low T)

• M. Yahyaoui et al., Combustion and Flame 147 (2006) 67–78 (1-hexene, intermediate and high T)

• M. Mehl et al., Comb. Flame 155 (2008) 756-772(1-, 2-, 3-hexene, high and low T)

• R. Bounaceur et al., Proc. Combust. Inst. 32 (1) (2009) 387-394(1-, 2-, 3-hexene, low T)

High and Low T Oxidation of Hexene Isomers

(M. Mehl et al., Comb. Flame 155 (2008) 756-772.)

At low temperature reactivity is controlled by the saturated portion of the fuel. At high temperature predictions suggest that the relative reactivity of the three HCs is inverted (no experimental data).

Mechanism developed in the context of Milano’s kinetic mechanism(Ranzi’s group)

Igni

tion

Del

ay T

ime

[ms]

(G. Vanhove et al., Proc. Comb. Inst. 30 (2005) 1065-1072.)

Alkene Oxidation ProcessesMain reaction pathways involved in alkene autoignition

RH

R

ROO

QOOH

β‐decomposition

Initiation

OOQOOH

Ketohydroperoxide

HORH

HORHOO

Waddington

Temperature

HO2 activation

HO2 Elimination

600K 750K 900K 1050K 1200K 1350K 1500K

+ OH

Reactivity of Hexene Isomers at Low Temperatures

· · ·

OO

OO

OO

H H

1-hexene 2-hexene 3-hexene

H

H

· ·

· ·

·

· ·

OO H

OO

OOH

O

O

Radical Branching

0 500 1000 1500

Pres

sure

/ ar

b. u

nits

time / μs

2-Hexene diluted in AirT

5 = 1021 K, P

5 = 10.4 atm

0 1000 2000Pr

essu

re /

arb.

uni

tstime / μs

2-Pentene diluted in AirT

5 = 993 K, P

5 = 10.8 atm

High pressure and low pressure shock tube data

• High pressure shock tube (example)

Experimental (NUI Galway)

Hexene Isomers: High Temperature

The ignition delay time of the three isomer cross at

about 1200 K

2-hexene shows the highest reactivity

Decomposition rates are controlling the ignition

process determining the composition of the radical

pool

3-hexene

2-hexene

1-hexene

1.00.6 0.7 0.8 0.91000K/T

10

100

1000

10000

1.1

Igni

tion

Del

ay T

ime

[μs]

Pressure 10 atm, φ = 1 in air

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0.6 0.8 1 1.2 1.41000K/T

1.6

Igni

tion

Del

ay T

ime

[μs]

3-hexene

1-hexene2-hexene

Pressure 10 atm, φ = 1 in air, Vanhove et al. 2005

Hexenes: Reaction Pathways Analysis

Main pathway above 1400 K

1-hexene

2-hexene

Pentene Isomers: High and Low Temperature

2-pentene

1-pentene

Pressure 10 atm, φ = 1 in air, Minetti et al. (1999)

Good agreement with the low and high temperature regions

No low temperature data for 2-pentene (future work)

0.01

0.1

1

10

100

1000

0.6 0.8 1 1.2 1.41000K/T

1.6Ig

nitio

n D

elay

Tim

e [m

s]

Pentene Isomers: Low Pressure

The model performs satisfactorily at these conditions. This validation gives us confidence in the high pressure predictions.

Igni

tion

Del

ay T

ime

[μs]

10

100

1000

10000

0.5 0.6 0.7 0.8 0.9

2-penteneφ =1.0φ =0.5

φ =2.0

1000K/T0.5 0.6 0.7 0.8 0.9

1000K/T

10

100

1000

10000

1-penteneφ =1.0

φ =0.5

φ =2.0

0.50 0.55 0.60 0.65 0.70 0.75 0.8010

100

1000 φ = 2.0 φ = 1.0 φ = 0.5

Igni

tion

Del

ay T

ime

/ μs

1000 K / T

φ = 2.0 φ = 1.0 φ = 0.5

2000 1800 1600 1400

1-pentene2-pentene

T / K

Pressure 1 atm, 1% pentene in argon diluent

Pentenes: Reaction Pathways Analysis

CH3

H

H

CH3

1/3

2/3

1/3

2/3

H

Main pathway above 1400 K

Alkenes: Conclusions• New set of experiments carried out to fill the gap in

the high temperature behavior of alkenes• High and low temperature mechanism for 1-, 2-

pentene and 1-, 2-, 3-hexene isomers incorporated in the kinetic mechanism

• Model validated successfully against ST data• Quantitative information provided to develop better

models for autoignition of more complex unsaturated fuels

Mechanism available:https://www-pls.llnl.gov/?url=science_and_technology-

chemistry-combustion-mechanisms

Small Hydrocarbon Kinetic Improvements

• Gallagher et al. C1-C4 kinetics combined with C0-C1 kinetics of Princeton as the base mechanism for the larger hydrocarbon kinetics (n-decane, n-dodecane, iso-octane, toluene, alkyl benzenes)

• Notes deficiencies in C2, C3 flame speed comparisons

• New work at Galway/Texas A&M on C1/C2 kinetics leads to significant improvements.

• Further revisions in Hydrogen/CO model for high pressure burning rates expected early this fall.

CH4/C2H6 Flame SpeedsBurning Velocities for Methane/Ethane

mixtures, P = 5 atm, Ti ~ 298 K

0.6 0.8 1.0 1.2 1.45

10

15

20

25

30 100 % C2H6

60/40 CH4 / C2H6

80/20 CH4 / C2H6

100 % CH4

Bur

ning

Vel

ocity

(cm

s-1)

φ



0.6 0.8 1.0 1.2 1.45

10

15

20

25

30

Dash - C3_49

100 % C2H6

60/40 CH4 / C2H6

80/20 CH4 / C2H6

100 % CH4

Bur

ning

Vel

ocity

(cm

s-1)

φ



0.6 0.8 1.0 1.2 1.45

10

15

20

25

30

Dash - C3_49Solid - C3_51.6

100 % C2H6

60/40 CH4 / C2H6

80/20 CH4 / C2H6

100 % CH4

Bur

ning

Vel

ocity

(cm

s-1)

φ

CH4/C2H6 Mixtures

010

2030

0

20

40

60

80

100

75

80

859095100

(100% C2H6)

Conditions of Current Study Sampling of Previous Studies

and below

Blen

d C

ompo

nent

CH

4

Pressure (atm) and above

Dilu

tion

(%)

• Studies Sampled Here:

• Burcat et al. (1971)

• Burcat et al. (1972)

• Cooke and Williams (1971)

• Cooke and Williams (1975)

• Crossley et. al (1972)

• de Vries and Petersen (2007)

• de Vries et al. (2007)

• Eubank et al. (1981)

• Herzler and Naumann (2009)

• Hidaka et al. (1999)

• Hidaka et al. (2000)

• Huang and Bushe (2006)

• Krishnan and Ravikumar (1983)

• Lamoureux and Paillard (2003)

• Lamoureux et al. (2002)

• Lifshitz et al. (1971)

• Petersen et al. (2007)

• Seery and Bowman (1970)

• Skinner and Ruehrwein (1957)

• Spadacinni and Colket (1994)

• Tranter et al. (2002)

• Tsuboi (1978)

• Zhukov et al. (2003)

CH4/C2H6 ST ignition Delay Times

6.5 7.0 7.5 8.0 8.5

100

1000

Mix 9 Mix 10 C4_51.6 San Diego JetSurf

Igni

tion

dela

y tim

e / μ

s

104 K / T

Mixture Blend Dilution Φ Pressure(CH4/C2H6) (%) (atm)

9 0 / 100 75 1 110 0 / 100 75 0.5 1


6.5 7.0 7.5 8.0 8.5

100

1000


Igni

tion

dela

y tim

e / μ

s

104 K / T


11 75/25 95 1 1012 50/50 95 1 10


7.5 8.0 8.5 9.0 9.5

100

1000


Igni

tion

dela

y tim

e / μ

s

104 K / T


21 0/100 85 1 1022 0/100 85 0.5 10

Changes to the sub-mechanismNew H2/O2 rates from recent Stanford University study

H + O2 <=> O + OHH2O2 (+M) <=> OH + OH (+M)H2O2 + OH <=> H2O + HO2

- new C2H4 + OH rate from recent Stanford paper- Alzueta's rate for HCCO + O2

- Klippensteins rate for CH2CHO decomposition (J. Phys. Chem. A 2006, 110, 5772-5781)

- Altered the branching ratio of C2H4 + O = CH2CHO + H (37%) / CH3 + HCO (63%) to 50:50

- San Diego Mech value for C2H5(+M) <=> C2H4+H (+M)- CH3 + CH3 <=> C2H5 + H chemically activated (Stewart et al. C&F 1989)- CH3 + CH3(+M) = C2H6 (+M) taken from Wang et al.

(JPC A 107:11414 (2003))

C2H4 Ignition

• Very important to alkane, cycloalkane, alcohol, ether and ester oxidation mechanisms among others:

• nC3H7 = C2H4 + CH3

• MCH oxidation → lots of C2H4

• C2H5OH = C2H4 + H2O• C2H5OC2H5 = C2H5OH + C2H4

• C2H5C(O)OC2H5 = C2H5C(O)OH + C2H4

C2H4 ignition delay times

Shock tube ignition delay times for C2H4with model predictions

7.5 8.0 8.5 9.0 9.5 10.0

100

1000

C2H4 in Air, 2 % C2H4 3 % O2, φ = 2.0, Paverage 10.1 atm

Igni

tion

Del

ay, μ

s

104 K / T

C4_50

7.8 8.0 8.2 8.4 8.6 8.8 9.0100

1000

C2H4 in Air, 1.0 % C2H4 3 % O2 φ = 1.0, Paverage 1.1 atm

C4_50

Igni

tion

Del

ay, μ

s

104 K / T

7.5 8.0 8.5 9.0 9.5 10.0

100

1000

C2H4 in Air, 2 % C2H4 3 % O2, φ = 2.0, paverage = 10.1 atm

Igni

tion

Del

ay, μ

s

104 K / T

C4_50

Improving model performance Identify a point where model performs poorly

Sensitivity analysisφ = 2.0, P = 8.8 atm, T = 1170 K

C2H3+O2<=>CH2CHO+OC2H4+CH3<=>C2H3+CH4

C2H4+HO2<=>C2H4O1-2+OHC2H4+OH<=>C2H3+H2O

H+O2<=>O+OHCH2CHO+O2=>CH2O+CO+OH

CH3+HO2<=>CH3O+OHH2O2(+M)<=>OH+OH(+M)C2H5+HO2<=>C2H5O+OH

C2H4+O<=>CH2CHO+HC3H8(+M)<=>CH3+C2H5(+M)

C2H4+O<=>CH3+HCOCH3+CH3(+M)<=>C2H6(+M)

CH2CHO<=>CH2CO+HC2H4+H(+M)<=>C2H5(+M)

CH3+HO2<=>CH4+O2

C2H5+O2<=>C2H4+HO2

C2H3+O2<=>C2H2+HO2

HO2+OH<=>H2O+O2

C2H3+O2<=>CH2O+HCO

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

C2H4 in Air, 2 % C2H4 3 % O2, φ = 2.0, p = 8.8 atm, T 1170 K

Sensitivity Coefficient

Sensitivity analysis

Inhibits reactivity

Promotes reactivity

Improving model performance

7.8 8.0 8.2 8.4 8.6 8.8 9.0100

1000

C2H4 in Air, 1.0 % C2H4 3 % O2 φ = 1.0, paverage = 1.1 atm

C4_51.1 C4_50

Igni

tion

Del

ay, μ

s

104 K / T

Ethylene

7.5 8.0 8.5 9.0 9.5 10.0

100

1000

C2H4 in Air, 2 % C2H4 3 % O2, φ = 2.0, paverage = 10.1 atm

Igni

tion

Dela

y, μ

s

104 K / T

C4_51.1 C4_50

Acknowledgements

• Dr. Marco Mehl – Olefin modelling

• Dr. Kenji Yasunaga – Olefin Experiments

• Drs. William Pitz/Charlie Westbrook

• Dr. S. Jahangirian – VPFR n-Decane species histories

Sub-mechanism Advancements for Surrogate Fuel Modelling

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