Reaction Models of Combustion Properties4 • Version 1.0+1.1 →JetSurF 2.0 n‐butyl‐,...

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Reaction Models of Fundamental Combustion Properties

Hai Wang

Enoch Dames, David Sheen & Rei Tangko

University of Southern California

2010 Fuel Summit, Princeton

H. Wang, E. Dames, B. Sirjean, D. A. Sheen, R. Tangko, A. Violi, J. Y. W. Lai, F. N. Egolfopoulos, D. F. Davidson, R. K. Hanson, C. T. Bowman, C. K. Law, W. Tsang, N. P. Cernansky, D. L. Miller, R. P. Lindstedt, A high‐temperature chemical kinetic model of n‐alkane (up to n‐dodecane), cyclohexane, and methyl‐, ethyl‐, n‐propyl and n‐butyl‐cyclohexane oxidation at high temperatures, JetSurF version 2.0, September 19, 2010 (http://melchior.usc.edu/JetSurF/JetSurF2.0).

• Version 1.0+1.1 → JetSurF 2.0 n‐butyl‐, n‐propyl‐, ethyl‐ and methyl‐cyclohexanes and cyclohexane.

n‐pentane to n‐dodecane

Some branched chain HCs + aromatics

• Key Revisions from version 1.0+1.1• Low temperature chemistry of cyclohexane and

methylcyclohexane added• H‐abstraction rates from Violi• ……

• Validation test sets > 200 (documented online)http://melchior.use.edu/JetSurF

JetSurF Status

Multispecies Time‐History DataDavidson, Hong, Pilla, Farooq, Cook & Hanson, Combustion and Flame (2010)

10 100 100010

Time [s]

1494K, 2.15atm300ppm heptane, =1

Solid lines: experiments; dashed lines: JetSurF 1.0

Multispecies Time Histories

Solid lines: experiments; dashed lines: JetSurF 1.0

10-5 10-4 10-3

Time (s)

10-5 10-4 10-3

Time (s)

nC7H16

300 ppm n-C7H16 - 3300 ppm O2 in Ar, T5 = 1365 K, p5 = 2.35 atm

What can we learn from the multispecies time‐histories?

• The model is accurate, but is it precise?

•Given the ~±5% experimental accuracy, can the data be utilized to improve model precision?

• To what extent the data improve model precision?

Propagation of Uncertainty

1 1...i ij ij

i j j kj k j

basis random variable

Data structure that describes a chemical model + associated uncertainty

,0 , ,1 1

r r r i i r ij i ji i j i

a x b x x

Predictions of a chemical model (e.g. laminar flame speed)+ associated uncertainty

ˆˆ,m m m

x ξ x

Represents some physics model,e.g. PREMIX

1‐atm C2H4‐air mixtures

0.5 1.0 1.5 2.0

Egolfopoulos & Law (1990)Faeth & co-workers (1998)Law & co-workers (2005)La

Equivalence Ratio,

Sheen et al. (2009)

10-5 10-4 10-3

Time (s)

10-3H2O

10-5 10-4 10-3

Time (s)

300 ppm nC7H16 / 3300 ppm O2 / Ar (T5 = 1494 K, p5 = 2.15 atm)

Multispecies Time Histories(Model Uncertainties)

JetSurF 1.0 is quite accurate

10-5 10-4 10-3

Time (s)

10-3H2O

10-5 10-4 10-3

Time (s)

JetSurF 1.0 is quite accurate… but aren’t we lucky!

Even less precise towards lower T5.

10-5 10-4 10-3

Time (s)

10-3H2O

10-5 10-4 10-3

Time (s)

10-5 10-4 10-3

Time (s)

300 ppm nC7H16 / 3300 ppm O2 / ArT5 = 1494 K, p5 = 2.15 atm

10-4 10-3

Time (s)

OH CO2

Analyses of Experimental Uncertainties

Dashed lines: ±10K T5 uncertainty; dotted lines: ±20% uncertainty on species concentration

0.5 1.0 1.5 2.0

Equivalence Ratio,

Method of Uncertainty Minimization (MUM‐PCE)

obs obs obs,0r r r r ξ

2* obs, ,2obs1 1 1

1 ˆˆminM M M M

r ir r i r ijr i i j ir

,00 *2obs1

minM r r

ˆˆ,m m m

x ξ x 0

0.5 1.0 1.5 2.0

Equivalence Ratio,

“best” model

least‐squares minimization

model + uncertainty

prediction + uncertainty

Sheen, et al. (2009)

2* * obs, ,2,... obs1 1 1

1 ˆˆ,... min ...M M M M

r ir r i r ijr i i j ir

1 1...i ij ij

i j j kj k j

0.5 1.0 1.5 2.0

Equivalence Ratio,

Method of Uncertainty Minimization (MUM‐PCE)

obs obs obs,0r r r r ξ

,00 *2obs1

minM r r

ˆˆ,m m m

x ξ x

0.5 1.0 1.5 2.0

Equivalence Ratio,

“best” model

least‐squares minimization

model + uncertainty

prediction + uncertainty

Sheen, et al. (2009)

10-5 10-4 10-3

Time (s)

10-3H2O

10-5 10-4 10-3

Time (s)

Model Precision Improved by the data

Impact on Flame Speed Predictions

0.7 0.9 1.1 1.3 1.5

Equivalence Ratio,

n‐heptane‐air mixtures (p = 1 atm, T0 = 353 K)

unconstrained – prior model

constrained – posterior modelOH, H2O, CO2 ( = 1, T5 = 1365 * 1495 K)

Multispecies Time HistoriesEffect of Experimental Uncertainties

0 5 10 15 20

1/(2 obs)

20% 10% 7% 5%

Uncertainty in Species Value, 2 obs

0 5 10 15 20

1/(2 obs)

20% 10% 7% 5%

Uncertainty in Species Value, 2 obs

CH3 (Series 2) only

OH (Series 1) only

All multi-species (Series 1 & 2)

Multispecies Time HistoriesEffect of Experimental Uncertainties

0.7 0.9 1.1 1.3 1.5

Equivalence Ratio,

posterior model (±20%)

posterior model (±5% - hypothetical)

(d)(d)

Model is Accurate, and (Looks) Precise (Too)with constrained joint parameter uncertainties

Equivalence Ratio,

2 sets of OH, H2O, CO2 profiles

2 sets of OH, H2O, CO2 profilesFlame speedIgnition delay

(s) 0.4% nC7H16 / 4.4 % O2 / Ar (p5 = 1 atm)

0.60 0.65 0.70 0.75

1000 K/T

Open diamond: Smith et al. (2005); filled circles: Davidson et. al. (2010)

Model is Accurate, and (Looks) Precise (Too)with constrained joint parameter uncertainties

Multispecies Global Multispecies+properties Global properties

Joint Parameter Uncertainties

JetSurF (Version 1.1) Release date: September 15, 2009

Main page JetSurF 1.1 download Performance How to cite Symbols: Data from D.F. Davidson, R.F. Hanson, “Cycloalkane Ignition Studies,” unpublished, June 29, 2009. Onset of OH emission. Lines: JetSurF v1.1 predictions.

0.65 0.70 0.75

0.381% methylcyclohexane - 4%O2 in Ar1p5 = 1.5 atm

1000 K / T

0.65 0.70 0.75 0.80

0.381% methylcyclohexane - 4%O2 in Ar1p5 = 3 atm

1000 K / T

0.65 0.70 0.75 0.80

0.191% methylcyclohexane - 4%O2 in Ar0.5p5 = 1.5 atm

1000 K / T

Main page JetSurF 1.1 download Performance How to cite Symbols: Data from J. Vanderover, M. A. Oehlschlaeger, “Ignition Time Measurements for Methylcyclohexane and Ethylcyclohexane‐Air Mixtures at Elevated Pressures,” International Journal of Chemical Kinetics 41 (2009) 82‐91. Onset of OH emission. Lines: JetSurF v1.1 predictions

0.75 0.80 0.85 0.90 0.95

0.4977% methylcyclohexane - 20.90%O2 in N20.25p5 = 15 atm

1000 K / T

0.75 0.80 0.85 0.90 0.95 1.00 1.05

1000 K / T

0.75 0.80 0.85 0.90 0.95 1.00 1.05

1000 K / T

0.80 0.85 0.90 0.95 1.00 1.05 1.10

0.9905% methylcyclohexane - 20.80%O2 in N21p5 = 50 atm

1000 K / T

Main page JetSurF 1.1 download Performance How to cite Symbols: Data from S. M. Daley, A. M. Berkowitz, M. A. Oehlschlaeger, “A shock tube study of cyclopentane and cyclohexane ignition at elevated pressures,” International Journal of Chemical Kinetics, 40 (2008) 624‐634. Onset of OH* emission. Lines: JetSurF v1.1 predictions.

0.75 0.80 0.85 0.90 0.95 1.00

0.5802% cyclohexane - 20.89%O2 in N2 0.25p5 = 15 atm

1000 K / T

0.75 0.80 0.85 0.90 0.95 1.00 1.05

1000 K / T

0.80 0.85 0.90 0.95 1.00 1.05 1.10

1000 K / T

0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10

1000 K / T

Cyclohexane Low‐Temperature Chemistry

Miller, Taatjes (2009)

Cyclohexane Ring‐Opening Reaction

k (s–1) = 5×1016 exp[ –88 (kcal/mol) / RT] (Tsang 1978)

Methylcyclohexane Ring‐Opening Reaction

• •

Ring‐Opening Reactions

CBS‐QB3 energy

→ Ho = 89.8 kcal/mol

→ Ho = 79.0 kcal/mol

CH3CH3

••

Ea = 71 kcal/mol

Ea = 88 kcal/mol

Summary

• JetSurF 2.0 is available online (still needs work).

•Major improvement from version 1.1• Added low temperature of cyclohexane

• Unresolved problems

• Low‐temperature chemistry for n‐butylcyclohexane not yet implemented

• Kinetics of alkylated cyclohexane thermal decomposition (ring opening through the carbene mechanism) currently unavailble)

Reaction Models of Combustion Properties4 • Version 1.0+1.1 →JetSurF 2.0 n‐butyl‐,...

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