Flame Kinetics and Transport of Flame Kinetics and Transport of AlkanesAlkanes and Aromatic Mi t resand Aromatic Mi t resAlkanesAlkanes and Aromatic Mixturesand Aromatic Mixtures

Sang Hee Won, Pascal Diévart, Jeffrey S. Santner, Hwan Ho Kim,  g yYiguang Ju

Department of Mechanical and Aerospace EngineeringDepartment of Mechanical and Aerospace EngineeringPrinceton University, Princeton, NJ 08544

M lti A C di ti C itt f C b ti R h (MACCCR)Multi Agency Coordination Committee for Combustion Research (MACCCR)Sept. 20 – 22, 2011, Argonne National Laboratory

1

PRINCETONMechanical and Aerospace Engineering

Questions to addressQuestions to address1. Do the MURI surrogate fuel models work for flame 

extinction?2. How to address the issue of kinetic and transport  

interaction between aromatics and alkanes in flames?3. How to isolate kinetic, fuel heating value, and transport3. How to isolate kinetic,  fuel heating value, and transport 

effects from the global flame experiments and obtain a general correlation?

4 Can we build the missing kinetic building block of the 2nd4. Can we build the missing kinetic building block of the 2generation jet fuel surrogate? 

n‐dodecane, i‐octane, n‐propyl‐benzene1,3,5 trimethyl–benzene?

5.     Can we collaboratively validate this mechanism (experiments)?(experiments)?

2

PRINCETONMechanical and Aerospace Engineering

Research ThrustResearch Thrust• Develop and validate MURI surrogate fuel formulations of Jet fuels

H/C ratio, DCN, TSI, and MW• Understand Kinetics and Transport Interaction b lk d i i lbetween alkanes and aromatics in Flames

• Develop a comprehensive correlation of flame ti ti d t t h i t i f tiextinction and extract chemistry information

• Develop a kinetic oxidation mechanism for 135 trimethyl benzenetrimethyl benzene

• Develop a high pressure spherical bomb for flame measurement of liquid fuelsflame measurement of liquid fuels

3

1. Flame validation of the 2nd surrogate fuel formulation of Jet fuels

4

PRINCETONMechanical and Aerospace Engineering

Diffusion Flame Experimental SetupDiffusion Flame Experimental Setup

• Extinction limits and OH measurements– Using FTIR measurements to check thermal decomposition and 

concentration variation: Concentration fluctuation < 1%– OH radical measurement: Q1(6) excitation ~ 282.93 nm

Heater & insulation

Nitrogen

Heater & insulationHeater

FuelT

T1 T2

To burner

Schematics of evaporation system

PRINCETONMechanical and Aerospace EngineeringExperimental Measurements of OH Concentration 

by using laser induced fluorescence 

• PLIF: Q1(6) transition (282.93 nm), linear regime, beam height 80 mmQuenching, Soot, PAH correctionsQuenching, Soot, PAH corrections

PAH LIFLII (soot)

OH LIF

Q1(6) line1

Stagnation plane

Schematic photo for Rayleigh scattering and PLIF

detuned subtraction

nPB diffusion flames

PRINCETONMechanical and Aerospace Engineering

Surrogate Model Flame Validation on Jet POSF 4658

Surrogate Fuel: Mole Fraction DCN H/C MW / g mol-1 TSI•1st generation surrogate model (3 components)

Surrogate Fuel: Mole Fraction DCN H/C MW / g mol TSIJet‐A POSF 4658 47.1 1.957 142.01 21.4

n-decane iso-octane Toluene0.4267 0.3302 0.2431 47.1 2.01 120.7 14.1

•2nd generation surrogate model (4 components)•n-dodecane/iso-octane/ propyl benzene / 1,3,5 trimethyl benzenep py , , y

7

PRINCETONMechanical and Aerospace EngineeringValidation: Extinction of Diffusion Flames

POSF 4658 vs. 1st generation surrogateg g

5000.2 0.3 0.4 0.5 0.6

Fuel mass fraction, Yf

400

Princeton JetA surrogateJetA

e, a

E [1/s

]

200

300

stra

in ra

te

100

Extin

ctio

n

00 0.03 0.06 0.09 0.12 0.15

E

Fuel mole fraction, Xf

Mass fraction does not match!Problem:

Mass fraction does not match!

PRINCETONMechanical and Aerospace EngineeringValidation: Extinction of Diffusion Flames

POSF 4658 vs. 1st and 2nd generation surrogatesg g400

s]

300

te a

E[1

/s

200

trai

n ra

t

100nctio

n st

JetAPOSF 4658

Extin

JetA POSF 4658

1st generation

2nd generationTf = 500 K and To = 300 K

00.05 0.09 0.13

Fuel mole fraction Xf

PRINCETONMechanical and Aerospace Engineering

Validation: Extinction of Diffusion FlamesPOSF 4658 vs. 1st and 2nd generation surrogates

400Why is the mean

300a E[1

/s]

ymolecular weight a big deal?

Why can such a simple

200rain

rate

JETAPOSF 4658

Why can such a simple mixture model mimic a real fuel extinction limit so well?

100ctio

n st

r JETA POSF 4658

3 comp. Surrogate

4 comp Surrogate

Where does the H/C ratio and fuel heating value contribute to the100

Ext

inc 4 comp. Surrogate value contribute to the

problem?

What is the role of 0

0.2 0.3 0.4 0.5

Fuel mass fraction Yf

aromatics?

2. Kinetic and transport interaction between aromatics and alkanes in flames?

11

18001.50E-0460 % d 40 % l

Example: Complexity in Flame Chemistry:Kinetic coupling between n-decane and toluene in flames

15001.00E-04

m3 s

]60 % n-decane + 40 % toluene

near extinction, Xf = 0.1, a = 176 1/s

C6H5CH2+ H = C6H5CH3

H Diffusion loss

1200

0 00E+00

5.00E-05 Tempem

ole/

cm

C6H5CH2+ H = C6H5CH3

900

-5.00E-05

0.00E+00 erature n ra

te [m

overall decomposition of n-decane

300

600

1 50E 04

-1.00E-04

[K]

Reac

tion

C10H22=C2H5+C8H17-1C10H22=nC3H7+C7H15-1

overall decomposition of toluene

0-2.00E-04

-1.50E-04

0 85 0 9 0 95 1 1 05 1 1

R C10H22=CH3+C9H19-1C6H5CH3+H<=>C6H5CH2+H2C6H5CH3+OH<=>C6H5CH2+H2OC6H5CH3+H<=>A1+CH3

0.1 mm

0.85 0.9 0.95 1 1.05 1.1

Axial coordinate [cm]Won, Sun, Dooley, Dryer, and Ju, CF 2010

Extinction limit: Alkanes, Iso‐alkanes, aromatics500

n-decane T 500 K d T 300 K

400

E[1

/s]

n-decanen-nonanen-heptaneJETA POSF 4658P i t S t

n-alkanesTf = 500 K and To = 300 K

300rate

aE Princeton Surrogate

iso-octanenPBtoluene

aromatics

200n st

rain

124TMB135TMB

aromatics

100inct

ion

0

100

Ext

Different kinetics or transport or heating values?How to extract kinetic information from the data?

00 0.05 0.1 0.15 0.2

Fuel mole fraction Xf

PRINCETONMechanical and Aerospace EngineeringA generic correlation for extinction limit:

Chemistry and TransportChemistry and TransportTheory of counterflow flame extinction

Extinction Damkohler number32

, 32

1 2 1( , , ) ( , ) expfO aF F F O F F

TY TLe P Le Le L LeD Y T T T T

Extinction Damkohler number

2,E F f a fDa e Y T T T T

E ti ti St i R t (f l dil t d b it )

iFF

e RTTC

QYa *

)(1 ,

Extinction Strain Rate (fuel diluted by nitrogen)

fpFTTCMM )(/

Transport Heat release/heat loss Fuel chemistry/reactivityRadical production rate

( Won et al. 2011, C&F )

By introducing a new concept:

Transport-Weighted Enthalpy:[fuel] Hc (MWfuel/MWnitrogen)-1/2

500

[1/s

]

n-decane

n-nonanen-heptane

iso-octane n-alkanes

300

400

n ra

te a

E

iso-octanenPBtoluene

124TMB135TMB

aromatics

200

300

tion

stra

in 135TMB

100

Extin

ct

T = 500 K and T = 300 Kiso-alkane

15

00.5 1 1.5 2 2.5 3

[Fuel]Hc(MWfuel/MWnitrogen)-1/2 [cal/cm3]

Tf = 500 K and To = 300 K

PRINCETONMechanical and Aerospace Engineering

Introducing:Introducing: Radical IndexRadical Index• Heat release and OH production/consumption 

pathwaysH O OH O CO OH CO H d H OH H O H– H + O2 = OH + O, CO + OH = CO2 + H and H2 + OH = H2O + H

– Occur mainly in the core reaction zone• Quasi‐steady‐state approximation of OH• OH formation rate, ζOH = [OH]max × δOH × a• Radical Index = ζOHfuel/ ζOHn‐alkaneOH OH

– at either maximum or Da >= 2Fuel Radical index

n‐alkanes 1.0

iso‐octane 0.70

Toluene 0.56

PB 0 67nPB 0.67

124TMB 0.44

135TMB 0.36

PRINCETONMechanical and Aerospace Engineering

A General Correlation for A General Correlation for Extinction vs. Radical IndexExtinction vs. Radical Index

• Extinction limits are proportional toT W i h d E h l TWE– Transport‐Weighted Enthalpy, TWE

– Radical Index, Ri (population rate of OH)500

R² = 0.97400

500

a E[1

/s]

n-decane

n-nonane

n-heptane

iso-octane

n-propyl benzene

200

300

stra

in ra

te n propyl benzene

toluene

1,2,4-trimethly benzene

1,3,5-trimethly benzene

100

200

Extin

ctio

n

17

00.5 1 1.5 2

Ri[Fuel]Hc(MWfuel/MWnitrogen)-1/2 [cal/cm3]

Tf = 500 K and To = 300 K

PRINCETONMechanical and Aerospace Engineering

RadicalRadical Index to predict extinction limitIndex to predict extinction limit

• 1st generation surrogate mixtures– nC10/iC8/toluenenC10/iC8/toluene– Ri1st gen. = Σ Xi × Rii = 0.79

n-decaneiso-octane

350

450

te a

E[1

/s]

iso octanetoluene1st generation surrogate for Jet-A POSF 4658Prediction from correlationPrediction from correlation

250

n st

rain

rat

150

Extin

ctio

n

18

500.02 0.06 0.1 0.14 0.18

Fuel mole fraction Xf

Tf = 500 K and To = 300 K

PRINCETONMechanical and Aerospace EngineeringRadical Index to predict extinction limitRadical Index to predict extinction limit

• 2nd generation surrogate– nC12/iC8/nPB/135TMB,  Ri2nd gen = 0.80 (Ri1st gen = 0.79)/ / / , 2nd gen ( 1st gen )

• S8 surrogate (nC12/iC8),   RiS8 sur = 0.86450

From Radical Index correlation

350

e a E

[1/s

] S8 surrogate (nC12/iC8)2nd generation surrogate of Jet-A POSF 4658 (nC12/iC8/nPB/135TMB)

250

n st

rain

rat

150

Extin

ctio

n

19

500.03 0.06 0.09 0.12 0.15

Fuel mole fraction, Xf

Tf = 500 K and To = 300 K

3 Kinetic Model Development for 1353. Kinetic Model Development for 135 trimethyl benzene: Ignition & flames

•Second generation surrogate model (4 components)•n-dodecanen dodecane•iso-octane•N-propyl benzene 1 3 5 t i th l b•1,3,5 trimethyl benzene

Lack of a kinetic mechanism!

20

PRINCETONMechanical and Aerospace Engineering1,3,5 trimethyl benzene Model Development 

1,3,5‐TriMethylBenzene A  similar oxidation pathway f

m Xylene Submodel Kinetic parameters modified

subset to the one of toluene was adopted

m‐Xylene SubmodelBattin‐Leclerc et al. 2006

and Gail and Dagaut et al., 2008

Kinetic parameters modified and adopted from similar reactions in toluene subset

TOLUENE SubmodelMetcalfe , Dooley, and Dryer, 2011

H2/O2 subset proposed by Burke et al. adopted

Thermodynamic parameters of di- and tri-methyl related species re-estimated

PRINCETONMechanical and Aerospace Engineering

Oxidation of 135‐TMB in flame configurations

1,3,5‐TMB

35dmb1ch2

H abstraction reactions(H, OH)

H addition

CH3 addition35dmb1ch2

abduct 1‐Ethyl‐3,5‐beta-scission+O

.

(2 aromatic rings) diMethylBenzene

3 5‐ 1 3 dimethyl

+O

3,5diMethylBenzAldehyde

1,3 dimethylphenyl  CH2O

+OCHO

Xylene radicals

H abstractionCHO

PRINCETONMechanical and Aerospace Engineering

Validation of 135TMB Model: Ignition Validation of 135TMB Model: Ignition 

Shock Tube Ignition delay for stoichiometric135TMB/air mixture at 20.6 atm

Oehlsclaeger et al. 2011

PRINCETONMechanical and Aerospace Engineering

Validation of 135TMB Model: Validation of 135TMB Model: extinction and flow reactorextinction and flow reactor

– Diffusion flame extinction at 1 atm, Tf = 500 K, To = 300 KFlow reactor oxidation at 12 5 atm 930 K 1111 ppm– Flow reactor oxidation at 12.5 atm, 930 K, 1111 ppm135TMB, 13300 ppm O2

24

4. Measurement4. Measurements of s of Flame SpeedFlame Speed of  of  surrogate fuelssurrogate fuelssurrogate fuelssurrogate fuels

25

PRINCETONMechanical and Aerospace EngineeringDevelopment of  “Spherical” Bomb for liquid fuelsDevelopment of  “Spherical” Bomb for liquid fuels

Pre-vaporizationchamber

P Thermocouple

Fan

Oven P Pressure gauge

Thermocouple

Liquid fuel injectionwith syringe

herm

ocou

ple

electrodes Heated tube

Air cylinder

To vacuum pump

Air or N2/O2

T

heater heater

(Pressure relief)

26

heater heater

Overview

PRINCETONMechanical and Aerospace EngineeringTransient Flame Trajectories and speedsTransient Flame Trajectories and speeds

J A POSF 4658 d i d 135TMB135TMB– JetA POSF 4658, n‐decane, iso‐octane, and 135TMB135TMB500

Unstretchedfl d

400

[cm

/s]

flame speed

Multi-stage flames at300

velo

city

Sb [

Equivalence

near limit conditions

100

200 0.7 0.8 0.91 0rn

ed g

as v

Equivalence ratio

0

100 1.0 1.1 1.2 1.4

Bu

Transition from ignition to propagation

27

0 500 1000 15000

Stretch rate [cm-1]Stretch rate at Critical Radius

Numerical modeling200 iso-C8H18/air

1atm, 298K, Phi=0.8 •ASURF code

s)

150 A•AdaptiveChemistry(PFA method)

Sb

(cm

/s

100 B

CKA = 320 s-1

KB = 450 s-1

KC = 470 s-1

•Adaptivegrids

50

C

0 200 400 600 8000

28

K (1/s)0 200 400 600 800

PRINCETONMechanical and Aerospace Engineering

Validation of 135TMB Model: Flame speedValidation of 135TMB Model: Flame speed

– Laminar flame speed at 1 atm, 400 K60

50

60

[cm

/s] at 400 K

40

velo

city

30

ar b

urin

g

20

Lam

ina

princeton [Spherical bomb]Uconn [Counterflow twin flames]135TMB model, Diévart et. al

100.5 0.7 0.9 1.1 1.3 1.5

Eqivalence ratio

PRINCETONMechanical and Aerospace EngineeringConclusion

h t d d i f l d l f j1. The 1st and 2nd generation surrogate fuel models for jet A were validated against extinction limits.

2 Aromatics play an important role in affecting flame extinction2. Aromatics play an important role in affecting flame extinction via kinetic and transport coupling.

3. A comprehensive correlation for diffusion flame extinction plimits of alkanes, isoalkane, aromatics, and real fuel was obtained by using Transport weighted enthalpy and radical indexindex.

4. Chemical kinetic model for 135TMB has been developed and validated through collaborative MURI team/RPI work. Thevalidated through collaborative MURI team/RPI work. The surrogate model  building blocks were completed.

5. A nearly constant pressure spherical bomb was developed to measure liquid fuel burning velocity and transient flame regimes at elevated pressures.  30

PRINCETONMechanical and Aerospace Engineering

AcknowledgementsAcknowledgements

• MURI Surrogate fuel project monitored by Dr. Julian Tishkoff

• AFRL research project monitored by Dr. Barry Kiel

31