Autoignition and Combustion of JP-8 and its

Surrogates at Moderate Pressures

ARO Grant # W911NF-09-1-0108.

K. SeshadriDepartment of Mechanical and Aerospace Engineering

University of California at San DiegoLa Jolla, California 92093-0411

Multiagency Coordination Committee for Combustion Research,Princeton, NJ

20—23 September 2010

Objectives & Approach

• Objectives:

– To develop surrogates that can reproduce selected aspects of combustionof JP-8 in laminar, nonuniform, nonpremixed and premixed flows.

• Approach

– Experimental: Conducted employing the counterflow configuration.Fuels tested are JP-8, potential surrogates of JP-8, and reference com-ponents. Measurements made include critical conditions of extinction,autoignition, and flame structure. The studies are to be carried out forvalues of pressure up to 25 bar.

– Kinetic Modeling: Carried out employing detailed and semi-detailedmechanism. The results are used to validate the chemical-kinetic mech-anisms.

Collaboration

• Professor Eliseo Ranzi at Dipartimento di Chimica, Materiali e IngegneriaChimica, Politecnico di Milano, Milano, Italy.

• Professor N. Peters at Institut fur Technische Verbrennung, RWTH Aachen,D-52056 Aachen, Germany.

Accomplishments

• Experimental:

– Nonpremixed combustion:

∗ Critical conditions of extinction, and autoignition measured for JP-8,and surrogates. Soot volume fraction measured at RWTH, Aachen.

∗ The structure of nonpremixed n-decane flame was measured.

– Premixed combustion:

∗ Critical conditions of extinction measured for JP-8, surrogates, andreference components.

– A High Pressure Combustion Experimental Facility (HPCEF) was beenbuilt. A methane/air flame was successfully stabilized in this facility atpressures up to 15 bar.

• Kinetic Modeling: Carried out for surrogates of jet fuels and referencecomponents.

Results of Previous Studies on Combustion in

Nonpremixed Flows

• In a previous study several batches of JP-8 and Jet-A, and fifteen possiblesurrogates of jet fuels were tested in nonpremixed systems.

• It was found that critical conditions of extinction and autoignition of allbatches of JP-8 and Jet-A are similar.

• Among the surrogates tested, the Aachen surrogate and Surrogate C, werefound to best reproduce autoignition and extinction characteristics of JP-8.

• The Aachen surrogate also accurately reproduced volume fraction of sootformed.

Recent Work on Surrogates

• SERDP surrogate made up of n-dodecane and m-Xylene.

• Utah/Yale surrogate (Jahangirian et al, C & F, 156, 2009) show goodagreement for decomposition products and soot precursors with those forjet fuels.

• Dooley et. al ( C & F, 2010) employing implicit methodology based onchemical group theory developed a surrogate made up of n-decane, iso-

octane and toluene. Validity was tested using variable pressure flow reactor,extinction of strained diffusion flames, autoignition in shock tube and rapidcompression machine.

Surrogates Tested

• The Aachen surrogate (developed at RWTH Aachen) is made up of n-

decane 80 %, trimethylbenzene 20 % by weight (H/C = 1.99).

• Surrogate C (developed at UCSD) is made up of 57 % n-dodecane, 21 %methylcyclohexane, 22 % o-xylene by weight (H/C = 1.92).

Extinction and Autoignition of Flames in

Nonpremixed Flows

Experiments & Kinetic Modeling

• Experimental

– Carried out at a pressure of 1.013 bar employing the counterflow config-uration.

– Fuel stream: Prevaporized liquid fuel diluted with nitrogen.

– Oxidizer stream: Air.

– Fuels Tested: JP-8 (4177), and the Aachen surrogate.

• Kinetic Modeling

– Mechanism developed at RWTH. It is made up of 900 elementary reac-tions among 129 species.

Schematic Illustration of Counterflow Configuration

L

T2 V2 Y

Flame

Air

vaporizedfuel, N2 T1 V1

YF,1

StagnationPlane

N2

N2heated Air

N2

N2

extinction auto-ignition

O2,2T2 V2 YO2,2

vaporizedfuel, N2 T1 V1

YF,1

Strain rate: a2 = a2(V1, ρ1, V2, ρ2)

Critical Conditions: depend on T1, YF,1, T2, YO2,2, and a2.

Extinction Experiments T1 = 473 K, T2 = 298 K, YO2,2 = 0.233. Experimentaldata YF,1 as a function of a2.

Autoignition Experiments YF,1 = 0.4, T1 = 473 K, and YO2,2 = 0.233. Experi-mental data obtained is T2 as a function of a2.

Measured Critical Conditions of Extinction

F,1

2 ,e - 1• The extinction characteristics of the Aachen surrogate is close to that of

kerosene (JP-8).

Critical Conditions of Autoignition

2,I

2 - 1• Symbols: Experimental data, Lines: Calculations

• Autoignition of the Aachen surrogate is close to that of JP-8.

• Calculated values of autoignition for the Aachen surrogate agrees well withthe measurements

Extinction of Flames in Strained

Premixed Flows

Experiments & Computations

2

φ 1 ,o x 1O 2• Carried out at p = 1.013 bar employing the counterflow configuration.

• Premixed reactant stream: Prevaporized liquid fuel mixed with oxygen andnitrogen. Inert stream: Nitrogen.

• The flame is on the premixed reactant stream side of the stagnation plane.

• Critical conditions of extinction depend on YF,1, YO2,1, T1, V1, T2, and V2.

Critical Conditions of Extinction

• The flow time is characterized by the strain rate, a1 on the premixed reactantstream side of the stagnation plane.

a1 =2|V1|

L

(

1 +|V2|

√ρ2

|V1|√

ρ1

)

.

• The chemical system is characterized by the equivalence ratio, φ

φ = νO2YF,1WO2

/(YO2,1WF)

and the quantity YO2,x

YO2,x = YO2,1/(

YO2,1 + YN2,1

)

.

Critical Conditions of Extinction

• Experiments

– Carried out for fixed values of T2 = 298K, T1 between 473 K and 483 K,and YO2,x = 0.18.

– Fuels tested are the alkanes (n-heptane, n-decane, n-dodecane), the aro-matics (o-xylene, trimethylbenzene) jet fuels JP-8 (4177), the Aachensurrogate, and Surrogate C.

– Data is obtained showing a1,E as a function of φ for 0.9≤φ≤1.25.

• Kinetic Modeling

– Performed by Professor E. Ranzi at Politecnico di Milano, Milano, Italy,

– The semi-detailed kinetic scheme is made up of more than 8000 elemen-tary and lumped reactions among more than 300 species.

Experimental Results of Extinction

1,E�1

• Symbols: Experimental data

• Critical conditions of extinction of Aachen surrogate and Surrogate C veryclose to those for JP-8

Comparison of Predictions of Kinetic Model with Experimental Data:Reference Fuels

• Symbols: Experimental data; Lines: Predictions of kinetic model.

• Good agreement for all fuels including trimethylbenzene and o-xylene

Comparison of Predictions of Kinetic Model with Experimental Data:Surrogates

• Symbols: Experimental data; Lines: Predictions of kinetic

• Excellent agreement of predictions with experimental data

The Structure of Nonpremixed n-Decane

Flame

Structure of n-Decane Flame

• Experimental

– Concentrations of stable species were measured by removing gas samplesfrom the reaction zone using a quartz microprobe and analyzing themin a gas chromatograph.

– The temperature profiles were measured using a bare Pt-Pt13%Rh (TypeR) thermocouple.

• Kinetic modeling performed using the semi-detailed mechanism developedat Politecnico di Milano.

21

YFuel = 0.306 (n-Decane)

Temperature and Species Profile Measurements

L = 10 mm

N2, O2

N2, Fuel

Microprobe

YO2= 0.233

Strain rate = 100 s-1Thermocouple

Pt - Pt13%Rh

Wire Diameter 25 m

Junction Diameter 85 m

Tip Opening 100 m

Tip O.D. 180 m

5 mm off Axis

Flame

Strain rate a = 4 V2 / L with 1 ·V12 = 2·V2

2

V2 = Exit velocity at oxidizer duct

Sampling of Stable Species in Nonpremixed Flame

(n-Decane flame)

Gas Chromatograph for Species Measurement

Agilent MicroGC 2000: 4 parallel columns with individual TCD detectors.

Sampling procedure: Sample was drawn from flame into a heated mixing

chamber up to 0.5 bar. Nitrogen was added to 1.2 bar and the mixture was

injected into gas chromatograph.

Column Carrier Gas Temperature Back-flush

Mole sieve Argon 348 K (75 C) yes

Plot U Helium 343 K (70 C) yes

Plot Q Helium 348 K (75 C) no

OV-1 Helium 348 K (75 C) no

H2

Chromatogram for one Sample Point(n-Decane Flame, 4.6 mm from Fuel Exit)

O2 N

2

CH

4

CO

CO

2

C2H

4

C2H

6

C2H

2

C3H

6

C3H

8

p-C

3H

4

a-C

3H

4

1-C

4H

8

H2O

1,3

-C4H

6

C5H

10

C6H

12

C8H

16

C7H

16

C6H

6

C7H

8

n-Decane (Species Profiles)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

2 3 4 5 6 7 8

Ma

ss F

ract

ion

Distance from Fuel Duct [mm]

CO2 ( 2)H2O ( 3)

CO ( 3)

H2 ( 50)

O2

n-C10H22

main species

Accuracy of species measurement: ±15-20%

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

2 3 4 5 6 7M

ass

Fra

ctio

n

Distance from Fuel Duct [mm]

C2H4

C2H2

CH4 ( 2)

C2H6

n-C10H22

intermediate species

n-Decane (Species Profiles)

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

2 3 4 5 6 7

Ma

ss F

ract

ion

Distance from Fuel Duct [mm]

C3H6

C3H8 ( 8)

Propyne

Propadiene ( 3)

n-C10H22

C3 hydrocarbons

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

2 3 4 5 6 7M

ass

Fra

ctio

nDistance from Fuel Duct [mm]

1-C4H8 ( 3)

1,3-C4H6 ( 2)

1-C5H10 ( 1.5)

1-C6H12

n-C10H22

C4, C5, C6 hydrocarbons

n-Decane (Temperature Profiles)

200

400

600

800

1000

1200

1400

1600

1800

2 3 4 5 6 7 8

Tem

per

atu

re [

K]

Distance from Fuel Duct [mm]

n-C10H22

Temperature measurement (uncorrected)

Temperature (corrected for radiation)

Accuracy of temperature measurement: ±80 K

High Pressure Combustion Experimental

Facility

High Pressure Combustion Experimental Facility

• A “High Pressure Combustion Experimental Facility” (HPCEF) has beenconstructed for carrying out experiments at pressures up to 25 bar.

• This facility will be used to study combustion of high molecular weighthydrocarbon fuels including JP-8 in laminar nonuniform flows.

• In the HPCEF different types of counterflow burners can be placed inside ahigh pressure chamber.

• A counterflow burner that can be used to carry out experiments on gaseousfuels has been built and tested at pressures up to 15 bar.

23

p = 4 bara2 = 100s-1

Yfu = 0.196Y02

= 0.233

p = 5 bara2 = 100s-1

Yfu = 0.174Y02

= 0.233

p = 6 bara2 = 100s-1

Yfu = 0.160Y02

= 0.233

p = 10 bara2 = 100s-1

Yfu = 0.185Y02

= 0.233

p = 15 bara2 = 100s-1

Yfu = 0.185Y02

= 0.233

a2 = 100s-1 Yfu = 0.185 Y02= 0.233

a2 = 120s-1 Yfu = 0.185 Y02= 0.233

a2 = 140s-1 Yfu = 0.185 Y02= 0.233

a2 = 160s-1 Yfu = 0.185 Y02= 0.233

a2 = 180s-1 Yfu = 0.185 Y02= 0.233

a2 = 200s-1 Yfu = 0.185 Y02= 0.233

p = 10 bar

p = 10 bar

p = 10 bar

p = 10 bar

p = 10 bar

p = 10 bar

Summary

• Experimental Studies show that the Aachen surrogate and Surrogate C ac-curately reproduce many aspects of nonpremixed and premixed combustionof JP-8.

• The semi-detailed kinetic model developed at Politecnico di Milano, Milano,Italy accurately reproduces experimental data on nonpremixed and premixedcombustion of Aachen surrogate and Surrogate C.

• The semi-detailed kinetic model developed at Politecnico di Milano, Milano,Italy accurately reproduces experimental data on combustion of aromaticfuels—o-xylene and trimethylbenzene.

• A High Pressure Combustion Experimental Facility has been built. Methaneflames have been stabilized at pressures up to 15 bar.

• Future experimental and modeling studies will focus on combustion char-acteristics of jet fuels, surrogates and reference components at moderatepressures.

Videos of Methane Flames Stabilized in the HPCEF

The flowfield is controlled by a computer. The entire process is almost com-pletely automated

• At pressure of 1 atm.

– At some selected value of the strain rate and composition of the reactantstreams, the flow field is established by the computer.

– A command is given for ignition. A flame is established.

– The remaining process is completely automated. The strain is increasedby the computer by selected increments until extinction takes place.Data is recorded.

– The experiment is repeated.

– The video was taken in the counterflow burner that is used in the HPCEFbut without the pressure chamber. Therefore the video is clear withoutreflections.

• At pressure of 10 atm.

– Procedure same as at 1 atm, but with the pressure chamber.