computational and experimental studies of jet fuel …leads to the fragmentation of heavier alkanes...
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Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Computational and ExperimentalStudies of Jet Fuel Combustion
Mitchell D. Smooke and Alessandro GomezDepartment of Mechanical Engineering
Yale UniversityNew Haven, CT 06520-8284
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Objectives• Examine flame structure of JP-8 doped
flames• Compare and contrast with promising
surrogate candidates• Model the surrogate(s) with semi-
detailed chemical kinetics• Reduce chemical kinetics scheme
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Experimental System• One-dimensional counterflow
flame– complex kinetics but simple
fluids• Liquid dispersion by the
electrospray, followed by sprayevaporation in the fuel line
• Perturbed baseline methaneflame– Use flame as a “controlled”
reactor by maintaining a fixedtime-temperature baseline
– Avoid condensation problemsand “cooking” the fuel in thetransfer lines
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
• 30µm tip size 100µm body (but 3Xprobe maintains comparable spatialresolution at atmospheric pressure)
• SiO2 for high temperature tolerance
• Small sampling flow rate (≈ 50µ l/min)
Microprobe Details
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
4 hours of flame burning and …..30 hours of off-line analysis!
GC/MS Configuration
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Experimental Conditions (non-Sooting Flames)• Baseline Flame
– Fuel stream XN2 = 0.935 XCH4= 0.065
– Oxidizer stream XN2 = 0.74 XO2= 0.26
• Dopant perturbation
– 4.2 103 ppm of either JP-8 or surrogate
• Max. Temp= 1750K
• Strain Rate= 102 s-1
• Zf (stoich. mixture fraction)= 0.77
• Flame on fuel side of stagnation plane
Non-sootingGSP
Fuel
Oxidizer
Flame
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Numerical Simulations•1D Simulation using self-similar transformation
•Dirichlet conditions imposed at the inlet
•221 Species × 5032 reactions
[E.Ranzi et al., Prog.Energ.Comb.Sci, 2001]
•Pseudo-time stepping + Newton’s Method
Experimental results have been shifted by 1.0mm to accountfor probe intrusiveness and other effects
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
From [Violi et al., Comb. Sci. Tech., 2002], designed to matchdistillation properties, smoke point behavior, laminar flame speedand validated for extinction limits in (Cooke et al., 2005)
• 10% iso-Octane
• 30% n-Dodecane
• 20% n-Tetradecane
• 20% Methylcyclohexane
• 15% o-Xylene
• 5% Tetralin
Surrogate Formulation
……but ready to test other promising alternatives (e.g., Aachen, SERDP, MURI, etc.)
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Results• Measured and computed mole
fractions for
• Large alkanes
• Ethane, ethylene, acetylene,methane
• Major species (CO, CO2 andO2)
• Aromatics
• Temperature measurementscorrected for radiation losses
• Zoom in on fuel side of the domain
• x = distance from fuel inlet
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Major Species and TemperatureJP-8 doped-
Symbols/continuous line Surrogate-doped (exp)-
Symbols/dashed line Surrogate-doped (comp)-
Continuous thick line
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
JP-8 vs. Surrogate: Large Alkanes
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Surrogate- Experiments vs. Computation: Large Alkanes
Surrogate-doped (exp)-Symbols/dashed line
Surrogate-doped (comp)- Continuous thick line
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
JP-8 vs. Surrogate: C4-C6 Species
JP-8 doped- Symbols/continuous line
Surrogate-doped (exp)- Symbols/dashed line
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
C2 species
JP-8 doped- Symbols/ continuous line
Surrogate-doped (exp)- Symbols/ dashed line
Surrogate-doped (comp)- Continuous thick line
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Aromatics
Surrogate-doped (exp)-Symbols/dashed line
Surrogate-doped (comp)- Continuous thick line
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Aromatics (close-up)
JP-8 doped- Symbols/ continuous line
Surrogate-doped (exp)- Symbols/ dashed line
Surrogate-doped (comp)- Continuous thick line
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Conclusions (Part 1)• The addition of jet fuel to a nonsooting baseline methane flame
leads to the fragmentation of heavier alkanes to smaller ones,down to C2-hydrocarbons and the appearance of peak aromaticconcentrations surviving further into the high temperatureregion.
• A 6-component surrogate captures the pyrolysis and oxidationbehavior of JP-8 reasonably well, with the most significantdiscrepancy for benzene, toluene and ethylene.
• The computational results using a semi-detailed kineticmechanism are in reasonably good agreement with theexperiments.
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
More flames?
With what feed streamcomposition?
Objective: span a broad range ofZf, from non-sootingflames to sooting ones
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
• Max. Temp= 1750K
• Strain Rate= 102 s-1
• Zf (stoich. mixture fraction)= 0.77
• Flame on fuel side of stagnationplane
Non-sooting Flames
GSP
Fuel
Oxidizer
Flame
• ↑ Max. Temp
• ↓ Strain Rate
• ↓ Zf
• Flame on oxidizer side of stagnationplane
Sooting Flames
GSP
Fuel
Oxidizer
Flame
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
2. Experimental Conditions (Incipiently Sooting Flames)
GSP
Fuel
Oxidizer
Flame
• Baseline Flame #2
– Fuel stream XN2= 0.728XC2H4= 0.272
– Oxidizer stream XN2= 0.807XO2= 0.184
• Dopant perturbation
– 2×103 ppm of either JP-8 or surrogate
• Max. Temp= 1989 K
• Strain Rate= 67.8 s-1
• Zf = 0.18
• Flame on oxidizer side of stagnationplane
≈0.6mm
Sooting
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Major Species and Temperature
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 1 2 3 4 5 6 7 8 9 10 11
Distance from fuel inlet [mm]
Mo
le f
rac
tio
n
300
700
1100
1500
1900
2300
Ethylene
CO2
CO
Temperature [K]
JP-8 doped- Symbols/ continuous line
Surrogate-doped (exp)- Symbols/ dashed line
Baseline (exp)- small dash line
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Surrogate Components
0
100
200
300
400
500
600
0 1 2 3 4 5 6 7
Distance from fuel inlet [mm]
pp
m
Methylcyclohexane
Isooctane
Dodecane
Tetradecane
Tetraline
Xylene
0
10
20
30
40
50
60
70
80
0 1 2 3 4 5 6 7
Distance from fuel inlet [mm]p
pm
Meth.Cyc.Hex
Heptane
Isooctane
Octane
Nonane
Decane
Undecane
Dodecane
Tridecane
Tetradecane
Pentadecane
JP-8 Alkanes
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
C1 and C2 Species
0.0E+00
1.0E-04
2.0E-04
3.0E-04
4.0E-04
5.0E-04
6.0E-04
7.0E-04
8.0E-04
9.0E-04
1.0E-03
0 1 2 3 4 5 6 7 8 9
Distance from fuel inlet [mm]
Mo
le f
racti
on
0.000
0.002
0.004
0.006
0.008
0.010
0.012
Ethane
Methane
Acetylene
JP-8 doped- Symbols/ continuous line
Surrogate-doped (exp)- Symbols/ dashed line
Baseline (exp)- small dash line
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Aromatics
0
20
40
60
80
100
120
140
160
1 2 3 4 5 6 7 8
Distance from fuel inlet [mm]
pp
m
Benzene
Toluene
JP-8 doped- Symbols/ continuous line
Surrogate-doped (exp)- Symbols/ dashed line
Baseline (exp)- small dash line
Soot band
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Chromatogram Comparison
• Grassy background
• Overlapping peaks
• 30 species identified and measured
• 20 species identified but notquantified
•Clean distinct peaks
•Possibility to track minor species
Surrogate JP-8
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Carbon Count Problem
Methane baseline flames (exp 1)CO and CO2 excluded from count
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Perturbation of Sampling Probe• The objective is to assess the probe perturbation
in terms of flame displacement by OH PLIF• A potentially useful byproduct is the concurrent
PLIF from PAH blends in the JP-8
PAH PLIF
OH PLIF
Nd:YAG(532 nm, ~60 mJ, 6 ns)
Dye Laser(566 nm, ~25 mJ)
BBO (x2)(~283 nm, ~4 mJ)
ICCDcamera
Flash LampTrigger Output
UG5 + WG305 Filter Set(52.1% Transmittance
@ 310 nm)
PIV Laser
PIVcamera
532 nm IF
Telescopeoptics
Burner
Energy meter
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Probe position above fuel
outlet
OH PLIF image
2.8 mm
3.8 mm
4.8 mm
5.8 mm
6.8 mm
7.8 mm
8.8 mm
9.8 mm
Flame shift ≤ 0.6 mm
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Conclusions (Part 2)• Experiments on an incipiently sooting ethylene flame show good
agreement between surrogate and JP-8 even with respect tobenzene and toluene, suggesting that the surrogate maycapture even the sooting behavior of JP-8, as intended by thematching of the smoke point in the surrogate design.
• A procedure was demonstrated to reduce the experimental timeto operate the burner for a complete flame scan toapproximately 4 hours, with 30 hours of automated off-lineGC/MS/FID chemical analysis.
• The JP-8 chemical analysis is invariably incomplete andaccounts for roughly only 20% of the overall carbon introducedas liquid fuel.
• OH PLIF showed a modest perturbation by the sampling probe.
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Future Work (pending renewal)
• Examine systematically other surrogate candidatesand their individual components (e.g., Aachen, MURI,SERDP);
• Tweak the chemical kinetic mechanism in thecomputational model to improve agreement withexperiments (in collaboration with Ranzi’s group inMilan);
• Use sensitivity tests in the chemical kinetic model forguidance in the chemical analysis;
• Design and test a high pressure chamber to performsimilar work at high pressures (up to 40 atm);
• Implement a reduced kinetics strategy.
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
References• Tosatto et al, to appear in the Proceedings of the 32nd International
Combustion Symposium, 2008• Bufferand et al., submitted to C&F, 2008• Jahangirian et al., in preparation, 2008
Acknowledgements
• Graduate students Luca Tosatto, Hugo Bufferand and Saeed Jahangirianperformed the bulk of the experiments and Bruno Coriton helped with theOH LIF experiment.
• Dr. James (Tim) Edwards (WPAFB) supplied the JP-8.• Research supported by
– AFOSR (Grant #FA9550-06-1-0018, Dr. Julian Tishkoff, Program Manager)and
– ARO DURIP (Grant # W911NF-07-1-0231, Dr. Ralph Antonien, ProgramManager)
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Back up
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
From JP8: aliphaticstoluene,xylene,ethylbenzene,n-alkylbenzenes,etc.
isopropylbenzeneetc.
benzene benzyl styrene
naphthalene
(toluene )
sootCourtesy of Charles Mc Enally
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
C2 Hydrocarbons in a JP-8-doped hydrogen flame (fullsymbols) and a surrogat-doped hydrogen flame (open
symbols).
Fuels Summit, NIST, Gaithersburg, Maryland, September 8-10, 2008
Flame A Flame B Flame C Flame D
Molar Composition
N2
C2H4
C2-C5 alkane (Ethane)
impurities
0.7278
0.2722
851 ppm
0.7340
0.2641
825 ppm
0.7339
0.2641
825 ppm
0.7339
0.2641
825 ppm
JP-8 (C11H21)
1953 ppm
Utah Surrogate
Methyl-Cyclohexane
Iso-Octane
m-Xylene
Tetraline
Dodecane
Tetradecane
Total=
394 ppm
197 ppm
295 ppm
98 ppm
591 ppm
394 ppm
1970 ppm
Aachen Surrogate
1,2,4-trimethylbenzene
n-Decane
Total=
450 ppm
1520 ppm
1970 ppm
Mass Flux (g/min/cm2) 1.619 1.684 1.683 1.682
Fuel
Side
Temperature (K) 417
Molar Composition
N2
O2
0.8070
0.1843
Mass Flux (g/min/cm2) 1.891 1.925 1.925 1.925
Oxidizer
Side
Temperature (K) 414
Strain Rate (s-1
) 67.78 69.54 69.53 69.52
zf 0.1798 0.1797 0.1799 0.1801
Sooting Flames B.C.
In the surrogate-doped flame,B, 14.2 103 ppm of C as C2H4in the baseline flame, A, arereplaced with 11.0 103 ppm ofC as JP-8