hypersonic fuels chemistry: n-heptane cracking and combustion andrew mandelbaum - dept. of...
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Hypersonic Fuels Chemistry:n-Heptane Cracking and Combustion
Andrew Mandelbaum - Dept. of Mechanical Engineering, Princeton University
Alex Fridlyand - Dept. of Mechanical Engineering, University of Illinois at Chicago
Prof. Kenneth Brezinsky - Dept. of Mechanical Engineering, University of Illinois at Chicago
Outline
•Project Background•Hypothesis•Experimental Apparatus and Methods•Results and Modeling
▫Heptane Pyrolysis▫Heptane Oxidation▫Heptane/Ethylene Oxidation
•Conclusions
Project Background
•Heat management•Very short reaction time requirements
Fig. 1: Cross-sectional diagram of a scramjet engine1
1. How Scramjets Work [online]. NASA. 2 Sept. 2006. 4 June 2011. http://www.nasa.gov/centers/langley/news/factsheets/X43A_2006_5.html.
Project Background
•Use fuel to cool engine structure
•Shorter cracking products may ignite more readily
Fig. 2: Ignition delay vs. temperature for various pure
gases and mixtures2
2. M. Colket, III and L. Spadaccini: Journal of Propulsion and Power, 2001, 17.2, 319.
Consequence, Questions Raised, Applications
•Injected fuel – different from fuel in tank•Effect on combustion products?•What causes the change in energy output –
physical or chemical differences?•Improved chemical simulations
▫Improved accuracy▫Use in engine modeling software▫Possibility for fuel composition customization
Hypothesis
•Heptane cracking products (primarily ethylene) will chemically influence combustion of remaining fuel
•Resultant species - differ in from non-cracked fuel alone and from existing heptane models
Low Pressure Shock Tube
•Designed to operate from 0.1-10 bar, 800-3000 K, 1-3 ms reaction time
•Explore oxidation chemistry at pressures relevant to hypersonic engine combustor
Fig. 3: Schematic drawing of low pressure shock tube and related assemblies
Methods• Perform pyrolysis and oxidation shocks at 4 bar
driver pressure• Examine stable intermediates and fuel decay
process using gas chromatography (GC-FID/TCD)
• Model used: n-Heptane Mechanism v3, Westbrook et al3, 4, 5
• Note: all graphs have x-error of ±5-10 K (from pressure transducers) and y-error of ±5-10% (from standards used in calibrations and GC error). Error bars are omitted for clarity
3. Mehl, M., H.J. Curran, W.J. Pitz and C.K. Westbrook: "Chemical kinetic modeling of component mixtures relevant to gasoline," European Combustion Meeting, 2009. 4. Mehl, M., W.J. Pitz, M. Sjöberg and J.E. Dec: “Detailed kinetic modeling of low-temperature heat release for PRF fuels in an HCCI engine,” S AE 2009 International Powertrains, Fuels and Lubricants Meeting, SAE Paper No. 2009-01-1806, Florence, Italy, 2009. 5. Curran, H. J., P. Gaffuri, W. J. Pitz, and C. K. Westbrook: Combustion and Flame,1998, 114, 149-177
Heptane Pyrolysis
• Pyrolyze to characterize decomposition and species formed
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 14500
10
20
30
40
50
60
T5 Calibrated [K]
He
pta
ne
Co
nce
ntr
atio
n [p
pm
]
Heptane Decomposition - Pyrolysis
Fig. 4: Concentration of heptane vs. T5 during pyrolysis
Pdriver=4 barRxn time: 1.5-1.8 ms
Heptane Pyrolysis (Continued)
• Ethylene is the primary product by concentration
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 14500
20
40
60
80
100
120
140
T5 Calibrated [K]
Eth
yle
ne
Co
nce
ntr
atio
n [p
pm
]
Ethylene Concentration - Pyrolysis
Fig. 5: Concentration of ethylene vs. T5 during pyrolysis
Pdriver=4 barRxn time: 1.5-1.8 ms
Heptane Pyrolysis (Continued)
•Possible directions for future research
Fig. 6: Concentration of acetylene, methane, and propylene vs. T5 during pyrolysis
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 14500
10
20
30
40
50
60
70
T5 Calibrated [K]
Co
nce
ntr
atio
n [p
pm
]
Acetylene, Methane, and Propylene Concentration
Acetylene
MethanePropylene
Heptane Pyrolysis - Modeling
•Model results to validate shock tube operation
950 1000 1050 1100 1150 1200 1250 1300 1350 1400-10
0
10
20
30
40
50
60
T5 [K]
Co
nce
ntr
atio
n [p
pm
]
Heptane Concentration vs. Final Temperature
Heptane Pyrolysis (Data)
Heptane Pyrolysis (Model)
Fig. 7: Comparison of pyrolysis data to model results for heptane decomposition
Pdriver=4 barRxn time: 1.5-1.8 ms
Heptane Oxidation – Modeling and Data
Fig. 8: Comparison of oxidation data to model results for oxygen concentration
900 950 1000 1050 1100 1150 1200 1250 1300 1350 14000
50
100
150
200
250
300
350
400
450
T5 [K]
Co
nce
ntr
atio
n [p
pm
]
Oxygen Concentration vs. Final Temperature
O2 Concentration (Data)
O2 Concentration (Model)
Pdriver=4 barRxn time: 1.5-1.8 msΦ=1.38
Heptane Oxidation – Modeling and Data (Cont’d)
Fig. 9: Comparison of oxidation data to model results for ethylene concentration
Pdriver=4 barRxn time: 1.5-1.8 msΦ=1.38
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 14500
20
40
60
80
100
120
T5 [K]
Co
nce
ntr
atio
n [p
pm
]Ethylene Concentration vs. Final Temperature
Ethylene Production (Data)
Ethylene Production (Model)
Heptane Oxidation – Modeling and Data (Cont’d)
Fig. 10: Comparison of oxidation data to model results for carbon monoxide production
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400-50
0
50
100
150
200
250
T5 [K]
Co
nce
ntr
atio
n [p
pm
]Carbon Monoxide Concentration vs. Final Temperature
CO Production (Data)
CO Production (Model)
Pdriver=4 barRxn time: 1.5-1.8 msΦ=1.38
Heptane with Ethylene Oxidation
Fig. 11: Normalized heptane concentration and ethylene concentration vs. T5 for neat mixture and cracked fuel mixture
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 14500
0.2
0.4
0.6
0.8
1
T5 Calibrated [K]
He
pta
ne
Co
nce
ntr
atio
n [p
pm
]
Normalized Heptane Decomposition - Neat vs. Cracked Mixture
Cracked Fuel Mix
Neat Heptane
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 14500
0.5
1
1.5
2
2.5
T5 Calibrated [K]
Eth
yle
ne
Co
nce
ntr
atio
n [p
pm
]
Normalized Ethylene Concentration - Neat vs. Cracked Micture
Neat Heptane (Data)
Cracked Fuel Mix (Data)
Neat Heptane (Model)
Cracked Fuel Mix (Model)
Heptane with Ethylene Oxidation
Figure 12: Carbon monoxide concentration vs. T5 for pure heptane oxidation and heptane with ethylene
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400-50
0
50
100
150
200
250
300
T5 Calibrated [K]
Ca
rbo
n M
on
oxi
de
Co
nce
ntr
atio
n [p
pm
]Carbon Monoxide Concentration - Neat vs. Cracked Micture
Neat Heptane (Data)
Cracked Fuel Mix (Data)
Neat Heptane (Model)
Cracked Fuel Mix (Model)
Pdriver=4 barRxn time: 1.5-1.8 msΦ=1.38
Conclusions and Future Work
•Heptane cracking products affect combustion of non-cracked fuel through chemical processes
•CO, CO2, and H2O production - energy output differences
•Future experiments - other cracking products and/or different reaction pressures
Acknowledgements•National Science Foundation, EEC-NSF
Grant # 1062943•University of Illinois at Chicago REU•Prof. Christos Takoudis and Dr. Gregory
Jursich•Arman Butt and Runshen Xu
Questions
6. http://www.af.mil/shared/media/photodb/photos/100520-F-9999B-111.jpg
6
Calibrations
• Temperature calibrations using TFE and CPCN• Known decomposition rates allow these species to be
used as chemical thermometers
Fig. 13: TFE and CPCN shock calibration results
575 625 675 725 775 825 875850
950
1050
1150
1250
1350
1450
1550
TFE and CPCN Calibrations for 1, 4, and 10 bar
W [m/s]
T5
[K]
Heptane with Ethylene Oxidation (Cont’d)
Fig. 14: Butene concentration vs. T5 for neat mixture and cracked fuel mixture
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 14500
1
2
3
4
5
6
7
8
9
10
T5 Calibrated [K]
Bu
ten
e C
on
cen
tra
tion
[pp
m]
Butene Concentration - Neat vs. Cracked Micture
Cracked Fuel Mix
Neat Heptane
Heptane with Ethylene Oxidation (Cont’d)
900 950 1000 1050 1100 1150 1200 1250 1300 1350 1400 14500
50
100
150
200
250
300
350
400
450
T5 Calibrated [K]
Oxy
gen
Con
cent
ratio
n [p
pm]
Oxygen Concentration - Neat vs. Cracked Micture
Cracked Fuel Mix
Neat Heptane
Fig. 15: Oxygen concentration vs. T5 for neat mixture and cracked fuel mixture
Heptane w/ Ethylene - Modeling
•Model cracked fuel mix with and without complete hydrogen balance to validate mixture
800 1000 1200 1400 1600 1800 2000-50
0
50
100
150
200
250
300
Temperature T5 [K]
CO
Con
cent
ratio
n [p
pm]
CO Concentration vs. Final Temperature
Neat CO Production
CO Production w/ H2 Balance
CO Production w/o H2 Balance
Fig. 16: Carbon monoxide concentration vs. T5 for neat mixture and mixtures with and without hydrogen balance
Heptane w/ Ethylene – Modeling (Cont’d)
•Decreased H2O output without H balance
800 1000 1200 1400 1600 1800 2000-50
0
50
100
150
200
250
300
350
Temperature T5 [K]
H2O
Con
cent
ratio
n [p
pm]
H2O Concentration vs. Final Temperature
Neat H2O Production
H2O Production w/ H2 Balance
H2O Production w/o H2 Balance
Fig. 17: Water concentration vs. T5 for neat mixture and mixtures with and without hydrogen balance