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
Fig. 1: Cross-sectional diagram of a scramjet engine1
• Heat management
• Very short reaction time requirements
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
Fig. 3: Schematic drawing of low pressure shock tube and related assemblies
• 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
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
Heptane Decomposition - Pyrolysis
60
Heptane Concentration [ppm]
50
Pdriver=4 bar
Rxn time: 1.51.8 ms
40
30
20
10
0
900
950
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450
T5 Calibrated [K]
Fig. 4: Concentration of heptane vs. T5 during pyrolysis
• Pyrolyze to characterize decomposition and species
formed
Heptane Pyrolysis (Continued)
Ethylene Concentration - Pyrolysis
140
Ethylene Concentration [ppm]
120
Pdriver=4 bar
Rxn time: 1.51.8 ms
100
80
60
40
20
0
900
950
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450
T5 Calibrated [K]
Fig. 5: Concentration of ethylene vs. T5 during pyrolysis
• Ethylene is the primary product by concentration
Heptane Pyrolysis (Continued)
Acetylene, Methane, and Propylene Concentration
70
Acetylene
Methane
Propylene
Concentration [ppm]
60
50
40
30
20
10
0
900
950
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450
T5 Calibrated [K]
Fig. 6: Concentration of acetylene, methane, and propylene vs. T5 during
pyrolysis
• Possible directions for future research
Heptane Pyrolysis - Modeling
Heptane Concentration vs. Final Temperature
60
Heptane Pyrolysis (Data)
Heptane Pyrolysis (Model)
50
Pdriver=4 bar
Rxn time: 1.51.8 ms
Concentration [ppm]
40
30
20
10
0
-10
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
T5 [K]
Fig. 7: Comparison of pyrolysis data to model results for heptane decomposition
• Model results to validate shock tube operation
Heptane Oxidation – Modeling and Data
Oxygen Concentration vs. Final Temperature
450
Pdriver=4 bar
Rxn time: 1.51.8 ms
Φ=1.38
400
Concentration [ppm]
350
300
250
200
150
100
O2 Concentration (Data)
O2 Concentration (Model)
50
0
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
T5 [K]
Fig. 8: Comparison of oxidation data to model results for oxygen concentration
Heptane Oxidation – Modeling and Data
(Cont’d)
Pdriver=4 bar
Rxn time: 1.51.8 ms
Φ=1.38
Ethylene Concentration vs. Final Temperature
120
Ethylene Production (Data)
Ethylene Production (Model)
Concentration [ppm]
100
80
60
40
20
0
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
1450
T5 [K]
Fig. 9: Comparison of oxidation data to model results for ethylene concentration
Heptane Oxidation – Modeling and Data
(Cont’d)
Pdriver=4 bar
Rxn time: 1.51.8 ms
Φ=1.38
Carbon Monoxide Concentration vs. Final Temperature
250
CO Production (Data)
CO Production (Model)
Concentration [ppm]
200
150
100
50
0
-50
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
T5 [K]
Fig. 10: Comparison of oxidation data to model results for carbon monoxide
production
Heptane with Ethylene Oxidation
Normalized Heptane Decomposition - Neat vs. Cracked Mixture
Normalized Ethylene Concentration - Neat vs. Cracked Micture
2.5
Cracked Fuel Mix
Neat Heptane
2
Ethylene Concentration [ppm]
Heptane Concentration [ppm]
1
Neat Heptane (Data)
Cracked Fuel Mix (Data)
Neat Heptane (Model)
Cracked Fuel Mix (Model)
0.8
0.6
0.4
1.5
1
0.5
0.2
0
900
950
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450
T5 Calibrated [K]
0
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
T5 Calibrated [K]
Fig. 11: Normalized heptane concentration and ethylene concentration vs. T5 for
neat mixture and cracked fuel mixture
1450
Heptane with Ethylene Oxidation
Carbon Monoxide Concentration - Neat vs. Cracked Micture
Pdriver=4 bar
Rxn time: 1.51.8 ms
Φ=1.38
Carbon Monoxide Concentration [ppm]
300
Neat Heptane (Data)
Cracked Fuel Mix (Data)
Neat Heptane (Model)
Cracked Fuel Mix (Model)
250
200
150
100
50
0
-50
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
T5 Calibrated [K]
Figure 12: Carbon monoxide concentration vs. T5 for pure heptane
oxidation and heptane with ethylene
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
6. http://www.af.mil/shared/media/photodb/photos/100520-F-9999B-111.jpg
Calibrations
TFE and CPCN Calibrations for 1, 4, and 10 bar
1550
1450
1350
T5 [K]
1250
1150
1050
950
850
575
625
675
725
775
825
875
W [m/s]
Fig. 13: TFE and CPCN shock calibration results
• Temperature calibrations using TFE and CPCN
• Known decomposition rates allow these species to
be used as chemical thermometers
Heptane with Ethylene Oxidation (Cont’d)
Butene Concentration - Neat vs. Cracked Micture
10
Cracked Fuel Mix
Neat Heptane
Butene Concentration [ppm]
9
8
7
6
5
4
3
2
1
0
900
950
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450
T5 Calibrated [K]
Fig. 14: Butene concentration vs. T5 for neat mixture and cracked fuel mixture
Heptane with Ethylene Oxidation (Cont’d)
Oxygen Concentration - Neat vs. Cracked Micture
450
Cracked Fuel Mix
Neat Heptane
400
Oxygen Concentration [ppm]
350
300
250
200
150
100
50
0
900
950
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450
T5 Calibrated [K]
Fig. 15: Oxygen concentration vs. T5 for neat mixture and cracked fuel mixture
Heptane w/ Ethylene - Modeling
CO Concentration vs. Final Temperature
300
CO Concentration [ppm]
250
Neat CO Production
CO Production w/ H2 Balance
CO Production w/o H2 Balance
200
150
100
50
0
-50
800
1000
1200
1400
1600
1800
2000
Temperature T5 [K]
Fig. 16: Carbon monoxide concentration vs. T5 for neat mixture and mixtures with
and without hydrogen balance
• Model cracked fuel mix with and without
complete hydrogen balance to validate mixture
Heptane w/ Ethylene – Modeling (Cont’d)
H2O Concentration vs. Final Temperature
350
H2O Concentration [ppm]
300
Neat H2O Production
H2O Production w/ H2 Balance
H2O Production w/o H2 Balance
250
200
150
100
50
0
-50
800
1000
1200
1400
1600
1800
2000
Temperature T5 [K]
Fig. 17: Water concentration vs. T5 for neat mixture and mixtures with and
without hydrogen balance
• Decreased H2O output without H balance