Hypersonic Fuels Chemistry: n-Heptane Cracking and Combustion

1. 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

2. Outline • Project Background • Hypothesis • Experimental Apparatus and Methods • Results and Modeling • Heptane Pyrolysis • Heptane Oxidation • Heptane/Ethylene Oxidation • Conclusions

3. 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.

4. 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.

5. 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

6. 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

7. 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

8. 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

9. Heptane Pyrolysis Pdriver=4 bar Rxn time: 1.5-1.8 ms • Pyrolyze to characterize decomposition and species formed Fig. 4: Concentration of heptane vs. T5 during pyrolysis

10. Heptane Pyrolysis (Continued) Pdriver=4 bar Rxn time: 1.5-1.8 ms • Ethylene is the primary product by concentration Fig. 5: Concentration of ethylene vs. T5 during pyrolysis

11. Heptane Pyrolysis (Continued) • Possible directions for future research Fig. 6: Concentration of acetylene, methane, and propylene vs. T5 during pyrolysis

12. Heptane Pyrolysis - Modeling Pdriver=4 bar Rxn time: 1.5-1.8 ms • Model results to validate shock tube operation Fig. 7: Comparison of pyrolysis data to model results for heptane decomposition

13. Heptane Oxidation – Modeling and Data Pdriver=4 bar Rxn time: 1.5-1.8 ms Φ=1.38 Fig. 8: Comparison of oxidation data to model results for oxygen concentration

14. Heptane Oxidation – Modeling and Data (Cont’d) Pdriver=4 bar Rxn time: 1.5-1.8 ms Φ=1.38 Fig. 9: Comparison of oxidation data to model results for ethylene concentration

15. Heptane Oxidation – Modeling and Data (Cont’d) Pdriver=4 bar Rxn time: 1.5-1.8 ms Φ=1.38 Fig. 10: Comparison of oxidation data to model results for carbon monoxide production

16. Heptane with Ethylene Oxidation Fig. 11: Normalized heptane concentration and ethylene concentration vs. T5 for neat mixture and cracked fuel mixture

17. Heptane with Ethylene Oxidation Pdriver=4 bar Rxn time: 1.5-1.8 ms Φ=1.38 Figure 12: Carbon monoxide concentration vs. T5 for pure heptane oxidation and heptane with ethylene

18. 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

19. Acknowledgements • National Science Foundation, EEC-NSF Grant # 1062943 • University of Illinois at ChicagoREU • Prof. Christos Takoudis and Dr. Gregory Jursich • Arman Butt and Runshen Xu

20. Questions 6 6. http://www.af.mil/shared/media/photodb/photos/100520-F-9999B-111.jpg

21. 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

22. Heptane with Ethylene Oxidation (Cont’d) Fig. 14: Butene concentration vs. T5 for neat mixture and cracked fuel mixture

23. Heptane with Ethylene Oxidation (Cont’d) Fig. 15: Oxygen concentration vs. T5 for neat mixture and cracked fuel mixture

24. Heptane w/ Ethylene - Modeling • Model cracked fuel mix with and without complete hydrogen balance to validate mixture Fig. 16: Carbon monoxide concentration vs. T5 for neat mixture and mixtures with and without hydrogen balance

25. Heptane w/ Ethylene – Modeling (Cont’d) • Decreased H2O output without H balance Fig. 17: Water concentration vs. T5 for neat mixture and mixtures with and without hydrogen balance