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 engine 1 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 mixtures 2 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 al 3, 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. Sj öberg 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 Pyrolyze to characterize decomposition and species formed Fig. 4: Concentration of heptane vs. T 5 during pyrolysis P driver =4 bar Rxn time: 1.5- 1.8 ms

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

11. Heptane Pyrolysis (Continued) Possible directions for future research Fig. 6: Concentration of acetylene, methane, and propylene vs. T 5 during pyrolysis

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

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

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

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

16. Heptane with Ethylene Oxidation Fig. 11: Normalized heptane concentration and ethylene concentration vs. T 5 for neat mixture and cracked fuel mixture

17. Heptane with Ethylene Oxidation Figure 12: Carbon monoxide concentration vs. T 5 for pure heptane oxidation and heptane with ethylene P driver =4 bar Rxn time: 1.5- 1.8 ms Φ=1.38

18. Conclusions and Future Work Heptane cracking products affect combustion of non-cracked fuel through chemical processes CO, CO 2, and H 2 O 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 Chicago REU Prof. Christos Takoudis and Dr. Gregory Jursich Arman Butt and Runshen Xu

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

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. T 5 for neat mixture and cracked fuel mixture

23. Heptane with Ethylene Oxidation (Cont’d) Fig. 15: Oxygen concentration vs. T 5 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. T 5 for neat mixture and mixtures with and without hydrogen balance

25. Heptane w/ Ethylene – Modeling (Cont’d) Decreased H 2 O output without H balance Fig. 17: Water concentration vs. T 5 for neat mixture and mixtures with and without hydrogen balance