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 engine 1 1. How Scramjets Work [online]. NASA. 2 Sept June

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.

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 bar, 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 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, 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 , Florence, Italy, Curran, H. J., P. Gaffuri, W. J. Pitz, and C. K. Westbrook: Combustion and Flame,1998, 114,

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: ms

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: ms

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

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: ms

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

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: ms Φ=1.38

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: ms Φ=1.38

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

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: ms Φ=1.38

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

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

Questions

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

Heptane with Ethylene Oxidation (Cont’d) Fig. 14: Butene concentration vs. T 5 for neat mixture and cracked fuel mixture

Heptane with Ethylene Oxidation (Cont’d) Fig. 15: Oxygen concentration vs. T 5 for neat mixture and cracked fuel mixture

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

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