Hypersonic Fuels Chemistry: n-Heptane Cracking and Combustion - PowerPoint Presentation

Hypersonic Fuels Chemistry:n-Heptane Cracking and Combustion Andrew Mandelbaum - Dept. of Mechanical Engineering, Princeton UniversityAlex Fridlyand - Dept. of Mechanical Engineering, University of Illinois at ChicagoProf. Kenneth Brezinsky - Dept. of Mechanical Engineering, University of Illinois at Chicago

Outline Project BackgroundHypothesisExperimental Apparatus and MethodsResults and ModelingHeptane PyrolysisHeptane OxidationHeptane/Ethylene OxidationConclusions

Project Background Heat managementVery short reaction time requirementsFig. 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 structureShorter cracking products may ignite more readilyFig. 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 tankEffect on combustion products?What causes the change in energy output – physical or chemical differences?Improved chemical simulationsImproved accuracyUse in engine modeling softwarePossibility for fuel composition customization

Hypothesis Heptane cracking products (primarily ethylene) will chemically influence combustion of remaining fuelResultant 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 timeExplore oxidation chemistry at pressures relevant to hypersonic engine combustorFig. 3: Schematic drawing of low pressure shock tube and related assemblies

Methods Perform pyrolysis and oxidation shocks at 4 bar driver pressureExamine stable intermediates and fuel decay process using gas chromatography (GC-FID/TCD)Model used: n-Heptane Mechanism v3, Westbrook et al3, 4, 5Note: 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

Heptane Pyrolysis Pyrolyze to characterize decomposition and species formedFig. 4: Concentration of heptane vs. T 5 during pyrolysis P driver =4 bar Rxn time: 1.5-1.8 ms

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

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

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

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

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

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

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

Conclusions and Future Work Heptane cracking products affect combustion of non-cracked fuel through chemical processesCO, CO2, and H2O production - energy output differencesFuture experiments - other cracking products and/or different reaction pressures

Acknowledgements National Science Foundation, EEC-NSF Grant # 1062943University of Illinois at Chicago REUProf. Christos Takoudis and Dr. Gregory JursichArman Butt and Runshen Xu

Questions 6. http://www.af.mil/shared/media/photodb/photos/100520-F-9999B-111.jpg6

Calibrations Temperature calibrations using TFE and CPCNKnown decomposition rates allow these species to be used as chemical thermometersFig. 13: TFE and CPCN shock calibration results

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

Heptane with Ethylene Oxidation (Cont’d) 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 mixtureFig. 16: Carbon monoxide concentration vs. T 5 for neat mixture and mixtures with and without hydrogen balance

Heptane w/ Ethylene – Modeling (Cont’d) Decreased H2O output without H balance Fig. 17: Water concentration vs. T 5 for neat mixture and mixtures with and without hydrogen balance