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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

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hypersonic fuels chemistry n heptane cracking and combustion

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

project background1
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
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
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
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

methods
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 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

heptane pyrolysis continued
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

heptane pyrolysis continued1
Heptane Pyrolysis (Continued)
  • Possible directions for future research

Fig. 6: Concentration of acetylene, methane, and propylene vs. T5 during pyrolysis

heptane pyrolysis modeling
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

heptane oxidation modeling and data
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

heptane oxidation modeling and data cont d
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

heptane oxidation modeling and data cont d1
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

heptane with ethylene oxidation
Heptane with Ethylene Oxidation

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

heptane with ethylene oxidation1
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

conclusions and future work
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
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
questions
Questions

6

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

calibrations
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
Heptane with Ethylene Oxidation (Cont’d)

Fig. 14: Butene concentration vs. T5 for neat mixture and cracked fuel mixture

heptane with ethylene oxidation cont d1
Heptane with Ethylene Oxidation (Cont’d)

Fig. 15: Oxygen concentration vs. T5 for neat mixture and cracked fuel mixture

heptane w ethylene modeling
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

heptane w ethylene modeling cont d
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

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