Shock Tube-Based Soot Formation Mechanism Refinement for Supersonic Aviation

The accurate prediction of soot formation and emissions from synthetic aviation fuels under high-temperature and -pressure conditions is a crucial step in the development of next generation propulsion systems. This work aims to reduce and refine the KAUST PAH Mechanism 2 (KM2), in combination with chemical kinetic data from the HyChem mechanism for the specific fuels assessed, to improve its predictive capabilities using experimental data collected from shock tube testing. Soot formation tendencies were obtained for commercial Jet-A, Gevo’s Alcohol-to Jet biofuel and a 50:50 blend of the two with ethylene in air at an equivalence ratio of Φ=10 and a total carbon content of 2.5%. Experimentation of high-temperature (1700-2080 K) and high-pressure (12 bar), was conducted at the University of Central Florida shock tube facility. Time-resolved soot volume fraction measurements were taken using a fixed-wavelength 632.8 nm HeNe laser and the laser extinction method. The collected data serves as the benchmark against which the KM2 mechanism is adjusted, enabling more accurate representation of soot formation under supersonic combustion conditions. A reduced version of the mechanism was developed to improve computational efficiency, followed by a sensitivity analysis targeting important aromatic species and soot precursors up to five aromatic rings. Adjustments to prominent reaction rates are made to draw model predictions of normalized soot yield closer to experimentally observed values. The resulting improvements to the KM2 model enhance its predictive capabilities for soot formation in SAF-based combustion, supporting the aviation industry's progress toward more efficient flight as fuel demands continue to grow.