Kinetic insight into composition effect on the laminar flame speeds of cracked endothermic hydrocarbon fuel for hypersonic vehicles

Hydrocarbon fuels are promising energy sources and coolants for hypersonic vehicles. A clear understanding on the oxidation mechanism discrepancies of different cracked endothermic hydrocarbon fuels is essential for the performance and thermal management of hypersonic vehicles. Kinetic analyses on the pathway flux, sensitivity, and producing rate were performed to reveal the intrinsic relationships between the composition variation and laminar flame speeds of different pyrolysis products. A skeletal mechanism containing 68 species and 326 reactions was developed and validated by the targeted properties of the pyrolysis products. Analyses showed the flame speed discrepancies were resulted from the kinetic effect of the composition variations. The main oxidation pathways and consumption rates of the key intermediates were hardly changed with composition variation in the pyrolysis products. Sensitivity analyses found the flame speeds of pyrolysis products were mainly affected by the H/O/OH addition reactions of C0–C2 species. Their sensitivity coefficients were independent of the composition variations. Analyses on the rate of product (ROP) indicated the composition variation has a significant effect on the ROPs of H/O/OH radicals. Pyrolysis products including compositions of higher H/C ratios can produce higher contents of H, O, and OH radicals for the flame, resulting in higher laminar flame speeds.