Ignition in a supersonic flow by a plasma jet of mixed feedstock including CH4

Ignition tests of hydrocarbon fuels in a supersonic airflow by plasma jet (PJ) torches of mixed feedstock, including methane (CH4), such as N2/CH4 and N2/CH4/O2 mixtures, were conducted. The Mach number of the airflow was 2.0, and the total temperature and total pressure of the main flow were those of room conditions. The wall pressure increase due to combustion of hydrocarbon fuels for the N2/CH4 PJ exceeded those of pure O2 and N2 PJs at high electric power input. Equilibrium calculations showed that the main species in high-temperature PJ, aside from N2, were H2, H, and HCN. Considering the slight impact of the HCN species on ignition delay time, the combustion enhancement by the N2/CH4 PJ was caused primarily by the existence of a large amount of H and H2 dissociated from CH4 molecules in the PJ. Moreover, the addition of O2 to the N2/CH4 feedstock further enhanced the combustion and stability of the N2/CH4 PJ. The existence of O2 increased the temperature and the number of H radicals in the PJ exhaust.