College of Chemical Engineering, Sichuan University, Chengdu 610065, P. R. China; Key Laboratory of Computational Physics, Yibin University, Yibin 644000, Sichuan Province, P. R. China; China Aerodynamics Research & Development Center, Mianyang 621000, Sichuan Province, P. R. China

Clean air at high temperature and velocity is used as the oxidant during fuel combustion in a hypersonic scramjet. In ground tests, however, the high-temperature air produced by combustion heating contains H2O and CO2 as contaminants. In this study, the influence of H2O and CO2 in air upon the equilibrium temperature and pressure, and the ignition delay time for ethylene combustion were investigated by a kinetics simulation method using a plug flow reactor. Different initial temperatures, pressures, and equivalence ratios were studied. We find that the presence of H2O promotes combustion whereas CO2 inhibits combustion. Both H2O and CO2 result in a decrease of the equilibrium temperature and pressure during ethylene combustion, and CO2 has a comparatively larger influence than H2O. The simulated result was used to interpret the experimental phenomena.