Thermochemical nonequilibrium is often associated with high-Mach-number flows. The objective of this study is to investigate the effect of thermochemical nonequilibrium on combustion characterization in a Mach 10 ethylene-fueled scramjet under near-actual flight conditions. The reactive flow is numerically studied using the Navier–Stokes equations based on thermal nonequilibrium (NEQ) and thermal equilibrium (EQ) models. Results indicate that the change in internal energy distribution affects chemical reaction rates, thereby altering the distributions of species and the heat release rate in the front section of the combustor. A quantitative comparison was conducted of combustion modes and reaction paths between EQ and NEQ. Although vibrational nonequilibrium affects the combustion mode and species distribution during the ignition stage in the front section of the combustor, the combustion field in the rear section under NEQ tends to converge with that under EQ. The final combustion efficiencies under EQ and NEQ are relatively close. Based on a comparison of the characteristic timescales, the underlying mechanism is that the high wall temperature and the high fuel temperature shorten the vibration–translation relaxation time. However, the significant hot vibrational nonequilibrium within the nozzle reduces the pressure, leading to a more than 10% decrease in specific impulse compared to the EQ case.
Wu et al. (2026) studied this question.