Numerical Simulation of Scramjet Combustion in Thermo-Chemical Non-Equilibrium Within an Arc-Heated Direct Connect Facility

Thermal nonequilibrium (TNE) effects are expected to influence scramjet combustion under both high-altitude flight and arc-heated ground-test conditions, where vibrational relaxation times are long. Building on previous numerical studies of an ethylene-fueled, cavity-assisted scramjet combustor driven by the University of Illinois Urbana–Champaign ACT-II arc tunnel, a two-temperature thermal nonequilibrium capability is implemented and verified within NCSU’s in-house reacting flow solver, REACTMB, and subsequently applied to this configuration. The formulation couples vibrational energy to a limited subset of dissociation reactions while retaining the baseline finite-rate chemistry framework. Results show that thermal nonequilibrium alters flame structure and delays chemical progress relative to a thermal-equilibrium formulation while maintaining a sustained flame and comparable downstream product levels. These findings highlight the sensitivity of scramjet combustion behavior to nonequilibrium effects even under simplified vibration–chemistry coupling.