Numerical Simulation of Oxygen-Enhanced Combustion in an Arc-Heated Direct Connect Scramjet Facility

Large-eddy simulations of operation of an axisymmetric isolator-combustor configuration experimentally tested at the University of Illinois’s ACT-II arc-heated combustion facility and equipped to study the influences of secondary oxidizer injection are presented in this work. Oxygen enrichment may have benefits in enabling stable, more efficient scramjet operation at higher altitudes and higher Mach numbers. Inflow conditions for the large-eddy simulations are generated from computations of flow within the arc heater – validation studies that compare predictions with laser absorption spectroscopy and wall pressure measurements are reported. Isolator-combustor LES results show that oxygen enrichment enables robust dual-mode operation at conditions that cannot maintain a flame without secondary oxidizer injection. Computational predictions show good agreement with experimental wall pressure measurements for cases with pure O2 injection but do not accurately predict the response when the O2 stream is shut down. Predictions show that the use of air as the oxidizing agent (for the same overall injectant mass ratio) can also enable stable dual mode operation, but the thrust potential is much less than with O2 injection. An analysis of the flame structure shows that CO is the dominant reaction product – levels are particularly high when pure O2 is the secondary oxidizer. The flame transitions from a non-premixed flamelet-like structure nearer to the injectors to a rich-premixed structure in the wakes of the injectors. Most of the heat release occurs under rich-premixed conditions.