Combustion oscillations in a scramjet engine combustor with transverse fuel injection

An analysis has been carried out for both non-reacting and reacting flows in a scramjet engine combustor with and without a cavity. Transverse injection of hydrogen is considered over a broad range of injection pressure. Strong unsteady flow characteristics were identified for a scramjet combustor. Large flow disturbances could be generated by shear layer instability that may be triggered by the interactions with shock waves. For all the cases studied, flow oscillations caused by the cavity override those induced by the interactions between shock waves and boundary layers. Transverse injected jet could be triggered to become unstable with disturbances arising from a shear layer or a cavity. The disturbed jet could penetrate deeper into the cross-flow and improve the mixing with air. Unstable flow characteristics for the reacting cases bore a close resemblance to those of non-reacting flows except for a rapid chamber pressure build-up to a higher level. As an extreme case of high pressure build-up. thermal choking occurred in the combustor, which might result in the combustor unstart due to the forward-running strong shock wave. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).