Combustion enhancement via tandem cavities within a Mach 8 scramjet combustor

Abstract

This paper presents a fundamental numerical investigation of an ethylene fuelled axisymmetric scramjet using single and tandem cavity flameholders. A scramjet profile was designed comprising a truncated Busemann diffuser, isolator, and a constant-to-divergent area combustor. Flight equivalent, Mach 8 flow was delivered to four combustor variants equipped with a single or one of three tandem cavities. Two tandem cavity pairs were positioned within the constant-area combustor, and the remaining was located at the combustor's diverging portion. Fuelling rates of 25%, 50% and 75% of stoichiometric fuel/air ratios were considered. Combustor performance was assessed on mixing and combustion efficiencies, heat release, and total drag. Tandem cavity pairs residing within the combustor's constant area region exhibited a 16% improvement to combustion and a 10% increase in heat release compared to the equivalently fuelled single cavity. There was minimal difference in drag for these configurations at high fuelling. Negligible benefits emerged from any tandem configuration at moderate fuelling rates, and positioning a tandem cavity at the diverging portion universally provided no benefit.