Investigation of Mixing and Combustion Characteristics in a Mach 8 Circular Scramjet Combustor

The turbulence details and flame dynamics in a cavity-assisted Mach 8 circular scramjet combustor have been elucidated by large-eddy simulation. The numerical results agree well with experimental measurements. The multiscale flow structures and complex flame patterns are clearly reproduced. Under the conjoint effect of cavity and shock, numerous vortices and strong turbulent fluctuations effectively promote the fuel mixing. The ethylene is ignited by the high-temperature and subsonic cavity and continues to burn in the supersonic airflow. The mixing efficiency and combustion efficiency increased by 42.3% and 25.7%, respectively, at the cavity section. During the combustion heat release increasing process, the location of shock-induced combustion shifts from the cavity trailing edge to the windward side of the fuel jet. Violent heat release and local high temperature in the cavity may result in the decomposition of combustion products. Due to the high total enthalpy and total temperature of the freestream, the autoignition plays a dominant role in most of the combustion region. The flame propagation, limited by the fuel concentration gradient, only contributes to combustion in areas such as flame boundaries and fuel nozzles.