Impact of Fuel Injection Distribution on Flame Holding in a Cavity-Stabilized Scramjet

This study investigated the impact of fuel injection distribution on flame stabilization and heat release in a cavity-stabilized scramjet. Experiments were conducted using a hydrogen air heater that provided vitiated air at an average stagnation temperature of 1570 K and stagnation pressure of 12.7 atm, accelerated to a Mach number of 2.2 at the combustor entrance. Ethylene was injected using two fuel injection locations, one upstream of the cavity and another in the cavity. Three different fuel injection distributions were studied for global equivalence ratios of 0.2, 0.3, and 0.4. Measurements included high-speed CH* chemiluminescence and shadowgraph, as well as wall-mounted pressure transducers. It was found that when the cavity fuel flow rate was low, the flame stabilized on the cavity shear layer and resulted in a gradual pressure rise in the combustor. A sufficiently high fuel flow rate in the cavity led to flame stabilization upstream of the cavity, in the fuel jet wake, and a more confined combustion zone. Shadowgraph imaging showed that injection of the fuel from the cavity floor at a sufficient momentum penetrated the shear layer over the cavity and enabled flame propagation upstream of the cavity. It was concluded that the heat release distribution and pressure profile in the combustor could be significantly influenced by the fuel injection distribution through its impact on the flame stabilization mode.