SPARK IGNITION PROCESS IN A SCRAMJET COMBUSTOR EQUIPPED WITH MULTI-CAVITIES AT MACH 4 FLIGHT CONDITION

The spark ignition process in the scramjet combustor equipped with multi-cavities at Mach 4 flight condition fueled by hydrogen was observed by the high speed camera and Schlieren system, at the inflow conditions of Ma=1.92, T0=846K, P0＝0.7MPa. The spark generation, the flame spreading and shock structures in the combustor with different ignition setups were captured. The results revealed that spark generates near the igniter, and grows to form flame in the cavity. The initial flame spreads along the cavity shear layer and ignites the fuel distributed downstream very quickly. With the pressure downstream rises up, the precombustion shock and the flame go against the stream and finally the whole fuel jet flame is ignited and stabilized. The expand angle of the upper wall and the disturbance caused by the upstream cavity have an obvious effect on the fuel diffusion and convection into the cavity and further affect the ignition. Hydrogen fuel injected into the cavity directly could improve the ignition performance greatly at the experimental status.