Inlet Unstart of an Ethylene-Fueled Model Scramjet with a Mach 4.5 Freestream Flow

Inlet unstart mechanism in an ethylene-fueled model scramjet is investigated using a pulsed arc-heated hypersonic wind tunnel simulating supersonic/hypersonic flight conditions (Mach 4.5, 6, and 9 flows). The inlet unstart is ca used by excessive heat release from ethylene combustion reactions with Mach 4.5 freestream flows of 500 K static temperature and 2,500 K stagnation temperature. Flame evolution during a test time of approximately 150 milliseconds is optically resolved by a fast framin g camera. An ethylene flame is auto-ignited in a region downstream of an ethylene jet where the high enthalpy flow is compressed and decelerated by incident/reflected shockwaves and development of boundary layers. This flame propagates upstream toward the inlet region upstream of the fuel jet to unstart the internal flow. Sudden decrease of combustor pressure and combustion heat release, and soot formation in the region upstream of the fuel jet ar e observed while the flow undergoes inlet unstart.