Hysteresis of combustion mode transition in solid rocket scramjet engine

To raise the level of understanding of combustion mode transition characteristics in solid rocket scramjet engine, direct connect test of mode transition in solid rocket scramjet engine is investigated. The flight condition of Mach number 6.0 and height of 26.0 km is simulated in direct connect test, and mass flow rate of inflow air is 4.0 kg/s. With adjusting the mass rate of fuel gas, subsonic combustion mode and supersonic combustion mode are observed in the same configuration of combustor. The max pressure of fuel gas generator in subsonic combustion mode is 3.152 MPa, the max mass flow rate of fuel gas is 0.533 kg/s, and working hours is about 7 s; the max pressure of fuel gas generator in supersonic combustion mode is 1.404 MPa, the max mass flow rate of fuel gas is 0.312 kg/s, and working hours is about 11 s. The result shows that at the same air-fuel ratio (14.0, 13.5, 13.0), the distribution of pressure along the engine in subsonic combustion mode is apparently higher than that in supersonic combustion mode. This phenomenon shows that under the same inlet flow condition and engine configuration, there may be subsonic combustion mode or supersonic combustion mode, and in other words, hysteresis of combustion mode transition appears. Analyzing the distribution of pressure along the engine during initial ignition stage of tests, it is found that hysteresis of combustion mode transition is caused by difference in ignition region of fuel gas.