Experimental study on combustion mode transition in an aero-ramp based scramjet

An experimental study was performed to investigate the characters of novel aero-ramp jets integrated gas pilot flame holder on dual-mode scramjet combustion. Experiments were conducted at direct connect facility with the combustion heated freestream, simulating Mach 5 flight enthalpy. Mode transitions were realized by changing fuel equivalence ratios at fixed fuel injected position. The experiments show that the combustor operated in the supersonic mode at fuel equivalence ratios below 0.17 and in the subsonic mode for equivalence ratios above 0.24. Hysteresis was observed in the transitional region between 0.22 and 0.24, as the mode of combustion was dependent on whether the fuel flow rate was increasing or decreasing. The flow fields near injectors were captured by high speed camera which can indicate the supersonic and subsonic combustion modes. One-dimensional performance analysis of the test data indicates that combustion efficiencies can reach 90% while flame holder was disposed at combustor section 2. These results indicate the importance of accounting for fuel mass flow rate varying direction in the transition region between subsonic and supersonic combustion regimes.