Experimental and numerical investigations of combustion mode transition in a direct–connect scramjet combustor

Direct–connect experiment and numerical simulation investigations on combustion mode transition were completed for inflow conditions of Mach number 3.0, total temperature 1500 K and total pressure 2.1 MPa. Pressure at centerline of combustor upper wall was measured. Numerical simulation results, containing Mach number distribution of combustion chamber, shock wave structure of isolator, and heat release rate of combustor, were compared at various equivalence ratios. The quantificational distinguish criterion of combustion mode (po/pipo/pi) was constructed using wall pressure popo of outlet and pipi of inlet for isolator. The combustor works in scram-mode when the pressure ratio is below 1.5, while it is in ram-mode when the value of po/pipo/pi is over 1.5. Two types of combustion mode could also be identified base on heat release distribution of combustion chamber and flow configuration of isolator. In scram-mode, the heat release is distributed equally, the flow in combustor is supersonic, and there is no large separation region in isolator. In ramjet mode, the heat release is distributed concentrated, the flow at the entrance of combustor and in the combustor are both subsonic, and there is large separation region and shock train in isolator.