Estimation of vitiation effects on flameholding and mode transition in a dual-mode supersonic combustor

To estimate the vitiation effects of test air on flameholding and mode transition in a direct-connected dual mode combustor, an experimental study was conducted with two types of air heater (electric heater and methane combustion heater) at various kerosene equivalence ratios. Total temperature, total pressure and Mach number of combustor entrance were matched in comparative tests. The lean blowout limits, wall pressures and mode transitions were compared. For clean air heater, the lean blowout limit occurred at the equivalence ratio of 0.105, while for methane combustion heater, it occurred at 0.135. Considering mode transition, the combustor operated in subsonic combustion mode at kerosene equivalence ratio above 0.30 with clean air; while for methane combustion heater, mode transition from supersonic to subsonic combustion occurred at equivalence ratio of 0.33. This indicated that the test data should be fully evaluated when using a combustion heater, especially in lean blowout limit and mode transition.