Supersonic combustion of hydrocarbons in a shape-transitioning hypersonic engine

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This paper presents the results of a series of shock tunnel experiments of a hydrocarbon-fuelled, Mach 8 shape-transitioning scramjet engine with a cavity combustor. The inlet of the scramjet transitions from a quasi-rectangular capture area to an elliptical throat, which results in a highly three-dimensional flowfield at the combustor entrance. The main focus of the work was to achieve ignition and combustion of hydrocarbon fuels at a high Mach number in a flight-candidate engine that has the necessary three dimensional flow path that is typical of “practical” scramjet engines. The engine was fuelled with a surrogate fuel mixture (64% ethylene and 36% methane by volume) which mimics the extinguishing characteristics of partially cracked JP-7 fuel. Experiments were performed with and without a hydrogen-pilot to demonstrate ignition and combustion. Static pressure measurements throughout the flow path were used in conjunction with experiments where combustion was suppressed, by using nitrogen instead of air as the main flow, to confirm a combustion-induced pressure rise for different injection and piloting strategies. Ignition and supersonic combustion of the surrogate fuel mixture was achieved in all cases where a hydrogen pilot was employed. The pilot hydrogen fuel was injected at the inlet of the engine. Simultaneous injection of the surrogate fuel mixture at the inlet and in the combustor (combined injection) and combustor-only injection did not achieve combustion.