Hydrocarbon-fueled scramjet combustor investigation

An experimental program to develop technology for a hydrocarbon-fueled scramjet engine for operation over the flight Mach number range from 3.5 to 7 is being conducted. As part of this program, a series of connectedpipe tests were performed to define scramjet combustor design criteria applicable to an engine concept which comprises a pair of modular axisymmetric combustors underslung on a supersonic/hypersonic missile. A novel air-breathing pilot was developed under this program and was tested to evaluate its flame stabilization and flame propagation characteristics. The air-breathing pilot also incorporates an external mainstream fuel injector which serves as the primary fuel injection stage for the supersonic combustor. During this program, it was demonstrated that the pilot promotes efficient combustion of either gaseous ethylene or preheated liquid Jet-A (JP-5) when it is injected into the supersonic mainstream flow as a primary fuel. The idea of using the airbreathing pilot and distributed primary and secondary fuel injectors to achieve efficient supersonic combustion over a wide range of equivalence ratios was also experimentally demonstrated. During staged fuel injection tests with gaseous ethylene fuel, high secondary fuel combustion efficiencies were achieved and smooth transitions from fully supersonic to dual-mode (supersonic/subsonic) operation were demonstrated. The air-breathing pilot was shown to isolate effectively the inlet from the combustion process even at the high combustor pressures experienced during dual-mode operation.