Conceptual Study of a Combined-Cycle Engine for an Aerospace Plane

Operating conditions and performances of a fixed-geometry combined-cycle engine for a single-stage-to-orbit aerospace plane were calculated with a simple simulation model. With the flow conditions calculated with the model, the cooling requirement of the engine and pitching moment of the plane were investigated. The engine was composed of an ejector-jet mode, a ramjet mode, a scramjet mode, and a rocket mode. The engine had a fixed geometry in its operation. Subsonic combustion was conducted with no second throat in the combustor under the ejector-jet mode and the ramjet mode. Propellants were liquid hydrogen and liquid oxygen. The coolant flow rate became larger than the fuel flow rate. The excessive flow rate decreased the specific impulse above Mach 9 and restricted application of the airbreathing engine mode up to Mach 11. The pitching moment of the plane would be balanced even in the space in the configuration with the combined-cycle engine mounted on the windward surface.