A new hybrid-rocket-based combined-cycle propulsion system concept

A new Hybrid-Rocket-Based Combined-Cycle (HRBCC) propulsion system concept, used for reusable launch vehicles or hypersonic vehicles, is presented in this paper. The HRBCC engine uses solid fuel hydroxyl terminated polybutadiene (HTPB), liquid oxidizer 98% hydrogen peroxide (98%H₂O₂) and ingested air for propellants. It combines ducted rocket, scramjet and hybrid rocket engine cycles into one compact engine. The hybrid rocket motor is embedded within the scramjet duct. A typical HRBCC engine operates in essentially three modes, such as ejectoijet mode, scramjet mode and rocket mode, with the variable inlet and nozzle geometry. During the ejectoijet mode the ducted hybrid rocket provides the bulk of the thrust for take-off and acceleration to transition speed (about 3Ma). In scramjet mode, the vehicle velocity reaches about 3-6 Ma and the flow through the engine is supersonic. When the vehicle reaches the outer limits of the atmosphere, the system transitions into hybrid rocket mode. In general, the principle advantages of this propulsion concept are showed as below, the exhaust fuel-rich hot-gas of the hybrid rocket motor may be benefits for the scramjet ignition and combustion stability; the engine structure is simple, because there is only one liquid oxidizer 98% H2O2 feeding system. It can be supplied by the catalyze decomposed 98% H2O2 gas-generator cycle; the sensitivity of engine performance to inlet air is decreased. If the inlet air is not enough, more 98% H2O2 can be injected to keep the best mixture ratio; the air drawn into the engine by the ejector effect provides significant thrust augmentation during boost.