A Rocket Based Combined Cycle engine, or RBCC engine, combines a rocket with one or more airbreathing engine cycles into a single propulsive device. During a typical launch profile this allows the engine to operate from static conditions at the beginning of the launch all the way to orbital insertion while maintaining optimum performance based on the prevailing conditions. However, to maintain these optimium conditions requires that the engine transition between operating as a pure rocket to an ejector (also called a ducted rocket or ram-rocket) to a ramjet to a scramjet back to a pure rocket once the atmosphere no longer contains enough oxygen to maintain combustion. Therefore, the engine must be designed both to accommodate existing rocket technologies while simultaneously providing for the ability to ingest atmospheric air.
This is the focus of our RBCC research and has led to the design of the Exchange Nozzle shown. The purpose of the Exchange Nozzle is to create a rocket flow path that is compatible with existing rocket technologies and yet allows for the incorporation of ‘cut-outs’ for the passage of air. By allowing the air to flow within the center of an annular rocket exhaust plume one can achieve much better mixing and performance from the engine as a whole. To accommodate a variety of designs and flight conditions the exchange inlet can be modified by changing any combination of the control inputs. Elements of this design have been tested in experimental airbreathing engines, optimized using genetic algorithms, and are currently being studied as part of a next generation space launch vehicle.