Investigation of several fundamental combustion problems in rocket-based combined-cycle engines

Multiple modes are involved in the operating process of a rocket-based combined-cycle (RBCC) engine, which operates efficiently in a wide range of Mach numbers and flight altitudes. Subsonic, transonic and supersonic flows co-exist in a RBCC combustor. The flow speed in a RBCC combustor is high, which leads to a very limited time of mixing between the fuel and the airstream. The reaction intensity in a RBCC combustor is strong and the combustion takes place in a confined space, in which complex wave structures are generated and reflected. The flow and combustion characteristics in a RBCC combustor is analyzed in terms of the strong shear property of the strut rocket jet, the diversity of combustion modes, and the intrinsic dynamic characteristics of combustion process. The growth of shear layers, the multiple combustion modes, the spatial distribution of heat release, and the combustion dynamics in a RBCC combustor are studied. The fundamental problems involved in high speed turbulent flow and combustion relevant to engine conditions are summarized. The detailed chemical kinetics model of a typical hydrocarbon fuel is simplified. A global reaction model for engineering simulation and a skeletal kinetics model for combustion mechanism study are respectively obtained and validated. Based on the study of the growth model of the reacting mixing layer featured with the rocket jet, the uncertainties of flow and combustion processes in the wide operating range under variable air inflow condition of RBCC engines, the simplification model of complex hydrocarbon fuels and the acceleration algorithm for the application of skeletal mechanism in engineering, the problems desired to be solved in the fundamental studies of RBCC engines are proposed in expectation of improving the understandings of multi-scale combustion mechanisms and optimization of the combustion organization method in RBCC engines.