Supersonic Combustion Processes

Abstract

Introduction With the broad range of flying conditions in the hypersonic regime, the processes in the supersonic combustion chamber are subject to large variations in thermodynamic conditions. At the low range of the hypersonic flight regime, the heat deposition in the combustion chamber is relatively large compared with the incoming flow energy; hence the heat deposition substantially reduces the air speed and a large pressure rise is experienced with possible flow separations. At the higher range of the hypersonic regime, close to Mach 25, which is considered the upper envelope of air-breathing propulsion, the heat addition may amount to only 10% of the incoming airflow enthalpy. The heat-release effects are less pronounced. The airspeed in the combustion chamber itself may be hypersonic, and the heat deposition is distributed over a longer distance following mixing and chemical reactions; the pressure rise associated with combustion is less pronounced and is mostly due to the internal geometry of the combustion chamber. The aerothermodynamic processes in the supersonic combustion chamber are complex and closely related. The comparable time scales lead to a closely coupled turbulent mixing and chemical reaction rates. Combustion cannot be initiated until mixing has been achieved at a molecular level, and, in turn, in regions where combustion has taken place, the temperature rise and the chemical composition changes modify the parameters responsible for mixing. This close coupling cannot be, in general, separated in the supersonic combustion chamber.