Staged injection in a dual-mode combustor for an air-breathing engine

The combination of a strut injector with a wall-mounted cavity has been experimentally investigated in the supersonic combustion test facility of the Institute for Flight Propulsion of the Technische Universität München. Preliminary work has been carried out on single-stage injection, using a strut for stabilization both of a hydrogen pilot flame and of a main methane flame. For this sake, the strut has been positioned in the constant cross-section portion of a modular, dual-mode combustor, the latter being directly connected to a Mach 2.2 Laval nozzle. The stabilization of both flames succeeded over a broad operation range, but the overall equivalence ratio could not be substantially increased due to limited penetration and mixing of the fuel into the supersonic air stream. The introduction of an additional injection stage further downstream in the combustor aimed to enhance the mixing level and the equivalence ratio. The second stage consists of a wall-mounted, open cavity. Fuel injection is performed in the direction opposite to the one of the main stream through a series of oval orifices on the cavity slanted rear wall. The cavity has been implemented in the diverging module of the combustion chamber in order to minimize the effects of the aerodynamic blockage of the fuel jet and the risk of thermal choking due to combustion. This paper outlines the results of the combination of different strut geometries with the cavity described above, for a reservoir total pressure of 1MPa and a total temperature of 1000K.