Investigations on multi-stage supersonic combustion in a model combustor

Staged injection is an approach to increase the overall equivalence ratio while reducing the risk of thermal choking in a supersonic combustor. The experiments presented in this paper were conducted to investigate the interaction between injection stages and to provide test data for the validation of numerical tools. Tests on multi-stage injection and combustion of gaseous hydrogen were performed at the connected pipe test facility of the Institute for Flight Propulsion of Technische Universitaet Muenchen. The first injection stage consists of a central strut injector. To increase the penetration depth of the fuel the geometry of the strut was slightly changed in comparison to already presented data. As the fuel of the first stage injected in the central region of the duct most of the unburnt oxygen is expected to be close to the upper and lower walls. For exploitation of the oxygen close to the walls the other stages are wall-mounted. To reach a high penetration depth and to minimize complexity holes perpendicular to the walls are used as wall injectors. To investigate the flow field without combustion helium was injected through the wall injectors matching the jet-tofreestream momentum flux ratio to that of a hydrogen jet in the experiments with combustion. The matched equivalence ratio was varied from 0 to 0.26 and Schlieren pictures were taken to visualize the flowfield around the wall injectors. Furthermore the wall pressure distribution was measured for comparison with the combustion test cases. Combustion experiments were conducted with single stage injection and two stage injection varying the equivalence ratios of the different stage. The wall pressure distribution was measured and chemiluminescence images of the flame were taken. The flame of the first stage was stabilized for all test conditions but the hydrogen injected through the second stage resulted just in a slight pressure rise.