RDC Operation and Performance with Varying Air Injector Pressure Loss

Abstract

Four different air injectors with an area of 14.4%, 23.0%, 28.7%, and 46.0% of the combustion annulus area are installed in a rotating detonation combustor (RDC) and tested in combination with two fuel injectors, five different outlet throat restrictions, and across an annulus mass flux range between 50 and 300 kg/s/m2. The equivalence ratio is fixed at 1 for all tests. The combination of injector and outlet area ratio dictates the fill Mach number and pressurization of the combustion chamber. This is underlined by an assessment of the injector stiffness in terms of the pressure ratio across it. With increasing injector area and increasing backpressurization, the stiffness decreases. This in turn influences the operating map of the device and presents limits for successful single wave operation. For each geometric configuration, a mass flux needs to be chosen that is sufficiently large to overcome the counter-rotating wave mode regime, but also does not lead to adverse longitudinal pulsations or coupling of the chamber dynamics to plenum acoustics. It is further demonstrated that the relative increase in stagnation pressure gain is also influenced by the injector and outlet combination, and that it may be imperative to implement mode control strategies to harness the full potential of an RDC. For the best configuration of this study, a stagnation pressure gain of -8% was recorded with a Kiel probe at the exhaust throat. The Kiel probe measurements are then compared to other published data, with which they are generally in good agreement. Lastly, the chamber Mach number is determined from the outlet throat area ratio as well as experimental data. The agreement of the results of these two approaches further substantiates the Kiel probe method’s usefulness and applicability in RDC experiments.