Numerical Study of Rotating Detonation Engines: A Discrete Inlet Flow-Field Analysis and Performance Evaluation with Varying Hydrogen and Methane Fuel Composition

Abstract

Pressure-gain combustion presents an exciting potential to increase engine efficiency over conventional engine cycles. The rotating detonation engine (RDE) is an engine concept which utilizes detonation to generate a pressure-gain combustion cycle. RDEs have a cylindrical geometry where a detonation wave continuously rotates around an annulus to produce thrust in the axial direction. However, since detonation is an extremely fast and volatile combustion mode, nonidealities in the cycle cause the control and stability of the engine to be difficult. These nonidealities include parasitic deflagration, mixture inhomogeneities, and multiple competing detonation waves. This study focuses on a stoichiometric, variable hydrogen and methane composition fuel RDE with air as the oxidizer. Specifically, an analysis was done of the effect of inlet number and increasing methane composition in combination with hydrogen fuel on the stability and performance parameters of an RDE. As the composition of methane increased, the performance values such as specific impulse and detonation wave velocity decreased up to 1000 seconds and 60 meters per second, respectively. The addition of methane in the fuel also decreased the range of inlet number in which the detonation wave was able to sustain itself. Two different scenarios produced the destabilization of the detonation wave: the coupling of parasitic deflagration and a slower detonation wave and the coupling of the Kevin-Helmholtz effect and the Rayleigh-Taylor phenomenon. However, the inclusion of methane in the fuel caused weaker reverse compression waves to be created and produced more uniform thrust. Therefore, for methane mixed with hydrogen fuel up to 15% of the mole fraction, performance and efficiency will decrease, but the detonation wave is more stable and has more uniform performance values over the cycle for certain inlet configurations. Once the methane mole fraction is greater than 15% of the fuel, the detonation wave can no longer sustain itself.