FUNDAMENTAL STUDY OF INJECTION, MIXING AND STABILITY IN MODEL ROTATING DETONATION ENGINES

Abstract

In light of the growing demand for more efficient aviation engines, detonation-based engines are being investigated as possible replacements to traditional rockets and jet engines. Rotating Detonation Engine (RDE) is one of the novel engine concepts, gaining much interest from the aero propulsion community, including both industry and academia. RDE is a continuous-detonation engine, which consists of an annular chamber where the reactants are injected axially while the detonation wave propagates along the chamber in an orthogonal direction to the flow axis. Potential advantages of RDEs include greater thermal efficiency, improved fuel economy, simpler design, reduced weight, better scalability, and possible exempt from combustion instability concerns. One of the purposes of this research is to better understand the nature of RDE propulsion concepts and pertinent interaction between various physical processes. The main focus is on the effect of injection and mixing on the detonation wave propagation and heat release inside RDE combustors. Complex interaction between detonation waves and injector flow-fields is investigated for various injector geometries and flow compositions. The effects of injection and mixing are investigated for two different types of injector geometry, including unlike impinging doublet injectors and recessed partially-premixed jet injectors. Counter propagating waves are observed in the detonation tunnel as well as in other RDE tests. Based on the present results, the onset of the counter-propagating waves can be attributed to the reignition of the unburned reactants trapped in the wake of the wave. By visualizing the injector internal flowfield, it was also shown that detonation wave propagates into the interior of the recessed injectors. This finding is important for properly predicting the refresh injection timing. Also, the RDE stability and mode selection phenomenon are investigated using Rayleigh criterion to provide physical explanations based on acoustic energy for sustenance of periodic motion. The experimental data for this analysis is acquired using simultaneous sampling of transient chemiluminescence and local pressure measurements in the extended linear model detonation engine. The results show that, in the case of decoupled detonation wave, there is a distinct time delay between the pressure peak and the peak in the chemiluminescence signal. The ensuing Rayleigh index analysis can be used to explain and predict RDE mode selection processes. The results provide both qualitative and quantitative insights on the effect of RDE geometry as well as on the detonation wave stability. They provide better understanding of the complex interaction between RDE combustor processes.