Low mass-flow operation of small-scale rotating detonation engine

Abstract

The primary goal of this research was to utilize a range of oxygen/ethylene mixtures in a small-scale Rotating Detonation Engine (RDE) at low mass flow rates to achieve operational detonation frequencies above the 20 kHz threshold of human hearing. A Micro-RDE was designed with an outer diameter of 28 mm and channel gap of 2 mm that yielded detonations at a wide range of testing conditions. Flow was induced via a Jets-in-Crossflow (JIC) scheme to achieve appropriate mixing of reactants before ignition with a pre-detonator device. Two aerospike nozzles of different diameter were tested to change the backpressure on the device and detonation wave speed and frequency were determined using high-speed imagery. Most successful tests yielded two detonation heads. Wave speeds were between 1100 and 1400 m/s and test frequencies were found to be above 31 kHz, well above the audible frequency. A secondary goal of this investigation was to investigate the mixing process within the RDE. Optical access was achieved by implementing a quartz outerbody. Optical imagery of the detonation channel was captured with a Shimadzu camera for detonations ranging from equivalence ratios (Φ) of 0.2–1.7. The fuel and air mixing processes were imaged at MHz rate revealing the local variations in the equivalence ratio that the bulk fluid flow was predominantly axial.