Experimental study on the propagation characteristics of the rotating detonation wave of a small-scale rotating detonation engine

Detonation combustion modes offer potential benefit over deflagration-based combustion due to rapid heat release and pressure-gain characteristics. A small-scale rotating detonation engine (RDE) is a compact detonation-based device capable of continuous and high-frequency operation. Small-scale RDEs are promising for propulsion related and laboratory-scale applications, especially for compact operation under low flow-rate conditions. In the present study, wave propagation behaviour in a small-scale RDE running on methane–oxygen was investigated experimentally using high-speed imaging. The combustor annulus had an inner diameter and outer diameter of 38 mm and 46 mm, respectively. The operating conditions were varied over equivalence ratios (φ = 0.8–1.2) and total mass flow rates (ṁtotal = 3.8, 4.0, and 4.2 g/s). The high-speed image sequences showed alternating single-wave and dual-wave propagation modes within the RDE annulus under the tested conditions. The wave propagation velocity and wave propagation frequency were determined from the recorded image sequences. The average wave propagation velocity was found to be significantly lower than the ideal Chapman–Jouguet value, indicating non-ideal wave behaviour under the present low flow rate operating conditions. Overall, the results provide useful insight into the propagation characteristics of a small-scale RDE operating with methane–oxygen mixtures at very low total mass flow rates.