Effects of chamber length on the structure of detonation waves in a non-premixed ethylene-oxygen rotating detonation engine

The present work has experimentally studied the effects of chamber length on flow fields of detonation waves in a non-premixed ethylene-oxygen rotating detonation engine (RDE). RDEs are constant-volume combustion devices offering higher performance than constant-pressure engines, with shorter chamber lengths that reduce weight and size, thereby improving efficiency. A comprehensive physical explanation for the stability and performance in RDEs at varied chamber lengths remains elusive. Experiments are performed at chamber lengths (30, 45, 60, 75, and 90 mm) and under a constant flow condition. Detonation waves are captured through a visible chamber wall and the RDE exit using two high-speed cameras simultaneously. Thrust and chamber pressure are measured to assess the performance of the RDE. Stable detonation wave cycles are observed at chamber lengths of 30 and 45 mm. At 60, 75, and 90 mm, the detonation waves demonstrate instability. This instability is attributed to interactions between combustion products from the previous cycle and an oblique shock in the current cycle, which may result in detonation quenching. The detonation wave speeds are reported as follows: 1414 m/s at the chamber length of 30 mm, and 1327 m/s at 90 mm. Pressure efficiency remains nearly uniform at 67%–69% for the chamber lengths of 45–90 mm, peaking at 76% for 30 mm. Thrust efficiency is consistently 79%–82% across the chamber lengths. The results provide insights into designing RDEs with an optimized chamber length, enabling stable detonation waves and minimizing detonation quenching, thereby improving RDE efficiency.