Experimental investigation on the effects of chamber characteristic length on the rotating detonation performance

To elucidate the coupled effects of the combustion chamber configuration and nozzle on rotating detonation propulsive performance, an experimental investigation was conducted under mass flow rates ranging from around 80 to 250 g/s using ethylene and 50% oxygen-enriched air. Five annular combustors with an increasing chamber characteristic length L * (from 439 mm to 563 mm), the ratio of chamber volume to the nozzle throat area, were tested with a fixed nozzle geometry. Five distinct propagation modes were identified, and the wave propagation mode evolutions with L * under varying the nominal inlet mass flow fluxes were categorized into stable, transition, and unstable regions. The results showed that the stable single-wave operational range progressively narrowed as L * increased. The chamber pressure and thrust exhibited a non-linear increase with the mass flow rate, while the characteristic velocity c * consistently decreased, indicating a reduced combustion efficiency at higher flow rates due to the shortened chemical reaction time. For L * increasing from 439 mm to 468 mm, a moderate enhancement in thrust and specific impulse is observed within the flow regime of 140–200 g/s. However, when L * was further increased to 563 mm, the propulsive performance declined over the whole range of flow rates investigated, indicating that L *=468 mm represents a critical dimension.