Impact of Varying Combustion Chamber Area in Rotating Detonation Engines

This numerical study investigates how changes in the combustion-chamber cross-sectional area affect wave dynamics and performance in the AFRL methane–oxygen rotating detonation rocket engine (RDRE). Three geometries were examined—diverging, nominal (constant area), and converging—while keeping all operating conditions fixed. The nominal and diverging cases sustained two co-rotating detonation waves, whereas the converging case sustained three waves that rotated in the opposite direction. Despite these differences in wave behavior, thrust and specific impulse remain similar across the three configurations. The spatiotemporal chamber averages show consistent pressure and temperature trends, with the converging case producing the highest pressure profile and the diverging case the lowest. Flow choking occurred mid-chamber for the diverging case and near the exit for the nominal and converging cases, indicating that a converging-diverging nozzle is not required to reach supersonic exhaust conditions. Overall, the combustion-chamber geometry has a strong influence on wave dynamics, but only a modest impact on global performance.