Scale effects on rotating detonation rocket engine operation

Rotating detonation rocket engines are propulsive devices employing detonation waves moving circumferentially around an annular channel that consume axially fed propellants. Theoretically, this provides benefits with respect to combustion pressure gain and thermodynamic efficiency when compared to deflagration-based combustors. To facilitate size scaling of these devices, the relationships between geometric parameters, performance, and wave dynamics have been investigated with gaseous methane-oxygen propellant. Empirical relations were derived between combustor geometry, fueling conditions, and engine operation, as well as correlation to thermodynamic parameters calculated with chemical kinetics codes. The radius of curvature effects were explored in annular combustors having outer diameters of 25 mm, 51 mm, and 76 mm with a fixed gap width of 5 mm. The injectors were scaled to have same oxidizer-to-fuel injector port area ratio, impingement distance, and injector-to-gap area ratio. Larger combustors had higher wave counts during operation at a given mass flux and equivalence ratio. Combustor axial pressures were found to be more dependent on propellant mass flux and equivalence ratio than geometry. Mass flux and the inner-to-outer radius ratio, the latter of which was related to other geometric ratios, dictated the operating mode transition thresholds and the number of resulting waves, respectively.