Simulations of two-phase methane/oxygen rotating detonation wave at cryogenic condition

This paper numerically investigates rotating detonation waves in a gaseous methane/cryogenic liquid oxygen mixture using a non-premixed injection pattern. Distinct differences are observed between the liquid-oxygen detonation engine and traditional liquid-fueled detonation systems: (1) the rotating detonation wave exhibits a strong propensity to form a counter-rotating mode at near-stoichiometric conditions, and (2) a considerable parasitic flame anchors near the inlet, reducing the detonation fraction. Both the counter-rotating mode, characterized by the coexistence of counter-propagating primary and secondary shocks, and the one-wave mode are observed; the specific mode depends on the initial oxygen droplet diameter and the global equivalence ratio. Significant local explosions occur near oxygen droplets immediately behind the leading shock, inducing numerous retrograde shocklets. These shocklets couple with the parasitic flame in the vicinity of the oxygen cluster, facilitating the formation of a secondary shock. Increased gaseous methane mass flow rate (e.g., ϕ = 2.0) or decreased global reactivity (e.g., ϕ = 0.25) reduces the secondary wave strength, resulting in a dominant one-wave operating mode. In the counter-rotating mode, the presence of secondary shocks substantially decreases the total pressure gain due to multiple shock collisions. The maximum mean thrust is observed at ϕ = 2.0, while the minimum is found at ϕ = 0.25. However, variations in the methane mass flow rate lead to an inverse trend in specific impulse. Stable propulsive performance is found in the one-wave mode compared to the counter-rotating mode.