A two-dimensional investigation to explore the velocity decrease mechanism of a detonation wave propagating within a rotating detonation engine (RDE) chamber was conducted focusing on the effect of injection conditions of the fuel and oxidizer. The injection is parameterized by the geometrical jet and the gas conditions (e.g. premixed or non-premixed). The total length of the injection nozzles constituted 20% of the length of the chamber's lower end under the RDE chamber simulation wherein the number of nozzles N ranged from 10 to 500 under premixed and 25 and 125 under the non-premixed condition. As the nozzle interval increased more burned gas existed in front of the detonation wave. Under the non-premixed condition for N = 25 the propagation velocity decreased to 84% of the CJ velocity and 82.4% of the injected C2H4 was burned by the detonation. Significant velocity decrease down to 86% of the CJ velocity was observed when C2H4 and O2 were placed separately with a large width of burned gas between them. The amount of incompletely combusted C2H4 was inversely proportional to the propagation velocity except in the case with an upper wall. This imply that burned gas has a larger effect on propagation velocity in the non-premixed condition.
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