Effect of injection parameters on instability of detonation waves in rotating detonation engines with an S-shaped isolator

In this study, the effects of three injection parameters on the propagation and instabilities of rotating detonation waves (RDWs) in a kerosene/air rotating detonation engine (RDE) with an S-shaped isolator are experimentally evaluated. The dimensionless parameter momentum flux ratio is considered a pivotal factor, and the influence of the injection geometry factors is analyzed. An empirical formula concerning the characteristic factor of oxidizer-fuel blending is derived to facilitate the RDE injection configuration design. The research reveals a significant correlation among the injection parameters, kerosene-air momentum flux ratios, and instability of RDWs. High dimensionless injection parameters do not necessarily result in a stable RDW phenomenon. Stable RDWs and unstable detonations are discussed under various injection parameters and momentum flux ratios. Additionally, a statistical analysis of the detonation instability is conducted, revealing two distinct cyclic categories: ignition-extinguishment-ignition and attenuation-recovery-attenuation. Two pathways of RDW instability propagation are identified to summarize the evolutionary processes of these variations and elucidate their mechanisms. Changes in the injection parameters cause the RDW to develop in two unstable orientations, resulting in the extinguishing and re-generating phenomenon of the RDW.