Numerical study on the propagation characteristics of detonation waves in a semi-confined channel affected by different inert gases

In rotating detonation engines, the lateral expansion of detonation waves within a semi-confined channel often leads to a velocity deficit in the wave and a reduction in combustion efficiency. Based on the OpenFOAM open-source computational platform, this paper numerically investigates the impact of different inert gases on the propagation characteristics of detonation waves in a semi-confined channel. The results show that: for gases with a large acoustic impedance ratio, such as Ar, CO₂ and N₂, the lateral expansion of the detonation wave forms an oblique shock wave - incident shock wave - detonation wave complex structure. The reflected wave formed at the inert gas boundary interacts with the existing transverse waves on the detonation wave front, the wave wrinkles, and the lower solid wall. As a result, the pressure ratio both behind and ahead of the reflected wave continuously increases, gradually enhancing its intensity until it eventually evolves into a new transverse wave. This process contributes to maintaining the stability of the detonation wave for a certain period. However, because the transverse waves continuously transmit into the inert gas, the intensity of the detonation wave still gradually decreases until it leads to detonation quenching. Owing to the physical properties of the inert gases affecting the intensity of the oblique shock waves (Ma_Ar > Ma_CO2 > Ma_N2), which in turn affects the propagation of the detonation wave, the propagation distance of the detonation wave is the shortest when the inert gas is N₂. For gases with a lower acoustic impedance ratio, such as He, the propagation of the detonation wave results in a complex structure of detached shock - transmitted shock wave - incident shock wave - detonation wave. In addition, the interaction between transverse waves and the compressed reaction zone can promote the formation of new transverse waves. The wave front maintains a large number of triple points, and the pressure ratio behind and ahead of the transverse waves remains at a high level, indicating that the wave intensity does not significantly decay. This sustained wave intensity contributes to the stability of the detonation wave. As a result, the detonation wave propagates farther in inert gases with a lower acoustic impedance ratio (He) compared to those with larger impedance ratios (Ar, CO₂, N₂).