Detonation onset due to the energy accumulation effect of shock wave focusing

Abstract

Shock wave focusing is a highly efficient and reliable method for detonation initiation, which is crucial for the successful operation of detonation engines. To refine the reflector design, a fair comparison of the energy accumulation abilities of different reflectors is necessary. In this study, seven different reflectors, namely, a 30° wedge reflector (WR30°), a 60° wedge reflector (WR60°), a 90° wedge reflector (WR90°), a 120° wedge reflector (WR120°), a reflector designed according to the Chester-Chisnell-Whitham relation (CCW), a parabolic reflector (PARA), and a semicylindrical reflector (SEMI), are investigated numerically. This study also includes a comparison between numerical and experimental results to confirm the accuracy of the simulations. The internal energy density near the apex zones of the reflectors is used as the metric to evaluate the energy accumulation abilities of different reflectors. The results show that the reflectors can be ranked in order of energy accumulation ability as follows: CCW > WR30° > WR60° > PARA > WR90° > WR120° > SEMI. This ranking is also supported by the corresponding numerical soot foils from each of the reflectors. The aforementioned reflectors have at least 2.5 times greater energy accumulation ability than the plane reflector, demonstrating the significant effect of shock wave focusing. Moreover, reflectors with longer converging depths appear to have a better energy accumulation effect. This study provides guidance for selecting different reflectors, which may contribute to higher detonation initiation reliability in detonation-based engines.