Efforts on high-frequency pulse detonation engines

Several attempts have been made on the studies of detonation-based propulsion. Deflagration-to-detonation transition (DDT) is usually used for detonation initiation as an efficient means. Many DDTenhancement methods, including using various physical and fluidic obstacles, introducing a predetonator, and employing the detonation branching scheme, have been developed and experimentally tested. In addition, shock reflection and focusing are also proposed for detonation initiation. Reliable and efficient detonation initiation methods should be determined according to specific applied conditions. Supply of propellants occupies a considerable proportion in a complete detonation cycle. Thus, rapid and efficient feed of fuel, oxidizer, and purge gas (if needed) plays a crucial role in high-frequency operations and many efforts have been made on this topic. Recent studies have provided some excellent solutions for high-frequency feed. Specific DDT enhancement methods for different tube configurations require more effort to provide a reference to which enhancement method is the optimal choice considering the DDT distance and time as well as the hardware complexity.