Optical and thrust measurement of a pulse detonation combustor with a coaxial rotary valve

Abstract

We developed a rotary valve for a pulse detonation engine (PDE), and confirmed its basic characteristics and performance. In a square cross-section combustor, we visualized a multi-shot of a pulse detonation rocket engine (PDRE) cycle at an operation frequency of 160 Hz by using a high-speed camera (time resolution: 3.33 μs, space resolution: 0.4 mm) and a Schlieren method. The propellant filling process and the purge process were confirmed, and each process was modeled. Moreover, we confirmed the processes of detonation wave generation and burned gas blowdown. In addition, we investigated the impact of shortening the passage width of a combustor and negative-time ignition (ignition time is earlier than the end-time of the propellant filling process) on the deflagration-to-detonation transition (DDT) distance and time. The DDT distance did not depend on the passage width of a combustor and decreased under the negative-time ignition condition. With a passage width of 20 mm, the DDT distance decreased by 22% under the negative-time ignition condition to a minimum value (76 ± 8 mm). The DDT time from spark time reached a minimum value (69 ± 14 μs) under the condition of a passage width of 10 mm and negative-time ignition. The detonation initiation time and the DDT distance were represented by the time until the flame expanded toward the tube-axis one-dimensionally from ignition (characteristic time). We also carried out thrust measurement using a PDRE system composed of a circular cross-section combustor and the newly developed valve. We obtained a stable time-averaged thrust in a wide range of operation frequency (40–160 Hz) and confirmed the increase of specific impulse due to a partial-fill effect. At a maximum operation frequency of 159 Hz, we achieved a maximum propellant-based specific impulse of 232 s and a maximum time-averaged thrust of 71 N.