To achieve reliable transmission of detonation wave to a pulse detonation engine (PDE) combustor, authors have proposed a PDE initiator, which consists of a predetonator and a reflector. A detonation wave propagates around the reflector changing its shape through three transition processes; from planer to cylindrical, toroidal, and planar again. Our previous study revealed that the transition to the cylindrical detonation wave upstream of the board plays a significant role in detonating hydrogen-air mixture in a 100-mm-diam-combustor. A self-sustainable condition of the cylindrical detonation wave is severe when the radius of the wave front is small. In cases using hydrogen-oxygen mixture as driver gas for the 100-mm-diam-combustor, we had to fulfill with driver gas entire upstream of the board at the critical condition for the transition to the cylindrical wave. On the other hand, curvature of the cylindrical detonation wave front becomes smaller with increasing radius of the front, so the self-sustainable condition of the cylindrical wave must be mitigated for a large bore combustor. In this study, we investigated the necessary filling diameter of the driver gas to detonate hydrogen-air cylindrical detonation by using a 500-mm-diam-cylindrical-combustor.

To achieve reliable transmission of detonation waves to a pulse detonation engine (PDE) combustor (detonation chamber), the authors propose a PDE initiator that uses a cylindrical reflector downstream of a predetonator exit. The detonation wave propagates around the reflector to change the wave shape in three transition stages: from a planar detonation wave in the predetonator to an expanding cylindrical detonation wave, from the cylindrical wave to a planar toroidal detonation wave, and from the toroidal wave to a planar

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