2025 Volume 68 Issue 3 Pages 136-144
Focusing a spherical shock wave formed by laser ignition in an elliptical cavity can initiate detonation. To clarify the effect of the detonability of premixture and shock intensity on detonation onset, laser ignition experiments were conducted with stoichiometric ethylene–oxygen premixture at the initial pressure of 5–200 kPa and laser emission energy of 50–150 mJ. The flow field was visualized by high-speed schlieren imaging. As a result, four different types of flow field were observed: moderate initiation, rapid initiation, general flame acceleration, and shock-only flow field. In the moderate initiation case, shock-flame complexes engulfed the leading shock wave and collided to cause a local explosion. In higher initial pressure, rapid detonation onset was observed when a local explosion occurred behind the leading shock. In the failed cases, although the initial shock, the reflected shock, and the combustion wave were observed, except in the shock-only case, a local explosion did not occur after the triple-points’ collision. Each case was classified as success or failure, and the success/failure distribution was compared with the critical energy of direct detonation initiation.
