Effect of ignition parameters on detonation initiation using toroidal shock wave focusing

Abstract

For fast detonation initiation, a novel compact initiator based on shock wave focusing has been proposed in our work. Two-dimensional numerical investigation was performed to understand the fast detonation initiation mechanism in hydrogen-air mixtures. Detailed evolution processes, namely, flame acceleration, shock wave focusing and detonation initiation were analyzed. Moreover, effects of ignition energy and energy release time on detonation initiation have been discussed thoroughly. The numerical results indicate that flame acceleration process can be divided into three stages: a) curling deformation of flame with low speed, b) tensile deformation of flame with medium speed, c) steady propagation of flame with high speed. After shock focusing, a highly compressed and heated region triggers the rapid detonation initiation. Further analysis indicated that detonation initiation time increases with the decrease of ignition energy. And the reason is mainly due to initial ignition delay differences controlled by ignition energy. In particular, once ignition energy is smaller than 12.5 mJ, mixtures will be no longer ignited. Besides, with the increase of energy release time, both the run-up time and distance of detonation initiation increase. The rapid release of energy can not only make mixtures ignited earlier, but also enhance initial flame velocity. As a result, when energy release time is reduced from 200 μs to 50 μs, the run-up time and distance are decreased by 50% and 32.5%.