The diffraction and re-initiation characteristics of gaseous detonations with an irregular cellular structure

Two-dimensional numerical simulations were performed in this study to look at the diffraction and subsequent evolution of an irregular structure detonation in a stoichiometric hydrogen-air mixture, propagating from a small-width pre-detonator (width d) into a larger-width testing channel (width D). By varying the ratio D/d from 1.1 to 5.5, three kinds of propagation modes and the corresponding dynamics of the irregular structure detonation waves are elucidated. The numerical results show that, for an irregular structure detonation wave, the D/ d range from 1.0 to 1.1 corresponds to the supercritical mode, the critical mode for D/d ranging from 1.2 to 5.0, and a D/d larger than 5.0 results in the subcritical mode. Compared to the equivalent numerical study for regular structure detonations, the critical width ratios for the supercritical mode and the critical mode are found different for irregular structure detonation. Detonation waves with an irregular structure are more likely to change from the supercritical mode to the critical mode. In the critical mode, the re-initiation process of an irregular structure detonation could originate in two ways, i.e., the Mach reflection of the diffracting lead shock LS to form the main triple point TP1 or self-sustained triple points (the TP2 similar to TP4) from the diffracting cellular detonation front. On the other hand, the re-initiation process of a regular structure detonation could result solely from the Mach reflection of the LS to form the TP1. By defining the distance between the backward-facing step and the explosion bubble HS formed by the collision of the new triple points as the characteristic distance L (mm), it is shown that the irregular structure detonation requires a longer characteristic distance L than the regular structure detonation to generate the HS at the centerline. The findings of this study offer potential avenues for optimizing pre-detonator and combustion chamber configurations in detonation engines.