Reinitiation mechanisms in hydrogen–air attenuated detonations

Detonation wave propagation and its interaction with obstacles are fundamental to industrial safety. In this study, detonation attenuation and reinitiation of stoichiometric hydrogen–air mixtures over a semi-cylinder are numerically studied with a calibrated chemical-diffusive model (CDM). Three regimes observed in experiments, including critical reinitiation, delayed reinitiation, and fully quenching, are well captured. It is demonstrated for the first time through a CDM model that the formation of transverse detonation by the Mach reflection behind the obstacle is a key factor for detonation reinitiation. For the critical reinitiation regime, a transverse detonation forms after a hotspot is directly triggered by the regular reflection near the obstacle. For the delayed reinitiation regime, a weak transverse detonation wave is generated by the Mach reflection on the obstacle, and then, it decays into a shock. The Mach shock leads to the detonation reinitiation. When the transverse detonation is not generated, the detonation is fully quenched by the cylinder. A flame diagnostic tool based on chemical explosive mode analysis highlighted the compressibility-induced ignition in the detonation reinitiation process. It is found that transverse detonations do not arise solely from the rapid consumption of the unburned pockets. Instead, they are initiated by the pressure amplification of reaction zones at interfaces between burned and unburned gases. The combustion rates in these zones are intensified through Richtmyer–Meshkov instabilities caused by the passage of transverse shock waves, which subsequently evolve into detonations.