Effect of the chain initiation reaction rate on direct initiation of detonation

The effect of the initiation step of a reaction mechanism on direct initiation of a self-sustained detonation has been studied numerically. For this purpose, the reaction mechanism has been simulated with a three-step chemical kinetics model that consists sequentially of the chain-initiation and chain-branching steps, followed by chain termination. A characteristic time τI is defined for each step of the mechanism, which includes effects of different kinetics parameters. It is shown that τI is a determining factor of the minimum allowable shock pressure. It is observed that the minimum shock pressure in the decaying period of critical initiation tends to the von Neumann pressure when τI becomes large. As a result, at large τI, the critical initiation becomes similar to the supercritical initiation. On the other hand, the amplification mechanism of the leading shock in the decaying period depends on τI.