Investigation of the Effect of Chain Initiation on Direct Initiation of Detonation

In this paper, the role of reaction mechanism in direct initiation of detonation is studied numerically. The combustion mechanism is presented using a three-step kinetics model, which consists of chain initiation, chain branching and chain termination. In this research, the role of chain initiation on the blast initiation is studied. To investigate the role of chemical mechanism, a characteristic time (τ) is defined for each step, which contains the effect of various kinetics parameters. Numerical simulation shows that extending the initiation characteristic time (I) causes an increase in the critical energy of direct initiation. To demonstrate the role of chain initiation on detonation initiation, shock pressure diagrams are presented for different values of I, and also for various initiation energies (E0). These diagrams show that for smaller Is, kinetics has a more important effect than for larger values of Is. Also, it is shown that by increasing the initiation energy, dependence of minimum value of the shock pressure on I is decreased. For large values of Is, the behavior of the wave in the critical initiation is almost independent of I; thus, detonation behavior for a given E0 nearly coincides with the respective Is. The relationship between a I and E0 depends on the value of I. For small I, this relationship is linear with a small slope, whereas for large I, it is linear with a large slope.