Comments on criteria for direct initiation of detonation

TLDR

Direct initiation of detonation by a blast wave into an explosive mixture is critically assessed, with current semiempirical theories relying on experimentally determined length‑scales and quenching effects of curvature or unsteadiness. The authors aim to develop an analytic initiation theory based solely on the explosive’s constitutive properties. They propose that initiation criteria must account for blast‑wave amplification through coherent coupling with chemical energy release. Analytic models, simulations, and experiments show that near‑critical initiation results from blast‑wave reacceleration from a sub‑CJ minimum, that hot spots markedly lower the critical energy, and these insights guide future rigorous theory development.

Abstract

The current status of the direct initiation problem, where a powerful source drives a blast wave into an explosive gaseous mixture to generate a Chapman–Jouguet (CJ) detonation, is critically assessed. The current theories which are most successful in estimating the critical energy required for initiation are semiempirical in nature, in that they involve an experimentally determined length–scale (typically cell size) to characterize the explosive mixture. The eventual analytic theory of initiation should be based exclusively on the constitutive properties of the explosive. To date, attempts at a comprehensive theory of initiation have invoked quenching of the reaction front by curvature or unsteadiness of the blast wave. Simple analytic models of initiation as well as numerical simulations and experiments, however, all indicate that initiation near the critical regime is the result of a reacceleration of the blast wave from a sub–CJ minimum. Hence, the criterion for initiation must take into account the amplification of the blast wave due to coherent coupling with the chemical energy release. The effect of 'hot spots' is also shown to have a pronounced effect in reducing the critical energy required for initiation. These results suggest directions which future investigations can pursue toward a rigorous theory of direct initiation.