Mechanistic insights into the initial explosion in the deflagration-to-detonation transition

This work presents an imaging study of the complex and often overlooked early-onset mechanisms of the deflagration-to-detonation transition (DDT). Columns of granular octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) doped with tungsten tracer particles are ignited thermally by hot wire and the resulting reactions are studied via high-speed X-ray radiography utilizing the Diamond Light Source synchrotron. The observed results provide insights into the initial development of the DDT process, resulting in a proposed mechanism for the slow initial steps in DDT for thermally ignited, low bulk-density granular explosive contained in a quasi-one dimensional tube configuration. In order to clarify the proposed mechanism, the terms preferential flow channel and matrix burning are adapted from the soil mechanics and hydrology literature to further elucidate the role of convective burning in DDT. The proposed mechanism helps to clarify the ongoing debate on the transport of gases in the Baer–Nunziato and reduced Baer–Nunziato models and suggests that applicability of each interpretation depends on which step in the mechanism is being described.