An elementary model for the transition from conductive to penetrative burning in gas-permeable explosives

The experimentally known phenomenon of spontaneous transition from slow conductive to fast penetrative (convective) burning in a confined gas-permeable explosive is discussed. A reduced quasi-linear model, involving only the most essential physical ingredients, is formulated. A good qualitative agreement between theoretical and experimental dependencies is obtained. Similar to the previously studied case of an inert porous matrix filled with an explosive gas, the transition is triggered by a localized autoignition in the extended resistance-induced preheat zone gradually formed ahead of the advancing deflagration. The conventional concept of penetrative burning is re-examined.