Initial stage of ignition process in powder explosive with a closed end

Simultaneous optical and piezometric measurements are used to obtain new data on the behavior of the layer of lightly compressed picric acid in the initial stage prior to convective combustion. The formation and development of the cavity resulting from the densification and motion of the explosive driven by the combustion products of the igniter are examined. The effects of the parameters of the igniter and explosive (length, initial density, particle sizes) and of the roughness of the walls of the shell channel on the development of the cavity are investigated. It is shown that for small heights of the explosive layer, cavity formation is accompanied by the development of a backward compression wave that propagates toward the igniter end. The parameters of this wave are determined.