Summary: When a detonation propagates in an explosive layer that only partially fills a channel, the rapidly expanding detonation products can form a piston and drive a precursor shock wave (PSW) in the air gap between the explosive layer and the channel confinement, ahead of the detonation as illustrated in Fig. 1a (see [V. Tanguay, A. J. Higgins, “The high-explosive channel effect: influence of boundary layers on the precursor shock wave in air”, J. Appl. Phys. 95, 6159 (2004; doi:10.1063/1.1715134)] and references therein). The experiments with nitromethane demonstrated that the phenomena [V. Tanguay et al., AIAA Paper 2005–0278 (2005)] is sensitive to the initial air pressure in the channel: at high enough initial pressure a precursor will not form. Taking into account that the detonation products pressure is hundreds of thousands of atmospheres, it is surprising that the initial air pressure as low as 10 to 20 atmospheres may be high enough to prevent the formation of PSW. This was also confirmed by the numerical simulations [V. Tanguay et al., AIAA Paper 2005–0278 (2005)] for a single value of air gap width.
For the entire collection see [Zbl 1165.74005].