Investigation of combustion phenomena associated with the flow of hot propellant gases-II: Gas velocity measurements by laser-induced gas breakdown

Abstract

The local and temporal distribution of gas velocity along the axis of the propellant gas flow ahead of the muzzle of a caliber 7.62 mm rifle is determined by using luminous tracers produced by a laser pulse. Within the main expansion zone of the flow field, maximum gas velocities of 2400 m/s are observed. After passing through the shock front which terminates this expansion zone, the flow is decelerated to ν < 150 m/s. Expansion starts anew at some distance from the shock front leading to gas velocities of several hundred m/s. This expansion is rapidly disturbed by the onset of secondary combustion causing a ‘breakdown’ of the flow. The effect is explained by the buildup of reverse pressure gradients between the shock front and the reaction zone.