Investigation of combustion phenomena associated with the flow of hot propellant gases. III: Experimental survey of the formation and decay of muzzle flow fields and of pressure measurements

Abstract

The development of the flow fields generated by firing a 7.62-mm caliber rifle is measured using a time-resolved spark shadograph technique. Two precursor flow fields are forced out ahead of the projectile. The propellant gas flow field forms upon separation of the projectile from the muzzle. While the first precursor develops in a nearly spherical manner, the development of the second precursor and the propellant gas blast field occur anisotropically. In the axial downstream direction the propagation velocity is higher than along the lateral direction. Motion of observable discontinuities is shown to follow time-displacement laws. In addition, the local and temporal pressure distribution in the muzzle blast field of the rifle was determined by immersing quartz probes in the flow. Within the main expansion zone of the flow, subatmospheric pressures of p > 0.2 × 10 5N/m 2 are observed. After passing through the shock fronts which terminate this expansion zone, the pressure increases to p > 1.5 × 10 5N/m 2. Expansion starts anew at some distance from the shock front, and the pressure decreases. This decrease is rapidly disturbed by the onset of combustion, and the buildup of reverse pressure gradients between the shock front and the reaction zone is observed. Further downstream, expansion commences anew until the gas-air interface is reached. At this interface the pressure increases indicating the deceleration of flow within the “contact surface.” The overpressure of the blast was shown to decrease both in-axis and lateral from p > 3.5 × 10 5N/m 2 near the muzzle to about p = 1.1 × 10 5N/m 2 at distance 2 m. The noted features of the flow and the interaction with the combustion processes are discussed in detail.