Convective burning of block charges prepared from seven-perforation propellant powder grains inhibited by polyvinyl butyral

The burning of block charges prepared from seven-perforation propellant powder grains inhibited with polyvinyl butyral is studied. The experiments are carried out in a constant-volume bomb, nozzle bomb with a post-combustion chamber, and a 23-mm laboratory gun device, setups that provide a wide range of combustion conditions. The progress of the combustion process and the motion of the projectile along the barrel are recorded using a set of piezoelectric sensors. The varied parameters are the amount of inhibitor, density of the monoblock (1.2–1.45 g/cm3), and the power of the igniter. The different combustion conditions achievable in the bomb and laboratory gun device enable to assess the impact of the pressure-rise rate on the rate of the convective burning of the block charge. Adjusting the properties of the latter makes it possible to vary the convective burning rate within 10–60 m/s, which is optimal for using the block charge for producing a shot. The results show that, when used in block charges, coarse seven-perforation propellant powders can provide, despite their own high burning progressivity, an equally high effect as the previously studied fine-grain propellant powders. At a given maximum pressure, the observed increase in the muzzle velocity for block charges exceed 12% as compared to a pour-density charge prepared from regular seven-perforation propellant powder. Based on numerical simulations, an analysis of the experimental data is performed and an explanation of the experimentally observed influence of the pressure rise rate on the convective burning rate of block charges is proposed.