The Effect of Coating the 5/7 Pyroxylin Propellant Particles by a Film of Polyvinyl Butyral on the Transition of Layer-By-Layer Burning to Convective Burning

The transition of layer-by-layer burning to convective burning is studied on samples of 5/7 pyroxylin powder granules with a density of 1.34 to 1.47 g/cm3 and porosity 7–15%. The experiments were carried out in a manometric bomb and a model rocket engine. We use the original particles and particles coated on the side surface with a film of polyvinyl butyral (PVB) in an amount of 4.1%. On samples with the initial particles, the transition to the convective regime occurs at a close-to-constant or slightly increasing pressure. The breakdown pressure of layer-by-layer burning increases with decreasing porosity. The use of coated particles leads to an increase in the duration of layer-by-layer burning. The transition of layer-by-layer burning to convective burning occurs at a falling pressure. The breakdown pressure decreases with decreasing porosity.