Improved Burn Rate Measurement of Deterred Gun Propellants with Multivariate Size Distribution

Deterred gun propellants with multivariate size distribution are widely used in small-calibre guns. While the surface treatment is used to increase the progressivity of the propellant and therefore the performance, the size distribution is due to variations in the production process. When standard models or methods for the burn rate measurement, e. g. according to STANAG 4115, are used to determine burning rates and burn rate parameters, they generally suffer from poor generalizability and are of little use for the simulation of the burning behaviour inside a gun. Therefore, a new model based on STANAG 4367 was developed, that addresses these issues. It describes the burning velocity with a depth-dependent Vieille's law and can also take into account a multivariate size distribution of the propellant grains and depth and pressure-dependent thermodynamic properties. The model is used to define an objective function to fit simulated dynamic vivacities to experimental data and thus determine burn rate coefficients in a modified Vieille's law. The method was validated by using synthetic dynamic vivacities as input data for the fitting procedure. To test the model, closed vessel experiments were conducted with a deterred double-base propellant. It is shown that the model gives an excellent description of the experimental data with reasonable burn rate coefficients and does not suffer from the drawbacks of other methods.