Characterisation and simulation of the influence of propellant geometric variability on gas delivery profiles

Abstract

Ballisticians do not currently take the significance of propellant grain geometry variance into account for the various solid propellants found within guns of various calibres (Baschung & Grüne, 2000). Conventional Internal Ballistic (IB) simulation codes assume that the geometry of propellant grains is uniform; however, variance in their geometry is present, and this has an impact on the performance of gun systems (Pocock, Locking, & Guyott, 2003). As a consequence, consideration needs to be given to the fact that propellant grains are variable in order to achieve improved accuracy during the IB simulation and burring rate calculation. The actual gas delivery profiles resulting from real-life propellant differ from the propellant gas delivery profiles provided by simulation models. This study focused on determining the geometric variability of representative grain shape, namely Ball Powder. Assumption of geometric variability distributions were implemented to describe and simulate the geometric variability. The initial goal of this study was to evaluate and characterise the effect of geometric variability among the grains on the combustion rates of propellants using both the closed vessel test and the dynamic firing test. A second goal of the study was to define, formulate and implement Probability Distribution (PDF) functions into the relevant IB calculation tools, i.e. calculation of burning rate and simulation of the Internal Ballistic (IB) cycle of guns. In summary, the identified samples that are characterised by their grain geometry show how they could influence the performance of the propellant, meaning that the IB simulation model results are affected by these phenomena. The results for both the tests and the simulation prove that the dimensions of the propellant grains are critical, even if the propellant samples have the same composition.