Approaching Solid Propellant Heterogeneity for Agglomerate Size Prediction

Abstract

Propellant microstructure is addressed for the interpretation and the prediction of agglomerate size in composite aluminized solid rocket propellants. Heterogeneity of propellant derives from random mixing of ingredients. In the bulk, particles arrange in repetitive local structures called pockets where fuel-rich composition is present. Those are privileged locations for agglomerate generation. Second-order spatial statistics is applied to propellants for characterization of the pocket structure. Average size and metal content of pockets are put in connection with experimental agglomerate data. Initial volumetric information come from numerical models of real propellant formulations which are generated by a packing code. An agglomeration model based on heterogeneity is also proposed. The algorithm supplies distributions of agglomerates for given propellants, based on microstructure geometric features and on a free parameter which is used to introduce pressure dependence. Currently, initial tuning is required. Fitting of experimental agglomeration data from four dierent propellants to the model demonstrate that the free parameter can be expressed as a a power function of pressure. Agglomerate size distributions resulting from the model reasonably match with experimental data.