Pocket Model for Aluminum Agglomeration Based on Propellant Microstructure

The propellant microstructure is addressed for the interpretation and the prediction of agglomerate size distribution in aluminized composite solid rocket propellants. Although the mixing process of a propellant is intrinsically random, repetitive fuel-rich local structures (pockets) are generated in the bulk. Pockets are privileged locations for agglomerate generation. In the present work, second-order spatial statistics are applied to model propellants for the characterization of the microstructure and for the definition of an agglomeration model. The model propellants used in this work are generated by a packing code on the basis of real formulations, which are experimentally characterized for validation purposes. The average size and the metal content of the pockets are derived from the interpretation of the radial distribution function. The model is capable of predicting the size distribution of the incipient agglomerates for given propellant microstructures, using one free parameter for the tuning. The fitting of experimental agglomeration data from four different industrial propellants suggests that the free parameter can be expressed as a power function of the combustion pressure and that the microstructure agglomeration model produces particle distributions that reasonably match with the experimental data.