Motor and Plume Particle Size Prediction in Solid-Propellant Rocket Motors

Models are developed for 1) agglomeration of powdered aluminum on the burning surface of a metallized composite solid propellant in order to predict average diameter of aluminum agglomerates as a function of propellant composition, pressure, burning rate, and size distribution of oxidizer particles and 2) the processes of coagulation and aerodynamic shattering of liquid aluminum-oxide droplets in an accelerating gas flow. The critical upper value of droplet diameter in the throat, which is calculated theoretically, is in agreement with the mean-mass diameter D 4 3 obtained by numerical simulation of a two-phase flow with coagulation and particle breakup. A formula is proposed for the average particle diameter at the nozzle exit, which is confirmed by agreement with the measured values of D 4 3 of aluminum-oxide particles in plumes of small, medium-sized, and large solid rocket motors. The proposed formula is also in agreement with Hermsen's correlation of measured diameters. Based on a comparison between theoretical calculations and numerous experimental data, the formula is recommended for prediction of the aluminum-oxide particle size in plumes of various types of solid rocket motors.