Agglomeration of Aluminized Solid Rocket Propellants

Abstract

Metal agglomeration is a massive problem for the combustion of aluminized solid rocket propellants. The tendency of metal particles to create metal/metal oxide agglomerates impairs energy conversion inside the nozzle and, because of two-phase-flow, specific impulse losses can easily reach 4-6 % and more. From this viewpoint it is important the capability to predict agglomerate size, which can give a pre-fire estimation of the delivered specific impulse. This work proposes a method for the evaluation of agglomerate sizes based on a statistical analysis of computer generated propellant surfaces. Investigations, carried out through a two-point probability function, highlight the existence of a characteristic length featuring the spatial displacement of large oxidizer grains (extending the Cohen’s pocket concept). These data are then used to draw a correlation between characteristic size, burning rate and mean agglomerates size for different propellants and operating pressures. A fair prediction capability was proven for this method, though its simplicity does not allow a complete matching with the experimental results.