Flame Height Effects on Agglomerate Size in Aluminized Solid Propellants

Solid rocket motors are one of the most used systems for space propulsion. Along with the numbers of advantages like simplicity, low cost, technological maturity and high thrust, this propulsion system exhibits relatively low gravimetric specific impulse among the thermochemical engine family. When metallized, solid propellants release droplets of molten aluminum (agglomerates) causing a further reduction of performance. This phenomenon depends on several parameters (e.g. burning rate, microstructure, propellant formulation, flame position, local temperatures etc.). This work focalizes the attention on the relation between agglomerate size and flame height. A theoretical investigation has been performed to select five representative formulations. An experimental campaign has been performed to characterize the materials in terms of burning rate, agglomerate size, and density. A simple code based on the GDF theory has been used to compute the flame height of interested formulations. Numerical and experimental data have been finally compared revealing a linear dependence of agglomerate size on the flame height, thus confirming the key role played by the flame in agglomerate growing and formation.