Computer model of aluminum agglomeration on the burning surface of a composite solid propellant

The process of agglomeration of aluminum particles on the burning surface of a ammonium perchlorate (AP)-based composite propellant is modeled using a computer algorithm. A random pack of particulate ingredients of given size and mass specifications is cast on the computer to simulate the propellant microstructure. The aluminum particles are tracked as the burning surface is regressed at an empirically inputted burning rate for a given propellant formulation, as the particles emerge at the burning surface, accumulate into filigrees, and get ignited by the near-surface leading-edge oxidizer-binder diffusion flamelets (LEFs) attached to the exposed areas of certain AP particles. An approximate heat transfer model is incorporated to estimate the ignition delays radially inward and outward from the LEFs into the filigrees accumulated over AP particles and surrounding binder/fine AP matrix layers. The delay influences the number of parent aluminum particles constituting a filigree and consequently the size of the agglomerate that the filigree rolls up into. The implementation of the algorithm is validated against experimental results available in the literature, which were specifically obtained to investigate the relationship between the decrease in the agglomerate size and attachment of LEFs over more and finer AP particles in the propellant with increase in pressure.