Flame Structure Simulation of Nonaluminized Composite Propellants

Composite solid propellants are heterogeneous mixing of reactive powders bound together by a combustible polymer matrix. Reactants distribution in solid phase influence flame structure because gas species are released separately from the burning surface during combustion. Diffusive mixing is the main responsible for effective oxidation of fuel gases produced by binder pyrolysis. Bidimensional flame structure simulations are presented in this paper. Nonaluminized propellants based on inert binder and crystalline oxidizer (AP/HTPB) are considered. Ideal laminate geometry is assumed in order to evaluate the effect of AP particles size on near-surface flame. Different laminas sizes are tested at constant pressure. The simulation is performed solving coupled simplified fluid dynamics and five-equation global reaction scheme. Gas temperature profiles along stream direction are discussed on the basis of different probing locations. Stretching of heterogeneous flame is made visible as the laminas size is increased together with a weakening of final diffusion flame in case of wide particles. The influence of premixed reaction on primary diffusion flames is also depicted by simulation as the AP laminas size is decreased.