Burning-rate behavior in aluminized wide-distribution AP composite propellants

Burning-rate behavior of aluminized, wide-distribution ammonium-perchlorate (AP), hydroxyl-terminated-polybutadiene (HTPB) binder composite propellants, both 2D laminates and 3D particulate propellants, is investigated experimentally. Very fine (2-μm) AP (FAP) is used at a high FAP/binder ratio (75/25) with either coarse (>200 μm) AP (CAP) particles (3D particulate propellants) or pressed AP slabs (simulating CAP particles in over-ventilated, 2D laminates). The results indicate that, while aluminum does not significantly alter the AP/binder flame structure, it can either increase the burning rate via radiative feedback or decrease it via inert heat-sink effects, depending on pressure (competing conductive heat feedback). Otherwise, the AP/binder flame structure is similar to that found previously for non-aluminized laminates, with minor differences. The FAP/HTPB-matrix burns with a one-dimensional premixed flame not hot enough to ignite aluminum, but hot enough to self-deflagrate if a modest amount of an external radiant flux (in the case considered, supplied by aluminum ignited downstream by the CAP/matrix flame) is present. The CAP/matrix interaction flame burns in either a split-diffusion or merged, partially premixed mode, depending on pressure and fuel-layer thickness. A correlation between the burningrate pressure exponent and the CAP/matrix flame-regime pressure dependence is found in terms of the Peclet number in accordance with a simple, conserved-scalar (mixture fraction) theory.