Effect of heterogeneity of solid propellants on their intrinsic stability of pyrolysis

A time-dependent quasi-one-dimensional computation of the pyrolysis of a pair of alternating slabs of solid fuel and solid oxidizer is performed. The geometry is representative of a two dimensionalized model of the burning surface of a composite propellant. It is recognized that the two components pyrolyze with different surface temperatures and rates of pyrolysis, owing to the difference in their activation energies of pyrolysis, heats of pyrolysis, and other thermo-physical properties. With the combination of ammonium perchlorate as the oxidizer and polybutadiene binder, it is found that the ratio of the pyrolysis rates of the two slabs tends to unity for fuel-rich equivalence ratios, indicating an approach to a steady state pyrolysis of the combination. On the other hand, for fuel-lean equivalence ratios, the removal of the ignition source leads to an abrupt fall in the regression rate of the binder, indicating that the pyrolysis cannot be self-sustained. As the mixture moves away from a fuel-rich composition, the time required to attain stability tends to be higher. The results are explained based on the stability of pyrolysis of the combination of ingredients, which is influenced by the difference in their activation energies of pyrolysis.