Pristine energetic materials degrade over time, resulting in a porous-propellant scenario. Safety and burning characteristics of such a degraded propellant will be considerably affected not only by porosity itself but by two-phase flow effects. A relative motion between the gas and condensed phases in both the solid-gas preheat region, bubbling melt layer as well as the exothermic reaction region is a fundamental aspect of multiphase deflagration in porous energetic materials. Our models of multiphase burning processes in porous solid propellants belong to a more general field of heterogeneous combustion.
Various intermediate phases exist in the context of solid-propellant burning, such as, for example, bubbling melt layers and a dispersed phase. There are models that assume a scenario where a gaseous flame is preceded simply by sublimation and/or pyrolysis reactions. In the context of 'unconfined' quasi-steady deflagrations, the approximation of small Mach number may imply that the gas pressure is independent of the spatial coordinate. However, under certain conditions, a confinement in the system may arise, thus causing a significant difference between the upstream and downstream values of the gas pressure, or overpressure. Consequently, growing overpressure leads to a rapid increase in the burning rate; i.e., a transition from conductive to convective burning.
In the problems described here, we addressed several models in combustion of porous solid propellants under confinement. The global combustion mechanism is adopted as a condensed-phase reaction (bubbling melt layer, sublimation and/or partial pyrolysis) followed by a gaseous flame to form the final gas-phase products.