A grain-scale modeling on the surface burning and agglomeration of the metalized solid propellants

This study delves into the dynamic behavior of reactive grains within metalized propellants during surface deflagration. Our grain-scale simulations account for both fast and slow deflagration processes involving two distinct metal fuels, namely zirconium and magnesium, with potassium perchlorate (KClO4) as the common oxidizer. Our primary goal is to develop a model and numerical technique capable of replicating the surface reactions observed in experiments. To achieve this, we utilize the compressible Navier-Stokes equations, incorporating the Arrhenius rate law and Johnson-Cook stress model. We pay particular attention to the melt layer, where surface burning occurs in an open atmosphere, and we develop a mechanism to describe the interaction between reactive grains and exhaust gases. We differentiate between two limiting scenarios: convective burning, where unreacted particles experience high-speed compression waves leading to reduced thermal diffusion within the cold reactant, and diffusive burning, characterized by insufficient pressure from particles undergoing both reaction and deformation to erode the burning surface. This results in pronounced agglomeration and the formation of gaseous metal oxides above the melt layer. The results shed light on critical factors influencing surface combustion, including the thermal softening of reactive particles, the time required for particle agglomerations, and tangential forces at multi-element interfaces within the grain-scale simulation domain.