Ignition and Combustion Mechanisms of Explosively-Dispersed Reactive Powder

A numerical study was conducted to explore the ignition and combustion of aluminum powder dispersed by a TNT charge. The simulations used a high-order numerical method for a compressible reactive gas that is coupled to a kinetic-theory-based granular multiphase model that is valid up to the packing limit. Scenarios where an annular shell of highly-packed monodisperse Al powder surrounding the TNT charge were considered with varying thickness, particle diameter, and particle packing. The results qualitatively show two different ignition and combustion modes of the explosively-dispersed powder observed in experiments. Prompt ignition, where the particles ignite almost immediately on the outer edge of the particle cloud, was observed if the particle layer is thin or loosely packed. The particles continue to burn in a non-premixed mode of combustion as they disperse outward. Delayed ignition was observed in scenarios where the particle layer is thick or the packing is high. The Al particles on the inner edge of the dispersing cloud ignite when they interact with the TNT fireball and secondary shocks. The Al-dust flame continues burns in a turbulent premixed mode of combustion from the inside towards the outside.