Mechanisms of prompt and delayed ignition and combustion of explosively dispersed aluminum powder

Abstract

A multidimensional numerical study was performed to explore the ignition and combustion mechanisms of an annular aluminum particle shell surrounding a trinitrotoluene (TNT) charge. The model equations consist of a fully compressible reacting gas coupled to a kinetic-theory-based Eulerian granular multiphase model. The parametric study explored the influence of thickness of the Al particle layer, initial Al packing, and diameter of the Al particles. The computed results show ignition and flame structures that are consistent with both delayed and prompt ignition of explosively dispersed reactive powder. In delayed ignition, the Al particles ignite several milliseconds after the dispersal when the particles interact with the surface of the TNT fireball during the negative phase of the blast. The resulting turbulent Al dust flame propagates from the inside toward the outside of the dispersed Al dust cloud. The results show that smaller-diameter Al particles ignite more quickly and propagate through the dispersed dust cloud more rapidly. Paradoxically, larger amounts of smaller Al particles are unburned after the turbulent flame propagates through the dust cloud in comparison to larger-diameter particles. Prompt ignition occurs when the Al particles ignite in the shock-heated air almost immediately as the particles start to disperse. The flame structure for prompt ignition scenarios is a non-premixed dust flame where the fuel and air are mixed by velocity slip between the gas and particles.

Experimental and computational investigation into the hydrodynamics and chemical dynamics of laser ablation aluminum plasmas

“…One such multi-physics code that offers this capability is HyBurn, which has been developed to model the extreme conditions and reactive multi-phase flows of post-detonation fireballs. 45,46 The code uses Eulerian methods combined with adaptive mesh refinements, granular compaction models, turbulent mixing methodologies, and gas-phase chemical reactions to simulate phenomena such as full-scale dust explosions, 47 particle-bed combustion, 48 deflagration-to-detonation transitions, 49 and shock-to-detonation transitions. 50 In this work, HyBurn will be employed to simulate the atmospheric mixing processes, plume hydrodynamics, and thermochemistry of aluminum LPPs.…”

Explosive dispersal of granular media

“…2018; Posey et al. 2021). Another prominent application involves blast mitigation by surrounding the explosive with a layer of particles (Milne et al.…”

“…In volcanic eruptions, the explosive expansion of pressurized gases through an initially concentrated dispersion of particles expels mixtures of pressurized gases and fragments of magma within volcanic conduits (Marjanovic et al 2018). For various commercial and military explosive systems, such as fire extinguishing devices using explosive dispersed dry powders (Klemens, Gieras & Kaluzny 2007), thermobaric and fuel-air bombs (Frost, Goroshin & Zhang 2010;Frost et al 2012), the explosive dispersal of granular media and the ensuing mixing of particulate matter with air are of particular importance to their reliable applications (Zhang et al 2015;Bai et al 2018;Posey et al 2021). Another prominent application involves blast mitigation by surrounding the explosive with a layer of particles (Milne et al 2014;Pontalier et al 2018).…”