Use of a hot-spot model to describe the influence of particle size and distance on combustion in a cloud

The combustion of particles in a cloud can be very different from single particle combustion. In addition to the size of the particles, the number density of particles or the mean distance between the particles plays an important role. Experiments show that if the distance between the particles in a cloud is large enough, particles burn in a similar manner to single particles. However below a certain distance, particles form a common flame front. In a parametric study, a hot-spot model is used to simulate the two burning regimes and to find the critical parameters for the transition between them. The results are discussed with reference to the combustion of metalized, gelled and solid propellants and dust explosions.