Influence of Gas-Dispersion Parameters of the Air Suspension Flow on the Flame Spread Velocity

The results of experimental studies on the effect of gas-dispersed parameters of the flow of an air suspension of aluminum particles—the average particle diameter d32 and excess air coefficient α—on the flame propagation velocity are presented. The dependences of the apparent flame propagation velocity, uf, on the coefficient of excess air α for ASD-1-grade aluminum powder with d32 = 17.4 µm and ASD-4-grade aluminum powder with d32 = 7.4 µm are obtained. It is established that the number of maxima and their location on the dependence graph uf(α) depend on the particle combustion mode, which in turn is determined by the particle size. For both powder grades, there is a maximum on the dependence graph uf(α) in the rich region (α ≈ 0.2). For aluminum particles with d32 = 17.4 µm, the flame propagation velocity decreases monotonically with increasing α. For particles with d32 = 7.4 µm, whose combustion occurs in the kinetic mode, there is a second maximum in the region of stoichiometric air suspension compositions (α ≈ 1.0). The number and location of maxima and their variation depending on the average diameter d32 allows us to draw certain conclusions about the combustion mechanism of aluminum particles.