Electric-spark ignition of flow of an aluminum particle-air mixture in a channel with a sudden expansion was studied experimentally using the model of hot-spot ignition. The critical radius of the initial site of ignition was determined, the dynamics of the process was studied, and the effect of turbulence intensity on the development of the hot spot was established.The ignition of a particle-gas cloud by a spark discharge is described using the hot-spot ignition model [1][2][3]. The problem of hot-spot ignition was considered in [4][5][6][7].In the thermal theory of ignition, the problem of hot-spot explosion reduces to analyzing the evolution of the initial temperature profile in the reactive medium and to determining the critical value of the FrankKamenetskii parameter δ cr = R 2 0 /at a , where R 0 is the radius of the hot spot, a is the thermal diffusivity of the substance, and t a is the adiabatic induction period [7]. A single spherical metal particle in a heated gas is a very convenient object for describing thermal explosion due to two features: the absence of a temperature distribution in the particle and the very simple and physically accurate expression for the heat transfer coefficient α. For fine particles, despite the possible high temperatures of thermal explosion, the role of the radiative component α r is usually insignificant. Hence, the Biot criterion can be written as Bi = α c r 0 /λ p = λ g /λ p , where α c is the conductive component of the heat-transfer coefficient, r 0 is the metal particle radius, and λ g and λ p are the thermal conductivities of the gas and particle, respectively. Thus, the problem reduces to the Semenov-Todes formulation [8].The laws of thermal explosion for single metal particles and their clouds differ because in clouds there is thermal interaction between particles. Thermal explosion for various laws of oxidation of metals was analyzed in [9]. For a linear law, zero order of heat release takes place and (as for the case of explosive particles) the critical value of the Semenov criterion is Se cr = 1/e. For parabolic and exponential laws, strong kinetic (more precisely, diffusive) deceleration of the reaction due to the buildup of the film oxide takes place. Under real conditions of thermal explosion, it competes with Arrhenius thermal self-acceleration. As a result, the preexplosion picture differs markedly from the classical one [8].Because of the peculiarity of the kinetic law, the dimensionless analysis has some special features. Instead of the common Se and Td criteria, the process is defined by the parameters Ω = 3Se get Td and γ = r 0 3δ 0 Td, wherek get (T 0 ), r 0 is the initial particle radius, ρ is the particle density, δ 0 is the initial thickness of the oxide film, T 0 is the ambient temperature, Q is thermal effect of the reaction, and k get is the preexponent [8]. It is known [10] that ignition lasts from the beginning of spark discharge to the establishment of steadystate flame propagation. Here there are at least two problems. One of them is the form...
