Structure of flames propagating through metal particle clouds and behavior of particles

Abstract

The structure of flames propagating through metal particle clouds and the behavior of metal particles near the flames have been examined experimentally. In the experiments, two types of iron particles with different diameter distributions were used. They were suspended in air and ignited by an electronic spark. The flames and individual particles were recorded using high-speed photomicrography, and the structure of flames and the behavior of particles were analyzed in detail. Each flame has a combustion zone of 3–5 mm in width. The combustion zone consists of luminous particles without gas-phase flame. Its leading edge is clear and smooth and moves at an almost constant velocity. The flame velocity depends on the particle size and particle cloud concentration, whereas the flammability limits for particle concentration depend mainly on only the particle size. At about 12 mm ahead of the leading edge of the combustion zone, particles start to accelerate in the direction of its propagation. When the particles approach close to the leading edge of the combustion zone, their velocities reach their maximum. On passing across the leading edge. They become bright and combustion would start. Then their velocities decrease. The velocity of particles at the leading edge of combustion zone is nearly proportional to the flame velocity.