Ignition of aerosolized reactive particles at high heating rates

This paper presents an experimental methodology, respective heat transfer model, and initial results describing ignition of rapidly heated, aerosolized powders of different materials. The experimental setup uses a CO₂ laser as a heat source. The interaction of the laser beam with particles is particle size-dependent and only a narrow range of particle sizes is heated effectively. Therefore, the heat transfer model needs to be only analyzed for the particles with this specific size, which greatly simplifies the interpretation of experiments. The powder is aerosolized inside a plate capacitor by charging particles contacting the capacitor's electrodes. A thin, laminar aerosol jet is carried out by an oxidizing gas through a small opening in the top electrode and is fed into a laser beam. The velocities of particles in the jet are about 1 m/s. The laser power is increased until the particles are observed to ignite. The ignition is detected optically. The ignition thresholds for spherical magnesium and aluminum powders were measured. The experimental data for magnesium, for which ignition kinetics is well known, were used to calibrate the detailed heat transfer model. The model was used to evaluate the ignition kinetics for aluminum powder.