Experimental study of stages in aluminum particle combustion in air

An experimental study of Al particle combustion in air is presented. Uniform Al particles were formed and ignited in air using a pulsed micro-arc discharge. Burning particle color temperatures were measured using a three-wavelength pyrometer, partially burned particles were quenched and cross-sectioned. Particle internal compositions were studied using a scanning electron microscope equipped with an x-ray energy dispersive spectroscopy detector and wavelength dispersive spectroscopy scan. Temporal variations of the particle diameter and the shape and size of the smoke cloud surrounding a burning particle were determined. The effect of an external electric field on Al particle combustion was also tested. Three distinct stages were identified in Al particle combustion, which correspond to different temperatures, internal particle compositions, and flame shapes. The transitions between the stages were shown to correlate with the internal phase transformations occurring in the burning Al droplets. Growing on spinning Al particles ''oxide caps'' were shown to cause rapid changes of trajectories of the burning particles. The temperature histories of burning Al particles were affected by the electric field, and a reduction in the total combustion time due to external electric fields was observed.