Peering through the flames: imaging techniques for reacting aluminum powders

Combusting metals burn at high temperatures and emit high-intensity radiation in the visible spectrum, which can oversaturate regular imaging sensors and obscure the field of view. Filtering the luminescence can result in limited information and hinder thorough combustion characterization. A method for "seeing through the flames" of a highly luminescent aluminum powder reaction is presented using copper vapor laser (CVL) illumination, synchronized with a high-speed camera. A statistical comparison of combusting aluminum particle agglomerates imaged using various filtration techniques shows the effectiveness of the high-speed camera with a CVL diagnostic approach. When ignited by an electrically induced plasma, aluminum particles are entrained as solid agglomerates that rotate about their centers of mass and are surrounded by emitted, burning gases. The average agglomerate diameter appears to be 160 μm when viewed with standard illumination and a high-speed camera. However, a significantly reduced diameter of 50 μm is recorded when imaged with CVL illumination coupled with a high-speed camera and a 511 nm notch filter. These results indicate alternative imaging techniques are required to resolve the complexities of metal particle combustion.