(760e) Combustion Dynamics of Aluminum Particle In Air

Experiments on combustion of single spherical Al particles with the sizes in the range of 2 – 20 μm were processed to determine the Al burn rate as a function of particle size, temperature, and preceding burn history.  In experiments, Al particles were ignited by a CO₂ laser beam in air at room temperature. Temperature history of Al particles was measured.  This temperature history was used in a heat transfer model formulated to determine the rate of heat release necessary to balance convection and radiation heat losses from the burning particle.  The rate of heat release was related to the rate of oxygen diffusion from air towards burning particle, and respective Stefan flow was included into the heat transfer model. The calculation considered three different combustion modes. In the first case, the oxide layer grows uniformly on the top of the Al particle.  The second case assumes the pure vapor-phase combustion so that no oxide is present on the particle surface.  Finally, the third case considers partial removal of the produced oxide, so that a fraction of the particle surface is covered by an oxide cap.  The size of the growing oxide cap was adjusted to match the experimental data for different particle sizes.  Additional experiments were performed to burn Al particles in air and collect and analyze combustion products to provide a reference point for the model development.