Mechanistic Model for Aluminum Particle Ignition and Combustion in Air

A mechanistic model for the ignition and combustion of an isolated aluminum particle burning in air is presented. The model consists of two stages, ignition and combustion. In the ignition stage, melting and heterogeneous surface reactions (HSR) are assumed to occur until a predefined transition temperature of the oxide is attained. In the combustion stage, a quasi-steady state diffusion flame is assumed, and a new conserved scalar formulation is presented that accounts for the deposition of metal oxide on the surface of the molten aluminum. A system of nonlinear ordinary differential equations that describes each stage self-consistently with the gas-phase analysis is developed. Representative results are presented for a range of ambient temperature conditions and compared to experimental measurements. Predictions of overall burn rates, particle velocity, and flame radius show good agreement with experimental data. Also discussed is the extension of the conserved scalar approach to include a more generalized oxidizing environment as well as HSR from nitride reactions during the quasi-steady burning stage.