Combustion response of an aluminum droplet burning in air

Abstract

The combustion in air of a 100 μm-diameter aluminum droplet is studied by direct Navier–Stokes simulations. The model only considers the gas phase and includes a reduced Al/O 2 kinetic scheme with 8 species and 10 reactions. The model is validated against experimental burn time data and appears to be fairly correct despite its simplicity. The unsteady combustion is then investigated by superimposing an acoustic disturbance to the mean flow. The velocity-coupled response is computed for different frequencies and slip Reynolds numbers. A resonance peak is found to occur when the acoustic time scale matches the gas diffusion time scale. For lower frequencies however (typically below a few kHz), a quasi-steady regime seems to hold out which means that assuming quasi-steady combustion (e.g., given by a D 2 model) is valid in this case. In this regime, the computed response corresponds with a theoretical expression obtained by a linearization of the Ranz–Marshall correction term. This implies that unsteady aluminum combustion is strongly dependent on convection effects.