Modeling transitional burning modes of aluminum particles

Aluminum particle burn-rates are known to be a strong function of particle size because the mode of combustion transitions from diffusion to kinetics controlled. To better understand the rate dependent diffusion and kinetic processes, a mixture fraction based particle burn model is developed. In this approach, the vapor phase equations are first recast in terms of mixture fraction space. The appeal of this formulation is it allows for computationally efficient solutions of the flame eigenvalue problem. Several cases are explored using the newly developed model for the burning of Al particles in air, carbondioxide and water-vapor environments. Predictions of burn-rates vs. particle size, reveal significant deviations from a diffusion control limited - highlighting the importance of accounting for finite-rate chemistry in modeling the burning of sub-micron Al particles. Lastly, estimates of flame speed are compared to experimental data for aluminum particle dust in air revealing a maximum in flame speed with decreasing particle size.