An unsteady PBE-CFD analysis of the asymmetric smoke-laden flame around a burning aluminum particle

Against the backdrop of our transition to a sustainable energy economy, metal powders are presently investigated as recyclable and carbon-free energy carriers that can be burned in air, while yielding condensed phase oxides as main reaction products. Aluminum not only qualifies as a potential metal fuel due to its high energy density, availability and handling safety, but has also been investigated in detail for its reaction kinetics. At present, the formation of nanosized oxide smoke droplets in the vicinity of burning aluminum particles poses major challenges to the recovery of oxides from the exhaust fumes of a dust flame and the closure of the metal fuel cycle. Here, we harness a kinetically detailed and spatio-temporally resolved single particle combustion model to estimate the pollutant and smoke charge emitted by a burning aluminum particle over the course of its conversion alongside the smoke’s size distribution. The smoke droplets’ sizes not only influence natural deposition mechanisms, but are also critical for the design of gas-smoke separation devices. Physically, the oxide smoke droplets are described in a Eulerian fashion using a population balance approach that is combined with tailored balances governing the gas-droplet dispersion’s mass, momentum and enthalpy. A particular feature is the incorporation of a time-varying particle morphology, including the growth of an oxide lobe following surface oxidation and smoke deposition. Our modeling framework is validated by comparing predictions of the particle burning times and residue sizes with available experimental data for different initial particle diameters. While the burning time scales with the initial diameter to the power of 1.83, the residue size is found to increase with a diameter exponent of 0.78.