Direct Numerical Simulation of single aluminum particle combustion in varying flow conditions

This study presents a comprehensive numerical investigation of single aluminum particle combustion under varying convective oxidizing flow conditions, using Direct Numerical Simulations. A three-dimensional, boundary-layer-resolved model is developed to capture the complex interplay of gas-phase chemistry, surface reactions, and multiphase transport phenomena. The model incorporates aluminum evaporation, aluminum suboxide reactions at the particle’s surface, and alumina formation both on the surface and in the gas phase. It also introduces an original scheme to account for the dissolution of alumina into the molten particle, based on parameters derived from molecular dynamics simulations. The model was validated against experimental burn time data. The unsteady combustion of a 125 μ m -aluminum particle in various flowing O 2 /N 2 conditions is then investigated in terms of standoff flame distance, gas-phase temperature and chemistry, particle temperature and surface chemistry. The results demonstrate that gas-phase reactions remain the dominant source of heat release, although surface reactions, particularly under highly oxygenated environments, play a significant role in modulating local combustion kinetics. The formation of liquid alumina at the particle’s surface, its partial dissolution into the molten aluminum, and the limited surface coverage even at high O 2 concentrations highlight the importance of coupling surface chemistry with thermal transport. While this mathematical model successfully reproduces the main macroscopic characteristics such as flame temperature, burn time–radius relationship, gas-phase composition, and fluxes, some discrepancies appear near the particle surface, i.e. at the microscale. These deviations can be attributed to radiative heat transfer effects which are not considered or to an incomplete understanding of surface reactions. Novelty and significance statement This is the first fully out-of-equilibrium 3D DNS model of aluminum combustion, free of symmetry constraints and explicitly coupling gas-phase and surface chemistry with flow dynamics (Reynolds numbers varying from 0.1 to 50). The model introduces no empirical closures or equilibrium assumptions inherited from droplet combustion; all governing physics are solved from first principles with fully resolved interfacial fluxes. The simulations provide new data highlighting (i) the critical role of surface reactions in governing combustion kinetics, particularly in highly oxygenated environments, and, (ii) the potential errors introduced when the evolving particle size and composition during combustion is neglected.