Coupling volume-of-fluid and chemical kinetics for direct numerical simulations of droplet combustion

Since the development of the d2 law, in 1952, numerical modeling of droplet combustion has predominantly relied on the assumption of spherical symmetry. In this work, we relax this hypothesis by introducing a strategy to combine interface-resolved phase change models with the direct solution of the combustion chemistry. The multiphase system is described using the geometric Volume-Of-Fluid approach, previously extended to simulate the evaporation of mixtures with variable thermodynamic and transport properties. Gas-phase chemical reactions are incorporated using an operator splitting technique, addressing the stiffness and non-linearity of the reactive step. The model is validated by comparing its predictions with experimental data and with a spherically-symmetric model, proving convergence and capturing the burning rates accurately. The impact of natural convective fluxes at different ambient pressures is quantified by suspending the droplet on a solid fiber in normal gravity conditions. Lastly, the multicomponent formulation is employed to predict droplet extinction resulting from water absorption. The model's implementation and simulation setups are publicly available on the Basilisk code website.