Detailed numerical simulation of an isolated droplet/particle combustion with applications to combustion of metals

A fully transient, one-dimensional (spherical symmetry) numerical model that uses detailed chemical kinetics, multi-component molecular transport mechanisms, condensation kinetics, and gas phase radiation heat transfer is developed. The model is used to simulate the combustion of a magnesium (Mg) droplet in pure oxygen (O₂) and carbon dioxide (CO₂). An Arrhenius-type rate expression is developed to obtain the condensation rate of the condensed phase magnesium oxide. The condensed phase oxide is treated as a gas phase species with low diffusivity. A coagulation model is used to simulate magnesium oxide particulate formation.; The predicted flame, temperature of Mg in O₂ is close to the vaporization-dissociation temperature of magnesium oxide (MgO) and the predicted flame temperature of Mg in CO₂ is close to the melting point of MgO. Both quasi-steady and transient simulations predict that a steep temperature gradient exists very close to the droplet surface. The droplet surface temperature is close to the metal boiling point. During combustion in carbon dioxide, the reaction between magnesium and carbon monoxide occurs very close to the surface and the model predicts formation of carbon near the surface.; For a 1-mm diameter magnesium droplet, the model predicts a burning rate constant equal to 1.14 s/mm2 for combustion of magnesium in oxygen and equal to 2.52 s/mm2 for combustion in carbon dioxide both at 1 atm pressure. Inclusion of gas phase radiation decreases the gasification rate and increases the burning time and for large droplets increases the extinction diameter. The coagulation model predicts formation of 0.03 micron and 0.2 micron diameter magnesium oxide particles at the flame location in oxygen and carbon dioxide, respectively.; A quasi-1-d reacting flow solver is developed. This solver is compatible with CHEMKIN, a chemical reaction mechanism package. The conserved variable form of the governing equations is used. A first order upwind difference scheme is used along with Van-Leer flux splitting for reacting gases. This solver along with the coagulation model can be used for the preliminary performance analysis of a rocket motor using an Mg-CO₂ propellant.