Modeling and simulation of titania synthesis in two-dimensional methane-air flames

The formation and growth of titanium dioxide nanoparticles in two-dimensional, non-premixed methane-air flames is investigated via direct numerical simulation. The simulations are performed by capturing the spatio-temporal evolution of the fluid, chemical, and particle fields. The fluid is described by the conservation of mass, momentum, and energy equations; species transport is augmented by the effects of methane-air combustion and the oxidation of titanium tetrachloride; and a nodal approximation to the general dynamic equation is used to represent the effects of nucleation, condensation and coagulation. Simulations are performed for two initial reactant concentration levels, 20% and 30% titanium tetrachloride by mass. The evolution of the temperature, chemical and particle fields as a function of space and size are presented. Results indicate that particle formation and growth is mixing limited in this study and the mean particle diameter and geometric standard deviation increase as the concentration level of the initial reactants increases. In general, high geometric standard deviations correspond to a large particle sizes.