Environmental & Climate Sciences Department Seminar

Two simple and efficient models for the description of multicomponent Fick diffusion in mixtures with high numbers of components have been recently developed [1]. Both models are based on the Kinetic Theory of Gases and make use of perturbation schemes in terms convenient dimensionless variables, leading to efficient algorithms for the calculation of mass diffusion fluxes in mixtures of interest in combustion science. The first model, termed Model 1, which is extremely simple, assumes that all components in the mixture are dilute in a single species, and provides an accurate description of the multicomponent fluxes by means of a perturbation scheme. In the second model, termed Model 1+M, the number of main species (those species which are not in the dilute limit) is increased from 1 to 1+M, with 1+M being at most an order O(10) number, and the perturbation strategy is only applied to the remaining dilute species, often in trace amounts. The performance of these two descriptions of multicomponent diffusion fluxes is compared to the formulation of Dixon-Lewis [2], used for instance in the Chemkin package [3], and also to the widely used mixture-average simplification. The results are illustrated with steady flamelets of hydrogen or dodecane, in order to compare computational costs when different number of species are involved. An unsteady auto-igniting counterflow diffusion flamelet of methane in a coflow of hot products is also considered. The different comparisons in terms of precision and cost show that Model 1+M can be more effective than the mixture-average approach in terms of computation time, while reproducing the results of Dixon-Lewis multicomponent diffusion [4]. REFERENCES [1] Arias-Zugasti, M., Garcia-Ybarra, P.L., Castillo, J.L., "Efficient calculation of multicomponent diffusion fluxes based on kinetic theory", Combust. Flame 163:540–556 (2016)