As suggested by the conservation of one species mass i is implemented in terms of a user-defined passive scalar, which represents the mass fractions w i . The molecular diffusion coefficient D m,i of an individual component i in the mixture is computed with the approximation of using the binary diffusion coefficients determined via the semi-empirical correlation of . The calculation of the molecular diffusion coefficients are precisely described in the supplementary information (SI Section S1). To guarantee the conservation of total mass, the equation of species mass conservation is solved for N -1 species and the N th species is determined by the definition that the mass fractions sum to unity: