quantity for partially premixed combustion. The relation between local equivalence ratio and mixture fraction is given by The stoichiometric mixture fraction defined earlier is the location where the local equivalence ratio . Scalar dissipation rate In turbulent combustion, a quantity called the scalar dissipation rate with dimensional units of that of an inverse time is used to define a characteristic diffusion time. Its definition is given by where is the diffusion coefficient of the scalar. Its stoichiometric value is . Liñán's mixture fraction Amable Liñán introduced a modified mixture fraction in 1991 that is appropriate for systems where the fuel and oxidizer have different Lewis numbers. If and are the Lewis number of the fuel and oxidizer, respectively, then Liñán's mixture fraction is defined as where The stoichiometric mixture fraction is given by . References Fluid dynamics Combustion