I need to calculate the spatially-resolved mixture fractions (with respect to both fuel and oxidizer) in a turbulent combustion chamber. The mixture fraction is defined as the mass originating from a single stream (usual fuel) over the total mass in a volume. This should be a fairly simple task, but a good portion of elemental C and O are also coming from diluent streams throughout the combustor. The chemical compositions of each stream, specifically, are fuel: CH4, oxid: O2, and diluent: CO2. I want to find specifically the fuel and oxidizer contribution to the mixture composition at each node. I believe mixture fraction is a built-in output in Chemkin but not Fluent.
If I have to calculate it manually, even if I neglect species diffusion, I still have more than 10 chemical species--way too many unknowns to calculate the mixture fractions from just mole and mass fraction outputs.
Is there a way to compute the mixture fraction for such a model?