Combustion modelling Fluent
 

I would like to know if combustion calculations start from the first iteration when a combustionmodel is used in fluent like premixed or non-premixed like will the solution start to calculate the combustion reactions of species present in the domain right from the first iteration or something else?

or

will normal flow equations be solved till the species are encountered and when will the combustion reactions solution actually begin.

THanks in advance.

Any help will be greatly appreciated