The initial guess for scalars can have a large effect on the convergence history of a combustion problem. For example, initial specification of a large concentration of fuel and oxidant in the domain can produce high, unrealistic temperatures that slow convergence. It is best to specify the concentrations in such a way that the reaction proceeds starting from the inlet and proceeds through the domain. This will help ensure reasonable flame temperatures during convergence.

In cases where the domain initially contains air, you should specify oxygen with a mass fraction of 0.232 and set each of the other species to Automatic. For temperature and other component mass fractions, you can safely choose Automatic as the option in most cases.