We consider two different types of flames: burner-stabilized flames and adiabatic, freely propagating flames. The conservation equations governing the two are the same, but the boundary conditions differ. In both cases the appropriate boundary conditions may be deduced from the early work of Curtiss and Hirschfelder.[35] For burner-stabilized flames is a known constant, the temperature and mass flux fractions () are specified at the cold boundary, and vanishing gradients are imposed at the hot boundary.

For freely propagating flames is an eigenvalue and must be determined as part of the solution [103]. Therefore, an additional constraint is required, or alternatively one degree of freedom must be removed from the problem. We choose to fix the location of the flame by specifying and fixing the temperature at one point. This is sufficient to allow for the solution of the flame speed eigenvalue . The user must select this point in such a way as to insure that the temperature and species gradients "nearly" vanish at the cold boundary. If this condition is not met then the resultant will be too low because some heat will be lost through the cold boundary. More details on boundary conditions are described in Boundary Condition Details .