The mass fraction of species and temperature fields can be measured or calculated in laminar counterflow diffusion flame experiments.
When calculated, a self-similar solution exists, and the governing equations can be simplified to only one dimension i.e. along the axis of the fuel and oxidizer jets.
For this, an average value of χ is computed known as Favre value[7] The basic assumption of a SLFM model is that a turbulent flame front behaves locally as a one dimensional, steady and laminar which proves to be a very useful while reducing the situation to a much simpler terms but it does create problems as few of the effects are not accounted for.
The steady laminar flamelet model is also used to predict chemical non-equilibrium due to aerodynamic straining of the flame by the turbulence.
Such transient effects also arise in turbulent flow, the scalar dissipation experience a sudden change.
N. Peters, Institut für Technische Mechanik RWTH Aachen, Four Lectures on turbulent Combustion.