For the combined Finite Rate Chemistry/Eddy Dissipation Model, the reaction rates are first computed for each model separately and then the minimum of the two is used. This procedure is applied for each reaction step separately, so while the rate for one step may be limited by the chemical kinetics, some other step might be limited by turbulent mixing at the same time and physical location.
It is also possible to apply different combustion models to each of the steps in a multi-step scheme. Some of the predefined schemes make use of this feature, regardless of the global model selection.
The combined model is valid for a wide range of configurations, provided the flow is turbulent. In particular, the model is valid for many reactions that range from low to high Damköhler numbers (chemistry slow/fast compared to turbulent time scale). Use of this model is recommended if reaction rates are limited by turbulent mixing in one area of the domain and limited by kinetics somewhere else. The Eddy Dissipation model can, however, be more robust than Finite Rate Chemistry or the combined model.
The following topics will discussed: