For multi-step reactions, there is the option of specifying a different combustion model for each reaction step. The choice of combustion model for each step is optional, and is made when the Reaction or Combustion Model check box is selected for a single-step reaction. Specification is carried out in the Reaction details view in CFX-Pre. For details, see Single Step: Basic Settings in the CFX-Pre User's Guide.

The available choices for a reaction-step specific reaction are Eddy Dissipation Model, Finite Rate Chemistry Model, and EDM/Finite Rate Chemistry Model. For details, see:

When a reaction contains a reaction-step specific combustion model, the model overrides the choice of combustion model set on the Fluid Domains form in CFX-Pre, except if the option on the Fluid Domains form is set to None.

Because of the behavior described in the paragraph above, it is important that you select a combustion model on the Fluid Domains form, even if you have selected models for each and every reaction step in a multi-step reaction.