Because FLUENT calculates all intermediate and product species automatically during the equilibrium calculation, certain species will be included that are generally not in chemical equilibrium. Principal among these are the NOx species. Specifically, the NOx reaction rates are slow and should not be treated using an equilibrium assumption. Instead, the NOx concentration is predicted most accurately using the FLUENT NOx postprocessor, where finite-rate kinetics are included (see Section 20.1). The NOx species can be safely excluded from the equilibrium calculation since they are present at low concentrations and have little impact on the density, temperature, and other species.
To force the exclusion of a species from the equilibrium calculation, click the Control tab in the Species Model panel (Figure 15.10.1).
Under Species Excluded From Equilibrium Calculation, enter the chemical formula for the desired species in the Add/Remove Species field. Next, click Add to add the species to the Species list or Remove to remove an existing species from the Species list.