### 9.13.2. Fluid Models

The models settings described in this section are set when creating a domain in CFX-Pre. For details, see Domains in the CFX-Pre User's Guide.

#### 9.13.2.1. Component Details

You should select Transport Equation for the NO component. A transport equation is solved for the NO component when NO is modeled, regardless of the combustion model used.

When running the EDM or Finite Rate Chemistry model, setting Transport Equation has the same effect as setting `Automatic`.

When running the Flamelet model, the flamelet library could also contain NO. In this case, specifying Transport Equation would activate the NO model discussed here. Specifying `Automatic` or `Library` would use NO from the library instead.

When the fuel nitrogen mechanism is added, the components HCN and HCO need to be specified with the same option as for NO. For example, when used in combination with the flamelet model, HCN and HCO should be set to `Transport Equation`.

#### 9.13.2.2. Boundary Conditions

For NO, the default value 0 is appropriate in many configurations. When a fuel nitrogen mechanism is used, the HCN component must be set at the boundary according to the nitrogen content in the fuel.

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