## 9.2. Using Combustion Models

To access Combustion Models in CFX, you must first set up a reacting fluid. This step is carried out in the Material details view. For details, see Material Details View: Reacting Mixture in the CFX-Pre User's Guide. There are a number of pre-defined reactions that can be selected, and the Reaction details view enables you to create custom reactions for use in CFX-Pre. For details, see Reactions in the CFX-Pre User's Guide.

If you want to specify any non-reacting components that will also be present in the domain, you can add them when creating the reacting mixture. Note that the thermodynamic properties for materials from the CFX-Pre database may not be appropriate (constant specific heat capacity) and may produce poor results if a passive component has a significant mass fraction.

The name of each material in the tree view indicates the range of validity for thermodynamical data. As an example `Carbon Monoxide at STP` has constant properties (density, specific heat capacity, and so on) for standard temperature and pressure. For reacting mixtures, materials from the `Gas Phase Combustion` material group should be used. These materials have variable properties and consistent reference enthalpies for heat release. These materials typically have the chemical formulae as their material name (for example, `CO`).

All liquids and solids in the MATERIALS library are defined with constant specific heat capacity. The variable `Cp` is included for all ideal gases except for `Air Ideal Gas`.

You may want to keep a CCL file containing any customized materials and reaction definitions and then import this file into CFX-Pre when needed.

Thermodynamic data for the material properties used in CFX-Pre was obtained from [26]

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