### 9.15.1. Fluid Models

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

#### 9.15.1.1. Soot Model

Set the Soot Model to `Magnussen` to enable the soot model.

#### 9.15.1.2. Fuel Material

The Fuel Material is a required parameter and should be set to the name of the fuel. In this release of CFX, only a single fuel is assumed to generate soot. If there are several fuel components, choose the one with the largest mass fraction and carbon content and increase model coefficients accordingly. For example, set the Fuel Carbon Mass Fraction and Nuclei Formation Pre Exponential Factor such that the correct value for the following product is obtained:

Fuel Carbon Mass Fraction * Nuclei Formation Pre Exponential Factor * Fuel Mass Fraction.

#### 9.15.1.3. Soot Material

The Soot Material is a required parameter indicating which material in the Library contains its properties description for Density, Absorption Coefficient, and so on.

#### 9.15.1.4. Fuel Consumption Reaction

This is an optional parameter, but you are strongly recommended to set an appropriate value for it. When using the EDM or Finite Rate Chemistry model, select the fuel break-up reaction. This reaction must be a single-step reaction.

The component specified for Fuel Material must be among the reactants of The Fuel Consumption Reaction and only those reactions are offered in the user interface.

If no Fuel Consumption Reaction is specified, a simplified version of the Magnussen model will be applied that is lacking some physical aspects (turbulence effects, soot combustion).

For the Flamelet or related combustion models (Burning Velocity Model, Extended Coherent Flame Model), the `Fuel Consumption Reaction` parameter is not available in the user interface. This is because these models define the fuel consumption by means of a Flamelet library, in contrast to a single reaction step. However, in this case the `Fuel Consumption Reaction` may be specified using CCL functionality (expert use), thereby enabling all features of the soot model in combination with models that do not use a single step for the primary combustion:

1. From the CFX-Pre user interface, create a separate Single Step reaction as follows:

   1. Reactants and products corresponding to the global reaction that is represented by the Flamelet library.

   2. All components of the new reaction should already exist in the Flamelet library.

   3. Set the combustion model under the reaction definition to Eddy Dissipation and/or Finite Rate Chemistry. Additionally, Finite Rate Chemistry requires specification of the Forward Reaction Rate.

2. From the CFX-Pre user interface, add the newly created reaction to the list of reactions that define the reacting mixture.

3. From the Command Editor in CFX-Pre, use CCL to set the parameter `Fuel Consumption Reaction` under `Soot Model` so that it references the new reaction. The following is an example of the CCL for a single phase case:

       FLOW:
         DOMAIN: <domain name>
           FLUID MODELS:
             COMBUSTION MODEL:
               SOOT MODEL:
                 Option = Magnussen
                 Fuel Material = CH4
                 Soot Material = Soot
                 Fuel Carbon Mass Fraction = 0.75
                 Fuel Consumption Reaction = <reaction name>
               END
             END
           END
         END
       END

   where `<domain name>` and `<reaction name>` are the names of the domain and new reaction, respectively.

#### 9.15.1.5. Fuel Carbon Mass Fraction

The mass fraction of carbon in the fuel should be entered (for example, for methane enter `0.75` or `12/16`).

#### 9.15.1.6. Soot Particle Mean Diameter

This is also an optional parameter. The default value is 178.5 angstrom (where 1 angstrom = 1.0*10-10 m).

Release 18.2 - © ANSYS, Inc. All rights reserved.