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19.2.3 Using the Autoignition Models

To activate the autoignition model, perform the following steps:

1.   Select Unsteady from the Time list in the Solver panel.

2.   Select an appropriate reaction model in the Define/Models/Species submenu.

Define $\rightarrow$ Models $\rightarrow$ Species $\rightarrow$ Transport & Reaction...

3.   The models in the Species Model panel that are compatible with the autoignition model are Species Transport, Premixed Combustion, and Partially Premixed Combustion.

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If you select Species Transport, you must also enable the Volumetric option in the Reactions group box.

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The Premixed Combustion and Partially Premixed Combustion models are only available for turbulent flows using the pressure-based solver.

4.   The Define/Models/Species submenu contains the Autoignition... model, which is now selectable. Select the Autoignition... model .

  • If Species Transport is selected in the Species Model panel, you can only select the Ignition Delay Model.

    Figure 19.2.3: The Ignition Delay Model in the Autoignition Model Panel
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  • If Premixed Combustion is selected in the Species Model panel, you can only select the Knock Model.

    Figure 19.2.4: The Knock Model in the Autoignition Model Panel
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  • If Partially Premixed Combustion is selected in the Species Model panel, you can select either the Knock Model or the Ignition Delay Model.

5.   When the Ignition Delay Model is enabled, the panel expands to include the modeling parameters for this model (Figure  19.2.5). The two correlation options that exist with this model are the Hardenburg and the Generalized. Depending on which correlation option is selected, the appropriate modeling parameters will appear in the panel.

Figure 19.2.5: The Ignition Delay Model for the Partially Premixed Combustion Model
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  • The Hardenburg option is typically used for heavy duty diesel engines. A Fuel Species is selected from the drop-down list and the Pre-Exponential, Pressure Exponent, Activation Energy, and Cetane Number are entered using the GUI. Default values of these parameters can be found in Table  19.2.1.

  • The Generalized option is described by Equation  19.2-3. Similarly to the Hardenburg option, a Fuel Species is selected from the drop-down list and the Pre-Exponential, Temperature Exponent, Activation Energy, RPM Exponent, Pressure Exponent, Equivalence Ratio Exponent, Octane Number, and Octane Number Exponent are entered using the GUI.

6.   When the Knock Model is enabled, the panel expands to include modeling parameters for this model (Figure  19.2.6). The two correlation options that exist with this model are the Douaud and the Generalized. Depending on which correlation option is selected, the appropriate modeling parameters will appear in the panel.

Figure 19.2.6: The Knock Model with the Partially Premixed Combustion Model Enabled
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  • The Douaud option is used for knock in SI engines. The modeling parameters that are specified in the GUI for this option are the Pre-Exponential, Pressure Exponent, Activation Temperature, Octane Number, and Octane Exponent (Equation  19.2-2).

  • The Generalized option (Equation  19.2-3) in the knock model requires the same parameters as in the ignition delay model.


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© Fluent Inc. 2006-09-20