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19.1.3 Using the Spark Model

To activate the spark 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.   Select Species Transport under Model in the Species Model panel and turn on Volumetric under Reactions.

4.   The Define/Models/Species submenu option contains the Spark Ignition... model, which is now selectable. Select the Spark Ignition... model. This will open the Spark Ignition Model Panel .

Figure 19.1.1: The Spark Ignition Model Panel

5.   Define the spark model as either Fixed Spark Size or Time-Varying Spark Radius.

When the Fixed Spark Size is enabled, the panel expands to include the main spark model inputs (Figure  19.1.2). The shape of the spark can be spherical, cylindrical or hexahedral in three dimensional simulations, or circular or quadrilateral in two dimensional simulations. Depending on the shape selected, appropriate inputs are highlighted or grayed out.

Figure 19.1.2: The Expanded Spark Ignition Model Panel

If the user selects the Time-Varying Spark Radius option, the spark is assumed spherical and will grow from an Initial Radius, $r_0$, to a Final Radius, $r_f$, over the spark
guiDuration, with a cube root dependence on time so that the radius will grow faster at the beginning and more slowly near the end. This time-dependent behavior is consistent with experimental findings (see Heywood [ 141]). The Time-Varying Spark Radius option is recommended as it has been found to be less sensitive to model parameters.

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