Defining Operating Conditions and Time-Step Size

Here, you set the crank angle at which the simulation begins and the duration of the analysis. You enable automatic time-step control, which adjusts the time-step size based on preset valve lift thresholds.

To set the start crank angle and the duration of the analysis:
  1. Right-click the Operating Conditions node and select Edit.
  2. In the Operating Conditions group box, set the following properties:
    Property Setting
    Start Angle 300.0 degCA
    Duration 420.0 degCA
    In general, you run an analysis over multiple engine cycles to reduce the effect of initial conditions on the final results. If your processing time is limited, you are advised to start the analysis some crank angles before the intake valve opens—for example at 300 deg crank angle. At this stage, you can assume that the flow in the cylinder is relatively steady compared to the intake and combustion phases.
  3. Click Apply, then Close.
The Graphics window still displays the engine geometry at TDC position. However, in the bottom left corner, the red-colored starred text indicates that the displayed imported geometry no longer represents your settings of 300 deg crank angle.


To set up the automatic time-step control:

  1. Right-click the Solvers node and select Edit.
    The Edit dialog displays the default time step settings, solver settings, auto-save settings, and wall treatment.
  2. In the Time Step Settings group box, activate Automatic.
  3. Click Apply, then Close.
  4. Save the simulation .