Setting up the Piston Motion

Here, you set the engine geometry properties that impact the piston motion and the cylinder displacement and compression ratio.

To set the geometry properties of the engine:
  1. Right-click the Engine > Cylinder node and select Edit.
  2. the Edit dialog, click the Motion tab.
  3. In the Engine Geometry group-box, set the following properties:
    • Bore—Simcenter STAR-CCM+ In-cylinder automatically calculates this value from the imported geometry.
    • Stroke
    • Crank Radius—this value is automatically calculated from the specified stroke.
    • Connecting Rod Length
    • Pin Offset
    • Zero CA Convention
    See Engine Reference—Cylinder Dialog: Motion.
To check if your setup is correct, you can calculate the displacement and compression ratio of the cylinder and compare the results to measurements.

To calculate the displacement and compression ratio:

  1. Click Apply.
    Simcenter STAR-CCM+ In-cylinder updates the geometry in the background to calculate the cylinder volume at TDC position with the valves closed. This value is required for the compression ratio calculation.

    The Displacement and Compression Ratio values for the cylinder are displayed.

  2. If the displayed values do not match your measurements, check your geometry properties again and correct them accordingly.
  3. If the piston of your imported geometry is not at TDC position, set one of the following properties:
    • Piston Position Offset: set the offset of the imported piston geometry from TDC.
    • Compression Ratio: set the compression ratio of your engine. Note that the default value assumes that the piston of your imported geometry is at TDC position.
  4. Click Apply.
    If you specify the piston position offset, Simcenter STAR-CCM+ In-cylinder displays the corresponding compression ratio and vice versa.
    Simcenter STAR-CCM+ In-cylinder automatically checks if the specified values result in an engine geometry where the piston touches any surfaces other than the liner or a symmetry surface. If it does, Simcenter STAR-CCM+ In-cylinder prints an error message in the Output window and restores the previous values. In that case, you are advised to investigate if the valve timing or compression ratio parameters are invalid.
  5. Click Close.
The Engine Geometry properties (except for Bore) and the Piston Position Offset define the motion of the piston. When you run the simulation, Simcenter STAR-CCM+ In-cylinder uses these properties to calculate the piston position for the respective crank angle and updates the geometry accordingly. However, as long as you do not start the simulation, the Graphics window displays the piston position using the default values. In the bottom left corner, the red-colored starred text indicates that the displayed piston is not at its correct position for the displayed crank angle. Additionally the warning triangle () on the Engine > Cylinder node indicates that this Engine Part requires an update.
  1. If you want to visualize the piston position according to your settings, click Update.