Geometry Requirements

For the automated setup of an internal combustion engine in Simcenter STAR-CCM+ In-cylinder, the geometry that you import must meet certain criteria. These criteria concern the file format as well as the positions and names of bodies and faces.

A full-cycle analysis of a four-stroke or two-stroke engine includes the gas exchange between cylinder and ports. Therefore, Simcenter STAR-CCM+ In-cylinder requires the import of a full single-cylinder engine geometry including cylinder, valves, and ports.

Furthermore, you can import geometries of additional parts that are static and attached to the engine, referred to as plenums. Examples of plenums are:

  • Pre-chambers—separate chambers attached to the cylinder head for jet ignition
  • Intake runners—tubes that channel intake air to the intake ports
  • Gas admission valves (GAVs)—valves that introduce gaseous fuel into the engine

A closed-cycle analysis usually investigates the injection and combustion process in a cylinder with all intake and exhaust valves closed. For axisymmetric cylinder geometries, Simcenter STAR-CCM+ In-cylinder allows you to model these stages of the engine cycle in only a sector of the actual cylinder geometry without considering the ports and valves in order to reduce runtime.

Depending on whether you want to perform a full-cycle analysis or a closed-cycle analysis using a cylinder sector model, Simcenter STAR-CCM+ In-cylinder requires that you import the engine geometry using one of the following file formats:

Engine Analysis File Format
Full-cycle

(using full engine geometry)

 A 3D model file saved as Boundary Representation (BRep) in one of the following CAD-based formats:
  • .x_t/.x_b - Parasolid Transmit file
  • .iges/.igs - IGES file
  • .step/.stp - STEP file
  • .vda - VDA file
  • .prt/.asm - Pro/ENGINEER file
  • .model/.exp/.session - CATIA V4 file
  • .catpart/.catproduct - CATIA V5 file
  • .sldprt/.sldasm - SolidWorks file
  • .prt - NX file
  • .par/.asm - Solid Edge files
  • .ipt/.iam - Inventor file
  • .3dm - Rhinoceros 3D Model file
  • .jt - JT Open B-rep file

The import process supports geometries that are geometrically and topologically valid from the Parasolid kernel point of view. Additionally, in your CAD package, the maximum tolerance value must be less than 5.0E-5 m.

Depending on the type of internal combustion engine—four-stroke or two-stroke— Simcenter STAR-CCM+ In-cylinder requires you to prepare the CAD bodies and faces of the engine geometry as described in one of the following sections:

Closed-cycle

(using cylinder sector)
  • *.csv - comma separated values file that contains the coordinates of a 2D spline that describes the profile of the cylinder sector in mm.

The knots of this spline must be at y = 0 and the cylinder axis must coincide with the z-axis.

The file must have two (X, Z) or three columns (X, Y, Z). For a three column table, Simcenter STAR-CCM+ In-cylinder ignores the Y column.

The import process supports the following types of 2D splines:

Full 2D Section
A closed spline that describes the profile of the cylinder sector with the piston at TDC position.


The spline must start with the definition of the piston at x=0, grow out radially towards the radius tip, and then go up along the liner. From there it continues with the defintion of the head back towards at the center (x = 0), and then grows down along the z-axis back to the starting point.
The first knot of the spline must match the last knot.
Piston Bowl Only (At BDC)
An open spline that describes the profile of the piston at BDC position.


This spline must start at x=0 and end at the radius tip.
Simcenter STAR-CCM+ In-cylinder automatically creates a flat cylinder head at z=0 and closes the spline between the end points of the cylinder head and the piston (black lines).
Head and Piston Bowl (At BDC)
An open spline that describes the profile of the piston and the cylinder head at BDC position.


The file must start with the definition of the piston spline followed by the spline for the head. The piston spline must start at x=0 and end at the radius tip. The spline for the head must start at (x,z) = (0,0) and end at the radius tip.
Simcenter STAR-CCM+ In-cylinder automatically closes the spline between the end points of the cylinder head and the piston (black lines).