Chapter 16

DIESEL ENGINE: SECTOR MODEL

Chapter 16 DIESEL ENGINE: SECTOR MODEL

The following tutorial data files are used in this chapter:

SECTOR_TUTORIALS/bowl.dbs

This tutorial describes the generation of a typical sector mesh, suitable for modelling diesel fuel injection and combustion. The main advantage of using a sector mesh is the run time reduction as you are only modelling a fraction of the actual cylinder volume. However, you cannot model the gas exchange phases as the sector mesh cannot handle valve opening and closing events. In addition, the piston bowl is assumed to be axisymmetric so you are unable to model valve pockets or similar features on the piston bowl. Therefore, sector meshing is best suited to modelling the fuel injection and combustion phase of axisymmetric cylinders.

The tutorial compliments the case described in Chapter 15 of this volume by using a similar cylinder geometry and the same operating conditions and engine characteristics. The piston geometry is now a 45° sector of the geometry used in Chapter 15, with the valve pockets removed. The generated volume mesh then only includes one of the eight fuel injectors. As the two cases share a similar set-up, this chapter only describes the es-ice sector meshing stage. To run the analysis, you must first go back to Chapter 15 to continue the physics set-up in es-ice and pro-STAR.

Figure 16-1 shows the bowl geometry used in this case and also an example of the analysis results to be expected from a sector mesh model.

Figure 16-1 Example of spray and liquid film results from a sector mesh analysis

Note that when producing piston bowl surface meshes for your own case, the bowl geometry must be at BDC. es-ice generates a spline that represents the bowl at TDC during the sector meshing process.

The steps to be followed in this tutorial are outlined below:

1.Import the piston bowl geometry surface

2.Create a 2D profile of the piston bowl shape

3.Generate a 2D template mesh

4.Generate a 3D sector mesh of the cylinder

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DIESEL ENGINE: SECTOR MODEL	Chapter 16
Importing the Bowl Geometry

Importing the Bowl Geometry

To import the geometry surface mesh:

•Launch es-ice in the usual manner

•In the Select panel, click Read Data

•In the Read Tool, click the ellipsis (...) button next to the DBase box and select bowl.dbs via the file browser

•Click the ellipsis (...) button next to the Get box and select 1 bowl geometry via the database browser

•In the Plot Tool, set the Views option to View 1 -1 1

•Click CPlot to display the imported bowl geometry shown in Figure 16-2

Figure 16-2 Bowl geometry surface

Defining the Bowl Shape

Based on the imported 3D surface mesh, es-ice requires a 2D profile of the bowl shape in order to generate a 2D section of the cylinder. The profile is used at a later stage to trim the 3D template and generate a cylinder volume mesh.

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Chapter 16	DIESEL ENGINE: SECTOR MODEL
	Defining the Fuel Injector

•Enter the following command to create a spline representing the 2D profile of the bowl:

Spline, 1, RadShell

If the bowl is not axisymmetric in your own case (e.g. it contains valve pockets), only include the axisymmetric part of the bowl in the current cell set before using the above command.

•In the Plot Tool, set Views View 0 -1 0 to display the spline, as shown in Figure 16-3

Figure 16-3 Displaying the spline representing the bowl

Defining the Fuel Injector

At this stage, you will create a coordinate system for the fuel injector. The origin of the coordinate system defines the point of injection and the z-axis defines the direction of the fuel spray. Alternatively, you can create the injector coordinate system after importing the model into pro-STAR.

•Enter the following command to create the injector coordinate system:

Local, 11, Cylinder, 1.5, 0, -1.2, 0, 0, 103

•In the Plot Tool, select the Local toggle button

•Click CPlot

•Enter the following command to view the injector coordinate system relative to the global coordinate system, as shown in Figure 16-4:

Zoom, MinMax, -30, -20, 165, 175, Plot

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DIESEL ENGINE: SECTOR MODEL	Chapter 16
Creating the 2D Template

Figure 16-4 Fuel injector coordinate system relative to the global coordinate system

Creating the 2D Template

The first step in creating the 2D template is to define the engine characteristics and operating conditions in the General parameters and Events parameters panels.

•In the Select panel, click Create Template

•In the Create Template panel, select Sector from the drop-down menu

•Click Events

•In the Events parameters panel (see Figure 16-5), set the Crank angle start (deg) to 680

•Set the Crank angle stop (deg) to 800

•Set the Engine RPM to 1100

•Set the Connecting rod length to 270

• Click Ok to accept the settings and close the panel

•In the Create Template panel, click Cylinder

•In the Cylinder parameters panel (see Figure 16-5), set the Piston stroke length to 158.54

•Click Ok to accept the settings and close the panel

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Chapter 16	DIESEL ENGINE: SECTOR MODEL
	Creating the 2D Template

Figure 16-5 Events parameters and Cylinder parameters panels

Next, create the 2D mesh template. In the following steps, you will set parameters in the Sector panel to define the cell count and cell distribution in certain parts of the template. For definitions and illustrations of these parameters, see Chapter 6, “Axisymmetric Sector Meshing” in the User Guide.

To begin creating the 2D mesh template:

•In the Create Template panel, click Make Sector

•In the Sector panel (Figure 16-6), click Create TDC Spline to create the bowl profile at the TDC position

•Set the Number of holes to 8 to define the total number of injectors in the cylinder

•Set the Azimuthal cells to 16

•Set the Minimum TDC layers to 5

•Select the Modify prisms toggle button and ensure that the adjacent value is set to 2

•Select the Edit toggle button and set the Radial cells to 60 (third column)

•Set the Axial cells to 130 (first column)

•Set the Axial block cells to 40 (first column)

•Click Create 2D

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DIESEL ENGINE: SECTOR MODEL	Chapter 16
Creating the 2D Template

Figure 16-6 Sector panel

Finally, create a plot of the 2D template overlaying the piston splines to check that enough cell layers have been defined to create a sector mesh.

•In the Plot Tool, select Geometry from the drop-down menu to activate the

Geometry window

•Enter the following command to remove the bowl surface mesh from the display:

CSet, None

•Select Workspace from the drop-down menu to activate the Workspace window

•Deselect the Fill toggle button

•Click DPlot to display the template on top of the bowl splines, as shown in Figure 16-8

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