Chapter 14	MULTIPLE CYLINDERS
	Saving the es-ice Model File

Figure 14-31 Multiple cylinder Star Controls > Time step control panel

Write Data

In the Write data view of the Star Controls panel:

•Accept the default settings and then click Write data to generate the files required by pro-STAR

Saving the es-ice Model File

Finally, save the model file and exit from es-ice.

•In the Select panel, click Write data to open the Write Tool

•Enter

save_es-ice.multiCylinderFinal and click Save to save the model file

•Close es-ice

The case can now be set up in pro-STAR, as described in Chapter 7 of this volume.

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Chapter 15

DIESEL ENGINE: FULL-CYLINDER CLOSED-CYCLE MODEL

Chapter 15 DIESEL ENGINE: FULL-CYLINDER

CLOSED-CYCLE MODEL

The following tutorial data files are used in this chapter:

CLOSED-CYCLE_POLYMESH/closed-cycleDiesel.dbs

CLOSED-CYCLE_POLYMESH/uisDiesel.dbs

PANELS/training.pnl

This chapter demonstrates an engine model set-up that uses the closed-cycle polyhedral meshing facility and includes a spray-optimised zone. A closed-cycle analysis occurs when all valves are closed and hence there is no gas exchange between the ports and cylinder. This stage of the engine cycle occurs during injection, ignition and the start of combustion, i.e. after the intake valves close and before the exhaust valves open. During this time, a number of important physical processes and property changes take place that must be accurately captured in the solution. A polyhedral mesh can usually model these highly dynamic conditions better than a trimmed mesh so it is often beneficial to use it under these conditions.

Polyhedral meshing also generates a spray-optimised mesh zone, employing hexahedral and pentahedral cells that are orthogonal to the spray direction. This type of mesh is better at tracking droplets and therefore better at modelling fuel injection. es-ice provides several parameters that can be used to modify the spray-optimised zone so that it matches the fuel spray characteristics. The interface between the spray zone and the surrounding polyhedral mesh has one-to-one cell connectivity which in turn improves solver stability and accuracy.

In order to model the piston motion, cell layers are added and removed between the upper and lower portions of the polyhedral mesh. The separation between these portions is determined by the ‘user intermediate surface’, which is a surface mesh imported into es-ice. In this tutorial, a user intermediate surface suitable for the current engine geometry and operating conditions is provided. Note that there are several points to consider when creating such a surface for your own cases, as described in “User intermediate surfaces” on page 6-34 of the User Guide.

This tutorial simulates the operation of a diesel compression-ignition engine in the interval between the intake valves closing and the exhaust valves opening (680 to 800 degrees crank angle). The fuel, n-dodecane with a cetane number of 60, is injected at 715.14 degrees crank angle for a duration of 7.11 degrees. A total of 0.8831×10–4 kg of fuel is injected through eight injectors during this period. The fluid in the cylinder is given an initial rotational velocity of 2,000 rpm about the z-axis, which induces turbulent fuel mixing after injection.

Table 15-1 summarises the engine characteristics and operating conditions.

Table 15-1: Engine characteristics and operating conditions

Bore	130 mm
Stroke	158.54 mm
Connecting Rod Length	270 mm
Speed	1100 rpm

The steps necessary to set up the tutorial are summarised below:

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DIESEL ENGINE: FULL-CYLINDER CLOSED-CYCLE MODEL	Chapter 15
Importing the Geometry

1.Import the engine geometry

2.Create the mesh using the closed-cycle polyhedral method

3.Set up the necessary Star Controls in es-ice

4.Set up the fuel injection, liquid film and analysis controls in pro-STAR

Importing the Geometry

The tutorial starts by importing a .dbs file containing a discretised surface that defines the engine geometry. Note that, as this tutorial is a closed-cycle analysis, the valves are closed and the ports are removed as they are not needed. Also, as for all es-ice geometry surfaces, the piston is at the TDC position (see Chapter 6, “Preparing the geometry” in the User Guide for more information on preparing geometry for closed-cycle analyses).

To import the surface:

•Check that closed-cycleDiesel.dbs is in your current working directory and then 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 closed-cycleDiesel.dbs via the file browser

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

•In the Plot Tool, click CPlot to view the imported geometry, shown in Figure 15-1

Figure 15-1 Closed-cycle engine geometry

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