Chapter 18 DIESEL ENGINE: POST-PROCESSING

The following tutorial data files are used in this chapter:

SECTOR_TUTORIALS/droplets.inp

SECTOR_TUTORIALS/scriptDroplets.sh

This chapter presents a tutorial for post-processing solution data for diesel models in both es-ice and pro-STAR.

es-ice can create scatter plots from information contained within a scatter data file (es-ice_phi-t.pos). This file is used here to create a scatter plot of equivalence ratio vs. gas temperature for every cell in the cylinder. Individual data sets are supplied at the crank angles specified by using the Postsetup tool in the Star Controls panel (see Chapter 17, “Post setup” of this volume).

pro-STAR can produce three-dimensional images displaying droplets within the model geometry; a feature that can be used to analyse spray characteristics inside the engine cylinder at any time step. A series of images can also be exported at each time step so that you can create animations of the transient solution using third-party software.

The tutorial covers the following operations:

1.Creating a scatter plot displaying equivalence ratio versus temperature

2.Creating a three-dimensional animation of fuel spray inside the cylinder throughout the simulation

Examples of general post-processing techniques are also given in Chapter 9 of this volume.

Creating a Scatter Plot

This section describes a scatter plot creation using the es-ice Graph Tool. The plot displays equivalence ratio versus temperature at 734 degrees CA.

First, load the es-ice scatter data file (es-ice_phi-t.pos) into the Graph Tool.

•Launch es-ice in the usual manner

•In the Select panel, click Post-process. The Graph Tool is included in the Post-process panel by default.

•Click the ellipsis (...) button and select es-ice_phi-t.pos from the file browser

•Select Scatter POS file from the drop-down menu

•Click Read

To plot a graph of equivalence ratio versus temperature at 734 degrees CA:

•Select item 2 in the list, labelled Phi-T: cylinder 1 angle 734

•Click Plot

Now modify the data range and add grid lines and labels to improve the graph appearance, as shown in Figure 18-1.

•Select the Domain toggle button

•Enter 0 and 3000 in the next two text boxes to cover a suitable data range

•Select Lines (as opposed to Ticks) from the drop-down menu and enter 6 in the adjacent box

•Set the Label to Temperature

•Select the Range toggle button

•Enter 0 and 10 in the next two text boxes to cover a suitable data range

•Select Lines (as opposed to Ticks) from the drop-down menu and enter 10 in the adjacent box

•Set the Label to Equivalence Ratio

Figure 18-1 Equivalence ratio versus temperature scatter plot

Creating a Spray Droplet Animation

This section gives an example of how you can use a pro-STAR input file (droplets.inp) to create an animation of fuel injection during the simulation.

Opening the input file with a text editor will display its contents, as shown in the following section. For clarity, the full command names have been used although the usual four-letter abbreviations can be substituted for them.

•Connect the events file and load the transient data

RESUME, , EVFILE, CONNECT TRLOAD, ,

•Create a custom colour table for use with the colour scale

CLRTABLE, POST, 1, 1.00, 0.00, 0.00, 1.0 CLRTABLE, POST, 2, 1.00, 0.20, 0.00, 1.0 CLRTABLE, POST, 3, 1.00, 0.40, 0.00, 1.0 CLRTABLE, POST, 4, 1.00, 0.55, 0.00, 1.0 CLRTABLE, POST, 5, 1.00, 0.70, 0.00, 1.0 CLRTABLE, POST, 6, 1.00, 0.80, 0.00, 1.0 CLRTABLE, POST, 7, 1.00, 0.90, 0.00, 1.0 CLRTABLE, POST, 8, 1.00, 1.00, 0.00, 1.0 CLRTABLE, POST, 9, 0.85, 1.00, 0.10, 1.0 CLRTABLE, POST, 10, 0.70, 1.00, 0.25, 1.0 CLRTABLE, POST, 11, 0.55, 1.00, 0.40, 1.0 CLRTABLE, POST, 12, 0.40, 1.00, 0.55, 1.0 CLRTABLE, POST, 13, 0.25, 1.00, 0.70, 1.0 CLRTABLE, POST, 14, 0.10, 1.00, 0.85, 1.0 CLRTABLE, POST, 15, 0.00, 1.00, 1.00, 1.0 CLRTABLE, POST, 16, 0.00, 0.90, 1.00, 1.0 CLRTABLE, POST, 17, 0.00, 0.80, 1.00, 1.0 CLRTABLE, POST, 18, 0.00, 0.70, 1.00, 1.0 CLRTABLE, POST, 19, 0.00, 0.55, 1.00, 1.0 CLRTABLE, POST, 20, 0.00, 0.40, 1.00, 1.0

•Specify a 20-colour scale with a user-defined value range of 0 to 0.2

CSCALE, 20, USER, 0, 0.1

•Set up the display items

PLLOCALCOOR, OFF, ALL PLDISPLAY, OFF, ALL PLDISPLAY, ON, LOGO PLDISPLAY, ON, HEAD PLDISPLAY, ON, MINMAX PLDISPLAY, ON, SCALE, ,8 PLMESH, OFF

•Set up the viewing position

VIEW, -1, 1, 1 CENTER, 40, 0, -42 DISTANCE, 60

•Select the Extended Graphics option and set up image output with a 1024 x 768 image resolution

TERMINAL, , EXTE

HRSDUMP, IMAGE, 1024, 768

•Specify the cylinder geometry colour

CLRTABLE, GEOM, 10, 0.6, 0.6, 0.6, 0.3 CTABLE, 501, FLUID, 10

CSET, ALL CMODIFY, CSET

•Collect the piston surface data into a cell set

CTABLE, 502, FLUID BSET, NEWSET, REGION, 6 CSET, NEWSET, BSET CMODIFY, CSET

•Set up the droplet display options

DOPTION, EDGE, OFF DOPTION, PERIMETER, 1

DOPTION, RADIUS, CONSTANT, 0.1 DOPTION, VECTOR, NONE, 1

•Increase the memory allocation

MEMORY, MAXDRP, 500000 MEMORY, MAXSC2, 1E7

•Set up a variable, it, which is incremented at each loop iteration and begin the loop definition

*SET, it, 1, 1 *DEFINE, NOEXECUTE

•Store the next time step

STORE, NEXT

•Set up a crank angle display label positioned in the lower-right corner of the

screen

*GET, TIME, time

*SET, CRANK, 1100 * TIME * 6 + 680 TSCALE, 4, 15

PLLABEL, 1, FORMAT, , 4, 10, 0.5 CRANK

F6.1, ' degCA'

•Merge vertices for a clear view of the display

CSET, ALL

VSET, NEWSET, CSET VMERGE, VSET

•Read and plot droplets at the current time step

PTREAD, , TIME DSET, ALL POPTION, GEOM CPLOT

DOPTION, FILL, COLOR, 0 DPLOT

•Create a pro-STAR “layer” for the droplet display

LAYER, DROP, STORE LAYER, DROP, HIDE

•Plot cell-averaged fuel scalar data on the piston surface

GETCELL, CONC, 1

CSET, NEWSET, TYPE, 502 CAVERAGE, CSET

POPTION, CONT CPLOT

•Create a layer for the fuel scalar display

LAYER, CONT, STORE LAYER, CONT, HIDE

•Show all layers

LAYER, ALL, SHOW REPLOT

•Create a counter for the filenames

*SET, itn, 1000 + it *SCOPY, itn, sitn, i4

•Export the current plot to a .gif file

*SSET, sname, image_1_{sitn} HRSDUMP, GIF, {sname}

•End the loop definition and then execute the loop for all time steps

*END

*LOOP, 0, 60

Note that useful information on creating post-processing input files can be found in the pro-STAR Commands and Post-Processing User Guide volumes of the STAR-CD documentation set.

Input files can be used with pro-STAR in batch mode to generate images and animations without opening the GUI. This facility is useful for producing consistent output from a number of different models and thus simplifying the comparison of results.

For Windows systems, off-screen rendering using pro-STAR is not currently supported. This means that the ability to use pro-STAR in batch mode to generate images and animations is not available. However, you can use input files within the pro-STAR GUI by issuing the following command:

IFILE, droplets.inp

Note that when importing an input file via the pro-STAR GUI, you need to add a c after the TRLOAD, , and VMERGE, VSET commands as the software prompts you to continue listing. This addition is not required when pro-STAR is running in batch mode as the software does not prompt for input.

An example of a Linux script for creating a droplet movement animation in batch is given below. The script employs third-party software (Gifsicle) to create animations and uses several .gif files. This software can be substituted by a different application if Gifsicle is unavailable.

•Run pro-STAR in batch mode, with input redirection to disable prompts, and load the sector.mdl model file

$STARDIR/bin/prostar gl -b << EOF star

y y

•Import the input file and run the commands

IFILE, droplets.inp

•Quit pro-STAR without saving and complete the input redirection

QUIT, NOSAVE

EOF

•Create an animation called droplets.gif using Gifsicle gifsicle -d 10 -l -o droplets.gif image*.gif

Figure 18-2 shows the fuel droplets and fuel concentration on the piston surface.

Figure 18-2 Fuel droplets and fuel distribution on piston surface.