Encyclopaedia Index

WORKSHOP - Combustion: ESCRS

Overview

The case considered is the zero-swirl gas-fired axisymmetric combustion chamber used in the experiments of Owen et al (16th Int. Symp. on Combustion, p105-117, 1976). The geometry comprises a 0.122m diameter tube into which natural gas (96%CH4) is injected at 288K axially to mix and burn with a coaxial annular air stream at 750K. The inlet air/fuel equivalence ratio is 0.9, and the combustor operating pressure is 3.8 atm. The length of the solution domain is taken as 4 furnace diameters.

Calculations can be made with one of 4 different combustion models, all part of the Extended Simple Chemically Reacting System (ESCRS):

  1. fast-chemistry model with a 1-step global irreversible methane reaction to form CO2 and H2O;
  2. as (1) but with an assumed double-delta pdf to account for the influence of concentration fluctuations;
  3. eddy-break-up finite-rate chemistry model with a 1-step global irreversible reaction; and
  4. as (3) but with a 2-step global reaction mechanism involving the intermediate CO.

The setup is based on library case C302. Results of the library case and comparisons with data are given in the Application Album.

Accessing PHOENICS-VR.

From the system level:

To enter the PHOENICS-VR environment, click on the PHOENICS icon on the desktop, or click on Start, programs, PHOENICS, PHOENICS.

From the commander level:

To enter the PHOENICS-VR environment, click on the 'Run vre' icon in the left column.

In PHOENICS-VR environment,

Start with an 'empty' case - click on 'File' then on 'Start New Case', then on 'Core', then click on 'OK'; to confirm the resetting.

To enter VR Editor:

This is the default mode of operation.

Within VR Editor.

Set the domain size and grid numbers:

Click on 'Menu' (Main Menu) on the VE-Editor panel; and set 'Combustion ESCRS' as the Title.

Click on 'Geometry'.

Click on 'Cartesian' under co-ordinate system; and select 'Cylindrical-polar' and then on 'OK'.

Leave 'Inner radius' at 0.0 and 'tolerance' at 1.e-3.

Change the x-domain size to 0.1 radians.

Change the y-domain size to 0.061 m.

Change the z-domain size to 0.488 m.

Set 'number of cells' to 1 in x-direction, 30 in the y-direction and 40 in the z-direction.

Click on 'OK' to close the Grid mesh settings dialog.

Click on 'OK' to exit from 'Menu'.

Click on 'Reset' button on the movement panel.

Click View -X and Up +Y

Click on 'Fit to Window'

 

Activate solution of the required variables and models

Click on 'Menu'; and then on 'Models'.

Leave 'Solution for velocities and pressure' to ON.

Click on ENERGY EQUATION; and then choose ENTHALPY and toggle STATIC to TOTAL.

Click on 'Turbulence models' and choose the KEMODL.

Click 'Top Menu' and 'OK' to close the Main Menu.

ESRCS model settings

The ESCRS model is set by a set of SCRS commands described in the Encyclopaedia. Please note that the SCRS commands can not be made in the VR-Editor.

The  VR-Editor settings and PIL settings need to be combined in the Q1 file in order to complete the entire setting of the input data.

Once the geometry and models settings are completed, click on 'File', open file for editing, 'Q1' to open and edit the Q1 file. Click 'Yes' when prompted to save the current VR settings to Q1.

Now add the PIL statements for the chosen model to Group 9 of the q1 file. The easiest way to do this is to highlight the text in the browser, right-click and copy it, then paste it into the Q1 at the end of Group 9.

There are four possible combustion models to activate. Click on the appropriate link to jump to the PIL settings for the required model.

  1. fast-chemistry model with a 1-step global irreversible methane reaction to form CO2 and H2O;
  2. as (1) but with an assumed double-delta pdf to account for the influence of concentration fluctuations;
  3. eddy-break-up finite-rate chemistry model with a 1-step global irreversible reaction; and
  4. as (3) but with a 2-step global reaction mechanism involving the intermediate CO.

Fast-chemistry model 

TEXT(ESCRS - Fast Chemistry
INTEGER(NSPEC,NELEM);NSPEC=7;NELEM=4
INTEGER(NCSTEP,NCREAC)
NCSTEP=1;NCREAC=1
SCRS(SYSTEM,NCSTEP,NCREAC,NELEM,FASTC)
SCRS(SPECIES,CH4,O2,H2,CO,H2O,CO2,N2)
SCRS(PROP,CHEMKIN,SCH4)

Click here to jump to the next step.

Fast-chemistry with double-delta pdf

TEXT(ESCRS - Fast Chemistry with double-delta pdf
INTEGER(NSPEC,NELEM);NSPEC=7;NELEM=4
INTEGER(NCSTEP,NCREAC)
NCSTEP=1;NCREAC=1
SCRS(SYSTEM,NCSTEP,NCREAC,NELEM,FASTC)
SCRS(SPECIES,CH4,O2,H2,CO,H2O,CO2,N2)
SCRS(PROP,CHEMKIN,SCH4)
SCRS(PDF,DDELTA)

Click here to jump to the next step.

1-step Eddy-breakup

TEXT(ESCRS - 1 Step Eddy-breakup
INTEGER(NSPEC,NELEM);NSPEC=7;NELEM=4
INTEGER(NCSTEP,NCREAC)
NCSTEP=1;NCREAC=1
SCRS(SYSTEM,NCSTEP,NCREAC,NELEM,FRATE*)
SCRS(SPECIES,CH4,O2,H2,CO,H2O,CO2,N2)
SCRS(PROP,CHEMKIN,SCH4)
SCRS(EBU,P,6.0)

Click here to jump to the next step.

2-step Eddy-breakup

TEXT(ESCRS - 2 Step Eddy-breakup
INTEGER(NSPEC,NELEM);NSPEC=7;NELEM=4
INTEGER(NCSTEP,NCREAC)
NCSTEP=2;NCREAC=2
SCRS(SYSTEM,NCSTEP,NCREAC,NELEM,FRATE*)
SCRS(SPECIES,CH4,O2,H2,CO,H2O,CO2,N2)
SCRS(PROP,CHEMKIN,STWO)
SCRS(EBU,P,6.0);SCRS(EBU,S1,1.0)

Common settings

The following PIL settings are common to all of the models. They should be pasted in after the model-specific lines.

REAL(YFUIN,YOXIN,YN2IN,TINA,TINF)
YFUIN=1.0;YOXIN=0.232;YN2IN=1.-YOXIN
TINA=750.;TINF=288.
STORE(MMWT,MCO,MCO2)
SCRS(FUIN,YFUIN,0.0,0.0,0.0,0.0,0.0,0.0,TINF)
SCRS(OXIN,0.0,YOXIN,0.0,0.0,0.0,0.0,YN2IN,TINA)

After the above editing is completed, save the Q1 file and exit the text editor. Allow the VR-Editor to reload the Q1 on exit from the file editor. We can now continue the rest of the settings through the VR-Editor.

 

CHEMKIN data file

The ESCRS uses a CHEMKIN link file to specify the elements and species present, and the reactions taking place. The first three options use the file SCH4.CKM, and the 2-step reaction uses STWO.CKM. Both files can be found in the directory /phoenics/d_earth/d_opt/d_chem.

The contents of SCH4.CKM are:

ELEMENTS C O H N END
SPECIES CH4 O2 H2 CO H2O CO2 N2 END
REACTIONS
2CH4 + 4O2 => 2CO2 + 4H2O 0. 0. 0.
END

The contents of STWO.CKM are:

ELEMENTS C O H N END
SPECIES CH4 O2 H2 CO H2O CO2 N2 END
REACTIONS
2CH4 + 3O2 => 2CO + 4H2O 0. 0. 0.
2CO + O2 => 2CO2 0. 0. 0.
END

To generate the CHEMKIN link file, click 'Run', 'Pre-processor', 'CHEMKIN Interpreter'. In the dialog that appears, click 'Browse', and navigate to the SCH4.CKM or STWO.CKM files. Select the appropriate one. Click OK to run the interpreter. The result should be the files sch4ckln, sch4mcln and sch4.lis or  stwockln, stwomcln and stwo.lis in the current working directory.

Specify properties

Click on 'Menu'; and then 'Properties'.

Toggle 'Use property table' to OFF

Set viscosity to 4.2E-05

Toggle 'Storage' for all properties to ON.

Click 'Page Dn' button and set

Click 'Conductivity', select 'CONST_PRANDTL_NO' and set Prl = 1.0;

Thermal expansion coefficient Beta =0.0;

Reference Press (Pa)=3.8E5;

Reference temp(K) = 0.0

 

Set Initial values

Click on 'Initialisation'.

Leave default values for all variables except for:

 

Source settings

Click on 'Sources'

Toggle 'Use Earth-Generated wall functions': EGWF to F

 

Enter numerical settings

Click on 'Numerics'.

Set 'Total number of iteration' to 400

Click 'Relaxation control' and set the following values:

Auto calculation of false time-steps (SARAH) - 0.005

  1. fast-chemistry model with a 1-step global irreversible methane reaction to form CO2 and H2O;
    P1 KE EP H1 DEN1 F
    -0.5 -0.2 -0.2 -0.2 -0.05 -0.5
  2. as (1) but with an assumed double-delta pdf to account for the influence of concentration fluctuations;
    P1 KE EP H1 DEN1 F
    -0.5 -0.2 -0.2 -0.2 -0.05 -0.5
  3. eddy-break-up finite-rate chemistry model with a 1-step global irreversible reaction;
    P1 KE EP H1 CH4 DEN1 F
    -0.4 -0.2 -0.2 -0.2 5.0E-4 -0.05 -0.4
  4. as (3) but with a 2-step global reaction mechanism involving the intermediate CO.
    P1 KE EP H1 CH4 CO DEN1 F
    -0.5 -0.2 -0.2 -0.2 1.0E-3 1.0E-3 -0.05 -0.2

Set Monitoring Options

Click 'Output' and 'Settings' next to Field Printout. Set 'OUTPUT 5 SPOT' and 'OUTPUT 6 TABL' to Y for CH4, (CO), TMP1 and DEN1. This will make the values of these variables at the probe location appear in the solver convergence monitor graph.

Click 'Top Menu' then 'OK' to close the Main Menu.

Create Objects and specify boundary conditions

Create the Oxidant Inlet

Click on 'Settings', 'New' and 'New Object'.

Change name to SCRSO.

Click on 'Size' and set Size of the object as:

Xsize:  0.1

Ysize: 0.016

Zsize: 0.0

Click on 'Place' and set POSITION of the object as:

Xpos: 0.0 0.1

Ypos: 0.0315

Zpos: 0.0

Click on 'General'.

Define Type: USER_DEFINED.

Click on 'Attributes'

Enter SCRSO in the 'NEW' input box, and click 'Apply'.

Change Type to 'LOW'

Set the Coefficient and value as shown below:

Variable P1 V1 W1 KE EP H1 CH4 F
Coefficient FIXFLU 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Value GRND1 0.0 19.6 15.4 6190.0 GRND3 0.0 0.0

 

Create the Fuel Inlet

Click on 'Settings', 'New' and 'New Object'.

Change name to SCRSF

Click on 'Size' and set Size of the object as:

Xsize:  0.1

Ysize: 0.0315

Zsize: 0.0

Click on 'General'.

Define Type: USER_DEFINED.

Click on 'Attributes'

Enter SCRSF in the 'NEW' input box, and click 'Apply'.

Change Type to 'LOW'

Set the Coefficient and value as shown below:

Variable P1 V1 W1 KE EP H1 CH4 F
Coefficient FIXFLU 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Value GRND3 0.0 0.91 0.033 0.31 GRND3 1.0 1.0

 

Create the outlet

Click on 'Settings', 'New' and 'New Object'.

Change name to Outlet.

Click on 'Size' and set Size as:

Xsize: 0.1

Ysize: 0.061

Zsize: 0.0

Click on 'Place' and set POSITION as:

Xpos: 0.0

Ypos: 0.0

Zpos: 0.488

Click on 'General'.

Define Type: OUTLET

Create the outer wall

Click on 'Obj'.

Change name to NWAL.

Click on 'Size' and set Size as:

Xsize: 0.1

Ysize: 0.0

Zsize: 0.488

Click on 'Place' and set Position as:

Xpos: 0.0

Ypos: 0.061

Zpos: 0.0

Click on 'General'.

Define Type: PLATE

 

Adjust grid distribution in Y and Z-direction

Click on 'Mesh toggle' button, and the grid will appears on the screen.

Click anywhere in the grid to bring up the 'Grid Mesh Settings' dialog.

Click on 'Edit all regions in Y direction'. Set 10 cells in each of the 3 regions. Click on 'OK'.

Click on 'Power/Ratio' for Z. Change from 1.0 to 1.4. This will compress the grid towards the inlet plane.

Click on 'OK'.

 

Set the Probe location

Move the probe to X=0.05, Y=0.006, Z =0.05. The convergence of the solver will be monitored at this point.

All the settings are now complete and the 'Solver' can be run.

Running the Solver.

In the PHOENICS-VR environment, click on 'Run', 'Solver' then 'Local solver(Earth)', and click on 'OK'; to confirm running Earth.

Using the VR Viewer.

In the PHOENICS-VR environment, click on 'Run', 'Post processor',then GUI Post processor (VR Viewer) Viewer)'. Click 'OK' on the file names dialog to accept the default files.

To view:

The image below shows the H2O mass-fraction distribution for option 3, single step Eddy-breakup.

To select the plotting variable:

To change the direction of the plotting plane, set the slice direction to X, Y or Z slice direction (927 bytes)

To change the position of the plotting plane, move the probe using the probe position buttons

probe position (927 bytes).

Saving the results.

In the PHOENICS-VR environment, click on 'Save as a case', make a new folder called 'COMBUST', select the new folder, and save as 'ESCRSn', where n is 1,2,3 or 4 depending on the combustion option.