CAT3410 Diesel Engine Emission Characterisation

OBJECTIVE

The objective of this study is to set up a flow simulation within CAT3410 diesel engine cylinder and study emission charateristics for two different types of piston profile: Open W and Omega.

The following engine parameters will be considered

Bore=0.13716m

Stroke=0.1651m

Connecting rod length=0.263m

Engine Speed=1600 rpm

The simulation process includes three major steps:

1. Preprocessing

    1.1. Geometry Import 

    1.2. Diagnosis

    1.3. Case Setup

2. Solving

3. Post Processing

   3.1. Plots (NOx, Soot and Unburnt Hydrocarbon)

   3.2. Animation

PROCEDURE

1. Preprocessing

1.1. Geometry Import:

The geometry of the open w piston was created by 'Make Engine Sector Surface' tool in converge.

Steps:

a. In the utility window click on extract profiles from surface.dat, open the Open W piston surface file

b. click on new file and again reopen the 'Make Engine Sector Surface' tool

c. Provide the values for bore, stroke and connecting rod values as 0.13716m, 0.1651m, 0.263m respectively

d. Untick the compression ratio and provide a value of 17.5

e. Then click on use bowl profile and import the bowl_piston from the files extracted in the earlier step

f. Enter the sector angle of 60 deg and click on make surface

For Open W piston: The geometry is given below:

Followed the same steps for Omega piston as well and the following figure was generated

1.2. Diagnosis: The diagnosis tool helps in identifying the different problems in the                    geometry. 

      The Diagnosis tool looks for the following geometric issues

     a. Intersection: Highlights number of triangles with piercing inbetween adjacent two                 triangles

     b. Nonmanifold Vertices: Checks for number vertex which are being shared between two           triangles

     c. Open Edge: This highlights the number of edges of a triangle which not shared by any           other triangle

     d. Normal Orientation: This highlights the number of traingles whose normal vector is               not pointing towards the interior of fluid domain

     e. Isolated Triangles: This checks for the number of triangle surrounded by any                         neighbouring triangles that have different boundary ID number

    Goto Diagnostics Dock>Find>

       

Since all the problem traingles are green ticked, there were no issues in the geometry

1.3. Case Setup:

Case Setup for Open W Piston:

Settings Values to be Entered/Selected
Application IC-Engine (Crank angle-based)
Material Tick on Reaction Mechanism
Gas simulation>No Change
Parcel Simulation> Add>DIESEL2
Global Transport Paramters>No  Change
Reaction Mechanism>Import the Mech.dat file provided
Species> Goto Parcel tab>add DIESEL2, Add HIROY_SOOT and NOX under the 'Passives' tab
Simulation Parameters Run Paramters> Transient
Simulation Time Parameter>
Start Time: -147 deg.
End time: 135 deg.
Initial time step:5e-07 s
Minimum time step:1e-08 s
Maximum time step: 2.5e-05 s
Solver Parameters> No Change
Boundary Conditions  Piston:
Boundary Type>Wall
Velocity Boundary Conditions: Wall Motion Type>Translating, Surface Movement>moving, select 'Law of Wall' from the list
Temperature Boundary Conditions: select 'Law of Wall' from the list, Temperature value>553k

Front and Back Face:
Boundary Type>Periodic
Periodic type>stationary
Angle>60deg
Matching Face>Back Face

Cylinder Wall:
Boundary Wall>Wall
Wall Motion Type>Stationary, select 'law of wall' from the list
Temperature Boundary Condition> Law of Wall, temp value>433k

Cylinder Head:
Boundary Type>Wall, Wall motion>stationary, select 'Law of Wall' in both velocity and temperature boundary condition, temp value> 523k

Assign: Incylinder Region to all the Boundaries
Initial Conditions & Events Regions and Initialization
Regions and Initialization
Add region>Incylinder Region
Stream ID: 0
Temperature: 355k
Enter Pressure value:197000.0Pa
Species: Add N2, O2, CO2, H2O and put the mole fractions as 0.23029, 0.76765, 0.0014304, 0.0006296 respectively

Passive: Hiroy_Soot: 0, NOx:0
Physical Models

Tick combustion and spray modelling
Turbulence Modeling-RNG-K Eplison is selected

Spray Modelling Setup:

Combustion Modelling Setup:

Grid Controls

Base Grid:
Enter the grid values for (dx, dy, dz) as per
dx = 0.0014 m; dy = 0.0014 m; dz =0.0014 m
Activated Adaptive Mesh Refinement and Fixed Embeddding from the menu
Adaptive Mesh Refinement-Add AMR Group>AMR groups>tick on Velocity and Temp
Select the Incylinder region under Avialable Region and click on => to shift it to active regions

Fixed Embedding-

 

Output/Post Processing

Post Variable Selection>Goto Species and add the following

Output Files Time Interval for writing 3D output data files: 2 deg
Time Interval for writing text output: 0.1 deg
Time Interval for restarting output: 5 s

Note:

1. For Omega piston all the setting were similar only the piston bowl profile was for Omega piston

2. Converge's Make Engine Sector Surface utility automatically flags the boundaries so no addtional boundary flagging is required.

 

2. Solving:After this all the input files was imported to a seperate folder. Converge creates .txt  files which contains all the values entered while setting up the case for respective settings done above. These input files will be processed by converge using Message Passing Interface (MPI) standard

For running the simulation, Cygwin tool was used instead of converge studio interface. Cygwin is a POSIX-compatible API which is based on command prompt is used to run the simulation

Steps:

a. Navigated to the folder location containing the input files

b. Entered the command> mpiexec.exe -n 2 converge.exe logfile & : This allows converge to run two processors (selection on number of processor cores present as per the system configuration, can use multiple cores if available) for the parallel processing and load balancing

c. Entered the command> taif -f logfile

d. After the simulation is over. Went back to converge studio>Post-Processing 3D

e. Enter Case Name>"Test", Change the File Type to Paraview VTK in-line binary format

d. Enter the address for the output files>Select all files>Select all Cell Variables>click on Convert

e. After the conversion of the post files to the binary output, open the Test.vtm (group file) file in Paraview

 

3. Post-Processing:

                  Fig 1: Open W Piston Vs Omega Piston Cell Count Plots

                  Fig 2: Open W Piston Vs Omega Piston Soot Plots

                  Fig 3: Open W Piston Vs Omega Piston NOx Plots

                  Fig 4: Open W Piston Vs Omega Piston Mean Temperature Plots

                  Fig 5: Open W Piston Vs Omega Piston CO Plots

                  Fig 6: Open W Piston Vs Omega Piston Spray Penetration Plots

                  Fig 7: Open W Piston Vs Omega Piston HC Plots

                  Fig 8: Open W Piston Vs Omega Piston C7H16 Plots (Unburnt HC)

Animation:

Open W Piston:

Soot

NOx

yC7H16

 

Omega Piston:

Soot

NOx and yC7H16

 

CONCLUSIONS:

1. The imep for Open W and Omega piston was generated using a tool called 'engine performance' available in the line plotting window.

For Open W Piston

imep: 1.24e06 Pa

Indicated power=imep*L*A*N/3600=5.37 KW

For Omega Piston

imep: 1.39e06 Pa

Indicated power=imep*L*A*N/3600=6.03 KW

2.The power generated by omega piston is more than open w owing to the higher indicated mean effective pressure

3. The temperature of the Omega piston is higher than Open w type, thus the higher NOx  formation can be observed. Omega piston gives out less soot and CO as compared to Open w type piston

4. Unburnt hydrocarbons are generated more in Omega piston as the spray penetration is lesser as compared to open w type thereby resulting to the less efficient atomization of the fuel. However, more soot is generated by Open type piston due to lower operating temperature. 


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