Surface preparation and Boundary Flagging of a PFI Engine

OBJECTIVES:

• Setup PFI engine in CONVERGE.

SCOPE:

• Clean up CAD and extract fluid domain.
• Prepare and verify FV model of PFI Engine.
• Understand the mesh movement in PFI Engine.

SOFTWARE USED:

• Converge, Case setup - To prepare FV model and setup cases of CHT.
• Converge, Post-Processing 3D - To convert .out files of converge to Paraview readable format.
• ParaView 5.7.0 - To perform Post Processing.

DESCRIPTION:

In this project, we are provided with PFI Engine ".stl" file as the input. This geometry is then imported to CONVERGE software. The geometry looks as below:

Fig 1. PFI Engine Geometry

The next step involves in running diagnosis for the imported geometry. This procedure is followed to make sure that there is no error in the fluid domain (i.e., with a closed fluid geometry). The the diagnostic tools is runned, the following errors are observed:

Fig 2. Error observed in the geometry when diagnosis tool is used.

Fig 3. Diagnosis dialog box

From the above figure we can observe the list of error that are found in geometry:

1. Intersections : 1574
2. Nonmanifold Problems : 5
3. Open Edges : 32
4. Normal Orientation : 214

Intersections: CONVERGE cannot use a surface containing triangles that intersect because an intersection would violate the concept of a consistent inside/outside orientation of the surface. This type of problem can be difficult to detect in a surface.CONVERGE Studio graphically represents parallel triangles that have been moved too close together and thus are considered intersecting.

Fig 4. Intersection Errors

Nonmanifold Problems: With the exception of special conjugate heat transfer cases, every edge in the geometry needs to be shared by exactly two triangles. If more than two triangles share a common
edge, thus forming a T-junction, this edge is a nonmanifold edge. It is impossible to have distinct inside and outside directions when a surface contains nonmanifold edges.

Fig 5. Nonmanifold Errors

Open Edges: In a closed triangulated surface, each triangle shares each of its three edges with exactlyone other triangle (except in special Conjugate Heat Transfer simulations). If an edge is part of only one triangle, this creates what is called a open edge.

Fig 6. Openedges error

Normal Orientation: CONVERGE requires the surface to have a properly defined inside (solved fluid side) and outside (non-fluid side). The normal vectors of all triangles (as defined by the right-hand rule) must point toward the fluid. One extra normal orientation step is required when a surface consists of multiple independent surfaces, as in the case of an object completely immersed within a fluid domain, such as a sphere immersed in (but not connected to) a box. For the immersed sphere, the normal vectors of the triangles must point away from the center of the sphere, since the solved fluid portion of the domain is outside of the sphere. The normal vectors of the box triangles must point inward, toward the sphere.

Fig 7. Normal Orientation error

These errors are cleared using basic geometric clean up tools. Once all these errors are cleared, we should get dialog box as shown below to make sure that the simulation run:

Fig 8. Diagnostc Tool box after clearing errors

Once these errors are clarified the next step involved is to split the boudaries and grouped using different boundaries:

Fig 9. Boundary Flagging - view tool bar

Fig 10. Geometry after boundary flagging is complete.

Once these steps are completed as per the above methods, we are at stage where the geometry preparation is completed and the next procedure is to setup the case for sunning the simulation.

The following are the input parameter for the IC Engine Simulation:

i. Engine Geometric Parameters

1. Bore =0.086 m
2. Stroke = 0.09 m
3. Connecting rod length = 0.18 m
4. RPM = 3000

ii. Run parameters

1. Simulation mode: No Hydro

iii. Simulation time parameters

1. Start time : -520 deg
2. end time : 120 deg

iv. Boundary conditions

1. Piston temperature - 450K
2. Liner temperature - 450K
3. Head temperature - 450K
4. Spark Plug temperature - 550K
5. Spark Plug electrode temperature - 600K
6. Exhaust ports temperature - 500K
7. Exhaut outflow - 1 bar
8. Exhaust outlflow temperature - 800k
9. Exhaust species concentration - Calculate the stoichiometric condition
10. Exhaust valve top temperature - 525K
11. Exhaust valve angle temperature - 525K
12. Exhaust valve bottom temeprature - 525K
13. Intake port - 1 temperature 425K
14. Intake port - 2 temperature 425K
15. Inflow pressure - 1 bar total pressure
16. Inflow temperature - 363K
17. Inflow species - Air
18. Intake valve top temperature - 480K
19. Intake valve angle temperature - 480K
20. Intake valve bottom temeprature - 480K

v. Initial conditions

• Intake port - 1 (closer to combustion chamber)
• ic8h18 - 0.025508
• o2 - 0.20157
• n2 - 0.77292
• Temperature - 390k
• pressure - 1 bar
• Intake port - 2 (away from combustion chamber)
• Air
• Temperature - 370K
• Pressure - 1 bar
• Cylinder
• Pressure - 1.85731 bar
• Temperature - 1360K
• Stoichiometric composition

vi. Injection Parameters

1. Fuel flow rate = 7.5e-4 Kg/second
2. Injection start time = -480.0
3. Injection duration = 191.2
4. Fuel temperature = 330K

The case setup is setup using the above parameters as follows:

i. IC Engine (crank angle-based)

Fig 11. IC engine dialog box

ii. Gas simulation

Fig 12. Gas simulation dialog box

iii. Reaction Mechanism

Fig 13. Reaction Mechanism

iv. Run parameters

Fig 14. Run Parameter

v. Simulation time parameters

Fig 15. Simulation Parameters

vi. Boundary

Fig 16. Boundary Conditions

vii. Regions and Initilization

Fig 17. Regions definition

viii. Base grid

Fig 18. Base Grid size

ix. Adaptive mesh refinement

Fig 19. Velocity based AMR

Fig 20. Temperature based AMR

x. Fixed embedding

Fig 21. Fixed Embedding

With the above parameters the case setup for IC engine is complete and is ready to be exported and run No-Hydro Simulation (i.e., simulation where the transport eqations are not solved but only the mesh is generated).

Fig 22. Exporting Input Files to run simulation

Once all the Input files are exported, it is ready for running the simulation using cigwin.The simulation summary is as follows once completed:

Fig 23. Simulation summary for No-Hydro

And the mesh movement is as follows:

Vid 1. PFI Engine mesh movement - No-Hydro Simulation