Surface Preparation and Boundary Flagging (PFI)

Aim: To perform No hydro simulation on SI8-PFI Engine model.

Geometry clean-up:

• Import the STL file in converge and run diagnosis in Converge CFD. The following are the error

1. Intersections
2. Nonmanifold problems
3. Open Edges
4. Normal orientation

Before cleaning the geometry, we have should flag a different boundary. Make use of boundary flag option to select the surface to assign them to an individual component. Use the Boundary fence option to assign fence to individual boundaries and flag them accordingly. The following are different boundary flag

• Piston

• Liner

• Cylinder head

• Exhaust Port

• Inlet Port

• Inlet Valve

• Exhaust Valve

• Spark Plug

When flagging the cylinder head we find that valve from intake port is superposing with the cylinder head, we can infer that the valve is pushed so high that it is part of the cylinder head as seen in the figure shown below:

To push the inlet valve in the downward direction we can use the option called translate. In translate select boundary in entity type. The direction vector can be obtained by the measure in the geometry tab. Select inlet valve bottom, inlet valve angle and inlet valve top boundary to be translated. The translated amount should be given 0.001.

To remove nonmanifold, delete nonmanifold triangle and patch them with patch option.

The problem triangle with normal orientation is due to the direction of the normal vector which has a different orientation from other triangles. To remove this error, we can use an option called normal in the transform tab.

The inlet port should be divided into two part, one part which has fuel spray and air and other part have air. To initialize fuel that comes into the combustion chamber we split the valve into two boundaries.

Case Setup:

• Select the IC engine in an application in begin case setup tab.

• The following are the data for the crank angle base.

• In the reaction mechanism, import the them.dat for the reaction mechanism of fuel

• Run parameter

Simulation mode: No hydrodynamic solver

• Simulation time parameters

Start time: -520 deg.

End time: 120 deg.

Initial time –step: 1e-07s

Minimum time-step: 1e-08s

Maximum time- step: 0.0001

• Boundary

Name	Region Name	Temperature (K)	Boundary Type	Wall Motion	Motion Profile
Piston	Cylinder region	450	Wall	Translating	Piston motion
inflow	Intake port -2 region	363	Inflow
Liner	Cylinder region	450	Wall	Stationary	Fixed
Cylinder head	Cylinder region	425	Wall	Stationary	Fixed
Exhaust port	Exhaust region	500	Outflow	Stationary	Fixed
Outflow	Exhaust region	800	Wall
Exhaust Valve top	Exhaust region	525	Wall	Translating	Exhaust_lift.in
Exhaust valve angle	Exhaust region	525	Wall	Translating	Exhaust_lift.in
Exhaust Valve bottom	Cylinder region	525	Wall	Translating	Exhaust_lift.in
Intake port	Intake port -1 region	425	Wall	Stationary	Fixed
Intake valve bottom	Cylinder region	480	Wall	Translating	Intake_lift.in
Intake valve top	Intake port -1 region	480	Wall	Translating	Intake_lift.in
Intake valve angle	Intake port -1	480	Wall	Translating	Intake_lift.in
Spark Plug terminal	Cylinder region	600	Wall	Stationary	Intake_lift.in
Spark Plug	Cylinder region	550	Wall	Stationary	Fixed
Intake port 2	Intake Port -2 Region	425	Wall	Stationary	Fixed

• The inflow boundary has a mass fraction of 1 which contain the constituents of air, Nitrogen (0.77) and Oxygen (0.23).
• The following reaction takes place in the combustion chamber:

• Stoichiometric Calculator at Outflow

Species	Moles	Molecular Weight (g/ mol)	Mass	Mass Fraction
`CO_2`	8	44.01	352.08	0.192304
`H_2 O`	9	18.01528	162.1375	0.088559
`N_2`	47	28.0134	1316.63	0.719137
Total			1830.847	1

• Region and initialization

The following are different region should be specific

• Cylinder Region

• Intake Port -1

• Intake Port -2

• Exhaust Region

• Events: The combustion chamber must be connected and disconnect from the intake and exhaust region based on the valve timing.

As the Intake port-1 and intake port -2 regions must remain open throughout the cycle. So, the permanent event should be specified.

• The RNG k-ε model is used for calculated turbulence.
• The base grid of dx=0.004, dy=0.004, and dz=0.004 is used.
• The fixed Embedding is provided to refine the grid at a specified location to improve the accuracy of our solution. At intake vale bottom and exhaust valve bottom the fixed embedding with permanent mode, the scale of 3 and embed layers of 1 is provided.

The cylinder type fixed embedding is provide at the combustion chamber and cylinder head. The below figure shows the fixed cylinder embedding.

• For writing output file the following parameter are provided

Time interval for writing 3D output data file: 2 deg.

Time interval for writing text output: 0.1 deg.

Time interval for writing restarting output: 10 deg.

• The following animation shows the movement of the piston, intake valve, and Exhaust valve according to the motion of the crack shaft.