Week 9: Project 1 - Surface preparation and Boundary Flagging (PFI)
Introduction
Fuel injection is the introduction of fuel in the internal combustion engine most commonly automotive engines by the means
of an injector. Port fuel injections long ago replaced carburetors in cars because of their efficiency and lower maintenance
requirements.
The fuel injector is installed in the intake manifold and they are cheap in production and do not have to withstand high
pressure from the combustion chamber. The fuel injector injects the fuel into the combustion chamber through the intake
valve owing to which the intake valve always remains and there is no carbon deposit in the intake valve. The major
disadvantage with respect to the other injection system is that it lacks efficiency (better fuel economy) with respect to the
other fuel delivery system.
Surface preparation and Boundary flagging
The geometry is loaded into the Converge-CFD environment and the diagnosis dock is selected. It was found that there are a
lot of errors viz Intersections(1574), Non manifold Problems(5), Open Edges(32), Normal orientation(214). Therefore
boundary flagging is required to hide the parts of the boundary to resolve all of the errors.
Piston
The piston boundary is selected by using the angle method from the boundary.
Inflow
The inflow boundary is selected by using the angle method
Liner
The liner is selected by using the boundary fence method, because by using the angle method the portion of the liner,
cylinder head, and the piston is selected. Therefore from the Geometry dock, "Fence" is selected and the "Arc" method is
selected from the top ribbon to flag the "Liner" using the "Boundary Fence" method.
Cylinder head
The cylinder head is selected by creating the fence around the intake and exhaust port, the other fence is already created
from the "Liner". The same is flagged by sing the "Boundary Fence" method. From the below snap it can be inferred that the
intake valve is so high that it is interfering with the cylinder head which forms the basis of intersection errors. In order to fix
these, the valve is pushed downwards to remove the intersection errors.
Exhaust port and Outflow
The exhaust port and the outflow are flagged by using the "Angle" method. After flagging, the two boundaries are hidden to
visualize the parts of exhaust valves.
Exhaust valve top, Exhaust valve angle, Exhaust valve bottom
The fences are marked as shown below to divide the exhaust valve into three boundaries. Once the boundaries are hidden
there are extra pieces that are visible which needs to be part of the exhaust port boundary. Thus "Box Pick" option is selected
from the top ribbon and the extra pieces are selected and flagged under the exhaust port boundary. The ring triangles need
to be part of the exhaust port. The extra pieces and the ring triangles are shown below.
Extra Pieces
Ring Triangle
Intake port
In order to select the "Intake port" the fence method is used. In the "Geometry" dock the "Fence" tab is selected and
"Reconstruct Fences From Existing Boundaries" is selected which will create the fences automatically from the Inflow and the
fences at the end of the intake port which is near to the cylinder head. The area is flagged by using the "Boundary Fence"
method.
Intake valve top, Intake valve angle, Intake valve bottom
The boundary fences already exist for the intake port. The new boundary fences are created for the intake valve bottom,
intake valve angle, intake valve top. The bottom region of the valve is selected by using the "Angle" method. In order to
select the angle portion of the valve, the fence is created at its two ends. The remaining portion is flagged to the Intake valve
bottom by using the option "Reconstruct Fences From the Existing Boundaries". The Intake valve bottom and angle
boundaries are hidden so that the portion which is left to flag is the Intake valve top boundary.
The new fence is created for the Intake valve top boundary as shown below and the "Boundary Fence" is selected to flag the
boundary.
Spark plug and Spark terminal
The Spark terminal is selected by using the Angle method. The fence is created around the Spark terminal by using
"Reconstruct Fences From Existing Boundaries". The base of the Spark plug is marked for fencing. The Spark plug is flagged
by using the "Boundary Fence" option method. The reason to flag them as separate boundaries because they are set at
different temperatures.
Intake port-2
The Intake port boundary is split into two boundaries, the main reason being is to create the Events. The Intake port is
closest to the valves and Intake port-2 is closest to the Inflow boundary where the species air is entering into the Engine.
Resolving Errors
Intersection Errors
The triangles of the intake port are intersecting with the triangles of the cylinder head. In order to resolve this "Measure" tab
is selected under which the "Arc normal" is selected. The three vertex points are selected from the intake valve (need to
make sure that the vertex points lie on the same circle). The "Apply" button is selected and the "Arc normal" is obtained. The
"Transform" tab is selected in which the "Translate" option is there and the following variables are written down in the
dialogue box.
The "Selected Boundary" option is enabled and the Intake valve top, Intake valve angle, Intake valve bottom boundaries are
selected. The Diagnosis is done for the geometry it was found that the Intersection Errors has come down to 3.
Open Edges
The area is open and as the Converge works on the finite volume method therefore it detects the open edges and expects us
to fix that.
In the "Geometry" dock select Repair and the Patch tab is selected. The Free edge loop (pick exactly one edge) is selected.
The method "By Open Edge" is selected from the main ribbon and the problem is rectified. Once the open edges are
converted into triangles the error comes down to 0.
The diagnosis is again run for the geometry and it is found that Intersection Errors, Open Edges, Non-manifold errors are 0.
Normal orientation
The normal vector should point inside the control volume not outside. Therefore in order to fix that the "Transform" option is
selected and the "Normal" tab is hit. The triangle is selected and the normal vector is selected which is pointing outwards and
then hit on apply.
Once these errors are resolved the diagnosis dock is clean.
Case-setup
The crank angle-based IC engine application type is selected.
Under "Gas simulation" the Equation of state is selected as "Redlich Kwong", the critical temperature is 133K and the critical
pressure is 3770000Pa and the therm.dat file is loaded under Gas thermodynamic data. The Turbulent Prandtl number is 0.9
and the Turbulent Schmidt number is 0.78 under Global Transport parameters. The PFI engine involves the combustion
process therefore the Reaction mechanism is selected and mech.dat is loaded. Under Run parameters, the parameters are
kept at their default values except the Simulation mode is selected as No hydrodynamic solver (for testing setup only). Under
Simulation time parameters start time is -480 deg, end time is 240 deg. The initial time step is 1e-07s and the minimum
time step is 1e-08s. The maximum time step is 0.0001s and the rest values are kept as default. The Solver parameters are
kept as default.
Boundary selection
The boundary selection and their parameters are tabulated as under
Species information at the Outflow boundary
Combustion of iso-octane will yield carbon dioxide, water, and nitrogen at the outlet.
The combustion is stoichiometric which means if we place the right amount of fuel corresponding to that the right amount of
end products are obtained.
Regions and initialization
The regions with parameters are tabulated below
Events
Events are created between the regions to regulate the flow between them. As the Events are activated between the regions
the Converge creates a disconnect triangle between them. Please note that these triangles are virtual triangles and should
not be created by the user. Events can be cyclic, sequential, and permanent.
Cyclic
Permanent
Setting up of Turbulence model
The Realisable
model is selected from the case-setup tree for the above-said simulation. Since the size of the eddies is restricted near the
wall and the maximum size of the eddies is formed away from the wall. It is well suitable for resolving flows in the
logarithmic flow region where y+ ranges from 30 to 300 and flow involving a high Reynolds number.
Base grid
The element size of 4e-3 was selected which is the default base grid.
Mesh on slices
Conclusion
The PFI surface preparation and the boundary flagging were done successfully using Converge-CFD and Cygwin command
prompt terminal.
The errors were obtained after the Diagnosis was removed successfully and set up for simulation.
The no-hydrosimulation setup was done successfully and the animation of the PFI Engine was uploaded successfully.
Fixed embedding was not used in the simulation setup as such the software uses an academic license and the use of the fixed
embedding exceeded the number of cells that is 5,12,000 cells.
The species information, the profile were uploaded successfully in their respective domain.