Project 1 - Surface preparation and Boundary Flagging

Port Flow Injection of SI Engine

The PFI estimates the simulates the full working of an SI-Engine. By definition in an SI-Engine pre-mixed air-fuel mixture is ignited with a spark plug.

The main steps involved in the process are:-

• Intake
• Mixture Formation
• Combustion
• Exhaust

The Star-CD software is commercially used for this software.

In this challenge, we wish to perform the boundary flagging and surface repair to the given PFI-CAD Model.

1.Boundary Flagging

To facilitate the surface repair, the Engine is split into various boundaries like the valve, piston etc.

Fig.1.1:-Boundaries Associated

Here there are two ports (inlet/exhaust ports) along with the inlet & exhaust valves present as the main boundaries.

Fig.1.2:- Boundaries involved in Intake & Exhaust Valves

Here, both the valves are seated on the cylinder head which also marks the top-dead-center for combustion

Fig.1.3:- Position of Cylinder Head wrt. Valves

The piston movement (for both compression & exhaust stroke) takes place in the liner. It houses the cylinder head on top & the Piston on the bottom.

Fig.1.4:- Liner in the Engine Assemble

The inlet & exhaust port houses the valves. The fresh air-fuel mixture & the combusted exhaust gas enters & exists via the Inlet & outflow respectively.

Fig.1.5: The Complete assemble of Engine

2.Surface Repair

The two main errors found in the challenge were Intersection Errors & Open edges.

Intersection Error

It occurs when two surface triangles intersect with each other. It leads to one surface piercing the other & coming out of it, which is not the case in actual engine assemble. An example of intersection error is given below.

Here two surface triangles inclined non-perpendicularly intersect each other to give pierced surface.

Here, the surface triangles pierce the coupling surface to create a pierced surface.

The magnified image of the above image is shown

Problem Application

The pierced surfaces can be found in a geometry by the Diagnostics tab.

Pierced surface error at the Inlet Valve angle, are shown in the original CAD.

Boundary Translation

To repair the intersecting errors, boundaries in the intake valve are translated by 0.5mm along its normal. This repairs all the pierced surfaces.

The normal is measured by the arc normal method.

Free Surface Error

It occurs due to missing surfaces, in most of the scenario the surface is mistakenly deleted by the user.

Due, to this inner volume extraction, becomes difficult & it is rectified by stitch & patch operation in Converge-CFD.

Problem Application

There were a few free edges in the Problem, especially in the piston region. Most of the free edges were patched.

Solution

By boundary flagging & surface repair we eliminate the issues such as non-manifold edges, free edges, non-manifold edges & pierced surfaces.

We also ensure that all the normal points to the interior to the surface and the surface diagnostics is run successfully.