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SI engine port design

SI engine port design

SI engine port design

Hi everyone.
I am new to this form and I am currently doing my master thesis on design of engine ports for a single cylinder engine. I am trying to find sources that can explain me the design factors and limitations of port design. In my case, it's a sngle cylinder engine with 2 valve. For the port orientation, I am in consideration of cross -flow port and a 90° port flow configuration. I am unable to find sources or papers that can explain this port configuration and the benfits and limitations of the same. I also plan to do CFD simulations to optimize the port. I would be really glad if anyone can help me in finding information of this type of port configuration


RE: SI engine port design

Have you read Heywood and/or Taylor? Beyond those introductory texts there are many thousands of papers and books on simulation and design of combustion systems, Gordon Blair authored several good ones.

Be aware if you haven't worked in combustion development that this is a rather deep rabbit hole of a subject, ports typically aren't "optimized" by themselves but as part of the entire combustion system to produce a desired in-cylinder motion and charge mixing in conjunction with the piston, valvetrain, and induction system as a whole.

RE: SI engine port design

You might consider, instead of starting with a clean sheet of paper, of finding some kind of foundational work within your own institution, or if necessary, outside, to build on. Typically research projects don't reach a final goal, but just move the ball down the field some distance. Rich sources for prior work will be SAE, ASME, and NASA (which, when it was NACA and during the aero piston engine development era, produced reams of worthwhile fundamental and practical studies on every riciprocating engine topic you could imagine).

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: SI engine port design

Ports do two things: They allow flow and they direct flow.
The amount of flow that ports allow affects power. The direction of air flow affects mixing and combustion and therefore is of interest when controlling emission output.

We measure air flow at various valve lift points on a flow bench with continuous flow across the port at a specific pressure differential across the valve. This may be 5, 10 or 28 inches of water depending upon the practice of the particular laboratory and the flow capacity of the bench.

The flow direction is measured on the cylinder side of the valve with a tiny wind turbine.
The orientation of the turbine is changed to measure the rotation of the incoming charge around the cylinder bore axis, swirl, and the rotation perpendicular to the bore axis, tumble.

All of these measurements at constant flow and pressure might or might not relate to the transient flow that occurs in an actual engine. The same holds for your CFD (colorful fluid dynamics) results. All practitioners hope that their methods are good indicators.

A common way to describe port flow is as a percentage of the speed of sound. This the ‘Z’ value in Chas. F. Taylors books.

As the application of turbochargers and superchargers suggest, increased flow is related to power production. In cylinder motion may or may not help power production.

It takes energy to create in-cylinder motion and this energy comes from the gas flowing into the cylinder. This energy would otherwise be used to fill the cylinder with more air. If the in-cylinder charge motion promotes more complete and/or more rapid combustion we may gain power by generating the motion.

Since a diesel depends entirely on in-cylinder air/fuel mixing and has a fuel that burns more slowly than gasoline it should not surprise you that more effort is put into generating in-cylinder motion in diesels.

In addition to Taylor, you may find Smokey Yunick’s book helpful. The manual from a flow bench manufacturer could be helpful.

Good luck.

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