Solidworks transient simulation

[Danschwind]

Beshr,

I'll try to answer you with a question: how have you calculated/defined your runner lenght and diameter?

[beshr]

Daniel,
I know that I have to determine the length of the runner such that it assures that the compression wave is located behind the valve just before it opens. But I didn't determine a specific value as the runner length is one of the parameters that I want to study its effect on the system.
I thought that the acoustic effects will be included in the simulation as I determine the boundary conditions at the outlets. Please, correct me if I am wrong and how to include it in the simulation?
Thanks.

[Danschwind]

I can't give you a precise answer to this question because I've never used a 3-D simulation to design my intake runner and plenum.

But, again: I highly advise you to ditch the 3-D simulation for now and start working on a 1-D simulation ASAP. All your questions will be answered with it.

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If your intake valve start opening when you piston is almost at TDC, will you want the peak of your reflection wave pressure to still happen at this moment?

[beshr]

First of all, I appreciate your advice and I think I will take it into consideration. Second of all, my basic answer would be yes, although I sense there is a point you want to make behind this question.

[Danschwind]

If the peak happens before the valve opens, you would be losing some of its momentum to reduce the backflow during overlap, right? When the overlap happens, usually covering a small range around TDC, your goal is to reduce backflow as much as you can, so that wasted momentum, that hit the back of the intake valve before it was losing its fight to the exhaust valve would make some difference, right?
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Short story, when I first joined my team back in 2011, there was a guy who was really really amazing with Fluid Mechanics designing the plenum. He and 2 other guys who were already seniors in the university spent 4 to 5 months just running some SW analysis of the geometry and trying their best to get to a point where the simulated flow rates between each cylinder to be as equal as possible. The plenum turn out to be a pain to fabricate, and when put to use, its performance was poorer than all cylinder-shaped plenums where the guys actually spent time calculating the runner lengths of both intake and exhaust to match the desired performance at the desired rpm. So, advising again: work your way on intake and exhaust lengths, use a simple plenum shape and after you get a satisfactory performance, you can do those tweaks at the geometry

[beshr]

Daniel,
Thank you so much for the advice and the information. Now, things make sense to me. I thought that the purpose of the compression waves were to act as a boost for the intake
charge. I didn't look at it this way.

[Danschwind]

The absolute orgasm for an engine guy is to have a forward pressure wave with peaks both at the overlap and when the valve is almost closed (you can think of that as a little "punch" on that last minute where not that much air is being sucked into the cylinder because the piston velocity is very low).

The word "boost" can be used, yes. But that "boost" during overlap is more like a "don't let the backflow ruin my performance" than a proper cleaning of the cylinder.

Dunno if Ricardo WAVE has a plot like this, but GT-Power has a "forward waves (or something like that)" that is very very very nice to analyse. You will spot a increase in pressure at the back of the valve during overlap, but the "back" wave (going from the cylinder to the intake) is generally higher in pressure than the "forward" one. Only under some circumstances you are able to have a bigger "forward" wave, and when that happens = POWAH!

[beshr]

Thank you very much for the information. It was very helpful discussion

[Danschwind]

I'm glad to help. If any engine guru want to add something, it would be nice