We've tried them both ways, but we seem to have the most luck with cylindrical plenums. I could guess it's due to the runners seeing different cross sections above it effecting the flow into the runner (more losses), but I really don't know.
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We've tried them both ways, but we seem to have the most luck with cylindrical plenums. I could guess it's due to the runners seeing different cross sections above it effecting the flow into the runner (more losses), but I really don't know.
'engine and turbo guy'
Cornell 02-03
Just out of curiosity, Electro, what school are you from?
When you say you are measuring the pressure and adjusting the runners, are you measuring acoustic pressure? What are you using? A microphone (from your school's acoustics lab) is very effective and easy to set up a prototype around.
For the question of piston position, the historical literature says to use 1/2 the stroke for the length of your cylinder. I would love for someone to tell me why, but I can't find out. From comparing my math models to my dyno results, it seems to be the best empirical match, though, so I continued using that assumption that was first published, as far as I can tell, by Engelman.
I don't like to differentiate between Helmholtz and organ pipe effects. They are the same phenomenon, different calculation methods and assumptions. I don't know if it is what you are getting at but I do not believe that there is both an organ pipe effect and a Helmholtz effect in your runner. There is, as you know, a strong acoustical effect that is determined by the geometry of your runner, port, and cylinder. There are also smaller acoustical effects based on your plenum, inlet, restrictor, throttle body, and filter geometries. Many call the latter the Helmholtz effect, others talk about it like it's magic, but the primary purpose of it in my opinion is to reduce the overall system impedance at the frequency your runners are designed around and, in a perfect world, prevent anti-resonances in any part of your system in the RPM range you will be operating in. Maybe I misunderstood your intent here, but it seems to me that many people feel that there are different phenomenon in play here when, in reality, they are really just the same equations with different variables stripped out in an attempt to model your geometry as either a pipe or a coke bottle.
I am not quite sure what you mean by spreading the distance between the runner-plenum junction; feel free to email me something more specific if you want at szimmerman_AT_spraycool.com. Dual plenums are a pain, though, because you have to individually tune the cylinders. I do believe that it is a great idea, though, because I think you can reduce the slope of your torque curve in your operating range without a significant reduction in peak torque. It takes extra time, analysis, and tuning though and resources are at a premium for this competition. If you have the time, the more challenging it is the more you will learn.
Is there an easier way to do it? Sure there is. Use the basic N=162/k*c*sqrt(A/(L*V))*sqrt((R-1)/(R+1)). That equation really changed the way intakes were designed. You will get fairly close and receive one resonant frequency, which was fine in the 60's when the analysis was on a 4000 RPM engine. It completely misses all the other frequencies where your system (or a part of it) goes into resonance. You don't really seem to be interested in an easy method. Your thorough method seems like it fits you much better. You will have much more to talk to the power-train judges than most people there.
I hope this will help in some small way. I would love to see every person designing intakes this year to pipe in and disagree (citing their own research/analysis.) Everybody would learn so much and acoustics is the big topic that is never really discussed and argued in depth on this forum.
Good luck.
Electro,
As you're in electrical engineering it might be easier for you to do the simulations in Spice. If you make an electrical equivalent circuit you can do frequency analysis with the click of a button. This will allow you to quickly see the effects on the frequency response if you change one value, and it's equally simple to add parasitic effects.
Igor
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On time, on budget or works.
Pick two.
Igor,
I looked at that method, and no matter how hard I tried, I couldn't make it make physical sense. I can make sense of electrical and mechanical effects, but can't seem to make the bridge. So I went with the idea that seemed "real" to me. If you have any insight on understanding that, by all means I'd love to hear it.
On another issue, as Sam pointed out, this topic (I agree) is not brought up very much on this forum. How about we start a thread and I'll get everyone to tell me why I'm way off. It'll be fun.
Sam,
Thanks a lot for the input. Regarding the "helmholtz equivelant" statement, I was thinking of the whole system resonating as a net volume with a restricted pipe to the exterior. What do you think of that equation for N? It sort of makes sense, but doesn't take into account any interference or geometry, but seems to have some feeling for total volume. Can this be the "net volume" of the system? (omitting the half stroked piston of course)
Mike
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Sam Zimmerman:
Ebere,
Many teams have tried cone-shaped plenums. What specific questions do you have? Share some specifics from your analysis/research and you will be able to get answers that better help you out. Try to ask very specific, preferably technical questions and I will try to either help you or maybe refer you to a paper.
Good luck. </div></BLOCKQUOTE>
Sir,
Please suggest some papers that give me some help on the basics of restrictor and plenum design, as the fluid mechanics is very complicated... and some that would help me ondesign procedures
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by crypto:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Sam Zimmerman:
Ebere,
Many teams have tried cone-shaped plenums. What specific questions do you have? Share some specifics from your analysis/research and you will be able to get answers that better help you out. Try to ask very specific, preferably technical questions and I will try to either help you or maybe refer you to a paper.
Good luck. </div></BLOCKQUOTE>
Sir,
Please suggest some papers that give me some help on the basics of restrictor and plenum design, as the fluid mechanics is very complicated... and some that would help me ondesign procedures </div></BLOCKQUOTE>
Find the sticky about design papers. Read those.
Mountain Lion Motorsports
Just make it phallic shaped somehow.
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