Plenum shape

[Ebere]

hello.. i was wondering if some of you have tried to use a plenum with a cone shape.... because we want to use a side entry restrictor, and we thougth that with that shape we could get an uniform distribution of the air... please if you have some information about this.... i´ll be very grateful

[Ebere]

hello.. i was wondering if some of you have tried to use a plenum with a cone shape.... because we want to use a side entry restrictor, and we thougth that with that shape we could get an uniform distribution of the air... please if you have some information about this.... i´ll be very grateful

[Jon @ Electromotive, Inc.]

Queens Unviersity has some good info on their engine journal

I think that will answer your question.

[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.

[Dallas Blake]

If you have any questions about what I've put on our webpages please feel free to email me or ask the questions on here.

We use a side entry tapered plenum. The taper is designed to counteract pressure headloss and equalize charge density to each cylinder

now the amount of taper that you put in your plenum will depend on many factors in your intake design but will be determined by the pressure difference you see across a side entry log style plenum with the same overall dimensions.

[Nitesh]

I know it's not exactly about the plenum shape, but are teams using velocity stacks in their plenum? It would help if someone could guide me to a link or two about reading materials for the same. Also, on a link found on this forum itself, there was a formula to calculate the required throttle body size but it obviously didn't take into consideration the restrictor as it wasn't FSAE specific. Could anyone help me in regard to the required Throttle body dimensions. i know of a thread where people have chipped in with the sizes they are using, and taking a cue from the same we used a 36mm one this year, but i feel i should be doing the calculations rather than picking up figures from the forums. any help would be appreciated. Thanks

[Maverik]

If you take the amount of air mass flow you know and the pressure vefore and after then you can use compressible flow calculations to figure out throttle body size.... well, entry size for the venturi design you are using which mandates a given size throttle body, or something along those lines... football preseason starting now go bucs!

[Ebere]

<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>
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Hello thank you for answering to my message... i have some doubts about the section change that should have the plenum to have an equal distribution of the air for each cilinder, maybe if you know some equation or something like it to calculate this, and also about its volume, because there are a lot of opinions about it, but there´s not some specific idea

[Sam Zimmerman]

There are many opinions on volume and I have not seen a specific equation on this. I also doubt very highly that you will find one.

I would hope that a certain RMIT and ex-Cornell guy would let me know where I am wrong on this, but here is my opinion. Your plenum is coupled to everything else in your intake and therefore affects throttle response, transient changes in air demand, and system acoustics, among others. You will not find a specific equation, only compromises.
What I was trying to get to was your definition of "uniform distribution of air." This will mean something completely different to an acoustics guy than a fluids guy. Basically, it is entirely possible to design an intake that when put on a flow bench shows perfectly even flow among all four cylinders, but when you run you engine you find that the inner 2 cylinders require more or less fuel than the outer 2 (or some other combo) because there can be different acoustic impedances at the runner/plenum junctions.
So, to cut to the chase, are you looking at your intake design from a fluid mechanics perspective or an acoustics perspective, or both? If your analysis is from an acoustics perspective, forget about the cone-shaped intake because it will cause you to lose all your acoustic benefits in the plenum due to the gradually weakening incoming wave. If you are looking at this from a fluids perspective, it should be pretty easy (if you are into CFD) to do some CFD analysis to design an even-flow intake.
Ideally, you would do an entire acoustical analysis/design, then CFD the entire system, build 2 or 3 prototypes, test, analysis, prototype, test, etc., etc. but no FSAE student has time for that in their schedule so I would suggest you pick an analysis method that you would like to learn about and beat the analysis and prototyping to death. If you intend to do an in-depth acoustical analysis, I would be glad to help you with what I remember. If you want to beat it to death with a CFD analysis, I would be useless.
I know this doesn't answer your initial questions but I feel you need to provide some analysis info to have your questions asked. Like you said, there are all kinds of opinions so eliminate the possibility of getting opinions and instead ask, "My analysis and/or testing shows this, I think ..., am I right? What does your analysis say?" I deal purely in prototypes in my current job and have found that no matter what you design, everyone from your boss to the janitor will give their opinion on how you should have done it. If you show those people your test results and ask how you can improve the data, that's when you get something valuable.

btw, Queens, I loved the web page. Great job documenting your work. I would do well to follow your lead in my job.

[Electro]

Sam, I have been approaching an intake design by acoustical analysis, but sure could use some more help. I am an electrical engineering student, and have little background in acoustics, but here's what I've got. I approached the obvious effect of rarefaction wave to plenum, returned pressure wave timed at 90 ish degrees to give the highest ram effect at valve closure (angle dependent on cam profile, chose half duration). On top of that, the inter-cylinder interference has an effect (as a function of the geometry of the plenum I assumed) and I didn't know how to treat that or analyze it so I chose to spread the distance between runner-plenum junction, or seperate 1-4 and 2-3 to individual plenums, joined by a third stub (two designs completed). But, alas, I realized the entire system must have some "Helmholtz" effective frequency, and calculating that depends on the position of the piston (same goes for the runner length, but I guess that can be averaged around the desired frequency?).

So this (and a few other factors, but this is getting long) all tells me I must be missing an easier way of doing this. Which brings me here, how else can you model or treat each effect of acoustic influence of the system? Acoustic impedance as some function of geometry?
As of now I plan on measuring the pressure and adjusting the runners and plenum to "tune" the system.

Any words of wisdom?

Thanks