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 (http://engsoc.queensu.ca/formulacar/enginepage.htm)

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>
----------------------------------------
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

[VFR750R]

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.

[Sam Zimmerman]

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.

[Igor]

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

[Electro]

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

[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

[Mikey Antonakakis]

<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.

[exFSAE]

Just make it phallic shaped somehow.