Questions about dynamic intakes

[GTMS]

My senior design project is to design a dynamic runner intake for GT Motorsports. I have a few questions that I hope someone can give me some guidance on.

1. Any good suppliers of dc servo motors for an application such as this?

2. Is there an upper limit to how large a plenum can be? A lower limit?

3. What have been the major shortcomings of these systems in the past?

I've heard about one successful implementation of a dynamic intake system, I think from Australia. Can anyone tell me which team this was?

Thanks

[GTMS]

My senior design project is to design a dynamic runner intake for GT Motorsports. I have a few questions that I hope someone can give me some guidance on.

1. Any good suppliers of dc servo motors for an application such as this?

2. Is there an upper limit to how large a plenum can be? A lower limit?

3. What have been the major shortcomings of these systems in the past?

I've heard about one successful implementation of a dynamic intake system, I think from Australia. Can anyone tell me which team this was?

Thanks

[Kamil]

We've had an active intake at UWA for 2 years now and we're still trying to improve it. The intake consumes a larger amount of resources to manufacture, is heavier than a static intake, and the control strategy is critical. Sealing is very important and thermal expansion needs to be considered. They're some of the obstacles we've had to overcome. As far as plenum volume goes, I'd be inclined to say go make some plenums and chuck them on the dyno, or make a plenum with an adjustable volume. I've heard of teams using 3L+ plenums with no throttle response issues. Maybe someone else can clarify that...

Kamil
UWA Motorsport

[D-Train]

The University of Adelaide also ran variable length runners at last year's comp. Not sure how successful it was though. Anyone from Adelaide care to comment? The thing looked great though, looked like a purchased part. I think it may have been rapid prototyped.

[GTMS]

I'm not sure about leakage really being so much of an issue, as all the moving parts are going to be contained within the plenum. As a side note, the plenum will be dynamic in volume as the design of the intake mandates it; we will have a very small plenum for idle and will open up at the same rate as the runners. My question is can one have too large of a plenum at high rpm?

[Kamil S]

I believe ETS ran a variable intake system, where the servos failed. You can try contacting them if you wish.

[Jersey Tom]

Have a backup, static intake that fits within your packaging constraints.

[Harry]

I've been told by guys with degrees in fluid dynamics that to have a truly effective dynamic intake, the cross-sectional area of the runners needs to change as wel as length. So we scrapped it.It'l be Hummoltz(sp?) tuning or a turbo this year.

[GTMS]

We already have a very good static intake, and it is more or less mapped. So the dynamic intake would just be in addition to what we already have.

While it is probably true that for an ideal dynamic intake you would want variable runner cross section as well, a non-varying cross section also works. We have done extensive runner length testing in the past, and have found that having a different runner length will shift the torque curve left or right relative to the rpm axis.

Again, I don't need discouragement, I want to know where I can get servo motors, if there is an upper limit to plenum volume, and what specific shortcomings there are.

Thanks

[DaveC]

We are going with a fairly large plenum this year, I have read up on plenums as large as 10x displacement without significant throttle response issues, but thats a subjective thing.

Changing runner cross section would help, but not as much as changing legnth. The other issue with changing cross section is how to handle the transition between the runners and the intake port if you found a way to change x section. I believe a static runner diameter that is smaller than stock would be better, though.

I also believe Helmholtz tuning is just about worthless as far as a fsae intake goes. Thats just my opinion, I'm sure many will disagree. I've seen poorly designed intakes that used Helmholtz design parameters, but it could have worked, it just requires more information than plugging resonator equations into a spreadsheet.

I've seen dynamic intake design discussed here, even with pics posted, search. I came to the conclusion that we can keep inside the powerband pretty easily without a dynamic intake, so it would be of minimum benefit for this application. Other applications might benefit a lot more, I know your design project is not specifically fsae oriented. If you really want to do a lot of extra work for minimal gains in fsae, a turbo is probably the best way to make your life more difficult.

[jjusb]

I don't see why a dynamic intake system would be "a lot of extra work for minimal gains in fsae".

My senior design project this year involved the design of a dynamic intake manifold that I hope will be installed in the 2007 car.

The system I designed shows huge gains in torque at low RPMs, and the torque curve is very, very flat from 4500 to 11000 rpm.

The development so far have been 3 months of transient CFD studies. The control system is not that complicated, and the construction would be the same as with the actual fixed intake (CNC machining of a mold and the final piece of some composite material).

I'm sure there is still a lot to do. Even when its built, there will be a lot of testing to do. It's not a project you'd want to try and complete in one FSAE year, but this is a project that WILL show gains, and in my opinion is worth trying.

Also, I don't see why you'd want to change cross-sectional area as well as runner lenght, basically you can change the tuning point using either of them.

As for plenum volume, last year's car had a plenum of 2,8L. We don't have big throttle response problems. Response is not as fast as we'd like it to be, but its just fine.

[Garlic]

I think its funny (and telling) how those with a dynamic intake on paper are saying how it's a pretty simple execution of the concept, while those who have done it properly say otherwise.

I may be mistaken but I beleive that UWA's intake is in it's 2nd year, and the first year it had issues (had heard it was not even operational). UWA may chime in if I am wrong. No other school, to my knowledge, has ever been able to make this work, and has never returned a year later with a dynamic intake after a year having one. And it has been tryed multiple times.

RPM rate of change is very quick on these cars. Sealing is VERY important. Not just to the outside world but internally. If it doesn't seal it doesn't do what you want. And the forces produced by vacuum are very large.

DaveC if you think Helmholtz does not matter in FSAE I can see why you think a dynamic intake would not be worth the effort. After all, if you say resonance does not apply to these cars, then all that's left is frictional effects, and so I'd expect you'd want your runner lengths to be as close to zero as possible. Certainly, I'd be real interested to hear why resonance is so insignificant on a FSAE car.

[Ben Inkster]

I hope I can clarify a few myths on this subject since I was the designer of the first UWA variable intake. A variable intake does not need to have a variable plenum volume, GTMS, I don't know what your design is but UWA does not have a variable plenum volume. The dynamic sealing is very important, any leakage within the manifold acts as a damper on your air column resonance and reduces the effect of a tuned intake. Change in runner diameter can be effective to tune an intake but it is much harder to vary and actuate. A large plenum volume will behave better for intake tuning but will reduce your throttle response (but like DaveC mentioned, not sure by how much) I think the bigger problem is packaging your plenum volume. The actuation of a variable intake is ultra important and we were lucky enough to have someone dedicated to the control system which is equally as important as the mechanical design. I think too much work went into this to just tell you what we used but we looked at our logged rpm data from practice and enduros to determine actuation speeds etc.

Garlic - UWA's first intake was operational at FSAE-A 2004 and it ran in the enduro. It did suffer from some issues but they were fixed by the time the car went to the US in 2005 and it ran in all events. The new 2005 UWA variable intake fixed the problems of the old one.

A variable intake is a large amount of work but so is a turbo, there are justifications for both. My justification for a variable intake was that it is light weight (compared to a turbo) and much easier to tune (compared to a turbo). Engine performance is a different strategy, a turbo will generate greater power and torque but (IMO) in a narrow, peaky engine range and create driving difficulties. The strategy with a variable intake is to create larger torque than a static manifold over a longer rpm range and make the car easier to drive.

On the subject of helmholtz tuning I agree with DaveC, Helmholtz becomes inaccurate at ~4000 rpm from there I would shift to continuous wave theory for greater accuracy. But if you have a 1D sim then use that.

Cheers
-Ben

[Garlic]

Ben- I'm showing my ignorance here. But what is the difference between Helmholtz and 'continuous wave theory'? Where might I find references to 'continous wave theory'?

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">and make the car easier to drive. </div></BLOCKQUOTE>

Exactly... what I found was that after drivers gained some experience, it is easy for them to keep the car in the effective powerband without resorting to dynamic intakes or turbocharging. While I certainly agree with jjusb that there is a lot to be gained on paper, that does not necessarily translate into a faster car. I believe if the driver can keep the car in the powerband without excessive shifting of gears, the large gains shown on paper dont really matter. Of course less shifting is better, but I believe you can get plenty of power in a fairly wide powerband with a static intake. These ideas apply to fsae, as I said other forms of motorsports might see more benefit from a dynamic intake, fsae cars do not require full throttle very much.

[Ben Inkster]

Garlic,
Helmholtz theory breaks a runner and plenum arrangement into a simple spring and mass approximation where the runner is represented as a mass of gas and the plenum is represented as a pneumatic spring. If you make the the system more and more complicated with more springs and more masses until it tends to and infinite number of masses and springs, you end up with the 1D continuous wave equation. This is a partial differential equation that can be solved with boundary equations and can be used for pipe networks with changes in cross sectional area and volume. If you want some references just type '1D wave equation' into your favourite search engine.

DaveC, if your drivers can drive in a narrow powerband than thats a great solution for you. All i can say is that UWA struggled for three years with narrow powerbands and it was a common complaint from all that drove the earlier cars and the slightest mistake would cost lot of time eg a mis-shift in a hairpin etc.

Cheers
-Ben

[Garlic]

Thanks Ben, I understand all that. I've used the basic Helmholtz in my own simulations before, combining the equations for more complicated stuff (and it does get complicated quickly, espcially with a restrictor!)

However you say Helmholtz becomes innacurate at _4000 RPM. Isn't 'continuous wave theory' just Helmholtz theory just taken to a proper resolution? Isn't saying that Helmholtz is worthless for FSAE, the same as saying 'continuous WAVE theory' is worthless as well?

[GTMS]

I appreciate all the response that I've gotten about this. Thanks guys.

All I really need to know, is what's the largest/smallest plenum volume that I can get away with? An artifact of my design is that the plenum volume is inversely proportional to runner length. I'm pretty sure that a very small volume will be great for low rpm operation and I can make this as small as I like, but I am concerned about whether or not a plenum can become too large at elevated rpms. These numbers are approximate, but I'm looking at around 7 liters of plenum volume when my runners will be the shortest (somewhere in the neighborhood of 12.5K to 13.5K rpm). I know this is a very large volume, but again, this is only at very high rpm.

Thanks guys.

[Garlic]

Well you've gotten some answers about plenum volumes that have been run, so there is your ballpark. I'm not sure what more you want?

Do you want someone to test different plenum volumes and report to you the results? Do you want someone to run thier 1D sim so you get your answers? Are you really willing to base your design on internet opinions, rather than your own testing?

It's not like this is some question about theory and you really need some experienced opinions to answer it or help you along. This is a case where you know the parameters you expect to have. So test them! Looks to me that you have your new car on the dyno. Mock up an intake, and test your range of values! This is the only way to start a project like a variable intake, know what is going to happen before you build it.

If you have a 1D sim at your team then it could at least give you some basic info, even if it isn't well correlated.

Sorry if this sounds harsh, but c'mon, its one thing to ask for opinions its another to repeatedly ask for specific info that you can easily gather on your own.

[Ben Inkster]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">However you say Helmholtz becomes innacurate at _4000 RPM. Isn't 'continuous wave theory' just Helmholtz theory just taken to a proper resolution? Isn't saying that Helmholtz is worthless for FSAE, the same as saying 'continuous WAVE theory' is worthless as well?
</div></BLOCKQUOTE>

Garlic, good point. I think what I meant to say was that helmholtz modelling using a very simple spring and mass system becomes inaccurate, but if the spring/mass model increases in complexity it would become more accurate, but continous theory is the infinitely complex helmholtz model expressed in a simple differential equation. I guess my hesitation with helmholtz comes from people looking up a simple helmholtz equation off the internet and applying it to a fsae intake manifold representing it as 1 mass and 1 spring.

-Ben

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I guess my hesitation with helmholtz comes from people looking up a simple helmholtz equation off the internet and applying it to a fsae intake manifold representing it as 1 mass and 1 spring. </div></BLOCKQUOTE>

This is what I was referring to, I was not saying resonance tuning is not necessary. I have seen people use the Helmholtz resonator equations with little other information, and come to mistaken conclusions.

GTMS, I have no more info to offer. As far as testing, I'd recommend either physical testing or CFD. For CFD not to leave lots of unanswered questions, you'll need both 3D CFD and a 1D Engine Simulator. Ricardo has a free license for Wave / Vectis for fsae teams. It will take quite a bit of effort to learn the software, gather data, etc. The design constraints imposed by a dynamic design may actually make physical testing easier, but the results may not be as good as well tuned CFD programs because you wont be able to run as many physical tests as computer sims. I believe a good physical test would be plenum volume, because the results are subjective. I'd want to have a few people drive the car at different plenum volumes and give their opinion of what they prefer. You can do the same for runner legnth, as there's some leeway for subjective results as well. Drivers may prefer a different runner legnth than what gives maximum area under the curve.

[Garlic]

You don't need a 3D CFD to answer these questions. 1D sims are more than capable of showing the effect of volumes and resonance, in fact, that's their primary use.

CFD becomes required when geometry evaluation is needed, especially for cylinder distribution. But for a strictly plenum volume evaluation, 1D sim is perfect.

[andrewd]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">A variable intake is a large amount of work but so is a turbo, there are justifications for both. My justification for a variable intake was that it is light weight (compared to a turbo) and much easier to tune (compared to a turbo). Engine performance is a different strategy, a turbo will generate greater power and torque but (IMO) in a narrow, peaky engine range and create driving difficulties. The strategy with a variable intake is to create larger torque than a static manifold over a longer rpm range and make the car easier to drive.

Cheers
-Ben </div></BLOCKQUOTE>

Sorry to burst your bubble benny, but think more in the range of 4000 rpm to just above 11000 (when the restrictor chokes) for the usuable boost range of a turbo.

[Scott Wordley]

For those who werent at FSE Australia 2005 and might doubt the benefits of UWAs variable intake keep in mind that they pretty much drove both enduros stuck in third gear and still flogged everyone. That car had torque everywhere.

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">But for a strictly plenum volume evaluation, 1D sim is perfect. </div></BLOCKQUOTE>

I fully agree. I am planning on using 3D CFD to fine tune the shape of some of the intake components, such as the plenum, restrictor, and interface between the intake primary and secondary runners and plenum. 1D did a great job determining the effects of generic volumes and legnths, but specific shapes are being designed with intuition and trial and error. It was all I could do this year to get 1D working in time to be of any use, and I got some grief for doing that instead of more physical testing, but I (and now many more people) think the final results of the effort were probably worthwhile, and will likely get us %90 there.

Scott, I have looked into a dynamic intake and definately agree it makes a huge difference. However, after experiencing some driver training sessions, I believe the real world difference is dependant on driver skill. The better drivers, who have become very good at shifting gears quickly, can keep the car in the powerband without issues. However, the dynamic intake looks like it might make enough of a difference to use 2 gears instead of 3, and that will benefit even very good drivers to some degree. How about a turbo car with a dynamic intake?... I wonder if that has ever been accomplished.

[Garlic]

Not trying to be a dick, but if you agree, then why'd you bring up CFD? It's useless for evaluation of plenum volumes as was being discussed.

[DaveC]

Youre not being a dick, thats why were here, to ask questions, compare notes, and hopefully learn something useful. Over the years I have noticed auto enthusiasts have strong opinions http://fsae.com/groupee_common/emoticons/icon_biggrin.gif http://fsae.com/groupee_common/emoticons/icon_eek.gif ,so do I, it makes for good entertainment.

Anyway, I used the Wave experiments panel to model a range of different parameters, including plenum volume. You dont get a single graph that way, but you can move a slider and watch the curves change with your experimental parameters. You can also label a parameter, and change that parameter in a constants table to be able to model different geometry at different engine speeds. That will at least give you a range of sizes to physically test.

[Mike Claffey]

DaveC, I would be a little careful before putting to much faith in wave experiment - I haven't used it for a while now but I remember it uses allot of assumptions and is a pretty rough indicator of what's going on.

Scott, the hairpin in 3rd gear was a pain in the ass but the car seemed to pull okay from 2000rpm.

[terra_dactile]

hi everyone,

In 2004 we (ETS) had a variable runner lenght intake system , but before copetition as mentioned above by kamil, the plastic gear of a servro motor blew up,
so for competition we had it set statically, at different lengths depending on the event,

In england in 2004, it blew up the night before the endurance day,we re glued it over night and we had serious problems with it during the endurnace event, later that summer it blew up again,

their were major advantages to haveing a variable length it is just very hard to keep up with the change in rpm seen during a real race , anyone who understands its purpose should know that if you are a lttle bit of the right length it can be worse than have a staic length because of the extra loss of volumetric efficiency related to the gemetry of a variable length intake, usually for it to work their are may sharp turn for the air to travel before entering the cylinder,

If UWA has had it on the car for two years their must be an advatage, if you get the thing to be at the right place at the right time, but you need a shit load of development to get it to work right,

Im no expert for this system but just thought i would shed some light on the possible problems of using one that is not timed right,

Jude Berthault
ETS Formula SAE 2003-Current
Steering System Leader
Brake System R&D

[Ben Inkster]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> quote:
A variable intake is a large amount of work but so is a turbo, there are justifications for both. My justification for a variable intake was that it is light weight (compared to a turbo) and much easier to tune (compared to a turbo). Engine performance is a different strategy, a turbo will generate greater power and torque but (IMO) in a narrow, peaky engine range and create driving difficulties. The strategy with a variable intake is to create larger torque than a static manifold over a longer rpm range and make the car easier to drive.



Sorry to burst your bubble benny, but think more in the range of 4000 rpm to just above 11000 (when the restrictor chokes) for the usuable boost range of a turbo. </div></BLOCKQUOTE>

Thanks for that insightful piece of info Bignuts (sarcasm)! They must be big for you to make open ended statements like that!

I specifically put IMO into that sentence because I do know the limits of my experience and I know that I haven't done much with turbo's. I based that opinion on torque curves from both Cornell and Wollongong, who are two turbo teams I respect the most and possibly have the most refined turbo's around and still can't stretch flat torque over a wide rpm range (~5000rpm). The Cornell dyno curve I'm referring to is here small turbochargers (http://fsae.com/eve/forums/a/tpc/f/125607348/m/5946004534/p/1)

However, I still think that both of these teams have awesome engine performance but it is a different philosophy to UWA. Now if you are claiming boost from 4000 to 11000 then how much is usable and what is your experience? Please back up your statements with something a little more credible or at least have 'Bignuts' and admit when you are speaking from opinion only.

So if you are going to call me 'Benny' then I am going to call you Smallnuts.

-Ben

[threehondas]

jjusb,

3 months of transient CFD? You would be better off spending that time on the dyno.

BB

[Pazza]

Hey

Scott- I was at FSAE 05 aswell and I saw UWA whoop everyones ass. I was speaking to some dude from UWA at the Espy after the event (I think his name was Marshy), and he was one of the drivers. I couldnt believe that they were making close to peak torque throughout their rpm range. Good stuff.

For my very small, uniSA team, I did the electrics, intake, ignition, exhaust and fuel setups. So i didnt have much time to work on complex setups. I made a static intake with a 3L volume and 10 and 12 inch runners. The runners were flanged, so the runner length could changed and dyno'd. The 12 inch runners made 43-47 ft.lbs from 7,000-10,000 rpm on the 01 F4i, but there was a large dip before this. However, I could only fab a 4-1 style exhaust manifold with a shitty merge collector because of monocoque space and money issues. So with a good 4-2-1 exhaust system I think we could have made ok torque curve.

I did some runner calcs, but it was all a bit of wank. If you have a choice, make a design and test it. You will learn more and its better than sitting infront of a computer. On the other hand, if you have as good of a team as UWA, get your buddies together and have some fun on WAVE.

I may be a little out of my league here as we finished 23-25 in the event. But we did only have 4 guys designing and building the car.

I was gonna post some pics of my setup but i dont know how to attatch photo's. How do you do it again?

Cheers

Sam

[Nathan C]

Hi guys,

I'm looking at a variable intake system as well this year - it looks possible, and if I can get it looking half as schmick as Adelaide's I'll be happy. One thing that's been bugging me beyond any issues with calculations and sims, though, is how to seal the damn thing! It probably seems like a really basic thing, but I'm fairly new at this and not sure what some of the best methods to properly seal this sort of thing are without having serious friction problems. Any suggestions (be as vague as you like if you think I'm asking for too many specifics) would be appreciated for someone who's probably bitten off more than he can chew here. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Ben Inkster]

Hey Nathan,

Sealing a variable intake is definetly not basic. I'm sure anyone from UWA, ETS, Adelaide and anyone else who has done one, would tell you that the internal dynamic sealing is a massive pain in the ass! and it is usually the root cause of failure on one of these systems.

I would focus a lot of your attention on this issue.

Cheers
Ben

[VFR750R]

As a rebuttal on our old dyno graph you referred to, how wide a torque curve do you need? Wide enough to cover 100% of rpm range you see on the track, wide enough to catch the next gear, wide enough to pull if your one gear off, or two...what do you guys think is a wide enough torque curve or is there such a thing? Maybe wide enough HP curve?

[VFR750R]

Oh, I just had a wild idea, how bout a variable runner diameter intake.

[Nathan C]

That was a thought I had, though the preliminary calcs I did indicated that it probably wasn't worth it for the pain it'd be to make it. Unless there's a way to do it that I haven't thought of yet, which is entirely possible...

[jpusb]

I still don't get how runner diameter can help since you can't change either head port & valve diameter "dynamicly".

http://fsae.com/groupee_common/emoticons/icon_confused.gif

[Mike Sadie]

GTMS,

there are a lot of high-torque, high-speed servos for RC sail boats that will most likely work. I found a servo that pretty much blows the rest out of the water. It is a digital coreless servo with titanium gears.

http://www.servocity.com/html/hsr-5995tg_ultra_torque.html