Helmholtz resonator calculation q's

[Angry Joe]

I've been messing with intake calculations and am looking at the Helmholtz multi-cylinder calculation now. There's an example on This Page (http://www.eng.ed.ac.uk/~jchick/Y5/thesis/FormulaStudent/public_html/pt7.htm) that is right out of the book I'm using.

I'm a little confused about where to model the plenum in this equation: should it be modelled as part of the intake, or as part of the 'dead' volume of the other cylinders?

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Angry Joe]

I've been messing with intake calculations and am looking at the Helmholtz multi-cylinder calculation now. There's an example on This Page (http://www.eng.ed.ac.uk/~jchick/Y5/thesis/FormulaStudent/public_html/pt7.htm) that is right out of the book I'm using.

I'm a little confused about where to model the plenum in this equation: should it be modelled as part of the intake, or as part of the 'dead' volume of the other cylinders?

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Alfonso Ochoa]

Check this website:
http://www.grapeaperacing.com/GrapeApeRacing/tech/intaketerms.cfm

I think it's clearer than the one you have.
Hope it helps you,

Alfonso Ochoa
F-SAE USB, Venezuela.
cabezota311@hotmail.com

[Richard Lewis]

Angry Joe, I don't think that page has a correct formula. If the formula is correct, then the variable definitions are incorrect.

The formula is supposed to output a value in Hertz, but none of the inputs are time dependant. I don't see how that is possible.

Perhaps I am making incorrect assumptions:
Vd=1 cylinders displacement
Rc=Compression ratio
and then the others as he's defined them.

The terms L1=1/A1 and L2=1/A2 strike me as being wrong. However, I am not sure what they should actually be. Does anyone have the Haywood book (1988) that can verify this formula for us?

-------------------------
UVIC Formula SAE Team
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[U of S Engine]

This is a page that I referenced for a small thermo report on compressible flow, and have partially used for our new intake design.

http://www.mecc.unipd.it/~cos/DINAMOTO/risuonatore/risuonatore.html

Kevin Hall
University of Saskatchewan
Engine Guy
www.engr.usask.ca/~formula (http://www.engr.usask.ca/~formula)

[Richard Lewis]

I ran and got the Heywood book, and found out the terms I thought weren't correct, weren't correct. They should be L/A not 1/A. The formula still isn't giving me any results that I can discern however.

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UVIC Formula SAE Team
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[Angry Joe]

I actually used the Heywood formula, I just used that site for an example. I also could not get the formula to work. I went trough the units and it came out as 1/(2*pi*cm), and my numbers were not even close.

Anybody know what's going on here?

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Charlie]

Here's what I have in my spreadsheet. I derived it from an equation in Winterbourne-Pearson and I don't remember the exact equation it came from.

Oscillations in Hz = (Speed of Sound*SQRT(Pipe cross-sectional area/(Pipe length* Mean cyl volume)))/2pi

Where mean cylinder volume is defined as 1/2 the displacement volume plus the entire clearance volume.

-Charlie Ping
Auburn University FSAE 1999-present

[Richard Lewis]

I have that one done as well... but I didn't see how both formula's could be correct, and the one you used charlie doesn't take the plenum volume into account at all...

-------------------------
UVIC Formula SAE Team
http://members.shaw.ca/drax77/UVICFSAEcar.jpg
http://uvic.fsae.ca

[Charlie]

I wasn't aware that the Heimholtz Equation took plenum volume into account. I know the Ohata & Ishida Eq. does. However I've gotten mixed results because it include an inlet pipe frequency that I cannot match to a restrictor accurately (IMO). If anyone know how to do this I'm all ears.

-Charlie Ping
Auburn University FSAE 1999-present

[Richard Lewis]

Has anyone used the formula Angry Joe posted with any sucess? Its from Internal Combustion Engine Fundamentals, by John B. Heywood. (1998)

Banging my head over that one, can't get results I can make heads or tales of. The resultant, which is supposed to be a frequency is coming out in 1/length units...

-------------------------
UVIC Formula SAE Team
http://members.shaw.ca/drax77/UVICFSAEcar.jpg
http://uvic.fsae.ca

[U of S Engine]

Are the ones at this link wrong

http://www.mecc.unipd.it/~cos/DINAMOTO/risuonatore/risuonatore.html

Kevin Hall
University of Saskatchewan
Engine Guy
www.engr.usask.ca/~formula (http://www.engr.usask.ca/~formula)

[Angry Joe]

Helmholtz doesn't seem too incorperate plenum volume, but the Heywood book is very vague about this. Their diagram does not seem to include a plenum.

http://www.we-todd-did-racing.com/wetoddimage.wtdr?i=wNTQ3MDk2czQxM2RmZDMxeTU0MQ%3D% 3D

Could it be incorperated into the intake portion? Or the extra volume created by the other cylinders? That alone doesn't explain the numbers I'm getting though.

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Brent Howard]

Most of these calculations are based on hemholtz which assumes an infinite void at the end of the intake runners. That's why you don't see a plenum volume. Basically intake desing is not an exact science and every model you use will give a different runner length. Don't worry too much about it though, because any length of area runner will give you an volumetric efficiency peak at some RPM that can be used as the running RPM based on gear ratio.

Brent

www.ucalgary.ca/fsae (http://www.ucalgary.ca/fsae)

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Brent Howard:
Don't worry too much about it though, because any length of area runner will give you an volumetric efficiency peak at some RPM <HR></BLOCKQUOTE>

True, but isn't that 'some RPM' precisely why we do these calculations in the first place? There are plenty of RPM ranges where the benefit is lost, and also some completely out of the engine's capable RPM range.

-Charlie Ping
Auburn University FSAE 1999-present

[Brent Howard]

Very true charlie. What i mean is calculate it using one of the models and pick a length that is near to the calculated values. For us we calculated values rangine from about 28-32 cm so we are going to pick a lenght in that range. None of the models are completly correct and all make assumptions that are not entirely correct. Basically I only meant that it's not a big deal if your peak RPM is 8000, or 8500.

Brent

www.ucalgary.ca/fsae (http://www.ucalgary.ca/fsae)

[Charlie]

I see. There is definitely nothing more accurate than physical testing, however it's always nice to see calculations verified.

I found a cool calculator online at the technicalF1.com forums. One of the members there wrote it. It contains a Heimholtz calculator. I used to to check my spreadsheet and they were close, but not exactly the same.

http://www.auburn.edu/~pingiii/temp/overdrive.exe

-Charlie Ping
Auburn University FSAE 1999-present

[Brent Howard]

I completly agree that physical testing is nearly the only way to actually come out with a good tuned intake design. What we were going to do this year, but it didn't work because of poor dyno data, was to run the calculations on the old intake, using the detroit dyno data. Then, compare the two and use the model that most closly reflects the real situation we had in detroit.

Brent

www.ucalgary.ca/fsae (http://www.ucalgary.ca/fsae)

[Charlie]

That's a great little program. I searched for it online but couldn't find it from google or altavista. So I uploaded it to my site.

-Charlie Ping
Auburn University FSAE 1999-present

[Angry Joe]

Very cool program. Do they want the entire displacement of the engine or just one cylinder? Same question for the runner area. I'm asking because when I use the area for one runner and the total displacement, I get numbers really close to our actual dyno results

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[This message was edited by Angry Joe on February 10, 2003 at 10:43 PM.]

[U of S Engine]

Conversely, when I enter the volume of one cylinder, I get numbers which seem close. Could someone please clarify these........I'm looking at you Charlie

Kevin Hall
University of Saskatchewan
Engine Guy
www.engr.usask.ca/~formula (http://www.engr.usask.ca/~formula)

[Marc Jaxa-Rozen]

Cylinder volume is for one cyl. only, as in the usual Helmholtz equations.

I just noticed the plenum volume effect is broken in the version I uploaded, I'll try to sort that out tonight.

[Charlie]

For 1 cyl only, yes. Might want to check the overdrive2's cylinder volume equation. According to Winterbourne, the volume is 1/2 displacement volume + total clearance volume. I think you might have 1/2 of both in your calcs.

Also, mind sharing how you incorporate the plenum volume into the Heimholtz Eq.? I figured it didn't work because there wasn't a way to do it.

-Charlie Ping
Auburn University FSAE 1999-present

[Richard Lewis]

Charlie, as was said earlier, there seems to be more than 1 Helmholtz equation. One assumes an infinite plenum volume (relative to runner volume I assume), and one does not. If I use the INfinite volume model I get a peak of ~14000rpm and if I use one that incorporates the FINITE volume it ends up being ~9000rpm. Most automotive plenums are larger in relation to their runners than the intake I am working with I guess, because the infinite model doesn't seem to be too accurate.

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UVIC Formula SAE Team
http://members.shaw.ca/drax77/UVICFSAEcar.jpg
http://uvic.fsae.ca

[Angry Joe]

I guess Overdrive 2 uses the infinite volume equation, since the numbers I got from the program are very close to the numbers I got by myself using that formula.

Can anyone post the version of Helmholtz that accounts for plenum volume? I can't find it in Heywood

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Alfonso Ochoa]

Can anyone please tell me how the Ohata model is? by a diagram or some picture with the variables names. Thanks,

Alfonso Ochoa.
cabezota311@hotmail.com

[Charlie]

It's in Winterbourne and Pearson. I don't have the book next to me right now, I highly suggest you buy it. Much of the confusion in this thread stems from people searching online for information that is best suited to come from a well-respected author.

-Charlie Ping
Auburn University FSAE 1999-present

[DJC]

The formula from Heywood is correct if you multiply by the speed of sound. I think that the plenum volume can be modeled into the volume of the extra runners.

Thanks,
DJC

[Kevin Hall]

Hey Guys

I'm having troubles finding the actual books you are talking about. Our school has squat, and I'd like to order them for myself. Thanks

Kevin

[Charlie]

As already mentioned, John Heywood's book is excellent, Winterbourne & Pearson's is also good, especially if you do engine simulation work.

Sorry don't have the book names here, but I believe I spelled the authors correctly, and it's easier to look up by author anyway.

-Charlie Ping
Auburn University FSAE 1999-present

[Marc Jaxa-Rozen]

It's Winterbone actually, look up his books on intake manifold design.

[Angry Joe]

Just checked our Library, found two books by Winterbone and Pearson. One is Theory of Engine Manifold Design, the other is Design Techniques for Engine Manifolds. The second seems like the better choice, but I got both of course. Oddly enough, each book has a different publisher.

Lehigh Formula SAE

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Sebastien Poulin]

to Marc Jaxa-Rozen and his Overdrive program

How do you convert natural frequencies into tuned engine speeds. This factor seems to be 76.536 but where does it comes from. I look in Heywood's but they say it's about twice the natural frequency.

Nice program and very accurate
Seb

[Marc Jaxa-Rozen]

That was based on an explanation in Stone's book (Intro to IC engines), but he does mention that it's not really such a simple correlation as matching the resonant frequencies to the piston freqs. So it's mostly a general indication, I guess.

Marc
École Nationale d'Aérotechnique

[Brent Howard]

Hey Everyone

It seems that everyone uses some variation of a helmholtz resonator to design the intake manifold and I was wondering if anyone uses or knows of a different model used? We are designing the intake as a 4th year design project and the gas dynamics professor that acts as our expert does not agree that the intake can be modelled using a helmholtz resonator. He said that the runner area was too large and the plenum volume too small to actually be anythig near a helmholtz resonator. Our volume for the plenum is about 2 times the engine displacement and the runners are 1.4" in diameter (the stock area for th eF4i engine). I disagree with the professor on this matter and feel that while the helmholtz resonator may not be a perfect model for hte intake it is sufficient to achieve a power curve that is to your liking by choosing a peak RPM value. And by the way the text we are using is the winterbourne one as well as a few internet sites which say basically the same stuff.

Thanks for any help

Brent

www.ucalgary.ca/fsae (http://www.ucalgary.ca/fsae)

[Marc Jaxa-Rozen]

Zero-D modelling such as the Helmholtz equation can only take you so far- in theory, it would be preferable to use some sort of 1D model (I like this program, and it's free- a rarity in this field: http://capella.colorado.edu/~laney/uflow.htm ) for more involved analysis...but there are so many variables involved that you might as well go with a general, Helmholtz-derived figure, and use dyno tuning to improve your design.

[Brent Howard]

Yeah...that's my feeling as well, however he is pressing the FEA idea for flow modelling.....I however feel that this is a bit much to expect us to learn for something that the changes are going to be fairly minimal. As well as the computer engineers motto of "garbage in = garbage out" which is definitly what we are going to get with any first attempt at computer modelling....i have no idea what type of results i should expect to recieve so anything i got out of the program i would take a fact, which is not a very good way to proceed.

Brent

www.ucalgary.ca/fsae (http://www.ucalgary.ca/fsae)

[Kevin Hall]

If your prof wants FEA, try to get the college to spring for Virtual 4 Stroke. That will give the most accurate simulation. The pulsating as well as the valve action would be truly difficult to properly model with basic CFD. Considering the CFD class I am in right now is just barely touching on the basics (still running numerical emthods in EXCEL, and switching to CFX in the lab today).

Have fun, whatever path you are forced to run along

Kevin Hall
U of S Engine Guy

[Nishant Jain]

Hey,

Was just reading up this chain and I would like to try the Overdrive program put up by Charlie Ping.

But the link's dead. Can anyone help with finding the software? Email it or upload it somewhere?

[Nishant Jain]

Has anyone used Stanford's Engine Simulation Program? I borrowed the book from the library which uses this program (Engines: An Introduction by John Lumley).

I'm wondering if the results are going to be worth the effort, or if there's a better option.

Any ideas?

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Nishant Jain:
Hey,

Was just reading up this chain and I would like to try the Overdrive program put up by Charlie Ping.

But the link's dead. Can anyone help with finding the software? Email it or upload it somewhere? </div></BLOCKQUOTE>

Sorry... I don't have this program anymore either!

[James Waltman]

Man, this thread is from the old days huh Charlie?

Here's a link to it if there's no objections from Marc.
http://www.wwufsae.com/Waltman/Resources/overdrive.exe

[Marc Jaxa-Rozen]

Hey,

Unfortunately there's a couple of errors in the software that pretty much make it useless, and I don't have the code or an updated version anymore...I think your best bet for this kind of method is to find the paper on acoustic intake design that was published by Sam Zimmerman a few years ago, and use that as a base.

Alternately, you might want to look into getting an educational license for Ricardo WAVE, as they offer excellent support for FSAE teams.

[Nishant Jain]

Thanks guys.

I'm working on the Ricardo license right now. Very eager to work on that. And having read the amazing tips and work-arounds put up here, it should be a less taxing experience for us.

As for the paper by Sam Zimmermann, I've been looking for it quite sometime since I read about it here on the forum. But seems like its not available online anymore. That link's died too. Again, can someone help?

[Mikey Antonakakis]

Go to the SAE site and look for it, you can buy it for about $11, that's what we ended up doing about a month ago. I don't have a link, sorry, but I'm sure you'll be able to find it there.

[James Waltman]

Link removed per Marc's request.

[alumasteel]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">As for the paper by Sam Zimmermann, I've been looking for it quite sometime since I read about it here on the forum. But seems like its not available online anymore. That link's died too. Again, can someone help? </div></BLOCKQUOTE>

Check with your university library first. Often libraries have subscriptions to professional publications like SAE, so you may be able to request it at no cost to you. I'm not sure how common that is overseas, but here in the states it's fairly standard. Otherwise, $11 is worth it in this case.