Plenum Chamber

[Jamie]

I am currently trying to design the air intake system, however it seems to be somewhat of a black art and seem to get different advice from different people, specifically on the plenum chamber. Its the big question, "how big should it be". Many people have suggested that it should be 2 times the total swept volume of the engine. However I recently attended a lecture given by a guy from Renault F1 and he suggested 4 times the size. I have also read articles on this website that say that people lost points due to an overly large plenum chamber without having a justification for it. Any thoughts?

[Dan Deussen @ Weber Motor]

Here is the essence on plemum size:

Larger Plenum Size
Advantages:
- better air distribution to all cylinders
- generally more peak torque

Disadvantages:
- sluggish throttle response
- more weight and harder packaging


Smaller Plenum Size
Advantages:
- snappy throttle response
- less weight and easier packaging

Disadvantages:
- worse air distribution to all cylinders
- generally less peak torque

Now in terms of throttle response your EFI calibration plays a big role here too. A well calibrated EFI system with quite a large plenum can eaily have better throttle response than a small planum with a crappy calibration.

Personally I would agree with the 2 to 4 times the plenum size idea. Your overall throttled system volume can be a bit bigger though.

[Cement Legs]

Originally posted by Jamie:
Many people have suggested that it should be 2 times the total swept volume of the engine.

Could you clarrify what you are including in the volume when you say total swept volume of the engine?

[Dan Deussen @ Weber Motor]

swept volume = displacement

typical FSAE engine CBR600F4 has a swept volume of 599cc = displacement of 599cc

[Cement Legs]

Originally posted by Dan Deussen @ Weber Motor AG:
swept volume = displacement

typical FSAE engine CBR600F4 has a swept volume of 599cc = displacement of 599cc

Tks... I wasnt sure if that included runner lengths.

[Kamil S]

Jamie,

Why don't you try running a Helmholtz resonator model, under what packaging constraints you have? You could make yourself a chart that displays runner lengths versus RPM, at different plenum volumes. It would give you a great idea of at least what is acoustically happening.

You could also use the articles at http://www.grapeaperacing.com

Hope this helps.

[Adam Coombes]

I am also designing an intake system this year and have a few queries (and i have read through a LOT of the threads on here first http://fsae.com/groupee_common/emoticons/icon_wink.gif )

I understand the different opperating characteristics of the large and small volume plenums, how would anyone recommend is the most effective way of tuning the distribution characteristics (im talking about the possibility of a tapered plenum shape, side entry) of a small volume plenum? CFD? This to me doesnt seem straight forward due to the non-constant nature of the pulsating flow.

I have seen many velocity stack/bell mouth designs and the majority of them appear to sit a reasonable distance from the 'floor' of the plenum, i understand this is to improve the pressure wave reflection effects as the mouth of the runner 'sees' a larger cross section (if you had say a cylindrical plenum) but if you have a flat bottom'd plenum and the area that the runner entrance 'sees' is the same on the floor of the plenum, is there any disadvantages of having a radiused entrance flush with the floor of the plenum?? That to me makes sense with view to flow efficincy, am i not seeing something??

Taper angles of runner pipes, most production bikes appear to have a slightly tapered bore throttle body set up, with a sharp taper just at the entrance to the intake port in the head, does anyone know why this is?! I would have thought the straighter the path the better, but the throttle body diameter appears to increase with most of the high powered sport bikes with each generation.
With us running restricted then the maximum flow rate through the runners is bound to be less than on the bike at max RPM, so would smaller diameter runners than the standard Throttle diameter make sense? Should the flow be accelerated down the runner into the inlet port, or be of constant velocity (and therefore cross sectional area)?

I realise that most of this stuff is of the try it and see variety, but i somehow dont seem to have the time or funding for that!! So i would be very gratefull if those members of the board who have had experience in this field could be so kind as to share your findings. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Cheers, Adam

Imperial College London

[DaveC]

I'm using Wave to get an idea of what works best, then I'll make up a some manifolds to test. Our small volume tapered plenum modeled VERY poorly... Just go to Ricardo's website, email them, and they'll give it to you for free. Wave is a 1D CFD engine sim program, it comes with a 3D CFD program (Vectis), and tools to help you convert 3D cad models to the 1D simulation. Without something like this, youre doing a LOT of guessing, and might be fabricating lots of stuff that may not work well.

Adam, check out this thread for more info...

http://fsae.com/eve/forums/a/tpc/f/125607348/m/17410099721

[Adam Coombes]

Dave,
Im already using WAVE, but i just dont trust its accuracy in modeling a small volume tapered plenum. I spose its just going to have to be the trial and error route then!
Cheers

[DaveC]

Thats a good point, the Wave approximation I used was Y-junctions of different volumes connected by zero legnth ducts, so the plenum stair-stepped down in volume rather than a continuous taper. So, the results could be flawed, but I'd bet its close enough to give you a clue. Also, increasing the y-junction volume and making them all the same volume made a significant improvement, maybe at the expense of throttle response...

Also, Wave cant tell the difference between a cylindrical or rectangular plenum (as far as I know)... so there is definately some room for the trial and error approach. Maybe next year the cylinder head ports and intake manifold will be in Vectis.