Intake Design Paper

[EPMAl]

Actually Sam, I was wondering if your methodology was taking into acount interference between cylinders or you calculated your system frequency on the assumption that the three other valves were closed during the whole cycle, thus not having pressure waves from the other cylinders interfering with the wave you're actually computing (from what I understand, you only used one cylinder as the wave source). I'm new to acoustics but to me, it seems we could have a more precise model if it was time-based which mean we could compute the interference effect between cylinders over an engine cycle (maybe using the acoustic pressure and velocity equations you presented in your work). After my post, I got your model running but still have some differences with your results.

The curves for the runner-plenum interface for close and open valves look good, but they still are offset which means the only thing that could move my curves on the x-axis would be my equivalence between frequency and engine speed. I'm using w=2*pi*(2*N/60); because i figured that the frequency had to be twice the engine speed divided by 60 (twice because the wave travels twice to go from the valve and back to the valve and divided by 60 to transfer rpm to revolution per seconds). I can't really figure out what goes wrong here. Also, does someone has an opinion on using mean cross sectional area of convergent or divergent tubes to approximate the speed the waves travels throught them. It just seems logic to me. Don't worry Sam, for the time I spent working on this, I'm really not looking for a quick turn-key. Right now, it just became personal between me and acoustics, haha.

[EPMAl]

Ok, sorry, I just saw, when I posted it that I didn't translate the figure. Those are the two curves at the runner-plenum interface with open valve (in blue) and closed valve (in greenish blue).

[Sam Zimmerman]

Originally posted by EPMAl:
Actually Sam, I was wondering if your methodology was taking into acount interference between cylinders or you calculated your system frequency on the assumption that the three other valves were closed during the whole cycle, thus not having pressure waves from the other cylinders interfering with the wave you're actually computing (from what I understand, you only used one cylinder as the wave source). I'm new to acoustics but to me, it seems we could have a more precise model if it was time-based which mean we could compute the interference effect between cylinders over an engine cycle (maybe using the acoustic pressure and velocity equations you presented in your work).

Nice work. I did not take into account the interference, but it would be a great next step. The only thing that I would caution on is trying to get too exact with the acoustics model and not moving on to the prototyping and testing. If the changes you are making to the model don't shift the graph by more than a couple hundred RPM, you might end up finding that you are picking the fly shit out of the pepper. Give it a try though, I never did and I would love to know the results.

Also, does someone has an opinion on using mean cross sectional area of convergent or divergent tubes to approximate the speed the waves travels throught them. It just seems logic to me. Don't worry Sam, for the time I spent working on this, I'm really not looking for a quick turn-key. Right now, it just became personal between me and acoustics, haha.

You have definitely thought this through. For the changing cross-section tubes you will have a continually changing impedance. I simply modeled this with a do loop, essentially modeling the tube with the changing cross-section as 'n' tubes in series, each with a length of n/L. Be careful to only add the effective length addition to the ends and not to each step, if that makes sense.

I hope I was understanding your questions correctly.

Good luck, that will be one pint. I like porters.

[speedracer_007]

the webpage link doesnt have the paper any more if anyone having could forward it to me at my email id i would really appreciate it
speedracer_sid@yahoo.co.in
Thanks

[EPMAl]

You'll have to buy it from sae.org . It costs about 12-13 USD. You can than download it right from the website.

[Gaanja]

Hi sam,

the paper is a great.

I have a few questions

1) The cam lift during the intake suction stroke changes the area available for the air to fill the cylinder. The changing area actually affects the impedance of the entire system. Is this taken care of by assuming the piston position to be at half stroke and the cam lift to be at average lift position calculated over the cyle?

2) is there a separate way of analysing the impedances of an intake that has a continuous area change? say one shaped like a flower vase? or do we do a finite element approach by dividing them into separate tubes of very small thickness along the cross section and then sum them up?

3)Is it worth the time to look at the effect of the position of the butterfly valve on the system at a given rpm?

[williams13nr]

I know this is from over a year ago, so sorry to bring it back but I can not find an answer to my problem.

I am using the impedance modeling approach to our intake as many teams have done in the past, and came across the same problem that EMPAI had back in Feb of 09 above. I can not reproduce the exact graphs that Sam produced in his papers, using all the values he used. The plots look close for the engine, but the frequencies do not coincide, and are off by ~2-3000 RPM. I tried to model the simple resonator as he does first in the paper, and got the values to be right on. I am also using w=2*pi(2*N/60) for the frequency, which I believe is what Sam used (found on another thread about this paper). I am confused because there is no difference in the calculation for the runner with cylinder open and the resonator other than the frequency, yet one matches and the other does not.

Has anyone been able to successfully reproduce Sam's exact plots for the impedance given the different runner lengths? Any help would be greatly appreciated.