Cylinder pressure

[Lightsun]

Hello everybody!This is my first post http://fsae.com/groupee_common/emoticons/icon_wink.gif
I'm working with a new CFD software to develop the aero package of our new car, and to have some training, I'm also developing the intake manifold. We are going to use a CBR600RR engine, but we won't have it until next month, and I would like to now aprox. which can be the lowest and the highest pressure inside the cylinder while the inlet valve is opened. I think that it's better to understand the behaviour of the air inside the manifold before I start to design more seriously, can anyone help me with some aprox. numbers?
Thank you!

[Lightsun]

Hello everybody!This is my first post http://fsae.com/groupee_common/emoticons/icon_wink.gif
I'm working with a new CFD software to develop the aero package of our new car, and to have some training, I'm also developing the intake manifold. We are going to use a CBR600RR engine, but we won't have it until next month, and I would like to now aprox. which can be the lowest and the highest pressure inside the cylinder while the inlet valve is opened. I think that it's better to understand the behaviour of the air inside the manifold before I start to design more seriously, can anyone help me with some aprox. numbers?
Thank you!

[Wesley]

Well, it depends a lot on your geometries. The amount of overlap (and the resultant scavenging) the engine speed, the exhaust lengths, everything has to do with your pressures generated - that's what you're trying to improve. The lower the cylinder pressure at IVO, the faster it fills. The higher the cylinder pressure at IVC, the more you've filled it. It's kind of what you're looking at maximizing...

[J.R.]

The best way to figure out how your engine will behave with different cylinder lengths are engine simulators. Ricardo Wave is free to FSAE teams, and we use GT Power which is ~$150 a chair. They take some time, but they are a great way to do engine development.

[Lightsun]

Thanks for your answers.
I've heard about Ricardo Wave, but I'm working with a software designer with their program, so I can't change to Ricardo now. I know that the pressure depends on the geometries, but what I really want to study is the behaviour of the air inside the intake manifold, not the behaviour of the engine (firstly, I'm studying the steam of air alone with the software, and later this month I'll study the engine performance). So maybe, someone has pressure numbers to fill the boundary conditions of my simulation, for example 1 bar, or 10 bars of pressure in the highest position of the piston, and 0.5 or 5 bars in the lowest position. I have no idea about which can be the numbers (I need to put the boundary conditions just at the end of the intake, on the upper face of the valve), and I just want something to get started with the simulation, and I hope in a few weeks I can put a pressure sensor in the intake of last year's car. So, can anyone tell me some aprox. data? Thank you!

[Mikey Antonakakis]

Well, that's kind of a complicated question to try and answer... but here goes.

Intake manifold pressure is somewhat proportional to engine volumetric efficiency, or how much air the engine DOES suck in compared to how much it CAN suck in. VE is pretty much directly proportional to torque, as well. But bottom line is, VE will, in a very simple model, not exceed 1. So you shouldn't ever see the pressure in the intake manifold exceed one bar. But then some people are crafty and design an intake with runners that will produce constructive interference of pressure waves and whatnot, to get a manifold pressure of over one bar. But with a naturally aspirated engine, this will just barely exceed one bar; I'd say, with a wild guess, 1.1 bar MAX. Now with respect to pistion position, the minimum pressures, which would occur sometime very soon after the intake valves open, would be close to vacuum in some engines. I'd say probably 0.1-0.2 bar would be an okay estimate, considering many engines pull 0.3 bar manifold pressure at idle. This very low pressure would occur after intake valve opening. The highest pressure would be sometime during the open phase of the intake valve, probably towards the middle to end of the opening, as a resonance "rams" the air into the port.

So I guess in summary, lowest pressure you could expect to see would be close to 0 bar, highest would be slightly over 1 bar, at least in some places in the manifold.

[rjwoods77]

Delphi and GM use cylinder pressure transducers from what I have seen. They look like a modified spark plugs. I would veer away from anything but a measured value since calculating leaves much room for error. Well for that matter so does measured if your setup sucks. I would start looking for sponsorship for something like that if you are really interested.

[kapps]

Measuring cylinder pressure gives some pretty serious data. A professor here did a lot of work with it back in the day. Remember, to get it right, you need to sample every degree or two of the crank, in every cylinder. With 720 degrees per fire and 10k+ rpm, you are going to have gigs of data very quickly.

[rjwoods77]

A couple things I dug up real quick:

http://www.ni.com/pdf/csma/us/361574a1.pdf

http://www.automotivetestsolutions.com/pressuretransduc...#pressuretransducers (http://www.automotivetestsolutions.com/pressuretransducersarticle.htm#pressuretransducers )

http://www.sae.org/technical/papers/900171

http://www.optrand.com/

http://www.optrand.com/Papers/fisita98/fisita98.htm

http://www.optrand.com/CALplug.htm

And if you really want to get crazy:

http://www.tvu.com/PCombCompleteweb.htm

[Mikey Antonakakis]

Maybe I'm the one that is reading his posts incorrectly, but I thought he was asking for intake manifold pressures? Like the pressure in the manifold (or maybe the port) at IVO and IVC. You're not having any compression between those two events so you wouldn't really see anything above atmospheric... I'm confused now, though.

[Wesley]

Yeah, he doesn't want combustion pressures, just intake event pressures.

But yeah, the lowest you could possibly see is 0, the highest as a starting point guess is 1 bar. It's a ballpark figure, but will give you order-of-magnitude accuracy.

[Lightsun]

Yeah, Wesley is right. I just want some data to have an order-of-magnitude idea. I was not sure to have 1 bar of maximum pressure and 0.1 of minimum pressure,because I don't have any experimental data. This weekend I'll try to put a pressure sensor in last year's car to have some more information, and I'll try to get a pressure Vs piston position diagram.
Thanks to everybody for your posts!

[J.R.]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by rjwoods77:
Delphi and GM use cylinder pressure transducers from what I have seen. They look like a modified spark plugs. I would veer away from anything but a measured value since calculating leaves much room for error. Well for that matter so does measured if your setup sucks. I would start looking for sponsorship for something like that if you are really interested. </div></BLOCKQUOTE>

Somehow I think a hundred thousand dollar setup (AVL Prices) is a little much for an SAE team, Rob.