Cylinder pressure during induction stroke?

[Azmio]

I am looking for cylinder pressure during induction stroke for an average NA engine? I am guessing that the vacuum is at its most when the piston reaches its maximum speed somewhere in the middle of the stroke.

 

[dcasto]

The maximum vacuum would be just before the valve starts to open on the intake, as soon as the valve opens, the pressure in the cylinder will rise (equalize) to the manifold pressure. The manifold pressure is at its maximum with no load as the throttle/trottle body is closed.

 

[patprimmer]

The piston is still on it's way up when the inlet valve opens.

For optimum performance, the inlet valve will be opened as soon as the inlet manifold pressure at the valve seat is higher than the exhaust manifold pressure at the valve seat.

This presupposes that the situation won't suddenly reverse and that the induction stroke is about to start.

The point varies greatly with engine speed.

Back to the OP

I don't know, but I think it will vary with manifold designs, rod length to stroke ratio, cam timing, engine speed.

I would GUESS it is around about maximum piston velocity

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

http://www.auto-ware.com/combust_bytes/pv.gif

for a bang blow suck squeeze diagram.

It really doesn't change much in this example (the near horizontal line at the bottom). I think Heywood has more detail.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dcasto]

Greglock, again, thanks. I'm a ChemE, I just know the physics and practicle parts. The vacuum doesn't change much, but I see that piston velocity isn't a factor, it's position of valves and piston in time. Thanks.

 

[Azmio]

i've been looking into dozens of PV diagram. Some of them shows the induction stroke as a horizontal line which means it doesnt change at all or maybe it is not scaled. Some pv diagram shows a small dip just below 0 bar as the piston is in the middle of the stroke.

The question that i have, how much below atmospheric pressure does it go. This will surely answer my question, is an IC engine an efficient air pump?

 

[dcasto]

see thread 71-158251