×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Cylinder pressure during induction stroke?

Cylinder pressure during induction stroke?

Cylinder pressure during induction stroke?

(OP)
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.

RE: Cylinder pressure during induction stroke?

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.

RE: Cylinder pressure during induction stroke?

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.

RE: Cylinder pressure during induction stroke?

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.

RE: Cylinder pressure during induction stroke?

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.

RE: Cylinder pressure during induction stroke?

(OP)
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?

RE: Cylinder pressure during induction stroke?

see thread 71-158251

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources