When a combustion happens inside the chamber how much pressure is the moles exerting inside the close container? How could one figure this out?

  • You want to know how much pressure is built (compression) just before the mixture is ignited, or do you want to know how much pressure the actual combustion causes?
    – JPhi1618
    May 25, 2016 at 13:40
  • Hmmm. I see this as nearly a duplicate to this question. The problem with the way this question is asked, is its not a fixed size chamber. And it's really pressure over time. Look at a crank rotation vs cylinder pressure map (they are available on line). It's a dynamic event, remember the spark firing starts BEFORE top dead center. It takes time for the explosion to propagate. Here's a typical image with pressure #'s
    – zipzit
    May 25, 2016 at 14:30
  • @zipzit, and idea what the unit of measure is for the vertical axis of that graph?
    – JPhi1618
    May 25, 2016 at 14:44
  • I would guess psi (pounds per square inch), but what do I know? I did a google image search for "crank rotation vs compression pressure", then looked for a likely chart. That particular image came from this page, but that doesn't begin to tell where the original came from.
    – zipzit
    May 25, 2016 at 14:48
  • According to the users manual for that software, "Cyl Pres" is the cylinder pressure in PSI. So if nothing else, the answer to the question is "in some cases, over 700 PSI of pressure is generated". Based on that one random image from Google.
    – JPhi1618
    May 25, 2016 at 15:30

1 Answer 1


There is no fixed pressure.. However it is not uncommon for ordinary petrol production engines to have an initial post spark pressure at peak power of around 68Atm's. Race petrol engines can be higher at more than 105Atm's

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