But, but Toby –
Yeah, you're right... I didn't think that one through quite all the way. I was
just
thinking about the difference between gauge pressure and total pressure (Total
= Gauge +
Atmosphere) - didn't consider the reason behind the reduced atmospheric
pressure at
altitude, that being fewer molecules per unit volume.
Thanks for clearing that up…
Gary McCormick
San Jose, CA (and 25 years past Chem 1A!)
-------------------------------------
Toby B wrote:
> But, but, Gary,
> (at the risk of starting another silly thread)
> If you start with a cylinder at 1 atm. and compress it to 1/9 its
> original volume, (14.7 x 9) you get 9 atm or something like 130 psi.
> But if you start with 1 atm. - 2.5 psi (14.7-2.5) and compress it to 1/9
> its volume, you only get around 110 psi.
>
> Or to think about it another way, in space there is no compression in
>a
> roadster (!) because there's no air to compress (leaving out the fuel
> vapor, of course). So as the air thins considerably, the number of
> molecules are reduced, and the pressures go down accordingly. Fewer
> molecules compressed into a closed space produce less pressure...
>
> And from experience- you need to reduce the amount of fuel at high
> altitudes since there's less air (and oxygen) and needs to be,
> correspondingly, less fuel...
>
> Or have the grey cells that were present for high school chem finally
> died?
> Toby
>
> Gary McCormick wrote:
>
> > Compression gage readings are PSIG (pounds per square inch - gage), which
>means the
> > additive pressure above and beyond atmospheric pressure. Short answer to the
> > question"Isn't altitude a factor?" is "No". Besides, the delta P between
>sea level and
> > 6400 ft ABS is only a tad over 2-1/2 psi.
> >
> > Gary McCormick
> > San Jose, CA (139 ft ABS)
> > ---------------------------
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