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Re: compression at altitude, etc.

To: Toby B <toby@wolfenet.com>
Subject: Re: compression at altitude, etc.
From: Gary McCormick <svgkm@halley.ca.essd.northgrum.com>
Date: Tue, 20 Jul 1999 08:26:44 -0700
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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