Re: [ST] for Brett - fuel economy

[Ken Nisula <knisula@xxxxxxxxx>]

My understanding is not that an oxygen molecule is
replaced, otherwise humid days would decrease the %O2
in the air below 21%, rather the water molecule can
absorb considerably more heat than air alone.  Thus
more energy from the internal combustion is used up
heating the excess water vapor in the fuel/air
mixture, rather than transferring to the overall
efficiency of the engine.  Thus the best combustion
weather is a cool, dry day!

Ken

--- David Jonas <kahonas@xxxxxxxxx> wrote:

> On 4/17/06, Emile Nossin <Emile@xxxxxxxxxx> wrote:
> >
> > ... moisture should make the air density higher).
> 
> 
> I had thought that moisture in the air actually
> decreased the density, hence
> why aircraft don't like humid days.  When a water
> molecule replaces one of
> oxygen, wouldn't it weigh less?  Atomic weight of 2
> Hydrogens and an oxygen
> (H2O) is significantly less than that of 2 oxygens
> (O2).
> 
> Somebody with a better grasp on chemistry and
> weather phenomena please
> correct me if I'm mistaken.
> 
> David
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