>Partial credit to a couple of the previous writers. But water neither
>displaces air nor increases oxygen content. For a given temperature and
>atmospheric pressure a cubic foot of air contains the same amount of
>oxygen no matter how much water it has in it. However, as an earlier
>writer noted, when it rains it is usually cooler. Therefore the air
>density is greater and more oxygen is available for combustion. By the
>same augment your car should run better in the winter or anytime its cold.
Not true.
A cubic foot of atmospheric gas contains only so many moles of gas molecules.
Be they
nitrogen, oxygen, water vapor, carbon monoxide, or whatever. A zero humidity
air
contains the highest level of oxygen, as well other gasses. The more water
vapor
present, the less other gasses are capable of being present at the same
pressure.
You can check this quickly by looking at the engine trim tables for triming in
jet
engines. Something I used to do in my spare time. The higher the humidity,
the lowe
the thrust, always. Same relation to atmospheric pressure, the lower the
pressure, the
lower the power. For the exact same reason, less combustable molecules of
oxygen per
cubic foot atmosphere.
>All these effects were well understood by World War II and many of the
>fighter planes of the day used water injection systems to purposely add
>water to the intake air. I believe the Auto Union GP cars of the late
>'30's also used water injection.
Yes, principly to reduce knock tendancy, and to allow other principles to be
maximized.
SAE has many papers on water injection systems, consistently showing that by
itself,
water injection at best has no effect on power, and usually reduces power.
However,
the reduction in knock tendancy allows modifications to the engine (such as
compression
increases, timing advances, etc) that can more then offset the power loss of
the water
injection itself.
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