On Tue, 10 Dec 2002, Simon Reinhardt wrote:

> IIRC, it's because the water flashes to steam. Therefore, properly
> timed water injection augments the gases produced by gasoline
> combustion, to produce a larger volume of "stuff" to push the piston
> more strongly on the power stroke.

That's probably part of it, but it also lowers combustion chamber
temperatures so higher compression can be run without detonation.  Turning
the water to steam requires heat energy.  One of Mazda's sports cars in
the early 90s had water injection (actually, washer fluid injection.)  If
you ran out of washer fluid, the ECU cut back on the turbo boost to
protect the engine.

Some military *jet* engines used water injection after the compression
stage for a power boost, as well, and in that case the increase in thrust
came from the mass the steam added to the exhaust.  (Force = mass *
accelleration)  The practice isn't used anymore because it makes for very
sooty, dirty exhaust (the water interferes with combustion)  and because
it's hard on engines.

             _ _
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