Mike Rapoport wrote:
: If you inject water into an engine with no other changes, power will go down
: a lot. I have used water injection to get a high compression engine to run
: on 92 octane fuel and the H2O decreases performance. Now if it were a
: turbocharged engine, I could increase the MP without detonation and produce
: more power, but that power would be the result of burning more air and fuel
: (not the water).

This could also be due to the poor ignition timing after this is
done. The timing (24 BTDC typical) will put the peak pressure pulse after
TDC. If you effectively retard this by slowing the burn with water
injection, the power will go down appropriately.

: Like you said, you are consuming energy to heat and vaporize the excess
: liquid. The energy used to heat the liquid to the boiling point and then
: effect a phase change is lost. You are puting liquid into an engine and
: having it come out the exhaust at a higher energy level (hotter and
: vaporized). That energy came from somewhere. It came from the power output
: of the engine.

Perhaps somewhat, but remember that typically almost 70% of the
energy in the fuel for a gasoline engine is *not* used to turn the crank,
but rather just makes your muffler glow a nice cherry red. It's the
integral of pressure, area, and crank throw that produces rotational
energy in the form of torque and RPM. I believe that water injection is
pretty much like high octane fuel. Some people (idiots, mostly) believe
that by putting fuel in their car that's higher octane than the car's
manual stipulates results in increased performance. All higher octane
does is let *OTHER* changes that can then be done (advanced timing,
increased CR, etc) to increase the power be performed and not damage the
engine. Water injection should amount to the same... all other things
equal, it will reduce the power somewhat. BUT if you do it, you can then
increase the CR, advance the timing, etc... and get more back out of it.


Imagine this: inject water into a high compression
: cylender and rotate the crank. The water will vaporize into steam. If what
: you are suggesting (that the steam is higher in volume and will drive the
: piston) where true, you could make an engine that would produce power and
: steam from water alone.

Man... if only I could get my carb set right for that....


: Try this: Lean to best power mixture in your airplane, note your speed or
: climb rate then go full rich and watch the performance decline.

Oh yeah... here in SW VA at 2100' field elevation, it about
vibrates off its mounts if you takeoff full rich on a 4200' DA day.
Doesn't climb too well either. Too rich is bad for everything except
CHT's.

-Cory


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