Geez Scott,
I've got 5 textbooks that cover water injection and they dont even come
close to explainin git as well as you did..way to go
"Scott Skylane" wrote in message
...
DeltaDeltaDelta wrote:
A couple of days ago, I saw a picture of a DC-8, i think, taking off,
trailing thick black smoke from the engines (they weren't on fire). The
description of the picture said that it was using water injection to
give
more power for takeoff. I also came across this when reading about the
P-47.
How does that system work? I presume it's different for pistons and
jets.

Triple Delta


Triple,

I am not sure about the jet physics. In the piston (large radial) world,
a water/alcohol mix is injected just downstream of the carburettor for
hight power operation. This has the effect of reducing combustion
chamber temperatures, thus allowing higher manifold pressures (i.e. HP)
without detonation. If you didn't inject water at these power settings,
the amount of excess fuel needed to keep the temps down would actually
flood the mixture, causing power loss.

The alcohol in the mix does virtually nothing to contribute to the power
output, it is there merely to keep the water fromm freezing at altitude.

Interestingly, Pratt & Whitney apparently stumbled upon this effect
while doing heavy rain water injestion tests in the early days.

Happy Flying!
Scott Skylane