Water on the big round engines is called ADI. (Anti Detonation
Injection. It lowers the combustion temperature and accomplishes
exactly that.

A jet engine produces thrust by the amount of mass it can push out the
back end. By injecting water you have increased that mass and the
thrust increases without a cooresponding increase in internal
temperature. More fuel can be added also for the same internal
temperature withour the water.

The alcohol in the water is there to keep it from freezing and plain
water would accomplish the same thing as far as performance.

Water was/is only used on the older low bypass engines because their
low speed thrust is low and the metals used can't stand the
temperatures of modern engines. Modern engines have much better
low-speed thrust because of the high bypass fan and the ability to run
at a much higher temperature because of the metalurgy.



On Fri, 9 Jul 2004 16:42:42 -0700, "Jim Baker"
wrote:


"DeltaDeltaDelta" wrote in message
...
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

3D.....See Rapoports answer for the technical explanation. Aircraft such as
the B-52 models prior to the G and the KC-135A used water injection takeoff
thrust if the weight and weather demanded it. It was a tremendous boost in
thrust in the B-52G and when the water ran out, a big deacceleration. As
you noticed, water injected takeoffs caused a lot of smoke.

JB