humid is better in turbines

[Greg Hermann]

At 1:46 AM 8/23/01, KasaRyan at aol.com wrote:
>Whoo Whee! opened up a can o worms on this one!
>
>Ok, one of the reasons I put in the explaination I did was that I knew that
>some early jet aircraft, the 707 among them, would dump hundreds of gallons
>of water into the combustion chambers of the engines on takeoff.  This
>probably lowered the temp slightly, but more importantly dramatically
>increased the volume of what was coming out the back of the engine, and also
>pushing on the turbine to compress more air.

This water injection trick was used in the days of turbo-JET engines as
opposed to turbo =FAN engines. (With a turbo -fan engine being nothing more
or less than a two shaft turbo-PROP turbine engine with a DUCTED propeller
(in the form of the fan).)

Any turbine engine runs a very lean mixture--lots of excess O2 going by the
combustors. They are limited on fuel by temperature--too much fuel, and the
exhaust driven turbine will fail and/or melt! What the water (which, as you
have implied, was injected in LIQUID form) REALLY did was act as an
internal coolant--allow the use of more fuel without going above the
critical exhaust gas temp.

More fuel = more power and thrust.

The mass of the water in the exhaust (as vapor) is really not as effective
for increasing thrust as more air would be (because of the light molecular
weight of H2O (18) as opposed to air (29). Also, this was a _very_ fuel
inefficient way to increase power and thrust. Consequently--the move to
fan-jets.

Greg


----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org