Re: Water injection ?

From:         gallope@admin.curtin.edu.au
Organization: Curtin University of Technology
Date:         31 Oct 95 00:31:28 
References:   1
Followups:    1
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gernot@vmars.tuwien.ac.at (Gernot Auer (Prak 1 Gerhard)) wrote:

>A friend of mine and myself were wondering about a label connected
>with a picture in the Airlines Magazine, displaying a 707 of broken
>up People Express Airline, describing the takeoff supported by
>'water injection'. Since I am no aircraft technician I can only guess
>it means to inject water into turbofans to increase power, which
>sounds pretty weird.

>Is there anyone who can support clues how 'water injection' in any way could
>effectively increase engine power?

Water Injection was (is?) most definitely used to increase thrust.
Of course not all engines have the facility available or fitted.

We used water injection regularly on the 747-200 with Pratt and
Whitney engines, on the route Bangkok - Athens.

It was a few years back, but if my memory serves me correctly...

Because Bangkok temperature was usually over the magical 29 degrees C
and we had a large fuel load, there was usually a problem getting
ariborne (even though the runway was around 11,000  ft long).
Solution - (distilled) water injection.
(The figure of 2,400 kgs of water sounds familiar, but I could be way
out. - anyone know for sure?)
The water was injected directly into the combustion chamber.
It gave us a couple of thousand pounds extra thrust on each engine
which was enough to get on our way. On lineup, as the engines were
stabilised, the pumps were turned on and a noticeable drop in EGT (and
from memory an * increase* in fuel flow)  was checked. Any water pump
failure before 80kts was an abort situation. Depending on the graphs,
sometimes one pump failure was acceptable between 80 kts and V1,
sometimes no pump failure was acceptable before V1.
The water injection allowed higher fuel flows and power without the
EGTs going over the limits . From memory a full load of water lasted
exactly 3 minutes. (about 1500')
If any pump failed early, the Flight Engineer had to be on the ball to
retard the thrust lever to stop excessive EGT.

Water Injection was certainly no friend of the engines, and put a lot
of extra strain on them. But it worked!.

TG