Re: Water injection , answered (?)

From: (William Osmun )
Organization: Netcom
Date:         31 Oct 95 00:31:28 
References:   1
Followups:    1
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>Is there anyone who can support clues how 'water injection' in any way
>could effectively increase engine power?

Engines use water injection as a way of increasing power available up
to the engines rated power.  An engine is rated for a given power at a
given set of conditions, say 25,000 lbs of thrust @ sea level @ 70
degrees F.  Well at 95 F at 2500 ft this engine would not be able to
put out 25,000 lbs thrust but maybe 20,000 lbs.  To get the thrust
output up to the rated thrust (25,000) they can inject water into the
intake.  What this does is increase the density of the air so that the
engine can perform as it should.  The water vaporizes, absorbing heat
from the air and cools it.  So instead of the engine seeing 95 degree F
air at density altitude of 2500 ft., it see's air with density equal to
70F air at sea level, it may even seem cooler.  Some users even use a
mixture of alcohol and water.  They use this only when a reserve of
power is needed, such as take off, as it requires quite a load of
water.  For example, a system for a Garrett TPE331-15AW uses about four
(4) gallons of water a minute.  This engine puts out 1650 HP, it's a
Turboprop but the principle is the same.  I don't think it's used as
much if at all on the newer turbofan engines but is still an option for
some turboprops.  Not unique to turbine engines though, it can be used
on piston engines also.