humid is better in turbines

[Malcolm Robb, LC 0112G]

The old smoky Joe KC135A's used it (water injection), and  Harriers still 
do. If you ever watch one at an air-show, you'll see steam coming from 
infront of the engine intake whilst its hovering. If the steam stops - run 
- coz Harriers can't without the water! This happened at an airshow in 
Germany many years ago. The pilot managed to land safely to save the 
aircraft crashing into the crowd. He then ejected, coz the engine had 
exploded by now ,and parachuted to safety. Unfortunatley the main part of 
the ejector seat came down in the crowd - landed on someone - and killed 
them.   Almost worthy of a Darwin award.

EFI Related:
I'd like to know the answers to cases #1 & #2 also too. 
http://www.aquamist.co.uk/dc/dc.html says the specifc heat capacity of 
evaporation for water is 2256kJ/kg. Anyone ever tried putting a humidity 
sensor in the inlet manifold ?


-----Original Message-----
From:	Roger Heflin [SMTP:rahmrh at cableone.net]
Sent:	Thursday, August 23, 2001 1:50 PM
To:	gmecm at diy-efi.org
Subject:	Re: humid is better in turbines

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.  The more force you chuck 
out
> the back, the more the plane goes forward!  Sir Issac had that one down, 
as
> far as Harry ricardo goes, I dont have his book on combustion chamber 
design,
> but I do believe he plugged away at it for a while.
>
> Roger, you seem to have the thermo book handy, so I would like this
> calculated.  If you have one gram(or cc) of water at 100C, and you add 
enough
> energy to vaporize it into gas, how much energy does this take, and at 1 
ATM,
> how much volume does it take up once vaporization is complete?  If you 
take 1
> cc of air at 100C, and you add the same amount of energy, is the 
resulting
> volume increase more or less than for the water which goes thru the state
> change.  (IS this PV=nRT? or something of that sort)
>
> I believe I was wrong on the water being in a liquid form on a humid day, 
but
> what if you use injection, and have liquid water in the combustion 
chamber.
>
> If this goes on too long, i will probably have to dust off the books and 
look
> it up myself.
>
You might need to, I won't be able to run the numbers until tonight.

I believe you have 2 test cases, all closed systems, I don't believe
humidity enterns in to it as water vapor acts as an ideal gas.

	case #1: 1 mole an ideal gas at 50C with xx joules then
		added to it what is the ending pressure.
	case #2: 1 mole (minus a small amount for the water) of an ideal
		gas and 1 mole of water (18ml) at 50C with xx joules added
		to it, what is the ending pressure?

I suspect strongly case #2 (same physical volume starting) will produce
a higher ending pressure, this requires that you get the water into the
combustion chamer as a liquid, and then add enough energy to convert it
to an ideal gas.    If it goes inth the combustion chamber as a gas, it
will act pretty much like an ideal gas, and no gain is made, and also it
would have displaced some oxygen coming in so reduced the amount of energy
that you could add to things.   I am pretty sure the Harrier jets do
this trick also to increase thrust, though only for short periods of time,
I suspect that the water is weight inefficient so you don't want to use
it for long times (only use to hover (harrier) and takeoff and other
emergencies).

				Roger
------------------------------------------------------------------------  
----
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

----------------------------------------------------------------------------
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