View Full Version : Water Injection

8th Oct 2000, 12:27
I am trying to find out information on water injection into turbine engines. Would anyone know if Qantas or Ansett, still use this method to assist take off performance. Also I need to find out approx. how much water is used in the process. Any other facts on the system, or if anyone can steer me towards any good books or websites, I have read through the rollys royce, and aircraft maintenance texts, but want to see if there is more information available

Any information would be appreciated

The Kelly Gang
8th Oct 2000, 12:42

I've moved this thread to Tech Log where it will get better exposure.


Dunnunda & Godzone Forum Moderator

Danish Pilot
8th Oct 2000, 14:04
Surmount: I know that some older larger radial piston engines had water injection, but I never heard about (I might be wrong) turbine engines with water injection. Some uses fuel to cool the turbine blade (some of the P&W JT9D if remember correct). On the piston engines, they used water to cool the cyl.head/piston of the engine. A pistion engine will have its highest performance slightly below max EGT, but the best fuel to air mix happens at max EGT. So you use the water to cool the proces down to a little below max EGT, and that gives the most HP. Try to ask some DC6 or DC7 drivers, they should know.

Crash & Burn
8th Oct 2000, 14:29
The Metro 23 (Garrett TPE331-12U turbo prop engines) uses a water/methyl alcohol mixture for high density altitude take-offs.

It's a mixture of 40% methyl alcohol & 60% distilled or demineralised water.

When the performance charts require it's use it's turned on just after you start rolling. It gives approximately a 30% increase in torque and is turned off at 500'.

The Metro has a 16 gallon tank for water/meth and you'll get approximately two take-off's out of one tank.

It's a bit of an eye opener for the passengers when you get to 500 feet, turn the water/meth off and suddenly get a 30% torque decrease!

8th Oct 2000, 14:38
From memory the 747 'classics' had around 2 tonnes of water injected over a 2 minute period. (please correct me if I am wrong here, someone in the know)

8th Oct 2000, 14:52
The theory of water injection into turbine (& piston) engs is that after compression (or supercharger) the air is hot - bloody hot actually, well over 250*C in JT9D. So, water is injected into the diffuser case where it vaporises, extracting heat from the air. Cooler air = more dense air = greater mass/unit volume (recall the compressor pumps volume, not mass) hence more mass flow and the ability to burn more fuel without a meltdown.
On the JT9D it was 600Kg/eng in 2.5 min. Felt nasty when the water ran out and the old bird died in the arse on a 38*C night ex BKK at about 1000ft. Only tried it with t/o eng fail once - very, very nasty!!! P&W went for demineralised water while other eng mfrs used water/methanol mix which gave a slight performance increase, but is diabolical to store and handle safely. Only used for t/o on JT9D. Other engs, eg TPE331 in Metro 23, also need it to satisfy ldg clb performance on 1 eng.
To answer the question, Qantas has no water inj capability on any of its B747 fleet. As I understand it, neither does Ansett.
As may be readily imagined, water inj is a fiddle which takes the engine very close to its temp limits, and a slight malfunction can be spectacular with a large shower of assorted nuts and bolts if it goes haywire - a blocked/distorted water inj nozzle will do it. Given that it was only ever used when weight limited your heart rate was always somewhat raised until the water ran out as you climbed away.

8th Oct 2000, 15:34
Sounds good though.

8th Oct 2000, 15:56
Thansk for the help guys

Very much appreciated :)

8th Oct 2000, 20:39
There was a thread I followed for a little while which will be able to answer you r questions for sure. http://www.pprune.org/ubb/NonCGI/Forum3/HTML/000901.html

Hew Jampton
8th Oct 2000, 21:43
The BAC 111 used to inject about 80 gallons of demin water for 'high performance' (joke) takeoff. The water was pumped out of barrels by hand, by the F/O during a very hot turnround!

All day breakfast
8th Oct 2000, 23:05
The Rolls Royce Dart's on the HS748's injected a watermeths mix to restore maximum power if hot or high.
If required the pumps were switched on and the water meths kicked in at something like 3/4's max rpm.
If I remember correctly the minimum quantity in each of the 2 tanks had to be 10 gallons if the system was to be used, and roughly 1/2 of this would be used on a takeoff or go around.
'Was funny to watch as it looked like a steam train hurtling along the runway at times!

9th Oct 2000, 00:03
Just some number on the JT9D Surmount.

600 Kg in 2.5 minutes calculates to a waterflow of 14.400 Kg/hr. This compares to a fuelflow in T/O of about 10.000 Kg/hr.

The waterinjectionsystem was powered by four waterpumps each requiring 48 KVA. They each require their own generator with just a little spare for the electronics. Galleypower was/is automatically switched off.

The best fun I had was when on one engine the watersystem just kept running after switchoff and on another the system switched offbut the fuelcontrol just kept on giving the extra mount of fuel.


9th Oct 2000, 06:59
Early model Boeing 707-100's used water injection with the JT3C-6 engine. Two pumps (one for left engines, one for right engines) fed demin water during takeoff for 2.5 minutes. When the water stopped, it felt as tho the power had been pulled back big-time, and in fact the thrust loss was 2,100 pounds per engine, and on a 10,600 pound/thrust engine, this was a LOT. These aircraft were affectionately known as "waterwagons". I flew these for awhile, and was pleased to move on to the B707-320 with fan engines.

crocodile redundee
9th Oct 2000, 11:30
As an ex LAME of the era at Qantas of 'wet' JT9D engines, I must concur with "justavagander" entirely. The engine ground runs were just as spectacular as those described. Added to that was the exorbitant cost of the demineralised water supplied by fuel agents. Water Injection was a great idea but in practice, the bad far outweighed the good. However, I was able to pay off my house mortgage quickly on the overtime earned thru all those engine changes due to overtemps from malfunctioning water injection systems!!!!!!

11th Oct 2000, 21:51
Surmount, I think I am right in saying that there was also an incident with water injection: it was a case of a twin flame-out on a BAC 1-11, Germany, I think, where water-methanol was accidentally filled into the injector systems instead of demin water. Memory is a bit foggy but I seem to recall that the water-methanol mixture didn't mix completely (probably lower density) with existing water in the system and on t/o the existing gallons of water in the tanks did very nicely until the mix came through, (abt 1000'?) whereupon there was a flame out. I can recall a superb piece of airmanship and a landing on an autobahn - some survivors - maybe someone else has a better recall...

Dan Winterland
11th Oct 2000, 23:56
Not only does the water cool the turbine, but the water vapourises incresing the volume, consequently the pressure and thus the thrust. The design of the engine is important - if it is close to the surge margin, then obviouslty this is not a good idea.

The Harrier/AV8B has about 40 secs worth of water injection for hot/heavy hovering.

international hog driver
16th Oct 2000, 04:17
I picked up some chopper work for a bit of fun a few weeks back and came across this.
Bell 206B - Allison C20 and so did the origional straight L Longranger (not L1 c28,L3/4 c30).
Anyway in the longranger it has water meth injection, about 2/3 water and 1/3 meth.

Operation is essentially the same as fixed wing but for different engine conditions. Basically pull collective to engine temp, limit but not the TQ limit, hit the meth and the above effects of lowering the temp and greater mass flow, The temp drop is between 50 and 90 degrees celcius depending on conditions.
The temp drop allows you to pull more collective (more fuel) back to the temp limit and hence more TQ (higher collective position) and get you off the ground.
Works well when you need it, essentially fire it off, increase TQ get airborne RFN and once through translation and into climb lower power and WM off.

Thats how it works in the fling wing world.