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A/c train
Topic Author
Posts: 674
Joined: Sun Jun 10, 2001 7:57 am

Water Injection

Wed Dec 19, 2001 7:16 am

A sure fire way of defining an aircraft which has engines using the water injection system on T/O is a stream of black smoke coming from the exhaust, but which a/c engines use this, apart from the 1-11 Spey? I dont see it very often.
regards
a/c
 
TWAalltheway
Posts: 142
Joined: Mon Jul 30, 2001 11:17 pm

RE: Water Injection

Wed Dec 19, 2001 8:13 am

hey,
I think I remember reading that early 707's used water injection in the J-57's. But the engines were refined in later models and the need was overcome. Also, B-52's used it as well. I think they use the same engines. See the photos.

Click for large version
Click here for full size photo!

Photo © Frank J. Mirande




Click for large version
Click here for full size photo!

Photo © Frank J. Mirande



TWA all the way!
 
david b.
Posts: 2894
Joined: Fri Jun 15, 2001 7:18 pm

RE: Water Injection

Wed Dec 19, 2001 9:30 am

Why does water need to be injected into the engine?
Cooling? But jet turbines are air cooled.
Teenage-know-it-alls should be shot on sight
 
JBC75
Posts: 17
Joined: Fri Sep 14, 2001 6:21 am

RE: Water Injection

Wed Dec 19, 2001 9:59 am

It provides extra thrust. That's the short answer anyway.
 
Rick
Posts: 125
Joined: Mon Dec 13, 1999 9:37 am

RE: Water Injection

Wed Dec 19, 2001 9:30 pm

Even with water injection to provide extra thrust, early 707's with water enjection still ate up almost every inch of runway on long cross country flight especially from hot high altitude airports. Just a note, they refered to the early 707's as "Water Wagons".
 
PerthGloryFan
Posts: 726
Joined: Fri Oct 27, 2000 9:48 pm

RE: Water Injection

Wed Dec 19, 2001 11:53 pm

A sure fire way of defining an aircraft which has engines using the water injection system on T/O is a stream of black smoke coming from the exhaust, but which a/c engines use this, apart from the 1-11 Spey? I dont see it very often.
"Water" injection is one of the causes of the smoke, but it is also an indication of the efficency (inefficiency) of the combustion process generally.
Turbo-props such as the RR Dart on Viscounts and F27s also used water injection and the exhaust wasn't that noticeable.

Why does water need to be injected into the engine?
Cooling? But jet turbines are air cooled.

Well it's actually a water-ethanol mix - vapourising water expands at a very significant rate, so injecting this mix into the fixed volume of the combustion chamber of a turbine produces an extremely high pressure that gets those blades spinning a fair bit faster.

I wouldn't of thought jet turbines are cooled at all actually - they mostly like it very hot - although the passage of the air through it does maintain a constant temperature - I believe fan temperatures of "reverse" style turbines like the PT6 can be problematic at shut down though.

cheers
PGF


 
A/c train
Topic Author
Posts: 674
Joined: Sun Jun 10, 2001 7:57 am

RE: Water Injection

Thu Dec 20, 2001 1:40 am

Perthgloryfan,
In order so turbines can survive in temps that are higher than melting temp, it is essential and I mean ESSENTIAL!, that both the NGV's and turbine rotor blades of most turbine assys, are extensively cooled internally using compressor air , heres five variations,
- Internal cooling
-FILM cooling
- Multi-pass cooling
- Platform cooling
- Transpiration cooling
, the blades are hollow, made of titanium/ nimonic alloys( in older engines),/ceramics/ single crystal blades. So they are heat resistant but will melt at high temps. The blade is fed air through the root of the blade, and out the tip, most blades used nowadays utilise, quintuple pass/multi feed/Internal cooling with extensive film cooling, some blades even have holes in the leading edge, the air inside the blade is sent through small pipe working, clever stuff!!, the air for this blade cooling is taken from the compressor because it is the next hottest part of the engine, LOST??, this is so the blade will not have to withstand such a dramatic temperature change, or ' Thermal cracking' as it's known.
Water Injection-
The water methanol/alcohol mix is sprayed at the compressor inlet or diffuser case, sometimes both are used, im not sure but I think on some a/c the pilot has Comp / diffuser individual selectors to control either.
You have to use de mineralised water which has a total solid content of not over 10 parts per million.
The sensitivity of the engine to the air entering the engine results in an appreciable loss in thrust available for t/o on a hot day or warm...., it is desirable to use some means of thrust augmentation,
10-30% added thrust, tap water will leave deposits on blades so not a good idea.
The water injection system was a pain in the arse anyway, I know of 1 1-11 were the NRV failed and the tanks burst, VC-10 should know quite a bit about this system with the 1-11 and all,
regards
a/c
 
VC-10
Posts: 3552
Joined: Tue Oct 26, 1999 11:34 am

RE: Water Injection

Thu Dec 20, 2001 5:54 am

I would dispute that water injection caused black smoke when used on the 1-11. A better indication is the fine water mist that appears under the belly approximatly in line with the engine intake and is the exhaust from the turbine water pump.

As A/c train states demineraised water is used and is stored in a single rubber bag tank at fwd of the aft cargo hold. The water is injected into the combustion chamber from two nozzles on each burner head and has the effect of increasing the air density and so thrust.

I did see the result of the compressor delivery air backfeeding to tank, as well as bulging out the fwd wall of the cargo hold it also left a distinct hump in the cabin floor.
 
TimT
Posts: 168
Joined: Sun Jun 03, 2001 1:38 pm

RE: Water Injection

Fri Dec 21, 2001 10:36 am

The early Pratt & Whitney JT8 engines smoked like a chimney-- in the 80's they did an EO mod "smokeless burner cans"
 
Guest

RE: Water Injection

Fri Dec 21, 2001 11:23 am

I understand that some of the old Metroliners had the Garrett TPE331-11 engines and that these were also water/ethanol injected. I have quite a bit of time flying the -10 engine and these were not injected.
 
DC-10inLB
Posts: 136
Joined: Mon Aug 21, 2000 5:48 pm

RE: Water Injection

Fri Dec 28, 2001 12:27 pm

The very early 707s, DC-8s and Convair 880s all had water injection.....basically anything with a turbo-jet had it at the time. Made the ingoing air denser thereby producing a little more thrust. Here are 2 fine examples of water injection at work.
Click for large version
Click here for full size photo!

Photo © Larry Pullen


Click for large version
Click here for full size photo!

Photo © Larry Pullen


Can you imagine the panic the environmentalists would be in if this were the case today?
 
747Teach
Posts: 176
Joined: Wed Nov 29, 2000 3:05 am

RE: Water Injection

Sat Dec 29, 2001 2:28 am

A/c train:
Oddly enough, no seems to have mentioned early 747 aircraft with the JT-9D engines (can't speak for CF-6 or Rolls) had water injection. The tanks were in the leading edge of the wing, at the very wing root. Each tank had a couple of transfer pumps, and were serviced from a panel under the belly. Some 747's still have the "tanks," which were actually a box-like structure, in the wing root. The plumbing routed down the leading edge and down through the pylon to a distribution point. The plumbing also had a sense line that ran down to the fuel control, and to a device called the regulator up towards the top of the engine casing. The lines then went to the fuel nozzles where the water was injected along with the fuel. On the flight deck, the flight engineer had a quanity indicator and some indicator lights and switches, and there were further indicating lights on the Captain's panel. I believe the switch to activate the system was on the First Officer's side. I'm sorry I don't have a maintenance manual reference for you, as the system has been deleted from our books. In our IPC the parts references still exist. Water injection is ATA chapter 82, if anyone has that reference available any more. Regards,
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: Water Injection

Sat Dec 29, 2001 3:01 pm

Actually, DC-10inLB, many of the older 707's and DC8's with turbojets did not have water injection, only a few models. And when the heavier (intercontinental) 707 was introduced, it had JT4 (no water) engines instead of JT3's. Convair 880...no water injection either.
 
DC-10inLB
Posts: 136
Joined: Mon Aug 21, 2000 5:48 pm

RE: Water Injection

Mon Dec 31, 2001 6:17 pm

My bad, the CV 880 just had very smokey noisey CJ-805s....But yes there were some older 8s and 707s with the water injection. Some of Western's early 707s had them i think
 
ERJPLT
Posts: 22
Joined: Fri Nov 09, 2001 1:41 am

RE: Water Injection

Tue Jan 01, 2002 12:35 am

Jet Guy,

You are correct in saying that the -11's have the injection system. Both the -11's and -12's have the CAWI( Continous Alcohol Water Injection) units. It was a mixture of water and ethynol, I believe it was a 60/40 mix(not definite). You could really feel it on departure when you had to kick it in for some added thrust. It would add 100 shaft HP, thus the -11 became 1200 SHP a side and the -12 became 1300 SHP a side.

David B.,
Basically the water injection system allows the engine to operate as if it were flying at a lower density altitude. The lowered temperature allows the additional thrust to be created. The nozzels were located at the air inlet and would produse a fine mist to mix with the air so that the P2T2 tube that measures temp/pressure for the engine will now indicate a lower temp than actually exists. On the Garret turboprop engines you would have to use a chart to determine the proper thrust for take off. For example, at 30 degrees celsius you would generally use about 80% thrust. By using the CAWI you could increase this to 100%. It was only used when you were pushing max gross weight because you are also weight restriced with the temp and runway limitations. You could use this for a total of 2 or 3 minutes before you ran out. Hope this helps.....

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