Water Injection into Jet Turbines

[MMEMatty]

I Understand 2nd Generation Jet Turbines (i.e. those used on the B-52, B-47 and that era) used to have exhaust water ingestion to boost power. How does this work? and why has it been scrapped?

Many Thanks.

Matty

[GlueBall]

SAA made use of water injection on early 74s to increase payload at high altitude JNB. The option reduces engine temperatures and therefore allowed higher T/O power settings.
:ooh:

[411A]

Water injection was used to increase mass flow thru the engine (not in the exhaust) and thereby allow a higher EPR during takeoff, while at the same time keeping EGT's in check.
Used no longer due to better material used in turbines.

Besides, the 'ole 'water wagons' were a bit@h to fly...:mad: :mad: :ooh:

[The Nr Fairy]

FWIW, Bell 206L (LongRangers) have water methanol injection fitted (I'm not sure if that's all types, but the MMEL specifies it an be inop for up to 120 days.

[ZFT]

GlueBall,

If I recall correctly, SAA also equipped 707C models with water injection giving a MTOW of 338,000 lbs.

It was a long time ago though so figure may be wrong.

[mustafagander]

Roughly speaking, the concept of water injection (with or without methanol) in a gas turbine is to reduce the temperature of the air entering the combustion zone. This achieves beneficial things like a more dense inlet flow, cooler inlet flow and greater mass flow. The cooler inlet flow was particularly helpful in the "G O Ds" when materials technology wasn't as well developed as now. The methanol is generally added for anti freeze, not extra cooling - think Metro which needs it for a potential 1EI missed approach in many places.

How it works is that water is injected into the diffuser case at the end of compression to cool the air. Compression causes considerable input of heat - as I recall it, the JT9 series diffuser case air temps run about 200*C at T/O power - so the water cools it. This means that combustion starts from a lower temp, so the turbine inlet guide vanes get a bit of relief - not much I grant you, but when they're so close to the limits of the materials every little bit helps. Also the water has mass, which is accelerated through the engine increasing mass flow. In the case of the JT9D it uses 600Kg per engine in 2.5 minutes.

The down side is that the system is rather complex and weighs quite a bit. From an operator's point of view, the complexities of the performance calculations were a veritable mine field given that we used it rather infrequently.

[BlueEagle]

In the Middle East we had Water/Meth. injection on the BAC1-11-200, think it may even have been fitted to the 'tropicalised' F27!

[411A]

Indeed it was, Blue Eagle, in every model of the FH227 and F.27 that I ever operated.

Take the FH227B for example. At higher altitude airfields, a 4000 pound increase in MTOW was possible with water/methanol.
A not insignificant amount, for this aircraft.

[Boss Raptor]

JT9D-59A as fitted to DC10-40 and A300 has water injection, exactly the same engine (literally identical in every way and not just different JT9 model) fitted to late B747-200's and redesignated as JT9D-7Q does not

All the Fokker F27-400 and 600 aircraft I have seen have water-methanol as standard, Dart 532-7R rings a bell?, the tanks are mounted at the rear of the engine pod behind the LG space and have a tendancy to break out of their mountings in the event of a heavy landing

[747FOCAL]

Boss Raptor - The 59A is equivelent to the -70A on the 747-200 not the 7Q which is slightly less fan diameter.

There are several operators out there that still use their water injection systems on the 747 Classics.

[NigelOnDraft]

Harrier / Pegasus uses it...

Carries 50gallons, which takes 90s to use. Gives up to ~2,000lb increase in thrust in the right circumstances (nearly 10%) - which in vertical operations can make all the difference between hovering and not, or getting off a short strip, Nominally 30s for takeoff, and 60s for landing (it doesn't start flowing until triggered as a certain JPT reached).

Injected, I think, after the combustion chamber, before the turbines. With water flowing, you get a slight increase in allowable RPM and JPT, but of course, a great increase in "effective JPT" (i.e. for a certain fuel flow and RPM, water reduces the JPT, AND you get a higher limit).

Your eyes water, and the engine cooks quickly, if you fail to land off your vertical landing before the water runs out!

NoD

[Compass Call]

BlueEagle

The BAC 1-11 used De-Mineralised Water only. To the best of my knowledge, the only 1-11 to use Water-Methanol crashed onto an autobahn in Germany immediately after take-off due to the turbines burning out. The Water-Methanol was pumped into this aircraft by mistake by ground staff who were unfamiliar with the requirements of the BAC 1-11.

Correct me if I am wrong but I believe that Water Injection is used for 'Thrust Augmentation' in jet engines. The water being injected along with the fuel in the combustion chambers and Water-Methanol is used for 'Thrust Restoration' in prop jets. The water-methanol being introduced into the early stages of the compressor.

CC

[BlueEagle]

Yup Compass Call you are right, the BAC1-11 was water injection, no Methanol, the memory dims with age!:D

[gas path]

Seem to remember the JT9d-3a with water injection, great fun on trim runs! that engine was unstable at the best of times let alone poking the thrust levers up to the take off range (above tandem bleed closure!) and then hitting the switch.:ooh:
I think BA were the first airline to mod it off, due in no part to reliabilty issues. (seem to remember P&W not being too pleased something about HPT life and warranty:hmm: )

[sky9]

Compass Call,

If my memory serves me right the German 1-11 out of Munich (1972/3) didn't use Water Methanol. The Engineers had used the containers to store aviation fuel so on Take Off additional fuel was injected into the engines.

I think that it was also the 1-11 400 and some 500 series that had the demin. water injection, not the 200.

[411A]

Yep, seem to remember likewise.
Jet fuel in the water/methanol tanks can not be good for engine reliability...:{

[Compass Call]

Sky9

You are right. It was the 475 and 500 series 1-11s that had water injection, not the earlier series. The 475 had the 500 wing & engines and a beefed-up undercarriage.

CC

[Ranger 1]

Demin water on BAC 1-11's, I can remeber it well, Dan Air 1-11 500's used to use it very frequently about 70 Gallons for depature out of here (BRS), we also frequently had to load 7x 10 Gallon barrels in the front hold for the return trip, from some short ,hot ,high airports, the aircraft had its own electric pump to up lift the stuff, it was contained in catering box kept in the hold, if it was missing it was a hand pump job!
Never saw a BA 1-11 use it though, I beleive they had no Demin facility on their aircraft (Dry engines).
Some Rolls Royce Dart engined aircraft were equipped with Water Methanol such as the HS748 2x tanks 30 gallons each, still used today. (just checked a 748!) :ok:

[gobfa]

All 1-11/500's with exception of those ordered by BA had de-min water injection system. At time I dealt with these aircraft (1970-74) a dry take off had a max of 43,522 kgs, wet increased it to 45,200kgs.

The speys fitted to 500's (non BA) had thrust of 12,500lbs believe the BA series were rated at 11,750 for commonality with speys fitted to the Trident fleet.

Another option BA took was not to have the fwd airstairs fitted to try and increase the payload available by taking lower rated engines.

[Flightmech]

I too remember working on both Dans & then BAF/British World 1-11's. So many barrels (demin) in the tanks and then so many in the hold for the return leg. Kept you fit i can tell you!. Also remember Air UK's F27's and the CAAFU 748's having the water methanol injection system, around 25 gals per side i believe. Those were the days!!

[BlueEagle]

Well Compass Call, we definitely had water injection on the Gulf Air BAC1-11s and they were neither the -475 or the -500 but they may have been -400, not -200 as I said earlier. A40-BB, BU and BX, (That was almost thirty years ago!).

[sky9]

I seem to remember from over 30 years ago that they were 1-11 432. Possibly ex Air Bahamas aircraft.

[BlueEagle]

Yes!!!! The light has just gone on, they were 432s. Thanks for that.

[ZQA297/30]

411A,
I think all variants of RR Dart engine used water methanol for "torque restoration".
I flew G-159, FH-227B, and HS-748 all used W/M.

Heard stories of a BW Viscount that had Avtur put in the WM tanks by ingenious refuellers who even modified refuelling nozzle to fit much smaller W/M overwing hole.
When injection cut in -tons of extra torque, luckily crew figured something was up and aborted T/O.

Going even further back I recall W/M was used on CV 440s, DC-6s and other heavy recips. It was called ADI (anti detonant injection), and allowed an extra 7.5 inches Manifold air pressure boost for takeoff. (Wet 62.5ins, dry 55 ins)

The principle was the same in all-increase mass airflow and decrease combustion temperature by using latent heat of evaporation for cooling.

[411A]

ZQA297/30,

You are quite correct about ADI.
Operated DC6B's for awhile, made a very big difference.
Altho the mix for ADI was slightly different, the principle was the same.
Water/methanol was also used in some models of the Allison 501 engine as well... (-D22C) on the Guppy, for example.

Strangely, many CurtisWright engines did not use ADI, don't know why.
Of course, the turbocompound engines had enough problems with PRT's.:uhoh:
But wow, when these engines worked good, they were the latest and greatest.
Especially the 1649 Constellation...a superb machine.:ok:
Put the DC7 to shame.

[Milt]

Salt Water Injestion

Navy web footed pilots know all about the results of salt water injestion into the engines of their choppers.

Salt deposits on some stages of the engine compressor reduce the mass flow resulting in rising combustion temperatures and power losses.

Short flights through rain cleans out the salt else precious ship's fresh water is used to wash out the salt after flight.

Old method - ~ 1960s - of cleaning compressor blades was to throw some walnut shells down the intake of the idling jet engine.

Are walnut shells still used or are we now higher tech?