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Water / methanol injection
I am hoping that John Farley will see this and respond.
I have been reading about water/meth injection in piston engines and I wonder whether it might be useful for very small gas turbines. Does anybody have experience or knowledge of this in aircraft engines. Some of the claims and descriptions are puzzling me. Since methanol has a lower calorific value (LCV) than petrol, I cannot see how it could boost power. The water, however, would reduce air temperature, making it 'easier' to compress. On the other hand, if they are referring to nitromethane, this would have the effect of enriching the oxygen content. So the question is, what is the chemical content of water / method used for gas turbines? |
Jack,
Cannot answer your chemistry queries but RAF Andovers had a Water/Meth system to boost engine performance. There was an obvious 'kick' when the system engaged as the RPM wound up. lm |
Thanks lm. I didn't know that - was that for the Air Dominance variant of the Handover?
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The HS748 and BAC 1-11 used Water Meth.
As I understand, the principle is for the water to lower the air temperature and the meth to stop it from freezing. I couldn’t resist this - the investigation concluded that it was not water meth in the tank. |
safetypee's very close -
Water provides evaporative cooling, but also more mass flow. The methanol is only for antifreeze. |
Jack,
I am unfamiliar with your ref to the 'Air Dominance' version. The Military variant with the rear ramp and clamshell doors was fitted with a Water/Meth system. From safetypee's input, it would seem logical that The Queen's Flight HS748s were similarly fitted. lm |
Doesn't the Harrier use water injection for extra power in the hover?
SSD |
The various Pegasus engines in UK Harrier variants up until those in the GR7A and GR9A had a JPT limit which when you hit it resulted in an auto reduction of fuel flow and so a cutback in RPM unless you tripped the limiters. So a 50 imp gall tank of plain water (demin ideally to avoid furring up of the injectors) was used. When this was switched on you were in effect pissing on the fire and so reducing hot end metal temps. This gave a lot more thrust – 1000 lb or more depending on the conditions.
When off doing shows etc unsupported one used to fill up the water tank from the local fire engine. The filler cap was on the top of the fuse above the wing and like a car. If asked "Wot you filling it up with water for mister?" the best answer was to look around as if to check for the black Omegas and say quietly. "Its the special fuel pellet I put in first that makes it work" We needed no antifreeze 'cos the tank was in the engine bay which stayed warm even in a high alt cruise. |
Water injection
Many thanks John.
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Didn't KC-135s and B-52s with turbojets rather than turbofans use it as well? Otherwise even the earth's curvature wouldn't have got those beasts airborne.
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Thanks chaps.
Thanks to all for contributions. The application I am looking at is very small gas turbines for model aeroplanes and UAVs. In models they are very heavy on fuel consumption and I suspect that there are considerable amounts of unburnt hydrocarbons being cast to the wind. The scale issue arises big time with residence time in the combustors being very short indeed. I was wondering whether spraying water and methanol (commonly used for model IC engines) laced with nitromethane would allow the spray to atomise in the compressor and make the whole thing more efficient. I guess the only way to find out is to buy one and try it out. Be ready for loud noises in North Wiltshire!!
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Zoom: correct, the P&W J57 powered versions of the B52 and KC135 had water injection.
Seeing John Farley's comments of filling up from the fire engine causes the thought that you had to check that what was going in, was indeed water! (Paninternational BAC111-515 Hamburg 06/09/71, Jet A1 instead of de-min. water, 21 fatalities.) |
The Trident 2 had water methanol fitted but it was removed. The problem was that the extra take off weight gained hardly exceeded the weight of the equipment and the water/meth.
As I recall the only indication was a green light twinkling away to show the system was working. The problem in a small engine would be getting the flow rate right. |
Originally Posted by Zoom
Didn't KC-135s and B-52s with turbojets rather than turbofans use it as well? Otherwise even the earth's curvature wouldn't have got those beasts airborne.
When I first got into tankers the system was set up with LEFT and RIGHT water injection. Finally some wizard realized that with a little different plumbing, you would NOT have assymetric thrust if one of the pumps failed and they went to an INB and OUTB system. (well, DUH!) The injection pumps had a very high electrical load and at times you could not get the engines to 'take water' so various methods were used including running the engines up to about 2.00 EPR and then turning the water pumps on (helluva shock on the engines). 'wet' EPR for takeoff was 2.85. A 'wet' takeoff was standard out of Thailand when carrying 165,000lbs of fuel for the fighters going north. Takeoff gross around 280 when added water and Vr speed around 170kts. |
Interesting paper here that seems to indicate that water injection could again have a future.
http://www-psao.grc.nasa.gov/Library...er_7_20_04.pdf |
Yep, also the first versions of the B-707 equipped with the PW JT3 used the "wet" take off thrust procedure.
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They were referred to as "water wagons", IIRC
Maybe early DC-8's too? |
I believe most RR Dart powered aircraft used water/methanol injection to either restore or boost engine power in hot/high operations. The RR Dart Mk529 was an example of a restored power engine while the Mk532 was a boosted engine. The Fairchild/Fokker F-27 series of aircraft as well as the Gulfstream G159 used water meth injection.
From the Fairchild manual: The Fairchild F-27 aircraft is equipped with a water/methanol system which provides maximum engine power without exceeding allowable turbine gas temperature when high ambient temperature necessitates fuel trimming. When operating at high power settings in high ambient temperatures, fuel flow must be trimmed to maintain engine temperature within acceptable limits. To restore the power lost by trimming, a controlled flow of water/methanol mixture is automatically injected to increase the mass flow through the engine. Although an increase in mass flow could be obtained by using water alone, this would not restore all the power lost by trimming since engine temperature would be lowered. By adding methanol to the water, engine temperature is raised to the correct level which, in conjunction with the increased mass flow, restores power lost by trimming. Thus, at sea level, with temperatures above ISA, engine power is restored to the value that would be obtained under ISA conditions. At altitudes above sea level, power is restored not to it's sea level value, but to the value which would be obtained at the particular altitude under ISA conditions by automatically correcting for pressure altitude. Power restoration takes place up to an altitude of 10,000 feet. The correct mixture for the above is critical. It is 63% +/- 1% of water and 37% +/- 1% of methanol by volume. W/M is extremely corrosive, so if you have to handle it personal protective devices are essential. |
Originally Posted by pigboat
I believe most RR Dart powered aircraft used water/methanol injection to either restore or boost engine power in hot/high operations. The RR Dart Mk529 was an example of a restored power engine while the Mk532 was a boosted engine. The Fairchild/Fokker F-27 series of aircraft as well as the Gulfstream G159 used water meth injection.
From the Fairchild manual: Gulfstream says essentially the same thing The correct mixture for the above is critical. It is 63% +/- 1% of water and 37% +/- 1% of methanol by volume. W/M is extremely corrosive, so if you have to handle it personal protective devices are essential. Once you got the Dart started, you 'trimmed' it up with small toggle switches on the center console. You were provided with wet and dry data in the summer days. As part of your flight kit, since the YS-11 had such poor ventilation and air conditioning, you carried a small towel to wipe the sweat from your brow after a few flights But then (being parochial and partial to cold beer) it did make the afternoon brew even more enjoyable. |
Hi all
We use water/meth injection on our Fairchild Metro 3 and 23's. All it does is help recover the lost power from low density air, ie Damm hot ! We use about 30 litres per takeoff on the 2 engines (TPE-331-12U) And the turbines love it ! I believe however the methanol is to stop the water freezing through the compressors and in the inlet when its extreamly cold. |
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