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Water in Jet Engines

04/25/2007 10:17 AM

while testing jet engines large mass of water is injected into the jet engines at very high preassure how does the jet engine able to hold the flame while the water is injected at very high pressure......the water comes out of the exhaust side without damaging the jet engine.....

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#1

Re: Water in Jet Engines

04/25/2007 11:05 AM

Good job, too. It wouldn't do for a jet engine either to get damaged or to go out while the plane is flying through a cloud...

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#2

Re: Water in Jet Engines

04/25/2007 11:21 AM

... actual question should be: HOW MUCH water can be injected into a jet turbine before it stops working? (as it actually happens)

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#4
In reply to #2

Re: Water in Jet Engines

04/25/2007 11:25 PM

Jet engines have ignition systems that are turned on when flying in rain, etc. to make sure they don't flameout. Don't know how much water an engine can take. Of course, it would depend on how large the engine is. I visited the Pratt & Whitney facility in West Palm Beach about 30 years ago. A friend of mine worked there and he showed me the test stands. They used a firehose to spray water into the engines. They also shoveled sand into the engines while running. They even threw dead chickens into them to simulate hitting birds.

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#20
In reply to #4

Re: Water in Jet Engines

04/26/2007 10:54 AM

There's footage somewhere of a guy getting sucked into an engine on the deck of an aircraft Carrier (sorry no reference in memory bank) - he lived.

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#5
In reply to #2

Re: Water in Jet Engines

04/25/2007 11:26 PM

Water injection has been used to increase thrust in jets too. Wikipedia mentions it in passing:

http://en.wikipedia.org/wiki/Water_injection_%28engines%29

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#14
In reply to #5

Re: Water in Jet Engines

04/26/2007 9:20 AM

At one time a lot of heavy jets used water injected, somewhere after the combustion chamber if I am not mistaken, to act sort of like an afterburner. I don't know if it is common practice now, but a lot of those same military heavies are still in service so I don't see why not.

I also remember the engine ignitors being put into "continuous ignition" mode when going through the pre-ascent checklist. I believe the concern was an air disruption causing a flameout more than any worry of water.

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#16
In reply to #14

Re: Water in Jet Engines

04/26/2007 9:34 AM

Greetings,

The aircraft Jet engines you mention do use a fuel/water mix to augment thrust. The rapid expansion of the water into a dense steam increases the net thrust.

This is still in use to day on several aircraft in the military.

The rate of water and fuel usage is incredible, but so is the power out put.

Not to many civilians con afford to fly around with an extra 2000 Lbs of water just to make use of a short air field on take off or some instant acceleration.

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#3

Re: Water in Jet Engines

04/25/2007 11:24 PM
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#6

Re: Water in Jet Engines

04/25/2007 11:53 PM

Greetings,

Water has also been used to help control the TPZ (Temp @ Primary combustion Zone) of Solar industrial Gas Turbine. This is called a Wet NoX system. The goal is to achieve and control 2800F at TPZ over a wide output range. The injecting ratio of H2O to Fuel is based on a tuning schedule that contains T1, TPZ and PCD variables.

Later versions of the low NOx emission do not use water, instead the use of a case bleed valve, IGVs and pilot fuel to the injectors are used to control TPZ.

This is how Solar Turbines can achieve there SoLoNox low emissions mode.

We also use online water washing to help clean the compressor section of the engine.

This practice is used routinely between shutdowns where a true water detergent was and rinse is performed.

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#7
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Re: Water in Jet Engines

04/26/2007 12:13 AM

Some old tractors used water injection to reduce temperature in the combustion chamber. This was done to prevent damage to the valves and other components which were not so heat tolerant as they are today.

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#8

Re: Water in Jet Engines

04/26/2007 2:51 AM

..and many years ago (30?) some companies were injecting small amounts of water into petrol engines to boost power and reduce emissions. Some were mixing it in the petrol itself as an emulsion, Tomorrow's World (BBC TV Program) showed some footage I remember.....

What became of it I haven't a clue.....does anyone els know?

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#18
In reply to #8

Re: Water in Jet Engines

04/26/2007 10:21 AM

Water & Humity reduces the octane requirement for internal combustion engines. Performance increase is due mostly knock (precombustion) prevention

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#19
In reply to #8

Re: Water in Jet Engines

04/26/2007 10:23 AM

Most engines these days have compression ratio's are at or below 8:1 and knock is not a problem as it was in the old 10:1 & 11:1 days.

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#9

Re: Water in Jet Engines

04/26/2007 3:19 AM

D:

In crude-fired boilers, water is misted into the combustion mix to create a flame vortex that has been shown to be more efficient at generating useful heat.

Since it's generally regarded as being incompressible, it's interesting that water was added to tractor fuel to affect the burn. How did that work?

Mark

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#10
In reply to #9

Re: Water in Jet Engines

04/26/2007 3:52 AM

....I would imagine that due to the way Diesel is sprayed under high pressure at around TDC of the compression stroke, the water was probably added to the diesel just before that......(Guessing!)

By the way, Diesel (petrol too!) is also basically incompressible like water, as most liquids are!! Which is why Hydraulics work as well as they do!!

But when used as a fuel, remember only a small spray is needed!!

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#11
In reply to #10

Re: Water in Jet Engines

04/26/2007 4:24 AM

The method for spraying water in to the combustion chamber was used also on small boat engines. The engine temperature had to reach it normal level before you could start spraying water into the combustion chamber. The water was sprayed through a dedicated nozzle and not through the Diesel-nozzle.

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#12
In reply to #9

Re: Water in Jet Engines

04/26/2007 5:31 AM

John Deere used water injection to reduce pre-detonation and increase performance in the Model D and Model GP until about 1930.

I did some google searches and found some interesting links on water injection.

The Hart Parr Tractor kerosene engine used water to prevent knocking (see fourth page):

https://www.asme.org/about-asme/who-we-are/engineering-history/landmarks/190-hart-parr-tractor

A Paper on "The Effects of Direct Water Injection on DI Diesel Engine Combustion". One point of interest is that it reduces NOx emissions and soot formation:

https://www.sae.org/publications/technical-papers/content/2000-01-2938/

Automotive Performance Parts - Water/methanol injection to improve horsepower:

https://www.snowperformance.net/Water-Methanol-FAQs-Gas-s/187.htm

A 1979 article on improving gas mileage with water injection:

https://www.motherearthnews.com/green-transportation/water-injection-zmaz79sozraw

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#13

Re: Water in Jet Engines

04/26/2007 5:36 AM

I just remembered, in our Turbine emergency Fire pumps in the Royal Navy (Rover gas Turbine from a car that Rover once built) nearly 40 years ago, we would clean them from time to time with water and (seperately) powdered walnut shells to get everything looking like new inside. I do not remember ever having to dismantle one, they were very reliable indeed.....

It was amazing just how much water the engines could take without the slightest problem when running.....you could even say that the engines completely disregarded the water.....the Walnut shells produced a lot of smoke if I remember correctly....

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#15
In reply to #13

Re: Water in Jet Engines

04/26/2007 9:25 AM

Greetings,

For a time the walnut shell method was the preferred method of compressor cleaning.

Later studies revealed that the walnut residue and fine powder was actually being pushed in to the PCD bleed and PCD Seal lines building up in the labyrinth seals causing damage to the seal journals of the engine.

Walnut shells have not been used for many years now because of that. The water / detergent wash is now the preferred method, but it requires that the engine be shut down and cool before the procedure.

The process is to bring the engine up to 25% NGP, (Speed of Gas Producer) spay the detergent water solution in to the air inlet of the engine. stop engine cranking and let the detergent soak for a period of time. Again crank engine up to 25% and rinse with water until the engine drain lines show clear water. On a dirty engine this may take two cycles to accomplish.

Once that is complete, restart the engine and let it dry out before loading.

The On-Line water wash uses just water and will only prolong the period of time between water / detergent washes.

In hot climates the induction of a FOG mist is used to reduce NoX, increase power output and extend the wash intervals.

T.

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#17

Re: Water in Jet Engines

04/26/2007 10:06 AM

A couple of things that have not yet been mentioned. First off modern aircraft jet engines are turbofan engines, not turbojet engines. Turbofan engines are actually two and in the case of the RB211 three jet engines all built on the same axis. The whole idea is that the majority of the air that is sucked into the front of the engine doesn't actually go through the combustion chambers but just comes out the back. It works like a gigantic fan and increases the overall efficiency as well as reducing the noise the engine creates. With a modern fan jet you can have up to 80% of the air that is sucked in the front bypasses the combustion chambers. As a result 80% of the water that is sucked in also bypasses the combustion chambers.

Secondly the compression ratio on a modern fan jet is something like 40 to 1. Since the amount of water that a given parcel of air can hold increases with temperature and pressure by the time you get to the combustion chamber most of the water will have evaporated and become water vapor.

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#21
In reply to #17

Re: Water in Jet Engines

04/26/2007 11:31 AM

I agree Masu. You are giving us the best answer, and I just want to add that the presence of water vapor in the combustion chamber means that we have more mass wich helps increasing compression because of the higher density inside it.

This trick has been used even in old cars equiped with carburatos (in spanish they were known as water carburators), let´s just remember that cars show some increase in power when moving across strong rains. If you haven´t experinced just try it in the next rain season.

The point is; I think (in case I do) we will never see enough water coming into a turbine out of the rain even in a rain storm, at least not enough to make it stop wich is good news for me who don´t like flying.

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#24
In reply to #21

Re: Water in Jet Engines

04/27/2007 3:29 AM

Mario, you are mentioning "cars show some increase in power when moving across strong rains. If you haven´t experinced just try it in the next rain season." The reason for some increase in power output is due to two different conditions:

1. The air is cooled down, and thus the air charge of the engine increase, and the average combustion pressure increase; -result: power output increase.

2. Rain water is added to the air going into the combustion chamber, and as stated in more of the messages, and when the water mist is changed to steam during combustion cycle the average pressure is raised; -power increase.

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#25
In reply to #24

Re: Water in Jet Engines

04/27/2007 9:21 AM

Right!. Thanks! that´s what I wanted to say.

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#26
In reply to #24

Re: Water in Jet Engines

04/27/2007 11:56 AM

Shhh, that's an oldschool ratrod secret.... misting water into the vehicle's intake via a mist nozzle and windshield washer. Only works at wide open throttle though.

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#27
In reply to #26

Re: Water in Jet Engines

04/27/2007 12:09 PM

Right!, just what happends when you step on the gas.

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#28
In reply to #21

Re: Water in Jet Engines

04/27/2007 2:21 PM

Hi Mario Gasca,

Thanks for the compliment. I must however disagree with your statement;

"the presence of water vapor in the combustion chamber means that we have more mass wich helps increasing compression because of the higher density inside it."

It's a common misconception that air that has water vapor or moisture in it is denser than dry air. In reality moist air is less dense than dry air and needs to be taken into account when flying an aircraft. Wikipedia have a good article on the density of air that explains it well.

With aircraft there is a thing call the International Standard Atmosphere ISA that everything is referenced to. When you calculate how and aircraft will perform, for example when taking off, you calculate how dense the atmosphere where you are is in relation to the ISA and this give you what is called the Pressure Altitude PA. To calculate the PA you take temperature, humidity, barometric pressure and altitude into account. Once you have a PA you can now use this to predict how the aircraft will handle.

The change in density may not seem to be great but it can affect the way an aircraft behaves and on a humid day aircraft require a longer take of run before becoming airborne.

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#29
In reply to #28

Re: Water in Jet Engines

04/27/2007 11:57 PM

Yes, the three H's of reduced aircraft performance, Heat, Humidity, and Height. All of these mean less dense air and therefore reduced performance.

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#22

Re: Water in Jet Engines

04/26/2007 12:38 PM

Hi:

I have been enjoying all the comments so far since I work at a Combined Cycle power plant. Years ago, I read an article about emergency power for fighter aircraft. I think it was on the Corsairs used in the Second World War which had a throttle quadrant that had a copper stop pin at full throttle. In case a fighter got into trouble with the nimble Zeros, the pilot could slam the throtle forward, shearing the pin and get an instant power boost by water injection. He could then get outta Dodge in a hurry for a little while and get home. It did ruin the engine, however. Somebody have more info on this?

Hank

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#23
In reply to #22

Re: Water in Jet Engines

04/26/2007 10:52 PM

Many of the articles I read ( and the last two links I posted earlier) while googling this topic mentioned WWII aircraft using water injection for a power boost, particularly the P51 Mustang. No mention was made of it ruining the engine though.

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#30

Re: Water in Jet Engines

05/13/2007 9:28 AM

Thanks for that link aurizon.

I took off once from Raliegh-Durham SC in a heavy rainstorm, and was looking out the window at #2 engine when it powered up for takeoff, and let me tell you, there was about a 10 foot radius all around the intake where all the rainwater was sucked into the engine. It looked like a tornado, all the rain was swirling around and into the engine, it looked pretty awesome, but I was really wondering just how much water that thing could take. Thanks again for the link!

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#31

Re: Water in Jet Engines

11/10/2008 1:44 PM

Actually , water (rain) can enter a high speed turbine and become steam.

Large amounts , however , have detrimental effects on the turbine vanes.

Temperature variations caused by cold water being applied to hot metal

causes stress , and possible turbine vane failure.

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