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Water Ingestion  
User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Posted (7 years 10 months 1 week 3 days 12 hours ago) and read 4368 times:

How do modern engines deal with extreme water ingestion? Numerous water ingestion test videos of modern high bypass turbofans dramatically display how much water gets shot out the bypass portion of the engine's exhaust.

However, I wonder how the core deals with this sort of water volume. Light sprinkles are one thing, but in a heavy shower, does the core pass water from the intake staright through the turbines and exhaust nozzle? Is the volume of water, even in extreme situations, proportionally low enough (to the volume/mass of air) to be vaporized and passed through the hot portion of the core as gas?

Of course, at some point, enough water ingestion will unstart the engine, but I'm interested in what happens to water that is ingested into the core at levels that the engine can remain functional.


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21 replies: All unread, jump to last
 
User currently offlineJben From Australia, joined exactly 8 years ago today! , 77 posts, RR: 4
Reply 1, posted (7 years 10 months 1 week 3 days 12 hours ago) and read 4370 times:

Water can do several things when it first hits the blades. It can bounce off, it can form very small droplets by the blades basically cutting the water droplets up into smaller droplets. The blades also act like a centrifuge, in that water that hits the blades, will actually be pushed to the outside and therefore less likely to enter the engine core.

Most of the water goes into the bypass duct, where it does basically nothing. Some of the water will enter the engine proper, and ordinarily this isn't a problem. There are situations where the engine will ingest enough water to cause the combuster to flame out.

Do remember there are situations where water is deliberately to increase the performance of an engine, called water injection. The B-47 used this approach quite successfully.


User currently offlineZeke From Hong Kong, joined Dec 2006, 9031 posts, RR: 75
Reply 2, posted (7 years 10 months 1 week 3 days 11 hours ago) and read 4359 times:

Quoting Jben (Reply 1):
The B-47 used this approach quite successfully.

If I recall correctly the B52, DC8, 707, and Metro have water/alcohol injection to increase the mass flow during takeoff.

Quoting Speedracer1407 (Thread starter):
Of course, at some point, enough water ingestion will unstart the engine, but I'm interested in what happens to water that is ingested into the core at levels that the engine can remain functional.

It would remain in the airflow, and increase the the mass flow form the powerplant. During heavy rain I select the ignition on as well, and ignition is automatically on when we select wing anti-ice on or the are flaps selected.



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User currently offlineKaddyuk From Wallis and Futuna, joined Nov 2001, 4126 posts, RR: 26
Reply 3, posted (7 years 10 months 1 week 3 days 7 hours ago) and read 4332 times:

Quoting Zeke (Reply 2):
It would remain in the airflow, and increase the the mass flow form the powerplant.

You're after Mass Air Flow, it will increase your mass airflow but not how you suggest. The Water will reduce the temperature of the air, which increases its density and therefore its mass (for a given volume).

Quoting Zeke (Reply 2):
If I recall correctly the B52, DC8, 707, and Metro have water/alcohol injection to increase the mass flow during takeoff.

It didnt work the same in all systems however. Some aircraft have Compressor Water Injection where the water is fed into the compressor and some have combustor water Injection where the water is injected into the engine just before the combuster (Normally with the Fuel Nozzles...)

Quoting Jben (Reply 1):
The blades also act like a centrifuge, in that water that hits the blades, will actually be pushed to the outside and therefore less likely to enter the engine core.

And in doing so will affect other items such as engine cooling (via Engine Bleeds)



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User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 4, posted (7 years 10 months 1 week 3 days 6 hours ago) and read 4318 times:

I have the video of the water ingestion test on the P&W 4086 when it was still in development. P&W had the engine inside of a test cell, where water was sprayed via a "ring manifold" into the intake of the engine; so much that water was pouring out of the back end of the engine, but it still ran.

User currently offlineBuzz From United States of America, joined Nov 1999, 697 posts, RR: 21
Reply 5, posted (7 years 10 months 1 week 3 days 5 hours ago) and read 4311 times:

Hi SpeedRacer1407, Buzz here. I'm looking for the book that shows air temperature in the compressor vs. engine station... it's in my boro book at work.
I'm impressed that the PW2000 engine on a 757 uses 14th stage at about 600 degrees to cool down the turbine section. I guess if you have a 27:1 compression ratio the air gets hot, even if you add water.

I don't recall how many pounds of air per second are inhaled. About 20% gets to be "burned", the rest is for cooling: a film of air is directed against burner louvers and nozzle guide vanes and turbine blades to keep from melting things.

I've noticed doing engine boroscope stuff, anything that's not air gets slung outwards like Jben in Aussie-Land was saying.

I don't know how much water it takes to strangle an engine, never had to do it!

g'day


User currently offlineJamie757 From , joined Dec 1969, posts, RR:
Reply 6, posted (7 years 10 months 1 week 3 days 1 hour ago) and read 4255 times:

Quoting N231YE (Reply 4):
I have the video of the water ingestion test on the P&W 4086 when it was still in development

Any chance that you could make some of this footage available to us?

 Smile

Rgds.


User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 7, posted (7 years 10 months 1 week 3 days ago) and read 4232 times:

Quoting Jamie757 (Reply 6):
Any chance that you could make some of this footage available to us?

Sure, give me about a week and I will have it up on YouTube, like my other two videos  smile .


User currently offlineFlyMatt2Bermud From United States of America, joined Jan 2006, 563 posts, RR: 7
Reply 8, posted (7 years 10 months 1 week 2 days 14 hours ago) and read 4113 times:

Here is a video in the meantime that may be of interest.
http://www.rolls-royce.com/education...chools/how_things_work/default.jsp

Click on "Journey through a jet engine." I am not an engineer but I would imagine with those temperatures and pressures most water is vaporized prior to introduction into the combustion section.



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User currently offlineJush From Germany, joined Apr 2005, 1636 posts, RR: 3
Reply 9, posted (7 years 10 months 1 week 2 days 13 hours ago) and read 4102 times:

For the video....
Better go to youtube it's easier i couldn't find it on that site.



Regds
jush



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User currently offlineAndz From South Africa, joined Feb 2004, 8451 posts, RR: 10
Reply 10, posted (7 years 10 months 1 week 2 days 4 hours ago) and read 4035 times:
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There was a similar video on GE's website showing testing of the GE-90.


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User currently offlineBAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 11, posted (7 years 10 months 1 week 2 days ago) and read 3979 times:

Quoting Zeke (Reply 2):
If I recall correctly the B52, DC8, 707, and Metro have water/alcohol injection to increase the mass flow during takeoff.

Just noticed something.

I don't know what a Metro is, (a Metroliner?) but all those other aircraft have turbojet motors, (if we're talking early B52s). Low or no bypass in other words.

Please bear with me here, but I need to go back to Newton's third law... A rocket makes thrust by throwing stuff out the back. Does this mean that the early turbojets could not throw enough air backwards to get good takeoff performance and so added water - which was heavier - to get off the ground?

Conversely, as a turbofan is hurling huge volumes of air backwards, it doesn't need to do this?

I always thought they used the water/alcohol injection to cool the core, like cars in a high state of tune do, (I have a turbo lump which does this as it stops the piston crowns from melting!).

Or is it both?

I realise this makes me look like a n00B, but I am one, so...



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User currently offlinePygmalion From United States of America, joined Jun 2006, 966 posts, RR: 38
Reply 12, posted (7 years 10 months 1 week 1 day 23 hours ago) and read 3960 times:

Adding water alcohol allows you to up the fuel delivery by keeping the combustor temps down. Without the extra cooling, you can't add the extra fuel without overheating. In the P3 when I was flying in the Navy, we used water alcohol in hot/high conditions to restore takeoff performance. The water alcohol tanks only lasted a minute or two but it was enough to get you into the air without running out of runway on a hot day with full payload/tanks.

User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 13, posted (7 years 10 months 1 week 1 day 22 hours ago) and read 3930 times:

Quoting BAe146QT (Reply 11):
I don't know what a Metro is, (a Metroliner?)

A Metro is the nickname for the Fairchild/Swearengen SA-227 (or similar varients); an older turboprop aircraft:


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Quoting BAe146QT (Reply 11):
Please bear with me here, but I need to go back to Newton's third law... A rocket makes thrust by throwing stuff out the back. Does this mean that the early turbojets could not throw enough air backwards to get good takeoff performance and so added water - which was heavier - to get off the ground? Conversely, as a turbofan is hurling huge volumes of air backwards, it doesn't need to do this?

Yes, jet engines operate in the basic principle of Newton's third law. And as you stated, the early turbojets were fairly "weak." Compare the P&W JT3C (turbojet) used on the early 707/DC-8 with a maximum thrust of around 13,500lbs. In its turbofan form, the JT3D, it developed 21,000lbs, and was used on later 707/DC-8. Also, many of the older aircraft were re-engined with it.

This also may help, the source is cited below:

Quote:
According to the theorem of momentum, thrust depends not only on the increase of airsteam velocity, but also on mass flow rate. As mass flow rate is linked to air density (mass=density*volume), a variation of properties of the air will cause thrust to be increased [or decreased].
...This explains why thrust is less at airports located high (low pressure)...or on hot days even at airports at sea level...As a result either the takeoff run will have to be increased, or the payload of the aircraft lowered, to accommodate the unfavorable temperature or altitude effects.
Now for the water injection method to increase thrust:
The temperature of the engine airflow can be lowered by injecting water upstream of the compressor. As the water vaporizes, temperature will drop causing density, hence mass, to increase, which directly provides additional thrust due to increased mass flow rate.
With advent of high bypass-ratio engines, and their large amounts of takeoff thrust, water injection was superseded by technological progress. (Pages 182-183, section 8.2)

Hunecke, Klaus. Jet Engines. Motorbooks International, Shrewsbury: 1997.

I know the book didn't comment on this: but as you thought, it was realized that water injection was inefficient as its reservoir (tank) robbed space that could have been used for more fuel or left empty to allow for more payload/passengers.


User currently offlineJamie757 From , joined Dec 1969, posts, RR:
Reply 14, posted (7 years 10 months 1 week 1 day 17 hours ago) and read 3875 times:

Quoting Jush (Reply 9):
For the video....
Better go to youtube it's easier i couldn't find it on that site.

Thanks for the link, fascinates me to watch stuff like this!

 Smile

Rgds.


User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 15, posted (7 years 10 months 1 week ago) and read 3780 times:

Quoting Jamie757 (Reply 6):
Any chance that you could make some of this footage available to us?

It's not as detailed as the RR video, but it does have the bird ingestion test as well:

*Sorry about the video quality, this was recorded from broadcast T.V. almost 10 years ago.



21st Century Jet, Episode III. Skyscraper Productions. 1995. Videocassette. Channel Four Television Company, LTD.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 4000 posts, RR: 34
Reply 16, posted (7 years 10 months 1 week ago) and read 3775 times:

There was a version of the JT9D withwater injection. I remember when the Air India arrived at BAH in the summer (36degC OAT). It needed 600 gallons of water in the tank, and we only had a manual pump! The poor guys were pumping for ages.
The water pump was there for our BAC 111-400 which had the Spey 511-14W engine. This injected water into the fuel nozzles to allow more fuel in. Water injection died out in the late 70s as better turbine blade materials allowed higher operating temps.
By the way we always used water ( a very special demineralized water) not water/meth. At lift off a valve opened on the water tank and it all drained out.


User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 17, posted (7 years 10 months 5 days ago) and read 3644 times:

Quoting TristarSteve (Reply 16):
There was a version of the JT9D withwater injection.

The early 747-100s/200s had the option for the water-injected JT9D-3AW or the -7AW.

As for water/meth, I know its primary use was for WWII aircraft as an emergency power reserve (its technical name was ADI: Anti-Detonation Injection). Its purpose was to cool the induction air enough to allow for higher manifold pressures, increasing power output, but with no increase in the octane of the fuel and without causing detonation.

Early gas turbine engines may have used water/methanol, but the last aircraft to use water injection used demineralized water only.


User currently offlineTristarsteve From Sweden, joined Nov 2005, 4000 posts, RR: 34
Reply 18, posted (7 years 10 months 4 days 23 hours ago) and read 3631 times:

Quoting N231YE (Reply 17):
Early gas turbine engines may have used water/methanol

The HS748 with Dart 532 used water/methanol
http://www.hal-india.com/Enginebangalore/products.asp
The Dart series of Engines were manufactured since 1966 under licence from Rolls Royce, UK. At present, these Engines are being repaired and overhauled. Two Dart Engines power HS-748 aircraft.

This engine has two-stage Centrifugal Compressors, three- stage Turbine and utilises water methanol injection to increase the shaft Horse Power.

[Edited 2006-10-31 20:41:04]

User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 19, posted (7 years 10 months 3 days 18 hours ago) and read 3534 times:

Quoting Tristarsteve (Reply 18):

Thanks for your input. I thought the Darts had water/methanol injection, but wasn't sure, so I emphasized "may." But you confirmed it.


User currently offlineTimT From United States of America, joined Jun 2001, 168 posts, RR: 0
Reply 20, posted (7 years 10 months 3 days 12 hours ago) and read 3507 times:

Turn on the ignitors and there's a very low chance of putting out the fire. In fact, most company ops call for ignitors on when in rain. And really, most jets like some water. As mentioned, it cools the combustion and makes for more power. From the MX side, it helps clean the compressor blades and vanes, allowing more air and cooler temps when it's dry. In another life, we would do a water wash of an engine in the test cell before we ran it- just to clean the innards'

User currently offlineBAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 21, posted (7 years 10 months 3 days 1 hour ago) and read 3458 times:

Thnks for the answers to my questions above, folks. Quite an education.  thumbsup 


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