ambanmba
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What Is This "Smoke" From Under A340 Engines?

Sat Aug 22, 2009 11:30 am

Was passing through AKL today and happened to notice that all 4 engines on this EK 340 (A6-ERI) had some type of "smoke" (steam?) coming from what looked like a port at the bottom of the engine.

What is this from? Nobody seemed to worried about it and the flight was dispatched on time.



ambanmba
Concorde 300/10/19/20/21/30/40/80 707/17/27/37/47/57/67/77 AT7 146 CRJ DC3/9/10 DHC8 F100 L1011 MD11/80 S340 T154M Y7C
 
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jetmech
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RE: What Is This "Smoke" From Under A340 Engines?

Sat Aug 22, 2009 12:36 pm

Quoting Ambanmba (Thread starter):
What is this from?

That smoke you can see is fine oil mist. On modern turbofans, the main bearings are sealed by a non contact seal known as a labyrinth seal or knife edge seal. These seals have "fingers" that form a narrow passage with the rotating shaft.

Air is bled from the compressor section and blown across this seal into the bearing cavity, thus, any oil that tries to leave the bearing cavity faces an opposing "wall" of pressurised air.







After oil has passed through and lubricated the bearing, it ends up mixing with this sealing air. This air / oil mixture is then scavenged back to the oil tank. Before it gets to the tank, the mixture is passed through an air / oil separator.

This uses centrifugal forces to de-aerate the air / oil mix, and return liquid oil to the oil tank. The separated air is then ejected overboard from the engine. Obviously, not all the oil can be removed in the centrifugal separator. A small amount of oil is ejected overboard with the sealing air, which can form a visible vapour.

Regards, JetMech

[Edited 2009-08-22 05:43:35]
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
ambanmba
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RE: What Is This "Smoke" From Under A340 Engines?

Sat Aug 22, 2009 1:07 pm



Quoting JetMech (Reply 1):
That smoke you can see is fine oil mist.

Thanks for the quick, informative and detailed answer. This is why A.net is so great!

Cheers,

ambanmba
Concorde 300/10/19/20/21/30/40/80 707/17/27/37/47/57/67/77 AT7 146 CRJ DC3/9/10 DHC8 F100 L1011 MD11/80 S340 T154M Y7C
 
Tristarsteve
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RE: What Is This "Smoke" From Under A340 Engines?

Sat Aug 22, 2009 6:46 pm

Don't worry I get the same question from flight crew every month or so.
You can see that the smoke in your picture is coming out of a mast. On the older RB211, including most of those on our B767s, there is no mast, just a grill in the cowling. So this smoke ends up as an oily streak on the cowlings. Amazing how many pilots ask about the oil leak. So I ask them how much oil they have lost, answer nil. These engines use very little oil, despite the smoke at idle. (For the Trent, I suppose a litre every 20 hours is about average) As soon as the engine is spooled up, the air/oil separator works and the oil is contained in the engine.
 
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jetmech
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RE: What Is This "Smoke" From Under A340 Engines?

Sun Aug 23, 2009 2:45 am

Quoting Ambanmba (Reply 2):

No worries.

Quoting TristarSteve (Reply 3):
As soon as the engine is spooled up, the air/oil separator works and the oil is contained in the engine.

I see. This makes sense. I also often saw Trents and RB's smoking visibly as the aircraft taxied in, and have often wondered why I did not need to add any oil upon checking. It didn't occur to me that the separator lost some effectiveness at lower RPM's.

Regards, JetMech

[Edited 2009-08-22 19:48:11]
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
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jetmech
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RE: What Is This "Smoke" From Under A340 Engines?

Sun Aug 23, 2009 6:13 am

Just to add further, the following is a diagram of a centrifugal air / oil separator. The air / oil mixture scavenged from the bearing cavity is admitted to the device via the pipe labelled with number 18 which sprays the mixture tangentially into the separator via the inlet labelled with number 19.

The centrifugal forces fling the oil onto the walls of the device, with liquid oil collected and sent to the oil tank via the pipe labelled with number 21. The sealing air is ejected overboard via the pipe labelled with number 14.

http://www.freepatentsonline.com/6709476-0-large.jpg

http://www.freepatentsonline.com/6709476-0-large.jpg

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
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HAWK21M
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RE: What Is This "Smoke" From Under A340 Engines?

Sun Aug 23, 2009 7:13 am

The Breather port.As mentioned above.

Post lubrication the Oil vapours before returning to the Oil tank via the scavenge pumps are passed thru an centrifugal air-oil seperator,the oil is seperated & returned to the tank.The air with small amount of oil fumes are thrown overboard thru the breather port.

regds
MEL.
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baroque
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RE: What Is This "Smoke" From Under A340 Engines?

Tue Aug 25, 2009 2:03 pm



Quoting JetMech (Reply 4):
I see. This makes sense. I also often saw Trents and RB's smoking visibly as the aircraft taxied in, and have often wondered why I did not need to add any oil upon checking.

OK we can work out that you have a whole Trent in pieces on the floor of your office, but the question is do you have one of each of the current ones, or are they sufficiently similar that you can "make do" with just a T500?  angel 
 
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jetmech
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RE: What Is This "Smoke" From Under A340 Engines?

Wed Aug 26, 2009 8:00 am



Quoting Baroque (Reply 7):
Trent in pieces on the floor of your office,

I wish! I do have a cutaway picture of the T-500 from Flight International, which proudly sits on my wall.

Quoting Baroque (Reply 7):
are they sufficiently similar that you can "make do" with just a T500?

The various RB's and Trent's are broadly similar (3 shaft layout) but differ somewhat in detail. The G2 for example, dumps the sealing air overboard from the side of the cowling, not the bottom like the T-500. The breather dump mast can be seen directly above the mechanics head in the following photo.


View Large View Medium
Click here for bigger photo!

Photo © Andrew Hunt - AirTeamImages



Nonetheless, I suspect they would all utilise a centrifugal air / oil separator, which if they did, would function with an identical principle of operation, i.e. using centrifugal forces and density differences to separate two fluids.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
baroque
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RE: What Is This "Smoke" From Under A340 Engines?

Wed Aug 26, 2009 1:36 pm

Quoting JetMech (Reply 8):
I wish! I do have a cutaway picture of the T-500 from Flight International, which proudly sits on my wall.

If I find any bits that fell off them on SYD to MEL (straight over our house), if I survive the experience, I will be sure to send them to you to make up this serious deficiency!

[Edited 2009-08-26 06:36:57]
 
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vzlet
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RE: What Is This "Smoke" From Under A340 Engines?

Wed Aug 26, 2009 3:27 pm

Similar effect on a smaller scale here:

View Large View Medium
Click here for bigger photo!

Photo © Mark Carlisle

"That's so stupid! If they're so secret, why are they out where everyone can see them?" - my kid
 
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HAWK21M
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RE: What Is This "Smoke" From Under A340 Engines?

Wed Aug 26, 2009 6:00 pm



Quoting JetMech (Reply 8):

Looks like a slurp of Two qts.
 Smile
regds
MEL.
I may not win often, but I damn well never lose!!! ;)

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