mozart
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Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 6:22 pm

Someone told me that fuel temperature is an issue when doing polar flights, e.g. EWR-HKG on the 777.

What are the lower limits of fuel temperature on the 777? What happens if temperature drops below that? Is there a fuel heat mechanism on the 777? Is it automatic or do pilots have to engage it manually?
 
B747forever
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 6:27 pm

Maybe the Tech forum would be better for this question.
Work Hard, Fly Right
 
LawnDart
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 6:40 pm



Quoting Mozart (Thread starter):
What are the lower limits of fuel temperature on the 777? What happens if temperature drops below that?

Jet-A will begin freezing at -40C...little wax crystals begin to form and they can clog up the fuel line and cause an engine shut down.

Quoting Mozart (Thread starter):
Is there a fuel heat mechanism on the 777? Is it automatic or do pilots have to engage it manually?

No fuel tank heater that I know of...many airlines use a fuel temp prediction model developed by Boeing (for Boeing aircraft) that calculates the temp of fuel along the route to be flown. It is up to the dispatcher and pilot to avoid areas that would cool the fuel to freezing.
 
graphic
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 6:52 pm



Quoting LawnDart (Reply 2):

Jet-A will begin freezing at -40C...little wax crystals begin to form and they can clog up the fuel line and cause an engine shut down.

-40 doesn't seem like that cold when you're talking about FL350 or FL400 in the wintertime, even over the continental US.
Demand Media fails at life
 
Mir
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 7:06 pm

There are heat exchangers that use heat from hot engine oil to warm the fuel, but I believe that it only works on the fuel in the lines from tank to engine, and doesn't actually heat the fuel in the tank itself.

I also agree that Tech/Ops would be a better place to ask this.

-Mir
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LawnDart
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 7:10 pm



Quoting Graphic (Reply 3):
-40 doesn't seem like that cold when you're talking about FL350 or FL400 in the wintertime, even over the continental US.

You're correct - it's not. The time it takes for that much fuel at, say, 10C to cool to freezing takes a while. It can happen, though.
 
777236ER
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 7:25 pm

Between the tropopause and stratosphere (36089ft to 65617ft), ISA temperature is -56deg C. At the poles it's much colder. The thermal inertia of Jet A/A-1 means it takes a very long time for large volumes to cool down.
Your bone's got a little machine
 
LHR777
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 7:38 pm

Jet-B freezes at -40c, Jet-A freezes at -47c.

Our aircraft come in from the US with Jet-B, and refuel in the UK with Jet-A. If an aircraft arrives from the US with Jet-B and is departing LHR on a polar-route, such as NRT, the Jet-B is then pumped into the centre tank, and topped-up with Jet-A. This is so that the Jet-B is burned first, before it reaches below -40c.
 
wowpeter
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 7:43 pm

Just fly faster, that's what we do on the A340-600 for the CX JFK to HKG route. Just flying 0.01 to 0.02 Mach faster makes a huge temperature difference as it increases the fricition on the surface of the wing. An alternative method (only after speeding up doesn't work) is to decent to a lower altitude. Caution should be taken as descending at some area around the pole could actually be colder (depending on the height of the Tropopause). Also at JFK during winter, the ground engineer will actually give us the actual fuel freeze point for the fuel loaded that day. Just so that we got a more accurate fuel freeze figure then -40C.

Peter
 
Fly2HMO
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sat Nov 24, 2007 10:28 pm



Quoting Wowpeter (Reply 8):
Also at JFK during winter, the ground engineer will actually give us the actual fuel freeze point for the fuel loaded that day.

How is that calculated? Mathematically? Or will they just shove a a gallon of Jet-A into a liquid-nitrogen-cooled freezer?  scratchchin 
 
Lemmy
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sun Nov 25, 2007 3:08 am

On the 777, the crew will get a "FUEL TEMP LOW" EICAS message when the fuel reaches -37C for Jet A. The crew, however, can set a different warning value if they know that their fuel has a different freezing point.

Tons more great information on polar flights here:
http://www.boeing.com/commercial/aer...e/aero_16/polar_story.html#3[/url]
I am a patient boy ...
 
CosmicCruiser
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sun Nov 25, 2007 5:46 pm



Quoting LHR777 (Reply 7):
Jet-A freezes at -47c.

In the U.S. we use JetA frz temp -40; in Europe and Alaska we get JetA-1 frz temp -47.

On the MD-11 we input fuel type into the FMS and that verifiys the frz temp. Approaching that temp we get "cold fuel recirculation" where fuel gets moved around to mix and somewhat warm. The temp probe is in tank #3 and the tail tank.

The only time I've ever seen cold fuel recirc was CDG-SFS, 12 hr. flight, in the winter.
 
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NWOrientDC10
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sun Nov 25, 2007 8:02 pm



Quoting LHR777 (Reply 7):
Jet-B freezes at -40c, Jet-A freezes at -47c.



Quoting 777236ER (Reply 6):
Between the tropopause and stratosphere (36089ft to 65617ft), ISA temperature is -56deg C.

At higher altitudes where the air pressure is lower than on the ground, the freezing point of Jet-A/B (and other compounds) should also be lower. Is this taken into account?

Good Day  Smile

Russell
Things aren't always as they seem
 
wilco737
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sun Nov 25, 2007 8:08 pm



Quoting CosmicCruiser (Reply 11):
The only time I've ever seen cold fuel recirc was CDG-SFS, 12 hr. flight, in the winter.

I have never seen that warning yet Big grin We never fly 12 hours! WAY to long  Wink And we dont have any polar routes anymore and our average flight time is 6 hours, so not long enough to get that warning... but must be cool seeing Mrs. Douglas recirc the fuel Big grin

WILCO737 (MD11F)
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A342
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RE: Fuel Temp On 777: How Cold Is Still OK?

Sun Nov 25, 2007 9:10 pm



Quoting LHR777 (Reply 7):
Jet-B freezes at -40c, Jet-A freezes at -47c.

As already said, A freezes at -40C and A1 at -47C. Jet B, being a wide-cut fuel (containing not only kerosene, but also gasoline) freezes at -50C.

If anybody has a question about aviation fuels, whether Jet or Avgas, I'm sure the answer can be found here:

http://www.chevronglobalaviation.com...view.pdf#pagemode=bookmarks&page=1
Exceptions confirm the rule.
 
KELPkid
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RE: Fuel Temp On 777: How Cold Is Still OK?

Mon Nov 26, 2007 3:42 am



Quoting LHR777 (Reply 7):
Our aircraft come in from the US with Jet-B

Unless they're starting out from FAI, I seriously doubt it. Jet-A is the standard jet fuel in the continental U.S. I think you may be confusing Jet-A1 (used extensively in Europe) with Jet-A. Jet-A has a slightly higher (7 deg. C) freezing point than Jet-A1 (-40 deg. C for Jet-A, -47 deg. C for Jet-A1).
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
wowpeter
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RE: Fuel Temp On 777: How Cold Is Still OK?

Mon Nov 26, 2007 6:34 am



Quoting Lemmy (Reply 10):
How is that calculated? Mathematically? Or will they just shove a a gallon of Jet-A into a liquid-nitrogen-cooled freezer?

Actually I don't know how do they calculate the fuel freeze figure. I am operating to JFK again in Dec, maybe I will ask the ground engineer how they do that.
 
dl757md
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RE: Fuel Temp On 777: How Cold Is Still OK?

Mon Nov 26, 2007 7:40 am

Quoting Mir (Reply 4):
There are heat exchangers that use heat from hot engine oil to warm the fuel, but I believe that it only works on the fuel in the lines from tank to engine, and doesn't actually heat the fuel in the tank itself.
There are right and center hydraulic system heat exchangers in the right main fuel tank and left hydraulic system heat exchanger in the left main fuel tank that cool the hydraulic fluid and heat the fuel. The primary function is of course hydraulic fluid cooling but it will warm the fuel a bit....the exact amount in normal ops I'm not sure of.

The operation of the fuel boost pumps in the tanks is another source of heat. Again it's quite small in relation to the amount of fuel but it does make some difference.

DL757Md

[Edited 2007-11-25 23:43:57]

[Edited 2007-11-25 23:44:22]
757 Most beautiful airliner in the sky!
 
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zeke
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RE: Fuel Temp On 777: How Cold Is Still OK?

Mon Nov 26, 2007 8:23 am



Quoting KELPkid (Reply 15):
Unless they're starting out from FAI, I seriously doubt it. Jet-A is the standard jet fuel in the continental U.S. I think you may be confusing Jet-A1 (used extensively in Europe) with Jet-A. Jet-A has a slightly higher (7 deg. C) freezing point than Jet-A1 (-40 deg. C for Jet-A, -47 deg. C for Jet-A1).

I agree, I normally get Jet A in the states, but it conforms with the Jet A1 freezing temp, as previously indicted, we get the actual fuel freezing temp from the fuel supplier.

The temp limit on the 340 is the fuel freezing temp + 5 deg, so -42 for Jet A1.

Quoting Wowpeter (Reply 8):
Just fly faster, that's what we do on the A340-600 for the CX JFK to HKG route. Just flying 0.01 to 0.02 Mach faster makes a huge temperature difference as it increases the fricition on the surface of the wing. An alternative method (only after speeding up doesn't work) is to decent to a lower altitude.

Can always transfer fuel out of the tail or outers as well, that is where it gets cold first.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
thegeek
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RE: Fuel Temp On 777: How Cold Is Still OK?

Mon Nov 26, 2007 9:21 am

At the risk of going off on a tangent, if the fuel is that cold, has any engine manufacturer thought about using the fuel as a heat sink for an inter cooler in the LP/IP compressor? Why? Would reduce the amount of work done by the compressor without actually wasting any heat. My calculations are (assuming a theoretical adiabatic compression) that for a 20:1 pressure ratio and a 15 degrees C intake temp gives a compressor outlet temperature of 404 degrees C. If after a 4:1 pressure ratio rise, the air is cooled from 155 degrees C to 65 degrees C gives a compressor outlet temperature of 262 degrees C. The specific heat of the fuel is significantly greater than the air. Compressor work equivalent to 52 degrees C heating of the core flow is saved. More intercooler stages could save more work, but with a law of diminishing returns.

Main trouble is that it might be necessary to find a liquid that is not flammable and can't freeze in the compressor, and use a heat exchanger to prevent the risk of a fuel leak in the compressor.
 
xv408
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RE: Fuel Temp On 777: How Cold Is Still OK?

Mon Nov 26, 2007 1:00 pm

One factor to consider is that the aircraft is not exposed to the static temperature at speed, but the total temperature. If my memory serves correctly, the equation is
Tt/Ts=1+0.2M^2.
This gives an effective air temperature at 0.8M, OAT -56degC, of -28deg C. Note this is not a frictional effect, but the effect of speeding the air up to the speed of the aircraft.

Quoting Thegeek (Reply 19):
At the risk of going off on a tangent, if the fuel is that cold, has any engine manufacturer thought about using the fuel as a heat sink for an inter cooler in the LP/IP compressor?

Interrcoolers have been considered, but are considered too heavy for the return on performance in aircraft. There is also a loss of pressure through any heat exchanger to be taken into consideration. This is also the case for cooling the cooling air in the turbines, although there are limited applications of this.
However, in ground-based installations, intercoolers are not that scarce. See this link for a Rolls-Royce marine unit:
http://marine.rolls-royce.com/WR-21-marine-gas-turbine-engines/
http://en.wikipedia.org/wiki/WR-21
 
soon7x7
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RE: Fuel Temp On 777: How Cold Is Still OK?

Mon Nov 26, 2007 10:10 pm



Quoting Thegeek (Reply 19):

You took the words right out of my mouth!...geeeeeeeeeeeeeez!...you need to go to surfing or something...my hats off too you for understanding that ,actually I do understand what your getting at but would never in my lifetime try to figure that out...at least...without being paid to do it...Better Idea...I'm going surfing!...later...j
 
tdscanuck
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RE: Fuel Temp On 777: How Cold Is Still OK?

Tue Nov 27, 2007 1:24 am



Quoting Mozart (Thread starter):
What are the lower limits of fuel temperature on the 777? What happens if temperature drops below that? Is there a fuel heat mechanism on the 777? Is it automatic or do pilots have to engage it manually?

If temperature goes too low, the fuel will wax up and the fuel filters will go in to bypass. You'll still fly, but the engines will be pissed off.

Quoting Mir (Reply 4):
There are heat exchangers that use heat from hot engine oil to warm the fuel, but I believe that it only works on the fuel in the lines from tank to engine, and doesn't actually heat the fuel in the tank itself.

On a Boeing, they're in the tank but the thermal mass of the fuel is so large compared to the heat load from the hydraulic system that it doesn't really improve your freeze margin.

Quoting Thegeek (Reply 19):
At the risk of going off on a tangent, if the fuel is that cold, has any engine manufacturer thought about using the fuel as a heat sink for an inter cooler in the LP/IP compressor? Why?

There are quite a few reasons why intercoolers aren't that good an idea on jets: LP/HP Intercooling Idea? (by Grunf Jan 16 2007 in Tech Ops)?threadid=180740&searchid=180740&s=intercooler#ID180740

Tom.
 
thegeek
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RE: Fuel Temp On 777: How Cold Is Still OK?

Tue Nov 27, 2007 7:03 am

I don't swallow that it will be too heavy. I assume the reasons why this has never been tried are more to do with the validity of my assumptions, but the link suggests a more suitable thread, so I will take it there.
 
XT6Wagon
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RE: Fuel Temp On 777: How Cold Is Still OK?

Tue Nov 27, 2007 9:10 am

If they needed to heat the fuel, it would be easy enough to simply pump the fuel. Not only do they heat the fuel if they are submerged, but they heat the fluid pumped by a good amount. I suspect that if they wanted to put a heating system into any of the tanks, a simple "backup" pump that simply pumps the fuel back into its own tank in normal usage would do. Little bit of extra plumbing and it would actually work as a backup pump too.

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