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Fuel Temp On 777: How Cold Is Still OK?  
User currently offlineMozart From Luxembourg, joined Aug 2003, 2152 posts, RR: 13
Posted (6 years 4 months 4 weeks 11 hours ago) and read 4893 times:

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?

24 replies: All unread, jump to last
 
User currently offlineB747forever From Sweden, joined May 2007, 17004 posts, RR: 10
Reply 1, posted (6 years 4 months 4 weeks 11 hours ago) and read 4890 times:

Maybe the Tech forum would be better for this question.


Work Hard, Fly Right
User currently offlineLawnDart From United States of America, joined May 2005, 968 posts, RR: 3
Reply 2, posted (6 years 4 months 4 weeks 11 hours ago) and read 4859 times:



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.


User currently offlineGraphic From , joined Dec 1969, posts, RR:
Reply 3, posted (6 years 4 months 4 weeks 11 hours ago) and read 4820 times:



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.


User currently onlineMir From United States of America, joined Jan 2004, 21103 posts, RR: 56
Reply 4, posted (6 years 4 months 4 weeks 11 hours ago) and read 4775 times:

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



7 billion, one nation, imagination...it's a beautiful day
User currently offlineLawnDart From United States of America, joined May 2005, 968 posts, RR: 3
Reply 5, posted (6 years 4 months 4 weeks 11 hours ago) and read 4758 times:



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.


User currently offline777236ER From , joined Dec 1969, posts, RR:
Reply 6, posted (6 years 4 months 4 weeks 10 hours ago) and read 4726 times:

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.

User currently offlineLHR777 From , joined Dec 1969, posts, RR:
Reply 7, posted (6 years 4 months 4 weeks 10 hours ago) and read 4682 times:

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.


User currently offlineWowpeter From Hong Kong, joined Oct 2006, 145 posts, RR: 0
Reply 8, posted (6 years 4 months 4 weeks 10 hours ago) and read 4663 times:

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


User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 9, posted (6 years 4 months 4 weeks 7 hours ago) and read 4493 times:



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 


User currently offlineLemmy From United States of America, joined Dec 2004, 258 posts, RR: 0
Reply 10, posted (6 years 4 months 4 weeks 3 hours ago) and read 4390 times:

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 ...
User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2254 posts, RR: 16
Reply 11, posted (6 years 4 months 3 weeks 6 days 12 hours ago) and read 4254 times:



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.


User currently offlineNWOrientDC10 From United States of America, joined Mar 2005, 1404 posts, RR: 4
Reply 12, posted (6 years 4 months 3 weeks 6 days 10 hours ago) and read 4209 times:
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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
User currently offlineWILCO737 From Greenland, joined Jun 2004, 8906 posts, RR: 76
Reply 13, posted (6 years 4 months 3 weeks 6 days 10 hours ago) and read 4206 times:
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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)
 airplane 



It it's not Boeing, I am not going.
User currently offlineA342 From Germany, joined Jul 2005, 4675 posts, RR: 3
Reply 14, posted (6 years 4 months 3 weeks 6 days 8 hours ago) and read 4189 times:



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.
User currently onlineKELPkid From United States of America, joined Nov 2005, 6265 posts, RR: 3
Reply 15, posted (6 years 4 months 3 weeks 6 days 2 hours ago) and read 4111 times:



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 :-)
User currently offlineWowpeter From Hong Kong, joined Oct 2006, 145 posts, RR: 0
Reply 16, posted (6 years 4 months 3 weeks 5 days 23 hours ago) and read 4085 times:



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.


User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 17, posted (6 years 4 months 3 weeks 5 days 22 hours ago) and read 4075 times:

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!
User currently offlineZeke From Hong Kong, joined Dec 2006, 8643 posts, RR: 75
Reply 18, posted (6 years 4 months 3 weeks 5 days 21 hours ago) and read 4061 times:



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
User currently offlineThegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 19, posted (6 years 4 months 3 weeks 5 days 20 hours ago) and read 4055 times:

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.


User currently offlineXv408 From United Kingdom, joined Nov 2006, 52 posts, RR: 0
Reply 20, posted (6 years 4 months 3 weeks 5 days 17 hours ago) and read 4013 times:

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


User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Reply 21, posted (6 years 4 months 3 weeks 5 days 8 hours ago) and read 3919 times:



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


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 22, posted (6 years 4 months 3 weeks 5 days 4 hours ago) and read 3871 times:



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.


User currently offlineThegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 23, posted (6 years 4 months 3 weeks 4 days 23 hours ago) and read 3837 times:

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.

User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3321 posts, RR: 4
Reply 24, posted (6 years 4 months 3 weeks 4 days 21 hours ago) and read 3817 times:

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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