AVSIG: JetA freeze concern? wwswsigarch.jpg (7236 bytes)

✈ . . . . . . ✈ . . . . . ✈ . . . . ✈ . . . ✈ . . ✈ . ✈ . . ✈ . . . ✈ . . . . ✈ . . . . . ✈ . . . . . . Touch-and-Go to our Live Forum (This is a Read-only Archive of the 2004-2017 AVSIG Forum)


AVSIG Discussion Sections >> Training & Proficiency

Pages: 1 | 2 | 3 | >> (show all)
Dave Siciliano (ADS)
Top Gun


Reged: 05/17/04
Posts: 8469
Loc: ADS (Dallas, TX)
JetA freeze concern?
      #389251 - 04/09/14 11:41 AM

Can you tell, I just returned from recurrent training (g). We always discuss a lot of things and sometimes don't really settle all of them.
So, in the course of events, we discuss the systems on the KA and it looks as if fuel isn't heated until it enters the Fuel Control Unit area where engine oil heats the fuel. So, I wonder why Jet A in the tanks (bladders) or making it's way to the fuel control unit doesn't freeze or turn to thick goop too dense to fly. The general freeze point for Jet A is -40 which is where C and F cross. Obviously, turbine and jet aircraft at altitude often get below -40. Any thoughts on why this isn't an issue? We don't have a fuel temp probe on my plane. I know some do.

Best,

Dave

Edited by Dave Siciliano (ADS) (04/09/14 12:07 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ralph Jones
Top Gun


Reged: 08/31/01
Posts: 21214
Loc: 4CO2
Re: JetA freeze concern? [Re: Dave Siciliano (ADS)]
      #389252 - 04/09/14 01:21 PM

That's a challenging problem in heat transfer. The rate of heat removal will depend on the ambient temperature, the amount of fuel in the tank, and the amount of empty space above the fuel (which serves as an insulator that gets thicker as fuel is consumed). I'm guessing that at the operational altitudes of your type, and the mission durations, the fuel just doesn't have time to get fully cooled.

Might be interesting to pull a fuel sample immediately after a landing and stick a thermometer in it.

--------------------
Ralph Jones
LS-4a N49LS 6R


Post Extras: Print Post   Remind Me!   Notify Moderator  
Russell Holton
AVSIG Member


Reged: 07/07/05
Posts: 14136
Re: JetA freeze concern? [Re: Ralph Jones]
      #389253 - 04/09/14 01:31 PM

Quote:

I'm guessing that at the operational altitudes of your type, and the mission durations, the fuel just doesn't have time to get fully cooled.



It would also depend on the starting temperature. It would be interesting to know, since at some point that assumption may not work - like flying out after overnighting in a very cold place.

Are there any restrictions on "starting temperature"?

Edited by Russell Holton (04/09/14 01:34 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
Re: JetA freeze concern? [Re: Dave Siciliano (ADS)]
      #389254 - 04/09/14 01:33 PM

Dave -- Interestingly, Shem recently posted an article on this subject:

http://airlinesafety.wordpress.com/2014/04/03/cold-fuel/


Post Extras: Print Post   Remind Me!   Notify Moderator  
Randy Sohn
Gradn Exlated Ordre of teh Fyling Fingres


Reged: 08/31/01
Posts: 23187
Loc: Savage, MN - U.S.A.
Re: JetA freeze concern? [Re: Dave Siciliano (ADS)]
      #389255 - 04/09/14 02:08 PM

Quote:

and it looks as if fuel isn't heated until it enters the Fuel Control Unit area where engine oil heats the fuel. So, I wonder why Jet A in the tanks (bladders) or making it's way to the fuel control unit doesn't freeze or turn to thick goop too dense to fly




Dave, it definitely WAS a concern, just one more thing we had to think about when accepting or not accepting some routes, generally to Asia.

best, randy


Post Extras: Print Post   Remind Me!   Notify Moderator  
Bruce Gorrell [EQY]
Top Gun


Reged: 04/29/04
Posts: 7864
Loc: Charlotte, NC
Re: JetA freeze concern? [Re: Dave Siciliano (ADS)]
      #389269 - 04/09/14 09:47 PM

Quote:

Can you tell, I just returned from recurrent training (g). We always discuss a lot of things and sometimes don't really settle all of them.
So, in the course of events, we discuss the systems on the KA and it looks as if fuel isn't heated until it enters the Fuel Control Unit area where engine oil heats the fuel. So, I wonder why Jet A in the tanks (bladders) or making it's way to the fuel control unit doesn't freeze or turn to thick goop too dense to fly. The general freeze point for Jet A is -40 which is where C and F cross. Obviously, turbine and jet aircraft at altitude often get below -40. Any thoughts on why this isn't an issue? We don't have a fuel temp probe on my plane. I know some do.

Best,

Dave




See http://en.wikipedia.org/wiki/Fuel_system_icing_inhibitor


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mase Taylor
Top Gun


Reged: 04/29/04
Posts: 9446
Loc: SOCAL
Re: JetA freeze concern? [Re: Bruce Gorrell [EQY]]
      #389271 - 04/09/14 10:11 PM

Prist?

--------------------
Fly The Airplane As Far Into The Crash As Possible. - Bob Hoover 1922-2016 R.I.P.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Russell Holton
AVSIG Member


Reged: 07/07/05
Posts: 14136
Re: JetA freeze concern? [Re: Mase Taylor]
      #389272 - 04/09/14 11:14 PM

If you need your paranoia levels raised:

The Price of No Prist

Also, google "Beechjet double flameout"


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mac Tichenor (DAL)
Top Gun


Reged: 06/04/04
Posts: 1857
Re: JetA freeze concern? [Re: Dave Siciliano (ADS)]
      #389273 - 04/09/14 11:39 PM

Dave - if the KA PT6 installation is like the Socata TBM's, the unused heated fuel is rerouted from the FCU back to the tanks. I don't know exactly how much fuel that is, but I think one can make a reasonable estimate.

(All of this is based on the TBM's numbers) Fuel flow for max power at sea level is about 90 GPH, and at FL310 (its highest and coldest altitude) is about 45 GPH. The amount of fuel delivered to the FCU is related (proportional?) to Ng (gas generator turbine RPM) which, at cruise power, only varies about 5% between sea level and FL310. So I think a reasonable guess is that around 40 - 45 GPH, or 3/4 gallon per minute of heated fuel is being returned to the tanks at FL310. (The two tanks hold 146 gallons each.)

I don't know how much the oil/fuel heat exchanger raises the fuel temperature. The oil temp at cruise is about 67 degrees C.

I've had a number of flights this winter with the OAT below -50C, and this has been on my mind. But, other than the BA accident where frozen fuel was implicated, I'm not aware of any reported problems attributable to this. Are you? The TBM fleet has over 1 million hours and the KA fleet, I'm sure, many times that. So it seems to me, if it occurred with any frequency, it would be in the lore.

I found a thermometer on Amazon that will measure down to -40C, so I ordered it and will report some readings once I get it.

Mac

p.s., I believe that Prist is useful in keeping suspended water in Jet A from freezing but does not serve to reduce the freezing point of the fuel itself.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mase Taylor
Top Gun


Reged: 04/29/04
Posts: 9446
Loc: SOCAL
Re: JetA freeze concern? [Re: Russell Holton]
      #389274 - 04/10/14 02:59 AM

Quote:

If you need your paranoia levels




Aargh.

--------------------
Fly The Airplane As Far Into The Crash As Possible. - Bob Hoover 1922-2016 R.I.P.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | >> (show all)



Extra information
0 registered and 7 anonymous users are browsing this forum.

Moderator:  Mike Overly 

Print Topic

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled

Rating:
Topic views: 6767

Rate this topic

Jump to

Contact Us AVSIG

Powered by UBB.threads™ 6.5.5

Logout   Main Index    AVSIG Aviation Forum