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News: The latest PSX update (version 10.42 from 16 August 2018) is available at: http://aerowinx.com/board/index.php?topic=4191.0

Author Topic: Fuel Temperature Reduction Rate  (Read 467 times)

G-CIVA

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Fuel Temperature Reduction Rate
« on: Fri, 20 Jul 2018 08:10 »
Hardy,

I am not seeing the fuel temperature fall toward the TAT as quickly as this representative graph from Boeing suggests, neither have I seen it fall at the rate at which the post I have linked would also suggest.



http://aerowinx.com/forum/topic.php?id=2327

On my current flight (ICN-ANC) the fuel was pumped in at +18'C, enroute the TAT started off at approx -18'C at FL330 & has fallen as I have climbed to -23'C (SAT -55'C) at FL370.  Some 6hrs 50mins into the flight the Fuel Temperature is sitting steadilly at +2'C.

I have never seen a temperature reduction or 'fall' rate as depicted in the Boeing illustration, which seems to indicate a fairly rapid initial reduction in temperature, before a slower reduction toward a 'stabilisation' approx 3'C above the TAT.

Without becoming an absolute PITA could it be time to perhaps revisit/refine the Fuel Temperature reduction/lapse rate?

I can send you the whole Boeing document via e-mail if you wish.

Best

« Last edit: Fri, 20 Jul 2018 08:26 by G-CIVA »
Steve Bell
aka The CC

Hardy Heinlin

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Re: Fuel Temperature Reduction Rate
« Reply #1 on: Fri, 20 Jul 2018 09:27 »
Please not again ...

These are approximations. What are you expecting?

The most critical point is the fueling. How do you know the airport fuel temp was 18° and not 30°?

I just retested it: My fuel temp drops by 50° after 3000 nm. E.g. when starting with 30°, I get -20° after 3000 nm. Your example starts at 5 and ends at -45. It's the same.


Here's the above quoted thread in the new forum software (in use since 2015). Please ignore the old forum software; it doesn't show texts that contain any non-ASCII characters (e.g. the degree character).

http://aerowinx.com/board/index.php?topic=2327.0
« Last edit: Fri, 20 Jul 2018 10:09 by Hardy Heinlin »

Phil Bunch

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Re: Fuel Temperature Reduction Rate
« Reply #2 on: Fri, 20 Jul 2018 23:52 »
An aside:

These fuel temp threads remind me of supersonic aircraft and their very different issues re fuel temperature.  I hope this isn't too far off-topic.

Below is a map of the Concorde's skin temperature:




---------------------
Perhaps the solution to the 747's low fuel temp concerns would be to redesign it for supersonic speeds! 
Best wishes,

Phil Bunch

DougSnow

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Re: Fuel Temperature Reduction Rate
« Reply #3 on: Sun, 22 Jul 2018 16:25 »
CC

We use the Boeing Fuel Temp Prediction Program in our Flight Planning System at work. The FTPP models how fuel lies within and flows from the tanks to the engines and is detailed to aircraft type. Some factors for fuel temp is how much of the internal tank structure is exposed to the very low TATs at altitude, and of course those TATs at altitude.  Also, you never use an FTPP prediction for an aircraft type it wasn't designed for.

The chart shows that after 4-5 hours in flight, resulting fuel temp isnt really affected by the fuel temp as it was loaded - it has reached an equilibrium temp, and is now more affected by the air temps outside the aircraft.

The FTPP will throw an alert if the temp is predicted to get within 3 degs C of the fuel freeze point temp, which requires the dispatcher to adjust the flight thru the area of the cold fuel (either adjust the altitude, increase speed, or in some cases both). Also, with the trop at a low altitude, it may be better to increase the altitude to get to warmer air aloft. We also require the flight plan to be remarked so the crew is aware of what was done. Our dispatchers will do something when the FTPP alerts as min fuel temp is an Airplane Flight Manual Chapter 1 limitation.

Hardy Heinlin

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Re: Fuel Temperature Reduction Rate
« Reply #4 on: Sun, 22 Jul 2018 23:23 »
The chart shows that after 4-5 hours in flight, resulting fuel temp isnt really affected by the fuel temp as it was loaded ...

Yes, after 4 to 5 hours. But in the initial phase the reduction rate is higher if the difference is higher; this is modelled in PSX and is shown on that Boeing chart. I'm just saying that these empirical values in the initial phase are approximations. 5 hours are 25% more than 4 hours.

Developing and testing a simulation of this stuff is very time consuming as it has to be flown in real time; the time acceleration function in PSX may influence the result because of the normal rounding and time frame granularity combined with those tiny temperature changes along extreme distances.

Perhaps I was misunderstanding what Steve wrote. Did the fuel temp stay at 2° for the remainder of the flight while the TAT was -23°? That would be a difference of 25°. If so, we're talking about the time after the initial phase. The difference should then slowly decrease to less than 5°. If not, something's wrong.


|-|ardy
« Last edit: Sun, 22 Jul 2018 23:36 by Hardy Heinlin »

United744

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Re: Fuel Temperature Reduction Rate
« Reply #5 on: Fri, 10 Aug 2018 03:19 »
Ahhhhhhhhhhh!!!!!!!!!!! It's not just me!!!

@Hardy: correct - the temperature delta between TAT and fuel temp REMAINS 20 degrees or more above TAT.

I have NEVER had a flight where fuel temp remotely became an issue, even when I set the OAT to ISA-20.

For me, it typically reaches about +3 deg. C and doesn't drop any lower. TAT is -25 deg. C or lower. The fuel temp never gets close to TAT at all.

If you search the forum, you will find posts by me on this issue previously.
« Last edit: Fri, 10 Aug 2018 03:30 by United744 »

Hardy Heinlin

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Re: Fuel Temperature Reduction Rate
« Reply #6 on: Fri, 10 Aug 2018 05:02 »
Your last post I found on this subject is from 2014:

http://aerowinx.com/board/index.php?topic=2327.msg23144#msg23144

We're now in 2018 and there have been a zillion updates.

When you're writing "Ahhhhh!!!!" -- is this a mental flashback to version 10.0.0 from 2014, referring to an effect that has been updated in PSX but not updated in your memory? Such mental effects happen sometimes to everyone of us. Or are you referring to the latest PSX version? If so, I need exact data so that I can try to reproduce the effect. Please understand that I can't work with vague phrases like "I never had ..." etc.

In my PSX code I see this:

The target fuel temp is always TAT + 1 + X.

X is a thrust dependent parameter and varies between circa 3 and 4.

So the target fuel temp is always TAT plus 4 or 5.

And here's the closure rate:

When delta is 60° or higher, the rate is maximum.
At delta 40° or higher, it's 50% of maximum rate.
At delta 20° or higher, it's 33% of maximum rate.
At delta 10° or higher, it's 25% of maximum rate.
Below delta 10° it's 20% of maximum rate.

The result should be a curve similar to that on the above Boeing diagram (which doesn't show any TAT, by the way).


|-|ardy

Hardy Heinlin

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Re: Fuel Temperature Reduction Rate
« Reply #7 on: Fri, 10 Aug 2018 17:43 »
I did some further tests and noticed my curves are similar to the green curve on that Boeing diagram -- if the initial fuel temp is already low. If it's higher initially, my curve should be steeper at the start -- indeed. In that part the original PSX version 10.0.0 wasn't that bad. The compromises thereafter were not perfect. I'll try to tune this stuff a bit further ...


Regards,

|-|ardy

Hardy Heinlin

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Re: Fuel Temperature Reduction Rate
« Reply #8 on: Sat, 11 Aug 2018 03:03 »
Initial part of the curve is now steeper in PSX 10.41:

http://aerowinx.com/board/index.php?topic=4191.0


Regards,

|-|ardy

G-CIVA

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Re: Fuel Temperature Reduction Rate
« Reply #9 on: Sun, 12 Aug 2018 14:11 »
Hardy,

Thanks for taking another look at this .... the faster temperature reduction rate with a warmer initial fuel temperature looks much better now.

Best

Steve
Steve Bell
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United744

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Re: Fuel Temperature Reduction Rate
« Reply #10 on: Fri, 17 Aug 2018 03:11 »
I'll check later! I wasn't aware it had been updated (I do read most of the release notes, though not all).

I fly PSX quite often, so my observations are through various versions, not just the initial release. :)