Pinkman,So you are convinced that no other aircraft departing China with Chinese fuel on a long haul sector to Europe or US has ever experienced the range of temperatures that has affected the 777s with TRENT 800 powerplants?:ugh:

Hot Dog
 

Again you ask the wrong question :ugh:

YES! I am saying that that particular set of circumstances has not happened before:

THAT batch of fuel
THAT powerplant/airframe combination
THAT temperature for
THAT duration

and THAT is why I keep saying stop focussing on THAT powerplant and look at the entire set of circumstances including the fuel.

You are obviously intelligent... why are you thinking in such a one-dimensional way? :ugh::ugh::ugh:

Pinkman

Ok Pinkman, the answer to the question is: It will not affect other engine/airframe combinations.

Aren't you glad it has no effect on your glider.:ok:

Hot Dog
 

But you dont know that, do you? You don't know because there is no evidence to support it either way except in hot-dog land where if something hasn't happend yet, it can't happen in the future.

How did you know I glide?

Dear Pinkman, I have lived in hot-dog land exactly 20 years longer than you have and amassed 20,000 hours in various jet aircraft and flight simulators as a check and training airman. I think you'll agree that after a while in this industry, with the evidence and history at hand; one can arrive at a fairly intelligent assumption on the subject at hand. However, I will not scuttle your theories any further as I consider this conversation terminated. Happy gliding, a great sport! Cheers,HD.

Umm, girls, wind back the fingernails. Vapilot2004 (link 2361) said . Good point. Missable perhaps because the certification and design used familiar and well-accepted principles, and the BA038 flight probably strayed into new territory.

I wonder if we were previously on the edge of an (as-yet undefined and only just realised) envelope and have stepped outside that envelope with this combination of aircraft, route, cold soak, fuel, testing, and specification. Not just an issue specific to the manufacturer or supplier, but rather a global issue with global consequences for the present system. Which includes engine and airframe manufacturers, and certification authorities (and not to forget the operators and crew).

Don’t Hang Up hinted at the new territory. I think it is wider than BA038 and similar operations. The new territory encompasses specifications, design and test methods, and presenting the biggest challenge of all - it questions how we will deal with the much bigger issue of the new bio-fuels. There is much work to be done (as PG said). And I think we are only at the start.

PS - Pinkman picked fuel as the cause of BA038 about a year ago, and Hotdog (The Reverend) has been contributing wisdom here for many years.

Everyone knows. If it's supposed to be secret don't put it in your public profile!

Doh! :ugh:

I went to fly a Canberra PR9 prototype back in 1964 and on looking round the cockpit I noticed a switch labelled Fuel Filter Heater. I asked "Wot's that for?" "To stop ice bunging up the works" "When should I put it on?" "When you fly high" "OK" I said.

Read Page 7 / Also page 8 19 feb '08 #151
 

From 19 Feb, '08 Posts #126 and #127. See if I got close. I didn't accept the "in spec." from the beginning, so far as it eliminated the Fuel as a cause here. Always be sceptical of reports, or conclusions from any source.

Then there was that off type 777 at LAX with its rollback. Fifty feet of ice making Fuel Line is too much. Interesting read, the "Beginning". The military have been flying at 50,000 feet for fifty years, and higher, this "new" behaviour of systems, Fuel, and Ice is sounding like a red herring.

A simple consideration of the simplest causes leaves, Chinese Fuel, and/or the way the 777Trent reacts as built and engineered to conditions extant for all the history of flight; and oh yes, to Chinese Fuel.

The Lear, a Twin, is certified to 51,000 feet. They fly to China. They also have Fuel line architecture much smaller in cross-section than the 777.
Can we scale back the handwringing regarding the state of ETOPS as impacted by "mysterious new forces?" Thanks in advance.

AF

Some clarification.

T800 is not likely to have a heater matrix bypass installed as part of the FOHE, the modification concerns creating a flush fitting matrix where ice cannot accrete to the protruding ends of the matrix.

Where T800 is different, is FMU spill return. It does not recirculate back around the FCOC whereas the GE, P&W and all RR architectures (except T800) recirc spill back through FCOC.

John Farley and airfoilmod – you are of course both right in your facts.

What got me was ethereal and not facts – call it gut feel, call it smelling something, call it vibrations in the ether, call it ‘away with the fairies’. I have no facts. I have no analysis. I have no scientific dissertation. If I told you the background to my concern, most people would laugh out loud - to avoid my further embarrassment, I’ll say that it is based on an “organic chemical”, as are jet fuel and biofuel blends.

I still think that there is a global issue coming with global consequences for the present fuels system. It's not just Chinese fuel. Arguable and dismissible. My only defence is that I sometimes have a disconcerting ability to see this sort of change. That sounds a bit arrogant, so let me apologise and offer Ernest Gann’s defence (as in the loose elevator bolt over California AFAIR) – blind dumb luck leads me to my conclusions.

DakMan
 

Taking note of your clarification, I would question the efficacy of shortening the tubes to terminate flush with the tubesheet. As it is, migrating Ice, when encountering the current design, has the ability to pass by the openings of the tubes and collect between them, for a time, held out of harm's way. The mod may have the advantage of collecting the tube openings closer to the Oil, (the Heat source), but the volume of Ice has nowhere to go but collect at the respective openings into the cannister. From a manufacturing standpoint, it appears a less complicated termination, (the Fix), simply with better access for the welder.

John Farley's anecdote about the Canberra is most instructive, a simple solution provided by a straightforward anticipation of the problem. A filter to remove solids (Ice) from the Fuel Flow, combined with a Heater to melt the Ice and return it? The Canberra was a very high flier; one should question the approach by Boeing/RR about the 777 design.

Over Run - I admit to the same experience. One who ignores any of his senses in flight is not using all his skills.

AF

I would guess that the intention is to provide a smooth rapid flow into the tubes to hasten the icy slurry through. The pockets around the protruding tube ends will be stagnant areas and encourage the stuff to stick.

I have been revisiting the fuel system diagram posted by Jet II at post 467, and it shows the LP fuel filter after the FCOC, which also seems to me to be an unusual arrangement.

Anyone out there know why the T800 is like that?? :confused:

Sooty

sooty
 

Without adding pressure by placing the HP in front of the FOHE, there will be no real change in Ice migration at the Face, as I see it. Clipping the tubes flush seems an improvement, but hardly a solution. As the migrating Ice hits the entry, it still has the same cross section to contend with, and I still think of the interstices between tubes as a plus for temporary "storage" of the slurry. The closer proximity to the Oil entry in the cannister is a plus, though.

The HP pump is a geared, or lobed mechanism, a positive contact type that would certainly serve to crunch solids or gels into a pumpable mass.

Placing this unit in Front of the FOHE would prevent solids from accessing the Face, as GE does. It was the Plug at the Face that caused cavitation, the HP has no flow/fault relief valve to relieve pressure when draw is prevented. Including the products of spill to cycle through the HP feed would be an alternate supply, or direct connect to HP from FOHE Face bypass would prevent cavitation also. But this would preclude using check valves in the spill return, otherwise cavitation could occur.

Airfoilmod

I was allways under the impression that having the HP fuel downstream of the FOHE was a failsafe design. The theory being that if a pipe within the exchanger ruptures the oil is at a higher pressure than the fuel. This leads to the oil contaminating the fuel system but the engine can combust this. Conversely If the fuel were to contaminate the oil system the lubricating properties of the oil would quickly be lost causing damage to the engine.

I Can't remeber the architecture of the GE system so I don't know how they get round this ?

Spannerz
 

What I'm after is the masticating ability of the gears in the HP to blend the Ice back into the Fuel. Bernd posted a while back that GE's HP is upstream of the FOHE.

If it takes different metallurgy for the pipes in the FOHE, or a pressure sensor in the oil portion of the cannister, or a bypass around the FOHE downstream the HP and directly to the nozzles, these are design considerations. It seems to me, though, that if the Oil gets into the Fuel system, it will deplete and cause engine damage anyway. One way round this HP FOHE is a partial bypass. Why direct 100% of the Fuel through the FOHE? Why not a portion of it, enough to cool the oil only.

The FOHE has been shown to be the weak link. Are there others? The Ice picture from the Reports is daunting, no doubt. There remain two issues:
Refitting the Trent/777 immediately, and an intense program of Fuel Research.

I would have to dig the notes out again but I think with oil contaminating LP fuel the rate of oil depletion is much less than HP fuel contaminating the oil thus buying valuable time with the engine still running.

Like you the I found the picture of the Ice accretion very worrying and the modified FOHE can't come soon enough. Practically the retro-fitting of the new units won't happen overnight, with 500+ Trent 800's on wing manufacturing and supplying the units post certification is a logistical challenge in its self.

More research into fuel will definitely be a good thing. The fact that a lot of the design regulations are based on 50 year old research indicates to me that this is long overdue !

I'll admit upfront that I am not an engineer - I am a refining & fuels guy with the oil industry. But I was struck by the fact that AAIB interim report 2 clearly reported that ice accumulated on the face of the FOHE and melted fairly rapidly until the test rig became too cloudy to see what was going on. Surely the idea must be to increase the transfer of heat between oil & fuel. How does remachining the physical face of the FOHE achieve that? Surely you either have to increase the recirculation rate of the oil or elongate the matrix to improve heat transfer. As I am clueless here I am happy to be abused on this!

Pinkman

Pinkman
 

As I see it, the extension of the tubes past the Face into a 100% Fuel (cold) environment allowed Ice to accumulate and prevented it from reaching the hotter portions of the HE, the Face. As Sooty says, the goal seems to be to expedite the Ice's migration directly to the Face itself. The schematic I have seems to show the From Engine Oil entering the FOHE at the Fuel exit. The FOHE Away Oil (cooled) seems to be exiting at the Face FOHE. I'd like to be wrong, since I think the Hottest Oil should be at the FOHE's Face.

My question is the region between all the tubes can accomodate some volume of Ice, and trap it out of Harm's way (theoretically), unless the slug of Ice is too large for this and then plugs the 1080 openings. In any case, though helpful, I don't think the foreshortening of the tubes to the Face accomplishes enough to solve the problem.

BA038 Rolled Back after an increase in Fuel was commanded, and the Thrust increased. Did the vibration of added thrust shake loose a quantity of Ice that then occluded the FOHE's? If so, what purpose does the AD's call for occasional max thrust solve? Then return to Idle to melt whatever accumulation has presented? The AD seems insufficient. The GE and Pratt engines, not having had a rollback (seemingly) does not mean they won't or that they haven't and weren't diagnosed properly. The RR fix seems short of the mark. If the AD is used, should it coincide to proximity to an alternate?

AF

I would again point out that the ice accretion photo, tests, etc.... have all come from UNREPRESENTATIVE tests using unrepresentative fuel.

Before trying to redesign everything, a proper understanding of what actually happened and the "new" fuel/ice behaviour is needed.


(I will now go back to sleep until the "accumulation" of posts ignring the facts starts to build-up to a critical level again.)

.

No, the rate of heat exchange has been designed the way it is. Having more heat exchanged may make the oil too cold. The other name for the FOHE is "Fuel Cooled Oil Cooler", which clearly states is primary function: cooling the oil. Heating the fuel is only a secondary effect.



Countercurrent flow heat exchangers are much more efficient than parallel flow desings. The design goal of the FOHE was not to melt ice on its fuel inlet face, but to cool the oil, and weight being a critical parameter in aviation, this was obviously the right engineering decision. I'd be surprised to see a lot of parallel flow HEs anywhere.


Bernd

Sooty
 

This is a normal arrangement, LP Pump - Oil Cooler - LP filter (with bypass) - HP Pump. Nothing unusual in that system and it's comon to all 3 big manufacturers.

Again, where T800 is different is the return circuit of spill flow (that flow delivered to the FMU in excess of what the burnt flow demand is) which is not an inconsiderable amount of fuel. On T800 it spills around the HP system in most other applications it spill around the LP system therefore introducing a large heat source into the FCOC.

Also, it is normal practice to arrange the flow path so that the hottest oil is cooled by the coldest fuel.

However, the effective "fix" is, in my opinion, treating the symptom not the cause, which is essentially fuel with high entrained water content.

Controlled testing of the engine fuel system whereby a "slug" of ice or "snowball" is introduced into the LP inlet is extremely difficult to control and replicate that which develops in the aircraft system.

As has been previously stated the engine fuel system has been optimised within the aircraft flight envelope, I do not know the intimate detail but it appears that there may have been some envelope excursion with BA0038 which the engine fuel system was not designed to accommodate, combined with the upload of fuel that may have had a high water content and the result could be considered as academic.

For information engine fuel system ice testing is carried out at a concentration level of ~260ppm.

Dak Man, Phil Gollin
 

That is why I continually ask what the results were from analysis of the 'retention' samples from the airport tankage. Practices vary; in the old days deliveries often had a representative sample from the bowser taken and it was sealed in something resembling a kilner jar with wire seals and a lead crimp.

Nowadays with hot hydrant systems the procedures aren't much changed: Ideally (i.e. CAP 748) there should still be a sample taken:


g) immediately prior to fuelling an aircraft.

Soooo.. again, I ask, where are the samples, were they subject to a proper Chain of Custody arrangement, and what are the analysis results?
It would be nice to see some records of the last delivery into tankage and the total rainfall increments between the delivery and the fuelling.

Pinkman

Why is this?

Is this not the opposite of bsieker's assertion ?


JD
:)

Basic thermodynamics, really.

Ideally, a countercurrent flow HE can make the "hot" fluid (oil) at its exit almost as cold as the "cold" fluid (fuel) at its inlet (when it is coldest).

Ideally, a parallel flow HE can make the "hot" fluid (oil) at its outlet only almost as cold as the "cold" fluid (fuel) at its outlet (when it is warmest).


It is. And I think Dak Man might have been momentarily confused when he wrote it.

Because what he said also means that the hottest fuel would be used to cool the coldest oil, which would be inefficient.


Bernd

Countercurrent exchange - Wikipedia, the free encyclopedia
Here is a very basic diagram on the difference between the two. Showing that counter current exchange is the more efficient. This of course will only apply if the lube oil bypass on the FOHE is closed. If it is open then little heat is transferred to the fuel. As the lube oil flow through the shell side of the FOHE is a torturous path across the many tubes and around the baffle plates, it would be interesting to know how far the bypass needs to be open before there is no flow on the shell side of the exchanger and therefore no heat input to the fuel. Are we sure that this exchanger arrangement is counter current flow? If it is concurrent then less heat transferred to the fuel even when it is fully in service.

Keep in mind
 

The Fuel flow is 6,000 pph at Idle, and the Fuel is very cold.

The Oil Flow is what? Far far less?

The Oil side of the HE is exposed to almost static low temps, it affects the Fuel very little.

At the critical time being discussed, (FOHE plug, Face) the Hottest Oil would be most effective at melting the Ice, per AD. But remember, as I pointed out a while back, the FOHE is not intended to be an Ice melter, it is an Oil cooler. So the design of concurrent or counter is not relevant to the discussion; except insofar as an installation is now intended to accomplish that which it was not designed to do. Solving the Plug problem doesn't solve the Ice problem. Until Pipe Ice is eliminated, someone's tilting at windmills. The Trent may be taking the fall for a problem no engine was designed to function with, but happened to be more vulnerable to, (the Ice), by chance, than the other engines.

AF

Perhaps my post was slightly misleading, there is no hottest or coldest fuel "end", the fuel temp is what it is and is largely uniform as it enters the FCOC, again remember that it's an oil cooler - not a fuel heater but you can take "benefit" from the hottest oil in raising fuel temps at what is evidently a critical point in the system, i.e the heater matrix end plate.

The fix that I mentioned is, in my opinion, little more than a sticking plaster, if the focus is to be an engine fuel system orientated fix then it should be focussed on getting a bit more heat to fuel in the FCOC loop, and as I have said previously this is normally achieved via the FMU spill return to LP rather than HP as in the T800.

However, in saying that, does anyone know what Fuel Return to Tank (FRTT) philosophy is for B777 / T800, this may well be an insufficient Flow Number (FN) for these extremely long sector cruises and not prevent the tank fuel volumes dropping below say, -8 Deg C.

I suspect that if system testing is done with fuel in the sticky ice temperature window then lots of engine fuel systems will, shall we say, "fall down" which is a huge can of worms. It's perhaps somewhat fortunate that it was a T800 where a fix is easily "sold". If it had been a GE90 where I believe the FCOC loop is in the HP fuel circuit, therefore intrinsically hotter, then the proverbial would be hitting the fan. As an aside the problem with HP side FCOC loops is matrix tube failure, as significant oil dilution would occur leading to lubrication / bearing "issues".

Again, fundamentally the engine is being asked to deal with an aircraft fuel system phenomena, not exactly chicken and egg.

DakMan
 

If HP upstream is problematic for tube failure, why did GE choose the design? The Fuel as heating fluid may not be GE's strong suit, but it's HP design. Again, the Fuel does not gain much Heat, it wasn't the design issue. The idea would be to Heat the first place Ice forms, which is not the FOHE. As a final fix, if it is the FOHE that is to remediate the Icing problem Plug, it's the same as accepting the presence of Pipe Ice. As a final fix, that is ludicrous, for reasons stated above.

AF

GE filter ??
 

I can understand the suggestion that placing the FOHE after the HP pump may protect the GE system by "mashing" the ice to slurry in the pump, but doesn't the GE arrangement have an LP filter? :confused:

If so, the ice would collect there, and presumably melt eventually, and any blockage would be relieved by the bypass.

Redesign - Can we all have a go?
 

With nice clean fuel and nice clean oil, it doesn't matter which flows through the little tubes, and which flows round them.

But if the fuel is lumpy, perhaps because some water has been pumped into it via an exceptionally cold main tank, it might be better to put the nice engine oil through the little tubes, and let the lumpy fuel go round the outside.

It's a viscosity
 

Thing. And Ice wasn't a design constraint. IMO.

Sooty - I can't find the GE schematic. The RR has an LP Filter downstream the FOHE, and appears to be embedded in an Oil flow system as is the Fuel. The LP seems to be an Impellor design, the HP a lobed, or geared design. So the Fuel goes unimpeded from Tank to LP to FOHE. (Roughly).

Only in Hindsight, and knowing Pipe Ice is a Real problem, are all these comments pertinent. But it would seem that putting the FOHE as the skinny kid, closer to the Nozzles, may have prevented Trent from taking the flak. But then we wouldn't be aware of the Problem at all. Perhaps never. So far, a totalled Bird, a broken leg and some brown Laundry offloaded Delta at Atlanta. So Far.

RightBase - To be fair, the FOHE wasn't designed strictly for high and cold. Down low, and warm, the Oil is in more need of cooling than up high, where most everything's cold to begin with. To get best exposure to the Fuel (which isn't so cold when low,) the design (IMO) slows the Fuel down, by necking down the cross section and adding surface area F/O.
Gives the transient Fuel more time to soak up some calories. Ice? What Ice. The increase in pressure and slower velocity becomes problematic up high, especially when Pipe Ice can occlude the passage. Which is what is frustrating, where the Oil isn't so hot, and the Fuel is very cold, the need for an FOHE is debatable, especially when Thrust is way short of TOGA or Cl. Hence, why not a (relatively) simple bypass for the Fuel? The Oil has one, it bypasses the FOHE when it cools down, Shouldn't the Fuel bypass at the same time? Or in an Icing regime?

AF

What happens if fuel enters engine below 3C?
 

Warning: I'm non-professional; not crew, not engineer - just guest here, thanks.

The thread has now turned to an area that intrigued me some time ago (419, page 21) and caused me to write the following.

The question was not answered then but I'm hoping one of you will be kind enough this time.

Thanks in advance.

Regards, Tanimbar

Sooty GE90 Architecture
 

ImageShack - Image Hosting :: ge90dacb777.tif

Indeed Sooty the GE90 does have an interstage LP filter which would go into bypass if clogged with ice. When in bypass the ice can migrate and block the bypass loop, cavitating the HP pump and ceasing all flow to the FMU.

Edit.

Having had a closer look at the GE90 schematic I was mistaken here, the LP filter (and hence bypass) is in the HP loop so the chances of ice ever getting there is slim as it would get mashed in the HP Gear Stage. However there is no bypass loop for the interstage strainer :(

Maybe it's the right amount of ice......
 

...to collect in a GE90 interstage strainer (or block a T800 FOHE) but not enough to fill the strainer and overspill into the bypass. I wonder if there are any records of GE90s with transient high strainer dp or bypass opening - would the pilot be aware of it?

It may be that variable conditions (and thus probably variable quantities of ice released) make the GE90 also an accident waiting to happen. :eek:

Sooty

Tanimbar
 

Fuel systems are routinely Qualification tested with fuel temperatures down to -54°C in the tank and -45°C at the LP inlet. It's fuel in the region of -8°C that is causing the headaches.

DAK Man -I'm just curious but didn't make this clear
 

You said,
.

I know. I should have made it clear that my question arises purely from curiosity. I'm not implying anything by asking, "What happens next if fuel at or below 3C enters an RR engine inlet?".

Regards, Tanimbar

Tanimbar
 

Nothing untoward.

This table you mentioned seems a bit suspicious to me.

As I've said the engine fuel system is designed to accept fuel (with 260ppm of water present) at the LP inlet down to -45°C (fuel temp) without issue (and they do). What is now evident is that this is possibly not the worst case scenario due to the type and formation of ice present.

This kind of system icing testing has in the past prompted modifications to FMU Flow Washed Filters where sevo flows are traditionally tapped off. Obviously if a flow washed filter becomes clogged (it shouldn't because as it's name applies the filter is constantly "flow washed") then you can lose control of the engine as VSVA contol et al are servo flow controlled / powered.

Dak Man - are we discussing the same thing?
 

Thanks for the reply. I think we might not be discussing the same thing.

If I understand the Airbus article properly ( http://www.airbus.com/store/mm_repos...6_low_fuel.pdf ) then the 'minimum engine inlet temperature' is the minimum temp. the fuel should be AFTER passing through the 'oil cooling system', i.e. the fuel is about to be burnt.

To quote from the article, paragraph entitled Minimum Inlet Temperature,

Of course, I might be completely misunderstanding the terms used and their meaning, in which case I'll find a dark corner .......

Regards, Tanimbar