DERG
 

While not knowing this engine initimately it is usual for RR engines oil to be cooled by cold fuel with the heat exchange also warming the fuel.
I may be wrong but your post no4 about 'robbing cool air' is probably completely wrong..now what is your point exactly? :ugh:

quite a few threads that wander into the technical side of things have newbie posters who post questions to confirm the answer to an already made up mind. Sometimes you might notice this when hidden in the text is the "given that you are still be beating your wife"

Or worse yet when the answers don't come in the way that they have expected they try and divert the subject rather than listen and learn.

Yes, it is almost more than one can bear.

Try the gym, Bench Press should do it.

Conjecture and substituting facts with opinions doesn't carry much weight. Neither does being tetchy. All in all, it's much like the Emperor; Much huffing and puffing and strutting about, while actually being nothing more than bare.

KUMOOZ

Oil cooling is indeed accomplished at the Fuel Oil Heat Exchanger.

It is the cooler of preference, though there is also An Air Cooler for engine and gearbox Oil. The FOHE is bypassed at Cruise and Descent in favor of the Air Cooler.

There is no provision for Fuel Heating via the FOHE. It has been piggybacked by the AD on TRENT 700 installed on the 777. The manual I have leaves that function out of the Operator's handbook. The GE90 does include a reference to Fuel Heating in its OM. For what its worth.

bear

DERG = ssg = johns? Strange similarities.

The GP7200 runs an oil temperature of 163℃ at the oil outlet, with transient operations of 177℃ limited to 20 minutes for comparison purposes to the Trent 900.

Indeed, lubricating oil is cooled using fuel from the wings during takeoff and climb.

There is also a minimum oil temperature that must be reached prior to takeoff.

Turbine D

DERG asked me about my experience in test cell ops. I have located the TCDS, and scavenge temp limits are: 160C continuous, 170C 5 minutes.

I never recorded oil temps - my focus was aero/thermo parameters, and I had my hands full with that. The local throttle jockeys took care of the mechanical numbers, but in several hundred hours of aggressive operation, they never had a oil temp problem on my engines. :)

Thank You
 

"B757 with RB211-535E4 engines. Cruise oil temps (off the EICAS) are rarely in three digits. They use a little bit of oil, but powerplant engineers monitor uplifts. If it gets excessive, shop visit time."

Thank you for this post. This is the info I am seeking.

What do I want to know? Some of us are wondering just WTF is going on with this T970 series and the "RR total care" contract. Just how is the oil top up recorded, YES how and where... and who looks at the record. Do you see the issue here? If the only people overseeing the engine are RR then clearly an operator has little control over the equipment used. Moreover the operator may be taking risks that are unacceprtable.

Turbine D thank you that helps.
Brian.. I have never used other screen names.
Bear..thank you..complex but constructive.
Lomapeso..oh yes..we know your classification well..you need a nanny on the shop floor in case you trip and fall. You are stardust, you are golden.

KBP If you have the inclination go get a litre of turbine oil and heat it up on a domestic cooker. If you can measure the temp at 150C. See what happens above 150C. There is no danger involved in this home experiment. But you may be surprised.

SteveF: I am damn sure the A388 of Lufthansa had this record, I am also sure that Singapore had it. But I am uncertain if Qantas had it. I am not saying Qantas was negligent in not having a hard copy paper record. What I am saying is that under the RR Total Care programme they may well have been led to believe they did not require one.

As I requested I would be grateful what the guys are seeing in daily use on their oil temp guages. The 180C running temp of the T972 as used in this A388 seems a lot higher than any other engine in civil aviation.

All replies welcome.

There is no Air/Oil Cooler on the Trent 900.Only a Fuel/Oil Heat Exchanger is installed.The GP 7200 has got both devices.RR and EA using Air/Oil Cooler for VFG Oil.

VFG oil?
 

what is this please?

VFG is a Variable Frequency Generator mounted on the accessory gearbox.It supplies 115V AC with a frequency between 370 to 770 Hz related to the engine speed.

One source I have informs me that the GE90 oil temp is measured at the supply side, not scavenge, and thus runs somewhat cooler on the readout.

Be careful in comparing apples to apples! :=

DERG,

I don't need to heat anything on a cooker to know what will happen. Even if I did, I would not be surprised by the result.

1 litre of oil heated to 200°C would have lost 3% mass after 6.5 hours.

End of story.

Would that be anything like the Trent 700 on the A330?

Thank you!
 

Thank you for the replies so far.

KBPsen Sure at standard temp and pressure, but the jet engines don't work at std temps and pressures. Back in 1971 I studied Kelvin's Gas Laws. I am sure you did too. You are not thick, I can tell.

Barit: excellent point YES.

no-hoper: thank you, please feel free to add to this thread. This Trent oil temperature issue fascinates.

spannersatcz..nice screen name! That is exactly what I want to know too!

Additional comments. GE/PandW/EA recently issued a notice to check oil lines for coking and fractures as a consequence of the Qantas incident on the A-388.

The RR Trent has more bearing surface area to cool than EA products. We know that the running temp of the Trent 972 is 180C. We have been told that the running temps of GE/GA/Pand W engines is less.

Would be grateful if others could please advise what temps they are seeing in day to day use in a/c they fly.

DERG:
MIL-PRF-7808 is a lubricating oil that must meet the following spec: Flash point 210° C (~ 410° F). I appreciate that an ambient pressure less than atmospheric would likely induce a flash to vapor at lower temps.

But lubricating oil in a jet engine is a fluid / liquid, under pressure.

Why do you feel that a fluid under pressure will flash?

I guess my question to you is: at what point when operating at cruise altitude do you believe that the lubricating oil is operating at ambient (20K feet, 30K feet 35K feet) pressures? The oil system remains under positive pressure, and contained ... or it leaks and sprays oil and you run out post haste and the issue of "flash" is far less than it is oil starvation.

I'll bite.

How is the application of Kelvin' Gas Laws utile in our discussion of oil properties when we are discussing a closed fluid circulating system under positive pressure? Is it your position that the lube is sprayed/applied by the system, before scavenge, to components that are operating at ambient pressure for the altitude? :confused:

Happy to understand your point better, if you'll elaborate a bit.

Thanks.

Lonewolf
 

Thanks for your reply. Everytime I try to log on to this site I get like 5/6 refusals so if I don't get back and reply you prolly will guess that I am onto an embarrasing scent. Too close to the truth for the well being of RR plc.

"Flash point 210° C (~ 410° F). I appreciate that an ambient pressure less than atmospheric would likely induce a flash to vapor at lower temps." Thanks for that info. The bearing chamber that RR uses is unique and patented. It uses pressure differentials to work as designed. So YES reduced pressure/partial vacuum lowe flash point. We know the T972 ran at 180C cruise so a spontaneous ignition inside the chamber is within probablilty. So the oil temp only has to rise about 9% to attain that unstable state at one atmosphere pressure.

"But lubricating oil in a jet engine is a fluid / liquid, under pressure." Not in this case it ain't. Especially if a pipe was fractured as the ATSB has identified.


"I guess my question to you is: at what point when operating at cruise altitude do you believe that the lubricating oil is operating at ambient (20K feet, 30K feet 35K feet) pressures? The oil system remains under positive pressure, and contained ... or it leaks and sprays oil and you run out post haste and the issue of "flash" is far less than it is oil starvation."

This happened at about 5K feet I think under about 85% load on TO. There is evidence that a lot of these T970s had oil leaks. The basic principal of by pass jet propulsion demands controlled pressures and are independent of outside air pressure. This is not the case with ambient temperatures at TO thrusts.

Kelvin Gas Pressure Law. Any liquid unless at absolute zero temp has an atmosphere just above the liquid state. This depends on both temp and pressure and is governed by a gas contsant value which I forget..ahem..I was 17 when I did this stuff.

Using the Kelvin laws I believe that the 9% temp leeway preventing a spontaneous combustion is not only possible but likely. Throw in a fractured oil pipe and a few places where the oil has accumulated and bingo you have an explosion.

I have to say if that 210C flash point is correct I want to know just WTF this company are seeking to achieve with this engine design.

DERG

An items not noted, as of yet, in your thread relative to oil temperature:

It is called "soak back". Soak back occurs when the engine is shut down and the oil coating the walls of the sump or in the tubing is heated above normal operational conditions verses if the engine was running and oil was flowing. It happens to sumps, tubing and bearing locations in very close proximity to hot components such as the frame between the HPT rotor and the IPT rotor. "Soak back" is a factor in the design of sumps and the location of the oil lines, but it is still probably the leading cause of the formation and build up of coke.

Turbine D