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#4728866 - 04/16/18 01:14 PM PAO/GrIII based oil in jet turbines>
PeterPolyol Offline


Registered: 03/06/16
Posts: 1351
Loc: toronto
General question: Are there any PAO/GrIII based turbine oils in use today or are they still unmatched with ester bases?

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#4729114 - 04/16/18 05:52 PM Re: PAO/GrIII based oil in jet turbines> [Re: PeterPolyol]
Cujet Offline


Registered: 02/15/03
Posts: 7238
Loc: Jupiter, Florida
I don't know of any G-III oils in turbine engines.

In fact, we are switching to HTS (high thermal stability) oils in much of our equipment.
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#4729214 - 04/16/18 07:17 PM Re: PAO/GrIII based oil in jet turbines> [Re: PeterPolyol]
Tom NJ Offline


Registered: 07/27/06
Posts: 2125
Loc: Virginia
No, PAOs and Group IIIs cannot possibly pass the high temperature oxidation and coking specifications in MIL-PRF-23699G, MIL-PRF-7808L, and AS5780B specifications needed for aviation turbine engines. In fact these highly paraffinic hydrocarbons are coke producers in high temperature thin film environments due to their utter lack of polarity. All jet engine oils are based 100% on polyol esters, and even small percentages of these hydrocarbons would be troublesome.

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#4729372 - 04/16/18 09:16 PM Re: PAO/GrIII based oil in jet turbines> [Re: Tom NJ]
PeterPolyol Offline


Registered: 03/06/16
Posts: 1351
Loc: toronto
Originally Posted By: Tom NJ
No, PAOs and Group IIIs cannot possibly pass the high temperature oxidation and coking specifications in MIL-PRF-23699G, MIL-PRF-7808L, and AS5780B specifications needed for aviation turbine engines. In fact these highly paraffinic hydrocarbons are coke producers in high temperature thin film environments due to their utter lack of polarity. All jet engine oils are based 100% on polyol esters, and even small percentages of these hydrocarbons would be troublesome.


Wow didn't expect that bit!
Thank you for the comprehensive rundown, Tom.

Cujet, what type of oil were you using?

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#4729523 - 04/17/18 03:22 AM Re: PAO/GrIII based oil in jet turbines> [Re: PeterPolyol]
FowVay Offline


Registered: 06/02/02
Posts: 2685
Loc: Southeastern USA
Even with polyol ester oils coking is a major concern. I work the GE CF6 engine at my company and see the horrors of high temperatures every day. Our engine uses ball and roller bearings that are lubricated with a nozzle sprayer. Each main line bearing group has its own sump with a chip detector to monitor debris activity. The rear of the engine (turbine rear frame) houses the #6 roller bearing and this is where much of the problems originate. It is a routine maintenance item to remove and de-coke the supply and scavenge oil tubes because they will develop coking inside the oil flow galley and restrict oil to the bearing. These aren't tiny little oil lines either. These things are .5"- .7" in diameter. The tubes are routed through the frame strut and exposed to the direct heat of the exhaust gas path. I personally don't see how anything can survive this environment but these engines are incredibly durable.
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#4729685 - 04/17/18 08:49 AM Re: PAO/GrIII based oil in jet turbines> [Re: FowVay]
Tom NJ Offline


Registered: 07/27/06
Posts: 2125
Loc: Virginia
Originally Posted By: FowVay
Even with polyol ester oils coking is a major concern.


FowVay, as you probably know, there are different grades of jet turbine engine oils with the differences mostly related to coking tendency. The older 2nd generation products such as Eastman 2380 (formerly Air BP and Exxon), Mobil Jet II, and AeroShell 500 often created coking issues in certain engines, such as the Pratt JT8D-200 series, RR Trents, and some others depending on operating conditions. Mobil Jet 254 and AeroShell 560 are 3rd generation oils with improved coking tendencies, and today the 4th generation oils are even better. These include Eastman 2197, Mobil Jet 387, and AeroShell Ascender. All of these generations use polyol esters exclusively, and even though the additives play the major role in coking, there are coking differences among the various polyol esters as well.

The Eastman 2197 led the way and set the standard for 4th generation oils, utilizing both a low coking polyol ester and an advanced anti-oxidant. This oil was developed by Exxon in the 1990s, and I worked closely with them in the development of the patented polyol ester. It is the largest selling 4th generation oil. I also developed the base ester for Shell's Ascender.

The high temperature capacity of modern jet engine oils is probably maxed out and I wouldn't expect a 5th generation oil any time soon as even some the 4th generation oils are still in the approval process. Since it takes a good ten years to develop and approve a new oil, probably a lot more with a different chemistry base oil, polyol esters will continue to be the exclusive base oil for many years. Current engines are designed around the performance of current oils, not the other way around.

If you are using older generation oils in your CF6 engines you may want to consider changing to a 4th generation oil. If you are using military spec oils instead of branded products, the 23699 HTS oils are also low coking.

Tom NJ

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#4730163 - 04/17/18 05:06 PM Re: PAO/GrIII based oil in jet turbines> [Re: PeterPolyol]
FowVay Offline


Registered: 06/02/02
Posts: 2685
Loc: Southeastern USA
Tom, Eastman 2197 is the specified fill for all of our engines and IDG. I can only imagine how bad it would be with a lesser product.
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#4730275 - 04/17/18 06:38 PM Re: PAO/GrIII based oil in jet turbines> [Re: PeterPolyol]
Cujet Offline


Registered: 02/15/03
Posts: 7238
Loc: Jupiter, Florida
We have a Eurocopter EC135, (twin engine) with the Turbomeca Arrius 2B1_A1 engines. In 1050 hours, weve had 3 catastrophic engine failures.

2 of those were oil coking taking out the aft bearing. 2380 oil.
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#4730340 - 04/17/18 07:33 PM Re: PAO/GrIII based oil in jet turbines> [Re: FowVay]
Tom NJ Offline


Registered: 07/27/06
Posts: 2125
Loc: Virginia
Originally Posted By: FowVay
Tom, Eastman 2197 is the specified fill for all of our engines and IDG. I can only imagine how bad it would be with a lesser product.


I agree. Eastman 2197 is top of the heap - if you are still getting coking not much you can do from the oil side.

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#4730346 - 04/17/18 07:38 PM Re: PAO/GrIII based oil in jet turbines> [Re: Cujet]
Tom NJ Offline


Registered: 07/27/06
Posts: 2125
Loc: Virginia
Originally Posted By: Cujet
We have a Eurocopter EC135, (twin engine) with the Turbomeca Arrius 2B1_A1 engines. In 1050 hours, weve had 3 catastrophic engine failures.

2 of those were oil coking taking out the aft bearing. 2380 oil.



2380 was formulated in the early 1960s, so there are better choices available for high coking engines.

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#4730638 - 04/18/18 05:46 AM Re: PAO/GrIII based oil in jet turbines> [Re: PeterPolyol]
john_pifer Offline


Registered: 07/08/12
Posts: 2030
Loc: Nashville, TN via Memphis
Most of our customers use the Mobil Jet II in their Embraers that have the CF34 GE.
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#4730709 - 04/18/18 07:55 AM Re: PAO/GrIII based oil in jet turbines> [Re: Tom NJ]
Cujet Offline


Registered: 02/15/03
Posts: 7238
Loc: Jupiter, Florida
Originally Posted By: Tom NJ
Originally Posted By: Cujet
We have a Eurocopter EC135, (twin engine) with the Turbomeca Arrius 2B1_A1 engines. In 1050 hours, weve had 3 catastrophic engine failures.

2 of those were oil coking taking out the aft bearing. 2380 oil.



2380 was formulated in the early 1960s, so there are better choices available for high coking engines.


True. Unfortunately, the use of any of the approved HTS (high thermal stability) oils require an recent overhaul first. This helicopter engine is unique, in that it has a larger and complex gearbox mounted directly to the compressor inlet. The various oil passages go through the machined face of the compressor housing-to gearbox interface. The original seals are incompatible with HTS oils and attempts to use HTS oils cause seal failure in short order. During overhaul, HTS compatible seals and o-rings are employed.

Put another way, the only commonly available oils approved for use in this engine, prior to a recent overhaul, are 2380 and Mobil Jet II.



Edited by Cujet (04/18/18 07:59 AM)
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#4730719 - 04/18/18 08:05 AM Re: PAO/GrIII based oil in jet turbines> [Re: Cujet]
Tom NJ Offline


Registered: 07/27/06
Posts: 2125
Loc: Virginia
Ah that makes sense Cujet. The anti-oxidant class used in some of the HTS oils has compatibility issues with certain seals. The exception I know of among HTS oils is AeroShell Ascender which uses a different type of anti-oxidant package that they say is compatible with all seals. In fact seal compatibility was a development target for this oil. You may want to check whether Ascender is approved for your engine yet.

Tom

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#4731062 - 04/18/18 02:26 PM Re: PAO/GrIII based oil in jet turbines> [Re: PeterPolyol]
BusyLittleShop Offline


Registered: 12/09/11
Posts: 859
Loc: Ca USA
I gleaned what I could from MSDS reports... turbine oils are low
viscosity much like ATF... funny no one worries about premature wear
of their turbine gears or their automatic transmission gears...



Shell
AeroShell Ascender_TDS
23cSt @ 40C
5.40cSt @ 100C

AeroShell Turbine Oil 2_
10.5cSt @ 40C

AeroShell Turbine Oil 390
12.9cSt @ 40C
3.4cSt @ 100C

AeroShell Turbine Oil 500
25.2cSt @ 40C
5.1cSt @ 100C

AeroShell Turbine Oil 555
29cSt @ 40C
5.4cSt @ 100C

AeroShell Turbine Oil 560
23cSt @ 40C
5.2cSt @ 100C

AeroShell Turbine Oil 750
36cSt @ 40C
7.5cSt @ 100C

Exxon
Exxon Jet 254
26.4 cSt @ 40C (102 F)
5.3 cSt @ 100C (212 F)
cSt @ -40 C (-40 F) 11,500
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#4731134 - 04/18/18 03:17 PM Re: PAO/GrIII based oil in jet turbines> [Re: BusyLittleShop]
Tom NJ Offline


Registered: 07/27/06
Posts: 2125
Loc: Virginia
The are three classes of jet turbine oils, usually referred to by their viscosity @ 100C, those being 3 cSt, 5 cSt, and 7.5 cSt. The 3 cSt oils are used mainly by air forces who may operate bases in very cold regions, so these oils are designed for engine start-ups down to -51C (-60F). The 5 cSt oils are used by commercial airlines and other military services and are deigned to allow engine start-ups down to -40C (-40F). The 7.5 cSt oils are for turboprop engines and the added viscosity is needed to lubricate the reduction gears.

Turbine engines are high speed concentric shaft engines that operate in a hydrodynamic regime, so the oils for the most part do not require high viscosity or extreme pressure additives. Instead they contain an ashless phosphate ester anti-wear additive. The oils serve as much as a coolant as they do a lubricant, and must be able to withstand and flow at the temperature extremes, both high and low, encountered by jet engines. Only polyol esters meet these requirements, except that some diesters and complex esters are used in the 7.5 cSt oils.

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