Turbine Oil

[Stationair8]

Why do turbine engines use synthetic oil instead of mineral oil?

[Landroger]

Why do turbine engines use synthetic oil instead of mineral oil?

Not being an expert, I suspect the answer is; because they can! I was told by a guy in the oil industry that with synthetic oil, the refinery pretty much reduce 'ordinary oil' to its component molecules and then put them all back the way they want them.

That way, the oil will be 'fine tuned' to do exactly what the engine and the operational regime requires.

Other than that, I haven't a clue. :)

Roger.

[gulfairs]

Mineral oil(dead dinosoars) is not able to stand the temeratures required in the bearings near and down wind of the hot section.
Synthetic lubrication is ok up to what ever a gas turbine can produce without serious break down or any breakdown.

[Brian Abraham]

Advantages of synthetic oil

1.Measurably better low- and high-temperature viscosity performance at service temperature extremes
2. Better chemical & shear stability
3. Decreased evaporative loss
4. Resistance to oxidation, thermal breakdown, and oil sludge problems
5. Extended drain intervals with the environmental benefit of less oil waste.
6. Improved fuel economy in certain engine configurations.
7. Better lubrication during extreme cold weather starts
8. Longer engine life
9. Superior protection against "ash" and other deposit formation in engine hot spots and reduced chances of damaging oil passageway clogging.

I stand to be corrected, but all aviation synthetic piston oils are a mineral/synthetic mix, rather than straight synthetic as available for motor vehicles. Reason being that synthetics do not hold lead in suspension as well as mineral oil.

The lower friction of synthetics make them unsuitable for break-in where friction is desirable to cause wear, hence the reason to use straight mineral oil on new/overhauled/cylinder or piston change for the maintenance manual stipulated period - often 50 hours.

At Esso, in Bass Strait, we were using one of the AFM approved oils in the S-76 gearboxes - Dexron, which is an oil produced by various manufacturers to a General Motors specification for use in automotive automatic gearboxes. The name Dexron is a GM copyright.

We were finding that in hot weather the main gearbox oil pressure would eventually drop below permissible limits. Lab checks found the oil still passed specs, and the conclusion eventually drawn was that the long chain molecules were being chopped into shorter chains by the shearing action imposed as the oil sprayed from the jets.

The accountants deemed that Dexron, being one third the price of the alternative Mobil Jet, continued oil changes were the way to go. After having to rescue me from off shore a few times, it was decided that Mobil Jet had some merits, and changed.

Reliable Performance For Confident Operations, AeroShell Turbine Oil 560 - Shell Aviation (http://www.shell.com/home/content/aviation/products/lubricants/turbine_engine_oils/oil_560/)
Piston Engine Oils - Shell Aviation (http://www.shell.com/home/content/aviation/products/lubricants/piston_engine_oils/)

[thermostat]

That was a great reply from Brian A. He hit it on the head. The friction reduction properties of synthetics reduces heat and wear. The very wide temperature range of synthetics allow for extreme high and low temperature operation of hot engine and cold high altitude flight. You would lose your 5 million dollar engine in perhaps 30 minutes if you used a mineral oil, it's simply crap.