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Turbine Engine Oil Guides

What is a Turbine Engine Oil?

Turbine Engine Oils (TEOs) are speciality lubricants designed to support the operation of turbine engines. First developed during the 1940’s, turbine engines can now be seen on almost all commercial aircraft currently in operation. While aviation is the main market place for these oils, there are other applications, especially in the power industry, where turbine engines are used.
Unlike piston engines, that convert an up and down movement from a piston into motion, turbine engines combine compressed air with the chemical reaction from the fuel within the engine to drive fan blades. This means that turbine engines reach much higher temperatures, and this has driven innovation in mineral TEOs, and subsequently synthetic TEOs.
There are two main functions of a TEO. Firstly, they lubricate the engine, including the gearbox, shafts and associated accessories, protecting them from damage and ensuring smooth operation while running. The other benefit is their use as a heat transfer fluid, cooling the engine in temperatures reaching 1000°c, in turn extending the life of the oil up to 25,000 hours of operation.




Specifications in TEOs

The main specifications that govern TEOs are MIL-PRF-23699 and SAE-AS-5780. Each specification has a number of different vendor options available, with Silmid stocking product from Shell Aviation, Eastman Aviation Solutions, Exxon Mobil and Nyco SA.


MIL-PRF-23699

The original US Military specification, this has been in existence for over 50 years and was formerly known as MIL-L-23699. This specification is divided into two further subcategories, defining differences in high temperature performance and thus their ability to reduce coking – the formation of carbon deposits within the engine.




SAE-AS-5780

Innovations in engine design, including the Trent 1000 by Rolls Royce, created further temperature problems that the MIL-PRF-23699 HTS grade could no longer adequately cover. This coincided with a shift in focus from military specifications, to commercial ones, namely those developed by the Society of Automotive Engineers (SAE). Their SAE-AS-5780 specification provides a more stringent framework for testing of such oils including their thermal stability, lower coking properties and improved load carrying capacity.
These oils are again categorised under two different subheadings – standard performance and high performance.

Type SPC – Standard Performance Category

*AeroShell Turbine Oil 560 is classed as an SPC grade oil under the SAE specification, but has a higher performance level than other SPC oils due to its MIL-PRF-23699 HTS qualification.


Type HPC – High Performance Category

It is important to note that receiving an SAE or MIL qualification does not complete the approval process, and separate approval should be sought from the engine manufacturer, through either engine development projects or a complete flight evaluation.