Strict requirements for oil…

In the past decennia, a lot has been written about the lubricating oil used in jet engines. In our short article Oils for Jet Engines we also highlighted on this topic.

Super oil for jet engines

Jet engine oil is not an “ordinary” oil, like the oil used in your car’s engine. Jet engine oil is used under very extreme conditions: at the engine inlet, temperatures of -50 to -60º C are quite common at nowadays’s usual cruising levels of 10-13 km. A strong compressor section is located directly behind the air inlet and here the temperature will quickly rise to well above 400º C, as result of the compression. In the aft section of the engine, behind the combustion chamber, we find the turbine. In this “hot section”, temperatures of well over 1,000º C occur frequently. And in all these different sections need to be lubricated (and cooled) by the same engine oil. Admittedly, any direct contact with these extremely hot parts is avoided as much as possible, but it will be obvious that jet engine oils need to have stable properties over a very wide temperature range in order to guarantee a proper lubrication under all prevailing circumstances.


Organophosphates, the solution?

As later jet engine generations delivered higher performance levels (more thrust), this implied higher and higher turbine temperatures. As a result the demands for lubricating oils became higher and higher, too. Soon the “normal” mineral oils could no longer meet those requirements, as these would freeze in the cold sections and  quickly loose their lubricating properties or even burn in the hot parts. The solution came as entirely synthetic oils were developed, which contained several special additives to guarantee stable lubrication even under extreme conditions. Organophosphates play an important role here, they turned out to be indispensable for the production of modern jet engines. And besides engine oil, the hydraulic fluids used on board contain large quantities of these chemical compounds, too, for the same reasons. They have excellent lubricating properties and are highly fire and corrosion resistant. The egg of Columbus, so it seemed…

Highly toxic compounds

The use of Organophosphates came with some serious problems though: in daily practice, some leakage of both engine oil and hydraulic fluid appeared to be unavoidable, even during normal operating conditions. A (relatively small) part of these substances will end up in the air that crew and passengers are breathing, with all health issues caused by that. During a so-called Fume Event, this even causes a serious pollution of the cabin air with a mix of highly toxic substances. Overigens wordt (naast bemanningen en passagiers) met name onderhoudspersoneel ook veelvuldig blootgesteld aan (al dan niet verhitte) dampen van motorolie en hydraulische vloeistoffen. Incidentally, in addition to crews and passengers, maintenance personnel in particular are also frequently exposed to (heated or not) vapors of engine oil and hydraulic fluids.

Aerotoxic Syndrome patients around the world know only too well how serious the resulting health threats can be.

In the meantime, parties are working on solutions…

The problems with air contamination on board and the health risks caused by them have been persistently downplayed or even completely denied by the airline industry for decades. They obviously do not want any negative publicity, let alone million dollar claims for health damage liability. Nevertheless, several parties are working hard to develop less toxic oils. In 2016, the Fraunhofer Gesellschaft in Germany applied for a patent on a TCP-free jet engine oil.

Oil manufacturer NYCO is also among the parties who have been researching for alternative oil types that are less harmful to the environment and less toxic to those exposed to them. They have been offering a TCP free engine oil for a few years now, so far Icelandair is one of the few airlines that switched to this oil for their fleet. However, there are still some doubts whether this oil is so much safer, as several of the TCP replacing additives might be carcinogenic and detrimental for fertility. Recently (November 2021) NYCO published a patent for the use of oils comprising non-neurotoxic anti-wear additives“.

Interesting developments indeed, but we’ll have to wait and see to what extent those claims of “non-neurotoxic” will be fulfilled. The (highly technical) document is not very transparent for the non-specialist reader. Also we’ll have to wait and see how soon those oil types will be available and which airlines will be willing to use them. No doubt that cost and world wide availability will be important factors to consider there.