Technical Articles - As published in The Blue

Shell led a number of industry firsts in this area. In the 1950s Shell was the first to develop Ashless Dispersant additives for use in aviation piston engine oils. Prior to this the only oils available were the straight mineral grades, which now tend only to be used for engine break in. The introduction of Ashless Dispersant additives with the AeroShell “W” range of oils introduced a step change in oil performance for many engines.

Dispersants improved engine cleanliness as well as making the oil more efficient at carrying particles in suspension to be extracted by the filter. Other additives improved the oil’s performance and longevity; anti-oxidants extended oil life, anti-foam additives helped improve lubrication by prevented air from becoming entrapped within the oil. These oils are now an industry standard with all other companies following Shell’s lead.

Shell’s next piston engine oil revolution was to introduce a semi-synthetic multigrade. For the first time, this allowed operators to take advantage of modern synthetic oil technology, with it’s improved thermal and oxidation stability, as well as have an oil which could be used in any climate.

Whilst other companies have struggled to apply synthetic oil technology to Avgas engines – witness the problems leading to the mandated withdrawal of AV-1, the synthetic multigrade produced by what is now ExxonMobil - Shell continued to be able to offer exemplary service with the only approved synthetic based aviation lubricant, AeroShell Oil W 15W-50.

To this day this oil has the best low temperature flow properties of any oil on the market. The result is that, when the engine is first started, AeroShell Oil W 15W-50 will reach moving parts more rapidly than any other oil; an effect which is even more pronounced when operating in low temperatures. This is significant when there are estimates that up to 80% of engine wear happens in the first few seconds after start.

More recently, Shell Aviation recognised the demands of private owners who used their aircraft less frequently than the average. This led to the introduction of advanced additives to combat corrosion and engine wear, particularly scuffing damage caused when the engine is first started. This was, again, a new approach for blended aviation oils which was pioneered by Shell, resulting in this additive combination being offered in AeroShell Oil W 15W-50 and AeroShell Oil W100 Plus.

Only recently are we starting to see other oil companies attempting to emulate the performance of these ground-breaking oils with their own versions of this technology, but Shell yet again has the advantage of experience, which only comes from being technical leaders and first to market.

Building on this heritage and unrivalled technological strength, Shell Aviation has again produced another lubricants ‘first’ for General Aviation. After 7 years of development and testing, Shell are proud to announce that we have developed a new oil suitable for use in the emerging compression ignition (commonly referred to as ‘Diesel’) aircraft engines. This oil is the fully synthetic AeroShell Oil Diesel 10W-40.

Whilst these new technology engines were still in their early development stages, Shell fostered close ties with a number of manufacturers - SMA, Thielert and Delta Hawk – to develop and test oil formulations.

As many of you will know, these engines are unique in using Jet A-1 as a fuel, rather than the more common diesel fuel used in their automotive cousins. This leads to some interesting design considerations for the engine manufacturer, including combustion performance and fuel lubricity, but the choice of fuel also has an impact upon the design of a suitable lubricant. Let me outline a few of the considerations.

Sulphur is commonly found in Jet fuel in far higher concentrations than found in Avgas 100LL, or even in modern diesel fuels. Exhaust gases containing Sulphur can combine with water to form Sulphuric Acid. This can result in high levels of acidity in the oil, leading to corrosion, if the lubricant is not designed to neutralise this acid. However, too much alkalinity in the oil can lead to piston wear problems, so careful balancing of oil properties with the fuel is significant.

Compression Ignition engines produce far more particulates during combustion than comparable gasoline engine. Many people will be familiar with this, having seen black smoke out of the exhaust of some diesel engined road vehicles. These particles also find their way into the oil, where they can cause sludging and compromise lubrication. Because of this, the dispersancy additives need to be of much higher performance when compared to oils used in gasoline engines. This prevents sludge and ensures that the oil is able to carry the particles to the filter for removal.

Shell has considered all of this, and more, in the design of AeroShell Oil Diesel 10W-40. AeroShell Oil Diesel 10W-40 also contains performance additives such as a powerful surface acting additives which bonds to the surface of highly loaded engine parts to reduce wear; again new technology for aviation engines.

Rather than just rely upon lab testing, Shell Aviation believes in proving the concept in use. It is for this reason that we forged partnerships with the engine manufacturers to develop and prove the oil during the engine development programs. Shell's development of an aviation specific diesel engine oil started in 1997, so has already enjoyed many years of successful testing and use even before being offered to the market.

Shell is again the first to be able to offer fully tested, technical innovation. It is due to this approach, as well as our technical expertise, that Shell now has a proven product available, blended and bottled, which is fully approved by the two central aviation diesel engine manufacturers, SMA and Thielert.

Happy flying.