Oil Stress Analysis Gave Key to Shell’s Unique New Lube Oil

By George Backwell at August 04, 2012 08:47
Filed Under: Research & Development

No need to keep different multiple spec lube oils on board any longer say Shell Marine Products as they launched their lube oil, Alexia S4 a few days ago. Their new oil is a ‘one-stop’ solution lube for all climates, all seasons, in a wide range of vessel types with low-speed two-stroke engines, including those steaming at slow and ultra-slow engine speeds. As if that were not enough, Shell also say that the new formulation better protects engines.

VLCC: Photo courtesy of Shell

Fundamentally though, the introduction of this oil for low-speed, two-stroke marine diesels was founded upon a breakthrough in the understanding of oil stress in this type of  engine, as will be seen.

Lube Oil Stress in Slow-speed Marine Diesels

Oil stress, the single most important factor that governs the lifetime and performance of an engine lubricant, is the name given to those factors which degrade lubricants, making them less effective. Research on oil stress has been done for many years at Shell’s Hamburg, Germany, Marine & Power Innovation Centre, and Alexis S54 is the latest product to come out of work done there.

Oil stress in four-stroke engines had been well documented, but comparatively less so in two-stroke engines, which have no oil sump. The two-stroke engine’s total loss lubrication system making it difficult to accurately monitor the actual oil condition on the liner surfaces of individual cylinders.

However, a comparatively recent R&D collaboration between Shell and  Wärtsilä came up with a solution; a special sampling system to capture and then examine the ‘white mist’ that appears every time the piston rings go past the charge air inlet ports in the cylinder liner. When analysed  researchers found that lube oil samples collected from this mist had very different characteristics from samples collected from existing (less truly indicative) drain oil sources.

Oil Stress Resarch: Photo courtesy of Shell

Researchers discovered that there were four types of stress in two-stroke engines to consider – Humidity Stress, Insoluble Stress, Acid Stress and Thermal Stress – far more rapid and  complex than in  four-stroke engines. With this knowledge in mind they set about finding a combination of additives that would best ameliorate those stresses, eventually coming up with Alexia S4.

Proving the New Lube Oil

Tests in laboratory engines under simulated slow steaming conditions demonstrated that Shell Alexia S4 provided up to a 20% improvement in overall engine wear, compared to Shell’s existing cylinder oil and out-performed all other oils tested.

The oil was also extensively tested during more than 25,000 hours of operational sea trials, by customers and the original engine manufacturers MAN and Wärtsilä. Here it proved its ability to protect engines running on distillates (for up to 1,000 hours in certain engines) and residual fuels containing 0.2% to 3.75% sulphur content in a range of locations and climates, including the Antarctic, the Middle East and South America.

With technical support and a switch to Alexia S4, one specific trial showed a 33% reduction in oil feed-rate.




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