Marine engine lubrication

Abstract

Trunk piston marine engine lubrication, when the engine is fueled by heavy fuel oil, is effected by a composition comprising a major amount of an oil of lubricating viscosity containing at least 50 mass % of a Group II basestock, and respective minor amounts of an overbased metal hydrocarbyl-substituted hydroxybenzoate detergent other than such a detergent having a basicity index of less than two and a degree of carbonation of 80% or greater and at least 1 mass % of a hydrocarbyl-substituted carboxylic acid, anhydride, ester or amide thereof. Asphaltene precipitation in the lubricant, caused by the presence of contaminant heavy fuel oil, is prevented or inhibited.

Description

FIELD OF THE INVENTION[0001]This invention relates to a trunk piston marine engine lubricating composition for a medium-speed four-stroke compression-ignited (diesel) marine engine and lubrication of such an engine.BACKGROUND OF THE INVENTION[0002]Marine trunk piston engines generally use Heavy Fuel Oil (‘HFO’) for offshore running. Heavy Fuel Oil is the heaviest fraction of petroleum distillate and comprises a complex mixture of molecules including up to 15% of asphaltenes, defined as the fraction of petroleum distillate that is insoluble in an excess of aliphatic hydrocarbon (e.g. heptane) but which is soluble in aromatic solvents (e.g. toluene). Asphaltenes can enter the engine lubricant as contaminants either via the cylinder or the fuel pumps and injectors, and asphaltene precipitation can then occur, manifested in ‘black paint’ or ‘black sludge’ in the engine. The presence of such carbonaceous deposits on a piston surface can act as an insulating layer which can result in the ...

AI Technical Summary

Benefits of technology

[0010]A second aspect of the invention is the use of a detergent (A) in combination with a carboxylic acid, anhydride, ester or amide (B) as defined in, and in the amounts stated in, the first aspect of the invention in a trunk piston marine lubricating oil composition for a medium-speed compression-ignited marine engine, which composition comprises an oil of lubricating viscosity in a major amount and contains 50 mass % or more of a Group II basestock, to improve asphaltene handling during operation of the engine, fueled by a heavy fuel oil, and its lubrication by the composition, in comparison with analogous operation when the same amount of detergent (A) is used in the absence of (B).

Problems solved by technology

The presence of such carbonaceous deposits on a piston surface can act as an insulating layer which can result in the formation of cracks that then propagate through the piston.

If a crack travels through the piston, hot combustion gases can enter the crankcase, possibly resulting in a crankcase explosion.

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