Marine engine lubrication

Abstract

Lubricant additives comprising as overbased metal hydrocarbyl-substituted hydroxybenzoate detergent dispersed in diluent and a polyalkenyl-substituted carboxlic acid anhydride dispersed in a diluent oil containing 50 mass % or more of a basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof are blended, in minor amounts, with a high saturates content oil of lubricating viscosity, in a major amount, to give trunk piston marine engine lubricating oil composition for a medium-speed four-stroke compression-ignited marine engine.

Description

FIELD OF THE INVENTION[0001]This invention relates to trunk piston marine engine lubrication for a medium-speed four-stroke compression-ignited (diesel) marine 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 formation of cracks that then propagate through ...

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