Marine Engine Lubrication

Abstract

Trunk piston marine engine lubrication comprising a major amount of (A) an oil of lubricating viscosity that comprises an oil-soluble ester basestock, or that comprises greater than 0.1 to less than 90 mass % of an oil-soluble ester basestock and, as 50 mass % or more of the remainder of the oil of lubricating viscosity, a high saturates basestock; (B) a minor amount of a metal alkyl salicylate detergent; and (C) greater than 0.1 to less than 10 mass %, of an oil-soluble polyalkenyl-substituted carboxylic acid anhydride, wherein the or at least one polyalkenyl group is derived from a polyalkene having a number average molecular weight of from 200 to 3,000. Asphaltene precipitation in the lubricant composition, caused by the presence of contaminant heavy fuel oil, is prevented or inhibited.

What is claimed is: 
     
         1 . A trunk piston marine engine lubricating oil composition for improving asphaltene handling in use thereof, in operation of the engine when fuelled by a heavy fuel oil, which composition comprises, or is made by admixing:
 (A) an oil of lubricating viscosity, in a major amount, which is either an oil-soluble ester basestock (A1); or comprises greater than 0.1 to less than 90 mass % of an oil-soluble ester basestock (A1) and, as 50 mass % or more of the remainder of the oil of lubricating viscosity, a basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof (A2);   (B) an oil-soluble metal detergent, in a minor amount; and   (C) an oil-soluble polyalkenyl-substituted carboxylic acid anhydride, in a minor amount of from greater than 0.1 to less than 10 mass, the, or at least one, polyalkenyl group being derived from polyalkene having a number average molecular weight of from 200 to 3000.   
     
     
         2 . The lubricating oil of  claim 1 , wherein, in the oil of lubricating viscosity, the basestock (A2), when present, contains more than 60 mass %, of the basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof. 
     
     
         3 . The lubricating oil of  claim 1 , wherein the basestock (A2), when present, is a Group II, Group III or Group IV basestock. 
     
     
         4 . The lubricating oil of  claim 1 , wherein the metal detergent (B) is a metal hydrocarbyl-substituted hydroxybenzoate detergent. 
     
     
         5 . The lubricating oil of  claim 4 , wherein the metal detergent (B) is a calcium alkyl salicylate detergent. 
     
     
         6 . The lubricating oil of  claim 4 , wherein the metal detergent (B) is C 9  to C 30  alkyl-substituted. 
     
     
         7 . The lubricating oil of  claim 4 , wherein the metal detergent (B) is C 20  or higher alkyl-substituted. 
     
     
         8 . The lubricating oil of  claim 1 , wherein the polyalkenyl substituent in the anhydride (C) has from 8 to 400 carbon atoms. 
     
     
         9 . The lubricating oil of  claim 1 , wherein the polyalkenyl substituent in the anhydride (C) has a number average molecular weight of from 350 to 1000. 
     
     
         10 . The lubricating oil of  claim 1 , wherein the polyalkenyl-substituted carboxylic acid anhydride (C) is a succinic anhydride. 
     
     
         11 . The lubricating oil of  claim 10 , wherein the succinic anhydride (C) is a polybutene succinic anhydride. 
     
     
         12 . The lubricating oil  claim 1 , wherein the ester basestock (A1) is present in an amount of 10 to 90 mass %. 
     
     
         13 . The lubricating oil of  claim 1 , wherein the ester basestock (A1) has a kinematic viscosity of 2 to 10 mm 2 s −1  at 100° C. 
     
     
         14 . The lubricating oil of  claim 1 , wherein the ester basestock (A1) is a polyol ester basestock. 
     
     
         15 . The lubricating oil composition of  claim 1 , further including a heavy fuel oil content. 
     
     
         16 . A method of operating a trunk piston medium-speed compression-ignited marine engine comprising:
 fuelling the engine with a heavy fuel oil; and   (iii) lubricating the crankcase of the engine with a composition as claimed in  claim 1 .   
     
     
         17 . A method of dispersing asphaltenes in a trunk piston marine lubricating oil composition during the lubrication of surfaces of the combustion chamber of a medium-speed compression-ignited marine engine and operation of the engine, which method comprises:
 (i) providing a composition as claimed in  claim 1 ;   (ii) providing the composition in the combustion chamber;   (iii) providing heavy fuel oil in the combustion chamber; and   (iv) combusting the heavy fuel oil in the combustion chamber.