Lubricant composition

Abstract

A marine diesel cylinder lubricant composition having a total base number of at least 30. The composition includes at least 40 weight per cent of an oil of lubricating viscosity, at least one detergent prepared from at least two surfactants, preferably phenate and sulphonate surfactants, at least one boron-containing dispersant providing at least 100 ppm of boron, and at least one zinc-containing antiwear additive, preferably a zinc dihydrocarbyl dithiophosphate, providing at least 230 ppm, preferably at least 250 ppm, of zinc. The marine diesel cylinder lubricant composition exhibits reduced wear even when used with high sulphur fuels.

1 . A marine diesel cylinder lubricant composition having a total base number of at least 30 and comprising: 
 at least 40 mass per cent of an oil of lubricating viscosity,    a detergent prepared from at least two surfactants,    a boron-containing dispersant providing at least 100 mass ppm of boron, and    a zinc-containing antiwear additive.    
     
     
         2 . The composition of  claim 1  in which the detergent includes at least 5 mass per cent of phenate and at least 5 mass per cent of sulphonate, based on the total amount of the detergent.  
     
     
         3 . The composition of  claim 1  in which the detergent includes a salicylate surfactant.  
     
     
         4 . The composition of  claim 1  in which the lubricant has a base number of at least 35.  
     
     
         5 . The composition of  claim 1  in which the dispersant includes at least 150 mass ppm of boron, based on the total amount of the composition.  
     
     
         6 . The composition of  claim 1  in which the antiwear additive includes at least 275 mass ppm of zinc.  
     
     
         7 . The composition of  claim 1  in which the antiwear additive is an oil-soluble salt of a dihydrocarbyl dithiophosphoric acid represented by the following formula:  
         [(RO)(R 1 O)P(S)S] 2 Zn  
       where R and R 1  are the same or different hydrocarbyl radicals containing from 1 to 18 carbon atoms.  
     
     
         8 . The composition of  claim 1  which also includes an aminic or phenolic antioxidant.  
     
     
         9 . A method of operating a marine diesel engine including a cylinder, which method comprises: 
 fueling the engine with a fuel having a sulphur content of at least 3.0 mass per cent, and    lubricating the cylinder with a marine diesel cylinder lubricant composition having a total base number of at least 30 and comprising: 
 at least 40 mass per cent of an oil of lubricating viscosity,  
 a detergent prepared from at least two surfactants,  
 a boron-containing dispersant providing at least 100 mass ppm of boron, and  
 a zinc-containing antiwear additive.