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 basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof, and respective minor amounts of an over-based 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.

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 an oil of lubricating viscosity, in a major amount, 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, and, in respective minor amounts:
 (A) 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, where degree of carbonation is the percentage of carbonate present in the overbased metal hydrocarbyl-substituted hydroxybenzoate detergent expressed as a mole percentage relative to the total excess base in the detergent; and   (B) a hydrocarbyl-substituted carboxylic acid, anhydride, ester or amide thereof, wherein the or at least one hydrocarbyl group contains at least eight carbon atoms, the acid, anhydride, ester or amine constituting at least 1 mass % of the lubricating oil composition.   
     
     
         2 . The composition as claimed in  claim 1  wherein (A) has
 (A1) a basicity index of two or greater and a degree of carbonation of 80% or greater; or 
 (A2) a basicity index of two or greater and a degree of carbonation of less than 80%; or 
 (A3) a basicity index of less than two and a degree of carbonation of less than 80%. 
 
     
     
         3 . The composition as claimed in  claim 1  wherein (B) is depicted as: 
       
         
           
           
               
               
           
         
         where R 1  represents a C 8  to C 100  branched or linear hydrocarbyl; 
         X and Y each independently represents OR 2  and OR 3 , where each R 2  and R 3  independently represents a hydrogen atom or an alkyl, aryl or aralkyl group, or X and Y together represent —O—; and/or are depicted as
   R 1 CH 2 COR 4    (II)
 
 
         where R 1  is as defined as above; and 
         R 4  represents OR 5  or NR 6 R 7 , where each R 5 , R 6  and R 7  independently represents a hydrogen atom or an alkyl group. 
       
     
     
         4 . The composition as claimed in  claim 1  wherein the metal in (A) is calcium. 
     
     
         5 . The composition as claimed in  claim 1  wherein the hydrocarbyl-substituted hydroxybenzoate in (A) is a salicylate. 
     
     
         6 . The composition as claimed in  claim 1  wherein the oil of lubricating viscosity contains more than 60 mass % of a basestock containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur or a mixture thereof. 
     
     
         7 . The composition as claimed in  claim 1  wherein the hydrocarbyl group in (B) has from 8 to 400 carbon atoms. 
     
     
         8 . The composition as claimed in  claim 1  wherein, in the acid or derivative (B), the hydrocarbyl substituent is derived from a polyolefin. 
     
     
         9 . The composition as claimed in  claim 1  wherein (B) is a succinic acid or a succinic anhydride. 
     
     
         10 . The composition as claimed in  claim 9  wherein (B) is a polyisobutene succinic acid or anhydride. 
     
     
         11 . The composition as claimed in  claim 1  having a TBN of 20 to 60. 
     
     
         12 . (canceled) 
     
     
         13 . A method of operating a trunk piston medium-speed compression-ignited marine engine comprising
 (i) fueling the engine with a heavy fuel oil; and   (ii) lubricating the crankcase of the engine with a composition as defined in  claim 1 .   
     
     
         14 . A method of dispersing asphaltenes in a trunk piston marine lubricating oil composition during its 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 defined 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.