Low-Ash Lubricating Oils for Diesel Engines

Abstract

The lubricant for a sump-lubricated, compression-ignited engine may contain an amount of a C12-C24 carboxylic acid-based fuel additive or component obtained by migration from the fuel. Good lubricant performance is obtained by including in the lubricant a boron-containing additive in an amount to provide about 2 to about 500 ppm B to the lubricant, provided that the total sulfated ash level is less than 0.8 weight percent.

1 . A method for lubricating a sump-lubricated, compression-ignited engine which is fueled by a liquid fuel containing fatty acid-based fuel additive or component, wherein said fatty acid-based fuel additive or component is susceptible to or does migrate into the lubricant in the sump of said engine, said method comprising supplying to said engine a lubricant which comprises:
 (a) an oil of lubricating viscosity;   (b) a boron-containing additive in an amount to provide about 2 to about 500 ppm B to the lubricant; and   (c) an overbased detergent having a TBN (oil free basis) of at least 400;   said lubricant having a total sulfated ash level of less than about 0.8 weight percent.   
     
     
         2 . The method of  claim 1  wherein the fatty acid-based fuel additive or component comprises a fatty acid or a condensation product or salt thereof. 
     
     
         3 . The method of  claim 1  wherein the fatty acid-based fuel additive or component comprises a methyl ester of a C12-24 acid. 
     
     
         4 . The method of  claim 1  wherein the fatty acid-based fuel additive or component comprises a mixture of fatty acids having about 14 to about 22 carbon atoms. 
     
     
         5 . The method of  claim 1  wherein the fatty acid-based fuel additive or component comprises tall oil fatty acids. 
     
     
         6 . The method of  claim 1  wherein the fatty acid-based fuel additive or component is present in the lubricant, resulting from migration from the fuel, in an amount of about 0.5 to about 5 percent by weight. 
     
     
         7 . The method of  claim 1  wherein the boron-containing additive comprises a borated dispersant. 
     
     
         8 . The method of  claim 7  wherein the borated dispersant comprises a borated succinimide dispersant containing about 0.5 to about 5 weight percent boron (oil free basis). 
     
     
         9 . The method of  claim 1  wherein the amount of the boron-containing additive is about 0.1 to about 4 percent by weight. 
     
     
         10 . The method of  claim 1  wherein the sulfated ash level of the lubricant is about 0.2 to less than about 0.8 weight percent. 
     
     
         11 . The method of  claim 1  wherein the phosphorus content of the lubricant is less than about 0.12 percent by weight. 
     
     
         12 . A lubricant comprising
 (a) an oil of lubricating viscosity;   (b) a boron-containing additive in an amount to provide about 2 to about 500 ppm B to the lubricant;   (c) an overbased detergent having a TBN (oil free basis) of at least 400; and   (d) about 0.5 to about 5 percent by weight of a fatty acid-based fuel additive or component comprising a mixture of fatty acids having about 14 to about 22 carbon atoms or a condensation product or salt thereof. said lubricant having a total sulfated ash level of less than about 0.8 percent.   
     
     
         13 . A composition prepared by admixing the components of  claim 12 . 
     
     
         14 . The composition of  claim 13  wherein the admixing of the components occurs within an internal combustion engine and arises from operation of said engine. 
     
     
         15 . The composition of  claim 14  wherein said internal combustion engine is a compression-ignited engine comprising a lubricant sump. 
     
     
         16 . The method of  claim 1  wherein the amount of the fatty acid-based fuel additive or component is about 0.1 to about 3 percent by weight. 
     
     
         17 . The lubricant of  claim 12  wherein the amount of the fatty acid-based fuel additive or component is about 0.5 to about 3 percent by weight. 
     
     
         18 . A lubricant comprising
 (a) an oil of lubricating viscosity;   (b) a boron-containing additive in an amount to provide about 2 to about 500 ppm B to the lubricant; and   (c) about 0.5 to about 3 percent by weight of a fatty acid-based fuel additive or component comprising a mixture of fatty acids having about 14 to about 22 carbon atoms or a condensation product or salt thereof;   
       said lubricant having a total sulfated ash level of less than about 0.8 percent.