Lubricant compositions for direct injection engines

Abstract

The invention is directed to a method for reducing low speed pre-ignition events in a spark-ignited direct injection internal combustion engine by supplying to the sump a lubricant composition which contains an oil of lubricating viscosity and an overbased sodium detergent. The metal overbased detergent may be selected from sulfonate detergents, phenate detergents, and salicylate detergents, including sulfonate detergents with a metal ratio of at least 5.

What is claimed: 
     
         1 . A method for reducing low speed pre-ignition events in a spark-ignited direct injection internal combustion engine comprising supplying to the engine a lubricant composition comprising a base oil of lubricating viscosity and an overbased sodium detergent. 
     
     
         2 . The method of  claim 1 , wherein the engine is operated under a load with a break mean effective pressure (BMEP) of greater than or equal to 10 bars. 
     
     
         3 . The method of  claim 1 , wherein the engine is operated at speeds less than or equal to 3,000 rpm. 
     
     
         4 . The method of  claim 1 , wherein the engine is fueled with a liquid hydrocarbon fuel, a liquid nonhydrocarbon fuel, or mixtures thereof. 
     
     
         5 . The method of  claim 4 , wherein the engine is fueled by natural gas, liquefied petroleum gas (LPG), compressed natural gas (CNG), or mixtures thereof. 
     
     
         6 . The method of  claim 1 , wherein the overbased sodium detergent comprises one or more of a sulfonate detergent, a phenate detergent, a salicylate detergent, and combinations thereof. 
     
     
         7 . The method of  claim 1 , wherein the lubricant composition further comprises at least one other additive selected from an ashless dispersant, an ashless antioxidant, a phosphorus-containing anti-wear additive, a friction modifier, a polymeric viscosity modifier, and a metal-containing detergent other than a sodium detergent 
     
     
         8 . The method of  claim 6 , wherein the overbased sodium detergent comprises a sulfonate detergent. 
     
     
         9 . The method of  claim 6 , wherein the overbased sodium detergent comprises a salicylate detergent. 
     
     
         10 . The method of  claim 1 , wherein the overbased sodium detergent has a metal ratio of 5 to 30. 
     
     
         11 . The method of  claim 1 , wherein the overbased sodium detergent is present in an amount from 0.2 to 8 weight percent of the lubricant composition. 
     
     
         12 . The method of  claim 1 , further comprising at least one metal-containing detergent selected from calcium detergents, magnesium detergents, or a combination thereof. 
     
     
         13 . The method of  claim 3 , wherein the lubricating composition further comprises a polyalkenyl succinimide dispersant in an amount from 0.5 to 4 weight % of the composition. 
     
     
         14 . The method of  claim 1 , wherein the lubricating composition comprises at least 50 weight % of a Group II base oil, a Group III base oil, or mixtures thereof. 
     
     
         15 . The method of  claim 1 , wherein the overbased sodium detergent comprises a sulfur-coupled phenate detergent. 
     
     
         16 . The method of  claim 1 , wherein the overbased sodium detergent is present in an amount to provide 0.1 weight percent to 0.9 weight percent sulfated ash to the lubricating composition. 
     
     
         17 . The method of  claim 1 , wherein there is a reduction in the number of LSPI events of at least 10 percent. 
     
     
         18 . The method of  claim 1 , wherein the low speed pre-ignition events are reduced to less than 20 LSPI events per 100,000 combustion events.