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 ashless antioxidant. The ashless antioxidant may be selected from phenolic compounds, aryl amine compounds, and sulfurized olefins, especially 2,6-hindered phenols and diarylamine compounds.

What is claimed: 
     
         1 . A method for reducing low speed pre-ignition events in a spark-ignited direct injection internal combustion engine wherein the engine is equipped with a turbocharger and is operated under a load with a brake mean effective pressure (BMEP) of greater than or equal to 10 bars at speeds less than or equal to 3,000 rpm, comprising supplying to the engine a lubricant composition comprising:
 a base oil of lubricating viscosity; and   two or more different antioxidants selected from a phenol antioxidant, an arylamine antioxidant, and a sulfurized olefin antioxidant, where each of the two or more antioxidant are present in an amount of at least 0.1 weight percent and the total amount of the two or more antioxidants is from 0.5 to 5 weight percent of the lubricant composition.   
     
     
         2 . The method of  claim 1 , wherein the engine is fueled with a liquid hydrocarbon fuel, a liquid non-hydrocarbon fuel, or mixtures thereof. 
     
     
         3 . The method of  claim 1 , wherein the engine is fueled by natural gas, liquefied petroleum gas (LPG), compressed natural gas (CNG), or mixtures thereof. 
     
     
         4 . The method of  claim 1 , wherein the lubricant composition further comprises at least one other additive selected from an ashless dispersant, a metal containing overbased detergent, a phosphorus-containing anti-wear additive, a friction modifier, and a polymeric viscosity modifier. 
     
     
         5 . The method of  claim 1 , wherein the phenol antioxidant is derived from a 2,6-dialkyl phenol. 
     
     
         6 . The method of  claim 1 , wherein the arylamine antioxidant wherein the arylamine antioxidant is a diarylamine compound. 
     
     
         7 . The method of  claim 1 , wherein the sulfurized olefin is present in the lubricant composition in an amount ranging from 0.2 to 2.5 weight %. 
     
     
         8 . The method of  claim 1 , wherein the lubricating composition further comprises a polyalkenyl succinimide dispersant in an amount from 0.5 to 4 weight % of the composition. 
     
     
         9 . 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.