Lubricant compositions for direct injection engine
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 dispersant. The ashless dispersant may be selected from succinimide compounds prepared from aliphatic or aromatic amines.
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;
0.5 to 2.2 wt % of a borated polyisobutylene based succinimide dispersant;
0.1 to 3 wt % of at least one ashless antioxidant; and
0.2 to 1 wt % of a magnesium detergent selected from one or more of an overbased alkylbenzene sulfonate detergent and a magnesium sulfur-free phenate detergent.
2. The method of claim 1 , wherein the engine is operated under a load with a brake 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 non-hydrocarbon 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 polyisobutylene succinimide compound is prepared from an amine comprising one or more of aliphatic polyamines, aromatic amines, polyether amines, and mixtures thereof.
7. The method of claim 1 , further comprising from 0.1 to 5 wt % of a boron-free ashless dispersant.
8. The method of claim 7 , wherein the boron-free ashless dispersant is a polyisobutylene succinimide dispersant prepared from a polyisobutylene having an average number molecular weight (M n ) of from 500 to 5000.
9. The method of claim 1 , wherein the at least one ashless antioxidant is a sulfurized olefin.
10. The method of claim 1 , wherein the at least one ashless antioxidant includes two or more antioxidants where each antioxidant is present in the lubricating composition in an amount of at least 0.1 wt %.
11. The method of claim 10 , wherein the total amount of antioxidant present in the lubricating composition is from 0.5 to 5 wt %.
12. The method of claim 11 , wherein each antioxidant is present in an amount of 0.25 to 3 wt %.
13. The method of claim 1 , wherein the lubricant composition further comprises at least one other additive selected from a metal containing overbased detergent, a phosphorus-containing anti-wear additive, a friction modifier, and a polymeric viscosity modifier.
14. The method of claim 1 , wherein the lubricating composition comprises at least 50 weight % of Group II base oil, Group III base oil, or mixtures thereof.