Engine lubricants for siloxane deposit control

Abstract

A zinc free or substantially zinc free lubricant having a sulfated ash content of less than about 1.0 percent and including (a) an oil of lubricating viscosity; (b) 0.03 to about 3.0 weight percent of a phosphite compound; (c) an metal containing detergent; (d) a polyisobutylene succinimide dispersant derived from an ethylene polyamine and having a carbonyl to nitrogen ratio equal or greater than 1; (e) at least one other dispersant; (f) a boron containing compound in amount to provide at least 25 ppm boron to the lubricant composition is useful for inhibiting siloxane deposits in a stationary gas engine fueled by natural gas having a high silicon concentration.

1 . A method for lubricating a natural gas fueled, sump-lubricated, stationary gas engine comprising supplying to the engine a lubricant composition comprising:
 (a) an oil of lubricating viscosity;   (b) 0.03 to about 3.0 weight percent with respect to the lubricant of a phosphite compound;   (c) a metal containing detergent;   (d) at least a first dispersant, wherein the first dispersant is a polyisobutylene succinimide dispersant derived from an ethylene polyamine and having a carbonyl to nitrogen ratio equal or greater than 1;   (e) at least one other dispersant selected from the group consisting of a succinimide dispersant having a carbonyl to nitrogen ratio less than 1, a Mannich dispersant, a succinamide dispersant, and a polyisobutylene succinic acid ester dispersant;   a boron containing compound in amount to provide at least 25 ppm boron to the lubricant composition;   wherein the lubricant composition is free or substantially free of zinc, and   wherein the lubricant composition has a sulfated ash content of less than about 1.0 wt. %.   
     
     
         2 . The method of  claim 1  wherein the phosphite compound comprises a phosphite ester selected from the group consisting of phosphite diesters, phosphite triesters and mixtures thereof. 
     
     
         3 . The method of  claim 1  wherein the phosphite compound comprises a phosphite having the following formula
   (R 1 O) 3 P 
 
       wherein each le independently is hydrogen or a hydrocarbyl group having 1 to 36 carbon atoms. 
     
     
         4 . The method of  claim 1  wherein the phosphite compound comprises a phosphite diester having ester groups of 2 to 10 carbon atoms and a phosphite diester having ester groups of 12 to 30 carbon atoms. 
     
     
         5 . The method of  claim 1 , wherein the phosphite compounds comprises dibutyl phosphite. 
     
     
         6 . The method of  claim 1  wherein the phosphite compound provides 0.001 wt. % to 0.05 wt. % phosphorus to the lubricant composition. 
     
     
         7 . The method of  claim 1 , wherein the total amount of dispersant is 1.0 wt % to 6.0 wt. % of the lubricant composition. 
     
     
         8 . The method of  claim 1 , wherein the first dispersant is present in an amount of 0.1 wt % to 2 wt % of the lubricant composition. 
     
     
         9 . The method of  claim 1 , wherein the second dispersant comprises a succinimide dispersant having a carbonyl to nitrogen ratio less than 1. 
     
     
         10 . The method of  claim 1 , wherein the metal containing detergent is selected from the group consisting of phenate detergents, sulphonate detergents, salicylate detergents, salixarate detergents, saligenin detergents and mixtures thereof. 
     
     
         11 . The method of  claim 1 , wherein the metal containing detergent comprises a salicylate detergent. 
     
     
         12 . The method of  claim 1 , wherein the salicylate detergent has a Total Base Number of about 200 to about 700 on an oil free basis. 
     
     
         13 . The method of  claim 1 , wherein the metal of the metal containing detergent is selected from the group consisting of magnesium, and calcium and mixtures thereof. 
     
     
         14 . The method of  claim 1 , wherein the lubricant composition comprises at least a third dispersant, wherein the third dispersant is a polyolefin succinic acid ester dispersant. 
     
     
         15 . The method of  claim 1 , wherein the lubricant composition has a silicon concentration greater than 125 ppm. 
     
     
         16 . The method of  claim 1 , wherein the engine is fueled by natural gas having a silicon concentration greater than about 10 mg/m 3−  as measured by gas chromatography mass spectrometry. 
     
     
         17 . The method of  claim 1 , wherein the boron containing compound comprises a borate ester having at least one hydrocarbyl group of 8 to 30 carbon atoms. 
     
     
         18 . The method of  claim 1 , wherein the boron containing compound comprises a borated dispersant. 
     
     
         19 . The method of  claim 1 , wherein the lubricant composition has 50 to about 500 ppm phosphorus. 
     
     
         20 - 21 . (canceled) 
     
     
         22 . A lubricant comprising:
 (a) an oil of lubricating viscosity;   (b) 0.03 to about 3.0 weigh percent with respect to the lubricant composition of a phosphite compound;   (c) a metal containing detergent;   (d) at least a first dispersant, wherein the first dispersant is a polyisobutylene succinimide dispersant derived from an ethylene polyamine and having a carbonyl to nitrogen ratio equal or greater than 1;   (e) at least one other dispersant selected from the group consisting of a succinimide dispersant having a carbonyl to nitrogen ratio less than 1, a Mannich dispersant, and a polyolefin succinic acid ester dispersant;   (f) a boron containing compound in amount to provide at least 25 ppm boron to the lubricant composition;   wherein the lubricant composition is substantially free of zinc,   wherein the lubricant composition has a sulfated ash content of less than about 1.0 percent.