Methods of improving the performance of combustion engine after-treatment devices

A method of improving the performance of an after-treatment device for a combustion engine, the method comprising:

• lubricating the combustion engine with a lubricating oil composition and combusting a fuel in the lubricated engine generating an exhaust stream including soot and/or ash particles derived from the combustion, wherein the lubricating oil composition includes one or more base oils of lubricating viscosity and an additive package including at least one oil-soluble silicon-containing compound providing from about 150 to about 250 ppm of silicon to the lubricating oil composition and wherein the silicon-containing compound is selected from undecyltriethoxysilane, tetradecyltriethoxysilane, hexadecyltrimethoxy silane, or combinations thereof and wherein the lubricating oil composition includes greater than 1 weight percent to 6 weight percent of zinc dialkyldithiophosphate;
• contacting the after-treatment device with the exhaust stream including the soot and/or the ash particles from the combustion;
• measuring oxygen storage capacity and/or CO T50 light-off temperature of the after-treatment device after at least about 120,000 miles of operation;
• and
• when measured by oxygen storage capacity, then the oxygen storage capacity of the after-treatment device after at least about 120,000 miles of operation is no more than 30 percent less than an initial oxygen storage capacity of the after-treatment device;
• or
• when measured by CO T50 light-off temperature, then the CO T50 light-off temperature of the after-treatment device after at least about 120,000 miles of operation is no more than 5 percent higher than an initial CO T50 light-off temperature of the after-treatment device.