Method for preventing exhaust valve seat recession

Abstract

A method for preventing or inhibiting exhaust valve seat recession in a natural gas fueled internal combustion engine is disclosed. The method involves lubricating the engine with a lubricating oil composition comprising (a) a major amount of an oil of lubricating viscosity, and (b) a minor amount of a natural gas engine oil additive package, wherein the lubricating oil composition is substantially free of each of any zinc compounds and alkaline earth metal salts of a condensation product of an alkylene polyamine, an aldehyde and a substituted phenol.

Description

BACKGROUND OF THE INVENTION[0001]1. Technical Field[0002]The present invention generally relates to a method for preventing or inhibiting exhaust valve seat recession in natural gas fueled internal combustion engines.[0003]2. Description of the Related Art[0004]Natural gas fueled engines are engines that use natural gas as a fuel source. Lubricating oils with high resistance to oxidation, nitration and viscosity increase are generally preferred for lubricating oils used in natural gas engines because of the conditions related to this type of engine.[0005]Natural gas has a higher specific heat content than liquid hydrocarbon fuels and therefore it will burn hotter than liquid hydrocarbon fuels under typical conditions. In addition, since it is already a gas, natural gas does not cool the intake air by evaporation as compared to liquid hydrocarbon fuel droplets. Furthermore, many natural gas fueled engines are run either at or near stoichiometric conditions, where less excess air is a...

AI Technical Summary

Benefits of technology

[0017]In accordance with one embodiment of the present invention, there is provided a method for preventing or inhibiting exhaust valve seat recession in a natural gas fueled engine, the method comprising lubricating the engine with a lubricating oil composition comprising (a) a major amount of an oil of lubricating viscosity, and (b) a minor amount of a natural gas engine oil additive package, wherein the lubricating oil composition is substantially free of each of any zinc compounds and alkaline earth metal salts of a condensation product of an alkylene polyamine, an aldehyde and a substituted phenol.

[0018]In accordance with a second embodiment of the present invention, there is provided a method for enhancing the life of an exhaust valve in a natural gas fueled engine as evidenced by protection or inhibition in exhaust valve seat recession in the natural gas fueled engine, the method comprising lubricating the engine with a lubricating oil composition comprising (a) a major amount of an oil of lubricating viscosity, and (b) a minor amount of a natural gas engine oil additive package, wherein the lubricating oil composition is substantially free of each of any zinc compounds and alkaline earth metal salts of a condensation product of an alkylene polyamine, an aldehyde and a substituted phenol.

[0019]In accordance with a third embodiment of the present invention, the use of a lubricating oil composition comprising (a) a major amount of an oil of lubricating viscosity, and (b) a minor amount of a natural gas engine oil additive package, wherein the lubricating oil composition is substantially free of each of any zinc compounds and alkaline earth metal salts of a condensation product of an alkylene polyamine, an aldehyde and a substituted phenol for the purpose of preventing or inhibiting exhaust valve seat recession in a natural gas fueled engine is provided.

[0024]By lubricating a natural gas fueled internal combustion engine with a lubricating oil composition comprising (a) a major amount of an oil of lubricating viscosity, and (b) a minor amount of a natural gas engine oil additive package, wherein the lubricating oil composition is substantially free of each of any zinc compounds and alkaline earth metal salts of a condensation product of an alkylene polyamine, an aldehyde and a substituted phenol, exhaust valve seat recession in the natural gas fueled engine is advantageously prevented or inhibited as compared to a corresponding lubricating oil composition in which a zinc compound such as a zinc dihydrocarbyl dithiophosphate compound is present therein. This is unexpected as zinc dihydrocarbyl dithiophosphate is a known antiwear agent which contributes to the ash formed on the exhaust valve and typically used in a natural gas engine lubricating oil composition.

Problems solved by technology

This condition of running continuously near full load places severe demands on the lubricant.

For example, by subjecting the lubricating to a sustained high temperature environment, the life of the lubricant is often limited by oil oxidation processes.

Also, since the rate of formation of nitrogen (NOx), increases exponentially with temperature, natural gas fueled engines may generate NOx concentrations high enough to cause severe nitration of lubricating oil.

In general, exhaust valve recession is wear which occurs at the valve and valve seat interface and is the most pronounced form of valve wear in natural gas fueled engines.

When the valve is prevented from seating properly, it can cause engine roughness, poor fuel economy and excessive emissions.

Although natural gas fueled engines typically use very hard corrosion-resistant material for the valve face and seat mating surface to give extended cylinder head life, it does not completely eliminate valve recession.

The combustion of liquid hydrocarbon fuels such as diesel fuel often results in a small amount of incomplete combustion (e.g., exhaust particulates).

Too little ash or the wrong type can accelerate valve and seat wear, while too much ash may lead to valve guttering and subsequent valve torching.

Too much ash can also lead to loss of compression or detonation from combustion chamber deposits.

In addition, a problem associated with the use of zinc dialkyldithiophosphate is that their phosphorus and sulfur derivatives poison the catalyst components of the catalytic converters.

However, simply decreasing the amount of zinc dialkyldithiophosphate presents problems because this necessarily lowers the antiwear properties and oxidation inhibition properties of the lubricating oil.

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