Lubricity
Under various conditions, the ability of engine oil to reduce friction, slow down wear and prevent metal sintering is called engine lubricity.
The viscosity of engine oil is an important indicator for evaluating lubricity.
Low-temperature operability
The performance of engine oil that ensures easy starting and reliable oil supply under low-temperature conditions is called low-temperature operability of engine oil.
The low-temperature operability of engine lubricating oil includes two aspects: facilitating low-temperature starting and reducing starting wear.
The indicators for evaluating the low-temperature operability of engine lubricating oil mainly include low-temperature dynamic viscosity, boundary pumping temperature and pour point.
Viscosity-temperature property
The property of lubricating oil that changes viscosity due to temperature rise and fall is called viscosity-temperature property.
Good viscosity-temperature property means that the viscosity of the oil changes little with temperature.
The effect of temperature on the viscosity of oil: the viscosity decreases when the temperature increases; the viscosity increases when the temperature decreases.
Adding viscosity index improver to base oil can improve the viscosity-temperature property of oil.
The engine oil formulated with low-viscosity base oil and viscosity index improver, which has good viscosity-temperature property and can meet the requirements of low and high temperature use at the same time, is called thickened engine oil or commonly known as multi-grade oil.
The index for evaluating the viscosity-temperature property of engine oil is the viscosity index.
The ability of engine oil to inhibit the formation of carbon deposits, lacquer film and sludge or to remove these deposits is called the clean dispersibility of engine oil.
The harm of carbon deposits to engine operation includes:
1.It increases the tendency of the engine to produce detonation.
2.Carbon deposits form a high-temperature source, which is easy to produce surface ignition, and can cause the engine power loss of 2%-15%.
3.Carbon deposits are deposited between the spark plug electrodes, which will cause the spark plug to short-circuit, resulting in reduced power and increased fuel consumption.
4.The valve is not closed tightly, and high-temperature carbon particles will also cause the valve and valve seat to burn.
5.Carbon deposits enter the crankcase, causing the lubricating oil to deteriorate and block the filter.
Generation of carbon deposits:
Carbon deposits cover high-temperature areas such as cylinder heads, spark plugs, injectors, and piston tops, and are thick solid carbon-like substances. It is the deposition of substances such as smoke and other substances decomposed at high temperatures when the combustion is incomplete or the engine oil enters the combustion chamber.
The hazards of paint film are:
1.Reduce the flexibility of piston rings, and even cause sticking rings, which makes piston rings lose their sealing function and reduce power.
2.The paint film has poor thermal conductivity, causing piston overheating and cylinder pulling.
The formation of paint film:
The paint film is a solid, glossy paint-like film, which is mainly produced in the piston ring area and piston skirt. It is mainly hydrocarbons at high temperature and metal catalysis. Under the action of oxidation and polymerization, colloids, asphaltene and other high molecular polymers are generated.
The factors affecting the formation of high-temperature deposits are: (carbon deposits and paint films are both high-temperature deposits)
1.The design and operating conditions of the engine.
2.The properties of fuel and lubricating oil.
The hazards of sludge are mainly:
1.It causes the engine oil to age and deteriorate, and the lubricity decreases.
2.It blocks the lubrication system.
The formation of sludge:
Sludge is a relatively stable condensate of oil-water emulsion and various impurities. Cars driving in cities stop and start from time to time, and the engine runs at low temperature for a long time, which is easy to produce sludge in the oil pan.
Factors that affect sludge formation are: (sludge belongs to low-temperature deposits)
1.Operating conditions of the engine.
2.The properties of fuel and lubricating oil.
The base oil of engine oil itself does not have the cleaning and dispersing properties, but is obtained by adding detergents and dispersants. It is mainly evaluated through corresponding engine tests.
Antioxidation
Under certain conditions, the ability of engine oil to resist oxidation and deterioration is called the antioxidation of engine oil.
It is an important factor in determining whether the engine oil is easy to deteriorate during use, and the tendency to corrode parts and generate deposits is an important factor in determining the service life of engine oil.
5) Good corrosion resistance:
The ability of engine oil to resist corrosion of metals by corrosive substances is called the corrosion resistance of engine oil.
The indicator for evaluating the corrosion resistance of engine oil is the neutralization value, which is also evaluated through corresponding engine tests.
Anti-foaming
The property of engine oil to eliminate foam is called the anti-foaming property of engine oil.
When the engine oil is violently stirred and air is mixed into the oil, foam will be generated. If the foam is not eliminated in time, it will cause faults such as air blockage and insufficient oil supply.
The indicators for evaluating the anti-foaming properties of engine oil are foam generation tendency and foam stability.
