Engine Oil Explained!

With increased electrification of vehicles, lubrication challenges are created for conventional engines. The staggering variety of engine oils in the market can be confusing. Basic functions of a lubricant is to provide anti-wear properties, avoid build-up of deposits and provide resistance to corrosion. Their compositions are extremely complex to sum up in this article.

Modern lubricants consist of a good quality base oil (mineral, synthetic or a mixture of both), viscosity modifiers, dispersants, detergents, anti-oxidants, anti-wear agents, friction modifiers and corrosion inhibitors.

Viscosity modifiers provide stability of viscosity across a wide range of temperatures. Hence, improving fuel-economy.

Friction modifiers also improve fuel economy by maintaining a minimum viscosity. In vehicles with diesel particulate filter (DPF), a process called "forced regeneration" takes place. During bottom dead center of combustion stroke, small amount of fuel is injected to later burn the accumulated soot in the DPF. Post combustion fuel-injection causes cylinder wall-wetting and causing lubricant contamination. In particular bio-diesels, which are less volatile (do not evaporate easily) than conventional diesel, causes serious loss in lubricant viscosity.

Anti-oxidants are particularly useful in vehicles using bio-fuels and high power density motors. Turbine temperatures in gasoline direct engines (GDI) can easily exceed 1000 degree Celsius. After highway/autobahn driving, shutting of the GDI engine causes a condition called "heat soak" (dramatic rise in turbine temperature). This causes oxidation (build-up) on turbo-shaft. In GDI engines, cylinder wall-wetting is also caused and increasing levels bio-fuel compositions are notorious for causing oxidation.

Anti-wear agents protect highly loaded components by creating a thin-layer of film on their surfaces. Anti-wear and anti-oxidant, zinc dialkyldithiophosphate (ZDDP) is extremely effective is performing its function. However, it is known to reduce catalytic converter efficiency.

Detergents maintain basicity, as combustion and un-burnt fuel cause formation of harmful acids. Detergents and anti-wear agents contains Sulphur. Low quality base oils also contain greater quantities of Sulphur. GDI engines are also prone to low-speed ignition (knock) and tiny engine oil drops are identified as the focal point of causing this condition. When small amounts of engine oil burns in the combustion chamber Sulphated ash is formed. Which blocks the catalytic converter and reducing its efficiency.

Dispersants restrict the build up of deposits and sludge from contaminants. They attach themselves to small soot particles and adjacent ones.

Corrosion inhibitors prevent acids (in extreme running condition) and moisture (in factory engine oil filled or plug-in hybrid vehicles) from damaging the crucial internal components.

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