Lubricants-
engine and its oil
 The
main purpose of lubricants is to lubricate moving parts of the vehicle
to reduce friction and wear and tear by providing smoothing, trouble
free performance for increased length of time.
A lubricant is a blend of base oils and performance enhancing additives
as required by engine, gear box and other application areas. At the
refinery, the crude oil is refined into gasoline, diesel, kerosene, LPG,
naphtha and base stocks (Lube). This base stock is further processed,
blended and strengthened with required properties to make different kind
of lubricants.
Of the all the lubricants engine oil is the most import. Lubricants for
gasoline and diesel engine are different as the load, cycles and fuels
are different. The oil in an engine does more than just reduce friction
between its moving parts. It also helps to seal the high-pressure
combustion gases inside the cylinders, to impede the corrosion of metal
parts, to absorb some of the harmful by-products of combustion, and to
transfer heat from one part of the engine to another.
Combustion of rich air-fuel mixture during starting, idling and warm up
form deposits. These deposits in the form of varnish, sludge, soot and
carbon, interfere with proper engine operation.
The engine oil keeps all the deposit forming material in suspension and
gets rid of them by oil filter, or draining out at proper intervals.
Engine oil is stored in the oil pan or sump at the bottom of the
engine. A pump forces the oil through a filter and then through a series
of passages and galleries to lubricate the engine’s moving parts.
The flow of also cools these parts. Rapidly moving engine parts actually
float on a thin film of oil and never make contact with one another.
This is called hydrodynamic lubrication and usually begins when an
engine reaches the idle speed. Most engine wear occurs when a cold
engine is first started, before the oil reaches its normal operating
pressure and flow.
Diesel Engine Lubricating Oil
The main function of lubricant for diesel engine is the same as
mentioned for gasoline engine. As the load in diesel engine is much
higher it should have adequate antiwear properties. Diesel fuel contains
a high level of Sulphur which burns to form oxides of sulphur , which in
turn in the presence of water, form sulphur acids resting in high
corrosion of engine parts. Hence the need of alkalinity reserve in the
oil which is represented by its TBN or Total Base Number. Generally, the
higher TBN value more the alkalinity reserve or acid neutralizing
capacity the oil contains.
Synthetic Oil
T The advent of synthetic oil more than fifty years back opened up
vastly improved and new alternative lubricant to mineral oil. But being
very expensive, it is confirmed to the arcane world of motor sports and
used for high performance cars. They are also widely used in developing
countries for a number of reasons like improved overall engine
performance, low oil consumption, long drain periods, less engine wear,
improved engine cleanliness and faster starting. Taking into
consideration the price tag and its efficacy, the option is left for
consumer’s discretion.
Additives- what they do
Plain mineral oils cannot provide all the necessary functional
properties that an engine requires. These plain mineral oils need
fortification with chemicals/additives which when used in small
quantities, import or enhance the desirable functional properties. Some
of the types and reasons for their use are as follows:
Dispersants: Keeps sludge, carbon and other deposit-
precursors suspended in oil.
Detergents: Keeps the engine parts clean from
deposits.
Rust/Corrosion Inhibitors: Prevents or controls
oxidation of oil, formation of varnish, sludge and corrosive compounds,
limit viscosity increase.
Extreme Pressure (EP), Anti wear and friction modifiers:
These form protective film on the engine parts and reduce wear and tear.
Metal deactivators: Forms surface films so that metal
surface does not catalyze oil oxidation.
Pour Point Depressant: Lowers freezing point of oils
assuring free flow at lower temperatures.
Anti-foamants: Reduces foam in crankcase and blending.
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