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Lubricity is the measure of the reduction in
friction Friction is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related en ...

friction
and or
wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion In earth science, erosion is the action of surface processes (such as Surface runoff, water flow or wind) tha ...

wear
by a
lubricant A lubricant is a substance that helps to reduce friction Friction is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and b ...
. The study of lubrication and wear mechanisms is called
tribology Tribology is the science and engineering of interacting surfaces in relative motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in which an object changes its position (ma ...
.


Measurement of lubricity

The lubricity of a substance is not a material property, and cannot be measured directly. Tests are performed to quantify a lubricant's performance for a specific system. This is often done by determining how much
wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion In earth science, erosion is the action of surface processes (such as Surface runoff, water flow or wind) tha ...

wear
is caused to a surface by a given wear-inducing object in a given amount of time. Other factors such as surface size, temperature, and pressure are also specified. For two fluids with the same viscosity, the one that results in a smaller wear scar is considered to have higher lubricity. For this reason, lubricity is also termed a substance's ''anti-wear property''. Examples of
tribometer A tribometer is an instrument that measures tribological Tribology is the science and engineering of interacting surfaces in relative Motion (physics), motion. It includes the study and application of the principles of friction, lubrication a ...

tribometer
test setups include "Ball-on-cylinder" and "Ball-on-three-discs" tests.


Lubricity in diesel engines

In a modern
diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of the diesel fuel, fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the die ...

diesel engine
, the fuel is part of the engine lubrication process.
Diesel fuel Diesel fuel in general is any liquid fuel Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy In physical sciences Physical science is a branch of natural science that studies abi ...
naturally contains compounds that provide lubricity, but because of regulations in many countries (such as the
US
US
and the EU countries), sulphur must be removed from the fuel before it can be sold. The hydrotreatment of diesel fuel to remove sulphur also removes the compounds that provide lubricity. Reformulated diesel fuel that does not have biodiesel added has a lower lubricity and requires ''lubricity improving additives'' to prevent excessive engine wear. ''Diesel Fuel Lubricity'' Authors: Paul Lacey and Steve Westbrook (Southwest Research Institute) SAE paper 950248, International Congress and Exposition, Detroit, Michigan, February 27-March 2, 1995 (Retrieved via Google from a publication of the National Biodiesel Board, entitled ''Lubrication'')


See also

* Boundary lubrication *
Superlubricity Superlubricity is a regime of motion in which friction vanishes or very nearly vanishes. What is a "vanishing" friction level is not clear, which makes the term superlubricity quite vague. As an ''ad hoc'' definition, a kinetic Friction, coefficien ...
*
Tribology Tribology is the science and engineering of interacting surfaces in relative motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in which an object changes its position (ma ...


References

{{Reflist
Fluid dynamics Fluid dynamics is a mathematical discipline within continuum mechanics Continuum mechanics is a branch of mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned with the motions of physical objects, more specifically ...
Tribology