Functions & Properties Of Good Lubricating Oil - SKengineers

 

LUBRICATION SYSTEM IN I.C. ENGINES

Ø  INTRODUCTION :

·        Lubrication of moving parts by means of oil, grease etc. is essential for proper functioning and to reduce friction between the moving parts of automobiles.

Ø  PURPOSE AND FUNCTIONS OF LUBRICATION :

·        To make the moving parts function properly by reducing friction.

·        By reducing friction wear of moving parts will be minimized.

·        Lubricating oil will take up the shocks/vibrations by small extent.

·        Corrosion of parts will be prevented.

·        To reduce noise.

·        Because of lubricating oil film between piston rings and cylinder walls, it does not allow any leakage of gases across the rings.

Ø  PROPERTIES OF GOOD LUBRICATING OIL :

·        Viscosity

·        Flash point

·        Fire point

·        Cloud point

·        Pour point

·        Oiliness

·        Corrosion

·        Colour

·        Dilution

·        Emulsification

·        Physical stability

·        Chemical stability

·        Sulphur content

·        Specific gravity

·        Neutralization number

·        Adhesiveness

·        Film strength

·        Cleanliness

1.      VISCOSITY :

a)      It is a property which offers resistance to flow.

b)     Thick oils have high viscosity.

c)      Medium oils have medium viscosity.

d)     Thin oils have low viscosity.

e)     It is inversely proportional to temperature i.e. it decreases as the temperature rises.

f)       Lighter oils are recommended for automobile engines.

2.      FLASH POINT :

a)      It is the temperature at which lubricating oil will flash when a small flame is passed across it.

b)     It should be sufficiently high to avoid flashing of oil vapours at the temperature occurring in common use.

3.      FIRE POINT :

a)      If the oil is heated after the flash point has been reached the lowest temperature at which oil will burn continuously.

b)     The fire point should be high, so that oil does not burn in services.

4.      CLOUD POINT :

a)      It is the temperature at which oil changes from liquid state to solid state, when subject to low temperatures. In some cases oil starts solidifying which makes it to appear cloudly.

5.      POUR POINT :

a)      It is the temperature which oil will pour.

b)     The property must be considered because of its effect on starting of engines in cold climate.

6.      OILINESS :

a)      An oil is said to be oil when it has oiliness. This property is highly desirable in helping the lubricant to adhere the cylinder walls.

7.      CORROSION :

a)      A lubricant should reduce the corrosion of parts.

8.      COLOUR :

a)      It is not that important property.

b)     It is a test for checking the uniformity of any given grade / brand of oil.

9.      DILUTION :

a)      If the piston rings are worn out, then petrol vapour may leak into crank case and dilute the lubricating oil in the crank case.

10.   EMULSIFICATION :

a)      A lubricating oil when mixed with water, is emulsified and looses its lubricating property. The emulsification number is an index of an oil to emulsify with water.

11.   PHYSICAL STABILITY :

a)      It should be physically stable for a required range of temperature i.e. it should not solidify or vaporize.

12.   CHEMICALLY STABILITY : it should be chemically stable.

13.   SULPHUR CONTENT : It must be less otherwise it promotes corrosion.

14.   SPECIFIC GRAVITY : It is a measure of density of oil.

15.   NEUTRALISATION NUMBER : Oil may contain alkaline or acid products.

16.   ADHESIVENESS : It is a property because of which oil particles tick to metal surfaces.

17.   FILM STRENGTH : It is a property because of which oil retains a film between two surfaces at high speed and load.

18.   CLEANLINESS : It should be clean.