By Mahesh Jadhav, SRF at IARI, New Delhi

1. Dr. M. L. Jadhav
Farm Power and Equipment
ICAR-Central Institute of Agricultural
Engineering, Bhopal

2. 1. The primary objective of lubrication is to reduce friction, wear, and
power loss. Lubrication accomplishes this requirement by interposing
a film of oil between the sliding surfaces (Reduce frictional effect).
2. Lubricating oils in internal combustion engines also function to cool
surfaces, such as the pistons, by absorbing heat and dissipating it
through cooling surfaces and radiators (Cooling effect).
3. Serves as a seal between piston rings and cylinder (Sealing effect).
4. Removes the foreign material between the engine working parts
(Cleaning effect)
Need of lubrication

3. • Lubricants commonly used in engines either are derived from mineral
oils or are classified as synthetic.
• The synthetic oils available are based on esters derived from animal
or vegetable oils, and another group is derived from hydrocarbons.
• However, lubricants that are derived from mineral oils predominate.
• Mineral lubricants are obtained from crude petroleum and change
very little on exposure to air.
• A great variety of lubricants are produced, ranging from light oils to
heavy greases.
Types of lubricants

4. 1. Viscosity
• Viscosity is the internal resistance of a fluid as one layer is moved in
relation to another layer.
• The viscosity of an oil must be sufficient to support an oil film between
a bearing and its journal. Excessive viscosity, however, causes
unnecessary power consumption.
• Sir Isaac Newton deduced the following relationship for a fluid being
shear-stressed between two plates
Lubricant properties

5. • A fluid is said to be Newtonian if the viscosity is constant, except for
temperature changes
Where,
F = Force, N
μ = Absolute viscosity, Pa.s
A = Area, m2
v = Velocity, m/s
h = clearance between plates, m

6. • The absolute value of μ can be determined by several methods. The two
most common methods are based on
Cannon-Fenske viscometer
capillary tube type for laminar flow
MacMichael viscometer
rotational type

7. Video of Cannon-Fenske viscometer

8. • In practice, determining the viscosity by Newton's method is difficult,
so several other methods have been devised, all based upon flow
through a capillary tube or orifice.
• Flow through a capillary tube can be related to viscosity by Poiseville's
law as follows
Where,
p = pressure difference, dynes per cm2
r = radius of tube, cm
t = time, s
V = volume of liquid, cm3
l = length of the tube, cm
μ = absolute viscosity, poises

9. • All capillary tubes are seriously affected by emulsions and dirt so that in
an effort to further simplify the determination of viscosity there are several
short-tube, or orifice-type, viscometers in general use.
• Although the orifice type requires less time for a determination, it does
not result in the precision of the capillary type.
• The orifice-type viscometer is an empirical instrument in that the viscosity
cannot be computed directly.
• Instead, the viscosity is reported as the time in seconds required for a
known quantity of oil, at a constant temperature, to flow through the
orifice.
• Thus the viscosity of an oil, as determined by the Saybolt Universal
Viscometer, is reported in Saybolt Universal Seconds (SUS or SSU).
• The viscosity of motor oil is usually reported in SUS.
• For more viscous fluids, a larger orifice is used and the results are
reported in Saybolt Furol Seconds.

10. Saybolt Universal Viscometer
• This instrument measures the time for
60 cm3 of a sample to flow through a
tube 1.76 mm in diameter and 12.25
mm long at a constant temperature.
• The resulting time in seconds is called
Saybolt Universal Seconds (SUS or
SSU).
• for SUS greater than 32, the equivalent
kinematic viscosity in centistokes v is
closely approximated by

11. Video of Saybolt Universal Viscometer

12. • Oil, as used in the crankcase of most internal combustion engines, is
normally classified in two ways.
1. SAE number
2. Quality
• The SAE has adopted for convenience a series of numbers that constitute a
classification for crankcase lubricating oils in terms of viscosity only.
• Other factors of oil character or quality are not considered.
• Viscosity numbers without an additional symbol are based on the viscosity
at 99°C.
• Viscosity numbers with the additional symbol W(winter) are based on the
viscosity at - 18°C.
• The viscosity of crankcase oils included in this classification is not less
than 39 s at 99°C, Saybolt universal.
Classification of Oil

13. • Viscosity index expresses the variation in viscosity with a change in
temperature.
• An oil with a high viscosity index (VI) has less change in viscosity with a
change in temperature than an oil with a low VI.
• Refineries have no problem producing oil of the correct viscosity for a
constant operating temperature, but the necessity of starting an engine at a
low temperature and running it at a higher temperature complicates the
problem.
• The variation of temperature within the engine also adds to the problem.
• Therefore, an oil with a high viscosity index is desirable.
• Multi-grade motor oils have been especially compounded to have a high
viscosity index.
• Engines subjected to wide temperature variations would normally benefit
from using a multi-grade oil, whereas engines subjected to relatively
constant temperatures would not be benefited due to more cost.
Viscosity index

14. • The system considers two things:
(1) the type of service and (2) the type of engine and fuel it uses.
Classification by Service
API Engine Service Description
CA Light-duty diesel; Engine service; Service typical of diesel engines, and
occasionally gasoline engines, operated in mild to moderate duty with
high-quality fuels.
CB Moderate-duty diesel; Engine service; Service typical of diesel engines
operated in mild to moderate duty but with lower-quality fuels that
necessitate more protection from wear and deposits.
Occasionally has included gasoline engines in mild service.
CC Moderate-duty diesel and gasoline engine service
Service typical of lightly supercharged diesel engines operated in
moderate to severe duty and includes certain heavy-duty gasoline
engines.
CD Severe-duty diesel; Engine service; Service typical of supercharged diesel
engines in high-speed, high-output duty requiring highly effective
control of wear and deposits.

15. Flash point and Fire point
• Flash point is the lowest temperature at which oil is to be heated until
sufficient inflammable vapour come off which produces a momentary flash
when brought to flame.
• When the vapours are released continuously and the flame persists for
longer period, then that temperature is called fire point.
• A good lubricant has its flash and fire point above the temperature at which
engine work, so that fire hazards are reduced.
Other important properties
Cloud point and Pour point
• When lubricating oil is cooled, the temperature at which wax and other
substance in the oil crystallize and separate out from oil is called Cloud
point.
• The lowest temperature at which the oil ceases to flow when cooled is
called Pour point.
• Cloud point and Pour point indicates the suitability of lubricant for use in
cold conditions. A good lubricant required to give service at low
temperature should possess low pour point and cloud point.

16. Volatility
• A good lubricant should have low volatility at working temperature.
• Measured by Reid vapour test.
Other important properties
Carbon Residue
• Lubricating oil has higher percentage of carbon in the combined form.
• A good lubricant should not deposit carbon when used at high temperature.
• Measured by Ramsbottom coking method

17. • Hydrodynamic theory
Lubrication Theories
• Boundary layer theory

18. 1. Petro-oil lubrication system
• This system is used in scooters and motor cycles, particularly for two stroke
engines about 3 to 6% of lubrication oil is added with petrol in the tank.
• The mixture fed in to the engine cylinder during the suction stroke.
• The droplets of the partials cause the lubricating effect in the engine
cylinder.
• The petrol evaporates when the engine is working.
• The lubricating oil is left behind in the form of mist.
• The parts of the engine such as piston, cylinder walls and connecting rod
are lubricated by being waited with the oil mist left behind.
• When the added oil is less, there will be insufficient lubrication and even
result in seizure of the engine.
• If the added oil is more, it will lead to excess exhaust smoke and carbon
deposits in the cylinder exhaust port and spark plugs.
• This method is not much effective in large engines.
Types of lubrication system

19. 2. Splash lubrication system
• In this system, the lubricating oil is filled in the sump or trough at the
bottom of the crank case by means of a gear pump or by gravity.
• Scoops (it is like a spoon) are attached to the big end of the connecting rod.
• Scoops dips into the oil trough and splashes oil out of the pan.
• The splashing action of oil maintains a fog or mist of oil that drenches the
inner parts of the engine such as bearings, cylinder walls, pistons, piston
pins, timing gears etc.
• For effective functioning of the engine, proper level of clean and undiluted
oil should be maintained in the oil pan.
• Lubrication depends largely upon the size of oil holes and clearances.
• No uniform lubrication and when the rings are worn, the oil passes the
piston into combustion chamber, causing carbon deposition, blue smoke
and spoiling the plugs.
• There is every possibility that oil may become very thin through crankcase
dilution.
• worn metal, dust and carbon may be collected in the oil chamber and be
carried to different parts of the engine, causing wear and tear

20. 3. Forced feed or pressure lubrication system
• In this system, the oil is pumped directly to the crankshaft, connecting rod,
piston pin, timing gears and camshaft of the engine through suitable paths
of oil.
• Usually the oil first enters the main gallery in the crankcase casting.
• From there, it goes to each of the main bearings through holes.
• From main bearings, it goes to big end bearings of connecting rod through
drilled holes in the crankshaft.
• From there, it goes to lubricate the walls, pistons and rings.
• There is separate oil gallery to lubricate timing gears.
• Lubricating oil pump is a positive displacement pump, usually gear type or
vane type.
• The oil also goes to valve stem and rocker arm shaft under pressure through
an oil gallery.
• The excess oil comes back from the cylinder head to the crankcase.
• This system is commonly used on high speed multi cylinder engine in
tractors, trucks and automobiles.

21. 4. Combination of splash and forced feed system
• In this system, the engine component, which are subjected to very heavy
load are lubricated under forced pressure, such as main bearing, connecting
rod bearing and camshaft bearing.
• The rest of the parts like cylinder liners, cams, tappets etc. are lubricated by
splashed oil.

22. 1. Excessive oil consumption:
(a) More oil goes to combustion chamber and gets burnt
(b) Some leakage occurs in some part of the line
(c) Loss of oil in form of vapour through ventilating system
• Oil can enter the combustion chamber through rings and cylinder walls,
worn piston rings and worn bearings.
Troubles in lubrication system
2. Low oil pressure :
(a) Weak relief valve spring
(b) Worn oil pump
(c) Cracked oil line
(d) Obstruction in the oil lines
(e) Very thin oil
(f) Worn out bearings
• Care should be taken to remove these defects as far as possible to increase
the oil pressure in the lubricating system.
• Sometimes defective oil pressure indicator shows low oil pressure. This
should be checked.

23. Troubles in lubrication system
3. Excessive oil pressure:
(a) stuck relief valve
(b) strong valve spring
(c) clogged oil line
(d) very heavy oil
• These defects should be removed to reduce the excessive oil pressure in the
lubricating system. Sometimes defective oil pressure indicator records high
oil pressure. Care should be taken to check this defect.

24. Care and maintenance of
lubrication system
The following care and maintenance should be taken to work lubrication
system properly
• A good design of oil circulation system should be chosen.
• Correct grade of lubricant ensures long and trouble free service.
• Oil should be maintained at desired level in the oil chamber.
• Oil should be cleaned regularly and after specified period of use, old
filters should be replaced by new filters.
• Connections, piping, valves and pressure gauge should be checked
regularly.
• Oil should be changed regularly after specified interval of time. Before
putting the new oil, the crankcase should be cleaned and flushed well
with a flushing oil.
• Precautions should be taken to keep the oil free from dust and water.