UNIT 5

I. C. Engines [AE 304]

Dr. Roop Lal

Lecture 3: Unit V: Engine Testing, Supercharging, Lubrication and Engine

Cooling: Lubrication principles, function of lubricating system, properties of
lubricating oil, additives,

1. INTRODUCTION
Lubrication is essentially required in motor vehicle maintenance. To supply
lubricating oil between the moving parts is simply termed as lubrication.
Lubrication of all moving parts (other than nylon, rubber bushel or pre-
lubricated components) is essential to reduce friction, wear and to prevent
seizure. Lubrication must be done properly, and right type of lubricant
should be used. Improper or inadequate lubrication of the engine will cause
serious trouble such as scored cylinders, worn or
burned-out bearings, misfiring cylinders, dirty spark plugs, stuck piston
rings, engine deposits and sludge and excessive fuel consumption.
2. OBJECTS OF LUBRICATION
The primary objects of lubrication are as follows:
1. To reduce friction between the moving parts.
2. To reduce wear of the moving parts.
3. To act as a cooling medium for removing heat.
4. To keep the engine parts clean, especially piston rings and ring grooves,
oil ways and filters.
5. To absorb shocks between beatings and other engine parts thus reducing
engine noises and extending engine life.
6. To form a good seal between piston rings and cylinder walls
7. To prevent deposition of carbon, soot and lacquer.
8. To absorb and carry away harmful substances resulting from incomplete
combustion.
9. To prevent metallic components from corrosive attack by the acid formed
during the combustion process.
10. To resist oxidation which causes sludge and lacquers.

3. LUBRICATING SYSTEMS
In motor vehicles, there are two separate systems of lubrication:
1. Engine Lubrication System
2. Chassis Lubrication system
The engine lubrication system may be either pressure type or splash type

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although various combinations of these two systems are used. A single system
lubricated the entire engine of all present day motor vehicles. Only equipment
outside the engine, such as starter, generators, water pump and distributors, are
separately lubricated. This system circulates the oil from a common reservoir or
sump to the main bearings connecting rod bearings, wrist pins, camshaft
bearings and cams, cylinder wails, valves and timing drive. The pump is located
at the bottom of the crank case. All modem American passenger cars and trucks
use the pressure system in which oil is forced under pressure by a geared pump
to the various rotating and reciprocating parts. In splash system the connecting
rod end has a dipper which splashes the oil on the various parts as it travels
through the oil while moving the connecting rod.
In chassis lubrication system each lubricating point is lubricated separately.
About 34 points are to be lubricated in the chassis of a modern passenger car.
These points may vary from 21 to 45 depending upon the design and
construction of vehicle. No single universe lubricant has yet been devised for all
these points. Some of the points require lubrication more often than others
4. FUNCTIONS OF LUBRICATING OIL
There are five important functions of the lubricating oil in an automotive
engine
1. To minimize friction and wear.
2. To cool by carrying away heat.
3. To seal the pistons and thus preventing escape of gases in the cylinders
with consequent loss of power
4. To cushion the parts against vibration and impact.
5. To clean the parts as it lubricated them, carrying away impurities.
The magnitude of the retarding frictional force mainly depends upon the
following three factors:
1 Nature of the surface: Friction is low when surface are smooth
and highly polished. Rough surface produce high frictional forces.
2 Pressure which forces the surface together: Friction is low when
pressure is low. High pressure produces high frictional forces.
3 Kind of material: Friction is low when material is hard. Soft
materials produce high frictional forces.

There is always friction between two surfaces when they rub against each
other no matter how highly polished surfaces are, such as shaft in a bearing,
piston in a cylinder. Irregularities of the highly polished surface can be

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examined under a magnifying glass or microscope. The high points of one

irregular surface strike the high points of other irregular surface when they
are rubbed each other. If there is no lubrication between the two surfaces, the
heat generated would bind or bum out the surfaces. Also there would be
considerable wear and power loss. If the surfaces are lubricated, like the
engine bearing, the shaft would float on a film of lubricant, and thus all
friction takes place in the film of lubricant. The greasy slippery particles of
the oil film slide on each other, minimizing the amount of friction, wear and
heat generated. An adequate amount of lubricating oil must be fed
continuously to the bearing, so that a film of oil is maintained in the bearing
under practically all operating conditions.
The thickness of the film between the bearing and journal depends upon the
load and speed and also upon the type of the lubricant. The film is thinner at
higher load, lower speed and lighter oil. The heavier oil often causes rise in
temperature of the bearing. Also, a heavier oil increases the friction.
Therefore, oil companies recommend the use of the lightest oil in automotive
engines, which can maintain an oil film of satisfactory thickness and can
provide satisfactory boundary lubrication when the engine is starting from
rest.

5. HYDRODYNAMIC THEORY OF LUBRICATION

When the shaft rotates in a bearing it takes an eccentric position in the
bearing, as shown in Fig. 1. This is due to the loading of the journals W and
the direction of rotation. The oil film is maintained by the wedding action as
the oil is toned into the wedge at the bottom by the pressure generated when
the oil is carried from the wide space A and fared into the narrow space B at
the bottom by rotating journal to which the oil adheres. This is called the
hydrodynamic theory of lubrication. From the above theory it is clear that
the oil film is maintained, only when the journal is in motion. When the
journal comes to rest the oi1 film is squeezed out. When the engine, is first
started, by boundary lubrication comes into play until the oil film is built-up
by the rotating journal. The qualities of lubricant called adhesiveness and
film strength help the lubricant to enter the metal pores and cling to the
surfaces of the beatings and journals keeping them wet when the journals are
at rest, and preventing metal-contact until the film of lubricant is built-up.

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Figure 1: Shaft takes an eccentric position in the bearing when in

operation

6. PROPERTIES OF LUBRICANTS
An engine lubricating oil must have certain properties for its satisfactory
function, as follows :
1. viscosity. 2. Flash point. 3. Fire point.
4.Cloud point 5. Pour point. 6. Oiliness.
7. Corrosion. 8. Colour. 9. Dilution.
10. Emulsification. 11. Physical stability. 12. Chemical stability.
13. Sulphur content 14. Specific gravity. 15. Neutralization
number.
16. Adhesivemss. 17. Film strength. 18. Cleanliness.

1. Vlscosity. Viscosity is a measure of the resistance to flow or internal

friction of an oil.
Viscosity essentially means body a heavy oil has high viscosity, a light oil
low viscosity and medium oil and medium viscosity. The viscosity of an oil
is usually specified as the time in seconds that it takes for a given amount of
the oil to flow by gravity through a standard sized orifice at a given
temperature. Viscosity is one of the most important properties of engine
lubricating oil. It is used universally to grade lubricants. Viscosity is
inversely proportional to temperature. It decreases as the temperature rises
and increases as it falls. That is why the lighter oil is recommended for
automobile engines in winter than in summer. It also explains why engines

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are so hard to start in very cold weather.

The viscosity is measured by viscometer. There are many types of
viscometers, the most important types an as follows:
(a) Saybolt universal viscosimeter. (b) Redwood viscosimeter.
(c) Engler viscosimeter. (d) Barbey viscosimeter.

The unit of viscosity is given as "seconds say bolts" or seconds Redwood"

etc. Temperature is also specified with the viscosity. For example, if an oil
has a viscosity of 50 at 210oF, it means that 50 seconds were required for the
measured volume of onto flow through the standard tube under gravity at
210oF

2. Flash point: The flash point has been defined as the lowest temperature at
which the lubricating oil will flash when a small flame is passed across its
surface. When the oil is heated, it leaches a temperature at which, if a small
flame is brought near it, a flash spreads across the oil. It happens due to the
volatilization of the light particles in the oil. The flash point of the oil should
be sufficiently high so as to avoid flashing of oil vapours at the temperature
occurring in common use.

3. Fire point if the oil is heated further after the flash point has been
reached, the lowest
Temperature at which the oil will burn continuously is called the fire point.
The fire point also must be high in a lubricating oil, so that the oil does not
bum in service.
4. Cloud point. The oil changes from liquid state to a plastic or solid state
when subjected to low temperatures. In some cases the oil starts solidifying
which makes it to appear cloudy. The temperature at which this takes place
is called the cloud point.

5. Pour point. It is the lowest temperature at which the lubricating oil will
pour. The pour point of an oil is indication of its ability to move at low
temperatures. This property must be considered because of its effect on
starting an engine in cold weather and on free circulation of oil through
exterior feed pipes when pressure is not applied.
6. Oiliness. It is the characteristic property of an oil. An oil is said to be oil
when it has
oiliness. This property is highly desirable in helping the lubricant to adhere
to the cylinder walls.

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7. Corrosion. Corrosion has been defined as the destruction of a solid body

by chemical or electro chemical action which starts unintentionally from its
outer surface. A lubricant should not corrode the working parts and it must
stain its properties even in the presence of foreign matter and additives.
8. Colour. Colour of a lubricating oil is not of so much importance for its
property expect as a lest for checking the uniformity of any given grade or
brand of oil.

9. Dilution. During the combustion petrol vapour may escape past the piston
rings if the rings are worn or broken. Considerable amount of such hens
mixed with the crankcase oil and dilutes it, thus affecting its lubricating
property. The rest to determine the amount of dilution in crankcase oil
indicates how far an oil could be used when mixed with petrol vapour.
Crankcase ventilation is however, adopted to escape the petrol fumes.

10. Emulsification. A lubricating oil, when mixed with water is emulsified

and loses its
lubricating property. The emulsification number is an index of the tendency
of an oil to emulsify with water.

11. Physical stability. A lubricating oil must be stable physically at the

lower and the
highest temperatures between which the oil is to be used. At the lowest
temperature there should not be any separation of solids, and at the highest
temperature it should not vaporize beyond a certain limit.

12. Chemical stability. A lubricating oil should also be stable chemically.

There should not be any tendency for oxide formation. The oxidation
products, being sticky, clog the working parts, cause the faulty piston rings
and valve action. The oil should also not decompose at high temperatures to
form carbon which makes spark plug and valves faulty to function.

13. Sulphur content if sulphur is present in considerable amount in the

lubricating oil it
promotes corrosion. The corrosion test shows the amount of sulphur content.
The scale used is the one recommended by Americal Petroleum Institute and
the result is called the API gravity.

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15. Neutralization number. An oil may contain impurities that are not
removed while refining. It may contain alkaline or acid products. The
neutralization number test is a simple procedure to determine acidity or
alkalinity of an oil. It is the weight in milligrams of potassium hydroxide
required to neutralize the acid content of one gram of oil

16. Adhesiveness. It is the property of lubricating oil due to which the oil
particles stick
with the metal surfaces.

17. Film strength. It is the property of a lubricating oil due to which the oil
retains thin film between the two surfaces even at high speed and load. The
film does not beak and the two surfaces do not come in direct contact.
Adhesiveness and film strength cause the lubricant to enter the metal pores
and cling to the surfaces of the bearings and journals keeping them wet
when the journals are at rest and preventing metal to metal contact until the
film of lubricant is built-up
18. Cleanliness. A lubricating oil must be clean. It should not contain dust
and dirt particles. These impurities may either be filtered out or removed
with the change of oil at periodic intervals. Further, the oil must contain
agents, called detergents which remove the impurities from the engine parts
during oil, circulation.
7. ADDITIVES IN OIL Any mineral oil, by itself, does not have all the
properties as described in the previous articles To give the desired
properties, certain additives are mixed in the oil during the manufacturing
process.
These additives are as follows:
1. Viscosity-index improved. 2.Pour-point depressants.
3. Oxidation inhibitors. 4. Corrosion inhibitors.
5. Rust inhibitors. 6. Foam inhibitors.
7. Detergent-dispersants. 8. Extreme-pressure agents.
8. SAE Numbers
The Society of Automotive Engineers (SAE) rates oil viscosity in two
different way, for winter and for other than winter. Winter grade oils are
o o
tested at 0 and 210 F. There are three grades, SAE 5 W. SAE 10 W and
SAE 20 W, the 'W ' indicating winter grade. For other than winter use, the
grades are SAE 20, SAE 30, SAE 40 and SAE 50, all without the 'W ' suffix.
Some oil have multiple ratings, which means they are equiva]ent, in

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viscosity, to several single rating oils. For example SAE 10 W 30 W oil is

comparable to SAE 10 W, SAE 20 W and SAE 30 oils.
Some oils become so thick at low temperatures that they will not pour at all.
Certain additives can be put into oil which will lower the temperature to a
point at which the oil become too thick to flow. Such additives keep
the oil fluid at low temperatures for adequate engine lubrication during cold
weather starting and initial operation.
At high temperature, when oil is agitated with or sprayed into the air in the
crankcase, the oil oxidation takes place. When the oil is oxidized, it breaks
down to form various harmful substances, which coat engine parts with an
extremely sticky, wax like material. This may clog oil channels and tend to
restrict the action of piston rings and valves. Oil oxidation may produce
corrosive materials also in the oil, that will corrode bearings and other
surfaces. Certain chemicals, known as oxidation inhibitors are added in the
lubricating onto resist oxidation.

9. Service Rating of Oil

The lubricating oils is rated as to its viscosity by number, it is also rated by
service designation. i,e., it is rated according to the type of service for which
it is best suited. There are six services ratings- three for gasoline and
three for diesel engines.
For gasoline engines:
MS oil. MM oil ML oil.
For diesel engines :
DG oil. DS oil. DM oil.

10. TYPES OF LUBRICANTS

The lubricants are of three types :
1. Solid lubricants: graphite, mica, soap stone or steatite.
2. Semi-solid lubricants: grease.
3. Liquid lubricants: mineral oil, vegetable oil, animal oil, etc.
Graphite and Mica are examples of solid lubricants. Graphite is often mixed
with oil to lubricate automobile springs. Graphite has low co efficient of
friction and is stable at high temperature. Semi solid lubricants such as
grease, are used in chassis lubrication. Grease is widely used in automobiles
at places where retention of liquid lubricants is difficult and where high
temperatures are encountered, like in axles.

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Greases are defined according to their purpose, like water pump grease,
chassis grease, multipurpose grease, or by the type of soap base, as follows:
1. Calcium-based grease are fairly water proof and are useful for water
pumps, chassis and wheel beatings
2. Sodium-based creases are able to withstand moderably high temperatures
and tend to absorb water, which reduces rusting problem
3. Aluminium based greases have good staying – put properties when
combined with a chemical, but not suitable for high temperature. They an
used on exposed chains, transmissions, chassis and flame fittings.
4. Lithium - based greased. One type of lithium based creases can do all
the jobs, and sometimes called multipurpose grease. It is used in wheel
bearings, chassis fittings, Erase cups, universal joints and water pumps
Greases are given a penetration number, which is the depth, in tenths of a
millimeter, to which a specially shaped cone will sink, point downwards,
into grease at temperature of 25oC. Two values are adopted:

1. The worked penetration number,

2. The unworked penetration number.
Liquid lubricants are used in automobile engine lubricating systems such
as transmission and rear axle system.
Lubricating oils are classified according to their source: as animal,
vegetable, mineral.

Animal oils are obtained from the animal fats such as Lard and Fish,
Whale, Tallow, etc. They are not suitable for automotive engine
lubrication because they are oxidized easily and become gummy after
some use.
Vegetable oils are obtained from linseed, rope seed, Hazel nut, palm
olive, caster, etc. These oil also are not suitable for automotive engine
lubrication because they are oxidized easily and become gummy after
some use.
Mineral oils are obtained from petroleum and chiefly contains
hydrocarbons. Mineral oils are almost entirely used for lubricating
automotive engines, because they have good lubricating properties. They
are cheap and more plentiful than the other types. Also they are free from
acid and do not attack metals.
Application:
1. Very heavy pressure and slow speed: Graphite, soapstone.
2. Heavy pressure and high speed: Palm oil, rape oil, castor oil, medium

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mineral oils.
3. Heavy pressure and slow speed: Grease, palm oil, lard oil, tallow oil.
4. Light pressure and high speed: Sperm oil olive oil, light mineral oils.
5. Ordinary machinery: Rape oil, lard oil, tallow oil, heavy mineral oils.
6. Steam cylinders: Lard oil, tallow oil, tape oil, heavy mineral oils.
7. Clock and watches: Hezel - nut oil, neat's foot oil, olive oil, sperm oil,
light mineral oils.
11. LUBRICATING PARTS
The engine parts which are to be lubricated an as follows :
1. Main crankshaft bearings. 2. Big end bearings.
3. Small end bearings. 4. Cam shaft bearings
5. Piston rings and cylinder walls. 6. Timing gears.
7. Valve mechanism.
12. LUBRICATING SYSTEMS
The different systems for lubricating the automobile engine are as follows :
1. Petroil system. 2. Splash system.
3. Pressure system. 4. Semi-pressure system.
5. Dry sump system.
1. Petroil system. This system of lubrication is generally adopted in two-
stroke petrol engine like scooters and motor cycles. It is the simplest form of
lubricating system it does not consist of any part, like oil pump. for the
propose of lubrication. But the lubricating oil is mixed into the petrol itself
while filling in the petrol tank of the vehicle, in a specified ratio. When the
fuel goes into crank chamber during the engine operation, the oil particles go
deep into the bearing surfaces and lubricate them. The piston rings, cylinder
walls, piston pin, etc. are lubricated in the same way. If the engine is allowed
to remain unused for a considerable time, the lubricating oil separates from
petrol and leads to clogging of passages in the carburetor, resulting in the
engine starting trouble. This is
The main disadvantage of this system.

2. Splash system: In this system of lubrication, the lubricating oil is stored

in an oil trough or sump. A scoop or dipper is made in the lowest part of the
connecting rod. When the engine runs, the dipper dips in the oil once in
every revolution of the crankshaft and cause the oil to splash on the cylinder
walls. This action affects the lubrication of the engine walls, piston ring,
crankshaft bearings and big end bearings.
Splash system mostly works in connection with pressure system in an
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engine, some parts

being lubricated by splash system and the other by pressure system.

Figure 2: Splash System of Lubrication

3. Pressure system: In this system of lubrication, the engine parts are lubricated
under pressure feed. The lubricating oil is stood in a separate tank or the sump,
from where an oil pump takes the oil through a strainer and delivers it through a
filter to the main oil gallery at a pressure of 2 to 4 kg/cm2. The oil from the main
gallery goes to the main bearings, from where some of it after lubricating the
main bearing, falls back to the sump, some is splashed to lubricate the cylinder
walls and the remaining goes through a hole to the crankpin. From the crank pin
it goes to the piston pin through a hole in the connecting rod web, where it
lubricated the piston rings.
For lubricating camshaft and timing gears, the oil is led through a separate oil
line from the oil gallery. The valve tappets are lubricated by connecting the
main gallery to the tappet guide surfaces through drilled holes.

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Figure 3: Pressure System of Lubrication

An oil pressure gauge at the instrument panel indicates the oil pressure in the
system. Oil filters and strainers in the system clear off the oil from dust, metal
particles and other harmful particles.

4. Semi - pressure system: It is the combination of splash system and pressure

system. Some parts are lubricated by splash system and some pars by pressure
system. Almost all the four stroke engines are lubricated by this system.
5. Dry sump system: The system in which the lubricating oil is stored in the oil
sump is called wet sump system, like the pressure system. But the system in

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which the lubricating oil is not kept in the oil sump is known as dry sump
system. In this system, the oil is carried in a separate tank from where it is fed to
the engine.

Figure 5: Dry Sump Lubrication

The oil which falls into the oil sump after lubrication is send back to the oil tank
by a separate delivery pump. Thus, the system consists of two pumps, one to
feed the oil and the other to deliver it back to the oil tank. This system is used in
situations where the vehicle has to change its position continuously, like in
aircrafts. The main advantage of this system is that there is no chance of
breakdown the oil supply during up and down movement of the vehicle.
13. PARTS OF LUBRICATINGSYSTEM
The lubricating system in a four-stroke engine consists of the following parts
:
1. Oil sump or tank. 2. Oil Pump 3. Oil cooler.
4. Oil filter and strainer 5- Oil pressure gauge. 6. Oil pressure
indicating light
7. Oil level indicator.
OIL PUMP
Oil pump is generally located inside the crankcase below the oil level. The
function of the oil pump is to supply oil under pressure to the various engine
parts to be lubricated. The different types of the oil Pumps used for engine
lubrication an as follows:
1. Gear pump 2. Rotor pump.
3. Plunger pump 4. Vane pump.

Gear pump. It consists of two meshed spur gears enclosed in a housing. There
is very little
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Clearance between the gear teeth and housing. One gear is attached to a shaft
which is driven through suitable gears from the camshaft or crank shaft of the
engine. The other gear is free to revolve on its own bearing. When the pump is
in action, the oil is driven between the gear teeth from the inlet side, carried
around between the gears and pump housing, and forced out the outlet side. The
pressure and quantity of the supplied by the pump depend upon the speed of the
gears.
This type of pump is almost universally used in the automotive engine, due to
its simplicity in construction. It can deliver oil at a pressure of about 2 – 4
kg/cm2. A pressure relief valve is also provided in many oil pumps to relief the
excessive pressure due to high engine speeds or clogged oil lines.

Figure 6: Gear pump with pressure relief valve

Rotor Pump. It consists of an inner and outer rotor within the pump body in
place of gears, that is, two Bean mesh internally. The external gear has the
number of teeth one more than on the internal gear. The oil is displaced from
the inlet to the outlet side in the same way as in the gear pump.

Figurer 7: Rotor Pump Figurer 8: Plunger Pump

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Plunger pump. It consists of plunger which reciprocates in the pump body,

while moving up, the plunger sucks oil from the inlet and while moving down it
forces out the oil from the outlet. This type of pump is used to deliver oil under
low pressure to the troughs of splash systems.
Vane pump. It consists of a cylindrical casing with outlet and a inlet, and drum.
The drum is mounted eccentrically in the casing and contains two vanes with
spring. When the drum rotates, the vanes sweeps the oil from the inlet to the
outlet side. Because the drum is mounted eccentrically, the volume between the
drum and the casing constantly decreases and oil pressure increases at the
outlet.

Figure 8: Vane pump.

Figure 11: Cartridge type of filter Figure 12: Edge type of filter

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Figure 15: Oil Cooler

OIL COOLER
The purpose of an oil cooler is to cool the lubricating oil in heavy duty engines
where the oil
Temperature become quite high. Because the viscosity of the oil deceases with
the temperature rise and also the oil film may beak at high temperatures, the oil
must be kept cold in the lubricating system.
An oil cooler is just like a simple heat exchanger. The oil may be cooled in
it either by cold water from the radiator or the air stream. Water type oil coolers
are more commonly used in lubricating system because they act as reversible
coolers. At the time of starting when the water is hotter than the oil, the oil is
heated to provide complete circulation in the system. At higher temperatures,
when the oil becomes hotter than water, the water cools the oil. A water type oil
cooler, as shown in Fig. 15, simply consists of tubes in which oil circulate.

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