Engine Basics Explained

Presentation Title: Engine Basics
Subject: Automotive Technology
Prepared by: Eng.
Internal Code: Tech.1.U1.01

Question bank
Presentation
Presentation
Lesson plan
Practical

Lesson Goals
After finishing this content you will be able to:
1. Explain how a four-stroke cycle gasoline engine operates.
2. List the various characteristics by which vehicle engines are classified.
3. Discuss how a compression ratio is calculated. Explain how engine size is determined.
4. Describe how displacement is affected by the bore and stroke of the engine.
5. List the engine parts
6. Explain the difference between 4-stroke and 2-stroke engines

Lesson Content
1. Evolution of the motor vehicle
2. Design of the motor vehicle
3. General Introduction
4. Classification of engines
5. Engine Operation
6. The Firing order or firing interval
7. Engine measurement
8. Engine construction overview
9. Two Stroke Engine’s Operation
10.Comparison between two stroke and four stroke engines
11.Working principle of diesel engine
12.Comparison between Diesel and gasoline engines

Evolution of the motor vehicle

Operational units
1-Engine
2-Drive train
3-Vehicle body
4-Suspension
5-Electrical system

1-Engine
Operational unit: Power unit

2-Drive train
Operational unit: Power transfer unit

3-Vehicle body
Operational unit: Support and load- bearing structure

4-Suspension
Operational unit: Electro- hydraulic system

5-Electrical system
Operational unit: Electrical and electronic system

General Introduction
Engine : Engines use energy to produce power. The chemical energy in
fuel is converted to heat energy by the burning of the fuel at a con trolled
rate. This process is called combustion.

GeneralIntroduction
The purpose and function of an engine is to convert the heat energy
of burning fuel into mechanical energy. In a typical vehicle, mechanical energy
is then used to perform the following:
• Propel the vehicle.
• Power the air-conditioning system and power steering.
• Produce electrical power for use throughout the vehicle.
purpose and function

GeneralIntroduction
1-Internal combustion engine
If engine combustion occurs
within the power chamber
2-External combustion engine
itself, such as a steam engine
burns fuel outside of the engine
All cars use internal combustion engine

Classification of engines
Multi Cylinders
According to No of Cylinders
Single Cylinder

According to No of Strokes
Four Stroke Two Stroke
Cycle (Power)
Two
Revolutions
Of the Crankshaft
One
Revolutions
Of the Crankshaft

According to Cylinders Arrangement

According to Engine Position
longitudinally crosswise (transversely).

According to the system of Ignition
Spark Ignition Engines Compression Ignition Engines
Spark Plug
Gasoline Engines
Combustion
Diesel Engines
Combustion
Compression
In which the engine starts combustion
Process by use of a spark plug
In which engine starts combustion process when
the air-fuel mixture self ignites due to high temperature
In the combustion chamber caused by compression

According to the system of Cooling
Water Cooled Air Cooled

Engine Operation
How engines work?

Engine Operation
FOUR-STROKE CYCLE OPERATION
Engine cycles are identified by the number of piston strokes required to complete the cycle.
Intake
Compression
Power
Exhaust
During one stroke, the crankshaft rotates 180 degrees (1/2
revolution).
A cycle is a complete series of events that continually repeats. Most
automobile engines use a four-stroke cycle.
One engine Cycle

Engine Operation
What is a Piston Stroke ?
The stroke of an engine is the distance the piston travels from top dead center (TDC) to bottom dead center
(BDC). This distance is determined by the throw of the crankshaft.
The longer this distance is, the greater the amount of air-fuel mixture that can be drawn into the cylinder.
The more air-fuel mixture inside the cylinder, the more force will result when the mixture is ignited.
TDC
BDC
Stroke

Engine Operation
FOUR-STROKE CYCLE OPERATION
Intake stroke: The intake valve is open and the piston inside
the cylinder travels downward, drawing a mixture of air and
fuel into the cylinder.
Compression stroke: As the engine continues to rotate,
the intake valve closes and the piston moves upward in
the cylinder, compressing the air-fuel mixture
Power stroke: When the piston gets near the top of the cylinder,
the spark at the spark plug ignites the air-fuel mixture,
which forces the piston downward.
Exhaust stroke: The engine continues to rotate, and the piston
again moves upward in the cylinder. The exhaust valve
opens, and the piston forces the residual burned gases out of
the exhaust valve and into the exhaust manifold and exhaust
system.
Hint:
Each cycle (four strokes) of events requires that the engine crankshaft make
two complete revolutions, or 720 degrees (360 degrees * 2 + 720 degrees).
Each stroke of the cycle requires that the crankshaft rotate 180 degrees.

Engine Operation
THE 720-DEGREE CYCLE
The greater the number of cylinders, the closer together the power strokes of
the individual cylinders will occur. The number of degrees that the crankshaft
rotates between power strokes can be expressed as an angle.
To find the angle between cylinders of an engine, divide the number of cylinders
into 720 degrees.
Angle with 3 cylinders: 720/3 = 240 degrees

The Firing order or firing interval
• The firing order is the sequence of power delivery of each cylinder in a multi-cylinder
reciprocating engine.
• This is achieved by sparking of the spark plugs in a gasoline engine in the correct order, or by
the sequence of fuel injection in a Diesel engine.
1-2-4-3 1-3-4-2
The common firing order of 4 stroke 4 cylinder IC engine is 1-3-4-2 and 1-2-4-3.
1-2-4-3

The Firing order or firing interval
Firing Table

Engine measurement
ENGINE SIZE
1- Bore: The diameter of a cylinder is called the bore. The larger the bore, the greater the area on
which the gases have to work. Pressure is measured in units, such as pounds per square inch (PSI).
Engine size is determined by the number of cylinders, the cylinder diameter, and the amount of
piston travel per stroke.
This distance is determined by the throw of the crankshaft.

ENGINE SIZE
2- Piston Displacement: Engine size is described as displacement. Displacement is the cubic inch (cu.
in.) or cubic centimeter (cc) volume displaced or how much air is moved by all of the pistons.
• Volume the piston displaces as it travels from BDC to TDC
• Found by comparing cylinder diameter and piston stroke
The formula is:
Cubic inch displacement = 𝝅𝑹𝟐 * Stroke * Number of cylinders
R = Radius of the cylinder or one-half of the bore.
𝝅𝑹𝟐 part is the formula for the area of a circle.
Engine measurement

DEFINITIONS:
Force
• Pushing or pulling action
• Measured in pounds or newtons
• When a spring is compressed, an outward movement
and force is produced
Force, Work and Power
Engine measurement

Work
• achieved when a certain amount of mass (weight) is
moved a certain distance by a force.
• Measured in foot-pounds or joules
• Formula for work:
work = distance moved × force applied
DEFINITIONS:
Engine measurement

power
• The term power means the rate of doing work.
• Power equals work divided by time.
• Measured in foot-pounds per second or per minute
• Formula for power:
power =
distance × force
time
Engine measurement

Force= P × Ap
Work = F × D
Power =
𝑊𝑜𝑟𝑘
𝑡𝑖𝑚𝑒
Combustion Products (Gases)
D
Mechanical Energy
Engine measurement

Compression Ratio
Compression ratio (CR)
Is the ratio of the volume in the cylinder above the piston when the piston is
at the bottom of the stroke to the volume in the cylinder above the piston
when the piston is at the top of the stroke.
This engine has eight times the volume at BDC, producing an 8:1
compression ratio
Engine measurement

Compression Ratio
Formula for compression ratio:
compression ratio =
cylinder volume at BDC
cylinder volume at TDC
Hint:
Any time an engine is
modified, the compression ratio should
be checked to make sure it
is either the same as it was originally.
Engine measurement

Engine Torque
Definition of torque: The definition of torque is a force (lb) applied to an object
times the distance from that object (ft). Therefore, based on the definition of the term,
torque should be:
Torque = Force × Distance
Torque is the term used to describe a rotating force that
may or may not result in motion.
Engine measurement

Engine Torque
Torque at crankshaft:
• Rating of the turning force at the engine
crankshaft
• When combustion pressure pushes the piston
down, a strong rotating force is applied to the
crankshaft
Engine measurement

ENGINE CONSTRUCTION OVERVIEW
BLOCK All automotive and truck engines are constructed
using a solid frame, called a block. A block is constructed of
cast iron or aluminum and provides the foundation for most of
the engine components and systems.
ROTATING ASSEMBLY Pistons are installed in the block and
move up and down during engine operation. Pistons are connected
to connecting rods, which connect the pistons to the crankshaft. The
crankshaft converts the up-and-down motion of the piston to rotary
motion, which is then transmitted to the drive wheels and propels
the vehicle.
CYLINDER HEADS All engines use a cylinder head to seal the
top of the cylinders, which are in the engine block. The cylinder
head also contains both intake valves that allow air and fuel into the
cylinder and exhaust valves.

1. Cylinder Block
2. Cylinder & Cylinder Liner
3. Cylinder Head
4. Camshaft
5. Valve
6. Push rod
7. Piston
8. Piston Rings
9. Connecting rod
10. Crank Shaft
11. Combustion Chamber
12. Spark Plug
13. Water Jacket
14. Intake Manifold
15. Exhaust Manifold
16. Oil Pan (Sump)
17. Crankcase

1. Cylinder Block
• is the body of the engine that containing the
cylinders, Coolant passages and Lubricating
Passages
• It is formed by casting
• Covered with water jacket or cooling fins
• Made from cast iron or aluminum alloy
Characteristics
1. High Rigidity To withstand high pressure
2. High conductivity to dissipate heat
3. low coefficient of expansion To resist shrinkage

2. Cylinder & Cylinder liner
Is the cylindrical hollow space inside the cylinder block that contains
the piston
In smaller Engines
The Cylinder, water jacket & the frame are made as one piece.
In larger Engines
These parts are manufactured separately
The cylinders are provided with liners To be replaced
easily in case of wear

Cylinder liner (Cylinder Sleeve)
Is a metal pipe shaped inserts that fit into the cylinder block
They act as Cylinder walls for the piston to slide up & down on.
Is made from high quality materials as grained cast iron or nickle cast iron
or nickel chromium cast iron.
Dry liner Wet liner
Types of cylinder liner

The outside of a dry sleeve touches the walls of the cylinder block which provides support for
the sleeve.
Dry liner
When a cylinder is damaged, the original cylinder must be bored
almost as large as the outside of the sleeve. Then, the sleeve is pressed
into the oversized hole. This allows the use of the original piston size.

Wet liner
• Have a flange at the top.
• The cylinder head gasket keeps the top of the sleeve
from leaking
• A rubber of copper o-ring is used at the bottom of a
wet sleeve to prevent coolant leakage into the
crankcase

• Is mounted on the top of the cylinder block to confines the pressure
of combustion and directs it down the piston.
• It contains the spark plug, fuel injectors, and valves.
• It is made of cast iron or aluminum alloy.
3. Cylinder Head
The cylinder head are sealed to the cylinder block to prevent gases
from escaping by the use of a head gasket on liquid-cooled engines

Intake port of air & exhaust ports of burned gases are cast into the cylinder head.
3. Cylinder Head

Valve guides and seats are machined through the cylinder head for the valves. The
valves fit into and slide in these guides.
3. Cylinder Head
Valve Seats
Valve guide

4. Cam Shaft
• Is a rotating shaft that used for opening and closing
valves at the proper time of the cycle.
• It is driven by the crankshaft at half its speed by a belt or
chain in 4 stroke engine
• As the camshaft rotates, the cam lobe exerts a thrust
against the valve that overcomes the valve spring
pressure & the gas pressure in the cylinder, causing the
valve to open.

4. Camshaft
• Overhead Camshaft Engine (OHC)
• The Valve train consist of the valves, camshaft,
and other associated parts
• The cylinder head houses the camshaft
Single Overhead Camshaft (SOHC)
Double Overhead Camshaft (DOHC)

4. Camshaft
1. Directly through the lifters
2. By rocker arm

4. Camshaft
• Has a cam for the intake valves and
one for the exhaust valves.
• DOHC are frequently used on engines
that have more than two valves per
cylinder

4. Camshaft
1. Directly through the lifters
2. By rocker arm

4. Camshaft
• A v-type DOHC engine has 4 camshafts – two for each bank

4. Camshaft
Pushrod Engines (Overhead valve Engines)
• The cam is in the cylinder block.
• Consist of the valves, camshaft, valve lifter, pushrod &
rocker arm.
• The cam acts on a valve lifter, which in turn acts on a
pushrod to move the rocker arm and open the valve.

Cam follower (valve tappets) or (valve lifters)
4. Camshaft

Intake Valve
• Intake valves control the inlet of cool, low-
pressure induction
• Made of materials such as chrome, nickel, or
tungsten steel.
Exhaust Valve
• Exhaust valves handle hot, high-pressure
exhaust gases.
• This means that exhaust valves are exposed to
more severe operating
• conditions.
• Made of more heat resistant metals such as
nichrome, silicon-chromium, or cobalt-chromium
alloys.
5. Valves

5. Valves
The valve is held in place and is positioned in the head by the valve guide. The portion
of the valve that seals against the valve seat in the cylinder head is called the valve face.
PARTS INVOLVED
• A valve spring holds the valve against the seat.
• The valve keepers (also called locks ) secure the
spring retainer to the stem of the valve. For valve
removal, it is necessary to compress the spring and
remove the valve keepers. Then the spring, valve
seals, and valve can be removed from the head.

Valve stem
Valve head
Valve seat
Connects to the valve to the mechanical
elements in the engine that operate the
valve by creating a force to move
Contains a fillet that leads into a seat face
that is machined at a specified angle to
match the machining of the valve seat to
which it will match.
Is heavily impacted by heat & Corrosion,
which is why, as a rule, it is hard-faced with
special alloys.
5. Valves

5. Valves
INTEGRAL SEATS
Valve Seats
INSERT SEATS
Integral valve seats are machined directly
into the cast-iron cylinder head and are
induction hardened to prevent wear.
Insert valve seats are a separate part that is
interference fitted to a counterbore in the
cylinder head.

5. Valves
VALVE SPRINGS
A valve spring holds the valve against the seat when the valve is not being opened.
One end of the valve spring is seated against the head.
A retainer and two split keepers hold the spring
in place on the valve.

5. Valves
VALVE SIZE RELATIONSHIPS
The intake valve is larger than the exhaust valve because the intake charge is being
drawn into the combustion chamber at a low speed due to differences in pressure
between atmospheric pressure and the pressure (vacuum) inside the cylinder. The
exhaust is actually pushed out by the piston and, therefore, the size of the valve does not
need to be as large, leaving more room in the cylinder head for the larger intake valve.

• Metal rod which transfer force from the lifter to the rocker arm.
• Used in cam-in-block engine.
5. Push Rod

Transfer the valve train motion to the valve.
6. Rocker Arm

7. Piston
• Is a cylinder mass that transfers the pressure forces in the combustion
chamber to the crankshaft.
• the top surface of the piston is called the crown which can either be flat
or of a concave shape.
• pistons are made of cast iron or steel or aluminum alloy.
Characteristics:
1. Rigidity to withstand high pressure
2. Good heat conductivity to dissipate heat
3. low coefficient of expansion
4. light

7. Piston
Wrist Pin
Makes the connecting between the piston & the connecting rod.

8. Piston Rings
Compression rings
• Metal rings that seal between the piston and the cylinder wall
to prevent high pressure gases from escaping into the
crankcase.
Oil rings
• Below the compression rings
• Prevent oil from escaping into the combustion chamber.
General Functions:
1. Compression gas sealing (Compression ring)
2. Lubricating oil film control(Oil ring)
3. Heat transfer
4. Support piston in the cylinder

• Connecting the piston with the rotating crankshaft and help in
converting the reciprocating motion of the piston to rotary motion at
the crankshaft.
• It connected to the piston using a pin
• Made of steel or aluminum alloy
8. Connecting Rod

Power from expanding gases in the combustion chamber is delivered to the crankshaft through
the piston, piston pin, and connecting rod. The connecting rods and their bearings are attached
to a bearing journal on the crank throw.
9. Crankshaft
The crankshaft includes the following parts.
1. Main bearing journals
2. Rod bearing journals
3. Crankshaft throws
4. Counterweights
5. Front snout
6. Flywheel flange
7. Keyways
8. Oil passages

Is the space in the cylinder between the cylinder head and the piston face
9. Combustion Chamber

10. Spark Plug
is a device for delivering electric current from an ignition system to the combustion chamber of a spark-
ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing
combustion pressure within the engine.

11. Exhaust Manifold
Is a part of the engine that collects engine exhaust gases from the cylinders.

12. Intake Manifold
Is a part of the engine that supplies the fuel/air mixture to the cylinders.

13. Oil pan
The oil pan is where engine oil is used for lubricating the engine. Another name for the oil pan is a
sump . As the vehicle accelerates, brakes, or turns rapidly, the oil tends to move around in the pan.

14. Gaskets

Two Stroke Engine’s Operation
TWO STROKE CYCLE ENGINE
In such engines, the whole sequence of events i.e. suction,
compression, power and exhaust are completed in two strokes
of the piston and in one complete revolution of the crankshaft.
There is no valve in this type of engine. Air movement (charge)
takes place through holes called ports in the cylinder.
The crankcase of the engine is air tight in which the crankshaft
rotates.

When the piston moves up the cylinder, it covers two of the ports,
the exhaust port and the transfer port, which are normally almost
opposite to each other.
This traps a charge of fresh mixture in the cylinder and further
upward movement of the piston compresses this charge.
Further movement of the piston also uncovers a third port in the
cylinder suction port.
More fresh mixture is drawn through this port into the crankcase.
Just before the end of this stroke, the mixture in the cylinder is
ignited as in the four stroke cycle.
First stroke (suction + compression)

Second stroke (Power + exhaust)
The rise in pressure in the cylinder caused by the burning gases forces the
piston to move down the cylinder.
Further downward movements of the piston uncover first the exhaust
port and then transfer port.
When the piston goes down, it covers and closes the suction port,
trapping the mixture drawn into the crankcase during the previous stroke
then compressing it.
This allows the burnt gases to flow out through exhaust port. Also the
fresh mixture under pressure in the crankcase is transferred into the
cylinder through transfer port during this stroke.

Comparison between two stroke and four stroke engines

Four stroke engine Two stroke engine
one power stroke for every two
revolutions of the crankshaft
one power stroke for each
revolutions of the crankshaft
Particulars
1. No. of power stroke
Small
Large
(about 1.5 times of 4 stroke)
2. Power for the same
cylinder volume
Valve mechanism is
Present
Ports instead of valves
3. Valve mechanism
Complicated and expensive Simple construction, and are
cheap
4.
Construction and cost
Little High (about 15% more)
5. Fuel consumption
Easy Difficult
6. Removal of exhaust gases
Good Poor
7. Durability
High Low
8. Stability of operation
Equipped with an independent
lubricating oil circuit
Using fuel, mixed with
lubricating oil
9. Lubrication
Comparison between two stroke and four stroke engines
Little Much
10. Oil consumption
Not so much Much because of mixed fuel
11. Carbon deposit inside cylinder

On the intake stroke, the piston passes TDC, the intake
valve(s) opens, and filtered air enters the cylinder, while the
exhaust valve(s) remains open for a few degrees to allow all
of the exhaust gases to escape from the previous combustion
event.
On the compression stroke, after the piston passes BDC,
the intake valve(s) closes and the piston travels up to TDC
(completion of the first crankshaft rotation).
On the power stroke, the piston nears TDC on the
compression
stroke and diesel fuel is injected into the cylinder by the
injectors. During this power stroke, the piston passes TDC
and the expanding gases force the piston down, rotating the
crankshaft.
{On the exhaust stroke, as the piston passes BDC, the
exhaust
valve(s) opens and the exhaust gases start to flow out of
the cylinder. This continues as the piston travels up to TDC,
pumping the spent gases out of the cylinder.
Working principle of diesel engine

Diesel engine petrol engine
Its compression ratio varies from 14:1 to 22:1 Its compression ratio varies from 5:1 to 8:1
It uses diesel oil as fuel. It uses petrol (gasoline)
Only air is sucked in cylinder in suction stroke.
Mixture of fuel and air is sucked in the cylinder in
suction stroke.
It has got ‘fuel injection pump’ and injector
It has got no fuel injection pump and injector,
instead it has got carburetor and ignition coil.
Fuel is injected in combustion chamber where
burning of fuel takes places due to heat of
compression.
Air fuel mixture is compressed in the combustion
chamber when it is ignited by an electric spark.
Engine weight per horse-power is high. Engine weight per horsepower is comparatively low.
Operating cost is low. Operating cost is high.
Comparison between diesel engine and petrol engine

Stroke Piston
travel
Exhaust valve Intake valve
Intake
Power Down close
Compression Up close
Exhaust
Choose the correct answer
On a four-stroke engine, during the compression stroke, which
statement
is correct?
A • Pressure will increase but temperature will remain constant.
B • Pressure and temperature will remain constant.
C • Pressure will remain constant but temperature will increase.
D • Pressure and temperature will increase in the cylinder.
How many revolutions will the camshaft do if the crankshaft rotates 80
times ?
A • 100 B • 160 C • 80 D • 40
Which one of the following statements in relation to the four-stroke
cycle is
false?
A • The inlet valve opens on the exhaust stroke.
B • The exhaust valve opens on the firing stroke.
C • Valve overlap occurs when both inlet and exhaust valves are open.
D • The inlet valve opens on the induction stroke.
The camshaft is turned by the………………
A . Flywheel b . Crankshaft
C . Connecting rod d . Crank case
The engine converts heat energy to ……………………
Cylinder head contains
a- Intake manifold ports b- Combustion chamber
c- Cooling system d- All of the above
The crank shaft rotates ......... the revelations of the CAM shaft
a- Half b- Equal
c- Twice d- None of the above
Cylinder head is fixed ....... the engine block
a- Above b- Next to
c- Under d- Inside
The timing belt( or timing chain ) is a joint between ...... and .......
Fixed parts of the engine are...................
Complete The table

REFERENCES:
1. https://x-engineer.org/automotive-engineering/internal-combustion-
engines/performance/power-vs-torque/
2. http://www.performanceunlimited.co.uk/brands/l-a-sleeve/
3. https://www.goetzeparts.in/products/cylinder-liners.html
4. https://www.researchgate.net/figure/Construction-of-wet-cylinder-
liner_fig1_312574938
5. https://www.samarins.com/glossary/dohc.html
6. AUTOMOTIVE TECHNOLOGY Principles, Diagnosis, and Service book 4th edition
7. Modern Automotive Technology book, 2nd English edition

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