Unit 2 -IC Engine, EVs and Hybrid EVs Dr.

Deepak Kumar, DGI, Greater Noida

IC Engine
An internal combustion engine (IC engine) is a type of heat engine where the
combustion of fuel occurs internally, rather than being ignited externally by a flame. In
simple terms, it's a device that converts chemical energy stored in fuel into mechanical
energy, which is used to perform work, such as powering vehicles or generating
electricity.
The basic components of an internal combustion engine include:

1. Cylinder: This is the main chamber where the combustion of fuel takes place. IC
engines can have one or more cylinders arranged in a linear or radial configuration.
2. Piston: A piston is a cylindrical component that moves up and down within the cylinder.
It's typically connected to the crankshaft via a connecting rod. The piston's movement
is what helps to compress the air-fuel mixture and convert the energy from combustion
into mechanical motion.
3. Crankshaft: The crankshaft is a rotating shaft connected to the pistons via connecting
rods. It converts the reciprocating motion of the pistons into rotational motion, which
can then be used to drive other components, such as the wheels of a vehicle or a
generator.
4. Combustion chamber: This is the space within the cylinder where the air-fuel mixture
is ignited and burned. It's designed to promote efficient combustion and maximize
power output.
5. Valves: Valves are used to control the flow of air and fuel into the combustion chamber
and the exhaust gases out of the chamber. IC engines typically have intake valves to
allow air and fuel into the cylinder and exhaust valves to expel the combustion gases.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

6. Spark plug (for gasoline engines): In gasoline engines, a spark plug is used to ignite
the air-fuel mixture within the combustion chamber. When an electrical current is
applied to the spark plug, it generates a spark that ignites the mixture, initiating the
combustion process.
7. Fuel injector (for diesel engines): In diesel engines, fuel is injected directly into the
combustion chamber rather than being mixed with air before entering the cylinder. Fuel
injectors are used to precisely control the timing and amount of fuel injected into the
cylinder.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida
oto
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Unit' lat
Engines:
An engine is a mechanical device that converts various forms of energy into mechanical work
or power.
b
It is a fundamental component in many machines and vehicles, providing the necessary force
toperform tasks such as propulsion, generating electricity, or powering machinery,.

Classification of engine:
1. Fuel Type:
Gasoline Engines: These engines run on gasoline (petrol) as their primary fuel
source. They are commonly found in most passenger cars and small vehicles.
Diesel Engines: Diesel engines use diesel fuel, which is typically more energy
dense than gasoline. They are known for their efficiency and are often used in
trucks, buses, ships, and industrial machinery.
Natural Gas Engines: These engines use natural gas as their fuel source. They
are often used in buses, some vehicles, and stationary power generation.
2. Cycle Type:
Four-Stroke Engines: These engines operate on a four-stroke cycle, including
intake, compression, power, and exhaust strokes. They are widely used in
automobiles, motorcycles, and industrial applications.
Two-Stroke Engines: Two-stroke engines complete a cycle in two strokes: one
for compression and power, and another for exhaust and intake. They are
simpler in design but less fuel-efficient and less common in modern
applications.
3. Application:
Automotive Engines: Engines used in cars, trucks, and other passenger
vehicles.

Marine Engines: Engines designed for use in boats and ships.

Aireraft Engines: Engines used in airplanes, helicopters, and other aircraft.
Industrial Engines: Engines used in various industrialapplications, including
generators, pumps, and heavy machinery.
4. Design and Configuration:
Inline Engines: Cylinders are arranged in a straight line.
V-Shaped Engines: Cy linders are arranged in a Vshape, typically with two
banks of cylinders.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Boxer or Flat Engines: Cylinders are horizontally opposed, with two banks of
cylinders facing each other.
Radial Engines: Cylinders are arranged in a circular pattern around a central
crankshaft, often used in aircraft.

Wankel Rotary Engines: These engines use a rotary design with no pistons
and have a unique triangular rotor.
5. Cooling Method:
Liquid-Cooled Engines: Engines that use a liquid coolant (typically water and
antifreeze) to regulate temperature.
Air-Cooled Engines: Engines that rely on airflow over external fins or cooling
fins to dissipate heat.
6. Number of Cylinders:
Engines can be classified by the number of cylinders they have, such as 4
cylinder, 6-cylinder, or 8-cylinder engines.
7. Hybrid and Electrie Engines:
Hybrid Engines: These engines combine an internal combustion engine
(usually gasoline) with an electric motor and a battery. They are used in hybrid
vehicles.

Electric Motors: Fully electric vehicles (EVs) use electric motors powered by
batteries, with no internal combustion engine.
8. Compression Ignition (CT) vs. Spark Ignition (SI):
Engines can be classified based on their ignition method, either compression
ignition (as in diesel engines) or spark ignition (as in gasoline engines).

Spark-Ignition (S) engine:

A Spark-Ignition (SI) engine, often referred to as a gasoline engine,
They operate on the Otto cycle. (unsat
It is commonly used in automobiles, motorcycles, and smaller equipment like
lawnmowers and generators.
The distinguishing feature of a SI engine is its reliance on a spark plug to ignite a
mixture of air and gasoline (or another hydrocarbon-based fuel) within the engine's
cylinders. volme

Compression-Ignition (CI) Engine:

CI engines are often referred to as diesel engines.
They operate on the Diesel cycle and rely on the heat generated by compressing air
to ignite diesel fuel injected into the cylinder.

o to
Airr fuel mixve
Auel mihre
|Gompesim ymih No
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Dieselengines are known for their high compression ratios, which result in high
thermal efficiency and torque.
They are commonly used in trucks, buses, ships, and industrial equipment.
Four-Stroke SI Engine:
1. Intake: During the first stroke (intake stroke), the intake valve opens, and the piston
moves downward. This creates a vacuum in the cylinder, drawing in an air-fuel mixture
from the carburetor or fuel injection system.
2. Compression: In the second stroke (compression stroke), both the
intake and exhaust
valves close. The piston moves upward, compressing the air-fuel mixture. The
compression ratio determines the degree of compression.
ignites the
3. Power: When the piston reaches the top of its stroke, a spark plug
compressed air-fuel mixture. This ignition initiates a rapid combustion, creating a high
power stroke and is
pressure force that pushes the piston downward. This is the
responsible for generating mechanical work.
4. Exhaust: After the power stroke, the exhaust valve opens, and the piston moves upward
again, expelling the burned gases from the cylinder. This is the exhaust stroke.

Four-stroke cycle intake exhaust

valves closed valves closed valve closed valve open
intake valve spark piug
open
exhaust valve
closed
air-fuel exhaust
mixture spark plug
firing gases
cormbustion
chamber
piston
connecting
rod

crankshaft

compression power exhaust

intake
Air-fuel mixture Air-fuei mixture Explosion torces Piston pushes out
is drawn in. is compressed. piston down. burned gases.
2007 Encyclopedia Britannica, Inc.
 Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

INTERNAL COMBUSTION ENGINE & GAS TURBINES

Module -I
INTRODUCTION

Heat engine:
Aheat engine is a device which transforms the chemical energy of a fuel into thermal energy
and uses this energy to produce mechanical work. It is classified into two types Se

(a) External combustion engine

(b) Internal combustion engine

External combustion engine: ghtweig

gr

Inthis engine, the products of combustion of air and fuel transfer heat to a second fluid which USBa0
is the working fluid of the cycle.
Examples:
*In the steam engineor a steam turbine plant, the heat of combustion is employed to generate
steam which is used in a piston engine (reciprocating type engine) or a turbine (rotary type
engine) for useful work.

*In a closed cycle gas turbine, the heat of combustion in an external furnace is transferred to
gas, usually air which the working fluid of the cycle.
Internal combustion engine:
In this engine, the combustion of air and fuels take place inside the cylinder and are used as
the direct motive force. It can be classified into the following types:

1. According to the basic engine design- (a) Reciprocating engine (Use of cy linder piston
arrangement), (b) Rotary engine (Use of turbine)
2. According to the type of fuel used- (a) Petrol engine, (b) diesel engine, (c) gas engine
(CNG, LPG),(d) Alcohol engine (ethanol, methanol etc)
3. According to the number of strokes per cycle- (a) Four stroke and (b) Two
stroke engine
4. According to the method of igniting the fuel- (a) Spark
ignition engine, (b) compression
ignition engine and (c) hot spot ignition engine
5. According to the working cycle- (a) Otto cycle
(constant volume cycle) engine, (b) diesel
cycle (constant pressure cycle) engine, (c) dual combustion cycle
(semi diesel cycle) engine.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

6. According to the fuel supply and mixture preparation- (a) Carburetted type (fuel supplied
manifold,
through the carburettor), (b) Injection type (fuel injected into inlet ports or inlet
fuel injected into the cylinder just before ignition).
7. According to the number of cylinder- (a) Single cylinder and (b) multi-cylinder engine

8. Method of cooling- water cooled or air cooled

9. Speed of the engine- Slow speed, medium speed and high speed engine
10. Cylinder arrangement-Vertical, horizontal., inline, V-type, radial, opposed cylinder or
piston engines.
11. Valve or port design and location- Overhead (I head), side valve (L head); in two stroke
engines: cross scavenging, loop scavenging, uniflow scavenging.
12. Method governing- Hit and miss governed engines, quantitatively governed engines and
qualitatively governed engine
14. Application- Automotive engines for land transport, marine engines for propulsion of
ships, aircraft engines for aircraft propulsion, industrial engines, prime movers for electrical
generators.

Comparison between external combustion engine and internal combustionengine:

External combustion engine Internal combustion engine
*Combustion of air-fuel is outside the engine*Combustion of air-fuel is inside the engine
cylinder (in a boiler) cylinder (in a boiler)
*The engines are running smoothly and * Very noisy operated engine
silently due to outside combustion
*Higher ratio of weight and bulk to output* It is light and compact due to lower ratio of
due to presence of auxiliary apparatus like weight and bulk to output.
boiler and condenser. Hence it is heavy and
cumbersome.
*Working pressure and temperature inside* Working pressure and temperature inside
the engine cylinder is low; hence ordinary the engine cylinder is very much high; hence
alloys are used for the manufacture of engine special alloys are used
cylinder and its parts.
*It can use cheaper fuels including solid fuels *High grade fuels are used with proper
filtration
*Lower efficiency about 15-20% *Higher efficiency about 35-40%
Higher requirement of water for dissipation *Lesser requirement of water
of energy through cooling system
*High starting torque *ICengines are not self-starting

Main components of reciprocating IC engines:

Cylinder: It is the main part of the engine inside which piston reciprocates to and fro. It
should have high strength to withstand high pressure above 50 bar and temperature above
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

2000 °C. The ordinary engine is made of cast iron and heavy duty engines are made of steel
alloys or aluminum alloys. In the multi-cylinder engine, the cylinders are cast in one block
known as cylinder block.

Cylinder head: The top endof the cylinder is covered by cylinder head over which inlet and
exhaust valve, spark plug or injectors are mounted. Acopper or asbestos gasket is provided
between the engine cylinder and cylinder head to make an air tight joint.
Piston: Transmit the force exerted by the burning of charge to the connecting rod. Usually
made of aluminium alloy which has good heat conducting property and greater strength at
higher temperature.
Figure 1shows the different components of IC engine.

Cylinder head
Spark plug

Inlet valve:
Wow airh
allo
into the
Valve stem combustion
chamber

Exhaust valve lgniting antuel

to allow burnt mixture
fuel out of the
combustion TDdn Combustion
chamber chamber
-Piston rings
Clearance volume Piston
Cylinder Gudgeon pin
-Pistoncylxler
BDC
Connecting
rod

Crankshat

Direction Crank case

rotation

Fig. 1. Different parts of IC engine

Piston rings: These are housed in the circumferential grooves provided on the outer surface
of the piston and made of steel alloys which retain elastic properties even at high temperature.
2types of rings- compression and oil rings. Compression ring is upper ring of the piston
which provides air tight seal to prevent leakage of the burnt gases into the lower portion. Oil
ring is lower ring which provides effective seal to prevent leakage of the oil into the engine
cylinder.

Connecting rod: It converts reciprocating motion of the piston into circular motion of the
crank shaft, in the working stroke. The smaller end of the connecting rod is connected with
the piston by gudgeon pin and bigger end of the connecting rod is connected with the crank
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

are used for the manufacture of

with crank pin. The special steel alloys or aluminium alloys
connecting rod.
rotary motion with the
Crankshaft: It converts the reciprocating motion of the piston into the
for the manufacturing of the
help of connecting rod. The special steel alloys are used
crankshaft. It consists of eccentric portion calledcrank.
and also serves as sump for
Crank case: It houses cylinder and crankshaft of the IC engine
the lubricating oil.
is to maintain its speed
Flywheel: It is big wheel mounted on the crankshaft, whose function
stroke, which is returned
constant. It is done by storing excess energy during the power
during other stroke.
Terminology used in ICengine:

1.Cylinder bore (D): The nominal inner diameter of the working cylinder.
2. Piston area (A): The area of circle of diameter equal to the cylinder bore.
3. Stroke (L): The nominal distance through which a working piston moves between two
successive reversals of its direction of motion.

4. Dead centre: The position of the working piston and the moving parts which are
mechanically connected to it at the moment when the direction of the piston motion is
reversed (at either end point of the stroke).
(a)Bottom dead centre (BDC): Dead centre when the piston is nearest to the crankshaft.

(b)Top dead centre (TDC): Dead centre when the position is farthest from the crankshaft.

5. Displacement volume or swept volume (V,): The nominal volume generated by the
working piston when travelling from the one dead centre to next one and given as,
V=A x L
6. Clearance volume (V): the nominal volume of the space on the combustion side of the
piston at the top dead centre.

7. Cylinder volume (V): Total volume of the cylinder.

V= V,+ Ve

8. Compression ratio (r): r= Vc

Fonr stroke engine:

Cycle of operation completed in four strokes of the piston or two revolution of the
piston.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Four Stroke Engine:

1) Four Stroke SI engine:

Working of Four-Stroke SI Engine:

1. Intake Stroke: The piston moves down, creating a vacuum in the cylinder. The intake
valve opens, allowing the air-fuel mixture to enter the cylinder.
2. Compression Stroke: The intake valve closes, and the piston moves up, compressing
the air-fuel mixture.
3. Power Stroke: When the piston reaches the top, the spark plug ignites the compressed
air-fuel mixture. The resulting explosion forces the piston down, generating power.
4. Exhaust Stroke: As the piston moves up again, the exhaust valve opens, allowing the
burned gases to exit the cylinder.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Working of Four-Stroke CI Engine:

1. Intake Stroke: The piston moves down, creating a vacuum in the cylinder. The intake
valve opens, and air is drawn into the cylinder.
2. Compression Stroke: The intake valve closes, and the piston moves up, compressing
the air to a very high pressure and temperature.
3. Injection Stroke: Near the top of the compression stroke, fuel is injected into the highly
compressed air, where it instantly ignites due to the high temperature and pressure.
4. Power Stroke: The burning fuel expands rapidly, forcing the piston down with
significant force.
5. Exhaust Stroke: The exhaust valve opens, and the piston moves up again, expelling
the burned gases out of the cylinder.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Difference Between four stroke SI and CI Engine:

Feature SI Engine CI Engine

Ignition
Spark plug Compression
Method

Fuel Gasoline Diesel

Compression
Lower (6:1 - 10:1) Higher (16:1 - 20:1)
Ratio

Applications Cars, motorcycles Trucks, buses, machinery

Smoother operation, quieter, Higher torque, fuel efficient,

Advantages
quicker starts durable

Lower fuel efficiency, higher

Disadvantages Noisier, higher initial cost
emissions

Merits and demerits of a four-stroke engine:

Merits:
1. Efficiency: Four-stroke engines are known for their fuel efficiency.
2. Lower Emissions: They produce fewer harmful emissions compared to other types of
engines.
3. Durability: They tend to have a longer lifespan and require less maintenance.
4. Smooth Operation: They provide a smoother driving or riding experience.
5. Fuel Versatility: They can run on different types of fuels, offering flexibility.

Demerits:
1. Complexity: Four-stroke engines are more complex and can be harder to repair or
maintain.
2. Heavier: They are usually heavier than other types of engines, affecting vehicle
performance.
3. Lower Power-to-Weight Ratio: Despite being heavy, they might not offer as much
power relative to their weight.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

4. Slower Acceleration: They can take longer to reach high speeds compared to other
engines.
5. Higher Initial Cost: They may be more expensive to purchase upfront, although they
can save money in the long run due to lower maintenance costs.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Two stroke Engine:

A two-stroke engine is a type of internal combustion engine that completes a power cycle with
two strokes (up and down movements of the piston) during one revolution of the crankshaft.
These engines are commonly found in applications where a lightweight and simple design are
desired, such as in motorcycles, chainsaws, outboard motors, and small handheld equipment.

1. Intake and Compression Stroke:

 As the piston moves downward from the top of the cylinder (top dead center),
it uncovers the intake port. This allows a mixture of air and fuel to enter the
combustion chamber while simultaneously compressing any residual exhaust
gases out through the exhaust port.
 The upward movement of the piston compresses the air-fuel mixture in the
combustion chamber, preparing it for ignition.
2. Power and Exhaust Stroke:
 Near the top of the compression stroke, a spark plug ignites the compressed air-
fuel mixture. The resulting explosion generates high pressure, driving the piston
downward with force.
 As the piston descends, it uncovers the exhaust port, allowing the burned gases
to exit the combustion chamber.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Scavenging Process
The scavenging process in a two-stroke engine is crucial for ensuring efficient operation and
maximizing power output. Scavenging refers to the removal of exhaust gases from the
combustion chamber and their replacement with a fresh mixture of air and fuel. This process
occurs during the exhaust stroke and the beginning of the intake stroke
Why is Scavenging Important?
Incomplete scavenging can lead to several problems:
 Reduced Power Output: If leftover exhaust gases take up space in the cylinder, there's
less room for the fresh air-fuel mixture. This leads to a weaker combustion event and
less power generation.
 Incomplete Combustion: Residual exhaust gases can hinder the proper mixing of the
air-fuel mixture, leading to incomplete combustion. This results in wasted fuel,
increased emissions, and rough engine operation.
 Higher Emissions: Incomplete combustion can lead to the formation of harmful
pollutants like carbon monoxide and hydrocarbons.

Types of Scavenging:
There are two main types of scavenging processes depending on the engine design:
1. Crossflow Scavenging: This is the most common type used in modern four-stroke
engines. Here's how it works:
o The intake and exhaust valves are positioned on opposite sides of the cylinder
head.
o During the intake stroke of the piston, fresh air (or air-fuel mixture) enters
through the intake valve on one side.
o The momentum of the incoming air pushes the exhaust gases out the exhaust
valve on the other side.
o Some overlap in the timing of the intake and exhaust valve opening allows for
a more thorough purging of exhaust gases.
2. Uniflow Scavenging: This type is primarily used in two-stroke engines:
o The intake and exhaust ports are located at opposite ends of the cylinder.
o The piston itself controls the opening and closing of these ports as it moves up
and down.
o As the piston moves down, it uncovers the intake port, allowing fresh air (or air-
fuel mixture) to enter the bottom of the cylinder.
o The rising pressure from the incoming charge pushes the exhaust gases out the
exhaust port located near the top of the cylinder.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Merits and Demerits of 2 stroke engine

Merits of 2-Stroke Engines:

 Simple Design: Two-stroke engines are significantly simpler than four-stroke engines.
They lack valves, relying on ports controlled by the piston movement for intake and
exhaust. This simpler design translates to:
o Lighter weight: Makes them ideal for applications where weight matters, like
chainsaws, motorcycles, and some small airplanes.
o Lower manufacturing cost: Due to fewer parts, they are generally cheaper to
produce.
 High Power-to-Weight Ratio: Because every downward stroke of the piston is a
power stroke, two-stroke engines can deliver more power relative to their weight
compared to four-stroke engines.
 Simple Maintenance: The lack of complex valve mechanisms makes them easier to
maintain in some cases.
Demerits of 2-Stroke Engines:
 Lower Fuel Efficiency: Two-stroke engines tend to burn more fuel and oil compared
to four-stroke engines. This is because some of the fresh air-fuel mixture can escape the
cylinder during the scavenging process along with the exhaust.
 Higher Emissions: Inefficient fuel burning and incomplete combustion in two-stroke
engines lead to higher emissions of pollutants like hydrocarbons and carbon monoxide.
This is why they are becoming less common due to stricter emission regulations.
 Shorter Lifespan: The constant mixing of fuel and oil in the crankcase reduces
lubrication effectiveness, leading to increased wear and tear on engine components
compared to four-stroke engines.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

 Noisier Operation: Two-stroke engines generally run noisier than four-stroke engines
due to the simpler port design and the need for higher exhaust gas velocity for effective
scavenging.
 Limited Application: Their drawbacks make them less suitable for applications where
fuel efficiency and emissions are critical, such as cars.

Difference between Two stroke and Four Stroke Engine:

1. Number of Strokes per Cycle:
 Two-Stroke Engine: Completes one power cycle with two strokes of the
piston—intake and compression combined with power and exhaust combined—
per revolution of the crankshaft.
 Four-Stroke Engine: Completes one power cycle with four strokes of the
piston—intake, compression, power, and exhaust—per two revolutions of the
crankshaft.
2. Fuel Delivery:
 Two-Stroke Engine: Typically mixes fuel and oil together, which is then
introduced into the combustion chamber during the intake stroke. This mixture
lubricates engine components as it burns.
 Four-Stroke Engine: Usually has separate systems for fuel and lubrication. Fuel
is introduced during the intake stroke, and oil is circulated in the engine
separately to lubricate moving parts.
3. Lubrication:
 Two-Stroke Engine: Relies on oil mixed with fuel for lubrication. This oil is
burned along with the fuel during combustion, necessitating regular
replenishment of the oil-fuel mixture.
 Four-Stroke Engine: Has a dedicated lubrication system that circulates oil to
lubricate moving parts such as the crankshaft, piston, and valves. The oil is not
burned during combustion and is typically changed less frequently than in a
two-stroke engine.
4. Power and Efficiency:
 Two-Stroke Engine: Tends to have a higher power-to-weight ratio due to its
simpler design and higher power output per revolution. However, it is generally
less fuel-efficient and emits more pollutants due to incomplete combustion and
mixing of fresh fuel with exhaust gases.
 Four-Stroke Engine: Often provides better fuel efficiency and lower emissions
compared to a two-stroke engine. It typically delivers smoother power delivery
and operates with more precision, but it can be heavier and more complex.
5. Maintenance and Emissions:
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

 Two-Stroke Engine: Requires more frequent maintenance due to the mixing of

oil with fuel and the potential for carbon buildup. It also tends to emit higher
levels of hydrocarbons and particulate matter.
 Four-Stroke Engine: Generally requires less frequent maintenance and produces
lower emissions, making it more environmentally friendly. However, it can have
more components that may require periodic adjustment or replacement.
In a simple way to understand only :

Two-Stroke Engine Four-Stroke Engine

Strokes per Cycle 2 4

Valves No valves (uses ports) Intake and exhaust valves

Lubrication Mixed with fuel (less efficient) Separate oil system (more efficient)

Efficiency Lower Higher

Emissions Higher Lower

Power-to-Weight Ratio Higher Lower

Complexity Simpler design More complex design

Cost Lower Higher

Noise Noisier Quieter

Applications Chainsaws, motorcycles Cars, trucks, most generators

Difference Between SI and CI engine:

1. Spark Ignition (SI) Engine:
 Ignition Method: In SI engines, ignition of the air-fuel mixture is initiated by
a spark plug. The spark plug generates an electric spark that ignites the
compressed air-fuel mixture at the right moment in the engine cycle.
 Fuel Type: SI engines typically use gasoline or petrol as fuel, which is highly
volatile and requires a spark to ignite.
 Compression Ratio: SI engines usually have lower compression ratios
compared to CI engines due to the need to prevent premature ignition
(knocking) of the fuel-air mixture.
 Applications: SI engines are commonly found in automobiles, motorcycles,
lawnmowers, and small engines where relatively low compression ratios and
precise control over ignition timing are required.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

2. Compression Ignition (CI) Engine:

 Ignition Method: In CI engines, ignition of the air-fuel mixture is achieved by
the heat generated during compression. The air-fuel mixture is compressed to a
high temperature and pressure, causing it to ignite spontaneously without the
need for a spark plug.
 Fuel Type: CI engines typically use diesel fuel, which ignites under high
temperature and pressure without the need for a spark.
 Compression Ratio: CI engines have higher compression ratios compared to
SI engines. This higher compression ratio is necessary to raise the temperature
of the air-fuel mixture to the point where spontaneous ignition occurs.
 Applications: CI engines are commonly used in heavy-duty vehicles such as
trucks, buses, ships, and industrial equipment where high torque, fuel efficiency,
and durability are required.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Electric vehicles and hybrid vehicles:

Electric vehicles:
 Electric vehicles (EVs) are automobiles that rely primarily or entirely on electric
propulsion, replacing traditional internal combustion engines with electric motors and
batteries.
 An electric vehicle (EV) uses one or more electric motors for propulsion.
 EVs rely on electricity stored in a battery pack. This battery pack is the heart of the
EV and holds the energy that powers the vehicle
The main components of electric vehicles (EVs) include:

1. Battery Pack: The battery pack is the primary energy storage unit in an EV. It typically
consists of lithium-ion batteries, which store electrical energy to power the vehicle's
electric motor.
2. Electric Motor: The electric motor is the engine of the EV. It receives the AC
electricity from the inverter and converts it into mechanical energy (rotation). This
rotation is then transferred to the wheels via the drivetrain, propelling the vehicle
forward. There are different electric motor types used in EVs, with AC induction motors
being the most common due to their simplicity and durability.
3. Power Inverter: The power inverter converts the direct current (DC) electricity from
the battery into alternating current (AC) electricity required by the electric motor. It
also controls the speed and torque of the motor.
4. Charging Port: EVs have a charging port where external power sources can be
connected to recharge the battery pack. Different types of charging ports are available,
including standard household outlets, dedicated charging stations, and fast-charging
stations.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

5. Onboard Charger: The onboard charger converts AC electricity from the charging
port into DC electricity to charge the battery pack. It regulates the charging process and
manages the flow of electricity into the battery.
6. Thermal Management System: EV batteries and electric motors generate heat during
operation, and a thermal management system is essential to regulate their temperature.
This system includes cooling mechanisms to prevent overheating and maintain optimal
performance and longevity.
7. Vehicle Control Unit (VCU): The VCU acts as the central control unit of the EV,
managing various functions such as motor control, battery management, regenerative
braking, and thermal management. It monitors and coordinates the operation of
different components to ensure efficient and safe vehicle operation.
8. Electric Power Steering: Electric power steering systems assist the driver in steering
the vehicle using an electric motor instead of hydraulic power. This system improves
efficiency and allows for advanced driver assistance features.
9. Braking System: EVs may use regenerative braking systems to capture energy during
braking and recharge the battery pack. However, they still require traditional hydraulic
or electric braking systems for deceleration and stopping.

Advantages of Electric Vehicles (EVs)

 Reduced Emissions: EVs produce zero tailpipe emissions, meaning they don't
contribute directly to air pollution in cities and around us. This helps improve air quality
and public health.
 Lower Operating Costs: Electricity is generally cheaper than gasoline, and EVs
require less maintenance compared to gasoline vehicles. EVs have fewer moving parts,
so there's less wear and tear on the engine and fewer fluids to change.
 Increased Efficiency: Electric motors convert a higher percentage of electrical energy
into usable power compared to internal combustion engines in gasoline vehicles. This
translates to more miles driven per unit of energy consumed.
 Quieter Operation: EVs generate significantly less noise pollution compared to
gasoline vehicles. This can be a major benefit in urban areas and for reducing noise
complaints.
 Tax Credits and Incentives: Many governments offer tax credits and incentives for
purchasing EVs, making them more affordable.
 Performance: Electric motors can deliver instant torque, which can provide a more
responsive and exhilarating driving experience compared to gasoline vehicles.
Disadvantages of Electric Vehicles (EVs)
 Limited Range: Battery range is a major concern for EVs, as they typically have a
shorter driving range on a single charge compared to a full tank of gas in a gasoline
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

vehicle. This can cause range anxiety for drivers who worry about running out of power
on long trips.
 Charging Time: While charging times are improving, it can take several hours to fully
recharge an EV battery pack compared to minutes for refueling a gasoline vehicle. This
can be inconvenient for long trips or if there aren't many charging stations available.
 Higher Initial Cost: Electric vehicles generally have a higher upfront purchase cost
compared to gasoline vehicles. Battery technology is still evolving, and the cost of
batteries is a significant factor in the overall price of the vehicle.
 Battery Degradation: EV batteries degrade over time and capacity reduces with
extended use, eventually requiring replacement. Battery replacement can be expensive.
 Limited Charging Infrastructure: The availability of charging stations, especially
fast-charging stations, is still limited in some areas. This can make it difficult to find a
place to charge on long trips.
 Environmental Impact of Battery Production: The mining and manufacturing of
battery materials for EVs can have environmental and social impacts.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Hybrid electric vehicles (HEVs)

Hybrid electric vehicles (HEVs) are a type of vehicle that bridges the gap between traditional
gasoline-powered cars and fully electric vehicles (EVs). They combine an internal combustion
engine (ICE) with an electric motor and battery pack to achieve better fuel economy and reduce
emissions compared to gasoline vehicles.

Type of HEVs
1. Parallel Hybrid: Uses both the internal combustion engine and electric motor to
power the vehicle simultaneously.
2. Series Hybrid: The internal combustion engine acts as a generator to recharge the
battery, while the electric motor drives the wheels.
3. Series-Parallel Hybrid: Combines elements of both parallel and series hybrids for
improved efficiency and performance.
4. Plug-In Hybrid: Similar to a regular hybrid but with a larger battery that can be
charged from an external power source.

Indepth:

1. Parallel Hybrid Electric Vehicles (PHEVs):

 In PHEVs, both the internal combustion engine (ICE) and the electric motor are
mechanically connected to the vehicle's transmission and drive the wheels
simultaneously.
 The electric motor assists the ICE during acceleration, reducing fuel
consumption and emissions.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

 PHEVs can operate in electric-only mode for short distances, relying solely on
the electric motor and battery pack, or in hybrid mode, where both the ICE and
electric motor contribute to propulsion.
2. Series Hybrid Electric Vehicles (SHEVs):
 In SHEVs, the internal combustion engine (ICE) is used solely as a generator to
produce electricity, which powers the electric motor that drives the wheels.
 The ICE does not directly drive the wheels but operates at its most efficient
speed to generate electricity for the electric motor and recharge the battery pack.
 Series hybrids offer greater flexibility in powertrain design and can potentially
achieve higher fuel efficiency, especially in urban driving conditions where
frequent starts and stops are common.
3. Series-Parallel Hybrid Electric Vehicles:
 Series-parallel hybrids combine elements of both parallel and series hybrid
configurations to achieve optimal efficiency and performance.
 These hybrids can operate in various modes, including electric-only mode,
hybrid mode (ICE and electric motor working together), and series mode (ICE
acting as a generator).
 Series-parallel hybrids offer a balance between electric-only driving capability
and the range of the internal combustion engine.
4. Plug-In Hybrid Electric Vehicles (PHEVs):
 PHEVs are similar to conventional hybrids but have larger battery packs that
can be charged from an external power source, such as a wall outlet or charging
station.
 This allows PHEVs to operate in electric-only mode for longer distances,
reducing reliance on the internal combustion engine and further lowering fuel
consumption and emissions.
 PHEVs offer the flexibility to drive using electricity from the grid or switch to
hybrid mode when the battery charge is depleted.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

HEV drive train components:

In a hybrid electric vehicle (HEV), the drivetrain combines the power of an internal combustion
engine (ICE) and an electric motor with a battery pack to achieve efficient and eco-friendly
transportation. Here's a breakdown of the key HEV drivetrain components:
1. Internal Combustion Engine (ICE):
 This is a gasoline engine similar to those found in traditional gasoline-powered
vehicles. However, in HEVs, the ICE is typically smaller and tuned for efficiency rather
than high performance.
2. Electric Motor:
 Acts as the other half of the power source, providing electric propulsion to the vehicle.
HEVs can use different electric motor types, with AC induction motors being common
due to their simplicity and durability.
3. Power Electronics:
 This group of components manages the flow and conversion of electricity within the
HEV drivetrain. Key players include:
o Power Inverter: Converts the DC (Direct Current) electricity from the battery
pack into AC (Alternating Current) electricity required by the electric motor. It
also controls the motor's speed and direction by regulating the frequency and
voltage of the AC output.
o DC-DC Converter: Steps down the high voltage DC output from the battery
pack to a lower voltage level suitable for powering the vehicle's low-voltage
auxiliary systems like lights and informationtainment systems.
4. Regenerative Braking System:
 A key feature in HEVs, this system captures energy during braking that would otherwise
be wasted as heat.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

 When the brakes are applied, the electric motor acts like a generator. It converts the
car's kinetic energy from slowing down into electricity, which is then used to recharge
the battery pack.
5. Drivetrain:
 Transfers the mechanical power to the wheels, but unlike traditional gasoline vehicles,
HEV drivetrains are generally simpler due to the absence of a complex transmission
system.
 It may include:
o Reduction Gears: Adjust the electric motor's high-speed rotation to a slower,
higher torque output suitable for driving the wheels.
o Differential: Allows the inner and outer wheels to rotate at different speeds
when cornering.
6. Transmission (in some HEVs):
 Unlike traditional gasoline vehicles that require multiple gears for varying speeds and
loads, some HEVs might use a single-speed reduction gear.
 However, some HEVs do incorporate a multi-speed transmission to improve efficiency
across a wider range of driving conditions. These transmissions are typically simpler
than those found in gasoline vehicles.
7. Battery Pack:
 Stores the electrical energy that powers the electric motor. Made up of numerous
lithium-ion battery cells connected in series and parallel configurations to achieve the
desired voltage and capacity.
 Battery Management System (BMS): This electronic system monitors factors like
cell voltage, temperature, and current flow within the battery pack, ensuring safe and
efficient operation.
8. Engine Control Unit (ECU) and Hybrid Control Unit (HCU):
 These are the brains of the HEV.
o ECU: Controls the operation of the gasoline engine, optimizing performance
and fuel efficiency.
o HCU: Manages the overall powertrain operation, determining the optimal
combination of electric motor and gasoline engine power based on driving
conditions and battery charge level. It communicates with both the ECU and the
power inverter to ensure smooth and efficient operation.
Unit 2 -IC Engine, EVs and Hybrid EVs Dr. Deepak Kumar, DGI, Greater Noida

Benefits of Hybrid Electric Vehicles:

 Improved Fuel Economy: Hybrids achieve significantly better fuel economy
compared to traditional gasoline-powered vehicles, reducing fuel costs and
greenhouse gas emissions.
 Reduced Emissions: While hybrids still use gasoline, they emit less CO2 and other
pollutants due to the increased reliance on electric power, especially for PHEVs.
 Regenerative Braking: Captures energy that would otherwise be wasted during
braking, improving overall efficiency.
 Smoother Operation: The combination of electric motor and gasoline engine can
provide a smoother and more responsive driving experience.
Drawbacks of Hybrid Vehicles:
 Higher Initial Cost: Hybrids generally have a higher upfront purchase cost compared
to gasoline vehicles due to the more complex powertrain technology.
 Battery Degradation: Like all batteries, EV batteries in hybrids degrade over time
and eventually require replacement, adding an extra cost.
 Less Cargo Space: In some hybrids, the battery pack placement might eat into cargo
space compared to gasoline counterparts.
 Limited All-Electric Range (for HEVs): HEVs cannot travel long distances solely
on electric power compared to PHEVs.