energy sources syllabus: energy resources introduction

Electrical and Mechanical Technology Unit 4

Mr. S.Rajesh, B.Tech (ME) & M.Tech (MD), Asst. Prof. VLITS 1

ENERGY SOURCES

Syllabus: Energy Resources: Renewable and Non-Renewable Energy, conversions

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INTRODUCTION:

Energy is required to do any kind of work. Energy is a Greek word in which ‘en’ means

ergon (in work or work content).

Primitive man depends on manual work. Later on he started using animal power to supplement manual energy to enhance his work output. Gradually, he learnt harnessing energy from wind and falling water to further enhance the work output. In 1785, steam engine by James Watt drought industrial revolution. It was the beginning of mechanical age or age of machines. Later the inventions of IC Engines (late 19th century) and Nicokla Tesla`s invention of Induction Motor in 1888 (beginner of Electrical Age), all these led to increase of energy requirement by leaps and bounds (un-stoppable).Thus with the progress of human civilization the energy consumption also accelerated.

Access to modern energy services is fundamental to fulfilling basic social needs, driving economic growth and fuelling human development. This is because energy services have an effect on productivity, health, education, safe and potable water and communication services. Modern services such as electricity, natural gas, modern cooking fuel and mechanical power are necessary for improved health and education, better access to information and industrial as well as agricultural productivity. Access to energy is a fundamental pre-requisite for modern life and a key tool in eradicating extreme poverty across the globe. Broadly, there are four major energy end use sectors: Commercial, Industrial, residential and Transportation.

Classification of Energy Sources:

Energy resources can be classified on the basis of following criteria:

Based on Usability of Energy Primary resources Secondary Resources

Based on Traditional Use Conventional Energy Non-Conventional Energy

Based on Long-Term availability Non-renewable Renewable

Based on Commercial application Commercial energy resource Non-commercial energy

Based on origin Fossil fuels energy Nuclear energy Hydro energy



Solar energy Wind energy Biomass energy Geothermal energy Tidal Energy Ocean thermal energy Ocean wave energy

1. Based on usability of energy:

a) Primary resources: These include resources embodied in nature prior to undergoing any human-made conversions or transformations. This only involves extraction or capture. Examples of primary energy resources are coal, crude oil, sunlight, wind, running rivers, vegetation and radioactive material like uranium etc. These resources are generally available in raw forms and are therefore, known as raw energy resources.

b) Secondary resources: The energy resources supplied directly to consumer for utilization after one or more steps of transformation are known as secondary or usable energy, e.g. electrical energy, thermal energy (in the form of steam or hot water), refined fuels or synthetic fuels such a hydrogen fuels, etc.

2. Based on Traditional Use: (a) Conventional: Energy resources, which are being traditionally used, for many decades

and were in common use around oil crisis of 1973, are called conventional energy resources, e.g. fossil fuels, nuclear and hydro resources.

(b) Non-conventional: Energy resources, which are considered for large-scale use after the oil crisis of 1973, are called non-conventional energy sources, e.g. solar, wind, biomass, etc.

3. Based on Long-Term Availability: (a) Non-renewable: Resources, which are fine and do not get replenished after their

consumption, are called non-renewable e.g. fossil fuels, uranium etc. They are likely to deplete with time.

(b) Renewable: Renewable energy is energy obtained from sources that are essentially inexhaustible. Example of renewable resources includes wind power, solar power, geothermal energy, tidal power and hydroelectric power.

4. Based on Commercial Application: (a) Commercial Energy Resource: The energy sources that are available in the market for a

definite price are known as commercial energy. The most important forms of commercial energy.

(b) Non-Commercial Energy: The energy sources that are not available in the commercial market for a price are classified as non-commercial energy. Examples of non- commercial energy. Examples of non-commercial energy are firewood, agro waste in rural areas, and solar energy for water heating, animal power for transport, irrigation and crushing of sugarcane.

RENEWABLE SOURCES OF ENERGY:



There is a fear that the fossil fuels will get exhausted by the next century. Therefor, other forms of systems based on non-conventional and renewable source of energy are being tired by many countries. The renewable source of energy may be defined as energy sources which are continuously produced in nature and are essentially inexhaustible are called renewable energy sources.

1. Direct solar energy 2. Wind energy 3. Tidal energy 4. Hydel energy 5. Ocean thermal energy 6. Bio energy 7. Geo thermal energy 8. Fuel wood 9. Fuel cells 10. Solid wastes 11. Hydrogen

Wind energy: Wind energy is the energy contained in the force of the winds blowing across the

earth surface. Wind energy is defined as the kinetic energy associated with the movement of large masses of air over the earth’s surface. The circulation of the air in the atmosphere is caused by the non-uniform heating of the earth’s surface by the sun. The air immediately above warm area expands and becomes less dense. It is then forced upwards by a cool denser air which flows in from the surrounding areas causing wind. Power in the wind:

Wind possesses kinetic energy by virtue of its motion. Any device capable of slowing down the mass of moving air, like a sail or propeller, can extract part of this energy and convert into useful work. The kinetic energy of one cubic meter of air blowing at a velocity V is given by,

In one second, a volume element of air moves a distance of V m. The

total volume crossing a plane, one square meter in area and oriented normal

to the velocity vector in one second is therefore V m3. The rate at which

the wind energy is transferred, i.e., wind power is given by,

No device, however well designed can extract all the wind energy because the wind

would have to be brought to halt and this through the rotor. It has been found that for maximum power output the exit velocity is equal to one-third of the entrance velocity. Thus a maximum of 60% of the available energy in the wind is converted into mechanical energy.



Wind energy conversion: A windmill is the oldest device built to convert the wind energy into

mechanical energy used for grinding, milling and pumping applications. It

consists of a rotor fitted with large sized blades. Now improvement in

performance is achieved by applying sound engineering and aerodynamic

principles. Nowadays the wind energy is used to produce electrical energy.

Wind energy is converted into mechanical energy in wind turbines. These

wind turbines are coupled to generators electrical energy.

Hydro Power Plant:

In hydroelectric power plants the potential energy of water due to

its high location is converted into electrical energy. The total power

generation capacity of the hydroelectric power plants depends on the head

of water and volume of water flowing towards the water turbine. The hydroelectric power plant, also called as dam or hydro power plant, is used for generation of electricity from large river that has sufficient quantity of water throughout the river. In certain cases where the river is very large, more than one dam can built across the river at different locations. Working Principle of Hydroelectric Power plant The water flowing in the river possesses two type of energy: (1) The kinetic energy due to flow of water and (2) Potential energy due to the height of water. In hydroelectric power and potential energy of water is utilized to generate electricity.



NON-RENEWABLE ENERGY SOURCES: Energy sources which have been accumulated over the ages and not quickly replenish able when they are exhausted. 1. Fossil fuels. 2. Nuclear fuels.

Working principle of a nuclear power station The schematic diagram of nuclear power station is shown in A generating station in which nuclear energy is converted into electrical energy is known as nuclear power station. The main components of this station are nuclear reactor, heat exchanger or steam generator, steam or gas turbine, AC generator and exciter, and condenser.

The reactor of a nuclear power plant is similar to the furnace in a

steam power plant. The heat liberated in the reactor due to the nuclear

fission of the fuel is taken up by the coolant circulating in the reactor.

A hot coolant leaves the reactor at top and then flows through the tubes of

heat exchanger and transfers its heat to the feed water on its way.

The steam produced in the heat exchanger is passed through the

turbine and after the work has done by the expansion of steam in the

turbine, steam leaves the turbine and flows to the condenser. The

mechanical or rotating energy developed by the turbine is transferred to

the generator which in turn generates the electrical energy and supplies to

the bus through a step-up transformer, a circuit breaker, and an isolator.

Pumps are provided to maintain the flow of coolant, condensate, and feed

water.



Questions:

1. What are the classifications of energyresources? 2. What are conversions of energy? 3. Write a brief notes on the following

i. Fossil fuels energy ii. Nuclear energy

iii. Hydro energy iv. Solar energy v. Wind energy

vi. Biomass energy vii. Geothermal energy

viii. Tidal Energy ix. Ocean thermal energy x. Ocean wave energy

4. What are renewable and non-renewable resources?



THERMODYNAMICS

Syllabus: Thermodynamics: Thermodynamic Principles and Laws

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INTRODUCTION:

Thermodynamics is an axiomatic science which deals with the relations among heat, work and properties of system which are in equilibrium. It describes the state and the change in state of physical systems.

Thermodynamics basically entails four laws or axioms, known as Zeroth, First, Second and Third law of Thermodynamics.

Zeroth law deals with thermal equilibrium and establishes a concept of temperature. First law throws light on the concept of internal Energy. Second law indicates the limit of converting heat into work and introduces the principle

of increase of entropy. Third law defines absolute zero of entropy (low temp to higher temp with external

agent). Importance of Thermodynamics:

IMPORTANT TERMS AND DEFINITIONS:

System: A system is the finite quantity of matter or a prescribed region of space.

Boundary: The actual or a hypothetical envelope enclosing the system is known as boundary of the system.

Closed System: If the boundary of the system is impervious to the flow of matter it is called a closed system.

Open System: An open system is one in which matter flows or out of the system.

Isolated System: A neither system that exchanges nor matter with any other system or with environment is known as isolated system.

Adiabatic System: An adiabatic system is one which is thermally insulated from surrounding, i.e., it does not exchange hear with surroundings.

Isothermal System: An isothermal system is one which maintains constant temperature.



Isobar System:An isobar system is one which maintains constant temperature.

Intensive Properties: Intensive Property is that property which does not depend on mass of the system, e.g. pressure, temperature.

Extensive Property: Extensive Property is related with mass of the system, e.g. volume, energy

Phase: A phase is quantity of matter which is homogeneous throughout in chemical composition and physical structure.

Homogeneous System: A system which consists of single phase is termed as homogeneous system

Heterogeneous System: A system which consists of two or more phases is called Heterogeneous System.

Point Function: The state of substance in equilibrium may be represented by a point on any co-ordinate axis corresponding pressure, temperature, specific volume etc. These properties are point functions.

Path Function: The items such as heat and work are not independent of the type of the process. Hence these are called as path functions.

State: Each unique condition of the system is known as a state.

Process: A Process occurs when the system undergoes a change in state or an energy transfer at a steady state.

Cycle: Any process or series of processes whose end states are identical is termed as a cycle.

Irreversible Process: An irreversible process does not trace the same path when reversed.

Thermal Equilibrium: In thermal equilibrium, the temperature will be the same at all points of the system and does not change with time.

Mechanical Equilibrium: In this there are no unbalanced forces within the system.



Chemical Equilibrium: In chemical equilibrium, no chemical reaction takes place in the system and chemical composition which is same throughout the system does not vary with time.

Thermodynamic Equilibrium: A system is in thermodynamics equilibrium if it has achieved the thermal, chemical and mechanical equilibrium.

THERMODYNAMIC LAWS:

1. ZEROTH LAW OF THERMODYNAMICS

The zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

or

If a body A, be in thermal equilibrium with two other bodies, B and C, then B and C are in thermal equilibrium with one another.

2. FIRST LAW OF THERMODYNAMICS

In early part of nineteenth century scientists developed the concept of energy and hypothesis that “energy can neither be created nor destroyed”, which came to be known as law of

conservation of energy.

The first law of thermodynamics can be stated as, “when a system undergoes a

thermodynamic cycle then the net heat supplied to the system from the surroundings is equal to the network done by the system on its surroundings”.

ʃ dQ = ʃ dW

Where ʃ represents the sum for a complete cycle

Q = W

ΔQ = ΔW

Hence, ΔQ - ΔW = ΔE

Performance of Heat engine:

A heat engine is used to produce maximum work from a given positive heat transfer. The measure of success is called the thermal efficiency of the engine and is defined by the ration of

ɳ = W/Q

Where W= net work transfer from engine

Q = heat transfer to the engine

3. SECOND LAW OF THERMODYNAMICS:

Before going for the second law of thermodynamics, let us highlight the shortcomings of first law of thermodynamics.

https://en.wikipedia.org/wiki/Thermodynamic_systems

https://en.wikipedia.org/wiki/Thermal_equilibrium



Limitations of First Law of Thermodynamics: First law does not provide a clear idea about the direction of absorption or evolution of heat. The information provided by the first law of thermodynamics are not enough to predict the spontaneity or feasibility of a process.

There are two classical statements of the second law of thermodynamics, known as Kelvin-Planck statement and Clausisus statement.

Kelvin-Planck statement: “It is impossible to construct an engine, which while operating in

a cycle produces no other effect except to extract heat from a single reservoir and do equivalent amount of work”.

Clausisus Statement: “It is impossible for a self-acting machine working in a cyclic process unaided by any external agency, to convey heat from a body at a lower temperature to a body at a higher temperature”.

Entropy is an extensive property of a substance and is designated as S. It may be defined for a reversible process in accordance with the relation:

ds= (δQ/T) rev

or Incremental Entropy = ratio of heat exchange and absolute temperature

Enthalpy: Enthalpy is the most important thermodynamic properties of the substance which is the sum of internal energy (U) and workflow (pV) and is denoted by H.

H= U+ pV

4. THIRD LAW OF THERMODYNAMICS:

The third law of thermodynamics is stated as follows, regarding the properties of systems in equilibrium at absolute zero temperature.

“The entropy of a perfect crystal at absolute zero is exactly equal to zero”.

Questions:

1. What is Thermodynamics and give its importance? 2. Define System, its constituents, Types of systems with a neat sketch and examples. 3. Define the following

i. Phase ii. Thermodynamic equilibrium

iii. Intensive and extensive properties iv. Homogeneous and Heterogeneous state v. Cycle and irreversible cycles

4. What are thermodynamic laws and give their significance? 5. What is Zeroth law of thermodynamics? 6. What is First law of thermodynamics and give its limitations? 7. What is Second and Third law of thermodynamics. 8. Give Kelvin-Planck and Clausisus statements. 9. Define Entropy and its significance.



IC ENGINES

Internal Combustion Engines: Classifications, basic engine components and nomenclature, working principle, four-stroke and two-stroke petrol and diesel engines, comparison of CI and SI engines, comparison of four stroke and two stroke engines, simple problems such as indicated power, brake power, friction power, specific fuel consumption, brake thermal efficiency, indicated thermal efficiency and mechanical efficiency.

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INTRODUCTION

An Internal Combustion (I.C.) engine is basically a heat engine in which combustion takes place inside the engine. The fuel supplies the thermal (heat) energy when it burns inside the I.C. engine. E.g. petrol engine, diesel engine etc. An engine in which combustion takes place outside the engine is called External Combustion (E.C.) engine. E.g. Steam engine.

Many experimental engines were developed till 1878. But the breakthrough in engine technology was achieved when German engineer Otto built the famous Otto (petrol-operated) engine.

Car Engine Diesel Engine

THE BASIC PRINCIPLE OF OPERATION

The basic mechanism used in an IC engine is a piston which moves linearly inside the engine cylinder and force is applied on this piston due to fuel combustion. Due to this force acting on the piston, the piston moves and hence work is done which is utilized in various domestic and industrial applications. The reciprocating motion (linear motion) of the piston is converted into rotary motion with the help of linkages.

APPLICATIONS OF IC ENGINES

1. They find wide applications in transportation in the form of road, rail, airway and water way engines.



2. They are used in electrical power generation. 3. They are used in civil engineering (construction) and industrial applications. 4. IC engines have replaced steam engines used in transportation. 5. They are efficient than boilers since they are light in weight. CLASSIFICATION OF I.C. ENGINES

IC engines are classified based on: i. Nature of Thermodynamic cycle as: 1. Otto Cycle engine. 2. Diesel engine. 3. Dual combustion cycle engine.

ii. Type of Fuel used as: 1. Petrol Engine 2. Diesel engine. 3. Gas engine. 4. Bi-fuel engine.

iii. Number of strokes as: 1. Four stroke engine. 2. Two stroke engine.

iv. Method of ignition as: 1. Spark ignition engine, known as S.I engine. 2. Compression ignition engine, known as C.I. Engine.

v. Number of cylinders as: 1. Single cylinder engine. 2. Multi cylinder engine.

vi. Position of Cylinder as: 1. Horizontal engine. 2. Vertical engine. 3. V- engine. 4. Opposed cylinder engine. 5. Radial engine.

vii. Method of cooling as: 1. Air cooled engine. 2. Water cooled engine.

viii. Applications: 1. Stationary engines 2. Mobile engines. Parts of I.C. Engines:

Parts of IC Engine

1. Cylinder: The heart of the engine is the cylinder in which the fuel is burnt and the power

is developed. The inside diameter is called bore. To prevent the wearing of cylinder



block, a sleeve will be fitted tightly in the cylinder. The piston reciprocates inside the cylinder.

2. Piston: The piston is a close fitting hollow cylindrical plunger moving to-and-fro in the

cylinder. The power developed by the combustion of the fuel is transmitted by the piston to the crankshaft through the connecting rod.

3. Piston rings: The piston rings are the metallic rings inserted into the circumferential

grooves provided at the top end of the piston. These rings maintain a gas-tight joint between the piston and the cylinder while the piston is reciprocating in the cylinder. They also help in conducting the heat from the piston to the cylinder.

4. Connecting rod: It is a link that connects the piston and the crankshaft by means of pin

joints. It converts the rectilinear motion of the piston into 5. Crank and crankshaft: The crank is lever that is connected to the end of the connecting

rod by a pin joint with its other end rigidly connected to a shaft called crankshaft. It rotates about the axis of the crankshaft and causes the connecting rod to oscillate.

6. Crank case: It is the lower part of the engine serving as an enclosure for the crankshaft

and also sump for the lubricating oil. 7. Valves: The valves are the devices which controls the flow of the intake and the exhaust

and from the cylinder. They are also called poppet valves. These valves are operated by means of cams driven by crankshaft through a timing gear and chain.

8. Fly wheel: It is a heavy wheel mounted on the crankshaft of the engine to maintain

uniform rotation of the crankshaft. I.C. ENGINE TERMINOLOGY:

1. Stroke: It is the distance travelled by the piston from the cover end to the crank end or from crank end to the cover end. It is denoted by L.

2. Bore: It is the diameter of the cylinder or outer diameter of the piston. It is denoted by D. 3. Top dead centre (TDC) or cover end: It is the extreme position of the piston, when the

piston is near cylinder head.



4. Bottom dead centre (BDC) or crank end: It is the extreme position of the piston, when the piston is near the crankshaft end.

5. Swept volume (Vs): It is the volume covered by the piston when the piston moves from TDC to BDC. It is denoted by Vs and is given by,

6. Clearance volume (Vc): It is the volume occupied by the charge at the end of

compression stroke when the piston is at TDC. 7. Compression ratio (C.R): It is the ratio of total volume of the cylinder to the clearance

volume. i.e., CR or r = Total volume/clearance volume

8. Piston speed: The total linear distance travelled by the piston per unit time is called

piston speed. It is expressed in m/min and is given by, Piston speed = 2LN m/min L = length of stroke in m

N = speed of the engine in rpm.

TWO - STROKE ENGINE: A 2 stroke engine performs only TWO strokes to complete one cycle. Crankshaft makes only one revolution to complete the cycle. The power is developed in every revolution of the crankshaft. Based on the type of fuel used they are classified as



1) 2-Stroke Petrol engine 2) 2-Stroke Diesel engine Two-Stroke Petrol Engine: The 2-stroke engine cylinder has inlet, exhaust and transfer ports on its circumference, as shown in figure.

Inlet port – admits fresh air-fuel mixture (charge) into the crankcase. Transfer port – transfers the charge from the crankcase into the cylinder. Exhaust port – discharges the burnt gases from the cylinder.

These ports are opened and closed by the reciprocating piston. The connecting rod and the crank convert the reciprocating motion of the piston into the rotary motion of the crankshaft.

Two Stroke Engine Parts

FIRST STROKE: Piston moves from TDC to BDC. The spark plug ignites the compressed petrol and air mixture (charge). The hot gases are released during combustion increasing the pressure in the cylinder which forces the piston downwards. The piston moves downwards performing the power stroke until the top of the piston uncovers the exhaust port. The burnt gases escape through the exhaust port. As the piston descends it covers the inlet port and uncovers the transfer port and charge flows from crankcase into the cylinder. This charge entering the cylinder drives out the remaining burnt gases through the exhaust port and the process is called scavenging. This process continues till the piston covers both exhaust & transfer port during the next ascending stroke. The crankshaft rotates by half rotation. SECOND STROKE: Piston moves from BDC to TDC. As the piston ascends, it covers the transfer port and the supply of charge to the cylinder is cut-off. Further upward movement covers exhaust



port and compression of the charge begins. In the meantime, inlet port opens and fresh charge enters the crankcase. Further ascend of piston will compress the charge in the cylinder. The compression ratio ranges from 7:1 to 11:1. After piston reaches TDC first stroke repeats again. The crank rotates by half rotation.

Fig. Two Stroke Petrol Engine

2-STROKE DIESEL ENGINE: The 2-stroke engine cylinder has inlet, exhaust and transfer ports on its circumference, as shown in fig.

Inlet port – admits fresh air into the crankcase. Transfer port – transfers Exhaust port – discharges the burnt gases from the cylinder.

These ports are opened and closed by the reciprocating piston. The connecting rod and the crank convert the reciprocating motion of the piston int FIRST STROKE: (Diesel engine) Piston moves from cover TDC to BDC. The injector injects a metered quantity of the diesel oil into the cylinder as a fine spray. The high temperature of compressed air ignites the injected diesel oil. The hot gases are released during combustion increasing the pressure in the cylinder which forces the piston downwards. The piston moves downwards performing the power stroke until the top of the piston uncovers the exhaust port. The burnt gasses escape through the exhaust port.



As the piston descends it covers the inlet port and uncovers the transfer port and air flows from crankcase into the cylinder. This air entering the cylinder drives out the remaining burnt gases through the exhaust port and the process is called piston covers both exhaust & transfer port during the next ascending stroke. The crankshaft rotates by half rotation.

SECOND STROKE: (Diesel engine) Piston moves from BDC to cover end TDC. As the piston ascends, it covers the transfer port and the supply of air is cut-off. Further upward movement covers exhaust port and compression of the air begins. In the meantime, inlet port opens and fresh air enters the crankcase. Further ascend of piston will compress the petrol and air mixture in the cylinder. The compression ratio ranges from 20:1 to 22:1. After piston reaches cover end first stroke repeats again. The crank rotates by half rotation.

Fig. Two Stroke DieselEngine

4-STROKE PETROL ENGINE: (S. I. ENGINE) Petrol engines works on the principle of theoretical Otto cycle, also known as cycle. It consists of cylinder, piston, connecting rod, crank, crankshaft, inlet valve, exhaust valve and spark plug. The spark plug fitted at the top of the cylinder initiates the ignition of the petrol, hence the name spark ignition engine.



1. SUCTION STROKE:

During this stroke the piston moves from TDC to BDC. The inlet valve is open and exhaust valve is closed. The crankshaft rotates by half a rotation. As the piston moves downwards, suction is created in the cylinder, as a result, fresh air-petrol mixture is drawn into the cylinder through the inlet valve. At the end of this stroke, the piston is in BDC, the cylinder is filled with air mixture and inlet valve closes.Horizontal line AB on the P-V diagram

2. COMPRESSION STROKE:

During this stroke the piston moves from BDC to TDC. Both the inlet valve and exhaust valves are closed. The crankshaft rotates by half a rotation. As the piston moves upwards, the fuel mixture in the cylinder will be compressed. The ratio of compression ratio in petrol engines ranges from 7:1 to 11:1, represented by the BC curve in the P-V diagram.



When the piston reaches TDC, the spark plug ignites the fuel mixture. Since the spark plug ignites the fuel (air-petrol), this type of engine is also called as spark ignition or S.I Engine. The combustion of fuel takes place increasing the pressure at constant volume, represented by the line CD in the P-V diagram.

3. WORKING OR POWER STROKE:

During this stroke the piston moves from TDC to BDC. Both the inlet valve and exhaust valves are closed. The crankshaft rotates by half a rotation. The high pressure of the burnt gases forces the piston downwards performing power stroke. The linear motion of the piston is converted to rotary motion of the crankshaft by connecting rod and crank. It is represented by curve on DE on PV diagram.

At the end of the stroke, the piston is in BDC, the exhaust valve opens which release the burnt gases to the atmosphere. This will bring pressure in the cylinder to atmospheric at constant volume, represented by the line EB in the P-V diagram.

4. EXHAUST STROKE:

During this stroke the piston moves from BDC to TDC. The inlet valve is closed and exhaust valve is open. The crankshaft rotates by half a rotation. As the piston moves towards the TDC, the burnt gases will be expelled out through the exhaust valve. Line BA on the P-V diagram. When the piston reaches the TDC, the exhaust valve closes and this completes the cycle.

4 STROKE DIESEL ENGINE: (C. I. ENGINE):

Diesel engines works on the principle of theoretical Diesel cycle, also known as constant pressure cycle. It consists of cylinder, piston, connecting rod, crank, crankshaft, inlet valve, and exhaust valve and fuel injector. The fuel injector fitted at the top of the cylinder supplies the measured quantity of diesel at high pressure.



Fig. Four Stroke Diesel Engine

1. SUCTION STROKE:

During this stroke the piston moves from TDC to BDC. The inlet valve is open and exhaust valve is closed. The crankshaft rotates by half a rotation. As the piston moves downwards, suction is created in the cylinder, as the end of this stroke, the piston is in BDC, the cylinder is filled with air and inlet valve closes. Horizontal line AB on the P-V diagram.

2. COMPRESSION STROKE:

During this stroke the piston moves from BDC to TDC. Both the inlet valve and exhaust valves are closed. The crankshaft rotates by half a rotation. As the piston moves upwards, the air in the cylinder will be compressed. The ratio 22:1, represented the BC curve in the P temperature increases and attains a temperature greater than the ignition temperature of diesel. Diesel is sprayed into the cylinder through the fuel injector.

During this stroke the piston moves from TDC to BDC. The inlet valve is open and exhaust valve is closed. The crankshaft rotates by half a rotation. As the piston moves downwards, suction is created in the cylinder, as a result, fresh air is drawn into the cylinder through the inlet valve. At the end of this stroke, the piston is in BDC, the cylinder is filled with air and inlet valve closes. Horizontal line AB on the P-V diagram.

The high temperature of the air ignites the diesel as soon as it is sprayed and undergoes combustion at constant pressure. Line CD on the P-V diagram. Since the compresses air ignites the diesel, this type of engine is also called as compression ignition or C.I Engine.

3. WORKING OR POWER STROKE:

During this stroke the piston moves from TDC to BDC. Both the inlet valve and exhaust valves are closed. The crankshaft rotates by half a rotation. The high pressure of the burnt gases forces the piston downwards performing power stroke. The linear motion of the piston is converted to rotary motion of the crankshaft by connecting rod and crank. It is represented by curve DE on PV diagram. At the end of the stroke, the piston is in BDC, the exhaust valve opens which release the burnt gases to the atmosphere. This will bring pressure in the cylinder to atmospheric at constant volume, represented by the line EB in the P-V diagram.

4. EXHAUST STROKE:



During this stroke the piston moves from BDC to TDC. The inlet valve is closed and exhaust valve is open. The crankshaft rotates by half a rotation. As the piston moves towards the TDC, the burnt gases will be expelled out through the exhaust valve. Line BA on the P-V diagram. When the piston reaches the TDC, the exhaust valve closes and this completes the cycle.

In 4 stroke engine, the 4 strokes constitute one cycle, hence the name 4 stroke cycle engine. The crankshaft makes two revolutions to complete one cycle. The power is developed in every alternate revolution of the crankshaft. 4 Stroke diesel engines produce higher power than 4 Stroke petrol engines.

COMPARISON OF 4 STROKE AND 2 STROKE ENGINE:

S.No. PRINCIPLE 4 STROKE 2 STROKE 1. Number of strokes per

cycle Four Two

2. Uses Cars, trucks, tractors, jeeps, buses, etc.,

Mopeds, scooters, motor cycles, etc.,

3. Power Developed In every alternate revolution of the crankshaft

In every revolution of the crankshaft

4. Flywheel Heavy Light 5. Admission of charge Directly to the engine

cylinder First to the crankcase & then transferred to the engine cylinder

6. Exhaust gases Driven through the outlet during exhaust stroke

Driven out by scavenging operation

7. Valves Opened & closed by mechanical valves

Opened & closed by piston

8. Noise Less High 9. Lubricating oil

consumption Less More

10. Fuel consumption Less More 11. Mechanical efficiency Low High

COMPARISON OF PETROL AND DIESEL ENGINE:

S.No. Principle Petrol Engine Diesel Engine 1. Cycle of operation Otto cycle (constant volume) Diesel cycle (constant

pressure) 2. Fuel used Petrol Diesel 3. Admission of fuel During suction stroke At the end of

compression stroke. 4. Charge drawn during

suction Air and petrol mixture Only air

5. Compression ratio 7:1 to 12:1 16:1 to 22:1 6. Type of ignition Spark ignition Compression or auto

ignition 7. Uses Scooter, motor cycle, car,

etc., Trucks, tractors, buses, etc.,



8. Engine speed High about 7000rpm Low from 500 to 3000rpm

9. Power output capacity Less More 10. Thermal efficiency Less High 11. Noise & vibration Almost nil High 12. Weight of the engine Less High 13. Initial cost Less More 14. Operating cost High Less 15. Maintenance cost Less Slightly higher 16. Starting of the engine Easily started Difficult to start in cold

weather 17. Exhaust gas pollution More Less

PERFORMANCE OF IC ENGINES

1. Mean effective pressure (MEP): The mean effective is defined as mean or average pressure acting on a piston throughout the power stroke. It is also the average pressure developed inside the engine cylinder of an IC engine. It is expressed in Bar.

( 1 bar = 105 N/m2) pressure of an engine.

The mean effective pressure of an engine is obtained diagram. The indicator diagram is the P-V diagram for one cycle at that load, drawn with the help of an indicator fitted on the engine. The indicated mean effective pressure is then calculated using the equation:

2. Indicated Power (IP): Indicated power is defined as the total power developed inside the engine cylinder due to combustion of fuel. It denoted by IP and is expressed in kW.

Where n = number of cylinders

Pm = Indicated mean effective pressure in Bar or in N/m2

L = Length of the stroke in m

A= Cross – sectional area of the cylinder in m2

A = πd2 / 4, where d = diameter of the cylinder bore or in m



N = engine speed in rpm

K =1/2 for 4-stroke engine

= 1 for 2 stroke engine.

3. Brake Power (BP): The net power available at the crank shaft of the engine for performing useful work is called brake power. It is denoted by BP and expressed in kW.

Where

N = Speed of the engine in rpm

Torque is measured by using either belt or rope brake dynamometer.

W = Net load acting on the brake drum, kg

R = Radius of the brake drum, m

T = Torque in N – m = W x R

4. Friction power (FP)= Indicated power – Brake power.

5. Mechanical Efficiency (ME): It is the efficiency of the moving parts of mechanism transmitting the indicated power to the crankshaft. Therefore it is defined as the ratio of the brake power and the indicated power. It is expressed in percentage.

6. Thermal Efficiency (TE): It is the efficiency of the conversion of the heat energy produced by the actual combustion of the fuel into the power output of the engine. Therefore it is defined as the ratio of power developed by the engine by the fuel in the same interval of time. It is expressed in percentage.

7. Brake Thermal Efficiency (BTE):It is defined as the ratio of the brake power to the heat

supplied by the fuel. It is expressed in percentage.



Where m = mass fuel supplied, kg/s CV = Calorific value of the fuel, kJ/kg BP = Brake power, kW

8. Indicated thermal efficiency (ITE): is defined as the ratio of brake power to the heat supplied by the fuel. It is expressed in percentage.

9. Specific fuel consumption (SFC): SFC is defined as the amount of fuel consumed by an

engine for one unit of energy that is produced. SFC is used to express the fuel efficiency of an IC engine. It measures the amount of fuel required to provide a given power for a given period. It is expressed in kg/MJ or kg/kW – hr. Questions: 1. What is an IC Engine and what are its applications? 2. What are the classifications of IC Engines? 3. Explain the basic components of IC Engines with a neat sketch. (or) Explain the terminology of IC Engines. 4. List out the difference between two-stroke and four-stroke. 5. Write the difference between Diesel and Petrol Engine. 6. Explain the working of two-stroke diesel and petrol engine with a neat sketch. 7. Explain the working of four-stroke diesel and petrol engine with a neat sketch. 8. Explain the working of any type of IC Engine with a neat sketch. 9. Define Suction stroke, Compression Stroke, Power Stroke and Exhaust Stroke. 10. Define the following MEP, IP, BP, FEP, ME, ITE, SFC.



Four Stroke

Two Stroke

All components 3D-View

energy sources syllabus: energy resources introduction

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