thermodynamic - andhra pradesh board of intermediate …bieap.gov.in/pdf/metpaperii.pdf · ·...

1.1 Introduction

1.2 Thermo dynamics

1.3 Types of System

1.4 Properties of Thermodynamics

1.5 Pressure

1.6 Volume

1.7 Temperature

1.8 Enthalpy

1.9 Atmospheric Pressure

1.10 Internal Energy

1.11 Specific heat

1.12 Summary

Learning ObjectivesAfter studying this chapter you will be able to know

1UNIT

ThermodynamicStructure

Mechanical Engineering Technician176

• Meaning of System in Thermodynamics.

• Types in thermodynamics Systems.

• About Pressure, Volume, Temperature, Enthalpy, atmospheric pressure,Internal energy, Specific heat

1.1 Introduction Thermodynamics is branch of science that deals transformation of energy

from one form to another.

Thermodynamics deals with the behaviour of gases and vapours whensubjected to variations of temperature and pressure and relationship betweenheat energy and mechanical energy.

1.2 Thermodynamics SystemA system in a prescribed region of space with definite boundary which

contains quantity of matter whose behaviour is to be studied

Fig. 1.1

Boundary : The actual envelope enclosing the system is the boundary.

Surrounding : Everything outside the system which has direct bearing onits behaviour is known as surrounding.

1.3 Types of Thermodynamics SystemsThere are three types of systems

1. Closed System.

2. Open System.

3. Isolated System.

Paper - II Mechanical Technology 177

Closed Systems : In closed system transfer of energy takes place i.ework and heat. But transfer of mass does not takes place.

Example 1. Compression of gas in a piston cylinder 2. Refrigerator ,3 heating of water in a chemical vessel.

Open System : In Open System both mass and energy transferred betweenthe system and surroundings.

Example: 1.Gas Turbine 2. Boiler delivering system 3 .Steam turbine.

Isolated System : An Isolated system cannot exchange both energy andmass with its surroundings. System and surrounding together form a universe.

1.4 Properties of Thermodynamics SystemsThe exact condition of a substance is called its state and variable. which

determine the state are known as its properties. The principal properties arepressure, Volume, Temperature, Internal energy, enthalpy and entropy. Thefundamental properties are pressure, volume an temperature.

There are two types of properties.

1. Intensive Properties.

2. Extensive Properties.

Intensive Properties. These properties do not depend on the mass of thesystem. Example: Temperature and pressure.

Extensive Properties. These properties depend on its mass of thesystem.Example: Volume.

Definitions of Properties

1.5 PressurePressure is a force applied over a unit area. In MKS system. the unit of

area is the square meter and the pressure is measured in kilograms per squaremeter {kg/m2}

Engineers measure pressure in kilograms per square centimetres {kg/cm2}In SI system the unit for pressure is the force one newton {N} Acting on asquare meter area {N/M2}

1.6 Volume (V)

Volume is defined as the space which the substance occupies and it ismeasured in cubic meter (m3)


1.7 TemperatureThe temperature of a substance may be define as measure of hotness or

degree of coldness, of a body. A body is said to be hot when it has a relativelyhigh temperature, it is said to be cold when it has relatively low temperature.ordinary temperatures are measured by thermometers. Very high temperaturesare measured by pyrometers it is measured in oC, oK, oF.

1.8 Enthalpy It is also called as total heat. Enthalpy is an energy term and is denoted by

H therefore H=U+PV

Where U is the internal energy, P is absolute pressure, and V is the volume.

1.9 Atmospheric PressureThe Atmospheric Surroundings the earth exerts a pressure in its surface,

Equivalent to its weight of air over a unit area of the earth’s surface is calledAtmospheric Pressure. The pressure of its atmospheric is recorded by a barmeter.

1.10 Internal Energy Internal Energy of a substance may be defined as the algebraic sum of

internal kinetic energy and the internal potential energy of its molecules.

If the temperature of a gas increased the molecular activity increases, sothe temperature decreased the molecular activity decreased, so the internal energyincreases if the temperature is decreased then the molecular activity decreased.

1.11Specific HeatThe Specific Heat of a substance may be defined as the amount of heat

that must be supplied to the substance to raise the temperature of unit mass ofthe substance through one degree

Specific Heat K=dq/ dT

Where dq is heat supplied per unit mass. dT is change in its temperature.

Test Your Understanding - IState with reasons whether the following statements are TRUE or FALSE

i) Thermodynamics is an science which deals with therelations among heat, work and properties of system.

ii) In Open system mass flows out of the system.


iii) The properties which do not depends on the mass of the system areknown as Extensive Properties.

iv) The properties which depends on the mass of the system are known asIntensive Properties.

v) If temperature increases internal energy decreased.

Terms Introduced in the Chapter1. Systems

2. Surroundings

3. Boundary

4. Enthalpy .

5. Atmospheric Pressure .

1.12 Summary1. Thermodynamics is an science which deals with the relations among

heat, work and properties of systems which are in equilibrium.

2. A system is a finite quantity of matter or a prescribed region ofspace.

3. If temperature increases internal energy increases.

4. The total heat of substance is known as enthalpy.

Questions for Practice1. Explain the terms system surrounding and boundry?

2. Explain the closed systems?

3. Explain the open systems?

4. Explain the isolated system?

5. Explain the terms pressure and temperature?

6. Explain the terms enthalpy and internal energy?

7. Explain the intensive properties?

8. Explain the extensive properties?


2.1 Introduction,

2.2 Zeroth Law of thermodynamics

2.3 First law of thermodynamics

2.4 Second law of thermodynamics

2.5 Summary

Learning Objectives After studying this chapter you will be able to know:

How and when the heat transfers takes place.

How the ratio of mechanical work to heat is always constant

Why the self acting machine is impossible.

2.1 IntroductionLaws of Thermodynamics are natural or fundamental laws formulated on

the basis of natural observations. They are not derived from any mathematics.

Laws of Thermodynamics are 1) Zeroth law of thermodynamics, 2) Firstlaw of thermodynamics, 3) Second law of thermodynamics.

2UNIT

Laws of ThermodynamicStructure


2.2 Zeroth Law of ThermodynamicsThis law states that if two systems each are in thermal equilibrium to a third

system then they three are in thermal equilibrium.

Examples: if we take three bodies i.e. A,B,C. A bodies hotter then Bbodies, and bring them into contact, we shall find after some time that both thebodies are equally hot. And then we bring them the bodies A, and C. intocontact we shall find after some time that the three bodies are equally hot.

TA = TB

TA = TC

Therefore TB = TC

i.e TA = TB = TC

2.3 First Law of ThermodynamicsThis law is the same as the law of the conservation of energy .which states

that energy can neither be created nor destroyed. Energy can be convertedfrom one from into another form.

It was established by the joule that heat and mechanical energies are mutuallyconvertible. Joule established experimentally that there is a numerical relationbetween the unit of heat and the unit of work and this relation is symbolicallyexpressed by the letter J. This relation is known as the Joule’s equivalent ormechanical equivalent of heat. According to this relation

1 Kcal = 427 kg-m.

A

B C


2.4 Second Law of ThermodyanamicsThis law states that ” it is impossible for self acting machine. Unaided by

any external agency to convey heat from a body of low temperature to a bodyat higher temperature” i.e. heat cannot itself pass from a cold body to hot body.This statement is known as second law of thermodynamics.

Test your Understanding - IState with reasons whether the following statements are TRUE or FALSE.

1. When two bodies are in thermal equilibrium with a third body separatelythen they are also in thermal equilibrium with each other.

2. First law of thermodynamics derived form the principal of conservationof energy.

3. The heat passes from lower temperature to higher temperature.

Terms Introduced in the Chapter1. Thermal equilibrium.

2. Mechanical equivalent of heat.

3. Self acting machine.

2.5 Summary1. The ratio of mechanical work to heat is always constant. This constant

is called as joule’s mechanical equivalent of heat.

2. Heat cannot flow from a cold body to a hot body without the aid ofexternal work.

Questions of practice1. Explain zeroth law of thermodynamics?

2. Explain first law of thermodynamics?

3. Explain second law of thermodynamics?

Structure3.1 Introduction

3.2 Boyles Law

3.3 Charle’s law

3.4 Avagadro’s law

3.5 Joule’s law

3.6 Regnault’s law

3.7 Characterisitic Gas Equation

3.8 General gas equation

3.9 Summary

Learning Objectives After studying this chapter, you will be able to know.

How the gas is obtained from liquid.

How the perfect gas is formed.

What happens when the gas is heated at constant temperature.

What happens when the gas is heated at constant pressure.

3UNIT

Laws of Perfect Gases


What happens when the gas is heated at constant volume.

When the gases contain equal number of molecules.

When temperature increases what happen in internal energy.

3.1 IntroductionA gas is a state of a substance whose evaporation from its liquid state is

complete.

A Vapor is a state of a substance whose evaporation from its liquid state ispartial. A vapor becomes dry when it is completely evaporated. Any furtherheating of a dry vapor is termed super heating and such a state of the vapor istermed super heated. The behavior of a super heated vapor approaches that ofa perfect gas. From thermodynamic point of view substances like air, oxygen,nitrogen, hydrogen with in certain temperature limits are regarded as gases.

The behavior of a perfect gas undergoing changes of temperature andpressure is governed by certain laws.

1. Boyle’s Law

2. Charle’s Law

3. Avagadro’s Law

4. Joule’s Law

5. Regnault’s law

3.2 Boyle’s LawIt states that when the gas is heated at constant temperature, the volume of

a given weight of gas is inversely proportional to the absolute pressure. Hence,volume increases as the absolute pressure decreases and vice verse.

Volume = V

Pressure = P

Temperature = T (constant)

Therefore V P

V = C x 1/p (Where C = constant)

Therefore PV = C


Applying the above law for initial and final states

P1V1 =P2V2 = PV= Constant.

Problems 1 : 4 m3 of air compressed at constant temperature to a finalvolume of 0.6 m3. If the initial pressure is 50kg/m2. What will be the finalabsolute pressure of the air in kg/cm2?

Given : Initial volume V1 = 4m3

Final volume V2 = 0.6 m3

Initial pressure P1 = 50 kg / m2

Final pressure P2 = ?

At constant temperature P1V1 =P2V2

i.e. 50 x 4 = P2 * 0.6

= P2 = 200 / 0.6 = 333 kg / m2

The change of pressure from kg per m2 to kg/cm2. Divide kg/m2 by 10,000(10,000m2 =1m2

P2 =333/104=0.0333kg/cm2.

3.3 Charle’s LawIt states that if a gas is heated at constant pressure its volume varies directly

with the absolute temperature.

V ( where P = Constant)

Therefore V=CT (where C = Constant)

V/T = constant

Applying the above law for initial and final states.

V1 / T1 = V2 / T2 = V / T = C

or

V1 / V2 = T1 / T2

Charle’s law also express if a gas is heated at constant volume its pressurevaries directly with the absolute temperature.

P ( where V = Constant)

P = CT ( where C is constant)


P / T = C

Applying the above law for initial and final states.

P1 / T1 = P2 / T2 = C

P1 / P2 = T1 / T2 = C

Worked Examples

2. A gas of volume of 2 cub . m and temperature is 27c receives heat atconstant pressure so that final volume is 4 cub . m calculated final temperature?

Given : Initial volume V1 = 2 cub.m

Initial temperature T1 = 27oC = 27 + 273 = 300 oK

Final volume V2 = 4 cub - m

Final Temperature T2 = ?

Therefore at constant pressure V1 / T1 = V2 / T2

= 2 / 300 = 4 / T2

Therefore T2 = 4 x 300 / 2 = 600 oK

Therefore T2 = 600 - 273 = 327oC

3. Gas with an initial pressure of 4 kg/cm2 and initial temperature of 40oc isheated at constant volume until the final pressure becomes 12kg/cm2 calculatethe final temperature of the gas.

Given initial pressure P1 = 4 kg / cm2

Initial temperature T1= 40oc = 40 + 273=313 oK

Final pressure P1=1.2 kg / cm2

Final temperature T2=?

at constant volume

P1 / T1 = P2 / T2

4/313 = 12 /T2

Therefore T2 = 12 x 313 / 4 = 939oK

T2 = 939 - 273 = 666oC

Final Temperature T2 = 666oC


3.4 Avagadro’s LawIt states that equal volume of all gases at the same temperature and pressure

contains the same number of molecules.

Example: One cubic meter of oxygen (O2 ) contains the same number ofmolecules as one cubic meter of hydrogen (O2) at same temperature and pressure.

3.5 Joule’s LawIt states that the internal energy of a gas is depend only its temperature. If

temperature increases the internal energy increases. If temperature decreasethe internal energy also decrease. Internal not depends on pressure and volume.

3.6 Regnault’s LawIt states the specific heat of a perfect gas at constant pressure is constant

and its volume at const volume is also constant it means that the two specificheats of a perfect gas don’t change with change in temperature. The ratio of thetwo specific heats cp and cv of any given gas is a constant.

Cp / Cv = Constant

3.7 Characteristic Gas EquationPerfect gas can change its thermodynamics state the pressure, volume, and

temperature, may all be varied. This one equation can be derived by combininglaws of Boyle’s and charle’s.

Let a kilogram of gas can be initially at pressure P , volume V, and absolutetemperature T, at state represented by ‘A’.

In state C pressure P1, volume V1 and temperature T1 but this change passesthrough state B at constant temperature. The pressure is P1, volume is V1 andtemperature T. and then changes from state B to state C at constant pressure.

The change from state A to B at constant temperature which follows theBoyle’s law

P,VT

P1 V1

TP1 V1T1

Constant Constant

Temperature Pressure

A B C


PV = P1V1

Therefore V1 = PV / P1 ---> Equation 1

The change from B to C being at constant pressure which follows theCharle’s law.

V1/V1 = T / T1

V1 = T V1 / T1

Comparing the values of V1 from equation I and II

PV / P1 = TV1 / T1

Therefore PV / T = P1V1 / T1 ---> Equation 2

If mass remains unchanged PV/T is constant. This constant is designatedby R and is called the “characteristic Gas constant and its value is different fordifferent gases.

Then PV = RT

for m kg of gas PV = mRT

3.8 General Gas EquationConsider of one kg of perfect gas with P1,V1,and T1 as initial values

Then P1V1 / T1= mR = Constant

Then P1V1=mRT1

Then P1V1/T1= mR = constant --> Equation 1

For final condition of gas P2 V2 = mRT2

P2 V2 / T2 = mR = constant --> Equatin 2

From equation 1 and 2

P1 V1 / T1 = mR = P2 V2 / T2 = Constant

Therefore P1 V1 / T1 = P2 V2 / T2 = PV / T Constant

Test your understandingsState with reasons whether the following statements are TRUE or FALSE

1. When the gas is heated at constant temperature V P.

2. When the gas is heated at constant volume P1/T


3. When the temperature increases the internal energy decreases.

4. In general gas equation the boyle’s law and charle’s law are combinetogether.

5. General gas equation is P1 V1 / T1 = P2 V2 / T2= PV /T

Terms Introduced in the Chapter

1. Perfect Gas

2. Specific heat of gas at constant volume

3. Specific heat of gas at constant pressure

4. Characteristic equation

5. General gas equation

3.9 Summary1. Boyle’s law V 1/P.

2. Charle’s law VT or PT

3. CP / CV = Constant

4. Internal energy U T

5. Characteristic gas equation PV=mRT

6. General gas equation P1 V1 / T1 = P2 V2 / T2

Short Answer Questions1. Define perfect gas?

2. Explain the Boyle’s law?

3. Explain the Charle’s law ?

4. State the Regnaults law ?

5. Explain the Joule’s law?

6. Explain the Avagadro law?

Essay Type Question7. Explain the characteristic gas equation ?


Numerical questions1. Calculate the final pressure of a gas having volume of 4 cub.m and

pressure 8 bar. Which is heated at constant temperature when the final volumeis 8 cub.m?

Ans. (1.5 bar)

2. A gas of volume of 2 cub.m and temperature is 27oc receives heat atconstant pressure so that final volume is 4 cub.m. Calculate final temperature.

Ans. ( 327oC )

3. A gas of volume of 0.2 cub.m is compressed in a cylinder to finalvolume 0.02 cub.m and pressure is 60 bar. Initial temperature and pressure are27oC and 3 bar respectively. Calculate final temperature.

Ans. (327oC )

4.1 Introduction

4.2 Types of Thermodynamic process

4.2.1 Constant Volume process

4.2.2 Constant pressure

4.2.3 Constant Temperature process

4.2.4 Adiabatic process

4.2.5 Polytropic process

4.3 Summary

Learning ObjectivesAfter studying this chapter, you will be able to know :

• The changes in temperature, pressure, volume when the gas is expanded or compressed.

• How to calculate the work done at different thermodynamic process

• How to calculate the change in internal energy at different Thermodynamic process

4UNIT

Thermodynamic Process inGases

Structure


• How to calculate the heat supplied, at different thermodynamicprocess.

4.1 IntroductionA thermodynamic process is a change in the state of a working substance

as a result of flow of energy. During the flow of energy, a change take s place inproperties of the substance and also in energy forms.

4.2 The different thermodynamic process may be classified

1. Constant volume process

2. Constant pressure process

3. Isothermal process

4. Adiabatic process

5. Polytropic process

4.2.1 Constant Volume Process

When a gas is heated in an enclosed vessel there is no change in volume,but increase in pressure and internal energy.

(1)Work done : if there is no change in volume

Workdone W = 0

(2) Change in internal energy

2

1

p

P1

P2

V1=V2VolumeV

Pressure


V1

V2

U=U2-U1 = mcv (T2-T1)

3) Heat transferred

Q= W + U = O + mcv (T2-T1) = mcv (T2-T1)

All the heat supplied during this process will be stored in the gas asinternal energy

(4)Relation between P, V and T drawing

P1V1/T1=P2V2/T2

Volume = constant i.e. V1=V2

There P1/T1 = P2/ T2

4.2.2 Constant Pressure ProcessNormal Lines Change

When a gas is heated at constant pressure, the volume increases withtemperature. Some external work is done due to increase in volume.

1) Workdone W = P.dv

P-V Plane

21

p

P1 = P2

V1 V2V

Work done

--> V


= P dv

= P(V2- V1)

We know that PV = mRT

Therefore PV2 = mRT2

PV1 = mRT1

Therefore W=mRT2 - mRT1

= mR(T2-T1)

(2)Change in internal energy

U = mCv (T2-T1)

(3)Heat supplied

Q=mCp (T2-T1)

4) Relation between P V and T

P1V1 = P2V2

T1 T2

P = Constant (ie P1 = P2 )

V1 V2

T1 T2

or V1 T1

V2 T2

4.2.3 Iso Thermal Proess or Constant Temperature ProcessIn this process temperature remain constant during expansion or

compression of the gas. If temperature constant product of pressure and volumealso remain constant.

V1

V2

=

=


Workdone : When heat is added the process is an expansion and work isdone by the gas. When heat is rejected, the process is compression and work isdone on the gas.

Fig. 4.1 PV Diagram

Therefore W = Pdv

but PV=P1V1 = C

Therefore P=P1V1/V

Hence W = P1V1 dv

v

= P1V1 dv

v

= P1V1 loge V2 - log eV1

= P1V1 loge (V2/V1)

= P1V1 log er (Where r =expansion ratio)

2) Change in internal energy U :

In this process temperature is constant

therefore change in internal energy is zero

V1

V2

V1

V2

V1

V2


i.e. U=U2-U1 = 0

3) Heat supplied Q

Therefore Q= change in internal energy + work done.

= O + P1V1 log er

= Q = P1V1 log er

4) Relation between P,V and T

P1V1 P2V2

T1 T2

Temperature constant

T1=T2

Therefore P1V1 P2V2

4.2.4 Adiabatic Process or Isentropic processIn adiabatic process

• No heat is added or rejected during the process

• During expansion work done by the gas

• During compression work should be done on te gas

• The process must be friction less

Fig. 4.2 Adiabatic Process

=

PV Curve


1. Work done W = P1V1 - P2V2

where PV=mRT

Therefore W = mRT1 - mRT2

mR (T1-T2)

Change in internal energy

U = mcv (T2-T1)

3) Heat supplied Q

Q = 0

4) Relation between P, V and T

P1VP2V

P1 / P2 = (V2 / V1)

T1 / T2 = (V2 / V1)

Therefore T1 / T2 = (P1 / P2)

4.2.5 Polytropic Process

This process can be described by the general equation. PVn = Constant nis having any value between zero to infinity ‘n’ is called polytropic index.

Fig. 4.3 PV Diagram

PVn = Constant


1) Workdone

W =( P1V1 - P2V2 / n -1 ) kg - m

we know PV = mRT

Therefore W= (mRT1 - mRT2 / n-1 ) kcal

= mR(T1 - T2) / n-1) kcal

2) Change in internal energy

U = mcv (T2-T1) kcal

3) Heat supplied

Q = workdone + change in internal energy

= W + U

= (mR(T1 - T2) / n-1) + mCv(T2-T1) kcal

4) Relation between P,V and T

P1V1n =P2V2

n

P1 / P2 =(V2/V1)n = (r)n

T1 / T2 = (V2/V1)n-1 = (r)n-1

Therefore T1 / T2 = (P1/P2) n-1/n

Test Your Understanding

State with reasons whether the following statements are TRUE or FALSE

1. An constant volume process workdone gives some value.

2. An constant pressure process workdone is zero.

3. In isothermal process temperature is constant.

4. In isothermal process, changes in internal energy is zero.

5. In adiabatic process heat is supplied to the gas.

6. In polytropic process ‘n’ is the polytropic index having any value fromzero to infinity.

Terms Introduced in the Chapter

1. Polytropic index (n)


2. Isothermal process

3. Adiabatic process

4.3 Summary1. In constant volume process workdone is zero because there is no change

in volume.

2. In constant pressure process workdone W=mR(T2-T1) change in internalenergy = mCv(T2-T1).

3. In Isothermal process change in internal energy is zero.

4. In adiabatic process no heat leaves or enters the system.

5. Polytropic process is known as general law for the expansion andcompression of gases.

Short Answer Type Questions1. Write the different types of thermodynamic processes.

2. Draw the P-V diagram of the constant volume process.

3. Draw the P-V diagram of the constant pressure process.

4. Draw the P-V diagram of the adiabatic process.

5. What is the difference between Isothermal and adiabatic process.

Long Answer Type Questions1. Explain the constant volume process and derive an expression,

Workdone, change in internal energy, heat supplied and relation betweenP,V and T.

2. Derive all expressions for constant pressure process.

3. Explain and derive all expressions for Isothermal process.

4. Explain and derive all expressions for adiabatic process.

5. Explain and derive all expressions for polytropic process.



5.2 Types of Fuels

5.3 Merits and demerits of liquid fuels

5.4 Merits and Demerits of Gaseous Fuels

5.5 Summary

Learning ObjectivesAfter studying this chapter, you will be able to know,

• What is the fuel and how it works.

• Substances which are present in a fuel

• About types of fuels.

• About calorific values of different fuels

• How to obtained different fuels

• About merits and demerits of fuels

• What are the requirements of good fuel.

5UNIT

Fuels and Combustion


5.1 IntroductionFuel is mainly composed of carbon, hydrogen, compounds of hydrocarbons

and small amount of other substances, such as sulphur, oxygen, nitrogen, etc.These elements will combine with oxygen and burned. The burning of fuel isknown as combustion. The amount of heat liberated during combustion of onekg of fuel is known as calorific value of fuel. Fuels are used in industry forproduction of heat and light. This heat is converted into mechanical work.

Classification of Fuels

Fuels are mainly classified into

1. Solid fuels a) Natural b) Artificial

2. Liquid fuels a) Natural b) Artificial

3. Gaseous fuels a) Natural b) Artificial

5.2.1 Solid Fuelsa) Natural Solid Fuels

1) Wood 2) Peat 3) lignite or brown coal 4) Bituminous Coal 5)Anthracite Coal

b) Artificial or Prepared Solid Fuels

1) Charcoal 2) Coke 3) Pulverized coal

Wood

It is a good domestic fuel. In some cases it is used as industrial fuel forboiler furnace. It consists of mainly carbon and hydrogen. The disadvantage ofusing wood as afule is its large moisture content and low thermal value. Thewood is converted into coal when burnt in the absence of air. The calorific valueof wood is 3200 k cal / kg.

Peat

It may be regarded as the first stage at which the fuel derived from woodand vegetable matter is recovered from earth. It contains 20 to 30% of watertherefore it has to be dried before use. The calorific value of peat is about 3500kcal / kg.

Lignite or Brown Coal

It is intermediate in character and composition between peat and coal.They are in black or earthy brown in colour. It contains 35 to 40 percent moisture


and lower carbon. The calorific value of lignite is 5000 k cal / kg.

Bituminous Coal

It represents the next stage of lignite in the coal formation. It is shiny blackin appearance and it contains 65% carbon and 25 to 35% volatile matter. Thecalorific value of bituminous coal is about 7,300 k cal / kg. It burns with a longyellow and smoky flame.

Anthracity Coal

It represents the final stage in the coal formation and it contains 90% carbonwith a very little volatile matter. It is smokeless and gives very little flame. Itscalorific value is about 8800 k cal / kg. It is usefull for steam raising and generalpower purposes.

5.2.2 Artificial or Prepared Solid Fuels

Charcoal

It is made by heating wood in absence of air or with limited supply of air atabove temperature of 3000c. the char coal produced. It contains about 90%carbon and its calorific value is 6,800 kcal/kg.

Coke

It is made from bituminous coal by heating continuously for 42 to 48 hoursin the absence of air in a closed vessel. This process is known as Carbonisationof coal. It is in dull black colour. It has 90% carbon, its calorific value about8000 kcal/kg.

Pulverised Coal

The low grade coal with a high ash content is powdered for mixing in air forcomplete combustion to producing high temperature. This pulverised coal iswidely used in the cement industry.

5.2.2 Liquid FuelsLiquid fueld are hydrocarbons. They can be classified as light oils and heavy

oils. They are commonly used for I.C. engines. Most of the liquid fuels arederived from natural petroleum. The crude oil is obtained from boreholes in theearths’s. The crude oil boiling at different temperatures and get petrol or gasoline,paraffin oil.


Petrol Or Gasoline

It is also know as gasoline. It is light and most volatile. Liquid fuels aremostly used in engines. The gasoline obtained by distillation of crude oil. It isdistilled at a temperature from 650c to 2200c.

Paraffin Oil or Kerosene

It is heavier and less volatile fuel than the petrol, and is used for heating andlighting fuel. It is obtained from crude petroleum by fractional distillation aftergasoline is produced. It is distilled at a temperature from 2200c to 3450c.

Heavy Fuel Oils

It is obtained by distillation of crude oil at about 2000c to 3600c. These areused in diesel engines. It is also known as Diesel oil.

Tar

Tar is an important by-product from the manufacture of coal gas. It is agood alternative to petrol for use as a fuel in I.C engines.

Alcohol

Alcohol is formed by formatation of vegetab matter is used as a commercialfuel. Its cost is higher than that of petrol cost.

5.2.3 Merits and Demerits of Liquied Fuelsa) Merits

1. Higher calorific value.

2. Lower storage capacity.

3. Better economy in handling.

4. No ashes.

5. Non-corrosin of boiler plates.

6. Higher efficiency.

b) Demerits

1. Higher cost

2. Greater risk of fire.

3. Costly containars are required for storage and transport.


5.2.4 Gaseous Fuels

Gaseous fuels may be classified into two classes. i) Natural gas ii) Preparedgases.

Natural Gas

The natural gas is usually found in or near the petroleum field under theearth’s surface. This is obtained by drilling holes under the ground. The gas isthe main methane(CH4) but ethance(C2H2), propance(C3H10) together with smallamount of other gases such as hydrogen sulphide, carbon dioxide, nitrogen arealso present to a lesset extent. Its Calorific value varies from 8500 to 9000 kcal/m3.

Prepared Gases

1) Coal gas 2) Producer gas 3) Water gas 4) Coke-over gas

1. Coal Gas

It is obtained by the carbonisation of coal. It consists mainly hydrogen,carbonmonoxide, carbon dioxide, hydrogen and marsh. It is also known astown gas. Its calorific value is about 5,000 to 6,300 k cal / m3.

2. Producer Gas

Producer gas is prepared by blowing a mixture of air and steam through ahot bed of coal or coke. It is a mixture of carbon monoxide, hydrogen , nitrogenand carbon dioxide. it has low calorific value but it is cheap.

3. Water Gas

This is produced by the action of steam on incadesent carbon in the formof coal or coke. It is a mixture of hydrogen and carbon monoxide. Its calorificvalue ranges from 11,500 to 23,000 kj/m3. This is also known as blue gas. Itburns witha bule flame.

4. Coke - Oven Gas

It is a by-product from coke oven. It is produced by high temperaturecarbonisation of bituminous coal. It calorific value ranges from 3,500 to 4,500kcal / m3. It is a mixture of methane and hydrogen and small amount of ethylene,carbon monoxide, carbon dioxide and nitrogen.

5.2.5 Merits and Demerits of Gaseous Fuelsa) Merits


1) Higher calorific value.

2) Lower storage capacity required.

3) Better economy in handling

4) No smoke and no ashes

5) Higher efficiency

6) They are free from impurities

7) They can be directly used in engines.

b) Demerits

1) They require costly containers for storage and transport.

2) Higher cost

3) Greater risk of fire.

5.3 Higher Calorific or Gross Calorific Value (H.C.V)The amount of heat liberated by the complete combustion of unit mass of a

fuel. When the temperature of the products of combustion is cooled down tothe temprature of the supplied air and fuel is called the gross or higher calorificvalue (H.C.V).

Net or Lower Calorific Value (L.C.V)

The amount of heat liberated by the complete combustion of unit mass of afuel. When the temperature of the products of combustion is cooled down to100oc and the steam formed during the combustion is not condensed is calledNet or Lower calorific value (L.C.V)

Test Your UnderstandingState with reasons whether the following statements are TRUE OR FALSE.

1. Fuel liberated a large amount of heat when it is burned.

2. Peat is dried before it can be used.

3. Lignite consists 90% carbon.

4. Coke is produced when the coal is heated strongly in the presence of air.

5. Liquid fuels are obtained from earth’s surface.


6. Natural gas is found in or near the petroleum fields.

7. Coal gas is also known as twon gas.

Terms Used in the Chapter1. Calorific value

2. Combustion

3. Coke

4. Higher calorific value

5. Lower calorific value

5.5 Summary1. The amount of heat liberated during combustion of one kg of fuel is

known as calorific value of fuel.

2. Fuels are mainly classified into a) Natural fuels b) Artificial fuels.

3. Almost all the liquid fuels are derived from natural petroleum.

4. The natural gas is usually found in or near the petroleum fields under theearth’s surface.

Short Answer Type Questions1. What is meant by term fuel ? What are its constituents.

2. Explain the term ‘Calorific value’.

3. Write the types of fuels.

4. Explain higher calorific value.

5. Explain lower calorific value.

Long Answer Type Questions1. Explain some solid fuels.

2. Explain briefly about liquid fuels.

3. Explain different types of gaseous fuels.

4. What are the merits and demerits of liquid fuels.

5. What are the merits and demerits of gaseous fuels.

6.1 Introduction

6.2 Types of Air Standard

6.3 Comparision of Otto cycle and Diesel Cycle

6.4 Summary

Learning ObjectivesAfter studying this chapter, you will be able to know,

• To calculate the efficiency of the engines.

• How the heat is utilised in the process.

• What are the operations and processes going in the carnot cycle.

• What are the operations and processes are going on in the otto cycle.

• What are the operations and processes are going on in the diesel cycle.

• What is the difference between otto and diesel cycle.

6.1 IntroductionA cycle is defined as a repeated series of operations occurring in a certain

order. It may be repeated by repeating the processes in the same order. When

6UNIT

Air Standard CyclesStructure


air is used as a working substance in thermodynamic cycle is called an air standardcycle.

6.1.2 Assumption1. Perfect gas is used as working substance.

2. The compression and expansion processes are adiabatic.

3. No chemical reaction

4. The mass of the gas is constant.

5. The specific heat of gas is constant.

6. The heating and cooling of air is carried out by bringing in hot body andcold body into contact with cylinder head respectively.

Types of Air Standard Cycles

1. Carnot cycle

2. Otto cycle (Constant volume cycle)

3. Diesel cycle (Constant pressure cycle)

1. Carnot Cycle

Fig. 6.1 Carnot Cycle

The carnot cycle was devised by Sadi carnot a French engineer in 1824and has the highest efficiency of all other cycles.

Isothermal Expansion

Adi

abat

ic E

xpan

sion

Isothermal Compression

Adi

abat

ic C

ompr

essi

on


It consists

1. Isothermal expansion

2. Adiabatic expansion

3. Isothermal compression

4. Adiabatic compression

In adiabatic process no heat is transferred. Heat is supplied to the systemduring Isothermal expansion and heat is rejected during Isothermal compression.

Workdone = Heat supplied - Heat rejected.

Heat supplied = mRT1 log er

Heat rejected = mRT2 log er

Therefore thermal efficiency

= Work done / Heat supplied

= (Heat supplied - Heat rejected) / Heat supplied

= (mRT1log er - - mRT2 log er ) / mRT1log er

= T1 - T2 / T1

Efficiency = 1 - T2 / T

6.2.2 Otto CycleThis cycle was devised by “OTTO” on this cycle petrol, and gas engines

are working. It consists of two adiabatic processes and two constant volumeprocesses.

In adiabatic process no heat is transferred. Heat is supplied and rejected atconstant volume process.

Work done : Heat Supplied - Heat rejected

Heat Supplied = mCv (T3 - T2 )

Heat rejected = mCv (T4 - T1)

Therefore Thermal efficiency = Workdone / heat supplied.

Therefore = Heat supplied - Heat rejected / Heat supplied.

= mCv (T3 - T2) - mCv (T4-T1) / mCv (T3-T2)


= (T3 - T2) - (T4-T1) / (T3 - T2)

Efficiency = 1 - (T4-T1) / (T3 - T2)

Fig. 6.2 Otto Cycle

If converting the temperature into volume ratio ‘r’

where ‘r’ = Compression ration

=V1 / V2 = V4 / V3

using the relation between volume and temperature during adiabatic processwe have

T3 / T4= (Vu / V3) = r

T2 / T1= (V1 / V2) = r

Therefore terhamal efficiency = 1 - 1/ (r

6.2.3 Diesel Cycle

It was also called as constant pressure cycle. Diesel engines work on this cycle

It consists of

1) Adiabatic compressions

2) Constant pressure (Heat supplied)

3) Adiabatic expansion

4) Constant volume (Heat rejection)

Con

stant

Vol

ume

Proc

ess

Adabatic Process

Constant volume ProcessAdabatic Process


Constant Pressure Process

In two adiabatic process no heat is transferred. In constant pressure processheat is supplied. In constant volume process heat is rejected

Fig. 6.3 Diesel Cycle

This cycle efficiency depends on the heat supply at constant pressure andheat rejection at constant volume. For higher thermal efficiency, the compressionratio should be high while the cut of ratio should be low.

The efficiency of a diesel cycle is higher than otto cycle. The compressionratio of these engines are 12 to 18.

Thermal efficiency = Workdone / Heat supplied

Work done = Heat Supplied - Heat rejected

where heat supplied = mCp (T3-T2)

Heat rejected = mCv (T4-T1)

Thermal efficiency = Heat supplied - Heat rejected

Heat Supplied

= mCp (T3-T2) - mCv (T4-T1)

mCp (T3-T2)

= 1 - Cv - (T4-T1) / Cp (T3-T2)

Constant Volume Process


= 1 - 1/r (T4-T1 / T3-T2)

Converting the temperature ratios into volume ratios

Compression ratio (C.R) = r = v1 /V4

Cut - off ratio V3 / V2

COMPARISION OF OTTO CYCLE AND DIESEL CYCLE

Test your UnderstandingState with reasons whether the following statements are TRUE

or False

• In air standard cycle perfect air is used as working substances.

• The specific heat of air is not constant in the air standard cycles.

• In carnot cycle, two adiabatic process, one Iso thermal processand one constant volume process are done.

• In carnot cycle heat is supplied at adiabatic expansion.

• The otto cycle consists two adiabatic and two Isothermalprocess.

• A Otto cycle heat is added at constant pressure process.

Sl.No. OTTO CYCLE1. It consists of two adiabatic and two constant volume process

2. Heat is added at constant volume.

3. Efficiency of Otto cycle de pends on compression ratio.

4. Otto cycle is less efficiency than diesel cycle.

5. It is used in petrol and gas engines.

DIESEL CYCLEIt consists of two adiabaticone constant pressureprocess.

Heat is added at constantpressure

Efficiency of diesel cycledepends on compressionratio and cut-off ratio.Diesel cycle is more efficientthan otto cycle.

Using in diesel engines.


• The Diesel engine consists one constant volume, one constant pressuretwo adiabatic process.

Terms Introduced in this Chapter1. Air standard cycle

2. Thermal efficiency

3. Compression ratio.

4. Cut-off ratio

6.4 Summary1. A thermodynamic cycle using air as working substances.

2. The specific heat of air is constant .

3. Mass of air in the cycle is constant.

4. In carnot cycle two Adiabatic two Isothermal process are done.

5. The Otto cycle consists two adiabatic process, two constant volumeprocess.

6. The Diesel cycle consists two adiabatic one constant volume and oneconstant pressure process.

7. Otto cycle is used in petrol and gas engines.

8. Diesel cycle is used in Diesel Engines.

Short Answer Type Questions

1. What is air standard cycle ?.

2. Draw the P-V diagram of Otto Cycle.

3. Draw the P-V diagram of Diesel cycle.

4. Draw the P-V diagram of Carnot cycle.

Long Answer Type Questions

5. Derive an expression for thermal efficiency of Carnot cycle.

6. Derive an expression for thermal efficiency of Otto cycle.

7. Derive an expression for thermal efficiency of Diesel cycle.

8. Write comparison between Otto cycle and Diesel cycle.


Structure

7.1 Introduction Heat engine

7.2 Classification of I.C Engines

7.3 Working principle of two stroke petrol enginers

7.4 Working principal of two stroke diesel enginer.

7.5 Working principal of four stroke petrol engine

7.6 Working principal of four stroke diesel engine

7.7 Comparison between two stroke and four stroke engines

7.8 Comparison between petrol and diesel engines

7.9 Carburetor

7.10 Fuel injection pump

Learning ObjectiveAfter studying this chapter,you will be able to know.

• How to classification of I.C Engines

• In engine what are the operations have been done

7UNIT

Internal Combition Engines


• How the two stroke engine works.

• How the four stroke engine works

• what are the difference between two stroke engine and four stroke engine.

• What are the difference between petrol engine and diesel engine.

• what is scavenging

• How the Carburator works.

• How the fuel injection pump works.

7.1 IntroductionIt is a form of heat engine where the fuel combustion takes place in a chamber

and the heat of combustion is converted into mechanical work. The conbustionof fuel takes place outside the cylinder chamber the engine is known as ExternalCombustion Engine(E.C Engine). The therma efficiency of an I.C engine is muchhigher than that of a stream engine. A modern I.C engine coverts about 40 to 45per cent of the heat of combustion of fuel into work.

Internal combustion engine can be started quickly within a short time.

7.2 Classification of I.C. Engines1. Type of fuel used

a) Petrol engines

b) Diesel engines

c) Gas engines

2. Number of stroke

a) two stroke engines.

b) four stroke engines.

3. Method of igniting fuel

a) spark ignition(e.e. Petrol engine)

b) compression ignition(i.e. Diesel engine).

4. Method of cooling system.

a) Air cooled engines

b) water cooled engines.


5. Number of cylinders

a) single cylinder engine

b) multi cylinder engine.

6. Cylinder arrangement

a) Horizontal

b) Vertical

c) V-type

d) Radial

e) Opposed piston

f) In-line.

7. Speed

a) low speed engines

b) medium speed engines

c) high speed engines

7.3 Working Principle of Two Stroke Petrol EngineThis engine works on two strokes i.e. upward stroke and downward stroke.

In this two strokes, ths suction, compression fuel ignition, working and exhaustof burnt fuel is takes place. The fig 7.1 shows the sequence of operations in atwo stroke petrol engine.

UPWARD STROKE: In this stroke the piston moves from bottom deadcenter to top dead center in the cylinder. Piston moves up, the air and fuelmixture inside the cylinder is compressed, and partial vacuum created in thecrank case. This causes fresh air fuel mixture from carburetor in drown into thecrank case through the inlet port. In this stroke the exhaust and transfer portsare covered by the piston. As the piston reaches the T.D.C. The mixturecompressed and it reaches high temperature and pressure. The spark plugignitedthe mixture. When the fuel mixture burnt high pressure gases exert forceon the piston. Hence piston moves downwards.

DOWNWARD STROKE: In this stroke the piston moves from T.D.Cto B.D.C. The inlet port is covered by the piston and fresh charge is compressedin the crank case. At the end of the stroke. The transfer port is uncovered.


Hence the fresh fuel mixture enter the cylinder throught the transfer port. At thisstage the exhaust port is uncovered, then the burnt gases go out of the cylinder.

This completes the one cycle and the crank case is ready to suck the freshair mixture.

Fig. 7.1 Two Stroke Petrol Engine

7.4 Working Principle of Two Stroke Diesel EngineThis engine works on two stroke i.e. upward stroke and downward stroke.

In this two strokes the suction, compression, fuel injection, working and exhaustof burnt fuel is takes place. the fig 7.2 shows the sequence the operations in atwo stroke Diesel engine.

UPWARD STROKE: In this stroke the piston moves from bottom deadcenter to top dead center in the cylinder. Piston moves up the air inside thecylinder is compressed, and partial vacuum created in the crank case. This causesfresh air from air filter is drown into the crank case through the inlet port. In thisstroke the exhaust and transfer port are covered by the piston. As the piston


reaches, the T.D.C the air compressed and it reaches high temperature andpressure. The injector injected the diesel in the compressed air resulting incombustion fuel.

Fig. 7.2 Diesel Engine

DOWNWARD STROKE: In this stroke the piston moves from T.D.Cto B.D.C. The inlet port is covered the piston and fresh air is compressed in thecrank case. At the end of this stroke the transfer port is uncovered. Hence, thefresh air enter the cylinder through the transfer port. At this stage the exhaustport is uncovered, then the burnt gases go out of the cylinder through the exhaustport.

This completes the one cyleand the crank case is ready to suck the freshair.

7.5 Four Stroke Petrol Engine Working PrincipleIn this engine the cyle is completed in four sequence of operations which

are

1. Suction stroke

2. Compression stroke

3. Working stroke

Injector


4. Exhaust stroke

For one cycle, crank completes two revolutions and one power strokecompleted.

SUCTION STROKE: In this stroke the piston in the cylinder movesfrom top dead center to bottom dead center. Hence partial vacuum created inthe cylinder, then inlet valve opens and air fuel mixture from carburator, is suckedinto the cyliner. At this time the outlet valve is closed.

COMPRESSION STROKE: In this stroke the piston move from bottomdead center to top dead center in the cylinder. The fuel air mixture in the cylinderis compressed then the temperature and pressure of the fuel mixture is increased.The spark plug ignite the fuel when the piston reaches the top dead center.Hence the fuel air mixture burns. This combustion creats high temperature andpressure on the top of the piston. At this time the suction and exhaust valves areclosed.

WORKING STROKE: The high pressure of the combustion fuel ofgases force the piston to move from top dead center to bottom dead center. Atthis time the suction valve and exhaust valves are closed.

EXHAUST STROKE: In this stroke the piston moves from bottom deadcenter to top dead center. The piston compresses the burnt gases. Then theexhaust valve is open. Hence the burst gases are forced out of the cylinderthrough the exhaust valve. At this time the inlet valve is closed.

Fig. 7.4 Four Stroke Petrol EngineI.V Inlet ValueE.V : Outlet ValueS.P : Spark Plug

S.P

PC

P = PistonC = CylinderC.R : Connecting Rod


7.6 Four Stroke Diesel Engine Working PrincipleIn this Engine the cyle is completed by two revolutions of the crank. It has

four sequence of operations.

1. Suction stroke.

2. Compression stroke

3. Working stroke

4. Exhaust stroke

SUCTION STROKE: In this sequence the piston in the cylinder movesfrom Top dead center(T.D.C) to Bottom dead Center(B.D.C). Hence a partialvacuum is created in the cylinder, then inlet valve opens and air from air filter issucked into the cylinder. At this time the outlet valve is closed.

COMPRESSION STROKE: In this stroke the piston moves from B.D.Cto T.D.C in the cylinder the air in the cylinder is compressed then the temperatureand pressure of the air increased. the injector spreayed the Diesel into thecompressed air, then the combustion of fuel takes place inside the cylinder. Thiscombustion of fuel creats high temperature and high pressure inside the cylinder.At this time the inlet valve and exhaust valves are closed

Fig. 7.5 Four Stroke Diesel Engine

I.V Inlet ValueE.V : Outlet Value

Injector

PC

P = PistonC = CylinderC.R : Connecting Rod


.WORKING STROKE: The high pressure of the combustion fuel ofgases force the piston to move from T.D.C to B.D.C. At this time the suctionand exhaust valves are closed.

EXHAUST STROKE: In this stroke the piston moves from B.D.C toT.D.C. The piston compresses the burnt gases then the exhaust valve is open.Hence the burnt gases are forced out of the cylinder through the exhaust valve.At this time the inlet valve is closed.

7.7 Comparision Between Four Stroke engine with Two Stroke Engine

Four stroke engine Two stroke engine

7.8 Comparision Between Petrol and Diesel Engine

Petrol Engine Diesel Engine

Scavenging in poor.Lubricating oil is need more.Cooling system is difficult.

wear of the cylinder is more.the thermal efficiency is low.the fuel consumption is high.it is simple in maintain.light in weightlighter flywheel is used.Crank completes one revolution of onepower stroke.Initial cost is less.

1. Scavenging is better.2. Lubricating oil is need low.3. Cooling system is simple in this engines.4. Wear of the cylinder is less.5. The thermal efficience is high.6. The fuel consumption is low.7. It is not simple in maintain.8. Heavier is weight.9. Heavier flywheel is required.10. Crank completes two revolu ̀ tions of one power stroke.11. Initial cost is high.

1. Petrol is used as a fuel.2. Spark plus is used.3. Starting of petrol engine is easy.4. Initial cost is low.5. The everage compression ratio is 5 to 9.6. Occupies less space.7. It works on otto cycle.8. Lighter in construction.9. High speed engines.

Diesel is used as a fuelFuel injector is used.Starting of Diesel engine is difficult.Initial cost is high.The everage compression ratio is 12 to20.Occupies more space.It works on diesel cycle.Heavy in construction.Low speed engines.


7.9 CarburettorThe air and petrol are mixed in the correct proportion in the carburettor

and are drawn into the cylinder during the suction stroke.

The main functions of the Carburettor are:

1. To maintain a small reserve of petrol at a constant level in the floatchamber.

2. To supply a fine spray of petrol to the air entering the cylinder.

3. To vapourise the petrol, and to produce uniform air-petrol mixture.

4. To maintain a correct mixture of petrol and air at all speeds.

Fig. 7.6 Carburettor

The fig 7.6 shows a simple carburettor. A float F is placed inside the floatchamber. the fuel is pumped into the float chamber through an opening ‘O’ atthe bottom. Two levers are hinged at the point K. One end of each lever isplaced inside the collar c of the valve spindle while the other end has a smallweight e which rest upon the float. When the fuel level rises the float moves inthe upward direction pushing the weights, and the valve V moves in the downwarddirection. The opening of the fuelpassage is therefore closed and incoming ofthe fuel into the float chamber is thus ended. When the fuel level is decreased,


the float moves in the downward direction. The weights also move in the samedirection. So the valve moves in the upward direction opening the passage ofthe fuel entrance and some amount of fuel is admitted. The function of the floatand the needle valve is to maintain a constant fuel level.

The float chamber is connected with the fuel jet which is placed inside anarrow passage of the intake pipe. This narrow passage B is called the venturytube and choke tube, the function of which is to increase the velocity of air nearthe fuel jet. When the air is taken inside the engine cylinder through the intakepipe, the fuel is vapurised from the jet orifice and mixed with the stream of air.But a greater portion of the fuel is atomixed. The vaporisation of the fuel dependsupon the nature of the fuel, the temperature and velocity of the air, and thepressure at the choke tube. The flow of mixture of air and fuel vapour to thecylinder is controlled by means of throttle valve T which is placed above the jet.

A rich mixture required at the time of starting. For this reason the chokevalve K fitted before the fuel jet to control the supply of air. By closing the pipepartially by the choke valve, the supply of air will be decreased with a decreaseof pressure inside the choke tube and vaparisation of the fuel will be increased.

If the speed of the engine increased there will be a decrease of pressureinside the intake pipe, and a rich mixture will be delivered.

7.9.1 Compound Jet Carburettor

Fig. 7.7 Compound Jet Carburettor


The fig... shows a compound jet carburettor. It is the modification of asimple plain tube carburettor where a constant flow nozzle and a constant fueljet has been introduced. Through the nozzle N a constant discharge of the fuel ismaintained inside the air well A, which remains at constant atmospheric pressure.the constant fuel jet c is connected with the air well and it is therefore independentof the pressure of the intake pipe. So the amount of fuel discharged remainsconstant. The constant flow jet is also called the compensating jet or the auxiliaryjet.

At normal speed the carburettor delivers a normal mixture. But when theengine speed increased, the suction increased and the main jet delivers a richmixture and the compensating jet delivers a lean mixture. At slow speed, themain jet delivers a lean mixture, where the compensating jet delivers a rich mixture.Therefore, in both cases, the carburettor delivers a normal mixture.

7.10 Fuel Injection PumpA fuel injection pump is used to supply a required quantity of fuel at high

pressure to the injectors at on each cylinder at required times.

Types of Fuel Injection Pumps

There are

1. Variable spill and variable stroke types.

2. Single-Cylinder type.

3. Multi-Cyliner type.

4. Jerk pump type.

5. Distributor type.

6. Cam operated type.


Cam-Operated Plunger Type

Fig 7.8 shows the fuel pump widely used in modern diesel engines. Theplunger of the fuel pump operated by a cam and it can be rotated in the plungercylinder to control the amount of fuel pumped to the nozzle. The vertical grooveA of the plunger leads into the helical groove D. Fuel oil flows to the fuel pumpunder gravity when the plunger uncovers the suction ports B and C on thedownward stroke. The space above the plunger is filled with oil at the beginningof the upward stroke. During the first part of the upward or delivery stroke, asmall quantity of oil is forced back into the suction space until the plunger closesthe suction ports B and C. From then on the fuel is put under pressure and thepump begins to force it through the delivery valve to the engine cylinder via thenozzle. Delivery begins as soon as the plunger has covered the ports on the wayup, and ends as soon as the sloping edge E of the helical groove D opens theport C, on the right side and permits the fuel to escape from the pressure spaceabove the plunger to the suction space through the port C. The pressure is thenrelieved and the delivery stops. The plunger P is rotated by the rack. The toothedrack is moved in or out by the governnor. Thus, by rotating the plunger, i.e. byalterning the angular position of the helical groove D of the fuel pump plungerrelative to the suction port C, the length of the effective stroke for which oil isdelivered is varied and hence the amount of fuel delivered to the engine is alsovaries.

Test your UnderstandingState with reasons whether the following statements are TRUE or FALSE.

1) In I.C engines the combustion of fuel takes place outside the enginecylinder.

2) The four stroke engine having ports.

3) The diesel engine having injector.

4) The two stroke engine having valves.

5) Petrol engines are high speed engines.

6) Fuel and air is mixed in the carburettor.

Terms Introduced in the Chapter1) Heat engine

2) Carburettor

3) Scavenging


4) Suction stroke

5) Compression stroke

6) Working stroke

7) Exhaust stroke

Summary

Heat Engine - which engine converts the heat energy into mechanical energyis called Heat Engine.

The four stroke engine consists

a) Suction stroke b) Compression stroke c) Working stroke d) Exhaust stroke

The two stroke engine consists a) Upward stroke 2) Downward stroke.

In petrol engine air and petrol mixture is drawn in suction stroke.

In diesel engine air is drawn in suction stroke.

The Carburettor has to vaporise and atomise the oil and mix it thoroughtlywith air at a fixed normal proportion.

The fuel punp has two main function. It must start the fuel injection at theproper crank angle, late in the compression stroke, and it must force through thenozzle into the cylinder, the exact quantity of fuel needed to produce the desiredpower.

Short Answer Type Questions1. Define Heat engine?

2. Write how the I.C Engine are classified.

3. Explain the scavenging.

4. Write the function of Carburettor.

Long Answer Type Questions1. With neat sketch explain the working principle of two stroke diesel

engine.

2. With neat sketch explain the working princple of two strokepetrol engine.


3. With neat sketch explain the working princple of four strokediesel engine.

4. With neat sketch explain the working princple of four stroke petrol engine.

5. With neat sketch explain the working principle of Carburettor.

6. With neat sketch explain the working princple of fuel injection pump.



8.2 Functions of a Pumps8.3 Classification of Pumps8.4 Applications of Pumps

8.5 Working Principle of Centrifugal Pump8.6 Working of Reciprocating Pump8.7 Working of Jet Pump

8.8 Working of Submersible PumpsLearning ObjectivesAfter studying this chapter, you will be able to know.

• The working principle of pumps

• How the pumps are classified

• Applications of pumps

• How the centrifugal pump works

8UNIT

Pumps


• How the reciprocating pump works

• How the jet pump works

• How the submersible pump works

8.1 IntroductionA pump is a mechanical device which converts the mechanical energy into

hydraulic energy. The hydraulic energy is in the form of pressure energy. Whena is interposed in a pipeline, it converts energy from an external source intohydraulic energy and transfers this energy to the liquid through the pipeline. Thusthe energy of the liquid is increased. The pumps are generally used for liftingliquids from a lower level to a higher level. Pumps are also used to increase thepressure energy without lifting the liquid.

8.2 Functions of the Pump1. It converts the mechanical energy into hydraulic energy.

2. It increases the kinetic energy and pressure energy of the liquid whichflows through it.

3. It lifts the liquid from lower level to higher level.

8.3 Classification of PumpsOn the basis of action involved in the working of pump, pumps are classified

as

I. Dynamic pumps

II. Displacement pumps

III. Special pumps

I. Dynamic pumps : In which the energy is countiously added to the pumpis called dynamic pumps.

Dynamic pumps are again classified into

Dynamic pumps

Centrifugal Propeller Screw Regenerative pump pump pump turbine pump


a. Centrifugal pump

In this pumps the pressure head is developed by centrifugal effect n theimpeller of the pump.

b. Propeller pump

In these pumps the pressure head, is developed by the propelling orlifting action of the vanes of the impellor.

c. Screw pumps

In these pumps the screws fitted in a casing develop the pressure head byrotating around themselves.

d. Regenerative turbine pump

In these pumps the pressure head is developed by the reverse turbine actionof the impeller.

II. Displacement pumps : in which the energy is periodically added to thepump is called displacement pumps. These displacement pumps are againclassified into

Displacement Pumps

Reciprocating pumps Rotary pumps

Piston Plunger Gear Vane CompardPiston Lobe

Single Double Differentialacting pump acting pump pump

a. Reciprocating pumps

In these pumps the movement of piston or plunger in a cylinder physciallydisplaces the liquid. If the cylinder is provided with a piston it is called as“piston’ pump and is called as ‘plunger’ pump if it is provided with a plunger.

b. Rotary pumps

These pumps displaces the liquid physically by means of rotating action ofthe components gears or vanes or comps etc provided in a casing.


c. Gear pump

These pumps are provided with two intermeching gears in a ca close fittingcasing. Each gear teeth acts like the plunger of a reciprocating pump. Duringrotation, each pair of teeth inter mesh on the suction side and provides suctioneffect. The liquid under pressure is carried to the other side and gets displaced.

d. Lobe pumps

These pumps are provided with a pair of rotors which, rotate with continuouscontrary motion with in a pumping chamber. A pair of timing gears is housed ina casing to facilitate the rotation of rotors. Thus these rotors pump liquid withchanging volumes.

Special Pumps

These are the pumps which, use either centrifugal action or reciprocatingaction and consists some spcial arrangement to discharge the fluid.

Types of Special pumps

SPECIAL PUMPS

TSubmersible Airlift Jet pumps pumps pumps

a. Submersible pumps

These are a variety of centrifugal pumps. The pumps and motor are submergedin the liquid which is to be pumped. Because of submergence of the pumps, thesuction lift requirement can be completely avoided and so the pump can dischargethe liquid to greater heights.

b. Air lift pumps

In these pumps the compressed air is introduced in a vertical pipe submergedin the fluid at a considerable distance below the static liquid level. This compressedair induces pressure to the fluid and causes lifting from greater depths.

c. Jet pumps

In these pumps a part of the fluid sucked is introduced in a vertical pipe submergedin the fluid at a considerable distance below the static liquid level. This compressedfluid induces pressure to the fluid and causes lifting from greater depth.


8.4Applications of PumpsThe centrifugal pumps can be used for pumping of liquid consisting debris

and dust particals. It is also used for pumping from greater depths to higherelevations.

The turbine pumps are used for pumping clean liquids and gases, hot andvolatile liquids.

The propeller pumps are used for lifting of pure liquids.

The screw pumps are used for fluids consisting debris.

The vane pumps are used for handling very thick and mud and semi solids.

The air lift pumps are used for pumping water, oil, corrosive fluids and sandyfluids.

The rotary pumps are used for pumping the pure liquid in a smooth andregular fashion.

The jet pumps are used for pumping pure liquids from greater depths.

For low discharges single acting pumps. For high discharge double actingpumps are used.

8.5 Centrifugal Pump

Fig. 8.1 Centrifugal Pump

Delivery Pipe

Blades

Impeller

Casing

Suction pipe

Strainer

Foot Valve


Main components of centrifugal pump.

1. Impeller

2. Casing

3. Suction pipe

4. Delivery pipe

1. Impeller

It is a rotor which is fitted with a series of backward curved blades or vanes.It is mounted on a shaft which is driven by an electric motor.

2. Casing

It is an air tight chamber which surrounds the impeller.

3. Suction pipe

Suction pipe is one through which water enters the pump. The lower end ofthe sunction pipe is fitted with a foot valve and strainer, and is dipped into thewater sump from where water is to be lifted. The upper end of the suction pipeis conneced to the centre of impeller.

4. Delivery pipe

It is a pipe through which water is delivered. Its lower end is connected tothe outlet of the pump. At outlet of the pump a delivery valve is provided tocontrol the flow from the pump into the delivery pipe.

8.5.1 Working Principle of Centrifugal PumpCentrifugal pump is shown in fig 8.1 To start the pump it must be primed i.e.

the suction pipe, casing and delivery pipe upto delivery value must be filled withwater to remove the air in the pump. This filling up of the pump water is calledpriming. After priming the delivery valve is kept closed and the electric motor isstarted to rotate the impeller. This causes the water to flow towards the innersurface of the casing by the centrifugal force. This flow create a vaccum at theeye of the impeller. Due to pressure difference, the water which is at atmosphericpressure in the sump enters the pump through suction pipe.

The blades of the impeller provide a diverging passage for the flow of waterwhich increases the pressure energy of the water. The pressure energy of wateris further increased when it flows through diverging passage provided in thecasing.


Advantages of centrifugal pump

1. Low cost2. Requires less floor space3. Operate at high speed4. Free from valves and glands5. Low maintenance cost6. Easy to install7. Uniform discharge8. Higher efficiency

Applications of Centrifugal pump

1. An irrigation2. Municipal water work3. Sewage pumping plants4. An Hydraulic elevators, lifts and cranes.5. An thermal power plants6. For rise protection

8.6 Reciprocating Pump

Fig. 8.2 Reciprocating Pump

Main parts of reciprocating pump

1. Cylinder 2. Connecting rod 3. Crank shaft

4. Suction pipe 5. Delivery pipe 6. Delivery valve 7. Strainer

1

2

3

4

5

6

7


Working principal of reciprocating pump

Fig. 8.2 shows the single acting reciprocating pump. There is one suctionpipe and one delivery pipe. In this pump the piston moving backward and forwardin the cylinder due to the rotation of the crank. During outward stroke, pistonmoves to the right and vaccum is created on the left side of the piston.

The atmospheric pressure acting on the liquid due to this, the liquid enteredthe cylinder through the suction pipe, at this time the suction value opened. Thisvalue is non0return value. On the inward stroke, the liquid in the cylinder iscompressed. This pressure of the liquid closes the suction valve and opens thedelivery valve and the liquid is forced into the delivery pipe. As the cranic rotatesthe suction and delivery strokes are repeated. At normal speed the deliveryvalve is opened to give a continuous supply of water. This type of pump issuitable for low head and high discharge.

8.6.1 Double Acting Reciprocating Pump

The fig. 8.3 shows the double acting reciprocating pump. It consists of twosuction pipes and two delivery pipes. One suction pipe and one delivery pipeson each side of the piston. In double acting pump, suction and delivery strokesoccur simultaneously. During outward stroke the suction valve S1 opens andwater is sucked into the cylinder. At the same time water is forced through thedelivery valve D2 at the back of the piston. During the inward stroke, water issucked through the suction valve S2 and water in front of the piston is forcedthrough the delivery valve D1. So in one complete revolution of crank water isdischarged twice.

Fig. 8.3 Double Acting Reciprocating Pump

Delivery pipes CylinderCrank

Connecting rod

Suction pipe

S1

D1D2

Suction pipe

Piston S2


8.7 Jet PumpMain parts of Jet Pump

1. A Conventional pump and motor

2. Suction pipe

3. Jet aseembly

4. Delivery pipe

Fig. 8.4 Jet Pump

Centrifugal deliverypump

Air Cock groundsurface

Water level

Suction pipe

Foot valve withstrainer

Jet Assembly

Pressure pipe

pope

Primary Unit

Pressure guage

Pipe


8.7.1 Working of Jet Pump

The pumping of fluid in the jet pumps consists of three stages. These are

i. Primmingii. Pressure regulatingiii. Pumping

i. Primming

When the pump is started for the very first time, it is to be primed by usingwater i.e. the water is to be poured through the ‘T’ joint keeping the air cock inopen condition until there is free flow of water from the air cock. Then the aircock is gradually closed while pouring the water. If there is any fall in water levelin the ‘T’ fitting after closing the air cock, then the piping system should bechecked for leakage.

ii. Pressure regulation

In jet pumps the maximum flow occurs only at particular operating pressure.So to get the maximum flow, the pressure valve is to be adjusted by loosening it,until maximum flow is maintained. Too much loosening of the screw will sometimeslower the pressure of the jet.

iii. Pumping

As and when the motor of the pump is started, initinally the water is enteredinto the suction pipe because of the centrifugal action of the pump. when thewater enters into the delivery pipe, then a part of it is allowed into the pressurepipe through the hose. Then by adjusting the pressure valve, the pressure of thewater in the pressure pipe is raised to the required extent. This water which isunder press is allowed to pass through the nozzle of the jet assembly. The highvelocity jet from the nozzle creates a low pressure at its tip and causes pull ofmore water from the suction pipe. The water then passes through the venturitube at high velocity along with the jet stream. When it passes upward in theenlarged part of the venturi the velocity of the stream decreases and the pressureincreases. This raised pressure force the water upto the suction limit of the pump.

8.7.2 Jet pump Application

1. These are used for water supply in nurseries, foresteries.

2. Used in small irrigation works and gardening.

3. For lifting more fluiid from greater dept

4. As a compressor it is sued for


i. For testing pressurized pipe-lines.

ii. For concrete fillings in under water works.

iii. for cleaning heat exchangers, boilers, boiler tubes and evaporators.

iv. For cleaning vessels in food processing plants.

v. For removal of scales from steel structures.

vi. For cleaning ferrous and non-ferrous castings

8.8 Submersible Pumps

The submersible pumps are basically centrifugal pumps. the main differencebetween these two pumps is in centrifugal pumps, the motor and the pump, arejoined by a long shaft and the suction end consists a long suction pipe. Where asin submersible pumps, both the motor and multistage centrifugal pumps areenclosed in a steel sheel and also it doesn’t provided with a suction pipe.

The main components of a submersible pumps are

i. Motor

ii. Pump

iii. Delivery pipe

8.8.1 Working of the Pump

The pumping of the water in submersible pumps is same as in centrifugalpump. The only difference is in submersible pumps, there is no suction pipe andhence the need of priming for pumping is not necessary.

The pumping in submersible pumps consists the following operations.

i. Priming before installationii. Pumping

i. Priming before installation

The motor must be filled with clean non-acid water and free of sand for thepurpose of priming before a submersible pump is installed.

ii. Pumping

The pump must be started by slightly opening the gate-valve. Then thedischarged water must be checked for the sand content, as excessive sand inthe water is harmful to the pump. If there is an appreciable amount of sandfound to be present, then the pump must run with partly opened gate-valve, until


the sand contents are reduced to acceptable quantity. Then the valve can beopened gradually to pump the water as per the capacity of the pump.

Fig. 8.5 Line diagram of Submersible pump

8.8.2 Application of Submersible pumps

1. For drinking water supply

2. For water supply in industries

3. For irrigation works

4. There are used where the ground water levels frequently changes.

5. To use in deep well operations.

Power Cable

Discharge Pipe

Check valve

Suction housing withstrainer

Pump

Motor


8.9 Comparision of Centrifugal Pump with Reciprocating Pump

Test your Understanding - IState with reasons whether the following statements are TRUE or FALSE

1. Pump converts the mechanical energy into the hydraulic energy.

2. The pumps in which the energy is continuously added those pumps are called displacement pumps.

3. In centrifugal pump rotating part is called impeller.

4. Centrifugal pump uses the centrifugal action.

5. Reciprocating pumps are a variety of displacement pumps.

6. The jet pump is a combination of reciprocating pump and an ejector.

7. Submersible pumps are a variety of reciprocating pumps.

Terms Introduced in the Chapter1. Dynamic Pumps

2. Displacement pumps

Sl. Centrifugal Pump

1. Smooth Flow

2. The Cost is low

3. It requires less floor space

4. Light weight

5. Efficiency is high

6. Torque is uniform

7. High speed

8. Simple construction

Reciprocating Pump

Unsteady flow

Cost is high

It requires more floor space

Weight is more

Low efficiency

Torque is not uniform

Low speed

Complicated construction


3. Special pumps

4. Centrifugal force

SummaryThe pumps in which the energy is continuously added to the pump to increase

the velocities of fluid called dynamic pumps. Displacement pumps are the pumpsin which the energy is periodically added to the movable parts of the pump.Sepcial pumps are the pumps which use either centrifugal action or reciprocationaction and consists some special arrangement to discharge the fluid. Submersiblepumps are a variety of centrifugal pumps. The pumps and motor are submergedin the liquid which is to be pumped. The jet pump is a combination of centrifugalpump and an ejector. Main components of jet pump are centrifugal pump, suctionpipe, jet assembly an ddelivery pipe.

Short Answer Type Questions1. Define pump

2. Mention the functions of pump

3. Mention the applications of pumps

4. Mention any two varieties of dynamic pumps

5. What is priming ?

Long Answer Type Questions1. Explain in detail the classification of pumps.

2. With neat sketch explain the working of centrifugal pump.

3. With neat sketch explain the working of reciprocating pump.

4. With neat sketch explain the working of jet pump.

5. With neat sketch explain the working of Submisable pump.

On Job Training1. Dismantling reciprocating pump and study the parts.

2. Toubleshooting in reciprocating pump and find remedies.

3. Dismantling centrifugal pump and study the parts.

4. To study the troubles shooting in centrifugal pump and find remedies.

5. Dismantling the jet pump and study the parts.


6. To study the troubles shooting in jet pump and find remedies.

7. Dismantling the submersible pump and study the parts.

8. To study the troubles shooting in jet pump and find remedies.

9. Dismantling the two stroke petrol engine and study the parts.

10. Assemble the two stroke petrol engine.

11. Dismantling the two stroke deisel engine and study the parts.

12. Assemble the two stroke deisel engine.

13. Dismantling the four stroke petrol engine and study the parts.

14. Assemble the four stroke, petrol engine.

15. Dismantling the four stroke deisel engine and study the parts.

16. Assemble the four stroke deisel engine.

thermodynamic - andhra pradesh board of intermediate …bieap.gov.in/pdf/metpaperii.pdf · ·...

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