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1 A PROJECT REPORT ON DESIGN AND FABRICATION TWO STROKE PETROL ENGINE TEST RIG PREPARED BY STUDENTS OF FINAL YEAR DIPLOMA IN MECHANICAL ENGINEERING UNIVERSITY POLYTECHNIC ALIGARH MUSLIM UNIVERSITY ALIGARH UTTAR PRADESH

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Page 1: A PROJECT REPORT ON DESIGN AND FABRICATION TWO … · FIGURE NO CAPTION OF THE FIGURE PAGE NO 1.1 Classification of Heat Engine 1 ... 1.5 Cylinder Head for an OHC Four-Cylinder Engine

1

A PROJECT REPORT ON DESIGN AND FABRICATION TWO STROKE

PETROL ENGINE TEST RIG

PREPARED BY STUDENTS OF FINAL YEAR DIPLOMA IN MECHANICAL

ENGINEERING UNIVERSITY POLYTECHNIC ALIGARH MUSLIM

UNIVERSITY ALIGARH UTTAR PRADESH

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CONTENTS

Contents i-ii

Declaration by the candidate iii

Certificate iv

Acknowledgements v

Abstract vi

List of figures vii

List of table’s viii

Chapters Pages

1. FUNDAMENTALS OF ENGINE 1-15

1.1 Engine 1

1.1.1 Heat Engine 1

1.1.2 Types of Heat Engine 1

1.1.3 External Combustion Engine 1

1.1.4 Internal Combustion Engine 2

1.2 Basic Engine Components 2

1.2.1 Engine Components 2

1.2.2 Nomenclature of Engine 6

1.3 Working Principle of Engine 8

1.3.1 Four-Stroke Spark Ignition Engine 9

1.3.2 Four-Stroke Compression Engine 11

1.4 Comparison of SI and CI Engine 12

1.5 Two-Stroke Engine 13

1.6 Comparison of Two-Stroke and Four-Stroke Engine 14

2. CLASSIFICATION OF ENGINE 16-20

2.1 Classification of IC Engines 16

2.1.1 Cycle of Operation 16

2.1.2 Types of Fuel Used 16

2.1.3 Method of Charging 17

2.1.4 Type of Ignition 17

2.1.5 Type of Cooling 17

2.1.6 Cylinder Arrangement 17

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2.2 Applications of IC Engines 19

2.2.1 Two-Stroke Engines 19

2.2.2 Four-Stroke Engines 20

3. ENGINE PERFORMANACE PARAMETERS 22-25

3.1 Indicated Thermal Efficiency 22

3.2 Break Thermal Efficiency 22

3.3 Mechanical Efficiency 22

3.4 Volumetric Efficiency 22

3.5 Relative Efficiency 23

3.6 Mean Effective Pressure 23

3.7 Mean Piston Speed 24

3.8 Specific Power Output 24

3.9 Specific Fuel Consumption 24

3.10 Air-Fuel Ratio 25

3.11 Calorific Value 25

4. TWO-STROKE SPARK IGNITION ENGINE TEST RIG 26-32

4.1 INTRODUCTION 26

4.1.1 Frame 26

4.1.2 Materials Used and Their Specifications 26

4.1.3 Mountings 26

4.1.3.1 Prony Brake Dynamometer 26

4.1.3.2 Shaft 27

4.1.3.3 Coupling 27

4.1.3.4 Fuel Bottle 27

4.1.3.5 Engine 27

4.2 CONCLUSIONS 28

BIBLIOGRAPHY 29

APPENDICES

Appendix-Photographs of Two-Stroke Petrol Engine Test Rig

A-1 Side View of Test Rig

A-2 Side View of Test Rig

A-3 Front View of Test Rig

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DECLARATION BY THE CANDIDATEs

We the students of final year Diploma in Engineering (Mechanical

Engineering), University Polytechnic, Aligarh Muslim University), Aligarh

hereby declare that we are fully responsible for the information, result and

conclusions etc. provided in this project “DESIGN AND FABRICATION OF

TWO-STROKE PETROL ENGINE TEST RIG” submitted to Aligarh Muslim

University, Aligarh for the of Diploma in Engineering (Mechanical Engineering).

We have completely taken care acknowledging the contributions of others

in this academic work. We further declare that in case of any violation of

intellectual property rights or copyrights found at any stage, we will be

responsible for that.

MOHAMMAD ZAMIL REZA NASEEM AKRAM

(11-DPIM 204) (11-DPIM 234)

MD OSAMA MD ARSHAD ANJUM

(11-DPIM 216) (11-DPIM 214)

MD SHAKIR ALAM FAIYAZ AHMAD

(11-DPIM 198) (11-DPIM 188)

MD INTEKHAB ALAM AFTAB HUSSAIN

(11-DPIM 199) (11-DPIM 236)

MD SAMIULLAH ANSARI

(11-DPIM 196)

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MECHANICAL ENGINEERING SECTION, UNIVERSITY

POLYTECHNIC

FACULTY OF ENGINEERING & TECHNOLOGY

ALIGARH MUSLIM UNIVERSITY, ALIGARH-202002(INDIA)

MOHAMMAD. YUNUS KHAN

B.Tech (Mech. Engg.), M Tech (Thermal Sc.)

CERTIFICATE

This is to certify that the thesis entitled “DESIGN AND FABRICATION OF TWO-

STROKE PETROL ENGINE TEST RIG” submitted by the students of Aligarh

Muslim University in partial fulfillment of the requirement for the award of Diploma in

Engineering (Mechanical Engineering) to the University Polytechnic, Aligarh Muslim

University, Aligarh is a record of their own work carried out under my supervision and

guidance.

To the best of my knowledge this thesis has been submitted in part or full

elsewhere in any other University for the award of any Degree or Diploma. It is further

understood that by this certificate the undersigned do not endorse or approve any

statement made, opinion expressed or conclusion drawn therein but approve the thesis

only for the purpose for which it is submitted.

Dated: (Mohammad Yunus Khan)

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ACKNOWLEDGEMENTS All praise to the Almighty Allah who gave me the valiantly to complete the work hard.

The successful completion of this project can be largely attributed to numerous persons with whom we have honor and privileged of being associated doing project work. Firstly, we owe my sincere thanks to my teachers and supervisor Mr. Mohammad Yunus Khan, Assistant Professor, Mechanical Engineering Section, for his unmatched support and valuable guidance with healthy criticism which were responsible to the completion of work.

We want to express my gratitude to Prof. Syed Iqbal Ali, Principal, University Polytechnic, Mr. Sabir Ali Khan, In charge, Mechanical Engineering Section. We are grateful to Mr. Jameel A. Siddiqui, Aleem Ahmad, Naseem Aziz, Shakeel Ahmad and Shoaib Ali for their untiring technical support. We are thankful to all the technical staff of the workshop for their support and encouragement.

Might be last but not least, all words of praise fall short and express themselves gratitude with full heart and soul to my parents and family members for their never ever ending support and fluidity in encouragement.

MOHAMMAD ZAMIL REZA NASEEM AKRAM

(11-DPIM 204) (11-DPIM 234)

MD OSAMA MD ARSHAD ANJUM

(11-DPIM 216) (11-DPIM 214)

MD SHAKIR ALAM FAIYAZ AHMAD

(11-DPIM 198) (11-DPIM 188)

MD INTEKHAB ALAM AFTAB HUSSAIN

(11-DPIM 199) (11-DPIM 236)

MD SAMIULLAH ANSARI

(11-DPIM 196)

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ABSTRACT

The two stroke engines were very popular throughout the 20th century in

motorcycles and small engine devices, such as chainsaws and outboard motors,

and were also used in some cars, tractors, etc. Now they are largely used in ships,

boats, etc. part of their appeal was their simple design (resulting low cost) and

often high power-to-weight ratio. The lower cost to rebuilt and maintain made

the two stroke engines incredibly popular.

Two stroke engines still have their applications where high power is

required in string trimmers and chainsaws. They are also used in mopeds, under

bones, scooters, tuk-tuks, snow-mobiles, lawn-mowers, etc.

In this project work, we have successfully designed and fabricated a two

stroke petrol engine test rig. We have modified a two stroke petrol engine that

was used in Bajaj Chetek scooter. The engine is fitted on a frame and its output

power is calculated from the extended shaft which is attached to the crankshaft

of the engine by means of a coupling.

This test rig is a breakthrough as there is no such two stroke petrol engine

test rig in our Polytechnic. Also, we have designed with expenses less than half

of its market price; therefore it is a considerable economical save too.

This test rig is an addition to the existing experimental setups and is

capable of performing various experiments such as performance analysis,

alternative fuel testing etc. This test rig will be for the students in the future.

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LIST OF FIGURES

FIGURE NO CAPTION OF THE FIGURE PAGE NO

1.1 Classification of Heat Engine 1

1.2 Cross-Section of a Spark Ignition Engine 2

1.3 Cylinder Block 3

1.4 Internal Construction of a V-6 Cylinder Block 3

1.5 Cylinder Head for an OHC Four-Cylinder Engine 3

1.6 Piston with the Piston Rings and Piston with Parts 4

1.7 Piston and Connecting Rod Assembly 6

1.8 Crankshaft 6

1.9 Camshaft and Cam 7

1.10 Top and Bottom Dead Centers 8

1.11 Working Principle of Four Stroke Si Engine 9

1.12 Ideal P-V Diagram Four Stroke Si Engine 10

1.13 Cycle of Operation of CI Engine 11

1.14 Ideal P-V Diagram for Four Stroke CI Engine 12

1.15 Crankcase Scavenged Two Stroke Engine 14

1.16 Ideal Indicator Diagram of a Two Stroke SI Engine 14

2.1 Engine Classification by Cylinder Arrangements 18

4.1 Two Stroke Spark Ignition Experimental Setup 26

LIST OF TABLE

TABLE NO CAPTION OF TABLE PAGE NO

1.1 Comparison of Two Stroke and Four Stroke Engine 14&15

4.1 Specification of Two Stroke Engine test Rig 28

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DEDICATED TO

MY LOVING PARENTS

AND

HONORABLE TEACHERS

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CHAPTER 1

FUNDAMENTALS OF ENGINE

1.1 ENGINE

An engine is a device that derives heat from the combustion of fuel and converts a part of

this energy into mechanical work. This is done by transforming one form of energy into

another form. Most of the engines convert thermal energy into mechanical work and

therefore they are called ‘heat engines’.

1.1.1 Heat Engine

Heat engine is a device which transforms the chemical energy and utilizes this thermal

energy to perform useful work. Thus, thermal energy is converted to mechanical energy

in a heat engine.

Heat engines can be broadly classified into two categories:

(i) Internal Combustion Engines (IC Engines)

(ii) External Combustion Engines (EC Engines)

1.1.2 Types of Heat Engine

Engines whether internal combustion or external combustion are of two types, viz.,

(i) Rotary engines

(ii) Reciprocating engines

A detailed classification of heat engines is given in Fig. 1.1. Of the various types of heat

engines, the most widely used ones are the reciprocating internal combustion engines, the

gas turbine and the steam turbine. The steam engine is rarely used nowadays.

Fig. 1.1 Classification of Heat Engines

1.1.3 External Combustion Engine

External combustion engines (EC Engines) are those in which combustion takes place

outside the engine whereas in internal combustion engines combustion takes place within

the engine. For example, in a steam engine or a steam turbine, the heat generated due to

the combustion of fuel is employed to generate high pressure steam which is used as the

working fluid in a reciprocating engine or a turbine. This fluid is then cooled, compressed

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and reused (closed cycle) or (less commonly) dumped and cool fluid pulled in (open

cycle air engine).

1.1.4 Internal Combustion Engine

The internal combustion engine (IC Engine) is a reciprocating heat engine in which fuel

mixed with correct amount of air is burnt inside a cylinder. The spark-ignition engine

usually runs on a liquid fuel. The fuel must be highly volatile so that it vaporizes quickly.

The fuel vapour mixes with air before entering the engine cylinders. This forms the

highly combustible air-fuel mixture that burns easily. The mixture then enters the

cylinders and is compressed. Heat from an electric spark produced by the ignition system

sets fire to, or ignites, the fuel mixture. As the mixture burns (combustion), high

temperature and pressure are produced in the cylinder. This high pressure, applied to the

top of the piston, forces it to move down the cylinder. The motion is carried by gears and

shafts to the wheels that drive the automobile.

1.2 BASIC ENGINE COMPONENTS

Even though reciprocating internal combustion engines look quite simple, they are highly

complex machines. There are hundreds of components which have to perform their

functions satisfactorily to produce output power.

1.2.1 Engine Components

A cross section of a single cylinder spark ignition engine with overhead valves is shown

in Fig. 1.2. The major components of the engine and their functions are briefly described

below.

Fig. 1.2 Cross-section of a spark-ignition engine

1.2.1.1 Cylinder Block

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The cylinder block (Fig. 1.3) is the foundation of the engine. All other engine parts are

assembled in or attached to the cylinder block. Most blocks are cast from gray iron (cast

iron) or iron mixed with other metals such as nickel and chromium.

Fig. 1.3 Cylinder Block

The block (Fig. 1.4) is a casting that has large holes for the cylinder bores. It also has

wafer jackets and coolant passages. Water jackets are the spaces between the cylinder

bores and the outer shell of the bloc. Coolant flows through these spaces to pick up heat

and carry it away from the engine.

Fig. 1.4 Internal construction of a V-6 cylinder block

1.2.1.2 Cylinder Head

Fig. 1.5 show disassembled cylinder heads for OHC and pushrod engines. Heads are cast

from cast iron or aluminum alloy. They are machined to take the various parts that are

attached to or installed in the heads. The cylinder head forms the top of the combustion

chamber. The piston and rings form the bottom. Each of the basic combustion-chamber

shapes produces a specific effect. The wedge increases the turbulence of the burning

mixture, but has high exhaust emissions. The hemispheric provides relatively slow

burning. The cup or bowl-in-piston improves turbulence in diesel, turbocharged, and

high-performance engines. The cylinder head is flat. The height and shape of the crescent

or pent-roof is easily varied to change the compression ratio and turbulence. Greater

turbulence causes the air-fuel mixture to bum faster.

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Fig. 1.5 Cylinder head for an OHC four-cylinder engine

1.2.1.3 Engine Cylinder

As the name implies it is a cylindrical vessel or space in which the piston makes a

reciprocating motion. The varying volume created in the cylinder during the operation of

the engine is filled with the working fluid and subjected to different thermodynamic

processes. The cylinder is supported in the cylinder block.

1.2.1.4 Piston

It is a cylindrical component fitted into the cylinder forming the moving boundary of the

combustion system. It fits perfectly (snugly) into the cylinder providing a gas-tight space

with the piston rings and the lubricant. It forms the first link in transmitting the gas forces

to the output shaft. Pistons must be strong to take these stresses. They must also be light

to reduce inertia loads on the bearings. Any object in motion resists any effort to change

its speed or direction of motion. This is inertia. When a piston stops at TDC or BDC and

starts to move in the other direction, it loads the bearings. Most automotive engines use

full-slipper pistons (Fig. 1.6). The skirts are cut away to save weight and to make room

for the counterweights on the crankshaft. Automotive pistons vary from 3 to 4 inches (76

to 122 mm) in diameter.

1.2.1.5 Piston Rings

Piston is fitted with piston rings (Fig. 1.6). The two types of piston rings are compression

rings and oil-control rings. Piston rings, fitted into the slots around the piston provide a

tight seal between the piston and the cylinder wall thus preventing leakage of combustion

gases. Compression rings seal compression and combustion pressures in the combustion

chambers. Oil-control rings scrap oil from the cylinder walls.

1.2.1.6 Combustion Chamber

The space enclosed in the upper part of the cylinder by the cylinder head and the piston

top during the combustion processes, is called combustion chamber. The combustion of

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fuel and the consequent release of thermal energy results in the building up of pressure in

this part of the cylinder.

Fig. 1.6 Piston with the piston rings ad piston with parts named.

1.2.1.7 Intake Manifold

The intake manifold is also a set of tubes. These tubes carry air or air-fuel mixture form

the throttle valves to the intake valve in the cylinder head.

1.2.1.8 Exhaust Manifold

Exhaust manifold is a set of tubes. It carries exhaust gas from the cylinder head to the

exhaust system. The manifold attaches to the head so the exhaust valve in the head align

with the tube openings and through which the product of combustion escape into the

atmosphere is called the exhaust manifold.

1.2.1.9 Spark Plug

It is a component to initiate the combustion process in a Spark-Ignition (SI) engines and

is usually located on the cylinder head.

1.2.1.10 Gudgeon Pin

It forms the link between the small and of connecting rod and the piston.

1.2.1.11 Connecting Rod

It interconnects the piston and the crankshaft and transmits the gas forces from the piston

to the crankshaft. The two ends of the connecting rod are called as small (little) end and

the big end (Fig. 1.7). Small end is connected to the piston by gudgeon pin and the big

end is connected to the crankshaft by crankpin.

1.2.1.12 Crankshaft

It converts the reciprocating motion of the piston into useful rotary motion of the output

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shaft (Fig. 1.8). In the crankshaft of single cylinder engine there is a pair of crank arms

and balance weights. The balance weights are provided for static and dynamic balancing

of the rotating system. The crankshaft is enclosed in a crankcase. It is a one piece casting

or forging of heat treated alloy steel. The output end of the crankshaft has the flywheel or

drive plate attached to it. The front end has the gear or sprocket that drives the camshaft,

the vibration damper and the drive belt pulley.

Fig. 1.7 Piston and connecting rod assembly

1.2.1.13 Flywheel

The net torque imparted to the crankshaft during one complete cycle of operation of the

engine fluctuates causing a change in angular velocity of the shaft. In order to achieve a

uniform torque and inertia mass in the form of a wheel is attached to the output shaft and

disc wheel is called flywheel.

1.2.1.14 Camshaft and Cams

The camshaft and its associated parts control the opening and closing of the two valves.

The associated parts are push rods, rocker arms, valve springs and tappets. This shaft also

provides the drive to the ignition system. The camshaft is driven by the crankshaft

through timing gears. Cams are made as integral parts of the camshaft and are designed in

such a way to open the valves at the correct timing mid to keep them open for the

necessary duration.

Fig. 1.8 Crankshaft

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1.2.2 Nomenclature of Engine

1.2.2.1 Cylinder Bore [d]

The nominal inner diameter of the working cylinder is called the cylinder bore and is

designated by the letter d and is usually expressed in millimeter (mm).

Fig. 1.9 Camshaft and cams

1.2.2.2 Piston Area (A)

The area of a circle of diameter equal to the cylinder bore is called the piston area and is

designated by the letter A and is usually expressed in square centimeter (cm2).

1.2.2.3 Stroke Length (L)

The nominal distance through which a working piston moves between two successive

reversals of its direction of motion is called the stroke and is designated by the letter L

and is expressed usually in millimeter (mm).

1.2.2.4 Stroke to Bore Ratio (L/d)

Stroke to Bore Ratio (L/d) ratio is an important parameter in classifying the size of the

engine. IF d < L, it is called under-square engine. If d = L, it is called square engine. If d

> L, it is called over-square engine. An over-square engine can operate at higher speeds

because of larger bore and shorter stroke.

1.2.2.5 Dead Centre

The position of the working piston and the moving parts which are mechanically

connected to it, at the moment when the direction of the piston motion is reversed at

either end of the stroke is called the dead center. There are two dead centers in the engine

as indicated in Fig. 1.10.

1.2.2.5.1 Top Dead Centre (TDC)

It is the dead centre when the piston is farthest from the crankshaft. It is designated as

TDC for vertical engines and inner Dead Centre (IDC) for horizontal engines.

1.2.2.5.2 Bottom Dead Centre (ODC)

It is the dead centre when the piston is nearest to the crankshaft. It is designated as BDC

for vertical engines and Outer Dead Centre (ODC) for horizontal engines.

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1.2.2.6 Displacement OR Swept Volume (Vs)

The nominal volume swept by the working piston when travelling form one dead centre

to the other is called the displacement volume. It is expressed in terms of cubic

centimeter (cc) and given by

Vs = Ax L = Ld 2

4

Fig. 1.10 Top and Bottom Dead Center

1.2.2.7 Cubic Capacity Or Engine Capacity

The displacement volume of a cylinder multiplied by number of cylinders in an engine

will give the cubic capacity or the engine capacity. For example, it there are N cylinders

in an engine, then

Cubic capacity = Vs xN

1.2.2.8 Clearance Volume (Vc)

The nominal volume of the combustion chamber above the piston when it is at the top

dead centre is the clearance volume. It is designated as Vc and expressed in cubic

centimeter (cc).

1.2.2.9 Compression Ratio (r)

It is the ratio of the total cylinder volume when the piston is at the bottom dead centre, VT

to the clearance volume, Vc. It is designated by the letter

C

s

C

sC

C

T

V

V

V

VV

V

Vr

1

1.3 WORKING PRINCIPLE OF ENGINE

If an engine is to work successfully then it has to follow a cycle of operation in a

sequential manner. The sequence is quite rigid and cannot be changed. In the following

sections the working principle of both SI and CI engines is described. Even through both

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engines have much in common there are certain fundamental differences. The credit of

inventing the spark-ignition engine goes to Nicolas A. Otto (1876) whereas compression-

ignition engine was invented by Rudolf Diesel (1892).

Therefore, they are often referred to as Otto engine and Diesel engine.

1.3.1 Four-Stroke Spark Ignition Engine

The engine in which the cycle of operations is completed in two revolutions (7200) of the

crank shaft or four strokes of the piston is known as the four stroke engine. One stroke is

completed when the piston moves from TOP DEAD Centre to Bottom Dead Centre or

when the crank rotates through 1800. If the combustion of the fuel-air mixture takes place

with the help of spark plug then it is known as four strokes Spark Ignition Engine. The SI

engine operates at a compression ratio of 6 to 10. The Cycle of operation for an ideal

four-stroke SI engine comprises following four strokes.

(i) Suction or intake stroke.

(ii) Compression stroke.

(iii) Expansion or power stroke and

(iv) Exhaust stroke.

The four-stroke engines manly use Petrol as a fuel. All the events of a four-stroke petrol

cycle namely suction, compression, combustion, expansion and exhaust are completed in

two revolutions of crankshafts

(i) Suction or intake Stroke

Suction stroke (0-1) as shown in (Fig. 1.11 (a)) starts when the piston is at the top dead

centre and about to move downwards. The inlet valve is open at this time and the exhaust

valve is closed. Now as the piston moves towards the BDC that increases the size of the

combustion space thereby reducing the pressure inside the cylinder below atmospheric

pressure. Therefore a vacuum is created that draws the charge consisting of air-fuel

mixture till the piston reaches its BDC position. The piton has now completed one stroke

and crankshaft has turned through 1800

i.e. half the revolution.

Fig. 1.11 Working Principle of Four-Stroke SI Engine

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(ii) Compression Stroke

The charge taken into the cylinder during the suction stroke is compressed by the return

stroke of the piston (1-2) as shown in (Fig. 1.12). This is called the compression stroke.

During this stroke both inlet and exhaust valves are in closed position, Fig. 1.11 (b). The

mixture which fills the entire cylinder volume is now compressed into the Clearance

volume. At the end of the compression stroke the mixture is ignited with the help of a

spark plug located on the cylinder head. In ideal engines it is assumed that burning takes

place instantaneously when the piston is the top dead centre and hence the burning

process can be approximated as heat addition at constant volume. During the burning

process the chemical energy of the fuel is converted into heat energy producing a

temperature rise of about 2000 0C (process 2-3) as shown in Fig. 1.12. The pressure at the

end of the combustion process is considerably increased due to the heat release from the

fuel.

Fig. 1.12 Ideal p-V Diagram for Four-Stroke SI Engine

(iii) Expansion/Power Stroke

The high pressure of the burnt gases forces the piston towards the BDC, (stroke 3-4) as

shown in Fig. 1.12; both the valves are in closed position, Fig. 1.4 (c). Of the four-strokes

only during this stroke power is produced. Both pressure and temperature decrease during

expansion.

(iv) Exhaust Stroke

At the end of the expansion stroke the exhaust valve opens and the inlet valve remains

closed, Fig. 1.11 (d). The pressure falls to atmospheric level a part of the burnt gases

escape. The piston starts moving from the bottom dead centre to top dead centre (stroke

5-0), Fig. 1.5 and sweeps the burnt gases out from the cylinder almost at atmospheric

pressure. The exhaust valve closes when the piston reaches TDC. At the end of the

exhaust stroke and some residual gases trapped in the clearance volume remain in the

cylinder. These residual gases mix with the fresh charge coming in during the following

its working fluid. Each cylinder of a four-stroke engine completes the above four

operations in two engine revolutions, one revolution of the crankshaft occurs during the

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suction and compression strokes and the second revolution during the power and exhaust

strokes. Thus for one complete cycle there is only one power stroke while, the crankshaft

turns two revolutions. For getting higher output from the engine the heat release (stroke

3-4) should be as small as possible. So, one should be careful in drawing the idea p-V

diagram shown in (Fig. 1.12).

1.3.2 Four-Stroke Compression Ignition Engine

The four-stroke CI engine is similar to the four-stroke SI engine but it operates at a much

higher compression ratio. The compression ratio of a SI engine is between 6 and 10 while

for a CI engine it is from 16 to 20. In the CI engine during suction stroke, air, instead of a

fuel-air mixture, is indicated.

Due to the high compression ratio employed, the temperature at the end of the

compression stroke is sufficiently high to self-ignite the fuel which is injected into the

combustion chamber. In CI engines, a high pressure fuel pump and an injector are

provided to inject the fuel into the combustion chamber. The carburetor and ignition

system necessary in the SI engine are not required in the CI engine. The ideal sequences

of operation for the four-stroke CI engine as shown in Fig. 1.13.

(i) Suction Stroke

Air alone is inducted during the suction stroke. During this stroke intake valve is open

and exhaust valve is closed, Fig. 1.13 (a).

(ii) Compression Stroke

Air inducted during the suction stroke is compressed into the clearance volume. Both

valves remain closed during this stroke, Fig. 1.13 (b).

Fig, 1.13 Cycle of Operation of CI Engine.

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(iii) Expansion Stroke

Fuel injection starts nearly at the end of the compression stroke. The rate of injection is

such that combustion maintains the pressure constant in spite of the piston movement on

its expansion stroke increasing the volume. Heat is assumed to have been added at

constant pressure. After the injection of fuel is completed (i.e. after cut-off) the products

of combustion expand. Both the valves remain closed during the expansion stroke, Fig.

1.13 (c).

(iv) Exhaust Stroke

The piston travelling from BDC to TDC pushes out the products of combustion. The

exhaust valve is open and the intake valve is closed during this stroke, Fig. 1.13(d) The

ideal p-V diagram is shown in Fig. 1.14.

Fig. 1.14 The ideal p-V diagram for a four stroke CI engine

Due to higher pressures in the cycle of operations the CI engine has to be sturdier than a

SI engine for the same output. This results in a CI engine being heavier than the SI

engine. However, it has a higher thermal efficiency on account of the high compression

ratio (of about 18 of against about 8 in SI engines) uses.

1.4 COMPARISON OF SI AND CI ENGINE

In SI and CI engines operating on four-stroke cycle, power can be obtained only in every

two revolution of the crankshaft. Since both SI and CI engines have much in common, it

is worthwhile to compare them based on important parameters like basic cycle of

operation, fuel induction, compression ratio etc. The detailed comparison is given below.

(i) Working Cycle

SI engine works on Otto Cycle or constant volume heat addition cycle whereas CI engine

works on Diesel cycle or constant pressure heat addition cycle.

(ii) Fuel

SI engine uses Gasoline, a highly volatile fuel which has which has high Self-ignition

temperature whereas in CI engine a non-volatile fuel i.e. Diesel oil is used which has

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comparatively low self-ignition temperature.

(iii) Fuel Intake

In SI Engines gaseous mixture of fuel-air is introduced during the suction stroke. A

carburetor and an ignition system are necessary. Modern engines have gasoline injection

where in CI Engine Fuel is injected directly into the combustion chamber at high pressure

at the end of the compression stroke. A fuel pump and injector are necessary.

(iv) Load Control

In SI Engine Throttle controls the quantity of fuel-air mixture introduced. Whereas, in CI

Engine the quantity of fuel is regulate. Air quantity is not controlled.

(v) Ignition

SI Engine requires an ignition system with spark plug in the combustion chamber.

Primary voltage is provided by either a battery or a magneto whereas, in CI Engine Self-

ignition occurs due to high temperature of air because of the high compression. Ignition

system and spark plug are not necessary.

(vi) Compression Ratio

In SI Engine the compression ratio is 6 to 10. Upper limit is fixed by antiknock quality of

the fuel whereas in CI Engine is 10 to 20 upper limited by weight increase of the engine.

(vii) Speed

Due to light weight and also due to homogeneous combustion, SI engines are high speed

engines whereas Due to heavy weight and also due to heterogeneous combustion. CI

engines are low speed engines.

(viii) Thermal Efficiency

In SI engines the lower compression ratio, the maximum value of thermal efficiency that

can be obtained is lower whereas in CI engine the compression ratio is maximum valve

of thermal efficiency that can be obtained is higher.

(ix) Weight

SI Engines are lighter in weight due to lower peak pressure but CI Engines are heavier

due to high peak pressure.

1.5 TWO-STROKE ENGINE

In two-stroke engines the cycle is completed in one revolution of the crankshaft. The

main difference between two-stroke and four-stroke engines is in the method of filling

the fresh charge and removing the burnt gases from the cylinder. In the four-stroke

engine these operations are performed by the engine piston during the suction and

exhaust strokes respectively. In a two-stroke engine, the filling process is accomplished

by the charge compressed in crankcase or by a blower. The induction of the compressed

charge moves out the product of combustion through exhaust ports.

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Therefore, no piston strokes are required for these two operations. Two strokes are

sufficient to complete the cycle, one for compressing the fresh charge and the other for

expansion or power stroke. Fig. 1.15 shows one of the simplest two-stroke engines, viz.,

the crankcase scavenged engine.

Fig. 1.15 Crankcase Scavenged Two-Stroke Engine

The air or charge is inducted into the crankcase through the spring loaded inlet valve

when the pressure in the crankcase is reduced due to upward motion of the piston during

compression stroke. After the compression and ignition, expansion takes place in the

usual way. During the expansion stroke the charge in the crankcase is compressed. Near

the end of the expansion stroke, the piston uncovers the exhaust ports and the cylinder

pressure drops to atmospheric pressure as the combustion products leave the cylinder.

Further, movement of the piston uncovers the transfer ports, permitting the slightly

compressed charge in the crankcase to enter the engine cylinder.

The top of the piston has usually a projection to deflect the fresh charge towards the top

of the cylinder before flowing to the exhaust ports. This serves the double purpose of

scavenging the fresh charge from flowing directly to the exhaust ports.

Fig. 1.16 Ideal Indicator Diagram of a Two-Stroke SI Engine

1.6 COMPARISON OF TWO-STROKE AND FOUR-STROKE ENGINES

S.No. Two-Stroke Engine Four-Stroke Engine

1. The thermodynamic cycle is The thermodynamic cycle is

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completed in two strokes of the

piston or in one revolution of the

crankshaft. Thus one power stroke

is obtained in each revolution of the

crankshaft.

completed in four strokes of the piston

or in two revolutions of the crankshaft.

Thus, one power stroke is obtained in

every two revolutions of the

crankshaft.

2. Because of one power stroke in one

revolution greater cooling find

lubrication requirements. Higher

rate of wear and tear.

Because of one power stroke in two

revolutions lesser cooling and

lubrication requirements. Lower rate

of wear and tear.

3. Two-stroke engines have no valves

but only ports (some two-stroke

engines are fitted with conventional

exhaust valve or reed valve).

Four-stroke engines have valves and

valve actuating mechanisms for

opening and closing for the intake and

exhaust valves.

4. Because of light weight and

simplicity du to the absence of

valve actuating mechanism, initial

cost of the engine is less.

Because of comparatively higher

weight and complicated valve

mechanism, the initial cost of the

engine is more.

5. Volumetric efficiency is low due to

lesser time for induction.

Volumetric efficiency is more due to

more time for induction.

6. Used where efficiency is important,

viz., in cars, buses, trucks, tractors.

Industrial engines, aeroplanes,

power generation etc.

Used where low cost, compactness and

light weight are important, viz., in

mopeds, scooters, motorcycles, hand

sprayers etc.

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CHAPTER 2

CLASSIFICATION OF ENGINE

2.1 CLASSIFICATION OF IC ENGINES

IC engines are classified on the basis of following categories.

2.1.1 Cycle of Operation

According to the cycle of operation, IC engines are basically classified into two

categories

(i) Constant volume heat addition cycle engine or Otto cycle engine. It is also called a

Spark-Ignition engine, SI engine or Gasoline engine.

(ii) Constant pressure heat addition cycle engine or Diesel cycle engine. It is also called a

Compression-Ignition engine, CI engine or Diesel engine.

2.1.2 Types of Fuel Used

Based on the type of fuel used engines are classified as:

(i) Engines using volatile liquid fuel like gasoline, alcohol, kerosene, benzene, etc. The

fuel is generally mixed with air to form a homogenous charge in a carburetor outside the

cylinder and drawn into the cylinder in its suction stroke. The charge is ignited near the

end of compression stroke by an externally applied spark and therefore these engines are

called Spark-Ignition engines.

(ii) Engines using gaseous fuels like natural gas, liquefied petroleum gas (LPG), blast

furnace gas and biogas. The gas is mixed with air and the mixture is introduced into the

cylinder during the suction process. Working of this type of engine is similar to that

engine using volatile fuels (SI gas engine).

(iii) Engine using solid fuels like charcoal, powdered coal, etc. Solid fuels are generally

converted into gaseous fuels outside the engine in a separate gas producer and the engine

works as a gas engine.

(iv) Engines using viscous (low volatility at normal atmospheric temperatures) liquid

fuels like heavy and light Diesel oils.

The fuel is generally introduced into the cylinder in the form of minute droplets by a fuel

injection system near the end of compression process. Combustion of fuel takes place due

to its coming into contact with the high temperature compressed air in the cylinder

therefore; these engines are called Compression engines (CI) engines.

(v) Engines using two fuels (dual-fuel engines)

A gaseous fuel or a high volatile liquid fuel is supplied along with air during the suction

stroke or during the initial part of compression through a gas valve in the cylinder head

an the other fuel (a viscous liquid fuel) is injected into the combustion space near the end

of the compression stroke.

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2.1.3 Method of Charging

According to the method of charging, the engines are classified as

(i) Naturally aspirated engines

Air or fuel-air mixture injected near to atmospheric pressure.

(ii) Supercharged engines

Air or fuel-air mixture below or above atmospheric pressure.

2.1.4 Types of Ignition

Spark Ignition engines require an external source of energy to initiate spark and thereby

the combustion process. A high voltage spark is made to jump across the spark plug

electrodes. In order to produce required high voltage there are two types of ignition

systems which are used. They are:

(i) Battery Ignition system

(ii) Magneto Ignition system

They derive their name based on whether a battery or a magneto is used as the primary

source of energy for producing the spark.

In the case of CI engines there is no need for an external means to produce the ignition.

Because of high compression ratio employed, the resulting temperature at the end of the

compression process is high enough to self-ignite the fuel when injected. However, the

fuel should be atomized into very fine particles. For this purpose a fuel injection system

is normally used.

2.1.5 Types of Cooling

Cooling is very essential for the satisfactory running of an engine. There we two types of

cooling systems in use and accordingly, the engines are classified as:

(i) Air-cooled engine

(ii) Water-cooled engine

2.1.6 Cylinder Arrangement

Another common method of classifying reciprocating engines is by the cylinder

arrangement. The cylinder arrangement is only applicable to multi-cylinder engines. Two

terms used in connection with cylinder arrangements must be defined first.

(i) Cylinder Row

An arrangement of cylinders in which the centerline of the crankshaft journals is

perpendicular to the plane containing the centerlines of the engine cylinders.

(ii) Cylinder Bank

An arrangement of cylinders in which the centerline of the crankshaft journals is parallel

to the plane containing the centerlines of the engine cylinders. A number of cylinder

arrangements popular with designers are described below.

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The details of various cylinder arrangements are shown in Fig. 2.1.

2.1.6.1 In-Line Engine

The in-line engine is an engine with one cylinder bank, i.e. all cylinders are arranged in

early, and transmit power to a single crankshaft. This type is quite common with

automobile engines. Four and six cylinder in-line engines are popular in automotive

applications.

2.1.6.2 ‘V’ Engine

In this engine there are two banks of cylinders (i.e., two in line engines) inclined at an

angle to each other and with one crankshaft. Most of the high powered automobiles use

the 8 cylinder ‘V’ engine, four in-lines on each side ‘V’. Engines with more than six

cylinders generally employ this configuration.

Fig. 2.1 Engine Classification by Cylinder arrangements.

2.1.6.3 Opposed Cylinder Engine

This engine has two cylinder banks located in the same plane on opposite sides of the

crankshaft. It can be visualized as two ‘in-line’ arrangements 180 degrees apart. It is

inherently a well-balanced engine and has the advantages of a single crankshaft. This

design is used in small aircrafts.

2.1.6.4 Opposed Piston Engine

When a single cylinder houses two pistons, each of which driving a separate crankshaft, it

is called an opposed piston engine. The movement of the pistons is synchronized by

coupling the two crankshafts. Opposed piston arrangement, like opposed cylinder

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arrangement, and is inherently well balanced. Further, it has the advantage of requiring

no cylinder head. By its inherent features, this engine usually functions on the principle

of two-stroke engines.

2.1.6.5 Radial Engine

Radial engine is one where more than two cylinders in each row are equally spaced

around the crankshaft. The radial arrangement of cylinders in most commonly used in

conventional air-cooled aircraft engine’s where 3, 5, 7 or 9 cylinders may be used in one

bank and two to four banks of cylinders may be used. The odd number of cylinders is

employed from the point of view of balancing. Pistons of all the cylinders are coupled to

the same crankshaft.

2.1.6.6 ‘X’ Type Engine

This design is a variation of ‘V’ type. It has four banks of cylinders attached to a single

crankshaft.

2.1.6.7 ‘U’ Type Engine

The ‘U’ type is a variation of opposed piston arrangement.

2.1.6.8 ‘H’ Type Engine

The ‘H’ type is essentially two ‘Opposed cylinder’ type utilizing two separate but

interconnected crankshafts.

2.1.6.9 Delta Type Engine

The delta type is essentially a combination of three opposed piston engine with three

crankshafts interlinked to one another. In general, automobile engines and general

purpose engines utilize the ‘in-line’ and ‘V’ type configuration or arrangement. The

‘radial’ engine was used widely in medium and large aircrafts till it was replaced by the

gas turbine. Small aircrafts continue to use either the ‘opposed cylinder’ type or ‘in-line’

or ‘V’ type engines. The ‘opposed piston’ type engine is widely use in large diesel

installations. The ‘H’ and ‘X’ types do not presently find wide application, except in

some diesel installations. A variation of the ‘X’ type is referred to as the ‘pancake’

engine.

2.2 APPLICATION OF IC ENGINES

The most important application of IC engines is in transport on land, sea and air. Other

applications include industrial power plants and as prime movers for electric generators.

2.2.1 Two-Stroke Engine

(i) Gasoline Engines

Small two-stroke gasoline engines are use where simplicity and low cost of the prime

mover are the main considerations. In such applications a little higher fuel consumption is

acceptable. The smallest engines are used in mopeds (50 cc engine) and lawn mowers.

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Scooters and motor cycles, the commonly used two wheeler transport, have generally

100-150 cc, two-stroke gasoline engines developing a maximum brake power of about 5

kW at 5500 rpm. High powered motor cycles have generally 250 cc two-stroke gasoline

engines developing a maximum brake power of about 10 kW at 5000 rpm. Two-stroke

gasoline engines may also be used in very small electric generating sets. Pumping sets

and outboard motor boats. However their specific fuel consumption is higher due to the

loss of fuel-air charge in the process of scavenging and because of high speed of

operation for which such small engines are designed.

(ii) Diesel Engines

Very high power diesel engines used for ship propulsion are commonly two-stroke diesel

engines. In fact, all engines between 400 to 900 mm bore are loop scavenged or uni-flow

type with exhaust valves. The brake power on a single crankshaft can be upto 37000 kW.

Nordberg, 12 cylinder 800 mm bore and 1550 mm stroke diesel engine develops 20000

kW at 120 rpm. This speed allows the engine to be directly coupled to the propeller of a

ship without the necessity of gear reducers.

2.2.2 Four-Stroke Engine

(i) Gasoline engines

The most important application of small four-stroke gasoline engines is in automobiles. A

typical automobile is powered by a four-stroke four cylinder engine developing an output

in the range of 30-36 kW at speed of about 4500 rpm. American automobile engines are

much bigger and have 6 or 8 cylinder engines with a power output upto 185 kW.

However, the oil crisis and air pollution from automobile engines have reversed this trend

towards smaller capacity cars.

Four-stroke gasoline engines were also used for buses and trucks. They were generally

4000 c, 6 cylinder engines with maximum brake power of about 90 kW. However, in this

application gasoline engines have been practically replaced by diesel engines. The four-

stroke gasoline engines have also been used in big motor cycles with side cars. Another

application of four-stroke gasoline engine is in small pumping sets and mobile electric

generating sets. Small aircraft generally use radial four stroke gasoline engines. Engines

having maximum power output from 400 kW to 4000 kW have been used in aircraft.

(ii) Diesel Engines

The four stroke diesel engine is one of the most efficient and versatile prime movers. It is

manufactured in sizes from 50 mm to more than 1000 mm of cylinder diameter and with

engine speed ranging from 100 to 4500 rpm which delivering outputs from 1 to 35000

kW. Small diesel engines are used in pump sets, construction machinery, air compressors,

drilling rigs and many miscellaneous applications. Tractors for agricultural application

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use about 30 kW diesels whereas jeeps, buses and trucks use 40 to 100 kW diesel

engines. Generally, the diesel engines with higher outputs than about 100 kW are

supercharged. Earth moving machines use supercharged diesel engines in the output

range of 200 to 400 kW. Marine applications, from fishing vessels to ocean going ships

use diesel engines from 100 to 35000 kW. Diesel engines are used both for mobile and

stationary electric generating plants of varying capacities. Compared to gasoline engines,

diesel engines are more efficient and therefore manufactures have come out with diesel

engines in personal transportation. However, the vibrations from the engine and the

unpleasant odour in the exhaust are the main drawbacks.

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CHAPTER 3

ENGINE PERFORMANCE PARAMETERS

The engine performance is indicated by the term efficiency . Five important engine

efficiencies and other related engine performance parameters are given below:

3.1 INDICATED THERMAL EFFICIENCY ( ith)

Indicated thermal efficiency is the ratio of energy in the indicated power, (i.p.), to the

input fuel energy in appropriate units.

fuelofvaluecalorificondfuelofMass

pi

skJondperfuelinenergy

skJpiith

sec/

.

]/[sec

]/[.

3.2 BRAKE THERMAL EFFICIENCY ( bth)

Brake thermal efficiency is the ratio of energy in the brake power, (b.p.), to the input fuel

energy in appropriate units.

fuelofvaluecalorificondfuelofMass

pi

sec/

.

3.3 MECHANICAL EFFICIENCY ( m)

Mechanical efficiency is defined as the ratio of brake power (delivered power) to the

indicated power (power provided to the piston).

pbpipf

pfpbpi

pi

pbm

...

...

.

.

It can also be defined as the ratio of the brake thermal efficiency to the indicated thermal

efficiency.

3.4 VOLUMETRIC EFFICIENCY ( v)

This is one of the very important parameters which decide the performance of four-stroke

engines. Four-stroke engines have distinct suction stroke and therefore the volumetric

efficiency indicates the breathing ability of the engine. It is to be noted that the utilization

of the air is what going to determine the power output of the engine. Hence, an engine

must be able to take in as much air as possible. Volumetric efficiency is defined as the

volume flow rate of air into the intake system divided by the rate at which the volume is

displaced by the system.

2/NVp

m

dispa

av

Whereap is the inlet density.

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An alternative equivalent definition for volumetric efficiency is

da

av

Vp

m

It is to be noted that irrespective of the engine whether SI, CI or gas engine, volumetric

rate of air flow is what to be taken into account and not the mixture flow. If pa is taken as

the atmospheric air density, then v represents the pumping performance of the entire

inlet system. If it is taken as the air density in the inlet manifold, they v represent the

pumping performance of the inlet port and valve only.

The normal range of volumetric efficiency at full throttle for SI engines is between 80 to

85% whereas for CI engines it is between 85 to 90%. Gas engines have much lower

volumetric efficiency since gaseous fuel displaces air and therefore the breathing capacity

of the engine is reduced.

3.5 RELATIVE EFFICIENCY (OR EFFICIENCY RATIO) (rel )

Relative efficiency or efficiency ratio is the ratio of thermal efficiency of an actual cycle

to that of the ideal cycle. The efficiency ratio is a very useful criterion which indicates the

degree of development of the engine.

efficiencydardsAir

efficiencythermalActualrel

tan

3.6 MEAN EFFECTIVE PRESSURE (Pm)

Mean effective pressure is the average pressure inside the cylinders of an internal

combustion engine based on the calculated or measured power out-put. It increases as

manifold pressure increases. For any particular engine, operating at a given speed and

power output, there will be a specific indicated mean effective pressure, imep, and a

corresponding brake mean effective pressure, bmep. They are derived from the indicated

and brake power respectively. Indicated power can be shown to be

100060.

LankPpi im

They, the indicated mean effective pressure can be written as

LAnk

ipPim

6000

Similarly, the brake mean effective pressure is given by

LAnk

bpPbn

6000

Where i.p = indicated power (kW)

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Pim = indicated mean effective pressure (N/m2)

L = Length of the stroke (m)

A = area of the piston (m2)

N = speed in revolution per minute (rpm)

n = number of power strokes

N/2 for 4- stroke and N for 2- stroke engines

K = number of cylinders

Another way of specifying the indicated mean effective pressure Pim is from the

knowledge of engine indicator diagram (p-V diagram). In this case, Pim, may be defined

as

diagramindicatortheofLength

diagramindicatortheofAreaPim

3.7 MEAN PISTON SPEED (SP)

An important parameter in engine applications is the mean piston speed, sp. It is defined

as LNS p 2

Where L is the stroke and N is the rotational speed of the crankshaft in rpm. It may be

noted that Sp is often a more appropriate parameter than crank rotational speed for

correlating engine behavior as a function of speed. Resistance to gas flow into the engine

or stresses due to the inertia of the moving parts limit the maximum value of Sp to within

8 to 15 m/s. Automobile engines operate at the higher end and large marine diesel

engines at the lower end of this range of piston speeds.

3.8 SPECIFIC POWER OUTPUT (Ps)

Specific power output of an engine is defined as the power output per unit piston area and

is a measure of the engine designer’s success in using the available piston area regardless

of cylinder size. The specific power can be shown to be proportional to the product of the

mean effective pressure and mean piston speed.

Specific power output, Ps = bp/A = constant x Pbm x Sp

As can be see the specific power output consists of two elements, viz., the force available

to work and the speed with which it is working. Thus, for the same piston displacement

and bmep, an engine running at a higher speed will give a higher specific output. It is

clear that the output of an engine can be increased by increasing either the speed or the

bmep. Increasing the speed involves increases in the mechanical stresses of various

engine components. For increasing the bmcp better heat release from the fuel is required

and this will involve more thermal load on engine cylinder.

3.9 SPECIFIC FUEL CONSUMPTION (SFC)

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The fuel consumption characteristics of an engine are generally expressed in terms of

specific fuel consumption in kilograms of fuel per kilowatt-hour. It is an important

parameter that reflects how good the engine performance is. It is inversely proportional to

the thermal efficiency of the engine.

Power

timeunitpernconsumptiofuelsfc

Brake specific fuel consumption and indicated specific fuel consumption, abbreviated as

bsfc and isfc, are the specific fuel consumptions on the basic of b.p. and i.p. respectively.

3.10 AIR- FUEL RATIO (A/F)

The relative proportions of the fuel and air in the engine are very important from the

standpoint of combustion and the efficiency of the engine. This is expressed either as a

ratio of the mass of the fuel to that of the air or vice versa.

In the SI engine the fuel –air ratio practically remains a constant over a wide range of

operation. In CI engines at a given speed the air flow does not very with load; it is the

fuel flow that varies directly with lad. Therefore, the term fuel-air ratio is generally used

instead of air-fuel ratio.

A mixture that constrains just enough air for complete combustion of all the fuel in the

mixture is called a chemically correct or stoichiometric fuel-air ratio. A mixture having

more fuel than that in a chemically correct mixture is termed as rick mixture and a

mixture that contains less fuel (or excess air) is called a lean mixture. The ratio of actual

fuel-air ratio to stoichiometric fuel-air ratio is called equivalence ratio and is denoted by

ratioairfueltricStoichiome

ratioairfuelActual

Accordingly, = 1 means stoichiometric (chemically correct) mixture, < 1 means lean

mixture and < 1 means rich mixture.

3.11 CALORIFIC VALUE

Calorific value of a fuel is the thermal energy released per unit quantity of the fuel when

the fuel is burned completely and the products of combustion are cooled back to the

initial temperature of the combustible mixture. Other terms used for the calorific value

are heating value and heat of combustion.

When the products of combustion are cooled to 250 C practically all the water vapour

resulting from the combustion process is condensed. The heating value so obtained is

called the higher calorific value or grass calorific value or the fuel. The lower or net

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calorific value is the heat released when water vapour in the products of combustion is

not condensed and remains in the vapour form.

CHAPTER 4

TWO STROKE SPARK IGNITION ENGINE TEST RIG

4.1 INTRODUCTION

The experimental setup consists of single cylinder, two stroke, and air cooled petrol

mounted on iron frame. It is connected to belt dynamometer. The schematic diagram of

the experimental setup is shown in Fig 4.1. Description of engine is in the following

headings.

Fig 4.1 Two Stroke Spark ignition Experimental Setup

4.1.1 FRAME

It is the most important part of the experimental setup. The frame is being made

considering the weight it has to bear and vibrations produced by the engine.

4.1.2 MATERIALS USED AND THEIR SPECIFICATIONS

(i) Rectangular frame

Two I shaped mild steel bars each of length 104 cm and width 11 cm each are used as the

longitudinal members of frame. They are connected with four flat mild steel plates to

form a strong rectangular frame.

(ii) Wheels

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Four rubber wheels with iron core in their centers are used. Each of 20 cm diameter and

thickness 5 cm. Each pair of wheel is connected by a solid circular shaft of diameter 2 cm

which in turn is welded with the frame to restrict its relative motion with the wheels.

4.1.3 MOUNTINGS

4.1.3.1 Prony Brake Dynamometer

Prony brake dynamometer is a type of absorptive dynamometer which consists of some

form of brakes in which provision is made for measuring the frictional torque on the

drum or a pulley. In the experimental setup, Prony brake dynamometer is used which

consist of a rubber belt placed around a pulley fixed to a shaft of engine whose power is

required to be measured. The rubber belt is bolted to the weight balance at each end. The

spring balances are hanged to the bolts fixed on a flat Iron piece at some distance. One

end is kept fixed and other has a valve which rotates thereby exerts pressure on the

pulley. As the pressure is exerted on the pulley, the weight carried by the engine can be

noted from the spring balance.

For measuring the power of the engine, the valve is rotated to exert a known weight. Now

the nuts are tightened until the shaft runs at constant speed. The constancy of the speed is

adjusted with the help of an accelerator. The speed of the shaft is measured by a

tachometer in terms of rpm by inserting its rotating end into the indentation at the end of

shaft. In this way power on the engine can be measured at different loads.

4.1.3.2 Shaft

The shaft made of mild steel is used having a length of 49 cm and diameter of 2 cm. One

end of the shaft is connected to the engine through coupling and other is connected to the

pedestal bearing.

4.1.3.3 Coupling

Two pieces of wooden coupling is used to connect the shaft from the dynamometer to

crankshaft of the engine.

4.1.3.4 Fuel Bottle

Fuel bottle having a capacity of 300 ml is used for storing the fuel. Accelerator

arrangement is done by wounding the accelerator wire on a bolt head which in turn is

fixed on a flat iron welded on the frame. The bolt is fixed in such a way that it has to do

horizontal motion only and is restricted from rotational motion.

4.1.4 ENGINE

A compact light weight portable engine with power takes off from the drum or pulley

which is connected to the crankshaft. Such types of engines are having wide applications

in automobiles such as two-wheelers and in marine like in boats, ships, etc. the technical

specifications of engine are given below.

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Table 4.1 Specifications of Engine Test Rig

Type Horizontal, totally enclosed spark ignition,

two stroke cycle, and petrol engine.

Make Bajaj chetak

Stroke length 57 mm

Bore 57 mm

Maximum power 7.50 bhp(5.93 kw)@5500 rpm

Maximum torque 10.8 Nm@3500 rpm

Capacity of fuel tank 300 ml

Circumference of brake wheel 364.24 mm

Ignition CDI Electrnic

Chassis type Monocoque

Cooling type Forced air cooled

Carburetor Spaco SI-20-20 mm venturi carburetor

Compression ratio 7.4/1.5:1

4.2 CONCLUSIONS

In this project work, we have successfully designed and fabricated a Two-Stroke Petrol

Engine Test Rig. It is an addition to the experimental setup installed in University

Polytechnic. It is made portable in order to overcome the space problems in the

Laboratory. Various experiments can be performed on this test rig such as estimation of

Brake Power, estimation of Brake Thermal Efficiency and Fuel Consumption Rate of

Two-stroke Engine.

Since there was no Two-Stroke petrol engine testing rig installed in labs of

polytechnic. So it was decided to design and fabricate the same. It is considerable

economical save since it has been designed and fabricate with less than half of the

expenses of its market value.

Overall it was a great experience for all of us to perform the project work in core of

our stream.

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BIBLIOGRAPHY

[1] V. Ganesan, “Internal Combustion Engines” Tata McGraw Hill Education Pvt. Ltd.

New Delhi.

[2] “Internal Combustion Engine” by M.L. Mathur and R.P. Sharma,Dhanpat Rai

Publication.

[3] “Internal Combustion Engine” by J.B. Heywood, Tata McGraw Hill Education Pvt.

Ltd. New Delhi.

[4] “A Text Book on Automobile Engineering” by Kirpal Singh, Standard Publishers and

Distributers.

[5] “The Automobile” by Harbans Singh Reyat, S. Chand Limited.

[6] “A Text Book on Automobile Engineering” by T.R.Banga,Natthana simha, Khanna

Publisher.

[7] William H. Crouse and Donald L. Anglin, “Automotive Mechanics”Tata McGraw

Hill Education Pvt. Ltd., New Delhi.

[8] http://en.wikipedia.org/wiki/Internal_combustion_engine.

[9] http://en.wikipedia.org/wiki/Two-stroke_engine.

[10] tnau.ac.in/eagri/eagri50/FMP211/pdf/lec02.pdf. [11] https://in.answers.yahoo.com/question/index?qid.

[12] en.wikipedia.org/wiki/Four-stroke engine.

[13] en.wikipedia.org/wiki/Petrol_engine.

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Photograph.A-1 Side View of test rig

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Photograph. A-2 Side View of Test Rig

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Photograph. A-3 front View of Test Rig