A Study On

The Effect of Engine Parameters & Biodiesel Blends on Vibration

Characteristics of DI-CI engine.

A project report submitted in partial fulfillment of

The requirements for the degree of

Bachelor of Engineering

(Mechanical Engineering)

By

Monika Godara

Ishwar Gehlot

Sahil Dhiman

Deepak Sharma

Guide:

S.Jindal, Associate Professor

Department of Mechanical Engineering,

College of Technology & Engineering, Udaipur.

Maharana Pratap University of Agriculture and Technology, Udaipur

1

Department of Mechanical Engineering,College of technology & Engineering, Udaipur

Maharana Pratap University of Agriculture and Technology, Udaipur

CERTIFICATE

This is to be certified that Monika Godara, Ishwar Gehlot, Sahil Dhiman

and Deepak Sharma of B.E. Final Year (Mechanical Engineering) have worked

sincerely under my guidance on the project topic “A Study on the Effect of Engine

Parameters & Biodiesel Blends on Vibration Characteristics of DI-CI engine.”

during session 2007-08. Their work was found satisfactorily.

This work has been carried out by the student own effort under my

guidance and supervision. The report is hereby approved for submission.

Place: Udaipur (Mr. S.Jindal)

Date: 15th July, 2008 Associate Professor

Department of Mechanical Engineering

2

A Study On The Effect Of Engine Parameters & Biodiesel

Blends On Vibration Characteristics Of DI-CI engine.

A Project Report Submitted in partial fulfillment of

The requirements for the degree of

Bachelor of Engineering

(Mechanical Engineering)

By

Monika Godara

Ishwar Gehlot

Sahil Dhiman

Deepak Sharma

Approved:

Project Advisor(s): Asso. Prof. S.Jindal

---------------------------

Examiner(s): ---------------------------

---------------------------

Dean/Head: Dr. B.P. Nandwana

---------------------------

3

Department of Mechanical Engineering

College of technology & Engineering

Maharana Pratap University of Agriculture and Technology, Udaipur

ACKNOWLEDGEMENT

I hope this report, which is the fruit of long dedicated hours of efforts and

consistent dedication, will be appreciated. No work can be perfect, without proper

guidance. I would like to express my deep gratitude and heartiest thanks to Project

guide Er. S. Jindal (Associate Professor, Mechanical Engineering), who infused

me with the spirit to work upon challenging field, which has its inception in such

time when there is a direct need for new orientation. I would also like to thank Er.

Vinay Vashistha, lab Assistant, Mr. K.L. Dameti, other staff of engine research lab

and dynamics lab.

I owe my gratitude to Dr. B.P. Nandwana (Head of Department,

Mechanical Engineering). I cannot retain to accord my humble and sincere

indebtness for aeon and filial affection. Their generous criticism kept the project

investigation stimulating and interesting.

My heart-felt thanks are to all the members of CTAE, who whole-heartedly

and patiently supported me in the completion of the report.

Last but not least, my efforts could never meet the success without the

blessings of God and my family. I can never think of repaying their affection, care

and encouragement without which it would have been difficult to reach the shores

Monika Godara

Ishwar Gehlot

Sahil Dhiman

Deepak Sharma

4

PREFACE

In accordance with the curriculum for “Bachelor’s Degree in

Engineering” by the Maharana Pratap University of Agriculture and Technology, a

project report must be given.

This report gives you an idea about the Effects of various engine

parameters and biodiesel blends on engine vibration. The report starts with basic

introduction of the engine and vibration. Then proceeding in a logical sequence

ends with effects of engine parameters and biodiesel blends on engine vibration.

Different test and their results with their consequent conclusion are

discussed in details. The report ends giving a conclusion of controlling engine

vibrations.

Monika Godara

Ishwar Gehlot

Sahil Dhiman

Deepak Sharma

5

Contents

Chapter

No.

Particulars Page No.

Certificate

Preface

Abstract

Acknowledgement

1.

2.

Introduction

1.1 Internal Combustion Engine

1.1.1 IC Engine components

1.1.2 Stages of Combustion

1.2 Air Fuel Ratio in CI Engines

1.3 Fuel

1.4 Direct injection system

1.4.1 Distributor and Inline pump direct injection

1.4.2 Unit direct injection

1.4.3 Common rail direct injection

1.5 Combustion Knock in CI Engines

1.5.1 Knocking in Diesel Engine

1.5.2 Methods of controlling diesel knock

1.6 Vibration

1.6.1 Vibration in Diesel Engine

Literature Review

2.1 Internal Combustion Engine

2.2 Vibration

6

3.

4.

2.2.1 Simple Harmonic Motion

2.2.2 Equations of Motion

2.2.3 Vibration Amplitude Measurement

2.2.4 Vibration Units

2.2.5 Displacement, Velocity and Acceleration

2.3 Vibration monitoring

2.4 Vibration Measurement Parameters

2.5 Effect of Engine Parameters on vibration

Conclusion

Engine Vibration Measurement and Analysis

3.1 Test Engine Description

3.1.1 Engine Specifications

3.2 Vibration measurement

3.3. Bio Fuel Used

3.4 Diesel Used

3.5 Engine Parameters

3.6 Test procedure

Result and Discussions

4.1 Compression ratio test

4.2 Load test

4.3 Injection pressure test

4.4 Blend test

4.5 Effect of lateral and axial vibrations

Summary

References

7

List of Figures

Figure No. Description Page No.

1.1

1.2

1.3

2.1

2.2

2.3

2.4

2.5

3.1

3.2

3.3

3.4

3.5

3.6

Working of four stroke diesel engine cycle

Stages of combustion in a CI engine

Solid fuel injection system for CI engine

Simple Harmonic Motion

Vibration Amplitudes

RMS Amplitude

Vibration Characteristics

Displacement, Velocity and Acceleration Curves

VIBXPERT – Vibration Measuring Instrument

Accelerometer and Magnetic Holder

Spiral Cable for Accelerometer

USB Cable for Communication

Route for Test Procedure

Positions of Accelerometer

8

List of Graphs

Graph No. Description Page No.

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

CR Test (Lateral Vibrations)

CR Test (Axial Vibrations)

Load Test (Lateral Vibrations)

Load Test (Axial Vibrations)

IP Test (Lateral Vibrations)

IP Test (Axial Vibrations)

Blend Test (Lateral Vibrations)

Blend Test (Axial Vibrations)

9

List of Tables

Table No. Description Page No.

3.1

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

Engine Specifications

CR Test (Lateral Vibrations)

CR Test (Axial Vibrations)

Load Test (Lateral Vibrations)

Load Test (Axial Vibrations)

IP Test (Lateral Vibrations)

IP Test (Axial Vibrations)

Blend Test (Lateral Vibrations)

Blend Test (Axial Vibrations)

10

Chapter 1

Introduction

1.1 Internal Combustion Engine:

Heat engines convert heat into work by the expansion or increase in volume of a

working fluid into which heat has been introduced by combustion of a fuel either

external to the engine or internally by the burning of a combustible mixture in the

engine itself,giving rise to what is called internal combustion engine. (Purohit 2003)

Internal combustion engine date back to 1876 when otto first developed spark

ignition engine and 1892 when diesel invented compression ignition engine. There

are at present three basic types of mass produced automotive engines the gasoline-

piston engine, diesel engine and wankel engine. Internal combustion engine(ICE)

burns fuel inside the engine. The engines used in automobiles are all internal

combustion engine.

IC engines can be divided into two types,reciprocating and rotary.Almost all

automobiles use the reciprocationg engines, in this engine piston moves up and

down. In the rotary engines rotor turns on rotate.

1.1.1 IC Engine components:

1. A piston sliding in cylinnder. The piston has two jobs; first to compress the

air charge, second, to receive the pressure of gases while they are burning

and expanding.

2. A cylinder head which closes the top end of cylinde so as to make a confined

space in which to compress the air and confine the gases while they are

burning and expanding.

3. Valves or ports to admit the air and to discharge the spent or exhaust gaeses.

4. Connecting rod to transmit force in either direction between piston and crank

shaft.

11

5. Crankshaft and main bearings which supprt the crankshaft and permit it to

rotate.

6. A supporting structure to hold the cylinder, crankshaft and main bearings in

firm relation to each other.

7. Fuel injection pump to force the oil into cylinder; and fuel injection nozzle to

break up the oil into fine spray as it enters the cylinder.

8. Camshaft, driven by cranksahft, to operate the fuel injection pump and also

to open valves.

9. Flywheel to store surpules energy on power stroke and to return the energy

when piston is pushed upward on compression stroke.

10. Governer or throttle, to regulate the amount of fuel supplied each stroke, and

thus control the engine speed.

11. Blower to force air into cylinder of two stroke engine. (Purohit 2003)

The piston engine is classified into two types:

Spark ignition engine

Compression ignition engine

Spark ignition engines use spark plugs and electric ignition system to ignite the fuel

in the engine cylinders.In spark ignition engine, the fuel and air are homogenously

mixed together in intake system, induced to intake valve to cylinder into cylinder

where it mixes with residual gases and is then compressed under normal operating

conditions, combustion is initiated towards end of compresssion stroke at spark plug

by an electric discharge.Combustion in CI engines is of normal and abnormal type.

(Ganesan 2006)

Compression ignition engine use diesels as the fuel, they donot have electric ignition

systems. Instead they use the heat of compression to ignite the fuel, when air is

compessed it gets very hot enough, to ignite the fuel. In CI engine only air is

compressed through high compression ratio raising its temperature and pressure to

12

a high value.Fuel is injected through one or more jets into highly compressed air in

combustion chamber.

Fig.1.1 Working of four stroke diesel engine cycle

1.1.2 Stages of Combustion:

The stages of combustion in CI engine are considered to be taking place in four stages. It

is divided into ignition delay, period of rapid combustion, the period of controlled

combustion and period of after burning. The details are explained below. V. Ganesan

(2006)

1. Ignition delay: This period is also called preparatory phase during which some

fuel has already been admitted and not yet ignited. This period is counted from

start of injection to point where pressure time curve separates from monitoring

curve indicated as start of combustion.

The delay period in CI engine exerts a very great influence on both engine design

and performance. It is of extreme importance because of its effect on both

combustion rate and knocking and also its influence on engine starting ability and

13

presence of smoke in exhaust. The fuel doesn’t ignite immediately upon injection

into combustion chamber. There is a definite period of inactivity between time

when first droplet of fuel hits the hot air in combustion chamber and time it starts

through actual burning process .This period is known as ignition delay period.

2. Period of rapid combustion: The period of rapid combustion also called

uncontrolled combustion, is that phase in which pressure rise is rapid. During

delay period droplets have had time to spread over wide area and fresh air is

always available around the droplets. Most of fuel admitted would have

evaporated and formed a combustible mixture with air. By this time, pre flame

reactions would have also been completed. The period of rapid combustion is

counted from end of delay period or beginning of combustion to point of

maximum pressure. The rate of heat release is maximum during this period.

It may be noted that pressure reached during period of rapid combustion will

depend on duration of delay period, longer the delay periods more rapid and

maximum is the pressure rise since more fuel have been accumulated in cylinder

during delay period. (Ganesan 2006)

Fig.1.2 Stages of combustion in a CI engine

14

3. Period of controlled combustion: The rapid combustion is followed by third stage,

the controlled combustion. The pressure and temperature in second stage is

already quite high. Hence the fuel droplets injected during second stage burn

faster with reduced ignition delay as soon as they find the necessary oxygen and

any further pressure rise is controlled by injection rate. The period of controlled

combustion is assumed to end at maximum cycle temperature.

4. Period of after burning: Combustion doesn’t cease with completion of injection

process. The unburnt and partially burnt fuel particles left in combustion chamber

start burning as soon as they come in contact with oxygen. This process continues

for certain duration called after burning period. Usually this period start from

point of maximum cycle temperature and continues over part of expansion stroke.

Rate of after burning depends on velocity of diffusion and turbulent mixing of

unburnt and partially burnt fuel with air. The duration of after burning phase

correspond to 70 to 80 degrees of crank travel from TDC. (Ganesan 2006)

1.2 Air Fuel Ratio in CI Engines:

In the CI Engines, for a given speed, and irrespective of load an approximately constant

supply of air enters the cylinder. Therefore CI engine can be termed as Constant Air

Supply Engine. The overall air fuel ratio may vary from 100:1 at no load to 20:1 at full

load. Generally in CI Engines the air –fuel ratio is leaner than stoichiometric. The

indicated thermal efficiency increases with leaner mixture but the mean effective pressure

and power output reduces, which results in larger size engine for a given power output.

The air fuel ratio must b as near to the chemically correct ratio. Thus CI engine must

always operate with excess air (air fuel ratio 20 to 23, i.e., excess air 35 to 50%). (Mathur

and Mehta 2002).

1.3 Fuel:

15

In IC engine, chemical energy of fuels is converted into heat energy by combusting the

fuel to generate power. In late 1920’s vegetable and seed oils were used as fuel for power

developing in IC engines. These early fuels were found less efficient for CI engines. So

fossil fuels like petroleum are invented. A form of fuel, derived from crude oil, “Diesel”

is used in CI engine. Diesel has good characteristics of a CI engine fuel. (Gupta 2006)

These characteristics are–

1. Ignition Quality: It is a measure of ability of a fuel to ignite after injection, thus

ensuring a progressive smooth burning and easy starting. It is measured in terms

of delay period. A fuel with lower self ignition temperature will ignite more

quickly when injected into the combustion chamber than the one with a higher

self ignition temperature. (Gupta 2006)

2. Volatility: The fuel should be sufficiently volatile in the operating range of

temperature to produce good mixing and combustion.

3. Engine Roughness: Fuel should have lubricating characteristics. There should

not be any presence of sulphur, ash, and residue in the fuel. The presence of these

components will cause engine wear and roughness.

4. Starting characteristics: The fuel should help in starting the engine easily. This

requirement demand high volatility to form a combustible mixture, and high

cetane rating in order that self ignition temperature is low. (Ganesan 2006)

India is among those countries which have high population growth rate. The demand for

mobility and automobiles is thus increasing day-by-day. At present the main source for

power generating for automobiles is the fossil fuels, which are depleting at a faster rate

year after year and are bound to exhaust in not too distant future. Economic and political

factors make supplies of petroleum uncertain and have given rise to tremendous price

escalation for developing countries where oil imports are imperative. The fossil fuels are

non-renewable and also unevenly deposited leading to the problem of energy

dependence. (Source-Annual report of ministry of petroleum and natural gas 2006-2007)

The idea of using biodiesel has been generated since the invention of internal combustion

engine. Biodeisel, short form for “biological oil”, is one of the alternative fuels that is

16

produced from renewable resources. Specifically, it is a mono alkyl ester produced from

vegetable oil, canola oil, soyabean oil or animal fats. Waste animal fats and used frying

oils (known as “yellow grease”) are also potential feedstock’s, just like petroleum-

derived diesel, biodiesel operates in diesel compression engines, including those used in

vehicles and stationary electrical generator units. It can be used in a 100 percent pure fuel

formulation or as a blended component with petroleum derived diesel. The most common

blend is called B20, which is 20 percent biodiesel and 80 percent petroleum diesel.

Essentially, no engine modifications are required, and biodiesel maintains the payload

capacity and range of petroleum-derived diesel. Level of utilization of biodiesel as a fuel

followed the two main crisis of the globe namely: fuel shortage and air pollution.

As far as air pollution is concerned, the environment affects our health and we and our

activities, affect the environment. In urban areas, vehicle account for over 50% of the air

pollution emitted. The targeted emissions from diesel operated vehicles are: NOx, carbon

mono oxide (CO), particulate matters (PM) and air toxics. This high level greenhouse gas

emission cause an increase in ground level ozone. Ground level ozone can cause aching

lungs, wheezing, coughing and headaches. Serious health problem also arises for those

people suffering from Asthma, emphysema and chronic bronchitis.

In developing countries, where they have little controls and other solutions such as CNG,

catalysts and DPFs are costly, some still untested, and many require infrastructure

changes.

Petroleum is lifehood of our civilization, but industry experts predicts that the word’s oil

supply will reach its maximum production and midpoint of depletion sometimes around

the year 2010 (source- Times of India). The world’s economy is fully dependent on fuel.

World oil demand is projected to rise from ~70 million barrel/day at present to ~92

million barrels/day in 2010 (EIA 1996). This has been spurred on by the fact that the

world’s current crude oil reserves are set to run out in the next 50 to 60 years, and since

biodiesel is derived from renewable resources they are not likely to run out as plants can

continue to grow on earth. (Source-Annual report of ministry of petroleum and natural

gas 2006-2007)

17

Among the alternative fuels believed to be the solution of the energy and the

environmental crisis, Biodiesel and Alcohol fuels are feasible fuels and much devotion

will be given to them. Since this time, a lot of researches have been conducted by

different scientists of the globe and of course attractive and appreciable results have come

out. As far as air pollution and the fuel consumption are concerned the blends of these

fuels with the fossil origin fuel are best. From extended researches 15:85% of alcohol to

diesel and 20:80% of biodiesel to diesel blends are most favorable fuels for engine and

also for the environmental concern.

1.4 Direct injection system:

An direct injection diesel engine delivers fuel direct into combustion chamber, where

combustion begins, assisted by injection pressure in the chamber. This system allows for

a rougher, noisy running engine, and because combustion is assisted by injection

pressure, injector pressures can be higher, which in the days of mechanical injection

systems allowed medium-speed running suitable for road vehicles (typically up to speeds

of around 2000 rpm). The injection pressure has the advantage of decreasing heat loss to

the engine's cooling system and providing the combustion burn, which advances the

efficiency by 5% – 10%. Direct injection engines were used in large-capacity, medium-

speed diesel engines in automotive, marine and construction. Direct injection technology

advanced in the 1980s. Indirect injection engines are costlier to build, not easy to produce

smooth, quiet-running vehicles with a simple mechanical system. In road-going vehicles

most prefer the greater efficiency and better controlled emission levels of direct injection.

18

Fig.1.3 Solid fuel injection system for CI engine

Modern diesel engines make use of one of the following direct injection methods:

1.4.1 Distributor and Inline pump direct injection:

The first incarnations of direct injection diesels used a rotary pump much like indirect

injection diesels; however the injectors were mounted in the top of the combustion

chamber rather than in a separate pre-combustion chamber. The problem with these

vehicles was the harsh noise that they made and particulate (smoke) emissions. Fuel

consumption was about fifteen to twenty percent lower than indirect injection diesels,

which for some buyers was enough to compensate for the extra noise.

This type of engine was transformed by electronic control of the injection pump,

pioneered by the Volkswagen Group in 1989. The injection pressure was still only around

300 bar (4350 psi), but the injection timing, fuel quantity, EGR and turbo boost were all

electronically controlled. This gave more precise control of these parameters which made

refinement more acceptable and emissions lower. The technology trickled down to the

mass market with cars being both more economical and powerful than indirect injection

competitors.

19

1.4.2 Unit direct injection:

Unit direct injection also injects fuel directly into the cylinder of the engine. However, in

this system the injector and the pump are combined into one unit positioned over each

cylinder. Each cylinder thus has its own pump, feeding its own injector, which prevents

pressure fluctuations and allows more consistent injection to be achieved. This type of

injection system, also developed by Bosch, is used by Volkswagen AG in cars (where it

is called a Pumpe-Düse-System — literally "pump-nozzle system") and by Mercedes

Benz ("PLD") and most major diesel engine manufacturers in large commercial engines

(CAT, Cummins, Detroit Diesel, Volvo). With recent advancements, the pump pressure

has been raised to 2,050 bar (205 MPa, 30127 psi), allowing injection parameters similar

to common rail systems.

1.4.3 Common rail direct injection:

In common rail systems, the distributor injection pump is eliminated. Instead, a high-

pressure pump pressurises fuel at up to 2,000 bar (202.65 MPa, 29391.9 psi), in a

"common rail". The common rail is a tube that branches off to computer-controlled

injector valves, each of which contains a precision-machined nozzle and a plunger driven

by a solenoid or piezoelectric actuators.

1.5 Combustion Knock in CI Engines:

Combustion knock in CI engines is associated with an extremely high rate of pressure

rise and also with heavy vibration accompanied by a knocking sound, thus causing

overheating of the piston and the cylinder head; drop in power, damage to bearings and

possible piston seizure.

The injection process of a fuel takes place over a definite period of time in terms of

degree crank angle. As a result, the first few drops which are injected into the chamber

pass through the ignition delay and a relatively small amount of fuel will be accumulated

in the chamber when actual burning additional droplets are being injected into the

20

chamber. Normally the fuel injected period is more than the delay period. If the delay

period of the injected fuel is short, the first fuel droplets will commence the burning

phase in relatively short time after injection, commences. As a result, the rate of burning,

the rate of burned mass of fuel will be such as to produce a rate of pressure rise that will

exert a smooth force on the piston.

If, on the other hand the delay period is longer, the burning of first few droplets is

delayed and therefore greater quantity of fuel droplets will accumulate in the chamber.

When the actual burning commences, the additional fuel may cause rapid rate of pressure

rise resulting in rough engine operation. If the delay period is too long, much fuel will be

accumulated resulting in instantaneous rise in pressure, such a situation produces pressure

waves striking on cylinder walls, piston crown and cylinder head, producing knock and

vibrations. Careful design of the injector pump, fuel injector, combustion chamber, piston

crown and cylinder head can reduce knocking greatly- modern engines using electronic

common rail injection have very low levels of knock. (Gupta 2006)

Engine knock or pinging occurs when some of the unburnt gases ahead of the flame in a

spark ignited engine spontaneously ignite. The unburnt gas ahead of the flame is

compressed as the flame propagates and the pressure in the combustion chamber rises.

The high pressure and corresponding high temperature of unburnt reactants can cause

them to spontaneously ignite. This causes a shock wave to traverse from the end gas

region and an expansion wave to traverse into the end gas region. The two waves reflect

off the boundaries of the combustion chamber and interact to produce high amplitude

standing waves.

1.5.1 Knocking in Diesel Engine:

Knocking is unavoidable to a greater or lesser extent in diesel engines, where fuel is

injected into highly compressed air towards the end of the compression stroke. There is a

delay period between the fuel being injected and combustion starting. By this time there

is already a quantity of fuel in the combustion chamber which will ignite first in areas of

greater oxygen density, before the rest of the charge. This sudden increase in pressure and

temperature causes the distinctive diesel 'knock' or 'clatter'. Careful design of the injector

pump, fuel injector, combustion chamber, piston crown and cylinder head can reduce

21

knocking greatly- modern engines using electronic common rail injection have very low

levels of knock. Engines using indirect injection generally have lower levels of knock

than direct injection engine, due to the greater dispersal of oxygen in the combustion

chamber and lower injection pressures providing a more complete mixing of fuel and air.

Knocking causes vibration in engine. Noises are produced due to this vibration. We all

know that noises are undesirable for an engine so the vibrations or the causes of knocking

should be eliminated or minimised.

1.5.2 Methods of controlling diesel knock:

1. The delay period suggests design and operating factors for reducing the delay

period. The delay period can also be reduced by reducing the degree of turbulence

as it will reduce heat loss. However, it will increase the combustion period and thus

reduce torque and thermal efficiency.

2. The delay angle is reduced (i.e. cetane no. is increased) by adding chemical dopes

called ignition accelerators. The two chemical dopes used are ethyl-nitrate and

amyl-nitrate in concentrations of 8.8 gm/litre and 7.7 gm/litre, respectively. The

chemical dopes increase the preflame reactions and reduce the flash point.

3. There would be high rate of pressure rise and high maximum pressure in the

uncontrolled combustion if large amount of fuel collects in the delay period. It can

be reduced by arranging the injector so that only a small amount of fuel is injected

at first. (Mathur and Mehta 2002)

1.6 Vibration:

Vibration can be considered to be the oscillation or repetitive motion of an object around

an equilibrium position. The equilibrium position is the position the object will attain

when the force acting on it is zero. This type of vibration is called "whole body motion",

meaning that all parts of the body are moving together in the same direction at any point

in time.

Vibration problem occur where there are rotating or moving parts in machinery. Apart

from the machinery itself, the surrounding structure also faces the vibration hazard

22

because of this vibrating machinery. The common examples are locomotives; diesel

engines mounted on unsound foundation, whirling of shafts, etc. the main causes of

vibration are as follows:

1. Unbalanced forces in the machine. These forces are produced from within the

machine itself.

2. Dry friction between the two mating surfaces. This produces what are known as self

excited vibration.

3. External excitation. These excitations may be periodic, random, or the nature of an

impact produced external to the vibrating system. (Groover 2004)

The effects of vibration are excessive stresses, undesirable noise, looseness of part and

partial or complete failure of parts. In spite of these harmful effects, the vibration

phenomenon does have some uses also, e.g. in musical instruments, vibrating screens,

shakers, stress relieving etc.

Elimination or reduction of the undesirable vibrations can be obtained by one or more of

the following methods:

1. Removing the causes of vibrations.

2. Putting the screens if noise is the objection.

3. Placing the machinery on proper type of isolators.

4. Shock absorbers.

5. Dynamic vibration absorbers.

The vibratory motion of a whole body can be completely described as a combination of

individual motions of six different types. These are translation in the three orthogonal

directions x, y, and z, and rotation around the x, y, and z-axes. Any complex motion the

body may have been broken down into a combination of these six motions. Such a body

is therefore said to possess six degrees of freedom. For instance, a ship can move in the

fore and aft direction (surge), up and down direction (heave), and port and starboard

direction (sway), and it can rotate lengthwise (roll), rotate around the vertical axis (yaw),

and rotate about the port-starboard axis (pitch).

23

The vibration of an object is always caused by an excitation force. This force may be

externally applied to the object, or it may originate inside the object. It will be seen later

that the rate (frequency) and magnitude of the vibration of a given object is completely

determined by the excitation force, direction, and frequency. This is the reason that

vibration analysis can determine the excitation forces at work in a machine. These forces

are dependent upon the machine condition, and knowledge of their characteristics and

interactions allows one to diagnose a machine problem. (Groover 2004)

1.6.1 Vibration in Diesel Engine:

In engine moving parts are present. These parts cause vibrations in engine. The vibration

is due to moving parts only are of lower frequency. But some high frequency vibrations

are also present there in engine due to abnormal combustion of charge (fuel-air mixture).

The development of combustion in diesel engine is strictly dependent on injection

parameters, like injection timing, mean injection pressure, injection number and fuel

quantity. It is well known that the variation of the injection parameters has an effect on

the engine block vibration.

Vibrations produced in diesel engine are mainly in two directions:

1. Vibrations in lateral direction.

2. Vibrations in longitudinal direction.

The piston impact on the cylinder liner is known as piston slap. This piston slap causes

the vibrations in lateral direction. Some higher frequency vibrations are also generated

due to the abnormal combustion. Lateral vibrations cause structural failure and the wear

due to this is more upto a great extent as compared to axial vibrations.

During abnormal combustion, multi point ignition occurs. This ignition causes rise in in-

cylinder pressure. The rise in in-cylinder pressure forces on piston, and due to this force

some high frequency vibrations are generated in longitudinal direction. Some high

frequencies vibrations are also due to piston movement in normal condition same as in

abnormal condition. But due to abnormal combustion the pressure rise in the cylinder is

24

to such an extent that causes some higher frequency vibrations. In axial direction shock

waves are formed. Speed of shock waves formed is less, as force exerted by them on

cylinder head and cylinder block is cushioned by dense foundation. (Kim 2002).

Our objective is to study the effect of various engine parameters and biodiesel blends on

vibrations in DI-CI engine.To obtain this objective we have to study the vibration

charactreistics by changing engine and biodiesel blends.

25

Chapter 2

Literature Reviews

The researches carried out in past related to the vibration characteristics according to

various engine parameters and biodiesel blends will be discussed in this chapter.

2.1 Internal Combustion Engine:

The first IC engine for commercial use was developed by a Frenchman, J.J.E.

Lenoir (1822-1900) in the year 1860. Coal gas and air mixture were drawn into the

engine cylinder during the first half of the piston stroke .At this point the charge

was ignited by a spark .This caused rise in pressure and the burned gases, the so

called products of combustion , delivered power to the piston for the second half of

the stroke .On the return stroke, the gases were discharged from the cylinder .The

return stroke was possible by using a large flywheel which stored energy during the

power stroke and dissipated energy during the return stroke, exactly in the same

manner as in the case of a steam engine. By the year 1865 about 5000 engines were

built in sizes up to 6 hp providing efficiency, however, not exceeding 5 percent, but

it was better than the efficiency of a small steam engine of those times. (Gupta 2006)

Nicolaus A.Otto (1832-1891) and Eugen Langen (1833-1895) developed a free piston

engine in 1867 in Germany. Air fuel mixture was taken in a cylinder and ignited by

a gas flame during the early part of the outward stroke to accelerate a free piston,

and a vacuum was thus generated in the cylinder. The piston was brought inward

by atmospheric pressure acting on the piston from the other side. During the inward

stroke the burned gas was exhausted through a slide valve. The piston rod was

connected by a rachet and a rack and pinion device to the flywheel mounted on the

output shaft.

In 1862, Alphonse Beau de Rochas (1815-1893), Frenchman, described the

principles of four –stroke cycle and the conditions under which maximum efficiency

could be obtained in IC engines. It gave an idea of ignited fuel at higher pressures,

26

nearly at the end of compression instead of burning the fuel at atmospheric

pressure. Increased cylinder volume with minimum surface to volume ratio,

maximum possible speed and higher expansion ratio were also suggested for higher

thermal efficiency.

Beau de Roches could not build any engine himself based on his principles. In 1876,

Nicolaus August Otto built an engine based on these principles. This engine worked

on the four stroke principle – intake, compression, expansion or power and exhaust

strokes. Ignition was nearly at the end of compression. Otto engine resulted in

reduced weight and volume and gave higher thermal efficiency. This was the

breakthrough that effectively founded the IC engine industry. By 1890, almost

50,000 of these engines had been sold in Europe and USA. (Gupta 2006)

By the 1880s, Dugald Clerk and James Robson of the UK and Karl Benz of

Germany developed the two stroke internal combustion engine. In this engine,

compression of the charge takes place during the inward or upward stroke and

expansion or power is obtained during the outward or down stroke. Exhaust and

intake processes occur during the end of the power stroke and at the beginning of

the compression stroke. In 1885, James Atkinson of England developed an engine

with an expansion stroke larger than compression stroke. The larger expansion

stroke was used to increase the efficiency of the engine. Efficiency could also have

been increased by increasing the compression ratio, but in order to avoid knocking

problems the compression ratio at that with the quality of fuel available had to be

kept below four.

In 1892, Rudolf Diesel (1858-1913) developed a different type of engine in which a

high compression ratio was used to ignite the fuel. Fuel was injected nearly at the

end of compression which was then ignited by hot compressed air. The efficiency of

the engine was increased due to higher compression and expansion ratios. The

knocking problem was also overcome. The present diesel engine is designed on the

same working principle.

Heat engines convert heat into work by the expansion or increase in volume of a

working fluid into which heat has been introduced by combustion of a fuel either

27

external to the engine or internally by the burning of a combustible mixture in the

engine itself. (Gupta 2006)

Internal combustion engine (ICE) burns fuel inside the engine. The engines used in

automobiles are all internal combustion engine.

The IC Engines can also be divided into two types – Spark Ignition Engine (SI) and

Compression Ignition Engine (CI).

Spark Ignition Engines use spark plugs and electric ignition system to ignite the fuel

in the engine cylinders.

The Compression Ignition Engine uses diesel as a fuel. These engines donot have

electric ignition systems as SI Engines. Instead they use the heat of compression to

ignite the fuel. Here air is compressed through a large compression ratio (12:1 to 22:1)

during the compression stroke raising its temperature and pressure. In this highly

compressed and highly heated air in the combustion chamber one or more jets of fuel are

injected in the liquid state, compressed to a high pressure of 110bar to 200bar by means

of a fuel pump. The injection process of a fuel takes place over a definite period of time

in terms of degree crank angle. As a result, the first few droplets which are injected into

the chamber pass through the ignition delay while the additional droplets are being

injected into the chamber. Normally, the fuel injected period is more than the delay

period. If the delay period of the injected fuel is short, the first few droplets will

commence the burning phase in a relatively short time after injection, and a relatively

small amount of fuel will be accumulated in the chamber when actual burning

commences. As a result, the rate of burned mass of fuel will be such as to produce a rate

of pressure rise that will exert a smooth force on the piston. If on the other hand, the

delay period is longer, the burning of the first few droplets is delayed and therefore a

greater quantity of fuel droplets will accumulate in the chamber. When the actual burning

commences, the additional fuel may cause rapid rate of pressure resulting in rough engine

operation. If the delay period is too long, much fuel will be accumulated resulting in

instantaneous rise in pressure. Such a situation produces pressure waves striking on

cylinder walls, piston crown and cylinder head, producing knock and vibrations. In fact,

the combustion mechanism of diesel engine is based on the auto ignition of the charge

28

and hence mild knock may always be present. When it exceeds a certain limit, the engine

is said to be knocking. This knocking tendency causes vibrations in engines. (Gupta

2006)

2.2 Vibration:

Vibration problem occur where there are rotating or moving parts in machinery. Apart

from the machinery itself, the surrounding structure also faces the vibration hazard

because of this vibrating machinery. The common examples are locomotives; diesel

engines mounted on unsound foundation, whirling of shafts, etc.

2.2.1 Simple Harmonic Motion:

The simplest possible vibratory motion that can exist is the movement in one direction of

a mass controlled by a single spring. Such a mechanical system is called a single degree

of freedom spring-mass system. If the mass is displaced a certain distance from the

equilibrium point and then released, the spring will return it to equilibrium, but by then

the mass will have some kinetic energy and will overshoot the rest position and deflect

the spring in the opposite direction. It will then decelerate to a stop at the other extreme

of its displacement where the spring will again begin to return it toward equilibrium. The

same process repeats over and over with the energy sloshing back and forth between the

spring and the mass -- from kinetic energy in the mass to potential energy in the spring

and back. (Groover 2004)

The following illustration shows a graph of the displacement of the mass plotted versus

time.

29

Fig.2.1 Simple Harmonic Motion

If there were no friction in the system, the oscillation would continue at the same rate and

same amplitude forever. This idealized simple harmonic motion is almost never found in

real mechanical systems. Any real system does have friction, and this causes the

amplitude of vibration to gradually decrease as the energy is converted to heat. The

following definitions apply to simple harmonic motion:

T = Period of the wave.

The period is the time required for one cycle, or one "round trip" from one zero crossing

to the next zero crossing in the same direction. The period is measured in seconds, or

milliseconds, depending on how fast the wave is changing.

F = Frequency of the wave, = 1/T

The frequency is the number of cycles that occur in one second, and is simply the

reciprocal of the period.

The unit for frequency is the Hz, named after Heinrich Hertz, the German scientist who

first investigated radio.

2.2.2 Equations of Motion: 

If the position, or displacement, of an object undergoing simple harmonic motion is

plotted versus time on a graph as shown above, the resulting curve is a sine wave, or

sinusoid, and is described by the following equation:

30

d= D sin ( t)

Where,

d = instantaneous displacement,

D = maximum, or peak, displacement

= angular frequency,

t = time

The velocity of the motion is equal to the rate of change of the displacement, or in other

words how fast its position is changing. The rate of change of one quantity with respect

to another can be described by the mathematical derivative, as follows:

Where,

v = instantaneous velocity.

Here we see that the form of the velocity function is also sinusoidal, but because it is

described by the cosine, it is displaced by 90 degrees. We will see the significance of this

in a moment.

The acceleration of the motion described here is defined as the rate of change of the

velocity, or how fast the velocity is changing at any instant:

Where,

a = instantaneous acceleration.

2.2.3 Vibration Amplitude Measurement: 

31

Fig.2.2 Vibration Amplitudes

Peak Amplitude is the maximum excursion of the wave from the zero or equilibrium

point.

Peak-to-Peak Amplitude is the distance from a negative peak to a positive peak. In the

case of the sine wave, the peak-to-peak value is exactly twice the peak value because the

waveform is symmetrical, but this is not necessarily the case with all vibration

waveforms, as we will see shortly.

Root Mean Square Amplitude (RMS) is the square root of the average of the squared

values of the waveform. In the case of the sine wave, the RMS value is 0.707 times the

peak value, but this is only true in the case of the sine wave. The RMS value is

proportional to the area under the curve; if the negative peaks are rectified, i.e., made

positive, and the area under the resulting curve averaged to a constant level, that level

would be proportional to the RMS value. (Groover 2004)

32

Fig.2.3 RMS Amplitude

 

The RMS value of a vibration signal is an important measure of its amplitude. It is

numerically equal to the square root of the average of the squared value of amplitude.

2.2.4 Vibration Units: 

The displacement is simply the distance from a reference position, or equilibrium point.

In addition to varying displacement, a vibrating object will experience a varying velocity

and a varying acceleration. Velocity is defined as the rate of change of displacement, and

Acceleration is defined as the rate of change of velocity.

The displacement of a body undergoing simple harmonic motion is a sine wave as we

have seen. It also turns out, that the velocity of the motion is sinusoidal. When the

displacement is at a maximum, the velocity will be zero because that is the position at

which its direction of motion reverses. When the displacement is zero, the velocity will

be at a maximum. This means that the phase of velocity waveform will be displaced to

the left by 90 degrees compared to the displacement waveform. In other words, the

velocity is said to lead the displacement by a 90-degree phase angle. (Groover 2004)

The acceleration waveform of an object undergoing simple harmonic motion is also

sinusoidal, and also that when the velocity is at a maximum, the acceleration is zero. In

other words, the velocity is not changing at this instant. Then, when the velocity is zero,

the acceleration is at a maximum, the velocity is changing the fastest at this instant. The

sine curve of acceleration versus time is thus seen to be 90 degrees phase shifted to the

left of the velocity curve, and therefore acceleration leads velocity by 90 degrees.

These relationships are shown here:

33

Fig.2.4 Vibration Characteristics

2.2.5 Displacement, Velocity and Acceleration:

A vibration signal plotted as displacement vs. frequency can be converted into a plot of

velocity vs. frequency by a process of differentiation, as we have defined earlier.

Differentiation involves a multiplication by frequency, and this means the vibration

velocity at any frequency is proportional to the displacement times the frequency. For a

given displacement, if the frequency is doubled, the velocity will also double, and if the

frequency is increased tenfold, the velocity is also increased by a factor of ten.

This means that a plot of vibration velocity will slope upwards as frequency rises

compared to the same signal plotted as displacement.

In order to obtain acceleration from velocity, another differentiation is required, and this

results in another multiplication by frequency. The result is that for a given displacement,

the acceleration is proportional to the frequency squared. This means that the acceleration

curve slopes upward twice as steeply as the velocity curve.

The relationship between levels of displacement, velocity, and acceleration versus

frequency in standard English units of mm peak-to-peak, mm per second peak, and mm

per sec2 RMS are expressed by the following equations:

34

35

Fig.2.5 Displacement, Velocity and Acceleration Curves

The three curves shown above display the same information, but the emphasis is

changed. Note that the displacement curve is difficult to read at higher frequencies, and

acceleration has enhanced higher frequency levels. The velocity curve is the most

uniform in level over frequency. This is typical of most rotating machinery, but in some

cases the displacement or acceleration curves will be the most uniform. It is a good idea

to select the units so the flattest curve is attained -- this provides the most visual

information to the observer. Velocity is the most commonly used vibration parameter for

machine diagnostic work.

2.3 Vibration monitoring: 

Vibration analysis, properly applied, allows the technician to detect small developing

mechanical defects long before they become a threat to the integrity of the machine and

thus provides the necessary lead-time to schedule maintenance to suit the needs of the

plant management. In this way, plant management has control over the machines.

Vibration measurement and analysis is the cornerstone of Predictive Maintenance, which

stands in sharp contrast to the historical "run-to-failure" type of maintenance practice.

Numerous studies, such as those conducted by the Electric Power Research Institute

36

(EPRI), have shown that on average, the cost to industry for maintenance will be reduced

by more than 50% if a predictive maintenance program is used instead of run-to-failure.

(Groover 2004)

The present work aims at investigating the possibility of using engine block vibration as a

mean to diagnose, outwardly, the combustion modifications induced by these parameters.

So, the possibility of following the combustion modification by means of two

accelerometers positioned at two different zones of the engine block has been analyzed,

defining a characteristic “signature” for each parameter. Classical Fourier analysis and

time-frequency analysis were used to define the degree of correlation between in-cylinder

pressure and vibration signals. It has been proved that injection pressure and injected

quantities, over an energy release threshold, really affect the vibration signals in a

peculiar way; injection timing affects the engine block vibration in a less evident way.

Carlucci et al. (2005)

2.4 Vibration Measurement Parameters: 

It is possible to examine the same vibration signal in terms of Acceleration, Velocity or

Displacement. It is seen that velocity at any frequency is proportional to the displacement

times the frequency and the acceleration at any frequency is proportional to velocity

times frequency, which means it is also equal to displacement times frequency squared.

Vibration displacement strongly emphasizes the lowest frequencies, and acceleration

strongly emphasizes the highest frequencies. When looking at the vibration spectrum of a

given machine, it is desirable to display the parameter that has the most uniform level

over the frequency range. This will maximize the dynamic range of the measured signal.

For most rotating equipment of medium size, it will be found that vibration velocity

produces the most uniform spectrum, and for this reason it is usually chosen as the

default parameter for machine monitoring.

2.5 Effect of Engine Parameters on vibration:

37

The development of combustion in diesel is strictly dependent on injection parameters.

The variation of the injection parameters has an effect on the engine block and head

vibrations. The need to minimize long and expensive machine failures on the application

in which the same machines play a crucial role has directed research towards the study of

new monitoring and diagnostic techniques.

For internal combustion engines, the new regulations demanding higher efficiency in

terms of emission and fuel consumption reduction, guide the technological development

towards more advanced injection systems. This is because the fuel injection mode, that

determines fuel droplet dimensions and related spatial distribution inside the combustion

chamber, strongly affects the ignition, combustion and pollutant formation processes.

Among the different techniques tested to analyze misfiring.

Azzoni et al. (1995) proposed an indicator based on the crankshaft velocity fluctuations.

This indicator is a function of the amplitudes of the zeroth, first and second orders of

engine cycle components, resulting from the angular velocity signal sampled on a cycle-

by-cycle basis and computed through a discrete Fourier transform. The authors proved

that this indicator is able to distinguish with sufficient precision the occurrence of misfire,

operating the engine in both stationary and acceleration and deceleration conditions.

Ball et al. (2000) tested a diagnostic system based on the measurement of environmental

noise. The sensitivity of the indicator, derived from the continuous wavelet transform,

was shown to some simulated malfunctioning, like a reduction of either the volumetric

compression ratio or the opening pressure of the injector. Further improvements of the

diagnostic method were required in order to distinguish among the different kinds of the

malfunctioning. Among the diagnostic techniques applied to internal combustion engines,

those based on the analysis of accelerometer data have earned a greater success.

Chun and Kim (1994) showed the possibility of obtaining a measure of a spark ignition

engine knock analyzing the oscillations measured at the upper part of the cylinder block

center.

Zurita et al. (1999), on the contrary, rebuilt the in-cylinder pressure history through the

signal provided by an accelerometer placed externally. Then, the in-cylinder pressure

trend was used as a diagnostic tool.

38

Othman (1989) used an accelerometer horizontally mounted on the side wall of a spark

ignition engine to monitor the combustion anomalies, like misfiring, and to adjust

automatically the air-fuel ratio and the ignition time of the spark plug.

Antoni et al. (2002) suggested the analysis of an internal combustion engine vibrations

using cyclostationarity to overcome the vibration non-stationarity. This approach,

combined with the synchronous sampling and not time sampling, makes possible the

definition of some malfunctioning indicators, like knock or misfiring. This approach,

however, revealing the presence of a malfunction, often did not supply useful information

about its nature.

Schmillen and Wolschendorff (1989) pointed out that the pressure oscillation amplitude

inside the combustion chamber was strongly dependent on the duration where

simultaneous autoignition takes place. This energy release, not uniform in space and

time, causes in-cylinder pressure oscillations, not uniform in space and time either.

Starting from these remarks,

Blunsdon and Dent (1994) figured out numerically the temporal trends of the in cylinder

pressure at different locations of the combustion chamber varying the injection profile ,

the number of subsequent injections, the timing of the different injections, the swirl ratio,

the injector position, and the thermal boundary conditions. The results showed that these

variables strongly affect the bulk motion settling inside the combustion chamber.

Many researchers have tried the biodiesel and its blends in Direct Injection Compression

Ignition (DICI). Agarwal (2007), Canakci (2007) and Crookes (2006), on these studies

suggest that the biodiesel can be easily used in existing engine without modifications

upto a blend ratio of 20 with improvement in emissions with a slight loss in Thermal

Efficieny. 100% Biodiesel can be used with some operating parameter modification like

the compression ratio, injection pressure, injection timing etc.

Tashtoush et al. (2006) studied several biofuels tested at different injection pressures in a

DI single cylinder diesel engine and observed that the injection pressure affects

significantly the combustion of fuel consumption.

39

Kim and Lee (2007) investigated the effect of spray angle and dual injection strategy on

exhaust emissions and concluded that the late timing splitted injections affected the

emissions and reduce the knock.

Ueki and Miura (1999) studied the effect of injection pressure on emissions in heavy duty

DI engines and concluded that the knock emissions by retarding injection time and

increasing the injection pressure.

Parlak et al. (2003) studied the effects of reducing compression ratio from the

performance and exhaust emissions in a low heat rejection in DICI engine and compared

it with a standard diesel engine with fix compression ratio. They found that reducing the

compression ratio in SDE lead to an unacceptable pressure rise associated with high

temperature in low heat rejection engine. Satisfactorily performance was obtained at

lower compression ratios.

Sayin et al. (2007) studied the influence of injection timing and different ethanol blends

with diesel and found that NOx and CO2 increasing amount of ethanol in the mixture and

at retarded injection timings.

Al-Baghdadi et al. (2004) studied the effect of compression ratio equivalence ratio and

engine speed on the performance and engine characteristics of a SI engine. He concluded

that the compression ratio and equivalence ratio have a significant effect on both

performance and emission characteristics of engine. Also, it was found that higher

compression ratio can be applied satisfactorily to increase the power output and

efficiency.

We will study vibration characteristics by varying following engine parameters:

Injection pressure

Compression ratio

Loads

1. Injection pressure: The spray characteristics are strongly dependent on

injection pressure. By increasing the injection pressure level, fuel droplets

40

speed and, as a result, mass flow injected increase. At the highest injection

pressure, the fuel spray penetrates more deeply in the combustion chamber

before reaching the ignition conditions, causing wall impingement in small

chambers. On the basis of hypothesis, the fuel spray break up is caused, by

the aerodynamic interaction with the gas in the chamber, whose relative

motion contributes to amplify unstable waves on the spray surface. An

increase of the injection pressure reduces the fuel droplets average

diameter and then improves the spray formation promoting droplet

vaporization. (Ganesan 2006)

2. Compression ratio: As compression ratio is increased from lower to

higher value the delay period reduces causing decrease in knocking. The

reason for decrease in knocking at higher compression ratio is that air

pressure and temperature increases and auto ignition temperature reduces

at higher compression ratio.

3. Loads: As load increases delay period decreases causing decrease in

knocking. The reason for decrease in knocking due to increase in loads

that due to increase in load operating temperature increases resulting in

decrease in knocking. (Ganesan 2006)

Conclusion of literature review:

From the review of presented literature it can be concluded that :

1. The performance of a DICI diesel engine depends greatly on the operating

parameters namely compression ratio, injection pressure, load and injection

timing.

41

2. The performance of such engine varies with different blends of biodiesel with

diesel.

3. With different operating parameters and with different blends the combustion

phenomenon leads to varying noise and vibration in the engine structure which is

detrimental to engine life.

Hence, a study on the measurement of vibration induced in the engine due to changes

in the operating parameters compression ratio, injection pressure, load and injection

timing needed to be studied to establish the relation between these parameters and

vibration signature. Further with different blends of biodiesel and diesel the effects on

vibration induced needs to be investigated.

42

Chapter 3

Engine Vibration Measurement and Analysis

So far we have discussed about the various engine parameters and biodiesel blends to

study their effect on engine vibrations. Now we will discuss about the engine vibration

measuring devices and test procedure by changing various engine parameters and

biodisel blends.

3.1 Test Engine Description:

The set up consists of single cylinder, four stroke, VCR (Variable Compression Ratio)

direct injection diesel engine. The engine is connected to eddy current type dynamometer

for loading. A specially designed tilting block arrangement is provided for changing

clearance volume of the combustion chamber. Set up is provided with necessary

instruments for combustion pressure and crank angle measurements. These signals are

interfaced to computer through engine indicator for P-θ and P-V diagrams. Provision is

also made for interfacing airflow, fuel flow, temperatures and load measurement. The set

up has stand alone panel box consisting of air box ,two fuel tanks for duel fuel test,

manometer, fuel measuring unit, transmitters for air and fuel flow measurements, process

indicator and engine indicator. Rotameters are provided for cooling water and calorimeter

water flow measurement.

The set up enables study of VCR engine performance for brake power, indicated power,

frictional power, brake mean effective pressure, indicated mean effective pressure, brake

thermal efficiency, indicated thermal efficiency, mechanical efficiency, volumetric

efficiency, specific fuel consumption, Air-Fuel ratio and heat balance. Windows based

Engine Performance Analysis software package “Enginesoft” is provided for on line

performance evaluation.

A piezoelectric sensor is installed in the pressure pipe of fuel before injector to pick up

the injection pressure signals which are also displayed through the software

superimposed with P-V diagram.

43

3.1.1 Engine Specifications:

1. Product VCR Engine test set up 1 cylinder, 4-stroke, Diesel

2. Make & Product

code

APEX- Model 234

3. Engine Make Kirloskar, Type one cylinder, 4-stroke Diesel,

water cooled, Power -3.5 kW at 1500 rpm, stroke 110

mm, bore 87.5 mm, 661 cc, CR 17.5, modified to VCR

engine CR range 12 to 18.

4. Dynamometer Type eddy current, water cooled, with loading unit.

5. Propeller shaft With universal joints

6. Air box M S fabricated with orifice meter and manometer

7. Fuel tank Two fuel tanks with total capacity 15 lit with glass fuel

metering column.

8. Calorimeter Type pipe in pipe

9. Piezo sensor Range 5000 PSI, with low noise cable for cylinder

pressure

10. Crank angle

sensor

Resolution 1 Degree, speed 5500 RPM with TDC

pulse.

11. Engine indicator Input Piezo sensor, crank angle sensor, no. of channels

2,commucation RS232

12. Digital

milivoltmeter

Range 0-200mV, panel mounted

44

13. Temperature

sensor

Type RTD , PT100 and Thermocouple, Type K

14. Temperature

transmitter

Type two wire , input RTD PT 100 , Range 0-100,

Deg C, Output 4-20mA and type two wire , input

thermocouple ,Range 0-1200 deg C, output 4-20 ma

15. Load indicator Digital, Range 0-50 Kg, supply 230 VAC

16. Load sensor Load cell, type strain gauge, range 0-50 kg

17. Fuel flow

transmitter

DP transmitter, Range 0-500 mm WC

18. Air Flow

transmitter

Pressure transmitter , Range 250 mm WC

19. Rotameter Engine cooling 40 – 400 LPH ;Calorimeter 10 -100

LPH

20. Pump Type Monoblock

21. Add on card Resolution 12 bit , 8/16 input , Mounting PCI slot

22. Software “Engine soft” Engine performance analysis software

23. Overall

dimensions

W2000 ×D2500 ×H 1500 mm

Table No. 3.1 Engine Specifications

45

3.2 Vibration measurement:

A portable hand held vibration monitoring instrument is used with piezoelectric

accelerometers for monitoring the engine vibrations for the study. The details of the

instrument are as under:

Make- PRÜFTECHNIK

Model- VIBXPERT Data collector and FFT analyzer

VIBXPERT is a high performance, full-featured FFT data collector and signal analyzer

which allows easy condition monitoring of equipment found in many industries such as

power generation, petrochemical, pulp and paper. VIBXPERT collects field data

including vibration information, bearing condition, inspection and process data and

integrates with PRÜFTECHNIK’s OMNITREND maintenance information platform.

46

Fig. 3.1 VIBXPERT – Vibration Measuring Instrument

Key features

• High measurement accuracy, high-speed data collection

• Collects Route and Off-Route data

• Almost every sensor can be connected

• 1 or 2 analog meas. channels (optional). Upgrade via passcode - no hardware changes

required.

• Two true synchronous channel capabilities for diagnosis of complex machinery faults

• Unlimited storage capacity via replaceable compact flash cards

• Overall values such as Acceleration, velocity, displacement can be measured.

The instrument allows convenient and clear data evaluation and archival on a PC.

Graphic trend plots are displayed; spectra and time signals can be analyzed in detail. All

measurement procedures and settings can be defined and edited using the OMNITREND

PC program. It brings together all the advantages of quick and reliable measurement

Collection.

Fig. 3.2 Accelerometer and Magnetic Holder

Fig. 3.3 Spiral Cable for Accelerometer

47

Fig. 3.4 USB Cable for Communication

3.3 Bio Fuel Used:

Biodiesel obtained from raw Ambadi Oil. The biodiesel has been prepared in the

laboratory by standard process using methanol and KOH as catalysts. The properties of

the biodiesel so obtained were as per acceptable standards adopted by researchers in

biodiesel research area.

3.4 Diesel Used:

High performance premium diesel fuel marketed by Bharat Petroleum in the brand name

“Speed Diesel” is used for normal engine tests under different loads and parameters.

3.5 Engine Parameters:

The performance of a DI-CI diesel engine depends greatly on the operating parameters:

compression ratio, injection presure, loads and blends of biodiesel (Ambadi oil). To

obtain the vibration characteristics of a DICI diesel engine we have taken the following

parameters within a feasible and optimum range:

1. Compression Ratio

2. Injection Pressure

3. Load

4. Blends

48

1) Compression ratio (CR) test:

According to the manufacturer the prescribed standard value of injection

pressure is 210 bar.

Rated power 3.5 kW at 1500 rpm which is obtained at 12 kg load.

Variable CR range: 18, 17.5, 17, 16.5, 16.

The maximum limit of C.R is taken as 18 as greater values are not

permitted. Minimum value is 16 as lesser values gives power loss in

engine. We have taken values of compression ratio with a difference of

0.5, as it gives a better view of the characteristics.

2) Load test:

According to the manufacturer the prescribed standard values of injection

pressure is 210 bar and compression ratio is 17.5.

Constant parameters are – Compression ratio 17.5, Injection pressure 210

bar.

Variable Load range: 0%, 25%, 50%, 75%, 100%, 125%.

The load range is taken from no load (0%) to over load (125%).

The load is increased from 0 to 15 kg at constant intervals of 3 kg.

3) Injection pressure (IP) test:

Constant parameter is – Compression ratio 17.5.

IP range: 100, 150, 200, 250. (bar)

The standard value of IP is 200 bar and we have taken upper and lower

limits of 250 and 100 bars respectively, as above the upper limit the spray

jet crosses the region of combustion thus the combustion is not proper and

below the lower limit due to very low IP the spray jet doesn’t reach the

combustion region.

49

4) Blends Test:

Constant parameters: Injection pressure 210 bar, Compression Ratio 17.5

Rated Power 3.5 kW at 1500 rpm which is obtained at 12 kg load.

As the biodiesel research is aimed at optimizing the engine performance

with maximum substitution of diesel, different blends are being worked

upon. The review of literature has shown that still scientists are trying to

work with pure biodiesel whereas many other studies concluded that B20

is the best for almost all kinds of biodiesel. Some studies with higher

blends gave good performance which can be attributed to the different

sources of raw vegetable oils used for making biodiesel.

Hence, to generalize the results of the study, we have selected different

blendes of biodiesel with diesel ranging from B0 to B100 (B0, B10, B20,

B50, B75 and B100)*. The tests at different load has been carried out with

diesel fuel, so the blendes were used for testing and measuring vibration

signals at a constant load set of full load only.

Note: B stands for biodiesel and 0, 10, 20, 50, 75, 100 repersent the percentage of biodiesel in biodiesel

blends.

3.6 Test procedure:

To perform the test to observe the effects of various engine parameters and biodiesel

blends on engine vibrations the following procedure is followed.

First of all we join the accelerometer cable and USB cable with VIBXPERT and then

another end of the USB cable is attached to a computer. The engine and cooling water

system is allowed to run.

A route is made in computer using PRÜFTECHNIK’s OMNITREND software and then

the route is downloaded to the VIBXPERT. The route is made as follows:

50

Fig.3.5 Route for Test Procedure

The accelerometer is attached, first to cylinder head and then to cylinder block to observe

the vibrations occurring in axial and lateral directions respectively. The VIBXPERT

provides values of amplitude from P-P, 0-P and RMS.

These values are then uploaded to the computer attached to VIBXPERT using USB

cable. A fresh route is then again made in the computer and downloaded to the

VIBXPERT and same procedure is followed.

Fig.3.6 Positions of Accelerometer

By changing various engine parameters different tests are performed following the same

procedure and the values obtained from the vibxpert of each test is used to observe the

effects of engine parameters and biodiesel blends on engine vibrations.

In biodiesel blend test the engine parameters are kept constant and only the biodiesel

blends are changed according to the prescribed manner.

51

Chapter 4

Result and Discussion

By following the test procedure various graphs are obtained by changing various

engine parameters and biodiesel blends. Now we will discuss the various

characteristics obtained from the graphs below.

4.1 Compression ratio test:

Constant parameters: Injection pressure 200 bars, Load 12 kg, Shaft speed 1500 RPM

C.R range: 18, 17.5, 17, 16.5, 16

C.R. Peak-Peak (mm/sec) Zero-Peak (mm/sec) RMS (mm/sec)

16 130.09 73.99 33.71

16.5 118.64 68.65 30.51

17 113.75 67.03 29.49

17.5 114.39 66.71 28.99

18 146.74 82.67 37.41

Table No. 4.1 CR Test (Lateral Vibrations)

0

20

40

60

80

100

120

140

160

15.5 16 16.5 17 17.5 18 18.5Compression Ratio

mm

/se

c.

Peak-Peak(mm/sec)

Zero-Peak(mm/sec)

RMS(mm/sec)

Graph 4.1 CR Test (Lateral Vibrations)

52

Table No. 4.2 CR Test (Axial Vibrations)

0

20

40

60

80

100

120

140

160

180

15.5 16 16.5 17 17.5 18 18.5

Compression Ratio

mm

/sec

.

Peak-Peak(mm/sec)

Zero-Peak(mm/sec)

RMS(mm/sec)

Graph 4.2 CR Test (Axial Vibrations)

Considering above characteristics it is found that the lateral vibration decreases from CR

16 to 17.5, at 17.5 least vibrations occur and maximum vibrations occur at CR 18.

Axial vibrations are decreasing continuously from maximum to minimum value with

increase in CR from 16 to 18.Vibrations are maximum at 16.5 and minimum at 18.

4.2 Load test:

CR Peak-Peak (mm/sec) Zero-Peak (mm/sec) RMS (mm/sec)

16 165.52 84.19 13.77

16.5 169.08 88.64 13.48

17 159.86 82.93 13.82

17.5 144.03 76.34 12.9

18 101.24 52.85 10.65

53

Constant parameters: Compression ratio 17.5, Injection pressure 200 bar, Shaft speed

1500 RPM

Load range: 0%, 25%, 50%, 75%, 100%, 125%

Load (%) Peak-Peak (mm/sec) Zero-Peak (mm/sec) RMS (mm/sec)

0 137.09 74.12 34.73

25 131.55 71.81 32.95

50 116.88 65.33 29.37

75 120.57 67.71 30.39

100 103.57 61.98 27.31

125 96.79 57.25 25.85

Table No. 4.3 Load Test (Lateral Vibrations)

Graph 4.3 Load Test (Lateral Vibrations)

Table No. 4.4 Load Test (Axial Vibrations)

Load (%) Peak-Peak (mm/sec) Zero-Peak (mm/sec) RMS (mm/sec)

0 67.79 42.75 9.21

25 77.06 41.16 9.39

50 101.84 53.53 10.56

75 121.09 66.63 11.29

100 114.1 59.15 10.98

125 92.89 52.2 10.06

54

Graph 4.4 Load Test (Axial Vibrations)

Considering above characteristics it is found that the lateral vibrations are decreasing

continuously from maximum to minimum value with increase in load from no load to

over load. Vibrations are maximum at 0% load and minimum at over load.

Axial vibrations increases with increase in load from 0% to 75% load,and after that

it decreaes.Maximum vibrations occur at 75%load and minimum at 0%load.

4.3 Injection pressure test:

Constant parameters: Compression ratio 17.5, Load 12 kg, Shaft speed 1500 RPM

I.P. range: 250, 200, 150, 100 (bar)

IP (bar) Peak-Peak (mm/sec) Zero-Peak (mm/sec) RMS (mm/sec)

250 102.39 61.18 26.6

200 121.87 72.05 31.72

150 145.51 81.91 37.22

100 162.14 89.11 40.44

Table No. 4.5 IP Test (Lateral Vibrations)

55

0

20

40

60

80

100

120

140

160

180

0 50 100 150 200 250 300

Injection Pressure (bar)

mm

/sec

.Peak-Peak(mm/sec)

Zero-Peak(mm/sec)

RMS(mm/sec)

Graph 4.5 IP Test (Lateral Vibrations)

Table No. 4.6 IP Test (Axial Vibrations)

IP (bar) Peak-Peak (mm/sec) Zero-Peak (mm/sec) RMS (mm/sec)

250 118.39 60.64 10.95

200 124.66 65.77 11.79

150 129.25 66.87 11.69

100 139.47 78.19 12.65

56

0

20

40

60

80

100

120

140

160

0 100 200 300

Injection Pressure (bar)

mm

/sec

.Peak-Peak(mm/sec)

Zero-Peak(mm/sec)

RMS(mm/sec)

Graph 4.6 IP Test (Axial Vibrations)

Considering above characteristics it is found that the both lateral and axial vibrations

decreases with increase in IP from 100 to 250 bar.

Both lateral and axial vibrations are maximum at 100 bar and minimum at 250 bar.

4.4 Blend test:

Constant parameters: Compression ratio 17.5, Load 12 kg, Injection pressure 200 bar,

Shaft speed1500 RPM

Blend range: B0, B10, B20, B50, B75, B100

Blend (D+B) Peak-Peak (mm/sec) Zero-Peak (mm/sec) RMS (mm/sec)

0 114.39 66.71 28.99

57

10 107.92 62.96 28.12

20 114.47 67.14 29.59

50 94.49 55.52 25.08

75 129.69 72.84 32.38

100 121.85 68.27 29.15

Table No. 4.7 Blend Test (Lateral Vibrations)

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120

Biodiesel Blends

mm

/sec

.

Peak-Peak(mm/sec)

Zero-Peak(mm/sec)

RMS(mm/sec)

Graph 4.7 Blend Test (Lateral Vibrations)

Blend (D+B) Peak-Peak (mm/sec) Zero-Peak (mm/sec) RMS (mm/sec)

0 144.03 76.34 12.9

10 127.1 64.96 11.9

20 130.01 66.94 12.31

50 108.7 56.57 11.06

75 117.35 63.28 12.14

100 116.42 61.86 11.86

58

Table No. 4.8 Blend Test (Axial Vibrations)

0

20

40

60

80

100

120

140

160

0 20 40 60 80 100 120Biodisesl Blendes

mm

/sec

Peak-Peak(mm/sec)

Zero-Peak(mm/sec)

RMS(mm/sec)

Graph 4.8 Blend Test (Axial Vibrations)

Considering above characteristics it is found that the lateral vibration varies with

variation in biodiesel blends. Almost same pattern is obtained for both lateral and axial

vibrations.

Lateral vibrations are maximum at B75 and minimum at B50, whereas axial vibrations

are maximum at B0 and minimum at B50.

4.5 Effect of lateral and axial vibrations:

Axial vibrations produced in engine causes wear and tear of engine cylinder, some

cavities are also formed in engine head due to fatigue. The parts of engine like ports,

valves, cylinder head gaskets are loosened due to all these failures the engine

performance is decreased to a great extent. But the shock waves formed due to axial

vibrations can be retarded by providing tight connections between the joints and the

material used for the joints should withstand the shocks and vibrations produced in axial

directions.

59

Lateral vibrations formed in the cylinder block produces shock waves in direction

perpendicular to axial direction. These shock waves causes wear and tear of the whole

engine assembly as well as foundation joints resulting in over all structural failure strong

foundation and suitable material able to withstand shocks and vibrations.

The vibrations produced in engine are undesirable, maximum engine failure is caused due

to lateral vibrations so in order to have smooth running of engine lateral vibrations should

be reduced to minimum.

60

Summary

The objective of our project is “A study on the effect of engine parameters and fuel

blends on vibration characteristics of a direct injection compression ignition (DI-CI)

engine”. The above objective has been carried out in order to see the vibration

characteristics of DI-CI engine by changing various parameters such as compression

ratio, injection pressure, loads and fuel blends.

A portable hand held vibration monitoring instrument is used with piezoelectric

accelerometers for monitoring the engine vibrations, i.e. VIBXPERT. To study the

vibrations occurring in engine in longitudinal (axial) and lateral directions, two

accelerometers were attached, one on head and another on cylinder block respectively.

The vibration characteristics and values of the amplitudes (0-P, P-P, RMS) in both the

directions are obtained automatically in the VIBXPERT.

By using the values of different amplitudes with there respective tests different graphs are

formed and by using these graphs different conclusions are made.

By considering the characteristics in compression ratio (CR) test it was found that lateral

vibrations were maximum at CR 18 and minimum at 17.5, whereas axial vibrations were

maximum at 16.5 and minimum at 18.

Referring the characteristics drawn for Load test, in lateral vibrations were maximum at

no or zero load and minimum at overload. On the other hand vibrations were least at zero

load and greatest at 75% load.

The injection pressure (IP) test both the vibrations characteristics were almost similar in

pattern and it was concluded that there is a linear decrement in vibration amplitudes with

the increase in IP from 100 to 250 bars.

By carrying out the test for the engine with using different blends it was found that both

the vibrations were minimum at B50, whereas the lateral vibrations were maximum at

B75 and axial vibrations were maximum at B0.

61

From Load test, IP test and biodiesel blend characteristics it is observed that lateral

vibrations are more than the axial vibrations produced in the engine.

As the lateral vibrations cause the structural failure of the engine set up, these vibrations

should be reduced to minimum.

By overall study of the objective gives ideas to observe the vibration characteristics

obtained by varying the various engine parameters and biodiesel blends. By knowing the

effects of engine parameters and biodiesel blends on the engine vibrations, the vibrations

can be controlled by varying the parameters. Hence the engine failure can be minimized.

62