Ns.seminar Report

LASER IGNITION SYSTEM

SEMINAR REPORT

Semester 7, 2014-2015

Submitted by

GAUTHAM SARANG

DEPARTMENT OF MECHANICAL ENGINEERING

RAJAGIRI SCHOOL OF ENGINEERING & TECHNOLOGY

KOCHI - 682039

RAJAGIRI SCHOOL OF ENGINEERING & TECHNOLOGY

KOCHI 682 039

DEPARTMENT OF MECHANICAL ENGINEERING

CERTIFICATE

This is to certify that the report on the Seminar titled LASER IGNITION SYSTEM is submitted by GAUTHAM SARANG in partial fulfillment of the requirements for the award of B.Tech Degree in Mechanical Engineering is

a bonafide record of the Seminar done by him during the SEVENTH

semester in the academic year 2014 - 2015.

Mr. Manoj G Tharian Mr. Sidheek P.A

Assistant Professor & HoD Assistant Professor

Department of ME Department of ME

RSET, Kakkanad RSET, Kakkanad

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Department of Mechanical Engineering, RSET, Kochi-682039

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ABSTRACT

Nowadays, applications of different lasers span quite broadly from

diagnostics tools in science and engineering to biological and medical uses. In this

presentation basic principles and applications of lasers for ignition of fuels are

concisely reviewed from the engineering perspective. The objective is to present

the current state of the relevant knowledge on fuel ignition and discuss select

applications, advantages and disadvantages, in the context of combustion engines.

Fundamentally, there are four different ways in which laser light can interact with

a combustible mixture to initiate an ignition event. They are referred to as thermal

initiation, nonresonant breakdown, resonant breakdown, and photochemical

ignition.

By far the most commonly used technique is the nonresonant initiation

of combustion primarily because of its freedom in selecting the laser wavelength

and ease of implementation.

Recent progress in the area of high power fiber optics allowed convenient

shielding and transmission of the laser light to the combustion chamber. However,

issues related to immediate interfacing between the light and the chamber such as

selection of appropriate window material and its possible fouling during the

operation, shaping of the laser focus volume, and selection of spatially optimum

ignition point remain amongst the important engineering design challenges. One

of the potential advantages of the lasers lies in its flexibility to change the ignition

location. Also, multiple ignition points can be achieved rather comfortably as

compared to conventional electric ignition systems using spark plugs. Also reduce

emissions of NOx to atmosphere. Although the cost and packaging complexities

of the laser ignition systems have dramatically reduced to an affordable level for

many applications, they are still prohibitive for important and high-volume

applications such as automotive engines.

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ACKNOWLEDGEMENT

I express my sincere thanks to the almighty whose divine intervention was

instrumental in successful completion of this work.

I hereby place in record, my sincere thanks, gratitude and graceful

acknowledgement to Mr. Manoj G Tharian, Assistant Professor & HoD,

Department of Mechanical Engineering, Rajagiri School of Engineering &

Technology.

I also express my sincere thanks to Mr. Sidheek P.A, Assistant Professor,

Department of Mechanical Engineering, Rajagiri School of Engineering &

Technology, Mr. James Mathew, Assistant Professor, Department of Mechanical

Engineering, Rajagiri School of Engineering & Technology, Mr. Jithin P.N,

Assistant Professor, Department of Mechanical Engineering, Rajagiri School of

Engineering & Technology, Mr. Mathew Baby, Assistant Professor, Department

of Mechanical Engineering, Rajagiri School of Engineering & Technology and

other staff members of the department for immense help provided by them.

GAUTHAM SARANG

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CONTENTS

ABSTRACT i

ACKNOWLEDGEMENT ii

LIST OF FIGURES vi

LIST OF TABLES vii

1. INTRODUCTION 01

2. INTERNAL COMBUSTION ENGINES 03

2.1 PARTS OF AN IC ENGINE 03

2.1.1 Cylinder Head 03

2.1.2 Cylinder Block And Cylinder Liner 03

2.1.3 Piston 04

2.1.4 Connecting Rod 04

2.1.5 Crankshaft 05

2.1.6 Crank Case And Sump 05

2.2 FOUR STROKE I C ENGINES 05

2.2.1 Working Principle Of A Four Stroke SI Engine 05

2.2.2 Four Stroke CI Engine 06

2.3 COMBUSTION IN SI ENGINES 07

2.4 COMBUSTION IN CI ENGINES 07

2.5 COMBUSTION IN CI ENGINES 07

2.5.1 COMBUSTION 08

2.5.2 KNOCK 08

2.5.3 AUTO IGNITION 09

2.5.4 SELF IGNITION 09

2.5.5 PRE-IGNITION 10

2.5.6 INDUCED IGNITION 10

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3. CONVENTIONAL SPARK IGNITION 11

3.1 THE FUNCTIONS OF AN IGNITION SYSTEM 12

3.2 SPARK PLUG 12

3.3 PROBLEMS OF A SPARK PLUG 13

3.4 DRAWBACKS OF SPARK IGNITION 14

4. LASER 15

4.1 PROPERTIES OF LASER LIGHT 15

4.2 LASERS AND THEIR EMISSION WAVELENGTHS 15

4.3 TYPES OF LASERS 16

4.3.1 GAS LASERS 16

4.3.2 CHEMICAL LASERS 16

4.3.3 EXCIMER LASERS 17

4.3.4 SOLID-STATE LASERS 17

4.3.5 SEMICONDUCTOR LASERS 17

4.3.6 DYE LASERS 17

5. LASER INDUCED SPARK IGNITION 18

5.1 REASONS FOR ADAPTING LASER IGNITION 19

5.2 METHODS OF ENERGETIC INTERACTIONS 20

5.2.1 THERMAL BREAKDOWN 20

5.2.2 RESONANT BREAKDOWN 20

5.2.3 NON RESONANT BREAKDOWN 21

5.2.4 PHOTOCHEMICAL MECHANISMS 21

5.3 PRINCIPLE OF LASER IGNITION 22

5.4 PHASES IN LASER IGNITION 23

5.5 WORKING 23

5.6 PARTS OF LASER IGNITION SYSTEM 24

5.4.1 POWER SOURCE 25

5.4.2 Nd:YAGLASER 25

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5.4.3 COMBUSTION CHAMBER WINDOW 26

5.4.4 OPTIC FIBER WIRE 27

5.4.5 FOCUSING UNIT 28

5.5 MULTIPOINT IGNITION 28

6. MINIMUM ENERGY REQUIRED FOR IGNITION 29

7. PRACTICAL LASER IGNITION REQUIREMENTS 30

7.1 MECHANICAL REQUIREMENTS 30

7.2 ENVIRONMENTAL REQUIREMENTS 30

7.3 PEAK POWER REQUIREMENTS 31

8. ADVANTAGES AND CHALLENGES ` 32

8.1 ADVANTAGES OF LASER IGNITION 32

8.2 DISADVANTAGES OF LASER IGNITION 33

8.3 CHALLENGES OF LASER IGNITION 33

9. CONCLUSION 34

10. REFERENCES 35

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LIST OF FIGURES

1. Fig 2.1 IC Engine 04 2. Fig 3.1 four stroke cycle 11 3. Fig 5.1 Resonant Laser-Induced Ignition 20 4. Fig 5.2 Nonresonant Laser-Induced Ignition 21 5. Fig 5.3 Photochemical Laser-Induced Ignition 22 6. Fig 5.4 Principle Of Laser Ignition 22 7. Fig 5.5 Time Scales in Laser Ignition 23 8. Fig 5.6 Optical breakdown in air generated 24

by a Nd:YAG laser

9. Fig 5.7 Laser Arrangement with Respect to Engine 25 10. Fig 5.8 Window Arrangement 27 11. Fig 5.9 Focusing Optics 28 12. Fig 5.10 Approach for Multipoint Ignition 28

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LIST OF TABLES

1. TABLE 4.1 Lasers And Their Emission Wavelengths 16

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CHAPTER 1

INTRODUCTION

Internal combustion engines are widely spread in our civilization. They

are used in energy production and industry and play a major role in transportation.

At the moment most of them are ignited by spark plugs which are the dominating

technology. They provide the advantages of already being on a highly advanced

development level and the possibility of low cost mass production. Nevertheless

this advanced development significantly restricts the potential for considerable

further improvements. Therefore the major objective for new types of ignition

systems is to provide development perspectives especially regarding the reduction

of fuel and energy consumption and the reduction of exhaust emissions. An

increase in efficiency and a simultaneously decreasing level of emissions are

needed. A possibility to achieve both is closely connected with the inflammability

limits of the ignition systems. If a system is able to ignite leaner gas-air mixtures,

the combustion takes place at a lower temperature. This results in reduced NOx

output. Additionally the ignition of leaner gas-air mixtures increases the fuel

efficiency of the combustion process.

The two most promising new types of ignition systems are the Laser

ignition and the Corona ignition. Both ideas are already known for several

decades. Nevertheless neither of them is in industrial use at the moment.

There have been series of advancements in the field of automobiles.

Modern science and technology have contributed to this fact. One such

advancement is the usage of laser for the combustion process in the combustion

chamber. Laser ignition is an emerging technology, still under development,

has a promising future.

With the advent of lasers in the 1960s, researchers and engineers

discovered a new and powerful tool to investigate natural phenomena and

improve technologically critical processes. Nowadays, applications of different

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lasers span quite broadly from diagnostics tools in science and engineering to

biological and medical uses. In this seminar basic principles and applications of

lasers for ignition of fuels are concisely reviewed from the engineering

perspective. The objective is to present the current state of the relevant knowledge

on fuel ignition and discuss select applications, advantages and disadvantages, in

the context of combustion of engines. Fundamentally, there are four different

ways in which laser light can interact with a combustible mixture to initiate an

ignition event. They are referred to as thermal initiation, non-resonant breakdown,

resonant breakdown, and photochemical ignition.

By far the most commonly used technique is the non-resonant initiation of

combustion primarily because of its freedom in selecting the laser wavelength and

ease of implementation. Recent progress in the area of high power fiber optics

allowed convenient shielding and transmission of the laser light to the combustion

chamber. However, issues related to immediate interfacing between the light and

the chamber such as selection of appropriate window material and its possible

fouling during the operation, shaping of the laser focus volume, and selection of

spatially optimum ignition point remain amongst the important engineering

design challenges. One of the potential advantages of the lasers lies in its

flexibility to change the ignition location. Also, multiple ignition points can be

achieved rather comfortably as compared to conventional electric ignition systems

using spark plugs.

.

Although the cost and packaging complexities of the laser ignition systems

have dramatically reduced to an affordable level for many applications, they are

still prohibitive for important and high-volume applications such as automotive

engines. However, their penetration in some niche markets, such as large

stationary power plants and military applications, are imminent. Lasers a type of

nonconventional ignition sources can contribute to a future performance

optimization.

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CHAPTER 2

INTERNAL COMBUSTION ENGINES

An engine is a machine designed to convert energy into useful mechanical

energy. Heat engines absorb energy in the form of heat and convert part of it into

mechanical energy and deliver it as work, the balance being rejected as heat.

These devices derive the heat energy from the combustion of a fuel. Based on the

location of the combustion process, heat engines are classified into internal

combustion and external combustion engines.

Internal combustion engines (IC engines) are those where the combustion

of the fuel takes place inside the engines. eg: Automobile engines.

In external combustion engines, combustion of fuel occurs outside the

engines and the working gas so heated is then admitted into the engines for

conversion and work extraction. eg: steam generated in a boiler is then admitted to

steam turbines for producing work.

2.1 PARTS OF AN IC ENGINE

The main components of a standard IC engine are briefly described below:

2.1.1 Cylinder Head

Cylinder head is the top cover of the cylinder and holds the inlet and

exhaust valves, their operating mechanisms, and the spark plug or fuel injector, as

the case may be. The valves along with their operating mechanism are together

called the valve gear.

2.1.2 Cylinder Block And Cylinder Liner

The cylinder head is fitted over the cylinder block and liner. The space

between the block wall and cylinder liner acts as the cooling water jacket.

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2.1.3 Piston

The piston is of cylindrical shape to fit the inside bore of the cylinder. Gas

tightness is ensured by means of the piston rings in the slots on the outer

cylindrical surface of the piston.

2.1.4 Connecting Rod

The Connecting rod is the link connecting the piston to the crankshaft for

transmission of the forces from and to the piston. The pin connecting it to the

piston is called the gudgeon pin and that connecting it to the crankshaft as the

crank pin.

Fig 2.1 IC Engine

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2.1.5 Crankshaft

The Crankshaft is a shaft with radial cranks, which converts the

reciprocating motion of the piston into rotary motion of the shaft.

2.1.6 Crank Case And Sump

Crank case is the engine casing having the main bearings in which the

crank shaft rotates. The bottom cover of the engine is the sump which usually acts

as a lubricating oil reservoir.

2.2 FOUR STROKE I C ENGINES

In a four-stroke engine, the cycle of operations is completed in four strokes of

the piston or two revolutions of the crankshaft. During the four strokes, there are

five events to be Completed, viz., suction, compression, combustion, expansion

and exhaust. Each stroke consists of 180 of crankshaft rotation and hence a four-

stroke cycle is completed through 720 of crank rotation. The cycle of operation

for an ideal four-stroke SI engine consists of the following four strokes:

1. Suction Stroke (0 -180)

2. Compression Stroke (180-360)

3. Expansion Stroke (360-540)

4. Exhaust Stroke (540-720)

2.2.1 Working Principle Of A Four Stroke SI Engine

Suction or Intake Stroke: Suction stroke 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. Due to the suction created by the motion of the piston

towards the bottom dead centre, the charge consisting of fuel-air mixture is drawn

into the cylinder. When the piston reaches the bottom dead centre the suction

stroke ends and the inlet valve closes. The charge taken into the cylinder during

the suction stroke is compressed by the return stroke of the piston. During this

stroke both inlet and exhaust valves are in closed position. The mixture that 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

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

place instantaneously when the piston is at 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 C

The pressure at the end of the combustion process is considerably

increased due to the heat release from the fuel. At the end of the expansion stroke

the exhaust valve opens and the inlet valve remains closed. 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 and sweeps the burnt gases out from the

cylinder almost at atmospheric pressure. The exhaust valve closes when the piston

reaches T DC. 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 cycle, forming 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 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 by two revolutions. For getting higher output from the engine the

heat release should be as high as possible and the heat rejection should be as small

as possible.

2.2.2 Four Stroke CI 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 an 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 inducted. 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.

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The ideal sequence of operations for the four-stroke CI engine is as follows:

i. Suction Stroke: Air alone is inducted during the suction stroke. During this stroke intake valve is open and exhaust valve is closed.

ii. Compression Stroke: Air inducted during the suction stroke is compressed into the clearance volume. Both valves remain closed during this stroke.

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 cutoff) the products of combustion expand. Both the valves remain

closed during the expansion stroke.

iv. Exhaust Stroke: The piston traveling from EDC to TDC pushes out the products of combustion. The exhaust valve is open and the intake valve is

closed during this stroke.

2.3 COMBUSTION IN SI ENGINES

Combustion is a chemical reaction in which certain elements of the fuel

like hydrogen and carbon combine with oxygen liberating heat energy and causing

an increase in temperature of gases. The conditions necessary for combustion are

The presence of a combustible mixture

Initiation for combustion

Stabilization and propagation of flame in combustion chamber.

In SI engines combustible mixture is generally supplied by the carburetor

and the combustion is initiated by an electric spark given by spark plug.

2.4 COMBUSTION IN CI ENGINES

In the CI engine, for a given speed, and irrespective of load, an

approximately constant supply of air enters the cylinder. The CI engine therefore

can be termed constant air supply engine. With change in load the quantity of fuel

is change, which changes the air-fuel ratio. The overall air-fuel ration may thus

vary from about 100:1 at no load and 20:1 at full load.

Whatever may be the overall air-fuel ratio in a CI engine due to injection

of fuel, there is a heterogeneous mixture with air-fuel ratio varying widely in

different areas within the chamber. There would be area where the mixture is very

lean or very rich. However there would be certain areas where the local-air-fuel

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ratio is within combustible limits and there under favorable conditions of

temperature, ignition occurs.

In full load condition the mixture slightly leaner than stoichiometric. The

poor distribution of fuel and its intermixing with air results in objectionable smoke

if operated near chemically correct ratio and (Air fuel ratio 20-23, i.e. excess air

35 to 50%) hence the CI engine must always operate with excess air.

2.5 TECHNICAL TERMS

2.5.1 COMBUSTION

Combustion is defined as the burning of a fuel and oxidant to produce heat

or work. Combustion includes thermal, hydrodynamic, and chemical processes. It

starts with the mixing of fuel and oxidant, and sometimes in the presence of other

species or catalysts. The fuel can be gaseous, liquid, or solid and the mixture may

be ignited with a heat source. When ignited, chemical reactions of fuel and

oxidant take place and the heat release from the reaction creates a self-sustained

process. The combustion products include heat, light, chemical species, pollutants,

mechanical work and plasma. Sometimes, a low-grade fuel, e.g., coal, biomass, or

coke, can be partially burned to produce higher-grade fuel, e.g., methane. The

partial burning process is called gasification. Various combustion systems, e.g.,

furnaces, combustors, boilers, reactors, and engines, are developed to utilize

combustion heat, chemical species, and work.

2.5.2 KNOCK

Knock is the most important abnormal combustion phenomenon. It

important because it puts a limit on the compression ratio at which an engine can

be operated, which in turn controls the efficiency and to some extent the power

output. It got the name knock because of the noise that results from the auto

ignition of a portion of fuel air mixture ahead of the advancing flame. As the

spark is ignited there is a formation of flame front and it starts propagating. As the

flame propagates across the combustion chamber, speed of flame front is

about 15 to 30 m/s ; the unburned charge ahead of the flame called the end

gas is compressed, raising its pressure, temperature and density. In case of

abnormal combustion the end gas fuel air mixture undergo fast chemical

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reactions, which results in auto ignition prior to normal combustion (i.e. the

flame front reaching it). During auto ignition a large portion of end gas releases

its chemical energy rapidly and spontaneously at a rate 5 to 25 times as in case of

normal combustion. This spontaneous ignition of the end gas raises the

pressure very rapidly and causes high frequency oscillations inside the

cylinder resulting in a high pitched metallic noise characterized as knock. During

this knocking phenomenon pressure waves of very large amplitudes propagate

across the combustion chamber and very high local pressures are produced

which are as high as 150 to 200 bars. Local 5% of the total charge is sufficient

to produce a very violent serve knock. The velocity reached during knock is of the

order of 300 to 1000 m/s.

2.5.3 AUTO IGNITION

The auto ignition temperature or kindling point of a substance is the lowest

temperature at which it will spontaneously ignite in a normal atmosphere without

an external source of ignition, such as a flame or spark. This temperature is required

to supply the activation energy needed for combustion. The temperature at which

chemical will ignite decreases as the pressure increases or oxygen concentration

increases. It is usually applied to a combustible fuel mixture.

2.5.4 SELF IGNITION

Spontaneous combustion or self-ignition is a type of combustion which

occurs without an external ignition source. Spontaneous combustion is a term used to

describe how something just ignited (spontaneously) but in fact spontaneous

combustion is more than usually, a slow process that can take several hours of

decomposition / oxidization with heat build up to a point of ignition.

The reasons for self-ignition:

A substance with a relatively low ignition temperature begins to release heat,

which may occur in several ways, such as oxidation or fermentation.

The heat is unable to escape, and the temperature of the material rises.

The temperature of the material rises above its ignition point

Combustion begins if a sufficiently strong oxidizer, such as oxygen, is

present.

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2.5.5 PRE-IGNITION

Pre-ignition is the phenomenon of surface ignition before the passage of

spark. The usual cause is an overheated spot, which by occur at spark plugs,

combustion chamber deposits, or exhaust valves. Mostly it is due to spark plug.

Exhaust valve usually run hot and sometimes when there is increase in heat load

for these valves there will be an increase in the temperature and may cause pre

ignition. Heat transfer principles indicate that the surface of the deposits is

hotter than the metal surface to which the deposits are attached. Hence, sufficient

deposits result in hot enough surfaces to cause pre ignition.

Pre-ignition is potentially the most damaging surface ignition phenomenon.

The effect of pre-ignition is same as very advanced ignition timing. Any process that

advances the start of combustion that gives maximum torque will cause higher

heat rejection because of the increased burned gas pressures and temperatures (due

to the negative work done during the compression stroke). Higher heat rejection

causes higher temperature components thus the pre ignition damage is largely

thermal which is evidenced by the fusion of spark plugs, piston and destruction of

piston rings.

2.5.6 INDUCED IGNITION

A process where a mixture, which would not ignite by itself, is ignited

locally by an ignition source (i.e. electric spark plug, pulsed laser, microwave

ignition source) is called induced ignition. In induced ignition, energy is

deposited, leading to a temperature rise in a small volume of the mixture, where

auto ignition takes place or the energy is used for the generation of radicals. In

both cases a subsequent flame propagation occurs and sets the mixture on fire.

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CHAPTER 3

CONVENTIONAL SPARK IGNITION

In a petrol engine, the fuel and air are usually pre-mixed before

compression. The pre-mixing was formerly done in a carburettor, but now (except

in the smallest engines) it is done by electronically controlled fuel injection.

In this system fuel entering the engine cylinder is ignited by means of a

spark. The required amount of fuel is induced into the cylinder during suction

stroke. This fuel is ignited during the compression stroke by a spark produced by a

spark plug. Due to the combustion of fuel large amount of heat and high pressure

gases are produced which expand causing linear motion of the piston

Fig 3.1 four stroke cycle

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3.1 THE FUNCTIONS OF AN IGNITION SYSTEM

The ignition system must provide an adequate voltage to initiate a

discharge across the spark plug electrodes and supply sufficient energy to ignite

the air-fuel mixture. This must occur for all the engines operating conditions and

at appropriate time on the compression stroke.

On the modern engines, it is normal for the ignition system to form a

subsection of an integrated management system, sharing sensors and circuits, with

fuelling and transmission control system.

However the ignition system does the following functions:

When the compression ratio is lower and self-ignition temperature is quite

high, an external source of ignition must be given.

This takes place close to the compression stroke.

The function of the ignition system is to propagate the flame and should

supply energy within a small volume.

The ignition should occur in a time interval sufficiently short time to

ensure that only a negligible amount of energy is lost other than to

establish the flame.

3.2 SPARK PLUG

A spark plug (also, very rarely nowadays, in British English: a sparking

plug), is an electrical device that fits into the cylinder head of some internal

combustion engines and ignites compressed fuels such as aerosol gasoline,

ethanol, and liquefied petroleum gas by means of an electric spark. Spark plugs

have an insulated central electrode which is connected by a heavily insulated wire

to an ignition coil or magneto circuit on the outside, forming, with a grounded

terminal on the base of the plug, a spark gap inside the cylinder. A spark plug is

composed of a shell, insulator and the central conductor. It pierces the wall of the

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combustion chamber and therefore must also seal the combustion chamber against

high pressures and temperatures without deteriorating, over long periods of time

and extended use.

The plug is connected to the high voltage generated by an ignition coil or

magneto. As the electrons flow from the coil, a voltage difference develops

between the central electrode and side electrode. No current can flow because the

fuel and air in the gap is an insulator, but as the voltage rises further, it begins to

change the structure of the gases between the electrodes. Once the voltage

exceeds the dielectric strength of the gases, the gases become ionized. The ionized

gas becomes a conductor and allows electrons to flow across the gap. Spark plugs

usually require voltage of 12,00025,000 volts or more to 'fire' properly, although

it can go up to 45,000 volts. They supply higher current during the discharge

process resulting in a hotter and longer-duration spark.

As the current of electrons surges across the gap, it raises the temperature

of the spark channel to 60,000 K. The intense heat in the spark channel causes the

ionized gas to expand very quickly, like a small explosion. This is the "click"

heard when observing a spark, similar to lightning and thunder.

The heat and pressure force the gases to react with each other, and at the

end of the spark event there should be a small ball of fire in the spark gap as the

gases burn on their own. The size of this fireball or kernel depends on the exact

composition of the mixture between the electrodes and the level of combustion

chamber turbulence at the time of the spark. A small kernel will make the engine

run as though the ignition timing was retarded and a large one as though the

timing was advanced.

3.3 PROBLEMS OF A SPARK PLUG

Lean mixture causes the increase in demand for the ignition energy.When

the air-fuel ratio is very high (that means the content of fuel in that mixture is very

less), for the combustion process to take place, the mixture demands more

energy.This leads to the erosion of the spark plug and thus reduced reliability and

lifetime of the spark plug. When the mixture demands more energy, the spark

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plug has to supply the required energy for the combustion to take place. This in

turn causes the electrodes to wear off, otherwise called as erosion of the spark

plug. The electrodes of the spark plug should be located near the combustion wall

to avoid disturbance of the precisely designed flow. The spark plug has to be

placed in correct position for its smooth working and to burn the mixture in much

effective way.

3.4 DRAWBACKS OF SPARK IGNITION

Location of spark plug is not flexible as it require shielding of plug from

immense heat and fuel spray.

It is not possible to ignite inside the fuel spray.

It requires frequent maintenance to remove carbon deposits.

Leaner mixtures cannot be burned.

Degradation of electrodes at high pressure and temperature.

Flame propagation is slow.

Multi point fuel ignition is not feasible.

Higher turbulence levels are required.

Economic as well as environmental considerations

All the above drawbacks are overcome in laser ignition system explained as

follows.

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CHAPTER 4

LASER

Light Amplification by Stimulated Emission of Radiation (LASER or

laser) is a mechanism for emitting electromagnetic radiation, often visible light,

via the process of stimulated emission. The emitted laser light is (usually) a

spatially coherent, narrow low-divergence beam,that can be manipulated with

lenses. Laser light is generally a narrow-wavelength electromagnetic spectrum

monochromatic light.

.

4.1 PROPERTIES OF LASER LIGHT

1. Monochromatic: Photons of one wavelength. In contrast, ordinary white

light is a combination of different wavelengths.

2. Directional: Laser light is emitted as a narrow beam and in a specific

direction. This property is referred to as directionality.

3. Coherent: The light from a laser is said to be coherent. This means that the

wavelengths of the laser light are in phase.

4.2 LASERS AND THEIR EMISSION WAVELENGTHS

Laser Type Wavelength (nm)

Argon fluoride (UV) 193

Krypton fluoride (UV) 248

Xenon chloride (UV) 308

Nitrogen (UV) 337

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Argon (blue) 488

Argon (green) 514

Helium neon (green) 543

Helium neon (red) 633

Rhodamine 6G dye (tunable) 570-650

Ruby (CrAlO3) (red) 694

Nd:Yag (NIR) 1064

Carbon dioxide (FIR) 10600

Table 4.1 Lasers And Their Emission Wavelengths

4.3 TYPES OF LASERS

4.3.1 GAS LASERS

The Helium-neon laser (HeNe) emits 543 nm and 633 nm and is very common

in education because of its low cost. Carbon dioxide lasers emit up to 100 kW at

9.6 m and 10.6 m, and are used in industry for cutting and welding. Argon-Ion

lasers emit 458 nm, 488 nm or 514.5 nm. Carbon monoxide lasers must be cooled

but can produce up to 500 kW. The Transverse Electrical discharge in gas at

Atmospheric pressure (TEA) laser is an inexpensive gas laser producing UV Light

at 337.1 nm.

4.3.2 CHEMICAL LASERS

Chemical lasers are powered by a chemical reaction, and can achieve high powers

in continuous operation. For example, in the Hydrogen fluoride laser (2700-2900 nm) and

the Deuterium fluoride laser (3800 nm) the reaction is the combination of hydrogen or

deuterium gas with combustion products of ethylene in nitrogen trifluoride.

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4.3.3 EXCIMER LASERS

Excimer lasers produce ultraviolet light, and are used in semiconductor

manufacturing and in LASIK eye surgery. Commonly used excimer molecules include F2

(emitting at 157 nm), ArF (193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm), and

XeF (351 nm).

4.3.4 SOLID-STATE LASERS

Solid state laser materials are commonly made by doping a crystalline solid host

with ions that provide the required energy states. For example, the first working laser was

made from ruby, or chromium-doped sapphire. Another common type is made from

Neodymium-doped yttrium aluminium garnet (YAG), known as Nd:YAG. Nd:YAG

lasers can produce high powers in the infrared spectrum at 1064 nm. They are used for

cutting, welding and marking of metals and other materials, and also in spectroscopy and

for pumping dye lasers. Nd:YAG lasers are also commonly doubled their frequency to

produce

Solid state lasers also include glass or optical fiber hosted lasers, for example,

with erbium or ytterbium ions as the active species. These allow extremely long gain

regions, and can support very high output powers because the fiber's high surface area to

volume ratio allows efficient cooling and its wave guiding properties reduce thermal

distortion of the beam.

4.3.5 SEMICONDUCTOR LASERS

Laser diodes produce wavelengths from 405 nm to 1550 nm. Low power laser diodes are

used in laser pointers, laser printers, and CD/DVD players. More powerful laser diodes

are frequently used to optically pump other lasers with high efficiency. The highest power

industrial laser diodes, with power up to 10 kW, are used in industry for cutting and

welding. External-cavity semiconductor lasers have a semiconductor active medium in a

larger cavity. These devices can generate high power outputs with good beam quality,

wavelength-tuneable narrow-line width radiation, or ultra-short laser pulses.

4.3.6 DYE LASERS

Dye lasers use an organic dye as the gain medium. The wide gain spectrum of

available dyes allows these lasers to be highly tunable, or to produce very short-duration

pulses (on the order of a few femtoseconds).

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CHAPTER 5

LASER INDUCED SPARK IGNITION

The use of laser ignition to improve gas engine performance was initially

demonstrated by J. D. Dale in 1978.

However, with very few exceptions, work in this area has for the last 20

years been limited to laboratory experimentation employing large, expensive and

relatively complicated lasers and laser beam delivery systems.

More recently, researchers at GE-Jenbacher, Mitsubishi Heavy Industries,

Toyota, National Energy Technology Lab and Argonne National Lab have

obtained and/or built smaller high peak power laser spark plugs.

Unlike many earlier laboratory laser systems, these smaller lasers are now

mounted directly onto the engine cylinder head so as to fire the laser beam directly

into the chamber. This arrangement allows the laser to become a direct

replacement for the traditional high voltage electrical spark-gap plug. Further

reductions in laser size, price and complexity will help the laser spark plug

become a commercial reality and a viable competitor to the traditional high

voltage spark-gap plug.

The Otto or SI engine is today characterized by low pollutant emissions.

The very efficient exhaust gas treatment makes power drives for nearly equal zero

emission operation possible. There is however need for improvement of fuel

consumption and the higher carbon dioxide emissions compared to the Diesel

equivalent.

Advancing the state of art of ignition systems for lean burn, stationary,

natural gas fuelled engines is crucial to meet increased performance requirements.

As the demand for higher engine efficiencies and lower emissions drive

stationary, spark-ignited reciprocating engine combustion to leaner air/fuel

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operating conditions and higher in-cylinder pressures, increased spark energy is

required to maintain stable combustion and low emissions.

To compensate power density losses due to leaner operation, high pressure

of initial charge is used to increase in-cylinder pressure at the time of combustion.

However, an important parameter is the ignition under extreme conditions, lean

combustible mixture and high initial pressure, requiring high voltage when using

conventional spark plug technology. Providing the necessary spark energy to

operate these engines significantly reduces the lifetime of spark plug and its

effectiveness in transmitting adequate energy as an ignition source. Laser ignition

offers the potential to improve ignition system durability, reduce maintenance, as

well as to improve engine combustion performance.

5.1 REASONS FOR ADAPTING LASER IGNITION

Since spark plugs are an integral part of the combustor liner, the ignition

kernel is usually located in the suboptimal quench zone of the combustor.

Lean mixtures along the liner increase the demand on ignition energy,

leading to an increased erosion of the spark plug electrodes, and thus to a

reduced reliability and lifetime of the igniter. Since spark plug ignition

shows a reduced ignitability of lean mixtures below an equivalence ratio

of 0.6

Laser ignition is a possible candidate to solve some of problems because it

allows uncoupling of the limiting link between the location of the ignition

source and the ignition kernel.

Lasers are able to ignite the mixture at the best thermodynamic and

aerodynamic conditions from almost any installation location. Therefore

laser ignition is more independent from variations of the local equivalence

ratio than other ignition concepts.

It is known that lasers are able to ignite leaner mixtures compared with

spark plug ignition because there are no electrodes surrounding the initial

flame kernel, which, in the case of the spark plug, cool down the kernel

and prevent it from evolving further into the combustion chamber.

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5.2 METHODS OF ENERGETIC INTERACTIONS

5.2.1 THERMAL BREAKDOWN

In the case of thermal interaction, ignition occurs without the generation of

an electrical breakdown in the combustible medium. The ignition energy is

absorbed by the gas mixture through vibrational or rotational modes of the

molecules; therefore no well-localized ignition source exists. Instead, energy

deposition occurs along the whole path in the gas. According to the characteristic

transport times therein, it no necessary to deposit the needed ignition energy in a

very short time. So this ignition can also be achieved using quasi continuous wave

lasers.

5.2.2 RESONANT BREAKDOWN

It involves non-resonant multi-photon dissociation of a molecule followed

by resonant photo ionization of an atom. As well as photochemical ignition, it

requires highly energetic photons. Therefore, these two types of interaction do not

appear to be relevant for this study and practical applications.

Fig 5.1 Resonant Laser-Induced Ignition

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5.2.3 NON RESONANT BREAKDOWN

In non-resonant ignition method, because typically the light photon energy

is in visible or UV range of spectrum, multi photon processes are required for

molecular ionization. This is due to the lower photon energy in this range of

wavelengths in comparison to the molecular ionization energy. The electrons thus

freed will absorb more energy to boost their kinetic energy (KE), facilitating

further molecular ionization through collision with other molecules. This process

shortly leads to an electron avalanche and ends with gas breakdown and ignition.

The multi photon absorption occurs in presence of losses (electron diffusion

outside the focused volume, radiation, collisional quenching of excited states,

etc.), thus demanding very high input beam intensities (through tightly-focused

high energy short-duration laser beam pulses) for a successful ignition process. To

assist the breakdown process, in some studies a metal needle is inserted just

behind the beam focused volume as an additional source of electrons. By far, the

most commonly used technique is the non-resonant initiation of ignition primarily

because of the freedom in selection of the laser wavelength and ease of

implementation.

Fig 5.2 Nonresonant Laser-Induced Ignition

5.2.4 PHOTOCHEMICAL MECHANISMS

In photochemical ignition approach, very little direct heating takes place

and the laser beam brings about molecular dissociation leading to formation of

radicals (i.e., highly reactive chemical species), see Fig. 1c. If the production rate

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of the radicals produced by this approach is higher than the recombination rate

(i.e., neutralizing the radicals), then the number of these highly active species will

reach a threshold value, leading to an ignition event. This (radical) number

augmentation scenario is named as chain-branching in chemical terms.

Fig 5.3 Photochemical Laser-Induced Ignition

5.3 PRINCIPLE OF LASER IGNITION

The laser beam is passed through a convex lens, this convex lens diverge

the beam and make it immensely strong and sufficient enough to start combustion

at that point. Hence the fuel is ignited, at the focal point, with the mechanism

shown above. The focal point is adjusted where the ignition is required to have.

Fig 5.4 Principle Of Laser Ignition

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5.4 PHASES IN LASER IGNITION

The different phases of laser ignition can be defined in chronological order

Electric breakdown and energy transfer from laser to plasma

Shock-wave generation and propagation

Gasdynamic effects

Chemical induction of branching chain reactions of radicals leading to

ignition

Turbulent flame initiation

Fig 5.5 Time Scales in Laser Ignition

5.5 WORKING

The process begins with multi-photon ionization of few gas molecules

which releases electrons that readily absorb more photons via the inverse

bremsstrahlung process to increase their kinetic energy. Electrons liberated by this

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means collide with other molecules and ionize them, leading to an electron

avalanche, and breakdown of the gas. Multiphoton absorption processes are

usually essential for the initial stage of breakdown because the available photon

energy at visible and near IR wavelengths is much smaller than the ionization

energy. For very short pulse duration (few picoseconds) the multiphoton processes

alone must provide breakdown, since there is insufficient time for electron-

molecule collision to occur. Thus this avalanche of electrons and resultant ions

collide with each other producing immense heat hence creating plasma which is

sufficiently strong to ignite the fuel. The wavelength of laser depend upon the

absorption properties of the laser and the minimum energy required depends upon

the number of photons required for producing the electron avalanche.

Fig 5.6 Optical breakdown in air generated by a Nd:YAG laser.

5.6 PARTS OF LASER IGNITION SYSTEM

A laser ignition device for irradiating and condensing laser beams in a

combustion chamber of an internal combustion engine so as to ignite fuel particles within

the combustion chamber, includes: a laser beam generating unit for emitting the laser

beams; and a condensing optical member for guiding the laser beams into the combustion

chamber such that the laser beams are condensed in the combustion chamber.

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Fig 5.7 Laser Arrangement with Respect to Engine

5.6.1 POWER SOURCE

The average power requirements for a laser spark plug are relatively modest. A

four stroke engine operating at maximum of 1200 rpm requires an ignition spark 10 times

per second or 10Hz (1200rpm/2x60). For example 1-Joule/pulse electrical diode pumping

levels we are readily able to generate high millijoule levels of Q-switched energy. This

provides us with an average power requirement for the laser spark plug of say

approximately 1-Joule times 10Hz equal to approximately 10 Watts.

5.6.2 Nd:YAGLASER

It is the most suitable laser beam generating unit in laser ignition system.

Nd:YAG (neodymium-doped yttrium aluminium garnet; Nd:Y3Al5O12) is a crystal that is

used as a lasing medium for solid-state lasers. The dopant, triply ionized neodymium,

typically replaces yttrium in the crystal structure of the yttrium aluminium garnet (YAG),

since they are of similar size. Generally the crystalline host is doped with around 1%

neodymium by atomic percent. They typically emit light with a wavelength of 1064 nm,

in the infrared. However, there are also transitions near 940, 1120, 1320, and 1440 nm.

Nd:YAG lasers operate in both pulsed and continuous mode. Pulsed Nd:YAG lasers are

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typically operated in the so called Q-switching mode: An optical switch is inserted in the

laser cavity waiting for a maximum population inversion in the neodymium ions before it

opens. Then the light wave can run through the cavity, depopulating the excited laser

medium at maximum population inversion.

5.6.3 COMBUSTION CHAMBER WINDOW

A laser ignition system or optical spark plug, in contrast to a

conventional electric spark plug ignition type system is located entirely outside

the combustion chamber. The energy necessary for ignition is delivered to the

engine purely optically. This implies a window to couple in the laser light. The

window is hence a key element in a future laser ignition system. Several concepts

are viable. One might think of a single central laser source from where optical

fibers deliver the laser pulses to the individual cylinders. At the cylinders, only a

focusing optics in needed. Another possibility would be to equip each cylinder

with its own laser plus focusing unit. The latter concept has more similarity with

todays spark plugs. In any case, a window is indispensable. The setup of a

window system is shown in the figure

That window has to meet three basic criteria. It must, for long term operation:

Withstand the thermal and mechanical stresses from the engine.

Withstand the high laser power necessary for ignition.

Exhibit a low propensity to fouling.

During combustion, the combustion chamber deposits can either be

organic (up to 300C) or inorganic in nature. When they form on the window,

they increasingly block the incoming laser light up to a point where no breakdown

can be produced any more. The formation of deposits on the window depends on

the temperature, the fuel and the engine oil. This is the main problem faced by

using a window in laser ignition.

Window must mainly withstand the influence of temperature, lubricating oil, fuel

and laser.

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The temperature on the window inside the combustion chamber is

influenced by its mounting position, engine speed, the thermal conductivity of the

window itself and the sealing material.

When we consider the lubricating oil, it contains many rather volatile

components that escape, decompose, burn subsequently lead to deposits. With

increasing residence time and thermal stressing of the engine oil, the volatile

fraction is reduced, and the influence of the oil on the window formation goes

down. Similar is the effect with the fuel.

When the laser beam passes a soiled window, an effect called ablation

occurs. The high intensity laser pulse is partly absorbed by the (black)

contaminations. These are quickly heated up so that they evaporate. Ablation is

ineffective with non-absorbing materials. It was found to work well with carbon

deposits.

Fig 5.8 Window Arrangement

5.6.4 OPTIC FIBER WIRE

It is used to transport the laser beam from generating unit to the focusing unit.

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5.6.5 FOCUSING UNIT

A set of optical lenses are used to focus the laser beam into the combustion

chamber. The focal length of the lenses can be varied according to where ignition is

required. The lenses used may be either combined or separated.

Fig 5.9 Focusing Optics

5.7 MULTIPOINT IGNITION

Laser ignition system can also be used for multipoint ignition in engines.

The laser beam generated will be divided 2 or more beams by means of diffraction

grating. Each beam is directed by optic fiber and focused into their respective

laser spark plugs.

Fig 5.10 Approach for Multipoint Ignition

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CHAPTER 6

MINIMUM ENERGY REQUIRED FOR IGNITION

The minimum ignition energy required for laser ignition is more than that

for electric spark ignition because of following reasons:

An initial comparison is useful for establishing the model requirements,

and for identifying causes of the higher laser MIE. First, the volume of a typical

electrical ignition spark is 103 cm3. The focal volume for a typical laser spark is

10-5 cm3. Since atmospheric air contains _1000 charged particles/cm3, the

probability of finding a charged particle in the discharge volume is very low for a

laser spark.

Second, an electrical discharge is part of an external circuit that controls

the power input, which may last milliseconds, although high power input to

ignition sparks is usually designed to last < 100 ns. Breakdown and heating of

laser sparks depend only on the gas, optical, and laser parameters, while the

energy balance of spark discharges depends on the circuit, gas, and electrode

characteristics. The efficiency of energy transfer to near-threshold laser sparks is

substantially lower than to electrical sparks, so more power is required to heat

laser sparks. Another reason is that, energy in the form of photons is wasted

before the beam reach the focal point. Hence heating and ionizing the charge

present in the path of laser beam. This can also be seen from the propagation of

flame which propagates longitudinally along the laser beam. Hence this loss of

photons is another reason for higher minimum energy required for laser ignition

than that for electric spark.

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CHAPTER 7

PRACTICAL LASER IGNITION REQUIREMENTS

7.1 MECHANICAL REQUIREMENTS

Laser spark plug designs must perform under engine mount shock and

vibration conditions. Testing to shock and vibration specifications for engine

mounted products will help to validate the durability and design life of the laser

spark plug. It appears that large stationary Advanced Reciprocating Engines

Systems (ARES) will most likely subject the laser spark plug to substantial long

term vibration and limited shock.

Automotive requirements are limited to shock and vibration compliance of

random vibration frequency testing at less than 15 gs.

7.2 ENVIRONMENTAL REQUIREMENTS

Lasers and optical instrumentation designed for outdoor use are typically

hermitically sealed backfilled with dry inert gas. Diode Pumped Solid State Lasers

are most sensitive to environmental temperature fluctuations as the diode pump

wavelength changes with temperature. This can be especially troublesome in Nd:

YAG and other crystal host lasers as their pump band width tends to be narrow.

Glass host DPSS lasers provide broad pump band widths allowing them to

traverse through -30 to +50 degrees C temperature operating range without the

need for diode thermal conditioning.

The ideal laser spark plug requires maximum performance over large

temperature ranges with minimum thermal conditioning. Decreasing the lasers

thermal conditioning requirements makes the laser design less complicated and

less expensive to build and maintain.

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7.3 PEAK POWER REQUIREMENTS

The peak power requirements for the laser spark are relatively high.

Formation of a plasma or laser spark in free space air is not difficult if you start

with Megawatt class (nanosecond pulse width - milli joule energy level) laser

pulses.

As the engine cylinder head pressure increases, the required laser pulse

peak power level for air breakdown decreases. With a multiple lens focusing

system it is plausible that one could reliably project a laser spark into a high

pressure cylinder head utilizing lower Kilowatt class pulse power densities.

Passive Q-switched lasers also allows for generation of a multiple laser

pulse output or pulse train. The first pulse of a pulse train initiates the plasma

and successive pulses feed more energy into the plasma causing the plasma to

expand. For neodymium lasers the pulses are typically separated by a few 10s of

microseconds. The net result of pulse train operation is longer sustained plasma

containing higher energy.

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CHAPTER 8

ADVANTAGES AND CHALLENGES

Location of laser plug is flexible as it does not require shielding from

immense heat and fuel spray and focal point can be made anywhere in the

combustion chamber from any point. It is possible to ignite inside the fuel spray as

there is no physical component at ignition location.

8.1 ADVANTAGES OF LASER IGNITION

It does not require maintenance to remove carbon deposits because of its

self-cleaning property.

High pressure and temperature does not affect the performance allowing

the use of high compression ratios.

Flame propagation is fast as multipoint fuel ignition is also possible.

Higher turbulence levels are not required due to above said advantages.

A choice of arbitrary positioning of the ignition plasma in the combustion

cylinder.

Absence of quenching effects by the spark plug electrodes.

Ignition of leaner mixtures than with the spark plug => lower combustion

temperatures => less NOx emissions.

No erosion effects as in the case of the spark plugs => lifetime of a laser

ignition system expected to be significantly longer than that of a spark

plug.

High load/ignition pressures possible => increase in efficiency.

Precise ignition timing possible.

Exact regulation of the ignition energy deposited in the ignition plasma.

Easier possibility of multipoint ignition.

Shorter ignition delay time and shorter combustion time.

Fuel-lean ignition possible.

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8.2 DISADVANTAGES OF LASER IGNITION

High system costs.

Concept is proven, but no commercial system available yet.

8.3 CHALLENGES OF LASER IGNITION

Propagation of laser pulse through fiber optics.

Development of a compact, robust and economic laser source.

Durability of windows.

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CONCLUSION

Although photochemical (resonant) ignition may be more energetically

efficient (less energy needed) than laser induced plasma ignition, the requirement

of a spectral match imposes imitations. Practical laser induced plasma ignition

systems, being less spectrally sensitive, can be made transferable across different

fuel/oxidizer mixtures. There are many technical advantages of the laser ignition

over conventional electric spark ignition system. Laser ignition is nonintrusive in

nature; high energy can be rapidly deposited, has limited heat losses, and is

capable of multipoint ignition of combustible charges. More importantly, it shows

better minimum ignition energy requirement than electric spark systems with lean

and rich fuel/air mixtures. It possesses potentials for combustion enhancement

and better immunity to spurious signals that may accidentally trigger electric

igniters. One of the potential advantages of the lasers lies in its flexibility to

change the ignition location. Also, multiple ignition points can be achieved rather

comfortably as compared to the conventional electric ignition systems using spark

plugs. Although the cost of the lasers has dramatically reduced to an affordable

level for many applications, it is still prohibitive for technologically important

applications such as automotive engines.

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REFERENCES

1. Laser Ignition in Internal Combustion Engines,Pankaj Hatwar,

DurgeshVerma; International Journal of Modern Engineering Research

(IJMER),Vol.2, Issue.2, Mar-Apr 2012 pp-341-345.

2. "Laser Plasma-Initiated Ignition of Engines", J. Tauer1, H. Kofler, K.

Iskra, G. Tartar And E. Wintner; 3rd International Conference on the Frontiers

of Plasma Physics and Technology

3. "Laser Ignition - a New Concept to Use and Increase the Potentials of Gas

Engines",Dr.GntherHerdin, DI Johann Klausner, Prof. Ernst Wintner;

ASME Internal Combustion Engine Division 2005 Fall Technical Conference,

Ottawa, Canada.

4. http://www.iitk.ac.in/erl/laserignition.html

5. http://www.faqs.org/patents/app/20080264371

6. http://en.wikipedia.org/wiki/Ignition_system

7. http://auto.howstuffworks.com/ignition-system4.html

8. http://www.seminarprojects.com/Thread-laser-ignition-system

9. http://www.lasers.org.uk/paperstore/Ignition2.pdf

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QUERIES

1. Is it possible for a laser to pass through optical fiber?

An optical fiber is a cylindrical dielectric waveguide (non-conducting

waveguide).The laser light in a fiber-optic cable travels through the core

(hallway) by constantly bouncing from the cladding (mirror-lined walls), a

principle called total internal reflection. Because the cladding does not absorb

any laser light from the core, the light wave can travel great distances.

2. In combined optics what is the focusing mechanism used?

A set of optical lenses are used to focus the laser beam into the combustion

chamber. The focal length of the lenses can be varied according to where

ignition is required. The lenses used may be either combined or separated. The

focusing mechanism used in both combined and separated optics are one and

the same but the difference is that, in combined optics the focusing lens is

integrated with the window. Where as in separated optics window and

focusing lens are two different parts.

3. What type of energy interaction is used for laser ignition?

By far, the most commonly used technique is the non-resonant initiation of

ignition primarily because of the freedom in selection of the laser wavelength

and ease of implementation.