Study of Laser Ignition System for Internal Combustion Engines

PAAVAI COLLEGE OF ENGINEERING Seminar Report
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STUDY OF LASER IGNITION SYSTEM
A PROJECT REPORT
Submitted by
ARAVIND KUMAR M S 622014102001
SANTHOSH KUMAR B 622014102325
DEEPAKKUMAR N 622014102701
in partial fulfillment for the award of the degree
of
BACHELOR OF ENGINEERING
in
AUTOMOBILE ENGINEERING
PAAVAI COLLEGE OF ENGINEERING, NAMAKKAL
ANNA UNIVERSITY::CHENNAI 600 025
APRIL 2018

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ACKNOWLEGEMENT
As the outset we wish to express our sincere gratitude and indebted need to our
esteemed institution of PAAVAI COLLEGE OF ENGINEERING, which has
given this opportunity to have sincere bases in management and fulfilment our most
cherish of reaming goal of becoming successful leader.
We wish to express our sincere thanks to chairman
Shri.CA.N.V.NATARAJAN,B.Com.,F.C.A., and Smt.MANGAINATARAJAN,
M.Sc., correspondent for providing us the need facilities to do our project work.
We express our thanks to our Director Administration
Dr.K.K.RAMASAMY,M.E., Ph.D., for his motivation to carrying out our project
work. We express our sincere thanks to our Principal Dr.M.DEVI,M.E.,Ph.D., for
her encouragement given to us in carrying on the project work.
We express our sincere gratitude to the head of the Department
Mr.J.NARENDRAN, M.E.,(Ph.D).,for Automobile Engineering who lead a
helping power, Whenever we are in need of it.
We express our sincere gratitude to the project coordinator
Mr.N.ARULMURTHI, M.E.,of Automobile Engineering who lead helping hand
power, whenever we are in need of it.
We express our sincere gratitude to the project guide
Mr.M.KATHIRESAN, M.E., of Automobile Engineering whole a helping hand
power, whenever we are in need of it.
We express gratitude to our parents and friends for their encouragement and
support throughout the project work.

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ABSTRACT
The increasing disadvantages of spark plug ignition system due to some
causes, it is becoming essential to find an alternative to the spark plug ignition
system. spark plug ignition system is unable to burn the fuel mixture completely
inside the combustion chamber,where as the alternative to it .The laser ignition
system burns air fuel mixture completely and runs the engine for a longer time
compared to spark plug ignition system.It is help to achieving the best performance
of vehicle. This project presents the overall scenario of the working of laser ignition
system which as the name suggests makes use of the laser.In this paper, mostly
considering performances of laser ignition and conventional spark ignition systems
are comparatively evaluated in terms of in-cylinder pressure variation, combustion
stability, fuel consumption, power output and exhaust emissions at similar operating
conditions of the engine due to the better outcome of this project yet to be aimed it.

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CONTENTS
SL No. TITLE PAGE NO.
LIST OF TABLES v
LIST OF FIGURES vi
LIST OF SYMBOLS viii
LIST OF ABBREVIATIONS IX
1 INTRODUCTION 1
2 LITERATURE REVIEW 5
3 STUDY OF IGNITION IN IC ENGINE 10
3.1 What is ignition 10
3.2 Ignition types 10
3.2.1 Compression Ignition (CI) 10
3.2.2 Induced Ignition 10
3.3 Conventional Spark Plug 11
3.4 Spark Plug Ignition 12

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4 IDENTIFICATION OF PROBLEMS IN
CONVENTIONAL IGNITION SYSTEM 14
5 REMEDY OF CONVENTIONAL IGNITION SYSTEM
PROBLEMS 17
6 LASER 18
6.1 Types of laser 21
7 LASER IGNITION 24
7.1 Types of laser ignition 25
7.2 Laser ignition along time 27
7.3 Ignition in combustion chamber 28
7.4 Mechanism of laser ignition 29
7.5 Principle of laser ignition 31
7.6 Arrangement of laser ignition system 31
7.6.1 Laser spark plug 34
7.7 Working of laser ignition system 35

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8 MODIFYING REQUIREMENTS OF LIS 38
8.1 Modification of Combustion chamber 38
8.2 Modification of Engine 38
8.3 Comparison of performance of SI with
respect to LI engines 40
8.4 Extended usage of laser Ignition 44
8.5 Advantages of laser ignition 46
8.6 Future Researches 47
8.7 Practical Laser Sparkplug Requirements 48
8.8 Application 50
9 CONCLUSION 51
10 REFERENCE 52

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LIST OF TABLES
Table No. TITLE Page No.
8.1 Technical data of the engine and the
ND: YAG laser 40
8.2 Estimated basic cost and performance requirements
for a laser spark plug 48

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LIST OF FIGURES
SL No. TITLE Page No.
3.1 Conventional spark plug 11
3.2 Four stroke engine cycle 13
5.1 laser ignition system 17
6.1 Principle components of a laser 18
6.2 Lasing action diagram 20
7.1 Optical breakdown in air generated by a
ND: YAG laser 24
7.2 Non resonant breakdown 26
7.3 Stages of ignition with respect to time 27
7.4 Ignition inside combustion chamber 28
7.5 Principle of laser ignition 31
7.6 Laser arrangement with respect to engine 32
7.7 Focusing unit 33
7.8 Laser spark plug 34

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7.9 Laser ignition system for multi cylinder engine 35
7.10 Plasma Formation by a Focused Beam 37
8.1 The q-switched Nd: YAG laser system 39
8.2 Comparison of performance parameters of SI
with respect to LI engines 41
8.3 Self cleaning property 42
8.4 Flame front propagation 43
8.5 Comparison of NOX emissions of
different ignition 44
8.6 Flame front 29 0 after ignition 45
8.7 Variation of ignition energy with respect to
combustion chamber temperatures 45
8.8 Mazda RX-9 16X rotary 50

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LIST OF SYMBOLS
I Intensity of an electromagnetic wave
E Electric field strength
D Diameter of the laser beam
M Beam quality
λ Wave length of laser beam
f Focal length of the optical element
T Temperature
P Pressure
k Boltzmann’s constant

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LIST OF ABBREVIATIONS
ND: YAG Neodymium-Doped Yttrium Aluminium Garnet
IMEP Indicated Mean Effective Pressures
COV Coefficient Of Variation
SIS Spark Ignition System
LIS Laser Ignition System
μs Nano Second
Mj Milli-Joule
Mpa Mega Pascal
MPI Multi Photon Ionization
DOHC Double-Overhead-Camshaft
PPM Particles Per Million
CH4 Methane
O2 Carbon Dioxide

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NOX Oxides Of Nitrogen
MEP Mean Effective Pressure
Is Build-Up Intensity
Es Build-Up Energy
MPE Minimum Pulse Energy For Ignition

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CHAPTER - 1
INTRODUCTION
It's widely accepted that the internal combustion engines will continue to
power our vehicles. Hence, as the global mobilization of people and goods increases,
advances in combustion and after-treatment are needed to reduce the environmental
impact of the continued use of IC engine vehicles. To meet environmental legislation
requirements, automotive manufacturers continue to address two critical aspects of
engine performance, fuel economy and exhaust gas emissions. New engines are
becoming increasingly complex, with advanced combustion mechanisms that burn
an increasing variety of fuels to meet future goals on performance, fuel economy
and emissions.
The spark plug has remained largely unchanged since its invention, yet its
poor ability to ignite highly dilute air- fuel mixtures limits the potential for
improving combustion efficiency. Spark ignition (SI) also restricts engine design,
particularly in new engines, since the spark position is fixed by the cylinder head
location of the plug, and the protruding electrode disturbs the cylinder geometry and
may quench the combustion flame kernel.
So, many alternatives are being sought after to counter these limitations. One
of the alternative is the laser ignition system (LIS) being described here. Compared
to a conventional spark plug, a LIS should be a favorable ignition source in terms of
lean burn characteristics and system flexibility . So, in this paper we'll be discussing
the implementation and impact of LIS on IC engines.

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Internal combustion engines play a dominant role in transportation and energy
production. Even a slight improvement will translate into considerable reductions in
pollutant emissions and impact on the environment. The two major types of internal
combustion engines are the Otto and the Diesel engine. The former relies on an
ignition source to start combustion, the latter works in auto ignition mode. Ignition
is a complex phenomenon known to strongly affect the subsequent combustion. It is
especially the early stages that have strong implications on pollutant formation,
flame propagation and quenching.
The spark ignited Otto engine has a widespread use and has been subject to
continuous, sophisticated improvements. The ignition source, however, changed
little in the last 100 years. An electrical spark plug essentially consists of two
electrodes with a gap in between where, upon application of a high voltage, an
electrical breakthrough occurs. A laser based ignition source, i.e. replacing the spark
plug by the focused beam of a pulsed laser, has been envisaged for some time. Also,
it was tried to control auto ignition by a laser light source.
The time scale of a laser-induced spark is by several orders of magnitude
smaller than the time scales of turbulence and chemical kinetics. In, the importance
of the spark time scale on the flame kernel size and NOx production is identified. A
laser ignition source has the potential of improving engine combustion with respect
to conventional spark plugs. The protection of the resources and the reduction of the
CO2 emissions with the aim to limit the greenhouse effect require a lowering of the
fuel consumption of motor vehicles. Great importance for the reduction lies upon
the driving source. Equally important are the optimization of the vehicle by the
means of a reduction of the running resistance as well as a low-consumption
arrangement of the entire powertrain system.

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The most important contribution for lower fuel consumption lies in the spark
ignition (SI) engine sector, due to the outstanding thermodynamic potential which
the direct fuel injection provides. Wall- and air-guided combustion processes
already found their way into standard- production application and serial
development, whereas quite some fundamental engineering work is still needed for
combustion processes of the second generation. Problems occur primarily due to the
fact that with conventional spark ignition the place of ignition cannot be specifically
chosen, due to several reasons. By the means of laser induced ignition these
difficulties can be reduced significantly. The combination of technologies (spray-
guided combustion process and laser induced ignition) seems to become of particular
interest, since the ignition in the fuel spray is direct and thus the combustion
initiation is secure and non-wearing.
Another approach is laser ignition of a homogeneous mixture. Laser ignition,
microwave ignition, high frequency ignition are among the concepts widely
investigated. The large majority of previous studies on LI have investigated the
fundamental processes of laser-induced gas breakdown for the application of gas
reciprocating engines, where mixtures of methane, hydrogen and air are most
commonly used. However, relatively few studies have concentrated on LI in
automotive gasoline IC engines , which is the main focus of this paper. Research
conducted at The University of Liver pool , is, to the authors’ knowledge, the only
LI research reported to date to use an otherwise unmodiﬁed production automotive
engine. Moreover, previous LI studies have used relatively long focal length (FL)
lenses to focus the beam through a port window of a combustion chamber, with FLs
ranging from 50 to 450mm . The beam energy required to create a plasma is higher
for longer FL lenses for a given beam diameter, due to the larger minimum waists
produced.

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Further more,the speciﬁc location of the plasma varies to a greater degree
along the path of the laser beam as the focal point volume is increased. This study
therefore investigates LI using shorter FL lenses ranging from 15 to 36mm, which
allows the optical plug to be compact in design, as the tight focuses achieved means
that beam expansion is not required.
The laser induced spark ignition has previously been found to be associated
with the laser pulse width, laser energy, the size of focusing spot, the composition
of mixture and its initial conditions. Studies have mainly focused on mixtures
containing hydrogen , methane or propane although some studies have also been
performed on hydrocarbon fuels such as dodecane, isooctane or Jet-A .In these
studies the ignition characteristics are usually expressed according to the energy
delivered by laser .
The protection of the resources and the reduction of the CO2 emissions with
the aim to limit the greenhouse effect require a lowering of the fuel consumption of
motor vehicles. Great importance for the reduction lies upon the driving source.
Equally important are the optimization of the vehicle by the means of a reduction of
the running resistance as well as a low-consumption arrangement of the entire power
train system. The most important contribution for lower fuel consumption lies in the
spark ignition (SI) engine sector, due to the outstanding thermodynamic potential
which the direct fuel injection provides. Wall- and air-guided combustion processes
already found their way into standard production application and serial development,
whereas quite some fundamental engineering work is still needed for combustion
processes of the second generation. Problems occur primarily due to the fact that
with conventional spark ignition the place of ignition cannot be specifically chosen,
due to several reasons. By the means of laser induced ignition these difficulties can
be reduced significantly.

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CHAPTER -2
LITREATURE REVIEW
Takuma Endo & Keisuke Kuwamoto[1]
Et.al.in his study findings revealed that laser ignition was superior to
the spark-plug ignition in the aspect of the early- stage rapid flame spread, although
it showed lower probability of successful ignition than that by the spark plug near
the lean-fuel ignitable limit. These findings suggest that the ignition in high-speed
flows is significantly influenced by the turbulence via the enhancement of heat
transport in particular. investigated laser ignition to hydrogen–air mixtures at high
pressures and their results showed that with increasing initial pressures the minimum
pulse energy was decreasing. Measurements and model calculations of ignition by
electrical sparks and non resonant laser sparks show that the minimum ignition
energy (MIE) for laser sparks is higher than for electrical sparks
J. Griffiths, M.J.W. Rileyb & Borman[2]
Et.al.in his study developed an Extensive research into the application LI for
various applications such as internal combustion engines and natural gas
reciprocating engines has been conducted .The potential for the application of lasers
in the ignition process was first identified shortly after the advent of pulsed laser
sources in J. Griffiths 1964 by et al., who demonstrated breakdown of air using a
focused ruby laser .The LI process typically involves the use of tightly focused UV
to near-IR laser radiation to locally ionize target molecules in a combustible mixture,
leading to full-scale combustion. Laser ignition, microwave ignition, high frequency
ignition are among the concepts widely investigated.

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J D Mullett , G Triantos, and S Keen[3]
Et.al.in his study was the Recent research in laser-induced ignition (LI) of
air–fuel mixtures in internal combustion (IC) engines has shown there to be many
potential advantages over conventional electrical spark ignition (SI) . Non-resonant
breakdown is the mechanism by which LI is performed in the tests presented in this
paper and is the most widely used and studied form of LI. Experimental studies have
been vital to extending the value of the theoretical examinations and in gaining a
further understanding of the combustion process. Combustion vessel and open flame
jet experimentation with methane (CH4) and other combustible gases have proven
invaluable in the search for better fuel economy and emissions and provide a better
understanding of the general ignition and combustion processe
Cangsu Xu n, Donghua Fang& Jian Ma[4]
Et.al. in his study In recent years, laser ignition has become an active research
topic because of its many potential beneﬁts over the conventional electric spark
ignition. Laser ignition of reactive mixtures can be divided into four categories: laser
thermal ignition, laser induced photochemical ignition, laser-induced resonant
breakdown ignition and laser induced spark ignition . Laser induced spark ignition
begins with the initial seed electrons produced from impurities in the gas mixture (e.
g dust, aerosol or soot particles). Experimental studies have been vital to extending
the value of the theoretical examinations and in gaining a further understanding of
the combustion process. Combustion vessel and open flame jet experimentation with
methane (CH4) and other combustible gases have proven invaluable in the search
for better fuel economy and emissions and provide a better understanding of the
general ignition and combustion process.

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Lydia Wermer a , James Hanssonb & Seong-kyun Im[5]
Et.al. in his study An experimental investigation was performed to study the
ignition and flame propagation behaviours of a methane diffusion jet flame (Re =
5500) when dual pulse laser-induced spark discharges were introduced in a mixing
layer. Initial electrons readily absorb more photons via the inverse bremsstrahlung
process to increase their kinetic energy. If the electrons gain sufficient energy, they
can collide with other molecules and ionize them, leading to an electron avalanche,
and breakdown the gas. This process is repeated until the spark plasma of high
temperature and high pressure is created. This extreme condition relative to the
ambient gas leads to the development of a rapidly expanding shock wave that is of
sufficient strength to ignite flammable mixtures.
J. D. Dale[6]
Et.al. in his study ,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. Experimental studies have been vital to extending the
value of the theoretical examinations and in gaining a further understanding of the
combustion process. Experimental studies have been vital to extending the value of
the theoretical examinations and in gaining a further understanding of the
combustion process. Combustion vessel and open flame jet experimentation with
methane (CH4) and other combustible gases have proven invaluable in the search
for better fuel economy and emissions and provide a better understanding of the
general ignition and combustion processes.

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M. D. Checkel, P. R. Smy[7]
Et.al. in his study used a gasoline-fueled stoichiometric operating internal
combustion engine for testing. And studied characterisation of laser ignition in
hydrogen–air mixtures in a combustion bomb at initial pressure of 3 MPa and
temperature 323 K and the results are compared with the laser ignition ones. They
found that the rate of pressure rise inside the combustion chamber was higher when
the mixture was ignited by laser plasma compared with spark plug ignition. Laser
ignition studies performed on internal combustion engines have allowed researchers
to directly study the effect that laser induced ignition has on the operating and
emissions characteristics of an operating engine. Past and recent studies have
indicated a higher and quicker combustion pressure rise with laser ignition.
J. Ma, D. Alexander, and D. Poulain[8]
Et.al. in his study ,The research performed by Ma et al., involved a motored
slider crank mechanism that was not self sustaining.Researchers from Japan's
National Institutes of Natural Sciences (NINS) are creating laser igniters that could
one day replace spark plugs in automobile engines. The team from Japan built its
laser from two yttrium aluminum- gallium (YAG) segments, one doped with
neodymium, the other with chromium. They bonded the two sections together to
form a powerful laser only 9 millimeters in diameter and 11 millimeters long (a bit
less than half an inch). The composite generates two laser beams that can ignite fuel
in two separate locations at the same time. This would produce a flame wall that
grows faster and more uniformly than one lit by a single laser. The laser is not strong
enough to light the leanest fuel mixtures with a single pulse. By using several 800-
picosecond-long pulses, however, they can inject enough energy to ignite the
mixture completely

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Kopecek, H., Lackner, M., Wintner, E., Winter[9]
Et.al. in his study This research is done to study the laser ignition of hydrogen
air mixture in a laser ignited internal combustion engine. In the research reported in
this paper, comparative study between conventional SI system and LI system were
carried out to investigate the technical potential of using LI system in a prototype
hydrogen fuelled engine. Engine performance, emission and combustion
characteristics for the two ignition systems are compared. So, many alternatives are
being sought after to counter these limitations. One of the alternative is the laser
ignition system (LIS) being described here. Compared to a conventional spark plug,
a LIS should be a favorable ignition source in terms of lean burn characteristics and
system flexibility . So, in this paper we'll be discussing the implementation and
impact of LIS on IC engines.
A.P. Yalin, M.W. Defoort, S. Joshi, D. Olsen, B. Willson, Y. Matsuura, M.
Miyagi[10]
Et.al. in his study This performed experiments to determine misfire limit and
knock limit of LI system. They reported increased misfire limit, and decreased
ignition delay for LI compared to SI engine. In the past, lasers that could meet those
requirements were limited to basic research because they were big, inefficient, and
unstable. Nor could they be located away from the engine, because their powerful
beams would destroy any optical fibers that delivered light to the cylinders. This
problem overcame by making composite lasers from ceramic powders. In this the
powders is heated and fuse into optically transparent solids and embeds metal ions
in them to tune their properties. Ceramics are easier to tune optically than
conventional crystals. They are also much stronger, more durable, and thermally
conductive, so they can dissipate the heat from an engine without breaking down.

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CHAPTER -3
STUDY OF IGNITION IN IC ENGINE
3.1 What is ignition
Ignition is the process of starting radical reactions until a self-sustaining flame
has developed. One can distinguish between auto ignition, induced ignition and
photo-ignition, the latter being caused by photolytic generation of radicals.
3.2 Ignition types
3.2.1 Compression Ignition (CI) or Auto Ignition
At certain values of temperature and pressure a mixture will ignite
spontaneously, this is known as the auto ignition or compression ignition.
3.2.2 Induced Ignition
A process where a mixture, which would not ignite by it, 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 subsequent flame
propagation occurs and sets the mixture on fire.
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 means collide with other molecules and ionize
them, leading to an electron avalanche, and breakdown of the gas.

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3.3 Conventional Spark Plug
Fig.3.1 Conventional spark plug
A spark plug (sometimes, in British English, a sparking plug, and,
colloquially, a plug) is a device for delivering electric current from an ignition
system to the combustion chamber of a spark-ignition engine to ignite the
compressed fuel/air mixture by an electric spark, while containing combustion
pressure within the engine. A spark plug has a metal threaded shell, electrically
isolated from a central electrode by a porcelain insulator.
The central electrode, which may contain a resistor, is connected by a heavily
insulated wire to the output terminal of an ignition coil or magneto. The spark plug's
metal shell is screwed into the engine's cylinder head and thus electrically grounded.
The central electrode protrudes through the porcelain insulator into the combustion
chamber, forming one or more spark gaps between the inner end of the central
electrode and usually one or more protuberances or structures attached to the inner
end of the threaded shell and designated the side, earth, or ground electrode(s).

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Spark plugs may also be used for other purposes; in Saab Direct Ignition when
they are not firing, spark plugs are used to measure ionization in the cylinders – this
ionic current measurement is used to replace the ordinary cam phase sensor, knock
sensor and misfire measurement function. Spark plugs may also be used in other
applications such as furnaces wherein a combustible fuel/air mixture must be ignited.
In this case, they are sometimes referred to as flame igniters.
3.4 Spark Plug Ignition
Conventional spark plug ignition has been used for many years. For ignition
of a fuel-air mixture the fuel-air mixture is compressed and at the right moment a
high voltage is applied to the electrodes of the spark plug.
When the ignition switch is turned on current flows from the battery to the
ignition coil. Current flows through the Primary winding of the ignition coil where
one end is connected to the contact breaker. A cam which is directly connected to
the camshaft opens and closes the contact breaker (CB) points according to the
number of the cylinders.
When the cam lobe Pushes CB switch, the CB point opens which causes the
current from the primary circuit to break. Due to a break in the current, an EMF is
induced in the second winding having more number of turns than the primary which
increases the battery 12 volts to 22,000 volts.
The high voltage produced by the secondary winding is then transferred to the
distributor. Higher voltage is then transferred to the spark plug terminal via a high
tension cable.
A voltage difference is generated between the central electrode and ground
electrode of the spark plug. The voltage is continuously transferred through the
central electrode (which is sealed using an insulator).

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When the voltage exceeds the dielectric of strength of the gases between the
electrodes, the gases are ionized. Due to the ionization of gases, they become
conductors and allow the current to flow through the gap and the spark is finally
produced. In this stroke the piston compresses the air-fuel mixture in preparation for
ignition during the power stroke (below).
The combustion leads to the production of high pressure gases. Due to this
tremendous force the piston is driven back to the bottom of the cylinder. As the
piston moves downwards, the crankshaft rotates which rotates the wheels of the
vehicle.
Fig 3.2 Four stroke engine cycle

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CHAPTER -4
IDENTIFICATION OF PROBLEMS IN CONVENTIONAL
IGNITION SYSTEM
Without a spark, there would be no way for fuel to ignite in the combustion
chamber. Spark plugs have been a critical component of the internal combustion
engine for years. Spark plugs are designed to transmit an electrical signal sent from
the ignition coil at a predetermined time to create a spark that ignites the air-fuel
mixture inside the combustion chamber. Each vehicle requires a particular type of
spark plug made from specific materials and with a designated spark plug gap that
is set by a mechanic during installation. Good spark plugs will burn fuel efficiently,
while bad or failing spark plugs can cause the motor not to start at all.
Spark plugs are similar to motor oil, fuel filters, and air filters in that they
require routine service and maintenance to keep your engine running strong. Most
vehicles sold in the United States require that their spark plugs are replaced every
30,000 to 50,000 miles. However, some newer cars, trucks and SUV's have advanced
ignition systems that ostensibly make spark plug replacement unnecessary.
Regardless of any warranties or claims made by a vehicle manufacturer, there are
still situations where a spark plug wears out or shows signs of failing.Listed below
are a few common symptoms of worn out spark plugs or spark plugs that have fouled
and need to be replaced by a SAE certified mechanic as soon as possible, so you can
continue driving your vehicle without issue.
1. Slow acceleration
The most common cause of poor acceleration on most vehicles is a problem
in the ignition system. Today's modern engines have multiple sensors that tell the
onboard computer and ignition system when to send electric pulses to fire the spark
plug, so the issue may be with a faulty sensor.

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However, sometimes the issue is just as simple as a worn out spark plug. A
spark plug is composed of materials that work together in order to produce a spark
hot enough to ignite the air-fuel mixture. When those materials wear out, the
effectiveness of the spark plug is reduced, which can significantly reduce the
acceleration of the vehicle.If you notice that your car is running sluggishly or does
not accelerate as quickly as it used to, it may be attributed to a spark plug that needs
to be replaced. However, you should contact a mechanic to inspect this issue as it
could be caused by multiple other factors including bad fuel filters, dirty or clogged
fuel injector, or issues with oxygen sensors.
2. Poor fuel economy
When a spark plug works correctly, it helps burn fuel efficiently in the
combustion cycle. When this occurs, your car can achieve better than average fuel
economy. When the plug is not functioning optimally, it is frequently due to the fact
that the gap between the spark plug electrodes is either too close or too far apart. In
fact, many mechanics will take out spark plugs, examine them, and adjust the gap to
factory settings as opposed to replacing the spark plug entirely. If your vehicle has
a reduction in fuel economy, it very well could be attributed to a worn out spark
plug.
3. Engine is misfiring
If the engine misfires, it's typically due to an issue in the ignition system. Most
of the time in modern cars it's due to a sensor malfunction. However, it may also be
caused by a spark plug wire or the tip of the spark plug that connects to the wire
being damaged. An engine misfire can be noticed by intermittent stumbling or
sputtering sounds from the engine. If the engine is allowed to keep misfiring, exhaust
emissions will increase, engine power will decrease, and fuel economy will drop.
Because of all the potential problems associated with engine misfiring issues, you
should contact a mechanic as soon as you notice an engine misfire.

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A professional mechanic can inspect the issue and determine the right course
of action to repair the problem.
4. Difficulty starting the vehicle
If you have trouble starting your vehicle, it could be a sign your spark plugs are
worn. However as noted above, the engine's ignition system is comprised of multiple
individual components that must work cohesively in order to function properly. At
the first sign of problems starting your car, truck or SUV, it's a good idea to contact
a certified mechanic to take a look at the cause.Regardless of what the issue might
be, the reality is that spark plugs will eventually wear out. Being proactive about
spark plug maintenance can extend the life of your engine by hundreds of thousands
of miles. The other problems are occurred in conventional spark plug ignition system
like as,
 Location of spark plug is not flexible as it requires shielding of plug from
immense heat and fuel spray.
 Ignition location cannot be chosen optimally.
 Spark plug electrodes can disturb the gas flow within the combustion
chamber.
 It is not possible to ignite inside the fuel spray.
 It requires frequent maintenance to remove carbon deposits.
 Leaner mixtures cannot be burned, ratio between fuel and air has to be
within the correct range.
 Degradation of electrodes at high pressure and temperature.
 Flame propagation is slow.
 Multi point fuel ignition is not feasible.
 Higher turbulence levels are required.
 Erosion of spark plug electrodes.

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CHAPTER -5
REMEDY OF CONVENTIONAL IGNITION SYSTEM
PROBLEMS
Laser ignition Laser ignition is an alternative method/Remedy for igniting
compressed gaseous mixture of fuel and air. The method is based on laser devices
that produce short but powerful flashes regardless of the pressure in the combustion
chamber. Usually, high voltage spark plugs are good enough for automotive use, as
the typical compression ratio of an Otto cycle internal combustion engine is around
10:1 and in some rare cases reach 14:1. However, fuels such as natural gas or
methanol can withstand high compression without self ignition. This allows higher
compression ratios, because it is economically reasonable, as the fuel efficiency of
such engines is high. Using high compression ratio and high pressure requires
special spark plugs that are expensive and their electrodes still wear out. Thus, even
expensive laser ignition systems could be economical, because they would last
longer. Laser plugs have no electrodes and they can potentially last for much longer.
Fig.5.1 Laser Ignition System

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CHAPTER - 6
LASER
The word LASER is an acronym. It stands for Light Amplification by the
Stimulated Emission of Radiation. By "radiation", however, the acronym refers to
a radiant vibration, not an emission of radioactive particles. In other words, the
emissions of lasers are in the form of light, and the frequencies can range anywhere
from infra-red to ultraviolet. Those lasers of interest to the laser display industry,
however, are mostly those whose output is visible (from red to deep blue).
As the acronym suggests, lasers work through a process called stimulated
emission. The lasers we typically employ are called ion gas lasers, due to the fact
that they utilize a gas or a mixture of gases as the lasing medium. These work
because certain gases are "easily" coerced to produce visible light through this
process.
Fig 6.1 Principle components of a laser

31
The stimulation comes in the form of electricity, which excites the atoms of
the gas: as the electrons in these atoms are given more energy, they tend to jump to
a higher orbit. These unnaturally high orbits, however, don't last long, and the
electrons fall back to their proper orbital shells, to be once again excited by the influx
of electricity. It is this process of the electrons returning to their original orbits that
creates the laser light we see (actually, it's more appropriate to call it a jump, for an
electron falls from orbit in a span of time infinitesimally small): During this jump
back down, the extra energy is released from each atom as a packet called a photon
(light). Moreover, if this photon collides with another already excited atom, that
atom is also stimulated to emit a photon...but this new photon will be vibrating
perfectly in step (in-phase) with the colliding photon, and will be traveling on the
exact same course. Photons are released, however, in haphazard directions. In order
to get them aligned into the tight beam of light with which we're familiar, the tubes
in which the atoms of gas are excited must be mirrored on both ends.
Any photon that now happens to randomly travel exactly perpendicular with
the mirrors on both ends (which inevitably happens) will cause a remarkable chain
of events: The drama begins with the photon's 'cloning' when it bounces off the
mirror and collides with another excited atom. Those two in-phase photons then
collide with two more excited atoms, making four photons traveling in-phase, and
exactly down the length of the laser tube. This process is then repeated in a geometric
progression of photons parading exactly down the laser tube, colliding with more
excited atoms, creating more photons, reflecting off the mirrors, and repeating and
amplifying the process over and over again. The laser light we see is finally released
through the front mirror, whose reflective coating was designed to be partially
transparent. In this way, a small percentage of those perfectly aligned photons is
allowed to escape, forming the thin, straight, coherent, and beautiful beams we call
LASER light.

32
Fig 6.2 Lasing action diagram
Different colors of light, as specific frequencies, are produced by different
gases. Argon gas, for instance, produces colors ranging from emerald green to
beautiful deep blues. Krypton gas produces a palette from deep reds to light blues.
A laser incorporating a mixture of these two gases can produce all the colors unique
to those individual gases... simultaneously. It is these Krypton/Argon mixed-gas ion
lasers that are typically utilized in laser projection hardware.
To sum up, laser light provides a quality of light unmatched by any other light
source in the world: It's coherent, meaning again that the waves of light are vibrating
perfectly in step with each other (in-phase); It's monochromatic, meaning that only
very pure, specific frequencies (colors) of light are created (though several
frequencies can be created simultaneously with the same laser); and it's low-
divergent, meaning it keeps its power contained within a narrow, barely widening
beam.

33
6.1 Types of laser
 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
μm and10.6 μm, 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 500kw.
The transverse electrical discharge in gas at atmospheric pressure (tea) laser is
an inexpensive gas laser producing uv light at 337.1 nm. Metal ion lasers are gas
lasers that generate deep ultraviolet wavelengths. Helium-silver (heag) 224 nm and
neon-copper (necu) 248 nm are two examples. These lasers have particularly narrow
oscillation line widths of less than 3 ghz (0.5 pico meters) making them candidates
for use in fluorescence suppressed raman spectroscopy.
 Chemical laser
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 tri
fluoride.
 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 (351nm).

34
 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 532 nm when a visible (green) coherent source is
required. ytterbium, holmium, thulium and erbium are other common dopants in
solid state lasers.
The ho-yag is usually operated in a pulsed mode, and passed through optical fibre
surgical devices to resurface joints, remove rot from teeth, vaporize cancers, and
pulverize kidney and gall stones. Titanium-doped sapphire (ti: sapphire) produces a
highly tunable infrared laser, used for spectroscopy. Solid state lasers also include
glass or optical fibre 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 fibre’s high surface area to volume ratio allows efficient
cooling and its wave guiding properties reduce thermal distortion of the beam.
 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.

35
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-tunable narrow-line width radiation, or ultra-short laser pulses.
Vertical cavity surface-emitting lasers (vessels) are semiconductor lasers whose
emission direction is perpendicular to the surface of the wafer. Vessel devices
typically have a more circular output beam than conventional laser diodes, and
potentially could be much cheaper to manufacture. As of 2005, only 850 nm vessels
are widely available, with 1300 nm vessels beginning to be commercialized , and
1550 nm devices an area of research.
Vessels are external-cavity vessels. Quantum cascade lasers are semiconductor
lasers that have an active transition between energy sub-bands of an electron in a
structure containing several quantum wells.
 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 femto seconds).

36
CHAPTER -7
LASER IGNITION
Laser ignition, or laser-induced ignition, is the process of starting combustion
by the stimulus of a laser light source.Laser ignition uses an optical breakdown of
gas molecule caused by an intense laser pulse to ignite gas mixtures. The beam of a
powerful short pulse laser is focused by a lens into a combustion chamber and near
the focal spot and hot and bright plasma is generated.
Fig 7.1 Optical breakdown in air generated by a ND: YAG laser.
At a wavelength of 1064 nm,at 532nm
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 means collide
with other molecules and ionize them, leading to an electron avalanche, and
breakdown of the gas. Multi photon 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.

37
For very short pulse duration (few picoseconds) the multi photon 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.
7.1 Types of laser ignition
Basically, energetic interactions of a laser with a gas may be classified into
one of the following four schemes as described in.
 Thermal initiation
In thermal initiation of ignition, there is no electrical breakdown of the gas
and a laser beam is used to raise the kinetic energy of target molecules in
translational, rotational, or vibrational forms. Consequently, molecular bonds are
broken and chemical reaction occur leading to ignition with typically long ignition
delay times. This method is suitable for fuel/oxidizer mixtures with strong
absorption at the laser wavelength. However, if in a gaseous or liquid mixtures is an
objective, thermal ignition is unlikely a preferred choice due to energy absorption
along the laser propagation direction. Conversely, this is an ideal method for
homogeneous or distributed ignition of combustible gases or liquids. Thermal
ignition method has been used successfully for solid fuels due to their absorption
ability at infrared wavelengths.
 Non-resonant breakdown
In non resonant breakdown ignition method, because typically the light
photon energy is invisible 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.

38
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. 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 7.2 Non resonant breakdown
 Resonant breakdown
The resonant breakdown laser ignition process involves, first, a non resonant
multi photon dissociation of molecules resulting to freed atoms, followed by a
resonant photo ionization of these atoms. This process generates sufficient electrons
needed for gas breakdown. Theoretically, less input energy is required due to the
resonant nature of this method.

39
 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), if the production rate 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.
7.2 Laser ignition along time
Laser ignition encompasses the nanosecond domain of the laser pulse itself to
the duration of the entire combustion lasting several hundreds of milliseconds.
Fig 7.3 Stages of ignition with respect to time

40
The laser energy is deposited in a few nanoseconds which lead to a shock
wave generation. In the first milliseconds an ignition delay can be observed which
has duration between 5 – 100 ms depending on the mixture. Combustion can last
between 100 ms up to several seconds again depending on the gas mixture, initial
pressure, pulse energy, plasma size, position of the plasma in the combustion bomb
and initial temperature.
7.3 Ignition in combustion chamber
Fig 7.4 Ignition inside combustion chamber
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. The focal point is adjusted where
the ignition is required to have. To provide more understanding of laser ignition, also
for higher initial temperatures than 200°C provided by the combustion chamber 1, a
new combustion chamber which can be heated up to maximum temperatures of
400°C was constructed (combustion chamber 2 ). Higher initial temperatures are
also interesting because they are nearer to engine like conditions.

41
7.4 Mechanism of laser ignition
It is well know that short and intensive laser pulses are able to produce an
“optical breakdown” in air. Necessary intensities are in the range between 1010 to
1011W/cm2
. At such intensities, gas molecules are dissociated and ionized within
the vicinity of the focal spot of a laser beam and hot plasma is generated. This plasma
is heated by the incoming laser beam and a strong shock wave occurs. The expanding
hot plasma can be used for the ignition of fuel-gas mixtures. By comparing the field
strength of the field between the electrodes of a spark plug and the field of a laser
pulse it should be possible to estimate the required laser intensity for generation of
an optical breakdown.
The field strength reaches values in the range of approximately 3×104V/cm
between the electrodes of a conventional spark plug. Since the intensity of an
electromagnetic wave is proportional to the square of the electric field strength I
∝E2
, one can estimate that the intensity should be in the order of 2 × 106 W/ cm2
.,
which is several orders of magnitude lower as indicated by experiments on laser
ignition. The reason is that usually no free electrons are available within the
irradiated volume. At the electrodes of a spark plug electrons can be liberated by
field emission processes.
In contrary, ionization due to irradiation requires a “multi photon” process
where several photons hit the atom at nearly the same time. Such multi photon
ionization processes can only happen at very high irradiation levels (in the order of
1010to 1011W/ cm2
.) where the number of photons is extremely high. For example,
nitrogen has an ionization energy of approximately 14.5 eV, whereas one photon
emitted by a Nd:YAG laser has an energy of 1.1 eV, thus more than 13 photons are
required for ionization of nitrogen.

42
The pulse energy of a laser system for ignition can be estimated by the following
calculation. The diameter d of a focused laser beam is
D = 2 × wf × M 2
× 2λf
πd
… … … … … … … … … … … (1)
where M2 is the beam quality, F is the focal length of the optical element and D is
the diameter of the laser beam with the wavelength λ. Now it is assumed that the
laser beam irradiates a spherical volume.
V = 4πw3
3
… … … … … … … … … … … … … … … … … … (2)
From the thermodynamical gas equation the number of particles N in a volume V is
N =
pv
kt
… … … … … … … … … … … … … … … … … … … (3)
With the pressure p, temperature T and Boltzmann’s constant k = 1.38 × 10 -23J/K.
Inside the irradiated volume, N molecules have to be dissociated where first the
dissociation energy Wd is required and finally 2N atoms are ionized (ionization
energy Wi). Using known values for Wd= 9.79 eV and Wi= 14.53 eV for nitrogen,
the energy for dissociating and ionizing all particles inside the volume can be
calculated as
W = (
πpd3
6kt
) × (Wd + 2Wi) … … … … … … … … … … … … … … (4)
For a spot radius of about 100 μm the equation gives a maximum energy of
approximately 1 mJ.Since not all particles inside the irradiated volume have to be
ionized, even smaller energies should be sufficient for generation of an optical
breakdown. It is assumed that the intensity which is necessary for the generation of
an optical breakdown processes is related to the pressure of the gas
I α 1/Pn
With n =1…5 depending on the mechanism of multi photon process. Higher
pressures, like in a combustion chamber should ease the ignition process what favors
the laser induced ignition.

43
7.5 Principle of laser ignition
Fig 7.5 Principle of laser ignition
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.
7.6 Arrangement 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.

44
Fig 7.6. Laser arrangement with respect to engine
 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 mill joule levels of Q-
switched energy. This provides us with an average power requirement for the laser
spark plug of say approximate ly 1-Joule times 10Hz equal to approximately 10
Watts.

45
 Combustion chamber window
Since the laser ignition system is located outside the combustion chamber a
window is required to optically couple the laser beam. The window must:
a) Withstand the thermal and mechanical stresses from the engine.
b) Withstand the high laser power.
c) Exhibit low propensity to fouling.
 Optic fiber wire
It is used to transport the laser beam from generating unit to the focusing unit.
 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 7.7 Focusing unit

46
7.6.1 Laser spark plug
Located at the top of each engine cylinder, spark plugs send a high-voltage
electrical power to plasma .That plasma spark ignites the compressed air-fuel
mixture in the cylinder, causing a controlled mini-explosion that pushes the piston
down.
Additionally, engine timing could be improved, as lasers can pulse within
nanoseconds, while spark plugs require milli seconds .In order to cause the desired
combustion, a laser would have to be able to focus light to approximately 100 giga
watts per square centimeter with short pulses of more than 10 milli joules each.
Previously, that sort of performance could only be achieved by large, inefficient,
relatively unstable lasers. The Japanese researchers, however, have created a small,
robust and efficient laser that can do the job. They did so by heating ceramic
powders, fusing them into optically-transparent solids, then embedding them with
metal ions in order to tune their properties.
Fig 7.8 Laser plug

47
7.7 Working of laser ignition system
Fig 7.9 Laser ignition system for multi cylinder engine
The laser ignition system has a laser transmitter with a fibre-optic cable
powered by the car’s battery. 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 mill joule 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 .It shoots the laser beam to a focusing
lens that would consume a much smaller space than current spark plugs. The lenses
focus the beams into an intense pinpoint of light by passing through an optical
window.

48
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. when the
fuel is injected into the engine, the laser is fired and produces enough energy (heat)
to ignite the fuel.
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. The plasma
generated by the Laser beam results in two of the following actions :
1. Emission of high energy photons
2. Generation of shock waves The high energy photons, heat and ionize the
charge present in the path of laser beam which can be seen from the propagation of
the flame which propagates longitudinally along the laser beam.
3.The shock waves carry energy out wards from the laser beam and thus help
in propagation of flame.
If the electrons gain sufficient energy, they can ionize other gas molecules on
impact, leading to an electron cascade and breakdown of the gas in the focal region.
It is important to note that this process requires initial seed electrons. These electrons
are produced from impurities in the gas mixture (dust, aerosols and soot particles)
which are always present. These impurities absorb the laser radiation and lead to
high local temperature and in consequence to free electrons starting the avalanche
process. In contrast to multi photon ionisation (MPI), no wavelength dependence is
expected for this initiation path.

49
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.
Fig 7.10 Plasma Formation by a Focused Beam

50
CHAPTER -8
MODIFICATION REQUIREMENTS OF LIS
8.1 Modification of Combustion chamber
As a feasibility test, an excimer laser has been used for ignition of
inflammable gases inside a combustion bomb. The laser used for the first
experiments was a Lambda Physik LPX205, equipped with an unstable resonator
system and operated with KrF, delivering pulses with a wavelength of 248 nm and
a duration of approximately 34 ns with maximum pulse energy of 400 mJ.10 The
combustion chamber has had a diameter of 65 mm and a height of 86mm, with a
resulting volume of 290cm3 and was made of steel.
The laser beam was focused into the chamber by means of a lens with a focal
length of 50 mm. Variations of pulse energies as well as gas mixtures have been
performed to judge the feasibility of the process. Results indicate that ignition-delay
times are smaller and pressure gradients are much steeper compared to conventional
spark plug ignition. Combustion can last between 100 ms up to several seconds again
depending on the gas mixture, initial pressure, pulse energy, plasma size, position of
the plasma in the combustion bomb and initial temperature.
8.2 Modification of Engine
Since the first feasibility could be concluded theoretical successful, an engine
will modifying for laser ignition. The engine is to modifying by a replacement of
the conventional spark plug by a window installed into a cylindrical mount. The
position of the focusing lens inside the mount can be changed to allow variations of
the location of the initial optical breakdown. If considering First experiment
conducting with laser ignition of the engine have been perform with an excimer
laser, later a q switched ND: YAG has been used.

51
The replacement of the excimer laser was mainly caused by the fact that
especially at very low pulse energies the excimer laser shows strong energy
fluctuations. Pulse energies, ignition location and fuel/air ratios have been varied
during the experiments. The engine has been operated at each setting for several
hours, repeatedly. All laser ignition experiments have been accompanied to be
conventional spark plug ignition as reference measurements.
A custom laser igniter was designing as a like-for-like replacement for the
existing standard igniter used with the SGT-400 pilot burner. The laser igniter
consisted of a clear aperture for transmission of the laser beam, and a-spherical
focusing optic with an effective focal length of 15.29 mm and an anti-reﬂective
coated N-BK7 output window. The laser-induced spark was located approximately
1 cm from the face of the burner. To ensure that no ingress of the combustible
gaseous mixture within the combustion chamber occurred, the tip of the ignition
lance was sealed with red silicone around the edge of the output window.
Fig 8.1 The q-switched Nd: YAG laser system

52
Table 8.1 Technical data of the research engine and the ND: YAG laser used for the experiments
Research engine Switched Nd:YAG
No.of cylinder 1 Pump source Flash lamp
No.of valves 1 Wave length 1064 or 532 nm
Injector Multi hole Energy 1064 or 532 nm
Stroke 85 mm Max.pulse energy 6 ns
Bore 88 mm Power consumption 1 kw
Displacement vol. 517 cm3 Beam Diameter 6 mm
Comp.ratio 11.6 Type Quantel brilliant
8.3 Comparison of performance of SI with respect to LI engines
Theoretically Compared to conventional spark plug ignition, laser ignition
reduces the fuel consumption by several per cents. Exhaust emissions are reduced
by nearly 20%. It is important that the benefits from laser ignition can be achieved
at almost the same engine smoothness level, as can be seen from . The results
presented show a direct comparison of combustion performance between a laser
ignited cylinder and a conventionally ignited cylinder, where the results are
displayed as ratios of COV &IMEP and performed better than SI in terms of
combustion stability for many of the focusing lenses and cavity aperture
combinations.

53
Fig 8.2 Comparison of performance parameters of SI with respect to LI engines
Additionally, a frequency-doubled Nd: YAG laser has been used to examine
possible influences of the wavelength on the laser ignition process. No influences
could be found. Best results in terms of fuel consumption as well as exhaust gases
have been achieved by laser ignition within the fuel spray. As already mentioned, it
is not possible to use conventional spark plugs within the fuel spray since they will
be destroyed very rapidly. Laser ignition doesn’t suffer from that restriction.
Another important question with a laser ignition system is its reliability. It is
clear that the operation of an engine causes very strong pollution within the
combustion Chamber. Deposits caused by the combustion process can contaminate
the beam entrance window and the laser ignition system will probably fail. To
quantify the influence of deposits on the laser ignition system, the engine has been
operated with a spark plug at different load points for more than 20 hours with an
installed beam entrance window.

54
As can be seen in fig the window was soiled with a dark layer of combustion
deposits. Afterwards, a cold start of the engine was simulated. Already the first laser
pulse ignited the fuel/air mixture. Following laser pulses ignited the engine without
misfiring, too. After 100 cycles the engine was stopped and the window was
disassembled.
Fig 8.3 Self cleaning property
As can be seen from fig 6.3 all deposits have been removed by the laser beam.
Additional experiments showed that for smooth operation of the engine the
minimum pulse energy of the laser is determined by the necessary intensity for
cleaning of the beam entrance window. Estimated minimum pulse energies are too
low since such “self-cleaning” mechanisms are not taken into account. Engine
operation without misfiring was always possible above certain threshold intensity at
the beam entrance window. For safe operation of an engine even at cold start
conditions increased pulse energy of the first few laser pulses would be beneficial
for cleaning of the beam entrance window.

55
Fig 8.4 Flame front propagation
The above figure explains the flame front propagation inside the combustion
chamber during combustion .Plasma had the maximum emission peak 14 ns after
the laser was fired and laser plasma UV-emission persisted for about 80 ns
.Minimum laser pulse energy (MPE) for ignition is decreases with increasing initial
pressure.The time of pressure rise in case of laser ignition is shorter than the spark
ignition.
Engines would produce less NOx if they burnt more air and less fuel, but they
would require the plugs to produce higher energy sparks in order to do so. Less NOx
emission.
6 ns
7 ns
8 ns
9 ns
10 ns
11 ns
12 ns
13 ns
14 ns
15 ns
16 ns
18 ns
20 ns
22 ns
25 ns
30 ns
35 ns
40 ns
45 ns
50 ns
60 ns
70 ns
80 ns

56
Fig 8.5 Comparison of NOX emissions of different ignition
8.4 Extended usage of laser Ignition
To fully utilize the potentialities of laser ignition, the developer must
understand and master the interrelationships in the engine perfectly. There is no
sense in utilizing only the NOX advantages with a costly system and not paying
attention to the specific fuel consumption. Consequently, additional measures must
be taken to maintain the fuel consumption level under conditions of extremely lean
operation and even to improve it. In this regard, researchers place great emphasis on
its experience with high turbulence to accelerate combustion (HEC concept).
However, there are also other innovative approaches possible with laser ignition.
One tested approach is so-called multi-point ignition, which has been investigated
not only in terms of the theoretical approach, but also through studies dealing with
combustion vessels.

57
Fig 8.6 Flame front 290
after ignition
As an example, Figure presents the result of the calculated flame front of a 4-
point Laser ignition after 29°CA in operation at Lambda 2.05. In this manner, the
spark duration (90 %) can be reduced approximately to less than half (NOx level 30
ppm) Another approach is to improve ignition conditions and flame propagation by
increasing combustion chamber temperatures. As well, this allows the required
ignition energies to be reduced considerably.
Fig 8.7 Variation of ignition energy with respect
to combustion chamber temperatures
Flame front 290
after ignition

58
With a very lean mixture it is possible to reduce the required ignition energy
by about 30 % by increasing the temperature by 50°C (from150 to 200°C). At full
load the temperatures at the firing point are a good deal higher. To be able to better
understand the interrelationships, the tests with the combustion vessel were extended
to a temperature level of 400°C. The results in the case of methane are presented in
Figure 6.7. Using this approach, the required ignition energy can be kept at less than
2 mJ up to Lambda 2.2 mJ. Knowledge of the global interrelationships is therefore
very important for the design of the laser.
8.5 Advantages of laser ignition
The main advantages of laser ignitions are given below:
 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 and 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, increasing 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.
 The thermodynamic requirements of a high compression ratio and a high
power density are fulfilled well by laser ignition.

59
8.6 Future Researches
Delivering the beam through free space and channeling it into the combustion
chamber through the optical plug achieved the best results – reducing the Coefficient
of Variation, making combustion smoother and more fuel efficient. The team was
particularly keen to deliver the beam via optical fiber, since this was likely to be less
susceptible to engine vibration and could facilitate improved engine layout. They
tried out a range of optical fibers, including silica and sapphire, and experimented
with different internal fiber structures, core sizes and beam coupling optics.
Delivering the beam via optical fiber proved to be more difficult than the
research team had hoped. The fiber didn’t respond well to engine vibration, which
increased the divergence of the output beam and reduced the beam mode quality.
Bending the fiber was also problematical and up to 20 per cent of the beam
energy was lost with small bend diameters, while tight bends caused the fiber to fail
altogether after a period. What’s more, the high density of laser energy can cause
immediate or long term degradation, leading to loss of beam transmission – and
therefore loss of ignition. Careful design of laser parameters, fiber coupling and
choice of optical media is crucial to avoid this. These problems can be solved with
further research.
From the perspective of dwindling oil resources laser ignition system is good
as it reduces the fuel consumption. From the environmental point of view it is very
significant since it considerably reduces the emission.
Seen as the current best alternative to conventional sparkplug ignition system.
Some of leading institutes and organizations researching and came with adaptive
results are,
 University of Liverpool in collaboration with Ford Motor Company
 National Energy Technological laboratory, United States of America
 Colorado University& National Institutes of Natural Sciences-Japan, etc.

60
8.7 Practical Laser Sparkplug Requirements
The simplest and least costly laser ignition design architecture would consist
of a compact high peak power laser transmitter head, and a sapphire window/lens
delivery system. The sapphire window is a well proven and reliable method of
providing a transparent bulkhead seal on high pressure combustion chambers such
as gas engine cylinder heads and the breeches of 155mm howitzers.
BMLIS (Breech Mount Laser Ignition System) lasers, mounted directly on to
the breech of large cannons, have over the last 20 years proven to be more reliable
than fiber optic laser beam delivery systems . In these laser applications the laser
window “self cleaning” or “burning free” effect is well known .
This is a laser ablation effect where ignition residue that collects on the
window surface is blown free and clear of the optical aperture with each laser
pulse.Many BMLIS, ARES and ARICE researchers are reaching the same
conclusions about the attractiveness and dependability of direct fire laser ignition
designs. Estimated basic cost and performance requirements for a practical laser
spark plug are listed in table 8.2.
Table 8.2 Estimated basic cost and performance requirements for a laser spark plug
Mechanical Laser and mounting must be hardened against shock and
vibration
Environmental Laser should perform over a large temperature range
Peak Power Laser should provide megawatts raw beam output
Average Power 1-laser per cylinder requires 10Hz for 1200rpm engine
operation
Lifetime 100 million shots – good, 500 million shots – better
Cost(ARES) Laser cost less than $3,000 each (100M pulse life ~ break
even)
Cost (Auto) Laser cost less than $600 each

61
The cost values shown for the natural gas engine laser spark plug are based
upon the estimated operational costs of an 800 Kilowatt 16-cylinder Waukesha
engine operating at 1200rpm with 16 lasers (one for each cylinder). At 1200 rpm the
laser operates 24 hours a day, 365 days a year at 10 Hz (1200 rpm/2 strokes/
60sec/min) for a total of approximately 315M pulses per year.
We may also envision smaller and less costly laser spark plugs for use in
common automobile and truck engines. These applications may make use of very
small low cost single emitter laser diodes to significantly reduce the laser spark plug
component cost.
Diode laser pumps are the most costly element employed in traditional side
and end pumped DPSS Lasers. The diode lifetime is the limiting factor in the laser
life time.The other criteria likes below,
 Cost
 Concept proven but no commercial system yet available
 Stability of optical window
 Laser induced optical damage
 Particle deposit
 Intelligent control
 Laser distribution
 Multiple pulse ignitions
 Multiple point ignitions

62
8.8 Application
Laser ignition may be used in various applications besides high-speed,
hypersonic aircraft. Examples include standard internal combustion engines, such as
in automobiles and aircraft, as well as industrial combustion facilities which generate
large amounts power. Laser ignition is considered as a potential ignition system for
non-hypergolic liquid rocket engines and reaction control systems which need an
ignition system. Conventional ignition technologies like torch igniters are more
complex in sequencing and need additional components like propellant feed lines
and valves. Therefore, they are heavy compared to a laser ignition system.
Pyrotechnical devices allow only one ignition per unit and imply increased launch
pad precautions as they are made of explosives.
 According to the latest international reports, Mazda’s upcoming rotary
sports car could feature laser ignition technology. This would replace the
spark plug ignition system which is currently applied to every petrol car
on the market. It’s also a setup a revolution in spark plug which has been
not change around since 1860.
 Ford Motor Co. and researchers at the University of Liverpool are
developing a car ignition system that swaps spark plugs for a laser beam
to start vehicles while generating fewer greenhouse gas emissions.
Fig 8.8 Mazda RX-9 16X rotar

63
CHAPTER - 9
CONCLUSION
In this paper, it is described the positive research work on laser ignitions which
can replace the conventional spark plug in near future very soon due to avoid the
drawbacks of spark plug ignition system . Main advantages are the free choice of the
ignition location within the combustion chamber and Significant reductions in fuel
consumption & exhaust gas. From the point of view of components development,
the main goal is the creation of a laser system which meets the engine- specific
requirements. Basically, it is possible to ignite mixtures with different laser systems.
The concept with the greatest development potential regarding efficiency and
miniaturization is the diode pumped solid-state laser. At present, a laser ignition plug
is very expensive as compared to spark plugs. But potential advantages will surely
bring it in to market for many practical applications.

64
CHAPTER - 10
REFERENCE
1) Takuma Endo & Keisuke Kuwamoto by “Comparative study of laser
ignition and spark-plug ignition in high-speed flows” Hiroshima 739-8527,
Japan.
2) J. Griffiths, M.J.W. Rileyb & Borman , by “Effect of flow velocity and
temperature on ignition characteristics in laser ignition of natural gas
and air mixtures” Brayford Pool, Lincoln, LN6 7TS, United Kingdom .
3) J D Mullett , G Triantos, and S Keen by “The influence of beam energy,
mode and focal length on the control of laser ignition in an internal
combustion engine” GSI Group, UK.
4) Cangsu Xu n, Donghua Fang& Jian Ma, by “A comparative study of laser
ignition and spark ignition with gasoline–air mixtures”, Zhejiang
University, Hangzhou 310027.
5) Lydia Wermer a , James Hanssonb & Seong-kyun Im a ,by” Dual-pulse
laser-induced spark ignition and flame propagation of a methane
diffusion jet flame” Department of Mechanical Engineering, USA.
6) J. D. Dale by “Advancing lean combustion of hydrogen-air mixtures by
laser induced ignition system” Brayford Pool, Lincoln, LN6 7TS, UK .
7) M. D. Checkel, P. R. Smy,by Application of High Energy Ignition Systems
to Engines, Prog. Energy Combust. Sci. 23, 379-398 (1997).
8) J. Ma, D. Alexander, and D. Poulain,by “Laser spark ignition and
combustion characteristics of methane-air mixtures,” Combustion and
Flame, pp. 492–506, 1998.

65
9) Kopecek, H., Lackner, M., Wintner, E., Winter, by Laser-Stimulated
Ignition in a Homogeneous Charge Compression Ignition Engine, SAE
2004 World Congress, paper No 2004-01-0937.
10) A.P. Yalin, M.W. Defoort, S. Joshi, D. Olsen, B. Willson, Y. Matsuura,
M. Miyagi, " Laser Ignition of Natural Gas Using Fiber Delivery" , ASME
Internal Combustion Engine Division 2005 Fall Technical Conference, ICEF-
2005-1336, pp. 1-9

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