LASER IGNITION SYSTEM REPORT ASHUTOSH GAUR

B.TECH. STUDY OF LASER IGNITION SYSTEM
A Project Report Submitted
In Partial Fulfillment of the Requirements
For the award of the Degree of
BACHELOR OF TECHNOLOGY
in
MECHANICAL ENGINEERING
by
ASHUTOSH GAUR (1413240043)
ARPIT SHARMA (1413240041)
GAURAV TIWARI (1413240074)
AVINASH K. SINGH (1413240047)
ANUJ K. SINGH (1413240037)
Under the supervision of
MR. VISHWAJEET RANJAN
DEPARTMENT OF MECHANICAL ENGINEERING
GREATER NOIDA INSTITUTE OF TECHNOLOGY
Plot no. 7, Knowledge Park – II, Greater Noida, U.P(201310)
Affiliated to Dr. A.P.J. Abdul Kalam Technical University, Lucknow,
(Formerly Uttar Pradesh Technical University, Lucknow, U.P.)
MAY, 2018
STUDYOFLASERIGNITIONSYSTEMMAY2018

STUDY OF LASER IGNITION SYSTEM
A Project Report Submitted
In Partial Fulfillment of the Requirements
For the award of the Degree of
BACHELOR OF TECHNOLOGY
in
MECHANICAL ENGINEERING
by
ASHUTOSH GAUR (1413240043)
ARPIT SHARMA (1413240041)
GAURAV TIWARI (1413240074)
AVINASH K. SINGH (1413240047)
ANUJ K. SINGH (1403240037)
Under the supervision of
Mr. VISHWAJEET RANJAN
DEPARTMENT OF MECHANICAL ENGINEERING
GREATER NOIDA INSTITUTE OF TECHNOLOGY, GREATER NOIDA
Affiliated to Dr. A.P.J. Abdul Kalam Technical University, Lucknow
(Formerly Uttar Pradesh Technical University, Lucknow, U.P.)
MAY, 2018

ii
GREATER NOIDA INSTITUTE OF TECHNOLOGY
PLOT NO. 7, K.P. II, GREATER NOIDA, UP-201310
Affiliated to Dr. A.P.J. Abdul Kalam Technical University, Lucknow, UP
(Formerly known as Uttar Pradesh Technical University, Lucknow)
CERTIFICATE
This is to certify that project report entitled “STUDY OF LASER IGNITION SYSTEM”
which is submitted by Ashutosh Gaur, Arpit Sharma, Gaurav Tiwari, Avinash k. Singh,
Anuj K. Singh in partial fulfillment of the requirements for the award of degree Bachelor of
Technology in Department of Mechanical Engineering from Greater Noida Institute of
Technology, affiliated to Dr. A.P.J. Abdul Kalam Technical University, Lucknow is a record
of the candidates own work carried out by them under my supervision. The matter embodied
in this project report is original and has not been submitted for the award of any other degree.
(Mr. VISHWAJEET RANJAN)
Supervisor
(Mr. ANUJ DIXIT) (Dr. SUDHIR KUMAR)
Project Co-ordinator Prof. & HOD ME
Deptt.

iii
DECLARATION
We hereby declare that this submission is our own work and that, to the best of our knowledge
and belief. It contains no material previously published or written by another person nor
material which to a substantial extent has been accepted for the award of any other degree
or diploma of the university or other institute of higher learning, except where due
acknowledgment has been made in the text.
Signature: Signature:
Name: Ashutosh Gaur Name: Arpit Sharma
Roll no: 1413240043 Roll no: 1413240041
Date: /05/2018 Date: /05/2018
Name: Gaurav Tiwari Name: Avinash k. Singh
Roll no: 1413240074 Roll no: 1413240047
Date: /05/2018 Date: /05/2018
Signature:
Name: Anuj K. Singh
Roll no: 1413240037
Date: /05/2018

iv
ACKNOWLEDGEMENT
It gives us a great sense of pleasure to present the report of B.Tech project undertaken during
B.Tech. Final Year. We express our sincere gratitude to our respected supervisor, Mr.
Vishwajeet Ranjan, (Assistant Professor, Department of Mechanical Engineering, Greater
Noida Institute of Technology, Greater Noida) for his invaluable inspiring guidance and
constant encouragement during the period of project work.
We owe special debt of gratitude to Mr. Anuj Dixit (Assistant Professor, Department of
Mechanical Engineering, Greater Noida Institute of Technology, Greater Noida) for his
constant support and guidance throughout the course of our work. His sincerity,
thoroughness and perseverance have been a constant source of inspiration for us. It is only
his cognizant efforts that our endeavors have seen light of the day.
We also take the opportunity to acknowledge the contribution of Professor Sudhir Kumar,
(Head, Department of Mechanical Engineering, Greater Noida Institute of Technology,
Greater Noida) for his full support and assistance during the development of the project.
We also like to acknowledge the contribution of all faculty members of the department for
their kind assistance during the development of our project. Last but not the least, we
acknowledge our friends for their contribution in the completion of this project.
Name: Ashutosh Gaur Name: Arpit Sharma
Roll no: 1413240043 Roll no: 1413240041
Date: /05/2018 Date: /05/2018
Name: Gaurav Tiwari Name: Avinash k. Singh
Roll no: 1413240074 Roll no: 1413240047
Date: /05/2018 Date: /05/2018
Signature:
Name: Anuj K. Singh
Roll no: 1413240037
Date: /05/2018

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ABSRACT
With the advent of lasers in the 1960s, researcher and engineers discovered a new and
powerful tool to investigate natural phenomena and improve technologically critical
processes. Nowadays, applications of different lasers span quite broadly from diagnostics
tools in science and engineering to biological and medical uses. In this report basic principles
and applications of lasers for ignition of fuels are concisely reviewed from the engineering
perspective. Recent progress in the area of high power fibre 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. 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.

vi
LIST OF CONTENTS
CERTIFICATE ii
DECLARATION iii
ACKNOWLEDGMENT iv
ABSTRACT v
CONTENTS vi
LIST OF FIGURE viii
LIST OF TABLES x
LIST OF ABBREVIATIONS xi
CHAPTER 1. INTRODUCTION
1.1 Introduction to Laser Ignition System 1
1.2 Ignition 2
1.3 Ignition types 2
1.4 Spark Plug Ignition 3
1.5 Limitation of Spark Ignition System 5
CHAPTER 2. LASER
2.1 Solid State Laser (ND: YAG) 7
CHAPTER 3. LITERATURE REVIEWS
3.1 Research Paper by Previous Scientist 12
3.2 Gaps In Literature Review 16
CHAPTER 4. LASER IGNITION SYSTEM
4.1 Principles of Laser Ignition System 18
4.2 Laser ignition along time 19
4.3 Ignition in combustion chamber 20
4.4 Mechanism of laser ignition 20
4.5 Arrangement of laser ignition system 22
4.6 Working of laser ignition system 25
4.7 Advantages of laser ignition system 27
CHAPTER 5. PREVIOUS EXPERIMENTS AND RESULT 28

vii
CHAPTER 6. FUTURE RESEARCHES & APPLICATIONS
6.1 Future Researches 35
6.2 Practical Laser Sparkplug Requirements 36
6.3 Application 37
CHAPTER 7. CONCLUSION 39
REFRENCES 40

viii
LIST OF FIGURES
Fig. No. Figure Description Page No.
Figure 1 Spark Plug 3
Figure 2 Four stroke engine cycle 4
Figure 3 Different colour LASER 7
Figure 4 ND : YAG laser 8
Figure 5 Population Inversion 9
Figure 6 Spontaneous Emission 10
Figure 7 Stimulated Emission 10
Figure 8 Optical breakdown in air generated 17
Figure 9 Non Resonant Breakdown 18
Figure 10 Stages of ignition with respect to time . 19
Figure 11 Ignition inside combustion chamber 20
Figure 12 Laser arrangement with respect to engine 22
Figure 13 Focusing unit 23
Figure 14 Laser Plug 24
Figure 15 Working of LIS 26
Figure 16 Arrangement of Laser Plug in cylinder head 27
Figure 17 Layout Of Experiment 28
Figure 18 Relation Between The IMEP And Equivalent Ratio 29
Figure 19 Flame Kernel Development Of Laser And Spark Ignition 30
Figure 20 Experimental setup for offline and online laser ignition
testing .
30

ix
Figure 21 Transmitted energy through the five optical plugs and
subsequent plasmas produced
31
Figure 22 Research Engine With The Q Switched ND : YAG Laser
System
32
Figure 23 Pressure Dependence On The Required Pulse Energy For
Successful Ignition
33
Figure 24 Comparison Of Fuel Consumption, Smoothness And
Emissions Between Spark And Laser Ignition
33
Figure 25 Spark Plug Ignition, Heavily Polluted On The Top And Self
Cleansing Of Optical Window On Down
34
Figure 26 Mazda RX 9 16X Rotar 38

x
LIST OF TABLES
Table No. Table Description Page No.
Table 1 Specification of test engine
28
Table 2
Technical data of the research engine and the Nd:Yag laser
used for the experiments
32
Table 3 Potential requirements of LIS
36

xi
LIST OF ABBREVIATIONS
Abbreviations Full Form
ND: YAG Neodymium-Doped Yttrium Aluminum Garnet
IMEP Indicated Mean Effective Pressures
COV Coefficient Of Variation
SIS Spark Ignition System
LIS Laser Ignition System
μs Micro Second
mj Milli-Joule
MPa Mega Pascal
MPI Multi Photon Ionization
DOHC Double-Overhead-Camshaft
PPM Particles Per Million
CH4 Methane
CO2 Carbon Dioxide

1
CHAPTER 1
INTRODUCTION
1.1 Introduction to Laser Ignition System
Since very long time, spark plugs have powered internal combustion engines.
Located at the top of each engine cylinder, spark plugs send a high-voltage
electrical spark across a gap between their two metal electrodes. That spark ignites
the compressed air-fuel mixture in the cylinder, causing a controlled mini-
explosion that pushes the piston down. One by product of the process is toxic
nitrogen oxides (NOx), which pollute the air causing smog and acid rain. 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. While this is
technically possible, the voltages involved would burn out the electrodes quite
quickly. Since lean mixtures have relatively slower flame speed than stoichiometric
mixtures, any technique which may provide increase in the air–fuel mixture burning
rate, would be beneficial. Flame speed in the lean burn SI engine can be increased
either by generating turbulence in the cylinder or by shortening the flame travel
distance for the same mixture strength. Reduction in flame travel path can be
realized by employing multiple spark plugs in each cylinder or by placing the
ignition point at an optimum location inside the combustion chamber. It is rather
challenging to install multiple spark plugs in multi-cylinder engines because of
already overcrowded cylinder head. Optimum spark location inside the combustion
chamber is also difficult in case of conventional spark ignition systems because
spark location is always very close to the top of combustion chamber. So the best
solution for this is Laser Ignition System, in which we use laser igniters instead of
conventional spark plug. Laser igniter ignite leaner mixtures without self-
destructing because they don't have electrodes. The operation of internal
combustion engines with lean gas-air mixtures, laser igniters results in increase of
fuel efficiencies and reduce green-house gas emissions by significant amounts.

2
1.2 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.
1.3 Ignition Types
1.3.1 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.
1.3.2 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.
1.3.3 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

3
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). 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.
Figure 1: Spark Plug
1.4 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

4
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
Figure 2: Four stroke engine cycle
ground electrode of the spark plug. The voltage is continuously transferred through
the central electrode (which is sealed using an insulator). 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.

5
1.5 Limitation of Spark Ignition System
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.

6
CHAPTER 2
LASER
LASER stands for Light Amplification by Stimulated Emission of Radiation. A
laser is a device which produces highly directional light. It emits light through a
process called stimulated emission of radiation which increases the intensity of
light. A laser is different from conventional light sources in four ways: coherence,
directionality, monochromatic, and high intensity. The light waves of ordinary
light sources have many wavelengths. Hence, the photons emitted by ordinary light
sources are out of phase. Thus, ordinary light is incoherent. On the other hand, the
light waves of laser light have only one wavelength. Hence, all the photons emitted
by laser light are in phase. Thus, laser light is coherent. The light waves from laser
contain only one wavelength or color so it is known as monochromatic light. The
laser beam is very narrow and can be concentrated on a very small area. This
makes laser light highly directional. The laser light spreads in a small region of
space. Hence, all the energy is concentrated on a narrow region. Therefore, laser
light has greater intensity than the ordinary light. Einstein gave the theoretical
basis for the development of laser in 1917, when he predicted the possibility of
stimulated emission.
In 1954, C.H. Townes and his co-workers put Einstein’s prediction for practical
realization. They developed a microwave amplifier based on stimulated emission
of radiation. It was called as MASER (Microwave Amplification by Stimulated
Emission of Radiation. Maser operates on principles similar to laser but generates
microwaves rather than light radiation. In 1958, C.H. Townes and A. Schawlow
extended the principle of masers to light. In 1960, T.H. Maiman built the first laser
device.
Lasers are classified into 4 types based on the type of laser medium used:
Solid-state laser
Gas laser
Liquid laser
Semiconductor laser

7
Figure 3: Different color LASER
2.1 (ND: YAG) Solid State Laser
Neodymium-doped Yttrium Aluminum Garnet (ND: YAG) laser is a solid state
laser in which ND: YAG is used as a laser medium. These lasers have many
different applications in the medical and scientific field for processes such as Lasik
surgery and laser spectroscopy. ND: YAG laser is a four-level laser system, which
means that the four energy levels are involved in laser action. These lasers operate
in both pulsed and continuous mode. ND: YAG laser generates laser light
commonly in the near-infrared region of the spectrum at 1064 nanometers (nm). It
also emits laser light at several different wavelengths including 1440 nm, 1320 nm,
1120 nm, and 940 nm.
2.1.1 Nd: Yag Laser Construction
Nd: YAG laser consists of three important elements: an energy source, active
medium, and optical resonator.
2.1.1.1 Energy Source
The energy source or pump source supplies energy to the active medium to achieve
population inversion. In Nd: YAG laser, light energy sources such as flashtube or
laser diodes are used as energy source to supply energy to the active medium.
In the past, flashtubes are mostly used as pump source because of its low cost.
However, nowadays, laser diodes are preferred over flashtubes because of its high
efficiency and low cost.

8
Figure 4: ND: YAG laser[16]
2.1.1.2 Active Medium
The active medium or laser medium of the Nd:YAG laser is made up of a synthetic
crystalline material (Yttrium Aluminum Garnet (YAG)) doped with a chemical
element (neodymium (Nd)). The lower energy state electrons of the neodymium
ions are excited to the higher energy state to provide lasing action in the active
medium.
2.1.1.3 Optical Resonator
The Nd:YAG crystal is placed between two mirrors. These two mirrors are
optically coated or silvered. Each mirror is silvered or coated differently. One
mirror is fully silvered whereas, another mirror is partially silvered. The mirror,
which is fully silvered, will completely reflect the light and is known as fully
reflecting mirror.
On the other hand, the mirror which is partially silvered will reflect most part of
the light but allows a small portion of light through it to produce the laser beam.
This mirror is known as a partially reflecting mirror.

9
2.1.2 Working of Nd:Yag Laser
Nd: YAG laser is a four-level laser system, which means that the four energy
levels are involved in laser action. The light energy sources such as flashtubes or
laser diodes are used to supply energy to the active medium.
In Nd:YAG laser, the lower energy state electrons in the neodymium ions are
excited to the higher energy state to achieve population inversion. Consider a
Nd:YAG crystal active medium consisting of four energy levels E1, E2, E3, and
E4 with N number of electrons. The number of electrons in the energy states E1,
E2, E3, and E4 will be N1, N2, N3, and N4. Let us assume that the energy levels will
be E1 < E2 <E3 <E4. The energy level E1 is known as ground state, E2 is the next
higher energy state or excited state, E3 is the metastable state or excited state and
E4 is the pump state or excited state. Let us assume that initially, the population
will be N1 > N2 > N3 > N4. When flashtube or laser diode supplies light energy to
the active medium (Nd:YAG crystal), the lower energy state (E1) electrons in the
neodymium ions gains enough energy and moves to the pump state or higher
energy state E4.
Figure 5: Population Inversion[16]
The lifetime of pump state or higher energy state E4 is very small (230
microseconds (µs)) so the electrons in the energy state E4 do not stay for long
period. After a short period, the electrons will fall into the next lower energy state
or metastable state E3 by releasing non-radiation energy (releasing energy without
emitting photons).
The lifetime of metastable state E3 is high as compared to the lifetime of pump
state E4. Therefore, the electrons reach E3 much faster than they leave E3. This

10
results in an increase in the number of electrons in the metastable E3 and hence
population inversion is achieved. After some period, the electrons in the metastable
state E3 will fall into the next lower energy state E2 by releasing photons or light.
The emission of photons in this manner is called spontaneous emission.
Figure 6: Spontaneous Emission[16]
The lifetime of energy state E2 is very small just like the energy state E4.
Therefore, after a short period, the electrons in the energy state E2 will fall back to
the ground state E1 by releasing radiation less energy.
When photon emitted due to spontaneous emission is interacted with the other
metastable state electron, it stimulates that electron and makes it fall into the lower
energy state by releasing the photon. As a result, two photons are released. The
emission of photons in this manner is called stimulated emission of radiation.
Figure 7: Stimulated Emission[16]

11
When these two photons again interacted with the metastable state electrons, four
photons are released. Likewise, millions of photons are emitted. Thus, optical gain
is achieved. Spontaneous emission is a natural process but stimulated emission is
not a natural process. To achieve stimulated emission, we need to supply external
photons or light to the active medium. The Nd:YAG active medium generates
photons or light due to spontaneous emission. The light or photons generated in the
active medium will bounce back and forth between the two mirrors. This
stimulates other electrons to fall into the lower energy state by releasing photons or
light. Likewise, millions of electrons are stimulated to emit photons. The light
generated within the active medium is reflected many times between the mirrors
before it escapes through the partially reflecting mirror.
Advantages of Nd:YAG laser
Low power consumption
Nd:YAG laser offers high gain.
Nd:YAG laser has good thermal properties.
Nd:YAG laser has good mechanical properties.
The efficiency of Nd:YAG laser is very high as compared to the ruby laser.

12
CHAPTER 3
LITERATURE REVIEW
3.1Research Paper by Previous Scientist
Mantri, H, and Ramtek, M [1] (2016), examine the various positions of laser
igniter and plot the performance graph showing the comparison of laser ignition
and spark ignition and he founds that the brake thermal efficiency and indicated
power are increases in engine with laser ignition system than the spark ignition
system in engine. This system can work even in high compression ratio,
compression rates, high temperature and high pressure. Specific fuel consumption
decreases in the laser ignition system as laser ignition system can operate on lean
mixtures. The significant reduction in combustion time and better time control can
be achieved by using multipoint laser ignition system.
Kothari, Modasara, A, et.al, [2] (2016), discusses the potential advantages and
control opportunities and considers the challenges faced, construction and working
of laser ignitor and the system requirements for laser ignitor. In order to generate
the laser Nd: YAG is chosen as laser active medium emitting at λem = 1064 nm,
and Cr: YAG as passive saturable absorber. There are four different ways in which
laser light can interact with a combustible mixture to initiate an ignition event
namely, Thermal initiation, Non resonant breakdown, Resonant breakdown, and
Photochemical ignition. Out of the above stated different ways non resonant
breakdown is more frequently used because of its freedom in selecting the laser
wavelength and ease of implementation. At present the laser ignition plug is very
expensive and commercially not yet available. They also explain types of laser
ignition system and working of laser ignition system.
Saxena, A. [3] (2015), described that how a revolutionary change has come after
the positive research work on laser igniters which can replace the conventional
spark plug in near future very soon. This replacement of conventional spark plugs
to laser igniters will be a milestone in automobile industry. Laser igniters will be
able to combust the fuel with lean air-fuel mixture as compare to conventional
spark plug, which helps to lower down the Nox emission and gives better fuel

13
efficiency and a better clean environment.
Harel.S, Sonawane.V et.al, [5] (2014), The thermodynamic requirements of a high
compression ratio and a high power density are fulfilled well by laser ignition.
Through this paper, the objective is to present the current state of the relevant
knowledge on fuel ignition and discuss selected applications, advantages, in the
context of combustion engines. Sustainability with regard to internal combustion
engines is strongly linked to the fuels burnt and the overall efficiency. Laser
ignition can enhance the combustion process and minimize pollutant formation.
This paper is on laser ignition of sustainable fuels for future internal combustion
engines. Ignition is the process of starting radical reactions until a self-sustaining
flame has developed. In technical appliances such as internal combustion engines,
reliable ignition is necessary for adequate system performance. Ignition strongly
affects the formation of pollutants and the extent of fuel conversion. Laser ignition
system can be a reliable way to achieve this. They show how does laser light can
interact with a combustible mixture to initiate an ignition event. In the end they
have discussed some experimental results regarding measurements of fuel
consumption and emissions which prove that laser ignition has important
advantages compared to conventional spark ignition systems.
Sharma.V, [6] (2014), Assistant professor of mechanical engineering department
has proposed the use of CNG in the IC engine, and found the drastic reduction in
the emission to the environment by the use of CNG in the engine and as we know
that the CNG plays a dominating role the transport and energy production.
Unfortunately, the spark plug cannot ignite the leaner mixture of fuel and air for
the longer time and also it produces exhaust emission and results in the reduction
of the efficiency of the engine and also reduces the NOx concentration in the
exhaust gas. Vikas Sharma has also explained the concept of ignition of the
combustibles, in CNG engine as the ignition of a combustible requires a high
voltage is applied to the electrodes of the spark plug.
Mullett, J. D, Dodd, R, et al [7] (2006), in this paper they tell us the four principles
of laser ignition system that are, Non resonant Breakdown Ignition, Resonant

14
Breakdown, Thermal initiation, Photochemical ignition. In this paper the
investigate the effects of laser parameter on LIS and the performance of LIS against
SI. It works on the principle of Non resonant breakdown principle in which begins
with the multiphoton ionisation of a few molecules in release of electron takes
place and thus is absorbed by laser head. After which an avalanche is created and
through which the kinetic energy of other molecule increases and thus breakdown
occur. Through this experiment the main focus is to reduce the energy required to
ignite the molecules when compared with SI ignitors and thus graph is plotted
between energies and found that energy of 4mJ. The experiment was conducted in
two modes first is offline and second was online. Result were drawn out through
graph mode from energy meter through offline mode in which laser before entering
the optical plug and existing through is plotted. In online mode the laser is passed
through engine and calculation takes place through optical plug.
M. Lackner, F. Winter, et al [8] (2006), In this paper laser-induced ignition of
hydrogen/air and biogas/air mixtures was investigated experimentally in a static
combustion bomb. The whole experiment was done with two modes in first, plane
window was inserted into the cylinder head of the engine. A focusing lens was
placed in front of that window in order to focus the laser beam down into the
combustion bomb called as “separate optics”. And in second mode, lens like
curvature was engraved directly into the window. By using such a special window,
no further lens was required called as “combined optics”. Schlieren photography
was applied to get information on the shock wave propagation and early flame
kernel development. In this paper it was found for the laser ignition tests with
hydrogen that with higher initial pressures the minimum pulse energy for ignition
(MPE) decreases. And secondly the work on the self-cleansing property of optical
window.

15
J. D. Dale et.al.[9] (2008), 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.
A.P. Yalin, M. Miyagi et.al [18] (2008) 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 powder 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.

16
3.2GAPS IN LITERATURE REVIEW
After reading above mentioned research /review papers we find some areas
where we can proceed our study because researches in these fields are still in
progress that makes our study feasible and we can complete our domain on some
of the points mentioned below,
Since the cost of this system is high so we can do some studies on reducing the
initial cost of the laser ignition system so that it can be implemented on
commercial level.
Multi Point ignition technique can be achieved by proposing a single-shot laser
and we can test its feasibility. We can get the advantage of rapid combustion
We can study the position of laser ignitor in the IC engine.
We can do research and study in improving the combustion stability by which
we can enable engine to be run under leaner condition with exhaust gas
recirculation(EGR) concentration, or at lower idle speed without increasing
noise, vibrations and harshness characteristics of the vehicles.
We might go under further studies in development of higher average power and
higher pulse frequency lasers, it is expected that a multi-strike laser ignition
system an associate combustion can reduce the probability of misfires under
high levels of dilutions.
We can do some studies for the stability and self-cleaning of optical window of
laser ignition system.

17
CHAPTER 4
LASER IGNITION SYSTEM
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
Figure 8: Optical breakdown in air generated by a ND: YAG laser.
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. 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
depends upon the absorption properties of the laser and the minimum energy
required depends upon the number of photons required for producing the electron
avalanche.

18
4.1 Principles of Laser Ignition System
4.1.1 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.
4.1.2 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. 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.
Figure 9: Non Resonant Breakdown

19
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.
4.1.3 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.
4.2 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.
Figure 10: Stages of ignition with respect to time[8]

20
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.
4.3 Ignition in Combustion Chamber
The laser beam is passed through a convex lens, this convex lens diverges 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.
Figure 11: Ignition inside combustion chamber
4.4 Mechanism of Laser Ignition
It is well known 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

21
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, 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. 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 × M2
× 2λf πd) 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. From the thermodynamic gas equation, the number of particles N in a
volume V is,(V = 4πw3)
, (N = pv kt )
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) For a spot radius of
about 100 μm the equation gives a maximum energy of approximately 1 mJ.

22
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.
4.5 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.
Figure 12: Laser arrangement with respect to engine.[6]

23
4.5.1 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 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.
4.5.2 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.
4.5.3 Optic Fiber Wire
It is used to transport the laser beam from generating unit to the focusing unit.
4.5.4 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.
Figure 13: Focusing unit

24
4.5.5 Laser 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.
Figure 14: Laser Plug
4.6 Working of Laser Ignition System
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

25
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.
The laser beam is passed through a convex lens, this convex lens diverges 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. 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.
Figure 15: Working of LIS
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

26
avalanche process. In contrast to multi photon ionization (MPI), no wavelength
dependence is expected for this initiation path.
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.
Figure 16: Arrangement of Laser Plug in cylinder head

27
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.
4.7 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.

28
CHAPTER 5
PREVIOUS EXPERIMENTS AND RESULT
1. The experiment was done for the development of unconventional natural gas
resources. Achieving lean burn with supercharging to attain high thermal efficiencies
with the help of laser igniters. The engine specification and setup is shown below in
table number 1,
Table 1: Specification Of Test Engine[11]
Base Engine NFD170
Bore*stroke 102*105
Displacement 857(cm3
)
Compression Ratio 12,14
Fuel Methane
Rotational Speed 1200
Ignition Timing MBT
Maximum Pressure 8
Figure 17: Layout Of Experiment[11]

29
The main result of the demonstration is the relation between the Indicated Mean
Effective Pressure(IMEP) and the equivalence ratio, is shown in figure 18. The
horizontal axis represents the equivalence ratio and the left side of the figure is
leaner. The side corresponds to the output from the engine. The spark and the laser
ignition results are represented by the square and circle points, respectively. Data
in normal aspiration. Without supercharging, are indicated as hollow characters,
and the color which are listed in the figure, represents the intake pressure. For
normal aspiration experiments, the laser maintained higher IMEP compared to the
spark plug ignition. Then for the case of supercharging, spark plugs that are
represented as red squares rapidly shifted towards rich side. This indicates that
spark plugs cannot ignite for the pre-mixture under high-pressure conditions. On
the other hand, it has been demonstrated that laser can maintain stable ignition
even in the supercharged condition up to an intake pressure of 1.8 atm, which is the
limit of the engine system.
Figure 18: Relation Between The IMEP And Equivalent Ratio[11]
Both LIS and SPI utilizes hot plasma but the physics behind the formation of both
sources is different and we take that benefit.

30
Figure 19: Flame Kernel Development Of Laser And Spark Ignition[11]
The LIS works in two phases first the laser ionizes the molecules and discharge the
electrons and then secondly the electron absorbs the laser energy through inverse
BREMESTRAHLUNG process. Fig19 shows the propagation of flame kernel in
LIS and SPI.
2. The below experiment was conducted at University of Liverpool and laser used for
the LI experiments was a ‘Mini-Q’ Q-switched Nd:YAG, manufactured by GSI
Group, operating at the fundamental wavelength of 1064 nm. Five different focal
length (FL) lenses (15, 18, 24, 30 and 36 mm) were tested individually in a
specifically designed optical plug. These were all uncoated BK7 Plano-convex
lenses, apart from the 36 mm FL lens, which had a visible to near infrared coating.
An uncoated sapphire window was sealed at the bottom of the optical plug for each
of these different lenses.
Figure 20: Experimental setup for offline and online laser ignition testing.[7]

31
The minimum beam waist produced by each lens was positioned at 4 mm from the
bottom of the plug (which is at the same location as the electrical discharge of the
spark plugs), as this was found from previous testing to be the optimum LI position for
this engine. Mirror (1) was installed on the optical bench for offline testing to direct
the beam into the optical plug, as shown in figure 20.
Figure 21: Transmitted energy through the five optical plugs and subsequent plasmas
produced[7]
The offline results for increasing the pulse energy into the five optical plugs are
illustrated in fig.21, which shows the transmitted energies through the plugs. The
peak of each curve indicates the minimum energy required to cause optical air
breakdown at atmospheric pressure for the respective FL lenses. After this point,
plasmas were formed which absorbed the incident energy. It can be seen from
figure 2 that at the higher plasma producing input energies, the transmitted energy
through the optical plugs and plasma becomes fairly constant, which indicates that
a percentage of the incident energy is being absorbed by the plasma. The lowest
minimum laser energy required for misfire free combustion was found to be 4 mJ
per pulse, also using the 15 mm FL lens in the optical plug. This compares to ~30
mJ in a ~1 ms electrical pulse for conventional SI. The minimum laser irradiance
required for LI was found to reduce when longer FL lenses were used, and
improved combustion performance and stability was achieved by using higher
laser energies.

32
3. A laser ignition system has been used for ignition of an internal combustion
engine. Since results have already been published, only a brief overview is given
here.
Table 2: Technical data of the research engine and the ND: YAG laser used for the experiments.[6]
Technical data of the research engine and the laser used for the experiments are
summarized in table2.
Figure 22: Research Engine With The Q-Switched Nd: Yag Laser System[6]

33
The experimental setup is shown in fig. 22.
Measurements on the dependence of the pressure on the required pulse energy for
ignition are summarized in fig.23.
Figure 23: Pressure Dependence On The Required Pulse Energy For Successful Ignition.[6]
Results indicate that the required pulse energy for successful ignition decreases
with increasing pressure.
Figure 24: Comparison Of Fuel Consumption, Smoothness And Emissions Between Spark And
Laser Ignition[1][6]
Results on consumption measurements are summarized in fig.24. Compared to
conventional spark plug ignition, laser ignition, laser ignition reduces the fuel

34
consumption by several per cents. Exhaust emissions are reduced by nearly 10%.
Additionally, a frequency-doubled Nd:YAG laser has been used to examine
possible influences of the wavelength on the laser ignition process. No influences
on the required pulse energy for successful ignition could be found. Fig.25 shows
the images of combustor taken by photography after the testing of almost 20hrs.
Figure 25: Spark plug ignition, heavily polluted on the left and self-cleansing of optical window
on right.[6]
It is observed that the optical window of laser plug cleans itself after several cycles
and so there is no suet deposition and whereas the spark plug is heavily polluted
after several hour running of engine.

35
CHAPTER 6
FUTURE RESEARCHES & APPLICATIONS
6.1 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.

36
6.2 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.
Table 3: Potential Requirements of LIS
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
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

37
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 costliest 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 like 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
6.3Application
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

38
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.
Figure 26: Mazda RX-9 16X Rotar

39
CHAPTER 7
CONCLUSION
i. The applicability of a laser-induced ignition system on direct injected
gasoline engine has been proven by many experiments conducted around
the world.
ii. Application of this system would be a great step in reduction of
environmental pollution.
iii. As we are shifting towards hybrid system for better fuel economy then we
can use this system also because the system is capable of burning leaner
mixture that results in lower fuel consumption.
iv. The optical window is capable of clean itself after several cycle so the
maintenance would be very less and life is also very long that is 150
million shots (good) and 600 million shots (better).
v. Ignition-delay times are smaller and pressure gradients are much steeper
compared to conventional spark plug ignition.
vi. At present, a laser ignition plug is very expensive compared to a standard
electrical spark plug ignition system and it is nowhere near ready for
deployment. But the potential and advantages certainly make the laser
ignition more attractive in many practical applications.

40
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41
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