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LASER IGNITION SYSTEM
SEMINAR REPORT
Semester 7, 2014-2015
Submitted by
GAUTHAM SARANG
DEPARTMENT OF MECHANICAL ENGINEERING
RAJAGIRI SCHOOL OF ENGINEERING & TECHNOLOGY
KOCHI - 682039
RAJAGIRI SCHOOL OF ENGINEERING & TECHNOLOGY
KOCHI 682 039
DEPARTMENT OF MECHANICAL ENGINEERING
CERTIFICATE
This is to certify that the report on the Seminar titled LASER IGNITION SYSTEM is submitted by GAUTHAM SARANG in partial fulfillment of the requirements for the award of B.Tech Degree in Mechanical Engineering is
a bonafide record of the Seminar done by him during the SEVENTH
semester in the academic year 2014 - 2015.
Mr. Manoj G Tharian Mr. Sidheek P.A
Assistant Professor & HoD Assistant Professor
Department of ME Department of ME
RSET, Kakkanad RSET, Kakkanad
Seminar Report
Department of Mechanical Engineering, RSET, Kochi-682039
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ABSTRACT
Nowadays, applications of different lasers span quite broadly from
diagnostics tools in science and engineering to biological and medical uses. In this
presentation basic principles and applications of lasers for ignition of fuels are
concisely reviewed from the engineering perspective. The objective is to present
the current state of the relevant knowledge on fuel ignition and discuss select
applications, advantages and disadvantages, in the context of combustion engines.
Fundamentally, there are four different ways in which laser light can interact with
a combustible mixture to initiate an ignition event. They are referred to as thermal
initiation, nonresonant breakdown, resonant breakdown, and photochemical
ignition.
By far the most commonly used technique is the nonresonant initiation
of combustion primarily because of its freedom in selecting the laser wavelength
and ease of implementation.
Recent progress in the area of high power fiber optics allowed convenient
shielding and transmission of the laser light to the combustion chamber. However,
issues related to immediate interfacing between the light and the chamber such as
selection of appropriate window material and its possible fouling during the
operation, shaping of the laser focus volume, and selection of spatially optimum
ignition point remain amongst the important engineering design challenges. One
of the potential advantages of the lasers lies in its flexibility to change the ignition
location. Also, multiple ignition points can be achieved rather comfortably as
compared to conventional electric ignition systems using spark plugs. Also reduce
emissions of NOx to atmosphere. Although the cost and packaging complexities
of the laser ignition systems have dramatically reduced to an affordable level for
many applications, they are still prohibitive for important and high-volume
applications such as automotive engines.
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Department of Mechanical Engineering, RSET, Kochi-682039
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ACKNOWLEDGEMENT
I express my sincere thanks to the almighty whose divine intervention was
instrumental in successful completion of this work.
I hereby place in record, my sincere thanks, gratitude and graceful
acknowledgement to Mr. Manoj G Tharian, Assistant Professor & HoD,
Department of Mechanical Engineering, Rajagiri School of Engineering &
Technology.
I also express my sincere thanks to Mr. Sidheek P.A, Assistant Professor,
Department of Mechanical Engineering, Rajagiri School of Engineering &
Technology, Mr. James Mathew, Assistant Professor, Department of Mechanical
Engineering, Rajagiri School of Engineering & Technology, Mr. Jithin P.N,
Assistant Professor, Department of Mechanical Engineering, Rajagiri School of
Engineering & Technology, Mr. Mathew Baby, Assistant Professor, Department
of Mechanical Engineering, Rajagiri School of Engineering & Technology and
other staff members of the department for immense help provided by them.
GAUTHAM SARANG
Seminar Report
Department of Mechanical Engineering, RSET, Kochi-682039
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CONTENTS
ABSTRACT i
ACKNOWLEDGEMENT ii
LIST OF FIGURES vi
LIST OF TABLES vii
1. INTRODUCTION 01
2. INTERNAL COMBUSTION ENGINES 03
2.1 PARTS OF AN IC ENGINE 03
2.1.1 Cylinder Head 03
2.1.2 Cylinder Block And Cylinder Liner 03
2.1.3 Piston 04
2.1.4 Connecting Rod 04
2.1.5 Crankshaft 05
2.1.6 Crank Case And Sump 05
2.2 FOUR STROKE I C ENGINES 05
2.2.1 Working Principle Of A Four Stroke SI Engine 05
2.2.2 Four Stroke CI Engine 06
2.3 COMBUSTION IN SI ENGINES 07
2.4 COMBUSTION IN CI ENGINES 07
2.5 COMBUSTION IN CI ENGINES 07
2.5.1 COMBUSTION 08
2.5.2 KNOCK 08
2.5.3 AUTO IGNITION 09
2.5.4 SELF IGNITION 09
2.5.5 PRE-IGNITION 10
2.5.6 INDUCED IGNITION 10
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3. CONVENTIONAL SPARK IGNITION 11
3.1 THE FUNCTIONS OF AN IGNITION SYSTEM 12
3.2 SPARK PLUG 12
3.3 PROBLEMS OF A SPARK PLUG 13
3.4 DRAWBACKS OF SPARK IGNITION 14
4. LASER 15
4.1 PROPERTIES OF LASER LIGHT 15
4.2 LASERS AND THEIR EMISSION WAVELENGTHS 15
4.3 TYPES OF LASERS 16
4.3.1 GAS LASERS 16
4.3.2 CHEMICAL LASERS 16
4.3.3 EXCIMER LASERS 17
4.3.4 SOLID-STATE LASERS 17
4.3.5 SEMICONDUCTOR LASERS 17
4.3.6 DYE LASERS 17
5. LASER INDUCED SPARK IGNITION 18
5.1 REASONS FOR ADAPTING LASER IGNITION 19
5.2 METHODS OF ENERGETIC INTERACTIONS 20
5.2.1 THERMAL BREAKDOWN 20
5.2.2 RESONANT BREAKDOWN 20
5.2.3 NON RESONANT BREAKDOWN 21
5.2.4 PHOTOCHEMICAL MECHANISMS 21
5.3 PRINCIPLE OF LASER IGNITION 22
5.4 PHASES IN LASER IGNITION 23
5.5 WORKING 23
5.6 PARTS OF LASER IGNITION SYSTEM 24
5.4.1 POWER SOURCE 25
5.4.2 Nd:YAGLASER 25
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5.4.3 COMBUSTION CHAMBER WINDOW 26
5.4.4 OPTIC FIBER WIRE 27
5.4.5 FOCUSING UNIT 28
5.5 MULTIPOINT IGNITION 28
6. MINIMUM ENERGY REQUIRED FOR IGNITION 29
7. PRACTICAL LASER IGNITION REQUIREMENTS 30
7.1 MECHANICAL REQUIREMENTS 30
7.2 ENVIRONMENTAL REQUIREMENTS 30
7.3 PEAK POWER REQUIREMENTS 31
8. ADVANTAGES AND CHALLENGES ` 32
8.1 ADVANTAGES OF LASER IGNITION 32
8.2 DISADVANTAGES OF LASER IGNITION 33
8.3 CHALLENGES OF LASER IGNITION 33
9. CONCLUSION 34
10. REFERENCES 35
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Department of Mechanical Engineering, RSET, Kochi-682039
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LIST OF FIGURES
1. Fig 2.1 IC Engine 04 2. Fig 3.1 four stroke cycle 11 3. Fig 5.1 Resonant Laser-Induced Ignition 20 4. Fig 5.2 Nonresonant Laser-Induced Ignition 21 5. Fig 5.3 Photochemical Laser-Induced Ignition 22 6. Fig 5.4 Principle Of Laser Ignition 22 7. Fig 5.5 Time Scales in Laser Ignition 23 8. Fig 5.6 Optical breakdown in air generated 24
by a Nd:YAG laser
9. Fig 5.7 Laser Arrangement with Respect to Engine 25 10. Fig 5.8 Window Arrangement 27 11. Fig 5.9 Focusing Optics 28 12. Fig 5.10 Approach for Multipoint Ignition 28
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LIST OF TABLES
1. TABLE 4.1 Lasers And Their Emission Wavelengths 16
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Department of Mechanical Engineering, RSET, Kochi-682039
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CHAPTER 1
INTRODUCTION
Internal combustion engines are widely spread in our civilization. They
are used in energy production and industry and play a major role in transportation.
At the moment most of them are ignited by spark plugs which are the dominating
technology. They provide the advantages of already being on a highly advanced
development level and the possibility of low cost mass production. Nevertheless
this advanced development significantly restricts the potential for considerable
further improvements. Therefore the major objective for new types of ignition
systems is to provide development perspectives especially regarding the reduction
of fuel and energy consumption and the reduction of exhaust emissions. An
increase in efficiency and a simultaneously decreasing level of emissions are
needed. A possibility to achieve both is closely connected with the inflammability
limits of the ignition systems. If a system is able to ignite leaner gas-air mixtures,
the combustion takes place at a lower temperature. This results in reduced NOx
output. Additionally the ignition of leaner gas-air mixtures increases the fuel
efficiency of the combustion process.
The two most promising new types of ignition systems are the Laser
ignition and the Corona ignition. Both ideas are already known for several
decades. Nevertheless neither of them is in industrial use at the moment.
There have been series of advancements in the field of automobiles.
Modern science and technology have contributed to this fact. One such
advancement is the usage of laser for the combustion process in the combustion
chamber. Laser ignition is an emerging technology, still under development,
has a promising future.
With the advent of lasers in the 1960s, researchers and engineers
discovered a new and powerful tool to investigate natural phenomena and
improve technologically critical processes. Nowadays, applications of different
Seminar Report
Department of Mechanical Engineering, RSET, Kochi-682039
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lasers span quite broadly from diagnostics tools in science and engineering to
biological and medical uses. In this seminar basic principles and applications of
lasers for ignition of fuels are concisely reviewed from the engineering
perspective. The objective is to present the current state of the relevant knowledge
on fuel ignition and discuss select applications, advantages and disadvantages, in
the context of combustion of engines. Fundamentally, there are four different
ways in which laser light can interact with a combustible mixture to initiate an
ignition event. They are referred to as thermal initiation, non-resonant breakdown,
resonant breakdown, and photochemical ignition.
By far the most commonly used technique is the non-resonant initiation of
combustion primarily because of its freedom in selecting the laser wavelength and
ease of implementation. Recent progress in the area of high power fiber optics
allowed convenient shielding and transmission of the laser light to the combustion
chamber. However, issues related to immediate interfacing between the light and
the chamber such as selection of appropriate window material and its possible
fouling during the operation, shaping of the laser focus volume, and selection of
spatially optimum ignition point remain amongst the important engineering
design challenges. One of the potential advantages of the lasers lies in its
flexibility to change the ignition location. Also, multiple ignition points can be
achieved rather comfortably as compared to conventional electric ignition systems
using spark plugs.
.
Although the cost and packaging complexities of the laser ignition systems
have dramatically reduced to an affordable level for many applications, they are
still prohibitive for important and high-volume applications such as automotive
engines. However, their penetration in some niche markets, such as large
stationary power plants and military applications, are imminent. Lasers a type of
nonconventional ignition sources can contribute to a future performance
optimization.
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Department of Mechanical Engineering, RSET, Kochi-682039
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CHAPTER 2
INTERNAL COMBUSTION ENGINES
An engine is a machine designed to convert energy into useful mechanical
energy. Heat engines absorb energy in the form of heat and convert part of it into
mechanical energy and deliver it as work, the balance being rejected as heat.
These devices derive the heat energy from the combustion of a fuel. Based on the
location of the combustion process, heat engines are classified into internal
combustion and external combustion engines.
Internal combustion engines (IC engines) are those where the combustion
of the fuel takes place inside the engines. eg: Automobile engines.
In external combustion engines, combustion of fuel occurs outside the
engines and the working gas so heated is then admitted into the engines for
conversion and work extraction. eg: steam generated in a boiler is then admitted to
steam turbines for producing work.
2.1 PARTS OF AN IC ENGINE
The main components of a standard IC engine are briefly described below:
2.1.1 Cylinder Head
Cylinder head is the top cover of the cylinder and holds the inlet and
exhaust valves, their operating mechanisms, and the spark plug or fuel injector, as
the case may be. The valves along with their operating mechanism are together
called the valve gear.
2.1.2 Cylinder Block And Cylinder Liner
The cylinder head is fitted over the cylinder block and liner. The space
between the block wall and cylinder liner acts as the cooling water jacket.
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Department of Mechanical Engineering, RSET, Kochi-682039
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2.1.3 Piston
The piston is of cylindrical shape to fit the inside bore of the cylinder. Gas
tightness is ensured by means of the piston rings in the slots on the outer
cylindrical surface of the piston.
2.1.4 Connecting Rod
The Connecting rod is the link connecting the piston to the crankshaft for
transmission of the forces from and to the piston. The pin connecting it to the
piston is called the gudgeon pin and that connecting it to the crankshaft as the
crank pin.
Fig 2.1 IC Engine
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2.1.5 Crankshaft
The Crankshaft is a shaft with radial cranks, which converts the
reciprocating motion of the piston into rotary motion of the shaft.
2.1.6 Crank Case And Sump
Crank case is the engine casing having the main bearings in which the
crank shaft rotates. The bottom cover of the engine is the sump which usually acts
as a lubricating oil reservoir.
2.2 FOUR STROKE I C ENGINES
In a four-stroke engine, the cycle of operations is completed in four strokes of
the piston or two revolutions of the crankshaft. During the four strokes, there are
five events to be Completed, viz., suction, compression, combustion, expansion
and exhaust. Each stroke consists of 180 of crankshaft rotation and hence a four-
stroke cycle is completed through 720 of crank rotation. The cycle of operation
for an ideal four-stroke SI engine consists of the following four strokes:
1. Suction Stroke (0 -180)
2. Compression Stroke (180-360)
3. Expansion Stroke (360-540)
4. Exhaust Stroke (540-720)
2.2.1 Working Principle Of A Four Stroke SI Engine
Suction or Intake Stroke: Suction stroke starts when the piston is at the top
dead centre and about to move downwards. The inlet valve is open at this time and
the exhaust valve is closed. Due to the suction created by the motion of the piston
towards the bottom dead centre, the charge consisting of fuel-air mixture is drawn
into the cylinder. When the piston reaches the bottom dead centre the suction
stroke ends and the inlet valve closes. The charge taken into the cylinder during
the suction stroke is compressed by the return stroke of the piston. During this
stroke both inlet and exhaust valves are in closed position. The mixture that fills
the entire cylinder volume is now compressed into the clearance volume. At the
end of the compression stroke the mixture is ignited with the help of a spark plug
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located on the cylinder head. In ideal engines it is assumed that burning takes
place instantaneously when the piston is at the top dead centre and hence the
burning process can be approximated as heat addition at constant volume. During
the burning process the chemical energy of the fuel is converted into heat energy
producing a temperature rise of about 2000 C
The pressure at the end of the combustion process is considerably
increased due to the heat release from the fuel. At the end of the expansion stroke
the exhaust valve opens and the inlet valve remains closed. The pressure falls to
atmospheric level a part of the burnt gases escape. The piston starts moving from
the bottom dead centre to top dead centre and sweeps the burnt gases out from the
cylinder almost at atmospheric pressure. The exhaust valve closes when the piston
reaches T DC. At the end of the exhaust stroke and some residual gases trapped in
the clearance volume remain in the cylinder. These residual gases mix with the
fresh charge coming in during the following cycle, forming its working fluid.
Each cylinder of a four stroke engine completes the above four operations in two
engine revolutions, one revolution of the crankshaft occurs during the suction and
compression strokes and the second revolution during the power and exhaust
strokes. Thus for one complete cycle, there is only one power stroke while the
crankshaft turns by two revolutions. For getting higher output from the engine the
heat release should be as high as possible and the heat rejection should be as small
as possible.
2.2.2 Four Stroke CI Engine
The four-stroke CI engine is similar to the four-stroke SI engine but it
operates at a much higher compression ratio. The compression ratio of an SI
engine is between 6 and 10 while for a CI engine it is from 16 to 20. In the CI
engine during suction stroke, air, instead of a fuel-air mixture, is inducted. Due to
the high compression ratio employed, the temperature at the end of the
compression stroke is sufficiently high to self-ignite the fuel which is injected into
the combustion chamber. In CI engines, a high pressure fuel pump and an injector
are provided to inject the fuel into the combustion chamber. The carburetor and
ignition system necessary in the SI engine are not required in the CI engine.
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The ideal sequence of operations for the four-stroke CI engine is as follows:
i. Suction Stroke: Air alone is inducted during the suction stroke. During this stroke intake valve is open and exhaust valve is closed.
ii. Compression Stroke: Air inducted during the suction stroke is compressed into the clearance volume. Both valves remain closed during this stroke.
iii. Expansion Stroke: Fuel injection starts nearly at the end of the compression stroke. The rate of injection is such that combustion
maintains the pressure constant in spite of the piston movement on its
expansion stroke increasing the volume. Heat is assumed to have been
added at constant pressure. After the injection of fuel is completed (i.e.
after cutoff) the products of combustion expand. Both the valves remain
closed during the expansion stroke.
iv. Exhaust Stroke: The piston traveling from EDC to TDC pushes out the products of combustion. The exhaust valve is open and the intake valve is
closed during this stroke.
2.3 COMBUSTION IN SI ENGINES
Combustion is a chemical reaction in which certain elements of the fuel
like hydrogen and carbon combine with oxygen liberating heat energy and causing
an increase in temperature of gases. The conditions necessary for combustion are
The presence of a combustible mixture
Initiation for combustion
Stabilization and propagation of flame in combustion chamber.
In SI engines combustible mixture is generally supplied by the carburetor
and the combustion is initiated by an electric spark given by spark plug.
2.4 COMBUSTION IN CI ENGINES
In the CI engine, for a given speed, and irrespective of load, an
approximately constant supply of air enters the cylinder. The CI engine therefore
can be termed constant air supply engine. With change in load the quantity of fuel
is change, which changes the air-fuel ratio. The overall air-fuel ration may thus
vary from about 100:1 at no load and 20:1 at full load.
Whatever may be the overall air-fuel ratio in a CI engine due to injection
of fuel, there is a heterogeneous mixture with air-fuel ratio varying widely in
different areas within the chamber. There would be area where the mixture is very
lean or very rich. However there would be certain areas where the local-air-fuel
Seminar Report
Department of Mechanical Engineering, RSET, Kochi-682039
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ratio is within combustible limits and there under favorable conditions of
temperature, ignition occurs.
In full load condition the mixture slightly leaner than stoichiometric. The
poor distribution of fuel and its intermixing with air results in objectionable smoke
if operated near chemically correct ratio and (Air fuel ratio 20-23, i.e. excess air
35 to 50%) hence the CI engine must always operate with excess air.
2.5 TECHNICAL TERMS
2.5.1 COMBUSTION
Combustion is defined as the burning of a fuel and oxidant to produce heat
or work. Combustion includes thermal, hydrodynamic, and chemical processes. It
starts with the mixing of fuel and oxidant, and sometimes in the presence of other
species or catalysts. The fuel can be gaseous, liquid, or solid and the mixture may
be ignited with a heat source. When ignited, chemical reactions of fuel and
oxidant take place and the heat release from the reaction creates a self-sustained
process. The combustion products include heat, light, chemical species, pollutants,
mechanical work and plasma. Sometimes, a low-grade fuel, e.g., coal, biomass, or
coke, can be partially burned to produce higher-grade fuel, e.g., methane. The
partial burning process is called gasification. Various combustion systems, e.g.,
furnaces, combustors, boilers, reactors, and engines, are developed to utilize
combustion heat, chemical species, and work.
2.5.2 KNOCK
Knock is the most important abnormal combustion phenomenon. It
important because it puts a limit on the compression ratio at which an engine can
be operated, which in turn controls the efficiency and to some extent the power
output. It got the name knock because of the noise that results from the auto
ignition of a portion of fuel air mixture ahead of the advancing flame. As the
spark is ignited there is a formation of flame front and it starts propagating. As the
flame propagates across the combustion chamber, speed of flame front is
about 15 to 30 m/s ; the unburned charge ahead of the flame called the end
gas is compressed, raising its pressure, temperature and density. In case of
abnormal combustion the end gas fuel air mixture undergo fast chemical
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Department of Mechanical Engineering, RSET, Kochi-682039
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reactions, which results in auto ignition prior to normal combustion (i.e. the
flame front reaching it). During auto ignition a large portion of end gas releases
its chemical energy rapidly and spontaneously at a rate 5 to 25 times as in case of
normal combustion. This spontaneous ignition of the end gas raises the
pressure very rapidly and causes high frequency oscillations inside the
cylinder resulting in a high pitched metallic noise characterized as knock. During
this knocking phenomenon pressure waves of very large amplitudes propagate
across the combustion chamber and very high local pressures are produced
which are as high as 150 to 200 bars. Local 5% of the total charge is sufficient
to produce a very violent serve knock. The velocity reached during knock is of the
order of 300 to 1000 m/s.
2.5.3 AUTO IGNITION
The auto ignition temperature or kindling point of a substance is the lowest
temperature at which it will spontaneously ignite in a normal atmosphere without
an external source of ignition, such as a flame or spark. This temperature is required
to supply the activation energy needed for combustion. The temperature at which
chemical will ignite decreases as the pressure increases or oxygen concentration
increases. It is usually applied to a combustible fuel mixture.
2.5.4 SELF IGNITION
Spontaneous combustion or self-ignition is a type of combustion which
occurs without an external ignition source. Spontaneous combustion is a term used to
describe how something just ignited (spontaneously) but in fact spontaneous
combustion is more than usually, a slow process that can take several hours of
decomposition / oxidization with heat build up to a point of ignition.
The reasons for self-ignition:
A substance with a relatively low ignition temperature begins to release heat,
which may occur in several ways, such as oxidation or fermentation.
The heat is unable to escape, and the temperature of the material rises.
The temperature of the material rises above its ignition point
Combustion begins if a sufficiently strong oxidizer, such as oxygen, is
present.
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2.5.5 PRE-IGNITION
Pre-ignition is the phenomenon of surface ignition before the passage of
spark. The usual cause is an overheated spot, which by occur at spark plugs,
combustion chamber deposits, or exhaust valves. Mostly it is due to spark plug.
Exhaust valve usually run hot and sometimes when there is increase in heat load
for these valves there will be an increase in the temperature and may cause pre
ignition. Heat transfer principles indicate that the surface of the deposits is
hotter than the metal surface to which the deposits are attached. Hence, sufficient
deposits result in hot enough surfaces to cause pre ignition.
Pre-ignition is potentially the most damaging surface ignition phenomenon.
The effect of pre-ignition is same as very advanced ignition timing. Any process that
advances the start of combustion that gives maximum torque will cause higher
heat rejection because of the increased burned gas pressures and temperatures (due
to the negative work done during the compression stroke). Higher heat rejection
causes higher temperature components thus the pre ignition damage is largely
thermal which is evidenced by the fusion of spark plugs, piston and destruction of
piston rings.
2.5.6 INDUCED IGNITION
A process where a mixture, which would not ignite by itself, is ignited
locally by an ignition source (i.e. electric spark plug, pulsed laser, microwave
ignition source) is called induced ignition. In induced ignition, energy is
deposited, leading to a temperature rise in a small volume of the mixture, where
auto ignition takes place or the energy is used for the generation of radicals. In
both cases a subsequent flame propagation occurs and sets the mixture on fire.
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Department of Mechanical Engineering, RSET, Kochi-682039
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CHAPTER 3
CONVENTIONAL SPARK IGNITION
In a petrol engine, the fuel and air are usually pre-mixed before
compression. The pre-mixing was formerly done in a carburettor, but now (except
in the smallest engines) it is done by electronically controlled fuel injection.
In this system fuel entering the engine cylinder is ignited by means of a
spark. The required amount of fuel is induced into the cylinder during suction
stroke. This fuel is ignited during the compression stroke by a spark produced by a
spark plug. Due to the combustion of fuel large amount of heat and high pressure
gases are produced which expand causing linear motion of the piston
Fig 3.1 four stroke cycle
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3.1 THE FUNCTIONS OF AN IGNITION SYSTEM
The ignition system must provide an adequate voltage to initiate a
discharge across the spark plug electrodes and supply sufficient energy to ignite
the air-fuel mixture. This must occur for all the engines operating conditions and
at appropriate time on the compression stroke.
On the modern engines, it is normal for the ignition system to form a
subsection of an integrated management system, sharing sensors and circuits, with
fuelling and transmission control system.
However the ignition system does the following functions:
When the compression ratio is lower and self-ignition temperature is quite
high, an external source of ignition must be given.
This takes place close to the compression stroke.
The function of the ignition system is to propagate the flame and should
supply energy within a small volume.
The ignition should occur in a time interval sufficiently short time to
ensure that only a negligible amount of energy is lost other than to
establish the flame.
3.2 SPARK PLUG
A spark plug (also, very rarely nowadays, in British English: a sparking
plug), is an electrical device that fits into the cylinder head of some internal
combustion engines and ignites compressed fuels such as aerosol gasoline,
ethanol, and liquefied petroleum gas by means of an electric spark. Spark plugs
have an insulated central electrode which is connected by a heavily insulated wire
to an ignition coil or magneto circuit on the outside, forming, with a grounded
terminal on the base of the plug, a spark gap inside the cylinder. A spark plug is
composed of a shell, insulator and the central conductor. It pierces the wall of the
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combustion chamber and therefore must also seal the combustion chamber against
high pressures and temperatures without deteriorating, over long periods of time
and extended use.
The plug is connected to the high voltage generated by an ignition coil or
magneto. As the electrons flow from the coil, a voltage difference develops
between the central electrode and side electrode. No current can flow because the
fuel and air in the gap is an insulator, but as the voltage rises further, it begins to
change the structure of the gases between the electrodes. Once the voltage
exceeds the dielectric strength of the gases, the gases become ionized. The ionized
gas becomes a conductor and allows electrons to flow across the gap. Spark plugs
usually require voltage of 12,00025,000 volts or more to 'fire' properly, although
it can go up to 45,000 volts. They supply higher current during the discharge
process resulting in a hotter and longer-duration spark.
As the current of electrons surges across the gap, it raises the temperature
of the spark channel to 60,000 K. The intense heat in the spark channel causes the
ionized gas to expand very quickly, like a small explosion. This is the "click"
heard when observing a spark, similar to lightning and thunder.
The heat and pressure force the gases to react with each other, and at the
end of the spark event there should be a small ball of fire in the spark gap as the
gases burn on their own. The size of this fireball or kernel depends on the exact
composition of the mixture between the electrodes and the level of combustion
chamber turbulence at the time of the spark. A small kernel will make the engine
run as though the ignition timing was retarded and a large one as though the
timing was advanced.
3.3 PROBLEMS OF A SPARK PLUG
Lean mixture causes the increase in demand for the ignition energy.When
the air-fuel ratio is very high (that means the content of fuel in that mixture is very
less), for the combustion process to take place, the mixture demands more
energy.This leads to the erosion of the spark plug and thus reduced reliability and
lifetime of the spark plug. When the mixture demands more energy, the spark
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Department of Mechanical Engineering, RSET, Kochi-682039
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plug has to supply the required energy for the combustion to take place. This in
turn causes the electrodes to wear off, otherwise called as erosion of the spark
plug. The electrodes of the spark plug should be located near the combustion wall
to avoid disturbance of the precisely designed flow. The spark plug has to be
placed in correct position for its smooth working and to burn the mixture in much
effective way.
3.4 DRAWBACKS OF SPARK IGNITION
Location of spark plug is not flexible as it require shielding of plug from
immense heat and fuel spray.
It is not possible to ignite inside the fuel spray.
It requires frequent maintenance to remove carbon deposits.
Leaner mixtures cannot be burned.
Degradation of electrodes at high pressure and temperature.
Flame propagation is slow.
Multi point fuel ignition is not feasible.
Higher turbulence levels are required.
Economic as well as environmental considerations
All the above drawbacks are overcome in laser ignition system explained as
follows.
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Department of Mechanical Engineering, RSET, Kochi-682039
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CHAPTER 4
LASER
Light Amplification by Stimulated Emission of Radiation (LASER or
laser) is a mechanism for emitting electromagnetic radiation, often visible light,
via the process of stimulated emission. The emitted laser light is (usually) a
spatially coherent, narrow low-divergence beam,that can be manipulated with
lenses. Laser light is generally a narrow-wavelength electromagnetic spectrum
monochromatic light.
.
4.1 PROPERTIES OF LASER LIGHT
1. Monochromatic: Photons of one wavelength. In contrast, ordinary white
light is a combination of different wavelengths.
2. Directional: Laser light is emitted as a narrow beam and in a specific
direction. This property is referred to as directionality.
3. Coherent: The light from a laser is said to be coherent. This means that the
wavelengths of the laser light are in phase.
4.2 LASERS AND THEIR EMISSION WAVELENGTHS
Laser Type Wavelength (nm)
Argon fluoride (UV) 193
Krypton fluoride (UV) 248
Xenon chloride (UV) 308
Nitrogen (UV) 337
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Argon (blue) 488
Argon (green) 514
Helium neon (green) 543
Helium neon (red) 633
Rhodamine 6G dye (tunable) 570-650
Ruby (CrAlO3) (red) 694
Nd:Yag (NIR) 1064
Carbon dioxide (FIR) 10600
Table 4.1 Lasers And Their Emission Wavelengths
4.3 TYPES OF LASERS
4.3.1 GAS LASERS
The Helium-neon laser (HeNe) emits 543 nm and 633 nm and is very common
in education because of its low cost. Carbon dioxide lasers emit up to 100 kW at
9.6 m and 10.6 m, and are used in industry for cutting and welding. Argon-Ion
lasers emit 458 nm, 488 nm or 514.5 nm. Carbon monoxide lasers must be cooled
but can produce up to 500 kW. The Transverse Electrical discharge in gas at
Atmospheric pressure (TEA) laser is an inexpensive gas laser producing UV Light
at 337.1 nm.
4.3.2 CHEMICAL LASERS
Chemical lasers are powered by a chemical reaction, and can achieve high powers
in continuous operation. For example, in the Hydrogen fluoride laser (2700-2900 nm) and
the Deuterium fluoride laser (3800 nm) the reaction is the combination of hydrogen or
deuterium gas with combustion products of ethylene in nitrogen trifluoride.
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4.3.3 EXCIMER LASERS
Excimer lasers produce ultraviolet light, and are used in semiconductor
manufacturing and in LASIK eye surgery. Commonly used excimer molecules include F2
(emitting at 157 nm), ArF (193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm), and
XeF (351 nm).
4.3.4 SOLID-STATE LASERS
Solid state laser materials are commonly made by doping a crystalline solid host
with ions that provide the required energy states. For example, the first working laser was
made from ruby, or chromium-doped sapphire. Another common type is made from
Neodymium-doped yttrium aluminium garnet (YAG), known as Nd:YAG. Nd:YAG
lasers can produce high powers in the infrared spectrum at 1064 nm. They are used for
cutting, welding and marking of metals and other materials, and also in spectroscopy and
for pumping dye lasers. Nd:YAG lasers are also commonly doubled their frequency to
produce
Solid state lasers also include glass or optical fiber hosted lasers, for example,
with erbium or ytterbium ions as the active species. These allow extremely long gain
regions, and can support very high output powers because the fiber's high surface area to
volume ratio allows efficient cooling and its wave guiding properties reduce thermal
distortion of the beam.
4.3.5 SEMICONDUCTOR LASERS
Laser diodes produce wavelengths from 405 nm to 1550 nm. Low power laser diodes are
used in laser pointers, laser printers, and CD/DVD players. More powerful laser diodes
are frequently used to optically pump other lasers with high efficiency. The highest power
industrial laser diodes, with power up to 10 kW, are used in industry for cutting and
welding. External-cavity semiconductor lasers have a semiconductor active medium in a
larger cavity. These devices can generate high power outputs with good beam quality,
wavelength-tuneable narrow-line width radiation, or ultra-short laser pulses.
4.3.6 DYE LASERS
Dye lasers use an organic dye as the gain medium. The wide gain spectrum of
available dyes allows these lasers to be highly tunable, or to produce very short-duration
pulses (on the order of a few femtoseconds).
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CHAPTER 5
LASER INDUCED SPARK IGNITION
The use of laser ignition to improve gas engine performance was initially
demonstrated by J. D. Dale in 1978.
However, with very few exceptions, work in this area has for the last 20
years been limited to laboratory experimentation employing large, expensive and
relatively complicated lasers and laser beam delivery systems.
More recently, researchers at GE-Jenbacher, Mitsubishi Heavy Industries,
Toyota, National Energy Technology Lab and Argonne National Lab have
obtained and/or built smaller high peak power laser spark plugs.
Unlike many earlier laboratory laser systems, these smaller lasers are now
mounted directly onto the engine cylinder head so as to fire the laser beam directly
into the chamber. This arrangement allows the laser to become a direct
replacement for the traditional high voltage electrical spark-gap plug. Further
reductions in laser size, price and complexity will help the laser spark plug
become a commercial reality and a viable competitor to the traditional high
voltage spark-gap plug.
The Otto or SI engine is today characterized by low pollutant emissions.
The very efficient exhaust gas treatment makes power drives for nearly equal zero
emission operation possible. There is however need for improvement of fuel
consumption and the higher carbon dioxide emissions compared to the Diesel
equivalent.
Advancing the state of art of ignition systems for lean burn, stationary,
natural gas fuelled engines is crucial to meet increased performance requirements.
As the demand for higher engine efficiencies and lower emissions drive
stationary, spark-ignited reciprocating engine combustion to leaner air/fuel
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operating conditions and higher in-cylinder pressures, increased spark energy is
required to maintain stable combustion and low emissions.
To compensate power density losses due to leaner operation, high pressure
of initial charge is used to increase in-cylinder pressure at the time of combustion.
However, an important parameter is the ignition under extreme conditions, lean
combustible mixture and high initial pressure, requiring high voltage when using
conventional spark plug technology. Providing the necessary spark energy to
operate these engines significantly reduces the lifetime of spark plug and its
effectiveness in transmitting adequate energy as an ignition source. Laser ignition
offers the potential to improve ignition system durability, reduce maintenance, as
well as to improve engine combustion performance.
5.1 REASONS FOR ADAPTING LASER IGNITION
Since spark plugs are an integral part of the combustor liner, the ignition
kernel is usually located in the suboptimal quench zone of the combustor.
Lean mixtures along the liner increase the demand on ignition energy,
leading to an increased erosion of the spark plug electrodes, and thus to a
reduced reliability and lifetime of the igniter. Since spark plug ignition
shows a reduced ignitability of lean mixtures below an equivalence ratio
of 0.6
Laser ignition is a possible candidate to solve some of problems because it
allows uncoupling of the limiting link between the location of the ignition
source and the ignition kernel.
Lasers are able to ignite the mixture at the best thermodynamic and
aerodynamic conditions from almost any installation location. Therefore
laser ignition is more independent from variations of the local equivalence
ratio than other ignition concepts.
It is known that lasers are able to ignite leaner mixtures compared with
spark plug ignition because there are no electrodes surrounding the initial
flame kernel, which, in the case of the spark plug, cool down the kernel
and prevent it from evolving further into the combustion chamber.
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5.2 METHODS OF ENERGETIC INTERACTIONS
5.2.1 THERMAL BREAKDOWN
In the case of thermal interaction, ignition occurs without the generation of
an electrical breakdown in the combustible medium. The ignition energy is
absorbed by the gas mixture through vibrational or rotational modes of the
molecules; therefore no well-localized ignition source exists. Instead, energy
deposition occurs along the whole path in the gas. According to the characteristic
transport times therein, it no necessary to deposit the needed ignition energy in a
very short time. So this ignition can also be achieved using quasi continuous wave
lasers.
5.2.2 RESONANT BREAKDOWN
It involves non-resonant multi-photon dissociation of a molecule followed
by resonant photo ionization of an atom. As well as photochemical ignition, it
requires highly energetic photons. Therefore, these two types of interaction do not
appear to be relevant for this study and practical applications.
Fig 5.1 Resonant Laser-Induced Ignition
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5.2.3 NON RESONANT BREAKDOWN
In non-resonant ignition method, because typically the light photon energy
is in visible or UV range of spectrum, multi photon processes are required for
molecular ionization. This is due to the lower photon energy in this range of
wavelengths in comparison to the molecular ionization energy. The electrons thus
freed will absorb more energy to boost their kinetic energy (KE), facilitating
further molecular ionization through collision with other molecules. This process
shortly leads to an electron avalanche and ends with gas breakdown and ignition.
The multi photon absorption occurs in presence of losses (electron diffusion
outside the focused volume, radiation, collisional quenching of excited states,
etc.), thus demanding very high input beam intensities (through tightly-focused
high energy short-duration laser beam pulses) for a successful ignition process. To
assist the breakdown process, in some studies a metal needle is inserted just
behind the beam focused volume as an additional source of electrons. By far, the
most commonly used technique is the non-resonant initiation of ignition primarily
because of the freedom in selection of the laser wavelength and ease of
implementation.
Fig 5.2 Nonresonant Laser-Induced Ignition
5.2.4 PHOTOCHEMICAL MECHANISMS
In photochemical ignition approach, very little direct heating takes place
and the laser beam brings about molecular dissociation leading to formation of
radicals (i.e., highly reactive chemical species), see Fig. 1c. If the production rate
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of the radicals produced by this approach is higher than the recombination rate
(i.e., neutralizing the radicals), then the number of these highly active species will
reach a threshold value, leading to an ignition event. This (radical) number
augmentation scenario is named as chain-branching in chemical terms.
Fig 5.3 Photochemical Laser-Induced Ignition
5.3 PRINCIPLE OF LASER IGNITION
The laser beam is passed through a convex lens, this convex lens diverge
the beam and make it immensely strong and sufficient enough to start combustion
at that point. Hence the fuel is ignited, at the focal point, with the mechanism
shown above. The focal point is adjusted where the ignition is required to have.
Fig 5.4 Principle Of Laser Ignition
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5.4 PHASES IN LASER IGNITION
The different phases of laser ignition can be defined in chronological order
Electric breakdown and energy transfer from laser to plasma
Shock-wave generation and propagation
Gasdynamic effects
Chemical induction of branching chain reactions of radicals leading to
ignition
Turbulent flame initiation
Fig 5.5 Time Scales in Laser Ignition
5.5 WORKING
The process begins with multi-photon ionization of few gas molecules
which releases electrons that readily absorb more photons via the inverse
bremsstrahlung process to increase their kinetic energy. Electrons liberated by this
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means collide with other molecules and ionize them, leading to an electron
avalanche, and breakdown of the gas. Multiphoton absorption processes are
usually essential for the initial stage of breakdown because the available photon
energy at visible and near IR wavelengths is much smaller than the ionization
energy. For very short pulse duration (few picoseconds) the multiphoton processes
alone must provide breakdown, since there is insufficient time for electron-
molecule collision to occur. Thus this avalanche of electrons and resultant ions
collide with each other producing immense heat hence creating plasma which is
sufficiently strong to ignite the fuel. The wavelength of laser depend upon the
absorption properties of the laser and the minimum energy required depends upon
the number of photons required for producing the electron avalanche.
Fig 5.6 Optical breakdown in air generated by a Nd:YAG laser.
5.6 PARTS OF LASER IGNITION SYSTEM
A laser ignition device for irradiating and condensing laser beams in a
combustion chamber of an internal combustion engine so as to ignite fuel particles within
the combustion chamber, includes: a laser beam generating unit for emitting the laser
beams; and a condensing optical member for guiding the laser beams into the combustion
chamber such that the laser beams are condensed in the combustion chamber.
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Fig 5.7 Laser Arrangement with Respect to Engine
5.6.1 POWER SOURCE
The average power requirements for a laser spark plug are relatively modest. A
four stroke engine operating at maximum of 1200 rpm requires an ignition spark 10 times
per second or 10Hz (1200rpm/2x60). For example 1-Joule/pulse electrical diode pumping
levels we are readily able to generate high millijoule levels of Q-switched energy. This
provides us with an average power requirement for the laser spark plug of say
approximately 1-Joule times 10Hz equal to approximately 10 Watts.
5.6.2 Nd:YAGLASER
It is the most suitable laser beam generating unit in laser ignition system.
Nd:YAG (neodymium-doped yttrium aluminium garnet; Nd:Y3Al5O12) is a crystal that is
used as a lasing medium for solid-state lasers. The dopant, triply ionized neodymium,
typically replaces yttrium in the crystal structure of the yttrium aluminium garnet (YAG),
since they are of similar size. Generally the crystalline host is doped with around 1%
neodymium by atomic percent. They typically emit light with a wavelength of 1064 nm,
in the infrared. However, there are also transitions near 940, 1120, 1320, and 1440 nm.
Nd:YAG lasers operate in both pulsed and continuous mode. Pulsed Nd:YAG lasers are
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typically operated in the so called Q-switching mode: An optical switch is inserted in the
laser cavity waiting for a maximum population inversion in the neodymium ions before it
opens. Then the light wave can run through the cavity, depopulating the excited laser
medium at maximum population inversion.
5.6.3 COMBUSTION CHAMBER WINDOW
A laser ignition system or optical spark plug, in contrast to a
conventional electric spark plug ignition type system is located entirely outside
the combustion chamber. The energy necessary for ignition is delivered to the
engine purely optically. This implies a window to couple in the laser light. The
window is hence a key element in a future laser ignition system. Several concepts
are viable. One might think of a single central laser source from where optical
fibers deliver the laser pulses to the individual cylinders. At the cylinders, only a
focusing optics in needed. Another possibility would be to equip each cylinder
with its own laser plus focusing unit. The latter concept has more similarity with
todays spark plugs. In any case, a window is indispensable. The setup of a
window system is shown in the figure
That window has to meet three basic criteria. It must, for long term operation:
Withstand the thermal and mechanical stresses from the engine.
Withstand the high laser power necessary for ignition.
Exhibit a low propensity to fouling.
During combustion, the combustion chamber deposits can either be
organic (up to 300C) or inorganic in nature. When they form on the window,
they increasingly block the incoming laser light up to a point where no breakdown
can be produced any more. The formation of deposits on the window depends on
the temperature, the fuel and the engine oil. This is the main problem faced by
using a window in laser ignition.
Window must mainly withstand the influence of temperature, lubricating oil, fuel
and laser.
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The temperature on the window inside the combustion chamber is
influenced by its mounting position, engine speed, the thermal conductivity of the
window itself and the sealing material.
When we consider the lubricating oil, it contains many rather volatile
components that escape, decompose, burn subsequently lead to deposits. With
increasing residence time and thermal stressing of the engine oil, the volatile
fraction is reduced, and the influence of the oil on the window formation goes
down. Similar is the effect with the fuel.
When the laser beam passes a soiled window, an effect called ablation
occurs. The high intensity laser pulse is partly absorbed by the (black)
contaminations. These are quickly heated up so that they evaporate. Ablation is
ineffective with non-absorbing materials. It was found to work well with carbon
deposits.
Fig 5.8 Window Arrangement
5.6.4 OPTIC FIBER WIRE
It is used to transport the laser beam from generating unit to the focusing unit.
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5.6.5 FOCUSING UNIT
A set of optical lenses are used to focus the laser beam into the combustion
chamber. The focal length of the lenses can be varied according to where ignition is
required. The lenses used may be either combined or separated.
Fig 5.9 Focusing Optics
5.7 MULTIPOINT IGNITION
Laser ignition system can also be used for multipoint ignition in engines.
The laser beam generated will be divided 2 or more beams by means of diffraction
grating. Each beam is directed by optic fiber and focused into their respective
laser spark plugs.
Fig 5.10 Approach for Multipoint Ignition
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CHAPTER 6
MINIMUM ENERGY REQUIRED FOR IGNITION
The minimum ignition energy required for laser ignition is more than that
for electric spark ignition because of following reasons:
An initial comparison is useful for establishing the model requirements,
and for identifying causes of the higher laser MIE. First, the volume of a typical
electrical ignition spark is 103 cm3. The focal volume for a typical laser spark is
10-5 cm3. Since atmospheric air contains _1000 charged particles/cm3, the
probability of finding a charged particle in the discharge volume is very low for a
laser spark.
Second, an electrical discharge is part of an external circuit that controls
the power input, which may last milliseconds, although high power input to
ignition sparks is usually designed to last < 100 ns. Breakdown and heating of
laser sparks depend only on the gas, optical, and laser parameters, while the
energy balance of spark discharges depends on the circuit, gas, and electrode
characteristics. The efficiency of energy transfer to near-threshold laser sparks is
substantially lower than to electrical sparks, so more power is required to heat
laser sparks. Another reason is that, energy in the form of photons is wasted
before the beam reach the focal point. Hence heating and ionizing the charge
present in the path of laser beam. This can also be seen from the propagation of
flame which propagates longitudinally along the laser beam. Hence this loss of
photons is another reason for higher minimum energy required for laser ignition
than that for electric spark.
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CHAPTER 7
PRACTICAL LASER IGNITION REQUIREMENTS
7.1 MECHANICAL REQUIREMENTS
Laser spark plug designs must perform under engine mount shock and
vibration conditions. Testing to shock and vibration specifications for engine
mounted products will help to validate the durability and design life of the laser
spark plug. It appears that large stationary Advanced Reciprocating Engines
Systems (ARES) will most likely subject the laser spark plug to substantial long
term vibration and limited shock.
Automotive requirements are limited to shock and vibration compliance of
random vibration frequency testing at less than 15 gs.
7.2 ENVIRONMENTAL REQUIREMENTS
Lasers and optical instrumentation designed for outdoor use are typically
hermitically sealed backfilled with dry inert gas. Diode Pumped Solid State Lasers
are most sensitive to environmental temperature fluctuations as the diode pump
wavelength changes with temperature. This can be especially troublesome in Nd:
YAG and other crystal host lasers as their pump band width tends to be narrow.
Glass host DPSS lasers provide broad pump band widths allowing them to
traverse through -30 to +50 degrees C temperature operating range without the
need for diode thermal conditioning.
The ideal laser spark plug requires maximum performance over large
temperature ranges with minimum thermal conditioning. Decreasing the lasers
thermal conditioning requirements makes the laser design less complicated and
less expensive to build and maintain.
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7.3 PEAK POWER REQUIREMENTS
The peak power requirements for the laser spark are relatively high.
Formation of a plasma or laser spark in free space air is not difficult if you start
with Megawatt class (nanosecond pulse width - milli joule energy level) laser
pulses.
As the engine cylinder head pressure increases, the required laser pulse
peak power level for air breakdown decreases. With a multiple lens focusing
system it is plausible that one could reliably project a laser spark into a high
pressure cylinder head utilizing lower Kilowatt class pulse power densities.
Passive Q-switched lasers also allows for generation of a multiple laser
pulse output or pulse train. The first pulse of a pulse train initiates the plasma
and successive pulses feed more energy into the plasma causing the plasma to
expand. For neodymium lasers the pulses are typically separated by a few 10s of
microseconds. The net result of pulse train operation is longer sustained plasma
containing higher energy.
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CHAPTER 8
ADVANTAGES AND CHALLENGES
Location of laser plug is flexible as it does not require shielding from
immense heat and fuel spray and focal point can be made anywhere in the
combustion chamber from any point. It is possible to ignite inside the fuel spray as
there is no physical component at ignition location.
8.1 ADVANTAGES OF LASER IGNITION
It does not require maintenance to remove carbon deposits because of its
self-cleaning property.
High pressure and temperature does not affect the performance allowing
the use of high compression ratios.
Flame propagation is fast as multipoint fuel ignition is also possible.
Higher turbulence levels are not required due to above said advantages.
A choice of arbitrary positioning of the ignition plasma in the combustion
cylinder.
Absence of quenching effects by the spark plug electrodes.
Ignition of leaner mixtures than with the spark plug => lower combustion
temperatures => less NOx emissions.
No erosion effects as in the case of the spark plugs => lifetime of a laser
ignition system expected to be significantly longer than that of a spark
plug.
High load/ignition pressures possible => increase in efficiency.
Precise ignition timing possible.
Exact regulation of the ignition energy deposited in the ignition plasma.
Easier possibility of multipoint ignition.
Shorter ignition delay time and shorter combustion time.
Fuel-lean ignition possible.
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8.2 DISADVANTAGES OF LASER IGNITION
High system costs.
Concept is proven, but no commercial system available yet.
8.3 CHALLENGES OF LASER IGNITION
Propagation of laser pulse through fiber optics.
Development of a compact, robust and economic laser source.
Durability of windows.
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CONCLUSION
Although photochemical (resonant) ignition may be more energetically
efficient (less energy needed) than laser induced plasma ignition, the requirement
of a spectral match imposes imitations. Practical laser induced plasma ignition
systems, being less spectrally sensitive, can be made transferable across different
fuel/oxidizer mixtures. There are many technical advantages of the laser ignition
over conventional electric spark ignition system. Laser ignition is nonintrusive in
nature; high energy can be rapidly deposited, has limited heat losses, and is
capable of multipoint ignition of combustible charges. More importantly, it shows
better minimum ignition energy requirement than electric spark systems with lean
and rich fuel/air mixtures. It possesses potentials for combustion enhancement
and better immunity to spurious signals that may accidentally trigger electric
igniters. One of the potential advantages of the lasers lies in its flexibility to
change the ignition location. Also, multiple ignition points can be achieved rather
comfortably as compared to the conventional electric ignition systems using spark
plugs. Although the cost of the lasers has dramatically reduced to an affordable
level for many applications, it is still prohibitive for technologically important
applications such as automotive engines.
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REFERENCES
1. Laser Ignition in Internal Combustion Engines,Pankaj Hatwar,
DurgeshVerma; International Journal of Modern Engineering Research
(IJMER),Vol.2, Issue.2, Mar-Apr 2012 pp-341-345.
2. "Laser Plasma-Initiated Ignition of Engines", J. Tauer1, H. Kofler, K.
Iskra, G. Tartar And E. Wintner; 3rd International Conference on the Frontiers
of Plasma Physics and Technology
3. "Laser Ignition - a New Concept to Use and Increase the Potentials of Gas
Engines",Dr.GntherHerdin, DI Johann Klausner, Prof. Ernst Wintner;
ASME Internal Combustion Engine Division 2005 Fall Technical Conference,
Ottawa, Canada.
4. http://www.iitk.ac.in/erl/laserignition.html
5. http://www.faqs.org/patents/app/20080264371
6. http://en.wikipedia.org/wiki/Ignition_system
7. http://auto.howstuffworks.com/ignition-system4.html
8. http://www.seminarprojects.com/Thread-laser-ignition-system
9. http://www.lasers.org.uk/paperstore/Ignition2.pdf
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QUERIES
1. Is it possible for a laser to pass through optical fiber?
An optical fiber is a cylindrical dielectric waveguide (non-conducting
waveguide).The laser light in a fiber-optic cable travels through the core
(hallway) by constantly bouncing from the cladding (mirror-lined walls), a
principle called total internal reflection. Because the cladding does not absorb
any laser light from the core, the light wave can travel great distances.
2. In combined optics what is the focusing mechanism used?
A set of optical lenses are used to focus the laser beam into the combustion
chamber. The focal length of the lenses can be varied according to where
ignition is required. The lenses used may be either combined or separated. The
focusing mechanism used in both combined and separated optics are one and
the same but the difference is that, in combined optics the focusing lens is
integrated with the window. Where as in separated optics window and
focusing lens are two different parts.
3. What type of energy interaction is used for laser ignition?
By far, the most commonly used technique is the non-resonant initiation of
ignition primarily because of the freedom in selection of the laser wavelength
and ease of implementation.