Laser ignition is an alternative method for igniting compressed gaseous mixture of fuel and air. The method is based on laser devices that produce short but powerful flashes regardless of the pressure in the combustion chamber

1. Chapter 1
INTRODUCTION
Laser ignition is an alternative method for igniting compressed gaseous mixture
of fuel and air. The method is based on laser devices that produce short but powerful
flashes regardless of the pressure in the combustion chamber. Usually, high voltage
spark plugs are good enough for automotive use, as the typical compression ratio of an
Otto cycle internal combustion engine is around 10:1 and in some rare cases reach 14:1.
However, fuels such as natural gas or methanol can withstand high compression without
self-ignition. This allows higher compression ratios, because it is economically
reasonable, as the fuel efficiency of such engines is high. Using high compression ratio
and high pressure requires special spark plugs that are expensive and their electrodes
still wear out. Thus, even expensive laser ignition systems could be economical,
because they would last longer. Laser plugs have no electrodes and they can potentially
last for much longer.
1.1 Laser
Lasers provide intense and unidirectional beam of light. Laser light is
monochromatic (one specific wavelength). A laser is a device that emits
electromagnetic radiations through a process of optical amplification based on
stimulated emission of photons. The term ‘LASER’ is an acronym for Light
Amplification by Stimulated Emission of Radiation. The emitted laser is unique in its
high degree of spatial and temporal coherence.
Spatial coherence means a fixed phase relationship between the electric fields
at different locations across the beam. Typically it is expressed through the output being
a narrow beam which is diffraction-limited, also known as a "pencil beam." Laser
beams can be focused to very tiny spots, achieving a very high irradiance. Temporal
coherence means a strong correlation between the electric fields at one location, but
different times.

2. 1.1.1 How Does a Laser Works
A laser is effectively a machine that makes billions of atoms pumps out trillions
of photons all at once so they line up to form a really concentrated beam of light. It’s
all starts with the electrons. The working of laser is explained with the help of following
figure. A red laser contains a long crystal made of ruby (shown as red bar) with a flash
tube shown with yellow zigzag lines wrapped around it. The flash tube looks a bit like
a florescent strip light, only it’s coiled around ruby crystal and it flashes every so often
like camera’s flash gun.
Fig No 1.1 Working of Laser
How do the flash tube and the crystal make laser light?
i. A high voltage electric supply makes the tube flash on and off.
ii. Every time the tube flashes, it "pumps" energy into the ruby crystal. The
flashes it makes inject energy into the crystal in the form of photons.
iii. Atoms in the ruby crystals soak up this energy in a process called absorption.
When an atom absorbs a photon of energy, one of its electrons jumps from
lower energy level to higher one. This puts the atom into an excited state, but
make it unstable. Because the excite state is unstable, the electron can remain
in its higher energy level for only few milliseconds. It falls back to its original

3. level, giving off energy it absorbed as a new photon of light radiation, shown
as small blue dot. This process is called spontaneous emission.
iv. The photons that atoms give off zoom up and down inside the ruby crystal,
traveling at the speed of light.
v. Every so often, one of these photons hits an already excited atom. When this
happens the excited atom gives off two photons of light instead of one. This is
called stimulated emission. Now one photon of light has produced two, so the
light has been amplified. In other word “Light amplification has been caused
by stimulated emission of radiation”.
vi. A mirror at one end of the laser tubes keeps photons bouncing back and forth
inside the crystal.
vii. A partial mirror at the other end of the tube bounces some photons back into
the crystal but let’s some escape.
viii. The escaping photons form a very concentrated beam of powerful laser light.
1.2 Types of laser
Gas
A Helium-Neon (HeNe) used mostly for holograms such as laser printing.
Chemical
Lasers that obtain their energy through chemical reactions. Used mostly for
weaponry.
Dye
Uses organic dye as the lasting medium, usually in the form of a liquid solution.
Used in medicine, astronomy, manufacturing, and more.
Solid-state
Uses a gain medium that is a solid (rather than a liquid medium as in dye or gas
lasers). Used for weaponry
Semiconductor
Also known as laser diodes, a semiconductor laser is one where the active medium
is a semiconductor similar to that found in a light-emitting diode. Applications include
telecommunication and medicine.

4. Chapter 2
CONVENTIONAL IGNITION SYSTEM
The protection of the resources and the reduction of the CO2 emissions with the
aim to limit the greenhouse effect require a lowering of the fuel consumption of motor
vehicles. Great importance for the reduction lies upon the driving source. Equally
important are the optimization of the vehicle by the means of a reduction of the running
resistance as well as a low-consumption arrangement of the entire power train system.
The most important contribution for lower fuel consumption lies in the spark ignition
(SI) engine sector, due to the outstanding thermodynamic potential which the direct fuel
injection provides. Wall- and air-guided combustion processes already found their way
into standard production application and serial development, whereas quite some
fundamental engineering work is still needed for combustion processes of the second
generation.
2.1 Spark plug Ignition
Conventional spark plug ignition has been used for many years. For ignition of
a fuel-air mixture the fuel-air mixture is compressed and at the right moment a high
voltage is applied to the electrodes of the spark plug. When the ignition switch is turned
on current flows from the battery to the ignition coil. Current flows through the Primary
winding of the ignition coil where one end is connected to the contact breaker. A cam
which is directly connected to the camshaft opens and closes the contact breaker (CB)
points according to the number of the cylinders. When the cam lobe Pushes CB switch,
the CB point opens which causes the current from the primary circuit to break. Due to
a break in the current, an EMF is induced in the second winding having more number
of turns than the primary which increases the battery 12 volts to 22,000 volts. The high
voltage produced by the secondary winding is then transferred to the distributor. Higher
voltage is then transferred to the spark plug terminal via a high tension cable. A voltage
difference is generated between the central electrode and ground electrode of the spark
plug. The voltage is continuously transferred through the central electrode, which is
sealed using an insulator. 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

5. become conductors and allow the current to flow through the gap and the spark is finally
produced. Following Figure shows the working of internal combustion engine with
standard spark ignition system.
Fig No 2.1.1 Standard Spark plug Ignition system
First the charge means mixture of air and fuel sucked into the combustion
chamber during suction stroke. At the time of suction stroke the inlet valve opens with
the help of cam shaft. After suction of charge into cylinder, it gets compressed during
compression stroke by increasing its pressure and temperature. At certain condition of
temperature and pressure of air-fuel mixture, the spark plug ignite this mixture at the
top dead centre of combustion chamber. Hence due high pressure of gaseous mixture,
the expansion stroke occur. This stroke is also called as power stroke as during this
stroke the mechanical power is developed. After power stroke, exhaust stroke occurs in
which the burned gasses pushed out from the exhaust valve operated by cam shaft. In
this way the cycle is continued and power develop continuously in the form of rotation
of crank shaft. But with this current ignition system, we cannot achieve higher
efficiency. It has some drawback over laser ignition system, which are mentioned
below.

6. 2.2 Draw back of conventional ignition system
a. Location of spark plug is not flexible as it requires shielding of plug from
immense heat and fuel spray
b. Ignition location cannot be chosen optimally.
c. Spark plug electrodes can disturb the gas flow within the combustion chamber.
It is not possible to ignite inside the fuel spray.
d. It requires frequent maintenance to remove carbon deposits.
e. Leaner mixtures cannot be burned, ratio between fuel and air has to be within
the correct range.
f. Degradation of electrodes at high pressure and temperature.
g. Flame propagation is slow.
h. Multi point fuel ignition is not feasible.
i. Higher turbulence levels are required.
j. Erosion of spark plug electrodes

7. Chapter 3
LASER IGNITION SYSTEM
3.1 Why Laser Ignition System
Regulations on NOx emissions are pushing us toward leaner air/fuel ratios
(higher ratio of air to fuel). These leaner air/fuel ratios are harder to ignite and require
higher ignition energies. Spark plugs can ignite leaner fuel mixtures, but only by
increasing spark energy. Unfortunately, these high voltages erode spark plug electrodes
so fast, the solution is not economical. By contrast, lasers, which ignite the air-fuel
mixture with concentrated optical energy, have no electrodes and are not affected.
Natural gas is more difficult to ignite than gasoline due to the strong carbon to hydrogen
bond energy. Lasers are monochromatic, so it will be much easier to ignite natural gases
and direct the laser beam to an optimal ignition location. Because of the requirement
for an increase in ignition energy, spark plug life will decrease for natural gas engines.
Laser spark plug ignition system will require less power than traditional spark plugs,
therefore outlasting spark plugs. Ignition sites for spark plugs are at a fixed location at
the top of the combustion chamber that only allows for ignition of the air/fuel mixture
closest to them. Lasers can be focused and split into multiple beams to give multiple
ignition points, which means it can give a far better chance of ignition.
Lasers promise less pollution and greater fuel efficiency, but making
small, powerful lasers has, until now, proven hard. To ignite combustion, a laser must
focus light to approximately 100 gig watts per square centimeter with short pulses of
more than 10 mill joules each. Japanese researchers working for Toyota have created a
prototype laser that brings laser ignition much closer to reality. The laser is a small
(9mm diameter, 11mm length) high powered laser made out of ceramics that produces
bursts of pulses less than a nanosecond in duration. The laser also produces more stable
combustion so you need to put less fuel into the cylinder, therefore increasing
efficiency. Optical wire and laser setup is much smaller than the current spark plug
model, allowing for different design opportunities. Lasers can reflect back from inside
the cylinders relaying information such as fuel type and level of ignition creating
optimum performance. Laser use will reduce erosion.

8. 3.2 Types of Laser Ignition
Basically, energetic interactions of a laser with a gas may be classified
into one of the following four schemes as described below.
i. Thermal breakdown
ii. Non-resonant breakdown
iii. Resonant breakdown
iv. Photochemical mechanisms
Thermal initiation
In thermal initiation of ignition, there is no electrical breakdown of the gas and
a laser beam is used to raise the kinetic energy of target molecules in translational,
rotational, or vibrational forms. Consequently, molecular bonds are broken and
chemical reaction occur leading to ignition with typically long ignition delay times.
This method is suitable for fuel/oxidizer mixtures with strong absorption at the laser
wavelength. However, if in a gaseous or liquid mixtures is an objective, thermal ignition
is unlikely a preferred choice due to energy absorption along the laser propagation
direction. Conversely, this is an ideal method for homogeneous or distributed ignition
of combustible gases or liquids. Thermal ignition method has been used successfully
for solid fuels due to their absorption ability at infrared wavelengths.
Non-resonant breakdown
In non-resonant breakdown ignition method, because typically the light photon
energy is invisible or UV range of spectrum, multi photon processes are required for
molecular ionization. This is due to the lower photon energy in this range of
wavelengths in comparison to the molecular ionization energy. 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.
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

9. gas breakdown. Theoretically, less input energy is required due to the resonant nature
of this method.
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.
3.3 Working of Laser Ignition System
Laser ignition is optical breakdown of gas molecules. A powerful short pulse
laser beam is focused by a lens into a combustion chamber and near the focal spot a hot
and bright plasma is generated Engine test runs were carried out with two different
approaches:
i. First, a 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 (“separated optics”).
ii. Second, a more sophisticated window was deployed. A lens-like
curvature was engraved directly into the window. By using such a
special window, no further lens was required (“combined optics”)
From the point of view of components development, the main goal is the
creation of a laser system which meets the engine-specific requirements. Basically, it
is possible to ignite mixtures with different types of lasers. The Following Figure shows
the laser arrangement.

10. Fig No 3.3.1 Arrangement of Laser system
From the point of view of components development, the main goal is the creation
of a laser system which meets the engine-specific requirements. Basically, it is possible
to ignite mixtures with different types of lasers. The laser ignition system has a laser
transmitter with a fibre-optic cable powered by the car’s battery. It shoots the laser
beam to a focusing lens that would consume a much smaller space than current spark
plugs. The lenses focus the beams into an intense pinpoint of light, and when the fuel
is injected into the engine, the laser is fired and produces enough energy (heat) to ignite
the fuel.
3.3.1 Focussing Lenses
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. For the selection of
lenses one experiment were carried out which is described further. A one-cylinder
research engine was used as a test engine. The research engine was equipped with a
four-valve DOHC cylinder head with a spray-guided combustion system of AVL List
GmbH. In a double-overhead-camshaft (DOHC) layout, one camshaft actuates the
intake valves, and one camshaft operates the exhaust valves. Gasoline was used as a
fuel. Engine test runs were carried out with two different approaches. First, a plane

11. 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
(“separated optics”). Second, a more sophisticated window was deployed. A lens like
curvature was engraved directly into the window. By using such a special window, no
further lens was required (“combined optics”). This is depicted schematically in
following Fig.
Fig No 3.3.2 Separated and combined optics
From the point of view of components development, the main goal is the
creation of a laser system which meets the engine-specific requirements. Basically, it
is possible to ignite mixtures with different types of lasers.
3.4 Laser Induced Spark Ignition
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

12. 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 No 3.4.1 Ignition in Combustion Chamber
The laser beam is passed through a convex lens, this convex lens diverge the
beam and make it immensely strong and sufficient enough to start combustion at that
point. Hence the fuel is ignited, at the focal point, with the mechanism shown above.
The focal point is adjusted where the ignition is required to have.
Following Fig shows the cress section of laser spark plug.
Fig No 3.4.2 Laser Spark Plug

13. 3.5 Advantages of Laser Ignition System
a. A choice of arbitrary positioning of the ignition plasma in the
combustion cylinder.
b. Effective ignition of leaner mixture at lower combustion temperature.
c. Less NOx emissions.
d. No erosion effects in case of spark plug.
e. Lifetime of laser ignition system expected to be significantly longer than
that of conventional spark plug.
f. High load ignition pressure possible.
g. High power output, hence higher efficiency.
h. Multipoint ignition is possible.
i. Shorter ignition delay time and shorter combustion time.
j. Precise ignition timing possible.
k. Fuel lean ignition possible.
l. Exact regulation of the ignition energy deposited in the ignition plasma.
3.6 Disadvantages of Laser Ignition System
i. High system costs.
ii. Concept proven, but no commercial system available yet.

14. Chapter 4
ENGINE EXPERIMENT
4.1 Introduction
As a feasibility test, an excimer laser has been used for ignition of inflammable
gases inside a combustion bomb. The laser used for the first experiments was a Lambda
Physik LPX205, equipped with an unstable resonator system and operated with KrF,
delivering pulses with a wavelength of 248 nm and a duration of approximately 34 ns
with maximum pulse energy of 400 mJ.10 The combustion chamber has had a diameter
of 65 mm and a height of 86mm, with a resulting volume of 290cm3 and was made of
steel. The laser beam was focused into the chamber by means of a lens with a focal
length of 50 mm. Variations of pulse energies as well as gas mixtures have been
performed to judge the feasibility of the process. Results indicate that ignition-delay
times are smaller and pressure gradients are much steeper compared to conventional
spark plug ignition.
4.2 Engine Experiments
Since the first feasibility experiments could be concluded successfully, an
engine was modified for laser ignition. The engine has been modified by a replacement
of the conventional spark plug by a window installed into a cylindrical mount. The
position of the focusing lens inside the mount can be changed to allow variations of the
location of the initial optical breakdown. First experiment with laser ignition of the
engine have been performed with an excimer laser, later a q switched ND: YAG has
been used.
Fig No 4.2.1 Experimental setup

15. The replacement of the excimer laser was mainly caused by the fact that
especially at very low pulse energies the exciter laser shows strong energy fluctuations.
Pulse energies, ignition location and fuel/air ratios have been varied during the
experiments. The engine has been operated at each setting for several hours, repeatedly.
All laser ignition experiments have been accompanied by conventional spark plug
ignition as reference measurements.
Table No 4.2.1 Technical data of the research engine and the ND: YAG laser used for the
experiments.
Research
engine
switched Nd:YAG
No. of
cylinders
Pump source Flash lamp
1
No. of valves 1 Wavelength 1064 or 532 nm
Injector Multi hole Max. pulse energy 160 mJ
Stroke 85 mm Pulse duration 6 ns
Bore 88 mm Power consumption 1 kW
Displacement
vol.
517 cm3 Beam diameter 6 mm
Comp. ratio 11.6 Type Quantel Brilliant
4.3 Results of Experiment
Results of the experiments are summarized in fig shows that laser ignition has
advantages compared to conventional spark plug ignition. Compared to conventional
spark plug ignition, laser ignition reduces the fuel consumption by several per cents.
Exhaust emissions are reduced by nearly 20%. It is important that the benefits from
laser ignition can be achieved at almost the same engine smoothness level, as can be
seen from fig.4.3.1. Additionally, a frequency-doubled Nd: YAG laser has been used
to examine possible influences of the wavelength on the laser ignition process. No
influences could be found. Best results in terms of fuel consumption as well as exhaust
gases have been achieved by laser ignition within the fuel spray. As already mentioned,

16. it is not possible to use conventional spark plugs within the fuel spray since they will
be destroyed very rapidly. Laser ignition doesn’t suffer from that restriction.
Fig No 4.3.1 Result Comparison
Another important question with a laser ignition system is its reliability. It is
clear that the operation of an engine causes very strong pollution within the combustion
Chamber. Deposits caused by the combustion process can contaminate the beam
entrance window and the laser ignition system will probably fail. To quantify the
influence of deposits on the laser ignition system, the engine has been operated with a
spark plug at different load points for more than 20 hours with an installed beam
entrance window. The window was soiled with a dark layer of combustion deposits.
Afterwards, a cold start of the engine was simulated. Already the first laser pulse ignited
the fuel/air mixture. Following laser pulses ignited the engine without misfiring, too.
After 100 cycles the engine was stopped and the window was disassembled. As seen to
the window, all deposits have been removed by the laser beam. Additional experiments
showed that for smooth operation of the engine the minimum pulse energy of the laser
is determined by the necessary intensity for cleaning of the beam entrance window.
Estimated minimum pulse energies are too low since such “self-cleaning” mechanisms
are not taken into account. Engine operation without misfiring was always possible
above certain threshold intensity at the beam entrance window. For safe operation of
an engine even at cold start conditions increased pulse energy of the first few laser
pulses would be beneficial for cleaning of the beam entrance window.

17. Chapter 5
CONCLUSION
The applicability of a laser-induced ignition system on engine has been proven. At
present, a laser ignition plug is very expensive comparatively. But potential advantages
will surely bring it in to market for many practical applications. Following are
conclusion drawn based on above discussion.
a. Laser ignition system allows almost free choice of the ignition location within
the combustion chamber, even inside the fuel spray.
b. Significant reductions in fuel consumption as well as reductions of exhaust
gases show the potential of the laser ignition process.
c. Minimum ignition energy is mainly determined by the necessary “self-
cleaning” mechanism at the beam entrance window from combustion deposits
and not by engine related parameters.
d. 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.
e. More importantly, it shows better minimum ignition energy requirement than
electric spark systems with lean and rich fuel/air mixtures.
f. Although the laser will need to fire more than 50 times per second to produce
3000 RPM, it will require less power than current spark plugs. The lasers can
also reflect back from inside the cylinders to relay information based on fuel
type used and the level of ignition, enabling cars to readjust the quantities of air
and fuel for optimum performance.
g. Applicability of the laser induced ignition as a future ignition system for
combustion engines with spray-guided combustion process could be proved
with basic research.

18. REFERENCES
Research papers-
a) Laser Ignition in Internal Combustion Engines - A Contribution to a
Sustainable Environment by M. Lackner*, F. Winter
b) Laser Ignition System for IC Engines by International Journal of Science
and Research (IJSR)
c) Laser Plasma-initiated Ignition Of Engines
d) Laser ignition system and method for internal combustion engine patent no
- US 8127732 B2
e) www.laserist.org