A take on the LASER Ignition System by you budding Mechanical engineers.

1. LASER IGNITION SYSTEM
By,
Avinash Bhagawati
Divyang Choudhary
Rishav Raj
6th SEM
Mechanical
Engineering

2. INTRODUCTION
It's widely accepted that the internal combustion engines
will continue to power our vehicles.
Hence, as the global mobilisation of people and goods
increases, advances in combustion and after-treatment
are needed to reduce the environmental impact of the
continued use of IC engine vehicles.
To meet environmental legislation requirements,
automotive manufacturers continue to address two
critical aspects of engine performance, fuel economy and
exhaust gas emissions.
New engines are becoming increasingly complex, with
advanced combustion mechanisms that burn an
increasing variety of fuels to meet future goals on
performance, fuel economy and emissions.
The spark plug has remained largely unchanged since its
invention, yet its poor ability to ignite highly dilute air-fuel
mixtures limits the potential for improving
combustion efficiency.
With

3. INTRODUCTION CONTINUED...
Spark ignition (SI) also restricts engine design,
particularly in new engines, since the spark position is
fixed by the cylinder head location of the plug, and the
protruding electrode disturbs the cylinder geometry and
may quench the combustion flame kernel.
So, many alternatives are being sought after to counter
these limitations.
One of the alternative is the laser ignition system (LIS)
being described here.
Compared to a conventional spark plug, a LIS should be
a favourable ignition source in terms of lean burn
characteristics and system flexibility.
So, in this paper we'll be discussing the implementation
and impact of LIS on IC engines.

4. PROCESSES & MECHANISMS
Spark Ignition System
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 become conductors and allows the
current to flow through the gap and the spark is finally produced.

5. LASER Ignition System
LI requires certain conditions to be met for two basic steps to take place, spark formation (generally limited
by breakdown intensity) and subsequent ignition (generally limited by a minimum ignition energy or MIE).
For example it's possible to provide sufficient energy for ignition with no spark formation or provide
insufficient energy with spark formation.
There are four mechanisms by virtue of which LI is able to ignite the air-fuel mixture.
They are,
1. Thermal initiation (TI)
2. Non-resonant breakdown (NRB)
3. Resonant breakdown (RB)
4. Photo chemical ignition (PCI)
Amongst the above mentioned mechanisms NRB is used the most.

6. SO, NOW WHAT'S THE
PROBLEM?
The following are the drawbacks of SI:
1. Location of spark plug is not flexible as it require shielding of plug from immense
heat and fuel spray.
2. It is not possible to ignite inside the fuel spray.
3. It require frequent maintenance to remove carbon deposits.
4. Leaner mixtures cannot be burned efficiently.
5. Degradation of electrodes at high pressure and temperature.
6. Flame propagation is slow.
7. Multi point fuel ignition is not feasible.
8. Higher turbulence levels are required.
To overcome the above mentioned disadvantages LIS is being sought after.

7. NON RESONANT BREAKDOWN
In NRB, the focused laser beam creates an electric field of sufficient intensity to cause dielectric breakdown of the air-fuel
mixture.
The process begins with multi-photon ionisation 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 ionise 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 ionisation 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.

8. NOW, HOW DOES IT WORK?
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 by passing through
an optical window, and when the fuel is injected into the engine, the laser is fired and produces
enough energy (heat) to ignite the fuel.

9. NOW, HOW DOES IT
WORK?...CONTINUED
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.
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 ionise 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.
The shock waves carry energy out wards from the laser
beam and thus help in propagation of flame as shown in the
above figure.

10. ADVANTAGES OF LIS
The following are the advantages of using a LIS:
1. Location of laser 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.
2. It does not require maintenance to remove carbon deposits because of the fact that whole system is
isolated.
3. Leaner mixtures can be burned as fuel ignition inside combustion chamber is also possible here
certainty of fuel presence is very high.
4. High pressure and temperature does not affect the performance allowing the use of high
compression ratios.
5. Flame propagation is fast as multipoint fuel ignition is also possible.
6. Higher turbulence levels are not required due to above said advantages.

11. NOX EMISSIONS IN DIFFERENT
IGNITION SYSTEMS IN MG/NM3

12. 1. SI
2. LI

13. CONCLUSION
Research to date on LI in engines has demonstrated improvements in combustion stability. With
proper control, these improvements can enable engines to be run under leaner conditions, with
higher Exhaust Gas Recirculation (EGR) concentrations, or at lower idle speeds without increasing the
noise, vibration and harshness characteristics of a vehicle.
LI gives significantly shorter power duration compared to SI. With the recent development of higher
average power and higher pulse frequency lasers, it is expected that a multi-strike LI system and
associated combustion control can reduce the probability of misfires under high levels of dilution.
The prospects for LI are also particularly exciting from a control perspective, from optical sensing of
the in-cylinder combustion, to the array of possible ignition activation and control mechanisms.
It is anticipated that this, combined with the capability to control the ignition location and timing, will
play a significant role in optimisation of future engines by dynamic feedback control.
The only limitations of the LIS is it's highly expensive setup.

14. REFERENCES
[1] Lackner, M., Winter, F., What is ignition? Combustion File 256, IFRF Online Combustion Handbook, ISSN
1607-9116, International Flame Research Foundation, Ijmuiden, The Netherlands, (2004).
[2] H. Kopecek, M. Lackner, F. Winter, E. Wintner, Laser ignition of methane air mixtures at pressures up to 4 MPa,
Journal of Laser Physics 13 (11), 1365 (2003).
[3] Kopecek, H., Lackner, M., Wintner, E., Winter, F., Laser-Stimulated Ignition in a Homogeneous Charge Compression
Ignition Engine, SAE 2004 World Congress, paper No 2004-01-0937, Detroit, MI, USA (2004).
[4] J. D. Dale, M. D. Checkel, P. R. Smy, Application of High Energy Ignition Systems to Engines, Prog. Energy Combust.
Sci. 23, 379-398 (1997).
[5] Ronney P.D., Laser versus conventional ignition of flames, Optical Engineering 33(2),510 (1994).
[6] Phuoc T.X., White F.P., Laser-induced spark ignition of CH4/air mixtures, Combustion and Flame 119, 203-216
(1999).
[7] Radziemski L.J., Cremers D.A., Laser-induced plasmas and applications, New York-Basel: Marcel Dekker Inc.,
(1989).

15. QUERIES, ANYONE?