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Laser ignition system (3) (1)


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Laser ignition system

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Laser ignition system (3) (1)

  4. 4. LASER IGNITION SYSTEM 2014 4 We the students of Vth semester of MECHANICAL ENGINEERING, have successfully completed the book report as a part of our curriculum as stated by MUMBAI UNIVERSITY. We have successfully completed the book report as described in this report by own skills and study as per instructions and guidance of Miss. Riddhi Popat. We clarify that we have not copied the report or its any appreciable part from any Literature in contravention of any academic ethics. Team Members- PRANITA POL 37 RAHUL PADWAL 39 SHREEDHARSANGOALKAR 42 ROHAN SAWANT 45 SUJIT SHETTY 51 RADHA SINGH 54
  5. 5. LASER IGNITION SYSTEM 2014 5 TABLE OF CONTENTS Abstract Acknowledgement List of figures Introduction Aimand scope 1.1 Introductionof system 1.2 Laser 1.2.1 Types of laser 1.3 Plasma 2.1 Laser ignitionsystem 2.2 Combustions 2.3 Laser igniters 2.4 present scenario 3.1 Comparison betweenspark and laser ignition 3.1.1 spark ignitionsystem 3.1.2 Laser ignitionsystem 3.2 Advantages 4.1 Discussion 4.2 Conclusion 5.0 References
  6. 6. LASER IGNITION SYSTEM 2014 6 ABSTRACT Laser ignition with its many potential advantages in comparison to conventional spark plug ignition has been investigated in detail. As ignition source several, to a certain extent exclusive prototype ns, Q- switched Nd:YAG lasers were used. Experiments were performed in a constant volume, high pressure/temperature combustion chamber and with two gasoline research engines. On one engine a mechanical & thermal robust, passive Q-switched, diode pumped Nd:YAG laser combined with special optimized optics was mounted directly on the research engine. Despite the harsh environment on the engine, the laser ignition system was able to operate the engine more than 10 hours. It turned out that the laser can ignite far leaner mixtures than with the conventional spark plug which means a significant reduction of NOx. Further on, the ignition delay and combustion time is shorter and the coefficient of variation (COV) of the induced mean effective pressure (IMEP) is significantly smaller. The use of this system should be initiated on heavy trucks and not on cars considering the high cost of the system.
  7. 7. LASER IGNITION SYSTEM 2014 7 ACKNOWLEDGEMENT It is indeed a matter of great pleasure and proud privilege to be able to present this Book report on "LASER IGNITION SYSTEM". The experience gained in the execution of a given book report is worth a milestone in a student’s life and the efforts taken to bring out the best in our capacity speaks volumes about the co-ordinated efforts. We are highly indebted the report guide Ms. RIDDHI POPAT for her invaluable guidance and appreciation for giving form and substance to this report. It is due to her enduring efforts; patience and enthusiasm, which has given a sense of direction and purposefulness to this book report and ultimately made it a success. We would like to tender our sincere thanks to the staff members for their co-operation. We would wish to thank the non - teaching staff and our friends who have helped us all the time in one way or the other. Really it is highly impossibleto repay the debt of all the people who have directly or indirectly helped us for preparing the book report.
  8. 8. LASER IGNITION SYSTEM 2014 8 LIST OF FIGURES 1.Laser ignition engine 2.Ruby laser 3.Plasma formation by a focused beam 4.Principle of laser ignition 5.Optical breakdown in air generated by Nd-Yag laser 6.Combustion chamber 7.Spray guided combustion using laser beam 8.Single and multipoint ignition 9.Setup of laser system for the first engine tests 10.Spark plug ignition in an internal combustion engine. 11.Laser ignition system for an internal combustion engine.
  9. 9. LASER IGNITION SYSTEM 2014 9 INTRODUCTION With the increasing disadvantage of spark plug ignition system, it is becoming essential to find an alternative to the spark plug ignition system.spark plug ignition system is unable to burn the fuel mixture completely inside the combustion chamber,whereas the alternative to it-the laser ignition system burns air fuel mixture completely and runs the engine for a longer time compared to spark plug ignition system. This project presents the overall scenario of the working of laser ignition system which as the name suggests makes use of the laser.
  10. 10. LASER IGNITION SYSTEM 2014 10 AIM AND SCOPE Our report on “Laser ignition system” seeks to share useful innovations both in thoughts and in practice with the aim of encouraging information exchange and the subsequent benefits that are borne of scrutiny, experimentation and debate . It is our hope that the work shared in this project will inform practices that strengthen the knowledge of the mentioned subject and encourage the access for the topic.
  11. 11. LASER IGNITION SYSTEM 2014 11 LASER IGNITION SYSTEM 1.1) INTRODUCTION For more than 150 years, spark plugs have powered internal combustion engines. Located at the top of each engine cylinder, spark plugs send a high-voltage electrical spark across a gap between their two metal electrodes. That spark ignites the compressed air-fuel mixture in the cylinder, causing a controlled mini explosion that pushes the piston down. One by product of the process is toxic nitrogen oxides (NOx), which pollute the air causing smog and acid rain. Engines would produce less NOx if they burnt more air and less fuel, but they would require the plugs to produce higher- energy sparks in order to do so. While this is technically possible, the voltages involved would burn out the electrodes quite quickly. In laser ignition system laser igniters on the other hand, could ignite leaner mixtures without self destructing because they don't have electrodes. The operation of internal combustion engines with lean gas air mixtures, laser igniters results in increase of fuel efficiencies and reduce green-house gas emissions by significant amounts. Figure 1.Laser Ignition Engine
  12. 12. LASER IGNITION SYSTEM 2014 12 1.2)LASER Lasers provide intense and unidirectional beam of light. Laser light is monochromatic (one specific wavelength). Wavelength of light is determined by amount of energy released when electron drops to lower orbit. Light is coherent; all the photons have same wave fronts that launch to unison. Laser light has tight beam and is strong and concentrated. To make these three properties occurtakes something called “Stimulated Emission”, in which photon emission is organized. Main parts of laser are power supply, lasing medium and a pair of precisely aligned mirrors. One has totally reflective surface and other is partially reflective (96 %). The most important part of laser apparatus is laser crystal. Most commonly used laser crystalis manmade ruby consisting of aluminum oxide and 0.05% chromium. Crystal rods are round and end surfaces are made reflective. A laser rod for 3 J is 6 mm in diameter and70 mm in length approximately. Laser rod is excited by xenon filled lamp, which surrounds it. Both are enclosed in highly reflective cylinder, which directs light from flash lamp in to the rod. Chromium atoms are excited to higher energy levels. The excitations meet photons when they return to normal state. Thus very high energy is obtained in short pulses. Ruby rod becomes less efficient at higher temperatures, so it is continuously cooled with water, air or liquid nitrogen. The Ruby rod is the lasing medium and flashtube pumps it. Figure 2. Ruby Laser
  13. 13. LASER IGNITION SYSTEM 2014 13 1.2.1)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 1.3)PLASMA The most dominant plasma producing process is the electron cascade process: Initial electrons absorb photons out of the laser beam via the inverse bremsstrahlung process. If the electrons gain sufficient energy, they can ionise other gas molecules on impact, leading to an electron cascade and breakdown of the gas in the focal region. It is important to note that this process requires initial seed electrons. These electrons are produced from impurities in the gas mixture (dust, aerosols and soot particles) which are always present. These impurities absorb the laser radiation and lead to high local temperature and in consequence to free electrons starting the avalanche process. In contrast to multiphoton ionisation (MPI), no wavelength dependence is expected for this initiation path
  14. 14. LASER IGNITION SYSTEM 2014 14 Figure 3.Plasma Formation by a Focused Beam 2.1)LASER IGNITION SYSTEM Laser ignition or laser-induced ignition, is the process of starting combustion by the stimulus of a laser light source. 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. Multiphoton absorption processes are usually essential for the initial stage of break down 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. The minimum ignition energy required for laser ignition is more than that for electric spark ignition because of following reasons: An initial
  15. 15. LASER IGNITION SYSTEM 2014 15 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 10^-3 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 reaches 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. Figure 4. Principle of laser ignition
  16. 16. LASER IGNITION SYSTEM 2014 16 Basically, energetic interactions of a laser with a gas may be classified into one of the following four schemes as listed below: 1) Thermal initiation  Ignition occurs without the generation of an electrical breakdown.  A laser beam is used to raise the kinetic energy of target molecules.  Molecular bonds are broken and chemical reaction occurs leading to ignition .  Long ignition delay times.  Best suited for solid fuels. 2) Non-resonantbreakdown  Laser light is tightly focused so that the intensity exceeds the breakdown threshold of the gas.  Once breakdown is achieved, a plasma spark is formed which absorbs the laser energy.  Energy is transferred to the combustion gases from the spark and starts the reaction  Commonly used technique because of the freedom in selection of laser wavelength and implementation. 3) Resonantbreakdown  Similar to non-resonant breakdown in that the end results is a plasma spark.  The wavelength of the laser must be tuned to the particular resonance.  This lowers the number of photons required for photo ionization, and hence the amount of energy required to cause breakdown. 4) Photochemicalmechanisms
  17. 17. LASER IGNITION SYSTEM 2014 17  This method starts ignition by creating radicals, and in general does not heat the gas as do the previous three methods.  If the productionrate of the radicals is higher than the neutralizing radicals then the highly active species will reach a threshold value, leading to an ignition event Figure 5. Optical breakdown in air generated by a Nd:YAG laser 2.2)COMBUSTIONS After a successful ignition event the flame propagates through the combustible. Usually, one can distinguish between different types of combustion processes. 1. Slow combustion processes (deflagrations): Reaction velocity is mainly determined by heat conductivity. Propagation velocity is less than the speed of sound.
  18. 18. LASER IGNITION SYSTEM 2014 18 2. Fast combustion processes (detonations): Reaction velocity is determined by a strong shock front moving at supersonic velocity. Propagation velocity is greater than the speed of sound. Figure 6. Combustion chamber Figure 7. Spray Guided Combustion using Laser Beam
  19. 19. LASER IGNITION SYSTEM 2014 19 2.3)LASER IGNITERS A new laser system invented by researchers could displace the venerable design of spark plugs, which has stood virtually unchanged for the past 150 years. Lasers, by contrast, could focus their beams into the middle of the column, from which point the explosion would expand more symmetrically – and reportedly up to three times faster than one triggered by a spark plug. Additionally, engine timing could be improved, as lasers can pulse within nanoseconds, while spark plugs require milliseconds. In order to cause the desired combustion, a laser would have to be able to focus light to approximately 100 Giga-watts per square centimeter with short pulses of more than 10 milli-joules each. Previously, that sort of performance could only be achieved by large, inefficient, relatively unstable lasers. The Japanese researchers, however, have created a small, robust and efficient laser that can do the job. They did so by heating ceramic powders, fusing them into optically transparent solids, and then embedding them with metal ions in order to tune their properties. Made from two bonded yttrium-aluminum-gallium segments, the laser igniter is just 9 millimeters wide and 11 millimeters long. It has two beams, which can produce a faster, more uniform explosion than one by igniting the air-fuel column in two locations at once –the team is even looking at producing a laser with three beams. While it cannot cause combustion with just one pulse, it can do so using several 800-picosecond-long pulses. Figure 8.Single & Multi-point Ignition
  20. 20. LASER IGNITION SYSTEM 2014 20 2.4)PRESENTSCENERIO 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 giga-watts per square centimeter with short pulses of more than 10 millijoules each. In the past, lasers that could meet those requirements were limited to basic research because they were big, inefficient, and unstable. Nor could they be located away from the engine, because their powerful beams would destroy any optical fibers that delivered light to the cylinders. This problem overcame by making composite lasers from ceramic powders. In this the powders is heated and fuse into optically transparent solids and embeds metal ions in them to tune their properties. Ceramics are easier to tune optically than conventional crystals. They are also much stronger, more durable, and thermally conductive, so they can dissipate the heat from an engine without breaking down. The composite generates two laser beams that can ignite fuel in two separate locations at the same time. This would produce a flame wall that grows faster and more uniformly than one lit by a single laser. The laser is not strong enough to light the leanest fuel mixtures with a single pulse. By using several 800- picoseconds-long pulses, however, they can inject enough energy to ignite the mixture completely. A commercial automotive engine will require 60 Hz (or pulse trains per second), Researchers have already tested the new dual-beam laser at 100 Hz. Researchers are also at work on a three-beam laser that will enable even faster and more uniform combustion. The laser-ignition system, although highly promising, is not yet being installed into actual automobiles made in a factory. Scientist team from Japan is, however, working with a large spark-plug company and with DENSO Corporation, a member of the Toyota Group.
  21. 21. LASER IGNITION SYSTEM 2014 21 Figure 9. Set-up of the laser systemfor the first engine tests 3.1)COMPARISON BETWEENSPARK& LASER IGNITION 3.1.1 Spark ignition System Conventional spark plug ignition has been used for many years and is a well established and reliable technology. The fuel-air mixture is compressed and at the right moment a high voltage is applied to the electrodes of the spark plug. For ignition of an inflammable gas mixture, the energy balance has to be positive within a small volume. The supplied energy together with the exothermal heat of the reaction have to be greater than the necessary activation energy and losses due to heat conduction or radiation. This technology has been used very successfully a million times in combustion engines from the very beginning till now. Nevertheless, problems occur due to the fact that the ignition location cannot be chosen optimally. Additionally, spark plug electrodes can disturb the gas flow within the combustion chamber.
  22. 22. LASER IGNITION SYSTEM 2014 22 Figure 10.Spark Plug Ignition in an Internal Combustion Engine  LIMITATIONS OF SPARK PLUG Spark plugs only ignite the area of the air-fuel mixture closest to them (the top), with much of the heat of the explosion being absorbed by the metal cylinder walls before it can reach down to the piston. The fuel inside the combustion chamber is not burnt completely by the conventional spark plug. Spark plug burn the air-fuel mixture which is slightly on richer side than air-fuel mixture, we can use in laser igniters. 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. 3.1.2 Laserignition system Laser ignition uses an optical breakdown of gas molecules caused by an intense laser pulse to ignite gas mixtures. The beam of a powerful short pulse laser is focused by a lens into a combustion chamber and near the focal spot a hot and bright plasma is generated, see fig. 11.
  23. 23. LASER IGNITION SYSTEM 2014 23 Figure 11.Laser Ignition System for an Internal Combustion Engine 3.2)ADVANTAGES The main advantages of laser ignitions are given below: 1) A choice of arbitrary positioning of the ignition plasma in the combustion cylinder 2) Absence of quenching effects by the spark plug electrodes 3) Ignition of leaner mixtures than with the spark plug; lower combustion temperatures and less Nox emissions 4) 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 5) High load/ignition pressures possible, increase in efficiency Precise ignition timing possible 6) Exact regulation of the ignition energy deposited in the ignition plasma 7) Easier possibility of multipoint ignition 8) Shorter ignition delay time and shorter combustion time
  24. 24. LASER IGNITION SYSTEM 2014 24 4.1)DISCUSSION 4.2)CONCLUSION In this paper, it is described that how a revolutionary change has come after the positive research work on laser igniters which can replace the conventional spark plug in near future very soon. This replacement of conventional spark plugs to laser igniters will be a milestone in automobile industry. Laser igniters will be able to combust the fuel with lean air-fuel mixture as compare to conventional spark plug, which helps to lower down the Nox emission and gives better fuel efficiency. 5) REFERENCES  H. Kopecek, S. Charareh, M. Lackner, C. Forsich, F. Winter, J. Kausner, G. Herdin, E. Wintner, "Laser Ignition of Methane-Air Mixtures at High Pressure and Diagnostics", Journalof Enginesand GasTurbine Power, 127 pp. 213-219  J.D. Dale, P.R. Smy, R.M. Clements, "Laser Ignited Internal Combustion Engine - An Experimental Study", Society of Automotive Engineers, 780329, pp. 1539-1548  T.X. Phuoc, "Laser Spark Ignition: Experimental Determination of Laser- Induced Breakdown Thresholds of Combustion Gases", Optical Communications, 175 pp. 419-423  D. Bradley, C.G.W. Sheppard, I.M. Suardjaja, R. Woolley, "Fundamentals of High-Energy Spark Ignition with Lasers", Combustion
  25. 25. LASER IGNITION SYSTEM 2014 25 and Flame,138pp. 55-77  A.P. Yalin, M.W. Defoort, S. Joshi, D. Olsen, B. Willson, Y. Matsuura, M. Miyagi, " Laser Ignition of Natural Gas Using Fiber Delivery",Proceedings of ICEF 2005, ASME InternalCombustion Engine Division 2005 FallTechnicalConference, ICEF-2005-1336, pp. 1-9  A.P. Yalin, A.R. Reynolds, S. Joshi, M.W. Defoort, B. Willson, Y. Matsuura, M. Miyagi, " Development of a Fiber Delivered Laser Ignition System for Natural Gas Engines", Proceedings of ICEF, ASME Internal Combustion Engine Division 2006 Spring Technical Conference, ICEF- 2006-1370, pp. 1-6