LASER IGNITION SYSTEM FOR INT
LASER IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINE
ERNAL COMBUSTION ENGINE
M.SrinivasnaikM.Srinivasnaik 11, Dr.T.V.V. Sudhakar , Dr.T.V.V. Sudhakar 22, Dr.B. Balunaik , Dr.B. Balunaik 33, Dr.A.SomiReddy, Dr.A.SomiReddy44
1 1
Research Scholar Department of Mechanical Engineering, Research Scholar Department of Mechanical Engineering,
JNTUH Kukatpally, Hyderabad-500085, India. JNTUH Kukatpally, Hyderabad-500085, India.
2 2
Principal And Professor in the Department of Mechanical Engineering Principal And Professor in the Department of Mechanical Engineering
Columbia Institute of Engineering and Technology, Raipur (CG)-493111, India. Columbia Institute of Engineering and Technology, Raipur (CG)-493111, India.
3 3
Professor in the Department of Mechanical Engineering Professor in the Department of Mechanical Engineering JNTUH Kukatpally, Hyderabad-500085, India. JNTUH Kukatpally, Hyderabad-500085, India.
4 4
Principal And Professor in the Department of Mechanical Engineering Principal And Professor in the Department of Mechanical Engineering Vivekananda Institute of Technology and Science, Karimnagar-505001, Vivekananda Institute of Technology and Science, Karimnagar-505001, India.India.
E-mail:[email protected],[email protected],[email protected],[email protected] E-mail:[email protected],[email protected],[email protected],[email protected]
Abstract: - Laser ignition is considered to be one of the most promising future ignition concepts for Abstract: - Laser ignition is considered to be one of the most promising future ignition concepts for internal combustion engines. It combines the legally required reduction of pollutant emissions and internal combustion engines. It combines the legally required reduction of pollutant emissions and higher engine efficiencies. In technical appliances such as internal combustion engines, reliable higher engine efficiencies. In technical appliances such as internal combustion engines, reliable ignition is necessary for adequate system performance. Economic as well as environmental ignition is necessary for adequate system performance. Economic as well as environmental constraints demand a further reduction in
constraints demand a further reduction in the fuel consumption and the the fuel consumption and the exhaust emissions of motorexhaust emissions of motor vehicles. At the moment, direct injected fuel engines show the highest potential in reducing fuel vehicles. At the moment, direct injected fuel engines show the highest potential in reducing fuel consumption and exhaust emissions.
consumption and exhaust emissions. Study of ignition of combustion processes is of greatStudy of ignition of combustion processes is of great importance. In most cases, a well-defined ignition location and ignition time is crucial for an IC importance. In most cases, a well-defined ignition location and ignition time is crucial for an IC engine. Spark plugs are well suited for such tasks but suffer from disadvantages, like erosion of engine. Spark plugs are well suited for such tasks but suffer from disadvantages, like erosion of electrodes or restricted positioning possibilities.
electrodes or restricted positioning possibilities. Thermodynamic requirements of a highThermodynamic requirements of a high compression ratio and a high power density are fulfilled well by laser ignition. Laser ignition can compression ratio and a high power density are fulfilled well by laser ignition. Laser ignition can enhance the combustion process and minimize pollutant formation. At present the laser ignition enhance the combustion process and minimize pollutant formation. At present the laser ignition plug is very expensive and commercially not get available.
plug is very expensive and commercially not get available. Keywords:
Keywords: Laser-ignition, Altern Laser-ignition, Alternative Fuels, emisative Fuels, emissions, Combustion psions, Combustion parameters.arameters.
1.
1.IntroductionIntroduction
Two things have to be considered while fuelling the internal combustion engines used for transportation Two things have to be considered while fuelling the internal combustion engines used for transportation purposes. The
purposes. The first thing first thing is one is one has to has to protect the protect the global environment. Tglobal environment. T he second thing he second thing is that is that the fossilthe fossil resources have to be preserved. in recent years, the concept of developing new clean vehicles has been resources have to be preserved. in recent years, the concept of developing new clean vehicles has been progressing
progressing worldwide. worldwide. The The clean clean vehicles vehicles are are driven driven by by clean clean energy energy sources sources such such as as electricity, electricity, fuelfuel cell, etc., However it is difficult to replace all conventional gasoline vehicles to clean vehicles cell, etc., However it is difficult to replace all conventional gasoline vehicles to clean vehicles immediately, because they still have several problems to get over. The costs
immediately, because they still have several problems to get over. The costs of the clean vehicles dependsof the clean vehicles depends upon the availability of the energy sources, the availability of refuelling and the recharging stations, upon the availability of the energy sources, the availability of refuelling and the recharging stations, vehicle performance, fuel cell lifetime, etc. Therefore the improvement of the efficiency of conventional vehicle performance, fuel cell lifetime, etc. Therefore the improvement of the efficiency of conventional internal combustion gasoline engines and the reductions of CO2 and harmful pollutant emissions have internal combustion gasoline engines and the reductions of CO2 and harmful pollutant emissions have become more impor
become more important today [1].tant today [1].
The global population by 2030 will be nearly 8 billion [2] and its primary energy demand will cross over The global population by 2030 will be nearly 8 billion [2] and its primary energy demand will cross over 700 EJ/year [3]. Also, the fossil fuel reserves are rather limited. Therefore there is a demand for 700 EJ/year [3]. Also, the fossil fuel reserves are rather limited. Therefore there is a demand for translating the fuel into higher energy prices, which leads to fuel inflation world over. In addition, our translating the fuel into higher energy prices, which leads to fuel inflation world over. In addition, our world is facing serious challenges such as environmental degradation and climate change, which are world is facing serious challenges such as environmental degradation and climate change, which are reportedly caused by the emissions of the petroleum fuelled vehicles. In order to control and arrest this reportedly caused by the emissions of the petroleum fuelled vehicles. In order to control and arrest this environmental damage, stringent emission norms have been adopted worldwide and they are becoming environmental damage, stringent emission norms have been adopted worldwide and they are becoming more and more stringent with time. Therefore to avoid the rapid depletion of fuel reserves, to slow down more and more stringent with time. Therefore to avoid the rapid depletion of fuel reserves, to slow down the increase in fuel prices and for stringent emission norm compliance, researchers worldwide are the increase in fuel prices and for stringent emission norm compliance, researchers worldwide are exploring alternate fuel options for running vehicles. These alternate fuels can be adopted in current exploring alternate fuel options for running vehicles. These alternate fuels can be adopted in current generation engines with minimal hardware modifications. Several alternative fuel candidates such as generation engines with minimal hardware modifications. Several alternative fuel candidates such as
biodiesel, compressed natural
biodiesel, compressed natural gas (CNG), gas (CNG), ethanolethanol, , hyhydrogen, drogen, hydrogen-Chydrogen-CNG NG mixtures (mixtures (HCNG),straighHCNG),straightt vegetable
vegetable oils (SVO), loils (SVO), liquefied iquefied petroleum gas petroleum gas (LPG) h(LPG) have been inave been investigated for thvestigated for their engineir enginee performance in or
performance in order to assess their technical feasibility in cder to assess their technical feasibility in current generation engines.urrent generation engines.
In a quest of running the internal combustion engines with improved thermal efficiency and lower In a quest of running the internal combustion engines with improved thermal efficiency and lower emissions, hydrogen has emerged as a prominent alternate fuel candidate with ultra-low emission emissions, hydrogen has emerged as a prominent alternate fuel candidate with ultra-low emission potential due
potential due to its eto its extremely clean emission xtremely clean emission spectrum. Compared to ospectrum. Compared to o ther fuels such ther fuels such as gasoline, das gasoline, d iesel,iesel, compressed natural gas (CNG), biodiesel etc., hydrogen has numerous advantages as an alternate compressed natural gas (CNG), biodiesel etc., hydrogen has numerous advantages as an alternate transportation fuel such as it can
transportation fuel such as it can be produced using various be produced using various renewable primary energy sources from waterrenewable primary energy sources from water (through electrolysis), from coal and biomass (through gasification), from natural gas (using steam (through electrolysis), from coal and biomass (through gasification), from natural gas (using steam methane reforming and various other ways) [4]. It does not contain carbon, hence does not emit any methane reforming and various other ways) [4]. It does not contain carbon, hence does not emit any greenhouse gas upon combustion. Hydrogen has higher calorific value resulting in more power output greenhouse gas upon combustion. Hydrogen has higher calorific value resulting in more power output upon combustion, higher auto-ignition temperature, low ignition energy, higher diffusivity and higher upon combustion, higher auto-ignition temperature, low ignition energy, higher diffusivity and higher flame propagation speed compared to gasoline. In addition to several advantages, hydrogen has few flame propagation speed compared to gasoline. In addition to several advantages, hydrogen has few disadvantages and limitations also. Due to very small ignition energy required to initiate combustion, disadvantages and limitations also. Due to very small ignition energy required to initiate combustion, chances of backfire and pre-ignition is higher in hydrogen fuelled engines. Density of hydrogen is very chances of backfire and pre-ignition is higher in hydrogen fuelled engines. Density of hydrogen is very low; therefore significantly larger volume of hydrogen is required compared to conventional fuel for the low; therefore significantly larger volume of hydrogen is required compared to conventional fuel for the same vehicle range. Among these, pre-ignition and backfire remain the biggest challenges for same vehicle range. Among these, pre-ignition and backfire remain the biggest challenges for commercialization of hy
commercialization of hydrogen engine. drogen engine. Researchers havResearchers have used several induction technie used several induction techniques, injectionques, injection strategies, and water induction in the intake manifold for hydrogen fuelled engine to eliminate/ control strategies, and water induction in the intake manifold for hydrogen fuelled engine to eliminate/ control engine backfire. For controlling NOx emissions, EGR and/or water injection into the intake manifold has engine backfire. For controlling NOx emissions, EGR and/or water injection into the intake manifold has been successfully attempt
been successfully attempted. Sustainability wited. Sustainability wit h regard h regard to internal coto internal co mbustion engines is mbustion engines is strongly linkedstrongly linked to the fuels burnt and the overall efficiency. Laser ignition can enhance the combustion process and to the fuels burnt and the overall efficiency. Laser ignition can enhance the combustion process and minimize pollutant formation. This paper is on laser ignition of sustainable fuels for future internal minimize pollutant formation. This paper is on laser ignition of sustainable fuels for future internal combustion engines. Ignition is the process of starting radical reactions until a self-sustaining flame has combustion engines. Ignition is the process of starting radical reactions until a self-sustaining flame has developed. In technical appliances such as internal combustion engines, reliable ignition is necessary for developed. In technical appliances such as internal combustion engines, reliable ignition is necessary for adequate system performance. Ignition strongly affects the formation of pollutants and the extent of fuel adequate system performance. Ignition strongly affects the formation of pollutants and the extent of fuel conversion [5].
conversion [5].
2. Literature Survey: 2. Literature Survey:
The conventional engine has been modified with a view to conduct feasibility Experiments using laser The conventional engine has been modified with a view to conduct feasibility Experiments using laser ignition [6]. The engine has been modified replacing the conventional spark plug by a window installed ignition [6]. The engine has been modified replacing the conventional spark plug by a window installed into a cylindrical mount. The position of the focusing lens inside the mount can be charged to allow into a cylindrical mount. The position of the focusing lens inside the mount can be charged to allow variations of the location of the initial optical breakdown. It has been observed that Compared to variations of the location of the initial optical breakdown. It has been observed that Compared to conventional spark plug ignition, laser ignition reduces the fuel consumption by several per cents. conventional spark plug ignition, laser ignition reduces the fuel consumption by several per cents. Exhaust emissions are reduced by nearly 20%. Another important question with a laser ignition system is Exhaust emissions are reduced by nearly 20%. Another important question with a laser ignition system is its reliability. It is
its reliability. It is clear that the operation of an engine causes clear that the operation of an engine causes very strong pollution within the combustionvery strong pollution within the combustion chamber. Deposits caused by the combustion process can
chamber. Deposits caused by the combustion process can contaminate the beam entrance window and thecontaminate the beam entrance window and the laser ignition system will probably fail.
laser ignition system will probably fail.
3. Background Study of Ignition in IC
3. Background Study of Ignition in IC EngineEngine 3.1.
3.1. IgnitionIgnition
Ignition is the process of starting radical reactions until a self-sustaining flame has developed. One can Ignition is the process of starting radical reactions until a self-sustaining flame has developed. One can distinguish between auto ignition, induced ignition and photo-ignition, the latter being caused by distinguish between auto ignition, induced ignition and photo-ignition, the latter being caused by photolytic g
photolytic generation of radicals.eneration of radicals. 3.2Types of Ignition
3.2Types of Ignition
A. Compression Ignition (CI) or Auto Ignition A. Compression Ignition (CI) or Auto Ignition
At certain values of temperature and pressure a mixture will ignite spontaneously, this is known as the At certain values of temperature and pressure a mixture will ignite spontaneously, this is known as the auto ignition or
auto ignition or compressicompression ion ignition.gnition. B. Induced Ignition
B. Induced Ignition
A process where a mixture, which would not ignite by it, is ignited locally by an ignition source (i.e. A process where a mixture, which would not ignite by it, is ignited locally by an ignition source (i.e. Electric spark plug, pulsed laser and microwave ignition source) is called induced ignition. In induced Electric spark plug, pulsed laser and 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, energy is deposited, leading to a temperature rise in a small volume of the mixture, where auto ignition takes place or the energy is used for the generation of radicals. In both cases subsequent flame ignition takes place or the energy is used for the generation of radicals. In both cases subsequent flame propagation occurs an
4. Conventional Sparking Plug Ignition 4. Conventional Sparking Plug Ignition Convention
Conventional spark plug ial spark plug ignition has been used for many years. For gnition has been used for many years. For ignition of a fuel-air mixture tignition of a fuel-air mixture the fuel-he fuel-air mixture is compressed and at the right moment a high voltage is applied to the electrodes of the spark air mixture is compressed and at the right moment a high voltage is applied to the electrodes of the spark plug.
plug.
4.1 Alternative ignition systems 4.1 Alternative ignition systems
In technical appliances like automatic burners and internal combustion engines, the electric spark plug In technical appliances like automatic burners and internal combustion engines, the electric spark plug has been in use for more than a century. For the ignition of especially fuel lean mixtures, alternatives to has been in use for more than a century. For the ignition of especially fuel lean mixtures, alternatives to conventional electric spark ignition systems have been devised: These are high-energy spark plugs, conventional electric spark ignition systems have been devised: These are high-energy spark plugs, plasma jet
plasma jet igniters, rail igniters, rail plug igplug igniters, tniters, torch jet orch jet igniters, and igniters, and pulsed-jet igniters, pulsed-jet igniters, exhaust gas exhaust gas recirculationrecirculation (EGR) ignition systems, laser-induced spark ignition and flame jet ig
(EGR) ignition systems, laser-induced spark ignition and flame jet ig niters.niters. 4.2 Drawback of Conventional Ignition System
4.2 Drawback of Conventional Ignition System • Location of spark plug is not
• Location of spark plug is not flexible as it requires shielding of flexible as it requires shielding of plug from immense heat and fuel Sprayplug from immense heat and fuel Spray and
and location cannlocation cannot be chosen ot be chosen optimally.optimally. • Spark plug electrodes can disturb
• Spark plug electrodes can disturb the gas flow within the combuthe gas flow within the combustion chamber.stion chamber. • It is not possible to ignite inside the fuel spray.
• It is not possible to ignite inside the fuel spray. • It requires frequent maintenance to re
• It requires frequent maintenance to re move carbon deposits.move carbon deposits. • Leaner mixtures cannot be burned, ratio b
• Leaner mixtures cannot be burned, ratio b etween fuel and air has to between fuel and air has to b e within the correct range.e within the correct range. •Degradation of electrodes at high pressure and
•Degradation of electrodes at high pressure and temperature.temperature. • Flame propagation is slow.
• Flame propagation is slow.
• Multi point fuel ignition is not feasible. • Multi point fuel ignition is not feasible. • Higher turbulence levels are required. • Higher turbulence levels are required. • Erosion of spark plug electrodes. • Erosion of spark plug electrodes. 4.3 Advantages of laser ignition
4.3 Advantages of laser ignition system.system.
Shorter ignition delay time and shorter combustion TimeShorter ignition delay time and shorter combustion Time
Exact regulation of the ignition energy deposited in the Exact regulation of the ignition energy deposited in the ignition plasmaignition plasma
Easier possibility of multipoint ignitionEasier possibility of multipoint ignition
High load/igniHigh load/ignition pressures possible thtion pressures possible that at is increase inefficiencyis increase inefficiency
Precise ignition timing possible No erosion effects as in the case of the spark plugs that is lifetimePrecise ignition timing possible No erosion effects as in the case of the spark plugs that is lifetime
of a laser ignition of a laser ignition
Absence of quenching effects by the spark plug Absence of quenching effects by the spark plug electrodeselectrodes
High load/ignition pressures possible that is High load/ignition pressures possible that is increase inefficiencyincrease inefficiency
4.4 Advantages of laser ignition over 4.4 Advantages of laser ignition over
Conventional spark ignition Conventional spark ignition
Life time of a Life time of a laser ignition system expected to blaser ignition system expected to be significantly longer than that of a spark pluge significantly longer than that of a spark plug
Leaner fuel can burn effectively because More intense spark Leaner fuel can burn effectively because More intense spark
Free choice of the ignition location wFree choice of the ignition location within the combustion chamberithin the combustion chamber
Laser ignition system could cope with aLaser ignition system could cope with a
stratified charge. stratified charge.
Flame propagation is relatively fast resulting in Flame propagation is relatively fast resulting in shorter combustion timeshorter combustion time
Easier possibility of multipoint ignitionEasier possibility of multipoint ignition
NOx emission NOx emission
Engines would produce less NOx if the
Engines would produce less NOx if they burnt more air and less y burnt more air and less fuel, but they would require the pfuel, but they would require the plugs tolugs to produce hig
produce higher energy sparks in order to her energy sparks in order to do so. Less NOx emissiondo so. Less NOx emission
5. Definition, production and characteristics of laser 5. Definition, production and characteristics of laser
The word LASER is actually an acronym for “light Amplification by Stimulated Emission of Radiation” The word LASER is actually an acronym for “light Amplification by Stimulated Emission of Radiation” [7-10].This expression can be comprehended better when the principle behind the generation of a laser [7-10].This expression can be comprehended better when the principle behind the generation of a laser radiation is understood which is illustrated schematically in Fig .1.1. All lasers are considered as optical radiation is understood which is illustrated schematically in Fig .1.1. All lasers are considered as optical amplifiers. These lasers work by pumping an active medium placed between two mirrors, one of which is amplifiers. These lasers work by pumping an active medium placed between two mirrors, one of which is partially tra
partially transmitting. The nsmitting. The active active laser laser medium medium is is a a collection of collection of specially specially selected selected atoms, atoms, molecules ormolecules or ions which can be in a solid, liquid or gaseous form and which will emit radiation as light waves when ions which can be in a solid, liquid or gaseous form and which will emit radiation as light waves when excited by the pumping action. No matter what the active laser medium consists (atoms, ions or excited by the pumping action. No matter what the active laser medium consists (atoms, ions or
absorbed energy for a very short, but random lifetime. When their life time expires, they give up their absorbed energy for a very short, but random lifetime. When their life time expires, they give up their energy in the form of a photon and return back to the former state until pumped again. The release of the energy in the form of a photon and return back to the former state until pumped again. The release of the photons in
photons in this this manner manner is called is called “Spontaneous Emission”. “Spontaneous Emission”. The photons The photons released in released in this wathis wa y travel y travel in allin all the directions in relation to the optical axis of the laser[11]. fig.1.2 if a photon collides with another the directions in relation to the optical axis of the laser[11]. fig.1.2 if a photon collides with another energized atom, etc, it causes it to release its photon prematurely and the two photons will travel along in energized atom, etc, it causes it to release its photon prematurely and the two photons will travel along in phase
phase until until the the next next collision, collision, thus thus building building a a steam steam of of photons photons of of increasing increasing density. density. This This action action ofof releasing a photon prematurely is called ‘Stimulated Emission’. Photons which do not travel parallel to releasing a photon prematurely is called ‘Stimulated Emission’. Photons which do not travel parallel to the optical axis of the laser are quickly lost from the system. Those which do travel parallel to the axis the optical axis of the laser are quickly lost from the system. Those which do travel parallel to the axis have their path length considerably extended by the optical feedback provided by the mirrors, before have their path length considerably extended by the optical feedback provided by the mirrors, before leaving the laser, through the partially transmitting mirror. This action not only servers as a
leaving the laser, through the partially transmitting mirror. This action not only servers as a n amplifier forn amplifier for photon
photon generation generation by by stimulated stimulated emission emission to to achieve achieve the the highly highly collimated collimated coherent coherent light light beam beam thatthat makes the laser so useful. Thus, in short, the principle of laser generation process involves the excitation makes the laser so useful. Thus, in short, the principle of laser generation process involves the excitation of lasing medium with external energy supply which results in spontaneous emission of photons and of lasing medium with external energy supply which results in spontaneous emission of photons and these photons oscillating along the optical axis of resonator mirrors stimulate further multiple emissions these photons oscillating along the optical axis of resonator mirrors stimulate further multiple emissions of similar energy and phase and thus get amplified. The amplified light that is the laser beam finally of similar energy and phase and thus get amplified. The amplified light that is the laser beam finally comes out of the partially transmitting mirror. fig 1.3. Hence, the laser beam is an “Electro Magnetic comes out of the partially transmitting mirror. fig 1.3. Hence, the laser beam is an “Electro Magnetic Radiation[12] “Fig 1.4. in the ultraviolet to infrared region the laser beam possess the following Radiation[12] “Fig 1.4. in the ultraviolet to infrared region the laser beam possess the following characteristics.
characteristics.
Monochromatic (single wavelength)Monochromatic (single wavelength)
Highly directional (travels long distances without beam sprHighly directional (travels long distances without beam spr eadingeading) and) and
Coherent.Coherent.
The out coming beam is focused and guided to the precise location using suitable optical systems consist The out coming beam is focused and guided to the precise location using suitable optical systems consist of lenses, mirrors etc. In contrast to laser light which is monochromatic, the ordinary light is a of lenses, mirrors etc. In contrast to laser light which is monochromatic, the ordinary light is a combination of many different wavelengths (colors). Lasers which emit light is highly directional. The combination of many different wavelengths (colors). Lasers which emit light is highly directional. The emitted light is a relatively a narrow beam which travels in specific direction. Whereas, the ordinary light emitted light is a relatively a narrow beam which travels in specific direction. Whereas, the ordinary light which is coming from the sum or a light bulb, or a candle is emitted in every direction away from the which is coming from the sum or a light bulb, or a candle is emitted in every direction away from the source.
source.
Figure.1.1 Schematic diagram showing the basic elements of laser and the generation of Laser Figure.1.1 Schematic diagram showing the basic elements of laser and the generation of Laser Radiation.
Radiation.
Figure.1.2 Schematic sketch showing the process of spontaneous emission from the excited active Figure.1.2 Schematic sketch showing the process of spontaneous emission from the excited active medium.
Figure.1.3 Schematic sketch showing the arrangement of mirrors to increase the path length for Figure.1.3 Schematic sketch showing the arrangement of mirrors to increase the path length for stimulated emission and amplification of laser power.
stimulated emission and amplification of laser power.
Figure.1.4 Electromagnetic spectrum showing the Wavelengths o
Figure.1.4 Electromagnetic spectrum showing the Wavelengths o f different lasers.f different lasers. 6. Mechanism of laser ignition
6. Mechanism of laser ignition
It is well know that short and intensive laser pulses are able to produce an “optical breakdown” in air. It is well know that short and intensive laser pulses are able to produce an “optical breakdown” in air. Necessary intensities
Necessary intensities are are in the in the range between 1range between 1 001010 to 10 to 101111W/cmW/cm2. At such intensities, gas molecules are2. At such intensities, gas molecules are dissociated and ionized within the vicinity of the focal spot of a laser beam and hot plasma is generated. dissociated and ionized within the vicinity of the focal spot of a laser beam and hot plasma is generated. This plasma is heated by the incoming laser beam and a strong shock wave occurs. The expanding hot This plasma is heated by the incoming laser beam and a strong shock wave occurs. The expanding hot plasma
plasma can can be be used used for for the the ignition ignition of of fuel-gas fuel-gas mixtures. mixtures. By By comparing comparing the the field field strength strength of of the the fieldfield between the
between the electrodes of electrodes of a spark pa spark plug and lug and the field of the field of a laser a laser pulse it pulse it should be possible should be possible to to estimate theestimate the required laser intensity for generation of an optical breakdown. The field strength reaches values in the required laser intensity for generation of an optical breakdown. The field strength reaches values in the range of approximately 3×10
range of approximately 3×1044V/cmV/cm between the electrodes of a conventional spark plug. Since the between the electrodes of a conventional spark plug. Since the intensity of an electromagnetic wave is proportional to the square of the electric field strength
intensity of an electromagnetic wave is proportional to the square of the electric field strength I I ∝∝ E E 2, one2, one can estimate that the intensity should be in the order of 2
can estimate that the intensity should be in the order of 2 ×× 101066 W/cmW/cm2, which is several orders of2, which is several orders of magnitude lower as indicated by experiments on laser ignition. The reason is that usually no free magnitude lower as indicated by experiments on laser ignition. The reason is that usually no free electrons are available within the irradiated volume. At the electrodes of a spark plug electrons can be electrons are available within the irradiated volume. At the electrodes of a spark plug electrons can be liberated by field emission processes. In contrary, ionization due to irradiation requires a “multiphoton” liberated by field emission processes. In contrary, ionization due to irradiation requires a “multiphoton” process
process where where several several photons photons hit hit the the atom atom at at nearly nearly the the same same time. time. Such Such multiphoton multiphoton ionizationionization processes
processes can can only only happen happen at at very high very high irradiation leirradiation levels vels (in (in the the order order of of 10101010to 10to 101111W/cmW/cm2) where the2) where the number of photons is extremely high. For example, nitrogen has an ionization energy of approximately number of photons is extremely high. For example, nitrogen has an ionization energy of approximately 14.5 eV, whereas one photon emitted b
14.5 eV, whereas one photon emitted b y a Nd:YAG laser hasy a Nd:YAG laser has an energy of 1.1 eV, thus
an energy of 1.1 eV, thus more than 13 photons are required for ionization of nitrogen.more than 13 photons are required for ionization of nitrogen.
The pulse energy of a laser system for ignition can be estimated by the following calculation. The The pulse energy of a laser system for ignition can be estimated by the following calculation. The diameter
diameter dd of a focused laser beam isof a focused laser beam is D=2x wf=2xM
D=2x wf=2xM22x(2x(2 λf/πd) λf/πd)..(i)..(i) Where
Where M M 22 is the beam quality, is the beam quality, FF is the focal length of the optical element andis the focal length of the optical element and D D is the diameter of theis the diameter of the laser beam with the wavelength
laser beam with the wavelength λ λ..
Now it is assumed that the laser beam irra
Now it is assumed that the laser beam irradiates a spherical volumediates a spherical volume V=4πwf
V=4πwf 33/3/3
From the thermo dynamical gas equation the number of particles
From the thermo dynamical gas equation the number of particles N Nin a volumein a volume VVisis N=pv/kt
N=pv/kt ..(ii)..(ii) With the pressure
With the pressure p p, temperature, temperature TT and Boltzmann’s constantand Boltzmann’s constant kk = = 11..3838 ×× 1010 -23-23 J/K J/K . Inside the irradiated. Inside the irradiated volume,
volume, N N molecules have to be dissociated where first the dissociation energy molecules have to be dissociated where first the dissociation energy WdWdis required and finallyis required and finally 2
2 N N atoms are atoms are ionized (ionization energyionized (ionization energy WiWi). Using known values for). Using known values for Wd Wd = 9= 9..7979 eV eV and and WiWi= 14= 14..5353 eVeV forfor nitrogen, the energy for dissociating and ionizing all p
nitrogen, the energy for dissociating and ionizing all p articles inside the volume can be articles inside the volume can be calculated ascalculated as W=
W= (πpd(πpd33/6kt) x (wd+2wt)..(iii)/6kt) x (wd+2wt)..(iii) For a spot radius of about 100
For a spot radius of about 100 μm μm the equation gives a maximum energy of approximately 1 mJ. Sincethe equation gives a maximum energy of approximately 1 mJ. Since not all particles inside the irradiated volume have to be ionized, even smaller energies should be not all particles inside the irradiated volume have to be ionized, even smaller energies should be sufficient for generation of an optical breakdown.
It is assumed that the intensity which is necessary for the generation of an optical breakdown processes is It is assumed that the intensity which is necessary for the generation of an optical breakdown processes is related to the pressure o
related to the pressure of the gas.f the gas. Iα 1/p
Iα 1/pnn ---(iv)---(iv) With
With nn =1…5 depending on the mechanism of multiphoton process. Higher pressures, like in a=1…5 depending on the mechanism of multiphoton process. Higher pressures, like in a combustion chamber should ease the ignition process what favours
combustion chamber should ease the ignition process what favours the laser induced ignition.the laser induced ignition. 7. Conclusion
7. Conclusion
Laser ignition system allows almost free choice of the ignition location within the combustion chamber, Laser ignition system allows almost free choice of the ignition location within the combustion chamber, even inside the fuel spray. Significant reductions in fuel consumption as well as reductions of exhaust even inside the fuel spray. Significant reductions in fuel consumption as well as reductions of exhaust gases show the potential of the laser ignition process. Laser i
gases show the potential of the laser ignition process. Laser i gnition is nonintrusive in nature; high energygnition is nonintrusive in nature; high energy can be rapidly deposited, has limited heat losses, and is capable of multipoint ignition of combustible 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 charges. More importantly, it shows better minimum ignition energy requirement than electric spark systems with lean and rich fuel/air mixtures. At present, a laser ignition plug is very expensive compared systems with lean and rich fuel/air mixtures. At present, a laser ignition plug is very expensive compared to a standard electrical spark plug ignition system and it is nowhere near ready for deployment. But the to a standard electrical spark plug ignition system and it is nowhere near ready for deployment. But the potential and advan
potential and advantages certainly make the laser ignition more attractivtages certainly make the laser ignition more attractive in many practical applications.e in many practical applications. Acknowledgment
Acknowledgment
I wish to express my sincere gratitude to Dr.T.V.V. Sudhakar Principal and professor, in the Department I wish to express my sincere gratitude to Dr.T.V.V. Sudhakar Principal and professor, in the Department of Mechanical Engineering Columbia institute of Engineering and Technology Raipur and Dr. Balunaik of Mechanical Engineering Columbia institute of Engineering and Technology Raipur and Dr. Balunaik Professor, Department of Mechanical Engineering JNTUH Kukatpally Hyderabad for introducing me to Professor, Department of Mechanical Engineering JNTUH Kukatpally Hyderabad for introducing me to this interesting field on Biodiesel. I am great full to them for their constant encouragement to pursue PhD this interesting field on Biodiesel. I am great full to them for their constant encouragement to pursue PhD studies at JNTUH. And thank full to the management, Director, administrator, principals and all Faculty studies at JNTUH. And thank full to the management, Director, administrator, principals and all Faculty members of VITS group of Institutions Karimnagar.
members of VITS group of Institutions Karimnagar. Reference
Reference
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