JP2008025378A - Laser ignition device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser ignition device having a structure wherein flexibility in a lens-mounting position is high and a laser beam-emitting window is hard to damage. <P>SOLUTION: The laser ignition device includes a laser light-source 11 for emitting the laser beam 20, a lens-barrel 12 having one end connected to the laser light-source 11 and the other end connected to a combustion chamber 9 of an engine, a laser emitting window 13 provided at one end of the combustion chamber 9 side of the lens-barrel 12, a lens 14 arranged in the lens-barrel 12 so as to condense the laser beam 20 in the combustion chamber 7. The lens 14 is composed of an optically isotropic ceramic. The lens 14 has improved translucency and improved thermal resistance, thus the lens 14 can be mounted in the vicinity of the combustion chamber exposed to high temperature. Further, the window for emission of the laser beam is effectively prevented from being damaged, because concentration of high-density energy to the laser-emission window can be avoided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser ignition device applied to an internal combustion engine, and more specifically to a laser ignition device used for an internal combustion engine for automobiles, power generation and the like.

  Conventionally, gasoline engines and diesel engines are known as typical internal combustion engines, but the former has a clean exhaust gas but is inferior in fuel efficiency, and the latter is excellent in fuel efficiency, but NOx, particulate matter (PM), etc. There was a problem of a large amount of harmful substance emissions. Therefore, from the viewpoint of protecting the global environment and preventing global warming, “premixed compression ignition technology”, which achieves a low fuel consumption and clean exhaust gas engine, is highly focused on self-ignition by highly compressing the air-fuel mixture. Yes. However, since the premixed compression ignition type engine has the disadvantage that the ignition is unstable, various ignition means for promoting ignition combustion have been proposed.

  Laser ignition, which is one of them, focuses high-power laser pulses at a focal point by a lens and ignites them using plasma generated at the focal point as a starting point. Compared with a spark plug conventionally used in a gasoline engine, laser ignition has advantages that ignition performance is not deteriorated even at a high compression ratio, and that ignition can be performed at an arbitrary position in the combustion chamber by adjusting the focal position. Furthermore, there is an advantage that it is not a source of electrical noise and there is no short circuit due to attached dirt. Therefore, in recent years, technological development relating to laser ignition has been advanced.

Since the laser device used for laser ignition is a precision instrument, it is desirable to install it at a position as far away from the engine as possible so as to avoid high temperature and vibration, and irradiate the combustion chamber with laser light transmitted through a fiber. However, since the pulse power required for ignition is high energy of mJ (millijoule) or more, it is actually difficult to transmit the fiber. Thus, a type of laser ignition device that is directly attached to the engine is known. (For example, refer to Patent Document 1).
JP-A-9-303244

  However, since the optical glass lens used in the conventional laser ignition device has low heat resistance, it is installed not at the vicinity of the combustion chamber where the temperature is very high but at a relatively low temperature. In other words, it is necessary to install the combustion chamber so as to be separated from the portion that is actually ignited, and the degree of freedom of the lens installation position is relatively small. In addition, in order to prevent the lens from being contaminated by the combustion gas generated in the combustion chamber, the space where the lens is installed is separated from the combustion chamber, and the laser light emitted from the laser light source is transmitted into the combustion chamber. A window is provided. The window itself needs to be provided at a position exposed to a high temperature so that the attached dirt is burned out in order to prevent a decrease in laser light transmittance. As a result, a distance is generated between the lens and the window, and the window is installed at a position relatively close to the focal point between the lens and the focal point (ignition point) in the combustion chamber. Therefore, the spot diameter of the laser beam when passing through the window is smaller than the spot diameter when being focused by the lens. In other words, there is a possibility that the energy density of the laser light at the time of passing through the window becomes high and the window is damaged. When the characteristics of the laser light are the same, the diameter of the laser light at the focal point (focal diameter) is inversely proportional to the focal length and the diameter of the laser light incident on the lens. In order to solve the above problems, it is conceivable to use a lens having a long focal length. However, if a lens having a long focal length is used, the energy density at the focal point cannot be increased, and the plasma generation property, and consequently Decreases ignitability. Further, in order to reduce the focal diameter using a lens having a long focal length, it is necessary to widen the diameter of the laser beam in advance using another lens, which leads to an increase in the number of parts and, consequently, an increase in cost.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a laser ignition device having a structure in which the degree of freedom of the lens installation position is high and the laser light irradiation window is hardly damaged. To do.

  In order to achieve the above object, a laser ignition device according to claim 1 is provided between a laser generating mechanism that emits laser light, the laser generating mechanism and a combustion chamber of an internal combustion engine, and the combustion chamber and the outside air. A laser beam irradiation window for emitting the laser beam into the combustion chamber, and an optical path of the laser beam between the laser generation mechanism and the laser beam irradiation window, and the laser beam And a lens that collects the light at the focal point in the combustion chamber, and the lens is made of an optically isotropic ceramic.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the lens also serves as the laser light irradiation window.

  Furthermore, a laser ignition device according to claim 3 is characterized in that, in addition to the configuration of the invention according to claim 1 or 2, the lens is made of YAG (yttrium aluminum garnet).

  In the laser ignition device according to the first aspect, the lens for condensing the laser beam and igniting the air-fuel mixture in the combustion chamber is made of an optically isotropic ceramic. Optically isotropic materials are desirable as lens materials because of their high transparency. In addition, since the lens is made of ceramics, it has excellent heat resistance and can be installed near the combustion chamber rather than a general optical lens. That is, the degree of freedom of the lens installation position, and thus the degree of freedom of design of the laser ignition device can be improved. Further, since the lens can be brought closer to the combustion chamber, that is, the laser light irradiation window, even when the laser light is collected by the lens, the spot diameter at the time of entering the laser light irradiation window is not reduced so much. Therefore, it is possible to avoid high-density energy from being concentrated on the laser light irradiation window, and it is possible to effectively suppress damage to the laser light irradiation window.

  Further, if the lens is made of ceramics, the material cost can be kept lower than when a single crystal bulk material is used as a material. Furthermore, it is possible to reduce the polishing cost by making the shape close to the lens during the molding of the ceramic.

  In the invention according to claim 2, the lens also serves as the laser irradiation window. As a result, the configuration can be further simplified, and the number of assembly steps and costs can be reduced by reducing the number of parts.

  In recent years, various transparent ceramic materials have been developed. Of these, ceramic YAG (yttrium aluminum garnet) is an aggregate of cubic YAG microcrystals, and therefore is an optically isotropic material and has high light transmittance. In general, a lens material is required to have a high refractive index and a small wavelength dependency of the refractive index in addition to a high light transmittance. The refractive index of YAG is 1.82, which is about the same as that of a high-refractive-index optical glass lens used for practical use. In the present invention, since the lens is used for condensing monochromatic laser light, it is not necessary to consider the wavelength dependence of the refractive index of the lens material. In addition to these, YAG is superior in heat resistance compared to optical glass, and YAG is suitable as a lens material for a laser ignition device. Conventionally, ceramics are inferior to single crystals in terms of quality, but now, with the establishment of a production process, it is possible to produce high-quality transparent YAG ceramics comparable to single crystal bulk bodies. Therefore, by forming the condensing lens with transparent YAG ceramics as in the invention according to claim 3, it is possible to design a laser ignition device including a high-quality lens while suppressing the manufacturing cost.

  Embodiments of a laser ignition device embodying the present invention will be described below with reference to the drawings.

<First Embodiment>
Hereinafter, a first embodiment of the laser ignition device according to the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view showing a schematic configuration when the laser ignition device 10 according to the first embodiment is mounted on a port injection type engine 1. FIG. 2 is a cross-sectional view of the laser ignition device 10 along the optical axis.

  As shown in FIG. 1, the engine 1 mainly includes a cylinder head 2, a cylinder block 3, and a piston 4 that reciprocates in the cylinder block 3. A space surrounded by the cylinder head 2, the cylinder block 3, and the piston 4 is a combustion chamber 9. The cylinder head 2 includes an intake port 5 that is an intake flow path, an intake valve 6 that opens and closes the intake port 5, an exhaust port 7 that is an exhaust flow path, an exhaust valve 8 that opens and closes the exhaust port 7, and the like. Yes. A fuel injection valve (not shown) for injecting fuel is provided in the intake port 5. The laser ignition device 10 is installed in the cylinder head 2 of the engine 1.

  As shown in FIG. 2, the laser ignition device 10 includes a laser light source 11, a lens barrel 12, a laser light irradiation window 13, and a lens 14.

  The laser light source 11 that emits laser light is not particularly limited, but a laser diode-excited solid laser is preferably used from the viewpoint of efficiency and output. As the laser medium, a material such as Nd: YAG or Yb: YAG which is excellent in stability and durability is preferable. Moreover, it is preferable that the laser pulse emission timing is controlled by the control of the active Q switch or by combining the excitation light control and the passive Q switch. The laser light source 11 corresponds to a “laser generation mechanism”.

  The lens barrel 12 is a cylindrical housing having one end connected to the laser light source 11 and the other end connected to the combustion chamber 9. The lens barrel 12 supports the lens 14 in the cylinder, and the laser beam 20 penetrates through the inside thereof. 11 to reach the combustion chamber 9. Although the material of the lens barrel is not particularly limited, it is preferable to use a metal having excellent heat resistance such as SUS304 in consideration of being installed in the vicinity of the combustion chamber.

  One end of the barrel 12 on the combustion chamber 9 side is open facing the combustion chamber 9, and the laser beam penetrating the barrel 12 is sealed at the opening from the outside air in the barrel. A laser beam irradiation window 13 for injecting 20 into the combustion chamber 9 is provided. Further, since the surface of the laser beam irradiation window 13 on the combustion chamber 9 side is directly exposed to the combustion atmosphere, dirt easily adheres with combustion gas or the like. Therefore, since the laser beam irradiation window 13 is provided at a sufficiently high temperature so that the dirt is burned out, heat resistance is required. Therefore, the material for the laser light irradiation window 13 is preferably a material having translucency and excellent heat resistance. Examples of suitable materials include ion crystalline materials such as translucent alumina, sapphire, and transparent YAG.

  The lens 14 irradiates the laser light 20 in the lens barrel 12 so that the laser light 20 penetrating the lens barrel 12 from the laser light source 11 is condensed at a desired position in the combustion chamber 9 through the laser light irradiation window 13. It is installed on the street. The lens 14 is made of an optically isotropic ceramic. Optically isotropic materials have high transparency, and ceramics are excellent in heat resistance, and therefore are suitable as lens materials. More preferably, it is composed of transparent YAG ceramics that are particularly excellent in both translucency and heat resistance.

  Next, the operation of the laser ignition device 10 according to the present embodiment configured as described above will be described. As shown in FIG. 2, when the laser light source 11 emits the laser light 20 at a desired pulse timing, the laser light 20 passes through the inside of the lens barrel 12 connected to the laser light source 11 and is supported in the lens barrel 12. The light enters the lens 14. The lens 14 focuses the incident laser beam 20 on the focal point 30 in the combustion chamber 9 through the laser beam irradiation window 13 provided at one end of the barrel 12 on the combustion chamber 9 side. On the other hand, as shown in FIG. 1, the air-fuel mixture formed by mixing the fuel injected from the fuel injection valve in the intake port 5 and the intake air is supplied into the combustion chamber 9 via the intake valve 6. Has been. At the focal point in the combustion chamber 9, the condensed laser beam 20 generates plasma in a part of the air-fuel mixture, whereby the air-fuel mixture can be ignited and burned.

  As described above, in the laser ignition device 10 of this embodiment, the heat resistance of the lens 14 is improved by configuring the lens 14 with an optically isotropic ceramic. As a result, the distance between the laser light irradiation window 13 and the lens 14 exposed to a high temperature can be shortened. That is, the degree of freedom of the installation position of the lens 14 is improved. Furthermore, since the increase in the energy density of the laser beam 20 at the time of incidence on the laser beam irradiation window 13 can be suppressed, the risk of damage to the laser beam irradiation window 13 can be reduced.

  Further, since the lens 14 is made of ceramics, the cost can be reduced as compared with a case where a single crystal bulk body is used as a material. In particular, when the lens 14 is made of transparent YAG ceramics, it is possible to obtain an apparatus including a high-quality lens having excellent translucency and heat resistance while suppressing cost.

<Second Embodiment>
Next, a laser ignition device 40 according to the second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view of the laser ignition device 40 along the optical axis. Hereinafter, with reference to FIG. 3, a configuration different from the first embodiment will be mainly described in the present embodiment. The schematic cross-sectional view when the laser ignition device 40 of this embodiment is mounted on the port injection type engine 1 is the same as FIG.

  As shown in FIG. 3, the laser ignition device 40 includes a laser light source 11 and a lens barrel 12 as in the first embodiment. On the other hand, unlike the first embodiment, the lens 14 also serves as the laser light irradiation window 13. That is, only the lens 14 is provided in the opening of the barrel 12 on the combustion chamber 9 side.

  The lens 14 is made of an optically isotropic ceramic, as in the first embodiment. More preferably, it is made of transparent YAG ceramics having high translucency and heat resistance. In the configuration of the present embodiment, the surface of the lens 14 on the combustion chamber 9 side is exposed to an extremely high temperature, but the transparent YAG ceramic has sufficient heat resistance.

  The operation of the laser ignition device 40 according to the second embodiment configured as described above will be described.

  As shown in FIG. 3, when the laser light source 11 emits the laser light 20 at a desired pulse timing, the laser light 20 passes through the inside of the lens barrel 12 connected to the laser light source 11 and is on the combustion chamber 9 side of the lens barrel 12. Is incident on a lens 14 provided at one end of the lens. The lens 14 focuses the incident laser beam 20 on the focal point 30 in the combustion chamber 9 and generates plasma in a part of the air-fuel mixture. With this plasma, the air-fuel mixture supplied into the combustion chamber 9 can be ignited and burned.

  As described above, in the laser ignition device 40 of the second embodiment, the lens 14 functions as a window that separates the combustion chamber 9 from the outside air and transmits the laser light 20 and also burns the laser light 20. It plays a role of collecting light in the chamber 9. That is, the laser beam irradiation window 13 of the first embodiment is omitted. Therefore, the configuration can be further simplified and the number of assembling steps and costs can be reduced by reducing the number of parts. In particular, when the lens 14 is made of transparent YAG ceramics, it is possible to obtain an apparatus including a high-quality lens having excellent translucency and heat resistance while suppressing cost.

  The configurations of the laser ignition devices shown in the first and second embodiments are examples, and it goes without saying that the present invention can be modified in various ways.

  For example, in the first and second embodiments, the laser ignition device according to the present invention is mounted on a port injection type engine, but the present invention can also be applied to other engines such as an in-cylinder injection type engine. In the first and second embodiments, the laser ignition device according to the present invention is provided in the vicinity of the top of the combustion chamber. However, the above configuration is an example, and the laser ignition device may be arranged at another position facing the combustion chamber. Is possible.

  In the first and second embodiments, the lens barrel 12 is provided between the laser light source 11 and the combustion chamber 9. However, the laser light 20 is condensed in the combustion chamber 9 by the lens 14. It only has to be. Thus, for example, the laser light 20 can be transmitted using an optical transmission tube or an optical fiber.

It is sectional drawing which shows schematic structure at the time of mounting the laser ignition apparatus 10 which concerns on 1st Embodiment to the port injection type engine. It is sectional drawing along the optical axis of the laser ignition apparatus 10 which concerns on 1st Embodiment. It is sectional drawing along the optical axis of the laser ignition apparatus 40 which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder head 3 Cylinder block 4 Piston 5 Intake port 6 Intake valve 7 Exhaust port 8 Exhaust valve 9 Combustion chamber 10 Laser ignition device 11 Laser light source 12 Lens tube 13 Laser beam irradiation window 14 Lens 20 Laser beam 30 Focus 40 Laser ignition apparatus

Claims (3)

A laser generating mechanism for emitting laser light;
A laser beam irradiation window provided between the laser generating mechanism and a combustion chamber of the internal combustion engine, isolating the combustion chamber and outside air, and emitting the laser beam into the combustion chamber;
A lens provided on an optical path of the laser light between the laser generating mechanism and the laser light irradiation window, and condensing the laser light at a focal point in the combustion chamber;
A laser ignition device comprising:
A laser ignition device, wherein the lens is made of an optically isotropic ceramic.   The laser ignition device according to claim 1, wherein the lens also serves as the laser light irradiation window. 3. The laser ignition device according to claim 1, wherein the lens is made of YAG (yttrium aluminum garnet).

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