JP2007303445A - Laser ignition device and laser ignition engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To contribute to an improvement in fuel economy of an internal combustion engine and to restraint on exhaust NOx emissions, by providing an igniter ignitable at multipoints, by irradiating a laser beam into a combustion chamber from an external part of a very small optical window, in a laser ignition device and an engine having the laser ignition device. <P>SOLUTION: This ignition device has a condensing optical system 4 in an external part of the combustion chamber 3 by optically connecting the inside and the outside of the combustion chamber 3 by arranging the optical window 2 on an upper side wall of a cylinder 1, and is formed by being connected to a YAG laser generator 6 and a ruby laser generator 7, by branching off the other end of an optical fiber 5 in a bifurcated shape, by connecting the optical fiber 5 to an upstream side, and ignites an air-fuel mixture by forming a focus at a different point in the combustion chamber 3 by the condensing optical system 4 in response to a difference in a wave length of the laser beam, by respectively shooting the laser beam from the YAG laser generator 6 and the ruby laser generator 7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser ignition device in an internal combustion engine, mainly a gas combustion engine, and an engine provided with the laser ignition device.

  In a gas combustion engine, in order to improve fuel efficiency and suppress NOx generation amount, there is a demand to reduce the fuel mixture ratio of the air-fuel mixture and make the fuel gas leaner and burn in abundant air. However, since the lean mixed gas has poor ignitability, ignition by the conventional spark plug does not provide sufficient ignition performance, and misfires and abnormal combustion occur, so there is a limit to the dilution of the fuel.

  Because the spark plug must be near the wall of the combustion chamber, even if the fuel is ignited from the spark plug, the initial energy of the combustion is absorbed by the cold wall and it is not possible to maintain the energy to continue combustion. It causes abnormal combustion. In addition, since the spark plug itself is designed to dissipate heat to the outside of the combustion chamber in order to prevent the spark plug from being burned in, the flame is also cooled by the spark plug, causing a misfire.

  On the other hand, it is desirable to provide a large number of ignition points in the combustion chamber in order to burn the flame-retardant rare gas so that misfire or abnormal combustion does not occur and to improve the combustion rate and the combustion speed. However, when igniting from multiple points using a spark plug, it is necessary to insert spark plugs corresponding to the number of ignition points, and it is difficult to increase the number of ignition points due to difficulty in arrangement in the cylinder.

  Therefore, as a method of igniting a plurality of ignition points separated from the wall surface in the combustion, a technique of applying a laser ignition device that ignites by absorbing the energy of laser light introduced into the combustion chamber into the fuel gas has been devised. For example, in Patent Document 1, a fly-eye type lens in which microlenses are integrated in an optical window for introducing laser light into a combustion chamber is installed, and the laser light irradiated on the optical window is divided into a plurality of light fluxes. A laser-type multi-point ignition device that focuses on a plurality of points is disclosed.

  As shown in FIG. 5, the laser-type multipoint ignition device disclosed in Patent Document 1 expands a laser beam irradiated from a laser source and introduced by an optical fiber or the like with an expander lens, and a condensing lens and a collimating lens. Then, the microlens array is irradiated with the collimated light having a predetermined diameter. The microlens array has a shape in which small-diameter microlenses are integrated, and the irradiated laser light is divided into a plurality of light beams corresponding to the number of microlenses, and each focuses on the combustion chamber to form a mixture. Ignite.

  According to the invention disclosed in Patent Document 1, a point at an arbitrary depth in the combustion chamber can be ignited by appropriately selecting the focal length of the microlens, so that the combustion energy is absorbed by the wall surface of the combustion chamber. And combustion can be reliably maintained. In addition, since it is possible to ignite multiple points from one optical window, the ignitability can be improved.

However, in the disclosed invention, the focal position is limited to a position directly below the optical window. Therefore, in order to disperse the ignition point over a wide range in the combustion chamber, it is necessary to make the aperture of the optical window very large. there were.
Japanese Patent Laying-Open No. 2005-147109

  The problem to be solved by the present invention is to provide a laser ignition device and an ignition device capable of performing multi-point ignition by irradiating laser light into the combustion chamber from the outside of a very small optical window in an engine equipped with the laser ignition device. In other words, it contributes to improvement of fuel consumption of the internal combustion engine and suppression of exhaust NOx.

  In order to solve the above problems, a laser ignition device according to the present invention is a laser ignition device that focuses laser light emitted from a laser generation system into a combustion chamber of an internal combustion engine and ignites an air-fuel mixture. It has a condensing lens system, and the laser generation system emits laser light having two or more different wavelengths, and the laser light emitted from the laser generation system is emitted into the combustion chamber according to the wavelength difference by the condensing lens system. The light is condensed at different points and the mixture is ignited.

  The laser generation system can be configured by combining two or more different generation devices such as a ruby laser generation device, a YAG laser generation device, and a wavelength tunable laser generation device. The laser light emitted from each laser generator is merged while being introduced by an optical fiber or a laser transmission tube, or the end portions of the optical fiber or laser transmission tube are bundled to form a condensing lens as one light beam. Irradiate the system.

  The condensing lens system is configured by incorporating optical lenses such as an expansion lens, a collimating lens, and a condensing lens in the laser optical path as necessary, and is formed so as to have a specific focal point in the entire system. A laser generation system is installed upstream of the condensing lens system, and a combustion chamber is located downstream through an optical window. The condensing lens system may be installed on the cylinder head in the same manner as the conventional spark plug, or may be installed so that the optical window opens on the upper side wall of the cylinder.

Since the refractive index of optical glass varies depending on the wavelength, and the focal length of the condensing lens depends on the wavelength of the irradiating light, the laser light with different wavelengths irradiated to the condensing lens system varies depending on the wavelength in different positions in the combustion chamber. Form a focus on. Therefore, in the laser light ignition device of the present invention, two or more focal points are formed by irradiating the condensing lens system with laser light having two or more wavelengths from the laser generation system and condensing it into the combustion chamber. It is characterized by multi-point ignition to the air-fuel mixture from the ignition point.

As described above, in the laser ignition device of the present invention, the air-fuel mixture can be ignited from multiple points, so that even fuel with poor ignitability can be reliably burned. Therefore, the lean limit of the air-fuel ratio can be improved, the fuel consumption of the internal combustion engine can be improved, and the exhausted NOx amount can be reduced.
As an example, when a YAG laser and a ruby laser are used, the wavelengths of the generated laser light are 1064 nm and 600 nm, respectively. For example, when a condensing lens formed of a material having a reference focal length of 100 mm is used, the difference in focal length is 2.5 mm.

  Moreover, in the laser ignition device of the present invention, it is not necessary to provide a plurality of ignition devices because multipoint ignition can be performed by providing one set of a condensing lens system and an optical window. Furthermore, since the condensing lens system only needs to have a diameter necessary for guiding and condensing the irradiated laser light, the condensing lens system and the optical window can have a very small aperture. it can. Therefore, when the laser ignition device of the present invention is mounted on an engine, the volume occupied by the ignition device in the cylinder can be made very small, and more space can be taken up by other devices such as intake and exhaust valves. The engine efficiency can be improved.

  In the laser ignition device of the present invention, since the wavelength dependence of the focal length of the condenser lens is utilized, it is desirable that the difference in wavelength of the irradiation laser light is large. For this reason, a plurality of laser generators having different laser generation mechanisms may be provided. For example, a wavelength conversion system using a nonlinear crystal is provided, and the fundamental wave generated from the laser generator is converted into a harmonic by the wavelength conversion system. At the same time, the condenser lens system can be irradiated.

  As an example, when the fundamental wave and the third harmonic of a YAG laser are used, the wavelength difference can be increased to 1064 nm and 355 nm, respectively, and the difference in focal position can be increased. When using a condensing lens made of a material with a reference focal length of 100 mm, the difference in focal length when using the fundamental wave of the YAG laser and the third harmonic is 5.8 mm, and the YAG laser and the ruby laser are The distance between the focal positions can be made larger than when it is used. Therefore, the effect of multipoint ignition can be ensured more reliably. Furthermore, when a wavelength conversion system is provided, the laser generation system can be configured with a single laser generator, so that installation costs and maintenance costs can be reduced.

  Furthermore, the distance between focal positions can be further increased by using an aspheric lens adjusted to increase the difference in focal length.

  Hereinafter, a laser ignition device and a laser ignition type engine of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic view of a laser ignition device in one embodiment of the present invention. An optical window 2 is provided on the upper side wall of the cylinder 1 to optically communicate the inside and outside of the combustion chamber 3. A condensing optical system 4 is provided outside the combustion chamber 3 separated by the optical window 2. Further, an optical fiber 5 is connected upstream of the condensing optical system 4, and the other end of the optical fiber 5 is bifurcated and connected to the YAG laser generator 6 and the ruby laser generator 7.

  FIG. 2 is an enlarged cross-sectional view of the condensing optical system 4. An extension lens 10 is disposed at the end portion of the optical fiber 5, and a collimating lens 11 and a condensing lens 12 are sequentially installed. Further downstream, the optical window 2 is connected.

In the laser ignition device of this embodiment, Y is set in accordance with the ignition timing of the engine.
Laser light is generated from the AG laser generator 6 and the ruby laser generator 7 and is incident on the optical fiber 5. The respective laser beams are combined in the optical fiber 5 and are irradiated onto the condensing optical system 4 as one light beam. The laser light reaching the condensing optical system 4 is widened by the expansion lens 10 and enters the collimating lens 11, is adjusted to a substantially parallel light beam, and enters the condensing lens 12.

  The condensing lens 12 condenses the laser light at different focal positions corresponding to the wavelengths of the two types of incident laser light, and forms two focal points 8 and 8 ′ in the combustion chamber 3 through the optical window 2. . Since the air-fuel mixture is filled in the combustion chamber 3 at the ignition timing, the laser light condensed in the combustion chamber 3 gives energy to the air-fuel mixture at each condensing position to generate a high temperature, and the air-fuel mixture becomes 2 Burn from the point.

  As described above, in the laser ignition device of the present embodiment, it is possible to perform multipoint ignition on the air-fuel mixture in the combustion chamber 3 only by providing the single condensing optical system 4 and the optical window 2. Therefore, the lean air-fuel mixture can be reliably ignited with a compact structure.

  The YAG laser generated by the YAG laser generator 5 has a wavelength of 1064 nm, and the ruby laser generated by the ruby laser generator 6 has a wavelength of 600 nm. When the focal length of the condensing lens 12 formed of a certain material provided in the condensing optical system 4 is 100 mm based on a light beam having a wavelength of 633 nm, it is about 102.4 mm for the YAG laser and about Ruby laser. Has a focal length of about 99.9 mm. Therefore, when the laser ignition device of the present embodiment is applied to a cylinder of about 200 mmφ to provide an ignition point at the center of the cylinder, the distance between the two ignition points is about 2.5 mm.

  FIG. 3 is a schematic view of a laser ignition device in the present embodiment. An optical window 2 is provided in the cylinder head 20, and a condensing optical system 4 is disposed above the optical window 2. An optical fiber 5 is connected upstream of the condensing optical system 4, and a YAG laser generator 6 is provided at the other end of the optical fiber 5. Further, a two-stage nonlinear crystal 21 is inserted into the optical fiber 5.

  FIG. 4 shows a conceptual diagram showing the arrangement of the nonlinear crystal of this example. LiB3O5 (LBO) is used as the non-linear crystal. For the second harmonic (SHG / Second Harmonic Generation) crystal 30 and the third harmonic (THG / Third Harmonic Generation) crystal 31, respectively, the wavelength of input / output light and those wavelengths The crystal length, cut angle, etc. are appropriately adjusted according to the refractive index.

  In the laser ignition device of the present embodiment, when a YAG laser fundamental wave having a wavelength of 1064 nm is oscillated from the YAG laser generator 6, a part of the fundamental wave is converted into a second harmonic wave having a wavelength of 532 nm by the second harmonic crystal 30. It enters the third harmonic crystal 31 together with the fundamental wave remaining without being converted. In the third harmonic crystal 31, a third harmonic wave having a wavelength of 355 nm, which is the sum frequency, is generated by the fundamental wave and the second harmonic wave, and the condensing optics together with the fundamental wave and the second harmonic wave that remain without being converted. It enters the system 4. The three kinds of lasers incident on the condensing optical system 4 are condensed by the condensing optical system 4 at different focal positions in the combustion chamber 3 according to the respective wavelengths, and the mixture is ignited at the three focal points 8. .

  Therefore, in the laser ignition device of the present embodiment, three ignition points can be formed only by providing one laser generator. Further, for example, since a larger wavelength difference can be obtained than when using a YAG laser and a ruby laser, the distance between focal positions can be further increased.

  In the present embodiment, since the laser ignition device is provided in the space where the spark plug is installed in the conventional cylinder, the laser light is condensed in the depth direction of the combustion chamber 3. When the piston is at the top dead center, the depth of the combustion chamber 3 becomes very small. Therefore, the focal length of the condensing optical system 4 has to be reduced, and the focal position relative to the wavelength difference of the laser beam is proportional to this. The difference is also reduced.

  However, in the laser ignition device of the present embodiment, since the difference in focal length can be further increased by utilizing the harmonics, even if the focal length of the condensing optical system 4 is small, a sufficient focal position difference can be obtained. It can be ensured, and the certainty of ignition by multipoint ignition can be sufficiently secured.

  As described above in detail, the laser ignition device of the present embodiment can ignite the air-fuel mixture from multiple points, so that even fuel with poor ignitability can be reliably burned. Therefore, the lean limit of the air-fuel ratio can be improved, the fuel consumption of the internal combustion engine can be improved, and the exhausted NOx amount can be reduced.

  Further, in the laser ignition device of the present embodiment, it is not necessary to provide a plurality of ignition devices because multipoint ignition can be performed by providing one set of the condenser lens system and the optical window. Furthermore, since the condensing lens system only needs to have a diameter necessary for guiding and condensing the irradiated laser light, the condensing lens system and the optical window can have a very small aperture. it can. Therefore, when the laser ignition device of this embodiment is mounted on an engine, the volume occupied by the ignition device in the cylinder can be made very small, and more space can be taken up by other devices such as intake and exhaust valves. The engine efficiency can be improved.

It is a schematic sectional drawing of the laser ignition device in one Example of this invention. It is an expanded sectional view of the condensing optical system 4 of a present Example. It is the schematic of the laser ignition apparatus in the 2nd Example of this invention. It is a conceptual diagram showing arrangement | positioning of the nonlinear crystal in a 2nd Example. It is a schematic sectional drawing of the conventional laser ignition device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Optical window 3 Combustion chamber 4 Condensing optical system 5 Optical fiber 6 YAG laser generator 7 Ruby laser generator 8, 8 'Focus 10 Expansion lens 11 Collimating lens 12 Condensing lens 20 Cylinder head 21 Non-linear crystal 30 2nd Harmonic crystal 31 Third harmonic crystal

Claims (6)

  A laser ignition device for condensing laser light emitted from a laser generation system in a combustion chamber of an internal combustion engine and igniting an air-fuel mixture, comprising a pair of condensing lens systems, wherein the laser generation system includes two or more laser generation systems Laser light having different wavelengths is emitted, and the laser light emitted from the laser generation system is condensed to different points in the combustion chamber according to the difference in wavelength by the condensing lens system to form an air-fuel mixture Laser ignition device characterized by igniting.   The laser generation system includes a laser generator and a wavelength conversion element made of a nonlinear crystal, and the laser generation system outputs a fundamental wave emitted from the laser generation apparatus and a harmonic whose frequency is multiplied by the wavelength conversion element. The laser ignition device according to claim 1, wherein:   The laser ignition device according to claim 2, wherein the laser generator generates a YAG laser.   4. The laser ignition device according to claim 1, wherein the condensing lens system is provided in a cylinder head portion.   4. The laser ignition device according to claim 1, wherein the condensing lens system is disposed on a side wall of the combustion chamber. A laser ignition engine comprising the laser ignition device according to any one of claims 1 to 5.

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