JP6848337B2 - Laser device, ignition device, and internal combustion engine - Google Patents

Description

The present invention relates to a laser device, an ignition device, and an internal combustion engine.

There is a laser ignition method as one method of igniting a predetermined ignition target such as a flammable gas. The laser ignition method is a method in which a pulsed laser is focused in an ignition target and plasma is generated by breakdown (dielectric breakdown) to ignite the ignition target. The laser ignition method is being researched and developed as an ignition method that replaces the plug ignition method that utilizes the discharge phenomenon between electrodes.

For example, a concave lens that diffuses the laser beam output from the resonator is arranged between the resonator that outputs the pulsed laser beam due to the resonance of the light and the convex lens that collects the laser beam output from the resonator. The laser ignition apparatus is disclosed (Patent Document 1). The light diffusing action of the concave lens increases the NA (numerical aperture) on the condensing side and improves the intensity of the breakdown.

As described above, the concave surface on the incident side (the side facing the resonator) of the concave lens that acts to improve the ignition performance is usually coated with a coating that prevents the reflection of the laser beam. However, since the concave lens is arranged at a position where the high-power pulsed laser beam output from the resonator is directly irradiated, the coating applied to the concave surface must be placed in a state of being easily deteriorated. When the coating deteriorates, the laser beam applied to the concave surface is reflected to the resonator side, and the reflected laser light is focused at the position on the resonator side of the concave surface. When a component such as a resonator is present at the condensing position of the reflected laser light, the component may be damaged by the energy of the reflected laser light. The potential for this damage increases as the coating deteriorates. By arranging the concave lens between the resonator and the convex lens in this way, the ignition performance is expected to be improved, but there is a concern about the problem of durability.

The present invention has been made in view of the above, and an object of the present invention is to improve performance without impairing durability.

In order to solve the above-mentioned problems and achieve the object, the laser apparatus according to one embodiment of the present invention has a resonator that receives light emitted from a light source and outputs laser light, and a resonator that outputs the laser light. A diffusion optical system having a concave surface for diffusing the laser light on the incident side of the laser light, a condensing optical system for condensing the laser light diffused by the concave surface, and a first holding for holding the resonator. A member, a second holding member for holding the diffusion optical system, and a third holding member for holding the first holding member and the second holding member are provided, and the resonator and the concave surface are provided. The distance between the first holding member and the second holding member is larger than the radius of curvature of the concave surface , and the third holding member holds the first holding member and the second holding member so as not to come into direct contact with each other. The first holding member is held so that a part of the holding member is exposed to the outside of the third holding member.

According to the present invention, it is possible to improve the performance without impairing the durability.

FIG. 1 is a diagram showing a configuration example of a laser device according to the first embodiment. FIG. 2 is a diagram showing a configuration example of the resonator according to the first embodiment. FIG. 3 is a diagram showing an example of the relationship between the distance between the resonator and the concave surface and the reflected focal point of the reflected light according to the first embodiment. FIG. 4 is a diagram showing an example of the relationship between the distance between the resonator and the concave surface and the reflected focal point of the reflected light according to the first comparative example. FIG. 5 is a diagram showing an example of the relationship between the distance between the resonator and the concave surface and the reflected focal point of the reflected light according to the second comparative example. FIG. 6 is a diagram showing a configuration example of the laser apparatus according to the second embodiment. FIG. 7 is a diagram showing a configuration example of the ignition device according to the third embodiment. FIG. 8 is a diagram showing a configuration example of an internal combustion engine according to a fourth embodiment.

Hereinafter, embodiments of a laser device, an ignition device, and an internal combustion engine will be described in detail with reference to the accompanying drawings.

(First Embodiment)
FIG. 1 is a diagram showing a configuration example of the laser device 1 according to the first embodiment. The laser device 1 includes a resonator 11, a diffusion optical system 12, a condensing optical system 13, and a window portion 15.

The resonator 11 is a device that receives the excitation light 10 emitted by the light source and resonates the light internally to output a high-power pulsed laser beam 21. The configuration of the resonator 11 is not particularly limited, but may be, for example, a configuration using the Q-switch method.

FIG. 2 is a diagram showing a configuration example of the resonator 11 according to the first embodiment. The resonator 11 according to this example includes a laser medium 61 and a saturable absorber 62. The material of the laser medium 61 may be, for example, Nd: YAG crystal or the like. The material of the saturable absorber 62 may be, for example, Cr: YAG crystal or the like. The laser medium 61 and the saturable absorber 62 may form a bonded, so-called composite crystal. The laser medium 61 is excited by the excitation light 10. The wavelength of the excitation light 10 is preferably the wavelength having the highest absorption efficiency in the YAG crystal. The surface on the incident side of the laser medium 61 and the surface on the injection side of the saturable absorber 62 are surfaces that have been subjected to optical polishing treatment, and serve as mirrors. A dielectric film corresponding to the wavelength of the excitation light 10 and the wavelength of the laser light 21 output from the resonator 11 is formed on the surface on the incident side of the laser medium 61 and the surface on the emission side of the saturable absorber 62. .. As a result, the light resonates and is amplified in the resonator 11.

The diffusion optical system 12 is an optical system that diffuses the laser beam 21 output from the resonator 11. The diffusion optical system 12 according to this example is one biconcave lens, and has a concave surface 41 on the incident side and a concave surface 42 on the ejection side. The concave surface 41 on the incident side is coated to prevent reflection of the laser beam 21. The laser beam 21 output from the resonator 11 directly irradiates the concave surface 41 on the incident side. In this example, one biconcave lens is used as the diffusion optical system 12, but the configuration of the diffusion optical system 12 is not limited to this, and for example, a plano-concave lens having a flat injection side is used. It may be.

The condensing optical system 13 is an optical system that condenses the laser beam 21 diffused by the diffusing optical system 12. The condensing optical system 13 according to this example includes a first plano-convex lens 13A and a second plano-convex lens 13B. The first plano-convex lens 13A has a convex surface 51 arranged on the ejection side and a plane 52 arranged on the incident side. The second plano-convex lens 13B has a convex surface 53 arranged on the incident side and a flat surface 54 arranged on the ejection side. The laser beam 21 that has passed through the first plano-convex lens 13A and the second plano-convex lens 13B is focused at the focal point 25. In this example, two plano-convex lenses 13A and 13B are used as the condensing optical system 13, but the configuration of the condensing optical system 13 is not limited to this, and for example, a biconvex lens or the like is used. It may be.

As described above, the laser beam 21 output from the resonator 11 is diffused by the diffusing optical system 12 and then condensed by the condensing optical system 13. Due to the action of the diffusing optical system 12, the NA of the condensing optical system 13 is increased, and the intensity of the breakdown at the focal point 25 is improved. The intensity of the breakdown can be adjusted by adjusting the radius of curvature of the diffusion optical system 12 and the condensing optical system 13. The required breakdown strength should be appropriately designed according to the usage situation, but it is preferable that the strength is such that the mixture of predetermined fuels such as gasoline and natural gas can be reliably ignited.

The window portion 15 is a member made of a transparent material arranged between the second plano-convex lens 13B and the focal point 25, and mainly serves as dustproof and the like. The material of the window portion 15 may be, for example, sapphire glass or the like.

The resonator 11, the diffusion optical system 12, and the condenser optical system 13 are the center of the cross section perpendicular to the resonance direction of the resonator 11, the center of the diffusion optical system 12 (the thinnest part), and the center of the condenser optical system 13. The thickest portion) is arranged so as to be located on one central axis 27.

FIG. 3 is a diagram showing an example of the relationship between the distance D between the resonator 11 and the concave surface 41 and the reflection focal point 72 of the reflected light 71 according to the first embodiment. The distance D according to this example is the distance from the end 31 on the diffusion optical system 12 side of the resonator 11 to the center of the concave surface 41. The distance D is larger than the radius of curvature R of the concave surface 41. More preferably, the distance D is greater than twice the radius of curvature R. For example, when the radius of curvature is 5.34 mm, the distance D is greater than 5.34 mm, more preferably greater than 10.68 mm.

As described above, when the relationship of D> R is established, the reflection focal point 72 of the reflected light 71 reflected by the concave surface 41 on the incident side of the diffusion optical system 12 is in the space between the resonator 11 and the diffusion optical system 12. Will be located. As a result, it is possible to prevent the reflection focal point 72, which has the highest energy of the reflected light 71, from being located in the resonator 11. As a result, even if the coating of the concave surface 41 is deteriorated and the laser beam 21 is reflected on the concave surface 41, the damage to the resonator 11 due to the energy of the reflected light 71 can be reduced. By making the distance D larger than twice the radius of curvature R, the beam diameter of the reflected light 71 irradiated to the end 31 of the resonator 11 becomes sufficiently large, so that the energy of the reflected light 71 is applied to the resonator 11. The damage can be further reduced.

FIG. 4 is a diagram showing an example of the relationship between the distance D between the resonator 11 and the concave surface 41 and the reflection focal point 72 of the reflected light 71 according to the first comparative example. The distance D according to the first comparative example coincides with the radius of curvature R of the concave surface 41. As described above, when the relationship of D = R is established, the reflection focus 72 is located at the end 31 of the resonator 11. As a result, when the coating on the concave surface 41 deteriorates, the energy of the reflected light 71 causes damage to the end portion of the resonator 11, for example, the surface (optically polished surface) of the saturable absorber 62 that functions as a mirror on the injection side. The possibility is high.

FIG. 5 is a diagram showing an example of the relationship between the distance D between the resonator 11 and the concave surface 41 and the reflection focal point 72 of the reflected light 71 according to the second comparative example. The distance D according to the second comparative example is smaller than the radius of curvature R of the concave surface 41. In this way, when the relationship of D <R is established, the reflection focus 72 is located in the resonator 11. As a result, when the coating on the concave surface 41 deteriorates, the energy of the reflected light 71 increases the possibility of damaging the inside of the resonator 11, for example, the laser medium 61, the saturable absorber 62, and the like.

Table 1 below shows a biconcave lens (diffuse optical system 12), a first plano-convex lens 13A (a part of the condensing optical system 13), a second plano-convex lens 13B (a part of the condensing optical system 13), and a window. A specific example of the shape of 15 is shown.

Table 2 below shows a specific example of the spacing between the components of the laser apparatus 1. As shown in FIG. 1, L1 is the length from the injection-side end 31 of the resonator 11 to the center (thinnest portion) of the incident-side concave surface 41 of the diffusion optical system 12. L2 is the length from the center (thinnest portion) of the concave surface 42 on the injection side of the diffusion optical system 12 to the plane 52 on the incident side of the first plano-convex lens 13A. L3 is the length from the center (thickest portion) of the convex surface 51 on the injection side of the first plano-convex lens 13A to the center (thickest portion) of the convex surface 53 on the incident side of the second plano-convex lens 13B. L4 is the length from the plane 54 on the injection side of the second plano-convex lens 13B to the plane on the incident side of the window portion 15. L5 is the length from the plane on the injection side of the window portion 15 to the focal point 25.

According to the first embodiment, the concave surface is formed by the relationship D> R between the distance D between the resonator 11 and the concave surface 41 of the diffusion optical system 12 and the radius of curvature R of the concave surface 41. The reflection focal point 72 of the reflected light 71 reflected by 41 is located in the space between the resonator 11 and the diffusion optical system 12. As a result, even if the coating on the concave surface 41 is deteriorated and the laser beam 21 is reflected on the concave surface 41, the damage to the resonator 11 by the reflected light 71 can be reduced. This makes it possible to improve the performance of the laser device 1 (certainty of breakdown at the focal point 25) and secure durability at the same time.

Hereinafter, other embodiments will be described with reference to the drawings, but the same reference numerals will be given to the parts that exhibit the same or similar effects as those of the first embodiment, and the description thereof will be omitted. There is.

(Second Embodiment)
FIG. 6 is a diagram showing a configuration example of the laser device 101 according to the second embodiment. The laser device 101 includes a resonator 11, a diffusion optical system 12, a condensing optical system 13, a window portion 15, a light source 111, an optical fiber 112, an external condensing optical system 113, a first optical system holding member 121, and a resonator holding member. Includes 122 (first holding member), second optical system holding member 123 (second holding member), and plug housing 124 (third holding member).

The light source 111 is a device that emits excitation light 10. The configuration of the light source 111 is not particularly limited, but may be, for example, a semiconductor laser or the like. Examples of the semiconductor laser include an edge emitting laser (EEL) and a vertical cavity surface emitting laser (VCSEL).

In comparison between EEL and VCSEL, when the excitation light 10 of the same energy is emitted, the beam diameter of the excitation light 10 emitted from the VCSEL is generally larger than the beam diameter of the excitation light 10 emitted from the EEL. .. For example, when the beam diameter of the excitation light 10 by the EEL is about 0.6 mm, the beam diameter of the excitation light 10 by the VCSEL is often about 1.5 mm. The beam diameter of the laser beam 21 output from the resonator 11 increases as the beam diameter of the excitation light 10 incident on the resonator 11 increases. Therefore, the beam diameter of the laser beam 21 output from the resonator 11 and applied to the concave surface 41 on the incident side of the diffusion optical system 12 is larger when VCSEL is used than when EEL is used. As the beam diameter of the laser beam 21 applied to the concave surface 41 becomes larger, the energy per unit area becomes smaller, so that the deterioration of the coating applied to the concave surface 41 becomes slower. Therefore, it is preferable to use VCSEL as the light source 111.

The optical fiber 112 transmits the excitation light 10 emitted from the light source 111 into the main body of the laser device 101 (the housing including the resonator 11, various optical systems 12, 13, 113, and the like). By using the optical fiber 112, the degree of freedom in designing the positional relationship between the light source 111 and the main body can be improved.

The external condensing optical system 113 is an optical system that condenses the excitation light 10 transmitted by the optical fiber 112 and irradiates the resonator 11. The external condensing optical system 113 according to this example includes a third plano-convex lens 113A and a fourth plano-convex lens 113B. The third plano-convex lens 113A has a convex surface 131 arranged on the ejection side and a plane 132 arranged on the incident side. The fourth plano-convex lens 113B has a convex surface 133 arranged on the incident side and a flat surface 134 arranged on the ejection side. The excitation light 10 emitted from the optical fiber 112 is focused by the third plano-convex lens 113A and the fourth plano-convex lens 113B so as to have a predetermined diameter at the incident side end 32 of the resonator 11. In this example, two plano-convex lenses 113A and 113B are used as the external condensing optical system 113, but the configuration of the external condensing optical system 113 is not limited to this, for example, a biconvex lens and a collimating lens. Etc. may be used.

The first optical system holding member 121 is a member that holds the external condensing optical system 113. The first optical system holding member 121 holds the third plano-convex lens 113A and the fourth plano-convex lens 113B so that their centers (thickest portions) are located on the central axis 27.

The resonator holding member 122 is a member that holds the resonator 11 and the first optical system holding member 121. The resonator holding member 122 holds the resonator 11 so that the center of the cross section in the direction perpendicular to the resonance direction of the resonator 11 is located on the central axis 27.

The second optical system holding member 123 is a member that holds the diffusion optical system 12 and the condensing optical system 13. The second optical system holding member 123 has the diffusing optical system 12 and the condensing optical system 13 having their centers (the thinnest part in the diffusing optical system 12 and the thickest part in the condensing optical system 13) on the central axis 27. Hold it so that it is located at. The second optical system holding member 123 is not in direct contact with the resonator holding member 122. The thermal conductivity of the second optical system holding member 123 is lower than the thermal conductivity of the resonator holding member 122.

The plug housing 124 is a member that holds the resonator holding member 122, the second optical system holding member 123, and the window portion 15. The plug housing 124 holds the resonator holding member 122 and the second optical system holding member 123 so that they do not come into direct contact with each other. A part of the resonator holding member 122 is held so as to be exposed to the outside of the plug housing 124. As a result, the structure is such that the heat of the resonator 11 is easily released to the outside. The thermal conductivity of the plug housing 124 is lower than the thermal conductivity of the resonator holding member 122. More preferably, the thermal conductivity of the plug housing 124 is lower than the thermal conductivity of the second optical system holding member 123.

The temperature of the resonator 11 becomes high due to the resonance amplification action of light during operation of the laser device 101. The deterioration of the coating applied to the concave surface 41 of the diffusion optical system 12 is accelerated by the high temperature. Therefore, it is necessary to have a structure that prevents the heat of the resonator 11 from being conducted to the diffusion optical system 12 while ensuring the heat dissipation of the resonator 11.

Therefore, in the present embodiment, the resonator holding member 122 and the second optical system holding member 123 are each composed of individual members and are not in direct contact with each other. The thermal conductivity of the second optical system holding member 123 is lower than the thermal conductivity of the resonator holding member 122. The thermal conductivity of the plug housing 124 is lower than that of the resonator holding member 122, and more preferably lower than that of the second optical system holding member 123. A part of the resonator holding member 122 is exposed to the outside of the plug housing 124.

Table 3 below shows examples of specific materials and thermal conductivity of the resonator holding member 122, the second optical system holding member 123, and the plug housing 124.

Table 3 is an example, and the materials and thermal conductivity of the resonator holding member 122, the second optical system holding member 123, and the plug housing 124 are not limited to the above. The resonator holding member 122 is required to have high thermal conductivity and the like. Although aluminum is exemplified here as a material suitable for the resonator holding member 122, other materials having high thermal conductivity such as copper and magnesium may be used. The second optical system holding member 123 is required to have low thermal conductivity, high rigidity, and the like. Here, SUS304 is exemplified as a material suitable for the second optical system holding member 123, but a material such as Inconel 625 may be used. The plug housing 124 is required to have low thermal conductivity, high rigidity, and the like. Here, Inconel 625 is exemplified as a material suitable for the plug housing 124, but a material such as Kovar or SUS304 may be used.

With the above configuration, even if the resonator holding member 122 is made of a material having a relatively high thermal conductivity, it becomes difficult for the heat of the resonator 11 to be conducted to the diffusion optical system 12. That is, according to the present embodiment, it is possible to avoid the temperature rise of the diffusion optical system 12 while ensuring the heat dissipation of the resonator 11. As a result, deterioration of the coating on the concave surface 41 can be suppressed, and damage caused by the reflected light 71 due to the concave surface 41 can be suppressed. This makes it possible to improve the performance of the laser apparatus 101 and secure the durability at a higher level.

(Third Embodiment)
FIG. 7 is a diagram showing a configuration example of the ignition device 201 according to the third embodiment. The ignition device 201 is a device that ignites the air-fuel mixture filled in the combustion chamber of the internal combustion engine. The ignition device 201 includes a laser device 101, a drive device 211, and a control device 212 according to the second embodiment.

The drive device 211 drives a light source 111 such as a VCSEL based on a control signal from the control device 212 that controls the internal combustion engine. The drive device 211 and the control device 212 are units that can be configured by using a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), or the like controlled by a program. The drive device 211 controls the amount and output timing of the excitation light 10 output from the light source 111 so that the laser light 21 focuses on the focal point 25 at the ignition timing in the combustion process of the internal combustion engine.

As described above, the performance of the internal combustion engine can be improved by using the ignition device 201, which has both the strength and durability of the breakdown, for ignition in the combustion process.

(Fourth Embodiment)
FIG. 8 is a diagram showing a configuration example of the internal combustion engine 301 according to the fourth embodiment. In FIG. 8, the configuration of the main part of the internal combustion engine 301 is schematically shown. The internal combustion engine 301 includes an ignition device 201, a fuel ejection mechanism 311, an exhaust mechanism 312, a combustion chamber 313, and a piston 314.

The outline of the operation of the internal combustion engine 301 is as follows.
(1) The fuel ejection mechanism 311 ejects a mixture of fuel and air into the combustion chamber 313 (intake process).
(2) The piston 314 rises and compresses the air-fuel mixture (compression step).
(3) The ignition device 201 emits the laser beam 21 so that a breakdown occurs in the combustion chamber 313. As a result, the air-fuel mixture is ignited, the combustion gas expands, and the piston 314 descends (combustion process).
(4) The piston 314 rises due to inertial force, and the exhaust mechanism 312 exhausts the combustion gas to the outside of the combustion chamber 313 (exhaust process).

In this way, a series of steps including intake, compression, combustion, and exhaust are repeated. The piston 314 moves in response to a change in the volume of gas in the combustion chamber 313 to generate mechanical energy. For example, gasoline, natural gas or the like is used as the fuel.

As described above, by using the ignition device 201 having both the strength and durability of the breakdown for ignition in the combustion process, it is possible to provide a high-performance internal combustion engine 301.

In the present embodiment, the piston engine that moves the piston 314 by burning the air-fuel mixture has been described, but the configuration of the internal combustion engine using the ignition device 201 (laser devices 1, 101) is not limited to this. Absent. The ignition device 201 can be adopted in an internal combustion engine having any configuration for burning a combustible gas to generate a combustion gas, and can also be applied to, for example, a rotary engine, a gas turbine engine, a jet engine, and the like. Further, the ignition device 201 may be used for cogeneration, which is a system that extracts power, heat, cold heat, etc. by utilizing exhaust heat and enhances energy efficiency comprehensively.

Further, the laser devices 1 and 101 can be applied to other than the internal combustion engine, and may be used, for example, in a laser processing machine, a laser peening device, a terahertz generator, or the like.

Although the embodiments of the present invention have been described above, the above embodiments are presented as examples and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and the equivalent scope thereof.

1,101 Laser device 10 Excitation light 11 Resonator 12 Diffuse optical system 13 Condensing optical system 13A First plano-convex lens 13B Second plano-convex lens 15 Window 21 Laser light 25 Focus 27 Central axis 31, 32 Ends 41, 42 Concave surface 51, 53, 131, 133 Convex surface 52, 54, 132, 134 Flat surface 61 Laser medium 62 Saturable absorber 71 Reflected light 72 Reflected focus 111 Light source 112 Optical fiber 113 External condensing optical system 113A Third plano-convex lens 113B Fourth plano-convex lens 121 First optical system holding member 122 Resonator holding member (first holding member)
123 Second optical system holding member (second holding member)
124 Plug housing (third holding member)
201 Ignition device 211 Drive device 212 Control device 301 Internal combustion engine 311 Fuel ejection mechanism 312 Exhaust mechanism 313 Combustion chamber 314 Piston

Japanese Unexamined Patent Publication No. 2010-14030

Claims (8)

A resonator that receives light emitted from a light source and outputs laser light,
A diffusion optical system having a concave surface for diffusing the laser beam on the incident side of the laser beam output from the resonator.
A condensing optical system that collects the laser beam diffused by the concave surface, and
A first holding member that holds the resonator and
A second holding member that holds the diffusion optical system and
A third holding member that holds the first holding member and the second holding member,
With
The distance between the resonator and the concave surface is larger than the radius of curvature of the concave surface.
The third holding member holds the first holding member and the second holding member so as not to come into direct contact with each other, and a part of the first holding member is outside the third holding member. A laser device that holds the first holding member so as to be exposed. The distance is greater than twice the radius of curvature,
The laser device according to claim 1. The thermal conductivity of the second holding member is lower than the thermal conductivity of the first holding member.
The laser apparatus according to claim 1 or 2. The thermal conductivity of the third holding member is lower than the thermal conductivity of the first holding member.
The laser device according to any one of claims 1 to 3. The thermal conductivity of the third holding member is lower than the thermal conductivity of the second holding member.
The laser device according to any one of claims 1 to 4. The light source is a vertical resonator surface emitting laser.
The laser apparatus according to any one of claims 1 to 5. The laser apparatus according to any one of claims 1 to 6 is provided.
The flammable gas is burned by irradiating the flammable gas with the laser beam focused by the condensing optical system.
Ignition system. The ignition device according to claim 7 is provided.
Converting the thermal energy generated by the combustion of the combustible gas into mechanical energy,
Internal combustion engine.

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