JP4772600B2 - Multi-point output laser ignition system - Google Patents

Description

  The present invention relates to a multipoint output laser ignition device used for performing multipoint ignition of an internal combustion engine, mainly a gas combustion engine, with a laser beam.

  In a gas combustion engine, in order to improve fuel consumption and suppress NOx generation amount, there is a demand to reduce the fuel mixture ratio of the mixed fuel and make the fuel gas more lean and burn in abundant air. However, the lean mixed gas has poor ignitability, and the ignition by the conventional spark plug does not provide sufficient ignition performance, and abnormal combustion such as misfiring and knocking occurs, which limits the dilution of 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.

  In order to burn a flame-retardant rare gas so that misfire or abnormal combustion does not occur, and to improve the combustion rate and combustion speed, it is desirable to provide a large number of ignition points in the combustion chamber. However, in the ignition by the spark plug, since the arrangement position of the spark plug is limited, the ignition point is limited to one point or two points, and combustion cannot be started simultaneously from multiple points.

  Therefore, as a method of igniting a plurality of ignition points distant 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 can be considered. However, in order to put it into practical use, it is necessary to develop technologies such as a method of propagating a high-power laser and a method of distributing a large number near the engine.

  For example, in Patent Document 1, a fly-eye type lens in which microlenses are integrated in an optical window that introduces laser light into a combustion chamber is installed, and the laser light irradiated to the optical window is divided into a plurality of light beams. A laser-type multi-point ignition device is disclosed in which a plurality of points are focused.

  As shown in FIG. 6, the laser-type multipoint ignition device disclosed in Patent Document 1 expands a laser beam guided by an optical fiber from one laser generation source with an expander lens, and collects a condensing lens and a collimator 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 produce mixed fuel. Multipoint ignition.

  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. Furthermore, since multiple points can be ignited from one optical window, the ignitability can be improved.

However, in the disclosed invention, a high-power laser is guided by an optical fiber, collimated, divided into a plurality of light beams by a microlens array, and converged to form a focal point. Therefore, an optical element having high quality is required, and there is a problem that the entire system becomes a precise and expensive device.
In addition, instead of dividing one high-power laser, a plurality of laser light sources may be provided to ignite each independently. In this case, a large number of systems are required, and the equipment cost is also expensive. There are difficulties in practical application.
Japanese Patent Laying-Open No. 2005-147109

  Therefore, the problem to be solved by the present invention is to provide a new multi-point output laser ignition device that is configured using a single laser resonator and does not use a laser splitting device.

In order to solve the above problems, a multipoint output laser ignition device of the present invention includes a laser resonator formed by sandwiching a laser medium with a pair of resonance mirrors including a reflection mirror and an output mirror provided with a plurality of output holes, A convergence optical system is provided for each of a plurality of output lasers output from the laser resonator.
The output hole is a portion having a small reflectance provided in a part of the output mirror. The output laser is transmitted through this output hole.

In the multipoint output laser ignition device of the present invention, a plurality of output holes are provided in the output mirror of the laser resonator, and a plurality of laser beams are emitted simultaneously. The laser beams are converged one by one by a converging optical system such as a microlens and condensed at different appropriate positions in the combustion chamber of the engine. The laser beams condensed at different positions pass energy to the air-fuel mixture filled in the combustion chamber at the condensing point to generate a high temperature and ignite the air-fuel mixture at multiple points. Since the fuel gas is ignited at multiple points where a plurality of laser beams are distributed in the combustion chamber, the combustion proceeds at once, the combustion time in the combustion chamber is shortened, and the output of the engine is improved.
In the multipoint output laser ignition device of the present invention, since a large number of laser beams are directly output from a single laser generator, it is not necessary to use a laser dividing device that is difficult to manufacture and handle precisely. In addition, there is no need to operate a plurality of laser generators synchronously.

When the intensity distribution of light in the output mirror exhibits a Gaussian distribution, the output holes are preferably arranged on concentric circles centered on the center of the output mirror.
A normal resonator combining a concave mirror and a concave mirror is configured so that the light intensity distribution in the reflecting mirror and the output mirror has a normal distribution with the central axis as a vertex in order to stabilize oscillation. When having such a light intensity distribution, if the distance from the central axis of the output hole is equal, the intensity of the output light will be equal. Therefore, it is preferable to arrange the output hole on a concentric circle centered on the central axis.

You may provide the collimator lens which makes the optical axis of the some output laser output from a laser resonator become mutually parallel.
The collimator lens that parallels the optical axes of the output lasers output from the laser resonator can be configured using, for example, a plano-convex lens. By collimating the optical axes of multiple output lasers with a collimator lens, the same converging optical system can be focused even if the distance between the laser resonator and the converging optical system changes. The size of the ignition device can be easily adjusted.

  The laser resonator may be an unstable resonator in which the reflecting mirror and the output mirror are a combination of a convex mirror and a convex mirror. In this case, since the light intensity on the output mirror surface becomes uniform, the intensity of the output laser obtained from the plurality of output holes becomes substantially equal. In an unstable resonator, the laser light emitted from the output hole provided at a position off the central axis also has an optical axis substantially parallel to the central axis. Therefore, a collimator lens for collimating the laser optical axis is used. By omitting, a more compact and simple laser ignition device can be obtained.

The converging optical system is preferably formed of a microlens.
The converging optical system required for each output laser can be formed by a microlens having a diameter of several millimeters or less. The microlens can form a necessary number of lenses having a required shape on a single substrate. By using such a microlens plate, the laser ignition device can be manufactured extremely compactly.

In addition, a transparent protective plate is provided on the output surface of the output laser that has become the convergent light so that the explosion pressure does not damage the optical system inside the ignition device when it is mounted on an engine and the combustion residue remains. It is preferable to protect the converging optical system from being contaminated. As the transparent protective plate, for example, a thick plate of quartz glass can be used.
The multipoint output laser ignition device of the present invention can be configured in the form of a small unit in which a laser generator and an optical system such as a microlens are integrated.

If the multipoint output laser ignition device of the present invention is applied to an engine, a plurality of laser beams can be directly generated from the laser generator and the mixture can be ignited from multiple points in the combustion chamber. And operation with less abnormal combustion.
Further, the laser multipoint ignition type engine equipped with the multipoint output laser ignition device of the present invention can reliably burn even a lean air-fuel mixture with poor ignitability, thus providing an engine with low fuel consumption and low NOx emissions. can do.

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

FIG. 1 is a schematic sectional view of a multi-point output laser ignition device in one embodiment of the present invention, FIG. 2 is a conceptual diagram showing an example of arrangement of output holes in an output mirror, and FIG. 3 is a simplified optical system after a laser resonator. FIG. 4 is a conceptual diagram showing another example of a laser resonator, and FIG. 5 is a conceptual perspective view showing a multi-point output laser ignition device attached to an engine combustion chamber.
FIG. 6 is a sectional view for explaining the prior art.

  The multipoint output laser ignition device 1 includes an output mirror 12, a reflecting mirror 13, a planoconvex lens 15, a convex microlens 16, and a protective transparent plate 17 that are opposed to each other with a laser medium 11 interposed therebetween. Used by attaching to the wall of the chamber 3.

The laser medium 11 is a substance that amplifies light by stimulated emission. The output mirror 12 and the reflecting mirror 13 constitute a Fabry-Perot resonator, and are adjusted so that light is fed back and the oscillation power condition and frequency condition are satisfied.
The output mirror 12 is provided with a plurality of output holes 14. The output hole 14 is a part where the light transmittance is high, and is a hole through which laser light is emitted. The laser light is emitted in a direction perpendicular to the reflecting surface of the output mirror.

Therefore, the plano-convex lens 15 is provided to collimate the output laser, and then converged by the microlens 16. The convergent light passes through the transparent protective plate 17 and forms a focal point 31 at a predetermined distance.
When the output laser passes through the plano-convex lens 15 and becomes parallel, the distance between the output mirror 12 of the laser resonator and the microlens 16 can be adjusted appropriately, so that it matches the engine to which the multipoint output laser ignition device 1 is applied. The length of the device can be adjusted.

The microlens 16 is formed as a convex lens having a diameter of several millimeters or less, and a microlens plate formed by the number of output lasers on a single substrate can be used.
Further, the protective transparent plate 17 is made of a material that transmits a convergent laser beam well, and a thick plate made of, for example, quartz glass designed to withstand pressure changes in the combustion chamber 3 is used.

The focal point 31 is formed at a position where when the multipoint output laser ignition device 1 is attached to the wall of the combustion chamber 3, the fuel gas is effectively ignited at an appropriate distance from the wall.
Further, it is preferable that the focal points 31 connected for each of a large number of output lasers are appropriately separated from each other so that combustion proceeds independently after ignition. Preferably, the volume in the combustion chamber 3 is divided into the same number of spheres that are in contact with each other as many as the number of output lasers, and the focal point is distributed to the center position of the spheres. By taking such an arrangement, the combustion speed in the combustion chamber 3 is most shortened.

When the diameter of the laser ignition device is small, in order to place the focal point in an appropriate wide range, a photorefractive element that directs the optical path of each laser beam to the outside by refraction, such as a prism, may be provided after the microlens 16. Good.
In addition, the photorefractive element can be provided as a single substrate formed by the number of output lasers.

As the combination of the reflecting mirror and the output mirror of the Fabry-Perot resonator, any of concave-concave, planar-planar, planar-concave, convex-concave, convex-convex can be selected.
In the concave-concave configuration shown in FIG. 1, the light 18 in the resonator is thin at the center and spreads at both ends, and the intensity of the light in the plane perpendicular to the axis has a Gaussian distribution. Can be realized relatively easily. Further, since the light intensity at the output mirror 12 has a Gaussian distribution, the closer the output hole 14 is to the center of the output mirror, the greater the intensity of the output laser.

  Since the ignition energy of the fuel gas is determined according to the gas component, gas concentration, oxygen concentration, etc., when performing multi-point ignition, it is required that the energy is substantially the same for each point. For this reason, the output hole 14 is preferably disposed on a concentric circle C centered on the center O of the output mirror 12 as shown in FIG.

Note that FIG. 3 shows that the output direction of the output laser is the normal direction of the concave mirror without parallelizing the optical axis of the laser beam, and the microlens 16 is placed on the optical axis while preserving the direction. It is the schematic which showed the provided structure.
In such a configuration, the output mirror 12 of the laser resonator is very close to the combustion chamber 3 of the engine, but the collimator lens 15 is not required and a low-cost laser ignition device is obtained.

  Also, as shown in FIG. 4, an unstable resonator having a convex-convex configuration can be adopted as the Fabry-Perot resonator. An unstable resonator in which both the output mirror 19 and the reflecting mirror 20 are convex surfaces has a large light spread 21 in the resonator, and the excited molecules can be effectively used for stimulated emission, so that the gain is large and large. Used to get output. In this unstable resonator, since the light intensity distribution in the output mirror 19 is relatively flat, the position of the output hole 14 can be determined relatively freely.

Further, since the optical axis of the output laser emitted from the output mirror 19 is substantially parallel to the central axis of the resonator, it is not necessary to provide the collimator lens 15 as in the configuration shown in FIG.
Note that the number of output lasers, the position of the focal point, and the like in the multipoint output laser ignition device 1 of this embodiment can be designed flexibly according to the scale of the engine, the composition of the air-fuel mixture, and the like.

The multipoint output laser ignition device 1 of the present embodiment is installed in a cylinder combustion chamber 3 of a gas combustion engine, for example, as shown in FIG. When the engine is equipped with the multipoint output laser ignition device 1, it becomes a laser multipoint ignition engine.
In the figure, a through-hole to the combustion chamber 3 is formed in a head equipped with an intake pipe 32 for introducing fuel gas and an exhaust pipe 33 for discharging exhaust gas, and the multipoint output laser ignition device 1 is attached to the through-hole. The laser supplied from the multipoint output laser ignition device 1 concentrates each laser energy at a large number of focal points 31 formed in the space in the combustion chamber 3 and ignites the fuel gas.

Since the focal points 31 having appropriate distances are ignited at the same time, and the combustion proceeds from the focal points 31, the fuel gas in the combustion chamber 3 burns out at a very high speed, and the engine has good combustion efficiency and misfires and abnormal combustion occur. You can drive less.
Further, since the engine equipped with the multipoint output laser ignition device 1 of this embodiment ignites multipoint, it can surely burn even a lean air-fuel mixture with poor ignitability, resulting in a low fuel consumption and low NOx emission engine. Can be provided.

The multipoint output laser ignition device of the present invention can be configured as a small unit in which a laser generator and an optical system of an output laser are integrated. Therefore, it is not necessary to use a light transport system to an ignition device that is difficult to handle.
Further, it is possible to design an efficient system as a whole in accordance with the laser power and frequency required according to the number of cylinders of the engine and the number of ignition points in the combustion chamber.

It is a schematic sectional drawing of the multipoint output laser ignition device in one Example of this invention. It is a conceptual diagram which shows the example of arrangement | positioning of the output hole in the output mirror in a present Example. It is the conceptual diagram which showed another aspect in a present Example. It is the conceptual diagram which showed another aspect in a present Example. It is a conceptual diagram which shows the state which equips the combustion chamber of an engine with the multipoint output laser ignition device of a present Example. It is a schematic sectional drawing of the conventional laser multipoint ignition device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multipoint output laser ignition device 11 Laser medium 12 Output mirror 13 Reflective mirror 14 Output hole 15 Plano-convex lens 16 Micro lens 17 Transparent protective plate 18 Light spread 19 Output mirror 20 Reflector 21 Light spread 3 Combustion chamber 31 Focus (ignition point) )
32 Intake pipe 33 Exhaust pipe

Claims (9)

  A laser ignition device for condensing and irradiating a laser beam into a combustion chamber of an internal combustion engine to ignite an air-fuel mixture, wherein a laser medium is formed by a pair of resonance mirrors including a reflecting mirror and an output mirror provided with a plurality of output holes. A multi-point output laser ignition device comprising: a laser resonator sandwiched and a converging optical system for each of a plurality of output lasers output from the output holes.   2. The multiplicity according to claim 1, wherein the laser resonator includes an output mirror having a Gaussian distribution of light intensity, and the output holes are arranged on concentric circles centered on the center of the output mirror. Point output laser ignition device.   The multipoint output laser ignition device according to claim 2, further comprising a collimator lens between the output mirror and the converging optical system.   2. The multipoint output laser ignition device according to claim 1, wherein the reflecting mirror and the output mirror constitute an unstable resonator in which a convex mirror and a convex mirror are combined.   5. The multipoint output laser ignition device according to claim 1, wherein the converging optical system is formed of a microlens.   6. The multipoint output laser ignition device according to claim 5, wherein the microlens is formed by forming a required number of lenses having a required shape on a single substrate.   7. The multipoint according to claim 1, wherein a light refracting element is provided behind the converging optical system and the optical axis of the output laser is refracted outward so that the focal point is arranged in a wide range. Output laser ignition device.   The multipoint output laser ignition device according to any one of claims 1 to 7, wherein a transparent protective plate is provided on a laser output surface of the multipoint output laser ignition device.   A laser multipoint ignition engine comprising the multipoint output laser ignition device according to any one of claims 1 to 8.

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