JP4836681B2 - Laser ignition device for easy optical window cleaning - Google Patents

Description

  The present invention relates to a laser ignition device that ignites an internal combustion engine with laser light.

  As an efficient operation method of an internal combustion engine, lean combustion using a lean air-fuel mixture has attracted attention. However, since misfire and knocking are likely to occur during lean operation, development of a laser ignition device that can control combustion relatively freely by selecting an ignition position and an ignition timing is in progress.

  A laser ignition device that ignites an air-fuel mixture in a cylinder of an internal combustion engine by irradiating it with a laser beam, so that it is not affected by severe pressure changes in the cylinder, with a transparent protective plate of quartz glass or sapphire. Separated from the combustion chamber. The optical window formed by the transparent protective plate gradually adheres and becomes dirty while the operation is repeated, but the laser light passing through the optical window is attenuated, and laser ignition cannot be performed.

  In Patent Document 1, a liquid fuel that is also an organic solvent is sprayed from an injection nozzle to form a mist, and a laser ignition internal combustion engine that is ignited by irradiating it with laser light that has passed through an optical window. A technique is disclosed in which a liquid fuel is directly sprayed onto an optical window and cleaned immediately after the compression stroke starts at each cycle after branching to maintain the laser transmittance of the optical window.

  The method disclosed in the literature uses liquid fuel as a solvent to clean the optical window and assimilate to the sprayed fuel after evaporation, so it does not adversely affect combustion. In addition, since it was made to inject into the optical window at the time of starting the compression stroke, it is easy to inject due to the low pressure in the combustion chamber, and the time to irradiate the laser light is long, so the fuel adhering to the window glass is completely evaporated. Thus, the laser beam transmitted through the optical window is not adversely affected.

However, since the disclosed method uses fuel as a solvent, it cannot be applied to a gas engine that uses gas fuel. If the method of evaporating liquid fuel with an optical window is applied to a lean mixed gas, the gas concentration is affected and normal lean combustion cannot be performed.
JP-A-6-249123

  Therefore, the problem to be solved by the present invention is to provide a laser ignition device in which an optical window can be easily cleaned and applied to a gas engine.

  In order to solve the above problems, a laser ignition device of the present invention ignites a laser beam by irradiating a combustion chamber of an internal combustion engine through an optical window, and the combustion chamber has two or more laser irradiation holes. Each of the laser irradiation holes is provided with a shutter that can be opened and closed, and a laser focusing unit including an optical window and a focusing optical system is detachably attached to each of the two or more shutters, and is detachably connected to the laser focusing unit. An optical fiber cable is connected to a laser switching element connected to the laser transmission means.

  The laser converging unit is a cylindrical unit having a function of irradiating a laser supplied by an optical fiber into a converging light by a converging optical system through an optical window. A joint mechanism such as a screw is provided on the end side of the optical window side so as to be detachably attached to the shutter, and a mechanism for jointing an optical fiber cable for supplying a laser is provided on the other end.

The laser switching element can be configured using a movable mirror that switches the optical path by changing the direction of the reflecting surface, an electro-optical element, or the like. Since the electro-optic element has a short switching time and can be controlled by an electric signal, it is easy to use even when an automatic operation is employed.
The shutter is preferably a ball valve. This is because a gas engine has a high maximum pressure in a cylinder, but a ball type valve has a structurally high pressure resistance and can easily withstand this level of pressure vibration.

When operating the internal combustion engine, the laser transmitted from the laser light source passes through the laser switching element and is supplied to the selected first laser converging unit. The light is transmitted, passes through the opening of the opened shutter, enters the combustion chamber through the laser irradiation hole, concentrates energy near the focal point, and ignites the mixture.
Normally, the shutter of the laser irradiation hole to which no laser is supplied is closed.

When the optical window is dirty and the laser transmittance is reduced, the closed shutter is opened, the laser switching element is switched at an appropriate timing, and the laser supply destination is changed from the dirty first laser focusing unit. The laser is ignited by switching to the second laser focusing unit.
For the sake of efficient combustion, the position of the ignition point is carefully specified in accordance with the fuel concentration distribution and the like. Therefore, the ignition point by the first laser focusing unit and the ignition point by the second laser focusing unit are preferably the same position. .

  When switching is completed, the shutter on which the first laser focusing unit is provided is closed, the optical fiber cable is disconnected from the first laser focusing unit, the dirty first laser focusing unit is then removed, and the optical window is appropriately cleaned. After removing, return to the original position.

When switching the laser focusing unit, avoid misfire by switching.
If a misfire occurs, the fuel concentration at the next ignition becomes excessive and the pressure in the combustion chamber becomes extremely high. For example, the switching of the laser does not overlap with the timing of ignition, for example, switching is performed in the exhaust stroke of the combustion cycle. Like that. For this reason, an interlock may be set so that the switching of the laser is always synchronized with the opening operation of the exhaust valve.
In addition, the switching time is sufficiently shortened so that the laser switching does not overlap with the ignition timing. Since the engine cycle is short, the laser switching element is composed of, for example, an electro-optical element using a Pockels cell.

  In the laser ignition device of the present invention, the laser focusing unit can be easily attached / detached even during operation of the internal combustion engine by switching to an alternative laser focusing unit and operating the shutter to shut off the combustion chamber. The optical window can be cleaned by any method.

Hereinafter, a laser ignition device with easy optical window cleaning according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of a laser ignition device in one embodiment of the present invention, FIG. 2 is a block diagram illustrating an operation method of the present embodiment, and FIG. 3 is a process diagram illustrating an operation procedure of the present embodiment.

  The laser ignition device in the present embodiment is provided with two or more laser irradiation holes 3 and 3 ′ in the wall 2 of the combustion chamber 1, and a shutter formed by a ball valve 11 or the like in each of the laser irradiation holes 3 and 3 ′. 10 and 10 ′ are attached, and laser focusing units 20 and 20 ′ are detachably attached to the shutters 10 and 10 ′ using joints 24 such as screws, and optical fiber cables are attached to the laser focusing units 20 and 20 ′. 30 and 30 ′ are connected, and the other ends of the optical fiber cables 30 and 30 ′ are connected to the laser switching element 40. A laser is supplied to the laser switching element 40 by an optical fiber cable 41 connected to the laser generator 50.

The laser generator 50 supplies a laser at the timing of performing laser ignition.
The laser supplied from the laser generator 50 is distributed by the laser switching element 40 to the operating laser focusing unit 20.
The laser switching element 40 is composed of an electro-optical element and has a function of distributing an incident laser to two or more paths. Since the electro-optic element has a short switching time and can be controlled by an electric signal, it is easy to use even when an automatic operation is employed.
The laser switching element 40 may be configured with a movable mirror. Even with a movable mirror, the optical path can be switched by mechanically changing the direction of the reflecting surface.

The laser focusing units 20 and 20 ′ are provided with a stopper 31 for fixing the optical fiber cables 30 and 30 ′ to the laser focusing unit so that the optical fiber cable can be attached and detached, and the position of the light emitted from the optical fiber cable. Confirm with good reproducibility.
The laser converging units 20 and 20 ′ are provided with a magnifying optical system 21 and a converging optical system 22 inside, and a thick optical window 23 made of quartz glass or sapphire glass provided at the end portion causes the internal equipment to control the high pressure of the combustion chamber. Block it so that it is not affected.

The magnifying optical system 21 converts the laser light emitted from the optical fibers 30 and 30 ′ into parallel rays once, and may be formed by a condensing lens and a collimating lens.
The converging optical system 22 is composed of a convex lens, and has a function of converging the laser light 4 and collecting it at the focal point 5.
The laser focusing units 20 and 20 ′ and the shutters 10 and 10 ′ can be detachably fixed by a joint mechanism 24.

  The joint mechanism 24 includes a male screw provided outside the end of the laser focusing units 20 and 20 ′ on the shutter 10 and 10 ′ side and a female screw provided on the shutter 10 and 10 ′, and is fitted to and detached from each other. It may be possible to fix it. In addition, when the pressure in the combustion chamber is low, it is possible to use a mechanism that can be easily attached and detached, such as a sage lock.

The shutters 10 and 10 'include ball valves 11 and 11' and a solenoid 12 that drives the ball valves. The ball valves 11 and 11 ′ are spherical valve bodies through which holes having the same diameter as the openings of the shutters 10 and 10 ′ pass, and a stem 13 that is advanced and retracted by a solenoid 12 is engaged with a rotating shaft.
When the solenoid 12 is driven, the stem 13 expands and contracts, the ball valve 11 rotates 90 degrees, and the through hole of the ball valve 11 is in an open state parallel to the opening axis of the shutter 10 and a closed state in which it is oriented in the vertical direction. It can be selected.

In the closed state shown on the right side of the figure, the ball valve 11 'of the shutter 10' tilts the through hole in a direction perpendicular to the opening axis to block the opening with the surface wall of the sphere, and the laser focusing unit 20 ' Is insulated from the combustion chamber 1 of the engine.
Further, in the open state shown on the left side in the figure, the ball valve 11 of the shutter 10 is focused laser light emitted from the laser focusing unit 20 so that the central axis of the through hole stands in a direction that coincides with the opening axis. 4 passes through the opening of the shutter 10 and is focused on the focal point 5 in the combustion chamber 1 to ignite the fuel gas in the chamber.

  In the laser ignition device of this embodiment, when the optical window 23 of the first laser focusing unit 20 being used is attached with soot or the like and the surface is contaminated and the transmittance of the laser is lowered, the procedure shown in FIG. The optical window 23 can be cleaned.

  That is, it is confirmed that the second laser focusing unit 20 ′ that has been serviced is attached to the second shutter 10 ′ that has been closed, and the second laser focusing unit 20 ′ is opened by opening the second shutter 10 ′. After being able to operate (S01), after waiting for an appropriate timing (S02), the laser switching element 40 is driven to switch the laser supply destination from the first laser focusing unit 20 to the second laser focusing unit 20 ′ ( S03), the second laser focusing unit 20 ′ performs laser ignition.

When switching the laser focusing unit, it is necessary to prevent misfire by switching.
When misfire occurs, the fuel gas remaining after combustion is added to normal fuel, so that the fuel concentration at the next ignition becomes excessive and the pressure in the combustion chamber 1 may become extremely large.

  Therefore, in order to protect the engine and the ignition device, it is necessary to prevent the laser switching from overlapping the timing of ignition. Therefore, an interlock may be provided so that laser switching does not always overlap with the ignition timing. For example, if switching is performed in the exhaust stroke of the combustion cycle, there is no risk of misfire due to laser switching because there is no overlap with the ignition timing.

Further, in order to prevent the laser switching from overlapping with the ignition timing, the time required for the switching needs to be sufficiently short with respect to the duration of the ignition.
Since the rotational speed of the engine is high, when the mechanism for mechanically driving the reflecting mirror and switching the optical path is driven manually, the switching time may be exceeded. Therefore, even when a mechanical mechanism is used, it is preferable to automatically drive with an electric signal.
Further, for example, an electro-optical element using the Pockels effect operates in a few ns. Therefore, if a laser switching device is configured with the electro-optical element and driven by an electrical activation signal, the switching time does not become a problem.
For this reason, in this embodiment, the laser switching element 40 is constituted by an electro-optical element.

The position of the ignition point by the second laser focusing unit 20 ′ is adjusted to be the same position as the ignition point 5 by the first laser focusing unit 20.
After switching the laser ignition, the first shutter 10 provided with the first laser focusing unit 20 is closed, and the optical fiber cable 30 is removed from the first laser focusing unit 20 (S04). Thereafter, the first laser focusing unit is removed from the first shutter 10 (S05).

  The removed optical window 23 of the first laser focusing unit 20 uses a solvent or is wiped with a soft cloth, or removes dirt by an appropriate method (S06). The first laser focusing unit 20 that has cleaned the optical window 23 is attached again to the first shutter 10 and the optical fiber cable 30 is attached so that it can be operated at any time (S07).

In addition, after removing the 1st laser focusing unit 20, you may mount | wear with the clean laser focusing unit prepared separately.
When the engine operation continues and this time the optical window 23 ′ of the second laser focusing unit 20 ′ is soiled, the second focusing unit 20 ′ is removed after switching to the first laser focusing unit 20 in the same procedure, What is necessary is just to wash | clean optical window 23 '.

  In the laser ignition device of the present invention, as described above, in order to smoothly switch the laser focusing unit, it is preferable that the focal position of the laser does not change even when the laser focusing unit is switched. In addition, in order to prevent the switching operation from overlapping with the timing of laser ignition, a laser switching element that can be switched at high speed is adopted, and a control circuit that switches in the exhaust stroke during the engine cycle that does not overlap with laser ignition is equipped. It is preferable to do.

  The laser ignition device of the present invention is operated by mounting a plurality of laser focusing units on the engine, and the laser focusing unit can be attached and detached without stopping the operation even during operation. And can be easily processed by any method.

It is a principal part schematic sectional drawing of the laser ignition device in one Example of this invention. It is a schematic block diagram of the laser ignition device of a present Example. It is the flowchart which showed the switching procedure in a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Combustion chamber wall 3, 3 'Laser irradiation hole 4 Laser light 5 Focus 10, 10' Shutter 11, 11 'Ball valve 12 Solenoid 13 Stem 20, 20' Laser converging unit 21 Enlarging optical system 22 Converging optical system 23, 23 'Optical window 24 Joint mechanism 30, 30' Optical fiber cable 31 Stopper 40 Laser switching element 41 Optical fiber cable 50 Laser generator

Claims (5)

A combustion chamber of an internal combustion engine is ignited by irradiating a laser beam through an optical window, the shutter having two or more laser irradiation holes in the combustion chamber and capable of opening and closing each of the laser irradiation holes A laser converging unit that irradiates the combustion chamber with the optical window and the converging optical system through the optical window is detachably attached to the shutter, and can be attached to and detached from the laser converging unit. A laser ignition device in which an optical fiber cable is connected to the optical fiber cable, the optical fiber cable is connected to a laser switching element, and the laser switching element is connected to laser transmission means.   The laser ignition device according to claim 1, wherein the shutter is a ball valve.   3. The laser ignition device according to claim 1, wherein the laser irradiated into the combustion chamber through the two or more laser irradiation holes has a focal point at the same position. 4.   4. The laser ignition device according to claim 1, wherein the laser switching element is configured using an electro-optic element. 5. The laser ignition device according to any one of claims 1 to 4, further comprising an interlock circuit assembled so that the switching of the laser does not overlap with the ignition timing.

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