JP4378516B2 - Laser ignition device and laser ignition method for internal combustion engine - Google Patents

Description

  The present invention relates to a laser ignition device and a laser ignition method for an internal combustion engine that forcibly ignites and burns a premixed gas or a layered gas mixture in a cylinder of the internal combustion engine.

Conventionally, an ignition system for an internal combustion engine that ignites a premixed gas or a layered gas mixture by a spark of a spark plug is used.
Further, as an ignition method for an internal combustion engine, a method has been proposed in which laser light is irradiated to a premixed gas or a layered gas mixture in a combustion chamber to ignite.
JP-T-2004-524478 JP-T 63-502682-

However, in the ignition method by spark discharge sparks, when the compression ratio is increased, the end gas self-ignites around the cylinder bore away from the ignition position of the ignition plug and knocking occurs. In this case, it is easy to wear and there is a problem in durability.
Further, in the conventional laser ignition system, in order to generate reliable ignition, the laser output must be increased, which causes problems such as an increase in the size of the apparatus and an increase in cost.

  The present invention solves the above-mentioned problems, reduces the laser output while ensuring reliable laser ignition, and achieves downsizing and cost reduction of the internal combustion engine including the ignition device. The purpose is to provide.

In order to solve the above problems, a laser ignition device for an internal combustion engine according to the present invention irradiates a pulse laser beam into a high-temperature / high-pressure premixed gas or a layered gas mixture in a cylinder of the internal combustion engine by a laser irradiation means, to generate, in the laser ignition device for the generated premix gas or an internal combustion engine for igniting the stratified mixture in the plasma into the cylinder to absorb the laser energy, pulse width of the pulse laser light provided to the cylinder, minimum ignition The pulse width of the pulse laser beam emitted from the laser irradiation means is made ultrashort by using a pulse width shortening device so as to have a pulse width as input energy .

  According to a second aspect of the present invention, in the laser ignition device for an internal combustion engine according to the first aspect of the invention, the laser irradiating means converges the pulsed laser beam into the cylinder using a condensing optical system.

  According to a third aspect of the present invention, in the laser ignition device for an internal combustion engine according to the first or second aspect of the invention, the laser irradiating means transmits a pulsed laser beam from a laser light source to the emitting part of the cylinder via the light transmitting means. It is characterized by that.

  According to a fifth aspect of the present invention, in the laser ignition device for an internal combustion engine according to the fourth aspect of the invention, the pulse width shortening device is arranged at an emission part of a cylinder of the internal combustion engine.

  According to a sixth aspect of the present invention, in the laser ignition device for an internal combustion engine according to the fourth aspect of the present invention, as the pulse width shortening device, an optical fiber as one of pulse laser beam optical transmission means has a pulse width shortening function. It is characterized in that no special device is required for the part.

  According to a seventh aspect of the present invention, in the laser ignition device for an internal combustion engine according to any one of the first to sixth aspects of the present invention, one laser light source and a plurality of internal combustion engine cylinders are connected by an optical transmission means.

  In the eighth aspect of the invention, a pulsed laser beam is irradiated into a high-temperature / high-pressure premixed gas or a layered gas mixture in a cylinder of an internal combustion engine to cause breakdown, and the generated plasma absorbs the laser energy so that In a laser ignition method of an internal combustion engine that ignites a premixed gas or a stratified gas mixture, the pulse width of the pulse laser beam irradiated into the cylinder is set to a pulse width that becomes a minimum ignition input energy.

According to the laser ignition device for an internal combustion engine of the present invention, a laser irradiation means irradiates a pulsed laser beam into a high-temperature / high-pressure premixed gas or a layered gas mixture in a cylinder of the internal combustion engine, and generates a breakdown. In the laser ignition device of an internal combustion engine that absorbs the laser energy into the plasma and ignites the premixed gas or the layered gas mixture in the cylinder, the laser irradiation means has a minimum pulse width of the pulse laser beam irradiated in the cylinder. With the configuration of the pulse width as the input energy, the laser output can be reduced to ensure reliable laser ignition, and the internal combustion engine including the ignition device can be made compact and the cost can be reduced.
At that time, according to the present invention, the pulse width shortening device can be used to obtain a pulse laser beam having an ultrashort pulse width with a laser light source having a normal pulse width.
Since the laser irradiation means uses a condensing optical system to focus the pulsed laser light in the cylinder of the internal combustion engine, laser ignition can be performed at a desired position in the cylinder of the internal combustion engine, so that heat efficient combustion is achieved. It becomes possible.
The laser irradiation means transmits the pulse laser light from the laser light source to the cylinder of the internal combustion engine by the light transmission means, so that the arrangement of the laser light source can be arranged at a position free from the influence of heat and vibration, and the degree of freedom of design is expanded. To do.
With the configuration in which the pulse width shortening device is disposed immediately before the cylinder of the internal combustion engine, it is possible to prevent the pulse laser beam having an ultrashort pulse width from damaging the optical transmission means such as an optical fiber.
As the pulse width shortening device, an optical fiber, which is one of the means for transmitting pulse laser light, has a pulse width shortening function and does not require a special device at the exit of the cylinder. The device can be made compact by utilizing the pulse width shortening function.
The apparatus can be made compact by a configuration in which one laser light source and a plurality of internal combustion engine cylinders are connected by optical transmission means.
Further , according to the laser ignition method for an internal combustion engine of the present invention, a plasma generated by irradiating a pulsed laser beam into a high-temperature / high-pressure premixed gas or a layered gas mixture in a cylinder of the internal combustion engine to generate breakdown. In the laser ignition method of an internal combustion engine that absorbs the laser energy to ignite the premixed gas or the stratified gas mixture in the cylinder, the pulse width of the pulse laser beam irradiated into the cylinder becomes the pulse width that becomes the minimum ignition input energy Thus, by providing a process for making the pulse width of the pulsed laser light emitted from the laser irradiation means ultrashort , the laser output can be reduced and reliable laser ignition can be achieved as in the ignition device for the internal combustion engine. Thus, the internal combustion engine including the ignition device can be made compact and the cost can be reduced.

  The laser ignition system of the internal combustion engine of the present invention irradiates the premixed gas or the layered gas mixture in the cylinder of the internal combustion engine with a pulsed laser beam to generate breakdown, and the generated plasma absorbs the laser energy and absorbs it. When the energy exceeds the minimum ignition energy corresponding to the fuel, the fuel / air pre-mixture or the layered mixture is ignited. The breakdown is said to be largely dependent on the peak value of the laser. That is, when the pulse width of the pulse laser beam is shortened, the peak value increases, so that the breakdown threshold value decreases. Therefore, we investigate the breakdown threshold due to the difference in the pulse width of the pulsed laser beam, and clarify the relationship between the laser energy required for ignition and the laser energy absorbed by the plasma generated by breakdown.

  FIG. 1 shows an experimental apparatus used for elucidating the laser ignition mechanism of the internal combustion engine of the present invention. In the experimental apparatus, the pulsed laser light emitted from the laser light source is branched by a beam splitter after the power is adjusted by a half-wavelength plate and a polarizing plate, and a part of it is a power meter (manufactured by MOLETRON: J25HR). The input energy is measured. The other of the branched pulsed laser light is condensed by a convex lens, irradiated in the atmosphere in a non-combustion experiment, and irradiated into the combustion chamber from a combustion chamber window in a combustion experiment and condensed at a focal point, and then a power meter (MOLECRON). Energy is measured by J25HR). The used lenses are three types of f = 50, 100, and 150 mm in the non-combustion experiment, and f = 50 mm in the combustion experiment. In the non-combustion experiment, dry air was flowed in order to prevent the temperature around the kernel from rising due to continuous transmission. The lasers used were Nd-YAG lasers with four pulse widths (FWHM) of 24 ps, 150 ps, 5 ns, and 20 ns. In the ignition experiment, the combustion chamber was at room temperature and normal pressure, and the equivalence ratio of methane-air premixed gas was changed from 0.6 to 1.0.

  FIG. 2 shows the relationship between the pulse width of the pulsed laser beam and the breakdown threshold value in the experimental apparatus shown in FIG. As shown in FIG. 2, when the pulse width of the pulse laser beam is shorter than nanoseconds, the breakdown threshold is small, and the difference with respect to the change in the pulse width is small. Conversely, when the pulse width of the pulsed laser light is on the order of nanoseconds, the exponential function of the breakdown threshold increases. This is because the breakdown depends on the power (energy density) of the laser, and the shorter the pulse width of the pulse laser light, the higher the power and the lower the breakdown threshold.

  FIG. 3 shows the relationship between the minimum ignition input energy and the pulse width of the pulse laser beam when the equivalence ratio is changed. As shown in FIG. 3, the change in the minimum ignition input energy due to the difference in the pulse width of the pulse laser beam is the smallest when the pulse width of the pulse laser beam is 150 ps regardless of the equivalence ratio, and the order is 5 ns and 24 ps. It has become. The difference between the pulse width of the pulse laser beam between 5 ns and 24 ps was small. Since the minimum ignition energy corresponding to the fuel is constant regardless of the laser, the result of this experiment is that if a laser with a pulse width of 150 ps is used, the amount of energy absorbed by the plasma is the largest, and the output of the laser Is the smallest.

Summarizing the results of the above experiments, the breakdown threshold becomes smaller as the pulse width of the pulse laser beam becomes shorter, but the energy absorption rate to the plasma generated thereafter is smaller. Considering ignition, it was found that using a laser with a short pulse width of the pulse laser beam under conditions where the minimum ignition energy is low, and using a laser with a long pulse width of pulse laser light under conditions where the minimum ignition energy is large did. As a result of the ignition experiment of the methane-air premixed gas, the minimum ignition input energy increased in the order of 150 ps, 24 ps, and 5 ns of the pulse width of the pulse laser beam. In other words, it has been found that the laser energy can be minimized by using a laser with a sub-nanosecond pulse width for laser ignition.

  Considering that the minimum ignition energy varies depending on the type of fuel, in general pulsed laser light with a long pulse width, the energy required for ignition is generally input to the plasma in the laser energy generated by the plasma. When the pulse width of the pulse laser beam is shortened, the energy for generating plasma is reduced, and as a result, the energy accumulated in the plasma is reduced, which may be lower than the minimum ignition energy corresponding to the fuel. The laser energy required for laser ignition can be minimized because the laser energy required for generating plasma by breakdown is small and the energy absorbed in the plasma exceeds the minimum ignition energy according to the fuel. It is important to select the pulse width of the light.

FIG. 4 shows an embodiment in which the present invention is applied to a laser ignition device for an internal combustion engine.
In FIG. 4, reference numeral 1 denotes a cylinder of the internal combustion engine, and a piston 9 is disposed in the cylinder 1 so as to freely reciprocate. A suction port 2 and an exhaust port 3 are opened in a combustion chamber 10 formed between the cylinder 1 and the piston 9. An intake pipe 4 having an intake valve 6 is installed at the suction port 2, and an exhaust pipe 5 having an exhaust valve 7 is installed at the exhaust port 3. A fuel / air premixed gas 8 (air in the case of a diesel) is supplied to the combustion chamber 10 from the intake pipe 4. The gas after combustion is exhausted from the exhaust pipe 5. The laser / light premixed gas 8 in the combustion chamber 10 of the cylinder 1 of the internal combustion engine is irradiated with pulsed laser light having an optimum pulse width from the laser light source 11. The laser light source 11 is desirably arranged at a position not affected by the heat and vibration of the cylinder 1 of the internal combustion engine. The pulsed laser light from the laser light source 11 is converged through a lens 14 at a desired position in the combustion chamber 10 of the cylinder 1 of the internal combustion engine via laser light transmission means 12 such as an optical fiber. Although it is possible to arrange the laser light source 11 directly on the cylinder 1 of the internal combustion engine, it is desirable to arrange the laser light source 11 at a position not affected by the heat and vibration of the cylinder 1 of the internal combustion engine. The pulsed laser light focused on the combustion chamber 10 generates breakdown in the premixed gas, generates plasma, and then absorbs the laser energy in the plasma and ignites the premixed gas. When the optimum pulse width of the pulse laser beam is very short, the pulse width shortening device 13 is installed in the laser beam transmission means using a laser light source having a pulse width of the pulse laser beam that is normally used. When the pulse width of the pulse laser beam is very short, there is a risk of damaging the laser beam transmission means 12 such as an optical fiber. Therefore, the pulse width shortening device 13 is connected to the cylinder 2 of the internal combustion engine that hits the final end of the laser beam transmission means 12. It is desirable to install at the laser beam irradiation position. Although not shown, one laser light source and a plurality of cylinders can be connected by an optical transmission means.

5A and 5B show an embodiment of a pulse width shortening device.
FIG. 5A shows the pulsed laser light from the laser light source, which is polarized and separated by the beam separator 15, and one of the linearly polarized components that has been polarized and separated is passed through the quarter-wave plate 16 and the lens 17. 18, is totally reflected in the generator cell 18, passes through the incident path, and is extracted from the beam separator 15 as pulsed laser light with a reduced pulse width. FIG. 5B shows an amplifying cell 19 disposed between the quarter-wave plate 16 and the lens 17 in the embodiment of FIG.

  Also, as another embodiment, as a pulse width shortening device, an optical fiber that is one of pulse laser beam optical transmission means has a pulse width shortening function, and a configuration that does not require a special device at the emission part of the cylinder can do. This utilizes the fact that a double clad optical fiber has a pulse width compression function. Since it is not necessary to install a pulse width shortening device at the emission part of the cylinder, the device can be made compact.

As a laser ignition method of an internal combustion engine, a cylinder is formed by irradiating a pulsed laser beam into a high-temperature / high-pressure premixed gas or a layered gas mixture in a cylinder of the internal combustion engine, generating a breakdown, and absorbing the laser energy in the generated plasma. In a laser ignition method for an internal combustion engine that ignites an internal premixed gas or a stratified gas mixture, the pulse width that makes the pulse width of the pulse laser light irradiated into the cylinder the minimum ignition input energy that exceeds the minimum ignition energy according to the fuel And

It is a figure which shows the experimental apparatus used in this invention. It is a figure which shows the relationship between a pulse width and a breakdown threshold value. It is a figure which shows the relationship between an equivalence ratio and minimum ignition input energy. It is a figure which shows one Embodiment of the laser ignition device of the internal combustion engine of this invention. (A) (b) It is a figure which shows one Embodiment of the pulse width shortening apparatus used for this invention.

Explanation of symbols

1: Cylinder of internal combustion engine 2: Suction port 3: Exhaust port 4: Intake pipe 5: Exhaust pipe 6: Intake valve 7: Exhaust valve 8: Fuel / air premixed air (in the case of diesel)
9: Piston 10: Combustion chamber 11: Laser light source 12: Laser light transmission means 13: Pulse width shortening device 14: Lens 15: Beam separator 16: 1/4 wavelength plate 17: Lens 18: Generator cell 19: Amplifier

Claims (7)

The laser irradiation means irradiates pulse laser light into the high-temperature / high-pressure premixed gas or layered gas mixture in the cylinder of the internal combustion engine, generates breakdown, and the generated plasma absorbs the laser energy to premix in the cylinder. In a laser ignition device of an internal combustion engine that ignites air or a layered mixture,
The pulse width of the pulse laser beam emitted from the laser irradiation means is set to a very short value by using a pulse width shortening device so that the pulse width of the pulse laser beam irradiated into the cylinder becomes a pulse width that is the minimum ignition input energy. A laser ignition device for an internal combustion engine. 2. The laser ignition device for an internal combustion engine according to claim 1, wherein the laser irradiating means converges the pulsed laser beam at a desired position in the cylinder using a condensing optical system. 3. The laser ignition device for an internal combustion engine according to claim 1, wherein the laser irradiation unit transmits a pulse laser beam from a laser light source to an emission part of the cylinder through the light transmission unit. 4. The laser ignition device for an internal combustion engine according to claim 1, wherein the pulse width shortening device is arranged at an emission part of a cylinder . The pulse width shortening device is characterized in that an optical fiber, which is one of the means for transmitting pulse laser light, has a pulse width shortening function, and no special device is required at the exit of the cylinder. 3. A laser ignition device for an internal combustion engine according to 3 . 6. The laser ignition device for an internal combustion engine according to claim 1, wherein one laser light source and a plurality of cylinders of the internal combustion engine are connected by optical transmission means . Pulsed laser light is radiated into a high-temperature / high-pressure premixed gas or layered gas mixture in a cylinder of an internal combustion engine to generate breakdown, and the generated plasma absorbs laser energy to cause premixed gas or layered gas mixture in the cylinder. In a laser ignition method for an internal combustion engine that ignites,
A step of making the pulse width of the pulse laser beam irradiated from the laser irradiation means ultrashort so that the pulse width of the pulse laser beam irradiated into the cylinder becomes a pulse width that is the minimum ignition input energy A method of laser ignition of an internal combustion engine characterized by the above .

Images