JP2009121247A - Laser ignition device, internal combustion engine and laser ignition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser ignition device capable of igniting a fuel in a combustion chamber with low energy, an internal combustion engine adopting the ignition device and a laser ignition method capable of igniting the fuel with low energy. <P>SOLUTION: The laser ignition device 10 is provided with a laser device 26 for outputting laser pulse to the fuel in the combustion chamber 14 of the engine 12 capable of adjusting power and pulse width of its output laser pulses and a laser control circuit 30 for operating the laser device 26 at an ignition timing. The laser control circuit 30 controls the laser device 26 so that a laser pulse LP2 of which peak power is lower than a laser pulse LP1 is output from the laser device 26 to plasma generated in the combustion chamber after the laser pulse LP1 having a peak power capable of generating the plasma in the combustion chamber 14 is output from the laser device 26. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser ignition device that ignites fuel using laser light, an internal combustion engine, and a laser ignition method.

Techniques for igniting fuel in a combustion chamber of an internal combustion engine using laser light are known (see, for example, Patent Documents 1 to 4). Patent Document 1 describes a technique in which laser light is spatially divided into a plurality of beams and irradiated toward a piston. Patent Document 2 describes a technique of oscillating a plurality of pulses of laser light having equal energy at time intervals that enable normal ignition. Patent Document 3 describes a technique in which a wedge substrate is used to irradiate a wide range of the upper surface of a piston with laser light. Patent Document No. 4 describes three techniques for controlling the laser pulse width to be the minimum energy required for ignition. In addition, a technique is known in which breakdown is enhanced by irradiating a two-pulse laser with equal energy and pulse width at intervals of picoseconds (see Non-Patent Document 1).
JP-A-9-303244 JP 2005-42591 A JP-A-7-217521 JP 2006-144726 A HOSODA, AOSHIMA, ITOH, TSUCHIYA "Enhancement of the Laser Breakdown of simple Gaseous and Liquid Materials under Intense Picosecond Double-pulse Excitation" 1999 Publication Board, Japanese Journal of Applied Physics

  However, in the so-called target breakdown in which the piston is irradiated with laser light, there is a problem that laser energy is consumed for the temperature rise (sensible heat) of the piston. In addition, in absorption laser ignition in which laser light is directly irradiated into the gas in the combustion chamber, there is a problem that energy loss tends to increase due to the laser light passing through the ignition position before plasma is generated. there were.

  In consideration of the above facts, the present invention provides a laser ignition device capable of igniting fuel in a combustion chamber with low energy, an internal combustion engine to which the ignition device is applied, and a laser capable of igniting fuel with low energy. The purpose is to obtain an ignition method.

  According to a first aspect of the present invention, there is provided a laser ignition device capable of adjusting a power and a pulse width of an output laser pulse and outputting a laser pulse toward fuel in a combustion chamber of an internal combustion engine, and an ignition At a timing, after a first laser pulse having a peak power capable of generating plasma in the combustion chamber is output from the laser device, a second laser pulse having a lower peak power than the first laser pulse is output from the laser device. And a control device for controlling the laser device so as to be output toward the plasma generated in the combustion chamber.

  In the laser ignition device according to the first aspect, the first laser pulse is output toward the fuel in the combustion chamber of the internal combustion engine from the laser device that is controlled by the control means at the ignition timing. Thereby, plasma is generated in the combustion chamber of the internal combustion engine. Next, a second laser pulse is output from the laser device toward the plasma. Thereby, the fuel is ignited.

  Here, in this laser ignition device, after the plasma is generated by the first laser pulse having a large peak power, the second laser pulse is output toward the plasma in which the laser energy is easily absorbed. In addition, it is possible to prevent the laser light from passing through the fuel.

  Thus, in the laser ignition device according to the first aspect, the fuel in the combustion chamber can be ignited with low energy.

  A laser ignition device according to a second aspect of the present invention is the laser ignition device according to the first aspect, wherein the control device has a pulse width of the second laser pulse larger than a pulse width of the first laser pulse. In addition, the laser device is controlled.

  In the laser ignition device according to claim 2, since the pulse width of the second laser pulse is wider than the pulse width of the first laser pulse, the pulse width of the second laser pulse is the same as the pulse width of the first laser pulse. Compared to the case, a large amount of energy can be absorbed in the plasma generated by the output of the first laser pulse, which contributes to stable ignition.

  The laser ignition device according to a third aspect of the present invention is the laser ignition device according to the second aspect, wherein the control device is configured such that the energy of the second laser pulse is larger than the energy of the first laser pulse. Control the laser device.

  In the laser ignition device according to claim 3, since the energy of the second laser pulse is larger than the energy of the first laser pulse, the plasma generated by the output of the first laser pulse can absorb larger energy, Contributes to more stable ignition.

  According to a fourth aspect of the present invention, there is provided a laser ignition device capable of adjusting a power and a pulse width of a laser pulse to be output, and outputting a laser pulse toward fuel in a combustion chamber of an internal combustion engine; After a first laser pulse having a peak power capable of generating plasma in the combustion chamber at the timing is output from the laser device, a second laser pulse having a larger energy and pulse width than the first laser pulse is emitted from the laser. And a control device that controls the laser device so that it is output from the device toward the plasma generated in the combustion chamber.

  In the laser ignition device according to the fourth aspect, the first laser pulse is output from the laser device, which is controlled by the control means at the ignition timing, toward the fuel in the combustion chamber of the internal combustion engine. Thereby, plasma is generated in the combustion chamber of the internal combustion engine. Next, a second laser pulse is output from the laser device toward the plasma. Thereby, the fuel is ignited.

  Here, in this laser ignition device, the plasma is generated by the first laser pulse having relatively low energy, and then the second laser pulse is output toward the plasma in which the laser energy is easily absorbed. The laser beam is prevented from passing through the fuel before. And the big energy of a 2nd laser pulse can be absorbed after the above-mentioned plasma production | generation.

  Thus, in the laser ignition device according to the fourth aspect, the fuel in the combustion chamber can be ignited with low energy. Moreover, since the pulse width of the second laser pulse is larger than the pulse width of the first laser pulse, instantaneously excessive peak power is suppressed and the apparatus is protected.

  The laser ignition device according to a fifth aspect of the present invention is the laser ignition device according to any one of the first to fourth aspects, wherein the control device is configured to control the pulses of the first laser pulse and the second laser pulse. The laser device is controlled so that the interval is 200 ns or less.

  In the laser ignition device according to claim 5, since the pulse interval between the first laser pulse and the second laser pulse is 200 ns, the energy of the second laser pulse is increased before the plasma expands and the plasma density decreases. Can be absorbed. Note that the pulse interval between the first laser pulse and the second laser pulse is more preferably 20 ns or less.

  An internal combustion engine according to a sixth aspect of the invention includes the laser ignition device according to any one of the first to fifth aspects as an ignition device for igniting the fuel in the combustion chamber.

  In the internal combustion engine according to claim 6, the air-fuel mixture in the combustion chamber is stably ignited by the laser ignition device according to any one of claims 1 to 5.

  According to a seventh aspect of the present invention, there is provided a laser ignition method for irradiating a first laser pulse having a peak power capable of generating plasma toward an air-fuel mixture of fuel and air, and the first pulse. And a second pulse irradiation step of irradiating a second pulse having a peak power lower than that of the first laser pulse toward a position where the first laser pulse is irradiated in the irradiation step.

  In the laser ignition method according to claim 7, when the first laser pulse is irradiated in the first pulse irradiation step, plasma is generated in the space irradiated with the first laser pulse. Next, in the second laser pulse irradiation step, a second laser pulse is output toward the plasma. The fuel is ignited by this ignition method.

  Here, in this laser ignition method, after the plasma is generated by the first laser pulse having a large peak power, the second laser pulse is output toward the plasma in which the laser energy is easily absorbed. Laser light is prevented from passing through the fuel.

  Thus, in the laser ignition method according to the seventh aspect, the fuel can be ignited with low energy.

  The laser ignition method according to an eighth aspect of the present invention is the laser ignition method according to the seventh aspect, wherein the second pulse irradiation step is more pulsed than the first laser pulse irradiated in the first laser pulse irradiation step. A second laser pulse having a large width is irradiated.

  In the laser ignition method according to claim 8, since the pulse width of the second laser pulse is wider than the pulse width of the first laser pulse, the pulse width of the second laser pulse is the same as the pulse width of the first laser pulse. Compared to the case, the plasma generated by the output of the first laser pulse can absorb a large amount of energy, contributing to stable ignition.

  A laser ignition method according to a ninth aspect of the present invention is the laser ignition method according to the eighth aspect, wherein, in the second pulse irradiation step, energy is higher than that of the first laser pulse irradiated in the first laser pulse irradiation step. Is irradiated with a second laser pulse.

  In the laser ignition method according to claim 9, since the energy of the second laser pulse is larger than the energy of the first laser pulse, the plasma generated by the output of the first laser pulse can absorb a larger energy, Contributes to more stable ignition.

  A laser ignition method according to a tenth aspect of the present invention is a first pulse irradiation step of irradiating a first laser pulse having a peak power capable of generating plasma toward an air-fuel mixture of fuel and air, and the first pulse. And a second pulse irradiation step of irradiating a second pulse having energy and a pulse width larger than those of the first laser pulse toward the position irradiated with the first laser pulse in the irradiation step.

  In the laser ignition method according to claim 10, when the first laser pulse is irradiated in the first pulse irradiation step, plasma is generated in the space irradiated with the first laser pulse. Next, in the second laser pulse irradiation step, a second laser pulse is output toward the plasma. The fuel is ignited by this ignition method.

  Here, in this laser ignition method, after the plasma is generated by the first laser pulse having a large peak power, the second laser pulse is output toward the plasma in which the laser energy is easily absorbed. Laser light is prevented from passing through the fuel. And the big energy of a 2nd laser pulse can be absorbed after the above-mentioned plasma production | generation.

  Thus, in the laser ignition method according to claim 10, the fuel can be ignited with low energy. In addition, since the pulse width of the second laser pulse is larger than the pulse width of the first laser pulse, excessively high peak power is prevented from being generated instantaneously, and, for example, components constituting the laser pulse output path are protected. The

  The laser ignition method according to an eleventh aspect of the present invention is the laser ignition method according to any one of the seventh to tenth aspects, wherein the second laser pulse irradiation step includes the first laser pulse irradiation step. The second laser pulse is irradiated within 200 ns after the first laser pulse is irradiated.

  In the laser ignition method according to claim 11, since the pulse interval between the first laser pulse and the second laser pulse is 200 ns, the energy of the second laser pulse is reduced before the plasma expands and the plasma density decreases. Can be absorbed. Note that the pulse interval between the first laser pulse and the second laser pulse is more preferably 20 ns or less.

  As described above, the laser ignition device and the internal combustion engine according to the present invention can ignite the fuel in the combustion chamber with low energy.

  The laser ignition method according to the present invention has an excellent effect that the fuel can be ignited with low energy.

  A laser ignition device 10 and an engine 12 that is an internal combustion engine according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 schematically shows a laser ignition device 10 and an engine 12 to which the laser ignition device 10 is applied. As shown in this figure, the laser ignition device 10 emits a laser beam toward the fuel mixture M injected into the combustion chamber 14 of the engine 12, and an ignition device for igniting the fuel by the laser beam. Has been.

  Specifically, the engine 12 includes a cylinder 16, a piston 18 that is slidable along the inner surface of the cylinder 16, and a cylinder head 20 that seals the open end of the cylinder 16. The combustion chamber 14 is a space between the piston 18 and the cylinder head 20 in the cylinder 16. Further, the engine 12 has a fuel injection valve 22 provided in the cylinder head 20.

  The fuel injection valve 22 is controlled by the engine controller 24 to spray (inject) fuel into the combustion chamber 14 at the end of the compression stroke. As a result, in the combustion chamber 14, an air-fuel mixture M of fuel and air is generated at the end of the compression stroke. The laser ignition device 10 is configured to ignite the air-fuel mixture M with laser light. The engine 12 may be a premixed type in which the air-fuel mixture M premixed with air is supplied to the combustion chamber 14 of the engine 12 in the intake stroke instead of the direct fuel injection type.

  The laser ignition device 10 includes a laser device 26 that outputs laser light, a laser emitting unit 28 that emits the laser light of the laser device 26 to the combustion chamber 14 of the engine 12, and a control device (control means) that controls the laser device 26. The laser control circuit 30 is configured as a main component. As the laser device 26, for example, a solid-state laser device such as a YAG laser is used.

  The laser device 26 and the laser emitting unit 28 are connected to an optical fiber 32 as an optical transmission unit so that the laser light output from the laser emitting unit 28 is guided to the laser control circuit 30 through the optical fiber 32. It has become. In this embodiment, the laser control circuit 30 includes a substantially cylindrical housing 34 fixed to the cylinder head 20, window glasses 35 and 36 that close both ends of the laser control circuit 30 so that laser light can pass through, and the housing 34. The lens includes a concave lens 38 and a pair of convex lenses 40 and 42 provided therein.

  The laser emitting unit 28 is configured to irradiate the laser beam guided by the optical fiber 32 to the ignition position IP which is a predetermined position in the combustion chamber 14 of the engine 12. This ignition position IP is one point in a region where fuel is sprayed by the fuel injection valve 22. In other words, the laser emission unit 28 is configured to irradiate the laser beam with the lens 42 narrowed down toward the ignition position IP.

  The laser control circuit 30 controls the laser device 26 so that the laser device 26 outputs pulsed laser light (hereinafter referred to as a laser pulse). In this embodiment, the laser control circuit 30 is configured to output a plurality of laser pulses to the laser device 26 per one ignition stroke (fuel spray) of the engine 12 based on a control signal from the engine controller 24. The laser device 26 is controlled.

  Specifically, the laser control circuit 30 is configured to output two laser pulses LP1 and LP2 from the laser device 26 as shown in FIG. The laser control circuit 30 is sufficient to cause breakdown in the combustion chamber 14 due to the laser power peak P1 (hereinafter referred to as peak power) P1 of the laser pulse LP1 as the first laser pulse output earlier in time. The laser device 26 is controlled so as to have a size. Further, the laser control circuit 30 is configured so that the energy of the laser pulse LP1 (time integration of the laser power) is sufficiently smaller than the energy required to ignite the mixture M with a single laser pulse. 26 is controlled.

  Specifically, the laser control circuit 30 is configured to control the laser device 26 so that the pulse width Wp1 of the laser pulse LP1 is equal to or less than 50 ns in half width (pulse width at half the laser power of the peak P1). ing. In this embodiment, the pulse width of the laser pulse LP1 is set to about 5 ns or less as a half-value width.

  Further, the laser control circuit 30 temporally makes the peak power P2 of the laser pulse LP2 as the second laser pulse output after the laser pulse LP1 smaller than a magnitude sufficient to cause breakdown in the combustion chamber 14. Thus, the laser device 26 is controlled. That is, the peak power P2 of the laser pulse LP2 is set smaller than the peak power P1 of the laser pulse LP1.

  On the other hand, the laser control circuit 30 is configured to control the laser device 26 so that Wp2 of the laser pulse LP2 is larger than the pulse width Wp1 of the laser pulse LP1 and has a half value width of about 200 ns or less. In this embodiment, the laser control circuit 30 is configured to control the laser device 26 so that the energy of the laser pulse LP2 is larger than the energy of the laser pulse LP1.

  Further, the laser control circuit 30 is configured to control the laser device 26 so that the pulse interval τ between the laser pulse LP1 and the laser pulse LP2 is equal to or less than a predetermined interval. Specifically, the laser control circuit 30 is configured to control the laser device 26 so that the pulse interval τ is 200 ns or less. In this embodiment, the pulse interval τ is set to 20 ns or less. In this embodiment, the pulse interval τ is determined from the output command of the laser pulse LP1 from the laser control circuit 30 to the laser device 26 and the output command of the laser pulse LP2 from the laser control circuit 30 to the laser device 26. Defined as interval to output.

  In the laser ignition device 10, the air-fuel mixture M in the combustion chamber 14 is ignited (ignited) by irradiating the ignition position IP with the laser pulses LP1 and LP2 described above.

  Next, the operation of the first embodiment will be described.

  In the engine 12 to which the laser ignition device 10 having the above configuration is applied, the reciprocating linear motion of the piston 18 is not shown in the drawing by repeating the suction stroke, compression stroke, expansion stroke, and exhaust stroke in this order in the cylinder 16. It is converted into the rotational motion of and generates power. Supplementally, at the end of the compression stroke, fuel is sprayed into the combustion chamber 14 by the fuel injection valve 22 to generate an air-fuel mixture M, and the laser ignition device 10 emits laser pulses LP1 and LP2 toward the air-fuel mixture M. By continuously irradiating, the mixture M is ignited. The expansion stroke is performed by the combustion of the fuel in the air-fuel mixture M.

  Ignition by the laser ignition device 10 will be described in detail. When the laser control circuit 30 determines that it is the ignition timing based on the signal from the engine controller 24, when the laser pulse LP1 is output from the laser device 26 controlled by the laser control circuit 30, the laser pulse LP1 is guided to the laser emitting section 28 via the optical fiber 32, and is irradiated to the ignition position IP in the combustion chamber 14 through the window glass 35, the concave lens 38, the pair of convex lenses 40 and 42, and the window glass 36 (first). 1 pulse irradiation step).

  When the laser pulse LP1 is irradiated toward the air-fuel mixture M in this way, the peak power P1 of the laser pulse LP1 exceeds the power sufficient to cause breakdown, and therefore breakdown occurs at the ignition position IP. For this reason, plasma is generated at the ignition position IP in the combustion chamber 14.

  Further, when the laser pulse LP2 is output from the laser device 26 controlled by the laser control circuit 30, the laser pulse LP2 is guided to the laser emitting unit 28 via the optical fiber 32, and the window glass 35, the concave lens 38, the ignition position IP in the combustion chamber 14 is irradiated through the pair of convex lenses 40 and 42 and the window glass 36 (second pulse irradiation step). That is, the laser pulse LP2 is applied to the plasma generated by the irradiation of the laser pulse LP1.

  Thereby, in the laser ignition device 10, a part of the energy of the laser pulse LP2 is absorbed by the plasma to further develop the plasma. When the plasma energy reaches the minimum ignition energy of the fuel, the fuel is ignited (ignited).

  As described above, in the laser ignition device 10, the plasma generated by the irradiation of the laser pulse LP1 having a large peak power P1 is irradiated with the laser pulse LP2, so that the energy of the laser pulse LP2 is efficiently absorbed by the plasma. . For this reason, the fuel can be ignited with small energy by combining the laser pulse LP1 and the laser pulse LP2.

  Further, in the laser ignition device 10, since the pulse width Wp1 of the laser pulse LP1 is small, in other words, since the energy of the laser pulse LP1 is small, even if the peak power P1 is increased, the optical components of the laser emitting unit 28 are damaged. It is prevented from occurring. On the other hand, in the laser ignition device 10, since the pulse width Wp2 of the laser pulse LP2 is large, that is, to irradiate the laser pulse LP2 with increased energy while keeping the peak power P2 low, the plasma generated by the irradiation of the laser pulse LP1 is generated. Can absorb a large amount of energy.

  In the laser ignition device 10, since the energy of the laser pulse LP2 is larger than that of the laser pulse LP1, in other words, plasma is first generated by the laser pulse LP1 having low energy, and the plasma absorbs the large energy of the laser pulse LP2. Therefore, the fuel can be ignited with less energy compared to the configuration in which the laser is ignited with one laser pulse.

  The effect of reducing the ignition energy by the irradiation of the laser pulses LP1 and LP2 will be supplemented with reference to the experimental results shown in FIGS. First, the experimental apparatus shown in FIG. 5 will be described. The experimental apparatus 100 includes a half mirror 102 that divides the laser light emitted from the laser apparatus 101, a laser energy meter 104 for detecting the energy of the laser light divided by the half mirror 102, and the residual that is divided by the half mirror 102. A quartz plate 106 that reflects a part of the laser light, a lens 108 that condenses the laser light that has passed through the quartz plate 106 onto the condensing part C, a lens 110 that returns the laser light that has passed through the condensing part C to parallel light, and a lens A quartz plate 112 that reflects a part of the laser light returned to parallel light at 110, a neutral density filter 114 that attenuates the laser light reflected by the quartz plate 106, and a laser light that is attenuated by the neutral density filter 114 A light receiving element (Pin photodiode) 116 for receiving light, a light reducing filter 118 for reducing laser light reflected by the quartz plate 112, and a light reducing filter The light receiving element (Pin photodiode) 120 that receives the laser light attenuated by 118, the lens 122 that condenses the light from the condensing unit C, and the wavelength of the laser light among the light condensed by the lens 122 is cut. It includes a filter 124, a light receiving element (Pin photodiode) 126 that receives light that has passed through the filter 124, and a gigascope (not shown) (sampling frequency 20 GHz) that records temporal changes in the output signals of the light receiving elements 116, 120, and 126. Has been. The rise time (step response) of each light receiving element 116, 120, 126 is 175 ps.

  In the experiment by the experimental apparatus 100, a laser pulse is output from the laser apparatus 101, the laser pulse before reaching the condensing part C is reflected by the quartz plate 106, and incident light is detected by the light receiving element 116. Further, the laser pulse transmitted through the condensing part C is reflected by the quartz plate 112 and detected by the light receiving element 120. Further, when plasma light emission (self-emission) occurs due to the generation of plasma in the condensing unit C, the light is detected by the light receiving element 126.

  FIG. 7B shows an experimental result when the laser device 101 generates a single laser pulse whose peak power is lower than a power sufficient to cause breakdown. From this figure, it can be seen that the incident light detected by the light receiving element 116 and the transmitted light detected by the light receiving element 120 substantially coincide. That is, in this case, almost all of the laser energy is transmitted without being absorbed by the condensing part C. FIG. 7A shows the experimental results when a single laser pulse having a peak power equal to or higher than a power sufficient to cause breakdown is generated from the laser apparatus 101. Before the breakdown occurs, it can be seen that the incident light and the transmitted light substantially coincide with each other as in the case of FIG. On the other hand, after the breakdown occurs, it can be seen that the transmitted light decreases with respect to the incident light. That is, it can be seen that after the generation of plasma due to the occurrence of breakdown, the energy of the laser pulse (energy corresponding to the area of the hatched portion) is absorbed by the plasma at the condensing part C.

  FIG. 3 shows the experimental results when the laser apparatus 101 outputs two laser pulses. FIG. 3B shows the experimental results when the peak power of each laser pulse is lower than the power sufficient to cause breakdown. From this figure, it can be seen that the incident light detected by the light receiving element 116 and the transmitted light detected by the light receiving element 120 substantially coincide. That is, in this case, almost all of the laser energy is transmitted without being absorbed by the condensing part C.

  On the other hand, FIG. 3A shows that the peak power P1 of the laser pulse LP1 irradiated earlier is higher than the power sufficient to cause breakdown, and the peak power P2 of the laser pulse LP2 is equivalent to FIG. 3B. The experimental results are shown when the power is less than sufficient to cause the breakdown. From this figure, it can be seen that the transmitted light is reduced with respect to the incident light from immediately after the occurrence of breakdown to the period in which the laser pulse LP2 is irradiated. That is, when breakdown occurs due to the laser pulse LP1, even a weak energy (power) laser pulse LP2 that cannot generate breakdown by itself is efficiently absorbed by the plasma generated by the laser pulse LP1 immediately after laser irradiation. I understand that In this experiment, plasma emission that was not observed in the experiment of FIG. 3B was observed. It can be seen that plasma light emission occurs immediately after breakdown occurs. It can also be seen that the plasma emission is enhanced in synchronism with the timing of incidence of the laser pulse LP2. That is, after the breakdown caused by the irradiation of the laser pulse LP1, the energy of the laser pulse LP1 and the energy of the laser pulse LP2 (the energy corresponding to the area of the hatched portion) are generated from the occurrence of the breakdown. It can be seen that plasma emission is enhanced by absorption by plasma. FIG. 3B shows the result when the pulse interval τ is approximately 8.7 ns. FIG. 3B shows an experimental result when the energy of the laser pulse LP2 is equal to or less than the energy of the laser pulse LP1.

  FIG. 4 shows plasma emission when the pulse interval τ between the laser pulse LP1 and the laser pulse LP2 is changed. It can be seen that the smaller the pulse interval τ, the greater the degree of enhancement of plasma emission by irradiation with the laser pulse LP2. Note that the greater the pulse interval τ, the smaller the degree of enhancement of plasma emission by irradiation with the laser pulse LP2, because the plasma generated by irradiation with the laser pulse LP1 expands with time and the plasma density decreases. It is believed that there is. Although illustration is omitted, it has been confirmed that when the pulse interval τ is 200 ns or more, plasma emission due to irradiation with the laser pulse LP2 is not observed. The same was true when a higher energy laser pulse LP2 was irradiated. In the laser ignition device 10 according to the first embodiment, since the pulse interval τ is set to 20 ns or less, the degree of enhancement of plasma emission by irradiation with the laser pulse LP2 is large.

  As described above, almost all of the energy irradiated before the breakdown is transmitted is not used as ignition energy. In the configuration in which ignition is performed with one laser pulse, the energy of the laser pulse is large, so that the energy that is transmitted before the breakdown occurs is large. On the other hand, in the laser ignition device 10, it is sufficient that the laser pulse LP1 has a peak power for generating a breakdown, so that the energy transmitted can be suppressed to a low level by reducing the energy. Then, by irradiating the plasma generated with the breakdown caused by the irradiation of the laser pulse LP1 with the laser pulse LP2, the plasma can absorb the energy required for ignition. That is, energy required for ignition can be stored in the ignition position IP.

  Therefore, the laser ignition device 10 can perform ignition while suppressing the total energy of the laser pulse LP1 and the laser pulse LP2 to be small as compared with a configuration in which ignition is performed by one laser pulse. Further, since the absolute value of the energy generated by the laser device 26 is reduced, the power consumption of the laser ignition device 10 can be reduced. Furthermore, the light source for laser excitation (for example, a flash lamp, a semiconductor laser, etc.) constituting the laser device 26 can be reduced. In addition, the cooling system can be simply configured, and the laser ignition device 10 can be downsized as a whole.

  In addition, since the pulse width Wp2 of the laser pulse LP2 is large as described above, the peak power P2 can be suppressed while increasing the energy of the laser pulse LP2, and the optical components constituting the laser emitting unit 28 can be protected. .

  Furthermore, since the engine 12 includes the laser ignition device 10 having the above-described configuration, the mixture M in the combustion chamber 14 is stably ignited with a small amount of energy.

  Next, a second embodiment of the present invention will be described. Note that components / portions that are basically the same as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof may be omitted, and illustration may be omitted.

  FIG. 6 schematically shows a laser ignition device 50 according to a second embodiment of the present invention and an engine 52 to which the laser ignition device 50 is applied. As shown in this figure, the laser ignition device 50 is a laser ignition in which a laser device 26 is provided outside the engine 12 in that a Q-switch type solid-state laser 54 as a laser device is disposed in a housing 34. Different from the device 10.

  In this laser ignition device 50, an LD (laser diode) laser 56 as a light source is provided outside the engine 52, and laser light from the LD laser 56 passes through an optical fiber 32 and a lens 58 to form a Q-switched solid-state laser. 54 is led. The lens 58 is disposed in the optical fiber 32.

  Further, the laser ignition device 50 includes an LD laser control circuit 60. Based on a control signal from the engine controller 24, the LD laser control circuit 60 injects fuel from the fuel injection valve 22 in the compression stroke of the engine 52, and then lasers the Q-switched solid-state laser 54 toward the ignition position IP. The LD laser 56 is controlled so that the pulse LP1 and the laser pulse LP2 are emitted.

  In this embodiment, the Q-switched solid-state laser 54 and the LD laser 56 correspond to the laser device in the present invention, and the LD laser control circuit 60 corresponds to the control device in the present invention. Other configurations of the laser ignition device 50 are the same as the corresponding configurations of the laser ignition device 10.

  Therefore, also with the laser ignition device 50 according to the second embodiment, the same effect can be obtained by the same operation of the laser ignition device 10. That is, a breakdown is generated by irradiation with a laser pulse LP1 having a high peak power to generate plasma, and this plasma is irradiated with a laser pulse LP2, thereby igniting the mixture M in the combustion chamber 14 with a small total energy. be able to.

  In each of the above-described embodiments, the example in which the two laser pulses LP1 and LP2 are irradiated is shown. However, the present invention is not limited to this, and for example, three laser pulses per one ignition stroke (fuel spray) of the engine 12 are used. The above laser pulse may be emitted toward the ignition position IP.

  In the above-described embodiment, an example in which the number of ignition positions IP is one in the combustion chamber 14 is shown. However, the present invention is not limited to this, and for example, a plurality of laser pulses ( (Laser pulses LP1, LP2, etc.) may be irradiated.

  Furthermore, in the above-described embodiment, an example is shown in which the optical fiber 32 is used to guide the laser pulse from the laser device 26 to the laser emitting unit 28 or the laser light from the LD laser 56 to the Q-switched solid-state laser 54. The present invention is not limited to this. For example, a laser or the like is used to guide a laser pulse from the laser device 26 to the laser emitting unit 28, or to guide a laser beam from the LD laser 56 to the Q-switched solid-state laser 54. May be.

  Furthermore, the present invention is not limited to the configuration and method of each embodiment described above, and any configuration that can irradiate the predetermined ignition position IP with the laser pulses LP1 and LP2 in this order is sufficient. Needless to say, various modified configurations are possible.

  Furthermore, in the above-described embodiment, an example in which the laser pulse LP2 has a larger pulse width and energy than the laser pulse LP1 has been shown. However, the present invention is not limited to this. For example, the energy of the laser pulse LP2 is the laser pulse. It is good also as a structure equivalent to the energy of LP1. Further, for example, the peak power P2 of the laser pulse LP2 may be large enough to cause breakdown alone.

1 is a schematic diagram showing a schematic overall configuration of a laser ignition device according to a first embodiment of the present invention. It is a diagram showing typically the shape of the laser pulse with which the laser ignition device concerning a 1st embodiment of the present invention irradiates. (A) is a diagram which shows the irradiation experiment result of the laser pulse imitating the irradiation pattern of the laser pulse in the laser ignition device according to the first embodiment of the present invention, and (B) is a diagram showing (A9) in FIG. It is a diagram which shows the irradiation experiment result of the comparative example laser pulse. It is a diagram which shows the difference in the plasma light emission at the time of changing the irradiation interval of the laser pulse in the laser ignition apparatus which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the experimental apparatus for performing experiment of FIG. 3, FIG. It is a schematic diagram which shows the schematic whole structure of the laser ignition apparatus which concerns on the 2nd Embodiment of this invention. It is a diagram which shows the irradiation experiment result of the laser pulse which concerns on the comparative example with embodiment of this invention, (A) is a diagram which shows the experimental result when a plasma is produced | generated, (B) does not produce | generate a plasma It is a diagram which shows the experimental result in a case.

Explanation of symbols

10 Laser ignition device 12 Engine (internal combustion engine)
14 Combustion chamber 26 Laser device 30 Laser control circuit (control device)
50 Laser ignition device 52 Engine (internal combustion engine)
54 Q-switched solid-state laser (laser device)
56 LD laser (laser device)
60 LD laser control circuit (control device)
LP1 laser pulse (first laser pulse)
LP2 laser pulse (second laser pulse)

Claims (11)

A laser device capable of adjusting power and pulse width of a laser pulse to be output, and outputting a laser pulse toward fuel in a combustion chamber of an internal combustion engine;
After a first laser pulse having a peak power capable of generating plasma in the combustion chamber is output from the laser device at the ignition timing, a second laser pulse having a peak power lower than the first laser pulse is output from the laser device. A control device for controlling the laser device so as to be output toward the plasma generated in the combustion chamber from
A laser ignition device comprising:   The laser ignition device according to claim 1, wherein the control device controls the laser device so that a pulse width of the second laser pulse is larger than a pulse width of the first laser pulse.   3. The laser ignition device according to claim 2, wherein the control device controls the laser device so that energy of the second laser pulse is larger than energy of the first laser pulse. A laser device capable of adjusting power and pulse width of a laser pulse to be output, and outputting a laser pulse toward fuel in a combustion chamber of an internal combustion engine;
After the first laser pulse having a peak power capable of generating plasma in the combustion chamber is output from the laser device at the ignition timing, the second laser pulse having energy and pulse width larger than those of the first laser pulse is A control device for controlling the laser device such that the laser device is output toward the plasma generated in the combustion chamber;
A laser ignition device comprising:   The laser ignition device according to any one of claims 1 to 4, wherein the control device controls the laser device so that a pulse interval between the first laser pulse and the second laser pulse is 200 ns or less. .   An internal combustion engine comprising the laser ignition device according to any one of claims 1 to 5 as an ignition device for igniting fuel in a combustion chamber. A first pulse irradiation step of irradiating the fuel with a first laser pulse having a peak power capable of generating plasma;
A second pulse irradiation step of irradiating a second pulse having a peak power lower than that of the first laser pulse toward the position irradiated with the first laser pulse in the first pulse irradiation step;
Including a laser ignition method.   8. The laser ignition method according to claim 7, wherein in the second pulse irradiation step, a second laser pulse having a pulse width larger than that of the first laser pulse irradiated in the first laser pulse irradiation step is irradiated.   9. The laser ignition method according to claim 8, wherein in the second pulse irradiation step, a second laser pulse having a larger energy than that of the first laser pulse irradiated in the first laser pulse irradiation step is irradiated. A first pulse irradiation step of irradiating the fuel with a first laser pulse having a peak power capable of generating plasma;
A second pulse irradiation step of irradiating a second pulse having energy and a pulse width larger than those of the first laser pulse toward the position irradiated with the first laser pulse in the first pulse irradiation step;
Including a laser ignition method.   11. The method according to claim 7, wherein, in the second laser pulse irradiation step, the second laser pulse is irradiated within 200 ns after the first laser pulse is irradiated in the first laser pulse irradiation step. The laser ignition method as described.

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