JP2008002279A - Combustion control device for laser ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the lean limit of an internal combustion engine by detecting a region where the fuel concentration of the air-fuel mixture is high and igniting ignition energy at a portion where the fuel concentration is high to burn the fuel in the lean burn engine combustion control device This contributes to improved fuel economy and reduced exhaust NOx.
SOLUTION: A measuring laser beam is irradiated into a cylinder 1 from a measuring laser beam emitting device 16 and a light amount is measured by an optical sensor 17, and a fuel concentration in an air-fuel mixture is determined from an absorption amount of the measuring laser beam with respect to fuel. In addition to the detection, the condensing optical system 8 and the electron optical element 9 are controlled according to the detection result to change the ignition position.
[Selection] Figure 1

Description

  The present invention relates to a combustion control device for a laser ignition internal combustion engine that ignites a lean air-fuel mixture with laser light.

  In a gas combustion engine, in order to improve fuel efficiency and suppress NOx generation amount, there is a demand to reduce the fuel mixture ratio of the air-fuel mixture and make the fuel gas leaner and burn in abundant air. However, since the lean air-fuel mixture has poor ignitability and misfires and abnormal combustion occur, there is a limit to the dilution of the fuel.

  Therefore, by devising the piston head and the direction of fuel introduction, etc., a part where the concentration of the air-fuel mixture is locally high in the engine cylinder is ignited, and the advantage of the lean burn engine is maintained by igniting the fuel rich part. However, techniques for ensuring ignition performance are being studied.

  For example, Patent Document 1 discloses a combustion control device as shown in FIG. The end portion of the intake port is opened in the circumferential direction of the cylinder, and the air-fuel mixture flowing into the cylinder from the intake port is arranged so as to form a lateral vortex in the cylinder circumferential direction, that is, a swirl. A fuel injection valve is provided upstream of the intake port, and fuel gas is added to the air introduced into the intake port.

  The air-fuel mixture flowing into the cylinder from the intake port forms a strong swirl at the top of the cylinder and forms a fuel-rich region in an annular shape. In the present disclosure, ignition performance during lean burn is ensured by igniting this fuel-rich part.

  As described above, in the disclosed invention described in Patent Document 1, a region having a higher fuel concentration is formed by devising the shape and opening direction of the intake port, and ignition energy is applied to the region, so that the lean burn is performed. Ignition performance is secured.

However, in the present disclosure, since there is no means for detecting the actual fuel distribution in the cylinder and means for moving the ignition position, the fuel rich state is changed due to changes in various conditions in the cylinder, such as a transition from engine startup to rated operation. The ignition energy is always applied to the same position even if the region moves. Therefore, a margin must be given to the amount of ignition energy and the fuel concentration so as to cope with changes in combustion conditions, and there is a limit to the efficiency.
Japanese Patent Laid-Open No. 05-302561

  The problem to be solved by the present invention is to detect a region where the fuel concentration of the air-fuel mixture is high in a combustion control device of a lean burn engine and ignite ignition energy at a portion where the fuel concentration is high to burn the fuel, This is to improve the lean limit of the internal combustion engine and contribute to improvement of fuel consumption and suppression of exhaust NOx.

  In order to solve the above-described problems, a combustion control device for a laser ignition type internal combustion engine according to the present invention is a laser ignition type internal combustion engine that focuses laser light in a cylinder and ignites a lean air-fuel mixture. It is equipped with a concentration measuring device to measure, an optical system that changes the focusing position of the laser beam, and a control device, and the control device detects the concentration change of the mixture based on the measurement result of the concentration measuring device and controls the optical system. The focusing position of the laser beam is corrected in a region where the fuel concentration is higher.

  The combustion control device for a laser ignition type internal combustion engine of the present invention measures the fuel concentration contained in the air-fuel mixture in the cylinder, detects the change in concentration, and controls so that the laser beam is condensed at a higher fuel concentration position. . Therefore, even when the entire air-fuel ratio is very lean, ignition energy can be applied to a region where high ignitability can be obtained and ignition can be performed reliably.

  Further, in the cylinder, the fuel concentration distribution in the cylinder is constantly changing due to, for example, changes in temperature conditions and rotation speed from engine startup to rated operation. Even during rated operation, the region where the fuel concentration is high in each combustion slightly changes. The combustion control device for a laser ignition type internal combustion engine of the present invention can detect a change in fuel concentration at any time and can always apply ignition energy at an optimal position following the movement of the high concentration region.

  Therefore, if the combustion control device for a laser ignition type internal combustion engine of the present invention is employed in a laser ignition type lean burn engine, high ignition performance can be ensured even when the fuel is lean, so that the lean limit of the mixture can be improved. it can. Furthermore, even if the combustion conditions change, a high ignition performance can always be obtained in response to the change in conditions, so the margin width given to the fuel concentration can be compressed.

  The concentration measuring device provided in the combustion control device of the laser ignition type internal combustion engine of the present invention is formed by, for example, a measuring laser light irradiation device and a light receiving device, and measures the absorption amount of the laser light to the fuel gas to determine the concentration of the mixture. Can be detected. In this case, for example, if the wavelength of the laser beam is about 3.4 μm, the fuel gas concentration can be measured by detecting the amount of absorption of the laser beam with respect to the CH group contained in the fuel gas.

  Further, the fuel concentration may be detected using a laser induced fluorescence method. For example, the fuel concentration can be measured by mixing a small amount of toluene or the like as a tracer in the fuel gas, irradiating the fuel gas with an ultraviolet laser, and detecting the fluorescence emitted from the tracer with a light receiving device.

  The optical system provided in the combustion control device of the laser ignition type internal combustion engine of the present invention can be formed by combining a condensing lens and an electro-optic element, and a spring and a piezo element are arranged on the condensing lens.

  The lens position is controlled by sandwiching both surfaces of a condensing lens formed of a multistage lens between a piezo element and a spring, and adjusting the voltage applied to the piezo element by the piezo element. By controlling the position of the lens, the focal length of the condensing lens system can be changed, and the condensing position on the optical axis of the laser light can be freely set.

Furthermore, by arranging an electro-optic element downstream of the condenser lens system and bending the laser light by the electro-optic element, the condenser position in the direction orthogonal to the optical axis of the condenser lens system can be changed. .
Therefore, by controlling the piezo element and the electro-optic element, the laser beam can be condensed at a free position in the cylinder and the ignition position can be controlled.

  The combustion control apparatus for a laser ignition type internal combustion engine according to the present invention may further include a knocking detection mechanism, and when the knocking is detected, the ignition timing of the laser beam may be adjusted according to the frequency of occurrence of knocking.

  As the knocking detection mechanism, an in-cylinder pressure measurement method, a vibration measurement method, and an ion current measurement method that are generally used can be used. However, knocking can be detected with very high sensitivity by measuring the emission signal during combustion.

  In the in-cylinder pressure measurement method, vibration measurement method, and ion current measurement method, the presence or absence of knocking is determined using a knocking high frequency superimposed on each measurement signal at the time of knocking. However, the inventor's research has revealed that the knocking high frequency is also superimposed on the emission signal at the time of combustion, and the knocking high frequency appears much more clearly than the index signal used conventionally.

  Therefore, the knocking detection mechanism provided in the combustion control device of the laser ignition type internal combustion engine of the present invention comprises an optical sensor and an arithmetic unit, measures the light quantity of the flame during combustion, and detects the high frequency contained in the light quantity signal. The presence or absence of knocking is determined. According to the knocking detection mechanism of this configuration, finer knocking can be detected with high sensitivity and accuracy compared to the conventional method.

  When knocking is detected by the knocking detection mechanism, the timing of laser ignition or the ignition position is adjusted based on the detection signal and by comparing the occurrence frequency and timing of knocking with past accumulated data.

  The combustion control device of the laser ignition type internal combustion engine of the present invention controls the ignition position so as not to cause abnormal combustion such as knocking or misfire. However, when knocking is detected by the knocking detection device, the ignition timing is set. Correct and control to continue normal combustion more stably.

As described above, according to the combustion control device for a laser ignition type internal combustion engine of the present invention, the fuel concentration in the cylinder is measured, and the ignition energy is applied to the region where the fuel concentration of the mixture is higher. High ignition performance can be ensured even in a lean case. Therefore, if the combustion control device for a laser ignition type internal combustion engine of the present invention is applied to the internal combustion engine, it is possible to improve the lean limit of the lean burn engine and contribute to the improvement of fuel consumption and the suppression of exhaust NOx.
Furthermore, if the combustion control device for a laser ignition type internal combustion engine of the present invention is provided with a knocking detection mechanism, combustion control can be further stabilized and abnormal combustion can be suppressed.

  Hereinafter, a combustion control device for a laser ignition type internal combustion engine of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a conceptual diagram of a combustion control device for a laser ignition type internal combustion engine in one embodiment of the present invention. A piston 2 is inserted into the cylinder 1, and a piston rod 3 is connected to the piston 2. The cylinder head 4 is provided with an intake port 5.

  An optical window 6 is provided at the center of the cylinder head 4, and an electro-optical element 7, a condensing optical system 8, and a laser emitting device 9 are sequentially provided above the optical window 6. Further, an optical fiber 10 is embedded in the cylinder head 4. One end of the optical fiber 10 reaches into the cylinder, and the other end is connected to the photomultiplier tube 11. The photomultiplier tube 11 transmits an electronic signal to an arithmetic unit (not shown).

  Three side optical windows 12 and 13 are opened on the side wall of the cylinder 1 at the left and right positions in the figure. An optical fiber cable 15 is in contact with the optical window 12 on the left side of the drawing via a collimating lens 14, and a measuring laser beam emitting device 16 is connected to the other end of the optical fiber cable 15. An optical sensor 17 is disposed outside the optical window 13 on the right side in the drawing. The optical sensor 17 transmits an electronic signal to an arithmetic device (not shown).

The combustion control apparatus of the laser ignition type internal combustion engine of the present embodiment measures the fuel concentration in the cylinder by such a configuration, detects a high concentration region, concentrates the ignition energy in the corresponding region, and ignites the air-fuel mixture. Further, the presence / absence of knocking is determined by the photomultiplier tube 11, and the condensing position of the laser beam is corrected to an appropriate position when knocking occurs.
A laser focusing position control method, a fuel concentration measurement method, and a knocking detection method will be sequentially described below.

  FIG. 2 is a configuration diagram conceptually showing the configuration of the electro-optical element 7, the condensing optical system 8, and the laser emitting device 9. The laser light emitted from the laser emitting device 9 passes through the condensing optical system 8, the electron optical element 7, and the optical window 6 in order, and is condensed in the cylinder 1.

  The condensing optical system 8 is formed of a collimating lens 21, a first condensing lens 22, and a second condensing lens 23 in order from the upstream side. The first condenser lens 22 is held between a piezo element 24 and a spring 25, and the piezo element 24 and the spring 25 are supported by a support portion 26. The piezo element 24 has the property that the volume increases or decreases according to the applied voltage. When the voltage applied to the piezo element 24 is increased, the piezo element 24 expands, and accordingly, the first condenser lens 22 moves to the left in the drawing. On the other hand, when the voltage applied to the piezo element 24 is decreased, the piezo element 24 contracts and is pushed by the spring 25 to move the first condenser lens 22 to the right in the drawing.

The electro-optical element 7 is configured to change the emission direction of incident light by an incoming control signal.
The laser light emitted from the laser emitting device 9 enters the collimating lens 21 in the air or through an optical fiber. After being collimated by collimating lens 21, it has a certain focal length by first condenser lens 22 and second condenser lens 23, and is emitted to electron optical element 7.

  The focal length of the laser light is determined by the distance between the first condenser lens 22 and the second condenser lens 23. Since the first condenser lens 22 is formed to slide in the optical axis direction in accordance with the voltage applied to the piezo element 24, the focal length of the laser light can be freely set by the voltage applied to the piezo element 24. It has become.

  The convergent laser light emitted from the second condenser lens 23 is bent in the target direction by the electron optical element 7, then passes through the optical window 6 and is collected in the cylinder 1 according to the bending direction and the focal length. Shine.

  Therefore, by controlling the voltage applied to the piezo element 24 and the control signal received by the electro-optic element 7, the bending direction of the optical axis and the focal length are manipulated to control the laser beam condensing position.

  FIG. 3 is a perspective view showing the configuration of the concentration measuring device arranged in the cylinder 1. An optical fiber cable 15 is connected to a measurement laser light emitting device 16 installed outside the cylinder 1, and six optical fibers in the optical fiber cable 15 reach the cylinder 1. Three of the six optical fibers are connected to an optical window 12 arranged in parallel to the motion axis of the piston 2 at regular intervals. The remaining three are connected to optical windows 12 arranged in a line perpendicular to the motion axis of the piston 2 at regular intervals. A collimating lens 14 is inserted between the optical fiber and the optical window 12.

  Six optical windows 13 are further opened at positions that are axially symmetric with respect to the six optical windows 12, and an optical sensor 17 is disposed outside the optical window 13. The optical sensor 17 is connected to the arithmetic device 18 to transmit a signal.

  The laser light emitted from the measurement laser light emitting device 16 is transmitted through six optical fibers in the optical fiber cable 15, adjusted to parallel rays by the collimating lens 14, and then the cylinder 1 through the optical window 12. Is irradiated. Further, the air-fuel mixture filling the cylinder 1 is transmitted and reaches the optical sensor 17 through the optical window 13. The optical sensor 17 converts the amount of received laser light into an electrical signal and transmits it to the arithmetic unit 18.

  If the laser light emitted from the measurement laser light emitting device 16 is a specific single wavelength light corresponding to the characteristic frequency of a specific component included in the fuel gas, the laser light is specifically absorbed according to the concentration of the fuel gas. The Therefore, a single wavelength laser having absorption characteristics with respect to typical components contained in the fuel gas is introduced into the cylinder from the optical window 12 to pass through the air-fuel mixture, and the amount of laser light transmitted without being absorbed is determined. If measured, the fuel concentration in the air-fuel mixture can be measured. For example, when a laser beam of about 3.4 μm is used, the laser beam is absorbed by a CH group and can be widely used for general fuel gas.

  In the present embodiment, the fuel concentration in the cylinder 1 is detected by irradiating a laser beam of about 3.4 μm from the measuring laser emitting device 16 and measuring the light quantity by the optical sensor 17. Three optical windows 13 and optical sensors 17 serving as laser light inlets are arranged horizontally and vertically. In the arithmetic unit, the measurement result of the optical sensor 17 arranged in the horizontal direction and the measurement result of the optical sensor 17 arranged in the vertical direction are analyzed by the arithmetic unit 18, respectively, and the calculation result is compared with the accumulated data and the fuel concentration is high. Calculate the position.

  Based on this result, an ignition position at which the air-fuel mixture can be burned most efficiently is determined, and ignition is performed by condensing the laser beam at the ignition position by the method described above. Furthermore, the fuel concentration is measured every time at a specific timing of the combustion cycle, the region where the fuel gas is contained at a high concentration is monitored, and the combustion energy is always applied to the optimum position following the movement of the high concentration region. .

Therefore, according to the combustion control device for a laser ignition type internal combustion engine of the present embodiment, even when a lean air-fuel mixture is burned, the distribution of the fuel concentration is measured and the laser light is collected in the region where the fuel is contained at a high concentration. Light and reliably ignite the mixture.

  Further, the combustion control device of the laser ignition type internal combustion engine of the present embodiment is provided with a knocking detection mechanism.

  In FIG. 1, an optical fiber 10 is embedded in a cylinder head 4, one end reaches the cylinder 1, and the other end is connected to a photomultiplier tube 11. The photomultiplier tube 11 converts light transmitted to the optical fiber 10 into electrons, and transmits a current proportional to the amount of light to the arithmetic unit. Therefore, the arithmetic unit can always monitor the amount of light emitted by the combustion in the cylinder 1. A semiconductor sensor such as a photodiode or a phototransistor may be used instead of the photomultiplier tube.

  When knocking occurs due to abnormal combustion in the cylinder 1, the amount of flame generated by combustion changes based on the knocking phenomenon in the cylinder, and a constant characteristic characteristic of the received light signal transmitted from the photomultiplier tube 11 is obtained. A high frequency signal is superimposed. The presence or absence of knocking is determined by detecting this high frequency signal.

  FIG. 4 is a graph showing a change in the light emission signal when knocking occurs. In the graph at the time of occurrence of knocking, the fluctuation of the received light signal that does not appear in the graph at the time of normal combustion clearly appears as a high frequency signal. The presence or absence of knocking can be determined by detecting the high frequency of the received light signal.

  When the arithmetic unit detects knocking, the ignition timing is adjusted based on the detection signal or by comparing the generation frequency and pattern of the high-frequency signal with the accumulated data, so that the combustion can be continued stably.

  FIG. 5 is a schematic view for explaining a fuel concentration measuring mechanism of a combustion control device for a laser ignition type internal combustion engine in a second embodiment of the present invention. Since the method other than the method for measuring the fuel concentration is the same as that of the first embodiment, illustration and description thereof are omitted.

  An optical window 42 is provided in a slit shape on the side wall of the cylinder 41, and an imaging device 44 is provided via the optical window 43 at a position that is approximately 90 degrees apart from the optical window 42 at the central angle. For the imaging device 44, a vidicon, an ICCD camera, or the like is used. On the outside of the optical window 42, a measurement laser emitting device 45, a cylindrical lens 46, and a collimating lens 47 are arranged. The collimating lens 47 is preferably a thin lens such as a Fresnel lens.

  The measurement laser light emitted from the measurement laser emitting device 45 is widened into a sheet shape by the cylindrical lens 46 and the collimating lens 47 and enters the cylinder 1 from the optical window 42. The imaging device 44 images the region irradiated with the sheet-like laser light from a substantially vertical direction, and transmits the image information to an arithmetic device (not shown).

  The combustion control device of the laser ignition type internal combustion engine of the present embodiment measures the fuel concentration using the laser excitation fluorescence method. In the laser excitation fluorescence method, a substance that emits fluorescence when excited by specific laser light is traced and mixed with fuel, and the fuel concentration is calculated by irradiating the laser with laser light and observing the fluorescence. If the fuel contains a substance that emits fluorescence when irradiated with a specific laser beam, it is not necessary to mix a tracer.

  In this embodiment, a small amount of toluene is mixed with the fuel as a tracer. When the cylinder 1 is filled with fuel gas containing toluene, the toluene absorbs the laser light irradiated into the cylinder 1 and emits fluorescence. Since the amount of generated fluorescent light has a correlation with the amount of toluene present, that is, the fuel concentration, the generated fluorescent light is photographed by the imaging device 44 and the image information is analyzed to measure the fuel concentration distribution on the laser light sheet. be able to.

  Therefore, if ignition energy is applied to a position where the air-fuel mixture can be most reliably burned based on the measured concentration distribution, high ignition performance can be obtained even when lean gas mixture is burned.

  In this embodiment, the laser beam is irradiated as one sheet, but if another laser beam is added so as to be orthogonal to the sheet-like laser beam, a three-dimensional fuel distribution can be obtained. Further, the high concentration region can be specified accurately, and the certainty of ignition can be improved.

  As described in detail above, according to the combustion control device of the laser ignition type internal combustion engine of the present embodiment, it is possible to analyze the fuel distribution in the cylinder and to apply the ignition energy to the region where the fuel concentration is higher. Even a lean mixture can be ignited reliably. Furthermore, even if the region where the fuel concentration is high moves, the ignition position can be changed following the transition of the concentration distribution, and high ignition performance can always be ensured. Accordingly, the lean limit of the lean burn engine can be improved, and the margin width given to the fuel concentration can be compressed in preparation for combustion conditions, which can greatly contribute to the improvement of fuel consumption and the reduction of exhaust NOx.

1 is a schematic cross-sectional view of a combustion control device for a laser ignition internal combustion engine in a first embodiment of the present invention. It is a conceptual diagram explaining the laser optical system for a measurement in 1st Example. It is a conceptual diagram explaining the fuel concentration measuring apparatus in 1st Example. It is a graph showing the change of the light emission signal at the time of knocking generation | occurrence | production. It is a conceptual diagram explaining the fuel concentration measuring apparatus in 2nd Example of this invention. It is the schematic of the conventional combustion control apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,41 Cylinder 2 Piston 3 Piston rod 4 Cylinder head 5 Intake valve 6, 12, 13, 42, 43 Optical window 7 Electro-optical element 8 Condensing optical system 9 Laser emitting apparatus 10 Optical fiber 11 Photomultiplier tube 14, 21 , 47 Collimating lens 15 Optical fiber cable 16, 45 Laser light irradiation device for measurement 17 Optical sensor 18 Arithmetic device 22 First condensing lens 23 Piezo element 24 Spring 25 Second condensing lens 26 Support unit 44 Imaging device 46 Cylindrical lens

Claims (8)

  In a laser ignition internal combustion engine that condenses laser light in a cylinder and ignites a lean air-fuel mixture, a concentration measuring device that measures the fuel concentration in the cylinder, an optical system that changes the condensing position of the laser light, and a control device And the control device detects a change in the concentration of the air-fuel mixture based on the measurement result of the concentration measuring device and controls the optical system to correct the condensing position of the laser light in a region where the fuel concentration is higher. A combustion control device for a laser ignition type internal combustion engine.   2. The laser ignition internal combustion engine according to claim 1, wherein the concentration measuring device comprises a measuring laser beam irradiation device and a light receiving device, and measures the concentration of the air-fuel mixture from the amount of absorption of the measuring laser beam into the fuel gas. Engine combustion control device.   3. The fuel gas concentration according to claim 2, wherein the measurement laser beam has a wavelength of about 3.4 μm, and the concentration measuring device measures the concentration of the fuel gas from the amount of absorption of the measurement laser beam with respect to the CH group. A combustion control device for a laser ignition type internal combustion engine.   The concentration measuring device comprises a measuring laser beam irradiation device and a light receiving device, and measures the concentration of the air-fuel mixture from the amount of fluorescent light emitted from the fuel gas by irradiating the measuring laser beam to the fuel gas. The combustion control device for a laser ignition type internal combustion engine according to claim 1.   The optical system is a combination of a condensing lens and an electro-optic element, and a spring and a piezo element are disposed on the condensing lens, and the voltage applied to the piezo element and the electro-optic element is controlled. 5. The combustion control device for a laser ignition type internal combustion engine according to claim 1, wherein the condensing position of the laser beam is controlled.   6. The apparatus according to claim 1, further comprising a knocking detection mechanism, wherein when the knocking detection mechanism detects knocking, the timing of ignition of the laser light is adjusted according to the frequency of occurrence of knocking. The combustion control device for a laser ignition type internal combustion engine.   The knocking detection mechanism includes an optical sensor and an arithmetic unit, and measures the amount of flame light during combustion, detects a high frequency included in the light amount signal, and determines whether knocking is present or not. A combustion control device for a laser ignition type internal combustion engine. A knocking detector comprising an optical sensor and an arithmetic unit, which measures a light emission signal of a flame at the time of combustion, and detects the presence or absence of knocking by detecting a high frequency contained in the light emission signal.

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