JP4842582B2 - Gas analyzer - Google Patents

Description

  The present invention relates to a gas analyzer that performs gas analysis by determining the temperature, concentration, chemical species, etc. of a gas by measurement.

  In general, a gas analyzer that measures the components of a gas by irradiating the gas flowing in the flow path with light and detecting the light transmitted through the gas is used. As this type of gas analyzer, For example, an in-line gas analyzer described in Patent Document 1 is known. In such a gas analyzer, two light-transmitting windows are formed so as to face or almost face each other on the pipe wall of the pipe through which the gas flows, and a part of each of these windows is left as a light-transmitting portion inside the pipe. A light-reflecting surface is formed, and a light source part including a light source and a Cassegrain mirror is provided outside the light transmission part of one window, and the light emitted from the light source passes through the Cassegrain mirror and enters the light transmission part of one window. On the other hand, it is provided so as to enter obliquely. Furthermore, a detector unit for detecting light of a plurality of wavelengths is provided outside the light transmission part of the other window, and the light exiting the light source part enters the pipe from the light transmission part of one window, and then After being reflected a plurality of times between the light reflecting surfaces of the two windows, the light is incident on the detector part via the light transmitting part of the other window. By using such a gas analyzer, the temperature, concentration, chemical species, etc. of the gas can be measured, and as a result, the components of the gas can be analyzed.

  Examples of the gas to be analyzed as described above include in-line gas used during semiconductor manufacturing as described in Patent Document 1, exhaust gas discharged from an internal combustion engine such as an automobile, exhaust gas discharged from a factory, and the like. .

JP 2004-53405 A

  Incidentally, the gas analyzer described in Patent Document 1 is configured so that light emitted from the light source is reflected a plurality of times between the light reflecting surfaces of the two windows and is incident on the detector unit. Scattered light is likely to be generated when the light for reflection is reflected, and the generated scattered light may be diffusely reflected and incident on the light detector portion together with the measurement light. As a result, there is a problem in that the scattered light enters as noise in the measurement light transmitted through the exhaust gas and the measurement accuracy is lowered.

  The present invention has been made in view of such problems, and the object of the present invention is to provide measurement light even if the measurement laser light transmitted through the gas to be analyzed is irregularly reflected or scattered. An object of the present invention is to provide a gas analyzer capable of preventing measurement of scattered light and improving measurement accuracy. That is, when a laser beam that passes through a gas is received, a gas analyzer that can prevent the scattered light generated for some reason from entering the light receiving unit together with the measurement light and improve the measurement accuracy. It is to provide.

  In order to achieve the above object, a gas analyzer according to the present invention irradiates a gas to be analyzed with laser light, and measures and analyzes the component concentration and temperature of the gas based on the laser light transmitted through the gas. The gas analyzer includes a sensor unit fixed to a path through which a gas to be measured flows, and the sensor unit includes a sensor base and a gas formed on the sensor base. A flowing gas passage hole, an irradiation unit for irradiating a laser beam fixed to the sensor base, a light receiving unit for receiving the irradiated laser beam, and a laser beam irradiated from the irradiation unit through the gas passage hole An irradiation light passage hole formed on the irradiation unit side and a transmission light passage hole formed on the light reception unit side so as to reach the light reception unit, the irradiation light passage hole and the transmission light passage hole; Less than Scattered light exclusion means for preventing scattered light incident on the irradiation light passing hole or the transmitted light passing hole at an incident angle different from the angle at which the laser light is incident on the peripheral surface of the transmitted light passing hole. Is characterized by being taken.

  In the gas analyzing apparatus of the present invention configured as described above, the laser light generated from the laser light generating means passes into the gas passage hole through which the gas passes from the irradiation light passage hole provided with the scattered light exclusion means. The transmitted laser light that has been irradiated and transmitted through the gas reaches the light receiving section through the transmitted light passage hole provided with the scattered light exclusion means. For this reason, the scattered light of the measurement laser light is prevented from reaching the light receiving portion, and the scattered light is not received by the light receiving portion, so that the scattered light is not mixed into the laser light transmitted through the gas, and the gas component The concentration, temperature, etc. of the gas can be measured with high accuracy, and the accuracy of gas analysis can be improved. In addition, it is preferable that a scattered light exclusion unit is also provided on the inner peripheral surface of the irradiation light passage hole.

  As another aspect, the sensor unit includes a reflecting member for reflecting the laser light emitted from the irradiation unit and guiding the laser beam to the light receiving unit outside the gas passage hole in the sensor base. A light passage hole for allowing the light to reach the reflecting member is formed, and the inner peripheral surface of the light passage hole receives scattered light that enters the light passage hole at an incident angle different from the incident angle of the laser light. The present invention is characterized in that a means for eliminating scattered light is provided so as to prevent the light from reaching. The gas analyzer configured in this manner reflects the laser beam so as to increase the transmission distance of the laser beam in the gas, and the scattered light generated at the reflection is reflected to the light receiving unit by the scattered light exclusion means of the light passage hole. In order not to make it reach | attain, scattered light is not mixed in the laser beam for a measurement, and a measurement precision can be improved.

  The scattered light exclusion means preferably includes a reflecting surface that reflects incident scattered light in a direction opposite to the incident direction, and the reflecting surface is an irradiation light passage hole, a transmitted light passage hole, and an inner peripheral surface of the light passage hole. It is preferable to include a threaded surface. According to this configuration, when scattered light is incident at an angle different from the angle at which the measurement laser light is incident, the scattered light is reflected by the scattered light exclusion means including the female thread surface in the direction opposite to the incident direction. Therefore, the scattered light does not reach the light receiving portion, and the measurement accuracy can be improved. The internal thread surface that forms the reflective surface can be easily formed by processing through the tap that forms the internal thread in the irradiation light passing hole, the transmitted light passing hole, and the light passing hole through which the laser light passes. can do. The female thread surface has a spiral inclined surface, and the scattered light other than the measurement laser light that passes through it strikes the inclined surface and is reflected in the opposite direction, so it is mixed with the measurement laser light as noise. Can be prevented.

  Moreover, it is preferable that the said scattered light exclusion means is a rough surface formed when roughing the inner peripheral surface of the said irradiation light passage hole, the transmitted light passage hole, and the light passage hole. According to this configuration, the rough surface formed on the irradiation light passage hole, the transmitted light passage hole, and the inner peripheral surface of the light passage hole is reflected by the rough surface even if scattered light is attenuated and reaches the light receiving unit. Since this is not possible, scattered light is not mixed in the received laser light, and the measurement accuracy can be improved.

  The light passage hole is preferably formed as a leading hole having a large diameter on the gas passage hole side and a small diameter on the reflecting member side. According to this configuration, the tip pore close to the reflecting surface is narrowed to a small diameter, and the diameter close to the gas passage hole on the incident side is large and easy to enter. Therefore, the noise can be greatly reduced without reaching the light receiving unit, and the measurement accuracy can be improved.

  The gas passage hole preferably has substantially the same cross-sectional shape as the cross-sectional shape of the path. That is, the cross-sectional shape of the path through which the gas flows is usually a circle like a pipe, and it is preferable that the shape of the gas passage hole is a circle substantially equal to the diameter of the pipe. If comprised in this way, even if a sensor part is fixed for the gas analysis in the path | route through which gas flows, disorder of gas flow can be prevented and it can prevent that the loss of gas flow increases. In particular, it is suitable when a large number of sensor units are installed in a gas flow path.

  The sensor units are preferably installed at a plurality of locations in the route. With this configuration, it is possible to measure the concentration and temperature of gas components at multiple points in the gas flow path, and easily measure and analyze changes in the concentration of gas components in the path in real time. Can do. In addition, since the sensor unit includes a laser beam irradiation unit and a laser beam receiver that has passed through the gas, the sensor unit can be easily installed.

  It is preferable that the sensor unit includes a heater for heating the reflecting member on the sensor base. In particular, it is more preferable to install in the vicinity of the reflecting member, and the set temperature of the heater is preferably set to a temperature that prevents condensation of moisture contained in the gas to be analyzed. According to this configuration, it is possible to prevent moisture contained in the gas from condensing on the surface of the reflecting member, thereby improving the reflectance of the laser beam and increasing the measurement accuracy. Also, when analyzing the exhaust gas discharged from the internal combustion engine, if the heater is energized and preheated before starting the internal combustion engine, the heat shock to the reflecting member such as the mirror due to the high temperature exhaust gas can be reduced, and the damage etc. Can be prevented, and deformation due to temperature change between the front surface and the back surface can be prevented.

  In the gas analyzer of the present invention, the gas to be analyzed is exhaust gas discharged from an internal combustion engine, and an exhaust gas flow path connected to the internal combustion engine is used as the path. According to this configuration, it is possible to analyze in real time the state of the exhaust gas discharged from the internal combustion engine through the exhaust passage, which is useful when checking the performance or testing of the internal combustion engine.

  Since the gas analyzer of the present invention irradiates the measurement laser beam into the gas passage hole through which the gas flows and receives the laser beam that has passed through the gas, it is hardly affected by the scattered light. It is possible to improve the accuracy of the concentration measurement and temperature measurement. In addition, no reference gas or auxiliary gas is required for the measurement, no large-scale equipment is required, and analysis can be performed at low cost.

  Hereinafter, an embodiment in which a gas analyzer according to the present invention is used in an automobile exhaust gas analyzer will be described in detail with reference to the drawings. FIG. 1 is a main part configuration diagram in which the exhaust gas analyzer according to the present embodiment is mounted on an automobile, FIG. 2 is a main part configuration diagram in a state in which the exhaust gas analyzer in FIG. 1 is mounted on an engine bench, and FIG. FIG. 4 is a front view showing a detail of the sensor unit in FIG. 3 and a cross-sectional view taken along line AA. FIG. 5 is a block diagram showing an overall configuration of an exhaust gas analyzer including a main configuration of a laser oscillation / light receiving controller and a signal analyzer.

  1-5, the exhaust gas analyzer of this embodiment is an apparatus which analyzes the exhaust gas discharged | emitted from the engine (internal combustion engine) 2 installed in the motor vehicle 1 as analysis object gas. Moreover, as shown in FIG. 2, it is an apparatus which analyzes the exhaust gas of the engine 2 installed in the engine bench 1A. The exhaust gas discharged from each cylinder of the engine 2 is merged in the exhaust manifold 3, introduced into the first catalyst device 5 through the exhaust pipe 4, further introduced into the second catalyst device 6, and then through the muffler 7 to the exhaust pipe 8. From the atmosphere. The exhaust path constituting the flow path (path) through which the exhaust gas flows is composed of the exhaust manifold 3, the exhaust pipe 4, the first catalyst device 5, the second catalyst device 6, the muffler 7, and the exhaust pipe 8, and is exhausted from the engine 2. The exhaust gas is purified by the two catalyst devices 5 and 6, muffled by the muffler 7, depressurized and released into the atmosphere. The muffler may have two main mufflers and sub mufflers.

  The plurality of members constituting the exhaust path are connected by bolts or the like with the flange portions in contact with each other. For example, the first and second catalytic devices 5 and 6 have exhaust pipe portions connected upstream and downstream of the large-diameter main body portion, and flange portions F and F are fixed to the end portions of these exhaust pipe portions by welding or the like. Has been. The muffler 7 has exhaust pipes connected to the upstream and downstream sides of the large-diameter main body, and flanges F and F are fixed to the ends of the exhaust pipes. The exhaust pipe 8 at the end is fixed directly to the muffler 7 by welding or the like. In this way, the plurality of members constituting the exhaust path are connected by the flange portion, and the cross-sectional shape through which the exhaust gas passes is formed in a circle having a diameter d.

  The exhaust gas analyzer 10 of the present embodiment includes a plurality of sensor units 11 to 14 installed at a plurality of locations in the exhaust path. The first sensor unit 11 is installed between the exhaust pipe 4 on the engine side upstream of the first catalyst device 5, the second sensor unit 12 is installed on the downstream side of the first catalyst device 5, and the third The sensor unit 13 is installed on the downstream side of the second catalyst device 6. The fourth sensor unit 14 is installed in the exhaust pipe 8 downstream of the muffler 7. The sensor unit 14 may be installed in the middle of the exhaust pipe or may be installed by being inserted into the opening at the end of the exhaust pipe. You may install a sensor part in the exhaust pipe for every cylinder of the upstream of the 1st sensor part 11 before merging with the exhaust manifold 3.

  The exhaust pipe 4, the first catalyst device 5, the second catalyst device 6, and the muffler 7 are connected by tightening the flange portions F and F with bolts, and the sensor portion 11 is installed between members constituting the exhaust path. , 12 and 13 are installed in a state of being sandwiched between the flange portions F and F. The flange portions F and F are formed at both end portions of the member constituting the exhaust path, and the joint surfaces of the flange portions intersect at right angles to the center line of the exhaust path. As a result, the sensor parts 11 to 13 are installed so as to cross the exhaust path between the flange parts F and F. The fourth sensor unit 14 performs analysis immediately before the exhaust gas is released into the atmosphere, and may be installed between the flanges F and F in the middle portion of the exhaust pipe 8 protruding from the muffler 7. In addition, what is necessary is just to set the number of installation of a sensor part arbitrarily.

  Each sensor part 11-14 is the same structure, and demonstrates the one sensor part 11 with reference to FIG. The sensor unit 11 has a sensor base 20 formed of a rectangular thin plate material, and an exhaust gas passage hole 21 having the same diameter d as the inner diameter d of the circular cross section of the exhaust pipe portion is formed at the center of the sensor base. The exhaust gas passes through the exhaust gas passage hole. The thickness of the plate-like sensor base 20 is preferably as thin as possible within a range in which the laser beam irradiation part and the light receiving part can be fixed. Specifically, the thickness of the sensor base 20 is preferably about 5 to 20 mm, for example. If it exceeds 20 mm, the flow of the exhaust gas tends to be disturbed, and if it is thinner than 5 mm, the mounting and fixing of the measurement laser light irradiation part and the light receiving part of the laser light transmitted through the exhaust gas become complicated. Moreover, it can be easily installed as required at any location in the exhaust path. The thickness of the sensor base 20 can be arbitrarily set.

  Thus, the shape of the exhaust gas passage hole 21 formed in the sensor base 20 is formed in a circle having the same diameter as the inner diameter of the exhaust pipe portion so as not to disturb the exhaust gas flow, and the sensor base 20 is formed thin. . For this reason, even if the sensor units 11 to 14 are installed in the exhaust path, the exhaust gas flow is not disturbed, and the exhaust can be performed smoothly with little pressure loss. For example, when the diameter of the exhaust gas passage hole 21 is about 30 ± 1 to 2 mm when the diameter is 30 mm, the disturbance of the exhaust gas flow is unlikely to occur. This range is a preferable range as substantially the same cross-sectional shape. As the plate material constituting the sensor base 20, a metal plate material or a ceramic plate material is used, but the material is not particularly limited.

  The sensor base 20 is fixed in a state of being sandwiched between the flange portions F and F, and a bolt, a nut, etc., not shown in the state of having the gaskets 22 and 22 sandwiched between the flange portions F and F and the sensor base 20. It is fixed by. The gasket 22 is made of asbestos or the like, and has an exhaust gas passage hole having the same diameter as the inner diameter of the exhaust pipe. With this configuration, even if the exhaust path is connected with the sensor base 20 sandwiched between the flange portions F and F, the exhaust gas does not leak in the middle, and the increase in the length of the exhaust path is small. FIG. 3 shows gaskets 22, 22 between a flange portion F welded to the downstream end of the exhaust pipe 4 and a flange portion F welded to the end of the exhaust pipe portion 5 a on the upstream side of the catalyst device 5. A configuration is shown in which the sensor base 20 is fixed by being sandwiched.

  The sensor base 20 is formed with two sensor holes 23 and 24 that penetrate the center of the plate thickness from the end surface toward the exhaust gas passage hole. The sensor hole 23 opens toward the exhaust gas passage hole 21 and constitutes an irradiation light passage hole formed so that the irradiated laser light can reach the light receiving part through the exhaust gas passage hole 21. The sensor hole 24 opens toward the exhaust gas passage hole 21 and constitutes a transmitted light passage hole formed so that the laser beam can reach the light receiving portion. The sensor holes 23 and 24 flow through the exhaust gas. The opening is perpendicular to the direction.

  The sensor unit 11 is a light receiving unit that receives an optical fiber 25A as an irradiating unit that irradiates a laser beam, is fixed to the sensor hole 23, and receives the laser beam irradiated from the optical fiber 25A and transmitted through the exhaust gas passing through the exhaust gas passing hole 21. The detector 26 </ b> A is fixed to the sensor hole 24. That is, the sensor unit 11 reflects the laser beam irradiated from the irradiation side optical fiber 25A so as to cross the exhaust path, is reflected by the two mirrors 30 and 31, is attenuated through the exhaust gas, and is received by the detector 26A. The mirror reflects the irradiated laser light and guides it to the detector.

  The sensor hole 23 communicates the exhaust gas passage hole 21 and the optical fiber 25 that is an irradiating portion, and constitutes an irradiation light passage hole through which the measurement laser light emitted from the optical fiber passes. Further, the sensor hole 24 communicates the exhaust gas passage hole 21 and the detector 26 which is a light receiving portion, and constitutes a transmitted light passage hole through which the laser light transmitted through the exhaust gas passes and reaches the detector 26. The scattered light for preventing the scattered light from reaching the light receiving portion when the scattered light is incident on the inner peripheral surfaces of the sensor holes 23 and 24 at an incident angle different from the incident angle of the laser light. Female thread surfaces 23a and 24a are formed as exclusion means. If there is at least a female threaded surface 24a on the light receiving side among the threaded surfaces formed in the sensor holes 23, 24, the scattered light received by the detector 26 can be largely removed.

  The female thread surface is preferably a 5 mm metric thread when the diameter of the sensor hole is about 5 mm, and is preferably threaded to match the diameter. Thus, by threading the inner peripheral surface of the sensor hole into a female screw surface, the scattered light passing through the sensor hole hits the inclined surface of the female screw surfaces 23a and 24a that is continuous in a spiral shape, and laser light is incident thereon. Therefore, the scattered light does not pass through the sensor hole together with the main measurement laser light. For this reason, it is possible to prevent the scattered light from being mixed with the laser beam for measurement.

As shown in detail in FIG. 4, the two mirrors 30 and 31 are attached to the outside of the circular exhaust gas passage hole 21 at the center of the sensor base 20 at opposing positions sandwiching the exhaust gas passage hole. Two sheets are arranged so that the surfaces are parallel to each other, and are fixed vertically so as to reflect the laser beam for measurement. That is, the mirrors 30 and 31 are arranged outside and parallel to the exhaust gas passage hole 21 with the exhaust gas passage hole interposed therebetween. The mirrors 30 and 31 are detachably fixed in two insertion grooves 32 and 33 formed in parallel to the outer peripheral side of the exhaust gas passage hole 21, and are irradiated to the exhaust gas passage hole 21 from the optical fiber 25 </ b> A. It has a function of causing light to reach the detector 26A. The mirrors 30 and 31 are formed in the shape of a rectangular substrate having a thickness of about several millimeters. A thin film of gold or platinum is formed as a reflective surface on one surface of the substrate, and MgF ₂ or SiO _{2 is used} as a protective layer thereon. _Two thin films are formed. Note that the protective film may not be formed.

Further, a photocatalytic layer may be formed on the surfaces of the mirrors 30 and 31. The photocatalyst layer is preferably a thin film of, for example, titanium dioxide (TiO ₂ ). The photocatalyst layer is formed as a thin film on the surface of the mirror by coating or coating. When the photocatalyst layer is titanium dioxide, this thin film absorbs and activates photocatalyst rays such as ultraviolet light, and the dirt adhering to the surface floats up. It functions to be discharged to the outside. Thus, it is preferable to form a photocatalyst layer on the surface of the mirror because the surface of the mirror can be cleaned.

  The insertion grooves 32 and 33 formed on the outer periphery of the exhaust gas passage hole 21 of the sensor base 20 are set to a size that allows the mirrors 30 and 31 to be inserted loosely. The insertion grooves 32 and 33 may penetrate the sensor base 20 and be opened on both sides, or may be formed on one side and closed on the other side. The mirrors 30 and 31 are fixed in the insertion grooves 32 and 33 by spacers 37 with mounting screws 36. If the mirror is damaged by heat shock or the like, it can be removed by loosening the mounting screw 36 to fix the new mirror. Further, when the mirror becomes dirty, it can be removed from the sensor base 20 and cleaned.

  Since the mirrors 30 and 31 are fixed by the mounting screws 36 via the spacers 37, the mirrors are prevented from vibrating due to vibrations of the engine or exhaust passages such as exhaust pipes. A spacer 37 is sandwiched to absorb the difference in thermal expansion between the mirror and the mounting screw, and functions as a cushioning material. As the spacer, those excellent in environmental resistance and elastically deforming are preferable. For example, a mica-based, carbon-based, or copper plate material is preferable. Thus, by fixing with the mounting screw via the spacer, it can be stably fixed without vibration even at a high temperature of about 800 ° C.

The mirrors 30 and 31 are manufactured by coating a reflecting material on the surface of a base material such as quartz, sapphire, or ceramic. As the coating material, it is preferable to select a material having a high reflectance suitable for the laser wavelength, such as gold or titanium oxide. Further, it is preferable to form a transparent coating such as SiO ₂ having excellent heat resistance and excellent environmental resistance on the uppermost surface as a coating for protecting the reflecting material. By using a mirror having excellent heat resistance and high reflectivity, accurate measurement can be performed. Further, when titanium oxide is used as a reflective material, it is preferable to measure the titanium oxide as it is because it is excellent in environmental resistance and effective as a photocatalyst for preventing contamination. .

  A light passage hole is formed between the inner peripheral surface of the exhaust gas passage hole 21 and the insertion grooves 32 and 33 for fixing the mirror so that the laser beam for measurement can reach the mirror. As the light passage hole, a penetrating slit, a penetrating light passage hole, or the like is formed. In the present embodiment, light passage holes 38, 38... Having a diameter of about several millimeters are formed so as to penetrate from the inner peripheral surface of the exhaust gas passage hole 21 to the insertion grooves 32, 33 in the direction orthogonal to the exhaust path. Passes through the inner peripheral surface of the exhaust gas passage hole 21 and the mirrors 30 and 31. With this configuration, when the measurement infrared laser light is irradiated into the exhaust gas passage hole 21 from the optical fiber 25 that is the irradiation unit, the measurement light reaches the lower mirror 31 through the lower light passage hole 38 and is Then, the light reaches the upper mirror 30 through the upper light passage hole 38, is reflected downward by the upper mirror, and is reflected by the upper and lower detectors 26 after being repeatedly reflected up and down. ing.

  When the scattered light is incident on the inner peripheral surface of the light passage hole 38 formed in the sensor base 20 at an incident angle different from the angle at which the laser light enters the light passage hole, Female screws 38a... Are formed as scattered light exclusion means for preventing light from reaching the light receiving section. This female thread can be easily formed by passing a tap through the through hole. Accordingly, the laser light emitted from the optical fiber 25A can reach the mirrors 30 and 31 through the light passage hole 38 in which the female screw 38a is formed.

  The optical fiber 25A and the detector 26A are connected to the laser oscillation / light reception controller 40, and infrared laser light emitted from the laser oscillation / light reception controller 40 is irradiated into the exhaust gas passage hole 21 of the sensor base 20 through the optical fiber 25A. The infrared laser beam transmitted therethrough is received by the detector 26A on the light receiving side, and is input to the laser oscillation / light receiving controller 40 via the signal line 28A. The intensity of light emitted from the optical fiber 25A, the intensity of light received through the exhaust gas and received by the detector 26A, and the like are supplied to a personal computer 55 as an analyzer. As described above, the exhaust gas analyzer 10 includes the plurality of sensor units 11 to 14, the laser oscillation / light reception controller 40, and the personal computer 55.

  Here, the laser oscillation / light reception controller 40 will be described with reference to FIG. The laser oscillation / light reception controller 40 is an irradiation device for irradiating infrared laser beams having a plurality of wavelengths, and receives signals having a plurality of frequencies from a signal generator such as a function generator (not shown) to the plurality of laser diodes LD1 to LD5. The laser diodes LD1 to LD5 irradiate infrared laser beams having a plurality of wavelengths corresponding to the respective frequencies. A plurality of frequency signals output from the signal generator of the laser oscillation / light reception controller 40 are supplied to the laser diodes LD1 to LD5 to emit light. For example, LD1 has a wavelength of about 1300 to 1330 nm and LD2 has a wavelength of 1330 to 1360 nm. The infrared laser beam having a wavelength band in which the wavelength band in which the peak wavelength of the component gas to be detected exists is continuous is set.

The wavelength of the infrared laser beam that passes through the exhaust gas is set in accordance with the component of the exhaust gas to be detected. Carbon monoxide (CO), carbon dioxide (CO ₂ ), ammonia (NH ₃ ), methane (CH ₄ ), When detecting water (H ₂ O), infrared laser beams having five wavelengths are used. For example, the wavelength suitable for detecting ammonia is 1530 nm, the wavelength suitable for detecting carbon monoxide is 1560 nm, and the wavelength suitable for detecting carbon dioxide is 1570 nm. The wavelength suitable for detecting methane is 1680 nm, and the wavelength suitable for detecting water is 1350 nm. Furthermore, when detecting the concentration of other exhaust gas components, infrared laser beams having different wavelengths are used in accordance with the number of exhaust gas components. Note that the gas concentration may be detected at different wavelengths even for the same component, and may be selected from different wavelengths.

  The infrared laser light emitted from each of the laser diodes LD1 to LD5 is guided to the duplexers 43 through the optical fibers 42 and is demultiplexed by the duplexers 43 according to the number of sensor units. In FIG. 5, the laser beams emitted from the laser diodes LD1 to LD5 in accordance with the three sensor units 11 to 13 are divided into three. The laser beams demultiplexed by the demultiplexers 43 are separated into signal light and measurement light by the demultiplexers 44A, 44B, 44C. The duplexers 44A are for the sensor unit 11, the duplexers 44B are for the sensor unit 12, and the duplexers 44C are for the sensor unit 13. The signal light divided by the five demultiplexers 44A for the sensor unit 11 is multiplexed by the multiplexer 45A through the optical fiber, and the combined signal light in a plurality of wavelength bands is the difference which will be described later through the optical fiber 47A. The light is guided to the mold photodetector 50A. On the other hand, the measurement light divided by the five demultiplexers 44A is multiplexed by the multiplexer 46A through the optical fiber and guided to the irradiating part of the sensor unit 11 by the optical fiber 25A.

  Further, the infrared laser light demultiplexed by the demultiplexers 43 is divided into signal light and measurement light by the five demultiplexers 44B for the sensor unit 12, and the signal light is divided into a plurality of signals by the multiplexer 45B. The signal light is obtained by combining the wavelength bands, and is guided to the differential photodetector 50B through the optical fiber 47B. The measurement light divided by the five demultiplexers 44B is multiplexed by the multiplexer 46B and guided to the irradiation part of the sensor unit 12 by the optical fiber 25B. Further, the infrared laser light demultiplexed by the demultiplexers 43 is divided into signal light and measurement light by the five demultiplexers 44C for the sensor unit 13, and the signal light is divided into a plurality of signals by the multiplexer 45C. It becomes signal light in the wavelength band and is guided to the differential photodetector 50C through the optical fiber 47C. The measurement light divided by the five demultiplexers 44C is multiplexed by the multiplexer 46C and guided to the irradiation unit of the sensor unit 13 by the optical fiber 25C.

  In FIG. 5, three sensor units 11 to 13 are shown. However, when more sensor units 14... Are installed, the demultiplexer 43 demultiplexes into more laser beams, and the demultiplexed laser beams. Are further divided into measurement light and signal light by a number of demultiplexers 44..., The signal laser light is multiplexed by a multiplexer 45, and then guided to a differential photodetector 50. Laser light for measurement is multiplexed by the multiplexers 46, and then guided to a larger number of sensor units 14.

  The exhaust gas analyzer 10 of the present embodiment is configured to reflect the infrared laser light for measurement by the mirrors 30 and 31 so as to increase the transmission distance in the exhaust gas, and the measurement repeatedly reflected by the mirrors 30 and 31 is performed. The laser beam for use is received by the detector. The detectors 26A, 26B, and 26C on the light receiving side connected to the light receiving units of the sensor units 11 to 13 are connected to the differential photodetectors 50A, 50B, and 50C of the laser oscillation / light receiving controller 40 via signal lines 28A, 28B, and 28C. Connected. The signal light combined by the multiplexers 45A, 45B, and 45C is guided to the differential photodetectors 50A, 50B, and 50C through the optical fibers 47A, 47B, and 47C.

  The three differential photodetectors 50A, 50B, and 50C are configured to take a difference between the transmitted laser light that has been transmitted and attenuated through the exhaust gas and the signal laser light that has not been transmitted through the exhaust gas. The signal laser light is input to a photodiode or the like and converted into an electric signal. An electrical signal corresponding to the difference between the signal light and the measurement light calculated by the differential photodetector is amplified by, for example, a preamplifier (not shown) and is passed through an A / D converter to a personal computer 55 that is a signal analysis device. Entered. The personal computer 55 analyzes the exhaust gas by calculating the concentration of the exhaust gas component and the temperature of the exhaust gas from the input signal.

  The exhaust gas analyzer 10 of the present invention transmits, for example, infrared laser light into exhaust gas, calculates the concentration of exhaust gas components based on the intensity of incident light and the intensity of transmitted light after passing through the exhaust gas, Is to analyze. That is, the concentration C of the exhaust gas component is calculated from the following formula (1).

C = −ln (I / I ₀ ) / kL (1)

In Equation (1), I is the transmitted light intensity, I ₀ is the incident light intensity, k is the absorptance, and L is the transmission distance. Therefore, the concentration C of the exhaust gas component is calculated based on the ratio of the transmitted light intensity (I) to the incident light intensity (I ₀ ), which is signal light, and the signal intensity (I / I ₀ ). Transmitted light intensity I, the detector 26A, 26B, are output through 26C, the incident light intensity _{I 0} is the optical fiber 47A, 47B, differential optical detectors 50A, 50B, the photoelectric converter such as a photodiode in the 50C through 47C Is output from. As the incident light intensity I ₀ in the present embodiment uses a signal light intensity that does not transmit the exhaust gas.

  The operation of the exhaust gas analyzer 10 of the present embodiment configured as described above will be described below. When measuring the concentration of the exhaust gas component, the signal generator of the laser oscillation / light reception controller 40 is operated to supply a signal to each of the laser diodes LD1 to LD5, and the infrared of a predetermined wavelength is transmitted from each of the laser diodes LD1 to LD5. Laser light is emitted. The infrared laser light emitted from each of the laser diodes LD1 to LD5 reaches the duplexers 43 through optical fibers 42, and is demultiplexed according to the number of sensor units.

  Thereafter, the demultiplexed infrared laser light is demultiplexed into measurement light and signal light by demultiplexers 44A... 44B. The one sensor unit 11 will be described in detail. The signal light demultiplexed by the five demultiplexers 44A is multiplexed by the multiplexer 45A to become a signal laser beam and guided to the differential photodetector 50A. The The measurement light demultiplexed by the five demultiplexers 44A is combined by the multiplexer 46A to become measurement laser light, and is guided to the irradiation part of the sensor unit 11 through the optical fiber 25A. Similarly, the other sensor units 12 and 13 are demultiplexed by the demultiplexers 43, and then demultiplexed into signal light and measurement light by the demultiplexers 44B, 44C, and the like, and are multiplexed by the multiplexers 45B and 45C. After being combined, the signal light is guided to the differential photodetectors 50B and 50C, combined by the multiplexers 46B and 46C, and the measurement light is guided to the sensor units 12 and 13.

  And the infrared laser light for measurement irradiated from the optical fibers 25A, 25B, and 25C of the sensor units 11 to 13 enters the exhaust gas passage hole 21 through which the exhaust gas passes through the sensor hole 23 that is the irradiation light passage hole. Irradiated. The infrared laser beam traverses the exhaust gas passage hole 21 which is an exhaust path, reaches the mirror 31 through the light passage hole 38, is reflected upward by the lower mirror 31, and then reaches the mirror 31 through the light passage hole 38 and reaches the upper side. The light is reflected downward by the mirror 30, and the transmission distance in the exhaust gas is increased by repeating the reflection. Finally, the light is received by the detectors 26A, 26B, and 26C through the sensor hole 24. That is, the infrared laser light for measurement is transmitted through the exhaust gas and attenuated, and the attenuated transmitted light is received by the detector that is the light receiving unit, and the light intensity of the transmitted light (measurement light) is measured.

  As shown in FIG. 6a, female threads 23a and 24a are formed on the inner peripheral surfaces of the sensor holes 23 and 24 as scattered light exclusion means, and the inner peripheral surfaces of the light passage holes 38 are also shown in FIG. 6b. Since the internal thread 38a is formed as the scattered light exclusion means, even if the scattered light S is generated, the scattered light is incident on the sensor hole or the light passage hole at an angle different from the original incident angle of the laser light R. Therefore, it is not reflected by the female thread surface in the opposite direction, for example, and mixed into the laser light and does not pass through the sensor holes 23 and 24 and the light passage hole 38.

  In addition, since the measurement infrared laser light is received across the plane perpendicular to the exhaust path in the exhaust gas passage hole 21 of the sensor section constituting the exhaust path, the concentration of the exhaust gas component in one orthogonal cross section And temperature can be measured in spots. That is, the concentration and temperature of the exhaust gas components in a certain range along the exhaust path are not measured, but the concentration and temperature of the exhaust gas components based on a predetermined plane crossing the exhaust path are measured. Therefore, spot-like measurement is possible.

  The measurement infrared laser light that has attenuated through the exhaust gas and reached the light receiving section is output as an electrical signal by the detectors 26A, 26B, and 26C, and is supplied to the differential photodetector 50A, via the signal lines 28A, 28B, 28C. 50B and 50C. On the other hand, the signal laser light is supplied to the differential photodetectors 50A, 50B, and 50C, and the differential photodetector detects the difference between the transmitted light (measurement light) and the signal light for each of a plurality of wavelength components, and transmits the transmitted light. The peak wavelength of the specific gas component is detected. In this way, the output from the differential photodetector is input to the personal computer 55 which is a signal analysis device. The personal computer 55 performs the concentration measurement and temperature measurement of the components of the exhaust gas based on the input peak wavelength for each of the plurality of frequency bands and analyzes it. Since the concentration and temperature of the exhaust gas component thus measured are not affected by scattered light, it is possible to measure with high accuracy and improve analysis accuracy.

  Each gas has its own absorption wavelength band, and many absorption lines exist in the absorption wavelength band, for example, as shown in FIG. FIG. 7a shows the signal intensity at the low temperature (= number of molecules), and FIG. 7b shows the signal intensity at the high temperature. Thus, since the signal intensity changes depending on the temperature, the temperature of the exhaust gas at the time of measurement can be calculated by measuring the signal intensity ratio.

  Then, as shown in FIG. 8, the absorption is measured by sweeping the oscillation wavelength of the laser light with respect to one of the absorption lines, for example, the wavelength λ1. The spectrum profile is measured by taking the ratio between this waveform and the waveform of the signal laser beam. Further, the temperature measurement can be obtained by measuring the spectrum profile for two different absorption lines λ1 and λ2 and taking the area ratio A1 / A2 (or the peak height ratio P1 / P2). . In the conventional wavelength modulation method, as shown in FIG. 8a, the concentration of the exhaust gas component is calculated based on the curvature of the tip of the absorption spectrum peak, but in the present invention, as shown in FIG. Since the concentration of the exhaust gas component is calculated, it is possible to calculate the concentration of the exhaust gas component that is not easily affected by pressure.

  The exhaust gas analyzer 10 of the present embodiment includes a sensor hole 23 that is an irradiation light passage hole through which the measurement laser light passes, a sensor hole 24 that is a transmission light passage hole, and a light passage hole 38 for causing the laser light to reach the mirror. , 38 are formed with female thread surfaces 23a, 24a, 38a as scattered light exclusion means, so that when scattered light due to irregular reflection in the exhaust gas passage holes and reflected by the mirrors 30, 31 are formed. Scattered light that occurs is unlikely to reach the light receiving part and is difficult to be received by the light receiving part. Scattered light is less likely to mix with the transmitted laser light received by the light receiving part, reducing noise caused by scattered light. Therefore, measurement accuracy can be increased.

  The sensor hole 23 to which the measurement laser light is irradiated constitutes an irradiation light passage hole, and the sensor hole 24 to which the laser light transmitted through the exhaust gas is received constitutes a transmission light passage hole. Scattering of these light passage holes The light exclusion means can be easily formed as the female thread surfaces 23a and 24a by screwing a thread cutting tap. In addition, the light passage holes 38 and 38 that communicate the exhaust gas passage hole 21 and the mirror can also be easily formed with a female thread surface 38a as a scattered light exclusion means on the inner peripheral surface by screwing a tap for threading. .

  In this measurement, a circular exhaust gas passage hole 21 having the same diameter as the cross-sectional shape of the exhaust path is formed in the sensor base 20 of the sensor unit, and the thickness of the sensor base 20 is thin, and laser light is emitted. Since the passing sensor holes 23 and 24 and the light passage holes 38 and 38 are formed small, the exhaust gas flows stably without disturbing the exhaust gas flow, so that the exhaust efficiency can be prevented from lowering. In addition, the laser beam that passes through the exhaust gas is reflected without disturbing the flow of the exhaust gas to increase the transmission distance in the exhaust gas and receive light, thereby increasing the attenuation, thereby enabling highly accurate measurement. . Note that the cross-sectional shape of the exhaust gas passage hole may be formed to be approximately the same as long as the flow of the exhaust gas is not disturbed.

  Another embodiment of the present invention will be described in detail with reference to FIG. FIG. 9 is a front view, a DD line cross-sectional view, a EE line cross-sectional view, and a FF line main part cross-sectional view of another embodiment of the sensor unit used in the exhaust gas analyzer according to the present invention. Note that this embodiment is different from the above-described embodiment in that the light passage hole through which the laser beam for measurement passes is formed in a tapered tip pore whose diameter gradually changes, and this tip pore serves as a scattered light exclusion means. A taper screw is formed. Other substantially equivalent configurations are denoted by the same reference numerals, and detailed description thereof is omitted.

  The sensor part 11A shown in FIG. 9 penetrates from the exhaust gas passage hole 21 formed at the center of the sensor base 20A to the groove part to which the mirror is fixed, and has the leading holes 38A. For example, the tip pore is tapered so that the diameter on the mirror side is small at about 2 mm, the diameter opened on the exhaust gas passage hole side is about 3 to 4 mm, and the diameter gradually increases toward the exhaust gas passage hole side. Is formed. As described above, since the front aperture 38A has a small diameter on the mirror side and a large opening side, the laser light incident on the mirror is easy to enter, and scattering that is likely to occur when the laser light is reflected by the mirrors 30 and 31. The amount of light that passes through the fine pores can be significantly removed.

  In addition, when the laser beam passes through the tip hole 38A, the scattered light is reflected by the tapered female screw surface 38b formed on the inner peripheral surface, and hardly passes through the tip hole 38A mixed with the laser beam. The scattered light can be prevented from being mixed with the laser beam for measurement. As a result, when measuring the concentration of the components of the exhaust gas based on the laser light transmitted through the exhaust gas, the measurement accuracy can be improved since the scattered light is not mixed with the measurement light. In particular, since the diameter of the hole facing the mirrors 30 and 31 is small at the tip hole 38A and the scattered light is difficult to pass when the laser light is reflected by the mirror, the scattered light is hardly mixed even if the number of reflections is large, Measurement accuracy can be increased.

  Although not shown in detail in FIG. 9, female screw surfaces are formed on the inner peripheral surfaces of the sensor holes 23 and 24 as scattered light exclusion means, as in the above embodiment. Further, although the fixing means for the mirrors 30 and 31 are not shown, they may be fixed with mounting screws in the same manner as the sensor section of FIG. 4, or may be fixed using other means. Although an example of a female screw surface has been shown as the scattered light exclusion means, a multi-stage slit or a step surface may be formed as the scattered light exclusion means.

  Another embodiment of the present invention will be described in detail with reference to FIG. FIG. 10 is a cross-sectional view of the main part of another embodiment of the sensor unit used in the exhaust gas analyzer according to the present invention. As shown in FIG. 10, the sensor unit 11 </ b> B of the present embodiment includes a dew condensation prevention heater H that prevents water droplets from adhering to the surfaces of the mirrors 30 and 31. That is, a mounting hole Ha is formed from the side in the sensor base 20B in the vicinity of the rear surface side of the mirror 31, and a heater H is mounted in the mounting hole. The mounting hole is formed in a cylindrical shape by a drill or the like, and a cylindrical heater H is inserted and fixed therein. The set temperature of the heater H is preferably set so that the surface temperature of the mirrors 30 and 31 is 150 to 200 ° C. By setting the temperature in this way, moisture to be attached to the surface of the mirror is removed. Vaporization can prevent condensation.

  Although FIG. 10 shows an example in which the heater H is fixed close to the lower mirror 31, the heater is similarly fixed to the upper mirror. In FIG. 10, a slit 39 is formed as a light passage hole through which the laser light passes toward the mirror. Scattered light eliminating means is also formed on the inner peripheral surface of the slit. The scattered light exclusion means may be a rough surface formed when the inner peripheral surface is roughened, or an uneven surface such as a satin finish. In addition, when the sensor base is formed of aluminum, scattered light exclusion means may be formed by setting the surface to a fine uneven surface (rough surface) by anodizing.

  The heater H is preferably energized before starting the engine. If energized in advance before starting, it is possible to prevent a heat shock caused by contact of high-temperature exhaust gas while the mirrors 30 and 31 are cold, and to prevent breakage of the mirror due to the heat shock. In particular, since the exhaust gas discharged from the engine is hot on the upstream side of the exhaust path, by energizing the heater in advance, it is possible to prevent thermal shock and prevent damage to the mirror. In addition, the surface of the mirror that comes into contact with the exhaust gas is hotter than the rear surface, and the mirror itself may be thermally deformed. The reflection of the laser beam can be stabilized, and the generation of scattered light can be prevented.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. For example, a laser beam irradiation unit and a light receiving unit may be disposed so as to face the gas passage hole of the sensor unit, and the laser beam may be directly received without using a reflecting member such as a mirror. Alternatively, a single mirror may be used so that the laser beam irradiated from the irradiation unit is reflected by the mirror only once and received.

  In addition, examples of light passage holes and tapered tip pores have been shown as light passage holes through which laser light passes. However, laser light passage holes are formed with slits, etc., and antireflection processing is applied to the inner peripheral surface of the slits. You may make it attenuate the scattered light by irregular reflection of light. Although an example of an infrared laser beam has been shown as the laser beam for measurement, it is needless to say that a visible laser beam or an ultraviolet laser beam may be used.

  Although the sensor base of the sensor unit is provided with an optical fiber as an irradiator and a detector as a light receiver, the sensor base may be provided with an irradiator such as a laser diode directly, and receives light instead of a detector such as a photodiode. It is good also as a structure which mounts the optical fiber for use. Moreover, a collimator lens may be provided in the irradiation part of the optical fiber, and laser light may be irradiated into the gas passage hole through the collimator lens.

  As an application example of the present invention, this gas analyzer can be used for exhaust gas analysis of combustion devices such as boilers, and in addition to automobile exhaust gas analysis, it is used for exhaust gas analysis of internal combustion engines used in ships, generators, etc. It can also be applied to. In addition to the exhaust gas analysis of a gasoline engine, exhaust gas analysis of a diesel engine can be performed, and further, it can be applied to the use of exhaust gas analysis of other internal combustion engines.

The principal part block diagram of one Embodiment which mounted the exhaust gas analyzer as a gas analyzer which concerns on this invention in the vehicle. The principal part block diagram of other embodiment which mounted the exhaust gas analyzer as a gas analyzer which concerns on this invention in the engine bench. The principal part block diagram of the exhaust gas analyzer containing the perspective view of the state which the principal part of one sensor part decomposed | disassembled. (A) is the front view which fractured | ruptured a part of sensor part of FIG. 3, (b) is the sectional view on the AA line of (a), (c) is the sectional view on the BB line of (a), (d ) Is a sectional view taken along the line CC of (c). The block diagram which shows the whole structure of the exhaust gas analyzer containing the principal part structure of a laser oscillation and light reception controller, and a signal analyzer. (A), (b) is a principal part expanded sectional view which respectively shows the state which excludes scattered light. The influence of the pressure of an absorption spectrum is shown, (a) is explanatory drawing of signal intensity at the time of low temperature, (b) is explanatory drawing of signal intensity at the time of high temperature. (A) is explanatory drawing which calculates the density | concentration of the component of exhaust gas from the conventional absorption spectrum, (b) is explanatory drawing which calculates the density | concentration of the component of exhaust gas from the absorption spectrum of this invention. Other embodiment of a sensor part is shown, (a) is a front view of a sensor part, (b) is a DD line sectional view of (a), (c) is a EE line sectional view of (a), (D) is sectional drawing of the principal part of the FF line | wire of the sensor base of (c). The principal part sectional view showing other embodiments of a sensor part.

Explanation of symbols

  1: automobile, 1A: engine bench, 2: engine (internal combustion engine), 3: exhaust manifold (exhaust path), 4: exhaust pipe (exhaust path), 5: first catalyst device (exhaust path), 6: second Catalyst device (exhaust path), 7: Muffler (exhaust path), 8: Exhaust pipe (exhaust path), 10: Exhaust gas analyzer (gas analyzer), 11-14, 11A, 11B: Sensor unit, 20, 20A, 20B: Sensor base, 21: Exhaust gas passage hole, 23: Sensor hole (irradiation light passage hole), 24: Sensor hole (transmission light passage hole), 23a, 24a: Female thread surface (scattered light exclusion means), 25: Light Fiber (irradiation part), 26: Detector (light-receiving part), 30, 31: Mirror, 38: Light passage hole, 38a: Female thread surface (scattered light exclusion means), 38A: Tip pore (light passage hole), 38b: Tapered female thread (scattered light exclusion) Stage), 39: slit (light passage hole), 40: laser oscillation / light receiving controller, 43: demultiplexer, 44A to 44C: demultiplexer, 45A to 45C, 46A to 46C: multiplexer, 50A to 50C: Differential-type photodetector, 55: personal computer (signal analysis device), H: heater, R: laser light, S: scattered light

Claims (7)

A gas analyzer that irradiates a gas to be analyzed with a laser beam and measures and analyzes the component concentration and temperature of the gas based on the laser beam transmitted through the gas,
The gas analyzer includes a sensor unit fixed to a path through which a gas to be measured flows,
The sensor unit is
A sensor base,
A gas passage hole through which the gas formed in the sensor base flows;
An irradiation unit for irradiating a laser beam fixed to the sensor base and a light receiving unit for receiving the irradiated laser beam;
An irradiation light passage hole formed on the irradiation portion side and a transmitted light passage formed on the light reception portion side so that the laser light emitted from the irradiation portion can reach the light reception portion through the gas passage hole. Holes ,
A reflecting member that is disposed outside the gas passage hole in the sensor base and reflects the laser beam irradiated by the irradiation unit and guides it to the light receiving unit;
A light passage hole for allowing the laser beam formed on the sensor base to reach the reflecting member, and
A rough surface for preventing reflection by attenuating the laser beam is formed on at least an inner peripheral surface of the transmitted light passage hole among the irradiation light passage hole and the transmitted light passage hole ,
The light passage hole has a rough surface for preventing reflection by attenuating the laser beam on the inner peripheral surface of the light passage hole, and the gas passage hole side has a large diameter and the reflection member side has a small diameter. A gas analyzer characterized in that it is formed as a tip pore . The gas analyzer according to claim 1 , wherein the rough surface is formed by subjecting the inner peripheral surface to a rough surface process. When the sensor base is formed of aluminum,
The gas analyzer according to claim 1 , wherein the rough surface is formed by subjecting the inner peripheral surface to an alumite treatment. The gas analyzer according to any one of claims 1 to 3 , wherein the gas passage hole has substantially the same cross-sectional shape as a cross-sectional shape of the path. The gas analyzer according to any one of claims 1 to 4 , wherein the sensor unit is installed at a plurality of locations in the path. The gas analyzer according to any one of claims 1 to 5 , wherein the sensor unit includes a heater that heats a reflecting member on the sensor base. The analyte gas is the exhaust gas discharged from an internal combustion engine, according to any one of claims 6 to the exhaust gas flow path connected to the internal combustion engine from claim 1, characterized in that the said path Gas analyzer.

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