Hydrogen flame ionization detector, gas analyzer, and gas analysis method

Abstract

The present invention provides a hydrogen flame ionization detector 100 for reducing a leakage current from a collector electrode to a peripheral member. The hydrogen flame ionization detector 100 mixes a sample gas and a hydrogen gas, burns the mixture in a combustion chamber 2S, and detects an ion current generated at that time. The hydrogen flame ionization detector 100 comprises an insulating block body 2 in which the combustion chamber 2S is formed, and a collector electrode 3 for detecting the ion current, the collector electrode 3 having a tip portion disposed inside the combustion chamber 2S. The collector electrode 3 is supported outside the combustion chamber 2S at a distance from the inner surface that forms the combustion chamber 2S.

Description

Hydrogen Flame Ionization Detector, Gas Analyzer, and Gas Analysis Method 【0001】 The present invention relates to a hydrogen flame ionization detector, a gas analyzer, and a gas analysis method. 【0002】 A hydrogen flame ionization detector mixes a sample gas and hydrogen gas and burns them in a combustion chamber, and detects the ion current generated at that time with a collector. 【0003】 Specifically, as shown in Patent Document 1, in a hydrogen flame ionization detector, a nozzle for ejecting a mixed gas of a sample gas and hydrogen gas and a collector for capturing ions generated when the mixed gas burns are arranged inside a detector housing. Further, the collector is held with respect to the detector housing by a ceramic insulator, a Teflon material, or the like. 【0004】 However, in a hydrogen flame ionization detector, since a hydrogen flame is formed inside, each part inside the detector housing becomes high temperature. Then, the electrical resistance value of each part such as the ceramic insulator holding the collector decreases. As a result, an unintended leakage current flows between the collector and the base electrode through the ceramic insulator, becoming a noise component with respect to the ion current. In particular, when the volume of the combustion chamber is reduced, the distance between the collector and the base electrode becomes short, so the influence of the above-mentioned leakage current may become more prominent. 【0005】 Japanese Patent Application Laid-Open No. 2000-206091 【0006】 Therefore, the present invention has been made in view of the above problems, and the main problem is to reduce the leakage current from the collector electrode to the peripheral members. 【0007】In other words, the flame ionization detector according to the present invention is a flame ionization detector that mixes a sample gas with hydrogen gas and burns it in a combustion chamber, and detects the ion current generated at that time, comprising an insulating block body having the combustion chamber formed inside, and a collector electrode whose tip is positioned inside the combustion chamber for detecting the ion current, wherein the collector electrode is supported outside the combustion chamber, away from the inner surface forming the combustion chamber. 【0008】 With this type of hydrogen flame ionization detector, since the collector electrode does not come into contact with the inner surface forming the combustion chamber, leakage current from the collector electrode to the inner surface forming the combustion chamber can be reduced. In addition, since the collector electrode is supported outside the combustion chamber, the support portion of the collector electrode is less likely to become hot due to the combustion of hydrogen gas, thus reducing leakage current from the collector electrode to the support portion. 【0009】 Here, the problem is that the electrical resistance (electrical insulation) decreases as each part becomes hot due to the hydrogen flame. In addition to constructing the block using a material with high electrical insulation, it is also conceivable to construct the block using a material that does not easily become hot, that is, a material with high thermal insulation. From the standpoint of electrical insulation, the block could be made of Teflon (electrical resistivity > 10 １８ It is preferable that the block be made of [Ω・m]. Furthermore, from the viewpoint of thermal insulation, it is preferable that the block be made of quartz glass (thermal conductivity: 1.38 [W / (m・k)]). 【0010】 In order to reduce the volume of the combustion chamber and miniaturize the hydrogen flame ionization detector, it is desirable that the collector electrode be needle-shaped, rod-shaped, or plate-shaped. In this case, the collector electrode is configured in a cantilevered state with its base end supported, and its tip positioned inside the combustion chamber. Alternatively, if the collector electrode is plate-shaped, it is conceivable that the base end be a rod-shaped portion in a cantilevered state, with the tip being a plate-shaped portion positioned inside the combustion chamber. 【0011】The block body has a first insertion hole that communicates with the combustion chamber and through which the collector electrode is inserted. Preferably, the collector electrode is inserted into the first insertion hole away from the inner surface forming the first insertion hole, so that its tip is positioned inside the combustion chamber. With this configuration, the collector electrode is supported outside the combustion chamber and the first insertion hole, so the support portion of the collector electrode is less likely to become hot due to the combustion of hydrogen gas, and the leakage current from the collector electrode to the support portion can be reduced. 【0012】 Preferably, the first through-hole has a shape that narrows continuously or gradually toward the combustion chamber, or has an equicross-sectional shape. With this configuration, the opening size of the first through-hole in the combustion chamber can be reduced while ensuring the distance between the inner surface forming the first through-hole and the collector electrode, thereby preventing the hydrogen flame from leaking out of the combustion chamber. 【0013】 The block body is provided with an electrode support portion that supports the base end of the collector electrode, and it is desirable that a heat insulating layer is formed between the electrode support portion and the combustion chamber. With this configuration, the heat transmitted from the block body to the electrode support portion can be reduced, the electrode support portion is less likely to become hot due to the hydrogen flame, and the leakage current from the collector electrode to the electrode support portion can be reduced. 【0014】 To miniaturize a flame ionization detector, it may be necessary to introduce a sample gas under reduced pressure in the combustion chamber. In this case, to reduce the pressure in the combustion chamber, it is necessary to seal the area around the collector electrode. Therefore, it is desirable that the block body be provided with a first insertion hole that communicates with the combustion chamber and through which the collector electrode is inserted without contact, an electrode support portion that supports the base end of the collector electrode, and a sealing portion that seals the space between the first insertion hole and the electrode support portion so as to surround the collector electrode. When performing reduced pressure gas flow in this configuration, for example, a pressure reduction mechanism that pulls the sample gas from the sealing portion can be considered. 【0015】The block body is provided with a first introduction passage for introducing hydrogen gas and sample gas into the combustion chamber, and a second introduction passage for introducing auxiliary combustion gas into the combustion chamber. Preferably, the first and second introduction passages are connected so as to face each other in the combustion chamber. With this configuration, the first and second introduction passages can be easily formed even when the block body is miniaturized. In addition, the hydrogen gas and sample gas and the auxiliary combustion gas can be easily mixed in the combustion chamber, making it easier to generate a stable hydrogen flame. 【0016】 In order to miniaturize the flame ionization detector, it is desirable that the block body has a flat plate shape. 【0017】 The hydrogen flame ionization detector of the present invention may further include a base electrode, the tip of which is positioned inside the combustion chamber, to which a predetermined bias potential is applied in relation to the collector electrode. In this configuration, in order to reduce leakage current from the base electrode, it is desirable that the base electrode is supported outside the combustion chamber, away from the inner surface forming the combustion chamber. 【0018】 Regarding the specific arrangement of the collector electrode and the base electrode, it is desirable that the collector electrode and the base electrode are arranged so that their tips face each other inside the combustion chamber. 【0019】 The hydrogen flame ionization detector of the present invention further comprises an ignition unit for igniting a hydrogen flame in the combustion chamber, the ignition unit having an ignition circuit connected to the collector electrode and the base electrode, and preferably the ignition circuit ignites the hydrogen flame by causing a discharge between the collector electrode and the base electrode. With this configuration, the hydrogen flame can be reliably ignited in the combustion chamber by generating a discharge (spark) between the collector electrode and the base electrode. Furthermore, an external ignition device and pilot flame are unnecessary, and the hydrogen flame ionization detector can be miniaturized and its structure simplified. 【0020】 Furthermore, a gas analyzer having the aforementioned flame ionization detector is also one aspect of the present invention. 【0021】Furthermore, it is desirable that the gas analyzer includes an introduction channel for sampling exhaust gas from an internal combustion engine and introducing it to the flame ionization detector, an exhaust channel for exhausting the exhaust gas that has passed through the flame ionization detector, and a heating mechanism for heating the introduction channel and the exhaust channel to a temperature above the dew point of the exhaust gas. With this configuration, it is possible to prevent condensation of moisture contained in the exhaust gas, prevent measurement errors caused by gas components dissolving in condensed water, and prevent malfunctions caused by condensed water. 【0022】 Furthermore, the gas analysis method according to the present invention is a gas analysis method using the flame ionization detector described above, characterized in that the introduction channel for sampling exhaust gas from an internal combustion engine and introducing it into the flame ionization detector, and the exhaust channel for exhausting the exhaust gas that has passed through the flame ionization detector, are heated to a temperature above the dew point of the exhaust gas. 【0023】 According to the present invention configured in this way, the leakage current from the collector electrode to the surrounding member can be reduced. 【0024】 This is a schematic diagram of a gas analysis system using a flame ionization detector in this embodiment. This is a cross-sectional view showing the main part of the flame ionization detector in the same embodiment. This is a cross-sectional view taken along line A-A showing the main part of the flame ionization detector in the same embodiment. This is a schematic diagram showing the acquisition circuit and calculation device of the flame ionization detector in the same embodiment. This is a schematic diagram showing the ignition part of the flame ionization detector in a modified embodiment. This is a cross-sectional view showing the main part of the flame ionization detector in a modified embodiment. This is a partially enlarged cross-sectional view showing the collector electrode in a modified embodiment. This is a cross-sectional view showing the main part of the flame ionization detector in a modified embodiment. This is a cross-sectional view showing the main part of the flame ionization detector in a modified embodiment. This is a cross-sectional view showing the main part of the flame ionization detector in a modified embodiment. This is a cross-sectional view showing the main part of the flame ionization detector in a modified embodiment. This is a (a) cross-sectional view and (b) longitudinal cross-sectional view showing the main part of the flame ionization detector in a modified embodiment. This is a schematic diagram showing the usage state of a vehicle-mounted exhaust gas analyzer in a modified embodiment. This is a schematic diagram showing the peripheral structure of the flame ionization detector in the exhaust gas analyzer in a modified embodiment. 【0025】A flame ionization detector according to one embodiment of the present invention will be described below with reference to the drawings. Note that all the following figures are schematic representations, with some omissions and exaggerations for clarity. The same components are denoted by the same reference numerals, and their descriptions are omitted as appropriate. 【0026】 <Configuration of the hydrogen flame ionization detector 100> The hydrogen flame ionization detector 100 of this embodiment mixes a sample gas with hydrogen gas and burns it in a combustion chamber, and measures the concentration of the target component contained in the sample gas based on the ion current generated at that time. 【0027】 Here, as shown in Figure 1, the hydrogen flame ionization detector 100 is installed on an exhaust gas flow path 10 which has a sampling section P1 for sampling the exhaust gas of the engine E, and measures the concentration of hydrocarbons, which are organic compounds, as the target components contained in the exhaust gas sample. 【0028】 Furthermore, a filter 11 and a suction pump 12 are provided on the exhaust gas flow path 10. The flame ionization detector 100 may also be incorporated into a vehicle-mounted exhaust gas analyzer. When incorporated into an exhaust gas analyzer, the flame ionization detector 100 is used for exhaust gas analysis together with other analyzers using different measurement principles, such as a laser analyzer. In addition, the flame ionization detector 100 may measure the concentration of volatile organic compounds (VOCs) in the atmosphere, or it may be used together with a gas chromatograph. Furthermore, the hydrogen flame ionization detector 100 may also measure the concentration of target components contained in the exhaust gas of various other equipment, such as (1) heat engines such as internal combustion engines, steam turbine engines or Stirling engines, (2) combustion equipment such as burners, boilers or combustion furnaces, (3) power generation equipment such as gas turbine generators, steam turbine generators or internal combustion engine generators (diesel generators), and (4) industrial furnaces such as high-temperature firing furnaces (ceramics firing furnaces, glass furnaces), metal melting furnaces (electric furnaces, molten steel furnaces), drying furnaces or heat treatment furnaces. 【0029】Specifically, as shown in Figures 2 and 3, the hydrogen flame ionization detector 100 comprises an insulating block body 2 with a combustion chamber 2S formed inside, and a collector electrode 3 whose tip is positioned inside the combustion chamber 2S for detecting ion current. The hydrogen flame ionization detector 100 also further comprises a base electrode 4 whose tip is positioned inside the combustion chamber 2S and to which a predetermined bias potential is applied between it and the collector electrode 3. The hydrogen flame ionization detector 100 is provided with an exhaust port (not shown) for exhausting exhaust gas produced by the combustion of the hydrogen flame. The hydrogen flame ionization detector 100 is also provided with an ignition unit (not shown) for igniting the hydrogen flame inside the combustion chamber 2S. 【0030】 The block body 2 is a flat plate shape formed from an insulator with low thermal conductivity, such as glass. A combustion chamber 2S is formed in the central part of this block body 2. This combustion chamber 2S is a space in which a mixture of sample gas and hydrogen gas burns to generate a hydrogen flame F, and is a space in which the mixture of sample gas and hydrogen gas mixes with a combustion aid. The combustion chamber 2S in this embodiment is a rectangular parallelepiped shape and is rectangular in plan view. This combustion chamber 2S does not include the first insertion hole 23, the second insertion hole 24, the first penetration part H1, and the second penetration part H2, which will be described later. The combustion chamber 2S can be in various shapes, such as a cylindrical shape or a polygonal prism shape. 【0031】 Furthermore, the block body 2 has a first introduction passage 21 for introducing hydrogen gas and sample gas into the combustion chamber 2S, and a second introduction passage 22 for introducing a combustion-supporting gas (e.g., air) into the combustion chamber 2S. The first introduction passage 21 is connected to a hydrogen gas supply passage 5 for supplying hydrogen gas and an exhaust gas passage 10. In this embodiment, the hydrogen gas supply passage 5 is connected to the upstream side of the hydrogen flame ionization detector 100 in the exhaust gas passage 10, and a mixed gas of hydrogen gas and sample gas is supplied to the first introduction passage 21. In addition, the second introduction passage 22 is connected to a combustion-supporting gas supply passage 7 for supplying a combustion-supporting gas (air). 【0032】The first inlet passage 21 and the second inlet passage 22 are connected so as to face each other in the combustion chamber 2S. Specifically, the first inlet passage 21 and the second inlet passage 22 are straight flow paths, and the first inlet passage 21 is connected substantially perpendicularly to the first surface (bottom surface in Figure 2) that forms the combustion chamber 2S. The second inlet passage 22 is connected substantially perpendicularly to the second surface (top surface in Figure 2) that is the inner surface of the combustion chamber 2S and faces the first surface. The openings of the first inlet passage 21 and the openings of the second inlet passage 22 in the combustion chamber 2S face each other. 【0033】 The collector electrode 3 is a straight, needle-shaped or rod-shaped electrode, and is supported outside the combustion chamber 2S without contacting the inner surface forming the combustion chamber 2S, that is, at a distance from the inner surface forming the combustion chamber 2S. Similarly, the base electrode 4 is a straight, needle-shaped or rod-shaped electrode, and is supported outside the combustion chamber 2S without contacting the inner surface forming the combustion chamber 2S, that is, at a distance from the inner surface forming the combustion chamber 2S. The collector electrode 3 and the base electrode 4 are each made of a precious metal, a non-precious metal, or an alloy, and in this embodiment, stainless steel is used. 【0034】 Here, the block body 2 has a first insertion hole 23 that communicates with the combustion chamber 2S and through which the collector electrode 3 is inserted. This first insertion hole 23 is connected to the combustion chamber 2S and has a shape that continuously narrows toward the combustion chamber 2S, and in this case, it has a tapered shape. The collector electrode 3 is inserted into the first insertion hole 23 without contacting the inner surface forming the first insertion hole 23, that is, at a distance (away from) the inner surface forming the first insertion hole 23, so that its tip is positioned inside the combustion chamber 2S. 【0035】Furthermore, the block body 2 has a second insertion hole 24 that communicates with the combustion chamber 2S and through which the base electrode 4 is inserted. This second insertion hole 24 is connected to the combustion chamber 2S and has a shape that continuously narrows toward the combustion chamber 2S, and in this case, it has a tapered shape. The base electrode 4 is inserted into the second insertion hole 24 without contacting the inner surface forming the second insertion hole 24, that is, at a distance (away from) the inner surface forming the second insertion hole 24, so that its tip is positioned inside the combustion chamber 2S. 【0036】 The first insertion hole 23 and the second insertion hole 24 are connected so as to face each other in the combustion chamber 2S. Specifically, the first insertion hole 23 is connected substantially perpendicularly to the third surface (right surface in Figure 2) that forms the combustion chamber 2S. This first insertion hole 23 opens into a part of the third surface that forms the combustion chamber 2S. The second insertion hole 24 is connected substantially perpendicularly to the fourth surface (left surface in Figure 2) that is the inner surface of the combustion chamber 2S and faces the third surface. This second insertion hole 24 opens into a part of the fourth surface that forms the combustion chamber 2S. The openings of the first insertion hole 23 and the openings of the second insertion hole 24 in the combustion chamber 2S face each other. With this configuration, the collector electrode 3 and the base electrode 4 are arranged so that their tips face each other inside the combustion chamber 2S. 【0037】 Furthermore, the block body 2 is provided with a first electrode support portion 25 that supports the base end of the collector electrode 3. The first electrode support portion 25 is provided outside the first insertion hole 23 relative to the combustion chamber 2S. Due to this first electrode support portion 25, the collector electrode 3 is cantilevered, and its tip is positioned inside the combustion chamber 2S. In other words, the base end of the collector electrode 3 is positioned outside the first insertion hole 23 relative to the combustion chamber 2S, and the part other than the base end does not come into contact with surrounding members. 【0038】Furthermore, a first heat insulating layer 26 is formed between the first electrode support portion 25 and the combustion chamber 2S, separating them. Specifically, the first heat insulating layer 26 is formed between the first electrode support portion 25 and the first insertion hole 23. In other words, the first electrode support portion 25 is located outside the first heat insulating layer 26 relative to the combustion chamber 2S. The first heat insulating layer 26 in this embodiment is composed of a first penetration portion H1 that penetrates the block body 2 from the front to the back. In other words, the air inside the first penetration portion H1 functions as the first heat insulating layer 26. This first penetration portion H1 intersects with the first insertion hole 23 and is formed to connect to the outside of the first insertion hole 23, and its width dimension L1 (in a plan view) perpendicular to the collector electrode 3 is configured to be larger than the outer opening width L2 of the first insertion hole 23. The first insulating layer 26 may be formed by containing nitrogen gas, argon gas, krypton gas, carbon dioxide, sulfur hexafluoride, or helium in the first penetration H1. In this case, the block body 2 is provided with a separate exhaust passage connected to the first insertion hole 23. 【0039】 Furthermore, the block body 2 is provided with a second electrode support portion 27 that supports the base end of the base electrode 4. The second electrode support portion 27 is provided outside the second insertion hole 24 relative to the combustion chamber 2S. This second electrode support portion 27 gives the base electrode 4 a cantilevered position, and its tip is positioned inside the combustion chamber 2S. In other words, the base end of the base electrode 4 is positioned outside the second insertion hole 24 relative to the combustion chamber 2S, and the part other than the base end does not come into contact with surrounding members. 【0040】Furthermore, a second heat insulating layer 28 is formed between the second electrode support portion 27 and the combustion chamber 2S, separating them. Specifically, the second heat insulating layer 28 is formed between the second electrode support portion 27 and the second insertion hole 24. In other words, the second electrode support portion 27 is located outside the second heat insulating layer 28 relative to the combustion chamber 2S. The second heat insulating layer 28 in this embodiment is composed of a second penetration portion H2 that penetrates the block body 2 from the front to the back. In other words, the air inside the second penetration portion H2 functions as the second heat insulating layer 28. This second penetration portion H2 intersects with the second insertion hole 24 and is formed to connect to the outside of the second insertion hole 24, and has a width greater than the outer opening width of the second insertion hole 24. 【0041】 The combustion chamber 2S, the introduction passages 21 and 22, and the insertion holes 23 and 24 of the block body 2 described above can be formed by laser etching on a glass substrate. Specifically, the areas within the glass substrate where the combustion chamber 2S, the introduction passages 21 and 22, and the insertion holes 23 and 24 are to be formed are irradiated with an ultrashort pulse laser to modify the substrate. Subsequently, the modified areas are selectively etched with an etchant such as potassium hydroxide (KOH) or hydrofluoric acid (HF) solution to form the combustion chamber 2S, the introduction passages 21 and 22, and the insertion holes 23 and 24. The combustion chamber 2S thus formed has, for example, a rectangular parallelepiped shape with a length of 3 mm, a width of 2 mm, and a height of 0.75 mm. The introduction passages 21 and 22 have, for example, a straight shape with a diameter of 0.25 mm. Furthermore, the insertion holes 23 and 24 have, for example, a tapered shape with a maximum diameter of 2 mm and a minimum diameter of 0.6 mm. In this configuration, the collector electrode 3 and the base electrode are needle-shaped electrodes with a diameter of 0.1 mm. The combustion chamber 2S, the introduction passages 21 and 22, and the insertion holes 23 and 24 of the block body 2 can also be formed by a 3D printer. 【0042】 In the configuration described above, as shown in Figure 4, an acquisition circuit 8 is connected to the collector electrode 3 to acquire the ion current, and the arithmetic unit 9 calculates the hydrocarbon concentration contained in the exhaust gas based on the output signal from the acquisition circuit 8. 【0043】The acquisition circuit 8 includes a lead wire 81 connected to the collector electrode 3 and an amplifier (operational amplifier) 82 that is connected to the lead wire 81 and amplifies and outputs the ionic current flowing through the collector electrode 3. A feedback resistor 83 is connected between the negative input terminal and the output terminal of the amplifier 82. 【0044】 The arithmetic unit 9 is composed of a general-purpose or dedicated computer having a CPU, an internal memory, an input / output interface, an AD converter, a display, and the like. Specifically, the arithmetic unit 9 has a function as a concentration calculation unit 91 that calculates the hydrocarbon concentration (specifically, THC concentration) contained in the exhaust gas using the output signal output from the acquisition circuit 8. The output signal is proportional to the hydrocarbon concentration contained in the exhaust gas. The hydrocarbon concentration calculated by the concentration calculation unit 91 can be displayed on the display 92. 【0045】 <Effect of this Embodiment> According to the hydrogen flame ionization detector 100 of this embodiment configured as described above, since the collector electrode 3 does not contact the inner surface forming the combustion chamber 2S, the leakage current from the collector electrode 3 to the inner surface forming the combustion chamber 2S can be reduced. Further, since the collector electrode 3 is supported outside the combustion chamber 2S, the support portion of the collector electrode 3 is not likely to become high in temperature due to the combustion of hydrogen gas, and the leakage current from the collector electrode 3 to the support portion can be reduced. 【0046】 Further, since the collector electrode 3 and the base electrode 4 are needle-shaped or rod-shaped, the volume of the combustion chamber 2S can be reduced and the hydrogen flame ionization detector 100 can be miniaturized. As a result, the hydrogen flame in the combustion chamber 2S can also be miniaturized. Therefore, the hydrogen flow rate required per unit measurement time can be reduced, and the capacity of the hydrogen cylinder for supplying hydrogen can also be reduced. Thereby, the safety can be further improved as compared with the prior art. In this regard, the hydrogen flame ionization detector 100 of this embodiment is particularly suitable for an in-vehicle exhaust gas measurement device. 【0047】Further, since the collector electrode 3 is configured to be supported outside the combustion chamber 2S and the first insertion hole 23, the support portion of the collector electrode 3 (the first electrode support portion 25) is less likely to become high in temperature due to the combustion of hydrogen gas, and the leakage current from the collector electrode 3 to the support portion can be reduced. Similarly, since the base electrode 4 is configured to be supported outside the combustion chamber 2S and the second insertion hole 24, the support portion of the base electrode 4 (the second electrode support portion 27) is less likely to become high in temperature due to the combustion of hydrogen gas, and the leakage current from the base electrode 4 to the support portion can be reduced. 【0048】 Since the first insertion hole 23 has a tapered shape that narrows toward the combustion chamber 2S, the opening size of the first insertion hole 23 in the combustion chamber 2S can be reduced while ensuring the distance between the inner surface forming the first insertion hole 23 and the collector electrode 3, and leakage of the hydrogen flame F to the outside of the combustion chamber 2S can be prevented. Similarly, since the second insertion hole 24 has a tapered shape that narrows toward the combustion chamber 2S, the opening size of the second insertion hole 24 in the combustion chamber 2S can be reduced while ensuring the distance between the inner surface forming the second insertion hole 24 and the collector electrode 3, and leakage of the hydrogen flame F to the outside of the combustion chamber 2S can be prevented. Note that the first insertion hole 23 and / or the second insertion hole 24 may have a tapered shape that expands toward the combustion chamber 2S. Thereby, the collector electrode 3 and / or the base electrode 4 can be efficiently led to the combustion chamber 2S. This is particularly effective when the collector electrode 3 has the shape of the plate-like portion 32. 【0049】 Since the first heat insulating layer 26 is formed between the first electrode support portion 25 and the combustion chamber 2S, the heat transmitted from the block body 2 to the first electrode support portion 25 can be reduced, the first electrode support portion 25 is less likely to become high in temperature due to the combustion of hydrogen gas, and the leakage current from the collector electrode 3 to the first electrode support portion 25 can be reduced. Similarly, since the second heat insulating layer 28 is formed between the second electrode support portion 27 and the combustion chamber 2S, the heat transmitted from the block body 2 to the second electrode support portion 27 can be reduced, the second electrode support portion 27 is less likely to become high in temperature due to the combustion of hydrogen gas, and the leakage current from the base electrode 4 to the second electrode support portion 27 can be reduced. 【0050】<Other Embodiments> The present invention is not limited to the embodiments described above. 【0051】 For example, the configuration of the ignition unit 6 of the hydrogen flame ionization detector 100 in the above embodiment may be as shown in Figure 5. This ignition unit 6 ignites a hydrogen flame using a collector electrode 3 and a base electrode 4, and has an ignition circuit 61 connected to the collector electrode 3 and the base electrode 4. This ignition circuit 61 ignites a hydrogen flame by burning the hydrogen gas supplied to the combustion chamber 2S through a discharge between the collector electrode 3 and the base electrode 4. In the configuration shown in Figure 5, the ignition circuit 6 and the acquisition circuit 8 can be switched and connected to the collector electrode 3 and the base electrode 4 by a switch unit 62. When igniting the hydrogen flame, the switch unit 62 connects the ignition circuit 61 to the collector electrode 3 and the base electrode 4. After the hydrogen flame is ignited, the switch unit 62 connects the acquisition circuit 8 to the collector electrode 3 and the base electrode 4. 【0052】 Furthermore, the first insertion hole 23 and the second insertion hole 24 in the above embodiment are not limited to a tapered shape, and as shown in Figure 6, they may have a uniform cross-sectional shape toward the combustion chamber 2S, which is the space where the hydrogen flame F is generated. In Figure 6, the combustion chamber 2S, the first insertion hole 23, and the second insertion hole 24 all have a circular cross-section, and the combustion chamber 2S and the first and second insertion holes 23 and 24 have the same cross-section. By making the first and second insertion holes 23 and 24 have a uniform cross-sectional shape, or by making the combustion chamber 2S and the first and second insertion holes 23 and 24 have the same cross-section, the processing of the block body 2 can be made easier. 【0053】Furthermore, although the collector electrode 3 in the above embodiment was a straight needle or rod shape, it may also be plate-shaped, as shown in Figure 7. Specifically, the collector electrode 3 has a rod-shaped portion 31 supported outside the combustion chamber 2S, and a plate-shaped portion 32 provided at the tip of the rod-shaped portion 31 and positioned inside the combustion chamber 2S. This plate-shaped portion 32 is provided perpendicular to the rod-shaped portion. The rod-shaped portion 31 is supported by the first electrode support portion 25 and is inserted into the first insertion hole 23 at a distance from the inner surface forming the first insertion hole 23, so that its tip is positioned inside the combustion chamber 2S. By having the plate-shaped portion 32 in this way, the collector electrode 3 can more easily capture the ion current and the ion current can be increased. As a result, the measurement accuracy can be improved. 【0054】 Furthermore, as shown in Figure 8, the first insertion hole 23 and the second insertion hole 24 in the above embodiment may have a shape in which at least one of the first insertion hole 23 or the second insertion hole 24 gradually narrows toward the combustion chamber 2S. Also, at least one of the first insertion hole 23 or the second insertion hole 24 may have a hole with an equal cross-sectional shape. 【0055】 Furthermore, as shown in Figure 9, the block body 2 may be configured without at least one of the first insulation layer 26 or the second insulation layer 28. In this case, the first electrode support portion 25 is provided in a manner continuous with the outer opening of the first insulation layer 26, and the second electrode support portion 27 is provided in a manner continuous with the outer opening of the second insulation layer 28. Although not shown in Figure 9, an exhaust port is provided in communication with the first insertion hole 23 or the second insertion hole 24 for exhausting exhaust gas generated by the combustion of the hydrogen flame. 【0056】Furthermore, as shown in Figure 10, the block body 2 may be provided with a first sealing portion 291 that seals the space between the first insertion hole 23 and the first electrode support portion 25, and a second sealing portion 292 that seals the space between the second insertion hole 24 and the second electrode support portion 27. The first sealing portion 291 is, for example, cylindrical in shape and seals the space between the first insertion hole 23 and the first electrode support portion 25 so as to surround the collector electrode 3 in the first through portion H1, which is a space. The second sealing portion 292 is, for example, cylindrical in shape and seals the space between the second insertion hole 24 and the second electrode support portion 27 so as to surround the base electrode 4 in the second through portion H2, which is a space. A pressure reduction mechanism for reducing the pressure in the combustion chamber 2S is connected to at least one of the first sealing portion 291 or the second sealing portion 292. This pressure reduction mechanism can be configured by a suction pump 12 provided in the exhaust gas flow path 10. This configuration enables a reduced-pressure gas flow, where the combustion chamber 2S is depressurized before introducing the sample gas, and allows for miniaturization of the hydrogen flame ionization detector 100. 【0057】 Furthermore, in the above embodiment, the first inlet passage 21 and the second inlet passage 22 are connected facing each other in the combustion chamber 2S, but the first inlet passage 21 and the second inlet passage 22 may be connected at any position relative to the combustion chamber 2S. 【0058】 Furthermore, in the above embodiment, the tip of the collector electrode 3 and the tip of the base electrode 4 are arranged facing each other inside the combustion chamber 2S, but the arrangement of their tips can be changed in various ways. For example, the tip of the collector electrode 3 and the tip of the base electrode 4 may be arranged to be parallel to each other or to intersect each other. 【0059】 Furthermore, although the block body 2 in the above embodiment was a single unit, it may be separated into multiple members. For example, as shown in Figure 11, the block body 2 may be separated into a first block member 2A, a second block member 2B, and a third block member 2C. 【0060】The first block member 2A has a combustion chamber 2S, a first insertion hole 23 that communicates with the combustion chamber 2S and through which the collector electrode 3 is inserted without contact, and a second insertion hole 24 that communicates with the combustion chamber 2S and through which the base electrode 4 is inserted without contact. The first block member 2A also has a first introduction passage 21 for introducing hydrogen gas and sample gas into the combustion chamber 2S, and a second introduction passage 22 for introducing a combustion aid gas (for example, air) into the combustion chamber 2S. 【0061】 The second block member 2B is provided at a distance from the first block member 2A. The second block member 2B has a first electrode support portion 25 that supports the base end of the collector electrode 3. 【0062】 The third block member 2C is provided at a distance from the first block member 2A. The third block member 2C is provided on the opposite side of the first block member 2A from the second block member 2B. A second electrode support portion 27 is formed on this third block member 2C to support the base end of the base electrode 4. 【0063】 These first block members 2A, second block member 2B, and third block member 3C are fixed to the upper surface of a common base member 20, for example, with the tips of the collector electrode 3 and base electrode 4 facing each other inside the combustion chamber 2S (see Figure 11(b)). Here, when fixing the first block member 2A to the base member 20, it may be fixed to the base member 20 via a holder member (not shown) that holds the first block member 2A. With this configuration, the first block member 2A can be securely held while being easily attached and detached during maintenance. The second block member 2B or the third block member 2C may also be fixed to the base member 20 via a holder member in the same way. 【0064】 Alternatively, block body 2 may be formed as a single unit by joining multiple members together. 【0065】In addition, as shown in Figure 12, the flame ionization detector 100 may be incorporated into a vehicle-mounted exhaust gas analyzer 200. A specific configuration of this exhaust gas analyzer 200 is shown in Figure 13. In Figure 13, analyzers with other measurement principles, such as laser analyzers, are omitted. In this configuration, the flow rate of exhaust gas discharged from the vehicle's tailpipe VH is measured, and the mass of THC discharged by the vehicle can be determined by multiplying the THC concentration measured by the flame ionization detector 100 by the measured exhaust gas flow rate. 【0066】 The exhaust gas flow path 10 has an upstream flow path (inlet flow path 10a) of the flame ionization detector 100 and a downstream flow path (exhaust flow path 10b) of the flame ionization detector 100. A sampling unit SP consisting of an inlet port P1 and a filter F is provided at the upstream end of the inlet flow path 10a. This sampling unit SP is heated to a predetermined temperature (for example, 190°C) by a sampling heating mechanism 13. A suction pump 12 is provided in the exhaust flow path 10b. This suction pump 12 is provided downstream of the flame ionization detector 100, but it may also be provided upstream of the flame ionization detector 100. 【0067】 Furthermore, the intake channel 10a and exhaust channel 10b are heated by a heating mechanism 14. The heating mechanism 14 includes an upstream heating mechanism 14a that heats the intake channel 10a and the hydrogen flame ionization detector 100 to above the dew point of the exhaust gas (for example, above the temperature at which THC can be measured, such as 190°C), and a downstream heating mechanism 14b that heats the exhaust channel 10b to above the dew point of the exhaust gas (for example, 55°C). The heating temperatures of the upstream heating mechanism 14a and the downstream heating mechanism 14b may be the same or different. The hydrogen gas supply channel 5 and the auxiliary gas supply channel 7 may also be heated to a predetermined temperature (for example, 60°C) by the heating mechanism 14c, or they may not be heated. By heating the hydrogen gas supply channel 5 and the auxiliary gas supply channel 7 to a predetermined temperature, the influence of ambient temperature fluctuations can be reduced. 【0068】Furthermore, in the exhaust gas flow path 10, a pre-measurement exhaust flow path 15 is connected to the upstream side (inlet flow path 10a) of the flame ionization detector 100, which exhausts a portion of the sampled exhaust gas. The pre-measurement exhaust flow path 15 is connected to the upstream side of a flow rate limiting unit 16, such as a capillary, which limits the flow rate in the inlet flow path 10a. With this configuration, a large flow rate of sample gas can be flowed up to just before the flame ionization detector 100 (in this case, the flow rate limiting unit 16), and only a portion of it can be flowed to the flame ionization detector 100. By bringing the connection point between the flame ionization detector 100 (in this case, the flow rate limiting unit 16) and the pre-measurement exhaust flow path 15 as close as possible, it is possible to suppress the decrease in responsiveness caused by the small flow rate of sample gas introduced into the flame ionization detector 100. 【0069】 Here, as the flame ionization detector 100 is miniaturized, its sensitivity becomes more susceptible to temperature changes in the sample gas (exhaust gas). For this reason, the upstream heating mechanism 14a that heats the introduction channel 10a individually controls the temperature of both the introduction channel 10a and the flame ionization detector 100. When the sample gas (exhaust gas) is diluted by the introduction of fuel gas or combustion aid gas in the combustion chamber 2S, the dew point becomes lower than that of the exhaust gas itself. In this case, it is sufficient to heat the sample gas to a level above the dew point of the diluted exhaust gas. 【0070】 Furthermore, the sampling unit SP and the flame ionization detector 100 are thermally insulated from each other, and the upstream heating mechanism 14a controls the temperature of the flame ionization detector 100 so that the detector sensitivity is not affected by changes in the ambient temperature of the sampling unit SP, etc. In addition, the flow rate limiting unit 16 and / or the flame ionization detector 100 may be further enclosed in an insulating housing 18 inside the housing 17 that thermally insulates the flame ionization detector 100 from the outside, thereby further reducing the influence of changes in ambient temperature. 【0071】In the above embodiment, the first introduction passage 21 introduced hydrogen gas and a sample gas into the combustion chamber 2S, and the second introduction passage 22 introduced a combustion-supporting gas (for example, air) into the combustion chamber 2S. However, the following configurations are also possible. For example, the first introduction passage 21 may introduce hydrogen gas and a combustion-supporting gas into the combustion chamber 2S, and the second introduction passage 22 may introduce a sample gas into the combustion chamber 2S. Alternatively, the first introduction passage 21 may introduce a combustion-supporting gas and a sample gas into the combustion chamber 2S, and the second introduction passage 22 may introduce hydrogen gas into the combustion chamber 2S. 【0072】 Alternatively, the hydrogen gas supplied to the flame ionization detector 100 may be generated by a water electrolysis device (not shown). With this configuration, when the flame ionization detector 100 is incorporated into a vehicle-mounted exhaust gas analyzer, it becomes unnecessary to mount a hydrogen cylinder on the vehicle, thereby improving safety. 【0073】 Furthermore, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from its spirit. 【0074】 According to the present invention, leakage current from the collector electrode to the surrounding member can be reduced. 【0075】 100...Hydrogen flame ionization detector 2...Block body 2S...Combustion chamber 21...First introduction passage 22...Second introduction passage 23...First insertion hole 24...Second insertion hole 25...First electrode support part 26...First insulating layer 3...Collector electrode 4...Base electrode

Claims

1. A hydrogen flame ionization detector for detecting an ion current generated when a sample gas and hydrogen gas are mixed and burned in a combustion chamber, comprising: an insulating block body with the combustion chamber formed inside; and a collector electrode whose tip is positioned inside the combustion chamber for detecting the ion current, wherein the collector electrode is supported outside the combustion chamber, away from the inner surface forming the combustion chamber.

2. The flame ionization detector according to claim 1, wherein the collector electrode is needle-shaped, rod-shaped, or plate-shaped.

3. The flame ionization detector according to claim 1 or 2, wherein the block body has a first insertion hole that communicates with the combustion chamber and through which the collector electrode is inserted, and the collector electrode is inserted into the first insertion hole away from the inner surface forming the first insertion hole, so that the tip of the collector electrode is located inside the combustion chamber.

4. The first insertion hole has a shape that narrows continuously or gradually toward the combustion chamber, or has an equicross-sectional shape, as described in claim 3.

5. The flame ionization detector according to any one of claims 1 to 4, wherein the block body is provided with an electrode support portion for supporting the base end of the collector electrode, and a heat insulating layer is formed between the electrode support portion and the combustion chamber.

6. The flame ionization detector according to any one of claims 1 to 4, wherein the block body is provided with a first through-hole that communicates with the combustion chamber and through which the collector electrode is inserted without contact, an electrode support portion that supports the base end of the collector electrode, and a sealing portion that seals the space between the first through-hole and the electrode support portion so as to surround the collector electrode.

7. The flame ionization detector according to any one of claims 1 to 6, wherein the block body has a first introduction passage for introducing hydrogen gas and a sample gas into the combustion chamber, and a second introduction passage for introducing a combustion aid gas into the combustion chamber, and the first introduction passage and the second introduction passage are connected so as to face each other in the combustion chamber.

8. The flame ionization detector according to any one of claims 1 to 7, wherein the block body is in the shape of a flat plate.

9. The flame ionization detector according to any one of claims 1 to 8, further comprising a base electrode whose tip is positioned inside the combustion chamber and to which a predetermined bias potential is applied in relation to the collector electrode, wherein the base electrode is supported outside the combustion chamber, away from the inner surface forming the combustion chamber.

10. The hydrogen flame ionization detector according to claim 9, wherein the collector electrode and the base electrode are arranged so that their tips face each other inside the combustion chamber.

11. The hydrogen flame ionization detector according to claim 9 or 10, further comprising an ignition unit for igniting a hydrogen flame in the combustion chamber, wherein the ignition unit has an ignition circuit connected to the collector electrode and the base electrode, and the ignition circuit ignites a hydrogen flame by discharging electricity between the collector electrode and the base electrode.

12. A gas analyzer having a flame ionization detector according to any one of claims 1 to 11.

13. The gas analyzer according to claim 12, comprising: an introduction channel for sampling exhaust gas from an internal combustion engine and introducing it to the flame ionization detector; an exhaust channel for exhausting the exhaust gas that has passed through the flame ionization detector; and a heating mechanism for heating the introduction channel and the exhaust channel to a temperature above the dew point of the exhaust gas.

14. A gas analysis method using a flame ionization detector according to any one of claims 1 to 11, comprising heating an introduction channel for sampling exhaust gas from an internal combustion engine and introducing it into the flame ionization detector, and an exhaust channel for exhausting the exhaust gas that has passed through the flame ionization detector, to a temperature above the dew point of the exhaust gas.

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