JP2009288220A - Specific gas concentration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a specific gas concentration sensor capable of accurately detecting either the concentration of NO<SB>X</SB>in a gas to be measured in which ammonia and NO<SB>X</SB>coexist or the concentration of the ammonia. <P>SOLUTION: The specific gas concentration sensor includes a first space on the upstream side and a second space on the downstream side serially arranged to each other; a first element in which a pair of electrodes are arranged in both surfaces of a solid electrolyte and of which either electrode of the pair of electrodes faces the first space; and a second element in which a pair of electrodes are arranged in both surfaces of a solid electrolyte and of which either electrode of the pair of electrodes faces the second space. After oxygen in the gas to be measured is pumped out by the first element such that NO may not be dissociated, NO in the gas to be measured is dissociated by the second element to pump out oxygen and extract a value of a current flowing through the second element as information indicating the concentration of NO<SB>X</SB>in the gas to be measured. A decomposing catalyst for decomposing ammonia in the gas to be measured into components other than NO<SB>X</SB>is provided for the more upstream side than the first space. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a specific gas concentration sensor, and more particularly to a specific gas concentration sensor for accurately detecting ammonia concentration and / or NO _x concentration in a gas to be measured in which ammonia and NO _x coexist.

Conventionally, as one aspect of the specific gas concentration detector, a NO _x concentration detector that detects the concentration of NO _x (nitrogen oxides such as NO and NO ₂ ) in the measurement gas, and an ammonia concentration in the measurement gas are used. ammonia concentration detector for detecting, furthermore, there is a detector for detecting respectively the NO _X concentration and the ammonia concentration in the measurement gas. In these detectors, instead of taking a part of the measured gas as a sample, a semiconductor sensor or solid electrolyte sensor is inserted directly into the measured gas, and the NO _x concentration and ammonia concentration are measured as electrical signals. A sensor that can be taken out is proposed.

Among them, as an example of the NO _X concentration detector, NO _X concentration detector in the measurement gas to the NO _X concentration can be accurately measured have been proposed. More specifically, a first pump cell having a pair of electrodes in the solid electrolyte layer and a first chamber having an oxygen concentration measurement cell as a part of the section screen, and a second pump cell having a pair of electrodes in the solid electrolyte layer A second chamber having a part of the section screen, a first diffusion resistance portion that communicates the first chamber with the gas space to be measured, and a second diffusion resistance portion that communicates the first chamber with the second chamber. a two-chamber tandem of the NO _X concentration detector, a measurement unit the oxygen concentration measuring cell is disposed in the vicinity of the second diffusion resistance portion, for measuring the current (first pump current) flowing through the first pumping cell, NO _x concentration provided with a measuring unit for measuring the current flowing through the second pump cell (second pump current) and a deriving unit for deriving the NO _x concentration in the gas to be measured from the first pump current and the second pump current A detector is disclosed (see Patent Document 1).

As an example of an ammonia concentration detector, ammonia can be detected in a wide range from a low concentration range to a high concentration range, and ammonia can be detected accurately even if NO _x is contained in the gas to be measured. Detection sensors have been proposed. More specifically, the gap between the opposing oxygen pump element and the oxygen concentration cell element is a processing space, and the electrode facing the processing space is made of a material having high catalytic activity for the ammonia oxidation reaction, and the back surface of the oxygen concentration cell element There is disclosed an ammonia detection sensor in which a side (opposite space) electrode is made of a material having low catalytic activity for an ammonia oxidation reaction. According to this ammonia detection sensor, when a gas to be detected containing ammonia and oxygen is introduced into the processing space and the opposite space, a difference occurs in oxygen consumption due to ammonia oxidation on both sides of the oxygen concentration cell element. Electric power is generated. Further, the oxygen pump element draws oxygen into the processing space, and controls so that the concentration cell electromotive force becomes a constant target value. Based on the current flowing through the oxygen pump element at this time, the ammonia concentration can be detected (see Patent Document 2).

Further, the NO _X and ammonia in the gas to be measured, have also been proposed simultaneously, gas analysis method that can be detected in real time. More specifically, by contacting a measurement gas containing NO _X and ammonia to the ammonia strong oxidation catalyst to convert the NO _X by oxidizing ammonia of the gas under measurement, the converted NO _X and the A first NO _x detection step for detecting the total amount of NO _x present in the gas to be measured, and the gas to be measured are brought into contact with an ammonia weak oxidation catalyst, and a part of the ammonia in the gas to be measured is removed. a second of the NO _X detection step is converted into NO _X, detects the total amount of the converted NO _X and NO _X of the measurement gas is oxidized, resulting in the first and second of the NO _X detection step A gas analysis method including a step of calculating the NO _x amount and / or the ammonia amount in the gas to be measured from the two detected values is disclosed (see Patent Document 3).

JP 2000-171438 A JP 2000-193639 A JP 2001-133447 A

By the way, in a vehicle equipped with a diesel engine, as an exhaust purification device for removing NO _{x in} exhaust gas discharged, a reduction catalyst for reducing NO _x using ammonia as a reducing agent is disposed in the exhaust passage. by supplying a reducing agent capable of generating ammonia upstream of the reduction catalyst, the exhaust gas purifying device for removing NO _X is used. In order to control the supply amount of the reducing agent in such an exhaust purification device, a sensor for detecting NO _x concentration or ammonia concentration (hereinafter referred to as “NO _x sensor” or “ammonia sensor”) is provided in the exhaust passage. May be provided. In particular, NO _X or ammonia flows out to the downstream side of the catalyst, as it is so as not to be released into the atmosphere, there is a case where NO _X sensor and the ammonia sensor is provided downstream of the reduction catalyst. As described above, when the NO _x sensor or the ammonia sensor is provided on the downstream side of the reduction catalyst, it is necessary to accurately detect the NO _x concentration or the ammonia concentration regardless of the relatively low concentration region. The sensor is required to have higher detection accuracy.

On the other hand, when ammonia is exposed to a high temperature, there is a possibility that NO _x is generated due to thermal decomposition. Therefore, in the NO _X concentration detector as described in Patent Document 1, when NO _X is generated by exposure of ammonia to a high temperature in the middle of reaching the first or second pump cell, this NO _X is generated. since nO _X will also be detected with, it may be impossible to detect the nO _X concentration contained in the gas to be measured accurately.

Further, the sensors described in Patent Document 2 and Patent Document 3 use a plurality of electrodes and oxidation catalysts having different ammonia oxidation efficiencies, and consider the ammonia oxidation efficiency of each electrode and oxidation catalyst in the gas to be measured. Is a sensor that detects ammonia concentration, or NO _x concentration and ammonia concentration, but it is highly dependent on the catalyst temperature and NO _x concentration measurement because the process of once oxidizing ammonia to NO _x is involved. There is a risk of errors in the detection results.

Therefore, the inventors of the present invention can solve such problems by making a configuration equipped with a decomposition catalyst that decomposes ammonia contained in the exhaust gas to be measured without generating NO _x. And the present invention has been completed. That is, an object of the present invention is to provide a specific gas concentration sensor that can accurately detect the NO _x concentration and / or the ammonia concentration in a gas to be measured in which ammonia and NO _x coexist.

According to the present invention, there is provided a specific gas concentration sensor for detecting a NO _x concentration in a gas to be measured, the first space on the upstream side arranged in series so that the gas to be measured flows in and the first gas sensor on the downstream side. A pair of electrodes are disposed on both surfaces of the two spaces and the solid electrolyte body, and a first element in which any one of the pair of electrodes faces the first space, and a pair of electrodes on both surfaces of the solid electrolyte body And an oxygen in the gas to be measured so that NO is not dissociated by the first element, and an electrode is disposed, and one of the pair of electrodes includes a second element facing the second space. After the gas is pumped out, the second element dissociates NO in the gas to be measured to pump out oxygen, and the current value flowing through the second element is taken out as information indicating the NO _x concentration in the gas to be measured. , Upstream of the first space, A specific gas concentration sensor (hereinafter sometimes referred to as a “first specific gas concentration sensor”) is provided that includes a decomposition catalyst that decomposes ammonia in the gas to be measured into components other than NO _x . The above-mentioned problem can be solved.

Another aspect of the present invention is a specific gas concentration sensor for detecting an ammonia concentration in a gas to be measured, and a first space and a second space that are arranged in parallel so that the gas to be measured flows. A reference in which a pair of electrodes are arranged on both surfaces of the solid electrolyte body, and one of the pair of electrodes faces the first space, while the other electrode has a reference gas different from the gas to be measured. A first element facing the gas space and a pair of electrodes are arranged on both surfaces of the solid electrolyte body, and one of the pair of electrodes faces the second space, while the other electrode is the reference gas space And a second element facing the first element, and a difference between current values flowing through the first element and the second element is extracted as information indicating an ammonia concentration in the gas to be measured. Upstream of the gas in the measured gas. Specific gas concentration sensor, characterized in that it comprises decomposing decomposition catalyst components other than NO _X and pneumoniae (hereinafter, may be referred to as "second specific gas concentration sensor.") Is.

According to still another aspect of the present invention, there is provided a specific gas concentration sensor for detecting ammonia concentration and NO _x concentration in a gas to be measured, wherein the first gas gas is arranged in parallel so that the gas to be measured flows. A pair of electrodes are disposed on both surfaces of the space and the second space, the third space arranged in series on the downstream side of the first space, and the solid electrolyte body, and one of the pair of electrodes is the first electrode A first element facing one space, the other electrode facing a reference gas space where a reference gas different from the gas to be measured is present, and a pair of electrodes on both sides of the solid electrolyte body, One of the electrodes faces the second space, the other electrode faces the reference gas space, and a pair of electrodes are arranged on both sides of the solid electrolyte body, Any one of the electrodes facing the third space An element, and after pumping out oxygen in the gas to be measured so that NO is not dissociated by the first element, dissociates NO in the gas to be measured by the third element and pumps oxygen out to the third element. The flowing current value is extracted as information indicating the NO _x concentration in the measured gas, and the difference between the current values flowing in the first element and the second element is extracted as information indicating the ammonia concentration in the measured gas. And a specific gas concentration sensor (hereinafter referred to as “third specific gas concentration sensor”) provided with a decomposition catalyst for decomposing ammonia in the gas to be measured into components other than NO _x on the upstream side of the first space. Is sometimes referred to as “.”.

  In configuring the specific gas concentration sensor of the present invention, it is preferable that a diffusion-controlled passage is provided in the flow path of the gas to be measured upstream of the first space, and a decomposition catalyst is provided in the diffusion-controlled passage.

According to the first specific gas concentration sensor of the present invention, after the ammonia contained in the gas to be measured is decomposed without generating NO _x in the decomposition catalyst, the gas to be measured is in the first space and the second space. Will flow into. Therefore, it is possible to accurately detect the NO _x concentration in the gas to be measured based on the value of the current flowing through the second element as the oxygen pump.

Further, according to the second specific gas concentration sensor of the present invention, the gas to be measured flows into the second space as it is, while in the first space, ammonia contained in the gas to be measured causes NO _x to be decomposed in the decomposition catalyst. After being decomposed without being generated, the gas to be measured flows into the first space. That is, the gas to be measured whose oxygen concentration is reduced by the amount used for the decomposition of ammonia flows into the first space. Therefore, the ammonia concentration in the gas to be measured can be accurately detected based on the difference between the current values flowing through the first element and the second element as battery elements.

According to the third specific gas concentration sensor of the present invention, the gas to be measured flows as it is into the second space, while ammonia contained in the gas to be measured is decomposed in the first space and the third space. after being decomposed without producing NO _X in, so the measurement gas flows into the first space and the third space. Therefore, when detecting the NO _x concentration in the gas to be measured, the first element and the third element are used as the oxygen pump, and the NO in the gas to be measured is determined based on the current value flowing through the third element. _X concentration can be detected with high accuracy. In addition, since the gas to be measured whose oxygen concentration is reduced by the amount used for the decomposition of ammonia flows into the first space and the third space, the first element is used when detecting the ammonia concentration in the gas to be measured. Using the second element as a battery element, the ammonia concentration in the gas to be measured can be accurately detected based on the difference between the current values flowing through the first element and the second element.

  Further, in the specific gas concentration sensor of the present invention, since the decomposition catalyst is provided in the diffusion-controlled passage, the amount of the decomposition catalyst used can be suppressed, an increase in cost can be suppressed, and the measured gas flowing into the first space can be suppressed. The ammonia can be reliably decomposed.

Embodiments relating to the specific gas concentration sensor of the present invention will be specifically described below with reference to the drawings. However, this embodiment shows one aspect of the present invention and does not limit the present invention, and can be arbitrarily changed within the scope of the present invention.
In addition, in each figure, what has attached | subjected the same code | symbol has shown the same member, and description is abbreviate | omitted suitably.

[First Embodiment]
The specific gas concentration sensor according to the first embodiment of the present invention is a first specific gas concentration sensor used as a NO _X sensor for measuring the NO _X concentration in the gas to be measured.
FIG. 1 is a cross-sectional view schematically showing the configuration of the first specific gas concentration sensor 10 of the present embodiment. The first specific gas concentration sensor 10 includes a measured gas flow path 15 formed by two solid electrolyte bodies 11 and 13, and the first space 17 and the measured gas flow path 15 are located in the middle of the measured gas flow path 15. A second space 19 is provided.

A first diffusion rate-limiting passage 21 is provided on the upstream side of the first space 17 of the gas flow path 15 to be measured, and a second diffusion rate-limiting passage 23 is provided between the first space 17 and the second space 19. Is provided. The first diffusion-controlling passage 21 and the second diffusion-controlling passage 23 are arranged such that a solid electrolyte body in which small holes or thin notches are formed is disposed in the gas flow path 15 to be measured, or a porous body such as alumina is used as the gas to be measured. It can be formed by filling the flow path 15. In the present embodiment, the first and second diffusion-controlling passages 21 and 23 are formed by disposing a solid electrolyte body in which a small hole or a thin cut is formed in the gas flow path 15 to be measured.
The gas G to be measured passing through the first diffusion rate controlling passage 21 and the second diffusion rate controlling passage 23 flows into the first space 17 or the second space 19 on the downstream side while receiving diffusion resistance. Yes. Therefore, even if the residence time of the gas to be measured in the first space 17 and the second space 19 becomes long and the composition of the gas to be measured outside the sensor changes, the first space 17 and the second space The influence on the gas G to be measured in 19 is reduced. As a result, the detection accuracy of the sensor is improved.

  Further, the first element 30 is provided facing the first space 17 of the measured gas flow path 15, and the second element 40 is provided facing the second space 19. The first element 30 is configured by arranging the first inner electrode 31 and the first outer electrode 33 on both surfaces of the solid electrolyte body 13, and the first inner electrode 31 faces the first space 17. The first outer electrode 33 faces the reference gas space 25. The second element 40 is configured by arranging the second inner electrode 41 and the second outer electrode 43 on both surfaces of the solid electrolyte body 13, and the second inner electrode 41 is in the second space 19. The second outer electrode 43 faces the reference gas space 25.

The fixed electrolyte body 13 constituting the first element 30 and the second element 40 is typically a ceramic body containing ZrO ₂ , for example, but is a conventionally known solid electrolyte body constituting an oxygen pump element. If there is, it can be suitably used.
The first and second inner electrodes 31, 41 and the first and second outer electrodes 33, 43 disposed on both surfaces of the solid electrolyte body 13 are each composed of a porous electrode capable of dissociating oxygen molecules, Similar to the solid electrolyte body, any conventionally known porous electrode can be suitably used.

  In the first specific gas concentration sensor 10 of the present embodiment, the first element 30 and the second element 40 are both used as oxygen pump elements, and the first element 30 and the second element 40 constituting the first element 40 are used. The inner electrode 31 and the first outer electrode 33, and the second inner electrode 41 and the second outer electrode 43 are connected to the external connection circuit 27 so that a voltage can be applied between the pair of electrodes. It has become.

Among these, in the first element 30, voltage is applied so that only NO is pumped out so that NO does not dissociate among NO _{X in} the gas G to be measured. At this time, in the first space 17, as shown by the following formula (1), NO ₂ is dissociated to generate NO and oxygen.
2NO ₂ → 2NO + O ₂ (1)
Therefore, the oxygen contained in the gas to be measured G and the oxygen generated in the first space 17 are pumped out from the first space 17 by the first element 30.

In the second element 40, a voltage is applied so as to dissociate NO in the measurement gas G and pump oxygen. That is, in the second space, as shown by the following formula (2), NO dissociates and nitrogen and oxygen are generated.
2NO → N ₂ + O ₂ (2)
Accordingly, oxygen generated in the second space 19 is pumped out from the second space 19 by the second element 40.

At this time, the current value flowing through the second element 40 indicates a current value according to the oxygen concentration pumped out from the second space 19, and this oxygen concentration indicates the NO _x concentration (the above formula (2)). Reference), by measuring this current value, the NO _x concentration in the gas to be measured can be detected.

Here, in the first specific gas concentration sensor 10 of the present embodiment, a decomposition catalyst having a function of decomposing ammonia without generating NO _x is applied to the solid electrolyte body forming the first diffusion-controlled passage 21. ing. The decomposition reaction of ammonia with this decomposition catalyst is performed as shown in the following formula (3).
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O (3)

That is, the NO _x concentration on the upstream side and the downstream side of the first diffusion rate controlling passage 21 having the function of an ammonia decomposition catalyst is not changed. Furthermore, since ammonia is removed from the gas to be measured G that has passed through the first diffusion-controlled passage 21, the gas to be measured G is in the first space 17 or the second space 19 on the downstream side of the first diffusion-controlled passage 21. In the meantime, the ammonia contained in the gas G to be measured does not thermally decompose and NO _x is not generated. Therefore, according to the first specific gas concentration sensor 10 of the present embodiment, oxygen is pumped from the first element 30 and the second element 40 as described above, and based on the value of the current flowing through the second element 40. Thus, the NO _x concentration in the measurement gas G can be detected with high accuracy.

[Second Embodiment]
The specific gas concentration sensor according to the second embodiment of the present invention is a second specific gas concentration sensor used as an ammonia sensor for measuring the ammonia concentration in the gas to be measured.
FIG. 2 is a cross-sectional view schematically showing the configuration of the second specific gas concentration sensor 50 of the present embodiment. The second specific gas concentration sensor 50 includes a first measured gas channel 54 and a second measured gas channel 55 formed by three solid electrolyte bodies 51, 52, and 53. A first space 57 is provided in the middle of one measured gas channel 54, and a second space 59 is provided in the middle of the second measured gas channel 55.

  In addition, a first diffusion-controlled passage 61 is provided on the upstream side of the first space 57 of the first measured gas channel 54, and on the upstream side of the second space 59 of the second measured gas channel 55. Is provided with a second diffusion-controlled passage 63. The first diffusion rate-limiting channel 61 and the second diffusion rate-limiting channel 63 are basically formed in the same manner as the diffusion rate-limiting channel described in the first embodiment.

Further, a first element 70 is provided facing the first space 57 of the first measured gas channel 54, and a second element 80 is facing the second space 59 of the second measured gas channel 55. Is provided. The first element 70 is configured by arranging the first inner electrode 71 and the first outer electrode 73 on both surfaces of the solid electrolyte body 51, and the first inner electrode 71 faces the first space. ing. The second element 80 is configured by arranging the second inner electrode 81 and the second outer electrode 83 on both surfaces of the solid electrolyte body 53, and the second inner electrode 81 is in the second space 59. Facing.
The configurations of the first element 70 and the second element 80 can be basically the same as those of the first element and the second element described in the first embodiment.

  Further, in the second specific gas concentration sensor 50 of the present embodiment, a first reference gas space 65 is formed on the opposite side of the first measured gas flow channel 54 across the first element 70, and the first A first outer electrode 73 constituting the element 70 faces the first reference gas space 65. Similarly, a second reference gas space 67 is formed on the opposite side of the second measured gas flow channel 55 with the second element 80 interposed therebetween, and the second outer electrode 83 constituting the second element 80 is connected to the second element 80. Two reference gas spaces 67 are faced. A common reference gas such as the atmosphere flows into the first and second reference gas spaces 65 and 67. The first reference gas space 65 and the second reference gas space 67 are not configured as separate spaces, but may be configured as one space.

  In the second specific gas concentration sensor 50 of the present embodiment, the first element 70 and the second element 80 are both used as battery elements, and the first element 70 and the second element 80 constituting the first element 70 are used. The inner electrode 71 and the first outer electrode 73, and the second inner electrode 81 and the second outer electrode 83 are each connected to an external connection circuit 69. The current value corresponding to the electromotive force generated in the first element 70 due to the difference in oxygen concentration between the first space 57 and the first reference gas space 65, and the second space 59 and the second reference gas space 67. The current value corresponding to the electromotive force generated in the second element 80 due to the difference in oxygen concentration is measured.

Here, in the second specific gas concentration sensor 50 of the present embodiment, a decomposition catalyst having a function of decomposing ammonia without generating NO _x is applied to the solid electrolyte body forming the second diffusion-controlled passage 63. ing. The decomposition reaction of ammonia with this decomposition catalyst is performed as shown in the following formula (4).
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O (4)

  For this reason, the ammonia to be measured flows into the first space 57 of the first measured gas channel 54 while the ammonia to be contained flows as it is, while the second space of the second measured gas channel 55 In 59, the gas G to be measured flows in a state where ammonia is decomposed and removed in the decomposition catalyst. That is, the gas to be measured G ′ flowing into the first space 57 and the gas to be measured G flowing into the second space 59 have different ammonia concentrations and reflect the oxygen concentration used for the decomposition of ammonia, Are different.

Therefore, in the second specific gas concentration sensor 50 of the present embodiment, the electromotive force generated in the first element 70 and the second element 80 due to the difference in oxygen concentration between the first space 57 and the second space 59. There is a difference between the generated electromotive force. Therefore, the difference in oxygen concentration is obtained from the difference between the measured current value flowing through the second element 80 and the current value flowing through the first element 70. Since the difference in oxygen concentration indicates the oxygen concentration used for the decomposition of ammonia, the ammonia concentration in the measured gas G is derived from the following equation (5) by measuring the difference in current value. Can do.
[NH ₃ ] = [O ₂ ] × 4/3 (5)

  Thus, according to the second specific gas concentration sensor 50 of the present embodiment, the oxygen concentration used for the decomposition of ammonia based on the difference between the current values flowing through the first element 70 and the second element 80. Therefore, the ammonia concentration in the measurement gas G can be detected with high accuracy.

[Third Embodiment]
The third specific gas concentration sensor according to the third embodiment of the present invention has functions of an NO _x sensor that measures the NO _x concentration in the gas to be measured and an ammonia sensor that measures the ammonia concentration in the gas to be measured. A third specific gas concentration sensor is also provided. The third specific gas concentration sensor of the present embodiment is basically configured by combining the first specific gas concentration sensor and the second specific gas concentration sensor.

  FIG. 3 is a cross-sectional view schematically showing the configuration of the third specific gas concentration sensor 100 of the present embodiment. The third specific gas concentration sensor 100 includes a first measured gas flow path 104 and a second measured gas flow path 105 formed by three solid electrolyte bodies 101, 102, 103. A first space 107 is provided in the middle of one measured gas channel 104, and a second space 108 and a third space 109 are provided in the middle of the second measured gas channel 105.

  In addition, a first diffusion-controlling passage 111 is provided on the upstream side of the first space 107 of the first measured gas channel 104. Similarly, a second diffusion-controlling passage 112 is provided on the upstream side of the second space 108 of the second measured gas channel 105, and the third space 109 is interposed between the second space 108 and the third space 109. A diffusion-controlled passage 113 is provided. These first to third diffusion-controlling passages 111, 112, and 113 can have the same configuration as the diffusion-controlling passage described in the first embodiment.

Further, the first element 120 is provided facing the first space 107 of the first measured gas flow path 104. The first element 120 is configured by arranging the first inner electrode 121 and the first outer electrode 123 on both surfaces of the fixed electrolyte 101, and the first inner electrode 121 faces the first space 107. is doing.
Similarly, the second element 130 is provided facing the second space 108 of the second gas flow channel 105 to be measured, and the third element 140 is provided facing the third space 109. The second element 130 is configured by arranging the second inner electrode 131 and the second outer electrode 133 on both surfaces of the solid electrolyte body 103, and the second inner electrode 131 faces the second space 108. is doing. The third element 140 is configured by arranging the third inner electrode 141 and the third outer electrode 143 on both surfaces of the solid electrolyte body 103, and the third inner electrode 141 is in the third space 109. Facing.

In the third specific gas concentration sensor 100 of the present embodiment, a first reference gas space 115 is formed on the opposite side of the first measured gas flow path 104 with the first element 120 interposed therebetween, and the first reference gas space 115 is formed. The first outer electrode 123 constituting the element 120 faces the first reference gas space 115. Similarly, a second reference gas space 117 is formed on the opposite side of the second measured gas channel 105 across the second element 130, and the second outer electrode 133 and the second outer electrode 133 constituting the second element 130 are formed. A third outer electrode 143 constituting the three elements 140 faces the second reference gas space 117. A common reference gas such as the atmosphere flows into the first reference gas space 115 and the second reference gas space 117. The first reference gas space 115 and the second reference gas space 117 are not configured as separate spaces, but may be configured as one space.
The configurations of the first to third elements 120, 130, and 140 are basically the same as those of the first element and the second element described in the first embodiment.

In the third specific gas concentration sensor 100 of the present embodiment, the first element 120 is used as a battery element, the second element 130 is used as an oxygen pump element and a battery element, and the third element 140 is used as an oxygen pump element. It is what is used. The first inner electrode 121 and the first outer electrode 123 constituting the first element 120, the second inner electrode 131 and the second outer electrode 133 constituting the second element 130, and the third element 140 are provided. The third inner electrode 141 and the third outer electrode 143 that are configured are connected to the external connection circuit 127, respectively.
Among these, when the first element 120 and the second element 130 are used as battery elements, an electromotive force generated in the first element 120 due to a difference in oxygen concentration between the first space 107 and the first reference gas space 115. And a current value corresponding to an electromotive force generated in the second element 130 due to a difference in oxygen concentration between the second space 108 and the second reference gas space 117 is measured. Yes. When the second element 130 and the third element 140 are used as oxygen pump elements, a predetermined voltage is applied between each pair of electrodes so that oxygen in the gas G to be measured is pumped out. It is configured.

Here, in the third specific gas concentration sensor 100 of the present embodiment, a decomposition catalyst having a function of decomposing ammonia without generating NO _x is applied to the solid electrolyte body that forms the second diffusion-controlled passage 112. ing. The decomposition reaction of ammonia with this decomposition catalyst is performed as shown in the following formula (6).
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O (6)

Therefore, the measured gas G ′ flows into the first space 107 of the first measured gas channel 104 while the ammonia contained therein remains as it is, while the second space 108 of the second measured gas channel 105. The gas to be measured G flows into the third space 109 in a state where ammonia is decomposed and removed by the decomposition catalyst. That is, the gas to be measured G ′ flowing into the first space 107 and the gas to be measured G flowing into the second space 108 have different ammonia concentrations and reflect the oxygen concentration used for the decomposition of ammonia, Are different. At this time, the NO _x concentration on the upstream side and the downstream side of the second diffusion rate controlling passage 112 is not changed.

Therefore, in the third specific gas concentration sensor 100 of the present embodiment, when the first element 120 and the second element 130 are used as battery elements, the difference in oxygen concentration between the first space 107 and the second space 108 is caused. As a result, a difference is generated between the electromotive force generated in the first element 120 and the electromotive force generated in the second element 130. Therefore, a difference in oxygen concentration is obtained from the difference between the measured current value flowing through the second element 130 and the current value flowing through the first element 120. Since the difference in oxygen concentration indicates the oxygen concentration used for the decomposition of ammonia, the ammonia concentration in the measured gas G is derived from the following equation (7) by measuring the difference in current value. Can do.
[NH ₃ ] = [O ₂ ] × 4/3 (7)

  Thus, in the third specific gas concentration sensor 100 of the present embodiment, the oxygen concentration used for the decomposition of ammonia is based on the difference between the current values flowing through the first element 120 and the second element 130. Therefore, the ammonia concentration in the measurement gas G can be detected with high accuracy.

On the other hand, in the third specific gas concentration sensor 100 of the present embodiment, when the second element 130 and the third element 140 are used as an oxygen pump element, the second element 130 causes the NO _{x in} the gas G to be measured. Among these, voltage is applied so that NO is not dissociated and only oxygen is pumped out. At this time, in the second space 108, as shown in the following formula (8), NO ₂ is dissociated and NO and oxygen are generated.
2NO ₂ → 2NO + O ₂ (8)
Accordingly, the oxygen contained in the gas to be measured G and the oxygen generated in the second space 108 are pumped out from the second space 108 by the second element 130.

In the third element 140, a voltage is applied so as to dissociate NO in the measurement gas G and pump oxygen. That is, in the third space 109, as shown in the following formula (9), NO is dissociated to generate nitrogen and oxygen.
2NO → N ₂ + O ₂ (9)
Therefore, oxygen generated in the third space 109 is pumped out from the third space 109 by the third element 140.

At this time, the current value flowing through the third element 140 indicates a current value corresponding to the oxygen concentration pumped out from the third space 109, and this oxygen concentration indicates the NO _x concentration (the above formula (9)). Reference), by measuring this current value, the NO _x concentration in the gas G to be measured can be detected.
At this time, since ammonia in the gas G to be measured is decomposed and removed in the second diffusion rate-limiting passage 112, the second space 108 or the third space 109 on the downstream side of the second diffusion rate-limiting passage 112 is provided. The ammonia contained in the measurement gas G does not thermally decompose and NO _x is not generated until it reaches, so that the NO _x concentration in the measurement gas G can be accurately detected. .

According to the specific gas concentration sensor described above, since a decomposition catalyst that decomposes ammonia without generating NO _x is provided, even when ammonia and NO _x coexist in the gas to be measured, It is possible to accurately detect either the ammonia concentration and / or the NO _x concentration. Therefore, it can be suitably used as a sensor provided in an exhaust system of a vehicle equipped with a diesel engine and used for exhaust purification control.

It is sectional drawing for demonstrating the structure of the 1st specific gas concentration sensor concerning the 1st Embodiment of this invention. It is sectional drawing for demonstrating the structure of the 2nd specific gas concentration sensor concerning the 2nd Embodiment of this invention. It is sectional drawing for demonstrating the structure of the 3rd specific gas concentration sensor concerning the 3rd Embodiment of this invention.

Explanation of symbols

10: first specific gas concentration sensor (NO _X sensor), 11.13: solid electrolyte body, 15: gas flow path to be measured, 17: first space, 19: second space, 21: first diffusion rate limiting Passage: 23: second diffusion-controlled passage, 27: external connection circuit, 30: first element, 31: first inner electrode, 33: second inner electrode, 40: second element, 41: second Inner electrode, 43: second inner electrode, 50: second specific gas concentration sensor (ammonia sensor), 51, 52, 53: solid electrolyte body, 54: first gas flow path to be measured, 55: second Gas flow to be measured, 57: first space, 59: second space, 61: first diffusion-controlled passage, 63: second diffusion-controlled passage, 69: external connection circuit, 70: first element, 71 : First inner electrode, 73: second inner electrode, 80: second element, 81: second inner electrode, 83 Second inner electrode, 100: third specific gas concentration sensor (NO _X and ammonia sensor), 101, 102, 103: solid electrolyte body, 104: first measurement gas flow channel 105: the second to-be Measurement gas flow path, 107: first space, 108: second space, 109: third space, 111: first diffusion controlled passage, 112: second diffusion controlled passage, 113: third diffusion controlled passage, 115: first reference gas space, 117: second reference gas space, 120: first element, 121: first inner electrode, 123: first outer electrode, 127: external connection circuit, 130: first Element 131: First inner electrode 133: First outer electrode 140: First element 141: First inner electrode 143: First outer electrode

Claims (4)

In a specific gas concentration sensor for detecting the NO _x concentration in the gas to be measured,
A first space on the upstream side and a second space on the downstream side arranged in series so that the gas to be measured flows,
A pair of electrodes are disposed on both surfaces of the solid electrolyte body, and a first element in which any one of the pair of electrodes faces the first space;
A pair of electrodes are disposed on both surfaces of the solid electrolyte body, and one of the pair of electrodes includes a second element facing the second space, and
After the oxygen in the gas to be measured is pumped out so that NO does not dissociate by the first element, the NO in the gas to be measured is dissociated by the second element and oxygen is pumped out and flows to the second element. The current value is configured to be taken out as information indicating the NO _x concentration in the measurement gas,
A specific gas concentration sensor comprising a decomposition catalyst for decomposing ammonia in the gas to be measured into components other than NO _x on the upstream side of the first space. In a specific gas concentration sensor for detecting the ammonia concentration in the gas to be measured,
A first space and a second space arranged in parallel so that the measurement gas flows;
A pair of electrodes are arranged on both surfaces of the solid electrolyte body, and one of the pair of electrodes faces the first space, while the other electrode has a reference gas different from the gas to be measured. A first element facing a reference gas space to be
A pair of electrodes disposed on both surfaces of the solid electrolyte body, and one electrode of the pair of electrodes faces the second space, while the other electrode faces the reference gas space; And having
A difference between current values flowing through the first element and the second element is configured to be taken out as information indicating the ammonia concentration in the gas to be measured.
A specific gas concentration sensor comprising a decomposition catalyst for decomposing ammonia in the gas to be measured into components other than NO _x on the upstream side of the first space. In the specific gas concentration sensor for detecting the ammonia concentration and the NO _x concentration in the gas to be measured,
A first space and a second space arranged in parallel so that the measurement gas flows;
A third space arranged in series downstream of the first space;
A pair of electrodes are arranged on both surfaces of the solid electrolyte body, and one of the pair of electrodes faces the first space, while the other electrode has a reference gas different from the gas to be measured. A first element facing a reference gas space to be
A pair of electrodes disposed on both surfaces of the solid electrolyte body, and one electrode of the pair of electrodes faces the second space, while the other electrode faces the reference gas space; ,
A pair of electrodes is disposed on both surfaces of the solid electrolyte body, and one of the pair of electrodes includes a third element facing the third space, and
After the oxygen in the gas to be measured is pumped out so that NO does not dissociate by the first element, the NO in the gas to be measured is dissociated by the third element and oxygen is pumped out and flows to the third element. A current value is taken out as information indicating the NO _x concentration in the measured gas, and a difference between current values flowing through the first element and the second element is taken out as information indicating the ammonia concentration in the measured gas. Is configured as
A specific gas concentration sensor comprising a decomposition catalyst for decomposing ammonia in the gas to be measured into components other than NO _x on the upstream side of the first space.   The diffusion-controlled passage is provided in the flow path of the gas to be measured upstream of the first space, and the decomposition catalyst is provided in the diffusion-controlled passage. Specific gas concentration sensor.

Images