CN114324533B - Nitrogen oxide sensor and method for measuring NO and NO in vehicle tail gas2Content method - Google Patents
Nitrogen oxide sensor and method for measuring NO and NO in vehicle tail gas2Content method Download PDFInfo
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- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 title claims abstract description 246
- 238000000034 method Methods 0.000 title claims abstract description 27
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 483
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 239
- 238000012360 testing method Methods 0.000 claims abstract description 125
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- CMIHHWBVHJVIGI-UHFFFAOYSA-N gadolinium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[Gd+3].[Gd+3] CMIHHWBVHJVIGI-UHFFFAOYSA-N 0.000 claims description 3
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum oxide Inorganic materials [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 claims description 3
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- 229910002091 carbon monoxide Inorganic materials 0.000 description 11
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- 230000008859 change Effects 0.000 description 7
- DOTMOQHOJINYBL-UHFFFAOYSA-N molecular nitrogen;molecular oxygen Chemical compound N#N.O=O DOTMOQHOJINYBL-UHFFFAOYSA-N 0.000 description 7
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Abstract
The invention relates to a nitrogen oxide sensor and a method for measuring the NO and NO 2 content in vehicle tail gas. The nitrogen oxide sensor includes: a gas test flow channel, a solid electrolyte matrix (6), a first platinum electrode (1), a second platinum electrode (2), a third platinum electrode (3), and a fifth platinum electrode (5); the solid electrolyte matrix (6) is provided with a test gas flow inlet (7), and the gas test flow channel extends to the inside of the solid electrolyte through the test gas flow inlet (7); the gas testing flow channel sequentially comprises a first chamber (8), a second chamber (9) and a third chamber (10), wherein NO 2 capturing particles (11) are distributed on the second inner wall of the second chamber. The NO 2 and the NO content in the automobile exhaust can be distinguished and measured through the nitrogen oxide sensor, and the detection effect is improved.
Description
Technical Field
The invention relates to the field of motor vehicle exhaust emission detection, in particular to a nitrogen oxide sensor and a method for measuring the contents of NO and NO 2 in vehicle exhaust.
Background
To meet the national vi emission regulations, nitrogen-oxygen sensors have been used on aftertreatment systems for light-duty diesel vehicles. The purpose of the nitrogen-oxygen sensor is to monitor the level of exhaust pollutant NO X in the aftertreatment system. However, the existing nitrogen-oxygen sensor can only monitor the content of NO, so that the total content of NO X is calculated, namely the sum of the contents of NO and NO 2. That is, the existing nitrogen-oxygen sensor cannot distinguish between NO and NO 2, which results in inaccurate measurement of NO X by the nitrogen-oxygen sensor.
NO X in the pollutants in the exhaust gas emitted from the diesel engine is only NO and NO 2. Other nitrogen oxides may be produced in extremely small amounts, but the proportion of NO X is also only negligible.
The BOSCH company nitrogen oxygen sensor in the prior art has two chambers, a first chamber and a second chamber. The working process of the nitrogen oxide sensor comprises the following steps:
The first step: when the exhaust gas enters the first chamber region, HC (hydrocarbon), CO (carbon monoxide), H 2 (hydrogen) and oxygen in the exhaust gas react to form H 2O、CO2 and the like.
A second step; exhaust gas flowing through the first chamber to the second chamber, wherein the exhaust pollutants leave NO X,NOX and NO 2. NO is easily catalyzed by Pt into N 2 and O 2, and the reaction formula is '2 NO- & gt N 2+O2'; whereas NO 2 is not substantially catalyzed by Pt. The NO is catalyzed by Pt to form O 2, which flows between the electrodes to produce a change in current/voltage that reflects the amount of NO in the exhaust. The amount of NO in the exhaust gas from the diesel engine is 90% or more of that in the NO X, so the measured amount of NO may be approximately representative of the amount of NO X.
In addition, there is a product LNT, lean NO X trap technology (lean NO X trap, LNT) in the after-treatment system of the diesel engine of the prior art to clean up exhaust gas pollutants. LNT can result in NO: the ratio of NO 2 is changed to be 2:1, 1:2 and the like, which further results in that the nitrogen-oxygen sensor cannot accurately measure the contents of NO and NO 2.
In summary, the nitrogen oxide sensor provided in the prior art cannot distinguish and detect the content of NO and NO 2 in the automobile exhaust, and cannot measure the accurate content of NO X.
Disclosure of Invention
The invention aims to provide a nitrogen oxide sensor and a method for measuring the NO and NO 2 content in vehicle tail gas, wherein the nitrogen oxide sensor can distinguish and measure the NO and NO 2 content in the vehicle tail gas.
In order to achieve the above object, a first aspect of the present invention provides a nitrogen oxide sensor including: a gas test flow channel, a solid electrolyte matrix, a first platinum electrode, a second platinum electrode, a third platinum electrode, and a fifth platinum electrode;
The solid electrolyte matrix is provided with a test airflow inlet, and the gas test flow channel extends to the inside of the solid electrolyte matrix through the test airflow inlet; the gas testing flow channel sequentially comprises a first chamber, a second chamber and a third chamber along the flow direction of the testing gas flow;
The second platinum electrode is covered on the outer wall of the solid electrolyte matrix and extends along the flow direction of the test airflow;
The first platinum electrode is covered on the first inner wall of the first chamber and is arranged opposite to the pole piece of the second platinum electrode, and the inner sides of the pole pieces of the first platinum electrode and the second platinum electrode are connected only through the solid electrolyte matrix;
The second inner wall of the second chamber is sequentially covered with the third platinum electrode and NO 2 capturing particles, the third platinum electrode is arranged opposite to the pole piece of the second platinum electrode, and the inner sides of the pole pieces of the third platinum electrode and the second platinum electrode are connected through the solid electrolyte matrix only; a reaction gap is formed between the third platinum electrode and the NO 2 capture particles;
the fifth platinum electrode is covered on the third inner wall of the third chamber and is arranged opposite to the pole piece of the second platinum electrode, and the inner side of the pole piece of the fifth platinum electrode and the inner side of the pole piece of the second platinum electrode are connected through the solid electrolyte matrix only;
a first power supply is arranged between the second platinum electrode and the first platinum electrode, a second power supply is arranged between the second platinum electrode and the third electrode, and a third power supply is arranged between the second platinum electrode and the fifth electrode;
a first electric signal measuring device is arranged between the third platinum electrode and the second platinum electrode; and a second electric signal measuring device is arranged between the fifth platinum electrode and the second platinum electrode.
Optionally, for the nox sensor, a NO 2 capturing layer is disposed in the second chamber, the third platinum electrode and the NO 2 capturing layer sequentially cover the second inner wall from inside to outside, and the NO 2 capturing layer includes the NO 2 capturing particles;
Optionally, the thickness of the NO 2 capturing layer is 6-12 μm;
optionally, the width of the NO 2 capturing layer is 4.5-7.5 mm;
optionally, the length of the NO 2 capturing layer is 6-10 mm.
Optionally, for the nitrogen oxide sensor, the NO 2 capture particles comprise ZnFe 2O4;
Optionally, the amount of the ZnFe 2O4 added in the NO 2 capturing particles is 40 to 60 wt%, preferably 45 to 55 wt%;
Alternatively, the particle size of the NO 2 capturing particles is 1 to 3. Mu.m, preferably 1.5 to 2.5. Mu.m.
Optionally, for the nox sensor, the nox sensor further includes a gas component detecting device for detecting an air-fuel ratio of the test gas flow in the first chamber.
Optionally, for the nitrogen oxide sensor, the nitrogen oxide sensor has an oxygen-deficient operating state and an oxygen-enriched operating state;
In the oxygen-deficient working state, the first platinum electrode is connected with the positive electrode of the first power supply, and the second platinum electrode is connected with the negative electrode of the first power supply;
in the oxygen-enriched working state, the first platinum electrode is connected with the negative electrode of the first power supply, and the second platinum electrode is connected with the positive electrode of the first power supply;
optionally, the nitrogen oxide sensor further comprises an electrode connection control device, and the electrode connection control device is in signal connection with the gas component detection device so as to determine the working state of the nitrogen oxide sensor according to the air-fuel ratio of the test gas flow.
Optionally, for the oxynitride sensor, the solid electrolyte matrix comprises ZrO 2 and a doping material; the doping material is selected from at least one of CaO, mgO and rare earth oxide, and the rare earth oxide is selected from at least one of Y 2O3、La2O3、Gd2O3、Sm2O3;
Optionally, in the solid electrolyte matrix, the grain size of the ZrO 2 is 5-50 μm, preferably 10-20 μm;
Optionally, in the solid electrolyte matrix, the particle size of the doping material is 5-50 μm, preferably 10-20 μm;
Optionally, the doping material is selected from at least one of Y 2O3 and CaO;
optionally, the volume fraction of the doping material in the solid electrolyte matrix is 7-10%, further 7.5-8.5%.
Optionally, for the nitrogen oxide sensor, a third platinum electrode of the second chamber is connected with a negative electrode of the second power supply, and the second platinum electrode is connected with a positive electrode of the second power supply;
The fifth platinum electrode of the third chamber is connected with the negative electrode of the third power supply, and the second platinum electrode is connected with the positive electrode of the third power supply.
Optionally, for the nitrogen oxide sensor, a reference airflow inlet and a reference runner extending along the reference airflow inlet towards the inside of the solid electrolyte matrix are further arranged on the solid electrolyte matrix;
A fourth platinum electrode is covered on the fourth inner wall of the reference flow channel, and the fourth platinum electrode is connected with the inner side of the pole piece of the second platinum electrode through the solid electrolyte matrix;
a third electric signal measuring device is arranged between the fourth platinum electrode and the second platinum electrode; a fourth electrical signal measuring device is arranged between the fourth platinum electrode and the first platinum electrode.
Optionally, for the nox sensor, the nox sensor further includes a sixth platinum electrode, where the sixth platinum electrode covers a fourth inner wall of the third chamber, and the fourth inner wall is disposed opposite to the third inner wall;
Optionally, a fifth electrical signal measurement device is disposed between the fourth platinum electrode and the sixth platinum electrode.
In a second aspect, the present invention provides a method for determining the NO and NO 2 content in the exhaust gas of a vehicle, using the nox sensor described in any one of the preceding paragraphs, the method comprising the steps of:
Flowing a test gas through the test gas flow inlet into the gas test flow channel and into the first chamber, the second chamber and the third chamber in sequence;
And determining the NO content and the NO 2 content in the test airflow according to the first electric signal value measured by the first electric signal measuring device and the second electric signal value measured by the second electric signal measuring device.
Optionally, for the method, the determining the NO content and the NO 2 content in the test airflow according to the first electrical signal value measured by the first electrical signal measurement device and the second electrical signal value measured by the second electrical signal measurement device includes:
Determining the NO 2 content in the test airflow according to the first electrical signal value; and determining the NO content in the test airflow according to the difference value between the second electric signal value and the first electric signal value.
Optionally, for the method, the method further comprises: and detecting the air-fuel ratio of the test air flow in the first cavity, and determining the working state of the nitrogen oxide sensor according to the air-fuel ratio of the test air flow.
Optionally, for the method, the determining the operating state of the nox sensor according to the air-fuel ratio of the test airflow includes:
When the air-fuel ratio of the test air flow is less than or equal to a set threshold value, the nitrogen oxide sensor is in an oxygen-deficient working state, the first platinum electrode is connected with the positive electrode of the first power supply, and the second platinum electrode is connected with the negative electrode of the first power supply;
when the air-fuel ratio of the test air flow is larger than a set threshold value, the nitrogen oxide sensor is in an oxygen-enriched working state, the first platinum electrode is connected with the negative electrode of the first power supply, and the second platinum electrode is connected with the positive electrode of the first power supply;
optionally, the set threshold of the air-fuel ratio ranges from 13.5 to 14.5.
Through the technical scheme, the nitrogen oxide sensor comprises three chambers, HC, CO and H 2 in a test air flow react with O 2 under the catalysis of the first platinum electrode of the first chamber to generate CO 2、H2 O and the like; the NO 2 trapping particles in the second chamber have excellent trapping and catalytic properties for NO 2, so that NO 2 in the test gas stream is trapped in the second chamber by the NO 2 particles and converted to NO and oxygen ions by the third platinum electrode, the oxygen ions move to the second platinum electrode under the action of the second power supply to generate an electrical signal change, thereby determining the content of NO 2 in the test gas stream, and only nitrogen oxides in the form of NO remain in the gas entering the third chamber from the second chamber, wherein the nitrogen oxides comprise the original NO in the test gas stream and the NO converted from NO 2 in the second chamber, and the total content of NO is measured in the third chamber, so that the initial NO content in the test gas stream is obtained according to the difference between the total NO content in the test gas stream and the NO 2 content measured in the second chamber, thereby achieving the purpose of distinguishing the NO content from the NO 2 content in the test gas stream. The nitrogen oxide sensor has the advantages of simple structure, convenient test and installation, and can rapidly and accurately measure the NO and NO 2 content in the test airflow, especially the tail gas of the vehicle.
Meanwhile, the NO 2 capturing particles are arranged in the second chamber, so that the NO 2 in the test air flow is captured and catalyzed, NO and NO 2 in the tail gas to be tested can be detected in a distinguishing mode, and the detection accuracy of the nitrogen oxide sensor is improved.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate the invention and together with the description serve to explain, without limitation, the invention. In the drawings:
FIG. 1 is a schematic diagram illustrating the construction of one embodiment of a NOx sensor of the present invention;
FIG. 2 is a schematic diagram illustrating the principle of the nitrogen oxide sensor of the present invention for converting oxygen into oxygen ions;
Fig. 3 is a schematic diagram showing the reaction principle of NO 2 in the second chamber of the nox sensor of the present invention to generate NO.
Description of the reference numerals
1-First platinum electrode, 2-second platinum electrode, 3-third platinum electrode, 4-fourth platinum electrode, 5-fifth platinum electrode, 6-solid electrolyte matrix, 7-test gas flow inlet, 8-first chamber, 9-second chamber, 10-third chamber, 11-NO 2 capture particles, 12-first power supply, 13-second power supply, 14-third power supply, 15-first electrical signal measuring device, 16-second electrical signal measuring device, 17-gas component detecting device, 18-reference flow path, 19-third electrical signal measuring device, 20-fourth electrical signal measuring device, 21-sixth platinum electrode, 22-fifth electrical signal measuring device, 23-heating resistor, 24-heating electrode, 25-sixth electrical signal measuring device
Detailed Description
The following describes specific embodiments of the present invention in detail with reference to the drawings. It should be understood that the detailed description and specific examples, while indicating and illustrating the invention, are not intended to limit the invention.
In the present invention, unless otherwise indicated, the terms "first," "second," "third," and the like are used merely to distinguish between different components and do not have the actual meaning of the order of connection before and after. In the present invention, the terms "upper" and "lower" are used to refer to the upper and lower parts of the device in normal use, and "inner" and "outer" are used to refer to the outline of the device, for example, "the inner sides of the first pole piece and the second pole piece" refer to the region of the middle interlayer of the two pole pieces, that is, the side of the first pole piece near the second pole piece, and the side of the second pole piece near the first pole piece.
As shown in fig. 1, a first aspect of the present invention provides a nitrogen oxide sensor including: a gas test flow channel, a solid electrolyte matrix 6, a first platinum electrode 1, a second platinum electrode 2, a third platinum electrode 3, a fourth platinum electrode 4 and a fifth platinum electrode 5;
The solid electrolyte matrix 6 is provided with a test airflow inlet 7, the test airflow enters a gas test flow channel through the test airflow inlet 7, and the gas test flow channel extends to the inside of the solid electrolyte matrix 6 through the test airflow inlet 7; the gas test flow passage sequentially comprises a first chamber 8, a second chamber 9 and a third chamber 10 along the flow direction of the test gas flow, and the test gas flow sequentially passes through the first chamber, the second chamber and the third chamber through the air flow passage; wherein the test air flow can be automobile exhaust;
The second platinum electrode 2 is covered on the outer side wall of the solid electrolyte matrix 6 and extends along the flow direction of the test gas flow;
The first platinum electrode 1 is covered on the first inner wall of the first chamber 8 and is arranged opposite to the pole piece of the second platinum electrode 2, the inner sides of the pole pieces of the first platinum electrode 1 and the second platinum electrode 2 are connected only through the solid electrolyte matrix 6, electrons and oxygen ions can be conducted in the solid electrolyte matrix, and the specific principle will be described in the following part;
The second inner wall of the second chamber 9 is sequentially covered with a third platinum electrode 3 and NO 2 capturing particles 11, the third platinum electrode 3 is arranged opposite to the pole piece of the second platinum electrode 2, and the third platinum electrode 3 is connected with the inner side of the pole piece of the second platinum electrode 2 only through a solid electrolyte matrix 6; by this arrangement, the test gas flow first contacts the NO 2 trapping particles 11 in the second chamber, NO 2 gas is trapped, and the trapped NO 2 reacts under the catalytic action of the third platinum electrode 3 due to the contact of the NO 2 trapping particles 11 with the third platinum electrode 3, converting NO 2 into NO;
the fifth platinum electrode 5 is covered on the third inner wall of the third chamber 10 and is arranged opposite to the pole piece of the second platinum electrode 2, the fifth platinum electrode 5 is connected with the inner side of the pole piece of the second platinum electrode 2 only through the solid electrolyte matrix 6, and the conduction of electrons and oxygen ions is carried out through the solid electrolyte 6;
A first power supply 12 is arranged between the second platinum electrode 2 and the first platinum electrode 1, a second power supply 13 is arranged between the second platinum electrode 2 and the third electrode 3, a third power supply 14 is arranged between the second platinum electrode 2 and the fifth electrode 5, and the first power supply 12, the second power supply 13 and the third power supply power to each chamber, namely electrons required by gas reaction are provided for reaction;
A first electrical signal measuring device 15 is arranged between the third platinum electrode 3 and the second platinum electrode 2; a second electrical signal measuring device 16 is provided between the fifth platinum electrode 5 and the second platinum electrode 2, and the first electrical signal measuring device 15 can measure the change of the electrical signal during the NO 2 reaction in the second chamber to generate NO, and the second electrical signal measuring device 16 can measure the change of the electrical signal during the NO reaction in the third chamber to generate N 2 and O 2.
In one embodiment, as shown in FIG. 1, the process of using the NOx sensor of the present invention to determine the NO and NO 2 content of a test gas stream includes:
The tail gas is taken as a test gas flow to enter the first cavity, hydrocarbon (CH), carbon monoxide (CO) and hydrogen (H 2) in the test gas flow react with O 2 under the catalysis of the first platinum electrode in the first cavity to generate CO 2、H2 O and the like, so that the test gas flow entering the second cavity only contains NO X, and the accuracy of the detection result of the nitrogen oxide sensor is improved;
The test air flow processed by the first chamber enters the second chamber, NO 2 capturing particles in the second chamber have excellent capturing and catalytic properties on NO 2, after NO 2 in the test air flow is captured by the particles, electrons are obtained at the third platinum electrode to generate NO and oxygen ions, the oxygen ions move to the second platinum electrode under the action of the second power supply to generate electric signal change, so that the content of NO 2 in the test air flow can be determined, the NO 2 in the test air flow is converted into NO through reaction in the second chamber, and only nitrogen oxides in the form of NO remain in the test air flow;
The test air flow processed by the second chamber enters a third chamber, NO in the air contains original NO in the test air flow and NO converted from NO 2 in the second chamber, the NO in the third chamber generates N 2 and O 2 under the catalysis of a fifth platinum electrode, O 2 obtains electrons at the fifth platinum electrode to form oxygen ions, the oxygen ions move to the second platinum electrode under the action of a third power supply to generate electric signal change, and the total content of the NO is measured through the electric signal change;
finally, the amount of NO initially contained in the test air flow is obtained according to the difference value of the total NO content in the test air flow and the NO 2 content measured in the second chamber, so that the purpose of distinguishing the NO content from the NO 2 content in the test air flow is achieved.
In one embodiment of the nitrogen oxide sensor provided by the present invention, the first platinum electrode 1, the second platinum electrode 2, the third platinum electrode 3 and the fifth platinum electrode 5 are each in the form of a coating, and in each platinum electrode, there are gaps between platinum particles, electrons and oxygen ions are allowed to circulate through the gaps in the platinum electrode, as shown in fig. 3, the inside of the platinum electrode includes individual platinum (Pt) particles, and there are gaps for electrons and oxygen ions to pass between each platinum particle.
In one embodiment, the thickness of the first platinum electrode 1 may be 9 to 11 μm, preferably 9.5 to 10.5 μm; the thickness of the second platinum electrode 2 may be 9 to 11 μm, preferably 9.5 to 10.5 μm; the thickness of the third platinum electrode 3 may be 9 to 11 μm, preferably 9.5 to 10.5 μm; the thickness of the fifth platinum electrode 5 may be 9 to 11 μm, preferably 9.5 to 10.5 μm.
In one embodiment, the thickness of the solid electrolyte matrix 6 between the second platinum electrode 2 and the first platinum electrode 1 of the first chamber may be 0.1 to 0.2mm, preferably 0.1 to 0.15mm; the thickness of the solid electrolyte matrix 6 between the second platinum electrode 2 and the third platinum electrode 3 of the second chamber may be 0.1 to 0.2mm, preferably 0.1 to 0.15mm; the thickness of the solid electrolyte matrix 6 between the second platinum electrode 2 and the fifth platinum electrode 5 of the third chamber may be 0.1 to 0.2mm, preferably 0.1 to 0.15mm.
In one embodiment of the nox sensor according to the present invention, as shown in fig. 1, a NO 2 capturing layer is disposed in the second chamber 9, the third platinum electrode 3 and the NO 2 capturing layer sequentially cover the second inner wall from inside to outside (the second inner wall is the innermost layer, in a specific form: the second inner wall-the third platinum electrode-the NO 2 capturing layer), and the NO 2 capturing layer includes NO 2 capturing particles 11. By coating the second inner wall with the third platinum electrode 3 and the NO 2 trap layer in this order, it is possible to connect with the solid electrolyte matrix 6, and a channel capable of allowing free movement of electrons and oxygen ions is formed between the third platinum electrode 3 and the second platinum electrode 2. In the invention, in order to achieve better NO 2 capturing and catalyzing effects, the thickness of the NO 2 capturing layer is 6-12 mu m, preferably 9-10 mu m; further, the width of the NO 2 capturing layer is 4.5-7.5 mm, preferably 5.5-6.5 mm; further, the NO 2 capture layer has a length of 6 to 10mm, preferably 7.5 to 8.5mm, where the length is along the direction of flow of the test gas stream.
In one embodiment of the nitrogen oxide sensor provided by the invention, the adopted NO 2 capturing particles 11 comprise ZnFe 2O4; further, the amount of ZnFe 2O4 added to the NO 2 capturing particles 11 may be 40 to 60 wt%, preferably 45 to 55 wt%; the particle size of the NO 2 capturing particles 11 may be 1 to 3. Mu.m, preferably 1.5 to 2.5. Mu.m. In the preferred embodiment, the capturing effect of the NO 2 capturing particles on the NO 2 is further improved, and the detection effect of the nitrogen oxide sensor for detecting the NO and the NO 2 in a distinguishing manner is further improved. Further, the NO 2 capturing particle 11 may further include at least one of MgFe 2O4 particles and CoFe 2O4 particles, which is not limited in this respect.
In one embodiment of the present invention, the nox sensor of the present invention further comprises a gas composition detecting means 17 for detecting the air-fuel ratio of the test gas flow in the first chamber 8.
In the present invention, the air-fuel ratio refers to the mass ratio between oxygen and the combustible gas containing H 2, CH and CO in the test gas stream. For example, in one embodiment, the gas component detecting device may detect the O 2 content (m 1) and the three kinds of gas contents (m 2) of H 2, CH, and CO in the test gas stream, and obtain the air-fuel ratio of the test gas stream according to the measured ratio between m1 and m 2.
In one embodiment of the present invention, the nitrogen oxide sensor has an oxygen-lean operating state and an oxygen-rich operating state;
In the oxygen-deficient working state, the first platinum electrode 1 is connected with the positive electrode of the first power supply 12, and the second platinum electrode 2 is connected with the negative electrode of the first power supply 12;
In the oxygen-enriched operating state, the first platinum electrode 1 is connected to the negative electrode of the first power supply 12, and the second platinum electrode 2 is connected to the positive electrode of the first power supply 12.
Specifically, in the oxygen-enriched operating state, the oxygen in the first chamber is sufficient to react with the non-nitrogen oxides in the test gas stream, so that the non-nitrogen oxide gases (HC, CO, H 2) in the test gas stream react under the catalytic action of the first power supply and the first platinum electrode, and the reaction formula is as follows:
CO+1/2O2→CO2 (1)
HC+O2→H2O+CO2 (2)
H2+1/2O2→H2O (3)
The CH in the formula (2) refers to hydrocarbon which is a harmful gas in automobile exhaust, and is generated by burning gasoline and diesel oil, and the hydrocarbon and nitrogen oxides can generate light blue smoke with irritation and larger hazard under the action of solar ultraviolet rays. The nitrogen hydride Compound (CH) in the exhaust gas in the first chamber of the nitrogen oxide sensor is fully reacted to generate carbon dioxide and water.
And based on the oxygen capturing property of the first platinum electrode, the oxygen rapidly moves to the second platinum electrode (connected with the positive electrode of the first power supply) in the form of oxygen ions (O 2-) when electrons (2 e - or 4e -) are obtained at the 'three-phase interface' of the first platinum electrode (connected with the negative electrode of the first power supply to obtain electrons). In the invention, the oxygen demand value can be preset according to the experience value of the test gas flow reaction, and oxygen exceeding the oxygen demand value in the first chamber can be used as redundant oxygen to obtain electrons at the first platinum electrode to form oxygen ions to move to the second platinum electrode.
Specifically, in the oxygen-deficient operating state, in order to fully combust non-nitrogen oxide combustibles in the test gas flow, oxygen can be supplemented into the first chamber, at this time, the first platinum electrode can be connected with the positive electrode of the first power supply, the second platinum electrode can be connected with the negative electrode of the first power supply, in this connection mode, electrons are obtained from the oxygen at the second platinum electrode to form oxygen ions, the oxygen ions move to the first platinum electrode and lose electrons at the first platinum electrode and escape in the form of oxygen molecules O 2, so that O 2 is supplemented into the first chamber, and the test gas flow fully generates the combustion reaction shown in the above reaction formulas (1) - (3) in the first chamber.
Through the different states of the oxygen-deficient working state and the oxygen-enriched working state, the connection modes of the first platinum electrode and the second platinum electrode and the anode and the cathode of the first power supply are changed, so that redundant oxygen can be formed into oxygen ions and moved to the second platinum electrode in the oxygen-enriched working state, the content of non-nitrogen oxides in the test air flow entering the second cavity can be reduced, and the detection accuracy is improved; under the working state of oxygen deficiency, oxygen ions existing at the second platinum electrode or oxygen ions newly generated by external oxygen at the second platinum electrode are moved to the first platinum electrode and lose electrons to generate oxygen so as to supplement oxygen in the first cavity, and the gas reaction effect is improved.
In one embodiment of the present invention, the nox sensor further comprises an electrode connection control device, which is in signal connection with the gas composition detection device 17 to determine the operation state of the nox sensor according to the air-fuel ratio of the test gas flow. Specifically, the electrode connection control device may be disposed inside the nox sensor or may be disposed outside the nox sensor, which is not limited in the present invention. In the embodiment, the switching between the oxygen-deficient working state and the oxygen-enriched working state of the nitrogen oxide sensor is further realized by arranging the electrode connection control device, so that the detection efficiency is improved.
In one embodiment according to the invention, the solid electrolyte matrix 6 in the oxynitride sensor comprises ZrO 2 and a doping material; further, the doping material is selected from at least one of CaO, mgO and rare earth oxide, and further selected from at least one of Y 2O3 and CaO; the rare earth oxide is at least one selected from Y 2O3、La2O3、Gd2O3、Sm2O3;
alternatively, the particle size of ZrO 2 in the solid electrolyte matrix 6 is 5 to 50. Mu.m, preferably 10 to 20. Mu.m;
Alternatively, the particle size of the doping material in the solid electrolyte matrix 6 is 5 to 50 μm, preferably 10 to 20 μm.
In a further embodiment, the volume fraction of doping material in the solid electrolyte is 7-10%, more preferably 7.5-8.5%.
For example, in one embodiment of the present invention, the solid electrolyte matrix 6 contains ZrO 2 and Y 2O3. Preferably, the particle size of ZrO 2 particles in the solid material matrix is 5 to 50. Mu.m, more preferably 10. Mu.m, and the particle size of Y 2O3 particles in the solid material matrix is 5 to 50. Mu.m, more preferably 10. Mu.m. The specific embodiment of the invention improves the ion conduction performance of the solid electrolyte matrix, and the added doping material can not only improve the concentration of oxygen ion vacancies, but also enable ZrO 2 to exist in a tetragonal or cubic form at low temperature, and larger gaps exist in a unit cell, so that oxygen ions are unobstructed in the vacancies, and the conductivity/oxygen ion flow rate of the solid electrolyte matrix is improved.
In the present invention, the working principle by converting oxygen into oxygen ions and conducting through the solid electrolyte matrix is shown in fig. 2. When a voltage (e.g., 1V) is applied across the two segments of the solid electrolyte, "region a" is connected to the negative (-) voltage and "region B" is connected to the positive voltage. The oxygen molecules (O 2) in the "a region" thereof receive electrons (4 e -) to form oxygen ions (O 2-), and the oxygen ions (O 2-) rapidly migrate to the Pt (platinum) electrode on the low oxygen concentration side ("B region" surface) through oxygen vacancies in the electrolyte, and the "B region" is "positive electrode (+)", so that the oxygen ions (O 2-) lose electrons again and are released as oxygen molecules (O 2).
In one embodiment of the nitrogen oxide sensor provided by the present invention, as shown in fig. 1, the third platinum electrode 3 of the second chamber 9 is connected to the negative electrode of the second power supply 13, the second power supply 13 supplies electrons to the third platinum electrode 3, and the second platinum electrode 2 is connected to the positive electrode of the second power supply 13. As shown in fig. 3, the second inner wall of the second chamber 9 is sequentially coated with the third platinum electrode 3 and the NO 2 capturing particles 11, NO 2 in the test gas flow entering the second chamber 9 is captured by the NO 2 capturing particles 11 in the reaction space formed between the particles of the NO 2 capturing particles 11, and electrons are obtained at the space of the third platinum electrode 3 to generate NO and oxygen ions, the reaction formula is as follows (4):
NO2+2e-→NO+O2- (4)；
The negatively charged oxygen ions (O 2-) generated by the reaction of formula (4) will move toward the second platinum electrode 2 through the solid electrolyte matrix 6 between the third platinum electrode 3 and the second platinum electrode. A first electrical signal value (e.g., a potential difference value or a current difference value) is generated between the second platinum electrode 2 and the third platinum electrode 3 by the movement of oxygen ions to be detected by the first electrical signal measuring means 15 of the nox sensor, and the detected first electrical signal can be converted into a number signal of reacted NO 2 to determine the content (w 1) of NO 2 in the test gas stream. And from the relationship of the number ratio (or molar ratio) of NO 2 to NO produced according to the formula (4) is 1:1, i.e., one NO gas molecule can be produced by 1 NO 2 gas molecule.
In one embodiment, the fifth platinum electrode 5 of the third chamber 10 in the nox sensor is connected to the negative electrode of the third power supply 14, the third power supply 14 supplies electrons to the fifth platinum electrode 5, and the second platinum electrode 2 is connected to the positive electrode of the third power supply 14. In this embodiment, after the reaction in the second chamber 9, the nitrogen oxides in the test gas flow exist only in the form of NO, and enter the third chamber 10 through the gas test flow channel, and the NO in the test gas flow is catalyzed at the fifth platinum electrode 5 of the third chamber 10 to generate N 2 and O 2, specifically, the following reaction formula (5):
2NO→N2+O2 (5)；
in this embodiment, the fifth platinum electrode 5 is connected to the negative electrode of the third power supply 15 to obtain electrons, and thus the oxygen generated by the above formula (5) is converted into oxygen ions by the electrons obtained at the fifth platinum electrode 5.
A solid electrolyte matrix 6 is provided between the second platinum electrode 2 and the fifth platinum electrode 5, so that oxygen ions obtained by electron-withdrawing oxygen at the second platinum electrode 5 move toward the second platinum electrode 2 through a channel in the solid electrolyte matrix 6, and this movement behavior causes a second electric signal value (for example, a potential difference value or a current difference value) to be generated between the fifth platinum electrode 5 and the second platinum electrode 2, to be detected by the second electric signal measuring means 16, and the amount of NO that has entered the third chamber is determined by converting the detected second electric signal into a signal of the amount of NO that has reacted (w 2).
Since the NO entering the third chamber contains not only the NO originally contained by the test gas stream entering the nox sensor through the test gas stream inlet 7, but also the NO generated by the reaction of NO 2 through the second chamber 9, and the number ratio (e.g., molar ratio) between NO 2 and the generated NO in the second chamber 9 is 1:1, the amount of NO originally contained by the test gas stream (the amount of NO contained in the exhaust gas) can be obtained by the difference (e.g., w2-w 1) between w2 and w 1.
Furthermore, the nitrogen oxide sensor provided by the invention is also provided with a reference airflow inlet and a reference runner 18 extending towards the inside of the solid electrolyte matrix 6 along the reference airflow inlet on the solid electrolyte matrix 6, and the reference runner 18 is connected with the atmosphere;
A fourth platinum electrode 4 is coated on the fourth inner wall of the reference flow channel 18, and the fourth platinum electrode 4 is connected with the inner side of the pole piece of the second platinum electrode 2 only through the solid electrolyte matrix 6;
In one embodiment, a third electrical signal measuring device 19 is provided between the fourth platinum electrode 4 and the second platinum electrode 2; a fourth electrical signal measuring device 20 is provided between the fourth platinum electrode 4 and the first platinum electrode 1. Further, the third electrical signal measuring device 19 and the fourth electrical signal measuring device 20 may be current measuring devices and/or potential measuring devices. The fourth platinum electrode 4 is also in the form of a coating layer having a thickness of 9 to 11. Mu.m, preferably 9.5 to 10.5. Mu.m.
In the invention, by setting the reference flow channel and the reference electrode as reference objects, the nitrogen oxide sensor can detect a potential difference value or a current difference value formed by gas reaction of the test gas flow during operation so as to determine the quantity of the gas reacted in the second chamber and the third chamber.
In one embodiment, in order to protect the nox sensor, the nox sensor of the present invention may further include a sixth platinum electrode 21, where the sixth platinum electrode 21 covers a fourth inner wall of the third chamber 8, and the fourth inner wall is disposed opposite to the third inner wall.
In a further embodiment, a fifth electrical signal measuring device 22 is provided between the fourth platinum electrode 4 and the sixth platinum electrode 21. The fifth electrical signal measuring device 22 may be a amperometric device and/or a potentiometric device.
In the preferred embodiment, the sixth platinum electrode is arranged in the nitrogen oxide sensor as the clamping electrode, so that the voltage in the nitrogen oxide sensor can be limited and protected, and the working stability and the safety of the nitrogen oxide sensor are improved.
In one embodiment, as shown in fig. 1, a heating resistor 23 is further disposed in the solid electrolyte matrix 6 in the nitrogen oxide sensor provided by the present invention, the heating resistor 23 is connected to the atmosphere in the reference channel 18 through the solid electrolyte matrix 6, and the other side corresponding to the one side of the fourth platinum electrode 4 disposed in the reference channel 18 is connected through the solid electrolyte matrix 6.
Further, a heating electrode 24 is provided in the solid electrolyte matrix 6 with respect to the heating resistor 23, and a heating voltage measuring device 25 is provided between the heating resistor 23 and the heating electrode 24, so that the heating resistor 23 is heated when the nitrogen oxide sensor is operated, and the resistance value of the heating resistor 23 can be measured by the heating voltage measuring device 25 to control the heating temperature of the heating resistor 23. Specifically, heating resistors in the oxynitride sensor is a common technical means in the art, and the present invention is not described herein.
In a second aspect of the invention, there is provided a method of determining the NO and NO 2 content in a vehicle exhaust, in which method the aforementioned nitrogen oxide sensor is employed, comprising the steps of:
flowing a test gas through the test gas flow inlet 7 into the gas test flow path and into the first chamber 8, the second chamber 9 and the third chamber 10 in sequence;
The NO content and the NO 2 content in the test air flow are determined according to the first electric signal value measured by the first electric signal measuring device 15 and the second electric signal value measured by the second electric signal measuring device 16.
Specifically, the test gas flow is made to flow into the first chamber 8, and after the non-nitrogen oxide gas reaction such as CO, CH, H 2 and the like contained in the test gas flow reacts as in the reactions of the formulas (1) - (3), only nitrogen oxides in the form of NO 2 and NO remain in the test gas flow; the test gas flow then flows into the second chamber 9, where NO 2 in the test gas flow reacts to form NO and oxygen ions (as shown in formula (3) above), where only nitrogen oxides in the form of NO remain in the test gas flow through the second chamber, and then flows into the third chamber 10; after the test gas flow enters the third chamber, the NO reacts to form N 2 and O 2 (as shown in formula (4)) and the reaction processes and reaction principles in the first chamber, the second chamber and the third chamber are described in detail in the foregoing, and are not described in detail herein.
Through the foregoing reaction, the first electrical signal value measured by the first electrical signal measuring device 15 can be converted to obtain the content (w 1) of NO 2 in the test gas flow that reacts in the second chamber according to the first electrical signal value; and the second electrical signal measuring device 16 measures a second electrical signal value, and the total amount (w 2) of NO reacted in the third chamber is obtained by converting the second electrical signal value; the NO content and NO 2 content in the test gas stream were finally determined by the difference between w2 and w 1. The specific process and principle in this step are already described in detail in the foregoing, and will not be repeated here.
In one embodiment of the present invention, the method for determining the NO and NO 2 content in the vehicle exhaust further comprises: the air-fuel ratio of the test air flow in the first chamber 8 is detected, and the operating state of the nox sensor is determined from the air-fuel ratio of the test air flow.
Specifically, determining the operating state of the nox sensor according to the air-fuel ratio of the test air flow includes:
When the air-fuel ratio of the test air flow is less than or equal to the set threshold value, the nitrogen oxide sensor is in an oxygen-deficient working state, the first platinum electrode 1 is connected with the positive electrode of the first power supply 12, and the second platinum electrode 2 is connected with the negative electrode of the first power supply 12;
When the air-fuel ratio of the test air flow is greater than the set threshold value, the nitrogen oxide sensor is in an oxygen-enriched working state, the first platinum electrode 1 is connected with the cathode of the first power supply 12, and the second platinum electrode 2 is connected with the anode of the first power supply 12. The set threshold value of the air-fuel ratio may be in the range of 13.5 to 14.5, preferably 14.3.
In the method provided by the invention, the specific principle of determining the working state of the nox sensor according to the air-fuel ratio of the test air flow is described in detail in the foregoing, and will not be repeated here.
The method for measuring the NO and NO 2 content in the tail gas of the vehicle provided by the invention realizes the distinguishing measurement of the NO and NO 2 content in the tail gas, and improves the detection effect.
The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the scope of the technical concept of the present invention, and all the simple modifications belong to the protection scope of the present invention. In addition, the specific features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various possible combinations are not described further.
Moreover, any combination of the various embodiments of the invention can be made without departing from the spirit of the invention, which should also be considered as disclosed herein.
Claims (24)
1. A nitrogen oxide sensor, characterized in that the nitrogen oxide sensor comprises: a gas test flow channel, a solid electrolyte matrix (6), a first platinum electrode (1), a second platinum electrode (2), a third platinum electrode (3) and a fifth platinum electrode (5);
The solid electrolyte matrix (6) is provided with a test airflow inlet (7), and the gas test flow channel extends to the inside of the solid electrolyte matrix (6) through the test airflow inlet (7); the gas testing flow channel sequentially comprises a first chamber (8), a second chamber (9) and a third chamber (10) along the flow direction of the testing gas flow;
the second platinum electrode (2) is covered on the outer wall of the solid electrolyte matrix (6) and extends along the flow direction of the test airflow;
The first platinum electrode (1) is covered on the first inner wall of the first chamber (8) and is arranged opposite to the pole piece of the second platinum electrode (2), and the inner sides of the pole pieces of the first platinum electrode (1) and the second platinum electrode (2) are connected only through the solid electrolyte matrix (6);
The second inner wall of the second chamber (9) is sequentially covered with the third platinum electrode (3) and NO 2 capturing particles (11), the third platinum electrode (3) is arranged opposite to the pole piece of the second platinum electrode (2), and the third platinum electrode (3) is connected with the inner side of the pole piece of the second platinum electrode (2) only through the solid electrolyte matrix (6); a reaction gap is formed between the third platinum electrode (3) and the NO 2 capturing particles (11); the second chamber (9) is internally provided with an NO 2 capturing layer, the third platinum electrode (3) and the NO 2 capturing layer are sequentially covered on the second inner wall from inside to outside, and the NO 2 capturing layer comprises the NO 2 capturing particles (11); the NO 2 capture particle (11) comprises ZnFe 2O4;
The fifth platinum electrode (5) is covered on the third inner wall of the third chamber (10) and is arranged opposite to the pole piece of the second platinum electrode (2), and the fifth platinum electrode (5) is connected with the inner side of the pole piece of the second platinum electrode (2) only through the solid electrolyte matrix (6);
A first power supply (12) is arranged between the second platinum electrode (2) and the first platinum electrode (1), a second power supply (13) is arranged between the second platinum electrode (2) and the third platinum electrode (3), and a third power supply (14) is arranged between the second platinum electrode (2) and the fifth platinum electrode (5);
A first electrical signal measuring device (15) is arranged between the third platinum electrode (3) and the second platinum electrode (2); a second electrical signal measuring device (16) is arranged between the fifth platinum electrode (5) and the second platinum electrode (2).
2. The oxynitride sensor according to claim 1, characterized in that the NO 2 capturing layer has a thickness of 6 to 12 μm; the width of the NO 2 capturing layer is 4.5-7.5 mm; the length of the NO 2 capturing layer is 6-10 mm.
3. The nitrogen oxide sensor according to claim 1, characterized in that the amount of ZnFe 2O4 added to the NO 2 capturing particles (11) is 40-60 wt%.
4. A nitrogen oxide sensor according to claim 3, characterized in that the amount of ZnFe 2O4 added to the NO 2 capturing particles (11) is 45-55 wt%.
5. The nitrogen oxide sensor according to claim 1, characterized in that the particle size of the NO 2 capturing particles (11) is 1-3 μm.
6. The nitrogen oxide sensor according to claim 5, characterized in that the particle size of the NO 2 capturing particles (11) is 1.5-2.5 μm.
7. The nitrogen oxide sensor according to any one of claims 1-6, characterized in that the nitrogen oxide sensor further comprises gas composition detection means (17) for detecting the air-fuel ratio of the test gas flow in the first chamber (8).
8. The nitrogen oxide sensor of claim 7, wherein the nitrogen oxide sensor has an oxygen-lean operating condition and an oxygen-rich operating condition;
In the oxygen-deficient working state, the first platinum electrode (1) is connected with the positive electrode of the first power supply (12), and the second platinum electrode (2) is connected with the negative electrode of the first power supply (12);
In the oxygen-enriched working state, the first platinum electrode (1) is connected with the negative electrode of the first power supply (12), and the second platinum electrode (2) is connected with the positive electrode of the first power supply (12).
9. The nitrogen oxide sensor according to claim 8, characterized in that the nitrogen oxide sensor further comprises an electrode connection control device, which is in signal connection with the gas composition detection device (17) for determining the operating state of the nitrogen oxide sensor depending on the air-fuel ratio of the test gas flow.
10. The nitrogen oxide sensor according to any one of claims 1 to 6, characterized in that the solid electrolyte matrix (6) comprises ZrO 2 and a doping material; the doping material is selected from at least one of CaO, mgO and rare earth oxide, and the rare earth oxide is selected from at least one of Y 2O3、La2O3、Gd2O3、Sm2O3.
11. The oxynitride sensor according to claim 10, characterized in that the particle size of ZrO 2 in the solid electrolyte matrix (6) is 5-50 μm;
In the solid electrolyte matrix (6), the particle size of the doping material is 5-50 mu m.
12. The oxynitride sensor according to claim 11, characterized in that the particle size of ZrO 2 in the solid electrolyte matrix (6) is 10-20 μm;
in the solid electrolyte matrix (6), the particle size of the doping material is 10-20 mu m.
13. The nitrogen oxide sensor of claim 11, wherein said doping material is selected from at least one of Y 2O3 and CaO.
14. The nitrogen oxide sensor according to claim 11, characterized in that the volume fraction of the doping material in the solid electrolyte matrix (6) is 7-10%.
15. The nitrogen oxide sensor according to claim 14, characterized in that the volume fraction of the doping material in the solid electrolyte matrix (6) is 7.5-8.5%.
16. The nitrogen oxide sensor according to any of the claims 1 to 6, characterized in that the third platinum electrode (3) of the second chamber (9) is connected to the negative pole of the second power source (13), the second platinum electrode (2) being connected to the positive pole of the second power source (13);
The fifth platinum electrode (5) of the third chamber (10) is connected with the negative electrode of the third power supply (14), and the second platinum electrode (2) is connected with the positive electrode of the third power supply (14).
17. The nitrogen oxide sensor according to any one of claims 1 to 6, characterized in that a reference gas flow inlet and a reference flow channel (18) extending along the reference gas flow inlet towards the inside of the solid electrolyte matrix (6) are also provided on the solid electrolyte matrix (6);
a fourth platinum electrode (4) is coated on the fourth inner wall of the reference flow channel (18), and the fourth platinum electrode (4) is connected with the inner side of the pole piece of the second platinum electrode (2) through the solid electrolyte matrix (6);
A third electrical signal measuring device (19) is arranged between the fourth platinum electrode (4) and the second platinum electrode (2); a fourth electrical signal measuring device (20) is arranged between the fourth platinum electrode (4) and the first platinum electrode (1).
18. The nitrogen oxide sensor according to claim 17, further comprising a sixth platinum electrode (21), said sixth platinum electrode (21) overlying a fourth inner wall of said third chamber (10), said fourth inner wall being disposed opposite said third inner wall.
19. The nitrogen oxide sensor according to claim 18, characterized in that a fifth electrical signal measuring device (22) is arranged between the fourth platinum electrode (4) and the sixth platinum electrode (21).
20. A method for determining the NO and NO 2 content in the exhaust gas of a vehicle, characterized in that a nitrogen oxide sensor according to any one of claims 1 to 19 is used, the method comprising the steps of:
Flowing a test gas through the test gas flow inlet (7) into the gas test flow channel and into the first chamber (8), the second chamber (9) and the third chamber (10) in sequence;
And determining the NO content and the NO 2 content in the test airflow according to the first electric signal value measured by the first electric signal measuring device (15) and the second electric signal value measured by the second electric signal measuring device (16).
21. The method according to claim 20, wherein said determining the NO content and the NO 2 content in the test gas stream from the first electrical signal value measured by the first electrical signal measurement device (15) and the second electrical signal value measured by the second electrical signal measurement device (16) comprises:
Determining the NO 2 content in the test airflow according to the first electrical signal value; and determining the NO content in the test airflow according to the difference value between the second electric signal value and the first electric signal value.
22. The method according to claim 20 or 21, characterized in that the method further comprises: an air-fuel ratio of the test air flow in the first chamber (8) is detected, and an operating state of the nitrogen oxide sensor is determined according to the air-fuel ratio of the test air flow.
23. The method of claim 22, wherein determining the operating condition of the nox sensor based on the air-fuel ratio of the test airflow comprises:
When the air-fuel ratio of the test air flow is less than or equal to a set threshold value, the nitrogen oxide sensor is in an oxygen-deficient working state, the first platinum electrode (1) is connected with the positive electrode of the first power supply (12), and the second platinum electrode (2) is connected with the negative electrode of the first power supply (12);
When the air-fuel ratio of the test air flow is larger than a set threshold value, the nitrogen oxide sensor is in an oxygen-enriched working state, the first platinum electrode (1) is connected with the negative electrode of the first power supply (12), and the second platinum electrode (2) is connected with the positive electrode of the first power supply (12).
24. The method according to claim 23, wherein the set threshold value of the air-fuel ratio is in a range of 13.5 to 14.5.
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