JP2010078378A - Granular substance detecting sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive granular substance detecting sensor capable of precisely separating Soot and SOF constituting a granular substance to detect them. <P>SOLUTION: The granular substance detecting sensor for detecting the granular substance contained in the exhaust gas discharged from an internal combustion engine includes a first measuring element 11 having an oxidation capacity for combusting the granular substance, a second measuring element 12 of which the oxidation capacity for combusting the granular substance is lower than that of the first measuring element 11, the first and second thermal electromotive force producing members 13 and 14, which produce electromotive force by the combustion heat of the granular substance, respectively connected to the first and second measuring elements 11 and 12, and a detection means 15 for detecting the amount of the granular substance on the basis of the difference between the thermal electromotive force produced by the first thermal electromotive force producing member 13 and the thermal electromotive force produced by the second thermal electromotive force producing member 14. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sensor for detecting particulate matter (hereinafter referred to as PM), and in particular, PM contained in exhaust gas discharged from a lean burn engine of an automobile, and PM contained in smoke emitted from a factory or the like. The present invention relates to a sensor that is used for detection of the above.

  PM contained in exhaust gas discharged from a lean burn engine such as a diesel engine is regarded as a causative substance such as air pollution, and reduction of the emission amount is a problem. In response to this, a technique for reducing PM emissions by improving combustion and a diesel particulate filter (hereinafter referred to as DPF) have been proposed, and PM emissions can be significantly reduced.

  The DPF is a porous filter made of ceramic or metal, and separates and collects PM from the exhaust gas by passing the exhaust gas containing PM. The PM collected in the DPF is burned and removed by raising the exhaust gas temperature by engine control or the like when a certain amount is accumulated. The amount of PM accumulated on the DPF is estimated based on travel distance, time, and engine information (engine speed, torque, etc.). The amount of accumulated PM is estimated from the degree of increase in the pressure loss of the DPF caused by PM accumulation by measuring the pressure difference between the upstream and downstream of the DPF.

On the other hand, a method for directly detecting PM in exhaust gas and estimating the amount of PM deposited on the DPF has also been proposed. Examples of the method include an optical method, an electric resistance method, a charge method, and a microwave method. Among these, the optical system is already on the market for measuring smoke of exhaust gas. Further, a vibration type mass detection method has also been proposed (see, for example, Patent Documents 1 to 3).
US Patent Application Publication No. 2003/0123059 US Pat. No. 6,786,075 JP 2006-208123 A

  However, conventionally proposed PM detection sensors (hereinafter referred to as PM sensors) are expensive and have problems in terms of performance assurance. For example, in the case of an optical PM sensor, the optical lens is contaminated by PM adhesion or the like in the exhaust gas. For this reason, it is difficult to use continuously for a long period of time, for example, periodic maintenance is required to avoid a decrease in PM detection sensitivity and accuracy.

  PM is mainly composed of soot made of solid carbon (hereinafter referred to as “Soot”) and a soluble organic substance (hereinafter referred to as “SOF”), and the soot is mainly collected in the DPF. Therefore, in order to improve the estimation accuracy of the PM accumulation amount on the DPF, it is desirable that the soot and SOF that constitute the PM can be detected separately. However, the conventionally proposed PM sensor could not detect Soot and SOF separately.

  Accordingly, there is a need for the development of an inexpensive PM sensor that can accurately detect and detect the Soot and SOF constituting the PM, and an object of the present invention is to provide a PM sensor that satisfies such a requirement. .

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, according to the PM sensor including the first measuring element having an oxidizing ability for burning PM and the second measuring element having an oxidizing ability for burning PM lower than that of the first measuring element, the above problem can be solved. As a result, the present invention has been completed. More specifically, the present invention provides the following.

  The invention according to claim 1 is a detection sensor for detecting particulate matter contained in exhaust gas discharged from an internal combustion engine, the first measuring element having an oxidizing ability to burn the particulate matter, An electromotive force is generated by the combustion heat of the particulate matter, connected to each of the second measurement element, the first measurement element, and the second measurement element having an oxidizing ability for burning the particulate matter lower than that of the first measurement element. A first thermoelectromotive force generating member and a second thermoelectromotive force generating member, a thermoelectromotive force generated by the first thermoelectromotive force generating member, and a thermoelectromotive force generated by the second thermoelectromotive force generating member. And a detecting means for detecting the amount of the particulate matter based on the difference.

  When the PM sensor according to the present invention is installed in the exhaust passage of the internal combustion engine, PM in the exhaust gas adheres to the first measurement element and the second measurement element. The 1st measuring element which has the oxidation ability which burns PM burns PM at temperature lower than 600 ° C which is the temperature which PM burns naturally. On the other hand, the second measuring element has lower oxidizing ability than the first measuring element, and PM is combusted on the first measuring element and PM is not combusted on the second measuring element. Difference in PM combustion heat occurs. The generated PM combustion heat acts on the first thermoelectromotive force generating member and the second thermoelectromotive force generating member connected to the first measuring element and the second measuring element, respectively, and different thermoelectromotive forces are generated. . Since the difference between these thermoelectromotive forces is proportional to the amount of PM, the amount of PM can be detected with high accuracy by capturing the difference in thermoelectromotive force.

  According to a second aspect of the present invention, in the particulate matter detection sensor according to the first aspect, the detection means does not burn the soot that constitutes the particulate matter, but burns soluble organic matter, and the soot. And the difference between the thermoelectromotive force generated by the first thermoelectromotive force generating member and the thermoelectromotive force generated by the second thermoelectromotive force generating member in each region of the second combustion region where the soluble organic matter burns. And detecting the amounts of each of the soot and the soluble organic matter.

  There is a difference in combustion temperature between Soot and SOF constituting PM, and Soot made of solid carbon has a higher combustion temperature than SOF which is an organic component. For this reason, when the temperature of the measuring element having PM oxidizing ability is in a temperature at which the soot cannot be combusted, that is, in the first combustion region, only the SOF is combusted and a thermoelectromotive force proportional to the combustion heat of the SOF is generated. On the other hand, when the temperature rises and the temperature at which the soot can be combusted, that is, in the second combustion region, a thermoelectromotive force is generated that is proportional to the sum of the combustion heat of the SOF and the combustion heat of the soot. Therefore, in each of the first combustion region and the second combustion region, detection for detecting a difference between the thermoelectromotive force generated by the first thermoelectromotive force generating member and the thermoelectromotive force generated by the second thermoelectromotive force generating member. According to the present invention provided with the means, the SOF and the Soot in the PM are accurately separated based on the difference between the thermoelectromotive force difference in the first combustion region and the thermoelectromotive force difference in the second combustion region. Can be detected.

  The invention according to claim 3 is the particulate matter detection sensor according to claim 1 or 2, wherein the first measurement element and the second measurement element are provided on the same porous body. To do.

  In the PM sensor of the present invention, the first measurement element and the second measurement element are provided on the same porous body. For this reason, according to this invention, a sensor can be reduced in size, it is advantageous on a layout, and material cost can be reduced.

According to a fourth aspect of the present invention, in the particulate matter detection sensor according to any one of the first to third aspects, the first measurement element and the second measurement element are at least Al ₂ O ₃ , SiO ₂ , MgO, and CaO. It is characterized by being a porous body formed from Amakusa porcelain clay.

A measurement element made of a porous material formed from Amakusa porcelain clay has sufficient heat resistance and mechanical strength in a temperature range (up to 800 ° C.) assumed for exhaust gas when used in an exhaust gas flow path. Regarding the mechanical strength, it is considered that SiO ₂ contained in Amakusa porcelain clay plays a role of a binder and develops a strength that can withstand use in an exhaust gas flow path.

  The invention according to claim 5 is the particulate matter detection sensor according to claim 4, wherein the first measurement element and the second measurement element are porous bodies formed using polyvinyl alcohol as a pore-forming agent. It is characterized by that.

  In order to form a porous body using Amakusa porcelain clay as a raw material, it is effective to add and mix a predetermined amount of a pore-forming agent. Specifically, polyvinyl alcohol (hereinafter referred to as PVA) as a pore-forming agent is added to Amakusa porcelain powder in a predetermined amount, mixed, molded, and then fired, whereby PVA is volatilized to form pores. That is, when forming the first measurement element and the second measurement element, PVA is used as a pore-forming agent, so that there are sufficient pores to separate the PM and gas components in the exhaust gas and permeate the gas components. A porous body is obtained. Therefore, according to the present invention, the PM can be detected with high accuracy because the measuring element capable of separating the PM and the gas component in the exhaust gas and transmitting the gas component is used.

  According to a sixth aspect of the present invention, in the particulate matter detection sensor according to any of the first to fifth aspects, the first measurement element includes at least Ag.

  When Ag is supported on the porous body constituting the first measuring element in order to provide high PM oxidation ability, PM can be oxidized and burned at a temperature lower than the temperature at which PM starts spontaneous combustion (600 ° C.). . This is because the outermost surface of Ag supported on the porous body is oxidized and covered with active oxygen atoms, and PM comes into contact therewith, so that oxidation combustion of PM at a low temperature becomes possible. It is done.

  According to the present invention, it is possible to provide a low-priced PM sensor that can separate and detect the Soot and SOF constituting the PM with high accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows the overall configuration of a PM sensor according to an embodiment of the present invention. As shown in FIG. 1, the PM sensor 10 is a sensor that is installed in an exhaust passage 20 of an internal combustion engine (not shown) and detects PM contained in exhaust gas discharged from the internal combustion engine. . The PM sensor 10 includes a first measuring element 11 having an oxidizing ability for burning PM, a second measuring element 12 having an oxidizing ability for burning PM lower than that of the first measuring element 11, and the first measuring element 11 and the second measuring element. A first thermoelectromotive force generating member 13 and a second thermoelectromotive force generating member 14 that are connected to each of the elements 12 and generate electromotive force by the combustion heat of PM, and heat generated by the first thermoelectromotive force generating member 13 Detection means 15 for detecting the amount of PM based on the difference between the electric power and the thermoelectromotive force generated by the second thermoelectromotive force generating member 14.

[Measuring element]
The first measuring element 11 and the second measuring element 12 are preferably porous bodies. In this embodiment, the first measuring element 11 and the second measuring element 12 are porous formed from Amakusa porcelain containing at least Al ₂ O ₃ , SiO ₂ , MgO, and CaO. A mass is used. Amakusa pottery is a raw material for pottery produced in the Amakusa region. The porous body formed using Amakusa porcelain clay has sufficient heat resistance and mechanical strength in the temperature range (maximum of 800 ° C.) assumed for the exhaust gas when used in the exhaust gas flow path. This is considered to be because SiO ₂ contained in Amakusa porcelain clay plays a role of a binder and develops strength that can withstand use in an exhaust gas flow path.

Specifically, in order to use this Amakusa porcelain powder and make a porous body, a predetermined amount of PVA is added as a pore-forming agent, mixed, molded, and then fired to evaporate organic PVA. As a result, pores are formed. The amount of PVA added is preferably Amakusa porcelain clay: PVA = 2: 1 to 4: 1 (weight ratio). About the porous body formed using PVA, when the magnitude | size of a pore is measured with a mercury porosimeter, they are 0.5 micrometer-6.0 micrometers. Further, when its gas permeability is measured, it is 30 mL · cm · cm ² / sec / atm or more, and it has sufficient gas permeability to separate the PM and the gas component in the exhaust gas and permeate the gas component. .

  The porous body itself formed from the above Amakusa porcelain is used for the second measuring element of this embodiment. As in the present embodiment, as the second measuring element, an element having no PM oxidation ability is preferably used. On the other hand, the first measuring element only needs to have higher PM oxidation ability than the second measuring element. In this embodiment, Ag is supported on the porous body formed from the above Amakusa porcelain clay. Is used. Specifically, a material in which Ag is supported by a dip coating method in which a porous material formed from Amakusa porcelain clay is immersed in an aqueous silver nitrate solution is used. The supported amount of Ag is preferably 5 to 30% by weight with respect to the porous body formed from Amakusa porcelain clay. Since Ag is excellent in PM combustion activity at a low temperature, it is possible to oxidize and burn PM at a low temperature on the first measurement element by supporting Ag.

  Here, “oxidation ability” represents the ability to oxidize and burn PM, and a measurement element with high oxidation ability can oxidize and burn PM efficiently at a lower temperature than a measurement element with low oxidation ability. . Further, “having no PM oxidizing ability” means that there is no ability to oxidize and burn any of Soot and SOF that constitute PM.

[Thermo-electromotive force generating member]
The members constituting the first thermoelectromotive force generating member 13 and the second thermoelectromotive force generating member 14 may be any members that generate electromotive force by heat generated by PM combustion. A thermocouple which is an electromotive force generating member is used. The first thermoelectromotive force generating member 13 and the second thermoelectromotive force generating member 14 use thermocouples made of the same material.

[Detection means]
The detection means 15 detects the amount of PM based on the difference between the thermoelectromotive force generated by the first thermoelectromotive force generating member 13 and the thermoelectromotive force generated by the second thermoelectromotive force generating member 14. Since the thermoelectromotive force generated in each thermoelectromotive force generating member is proportional to the PM combustion heat generated in each measuring element, the amount of PM can be detected by obtaining the difference between both thermoelectromotive forces.
Further, the detection means 15 generates the first thermoelectromotive force generating member 13 in each of the first combustion region in which the SOF is combusted without burning the soot constituting the PM and the second combustion region in which the soot and the SOF are combusted. The difference between the generated thermoelectromotive force and the thermoelectromotive force generated by the second thermoelectromotive force generating member 14 can be obtained, and the respective amounts of Soot and SOF can be detected based on the difference. Details of the reason for detecting the amounts of PM, Soot, and SOF will be described later.

According to PM sensor 10 provided with the above composition, the following effects are produced.
When the PM sensor 10 according to the present embodiment is installed in the exhaust flow path 20 of the internal combustion engine, PM in the exhaust gas adheres to the first measurement element 11 and the second measurement element 12. The first measuring element 11 having an oxidizing ability for burning PM burns PM at a temperature lower than 600 ° C., which is a temperature at which PM spontaneously burns. On the other hand, the second measuring element 12 has a lower oxidizing ability than the first measuring element 11, and as shown in FIG. 2, PM burns on the first measuring element 11 and on the second measuring element 12. Under a temperature at which PM does not burn, there is a difference in PM combustion heat between the two. The generated PM combustion heat acts on the first thermoelectromotive force generating member 13 and the second thermoelectromotive force generating member 14 connected to the first measuring element 11 and the second measuring element 12, respectively. Electric power is generated. Specifically, the thermoelectromotive force A generated by the first thermoelectromotive force generating member 13 is larger than the thermoelectromotive force B generated by the second thermoelectromotive force generating member 14. Since the difference between these thermoelectromotive forces is proportional to the PM amount, the PM amount can be detected with high accuracy by capturing the thermoelectromotive force difference AB.

  By the way, there is a difference in combustion temperature between Soot and SOF constituting PM, and Soot made of solid carbon has a higher combustion temperature than SOF which is an organic component. FIG. 3 shows the soot and SOF combustion regions. FIG. 3 shows carbon black (hereinafter referred to as “PM black”) as a substitute for PM in each of a porous body having no PM oxidation ability (second measurement element) and a porous body having PM oxidation ability (first measurement element). CB weight reduction rate when carrying CB) is replaced with PM reduction rate. Moreover, the combustion curve of FIG. 3 was obtained by the same measurement as the test example mentioned later.

Here, in FIG. 3, the temperature when the CB (PM) weight reduction exceeds 10% is called the soot combustion start temperature, and the CB 10% reduction temperature (600 on the porous body having no PM oxidizing ability) The region above (° C.) is called a PM (Soot) natural combustion region. Moreover, the region of CB10% decreasing temperature (T0) to 600 ° C. on the porous body having PM oxidizing ability is called a PM (Soot) oxidizing combustion region, and CB10% decreasing on the porous body having PM oxidizing ability. The region below the temperature (T0) is called the SOF oxidation combustion region. Thus, there is a large difference in the combustion region between the Soot and the SOF that constitute the PM, and by using the difference, the Soot and the SOF can be detected separately.
For example, SOF can be detected at a temperature that can sufficiently oxidize HC in a region below T0 (T1: about 300 ° C.), and PM can be detected at a CB50% decreasing temperature (T2: 500 ° C. in a region above T0. Degree). Here, the reason why CB is reduced by 50% is that the PM combustion rate is the highest when the CB reduction rate is 50%.

  When the temperature of the first measuring element having PM oxidation ability is in the SOF oxidation combustion region where the soot cannot be combusted, that is, in the first combustion region, only SOF is combusted and a thermoelectromotive force proportional to the combustion heat of SOF is generated. The mechanism of the PM sensor 10 when in the first combustion region is shown in FIG. The difference C1 between the thermoelectromotive force A1 of the first thermoelectromotive force generating member 13 where the SOF combustion occurs and the thermoelectromotive force B1 of the second thermoelectromotive force generating member 14 where the SOF combustion does not occur is the combustion heat of the SOF Is proportional to

  Further, when the temperature rises and the soot is combustible in the PM (Soot) oxidation combustion region, that is, in the second combustion region, a thermoelectromotive force is generated that is proportional to the sum of the combustion heat of the SOF and the combustion heat of the Soot. FIG. 5 shows the mechanism of the PM sensor 10 when in the second combustion region. The difference C2 between the thermoelectromotive force A2 of the first thermoelectromotive force generating member 13 where SOF and Soot combustion occurs and the thermoelectromotive force B2 of the second thermoelectromotive force generating member 14 where neither SOF nor Soot combustion occurs is: It is proportional to the combustion heat of PM (Soot + SOF).

  Therefore, as shown in FIG. 6, the first thermoelectromotive force generating member 13 generates the first combustion region (SOF oxidation combustion region) and the second combustion region (PM (Soot) oxidation combustion region). According to the present embodiment including the detection means 15 that detects the difference between the thermoelectromotive force and the thermoelectromotive force generated by the second thermoelectromotive force generating member 14, the heat generation in the first combustion region (SOF oxidation combustion region) is performed. Based on the difference between the power difference and the thermoelectromotive force difference in the second combustion region (PM (Soot) oxidation combustion region), it is possible to accurately separate and detect the SOF and the Soot in the PM.

In addition, a measuring element using a porous material formed from Amakusa porcelain clay has sufficient heat resistance and mechanical properties in the temperature range (maximum 800 ° C.) expected for exhaust gas when used in the exhaust gas flow path 20. Strength. This is considered to be because SiO ₂ contained in Amakusa porcelain clay plays a role of a binder and develops strength that can withstand use in the exhaust gas flow path 20. Moreover, since the porous body formed from Amakusa porcelain has sufficient gas permeability, PM contained in exhaust gas can be detected efficiently.

  According to the 1st measuring element 11 and the 2nd measuring element 12 which consist of a porous body formed using polyvinyl alcohol (PVA) as a pore formation agent, PM in a waste gas and a gas component are isolate | separated and a gas component is separated. Can be transmitted. For this reason, the 1st measuring element 11 and the 2nd measuring element 12 using the porous body formed using PVA have sufficient pores to separate the PM and the gas component in the exhaust gas and permeate the gas component. PM can be detected with high accuracy.

  Further, since Ag is supported on the porous body constituting the first measuring element 11, the PM can be oxidized and burned at a temperature lower than the temperature at which PM starts spontaneous combustion (600 ° C.). This is because the outermost surface of Ag supported on the porous body is oxidized and covered with active oxygen atoms, and PM comes into contact therewith, so that oxidation combustion of PM at a low temperature becomes possible. It is done.

  From the above, according to the PM sensor 10 according to the present embodiment, by detecting the combustion heat generated by the low-temperature oxidation combustion of PM by Ag as the thermoelectromotive force, it is inexpensive and can detect the separation between the Soot and the SOF. A possible high-precision PM sensor can be provided.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
For example, the first measurement element 11 and the second measurement element 12 can be provided on the same porous body. Specifically, by immersing a part of the porous body formed from Amakusa porcelain in an aqueous silver nitrate solution, Ag can be supported on a part thereof, and the first measurement element 11 and the second measurement element 12 are supported. Can be provided on the same porous body. According to this modification, the PM sensor can be reduced in size, which is advantageous in terms of layout and can reduce the material cost.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

<Test Example 1>
Conventionally, PM burning activity has been achieved for an element made of a porous material made of Amakusa porcelain clay (hereinafter referred to as a ceramic porous element) and an element in which Ag is supported (hereinafter referred to as an Ag-supporting ceramic porous element). The PM combustion activity was compared with a La _0.9 K _0.1 CoO ₃ porous body (hereinafter referred to as LKC porous body element) known as a porous body having s. The production of each element and the evaluation method were as follows.

[Production of element]
A predetermined amount of PVA as a pore-forming agent was added to Amakusa porcelain powder and mixed. The mixed powder was subjected to a molding process at 20 MPa for 10 minutes using a tablet molding machine. After the molding, firing was performed at 800 ° C. to obtain a ceramic porous body element having pores formed by volatilization of PVA.
Further, the obtained ceramic porous body element was immersed in a silver nitrate aqueous solution (dip coating method) to support 5% by weight of Ag, thereby obtaining an Ag-supporting ceramic porous body element.

  Further, a predetermined amount of PVA as a pore-forming agent was added to and mixed with the LKC precursor powder containing a predetermined amount of La, K, and Co constituting the LKC porous body and prepared by the evaporation to dryness method. The mixed powder was subjected to a molding process at 20 MPa for 10 minutes using a tablet molding machine. By firing at 1100 ° C. after molding, an LKC porous element having pores formed by volatilization of PVA was obtained.

[Evaluation methods]
Each manufactured device was loaded with 5.0% by weight of CB as an alternative to PM. About each element which carry | supported CB, TG measurement was performed on the following conditions, and PM combustion activity was evaluated by comparing those thermogravimetric changes. In the evaluation, a contact state between PM and the element in the exhaust gas was simulated by an LC method (loose contact method) in which CB was sprinkled on the element for a certain period of time using a spatula.

Measuring device: “DTG-60H” manufactured by Shimadzu Corporation
Sample: 5.0 wt% CB / element (about 10 mg)
Atmosphere: Temperature rise rate in air: 10 ° C./min up to 800 ° C. Contact state: Mixing for a certain time with a spatula

  FIG. 7 shows a TG chart obtained as a result of the TG measurement. Comparing the temperatures at which the weight loss due to CB combustion was greatest (hereinafter referred to as Tmax) for each element, the ceramic porous body had the highest temperature, followed by the LKC porous element. Met. In these elements, Tmax was around 600 ° C., whereas Tmax of the Ag-supporting ceramic porous body element was less than 500 ° C. From this result, it was confirmed that the element in which Ag is supported on the element made of a porous body formed from Amakusa porcelain can oxidize and combust PM at a lower temperature than the conventional one and has high PM combustion activity.

<Example 1>
The effect of the present invention was verified using exhaust gas discharged from a commercial diesel generator. For the verification, a test apparatus 50 shown in FIG. 8 was used. Specifically, the entire amount of exhaust gas discharged from the diesel generator 60 was taken into the test apparatus 50 and a PM detection test was performed. The test unit was installed in the quartz glass tube 61 (inner diameter φ50 mm), and an electric heater 56 was installed outside thereof to adjust the ambient temperature to a predetermined temperature. The temperature was set with reference to FIG. 3 as described above.

  In the quartz glass tube 61, a sensor element 51 made of a porous body having PM oxidizing ability and a reference element 52 made of a porous body not having PM oxidizing ability are arranged perpendicular to the gas flow, Thermoelectromotive force generating members 53 and 54 made of thermocouples were connected to each, and the voltage at the output end was measured. In addition, in order to measure gas temperature, the gas temperature sensor (not shown) which consists of thermocouples was installed between both elements.

The sensor element 51 and the reference element 52 were formed in a tablet shape having a diameter of 20 mm × 5 mm, holes were formed on the side surfaces, and thermocouples were inserted into the holes to form elements. A porous body serving as an element was produced by the following procedure.
The raw material used was Amakusa porcelain clay powder, which is a raw material for pottery produced in the Amakusa region. In order to obtain a porous body, PVA was added as a pore-forming agent so that the volume ratio was 1: 3 with respect to Amakusa porcelain clay. After the addition, the mixture was kneaded, the powder was filled in a mold, and uniaxial pressure molding was performed at 20 MPa for 10 minutes. The molded body was fired in air at 800 ° C. for 5 hours to produce a porous body. The porous body serving as the sensor element 51 was further immersed in an aqueous silver nitrate solution to carry Ag. The amount of Ag supported was 5% by weight.

The PM detection test was performed according to the following procedure.
The sensor element 51 and the reference element 52 were installed in the quartz glass tube 61, and the temperature was stabilized at 500 ° C. with the electric heater 56. Next, the diesel generator 60 was started in a no-load state, and exhaust gas was introduced into the test unit. After circulating the exhaust gas for a certain time, the diesel generator 60 was stopped. Meanwhile, the thermoelectromotive force output from the sensor element 51 and the reference element 52 was monitored, and the difference was calculated. The PM concentration in the exhaust gas is extracted from the test line with a constant flow rate of gas with a pump 57, filtered through a Teflon (registered trademark) filter 58, and the PM concentration is calculated from the difference in weight before and after the filter. did.

<Comparative Example 1>
The same operation as in Example 1 was performed except that the set temperature of the electric heater 56 was set to 350 ° C. instead of 500 ° C.

<Example 2>
The same operation as in Example 1 was performed except that a resistor corresponding to 31% of the rated output was connected to the diesel generator 60.

<Example 3>
The same operation as in Example 1 was performed except that a resistor corresponding to 44% of the rated output was connected to the diesel generator 60.

Consider the results of Example 1.
FIG. 9 shows the relationship between time and thermal electromotive force difference in the PM detection test of Example 1, and FIG. 10 shows the relationship between time and sensor temperature.
As shown in FIGS. 9 and 10, since the thermoelectromotive force from the sensor element 51 and the reference element 52 is the same before the diesel generator 60 is started, a difference in thermoelectromotive force does not occur. When the diesel generator 60 is started and exhaust gas is introduced into the test section, the PM (SOF + Soot) adhering to the sensor element 51 undergoes oxidative combustion, resulting in a difference in thermoelectromotive force from the reference element 52. The thermoelectromotive force difference decreases with time and becomes constant at a certain point. Although this is heated to 500 ° C. by the electric heater 56, the temperature of the test part is lowered by the flow of exhaust gas having a temperature lower than that, and the sensor temperature is stabilized at about 250 ° C. This is because only the SOF shows the difference in thermoelectromotive force generated by oxidative combustion.
Thereafter, when the diesel generator 60 is stopped, the thermoelectromotive force difference rises again and reaches a peak, and then starts to decrease, and the thermoelectromotive force difference disappears. This is because the exhaust gas no longer flows, and the electric heater 56 heats it again to 500 ° C., so that the soot accumulated without being oxidized and burned during the exhaust gas flow is oxidized and burned, resulting in a thermoelectromotive force difference. It is. Therefore, it has been found that by controlling the sensor temperature to a predetermined temperature, the soot and SOF in the PM can be detected separately.

Consider the results of Comparative Example 1.
FIG. 11 shows the relationship between the time and the thermoelectromotive force difference in the PM detection test of Comparative Example 1, and FIG. 12 shows the relationship between the time and the sensor temperature.
As shown in FIGS. 11 and 12, since the thermoelectromotive force from the sensor element 51 and the reference element 52 is the same before the diesel generator 60 is started, no difference in thermoelectromotive force occurs. When the diesel generator 60 is started and exhaust gas is introduced into the test unit, the temperature when the PM adheres to the sensor element 51 is as low as 350 ° C. because the set temperature of the electric heater 56 is 350 ° C. Burns and a thermoelectromotive force difference of the difference occurs. However, since the sensor temperature is lowered to 200 ° C. or less due to exhaust gas inflow, SOF cannot be oxidized and burned, and a difference in thermoelectromotive force from the reference element 52 does not occur.
After that, when the diesel generator 60 is stopped and the exhaust gas does not flow into the test section, even if it is heated by the electric heater 56, the attached soot does not undergo oxidative combustion, so no thermoelectromotive force difference occurs. From this result, it was found that accurate PM detection cannot be performed unless the sensor temperature is controlled at a temperature at which the soot can be oxidized and combusted.

Consider the results of Examples 2 and 3.
The relationship between the time and the thermoelectromotive force difference in the PM detection test of Examples 1 to 3 is plotted in FIG. 13, the relationship between the time and the sensor temperature is plotted in FIG. 14, and the relationship between the generated PM concentration and the thermoelectromotive force difference is plotted. The obtained figure is shown in FIG. Table 1 shows the PM concentration and the thermoelectromotive force difference immediately after starting the diesel generator 60 (part P in FIG. 13).

  In the second and third embodiments, the generation amount of PM is changed by changing the load of the diesel generator 60 with respect to the first embodiment. As shown in FIGS. 13 to 15 and Table 1, in Examples 2 and 3 in which a load is applied to the diesel generator 60 to reduce the PM generation amount, the difference in thermoelectromotive force is reduced as compared with Example 1. I understood that. It was also found that the degree of decrease is proportional to the load applied to the diesel generator 60. Therefore, from this result, it was confirmed that there is a good correlation between the thermoelectromotive force difference and the PM concentration.

It is a figure showing the whole PM sensor composition of the present invention. It is a figure for demonstrating the mechanism of this invention. It is a figure which shows the combustion temperature of Soot and SOF. It is a figure which shows the mechanism of PM sensor when it exists in a 1st combustion area. It is a figure which shows the mechanism of PM sensor when it exists in a 2nd combustion area | region. It is a figure for demonstrating the mechanism of this invention. 6 is a diagram showing a TG chart obtained as a result of Test Example 1. FIG. It is a figure which shows the whole structure of a test apparatus. It is a figure which shows the relationship between the time of Example 1, and a thermoelectromotive force difference. It is a figure which shows the relationship between the time of Example 1, and sensor temperature. It is a figure which shows the relationship between the time of the comparative example 1, and a thermoelectromotive force difference. It is a figure which shows the relationship between the time of Comparative Example 1, and sensor temperature. It is a figure which shows the relationship between the time of Examples 1-3 and a thermoelectromotive force difference. It is a figure which shows the relationship between the time of Examples 1-3, and sensor temperature. It is a figure which shows the relationship between PM density | concentration and a thermoelectromotive force difference.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 PM sensor 11 1st measuring element 12 2nd measuring element 13 1st thermoelectromotive force generating member 14 2nd thermoelectromotive force generating member 15 Detection means

Claims (6)

A detection sensor for detecting particulate matter contained in exhaust gas discharged from an internal combustion engine,
A first measuring element having an oxidizing ability to burn the particulate matter;
A second measuring element having an oxidizing ability for burning the particulate matter lower than that of the first measuring element;
A first thermoelectromotive force generating member and a second thermoelectromotive force generating member connected to each of the first measuring element and the second measuring element and generating electromotive force by the combustion heat of the particulate matter;
Detecting means for detecting the amount of the particulate matter based on the difference between the thermoelectromotive force generated by the first thermoelectromotive force generating member and the thermoelectromotive force generated by the second thermoelectromotive force generating member; A particulate matter detection sensor comprising:   The detection means includes the first heat in each of the first combustion region where the soot composing the particulate matter does not burn but the soluble organic matter burns, and the second combustion region where the soot and the soluble organic matter burn. The amount of each of the soot and the soluble organic matter is detected based on the difference between the thermoelectromotive force generated by the electromotive force generating member and the thermoelectromotive force generated by the second thermoelectromotive force generating member. Item 1. The particulate matter detection sensor according to Item 1.   The particulate matter detection sensor according to claim 1, wherein the first measurement element and the second measurement element are provided on the same porous body. The first measuring device and the second measuring element are all at least _Al 2 _{O 3,} SiO 2, MgO, and from the claims 1, characterized in that a porous body formed from Amakusa clay containing CaO 3 Or a particulate matter detection sensor.   The particulate matter detection sensor according to claim 4, wherein the first measurement element and the second measurement element are porous bodies formed using polyvinyl alcohol as a pore-forming agent.   The particulate matter detection sensor according to claim 1, wherein the first measurement element contains at least Ag.

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