JP2004340049A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of realizing effective combustion and removal of particulates with the aid of plasma, low manufacturing cost, and high capturing rate of particulates. <P>SOLUTION: Each of rod-shaped electrodes 9, 10 is inserted into part of a flow passage 5 not sealed with a plug 8 from the inlet side and outlet side of a filter body 7 of a porous honeycomb structure formed out of ceramic such as cordierite. Discharging is developed between the rod-shaped electrode 9 inserted from the inlet side and the rod-shaped electrode 10 inserted from the outlet side, and voltage is applied to generate plasma in the exhaust gas 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to an exhaust purification device for removing particulates from exhaust gas of an internal combustion engine such as a diesel engine.
[0002]
[Prior art]
Particulate matter (particulate matter) discharged from the diesel engine is mainly composed of soot composed of carbonaceous material and SOF component (Soluble Organic Fraction: soluble organic component) composed of a high-boiling hydrocarbon component. Although it has a composition containing a small amount of sulfate (mist-like sulfuric acid component), as shown in FIG. 6, an exhaust pipe 3 through which exhaust gas 2 from a diesel engine 1 flows as a measure for reducing this kind of particulates. It is considered that a particulate filter 4 is provided in the middle of the process.
[0003]
As shown in detail in FIG. 7, the particulate filter 4 mainly includes a filter body 7 having a porous honeycomb structure made of a ceramic such as cordierite or the like. The inlets of the passages 5 are alternately plugged with plugs 8, and the outlets of the channels 5 whose inlets are not plugged are plugged by plugs 8. Only the exhaust gas 2 that has passed through the partitioning porous thin wall 6 is discharged downstream, and particulates are collected on the inner surface of the porous thin wall 6.
[0004]
The particulates in the exhaust gas 2 are collected and deposited on the inner surface of the porous thin wall 6, and are spontaneously combusted and removed when the exhaust gas shifts to an operation region where the exhaust temperature is high. However, for example, in a vehicle such as a route bus in Tokyo that runs only on congested roads, since the operation at a required predetermined temperature or more does not continue for a long time, the amount of accumulation is larger than the amount of processed particulates. There is a possibility that the particulate filter 4 may be clogged upward.
[0005]
For this reason, development of a plasma-assisted exhaust gas purifying device has been promoted so that particulates can be satisfactorily burned and removed even in an operating region where the exhaust gas temperature is low. When plasma is generated, the exhaust gas 2 is excited, oxygen becomes ozone, NO becomes NO ₂ , and these exhaust gas excited components are in an activated state. However, it is possible to satisfactorily burn and remove the particulates.
[0006]
Prior art documents relating to a plasma-assisted exhaust gas purifying apparatus are also disclosed in, for example, Patent Document 1 below.
[0007]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2002-501813
[Problems to be solved by the invention]
However, in a conventional plasma-assisted exhaust gas purification apparatus, as described in Patent Document 1, a dielectric is formed between an outer electrode and an inner electrode made of perforated cylindrical stainless steel. A ceramic pellet is filled, and an exhaust gas 2 is flown so as to pass through a packed layer of the pellet to collect particulates in the exhaust gas 2, while discharging between the outer electrode and the inner electrode to generate a plasma. In general, the processing cost for the outer electrode, the inner electrode, and the pellets of ceramics is high, and the production cost is increased.
[0009]
In addition, since the substantial filter portion is constituted by the packed layer of pellets, there is also a problem that the mesh is too coarse and a high collection rate cannot be obtained as with a normal ceramic particulate filter.
[0010]
The present invention has been made in view of the above-described circumstances, and an exhaust purification device capable of effectively burning and removing particulates with the aid of plasma, and having a low manufacturing cost and a high particulate collection rate. It is intended to provide.
[0011]
[Means for Solving the Problems]
The present invention is directed to a filter main body formed of a porous material and having a large number of flow passages through which exhaust gas flows formed in a honeycomb shape, and alternately selecting one of an inlet side and an outlet side of each flow path of the filter main body. An exhaust purification device comprising: a plug to be sealed; and a particulate thin film in the exhaust gas that can pass through a porous thin wall defining each of the flow paths. From both the side and the outlet side, a rod-shaped electrode is inserted into some of the unsealed flow paths, and discharge occurs between the rod-shaped electrode inserted from the inlet side and the rod-shaped electrode inserted from the outlet side. Then, a voltage can be applied so as to generate plasma in the exhaust gas.
[0012]
Thus, in this way, the existing ceramic particulate filter is utilized as it is, and a low-cost rod-shaped electrode is inserted into a part of each flow path of the filter body to perform electrical wiring. A plasma-assisted exhaust gas purification device can be obtained, and a simple layout of the rod-shaped electrodes and a highly flexible layout are realized by using the honeycomb-shaped flow passage of the filter body, resulting in good workability in manufacturing. Therefore, the manufacturing cost is significantly reduced as compared with the related art.
[0013]
On the other hand, in use, the exhaust gas passing through the filter body always flows through the porous thin wall, and the particulates in the exhaust gas are collected on the porous thin wall. As high as the particulate filter, a high particulate collection rate is secured.
[0014]
In addition, when necessary, a voltage is applied between the rod-shaped electrodes to discharge in the exhaust gas, thereby exciting the exhaust gas. As a result, oxygen becomes ozone and NO becomes NO immediately in the vicinity of the collected particulates. _Since these exhaust gas excited components are in an activated state, the oxidation reaction of the particulates collected on the porous thin wall is promoted by the exhaust gas excited components, and the operation at a low exhaust gas temperature is performed. Even in the state, the particulates are favorably burned and removed.
[0015]
Further, in the present invention, it is preferable that the oxidation catalyst is integrally carried on the entire filter body. In this case, the oxidation reaction of the particulates collected in the filter body is promoted, and the ignition temperature is lowered. As a result, the flammability of the particulates in the operating state where the exhaust gas temperature is low is further enhanced, so that the better elimination of the particulates is achieved.
[0016]
Further, the surface of the rod-shaped electrode may be coated with an oxidation catalyst, or the rod-shaped electrode itself may be made of a catalyst metal that forms an oxidation catalyst. In this case, the particulates adhered and deposited on the rod-shaped electrode and its peripheral portion may be used. Is efficiently and early burned and removed with the assistance of combustion by the oxidation catalyst.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
FIGS. 1 to 5 show an example of an embodiment of the present invention, and the portions denoted by the same reference numerals as those in FIGS. 6 and 7 represent the same components.
[0019]
As schematically shown in FIGS. 1 and 2, the exhaust gas purifying apparatus of the present embodiment utilizes the ceramic particulate filter 4 described above with reference to FIG. 7 as a main component. More specifically, plugs 8 are used to plug a filter body 7 having a porous honeycomb structure made of ceramic such as cordierite from both the inlet side (left side in FIG. 1) and the outlet side (right side in FIG. 1). The rod-shaped electrodes 9 and 10 are inserted into some of the unsealed flow paths 5 (see FIG. 2), and the rod-shaped electrodes 9 inserted from the inlet side and the rod-shaped electrodes 10 inserted from the outlet side are reciprocated. It is configured such that a voltage can be applied to generate a plasma in the exhaust gas 2 by discharging between them.
[0020]
That is, the external connection terminal 12 is arranged to penetrate the end face of the casing 11 enclosing the filter body 7 on the entrance side, and the external connection terminal 13 is arranged to penetrate the end face of the casing 11 on the exit side. All of the inserted rod-shaped electrodes 9 are connected to the external connection terminals 12, and all of the inserted bar-shaped electrodes 10 from the outlet side are connected to the external connection terminals 13.
[0021]
A power supply 15 is connected to each of the external connection terminals 12 and 13 via a discharge control unit 14. In this embodiment, a battery mounted on a vehicle is assumed as the power supply 15. Then, the voltage of the power supply 15 is raised to an appropriate dischargeable voltage by the discharge control unit 14, and then the power is supplied to the rod-shaped electrodes 9, 10 via the external connection terminals 12, 13.
[0022]
Here, one of the rod-shaped electrodes 9 and 10 inserted into the filter body 7 from both the inlet side and the outlet side forms an anode and the other forms a cathode. If the layout is such that the distance between them is substantially equal, for example, a check pattern pattern in which the rod-shaped electrodes 9 and 10 are arranged in a staggered manner as shown in FIG. It is possible to form an alternating arrangement pattern in which the rod-shaped electrodes 9, 10 are arranged linearly with a phase shift, or a concentric pattern in which the rod-shaped electrodes 9, 10 are alternately arranged so as to form a concentric shape as shown in FIG. It is.
[0023]
In the present embodiment, the oxidation catalyst is integrally carried on the entire filter body 7, and the surface of each of the rod-shaped electrodes 9, 10 is also coated with the oxidation catalyst.
[0024]
In this way, the existing ceramic particulate filter 4 is utilized as it is, and the rod-shaped electrodes 9 and 10 with low processing cost are inserted into a part of each flow path 5 of the filter body 7 so as to be electrically connected. By performing simple wiring, a plasma-assisted exhaust gas purifying device can be obtained. In addition, by using the honeycomb-shaped flow path 5 of the filter body 7, simple installation of the rod-shaped electrodes 9 and 10 and a layout having a high degree of freedom can be realized. As a result, the workability in terms of manufacturing is improved, so that the manufacturing cost is significantly reduced as compared with the related art.
[0025]
On the other hand, in the use thereof, the exhaust gas 2 passing through the filter body 7 always flows through the porous thin wall 6, and the particulates in the exhaust gas 2 are collected on the porous thin wall 6. A high particulate collection rate, which is the same as that of the ceramic particulate filter described above, is secured.
[0026]
In addition, when necessary, a voltage is applied between the rod-shaped electrodes 9 and 10 by the discharge control unit 14 to cause a discharge in the exhaust gas 2, thereby exciting the exhaust gas 2. In the above, since oxygen becomes ozone and NO becomes NO ₂ , and these exhaust gas excited components are in an activated state, the oxidation reaction of the particulates collected on the porous thin wall 6 causes the exhaust gas to react with the exhaust gas. Accelerated by the excited components, the particulates are satisfactorily burned off even in an operation state where the exhaust gas temperature is low.
[0027]
Here, particularly in the present embodiment, since the oxidation catalyst is integrally supported on the entire filter main body 7, the oxidation reaction of the particulates collected in the filter main body 7 is promoted, and the ignition temperature decreases, As a result of further improving the flammability of the particulates in an operating state where the exhaust gas temperature is low, better combustion removal of the particulates is realized.
[0028]
Further, in the present embodiment, since the oxidation catalyst is also coated on the surfaces of the rod-shaped electrodes 9 and 10, the particulates adhered and deposited on the rod-shaped electrodes 9 and 10 and the periphery thereof support combustion by the oxidation catalyst. As a result, it is efficiently burned and removed early.
[0029]
Therefore, according to the above embodiment, it is possible to effectively burn and remove the particulates collected in the filter main body 7 with the assistance of the plasma even in an operation state in which the exhaust gas temperature is low such as during a light load operation. In addition, the manufacturing cost can be greatly reduced as compared with the related art, and a high collection rate of particulates can be secured, which is the same as that of the conventional ceramic particulate filter.
[0030]
It should be noted that the exhaust gas purification apparatus of the present invention is not limited to the above-described embodiment, and it goes without saying that various changes can be made without departing from the spirit of the present invention.
[0031]
【The invention's effect】
According to the exhaust gas purification apparatus of the present invention described above, various excellent effects as described below can be obtained.
[0032]
(I) According to the invention described in claim 1 of the present invention, even in an operation state where the exhaust gas temperature is low such as during a light load operation, the particulate matter collected in the filter body is effectively reduced by the assist of plasma. It is possible to significantly reduce the production cost as compared with the conventional ceramic particulate filter, and it is possible to secure a high particulate matter collection rate that is the same as that of a conventional ceramic particulate filter.
[0033]
(II) According to the invention described in claim 2 of the present invention, the oxidation reaction of the particulate matter collected in the filter main body can be promoted by the oxidation catalyst. More reliable burning and removal of particulates can be realized.
[0034]
(III) According to the third and fourth aspects of the present invention, the particulates adhered and deposited on each rod-shaped electrode and its peripheral portion can be burned and removed efficiently and early by efficiently assisting combustion with an oxidation catalyst. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram schematically showing an example of an embodiment for carrying out the present invention.
FIG. 2 is a cross-sectional view showing a state where a rod-shaped electrode is inserted into a flow path of the filter body of FIG.
FIG. 3 is a front view showing an example in which the rod-shaped electrodes of FIG. 1 are arranged in a check pattern.
FIG. 4 is a front view showing an example in which the rod-shaped electrodes of FIG. 1 are arranged in an alternating arrangement pattern.
FIG. 5 is a front view showing an example in which the rod electrodes of FIG. 1 are arranged in a concentric pattern.
FIG. 6 is a schematic diagram illustrating an arrangement state of a conventional particulate filter.
FIG. 7 is a sectional view showing details of the particulate filter of FIG. 6;
[Explanation of symbols]
2 Exhaust gas 5 Flow path 6 Porous thin wall 7 Filter body 8 Plug body 9 Rod electrode 10 Rod electrode 14 Discharge control unit 15 Power supply

Claims (4)

A filter body made of a porous material and having a large number of channels formed in a honeycomb shape through which exhaust gas flows, and a plug body for alternately plugging one of an inlet side and an outlet side of each channel of the filter body. An exhaust purification device comprising: a porous thin wall that partitions each of the flow paths, so that particulates in exhaust gas can be collected. From both sides, a rod-shaped electrode is inserted into a part of the unsealed flow path, and the rod-shaped electrode inserted from the inlet side and the rod-shaped electrode inserted from the outlet side are discharged between each other to exhaust gas. An exhaust gas purification apparatus characterized in that a voltage can be applied to generate plasma therein. 2. The exhaust gas purifying apparatus according to claim 1, wherein an oxidation catalyst is integrally carried on the entire filter body. The exhaust purification device according to claim 1 or 2, wherein an oxidation catalyst is coated on a surface of the rod-shaped electrode. 3. The exhaust gas purifying apparatus according to claim 1, wherein the rod-shaped electrode itself is made of a catalyst metal forming an oxidation catalyst.

Images