JP2006342730A - Exhaust processing system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a cohesive device capable of holding insulation with a simple constitution, without causing electric current leakage by a deposit of an exhaust particulate to an insulator part even in the presence of the exhaust particulate of the high concentration, in an exhaust processing system of an internal combustion engine using corona discharge. <P>SOLUTION: A corona discharge electrode 2 and a conductive net 3 being a dust collecting electrode are oppositely arranged in an exhaust passage 11 of the cohesive device 1. The corona discharge electrode 2 has a discharge part 22 positioned in a substantially central part of the exhaust passage 11, a conductive part 21 introducing high voltage from an external power source to the discharge part 22, and the insulator part 23 holding the outer periphery of the conductive part 21. A Pt carrying part projecting in a ring shape is arranged on the outer periphery of the insulator part 23, and the insulation is held by removing the sticking exhaust particulate by the catalytic action of Pt included on at least its outside surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust treatment apparatus including an aggregator that aggregates exhaust particulates contained in exhaust gas of an internal combustion engine by using corona discharge.

  In recent years, exhaust particulate (PM), which is a harmful substance discharged from a diesel engine, has become a major problem. As a method for treating exhaust particulates, for example, an apparatus is known in which after colliding with a collision guide member provided in an exhaust pipe and aggregating it, it is negatively charged by a charged body and electrically collected. However, agglomeration by collision does not provide a sufficient agglomeration effect, and there is a risk that the fine particles may be released through the apparatus without agglomeration.

Therefore, a method of electrostatically aggregating fine particles using corona discharge has been studied. Patent Document 1 below discloses an apparatus in which a plurality of linear discharge electrodes extending in the axial direction of a cylindrical body are arranged in a cylindrical body into which a gas containing smoke or exhaust particulates flows. In this device, a corona discharge is generated by applying a high voltage between the discharge electrode and the cylindrical body peripheral wall surrounding the discharge electrode as a dust collecting electrode. Due to this corona discharge, the fine particles in the exhaust are charged and moved to the dust collecting electrode side by electrostatic force and aggregate. As the aggregated particles grow, they fall by their own weight and can be recovered.
JP 2003-144799 A

Further, in Patent Document 2 below, a device in which a discharge electrode provided with a plurality of needle-like protrusions on the outer periphery of a round bar portion is arranged in an inner cylinder of a cyclone-structured agglomerator to generate corona discharge. Is disclosed. Fine particles aggregated and deposited on the inner cylinder wall are separated by a gas flow, and collected by a particle collector through a cyclone type particle separator.
JP-A-5-222915

  However, under the condition that exhaust particulates are present at a high concentration in the exhaust gas flowing into the aggregator, the exhaust particulates are likely to deposit on the exhaust particulates on the insulator portion that holds the discharge electrode. In this case, even if a negative high voltage is applied to the discharge electrode, a current flows in the accumulated exhaust particulates (current leakage), so it is difficult to generate negative ions in the exhaust passage to charge the exhaust particulates. There was a problem to become.

  To solve this problem, in the apparatus of Patent Document 2, the discharge pipe of the cyclone type particle separator is connected to the housing of the aggregator, and clean gas from the cyclone type particle separator is blown onto the insulator part to prevent adhesion of fine particles. is doing. However, the configuration is complicated, for example, a cyclone type particle separator is installed downstream and connection piping is required.

  Therefore, an object of the present invention is an agglomeration capable of maintaining insulation in an exhaust gas processing apparatus for an internal combustion engine using corona discharge, even in the presence of high-concentration exhaust particulates, without causing current leakage due to the accumulation of exhaust particulates on the insulator. It is to realize a vessel with a simple configuration, and to exhibit good discharge characteristics and enable efficient aggregation.

The exhaust treatment apparatus according to the first aspect of the present invention is provided with a discharge electrode and a dust collection electrode in an exhaust pipe of an internal combustion engine, and a high voltage is applied between these electrodes to generate corona discharge, thereby charging exhaust particulates. A coagulator for coagulation is provided.
In the aggregator, the discharge electrode includes a discharge part located substantially at the center of the exhaust passage formed in the aggregator, a conductive part for guiding a high voltage from an external power source to the discharge part, and an outer periphery of the conductive part. It has a lever part to hold. Furthermore, an insulation holding means having an oxidation catalyst layer that covers a part of the outer peripheral surface of the insulator portion in the circumferential direction is provided, and the exhaust particles adhering to the insulator portion are purified by the oxidation catalyst to maintain the insulation.

  In a state where high concentration exhaust particles are present, there is a problem that current leakage occurs through the exhaust particles adhering to the insulator of the discharge electrode exposed to the exhaust flow. The insulating holding means of the present invention oxidizes and removes the attached exhaust particulates by the action of the oxidation catalyst, so that the attached exhaust particulates are divided and no current leakage occurs. Thereby, corona discharge can be efficiently generated, and the exhaust particulates in the exhaust can be charged by the generated ions and electrostatically collected on the dust collecting electrode. Therefore, it is possible to maintain the insulation of the discharge electrode with a simple configuration and improve the agglomeration performance due to corona discharge without significant change in apparatus or configuration.

  In the invention of claim 2, the insulating holding means has a ring-shaped projecting portion projecting in a radial direction from the outer peripheral surface of the insulator portion, and an oxidation catalyst is contained in at least the outer surface of the insulating projecting portion as the oxidation catalyst layer. .

  Specifically, when the insulating holding means is constituted by a ring-shaped protruding portion, a step is formed between the insulator portion and the other surface, so that the effect of separating exhaust particulates can be enhanced and the surface area can be increased. Since it becomes large, the removal performance by an oxidation catalyst improves.

  In the invention of claim 3, the ring-shaped projecting portion is provided separately from the insulator main body.

  If the ring-shaped projecting portion is separated from the insulator main body, it is easy to manufacture, and the oxidation catalyst is easily supported, and the cost can be reduced while maintaining the cutting performance.

  In a fourth aspect of the present invention, the ring-shaped protrusion has an outer diameter shape with different diameters in which thin portions and thick portions are alternately formed in the circumferential direction.

  By making a part of the ring-shaped protrusion thin, the cost can be reduced, and the surface area is increased, so that the removal performance by the oxidation catalyst is improved.

  In the invention of claim 5, the oxidation catalyst is Pt.

  Pt is preferable because it is excellent in exhaust gas purification performance.

  In a sixth aspect of the present invention, the dust collecting electrode is a ground electrode disposed downstream or on the outer periphery of the discharge electrode.

  When a negative DC high voltage is applied to the discharge electrode, the exhaust particles in the vicinity are negatively charged by corona discharge, and move and aggregate to the downstream or outer peripheral ground electrode, so that they can be collected as aggregated particles.

  In the invention of claim 7, the dust collection electrode is made of a conductive net or a conductive porous body disposed across the exhaust passage at a position downstream of the discharge electrode.

  Preferably, when the dust collection electrode is formed of a conductive structure having a large number of air holes that do not prevent passage of the aggregated exhaust particulates, the aggregated particles can be easily collected.

  In the invention of claim 8, the discharge part of the discharge electrode has a plurality of protrusions protruding radially.

  If formed in this way, corona discharge can be uniformly generated in the exhaust passage.

  A first embodiment in which the present invention is applied to an exhaust treatment device for a diesel engine will be described below with reference to the drawings. FIG. 1 (a) shows a configuration of an aggregator 1 provided in an exhaust treatment device. In a housing H connected to an exhaust pipe of an engine, a corona discharge electrode 2 as a discharge electrode and a dust collection electrode are used. A certain conductive net 3 is arranged oppositely. The housing H is a cylindrical tube having a diameter larger than that of the exhaust pipe. The inside of the housing H is an exhaust passage 11 having a circular passage cross section, and is connected to a straight portion of the exhaust pipe at both end small diameter portions. The corona discharge electrode 2 is attached to the holding plate 13 that closes the opening 12 provided on the tube wall of the housing H so as to penetrate therethrough. In the corona discharge electrode 2, a male screw portion provided on the outer periphery of the insulator portion 23 is screwed into a female screw portion provided on the holding plate 13, and is fastened and fixed by a nut 14.

  The corona discharge electrode 2 includes a conductive portion 21 whose base end side (upper end side in the figure) protruding outside the housing H is connected to a DC high voltage power source (not shown), and a conductive part 21 provided on the distal end side (lower end side in the figure). The discharge part 22 to which a high voltage is guided through the part 21 and the insulator part 23 that holds the outer periphery of the conductive part 21 are included. The leading end side of the conductive portion 21 extends through the tube wall of the housing H in a direction crossing the exhaust flow in the exhaust passage 11, and the leading end portion of the conductive portion 21 exposed from the insulator portion 23 is the axis C of the exhaust passage 11. It bends in an L shape at the position and goes downstream along the axis C.

  As shown in FIG. 1B, the discharge part 22 of the corona discharge electrode 2 is fixed to the tip of the L-shaped bent part of the conductive part 21. For example, as shown in FIG. 1 (c), the discharge portion 22 is formed of a star-shaped flat plate having a large number of protrusions 2 a, and the protrusion 2 a is disposed so as to be directed in a radial direction with respect to the axis C of the housing H. . Thus, by forming a large number of protrusions 2a radially at the tip of the discharge portion 22, the discharge rate can be increased, and corona discharge can be generated uniformly in the exhaust passage 11 to enhance the agglomeration effect. Note that the shape of the discharge part 22 is not limited to a star shape, and it is only necessary that the plurality of protrusions 2a be positioned radially, and the number of protrusions 2a can be changed as appropriate.

  In FIG. 1 (a), the conductive net 3 is disposed across the passage so as to be orthogonal to the exhaust flow on the downstream side of the discharge portion 22 located substantially at the center of the exhaust passage 11. As shown in FIG. 2, the conductive mesh 3 is formed into a disk shape having a mesh through which exhaust gas can flow using a conductive material, and the outer peripheral edge is welded to the inner peripheral surface of the housing H. Fixed. The conductive net 3 is at ground potential. The mesh of the conductive net 3 is preferably a size that does not hinder the passage of the aggregated fine particles, for example, one side has a size of about 0.5 mm to 1 mm or more. Here, the exhaust fine particles usually have a particle size of about 0.01 μm to several μm, and the aggregated fine particles are usually coarse particles having a particle size of about 1 μm to 10 μm. If the mesh is large, the pressure loss is reduced, but the coagulation effect in the conductive net 3 is reduced. Therefore, the size of the mesh may be appropriately adjusted so as to obtain a desired coagulation effect.

  Features of the present invention will be described. As shown in FIGS. 1 (a) and 1 (b), the corona discharge electrode 2 has an insulating holding means on the outer periphery of the distal end portion of the insulator portion 23 protruding into the housing H and located near the central portion of the exhaust passage 11. A ring-shaped Pt carrier 4 is provided. The Pt support portion 4 is composed of a ring-shaped protruding portion that protrudes in the radial direction from the outer peripheral surface of the insulator portion 23, and an oxidation catalyst layer is formed by containing Pt as an oxidation catalyst on at least the outer surface thereof. Exhaust particulates adhering to the surface can be removed by catalytic action. A catalytic metal other than Pt can also be used as the oxidation catalyst.

  The outer diameter of the Pt support portion 4 only needs to be larger than that of the insulator portion 23, and the stepped portion is formed between the outer surface of the insulator portion 23, so that the exhaust particulates are easily divided in the axial direction. . Preferably, the projecting thickness of the ring-shaped projecting portion of the Pt carrier 4 is configured to be about 0.1 mm to 1 mm. If the protrusion thickness is less than 0.1 mm, the effect of dividing the exhaust particulates by the Pt carrier 4 is small, and if it is greater than 1 mm, the Pt carrier 4 is large, which is not economical. By forming the Pt carrying part 4 so that the formation width (the length in the axial direction) is, for example, about 1 mm, the effect of separating exhaust particulates can be obtained.

  The Pt carrying part 4 can be formed integrally with the insulator part 23, but a Pt carrying ring in which Pt which is an oxidation catalyst is carried on an insulating ring-shaped base material can be provided separately. Pt can be easily loaded. In this case, the Pt carrying ring may be fitted and fixed to the outer periphery of the insulator part 23 having a constant diameter, or the insulator part 23 may be divided into a plurality of parts and the Pt carrying ring may be sandwiched therebetween. When the insulator 23 is divided into a plurality of parts, a Pt carrying ring is inserted from the small diameter end of the discharge electrode 1 on which the insulator body is mounted, and a fixing insulator is inserted, and then, for example, a glass-containing adhesive is used. The fixing insulator is integrated by joining and fixing.

  The operation and effect of the aggregator 1 provided with the Pt carrier 4 of the present embodiment will be described with reference to FIGS. In a state in which exhaust gas flowing into the agglomerator 1 contains high-concentration exhaust particulates, the exhaust particulates easily adhere to the insulator portion 23 of the discharge electrode 2 protruding into the exhaust passage 11. FIG. 4B shows a configuration in which the insulator part 23 does not have the Pt support part 4 and exhaust particulates are deposited on almost the entire outer surface of the insulator part 23, so that it is applied to the discharge part 22 through the deposited exhaust particulates. Current leaks and corona discharge does not occur well. In contrast, as shown in FIGS. 3A and 3B, in the configuration of the present embodiment in which the Pt support portion 4 is provided in the insulator portion 23, exhaust particulates are deposited on the entire outer surface of the insulator portion 23. On the surface of the Pt carrier 4, the accumulated exhaust particulates react with oxygen (O 2) in the atmosphere by the catalytic action of Pt and are discharged as carbon dioxide (CO 2). As a result, exhaust particulates deposited on the outer surface of the Pt carrier 4 are removed, and the deposited exhaust particulates are divided in the axial direction in the Pt carrier 4, thereby preventing current leakage from occurring. it can.

  As a result, as shown in FIG. 4A, a negative DC high voltage (for example, −20 KV) is applied to the discharge part 22 through the conductive part 21 of the corona discharge electrode 2 from a DC high voltage power supply (not shown). Corona discharge can be generated in the vicinity of the protrusion 2a at the tip of the discharge portion 22. When electrons are emitted by corona discharge (1 in the figure), this electron causes gas molecules (oxygen) with high electron affinity to become negative ions (2 in the figure) and adhere to nearby exhaust particulates (PM). Is negatively charged (3 in the figure). The exhaust particulates (PM) move by the Coulomb force and the gas flow (4 in the figure) and are electrostatically collected by the conductive net 3 (5 in the figure). Electrons that negatively charge the exhaust particulates (PM) are emitted to the conductive net 3 (6 in the figure). The exhaust particulates collected in the conductive net 3 are aggregated into coarse particles, separated by the gas flow, passed through the conductive net 3, and then moved downstream. This facilitates the collection of exhaust particulates.

  FIG. 5 shows an example of the configuration of the exhaust treatment device including the aggregator 1. In the common rail diesel engine E, the agglomerator 1 having the above configuration is installed in the middle of the exhaust pipe E1 connected to the exhaust manifold. Yes. A DPF (diesel particulate filter) for collecting exhaust particulates is disposed downstream of the aggregator 1, and exhaust particulates discharged from the aggregator 1 are collected. At this time, since the exhaust particulates are aggregated into coarse particles, they are reliably collected by the DPF and periodically removed by combustion. Other harmful components in the exhaust gas are purified by the oxidation catalyst and NOx catalyst downstream of the DPF. Therefore, it is possible to prevent harmful components including exhaust particulates from being purified and discharged to the atmosphere.

  The second embodiment of the present invention will be described with reference to FIG. In the first embodiment, in the discharge electrode 2 of the aggregator 1, the outer diameter of the Pt carrier 4 provided in the insulator 23 is a constant diameter, but as shown in FIGS. 6 (a) and 6 (b). Alternatively, different diameter shapes may be used. Here, the ring-shaped projecting portion of the Pt support portion 4 has a gear shape in which thick portions and thin portions are alternately provided in the circumferential direction, and is an oxidation catalyst layer in which Pt is supported on at least the outer surface thereof.

  In this way, in addition to reducing the cost by reducing the thickness of the Pt carrier 4, the area of the outer surface of the ring-shaped protrusion, that is, the surface area of the oxidation catalyst layer having the action of removing exhaust particulates is increased. The oxidation performance of exhaust particulates can be improved.

  A third embodiment of the present invention will be described with reference to FIG. In each of the above embodiments, the ring-shaped projecting portion projecting in the radial direction is formed as the Pt carrying portion 4 provided on the insulator portion 23 of the discharge electrode 2, but the outer diameter thereof is a constant diameter. As shown, an oxidation catalyst layer that surrounds the outer surface of the insulator 23 with a predetermined width may be formed to form the Pt carrier 4. The Pt carrier 4 is formed, for example, by mixing Pt powder into the base material of the insulator 23. Alternatively, an extremely thin Pt carrying ring may be provided on the outer surface of the insulator part 23 to form the Pt carrying part 4, and both can be reduced in cost.

  A fourth embodiment of the present invention will be described with reference to FIG. In each of the above embodiments, the Pt carrier 4 provided on the insulator 23 of the discharge electrode 2 is provided at one place. However, as shown in FIG. 8, Pt is provided at a plurality of places (two in the figure) in the axial direction of the insulator 23. A carrier 4 can also be provided. In the figure, two Pt support portions 4 similar to those in the first embodiment are arranged at intervals, and an effect of preventing current leakage by reliably separating exhaust particulates deposited on the outer surface can be obtained.

  In this way, in addition to reducing the cost by reducing the thickness of the Pt carrier 4, the area of the outer surface of the ring-shaped protrusion, that is, the surface area of the oxidation catalyst layer having the action of removing exhaust particulates is increased. The oxidation performance of exhaust particulates can be improved.

  As described above, according to the present invention, the ability of agglomerating exhaust particulates by corona discharge can be enhanced with a simple configuration. Therefore, a high-performance and highly practical exhaust treatment device can be realized.

  In the above embodiment, the dust collection electrode is configured by the conductive net disposed downstream of the corona discharge electrode. However, the inner peripheral wall of the exhaust passage located on the outer periphery of the corona discharge electrode can be used as the dust collection electrode. In addition, although these conductive nets and the exhaust pipe inner peripheral wall are configured as ground electrodes, these potentials do not necessarily have to be ground potentials.

(A) is the schematic block diagram of the aggregator in the 1st Embodiment of this invention, (b) is a principal part enlarged view of (a), and is a side view which shows the schematic shape of a corona discharge electrode, (c) is a corona discharge. It is a front view which shows the discharge part shape of an electrode. It is a front view which shows schematic shape of the electroconductive net | network which is a dust collection electrode. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram for explaining the function and effect of the present invention, in which (a) shows a state in which exhaust particulates adhere to a corona discharge electrode, and (b) is a partially enlarged view of (a) showing a catalyst for exhaust particulates. It is a figure which shows the mode of the removal by reaction. (A) is a schematic diagram for explaining the operation of the aggregator, and (b) is a diagram showing a state in which exhaust particulates adhere to the corona discharge electrode in a configuration not including the insulating holding means of the present invention. is there. 1 is an overall schematic configuration diagram of an exhaust treatment device for an internal combustion engine including an aggregator. (A) is a side view which shows schematic shape of the corona discharge electrode in the 2nd Embodiment of this invention, (b) is the sectional view on the AA line of (a). It is a side view which shows schematic shape of the corona discharge electrode in the 3rd Embodiment of this invention. It is a side view which shows schematic shape of the corona discharge electrode in the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aggregator 11 Exhaust passage 2 Corona discharge electrode (discharge electrode)
21 conductive part 22 discharge part 23 insulator part 2a protrusion 3 conductive net (dust collecting electrode)
4 Pt carrying part (insulation holding means)

Claims (8)

An exhaust treatment apparatus is provided with an agglomerator that charges and agglomerates exhaust particulates by disposing a discharge electrode and a dust collecting electrode in an exhaust pipe of an internal combustion engine and applying a high voltage between these electrodes to generate corona discharge. And
The discharge electrode holds a discharge part located substantially at the center of an exhaust passage formed in the aggregator, a conductive part for guiding a high voltage from an external power source to the discharge part, and an outer periphery of the conductive part Insulation holding means is provided that has an insulator part and has an oxidation catalyst layer that covers a part of the outer peripheral surface of the insulator part in the circumferential direction, and purifies exhaust particulate adhering to the insulator part by an oxidation catalyst to maintain insulation. An exhaust treatment apparatus for an internal combustion engine, characterized in that   2. The internal combustion engine according to claim 1, wherein the insulating holding means has a ring-shaped projecting portion projecting in a radial direction from an outer peripheral surface of the insulator portion, and an oxidation catalyst is contained in at least an outer surface of the insulating projecting portion. Exhaust treatment equipment.   The exhaust treatment device for an internal combustion engine according to claim 2, wherein the ring-shaped protrusion is provided separately from the insulator main body.   The exhaust processing device for an internal combustion engine according to claim 2 or 3, wherein the ring-shaped projecting portion has an outer diameter shape with different diameters in which thin portions and thick portions are alternately formed in a circumferential direction.   The exhaust treatment device for an internal combustion engine according to any one of claims 1 to 4, wherein the oxidation catalyst is Pt.   The exhaust treatment apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein the dust collection electrode comprises a ground electrode disposed downstream or on the outer periphery of the discharge electrode.   The exhaust treatment apparatus for an internal combustion engine according to claim 6, wherein the dust collecting electrode is made of a conductive net or a conductive porous body disposed across the exhaust passage at a position downstream of the discharge electrode. The exhaust treatment device for an internal combustion engine according to any one of claims 1 to 7, wherein the discharge portion of the discharge electrode has a plurality of protrusions protruding radially.

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