JP2013124556A - Exhaust gas treatment device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas treatment device for electrically charging and agglomerating particulate matters in an exhaust gas using corona discharge in which the shape and the arrangement of a discharge electrode are optimized to efficiently treat the particulate matters without making a device structure complicated and without increasing the scale of the device structure, and thereby, the particulate matters are prevented from slipping through and the number of the particles is reduced.SOLUTION: A cylindrical pipeline-like dust collecting electrode 4 connected to an engine exhaust pipe is disposed and the inside is used as an exhaust gas passage 11 through which the exhaust gas containing the particulate matters passes and an electric dust collecting part 1 generating the corona discharge between the discharge electrode 3 and the dust collecting electrode 4 arranged in the passage center of the exhaust gas passage 11. The discharge electrode 3 has a plurality of discharge bodies 32 formed by radially arranging a plurality of projected electrodes 33 at the outer periphery along the center axis of the exhaust passage 11. The projected electrodes 33 adjacent to each other in the peripheral direction and the axial direction of the exhaust gas passage 11 are arranged so that regions 52 regulated by electric force lines 51 emitted from the respective projected electrodes 33 and reaching the dust collecting electrode 4 are brought into contact with each other on the surface of the dust collecting electrode.

Description

  The present invention relates to an exhaust gas treatment apparatus that collects and collects particulate matter contained in exhaust gas of an internal combustion engine using corona discharge.

  A direct-injection gasoline engine or diesel engine that injects fuel directly into a cylinder of a vehicle internal combustion engine has excellent fuel efficiency performance due to lean combustion, but has a problem that particulate matter (PM) is likely to be generated. Particulate matter is mainly composed of soot and soluble organic component (SOF), and in particular, fine suspended particulate matter (SPM) having a diameter of 10 μm or less, for example, may be suspended in the air for a long time. is there.

  As an exhaust gas aftertreatment device containing particulate matter, for example, in a diesel engine, a particulate filter having a honeycomb structure is generally installed. However, in order to collect minute suspended particulate matter (SPM), if the pore size of the particulate filter is reduced, clogging is likely to occur, and if the porosity is increased, slipping may occur. Further, in a direct-injection gasoline engine having lower thermal efficiency than a diesel engine, the particulate filter is not effective, and the fuel consumption may be further reduced due to the pumping loss.

  On the other hand, there is an electrostatic precipitator using corona discharge as a post-processing device that does not use a particulate filter. In general, an electrostatic precipitator has a configuration in which a corona discharge electrode and a ground electrode are opposed to each other and a corona discharge is generated by applying a high voltage between the two electrodes to charge and aggregate particulate matter. ing. It has been proposed to apply such an electric dust collector to an exhaust gas treatment device of a diesel engine or a direct injection gasoline engine. As conventional techniques, for example, there are Patent Documents 1 and 2.

  In Patent Document 1, a dust collection filter device including a dust collection electrode and a dust collection filter is provided on the inner periphery of a cylinder, and a discharge electrode is disposed in an exhaust gas passage formed inside the dust collection filter device. The discharge electrode generates an ionic wind that induces and forms a secondary flow in a direction perpendicular to the exhaust gas flow containing particulate matter. The discharge electrode main part and a plurality of disks or polygons arranged on the outer periphery thereof. It is constituted by a shaped discharge plate.

  Patent Document 2 has a configuration in which a discharge electrode is provided inside a tubular body, and a rod-shaped dust collection electrode is disposed downstream of the discharge electrode along the central axis direction of the flow path. Specifically, as shown in FIG. 12, the discharge electrode 101 disposed on the upstream side in the tubular body 100 is provided with a large number of needle-like discharge bodies 102 a that protrude in the flow path direction on both surfaces of the disk 102. Corona discharge is generated around it. The dust collecting electrode 103 forms an electric field between the rod-like body 104 having a length of twice or more of the inner diameter of the tube and the surrounding tube wall 105, and the particulate matter charged by corona discharge is supplied to the tube. Capture on the body wall. These corona discharge regions and electric field forming regions are combined to reduce the number of suspended particulate matter.

JP 2010-22949 A JP 2011-52544 A

  In recent years, exhaust gas regulations for automobiles have been further strengthened. Furthermore, regarding particulate matter, not only the reduction of the emission weight but also the regulation of the number of emitted particles has become important (PM particle number regulation). . However, it has been found that a conventional electrostatic precipitator using corona discharge does not necessarily have a sufficient processing capacity in order to cope with stricter discharge regulations.

  The dust collection filter device of Patent Document 1 employs a disk or polygonal discharge plate for the purpose of facilitating the manufacture and assembly of the discharge plate, but these shapes are optimal for improving the amount of discharge current. I can't say that. In addition, a plurality of discharge plates are arranged side by side in the axial direction to improve the processing capability. However, since the electric field intensity generated by each discharge plate is small, it is not easy to prevent the particulate matter from slipping through. Or in order to make up for this, there is a concern that the number of installed discharge plates increases, resulting in an increase in size and cost.

  The exhaust gas treatment device of Patent Document 2 distinguishes between an upstream corona discharge region and a downstream electric field forming region, so that charging by corona discharge and dust collection by an electric field are efficiently performed. However, in order to increase the amount of discharge current in the corona discharge region, the discharge electrode 101 has a complicated shape in which a large number of needle-like discharge bodies 102a protrude from both surfaces of the disk 102 serving as a support base. The dust collecting electrode 103 in the electric field forming region also requires the length of the rod-like body 104 to be 2 to 5 times the tube diameter, and there is difficulty in the strength and support structure of both electrodes. For this reason, the increase in cost by manufacture of an electrode and the enlargement of an apparatus cannot be avoided.

  Therefore, an object of the present invention is to optimize the shape and arrangement of the discharge electrode in an exhaust gas treatment apparatus that charges and aggregates particulate matter in exhaust gas discharged from an internal combustion engine using corona discharge. An object of the present invention is to provide an exhaust gas treatment apparatus that efficiently processes particulate matter flowing into the apparatus without complicating or increasing the size of the apparatus, and that has a high ability for preventing slip-through and reducing the number of particles. .

An exhaust gas treatment apparatus according to claim 1 of the present invention is provided with a cylindrical pipe-shaped dust collecting electrode connected to an exhaust pipe of an internal combustion engine, and the inside thereof is used as an exhaust gas passage through which exhaust gas containing particulate matter passes, An electric dust collecting part that generates corona discharge between the discharge electrode disposed in the center of the exhaust gas passage and the dust collecting electrode to generate ion wind is provided.
The discharge electrode is formed by arranging a plurality of discharge bodies radially arranged on the outer periphery along the central axis of the exhaust gas passage.
In addition, the protruding electrodes adjacent in the circumferential direction and the axial direction of the exhaust gas passage are such that regions defined by electric lines of force reaching each dust collecting electrode from each protruding electrode are in contact with each other on the dust collecting electrode surface. Is arranged.

  In the exhaust gas treatment apparatus according to the second aspect of the present invention, the discharge electrode arranges the protruding electrodes adjacent to each other in the circumferential direction and the axial direction so that electric lines of force formed by the protruding electrodes do not interfere with each other.

  In the exhaust gas treatment apparatus according to claim 3 of the present invention, the discharge electrodes are arranged such that the discharge bodies adjacent in the axial direction do not overlap the radial directions of the protruding electrodes on the outer periphery.

  In the exhaust gas treatment apparatus according to claim 4 of the present invention, the discharge electrode is formed by arranging the plurality of discharge bodies at equal intervals on the outer periphery of a rod-like support portion along the central axis of the exhaust gas passage.

  In the exhaust gas treatment apparatus according to claim 5, the discharge electrode has 4 or more and 12 or less protruding electrodes on the outer periphery of the discharge body, and an interval between the discharge bodies adjacent in the axial direction is 10 mm. Over 30 mm or less.

  In the exhaust gas treatment apparatus of the present invention, when a voltage is applied to the discharge electrode disposed in the cylindrical tube-shaped dust collecting electrode, a corona discharge is generated around the discharge electrode, and the generated ions and gas molecules face each other. Ion wind toward the dust collecting electrode. When the exhaust gas from the internal combustion engine is introduced into the electric dust collector, the particulate matter in the exhaust gas is charged, and is moved to the outer dust collecting electrode by the ionic wind and aggregates. Here, since the ions to be generated move along the electric lines of force formed between the discharge electrode and the dust collecting electrode, a region defined by the electric lines of force is formed in the entire area of the electric dust collecting part. It is necessary to

  In the discharge electrode of the present invention, when a plurality of discharge bodies having a plurality of protruding electrodes are arranged on the outer periphery along the central axis of the exhaust gas passage, the electric lines of force formed by the protruding electrodes are the dust collecting electrodes. Since the boundary is in contact with the surface, the electric field lines formed by the protruding electrodes are effectively formed in areas where the electric lines of force act in the circumferential direction and the axial direction, respectively. Therefore, an ion wind perpendicular to the exhaust gas flow is formed in the entire electric dust collector, and particulate matter in the exhaust gas is collected on the surface of the dust collector electrode without passing through the electric dust collector. Particulate matter aggregates on the surface of the dust collecting electrode to form aggregated particles, which greatly reduces the number of fine suspended particles.

  As described above, the discharge electrode of the present invention has an optimal arrangement in which the adjacent protruding electrodes are not too close and not too far apart in both the circumferential direction and the axial direction, and constitutes a compact and high-performance electric dust collecting part. . Therefore, it is possible to realize an exhaust gas treatment device that efficiently charges and aggregates particulate matter in the exhaust gas and generates a high ability to prevent slipping and reduce the number of particles without increasing the size and complexity of the device. .

  According to the exhaust gas treatment apparatus of the present invention, in the circumferential direction and the axial direction, the adjacent protruding electrodes are arranged so that the electric lines of force formed by the protruding electrodes do not interfere with each other. The amount of discharge current can be maximized. Therefore, it is possible to maximize the dust collection capability in the electric dust collection unit having a constant volume.

  According to the exhaust gas treatment apparatus of the present invention, since the positions of the projecting electrodes on the outer periphery do not overlap in the axial direction in the adjacent discharge bodies, the electric lines of force formed by the projecting electrodes are alternately positioned. Thus, there is no gap in the circumferential direction, reducing dead space. Therefore, it is possible to enhance the effect of preventing the exhaust particulates from slipping through the electrostatic precipitator.

  According to the exhaust gas treatment apparatus of claim 4 of the present invention, specifically, the discharge electrode is provided with a rod-like support portion disposed along the central axis of the exhaust gas passage, and a plurality of discharge bodies are disposed on the outer periphery thereof. In addition, a high dust collection effect can be obtained by arranging them at equal intervals so that the electric lines of force formed by the protruding electrodes are in contact with each other on the dust collection electrode surface.

  According to the exhaust gas treating apparatus of claim 5 of the present invention, specifically, the discharge electrodes have a number of protruding electrodes in the range of 4 to 12 on the outer periphery of the discharge body, and are adjacent in the axial direction. The interval between the matching discharge bodies is in the range of more than 10 mm and less than or equal to 30 mm, and the electric field lines formed by the protruding electrodes are arranged so as to be in contact with the dust collection electrode surface. A dust collection effect is obtained.

(A) is the whole schematic block diagram of the exhaust-gas-treatment apparatus in 1st Embodiment of this invention, (b) is the side view and front view of the discharge part which are principal parts, (c) It is the principal part enlarged view of the discharge part. is there. (A) is a schematic diagram of the electric dust collector in the first embodiment, (b) is a diagram for explaining the discharge characteristics between the protrusion and the flat plate. (A) is a figure for demonstrating the production | generation mechanism of ion wind, (b) is a typical figure showing the electric-force-line area | region which an adjacent protruding electrode forms. (A) is a figure which shows the relationship between an electrode shape, electric field strength, and discharge amount, (b) is a figure which shows the relationship between electric field strength and discharge amount. (A) is a figure which shows the relationship between the number of protrusions of a protruding electrode, and discharge current amount, (b) is a figure which shows the relationship between protrusion space | interval and discharge current amount. (A) is a figure which shows the relationship between the protrusion length of a protruding electrode, and the electric field strength of a protrusion tip, (b) is an electric field strength distribution map of a protruding electrode. (A) is a figure which shows the relationship between the protrusion tip radius of a protruding electrode, and electric field strength, (b) is a figure for demonstrating the calculation method of the electric field strength of the protruding electrode surface. It is one Example of the discharge electrode which optimized arrangement | positioning of a protruding electrode, (a) is a figure which shows the example of arrangement | positioning of the circumferential direction of a protruding electrode, (b) shows the example of arrangement | positioning of the axial direction of a protruding electrode. FIG. (A) is a typical figure which shows the mechanism of particulate matter (PM) reduction by the exhaust gas processing apparatus of this invention, (b) is a figure which shows the relationship between discharge current amount and PM number reduction rate. (A) is a figure which shows the influence when the space | interval of a protruding electrode is small, (b) is a figure which shows the influence when the space | interval of a protruding electrode is wide. (A) is a schematic diagram which shows the structure of the discharge electrode in 2nd Embodiment of this invention, (b) is a schematic diagram which shows the structure of the discharge electrode in 3rd Embodiment of this invention. . It is a whole schematic block diagram of the conventional exhaust gas processing apparatus.

  Hereinafter, a first embodiment in which the present invention is applied to an exhaust gas treatment apparatus for an internal combustion engine will be described with reference to the drawings. FIG. 1A is a cross-sectional view showing an overall schematic configuration of an exhaust gas treatment apparatus, and FIG. 1B is a side view and a front view of a discharge part 2 constituting an electrostatic precipitator 1, FIG. FIG. 2 is an enlarged perspective view of a part of the discharge electrode 3 which is a main part of FIG. The exhaust gas treatment apparatus of the present embodiment is an example applied to an automobile engine that is an internal combustion engine, and has a housing H connected in the middle of an engine exhaust pipe (not shown) in FIG. The electric dust collecting unit 1 is provided. The engine is a direct-injection gasoline engine or a diesel engine, and has a system in which fuel is directly injected into a cylinder from an injector.

  In the present embodiment, the electric dust collection unit 1 of the exhaust gas treatment apparatus includes a discharge unit 2 having a cylindrical tube-shaped dust collection electrode 4 as a part of a housing H made of a cylindrical tube and having a discharge electrode 3 therein. The electrostatic precipitator 1 is arranged. Inside the housing H is an exhaust gas passage 11 through which combustion exhaust gas (hereinafter referred to as exhaust gas) from the engine flows. Here, the left side of the figure is the upstream side of the exhaust gas flow, the right side is the downstream side, and the housing H Will be described as an inlet 12 into which exhaust gas from the engine is introduced. The housing H is connected to the vehicle body, and the dust collection electrode 4 is at ground potential.

  The discharge part 2 includes an insulator part 21 held and fixed to the wall of the housing H, and a discharge electrode 3 supported by the insulator part 21. The discharge electrode 3 has a rod-shaped support portion 31 disposed along the central axis of the housing H, and a large number of discharge bodies 32 disposed on the outer periphery of the rod-shaped support portion 31 at equal intervals. The insulator part 21 is a cylindrical body, the upper half part of the figure is exposed to the outside of the housing H, and the lower half part of the figure protrudes into the exhaust gas passage 11. A rod-shaped conductive portion 22 is inserted and held in the cylinder of the insulator portion 21, and its base end portion (upper end portion in the figure) is exposed to the outside of the housing H to form a terminal portion 23, which is not shown in the figure. Connected to power.

  The front end portion (lower end portion in the figure) of the conductive portion 22 protrudes downward from the cylinder of the insulator portion 21 and bends in an L shape at the center of the gas flow to constitute the rod-shaped support portion 31 of the discharge electrode 3. doing. As shown in FIG. 1B, the discharge body 32 of the discharge electrode 3 is a plate-like body arranged so as to face the gas flow, and a large number of protruding electrodes 33 are arranged radially on the outer periphery. These protruding electrodes 33 protrude in the radial direction and face the cylindrical dust collecting electrode 4 that concentrically surrounds the discharge electrode 3.

  Combustion exhaust gas flows into the exhaust gas passage 11 of the exhaust gas processing apparatus from an inlet 12 connected to an engine exhaust pipe (not shown). Combustion exhaust gas contains particulate matter (particulate matter; PM) composed of soot and soluble organic components (SOF), and the exhaust gas treatment device generates corona discharge in the electrostatic precipitator 1. The particulate matter passing through the inside is collected and collected using an ionic wind induced in a direction orthogonal to the flow of the exhaust gas. In particular, fine suspended particulate matter (SPM) is strictly regulated for release to the outside of the exhaust pipe, and it is required to reduce the number of particulate matter by charging aggregation.

  For this reason, in this invention, the discharge body 32 shape and arrangement | positioning of the discharge electrode 3 are set so that a particulate matter can be favorably collected in the whole region of the electric dust collection part 1. FIG. Specifically, a region to be the electrostatic precipitator 1 is determined by the length L of the rod-like support 31 of the discharge electrode 3 shown in FIG. A discharge space is formed. And the dust collection performance in the electric dust collection part 1 is set by optimizing the space | interval S in which the discharge body 32 is installed with respect to the length L of the rod-shaped support part 31, and the protrusion number N of the discharge body 32 outer periphery. To improve.

  As shown in FIG. 1C, in the present embodiment, each discharge body 32 has a substantially star-shaped flat plate shape, and needle-like protruding electrodes 33 that become thinner toward the tip end radially from a plurality of locations on the outer periphery. Is arranged in. The discharge body 32 has a mounting hole in the center of the plate surface, and is inserted and fixed to the outer periphery of the rod-like support portion 31 so that the plate surface faces the gas flow. As shown in the figure, each discharge body 32 has, for example, a shape in which protruding electrodes 33 protrude radially from eight locations on the outer periphery. In FIG. 1A, each protruding electrode 33 is orthogonal to the gas flow. The tip is opposed to the dust collecting electrode 4. In addition, for example, the protruding electrodes 33 are arranged at predetermined equal intervals at 10 positions in the axial direction including the tip of the rod-shaped support portion 31. The method of setting the arrangement (interval S and number of protrusions N) of the discharge bodies 32 is a characteristic part of the present invention, and will be described in detail below.

  FIG. 2 (a) is a diagram schematically showing the electrostatic precipitator 1 of the present embodiment. Here, a discharge body 32 provided with protruding electrodes 33 at eight locations on the outer periphery is used as a rod-like support 31. These are illustrated as being arranged at equal intervals at seven locations in the axial direction. Here, as shown in FIG. 2 (b), the discharge characteristics between the protruding electrodes 33 of the discharge body 32 and the dust collecting electrode 4 are flat plates (dust collecting electrodes) facing the protrusions (the protruding electrodes 33). It can be approximated as the discharge characteristic between 4). When a voltage (negative high voltage) is applied from the high voltage power source to the projecting electrode 33, the electric field concentrates around the projecting electrode 33, corona discharge is generated, and electrons are emitted.

As shown in FIG. 3A, the electrons (e) emitted from the protruding electrodes 33 collide with oxygen molecules (O ₂ ) present in the electrostatic precipitator 1 to generate oxygen ions (O ²⁻ ) Is generated. The generated oxygen ions (O ²⁻ ) move toward the dust collection electrode 4 on the lines of electric force while receiving the Coulomb force by the electric field. During this time, oxygen ions (O ²⁻ ) moving on the lines of electric force exchange momentum with other gas molecules such as nitrogen molecules (N ₂ ), carbon dioxide molecules (CO ₂ ), and the like. The flow generated by the exchange of momentum becomes an ionic wind, and the flow is in a direction orthogonal to the flow of exhaust gas flowing in the axial direction in the electrostatic precipitator 1.

Particulate matter (PM) in the exhaust gas flowing into the electric dust collector 1 is charged by contacting with surrounding electrons (e) and oxygen ions (O ²⁻ ). Then, while moving toward the dust collecting electrode 4 on the outer periphery by electrostatic force and ion wind, or agglomerates on the surface of the dust collecting electrode 4. In this way, the particulate matter (PM) can be charged and aggregated and collected, and in particular, the fine particulate matter (SPM) floating in the atmosphere can be collected by using the fine particles of 10 μm or less as the aggregated particles. Can be significantly reduced.

  In the present invention, in order to improve the aggregation effect of the particulate matter (PM), the discharge characteristics between the discharge electrode 3 and the dust collection electrode 4 that greatly contribute to the generation of ion wind are controlled. Specifically, the electric field strength around the discharge electrode 3 is increased by using the discharge body 32 having the plurality of protruding electrodes 33 and is defined by the lines of electric force formed between the dust collection electrode 4 and the electric field. It is preferable that the area is densely arranged in the entire area within the electric dust collector 1. Here, as shown in FIG. 2B, the virtual electric lines of force 51 radiated from the surface of the protruding electrode 33 and reaching the dust collecting electrode 4 correspond to the current density distribution on the dust collecting electrode 4 surface. In the region defined by the electric lines of force 51 (hereinafter referred to as electric line of force region 5), the current density increases toward the center, and the current density is substantially zero at the boundary. The electric field line region 5 can be defined by the radiation angle θ of electrons emitted from the projecting electrode 33, and the radiation angle θ of the electric field line region 5 formed by the projecting electrode 33 under the same conditions is constant. It becomes.

  Therefore, in the present invention, the electric field lines 5 corresponding to the protruding electrodes 33 of the discharge electrode 3 are in contact with each other in the circumferential direction and the axial direction of the electrostatic dust collecting portion 1 on the dust collecting electrode 4 surface. A plurality of discharge bodies 32 are arranged. FIG. 2A schematically shows this, and the electric field lines 5 formed by the protruding electrodes 33 of the discharge electrode 3 are projected onto the surface of the dust collecting electrode 4 developed in a planar shape. Region 52 is represented. In the vertical direction in the figure, eight regions 52 corresponding to the eight projecting electrodes 33 provided on the outer periphery of each discharge body 32 are arranged in contact with each other, and in the horizontal direction in the figure, in the axial direction. Corresponding to the seven discharge bodies 32 arranged, the regions 52 formed by the eight protruding electrodes 33 are arranged in contact with each other. These regions 52 are elliptical as shown in the figure, and represent that the radiation angle θ from each protruding electrode 33 is large in the circumferential direction and small in the axial direction.

  At this time, as shown in FIG. 3 (b), the electric field lines 5 formed by the adjacent protruding electrodes 33 are arranged without being overlapped or separated from each other, and the current density distribution, that is, the discharge current amount is reduced. Can be maximum. Therefore, it is important to set the shape of the protruding electrode 33 of the discharge body 32 and the interval between the protruding electrodes 33. In the present invention, in the circumferential direction (direction perpendicular to the gas flow) and the axial direction (gas flow direction). The dust collection performance is greatly improved by setting so that the elliptical regions 52 formed by the adjacent protruding electrodes 33 on the surface of the dust collection electrode 4 are in close contact with each other. These setting methods will be described next.

First, the shape of the discharge body 32 will be examined with reference to FIG. FIG. 4A compares the electric field strength and the discharge amount of the discharge body 32 having the protruding electrode 33 of the present invention and the conventional polygonal (for example, hexagonal) or disk-shaped discharge body. The electric field strength is a result calculated by simulation under the same conditions, and the discharge amount (discharge current amount) is calculated from the electric field strength and the discharge amount (discharge current amount) based on Ohm's law as shown in FIG. It was calculated from the relationship.
Here, from Ohm's law, I = σES
Where I: discharge current amount (A) σ: electrical conductivity (1 / Ωm) E: electric field strength (V / m) S: discharge section cross-sectional area (m ² )
That is, as the electric field strength increases, the amount of discharge current increases, and the shape of the discharge body 32 is optimally the shape having the protruding electrodes 33 that increase the electric field strength around the electrodes.

  Further, the number N of protrusions and the spacing S of the protruding electrodes 33 formed on the outer periphery of the discharge body 32 will be examined. FIG. 5A shows the relationship between the number of protrusions (N = 1 to 4) of the protruding electrode 33 and the amount of discharge current, and the amount of discharge current increases in proportion to the number of protrusions. Therefore, it is preferable that the number of the protruding electrodes 33 arranged on the outer periphery of the discharge body 32 be four or more.

  From this relationship, as the number of the protruding electrodes 33 arranged on the outer periphery of the discharge body 32 is increased, the amount of discharge current is expected to increase. Conventionally, in order to increase the amount of discharge current, the number is increased. It is said to be good. However, as shown in FIG. 5B, it has been found that when the protrusion interval is smaller than the predetermined range, the amount of discharge current decreases and rapidly decreases below 20 mm, particularly below 10 mm. For this reason, the increase in the number of the protruding electrodes 33 and the decrease in the protrusion interval adversely affects the dust collection performance.

  Therefore, it is preferable to set the number and interval of the projecting electrodes 33 to be optimum so that a desired discharge current amount can be obtained according to the shape or size of the discharge body 32 and the projecting electrodes 33. . 6A and 6B show the results of examining the influence of the protrusion length of the protruding electrode 33. FIG. As shown in FIG. 6B, the protruding electrode 33 is a needle-like electrode having a hemispherical tip, and the protruding length h (the protruding length from the proximal end to the distal end) is changed. The electric field strength distribution was calculated by a simulator. FIG. 6A shows the relationship between the projection length h (1 to 20 mm) and the electric field strength at the tip of the projection under the condition of a constant potential (10 kV). The electric field strength is increasing. However, if it exceeds 15 mm, the increase in electric field strength is small, and even if it exceeds 20 mm, no significant change can be expected. Therefore, preferably, the projection length h is appropriately selected so that a desired electric field line region 5 is formed between the projection length h and the dust collecting electrode 4 within a range of 20 mm or less. .

7A and 7B show the results of examining the influence of the protrusion tip radius of the protruding electrode 33. FIG. As shown in FIG. 7B, assuming that the tip of the protruding electrode 33 is spherical, the radius is r, the surface potential is V, and the vacuum dielectric constant is ε ₀ , the charge Q charged on the spherical surface is Is represented by the following formula.
Q = 4πε ₀ rV [C]
Further, the charge density ρ on the surface of the sphere and the electric field intensity E near the surface of the sphere are represented by the following equations, respectively.
ρ = Q [C] / 4πr ² [m ² ] = ε ₀ V / r [C / m ² ]
E = ρ [C / m ² ] / ε ₀ [F / m] = V / r [V / m]
From this relational expression, electric field strength E and radius r
Accordingly, the relationship between the electric field strength E and the radius r (0.1 to 1 mm) when the surface potential V is constant (10 kV) is as shown in FIG. 7A. The electric field strength on the surface is large. Therefore, it is preferable to appropriately select the radius r so that a desired electric field line region 5 is formed between the radius r and the dust collecting electrode 4 within a range of 1 mm or less.

  From the results of FIGS. 6 and 7, it can be seen that a higher electric field strength can be obtained by making the protruding electrode 33 have a sharp shape with a long protrusion length h and a small radius r at the protrusion tip. For this purpose, the discharge body 32 of the present invention has needle-shaped protruding electrodes 33 that are arranged so as to be thinner toward the tip, and is arranged in a star shape. Further, in the present invention, by optimizing the arrangement of the protruding electrodes 33, the amount of discharge current discharged to the discharge space between the dust collecting electrodes 4 is maximized. The specific method will be described next.

  FIGS. 8A and 8B show an embodiment of the discharge electrode 3 in which the arrangement of the protruding electrodes 33 is optimized according to the present invention. FIG. 8A shows the circumferential direction of the protruding electrodes 33. FIG. 8B shows an arrangement example of the protruding electrodes 33 in the axial direction. The discharge electrode 3 is housed in a housing H connected to a general vehicle direct injection gasoline exhaust pipe, and the protrusion electrode 33 has a protrusion length h and a protrusion tip radius shown in FIGS. It is set to a predetermined shape that is a suitable range of r. At this time, the discharge characteristics between each protruding electrode 33 and the dust collecting electrode 4 are as shown in FIG. 2B, and the emission of electrons emitted from each protruding electrode 33 by voltage application. The angle θ is constant. Therefore, the electric field lines 5 formed by the protruding electrodes 33 are arranged in the electric dust collecting unit 1 in close contact with the region 52 projected onto the surface of the dust collecting electrode 4 to maximize the dust collecting performance. Can be demonstrated.

  First, the radiation angle θ of the electric force lines 51 dominant in the electron emission is calculated, and the regions 52 in which the electric force line areas 5 formed by the plurality of protruding electrodes 33 are respectively projected onto the dust collecting electrode 4 are in close contact with each other. Thus, the number of the protruding electrodes 33 is determined. Specifically, as shown in the left diagram of FIG. 8A, the radiation angle θ in the circumferential direction of the electric lines of force is known from the relationship between the number of the protruding electrodes 33 of the discharge body 32 and the amount of discharge current. Can do. Here, the number of the projecting electrodes 33 was changed in the range of 2 to 16 and arranged on the outer periphery of the discharge body 32 at equal intervals. Further, the applied voltage was set at three stages of −10 kV, −15 kV, and −20 kV, and changes in the discharge current amount (corresponding to the area surrounded by the current density distribution curve in FIG. 2B) were examined.

  As a result, the discharge current amount reached a maximum when the number of needle-like projecting electrodes 33 (the number of needles n in the figure) was about 8, and a decrease in the discharge current amount was observed even below this. This is because in the region where the number of protruding electrodes 33 is 8 or less, the number of regions from which electrons are emitted increases in proportion to the number of protrusions (number of needles n), and the total discharge current amount increases. This tendency becomes more prominent as is larger. On the other hand, in the area of 8 or more protruding electrodes 33, although there was no significant change, the discharge current amount tended to decrease gradually in proportion to the number of protrusions (number of needles n). That is, as shown in the right diagram of FIG. 8A, when the number of the projecting electrodes 33 is eight, the regions 52 in which the electric lines of force 51 radiated to the outer periphery of the discharge body 32 are projected on the dust collecting electrode 4 are mutually connected. I have been in contact with you recently. However, if the number exceeds eight, the boundary of the region 52 projected onto the dust collecting electrode 4 overlaps and interference is likely to occur, and the peak value of the current density distribution is considered to be lowered.

  Therefore, in the configuration of this embodiment, the optimal number of the protruding electrodes 33 is 8 in the circumferential direction, and at this time, the radiation angle θ in the circumferential direction is 57 °. Moreover, if it is around eight, a substantially equivalent effect is acquired and it can select suitably in the range of 4-12 normally, Preferably 6-10.

  Further, as shown in FIG. 8B, the protruding electrodes 33 of the discharge body 32 are arranged at equal intervals in the axial direction, and the radiation angle in the axial direction of the electric lines of force 51 from the relationship between the interval and the discharge current amount. θ can be known. Here, the length L of the rod-like support portion 31 to which the protruding electrode 33 is attached is constant at 120 mm. The interval between the protruding electrodes 33 was changed within a range of 10 to 60 mm, and the applied voltage was set in two stages of −15 kV and −20 kV. As a result, the discharge current amount was maximized when the interval between the protruding electrodes 33 (electrode interval S in the figure) was 20 mm, and a decrease in the discharge current amount was observed even below or above. That is, the distance between the projecting electrodes 33 is around 20 mm, and the region 52 where the electric lines of force 51 are projected onto the dust collecting electrode 4 does not overlap and is in the closest state without separation.

  On the other hand, in the region where the electrode interval S exceeds 20 mm, the number of projecting electrodes 33 that can be arranged decreases as the interval increases, and the amount of discharge current tends to decrease. Further, in the region where the electrode spacing S is less than 20 mm, the region 52 where the electric lines of force 51 are projected onto the dust collecting electrode 4 overlaps and interferes easily, and the peak value of the current density distribution decreases, thereby reducing the discharge current amount. Decrease.

  Therefore, in the configuration of the present embodiment, the number of the protruding electrodes 33 is optimally arranged so that the electrode interval is 20 mm in the axial direction. At this time, the radial radiation angle θ is 34 °. Moreover, if it is around 20 mm, the substantially equivalent effect will be acquired and it can usually select suitably in 10 to 30 mm or less.

  As described above, in the present invention, the projection-like electrode 33 provided in the discharge electrode 3 is known in advance in the circumferential direction and the axial radiation angle, and the projection area on the dust collection electrode 4 is closely contacted. The number and interval of the electrodes 33 are adjusted. As a result, interference of electric lines of force reaching the dust collecting electrode 4 is prevented, the area where electrons are not emitted is minimized, the total discharge current amount is increased, and the discharge space in the electric dust collecting unit 1 is maximized. Can be used.

  FIG. 9A is a schematic diagram showing the mechanism of particulate matter (PM) reduction by the exhaust gas treatment apparatus of the present invention. In the discharge electrode 3 of the present invention, the interval between the adjacent protruding electrodes 33 is appropriately set, so that the electric lines of force 51 radiated from each protruding electrode 33 are not interfered with each other. And, it reaches the opposite dust collecting electrode 4 without being too far away. As a result, the amount of discharge current in the electrostatic precipitator 1 is increased, and an ion wind from each protruding electrode 33 toward the dust collecting electrode 4 is well formed. The particulate matter (PM) in the exhaust gas is transferred to the dust collecting electrode 4 on the outer peripheral wall surface by exchanging momentum with the flow of electrons or negative ions, where the particulate matter (PM) is aggregated. Aggregation can reduce the number of particulate matter (PM) discharged.

  FIG. 9B is a diagram showing the relationship between the discharge current amount and the PM number reduction rate, and when the discharge current amount is increased or decreased by adjusting the number of the discharge bodies 32 and the protruding electrodes 33 of the discharge electrode 3. It is the result of investigating the PM number reduction rate. As shown in the figure, it is presumed that the probability of colliding with the particulate matter (PM) is increased by increasing the discharge current amount.

  On the other hand, FIGS. 10A and 10B show the effects when the arrangement of the protruding electrodes 33 is not optimized. For example, as shown in FIG. 10A, when the interval between the protruding electrodes 33 adjacent in the axial direction is narrower than the preferred range (electrode interval S = 10 mm), the adjacent electric force lines 52 interfere with each other. As a result, the electric field strength around the tip of the protruding electrode 33 is reduced. As a result, the electric force line region 5 formed by the electric force lines 51 reaching the dust collection electrode 4 from the protruding electrode 33 changes, and the peak of the current density distribution in the dust collection electrode 4 becomes small. Since the desired current density distribution cannot be obtained, the total discharge current amount defined by the sum of the areas of the current density distribution becomes small.

  Further, as shown in FIG. 10B, when the interval between the protruding electrodes 33 adjacent in the axial direction is wider than the above preferable range (electrode interval S = 40 mm), the adjacent electric force lines 51 interfere with each other. Although there is nothing, the electric field lines 5 determined by the electron emission angle θ from the protruding electrode 33 are separated. As a result, a dead space is formed outside the electric field lines 5 formed by the protruding electrodes 33, and a space without discharge is formed. Therefore, it is easy for the particulate matter to slip through, and a desired concentration is obtained. Dust performance cannot be obtained.

  11A and 11B show the second and third embodiments of the present invention, in which the shape and arrangement of the discharge body 32 of the discharge electrode 3 are changed. The rest of the configuration is the same, and the configuration of the discharge electrode 3 as the main part will be described below. In the second embodiment of the present invention shown in FIG. 11A, the shape of the discharge body 32 is the same as that of the first embodiment of the present invention shown in FIG. 1, and eight protruding electrodes 33 are provided on the outer periphery. It is radially arranged at equal intervals. In this embodiment, as shown in the figure, the adjacent discharge bodies 32 are rotated by a predetermined angle so that the radial directions of the projection electrodes 33 do not overlap, and the tips of the projection electrodes 33 of each discharge body 32 are exhaust gas. When viewed from the front in the flow direction, they are positioned alternately.

  In this manner, when the two adjacent discharge bodies 32 are arranged at a predetermined interval, the interval between the two adjacent protruding electrodes 33 is maximized, and the electric field lines 5 formed by the protruding electrodes 33 are formed. Dead space is reduced. That is, in the developed view of the dust collecting electrode 4 shown in the figure, the areas 52 projected from the electric field lines 5 formed by the respective projecting electrodes 33 of the discharge body 32 are alternately arranged in the axial direction and are closer to each other. . Therefore, the effect of reducing slipping of the particulate matter (PM) flowing into the electric dust collection unit 1 is high, and the dust collection performance can be improved.

  FIG. 11B shows a third embodiment of the present invention, in which the shape of the discharge body 32 is arranged with a smaller number of protruding electrodes 33 than in the first embodiment of the present invention shown in FIG. . Specifically, four protruding electrodes 33 are arranged radially at intervals of 90 degrees on the outer periphery. Also in the present embodiment, as shown in the drawing, adjacent discharge bodies 32 are arranged so as to be rotated by 45 degrees so that the radiation directions do not overlap, and the tips of the protruding electrodes 33 of each discharge body 32 are viewed from the front. Sometimes they are staggered.

  In this case, since the interval between the protruding electrodes 33 of the discharge body 32 is separated from that of the first and second embodiments, the interval between the discharge bodies 32 adjacent in the axial direction can be further reduced. Therefore, the axial length of the exhaust gas treatment apparatus can be shortened and the whole can be made compact. Therefore, it is advantageous when the installation space is limited.

  As described above, according to the present invention, the discharge electrode 3 is optimally disposed so that the adjacent protruding electrodes 33 are not too close and not too far apart in both the circumferential direction and the axial direction, and is compact and has high performance. The dust collection part 1 is comprised. Therefore, it is possible to realize an exhaust gas treatment device that efficiently charges and aggregates particulate matter in the exhaust gas and generates a high ability to prevent slipping and reduce the number of particles without increasing the size and complexity of the device. .

  The exhaust gas treatment apparatus of the present invention is not limited to a direct-injection gasoline engine or diesel engine, but can be used to reduce particulate matter discharged from an internal combustion engine.

H Housing 1 Electric dust collecting part 11 Exhaust passage 12 Inlet part 2 Discharge part 21 Insulator part 22 Conductive part 23 Terminal part 3 Discharge electrode 31 Rod-shaped support part 32 Discharge body 33 Protruding electrode 4 Dust collecting electrode 5 Electric field line area 51 Electric field lines 52 area

Claims (5)

Discharge electrode disposed in the center of the exhaust gas passage, provided with a dust collection electrode in the form of a cylindrical pipe connected to the exhaust pipe of the internal combustion engine, and the inside thereof as an exhaust gas passage through which exhaust gas containing particulate matter passes And an electric dust collecting part that generates corona discharge and generates ion wind between the dust collecting electrode and the dust collecting electrode,
In the electric dust collector,
The discharge electrode is formed by arranging a plurality of discharge bodies radially arranged on the outer periphery along the central axis of the exhaust gas passage.
In addition, the protruding electrodes adjacent in the circumferential direction and the axial direction of the exhaust gas passage are such that regions defined by electric lines of force reaching each dust collecting electrode from each protruding electrode are in contact with each other on the dust collecting electrode surface. An exhaust gas treatment apparatus for an internal combustion engine, wherein   2. The exhaust gas treatment for an internal combustion engine according to claim 1, wherein the discharge electrodes are arranged such that the projecting electrodes adjacent in the circumferential direction and the axial direction do not interfere with the electric lines of force formed by the projecting electrodes. apparatus.   The exhaust gas treatment apparatus for an internal combustion engine according to claim 1 or 2, wherein the discharge electrodes are arranged such that the discharge bodies adjacent in the axial direction do not overlap the radial directions of the protruding electrodes on the outer periphery.   The exhaust gas of the internal combustion engine according to any one of claims 1 to 3, wherein the discharge electrode has the plurality of discharge bodies arranged at equal intervals on an outer periphery of a rod-like support portion along a central axis of the exhaust gas passage. Processing equipment.   The discharge electrode has 4 or more and 12 or less protruding electrodes on the outer periphery of the discharge body, and an interval between the discharge bodies adjacent in the axial direction is set in a range of more than 10 mm and 30 mm or less. Item 6. The exhaust gas treatment apparatus for an internal combustion engine according to any one of Items 1 to 4.

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