JP6886349B2 - Plasma reactor - Google Patents

Description

The present invention relates to a plasma reactor, and more particularly to a plasma reactor suitable for an apparatus for purifying exhaust gas of an internal combustion engine (engine).

Conventionally, by passing the exhaust gas of an engine or incinerator through a plasma field, CO (carbon monoxide), HC (hydrocarbon), NOx (nitrogen oxide) and PM (Particulate Matter) contained in the exhaust gas are particulate. A plasma reactor that treats harmful substances such as substances) has been proposed.

For example, discharge electrodes provided on a dielectric are provided in parallel at intervals, and a voltage is applied between the discharge electrodes to generate low-temperature plasma (non-equilibrium plasma) due to dielectric barrier discharge, thereby flowing between the discharge electrodes. Various techniques for oxidizing and removing PM in the exhaust gas have been proposed (see, for example, Patent Documents 1 to 3). More specifically, Patent Documents 1 to 3 are techniques in which a pair of discharge electrodes (conductive films) facing each other are provided, and a voltage is applied between the two discharge electrodes to generate plasma. In Patent Documents 1 and 2, a plurality of through holes are provided in each discharge electrode. In particular, in Patent Document 2, through holes are arranged in a plurality of types of arrangement patterns in one discharge electrode. Further, in Patent Document 3, the distance between adjacent discharge electrodes is configured to be different for each region.

Japanese Patent No. 4746986 (Fig. 3, etc.) Japanese Patent No. 4104627 (Fig. 3, etc.) Japanese Patent No. 4863743 (Figs. 4 to 6, 8 etc.)

By the way, when the plasma reactor is mounted on a vehicle or the like and used, the exhaust gas containing soot (PM) flows into the gas flow path formed between the adjacent discharge electrodes. It should be noted that the PM in the exhaust gas tends to be deposited on the upstream side portion of the gas flow path, particularly on the side portion where the flow velocity is relatively low in the upstream side portion, so that the deposited PM is the upstream end of the discharge electrode. There is a high possibility that it will adhere to the end of the part or the side.

However, in the prior art described in Patent Documents 1 and 2, although the portion serving as the starting point of the discharge exists at the edge of the through hole, the starting point of the discharge is located at the upstream end or the side end of the discharge electrode. There is almost no part that becomes. Further, in the prior art described in Patent Document 3, not only the upstream side end portion and the side portion side end portion do not have a portion serving as a starting point of electric discharge, but also the through hole itself does not exist. Therefore, in these cases, it is difficult to generate plasma at the upstream end and the side end, and it is difficult to remove the accumulated PM by using plasma.

As a result, there is a problem that the insulation between the adjacent discharge electrodes cannot be ensured because the adjacent discharge electrodes are electrically connected to each other via the PM. Further, when a laminated body of electrode panels including a discharge electrode is housed in a case and the case containing the laminated body is attached to an exhaust pipe, the discharge electrode and the case are electrically connected via PM. , There is a problem that the insulation between the discharge electrode and the case cannot be secured. Therefore, in these cases, since a leak current is generated, the amount of plasma generated with respect to the input power is reduced, and the purification efficiency of the exhaust gas may be lowered.

The present invention has been made in view of the above problems, and an object of the present invention is to improve reliability by ensuring insulation between adjacent discharge electrodes and insulation between a discharge electrode and a case. The purpose is to provide a possible plasma reactor.

As a means (means 1) for solving the above-mentioned problems, a plurality of electrode panels including a dielectric and a discharge electrode are provided in parallel at intervals, and a gas is passed between the plurality of electrode panels to form a dielectric. A plasma reactor that generates plasma by barrier discharge, the outer peripheral portion of the discharge electrode includes an upstream end portion located on the gas inflow side, a downstream end portion located on the gas outflow side, and the above. It is configured to include an upstream side end portion and a side portion side end portion located between the downstream side end portions, and the upstream side end portion has a shape having a corner portion in a plan view, and the discharge Some plasma reactors are characterized in that the discharge start voltage at the outer peripheral portion of the electrode is lower than the discharge start voltage at the central portion of the discharge electrode.

Therefore, in the invention described in the above means 1, the upstream end portion of the discharge electrode has a shape having a corner portion in a plan view. Since this corner portion is likely to be the starting point of discharge, discharge is generated at many points on the upstream end portion having the corner portion, and plasma is surely generated. Therefore, when PM in the exhaust gas deposited on the upstream end is oxidized and removed by using plasma, PM can be removed efficiently. As a result, conduction between adjacent discharge electrodes via PM and conduction between the discharge electrode and the case (in which the laminated body of the electrode panels are housed) also via PM are prevented, so that the conduction between adjacent discharge electrodes is prevented. Insulation and insulation between the discharge electrode and the case can be ensured. Therefore, the reliability of the plasma reactor can be improved.

The plasma reactor has a structure in which a plurality of electrode panels including a dielectric and a discharge electrode are provided in parallel at intervals. Here, examples of the material for forming the dielectric include _{ceramics such as alumina (Al 2} O ₃ ), aluminum nitride (AlN), and yttrium oxide (Y ₂ O ₃ ), and mixtures thereof. Examples of the material for forming the discharge electrode include tungsten (W), molybdenum (Mo), ruthenium oxide (RuO ₂ ), silver (Ag), copper (Cu), and platinum (Pt).

The discharge electrode preferably has a shape in which both the upstream side end portion and the side portion side end portion have corner portions in a plan view. By doing so, in addition to the upstream side end portion having the corner portion, the discharge is generated at many points at the side portion side end portion having the corner portion, and the plasma is surely generated. Therefore, PM accumulated on the upstream side end portion and the side side end portion can be efficiently removed by using plasma. Therefore, it is possible to prevent the conduction between the adjacent discharge electrodes and the conduction between the discharge electrodes and the case due to the accumulation of PM on the upstream side end portion and the side side end portion.

By the way, PM deposited on the side end portion tends to be particularly likely to be deposited in the region near the upstream side end portion. Therefore, the side end portion may have a shape in which the region near the upstream end portion has a corner portion in a plan view, and the other region has a shape having a corner portion in a plan view. You don't have to. That is, since it is sufficient to provide the corner portion only in a part of the side end portion, the manufacturing cost can be suppressed low.

Further, it is preferable that at least one of the upstream side end portion and the side portion side end portion of the discharge electrode has a shape having a convex portion in a plan view. Since this convex portion tends to be the starting point of electric discharge, electric discharge is generated at many points of the end portion having the convex portion, and plasma is surely generated. Therefore, the PM deposited on the end portion can be efficiently removed by using plasma. Therefore, it is possible to prevent the conduction between the adjacent discharge electrodes and the conduction between the discharge electrodes and the case due to the accumulation of PM on the end portion.

In particular, it is preferable that the convex portion of the upstream end portion has a sharpened shape in a plan view. In this case, since the convex portion is surely the starting point of the discharge, the discharge is generated at more places on the upstream end portion having the convex portion, and the plasma is surely generated. Therefore, the PM accumulated at the upstream end can be removed more efficiently by using plasma, so that the conduction between the adjacent discharge electrodes and the conduction between the discharge electrodes and the case due to the accumulation of PM can be reliably prevented. ..

When the plurality of discharge electrodes are composed of the first electrode and the second electrode adjacent to the first electrode, at least a part of the corner portion provided on the first electrode and the second electrode At least a part of the corner portions provided in the above may be arranged so as not to overlap each other. In this way, a dielectric barrier discharge is generated between the corner portion of the first electrode and the corner portion of the second electrode existing obliquely below the corner portion. As a result, plasma can be generated in a wider range at the upstream side end portion (or the side portion side end portion) having the corner portion. Therefore, PM accumulated on the upstream side end portion (or the side side end portion) can be reliably removed.

The schematic cross-sectional view which shows the plasma reactor in this embodiment. The perspective view which shows the plasma reactor. Top view showing a plasma reactor. Perspective view showing plasma panel laminate, clamp, power supply terminal and mat. The perspective view which shows the plasma panel laminate, the clamp and the power supply terminal. Schematic cross-sectional view showing an electrode panel. The perspective view which shows the electrode panel. The plan view which shows the electrode panel. Top view showing the electrode panel. In another embodiment, a plan view of a main part showing an electrode panel. In another embodiment, a plan view of a main part showing an electrode panel. In another embodiment, a plan view of a main part showing a discharge electrode. FIG. 5 is a plan view showing the relationship between the first electrode and the second electrode in another embodiment.

Hereinafter, an embodiment embodying the plasma reactor 1 of the present invention will be described in detail with reference to the drawings.

As shown in FIGS. 1 to 3, the plasma reactor 1 of the present embodiment is a device for removing PM contained in the exhaust gas of an automobile engine (not shown), and is attached to an exhaust pipe 2. .. The plasma reactor 1 includes a power supply 3, a case 10, and a plasma panel laminate 20.

The case 10 is formed in a rectangular tubular shape using, for example, stainless steel. The first cone portion 11 is connected to the first end portion (left end portion in FIG. 1) of the case 10, and the second cone portion 12 is connected to the second end portion (right end portion in FIG. 1) of the case 10. There is. Further, the first cone portion 11 is connected to the upstream side portion 4 (engine side portion) of the exhaust pipe 2, and the second cone portion 12 is connected to the downstream side portion 5 (opposite side to the engine side) of the exhaust pipe 2. Part) is connected. The exhaust gas from the engine flows into the case 10 from the upstream side portion 4 of the exhaust pipe 2 through the first cone portion 11, passes through the case 10, and then passes through the second cone portion 12. It flows out to the downstream portion 5 of 2.

As shown in FIGS. 1, 4, and 5, the plasma panel laminate 20 is housed in the case 10, and has an upstream end face 21 from which the exhaust gas flows in and a downstream end face 22 from which the exhaust gas flows out. It has a substantially rectangular parallelepiped shape with four gas non-passing surfaces 23, 24, 25, and 26. The upstream end surface 21 and the downstream end surface 22 are located on opposite sides of each other in the plasma panel laminate 20. The gas non-passing surfaces 23 to 26 are located between the upstream end surface 21 and the downstream end surface 22.

Further, the plasma panel laminated body 20 has a structure in which a plurality of electrode panels 30 are laminated. Each electrode panel 30 is arranged parallel to the passage direction F1 (direction from the first cone portion 11 to the second cone portion 12) of the exhaust gas flowing from the upstream end surface 21 side to the downstream end surface 22 side, and is equal to each other. They are provided in parallel with an interval (0.5 mm in this embodiment). More specifically, the plasma panel laminate 20 has a gas flow path 27 (see FIG. 1) through which exhaust gas passes between adjacent electrode panels 30. The gas flow path 27 includes an opening 28 that opens at the upstream end surface 21 and the downstream end surface 22.

As shown in FIG. 1, the first wiring 6 and the second wiring 7 are alternately electrically connected to each electrode panel 30 along the thickness direction of the plasma panel laminate 20. The first wiring 6 is electrically connected to the first terminal of the power supply 3, and the second wiring 7 is electrically connected to the second terminal of the power supply 3.

As shown in FIGS. 1, 6 to 9, the electrode panel 30 of the present embodiment has a first main surface 31, a second main surface 32, a first end surface 37, and a second end surface 38, and has a length of 100 mm. × It has a substantially rectangular plate shape with a width of 200 mm. The first main surface 31 and the second main surface 32 are located on opposite sides of each other in the thickness direction of the electrode panel 30. Further, the first end surface 37 and the second end surface 38 are located on opposite sides of the gas flow path 27 in the surface direction. Further, the electrode panel 30 has an upstream side surface 115 constituting the upstream end surface 21 of the plasma panel laminated body 20 and a downstream side surface 116 forming the downstream end surface 22 of the plasma panel laminated body 20. Further, the electrode panel 30 has a structure in which a discharge electrode 34 (thickness 10 μm) is built in a rectangular plate-shaped dielectric 33. In the present embodiment, the dielectric 33 is made _{of ceramic such as alumina (Al 2} O ₃ ), and the discharge electrode 34 is made of tungsten (W).

As shown in FIGS. 6 and 7, the dielectric 33 has a recess 35 that opens at the second main surface 32. The recess 35 extends in the lateral direction of the electrode panel 30 and opens at both end surfaces of the electrode panel 30. In the plasma panel laminate 20 of the present embodiment, the gas flow path 27 described above is configured between the inner surface of the recess 35 and the first main surface 31 of the electrode panel 30 adjacent to the lower layer side. Since the electrode panel 30 in the lowermost layer constituting the plasma panel laminated body 20 does not have the electrode panel 30 on the lower layer side, the recess 35 is not formed.

As shown in FIGS. 7 and 8, on both side portions of the recess 35 in the electrode panel 30, one conduction structure 40 for conducting the first main surface 31 side and the second main surface side 32 side is provided. Has been done. Each conductive structure 40 includes a through-hole conductor 41, a first pad 42, and a second pad 43. The through-hole conductor 41 penetrates the electrode panel 30 in the thickness direction. The through-hole conductor 41 provided in one of the conductive structures 40 penetrates the extending portion 36 extending from the discharge electrode 34 to the outer peripheral side. Further, the first pad 42 is formed on the first main surface 31 and is electrically connected to the end portion of the through-hole conductor 41 on the first main surface 31 side. On the other hand, the second pad 43 is formed on the second main surface 32, and is electrically connected to the end of the through-hole conductor 41 on the second main surface 32 side. The first pad 42 and the second pad 43 each have a rectangular shape, and the surfaces thereof are plated with Ni or the like.

As shown in FIGS. 4 and 5, the plasma reactor 1 includes three first clamps 50, 51, and 52 that sandwich and fix each electrode panel 30 (plasma panel laminate 20) from the gas non-passing surface 24 side. , Each electrode panel 30 is provided with three second clamps 53, 54, 55 for sandwiching and fixing each electrode panel 30 from the gas non-passing surface 26 side. Each clamp 50 to 55 is formed by bending a metal plate (for example, a stainless plate made of a material such as SUS430). Further, the first clamps 50 to 52 are arranged at equal intervals along the exhaust gas passing direction F1 on the gas non-passing surface 24, and the second clamps 53 to 55 are arranged on the gas non-passing surface 26 in the exhaust gas passing direction. They are evenly spaced along F1.

The first clamps 50 and 51 arranged on the upstream side portion and the central portion of the gas non-passing surface 24, and the second clamps 53 and 54 arranged on the upstream side portion and the central portion of the gas non-passing surface 26 are , Each electrode panel 30 has only a function of sandwiching in the stacking direction. On the other hand, the first clamp 52 arranged on the downstream side portion of the gas non-passing surface 24 and the second clamp 55 arranged on the downstream side portion of the gas non-passing surface 26 sandwich each electrode panel 30 in the stacking direction. In addition to the function, it has a function of electrically connecting to the discharge electrode 34.

Further, as shown in FIGS. 4 and 5, each clamp 50 to 55 includes a clamp main body 56 and a holding plate 57. The clamp body 56 extends in the stacking direction of the electrode panels 30. The pressing plate 57 is formed integrally with the clamp main body 56 and is arranged at both ends of the clamp main body 56. Each holding plate 57 is a leaf spring having elasticity and a folded structure. Each holding plate 57 is in pressure contact with the gas non-passing surface 23 and the gas non-passing surface 25 of the plasma panel laminated body 20, respectively. The double pressing plates 57 constituting the clamps 52 and 55 have a first pad 42 formed on the gas non-passing surface 23 (the first main surface 31 of the uppermost electrode panel 30) and the gas non-passing surface 25 (the gas non-passing surface 25 (). It is in pressure contact with the second pad 43 formed on the second main surface 32) of the lowermost electrode panel 30. The protruding length of the pressing plate 57 constituting the clamps 52, 55 from the clamp main body 56 is longer than the protruding length of the pressing plate 57 constituting the other clamps 50, 51, 53, 54 from the clamp main body 56. It has become.

As shown in FIGS. 2 to 5, the plasma reactor 1 includes a pair of power supply terminals 61 and 62. The power supply terminals 61 and 62 of this embodiment have the same structure as the spark plug. More specifically, the power supply terminals 61 and 62 include an external connection portion, a conductive seal containing metal powder, an insulator, a main metal fitting, talc, packings, and the like. The external connection portion is connected to the central shaft 63 via a conductive seal. The tip of the central shaft 63 is arranged in an insulator. The power supply terminal is not limited to that of the present embodiment, and may have another structure as long as the structure is such that the external connection portion and the case 10 are insulated by an insulator. ..

The tip of the power supply terminal 61 is exposed from the case 10, and the base end (central shaft 63) is in pressure contact with the holding plate 57 (specifically, the gas non-passing surface 23) of the first clamp 52. It is electrically connected to the holding plate 57). Similarly, the tip of the power supply terminal 62 is exposed from the case 10, and the base end (central shaft 63) is pressure-welded to the holding plate 57 (specifically, the gas non-passing surface 23) of the second clamp 55. It is electrically connected to the holding plate 57). The power supply terminals 61 and 62 project in the same direction. In the present embodiment, the tip of the power supply terminal 61 is connected to the first wiring 6 (see FIG. 1), and the tip of the power supply terminal 62 is connected to the second wiring 7 (see FIG. 1). It is designed to be connected.

As shown in FIGS. 1 and 4, a mat 71 forming a rectangular annular shape in a side view is interposed between the case 10 and the plasma panel laminate 20. The mat 71 has a function of fixing the plasma panel laminate 20 to the case 10. Further, the mat 71 covers the outer surface of the plasma panel laminate 20. More specifically, the mat 71 includes a substantially rectangular plate-shaped first mat piece 72 that covers the gas non-passing surface 23, a substantially rectangular plate-shaped second mat piece 73 that covers the gas non-passing surface 24, and a gas non-passing surface. It is composed of a substantially rectangular plate-shaped third mat piece 74 that covers 25 and a substantially rectangular plate-shaped fourth mat piece 75 that covers the gas non-passing surface 26. The mat 71 is formed by joining the mat pieces 72 to 75 to each other using adhesive tape or the like, if necessary. Here, as the material constituting the mat 71, for example, an insulating material such as a ceramic fiber, a metal fiber, or a foamed metal can be used.

Further, as shown in FIG. 4, the mat 71 of the present embodiment is formed with two notches 81 and 82 penetrating the mat 71 in the thickness direction. The first clamp 52 is located in the inner region of the notch 81, and the second clamp 55 is located in the inner region of the notch 82. More specifically, the notches 81 and 82 are composed of a groove 83 that penetrates the second mat piece 73 in the thickness direction and a pair of recesses 84 that penetrate the mat pieces 72 and 74 in the thickness direction, respectively. The groove 83 extends along the stacking direction of the electrode panels 30 and divides the second mat piece 73. On the other hand, the recess 84 is formed only in a part of the outer peripheral portion of the mat pieces 72 and 74 so as not to divide the mat pieces 72 and 74. The clamp main body 56 of the clamps 52 and 55 is arranged in the groove 83, and the holding plate 57 of the clamps 52 and 55 and the central shaft 63 of the power supply terminals 61 and 62 are arranged in the recess 84. There is.

As shown in FIGS. 7 to 9, the discharge electrode 34 penetrates in the thickness direction of the discharge electrode 34, and is composed of a plurality of first linear portions 91 and a plurality of second linear portions 92. It has a plurality of through holes 93. The length, width, and thickness of the first linear portion 91 and the second linear portion 92 are appropriately determined in consideration of the applied voltage and the like. Further, in the discharge electrode 34, a plurality of first linear portions 91 extend linearly along the passing direction F1 of the exhaust gas, and are spaced at regular intervals in a direction orthogonal to the passing direction F1 (width direction of the recess 35). It is provided with a space. Further, in the discharge electrode 34, a plurality of second linear portions 92 extend linearly along the width direction of the recess 35, and are provided at regular intervals in the passing direction F1. Therefore, the first linear portion 91 and the second linear portion 92 form a square grid of 0.5 mm square in a plan view. Along with this, the through hole 93 formed by the first linear portion 91 and the second linear portion 92 also forms a square shape having four corner portions 94 in a plan view.

As shown in FIGS. 8 and 9, the outer peripheral portion 101 of the discharge electrode 34 includes an upstream end portion 102 located on the side where the exhaust gas flows in and a downstream end portion 103 located on the side where the exhaust gas flows out. It is configured to include two side end portions 104 and 105. The upstream end 102 and the downstream end 103 are located on opposite sides of each other in the discharge electrode 34. The side end portions 104 and 105 are located between the upstream side end portion 102 and the downstream side end portion 103, and are located on opposite sides of each other in the discharge electrode 34.

As shown in FIG. 9, the upstream end of each first linear portion 91 is located at the upstream end 102. The upstream end of each first linear portion 91 has a shape having a convex portion (upstream convex portion 106) in a plan view. Each upstream convex portion 106 projects upstream from the edge 95 on the upstream side 115 side of the second linear portion 92 located on the most upstream side 115 side along the plane direction of the electrode panel 30. The tip of each upstream convex portion 106 is arranged so as not to be exposed from the upstream side surface 115. In other words, each upstream convex portion 106 is arranged so that its tip is separated from the upstream side surface 115. Here, the amount of protrusion of each upstream convex portion 106 from the edge 95 of the second linear portion 92 is equal to each other, and is 0.5 mm in the present embodiment. The upstream convex portion 106 of the present embodiment constitutes the upstream end portion of the first linear portion 91, but the upstream convex portion 106 has a configuration separate from that of the first linear portion 91. There may be. That is, the upstream convex portion 106 may be formed in a process different from that of the first linear portion 91. Further, the upstream convex portion 106 and the first linear portion 91 may be arranged offset in a direction orthogonal to the exhaust gas passage direction F1 (left-right direction in FIG. 9). Further, each upstream convex portion 106 has a pentagonal shape in a plan view, and the tip portion has a pointed shape having three corner portions 107 in a plan view. Of the three corners 107, the corner 107 located at the tip of the upstream convex portion 106 is a right angle (90 ° in the present embodiment), and the remaining two corners 107 are obtuse angles (the present embodiment). Is 135 °).

Further, the end of each of the second linear portions 92 on the first end surface 37 side is located at the side end portion 104, and the end of each of the second linear portions 92 is located at the side end portion 105. The end on the side of the second end surface 38 is located. The end portion of each of the second linear portions 92 on the first end surface 37 side has a shape having a convex portion (first side portion side convex portion 108) in a plan view over the entire side portion side end portion 104. doing. Further, the end portion of each second linear portion 92 on the second end surface 38 side has a shape having a convex portion (second side portion side convex portion 109) in a plan view over the entire side portion side end portion 105. Is made up of. Each first side convex portion 108 projects laterally along the plane direction of the electrode panel 30 from the edge 96 on the first end surface 37 side of the first linear portion 91 located closest to the first end surface 37 side. ing. The tip of each of the first side convex portions 108 is arranged so as to slightly protrude toward the first end surface 37 from the formation region of the recess 35 in a plan view and not to be exposed from the first end surface 37. Similarly, each of the second side convex portions 109 protrudes from the edge 97 of the first linear portion 91 located on the second end surface 38 side on the second end surface 38 side. The tip of each second side convex portion 109 is arranged so as to slightly project toward the second end surface 38 side from the formation region of the recess 35 in a plan view and not to be exposed from the second end surface 38. Here, the amount of protrusion of each first side convex portion 108 from the end edge 96 of the first linear portion 91, and each second side side convex portion from the end edge 97 of the first linear portion 91. The amount of protrusion of 109 is equal to each other, and is 0.7 mm in this embodiment. The side convex portions 108 and 109 of the present embodiment form a part of the second linear portion 92, but the side convex portions 108 and 109 are different from the second linear portion 92. It may be a body composition. That is, the side convex portions 108 and 109 may be formed in a process different from that of the second linear portion 92. Further, the side convex portions 108, 109 and the second linear portion 92 may be arranged offset in a direction parallel to the exhaust gas passage direction F1 (vertical direction in FIG. 9). Further, each of the convex portions 108 and 109 has a rectangular shape in a plan view, and the tip portion has a shape having two corner portions 110 in a plan view. Each corner 110 is a right angle.

As shown in FIGS. 1 and 9, the plasma reactor 1 of the present embodiment is used, for example, to remove PM contained in the exhaust gas. In this case, when a pulse voltage (for example, peak voltage: 5 kV (5000 V), pulse repetition frequency: 100 Hz) is applied between the power source 3 and the electrode panels 30 adjacent to each other, the opening edge and the convex portion 106 of each through hole 93 are applied. Dielectric barrier discharge occurs starting from the corners 107 and 110 of, 108 and 109, and plasma is generated between the discharge electrodes 34 due to the dielectric barrier discharge. The discharge start voltage (voltage for generating plasma) at the outer peripheral portion 101 of the discharge electrode 34 (specifically, the corner portions 107, 110 of the convex portions 106, 108, 109) is the central portion 100 (specifically, the voltage for generating plasma) of the discharge electrode 34. Specifically, it is lower than the discharge start voltage at the opening edge of the through hole 93). Then, due to the generation of plasma, PM contained in the exhaust gas flowing through the gas flow path 27 is oxidized (combusted) and removed.

Next, a method for manufacturing the plasma reactor 1 will be described.

First, a first to third ceramic green sheet to be a dielectric 33 is formed by using a ceramic material containing alumina powder as a main component. As a method for forming the ceramic green sheet, a well-known molding method such as tape molding or extrusion molding can be used. Then, each ceramic green sheet is laser-processed to form a through hole for the through-hole conductor 41. The through hole may be formed by punching, drilling, or the like.

Next, using a conventionally known paste printing device (not shown), the through holes for the through-hole conductor 41 are filled with a conductive paste (tungsten paste in this embodiment) to form the through-hole conductor 41, which is not fired. A through-hole conductor portion is formed.

Next, the first ceramic green sheet is placed on a support base (not shown). Further, a paste printing apparatus is used to print the conductive paste on the back surface of the first ceramic green sheet. As a result, an unfired electrode having a thickness of 10 μm, which serves as a discharge electrode 34, is formed on the back surface of the first ceramic green sheet. As a printing method of the unfired electrode on the first ceramic green sheet, a well-known printing method such as screen printing can be used.

Then, after the conductive paste is dried, the second ceramic green sheet and the third ceramic green sheet are laminated in order on the back surface of the first ceramic green sheet on which the unfired electrode is printed, and in the sheet laminating direction. Applying pressing force. As a result, each ceramic green sheet is integrated to form a ceramic laminate. Further, a paste printing device is used to print the conductive paste on the main surface of the first ceramic green sheet to form the unfired first pad 42, and the conductive paste is formed on the back surface of the third ceramic green sheet. The sex paste is printed to form the unbaked second pad 43. The third ceramic green sheet is laminated after being punched to match the shape of the recess 35.

Next, after performing a drying step, a degreasing step, etc. according to a well-known method, the ceramic green sheet and the unfired electrode are heated to a predetermined temperature (for example, about 1400 ° C to 1600 ° C) at which alumina and tungsten can be sintered. Perform simultaneous firing. As a result, the alumina in the first to third ceramic green sheets and the tungsten in the conductive paste are simultaneously sintered, and the dielectric 33, the discharge electrode 34, the through-hole conductor 41, the first pad 42 and the second pad 42 and the second. The pad 43 is formed by simultaneous firing, and the first to third ceramic green sheets serve as the electrode panel 30. At this time, the upstream end of each of the first linear portions 91 located at the upstream end 102 of the discharge electrode 34 has a shape having the upstream convex portion 106. Further, the end of each of the second linear portions 92 located at the side end 104 of the discharge electrode 34 on the first end surface 37 side has a shape having the first side convex portion 108, and the discharge electrode The end of each of the second linear portions 92 located on the side end portion 105 of 34 on the second end surface 38 side has a shape having the second side portion side convex portion 109.

After that, a laminating step is performed, and a plurality of the obtained electrode panels 30 are laminated to form a plasma panel laminated body 20. Next, the plurality of electrode panels 30 are sandwiched and fixed in the stacking direction by using clamps 50 to 55. At this time, the pair of pressing plates 57 constituting the clamps 52 and 55 are in pressure contact with the first pad 42 and the second pad 43. Further, by performing welding or the like, the central shaft 63 of the power supply terminal 61 is electrically connected to the tip of the holding plate 57 forming the first clamp 52, and the holding plate 57 forming the second clamp 55 is connected. The central shaft 63 of the power supply terminal 62 is electrically connected to the tip portion. Next, the mat 71 is attached so as to cover the outer surface of the plasma panel laminate 20, and then the case 10 is attached so as to cover the outer surface of the mat 71. After that, the first wiring 6 is connected to the tip of the power supply terminal 61, and the second wiring 7 is connected to the tip of the power supply terminal 62. Through the above process, the plasma reactor 1 is completed.

Therefore, according to the present embodiment, the following effects can be obtained.

(1) In the plasma reactor 1 of the present embodiment, the upstream convex portion 106 located at the upstream end 102 of the discharge electrode 34 has a shape having a square portion 107 in a plan view. Since the corner portion 107 is likely to be the starting point of discharge, discharge is generated at many points of the upstream end portion 102 having the corner portion 107, and plasma is surely generated. Therefore, PM in the exhaust gas deposited on the upstream end 102 can be efficiently removed by using plasma. As a result, conduction between adjacent discharge electrodes 34 via PM and conduction between the discharge electrode 34 and the case 10 via PM are prevented, so that insulation between adjacent discharge electrodes 34 and discharge electrode 34 are prevented. It is possible to secure the insulation between the case 10 and the case 10. Therefore, the reliability of the plasma reactor 1 can be improved.

(2) In the present embodiment, the clamps 52 and 55 electrically connected to the discharge electrode 34 are arranged at a location away from the upstream end 102, which is a location where PM is likely to be deposited. Will be prevented from adhering to the clamps 52 and 55. As a result, the conduction between the discharge electrode 34 and the case 10 via the PM and the clamps 52 and 55 is prevented, so that the insulation between the discharge electrode 34 and the case 10 is more reliably secured. Therefore, the reliability of the plasma reactor 1 is further improved.

(3) The plasma reactor 1 of the present embodiment is attached to the exhaust pipe 2 via the first cone portion 11 and the second cone portion 12. As a result, the resistance in the exhaust gas flow path through which the exhaust gas flows in the order of the upstream portion 4 of the exhaust pipe 2 → the first cone portion 11 → the plasma reactor 1 → the second cone portion 12 → the downstream portion 5 of the exhaust pipe 2 is reduced. Therefore, the pressure loss in the exhaust gas flow path can be suppressed. As a result, it is possible to prevent a decrease in engine output due to pressure loss.

The above embodiment may be changed as follows.

-In the above embodiment, both the upstream side end 102 and the side side end 108, 109 of the discharge electrode 34 have a shape having corners 107, 110 in a plan view. However, one of the upstream side end portion 102 and the side portion side end portions 108 and 109 may have a shape having a corner portion in a plan view. Further, as shown in FIGS. 10 and 11, only the upstream end portions 121 and 131 may have a shape having corner portions 122 and 132 in a plan view. The downstream end 103 of the discharge electrode 34 may have a shape having corners in a plan view.

In the above embodiment, the tip of the upstream convex portion 106 has a pointed shape having three corner portions 107 in a plan view. However, as shown in the discharge electrode 130 of FIG. 11, the tip portion of the upstream convex portion 133 may have a shape having two corner portions 132 in a plan view. Further, as shown in the discharge electrode 140 of FIG. 12, the upstream convex portion 141 may have a pointed shape having one corner portion 142 in a plan view. The tip of the upstream end may have a shape having four or more corners in a plan view.

In the above embodiment, the upstream side convex portion 106 of the upstream side end portion 102, the first side side convex portion 108 of the side side end portion 104, and the second side portion of the side side end portion 105. Of the lateral convex portions 109, only the upstream convex portion 106 had a shape that was pointed in a plan view. However, at least one of the first side convex portion 108 and the second side convex portion 109 may have a shape that is pointed in a plan view. Further, all of the upstream side end portion 102, the first side portion side convex portion 108, and the second side portion side convex portion 109 may have a shape that is pointed in a plan view.

In the above embodiment, the side end portion 104 of the discharge electrode 34 has a shape having a corner portion 110 in a plan view over the entire side side end portion 104. Further, in the above embodiment, the side end portion 105 of the discharge electrode 34 has a shape having a corner portion 110 in a plan view over the entire side portion side end portion 105. However, the side end portions 104 and 105 may have a shape in which only the region closer to the upstream side end portion 102 has a corner portion in a plan view. In this case, since it is sufficient to provide the corners only in a part of the side end portions 104 and 105, the manufacturing cost can be suppressed low.

As shown in FIG. 13, the plurality of discharge electrodes are the first electrode 151 (discharge electrode) provided on the first electrode panel (not shown) and the second electrode panel adjacent to the first electrode panel. It may be composed of a second electrode 152 (discharge electrode) provided on the electrode panel (not shown). Then, at least a part of the corner portion 153 provided on the first electrode 151 and at least a part of the corner portion 154 provided on the second electrode 152 may be arranged so as not to overlap each other. In FIG. 13, all of the upstream convex portions 156 (corner portions 153) located at the upstream end portion 155 of the first electrode 151 and the upstream side located at the upstream end portion 157 of the second electrode 152 are shown. All of the convex portions 158 (corner portions 154) are arranged so as to be offset in a direction orthogonal to the passing direction of the exhaust gas. In this way, a dielectric barrier discharge is generated between the corner portion 153 of the first electrode 151 and the corner portion 154 of the second electrode 152 located diagonally below the corner portion 153. As a result, plasma can be generated in a wider range at the upstream end portions 155 and 157 having the corner portions 153 and 154. Therefore, the PM deposited on the upstream end portions 155 and 157 can be reliably removed.

The first linear portion 91 and the second linear portion 92 constituting the discharge electrode 34 of the above embodiment had a square grid shape in a plan view, but formed a diamond shape or the like in a plan view. You may be doing it.

-The mat 71 of the above embodiment was configured by joining the first to fourth mat pieces 72 to 75 to each other. However, the mat may have an undivided structure.

The electrode panel 30 of the above embodiment is configured by incorporating the discharge electrode 34 in the dielectric 33. However, the electrode panel may be formed by forming the discharge electrode 34 on the surface of the dielectric 33.

-The plasma reactor 1 of the above embodiment has been used for purifying the exhaust gas of an automobile engine, but may be used for purifying the exhaust gas of an engine of a ship or the like, for example. Further, the plasma reactor 1 may be one that performs plasma treatment, and may not be one that treats exhaust gas, or may not be used for purification.

Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiments are listed below.

(1) The plasma reactor according to the means 1, wherein the voltage for generating plasma from the outer peripheral portion of the discharge electrode is lower than the voltage for generating plasma from the central portion of the discharge electrode.

(2) In the means 1, the electrode panel has a pair of main surfaces and a pair of end faces, and has a configuration in which the discharge electrode is built in the dielectric, and the outer peripheral edge of the discharge electrode. A plasma reactor characterized in that the distance from the end surface to the end surface is larger than the distance from the first surface of the discharge electrode to the main surface or the distance from the second surface of the discharge electrode to the main surface.

1 ... Plasma reactor 30 ... Electrode panel 33 ... Dielectric 34, 130, 140 ... Discharge electrode 100 ... Central portion 101 of the discharge electrode ... Outer peripheral portion 102, 121, 131, 155, 157 ... Upstream end portion 103 ... Downstream side end portions 104, 105 ... Side side end portions 106, 133, 141, 156, 158 ... Upstream side convex portion 108 as a convex portion ... First side side convex portion 109 as a convex portion ... As a convex portion Second side convex portion 107, 110, 122, 132, 142, 153, 154 ... Corner portion 151 ... First electrode as a discharge electrode 152 ... Second electrode as a discharge electrode

Claims (6)

A plasma reactor in which a plurality of electrode panels including a dielectric and a discharge electrode are provided in parallel at intervals, and gas is passed between the plurality of electrode panels to generate plasma by dielectric barrier discharge.
The outer peripheral portion of the discharge electrode is located between the upstream side end portion located on the gas inflow side, the downstream side end portion located on the gas outflow side, and the upstream side end portion and the downstream side end portion. Consists of including the side edge to which it is located
The upstream end portion has a shape having a corner portion in a plan view.
A plasma reactor characterized in that the discharge start voltage at the outer peripheral portion of the discharge electrode is lower than the discharge start voltage at the central portion of the discharge electrode. The plasma reactor according to claim 1, wherein both the upstream side end portion and the side portion side end portion have a shape having a corner portion in a plan view. The plasma reactor according to claim 2, wherein at least one of the upstream side end portion and the side portion side end portion has a shape having a convex portion in a plan view. The plasma reactor according to claim 3, wherein the convex portion of the upstream end portion has a shape that is pointed in a plan view. The plasma according to any one of claims 2 to 4, wherein the side end portion has a shape in which a region near the upstream end portion has a corner portion in a plan view. Reactor. The plurality of discharge electrodes consist of a first electrode and a second electrode adjacent to the first electrode.
The feature is that at least a part of the corner portion provided on the first electrode and at least a part of the corner portion provided on the second electrode are arranged so as not to overlap each other. The plasma reactor according to any one of claims 1 to 5.

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