JP2006144563A - Emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize a plasma assist type emission control device employing barrier discharge which implements easy manufacture of electrodes having a ventilation structure in which the surface is insulation-coated with a dielectric material. <P>SOLUTION: A plasma assist type emission control device is equipped with a flat-shaped electrode 15 (electrode plate) having a ventilation structure, a plurality of electrodes 18 which are arranged so as to sandwich a plasma generating space 16 having a uniform interval with respect to a surface of the flat-shaped electrode 15 and whose surfaces are insulation-coated with dielectric material 17, and a filter means formed in the flat-shaped electrode 15 itself, wherein exhaust gas 8 is made to flow so as to pass through the plasma generating space 16 and the flat-shaped electrode 15 from a clearance in a row group of electrodes 18 and voltage required for discharge can be applied between each flat-shaped electrode 15 and each electrode 18. The electrode 18 is inserted into the dielectric material 17 formed to be tubular so as to be subjected to an insulating coating on the electrode 18. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device that removes particulates from exhaust gas of an internal combustion engine such as a diesel engine.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot made of carbonaceous matter and SOF content (Soluble Organic Fraction) made of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. It has been done conventionally.

  This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.

  Particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, and are spontaneously combusted and removed when the exhaust gas moves to an operating region. For example, in a vehicle that travels only on a congested road such as a route bus in Tokyo, the accumulated amount is higher than the processing amount of particulates because the operation above the required predetermined temperature does not continue for a long time. There is a possibility that the particulate filter may be clogged.

  For this reason, plasma-assisted exhaust purification devices are being developed so that particulates can be burned and removed well even in the operating region where the exhaust temperature is low, and this type of exhaust purification device discharges into the exhaust gas to generate plasma. The exhaust gas is excited and active radicals such as O radicals and OH radicals are generated, and these exhaust gas excitation components are in an activated state, so even in an operation region where the exhaust temperature is low. It is possible to burn and remove the particulates (oxidation treatment) satisfactorily.

For example, in Patent Document 1 and Patent Document 2 below, ceramic pellets forming a dielectric material are filled between an outer electrode and an inner electrode made of cylindrical stainless steel that has been perforated, and a packed layer of the pellet is formed. A plasma-assisted exhaust purification system is proposed in which exhaust gas is allowed to flow and particulates in the exhaust gas are collected, while plasma is generated by discharging between the outer electrode and the inner electrode. Has been.
Japanese translation of PCT publication No. 2002-501813 Japanese translation of PCT publication No. 2002-511332

  In addition, although these patent documents 1 and 2 do not have a clear description, in the plasma assist type exhaust gas purification apparatus as in patent documents 1 and 2, either the outer electrode or the inner electrode (or both) is used. ) Is insulated with a dielectric material, thereby causing a barrier discharge to generate a low temperature plasma (non-thermal equilibrium plasma), and it is considered necessary to help burn and remove particulates more safely using the low temperature plasma. ing.

  That is, if either one (or both) of the outer electrode and the inner electrode is covered with a dielectric to cause barrier discharge, electrons will not fly directly from one electrode to the other. In addition, it is possible to stably generate low-temperature plasma (non-thermal equilibrium plasma) while preventing the transition to arc discharge, and it is possible to avoid an unexpected short circuit due to the deposition of particulates on the outer and inner electrodes. Because.

  However, in such a plasma assist type exhaust gas purification device that has been proposed in the past, the particulate packing in the exhaust gas is collected by traversing the packed bed of pellets together with each electrode. However, there is a problem that it is technically difficult to insulate and cover such an electrode with a dielectric because it has a ventilation structure composed of a metal mesh, a punching metal, or the like.

  For example, when insulatingly coating each electrode composed of a metal mesh or punching metal with a dielectric, means such as ceramic coating can be applied to each electrode, but coating on thin objects such as a metal mesh or punching metal Then, problems such as cracks and cracks are caused by the difference in thermal expansion.

  The present invention has been made in view of the above-described circumstances, and realizes a plasma-assisted exhaust purification device by barrier discharge so that a gas-permeable electrode whose surface is covered with a dielectric can be easily manufactured. It is an object.

  The present invention relates to an electrode plate having a ventilation structure, a plurality of electrode rods arranged with a plasma generation space at a uniform interval with respect to the surface of the electrode plate, and having a surface insulated by a dielectric, and an electrode plate And a filter means configured in at least one of the plasma generation spaces, the exhaust gas is allowed to flow through the plasma generation space and the electrode plates through the gaps between the electrode rod rows, and each electrode plate and each electrode rod Is a plasma-assisted exhaust purification device that can apply a voltage required for discharge between the electrode and the dielectric rod formed so as to form a tubular shape when forming an electrode rod whose surface is insulated. An electrode rod is inserted therein.

  In this way, an electrode rod whose surface is insulated and coated can be easily manufactured by simply inserting the electrode rod into a dielectric formed to have a tubular shape. An electrode plane is formed by arranging a plurality of plasma generation spaces with a uniform interval with respect to the surface of the plate, and a ventilation structure is also realized by passing through the gaps in the row group.

  Further, according to the structure in which the electrode rod is inserted into the tubular dielectric, even if the electrode rod is thermally expanded in the tubular dielectric, it expands independently of the outer dielectric. In addition, no cracks or cracks are generated in the outer dielectric, and the possibility of loss of insulation is avoided in advance.

  In actual use, when exhaust gas is allowed to flow through the plasma generation space and the electrode plate through the gap between the electrode rod rows, the exhaust gas is configured in at least one of the electrode plate and the plasma generation space. When the necessary voltage is applied between the electrode plate and each electrode rod when necessary, each electrode rod and electrode plate whose surfaces are insulated and coated are collected. As a result, a barrier discharge occurs between them, and as a result, low-temperature plasma (non-thermal equilibrium plasma) is generated in the plasma generation space. As a result, exhaust gas is excited and active radicals such as O radicals and OH radicals are generated. The particulates are effectively burned and removed (oxidized) with the help of the components.

  At this time, since the plurality of electrode bars are opposed to the electrode plate in a curved shape with a small curvature, an electric field that is locally stronger than when a pair of electrode plates are simply opposed to each other is formed. It is easy to generate low-temperature plasma without applying a very high voltage.

  In addition, regarding the same plasma-assisted exhaust gas purification apparatus, when forming an electrode bar whose surface is covered with insulation, an electrode material may be coated on the inner peripheral surface of a dielectric formed so as to form a tubular shape. In this way, an electrode rod having a surface that is simply covered with an insulating material can be manufactured simply by coating an electrode material on the inner peripheral surface of the dielectric formed to have a tubular shape.

  In addition, according to the structure in which the electrode material is coated on the inner peripheral surface of the tubular dielectric as described above, there is no gap between the outer dielectric and the inner electrode rod, and there is no waste between the two. The possibility that a serious discharge will occur is avoided in advance.

  Even if the electrode rod coated on the inner peripheral surface of the tubular dielectric is thermally expanded, the coating layer forming the electrode rod only becomes wrinkles locally, and the outer dielectric is cracked or cracked. There is no strong stress that can be generated.

  Furthermore, in the present invention, it is preferable to form a large number of edge portions on the surface of the tubular dielectric, and in this way, a strong electric field is easily formed locally at each edge portion, and low temperature plasma is formed. Can be further easily generated.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the first and second aspects of the present invention, an electrode rod is inserted into a dielectric formed to form a tube, or the inner circumference of the dielectric formed to form a tube. By coating the surface with an electrode material to form an electrode rod, it is possible to easily manufacture a gas-permeable structure electrode whose surface is covered with a dielectric as a group of a plurality of electrode rods. A plasma-assisted exhaust purification device can be realized.

  (II) According to the invention described in claim 1 of the present invention, since the outer dielectric does not crack or crack even if the electrode rod is thermally expanded in the tubular dielectric, the insulation is long. It can be kept stable over a period of time.

  (III) According to the invention described in claim 2 of the present invention, since the gap between the outer dielectric and the inner electrode rod can be eliminated, there is a possibility that wasteful discharge may occur between them. It can be avoided.

  (IV) According to the invention described in claim 3 of the present invention, since a strong electric field is likely to be locally formed at a large number of edge portions formed on the surface of the tubular dielectric, low temperature plasma is further generated. Can be made easier.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 to 4 show an example of an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes a diesel engine (internal combustion engine) equipped with a turbocharger 2, and intake air introduced from an air cleaner 3. 4 is introduced into the compressor 2a of the turbocharger 2 through the intake pipe 5 and pressurized, and the pressurized intake air 4 is distributed and introduced to each cylinder of the diesel engine 1 via the intercooler 6.

  Further, exhaust gas 8 discharged from each cylinder of the diesel engine 1 through the exhaust manifold 7 is sent to the turbine 2b of the turbocharger 2, and the exhaust gas 8 driving the turbine 2b is supplied to the plasma assist in the middle of the exhaust pipe 9. Particulates are collected through the exhaust gas purification device 10 and then discharged.

  This exhaust purification device 10 has a schematic structure as shown in FIGS. 2 and 3, and the required number thereof is collected by a casing 12 (only a part is shown in FIG. More specifically, a pair of flat plate electrodes 15 (electrode plates) forming a ventilation structure facing each other with a required gap therebetween, and each flat plate electrode 15 between each flat plate electrode 15. A plurality of electrode rods 18 arranged in parallel with a gap of several millimeters across a plasma generation space 16 with a uniform spacing with respect to the surface of the surface, and having a surface insulated by a dielectric 17. Both ends of each electrode rod 18 are supported by insulating structures 13 and 14.

  Here, in the example shown in FIGS. 2 and 3, the case where the plate electrode 15 itself is configured as a filter means is illustrated, and the plate electrode 15 is formed by a metal filter capable of collecting particulates. Has a ventilation structure.

  This type of metal filter includes micron-order metal fibers laminated and sintered, metal powder sintered bodies, metal mesh laminated and sintered, metal mesh sintered metal powder, etc. Should be adopted.

  However, a cordierite honeycomb filter, a ceramic fiber filter, a ceramic foam, an alumina pellet or the like can be interposed as a filter means in the plasma generation space 16, and in this case, the plate electrode 15 is not necessarily provided. It does not need to be configured as a filter means, and may be configured as a flat plate electrode 15 having a simple ventilation structure made of a metal mesh, punching metal, or the like. Of course, for the purpose of obtaining a high collection rate, the plate electrode 15 itself may be configured as a filter means, and a filter means may be used in the plasma generation space 16 together.

  Incidentally, when the plasma generating space 16 is filled with a dielectric granular material such as ceramic pellets to form a filter means, electric charges concentrate at each contact point of the granular material to form a strong local electric field, thereby reducing the temperature. Plasma is easily generated, and if a plurality of planes extending in the opposing direction of the plate electrode 15 and the electrode rod 18 are formed by the filter means interposed in the plasma generation space 16, creeping discharge along this plane is promoted. Therefore, low temperature plasma is likely to be generated.

  On the other hand, a gas inlet 20 for introducing the exhaust gas 8 into the introduction space 19 sandwiched between the two rows of the electrode rods 18 is opened in the front insulating structure 13, and the rear side The insulating structure 14 has a closed structure that blocks the flow of the exhaust gas 8, and the exhaust gas 8 introduced into the introduction space 19 from the upstream side through the gas inlet 20 passes through the gaps between the row groups of the electrode rods 18. It passes through the plasma generation space 16 and the plate electrode 15 and flows downstream.

  Further, the rear end of each electrode rod 18 penetrates the rear insulating structure 14 to form a power feeding portion 22 made of a conductor plate outside the insulating structure 14. In contrast, a power source 21 is connected through the housing 12 and each plate electrode 15 is grounded, and an AC high voltage (DC pulse high voltage) necessary for discharge is generated between each plate electrode 15 and each electrode rod 18. However, it is possible to apply).

  Here, in this embodiment, when the electrode rod 18 whose surface is insulated is formed, as shown in FIG. 4, the electrode rod 18 is inserted into a dielectric 17 formed in a tubular shape. Insulating coating of the electrode rod 18 is performed.

  In this way, the electrode rod 18 whose surface is covered with insulation can be easily manufactured simply by inserting the electrode rod 18 into the dielectric 17 formed to have a tubular shape. An electrode plane is formed by arranging a plurality of rods 18 with the plasma generation space 16 having a uniform interval with respect to the surface of the plate electrode 15, and a ventilation structure is also realized by passing through the gaps in the row group. become.

  Further, according to the structure in which the electrode rod 18 is inserted into the tubular dielectric body 17, even if the electrode rod 18 is thermally expanded in the tubular dielectric body 17, it expands independently of the outer dielectric body 17. As a result, the outer dielectric is not cracked or cracked, and the risk of loss of insulation is avoided.

  When the exhaust gas 8 introduced into the introduction space 19 from the gas inlet 20 is caused to flow through the plasma generation space 16 and the plate electrode 15 through the gaps between the row groups of the electrode rods 18 in actual use, Since the particulates are collected when the gas 8 passes through the flat plate electrode 15 forming the metal filter, a DC pulse high voltage (even with a DC pulse high voltage) is provided between each flat plate electrode 15 and each electrode rod 18 when necessary. As a result, barrier discharge occurs between each electrode rod 18 whose surface is insulated with a dielectric 17 and the plate electrode 15, thereby generating low-temperature plasma (non-thermal equilibrium plasma) in the plasma generation space 16. The exhaust gas 8 is excited to generate active radicals, and the particulates are effectively removed by combustion with the assistance of these exhaust gas excitation components (oxidation treatment). It is is will be.

  At this time, since the plurality of electrode rods 18 are opposed to the flat plate electrode 15 with a curved surface having a small curvature, an electric field that is locally stronger than when the pair of flat plate electrodes 15 are simply opposed to each other. It is possible to generate low temperature plasma without applying a very high voltage.

  Therefore, according to the above-described embodiment, by inserting the electrode rod 18 into the dielectric 17 formed in a tubular shape, a plurality of electrodes having a ventilation structure whose surface is insulated by the dielectric 17 are formed. Since it can be easily manufactured as a group of rods 18, it is possible to realize a plasma-assisted exhaust purification device by barrier discharge, and the electrode rod 18 is thermally expanded in the tubular dielectric 17. However, since the outer dielectric 17 is not cracked or cracked, the insulating property can be stably maintained for a long period of time.

  FIG. 5 shows another embodiment of the present invention. In constructing the electrode rod 18 whose surface is insulated, an electrode material such as silver is applied to the inner peripheral surface of the dielectric 17 formed in a tubular shape. The electrode rod 18 may be coated by pasting it into a paste form. In this way, the surface can be easily insulated by simply coating the inner peripheral surface of the dielectric 17 formed in a tubular shape with an electrode material. The electrode rod 18 is manufactured.

  In addition, according to the structure in which the electrode material is coated on the inner peripheral surface of the tubular dielectric body 17 as described above, there is no gap between the outer dielectric body 17 and the inner electrode bar 18. In addition, it is possible to avoid the possibility that wasteful discharge occurs during this time.

  Note that even if the electrode rod 18 coated on the inner peripheral surface of the tubular dielectric 17 is thermally expanded, the coating layer forming the electrode rod 18 cracks into the outer dielectric 17 only by locally becoming wrinkles. Strong stress that causes cracks or the like does not occur.

  Further, as shown in FIGS. 4 and 5, the electrode rod 18 is inserted into the dielectric 17 formed so as to form a tube, or the inner peripheral surface of the dielectric 17 formed so as to form a tube. When the electrode material is coated to form the electrode rod 18, as shown in FIG. 6, a large number of edge portions 17a are formed by performing processing such as engraving grooves on the surface of the tubular dielectric 17 in the circumferential direction. In this way, a strong electric field is easily formed locally at each edge portion 17a, and low temperature plasma can be more easily generated.

  Further, in the above description, the case where the gas-permeable electrode plate is the flat plate electrode 15 is illustrated, but as shown in FIG. 7, the cylindrical electrode 15 ′ is a cylindrical electrode as the gas-permeable electrode plate. In such a case, a plurality of electrode rods 18 are arranged in an annular shape with a plasma generation space 16 having a uniform interval with respect to the inner peripheral surface of the cylindrical electrode 15 '. You can do it.

  The exhaust emission control device of the present invention is not limited to the above-described embodiments. The electrode plate having a ventilation structure may be provided with a curved surface shape other than a cylindrical shape. Of course, various changes can be made without departing from the scope of the invention.

It is the schematic which shows an example of the form which implements this invention. It is a top view which shows schematic structure of the exhaust gas purification apparatus of FIG. It is sectional drawing of the III-III arrow of FIG. It is a perspective view which expands and shows the detail of the electrode rod of FIG. It is a perspective view which shows another example of a form of this invention. It is a perspective view which shows the modification of the dielectric material formed so that a tubular shape might be comprised. It is sectional drawing which shows the example which employ | adopted the cylindrical cylindrical electrode for the electrode plate of a ventilation structure.

Explanation of symbols

8 Exhaust gas 10 Exhaust gas purification device 15 Flat plate electrode (filter means)
15 'cylindrical electrode (filter means)
16 Plasma generation space 17 Dielectric 17a Edge portion 18 Electrode rod 21 Power source 22 Power feeding portion

Claims (3)

  An electrode plate having a ventilation structure, a plurality of electrode rods arranged with a plasma generation space at a uniform interval with respect to the surface of the electrode plate, and having a surface insulated by a dielectric, and the electrode plate and the plasma generation space And at least one of the filter means, the exhaust gas is allowed to flow through the plasma generation space and the electrode plate through the gap between the electrode rod rows, and between each electrode plate and each electrode rod. A plasma-assist type exhaust purification device capable of applying a voltage required for discharge, wherein an electrode rod is formed in a dielectric formed in a tubular shape when forming an electrode rod with an insulating coating on the surface. An exhaust emission control device characterized by having inserted.   At least one of an electrode plate having a ventilation structure, a plurality of electrode rods arranged in parallel with the surface of the electrode plate across the plasma generation space and having a surface insulated by a dielectric, and the electrode plate and the plasma generation space Filter means arranged on either side, and exhaust gas is allowed to flow through the plasma generation space and the electrode plates through the gaps between the electrode rod rows, and is necessary for discharge between each electrode plate and each electrode rod A plasma assist type exhaust gas purification device that can apply a voltage to an inner surface of a dielectric formed in a tubular shape when forming an electrode rod whose surface is insulated. An exhaust purification device characterized in that it is coated into an electrode rod.   The exhaust emission control device according to claim 1 or 2, wherein a large number of edge portions are formed on the surface of the tubular dielectric.

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