JP2007090240A - Exhaust gas purifying apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifying apparatus using plasma discharge, capable of preventing short circuit of a circuit due to moisture in the exhaust gas. <P>SOLUTION: This exhaust gas purifying apparatus has: insulating honeycomb structure; a casing disposed at the outer periphery of the honeycomb structure, functioning as an outer peripheral electrode and containing the honeycomb structure; and a rod-like discharge electrode retained on a central axis of the casing, the casing is disposed to form an angle of 30-90° in relation to the horizontal plane with the insulating honeycomb structure set at the lower part, and the discharge electrode is inserted into the casing from the upper part not to contact the honeycomb structure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus that purifies harmful components in exhaust gas from an internal combustion engine or the like using plasma discharge.

  Various harmful components are contained in exhaust gas discharged from internal combustion engines and incineration facilities used in automobiles and the like. Of these harmful components, NOx, SOx, and particulate matter (or particulates, hereinafter referred to as “PM”) are desired to be reduced. For diesel engines. In recent years, in particular, it has been strongly desired to reduce the emission of PM, and a particulate filter is used to remove this PM.

  This type of particulate filter has a porous honeycomb structure made of ceramics such as cordierite, and the inlets of each flow path partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. The outlets are sealed in the flow paths, and only the exhaust gas that has permeated through the porous walls that define each flow path is discharged downstream. Since PM in the exhaust gas cannot pass through the porous wall, PM is collected on the inner surface of the porous wall.

  In such a filter, the collected PM causes the filter to be clogged, resulting in an increase in ventilation resistance and a burden on the engine. Therefore, before the ventilation resistance due to this clogging increases, the PM is appropriately adjusted. It is necessary to burn off and regenerate the filter. However, in the normal operation state of a diesel engine, an exhaust temperature that is high enough to cause PM to self-combust is not obtained.

  Therefore, recently, it has been proposed that plasma is generated by discharge, PM is burned and removed by the oxidizing action of the plasma, and NOx and the like are purified by the oxidizing action of the plasma and the reducing action of the catalyst.

  There are various types of exhaust gas purification methods using such discharge plasma. For example, as shown in FIG. 1, a plasma reactor having a cylindrical outer peripheral electrode 1 and a discharge electrode 2 on the central axis of the outer peripheral electrode. Has been proposed (see, for example, Patent Document 1).

JP-A-6-335621

  FIG. 2 shows a conventional exhaust gas purification apparatus using a plasma reactor. In this exhaust gas purifying device, the discharge plasma device 3 and the PM collecting part or the exhaust gas purifying catalyst 4 are continuously arranged integrally in a case functioning as an outer peripheral electrode in the exhaust gas flow path, and the PM collecting part or the exhaust gas purifying is performed by corona discharge. Purification of PM and NOx in the catalyst 4 is promoted. However, in such an exhaust gas purification device, there is a problem that a short circuit may occur between the discharge electrode 2 and the outer peripheral electrode 1 due to moisture condensed in the exhaust pipe after the engine is stopped, and a high voltage cannot be applied. .

  An object of the present invention is to provide an exhaust gas purification apparatus using plasma discharge that can solve such problems and prevent a short circuit of a circuit due to moisture in the exhaust gas.

In order to solve the above problem, according to the first invention,
Insulating honeycomb structure,
In the exhaust gas purification apparatus, comprising: a case that houses the honeycomb structure and functions as an outer peripheral electrode that is disposed on an outer peripheral portion of the honeycomb structure; and a rod-shaped discharge electrode that is held on a central axis of the case With the insulating honeycomb structure portion facing down and at an angle of 30 to 90 ° with respect to the horizontal plane, and the discharge electrode is inserted into the case from above so as not to contact the insulating honeycomb structure. ing.

  In order to solve the above problem, according to the second invention, in the first invention, the insertion portion of the discharge electrode into the case is provided in a portion that is not directly exposed to the exhaust gas flow.

  According to the present invention, in the exhaust gas purification apparatus in which the discharge plasma apparatus and the honeycomb structure are continuously arranged integrally in the case, the case is 30 to 90 ° with respect to the horizontal plane with the insulating honeycomb structure portion facing down. The discharge electrode of the discharge plasma apparatus is inserted into the case so as not to come into contact with the insulating honeycomb structure from the top, so that the bottom portion even if moisture flows into the apparatus together with the exhaust gas. And a short circuit is prevented from occurring between the discharge electrode and the case.

  Hereinafter, an exhaust gas purification apparatus of the present invention will be described with reference to the drawings. As shown in FIG. 3, the exhaust gas purifying apparatus includes an insulating honeycomb structure 5, a case 6 for housing the honeycomb structure, which is disposed on the outer peripheral portion of the honeycomb structure 5 and functions as an outer peripheral electrode; And a rod-shaped discharge electrode 7 held on the central axis of the case 6. The case 6 is disposed with the insulating honeycomb structure 5 facing downward so as to form an angle of 30 to 90 ° with respect to the horizontal plane, and the discharge electrode 7 is disposed from above the case 6 into the case. And is held by an insulating alumina tube or insulator 8.

  The discharge electrode 7 is electrically connected to a power source 9, and the case 6 as an outer peripheral electrode is grounded. By causing the power source 9 to act on the basis of a control signal from a control unit (not shown), the discharge electrode 7 A corona discharge is caused between 7 and the case 6 so that plasma can be generated.

  As the insulating honeycomb structure 5, a porous particulate filter made of ceramic such as cordierite or an exhaust gas purification catalyst in which a catalyst metal such as a noble metal is supported on a ceramic honeycomb can be used.

  In this exhaust gas purifying apparatus, when exhaust gas discharged from an engine or the like flows, a power source 9 is actuated by a control signal from a control unit according to the amount of harmful components in the exhaust gas, and a corona between the discharge electrode 7 and the case 6 is applied. The discharge is sustained over a relatively wide range. Then, the exhaust gas passing through this portion is excited, NO and the like contained in the exhaust gas are activated as plasma by corona discharge, and highly active components flow into the honeycomb structure 5.

  When a particulate filter is used as the insulating honeycomb structure 5, PM is ignited at a lower temperature than before as a result of the oxidation reaction of PM collected by the particulate filter being promoted by the above-mentioned highly active component. Will be burned off. Further, when an exhaust gas purification catalyst is used as the insulating honeycomb structure 5, since the components in the exhaust gas flow in as highly active components, harmful components in the exhaust gas can be efficiently oxidized or reduced and rendered harmless.

  Incidentally, when the conventional exhaust gas purification apparatus as shown in FIG. 2 is installed in an automobile, it is installed in parallel to the floor surface of the vehicle and the exhaust gas is purified in this parallel direction. The exhaust gas also contains water vapor. Therefore, after the engine is stopped, the water vapor is condensed in the exhaust pipe to form water droplets. When this moisture enters the exhaust gas purification device, it accumulates at the bottom of the case 1 as the outer peripheral electrode, and discharge electrode A circuit is formed between the two. As a result, a state where a high voltage cannot be applied occurs.

  In the exhaust gas purifying apparatus of the present invention, the case is arranged vertically with respect to the vehicle floor so as to form an angle of 30 to 90 ° with respect to the horizontal plane. In addition, a short circuit can be prevented. Further, since the discharge electrode 7 is inserted so as not to come into contact with the honeycomb structure 5, even if moisture accumulates on the honeycomb structure 5, this moisture does not contact the discharge electrode 5, thereby preventing a short circuit. be able to.

  It is the attachment portion of the discharge electrode 5 to the case 6 that is most likely to cause a short circuit between the discharge electrode 5 and the case 6 that is the outer peripheral electrode. Thus, the discharge electrode 5 is fixed to the case 6. By preventing moisture from adhering to the attachment portion, it is possible to more effectively prevent a short circuit. Therefore, it is preferable to provide a portion where the discharge electrode 7 is inserted into the case 6 at a portion which is not directly exposed to the exhaust gas flow. In other words, as shown in FIG. 3, it is preferable to introduce the exhaust gas so that the exhaust gas flow is not applied to the portion where the discharge electrode 7 is inserted into the case 6.

  Water was sufficiently absorbed by the ceramic particulate filter, placed in the exhaust gas purification device as shown in FIG. 3, the engine was started, voltage was applied, and the time until PM collection in the filter worked was measured. . However, since a high voltage cannot be applied when the current value exceeds 10 mA, the time until the current value becomes 10 mA or less and the power switch is turned on every 30 seconds until electrostatic collection functions. Was measured. For comparison, the same particulate filter was used, and the same measurement was performed in the conventional exhaust gas purification apparatus shown in FIG. The results are shown in Table 1 below.

  From this result, it can be seen that the exhaust gas purification apparatus of the present invention can collect PM electrostatically at the same time as starting the engine, and can prevent a short circuit due to moisture.

It is a perspective view of the conventional plasma generator. 1 is a schematic view of a conventional exhaust gas purification device. 1 is a schematic view of an exhaust gas purification apparatus of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Perimeter electrode 2 Discharge electrode 3 Discharge plasma apparatus 4 PM collection part 5 Honeycomb structure 6 Case 7 Discharge electrode 8 Alumina tube 9 Power supply

Claims (2)

Insulating honeycomb structure,
An exhaust gas purification apparatus having a case housing the honeycomb structure and functioning as an outer peripheral electrode disposed on an outer peripheral portion of the honeycomb structure, and a rod-shaped discharge electrode held on a central axis of the case, The case is disposed so as to form an angle of 30 to 90 ° with respect to a horizontal plane with the insulating honeycomb structure portion facing down, so that the discharge electrode does not come into contact with the insulating honeycomb structure from the top into the case. Inserted exhaust gas purification device. The exhaust gas purifying apparatus according to claim 1, wherein an insertion portion of the discharge electrode into the case is provided in a portion that is not directly exposed to the exhaust gas flow.

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