JP2007182810A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device improved in energy efficiency, PM collection efficiency and the like. <P>SOLUTION: The exhaust emission control device has an insulative honeycomb structural body, an outer peripheral electrode disposed on an outer peripheral part of the honeycomb structural body and a bar electrode disposed on a central axis of the honeycomb structural body. The outer peripheral electrode and bar electrode are extended to an upstream side of exhaust gas flow in the honeycomb structural body. A plurality of discharge projections are provided on the part of the bar electrode, which is extended to the exhaust gas flow upstream side of the honeycomb structural body, and an insulative member is disposed on an inner peripheral surface of the part of the outer peripheral electrode, which is extended to the exhaust gas flow upstream side of the honeycomb structural body. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purifying apparatus for removing harmful components, particularly particulate matter (hereinafter referred to as PM), in exhaust gas from an internal combustion engine or the like by 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, it is desired to reduce NOx, SOx, and PM emissions. 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, an exhaust gas purifying apparatus (plasma reactor) has been proposed that generates plasma by discharge, burns and removes PM by the oxidizing action of the plasma, and purifies NOx and the like by the oxidizing action of the plasma and the reducing action of the catalyst. .

  FIG. 1 shows an example of a conventional exhaust gas purification device. The exhaust gas purification apparatus 10 has a case 11 that is incorporated between exhaust pipes L1 and L2 that constitute an exhaust system of an internal combustion engine, and exhaust gas is introduced into the case 11. In the case 11, the honeycomb structure 12, the outer peripheral electrode 13, and the rod-shaped electrode 14 are disposed. A power source 15 is connected to the rod-shaped electrode 14, and the outer peripheral electrode 13 is grounded. When the power source 15 is operated, a discharge is generated between the rod-shaped electrode 14 and the outer peripheral electrode 13 to generate plasma.

  In such an exhaust gas purifying apparatus, it has been proposed to install an electrically insulating hollow cylinder between the electrodes in order to avoid unnecessary energy consumption due to the occurrence of sparks between the electrodes (see Patent Document 1). ).

JP 2001-162134 A

  However, the above exhaust gas purification apparatus has room for improvement in terms of energy efficiency, PM collection efficiency, and the like. An object of the present invention is to provide an exhaust gas purifying apparatus that solves such problems and improves energy efficiency, PM collection efficiency, and the like.

In order to solve the above problem, according to the first invention,
Insulating honeycomb structure,
In the exhaust gas purifying apparatus having an outer peripheral electrode disposed on an outer peripheral portion of the honeycomb structure and a rod-shaped electrode disposed on a central axis of the honeycomb structure, the outer electrode and the rod-shaped electrode are connected to the exhaust gas of the honeycomb structure. A plurality of discharge protrusions are provided in a portion of the rod-shaped electrode that extends to the upstream side of the flow and extends to the upstream side of the exhaust gas flow of the honeycomb structure, and the exhaust flow of the honeycomb structure of the outer peripheral electrode An insulating member is disposed on the inner peripheral surface of the portion extending upstream.

According to the second invention to solve the above problem,
Insulating honeycomb structure,
An outer peripheral electrode disposed on an outer peripheral portion of the honeycomb structure; and a rod-shaped electrode disposed on a central axis of the honeycomb structure, wherein the outer peripheral electrode and the rod-shaped electrode are upstream of the exhaust gas flow of the honeycomb structure The rod-shaped electrode has a plurality of discharge protrusions at a portion extending upstream of the exhaust gas flow of the honeycomb structure, and the exhaust gas flow of the honeycomb structure of the outer peripheral electrode A plurality of processing units in which insulating members are arranged on the inner peripheral surface of the portion extending upstream are arranged in series from the upstream side to the downstream side of the exhaust gas flow.

  According to the present invention, by disposing an insulating member between the outer peripheral electrode and the rod-shaped electrode, it is possible to prevent the occurrence of sparks between the electrodes, to prevent a short circuit between the electrodes due to PM deposition, and to improve energy efficiency and PM collection efficiency. Can be improved. Further, by providing discharge protrusions on the rod-like electrode, it is possible to promote electron emission and improve energy efficiency. Furthermore, by combining these, before reaching the honeycomb structure, PM is charged by the micro discharge generated between the rod-shaped electrode upstream of the exhaust gas flow and the insulating member and collected by the honeycomb structure, and the exhaust gas is activated. To promote PM oxidation. Further, by combining a plurality of units having such a configuration, it is possible to prevent PM accumulation, particularly in the downstream unit, and promote PM oxidation.

  Hereinafter, one mode of an exhaust gas purification apparatus of the present invention will be described with reference to the drawings. As shown in FIG. 2, the exhaust gas purification device 20 includes a honeycomb structure 22, an outer peripheral electrode 23 disposed on the outer peripheral portion of the honeycomb structure 22, and a rod-shaped member disposed on the central axis of the honeycomb structure 22. It has an electrode 24.

  Here, the outer peripheral electrode 23 and the rod-shaped electrode 24 extend to the upstream side of the exhaust gas flow of the honeycomb structure 22, and the rod-shaped electrode 24 extends to the portion of the honeycomb structure 22 that extends to the upstream side of the exhaust gas flow. An insulating member 26 is disposed on the inner peripheral surface of a portion having a plurality of discharge protrusions 27 and extending to the exhaust gas upstream side of the honeycomb structure 22 of the outer peripheral electrode 23.

  The rod electrode 24 is connected to the power source 25 and the outer peripheral electrode 23 is grounded. However, the rod electrode 24 may be grounded and the outer peripheral electrode 23 may be connected to the power source. Alternatively, the rod-shaped electrode 24 and the outer peripheral electrode 23 may be connected to different poles of the power source 25. The rod-shaped electrode 24 is fixed to the honeycomb structure remaining on the downstream side of the exhaust gas flow in the radial center portion of the honeycomb structure 22.

  The exhaust gas purification device 20 is housed in a case 21 and connected to an exhaust pipe constituting an exhaust system of an internal combustion engine. However, the case 21 may be made of metal and used as an outer peripheral electrode. The exhaust gas containing PM flows from the left side to the right side of the drawing as shown by the arrow, and passes through the honeycomb structure 22 surrounded by the outer peripheral electrode 23.

Here, each component which comprises the exhaust gas purification apparatus 20 is demonstrated concretely.
The insulating honeycomb structure 22 is formed of a ceramic such as cordierite or alumina, and has a large number of cells extending in the flow direction of the exhaust gas. The honeycomb structure 22 may be a straight flow type or a wall flow type. Here, the honeycomb structure 22 has sufficient insulation, so that the conductivity is smaller than that of the PM, and when a voltage is applied, a current flows through the PM itself so that the PM is energized and combusted. Should.

The honeycomb structure 22 can be formed by grinding a part of a normal honeycomb carrier formed into a cylindrical shape, but may be manufactured by any other method as long as a desired shape can be obtained. Good. In addition, an oxidation catalyst such as CeO ₂ , Pt / CeO ₂ , Mn / CeO ₂ , Fe / CeO ₂ , and Pt / Al ₂ O ₃ may be supported on the cell walls of the honeycomb structure 22.

  The rod-shaped electrode 24 is formed of a material capable of applying a voltage between the rod-shaped electrode 24 and the outer peripheral electrode 23. As this material, a conductive material or a material such as a semiconductor can be used, and among these, a metal material is preferable. Specifically, copper, tungsten, stainless steel, iron, platinum, aluminum or the like can be used as the metal material, and stainless steel is particularly preferable from the viewpoint of cost and durability. The shape of the rod-shaped electrode 24 is generally a wire, but a hollow rod-shaped electrode can also be used.

  The rod-shaped electrode 24 can be formed of the same material as that of the rod-shaped electrode 24, and the discharge projection 27 provided at a portion extending and projecting from the honeycomb structure 22 to the upstream side of the exhaust gas flow. The plurality of needles are formed in a spine shape, and are arranged radially from the rod-shaped electrode 24 so that the tip thereof faces the outer peripheral electrode 23. Although the number of needle-like portions of the discharge protrusion 27 needs to be abnormal to some extent, an optimized number can be determined by experiment so as to charge the PM in the exhaust gas most satisfactorily.

  The outer peripheral electrode 23 is formed in a cylindrical shape by winding the same material as the rod-shaped electrode 24 around the honeycomb structure 22 as a metal mesh or a metal foil. Alternatively, the conductive paste can be applied to the honeycomb structure 22 and formed.

  The power supply 25 may generate a pulsed or steady DC voltage. As the applied voltage and the pulse period, general values for generating plasma can be used. For example, a pulse voltage of 50 kV and a pulse period of 2,000 Hz can be used.

  The insulating member 26 provided on the inner peripheral surface of the portion of the outer peripheral electrode 23 that extends to the upstream side of the exhaust flow of the honeycomb structure 22 is formed in a cylindrical shape from a ceramic or the like similar to the honeycomb structure 22. Can be formed. The insulating member 26 is preferably porous, and the pore diameter is more preferably 15 to 200 μm.

  As described above, by providing the discharge protrusion 27 on the rod-shaped electrode 24, the applied voltage can be reduced and the energy efficiency can be improved. Specifically, in the conventional exhaust gas purification apparatus as shown in FIG. 1, the applied voltage required to achieve a PM collection rate of 95% was 30 kV. The applied voltage dropped to 17 kV. Further, the provision of the insulating member 26 can suppress the occurrence of a short circuit between the rod-shaped electrode 24 and the outer peripheral electrode 23. That is, as shown in FIG. 3, in the conventional exhaust gas purifying apparatus in which such an insulating member is not arranged, the PM 16 is deposited, so that the rod-shaped electrode 14 and the outer peripheral electrode 13 are short-circuited by the PM 16 and the circuit Is formed and the insulation is destroyed. Then, it can no longer be discharged, and the PM collection rate and the exhaust gas purification rate are reduced. Therefore, as shown in FIG. 2, by arranging an insulating member on the inner peripheral surface of the outer peripheral electrode 23, a short circuit between the outer peripheral electrode 23 and the rod-shaped electrode 24 due to PM deposition can be prevented.

  Furthermore, in the present invention, the discharge protrusion 27 is provided on the rod-shaped electrode 24 and the insulating member 26 is provided on the inner peripheral surface of the outer peripheral electrode 23, whereby microdischarge can be generated and PM oxidation can be promoted. Specifically, as shown in FIG. 4, when the rod-shaped electrode 24 is a negative electrode, charges having a polarity opposite to the discharged charge are collected in the insulating member 26, and then a discharge phenomenon is reversed from the insulating member 26. Occurs and activates the exhaust gas and promotes PM oxidation.

  In the second aspect of the present invention, the exhaust gas purifying apparatus is a single processing unit, and a plurality of the processing units are arranged in series from the upstream side to the downstream side of the exhaust gas flow. Specifically, as shown in FIG. 5, in the exhaust gas purifying apparatus 50, a plurality of processing units 51 are arranged in series in a case 52 from upstream to downstream of the exhaust gas flow. Each processing unit 51 includes an insulating honeycomb structure 53, an outer peripheral electrode 54 disposed on an outer peripheral portion of the honeycomb structure, and a rod-shaped electrode 55 disposed on a central axis of the honeycomb structure. The electrode 54 and the rod-shaped electrode 55 extend to the exhaust gas flow upstream side of each honeycomb structure 53, and the rod-shaped electrode 55 extends to the exhaust gas flow upstream side of each honeycomb structure 53. A plurality of discharge protrusions 56 are provided at a part, and an insulating member 57 is disposed on the inner peripheral surface of the outer peripheral electrode 54 that extends to the upstream side of the exhaust flow of each honeycomb structure 53.

  As described above, the exhaust gas can be more activated by generating a micro charge between the discharge protrusion and the insulating member, but PM is also deposited on the honeycomb structure during this activation, and the deposition As a result, the exhaust gas purification ability decreases with time. Therefore, by dividing the honeycomb structure to form a repetitive structure of a plurality of units, particularly in the downstream unit, PM deposition is small, a clean surface can be maintained, and exhaust gas purification performance can be maintained high.

PM oxidation rate test and PM collection rate measurement test Using the experimental apparatus shown in Fig. 6, the engine operating conditions were: rotation speed = 1800 rpm, torque = 30 N · m, inlet gas temperature: 200 ° C, as follows: Then, the PM oxidation rate and the PM collection rate were measured.

  First, the engine was warmed up while throwing exhaust gas to the bypass side. After confirming the completion of warm-up, dynamo was set to a predetermined condition, and voltage application was started until the voltage value reached the maximum value to the exhaust gas purification device. Next, exhaust gas was flowed to the main side (exhaust gas purification device side), and the PM collection rate was measured at a rate of once every 5 minutes through a full dilution tunnel. Further, a part of the exhaust gas was used to see the change over time in the collection rate with a particle number measuring device (ELPI). In this way, the experiment was performed for 30 minutes, and the exhaust gas was turned to the bypass side and the experiment was completed. The sample after completion of the experiment was decomposed and pulverized, and was subjected to measurement of the amount of PM remaining in the DPF using MEXA 1370-PM manufactured by HORIBA. The PM oxidation rate was obtained from the collected rate measurement value and the present analysis value.

Specifically, the PM oxidation rate is the amount of incoming PM-(outgoing PM amount + remaining PM amount)
The amount of entering PM is obtained from the increase in the weight of exhaust gas entering the honeycomb structure through the quartz collection filter, and the amount of output PM is obtained from the increase in weight by passing the exhaust gas from the honeycomb structure through the quartz collection filter. The residual PM amount was obtained by disassembling the honeycomb structure after the experiment and measuring it with MEXA 1370-PM manufactured by HORIBA.

NOx purification rate measurement test (R / L repetition)
Engine operating conditions: rotational speed = 1800 rpm, torque = 60 N · m, inlet gas temperature: 300 ° C., the NOx purification rate was measured as follows.

  First, the engine was warmed up while throwing exhaust gas to the bypass side. After confirming the completion of warm-up, dynamo was set as a predetermined condition, the condition was commanded so that light oil could be added to the engine ECU, and voltage application to the exhaust gas purification device was started until the voltage value reached the maximum. Next, the exhaust gas was flowed to the main side (exhaust gas purification device side), and the amount of NOx reduced with respect to NOx in the incoming gas was determined from the analysis value of the NOX meter of MEXA 9100D made by HORIBA.

  As a result, the PM oxidation rate for 30 minutes from the start of the experiment was almost 0 g / hL only by providing the discharge protrusion on the rod-shaped electrode or by providing the insulating member on the surrounding electrode. It improved to about 0.5 g / hL.

  Further, when the PM oxidation rate and NOx purification rate with and without repetition of the processing unit were compared with each other, the PM oxidation rate at 300 ° C. was about 0.5 g / hL without repetition, The NOx purification rate was improved to 0.7 g / hL with repetition, and the NOx purification rate was increased to 35% with repetition while it was 30% without repetition.

  Moreover, when the time to dielectric breakdown with and without repetition of the processing unit was measured and compared, as shown in FIGS. 7 and 8, the time until dielectric breakdown was approximately doubled by making the processing unit into a repeated structure. Improved.

It is sectional drawing which shows the one aspect | mode of the conventional exhaust gas purification apparatus. It is sectional drawing which shows the one aspect | mode of the exhaust gas purification apparatus of this invention. It is a schematic diagram which shows the mode of PM deposition in the conventional exhaust gas purification apparatus. It is a schematic diagram explaining generation | occurrence | production of micro discharge. It is sectional drawing which shows the other aspect of the exhaust gas purification apparatus of this invention. It is the schematic which shows the structure of an experimental apparatus. It is a graph which shows the time to the dielectric breakdown when there is no repetition of a processing unit. It is a graph which shows the time to the dielectric breakdown in the case with repetition of a processing unit.

Explanation of symbols

10, 20, 50 Exhaust gas purification device 11, 21, 52 Case 12, 22, 53 Honeycomb structure 13, 23, 24 Outer electrode 14, 24, 55 Rod electrode 15, 25 Power source 26, 57 Insulating member 27, 56 Discharge protrusion

Claims (2)

Insulating honeycomb structure,
An exhaust gas purification apparatus having an outer peripheral electrode disposed on an outer peripheral portion of the honeycomb structure and a rod-shaped electrode disposed on a central axis of the honeycomb structure, wherein the outer peripheral electrode and the rod-shaped electrode are the honeycomb structure The rod-shaped electrode has a plurality of discharge projections at a portion extending to the exhaust gas flow upstream side of the honeycomb structure, and the honeycomb electrode of the outer peripheral electrode An exhaust gas purification apparatus, wherein an insulating member is disposed on an inner peripheral surface of a portion extending upstream of an exhaust gas flow of a structure. Insulating honeycomb structure,
An outer peripheral electrode disposed on an outer peripheral portion of the honeycomb structure; and a rod-shaped electrode disposed on a central axis of the honeycomb structure, wherein the outer peripheral electrode and the rod-shaped electrode are upstream of the exhaust gas flow of the honeycomb structure The rod-shaped electrode has a plurality of discharge protrusions at a portion extending upstream of the exhaust gas flow of the honeycomb structure, and the exhaust gas flow of the honeycomb structure of the outer peripheral electrode An exhaust gas purifying apparatus, wherein a plurality of processing units in which an insulating member is disposed on an inner peripheral surface of a portion extending upstream is disposed in series from upstream to downstream of the exhaust gas flow.

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