JP2005083346A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a plasma assist type exhaust emission control device reducing electric power consumption and discharging no noxious gas into the atmosphere. <P>SOLUTION: In a filter main body 7 comprised of a porous material for collecting particulates in exhaust gas 2 by making the exhaust gas 2 pass, a plasma regeneration type particulate filter 11 is constituted by providing bar-shaped electrodes 9 and tubular electrodes 10 to generate plasma inside the filter main body 7. The plasma regeneration type particulate filter 11 is stored inside a filter case 12 in the middle of an exhaust pipe 3. Oxidation catalysts 16, 17 are arranged in the vicinity of forward and backward positions of the plasma regeneration type particulate filter 11 inside the filter case 21 so as to obtain insulation effectiveness with respect to the plasma regeneration type particulate filter 11. <P>COPYRIGHT: (C)2005,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 composed of carbonaceous matter and SOF content (Soluble Organic Fraction) composed of high-boiling hydrocarbon components. As shown in FIG. 3, an exhaust pipe 3 through which exhaust gas 2 from a diesel engine 1 circulates is used as a measure for reducing this type of particulates. The exhaust pipe 3 has a composition containing a small amount of sulfate (mist-like sulfuric acid component). It is considered that the particulate filter 4 is provided in the middle of the above.

  As shown in detail in FIG. 4, the particulate filter 4 mainly includes a filter body 7 having a porous honeycomb structure made of ceramic such as cordierite, and each flow divided in a lattice shape in the filter body 7. The inlets of the passages 5 are alternately sealed by the plugs 8, and the flow paths 5 whose inlets are not sealed are sealed by the plugs 8. Only the exhaust gas 2 that has passed through the partitioning porous thin wall 6 is discharged downstream, and particulates are collected on the inner surface of the porous thin wall 6.

  Particulates in the exhaust gas 2 are collected and deposited on the inner surface of the porous thin wall 6 and are spontaneously burned and removed when the exhaust gas moves to an operation region where the exhaust temperature is high. However, for example, in a vehicle that travels only on a congested road such as a route bus in Tokyo, the accumulated amount is more than the particulate processing amount because the operation above the required predetermined temperature does not continue for a long time. There was a possibility that the particulate filter 4 would be clogged.

For this reason, a plasma-assisted exhaust purification device is being developed so that particulates can be burned and removed well even in an operating region where the exhaust temperature is low. In this type of plasma-assisted exhaust purification device, If discharge is generated to generate plasma, the exhaust gas 2 is excited, oxygen becomes ozone, NO becomes NO ₂ , and these exhaust gas excitation components are in an activated state. Thus, it is possible to satisfactorily burn and remove the particulates even in an operation region where the temperature is low.

The prior art documents related to the plasma assist type exhaust purification device are also mentioned in, for example, the following Patent Document 1.
Japanese translation of PCT publication No. 2002-501813

  However, in the conventional plasma-assisted exhaust purification device, since the power consumption required for regeneration of the particulate filter 4 is large, a large-capacity power supply that cannot be covered by the existing vehicle battery is required, There is a problem in that fuel consumption is deteriorated because charging corresponding to consumed power is required.

  Further, when the particulate filter 4 is regenerated, the particulates are incinerated at a relatively low temperature, and there is a concern that harmful gases such as high-concentration CO and HC are generated and discharged into the atmosphere.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to realize a plasma-assisted exhaust purification device that requires less power consumption and does not discharge harmful gases into the atmosphere.

  The present invention relates to a plasma regeneration by mounting an electrode on a filter body made of a porous material that allows exhaust gas to pass through and collects particulates in the exhaust gas so that plasma can be generated inside the filter body. And a plasma regeneration type particulate filter is accommodated in a filter case in the middle of an exhaust pipe, and the plasma regeneration type particulate filter is disposed in the filter case at the front and rear positions of the plasma regeneration type particulate filter. The present invention relates to an exhaust emission control device in which an oxidation catalyst is arranged close to a curate filter so as to obtain a heat retaining effect.

Thus, when the exhaust gas flowing into the filter case passes through the preceding oxidation catalyst, NO occupying most of the NOx in the exhaust gas becomes highly reactive NO ₂ , and the exhaust temperature The particulate oxidation reaction is greatly accelerated under the operating conditions where the temperature is about 250 ° C. or higher, and the combustion is removed well.

  However, if the operating conditions under light load such as when driving on a congested road in an urban area where the exhaust temperature greatly falls below 250 ° C continue for a long time, it will not be possible to achieve good combustion removal of the particulates. A voltage is applied between the electrodes mounted on the filter body when it is estimated that the amount is greater than or equal to the predetermined amount (it may be estimated from the differential pressure between the inlet side and the outlet side of the filter body, operation time, etc.) Then, discharge is performed in the filter body.

When a voltage is applied between the electrodes mounted on the filter body in this way to discharge the filter body, the internal gas is excited, oxygen becomes ozone, NO becomes NO ₂ , and these gas excitation components Is in an activated state, the oxidation reaction of particulates collected in the filter body is promoted by the gas excitation component, and the particulates are burned and removed well even under operating conditions where the exhaust temperature is low. become.

  At this time, the plasma regeneration type particulate filter is in a state of being insulated by being sandwiched between the front and back by an oxidation catalyst in the same filter case, so that the oxidation of the collected particulates starts and the temperature of the filter body rapidly increases. As a result, the particulates are easily incinerated. As a result, the incineration of the particulates can be completed in a shorter discharge time than before, and the power consumption can be reduced as compared with the prior art.

Also, harmful gas of a high concentration of CO and HC and the like generated by particulates is relatively incinerated at low temperature with the aid of such a plasma, harmless CO ₂ as it passes through the downstream oxidation catalyst Then, it is oxidized to H ₂ O and discharged.

  Furthermore, in the present invention, the plasma regeneration type particulate filter is divided into a plurality of small units and installed in parallel in the filter case so that a discharge voltage can be individually applied to each small unit. It is preferable.

  In this way, it becomes possible to regenerate the plasma regeneration type particulate filter by plasma individually for each small unit, so that it is possible to sufficiently cope with a relatively small capacity power source, As a result of division into a plurality of small units, the flammability of the particulates in units is improved, so that regeneration by plasma when the engine is stopped in a vehicle or the like equipped with an idle stop device is also realized.

  Further, in the present invention, it is preferable that the oxidation catalyst is integrally supported on the porous material constituting the filter main body. In this way, the oxidation reaction of the particulates collected in the filter main body is promoted and ignition is performed. As a result of lowering the temperature and further increasing the combustibility of the particulates in the operating state where the exhaust gas temperature is low, better combustion removal of the particulates is realized.

  In carrying out the present invention more specifically, a filter in which a large number of flow paths through which exhaust gas flows is formed in a honeycomb shape and the end portions on the inlet side and the outlet side of each flow path are alternately sealed. It is possible to adopt a main body. Furthermore, when such a filter main body is adopted, a rod-like electrode is inserted into the axial center of the filter main body, and a cylindrical electrode is attached to the outer peripheral surface of the filter main body. Good.

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

  (I) Particulates collected in the filter body can be effectively burned and removed with the assistance of plasma even in an operation state where the exhaust temperature is low, such as during light load operation. Because of the heat retention effect of the filter, the temperature of the filter body can be increased rapidly, making it easy to incinerate the particulates, so that the burning and removal of particulates can be completed in a shorter discharge time than before. A significant reduction can be achieved.

(II) High concentrations of harmful gases such as CO and HC generated by incineration of particulates at a relatively low temperature with the assistance of plasma are passed through an oxidation catalyst in the subsequent stage to harmless CO ₂ and H ₂ O. Oxidation can be performed and discharged, and the possibility that harmful gases remain in the exhaust gas finally discharged into the atmosphere can be avoided.

(III) Since NO which occupies most of the NOx in the exhaust gas can be changed to highly reactive NO ₂ by passing through the preceding stage oxidation catalyst, the particulate matter under operating conditions with a relatively high exhaust temperature can be obtained. Oxidation reaction can be greatly promoted, and by this, spontaneous combustion of particulates can be promoted without the assistance of plasma, and good combustion removal can be achieved.

  (IV) When the plasma regeneration type particulate filter is divided into a plurality of small units and installed in parallel in the filter case, and a discharge voltage can be individually applied to each small unit, It is possible to sufficiently cope with a relatively small-capacity power source, and it is also possible to realize regeneration by plasma when the engine is stopped in a vehicle or the like equipped with an idle stop device.

  (V) In the case of adopting a structure in which the oxidation catalyst is integrally supported on the porous material constituting the filter body, the oxidation reaction of the particulates collected on the filter body can be promoted by the oxidation catalyst. Therefore, it is possible to achieve more reliable particulate removal and combustion in the operation region where the exhaust gas temperature is low.

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

  1 and FIG. 2 show an example of an embodiment for carrying out the present invention, and portions denoted by the same reference numerals as those in FIGS. 3 and 4 represent the same items.

  As shown in FIGS. 1 and 2, in the exhaust purification apparatus of this embodiment, a rod-shaped electrode is formed on the filter body 7 similar to that shown in FIG. 4 so that plasma can be generated inside the filter body 7. 9 and the cylindrical electrode 10 are used. Here, the plasma regeneration type particulate filter 11 is used, and here, the plasma regeneration type particulate filter 11 includes a plurality of (four in the illustrated example) small units 11A and 11B. , 11C, and 11D and are installed in the filter case 12 in parallel.

  The rod-shaped electrode 9 is inserted into the axial center of the filter body 7 in each of the small units 11A, 11B, 11C, and 11D, and the cylindrical electrode 10 is attached to the outer peripheral surface of the filter body 7. Moreover, the rod-like electrode 9 of each small unit 11A, 11B, 11C, 11D is connected to the anode side of the power source 14 (battery) via the switching relays 13a, 13b, 13c, 13d, and each small unit 11A, 11B, The cylindrical electrodes 10 of 11C and 11D are connected to the cathode side of the power source 14 via the conductive support member 15 and the filter case 12, and are individually discharged for each small unit 11A, 11B, 11C, and 11D. This voltage can be applied.

  The support member 15 is for supporting the small units 11A, 11B, 11C, and 11D of the plasma regeneration type particulate filter 11 in the filter case 12, and the small units 11A, 11B, 11C, and 11D. It also serves as a partition wall that closes the gap between them.

  The plasma regenerative particulate filter 11 divided by the plurality of small units 11A, 11B, 11C, and 11D described above is accommodated in a filter case 12 in the middle of the exhaust pipe 3, and the filter case 12 At the front and rear positions of the plasma regeneration type particulate filter 11, oxidation catalysts 16 and 17 are disposed in proximity to each other so as to obtain a heat retaining effect with respect to the plasma regeneration type particulate filter 11.

  Here, the front and rear oxidation catalysts 16 and 17 are of a flow-through type in which an appropriate amount of platinum is supported on a honeycomb structure carrier made of a ceramic such as cordierite. The amount of platinum supported may be less than that of the preceding oxidation catalyst 16.

  The porous material constituting the filter main body 7 in each of the small units 11A, 11B, 11C, and 11D described above is integrated with an oxidation catalyst for the purpose of promoting the oxidation reaction of the particulates collected in the filter main body 7. Alternatively, it may be supported.

Thus, when the exhaust gas purification apparatus is configured in this way, when the exhaust gas 2 flowing into the filter case 12 passes through the preceding oxidation catalyst 16, NO occupying most of the NOx in the exhaust gas 2 reacts. It becomes highly NO ₂ , and the oxidation reaction of the particulates is greatly accelerated under the operating conditions where the exhaust temperature is about 250 ° C. or higher, so that it is burned and removed well.

  However, if the operating conditions under light load such as when driving on a congested road in an urban area where the exhaust temperature greatly falls below 250 ° C continue for a long time, it will not be possible to achieve good combustion removal of the particulates. Each small unit 11A, 11B, 11C, and 11D is estimated when the amount is estimated to be equal to or greater than a predetermined amount (it may be estimated from the differential pressure between the inlet side and the outlet side of the filter body 7 and the operation time). A discharge voltage is individually applied to discharge between the rod-shaped electrode 9 and the cylindrical electrode 10 to generate plasma in the gas inside the filter body 7.

In this way, the gas inside the filter body 7 is excited, oxygen becomes ozone, NO becomes NO ₂ , and these exhaust gas excitation components are in an activated state. Oxidation reaction of the particulates collected in the catalyst is promoted by the exhaust gas excitation component, and the particulates are burned and removed well even under operating conditions where the exhaust gas temperature is low.

  At this time, since the plasma regeneration type particulate filter 11 is in a state of being insulated by being sandwiched by the oxidation catalysts 16 and 17 in the same filter case 12 at the front and rear, the oxidation reaction of the collected particulates starts. As a result of the temperature of the main body 7 rapidly rising, the particulates are easily incinerated. As a result, the incineration of the particulates can be completed in a shorter discharge time than before, and power consumption can be reduced as compared with the prior art.

  Further, since the voltage is individually applied to the small units 11A, 11B, 11C, and 11D of the plasma regeneration type particulate filter 11 and discharged, the power supply 14 having a relatively small capacity can sufficiently cope with the discharge. In addition, as a result of dividing the particulates into a plurality of small units 11A, 11B, 11C, and 11D, the flammability of the particulates becomes good. As a result, when the engine is stopped in a vehicle or the like equipped with an idle stop device Plasma regeneration is also realized.

In addition, harmful gases such as high-concentration CO and HC generated by burning the particulates at a relatively low temperature with the assistance of such plasma are harmless when passing through the oxidation catalyst 17 at the subsequent stage. Oxidized to ₂ or H ₂ O and discharged.

  Therefore, according to the above embodiment, the particulates collected in the filter body 7 can be effectively burned and removed by the assistance of plasma even in an operation state where the exhaust temperature is low during light load operation or the like. In addition, the temperature of the filter body 7 can be rapidly increased by the heat retaining effect of the front and rear oxidation catalysts 16 and 17 so that the particulates can be easily incinerated, so that the particulates can be burned and removed in a shorter discharge time than before. Thus, the power consumption can be greatly reduced.

In addition, harmful gases such as CO and HC generated by incinerating particulates at a relatively low temperature with the assistance of plasma are passed through an oxidation catalyst 17 at the subsequent stage to harmless CO ₂ and H ₂ O. Oxidation can be performed and exhausted, and the risk of harmful gases remaining in the exhaust gas 2 finally exhausted to the atmosphere can be avoided.

Further, NO that occupies most of the NOx in the exhaust gas 2 can be made highly reactive NO ₂ by passing the oxidation catalyst 16 in the preceding stage, so that the particulates under the operating conditions where the exhaust temperature is relatively high. Thus, it is possible to promote the natural combustion of the particulates without the aid of plasma, thereby achieving good combustion removal.

  In particular, as shown in this embodiment, the plasma regenerative particulate filter 11 is divided into a plurality of small units 11A, 11B, 11C, and 11D and installed in parallel in the filter case 12, and each small unit 11A, In the case where the discharge voltage can be individually applied to each of 11B, 11C, and 11D, it is possible to sufficiently cope with a relatively small-capacity power supply 14, and an idle stop device is mounted. It is also possible to realize plasma regeneration when the engine is stopped in a vehicle or the like.

  Further, in the case of adopting a configuration in which the oxidation catalyst is integrally supported on the porous material constituting the filter body 7, the oxidation reaction of the particulates collected in the filter body 7 can be promoted by the oxidation catalyst. Therefore, it is possible to realize more reliable particulate removal and combustion in the operation region where the exhaust gas temperature is low.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment. The plasma regeneration type particulate filter may be constituted by a single unit, and an oxidation catalyst is not necessarily provided in the filter body. Needless to say, the shape and arrangement of the filter main body and the electrode are not limited to those shown in the drawings, and various modifications can be made without departing from the scope of the present invention.

It is sectional drawing which shows an example of the form which implements this invention. It is sectional drawing of the II-II arrow of FIG. It is the schematic which shows the arrangement | positioning state of the conventional particulate filter. It is sectional drawing which shows the detail of the particulate filter of FIG.

Explanation of symbols

2 Exhaust gas 3 Exhaust pipe 4 Particulate filter 5 Flow path 7 Filter body 9 Rod electrode (electrode)
10 Cylindrical electrode (electrode)
DESCRIPTION OF SYMBOLS 11 Plasma regeneration type particulate filter 11A, 11B, 11C, 11D Small unit 12 Filter case 16 Oxidation catalyst of a front | former stage 17 Oxidation catalyst of a back | latter stage

Claims (5)

  A plasma regenerative particulate filter comprising a filter body made of a porous material that allows exhaust gas to pass therethrough and collects particulates in the exhaust gas, and is equipped with an electrode so that plasma can be generated inside the filter body. And the plasma regenerative particulate filter is accommodated in a filter case in the middle of the exhaust pipe, and the front and rear positions of the plasma regenerative particulate filter in the filter case are located with respect to the plasma regenerative particulate filter. An exhaust emission control device in which an oxidation catalyst is arranged close to each other so as to obtain a heat retaining effect.   The plasma regenerative particulate filter is divided into a plurality of small units and installed in parallel in a filter case, and a discharge voltage can be individually applied to each small unit. The exhaust emission control device according to 1.   The exhaust emission control device according to claim 1 or 2, wherein an oxidation catalyst is integrally supported on a porous material constituting the filter body.   2. A filter main body in which a large number of flow paths through which exhaust gas flows is formed in a honeycomb shape and ends of the respective flow paths are alternately plugged is adopted. Or the exhaust gas purification device of 3.   The exhaust emission control device according to claim 4, wherein a rod-shaped electrode is inserted into an axial center portion of the filter body, and a cylindrical electrode is mounted on the outer peripheral surface of the filter body.

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