JP2011064068A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent clogging of an exhaust emission control catalyst by improving a flow of exhaust gas introduced to the exhaust emission control catalyst such as an oxidation catalyst while maintaining the compactization of a casing. <P>SOLUTION: An exhaust emission control device accommodates an oxidation catalyst 2 (exhaust emission control catalyst to pass exhaust gas therethrough for purification) in a casing 4 at some midpoint in an exhaust pipe 3, forces an inlet pipe 6 containing a plurality of air diffusing holes 8 to be inserted from a direction orthogonal to an axial center of the oxidation catalyst 2 with respect to an inlet chamber 5 defined at an inlet side of the oxidation catalyst 2 in the casing 4, and diffuses exhaust gas 7 introduced from an exhaust pipe on the upstream side through the inlet pipe 6 in the inlet chamber 5 through the medium of respective air diffusing holes 8, wherein air diffusing holes 8 are limitedly opened only on a side facing to the oxidation catalyst 2 of the inlet pipe 6 and the number of air diffusing holes 8 on a tip side of the inlet pipe 6 are reduced as compared with that in a midway part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

  Particulate matter (particulate matter) discharged from diesel engines is mainly composed of carbonaceous soot and SOF (Soluble Organic Fraction) consisting of high-boiling hydrocarbon components. Furthermore, 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. Has been performed conventionally.

  The particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the respective channels partitioned in a lattice shape are alternately sealed, and the channels are not sealed. The outlet is sealed, and only the exhaust gas that has permeated through the porous thin wall that defines each flow path is discharged downstream.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operation conditions, there are few opportunities to obtain exhaust temperatures that are high enough for particulates to self-combust, so a catalyst regeneration type that integrally supports an oxidation catalyst. Adoption of a particulate filter is being studied.

  That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.

  However, even when such a catalyst regeneration type particulate filter is used, the trapped amount exceeds the particulate processing amount in the operation region where the exhaust temperature is low, so such a low exhaust gas. If the operation state at the temperature continues, there is a possibility that the particulate filter will fall into an over trapped state without the regeneration of the particulate filter proceeding well.

  Therefore, a flow-through type oxidation catalyst is separately arranged in front of the particulate filter, and fuel is added to the exhaust gas upstream of the oxidation catalyst at the stage where the amount of particulate accumulation has increased. It is considered to perform forced regeneration.

  That is, the fuel (HC) added on the upstream side of the particulate filter undergoes an oxidation reaction while passing through the preceding oxidation catalyst, and the catalyst bed of the particulate filter immediately after the inflow of exhaust gas heated by the reaction heat. The temperature is raised, the particulates are burned out, and the particulate filter is regenerated.

  As a specific means for executing this kind of fuel addition, post-injection is added at the timing of non-ignition later than the compression top dead center following the main injection of fuel performed near the compression top dead center. What is necessary is just to add a fuel in gas.

  As shown in FIG. 3, when such a particulate filter 1 is installed in the middle of the exhaust pipe 3 together with the oxidation catalyst 2 in the previous stage, the preceding stage is placed in a casing 4 interposed in the middle of the exhaust pipe 3. The oxidation catalyst 2 and the particulate filter 1 are arranged and accommodated in series, and the inlet pipe 6 is inserted into the inlet chamber 5 defined on the inlet side of the oxidation catalyst 2 in the casing 4 to introduce the exhaust gas 7. As shown in the drawing, the inlet pipe 6 is connected to the axial direction of the oxidation catalyst 2 in the axial direction (left-right direction in FIG. 3) due to the layout relationship with the vehicle equipment (mounting parts). May be forced to be inserted into the entrance chamber 5 from a direction orthogonal to the direction.

  In such a case, conventionally, the diffuser hole 8 is opened in the entire portion of the inlet pipe 6 that has entered the inlet chamber 5, and the exhaust gas 7 introduced from the upstream exhaust pipe 3 is supplied to the inlet pipe 6. 6 is diffused through each air diffusion hole 8 and led to the inlet side end face of the oxidation catalyst 2.

  In addition, as prior art document information that technically discloses such a structure that introduces an exhaust gas by inserting an inlet pipe from a direction orthogonal to the axial center direction of the exhaust purification catalyst, for example, the following Patent Document 1 is disclosed. is there.

JP 2003-74335 A

  However, in the conventional structure as shown in FIG. 3, the pressure increases at the tip side where the flow of the exhaust gas 7 passing through the inlet pipe 6 hits the peripheral surface of the casing 4, and as shown in FIG. Many of them blow out from the air diffusion holes 8 on the front end side, and many of them abut against the cylindrical circumferential surface of the casing 4 immediately after blowing out, so that a flow in the circumferential direction of the circumferential surface is easily formed. As a result of the flow of the exhaust gas 7 being obliquely blown against the inlet side end face, there was a problem that soot easily adheres to the inlet side end face of the oxidation catalyst 2.

  That is, as shown in FIG. 5 in the schematic cross-sectional view of the vicinity of the inlet side end surface of the oxidation catalyst 2, when the exhaust gas 7 is blown obliquely toward the inlet side end surface of the oxidation catalyst 2, There is a problem that a vortex 9 is generated, and a portion where the vortex 9 is generated becomes a substantial stagnation place of the flow of the exhaust gas 7, and clogging is likely to occur due to deposition and deposition of soot here.

  In addition, Patent Document 1 presented earlier proposes a structure in which a diffuser hole (communication opening) of the inlet pipe is opened toward the side opposite to the exhaust purification catalyst. In such a structure, the exhaust gas blown out from the diffuser hole (communication opening) of the inlet pipe hits the end surface of the casing and reverses, and then flows toward the exhaust purification catalyst. It has been confirmed that the flow of the exhaust gas is easy to blow obliquely to the end face, and that the effect of suppressing clogging due to the deposition and deposition of soot as described above is small.

  That is, the flow of exhaust gas that has been reversed against the end surface of the casing flows to the exhaust purification catalyst side along the peripheral surface of the casing and reaches the inlet side end surface of the exhaust purification catalyst. While flowing into the outer peripheral portion, most of the flow forms a flow that disperses along the inlet side end surface of the exhaust purification catalyst, and the flow component along the inlet side end surface has a tilt angle with respect to the axial direction of the exhaust purification catalyst. Result in increasing.

  In FIG. 3, if the distance L (see FIG. 3) between the inlet pipe 6 and the entrance end surface of the oxidation catalyst 2 is sufficiently long, the exhaust gas 7 forms a flow along the axial direction of the oxidation catalyst 2. However, securing this long distance L hinders the casing 4 from being made compact and significantly deteriorates the mountability on the vehicle. Therefore, the exhaust gas is maintained while keeping the casing 4 compact. It is desired to improve the flow of 7.

  The present invention has been made in view of the above circumstances, and prevents clogging of the exhaust purification catalyst by improving the flow of exhaust gas introduced into the exhaust purification catalyst such as an oxidation catalyst while keeping the casing compact. The purpose is that.

  According to the present invention, an exhaust purification catalyst that purifies by passing exhaust gas is housed in a casing in the middle of an exhaust pipe, and the exhaust purification catalyst is placed in an inlet chamber defined on the inlet side of the exhaust purification catalyst in the casing. An inlet pipe having a large number of air diffusion holes is inserted from a direction orthogonal to the axial direction, and exhaust gas guided from an upstream exhaust pipe through the inlet pipe is diffused into the inlet chamber through the air diffusion holes. In the exhaust purification device, the diffuser holes are limitedly opened only on the side of the inlet pipe facing the exhaust purification catalyst, and the number of diffuser holes on the tip side of the inlet pipe is made smaller than the number of holes in the middle part. It is characterized by this.

  In this way, since all the air diffusion holes of the inlet pipe face the side facing the exhaust purification catalyst, the exhaust gas hits the cylindrical peripheral surface of the casing immediately after blowing out, and the circumference of the peripheral surface The exhaust gas that flows out of the air diffuser is directly removed from the exhaust gas. A flow toward the catalyst is formed, and a flow component in the axial direction of the exhaust purification catalyst in the entire flow of the exhaust gas is greatly increased as compared with the conventional case.

  When exhaust gas is introduced from the axial direction to the inlet end surface of the exhaust purification catalyst, no vortex is generated at the inlet of each flow path of the exhaust purification catalyst, so that no soot deposits occur here. However, even if temporarily attached, the exhaust gas flow is blown away immediately, and as described above, the flow component toward the axial direction of the exhaust purification catalyst is much larger than the conventional exhaust gas flow. When the number is increased, problems such as growth of clogs deposited and accumulated at the inlets of the respective channels and clogging can be avoided.

  In addition, since the number of diffuser holes on the tip side of the inlet pipe is reduced compared to the number of holes in the middle, a relatively large amount of exhaust gas is biased from the tip side of the high pressure inlet pipe into the inlet chamber. The flow distribution of exhaust gas introduced into the exhaust purification catalyst is made uniform, and the number of diffuser holes is reduced on the tip side of the inlet pipe close to the peripheral surface of the casing. The formation of the flow toward the circumferential direction of the peripheral surface of the casing is effectively suppressed.

  At this time, it is preferable that the region where the air diffusion holes are formed on the distal end side of the inlet pipe is gradually reduced in a tapered manner in the exhaust gas flow direction. In order to reduce the number of diffused holes in the exhaust gas, the diffused holes with less displacement of the exhaust gas blowing direction with respect to the axial direction of the exhaust purification catalyst are preferentially left.

  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 invention described in claim 1 of the present invention, the exhaust gas out of the entire flow of the exhaust gas without securing a long distance between the inlet pipe and the inlet side end surface of the exhaust purification catalyst. The flow component toward the axial direction of the purification catalyst can be greatly increased as compared with the prior art, and the flow direction of the exhaust gas introduced into the exhaust purification catalyst is made uniform, and the circumferential direction of the circumferential surface of the casing Therefore, it is possible to effectively prevent the clogging of the exhaust purification catalyst by improving the flow of the exhaust gas introduced into the exhaust purification catalyst while keeping the casing compact. it can.

  (II) According to the invention described in claim 2 of the present invention, in reducing the number of diffuser holes on the tip end side of the inlet pipe, the displacement of the exhaust gas blowing direction with respect to the axial direction of the exhaust purification catalyst is further increased. It is possible to preferentially leave a small number of air diffusion holes, and it is possible to further increase the flow component in the axial direction of the exhaust purification catalyst in the entire flow of the exhaust gas.

It is sectional drawing which shows an example of the form which implements this invention. It is a perspective view which shows the blowing condition of the exhaust gas from the inlet pipe of FIG. It is sectional drawing which shows a prior art example. It is a perspective view which shows the blowing condition of the exhaust gas from the inlet pipe of FIG. It is an enlarged view which shows typically the entrance side end surface vicinity of the oxidation catalyst of FIG.

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

  FIGS. 1 and 2 show an example of an embodiment for carrying out the present invention. In the same manner as described above with reference to FIGS. 3 to 5, a front stage is provided in a casing 4 interposed in the middle of the exhaust pipe 3. An oxidation catalyst 2 (an exhaust purification catalyst that purifies by passing exhaust gas) and a particulate filter 1 are arranged in series with respect to an inlet chamber 5 defined on the inlet side of the oxidation catalyst 2 in the casing 4. An inlet pipe 6 having a large number of air diffusion holes 8 is inserted from a direction orthogonal to the axial center direction of the oxidation catalyst 2, and exhaust gas 7 guided from the upstream exhaust pipe 3 through the inlet pipe 6 is supplied to each of the air diffusion holes. 8 is diffused into the inlet chamber 5, but the diffuser holes 8 are limitedly opened only on the side of the inlet pipe 6 facing the oxidation catalyst 2, and the diffuser at the tip side of the inlet pipe 6 is diffused. The number of pores 8 is less than the number of holes in the middle It is characterized in was small allowed.

  Here, in this embodiment, the region where the air diffusion holes 8 are formed on the tip side of the inlet pipe 6 is formed so as to be gradually tapered toward the flow direction of the exhaust gas 7. In reducing the number of diffuser holes 8 on the tip end side of the pipe 6, the diffuser holes 8 with less shift in the blowing direction of the exhaust gas 7 with respect to the axial direction of the oxidation catalyst 2 are preferentially left.

  Thus, if configured in this way, all the diffused holes 8 of the inlet pipe 6 are directed to the side facing the oxidation catalyst 2, so that the exhaust gas 7 is directed to the cylindrical peripheral surface of the casing 4 immediately after blowing out. It does not flow into the circumferential direction of the peripheral surface by abutting, or does not flow back to the oxidation catalyst 2 along the peripheral surface of the casing 4 along the peripheral surface of the casing 4. Most of the discharged exhaust gas 7 directly forms a flow toward the oxidation catalyst 2, and the flow component toward the axial center of the oxidation catalyst 2 out of the entire flow of the exhaust gas 7 is greatly increased as compared with the prior art. It will be.

  Then, when the exhaust gas 7 is introduced from the axial direction to the entrance end surface of the oxidation catalyst 2, no vortex is generated at the inlet of each flow path of the oxidation catalyst 2, so that soot deposits occur. Even if it temporarily adheres, it is immediately blown off by the flow of the exhaust gas 7, so that the flow component toward the axial direction of the oxidation catalyst 2 in the entire flow of the exhaust gas 7 as described above is conventional. If it is significantly increased, problems such as growth of clogs deposited and accumulated at the inlets of the respective channels and clogging can be avoided.

  Further, since the number of diffuser holes 8 on the distal end side of the inlet pipe 6 is reduced as compared with the number of holes in the middle portion, a relatively large amount of exhaust gas 7 is biased from the distal end side of the inlet pipe 6 having a high pressure. The tendency to introduce the gas into the inlet chamber is corrected, the flow distribution of the exhaust gas 7 introduced into the oxidation catalyst 2 is made uniform, and the air diffusion holes are formed at the front end side of the inlet pipe 6 near the peripheral surface of the casing 4. By reducing the number of holes of 8, the formation of the flow in the circumferential direction of the peripheral surface of the casing 4 is effectively suppressed.

  Therefore, according to the above embodiment, the axial center of the oxidation catalyst 2 in the entire flow of the exhaust gas 7 can be obtained without securing a long distance L between the inlet pipe 6 and the entry side end face of the oxidation catalyst 2. The flow component toward the direction can be significantly increased as compared with the conventional method, and the flow toward the circumferential direction of the peripheral surface of the casing 4 while achieving a uniform flow distribution of the exhaust gas 7 introduced into the oxidation catalyst 2. Therefore, the flow of the exhaust gas 7 introduced into the oxidation catalyst 2 can be improved while keeping the casing 4 compact, and the clogging of the oxidation catalyst 2 can be prevented. .

  Further, in reducing the number of the diffuser holes 8 on the distal end side of the inlet pipe 6, it is possible to preferentially leave the diffuser holes 8 with less deviation in the blowing direction of the exhaust gas 7 with respect to the axial direction of the oxidation catalyst 2. Further, the flow component in the axial direction of the oxidation catalyst 2 in the entire flow of the exhaust gas 7 can be further increased.

  Note that the exhaust purification apparatus of the present invention is not limited to the above-described embodiment, and the exhaust purification catalyst housed in the casing in the middle of the exhaust pipe is not necessarily oxidized in the front stage of the particulate filter. The catalyst is not limited to the catalyst, and may be an oxidation catalyst using the particulate filter itself as a carrier, or may be various catalysts such as a NOx occlusion reduction catalyst, a selective reduction catalyst, and a three-way catalyst. Of course, various modifications can be made without departing from the scope of the present invention.

2 Oxidation catalyst (exhaust gas purification catalyst)
3 Exhaust pipe 4 Casing 5 Inlet chamber 6 Inlet pipe 7 Exhaust gas 8 Aeration hole

Claims (2)

  An exhaust purification catalyst for purifying by passing exhaust gas is housed in a casing in the middle of the exhaust pipe, and the axial center direction of the exhaust purification catalyst with respect to an inlet chamber defined on the inlet side of the exhaust purification catalyst in the casing In an exhaust emission control device, an inlet pipe having a large number of air diffusion holes is inserted from an orthogonal direction, and exhaust gas guided from an upstream exhaust pipe through the inlet pipe is diffused into the inlet chamber through the air diffusion holes. The diffuser holes are limitedly opened only on the side of the inlet pipe facing the exhaust purification catalyst, and the number of diffuser holes on the tip side of the inlet pipe is made smaller than the number of holes in the middle part. Exhaust purification device.   2. The exhaust emission control device according to claim 1, wherein a region in which a diffuser hole is formed on the distal end side of the inlet pipe is gradually reduced in a tapered shape in the flow direction of the exhaust gas.

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