JP2009062875A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of reducing cost (reducing a noble metal quantity), by restraining catalyst performance to a necessary sufficient proper grade, while excellently maintaining exhaust emission control performance. <P>SOLUTION: This exhaust emission control device is mounted in the middle of an exhaust pipe 3 by embracing-holding a front stage oxidation catalyst 2 (an exhaust emission control catalyst for passing and purifying exhaust gas) and a particulate filter 1 by a shell 4, and is interposed with a cone 6 of diametrically expanding in the flowing direction of the exhaust gas 5 so as to gradually increase an inner diameter dp of the exhaust pipe 3 up to an inner diameter ds of the shell 4 on the inlet side of this shell 4. A dimensionless value ζ is set so as to become a range of 2.2-4.0 by dividing a distance L up to an inlet side end surface of the front stage oxidation catalyst 2 from an inlet of the cone 6 by a difference between the inner diameter ds of the shell 4 and the inner diameter dp of the exhaust pipe 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of a soot fraction composed of carbon and a SOF fraction (Soluble Organic Fraction) composed of a high-boiling hydrocarbon component. 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 mounted in the middle of the exhaust pipe 3 together with the preceding oxidation catalyst 2, the particulate filter 1 and the oxidation catalyst 2 are held by a shell 4 and exhausted. It is equipped in the middle of the pipe 3, and a cone 6 that expands in the flow direction of the exhaust gas 5 so as to gradually increase the inner diameter dp of the exhaust pipe 3 to the inner diameter ds of the shell 4 is interposed on the entrance side of the shell 4. Yes.

In addition, as prior art document information that technically discloses the arrangement state of the preceding oxidation catalyst 2 and the particulate filter 1, for example, there is the following Patent Document 1 by the same applicant as the present invention.
JP 2006-77591 A

  However, conventionally, the distance L from the entrance of the cone 6 to the entrance end surface of the oxidation catalyst 2 is determined in consideration of the circumstances such as productivity and mountability, and the catalytic performance (precious metal amount, etc.) of the preceding oxidation catalyst 2 is determined. ) Is adjusted so as to satisfy the exhaust purification performance, there is a possibility that a high-cost noble metal or the like is excessively used without sufficiently obtaining the catalyst performance to be originally exhibited.

  The present invention has been made in view of the above circumstances, and an exhaust emission control device capable of reducing the cost (reducing the amount of noble metal) by suppressing the catalyst performance to a necessary and appropriate grade while maintaining good exhaust emission purification performance. The purpose is to provide.

  In the present invention, an exhaust gas purification catalyst that passes exhaust gas to be purified is held by a shell and is provided in the middle of the exhaust pipe, and the flow direction of the exhaust gas gradually increases the inner diameter of the exhaust pipe to the shell inner diameter on the inlet side of the shell. In the exhaust purification device having a cone that expands to a diameter of 2, the dimensionless value obtained by dividing the distance from the inlet of the cone to the inlet end surface of the exhaust purification catalyst by the difference between the shell inner diameter and the exhaust pipe inner diameter is 2. It is characterized by being set to be in the range of 2 to 4.0.

  Thus, if the dimensionless value is set to be in the range of 2.2 to 4.0, the exhaust gas generated when the dimensionless value is made smaller than 2.2. It is possible to avoid the extreme deterioration of dispersibility, and the catalyst performance that should be originally exhibited can be sufficiently derived to obtain good exhaust purification performance.

  In fact, according to a verification experiment by the present inventors, it has been found that when the dimensionless value is made smaller than 2.2, the dispersibility of the exhaust gas is extremely deteriorated. When the dimensionless value is in the range of 2.2 to 4.0, the dispersibility of the exhaust gas is at a sufficiently high level and gradually becomes better as the value increases, and is almost flat. Is known.

  On the other hand, even if this dimensionless value is made larger than 4.0, the distance from the inlet of the cone to the inlet side end face of the exhaust purification catalyst only increases, and hardly contributes to the improvement of the dispersibility of the exhaust gas. It has been found that this will only worsen the mountability on the vehicle.

  According to the above-described exhaust purification apparatus of the present invention, the dimensionless value obtained by dividing the distance from the cone inlet to the inlet side end face of the exhaust purification catalyst by the difference between the shell inner diameter and the exhaust pipe inner diameter is 2.2 to By setting it to be in the range of 4.0, the exhaust gas dispersibility can be ensured at a sufficiently high level while avoiding an extreme deterioration of the exhaust gas dispersibility, which is originally exhibited. The catalyst performance should be fully extracted and good exhaust purification performance can be obtained, so that while maintaining the exhaust purification performance good, the catalyst performance can be suppressed to the appropriate and appropriate grade and the cost can be reduced. An excellent effect that (a reduction in the amount of noble metal) can be achieved can be achieved.

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

  FIG. 1 shows an example of an embodiment for carrying out the present invention. As in the case of FIG. 3 described above, an oxidation catalyst 2 in the previous stage (an exhaust purification catalyst for purifying exhaust gas through it) and particulates. The filter 1 is held in the middle of the exhaust pipe 3 by being held by the shell 4, and the exhaust gas 5 flows in the flow direction so as to gradually increase the inner diameter dp of the exhaust pipe 3 to the inner diameter ds of the shell 4 on the entrance side of the shell 4. With regard to the exhaust gas purification device having an enlarged cone 6, the distance L from the inlet of the cone 6 to the inlet side end surface of the preceding oxidation catalyst 2 is divided by the difference between the inner diameter ds of the shell 4 and the inner diameter dp of the exhaust pipe 3. Thus, the dimensionless value ζ is set to be in the range of 2.2 to 4.0.

  That is, if the dimensionless value ζ is set to be in the range of 2.2 to 4.0, the extreme dispersibility of the exhaust gas 5 generated when the value ζ is made smaller than 2.2. Such deterioration can be avoided in advance, and the catalyst performance that should be originally exhibited can be sufficiently extracted to obtain good exhaust purification performance.

  In fact, according to the verification experiment by the present inventor, for example, an experimental result as shown in a graph (showing the relationship between the uniformity [Uniformity Index] and the value ζ) in FIG. 2 is obtained. As is clear from the above, the dimensionless shape of the shell 4 regardless of whether the inner diameter ds of the shell 4 is large, medium, or small, or when the inner diameter dp of the exhaust pipe 3 is larger than the present one. It has been found that when the normalized value ζ is smaller than 2.2, the uniformity of the exhaust gas 5 is significantly lowered and the dispersibility is extremely deteriorated.

  Here, the data in which the inner diameter ds of the shell 4 is medium is the current data in which the inner diameter ds of the shell 4 is 199 mm and the inner diameter dp of the exhaust pipe 3 is 57.5 mm. The inner diameter dp of the shell 4 is expanded to 259 mm while keeping the inner diameter dp of the exhaust pipe 3 at the current 57.5 mm, and the data with the smaller inner diameter ds of the shell 4 is the current inner diameter dp of the exhaust pipe 3. The inner diameter ds of the shell 4 is reduced to 154 mm while keeping the inner diameter dp of the exhaust pipe 3 while the inner diameter dp of the exhaust pipe 3 is large. Is enlarged to 77.0 mm.

The uniformity is an evaluation of the dispersibility of the exhaust gas 5 by a deviating method, and is expressed by the following equation 1 [γ: uniformity, _Wi : local flow velocity, _Wmean : Average flow rate].

  The value in this uniformity is in the range of 0 to 1, and when the uniformity is 1, it represents an ideal flow and the axial flow velocity in the carrier is the same flow velocity everywhere. When 0 is 0, this represents a state in which the total flow rate flows to one cell and the flow rate of the other cells becomes 0. In a normal case, it is about 0.7 to 0.98.

  Further, as can be seen from the graph of FIG. 2, when the dimensionless value ζ is in the range of 2.2 to 4.0, the value ζ increases at a sufficiently high level of dispersibility of the exhaust gas 5. It has been found that it will be almost flat, gradually improving.

  On the other hand, even if the dimensionless value ζ is made larger than 4.0, the distance L from the entrance of the cone 6 to the entrance end surface of the oxidation catalyst 2 only increases, and the dispersibility of the exhaust gas 5 is improved. Has been found to contribute little, and can only worsen the ability to be mounted on a vehicle.

  As described above, according to the above embodiment, the distance L from the inlet of the cone 6 to the inlet side end face of the oxidation catalyst 2 is not divided by the difference between the inner diameter ds of the shell 4 and the inner diameter dp of the exhaust pipe 3. By setting the dimensioned value ζ to be in the range of 2.2 to 4.0, the dispersibility of the exhaust gas 5 is sufficiently prevented while avoiding an extreme deterioration of the dispersibility of the exhaust gas 5 in advance. It can be secured at a high level, and it can draw out the catalyst performance that should be originally exhibited to obtain a good exhaust purification performance, so that the catalyst performance is necessary and sufficient while maintaining the exhaust purification performance well. The cost can be reduced to an appropriate grade, and the cost can be reduced (the amount of precious metal can be reduced).

  Note that the exhaust purification apparatus of the present invention is not limited to the above-described embodiment, and the exhaust purification catalyst equipped in the middle of the exhaust pipe is not necessarily limited to the oxidation catalyst attached to the front stage of the particulate filter. It may be an oxidation catalyst using the particulate filter itself as a carrier, or may be various catalysts such as a NOx storage reduction catalyst, a selective reduction catalyst, a three-way catalyst, etc. Of course, 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 a graph which shows the relationship between uniformity and the dimensionless value (zeta). It is sectional drawing which shows the arrangement | positioning state of the oxidation catalyst of a front | former stage, and a particulate filter.

Explanation of symbols

1 Particulate Filter 2 Oxidation Catalyst (Exhaust Gas Purification Catalyst Purified by Passing Exhaust Gas)
3 Exhaust pipe 4 Shell 5 Exhaust gas 6 Cone L Distance from the entrance of the cone to the inlet side end face of the preceding oxidation catalyst dp Inner diameter of exhaust pipe ds Inner diameter of shell

Claims (1)

  An exhaust purification catalyst that purifies by passing exhaust gas is held by the shell and installed in the middle of the exhaust pipe, and the diameter of the exhaust pipe is increased in the exhaust gas flow direction so that the inner diameter of the exhaust pipe is gradually increased to the shell inner diameter on the inlet side of the shell. In the exhaust purification apparatus having a cone, the dimensionless value obtained by dividing the distance from the inlet of the cone to the inlet end face of the exhaust purification catalyst by the difference between the shell inner diameter and the exhaust pipe inner diameter is 2.2-4. An exhaust emission control device set to be in a range of zero.

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