JP2008267225A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device promoting the mixing of reducing agent with exhaust without increase in pressure loss or increase of noise. <P>SOLUTION: A nitrogen oxide reducing catalyst 16 is disposed in a cylindrical container 20, and an upstream chamber 22 and a downstream chamber 24 are disposed to the upstream and the downstream of the nitrogen oxide reducing catalyst 16 in the cylindrical container 20. The exhaust from an inlet pipe 14 connected to the upstream of an exhaust flow passage flows into the upstream chamber 22 from an outer peripheral side of the cylindrical container 20, an outlet pipe 28 connected to the downstream of the exhaust flow passage is disposed to the downstream chamber 24 to cross the downstream chamber 24, a lot of small holes 30 communicating to the downstream chamber 24 are formed to an outer periphery of the outlet pipe 28, and the exhaust is discharged to the downstream of the exhaust flow passage from the outlet pipe 28 through the small holes 30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for reducing and removing nitrogen oxides discharged from an internal combustion engine such as a diesel engine by adding a reducing agent upstream of a nitrogen oxide reduction catalyst.

  Conventionally, a nitrogen oxide reduction catalyst is disposed in the exhaust passage of an internal combustion engine, and a reducing agent, for example, ammonia water or urea water is injected and added to the upstream side of the nitrogen oxide reduction catalyst. 2. Description of the Related Art An exhaust emission control device that makes a nitrogen oxide harmless by performing a catalytic reduction reaction between an oxide and a reducing agent is known.

In such an exhaust purification device, it is necessary to promote mixing of the reducing agent and the exhaust. For example, as disclosed in Patent Document 1, a plurality of vanes that form a predetermined angle with respect to the exhaust flow direction in the exhaust passage. When the exhaust gas passes through the vane, a swirling flow is generated and mixing of the reducing agent and the exhaust gas is promoted.
JP 2006-183508 A

  However, such conventional devices have a problem in that vanes are arranged in the exhaust passage, which causes an increase in pressure loss, and may cause an increase in noise due to a swirling flow in the exhaust pipe.

  An object of the present invention is to provide an exhaust emission control device that can promote mixing of a reducing agent and exhaust gas without increasing pressure loss and noise.

In order to achieve this problem, the present invention has taken the following measures in order to solve the problem. That is,
In an exhaust emission control device for adding a reducing agent upstream of a nitrogen oxide reduction catalyst interposed in an exhaust passage of an internal combustion engine and reducing and removing nitrogen oxides in exhaust gas,
While arranging the nitrogen oxide reduction catalyst in a cylindrical container, providing an upstream chamber and a downstream chamber in the cylindrical container on the upstream side and the downstream side of the nitrogen oxide reduction catalyst,
Let the exhaust from the inflow pipe connected to the upstream side of the exhaust flow channel flow into the upstream chamber from the outer peripheral side of the cylindrical container,
An outflow pipe connected to the downstream side of the exhaust passage is provided in the downstream chamber across the downstream chamber, and a plurality of small holes communicating with the downstream chamber are formed on the outer periphery of the outflow pipe, so that the exhaust is discharged. The exhaust gas purification apparatus is characterized in that the exhaust gas is discharged from the outflow pipe to the downstream side of the exhaust passage through the small hole.

  The inflow pipe may be configured to pass through the cylindrical container in a radial direction of the cylindrical container and to be connected to the upstream chamber. Alternatively, the inflow pipe may be configured to pass through the cylindrical container in a tangential direction of the cylindrical container and to be connected to the upstream chamber. The outflow pipe may penetrate the cylindrical container in the radial direction of the cylindrical container, and may reach the inner wall on the opposite side across the downstream chamber. Furthermore, it is good also as a structure which has arrange | positioned the reducing agent oxidation catalyst in the said cylindrical container between the said nitrogen oxide reduction catalyst and the said downstream chamber.

  The exhaust emission control device of the present invention is provided with an upstream chamber and a downstream chamber on both sides of the nitrogen oxide reduction catalyst, and causes the swirling flow to flow into the upstream chamber from the outer peripheral side of the cylindrical container to promote stirring. Since the outflow pipes having a large number of small holes are provided in the downstream chamber, the pressure distribution of the exhaust is not biased, and the exhaust flows in a distributed manner, so that the pressure loss can be reduced, and the upstream chamber and the downstream chamber Exhaust noise can be reduced by the interference effect due to the expansion effect and small holes.

The best mode for carrying out the present invention will be described below in detail with reference to the drawings.
As shown in FIG. 1, reference numeral 1 denotes an exhaust purification device. The exhaust purification device 1 is interposed in an exhaust passage (not shown), and includes a front exhaust purification unit 2 and a rear exhaust purification unit 4. The front exhaust purification unit 2 includes an oxidation catalyst 6 and a diesel particulate filter (hereinafter referred to as DPF) 8, and a cylindrical container 10 that houses the oxidation catalyst 6 and the DPF 8.

  An inflow hole 12 connected to the upstream exhaust passage is formed in the container 10, and the exhaust gas flowing into the container 10 through the inflow hole 12 passes through the oxidation catalyst 6, then through the DPF 8, and then into the inflow pipe. 14 is configured to flow into the rear exhaust purification unit 4 via 14.

  The oxidation catalyst 6 changes the hydrocarbon in the exhaust gas to carbon dioxide and water, oxidizes the carbon monoxide and changes it to carbon dioxide. Moreover, it is a well-known thing which changes nitrogen monoxide to nitrogen dioxide among the nitrogen oxides in exhaust_gas | exhaustion. The DPF 8 is a well-known one that captures soot in the exhaust and burns it.

  The rear exhaust purification unit 4 includes a nitrogen oxide reduction catalyst 16 and a reducing agent oxidation catalyst 18 and a cylindrical container 20 that houses the nitrogen oxide reduction catalyst 16 and the reducing agent oxidation catalyst 18. The cylindrical container 20 has a substantially circular cross-sectional shape, is long in the axial direction, and is closed at both ends.

  The nitrogen oxide reduction catalyst 16 and the reducing agent oxidation catalyst 18 are arranged and housed in the middle of the cylindrical container 20, and the exhaust gas flows axially through the cylindrical container 20. It arrange | positions so that it may flow through the reducing agent oxidation catalyst 18 in an axial direction after passing through the reducing catalyst 16 in an axial direction.

  The nitrogen oxide reduction catalyst 16 is a catalyst used in a selective catalytic reduction method (SCR method) using ammonia as a reducing agent. For example, a support having a honeycomb structure such as aluminum oxide, zeolite, chromium oxide, titanium oxide, etc. It is a well-known thing formed by carrying. The nitrogen oxide reduction catalyst 16 changes the nitrogen oxide in the exhaust gas into nitrogen and water using a reducing agent. The reducing agent oxidation catalyst 18 is a well-known catalyst that oxidizes unreacted ammonia.

  An upstream chamber 22 is formed in the cylindrical container 20 between one end of the cylindrical container 20 and the nitrogen oxide reducing catalyst 16 on the upstream side of the nitrogen oxide reduction catalyst 16. A downstream chamber 24 is formed in the cylindrical container 20 between the other end of the cylindrical container 20 and the reducing agent oxidation catalyst 18 on the downstream side of the nitrogen oxide reduction catalyst 16.

  In the present embodiment, the cylindrical container 20 is formed to have a substantially constant cross-sectional shape in the axial direction, and the entire upstream end face of the nitrogen oxide reduction catalyst 16 in the axial direction is exposed to the upstream chamber 22. . Further, the entire downstream end surface of the reducing agent oxidation catalyst 18 in the axial direction is exposed to the downstream chamber 24.

  The inflow pipe 14 described above is connected to the upstream chamber 22. In this embodiment, the inflow pipe 14 is formed in a substantially U shape and is provided across the container 10 and the cylindrical container 20. The inflow pipe 14 passes through the outer peripheral wall of the container 10 and is connected to the inside of the container 10, and passes through the outer peripheral wall of the cylindrical container 20 and is connected to the upstream chamber 22.

  In addition, in the present embodiment, the inflow pipe 14 connected to the upstream side chamber 22 is cylindrical, as shown in FIG. 2, the opening direction of the inflow pipe 14 in the upstream side chamber 22 is the radial direction of the cylindrical container 20. The cylindrical container 20 is disposed so as to face the substantially central direction and face the wall surface of the cylindrical container 20 on the opposite side. Exhaust gas flowing into the upstream chamber 22 from the inflow pipe 14 passes through the center of the upstream chamber 22 and hits the opposite circular wall surface as shown by an arrow in FIG. It flows in the direction opposite to the inflow direction. As a result, a swirling flow of exhaust gas is generated in the upstream chamber 22.

  The connection between the inflow pipe 14 and the upstream side chamber 22 is not limited to this, and as shown in FIG. 3, the inflow pipe 14 penetrates the outer peripheral wall of the cylindrical container 20 and enters the upstream side chamber 22. You may arrange | position so that an edge may be opened and the opening direction may face the tangential direction of the upstream chamber 22 with a circle. The exhaust gas flowing into the upstream chamber 22 from the inflow pipe 14 flows along the circular wall surface of the upstream chamber 22 as indicated by an arrow in FIG. As a result, a swirling flow of exhaust gas is generated in the upstream chamber 22.

  On the other hand, the inflow pipe 14 is provided with an injection nozzle 26 so that a reducing agent using urea water can be injected and supplied toward the exhaust in the inflow pipe 14 and added to the exhaust. Since ammonia is difficult to handle, urea water is used as a reducing agent in this embodiment, and urea water generates ammonia by a hydrolysis reaction by exhaust heat, and this ammonia is converted into nitrogen oxides in the nitrogen oxide reduction catalyst 16. Used in the reduction reaction.

  The injection nozzle 26 for adding the reducing agent is not limited to the case where the injection nozzle 26 is provided in the inflow pipe 14 and is supplied by injection into the inflow pipe 14. As shown in FIG. 5, the reducing agent may be supplied by injecting and supplying the reducing agent from the injection nozzle 26 into the chamber 10 a of the container 10 on the downstream side of the DPF 8 of the upstream exhaust purification unit 2. .

  The downstream chamber 24 is provided with an outflow pipe 28 connected to the downstream side of an exhaust passage (not shown). As shown in FIG. 4, the outflow pipe 28 is provided through the outer peripheral wall of the cylindrical container 20, and the outflow pipe 28 passes through the center of the downstream side chamber 24 in the radial direction of the cylindrical container 20. And reaches the inner wall on the opposite side of the cylindrical container 20 and is in contact with the inner wall of the cylindrical container 20 to be closed. A large number of small holes 30 are formed in the outer periphery of the outflow pipe 28 in the downstream side chamber 24. The small holes 30 are arranged substantially uniformly on the outer periphery of the outflow pipe 28.

Next, the operation of the above-described exhaust purification device of this embodiment will be described.
First, when exhaust gas flows into the container 10 of the upstream exhaust gas purification unit 2 through the inflow hole 12, the exhaust gas passes through the oxidation catalyst 6 and the DPF 8, and the oxidation catalyst 6 converts hydrocarbons in the exhaust gas into carbon dioxide and water. Change, oxidize carbon monoxide to carbon dioxide. In addition, nitrogen monoxide in the nitrogen oxide in the exhaust gas is changed to nitrogen dioxide. In addition, the DPF 8 burns soot in the exhaust.

  Exhaust gas that has passed through the oxidation catalyst 6 and the DPF 8 flows into the upstream chamber 22 of the rear exhaust purification unit 4 through the inflow pipe 14. When the exhaust gas passes through the inflow pipe 14, a reducing agent is injected and supplied from the injection nozzle 26, and the reducing agent is added to the exhaust gas.

  The exhaust gas to which the reducing agent is added flows into the upstream chamber 22 from the inflow pipe 14. Exhaust gas that has flowed into the upstream chamber 22 from the inflow pipe 14 flows along the circular wall surface of the upstream chamber 22 and a swirling flow is generated, so that the reducing agent and the exhaust gas are mixed. Further, the exhaust gas flowing into the upstream chamber 22 is swirled in the upstream chamber 22 by the swirling flow, and thus is uniformly distributed to the inlet side end face of the nitrogen oxide reduction catalyst 16. In the present embodiment, exhaust gas is uniformly supplied to the end face side of the honeycomb structure carrier.

  When the exhaust gas to which the reducing agent is added passes through the nitrogen oxide reduction catalyst 16, the nitrogen oxide in the exhaust gas is changed into nitrogen and water and rendered harmless. When the exhaust gas passes through the reducing agent oxidation catalyst 18, unreacted ammonia is oxidized and the exhaust gas flows into the downstream side chamber 24.

  Exhaust gas that has flowed into the downstream chamber 24 flows into the outflow pipe 28 via the small hole 30 and is further discharged to the downstream exhaust passage. Since it flows into the outflow pipe 28 from the downstream side chamber 24 via the many small holes 30, there is little bias in the pressure distribution in the downstream side chamber 24, and the exhaust gas is discharged through the outflow pipe 28.

  Thereby, when the exhaust gas in the upstream chamber 22 flows through the nitrogen oxide reduction catalyst 16 to the downstream chamber 24, the pressure distribution in the downstream chamber 24 is less biased. In combination, the exhaust gas passes through the nitrogen oxide reduction catalyst 16 in a dispersed manner, and the pressure loss can be reduced.

  Further, since the exhaust gas is expanded when it flows into the upstream chamber 22 and the downstream chamber 24, particularly when it flows into the upstream chamber 22, the exhaust noise is reduced by the expansion effect. Further, when the exhaust gas is discharged from the outflow pipe 28 through the large number of small holes 30, the exhaust noise is reduced due to the interference effect.

  The present invention is not limited to such embodiments as described above, and can be implemented in various modes without departing from the gist of the present invention.

It is sectional drawing of the exhaust gas purification apparatus as one Embodiment of this invention. It is AA sectional drawing of FIG. It is sectional drawing equivalent to the AA line of FIG. 1 as another embodiment. It is BB sectional drawing of FIG. It is sectional drawing of the exhaust gas purification apparatus as another embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Exhaust gas purification device 2 ... Pre-stage exhaust gas purification part 4 ... Rear-stage exhaust gas purification part 6 ... Oxidation catalyst 10 ... Container 12 ... Inflow hole 14 ... Inflow pipe 16 ... Nitrogen oxide reduction catalyst 18 ... Reductant oxidation catalyst 20 ... Cylindrical container 22 ... Upstream chamber 24 ... Downstream chamber 26 ... Injection nozzle 28 ... Outflow pipe 30 ... Small hole

Claims (5)

In an exhaust emission control device for adding a reducing agent upstream of a nitrogen oxide reduction catalyst interposed in an exhaust passage of an internal combustion engine and reducing and removing nitrogen oxides in exhaust gas,
While arranging the nitrogen oxide reduction catalyst in a cylindrical container, providing an upstream chamber and a downstream chamber in the cylindrical container on the upstream side and the downstream side of the nitrogen oxide reduction catalyst,
Let the exhaust from the inflow pipe connected to the upstream side of the exhaust flow channel flow into the upstream chamber from the outer peripheral side of the cylindrical container,
An outflow pipe connected to the downstream side of the exhaust passage is provided in the downstream chamber across the downstream chamber, and a plurality of small holes communicating with the downstream chamber are formed on the outer periphery of the outflow pipe, so that the exhaust is discharged. An exhaust emission control device for discharging from the outflow pipe to the downstream side of the exhaust passage through the small hole.   The exhaust purification apparatus according to claim 1, wherein the inflow pipe passes through the cylindrical container in a radial direction of the cylindrical container and is connected to the upstream chamber.   The exhaust purification apparatus according to claim 1, wherein the inflow pipe passes through the cylindrical container in a tangential direction of the cylindrical container and is connected to the upstream chamber.   The said outflow pipe | tube penetrates the said cylindrical container to the radial direction of the said cylindrical container, and reaches the inner wall of the opposite side across the said downstream chamber. Exhaust gas purification device described in 1.   The exhaust emission control device according to any one of claims 1 to 4, wherein a reducing agent oxidation catalyst is disposed in the cylindrical container between the nitrogen oxide reduction catalyst and the downstream chamber.

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