JP2008127997A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of realizing excellent NOx reduction performance, by uniformly supplying a reducing agent to respective parts of a reducing catalyst, by promoting atomization and diffusion of the reducing agent supplied from a reducing agent supply means. <P>SOLUTION: An oxidation catalyst 34 and a DPF 35 are stored in an upstream side casing 31, and an SCR catalyst 40 and an oxidation catalyst 41 are stored in a downstream side casing 32, and both casings 31 and 32 are connected by a pipe 33b. A spray diffusion chamber 36 is formed on the downstream side of the DPF 35 in the upstream side casing 31, and an injection nozzle 38 of urea and a fin device 37 generating a swirling flow in exhaust gas are provided. The atomization and the diffusion are promoted by injecting a urea aqueous solution into the spray diffusion chamber 36 capable of an injection distance L with the field temperature higher than the inside of the pipe 33b and the large passage cross-sectional area. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine (hereinafter referred to as an engine), and more particularly to an exhaust gas purification device that provides a reducing agent supply means in an exhaust passage and supplies a reducing agent to a downstream reduction catalyst.

As an exhaust gas purification apparatus that purifies harmful components in exhaust gas using this type of reducing agent, for example, there is an apparatus equipped with an SCR catalyst (selective reduction type NOx catalyst) (see, for example, Patent Document 1). The technology of Patent Document 1 assumes application to a construction machine such as a hydraulic excavator or a bulldozer equipped with a diesel engine. In consideration of the characteristics of a vehicle having a relatively short overall length, the upstream particulate collection is performed. The collecting DPF and the urea denitration catalyst (SCR catalyst) on the downstream side are arranged in parallel and communicated with each other through the communication chamber so as to form a substantially U shape as a whole. The supply section for urea injection and the flow guide for stirring the injected urea aqueous solution are provided in the communication section. After the urea aqueous solution is injected from the supply section into the exhaust gas flowing through the DPF and stirred with the exhaust gas by the flow guide The reduction action of NOx is achieved using NH ₃ (ammonia) obtained by hydrolyzing urea with a urea denitration catalyst.

  However, trucks, buses, light commercial vehicles, and the like have restrictions different from those of the construction machines, and as a result, different characteristics are also required for the exhaust purification device. Since these vehicles have a relatively long overall length, it is not necessary to configure the exhaust purification device in a U-shape, but on the other hand, avoid the vehicle frame, the power train of the engine or transmission, or the rear wheel axle, etc. It is necessary to arrange each component.

Therefore, as shown in FIG. 3, as a general configuration, upstream upstream oxidation catalyst 34 and DPF 35 and downstream SCR catalyst 40 and downstream oxidation catalyst 41 are separated and accommodated in independent casings 31 and 32. These casings 31 and 32 are connected by small diameter pipes 33a to 33c to constitute an exhaust passage. Since the urea injection nozzle 38 corresponding to the supply part of Patent Document 1 and the fin device 37 for generating the swirl flow corresponding to the flow guide need to be provided on the upstream side of the SCR catalyst 40, these injection nozzles 38 and the fin device 37 are installed at the location of the pipe 33b. A urea aqueous solution is injected into the exhaust gas in the pipe 33b, and a swirling flow is generated by the fin device 37 to promote atomization / diffusion of the urea aqueous solution. I am trying.
JP-A-2005-155404

However, when the injection nozzle 38 and the fin device 37 are installed in the pipe 33b as described above, there arises a problem that atomization / diffusion of the urea aqueous solution cannot be sufficiently promoted.
That is, the temperature of the engine exhaust gas drops drastically when it flows into the pipe 33b from the casing 31 containing the pre-stage oxidation catalyst 34 and the DPF 35, so that the urea aqueous solution is injected into an atmosphere that is not so hot and is sufficiently atomized. I can not expect. Further, the sprayed urea aqueous solution collides with the inner wall of the pipe at a small injection distance L in the pipe 33b having a small passage cross-sectional area, which is a cause of the atomization failure.

As a result, in the configuration shown in FIG. 3, the atomization / diffusion of the urea aqueous solution is insufficient, and NH ₃ cannot be uniformly supplied to each part of the SCR catalyst 36, and a good NOx purification performance cannot be realized. there were.
The present invention has been made in order to solve such problems, and the object of the present invention is to promote atomization / diffusion of the reducing agent supplied from the reducing agent supply means to each part of the reduction catalyst. It is an object of the present invention to provide an exhaust gas purification apparatus for an internal combustion engine that can supply a reducing agent evenly and thereby realize a good purification performance.

  In order to achieve the above object, an invention according to claim 1 is provided in an exhaust passage of an internal combustion engine, and is disposed on the downstream side of an upstream casing in which an oxidation catalyst is accommodated and an upstream casing of the exhaust passage. A downstream casing that is connected to the upstream casing via a pipe line and that contains a reduction catalyst therein, and is provided on the downstream side of the oxidation catalyst in the upstream casing to supply the reducing agent into the upstream casing. And a reducing agent supply means.

Accordingly, the reducing agent is supplied from the reducing agent supply means into the upstream casing, and the reducing agent is guided to the downstream casing through the pipe and used for the purification action by the internal reduction catalyst.
As the reduction catalyst, for example, an SCR catalyst (selective reduction type NOx catalyst) for reducing NOx in exhaust gas using urea or ammonia or a storage type NOx catalyst for storing NOx in exhaust gas is applied. NOx in the exhaust gas is reduced on the SCR catalyst using urea or ammonia supplied as a reducing agent from the reducing agent supply means, and in the case of an occlusion type NOx catalyst, occlusion is achieved. When the NOx occlusion amount of the type NOx catalyst reaches a predetermined threshold value, fuel is supplied as a reducing agent from the reducing agent supply means, so that NOx is released and reduced from the NOx catalyst using the supplied fuel.

  In any case, in order for the reduction catalyst to exert a good purification action, it is necessary to promote atomization / diffusion of the reducing agent and supply the reducing agent evenly to each part of the reduction catalyst. It is desirable to inject the reducing agent into a high-temperature atmosphere with good atomization and to secure a long injection distance (distance in the injection axis direction in which the reducing agent spray moves with the injection energy) without blocking the reducing agent spray. .

In the present invention, an upstream casing that accommodates an oxidation catalyst is used as a space for supplying a reducing agent, and the upstream casing has a higher temperature in the field than the downstream pipeline, which is good. Since the atomization can be expected and the passage cross-sectional area is larger than that in the pipe line, the injection distance of the reducing agent can be sufficiently secured, so that the atomization / diffusion of the reducing agent can be promoted.
The invention of claim 2 is the wall flow type according to claim 1, wherein the particulate matter in the exhaust gas is collected between the oxidation catalyst in the upstream casing and the reducing agent supply means in the vicinity of the reducing agent supply means. These filters are arranged.

Therefore, by disposing a filter with a large heat capacity upstream of the reducing agent supply means, even if the exhaust gas temperature fluctuates according to the operating state of the internal combustion engine, an extreme temperature drop is suppressed at the position of the reducing agent supply means, This further promotes atomization / diffusion of the reducing agent.
According to a third aspect of the present invention, in the first or second aspect of the present invention, the agitation means for agitating the exhaust gas flowing in the upstream casing is provided in the vicinity of the reducing agent supply means in the upstream casing.

  Therefore, when the exhaust gas flowing through the upstream casing is stirred by the stirring means, atomization / diffusion of the reducing agent injected into the exhaust gas is further promoted. As the agitation means, for example, a method of causing a swirl flow in the exhaust gas by a fin device using fins is employed, so that a certain increase in exhaust pressure is inevitable, but agitation is performed in the upstream casing having a large passage cross-sectional area. By providing the means, an increase in exhaust pressure is suppressed to a minimum.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine of the first aspect of the present invention, by providing the reducing agent supply means in the upstream casing having a high field temperature and a large passage sectional area, the atomization is excellent. Injects the reducing agent into a high-temperature atmosphere and ensures a sufficient injection distance of the reducing agent, thus promoting atomization and diffusion of the reducing agent and supplying the reducing agent evenly to each part of the reduction catalyst for good purification. Performance can be realized.

According to the exhaust gas purification apparatus for an internal combustion engine of the second aspect of the invention, in addition to the first aspect, a filter having a large heat capacity is disposed upstream of the reducing agent supply means to suppress fluctuations in the exhaust gas temperature, thereby reducing the reducing agent. Can be further promoted.
According to the exhaust gas purification apparatus for an internal combustion engine of the invention of claim 3, in addition to claim 1 or 2, by providing a stirring means in the upstream casing having a large passage cross-sectional area, fuel consumption deterioration due to increased exhaust pressure, etc. Detrimental effects can be minimized.

Hereinafter, an embodiment in which the present invention is embodied in an exhaust emission control device for a diesel engine will be described.
FIG. 1 is an overall configuration diagram showing an exhaust emission control device for a diesel engine according to this embodiment. The engine 1 is configured as an in-line 6-cylinder engine. Each cylinder of the engine 1 is provided with a fuel injection valve 2, and each fuel injection valve 2 is supplied with pressurized fuel from a common common rail 3 and is opened at a timing according to the operating state of the engine. The fuel is injected into the inside.

  An intake manifold 4 is mounted on the intake side of the engine 1, and the intake passage 5 connected to the intake manifold 4 is opened and closed by an air cleaner 6, a compressor 7a of the turbocharger 7, an intercooler 8, and an actuator 9a from the upstream side. An intake throttle valve 9 is provided. An exhaust manifold 10 is mounted on the exhaust side of the engine 1, and an exhaust passage 11 is connected to the exhaust manifold 10 via a turbine 7b of a turbocharger 7 connected coaxially with the compressor 7a.

  During operation of the engine 1, the intake air introduced into the intake passage 5 through the air cleaner 6 is pressurized by the compressor 7 a of the turbocharger 7, and then distributed to each cylinder through the intercooler 8, the intake throttle valve 9, and the intake manifold 4. These are introduced into the cylinder in the intake stroke of each cylinder. In the cylinder, fuel is injected from the fuel injection valve 2 at a predetermined timing and ignited and burned in the vicinity of the compression top dead center, and the exhaust gas after combustion rotates through the exhaust manifold 10 and then rotates the turbine 7b and then passes through the exhaust passage 11. It is discharged outside.

  On the other hand, the intake manifold 4 and the exhaust manifold 10 are connected by an EGR passage 17, and an EGR valve 18 and an EGR cooler 19 that are opened and closed by an actuator 18 a are provided in the EGR passage 17. During operation of the engine 1, part of the exhaust gas is recirculated as EGR gas from the exhaust manifold 10 side to the intake manifold 4 side according to the opening degree of the EGR valve 18.

The intake manifold 4 is provided with a swirl valve 20 that is driven to open and close by an actuator 20a corresponding to the intake port of each cylinder. When each swirl valve 20 is closed, a swirl flow is generated in the cylinder.
The exhaust passage 11 is provided with the exhaust purification device of the present invention, and the exhaust purification device is accommodated in the upstream casing 31 and the downstream casing 32. Basically, the casings 31 and 32 and the silencer (not shown) are connected to each other via thin pipes 33a to 33c, and the exhaust passage 11 is constituted by these members. In order from the upstream side of the exhaust passage 11, the upstream casing 31 is connected to the turbine 7b of the turbocharger 7 via the first pipe 33a, and the upstream casing 31 is connected to the downstream casing via the second pipe 33b. 32. The downstream casing 32 is connected to the silencer via the third pipe 33c, and the rear end of the silencer is open to the atmosphere.

  Both the upstream casing 31 and the downstream casing 32 have a substantially cylindrical shape extending in the front-rear direction of the vehicle. The passage cross-sectional area through which the exhaust gas in both the casings 31 and 32 flows is set to be significantly larger than the passage cross-sectional area of the pipes 33a to 33c in order to accommodate each component of the exhaust gas purification device. The step between ~ 33c is tapered to reduce the flow resistance of the exhaust gas.

  The upstream casing 31 accommodates a pre-stage oxidation catalyst 34 on the upstream side of the interior, and a wall flow type DPF (diesel particulate filter) 35 on the downstream side. As will be described later, the DPF 35 is a particulate matter in the exhaust gas. There is an effect of collecting curate (hereinafter referred to as PM). The upstream casing 31 extends rearward from the accommodation position of the DPF 35 while maintaining the same cross-sectional shape. As a result, a space is formed on the downstream side of the DPF 35 in the upstream casing 31. Is referred to as a spray diffusion chamber 36.

  In the spray diffusion chamber 36, a fin device 37 (stirring means) for causing a swirling flow in the exhaust gas is installed. The fin device 37 of the present embodiment is configured by a large number of fins 37a erected on the inner peripheral wall of the upstream casing 31, and each fin 37a forms a predetermined angle in the circumferential direction with respect to the exhaust gas circulation direction. The principle of causing a swirling flow around the central axis of the upstream casing 31 is adopted.

However, the configuration of the fin device 37 is not limited to this and can be arbitrarily changed. Further, the agitation means is not limited to one that causes a swirling flow in the exhaust gas, but may be one that exerts an agitating action of the exhaust gas without causing a swirling flow as in the flow guide described in Patent Document 1, for example. Good.
An injection nozzle 38 (reducing agent supply means) is installed on one side of the outer peripheral wall of the upstream casing 31 so as to be positioned on the downstream side of the fin device 37, and the injection nozzle 38 is a urea aqueous solution pumped from a tank (not shown). As a reducing agent, it can be arbitrarily injected into the spray diffusion chamber 36. The injection direction of the injection nozzle 38 is set so as to be orthogonal to the exhaust gas flow direction and is set so as to be directed to the central portion of the upstream casing 31. A temperature sensor 39 is installed between the fin device 37 and the injection nozzle 38, and the temperature in the spray diffusion chamber 36 is detected by the temperature sensor 39.

On the other hand, the downstream casing 32 accommodates the SCR catalyst 40 (reduction catalyst) on the upstream side of the inside and the downstream oxidation catalyst 41 on the downstream side. As will be described later, the SCR catalyst 40 is contained in the exhaust gas. It has the effect of purifying NOx.
As described above, the exhaust emission control device of the present embodiment is configured. However, since the upstream casing 31 and the downstream casing 32 that contain a catalyst or the like require a considerable installation space, a vehicle frame, an engine, a transmission, and the like The power train or the rear axle is arranged apart from each other so as to avoid the rear wheel axle, and the layout is connected to each other by the second pipe 33b.

  On the other hand, the intake throttle valve 9, exhaust throttle valve 12, EGR valve 18, swirl valve 20 actuators 9a, 12a, 18a, 20a, fuel injection valve 2, fuel nozzle 14, injection nozzle 38, temperature sensor 39, etc. It is connected to an (electronic control unit) and driven and controlled by the ECU 51 based on detection information from sensors. For example, the ECU 51 operates the engine 1 by controlling the injection amount, injection pressure, and injection timing of the fuel injection valve 2 based on the operating state of the engine 1 such as the engine speed and load, and opens the EGR valve 18 by the actuator 18a. The EGR recirculation amount is adjusted by controlling the degree, and the opening of the swirl valve 20 is controlled by the actuator 20a to adjust the swirl flow.

The ECU 51 controls post-injection for forced regeneration of the DPF 35, urea supply from the injection nozzle 38 for NOx purification by the SCR catalyst 40, and the like. The NOx purification action by the SCR catalyst 40 will be described.
The DPF 35 has an action of collecting PM in the exhaust gas. In an operation state where the exhaust gas temperature of the engine 1 is relatively high, NO ₂ is generated from NO in the exhaust gas by the oxidizing action of the pre-stage oxidation catalyst 34, and the NO ₂ The PM collected in the DPF 35 by the oxidation reaction is continuously incinerated and removed, whereby the DPF 35 is regenerated. On the other hand, when the operation state in which such a continuous regeneration action cannot be obtained continues, post injection is appropriately executed after the main injection by the ECU 51, and the DPF 15 is made to be heated by the heat of the oxidation reaction of the fuel supplied onto the pre-stage oxidation catalyst 34. The DPF 35 is forcibly regenerated by raising the temperature and burning and removing PM. Note that CO generated during PM combustion in forced regeneration is oxidized to CO ₂ by the post-stage oxidation catalyst 41.

Further, since the SCR catalyst 40 needs to supply NH ₃ (ammonia) for NOx purification, the ECU 51 injects the urea aqueous solution injection amount from the injection nozzle 38 based on the operating state of the engine 1 and the detected value of the temperature sensor 39. To control. The injected urea aqueous solution is hydrolyzed by exhaust heat and water vapor in the exhaust gas to generate NH ₃ , and this NH ₃ reduces NOx in the exhaust gas to harmless N ₂ on the SCR catalyst 40 to purify NOx. On the other hand, surplus NH _{3 at} this time is oxidized to NO by the post-stage oxidation catalyst 41.

A hydrolysis catalyst that acts to hydrolyze urea into NH ₃ may be disposed upstream of the SCR catalyst 40, or an aqueous ammonia solution may be injected from the injection nozzle 38 instead of the aqueous urea solution. Also good.
In this embodiment, since the spray nozzle 38 is provided in the spray diffusion chamber 36 formed in the upstream casing 31 and the urea aqueous solution is sprayed from the spray nozzle 38 into the spray diffusion chamber 36, the following effects are obtained. It is done.

First, in order for the SCR catalyst 40 to exhibit NOx purification performance, it is necessary to promote the atomization / diffusion of the urea aqueous solution and supply NH ₃ to each part of the SCR catalyst 40 evenly. It is desirable to inject the urea aqueous solution in a good high temperature atmosphere and to secure a long injection distance L (distance in the injection axis direction in which the urea aqueous solution spray moves with injection energy) without blocking the spraying of the urea aqueous solution.

  Here, the inside temperature of the spray diffusion chamber 36 of the upstream casing 31 tends to be higher than that of the second pipe 33b on the downstream side. FIG. 2 is a diagram showing the average temperature during the transient mode operation at each position a to f of the exhaust purification device in correspondence with the configuration diagram of FIG. 1, and the outlet temperature with respect to the inlet temperature a of the pre-stage oxidation catalyst 34. b rises due to the oxidation action of the front-stage oxidation catalyst 43 and the heat capacity of the front-stage oxidation catalyst 43, and the temperature c in the spray diffusion chamber 36 after passing through the DPF 35 is kept substantially equal, but downstream thereof It can be seen that the temperature d in the second pipe 33b on the side is considerably lowered. Therefore, compared with the case where the urea injection nozzle 38 is arranged in the second pipe 33b as in the prior art shown in FIG. 3, in the present embodiment in which the injection nozzle 38 is arranged in the spray diffusion chamber 36, the atomization is good. A urea aqueous solution is injected into a high temperature atmosphere.

  In addition, the DPF 35 located upstream of the injection nozzle 38 in the upstream casing 31 has a large heat capacity and functions to suppress temperature fluctuations in the spray diffusion chamber 36 on the downstream side. Even if the exhaust gas temperature fluctuates according to the state, an extreme temperature drop is suppressed at the position of the injection nozzle 38. Due to the above temperature factors, the aqueous urea solution injected from the injection nozzle 38 into the spray diffusion chamber 36 is atomized and diffused well.

  Further, the upstream casing 31 that accommodates the front-stage oxidation catalyst 34 and the DPF 35 has a significantly larger passage cross-sectional area than the second pipe, and the urea aqueous solution is injected from the injection nozzle 38 toward the wide spray diffusion chamber 36. Therefore, it is easy to secure the injection distance L from the beginning. In addition, since the injection direction of the urea aqueous solution by the injection nozzle 38 is directed to the central portion of the downstream casing 31, the space in the spray diffusion chamber 36 is utilized to the maximum to ensure the injection distance L. As a result, a sufficient injection distance L of the urea aqueous solution can be secured, and the factor related to the injection distance L greatly contributes to the atomization / diffusion of the urea aqueous solution.

As a result, according to the exhaust purification apparatus of this embodiment, atomization / diffusion of the urea aqueous solution can be sufficiently promoted to supply NH ₃ evenly to each part of the SCR catalyst 40, thereby realizing good NOx purification performance. can do.
On the other hand, in the present embodiment, not only the injection nozzle 38 but also the fin device 37 is disposed in the spray diffusion chamber 36 having a large passage cross-sectional area, and the installation space for the fin device 37 has a margin, so urea. There is also an advantage that good atomization / diffusion of the aqueous solution and suppression of increase in exhaust pressure can be achieved at a high level.

  That is, if the fin shape of the fin device 37 is set so that a strong swirl flow can be generated in the exhaust gas, it is suitable for atomization / diffusion of the urea aqueous solution, but the exhaust pressure tends to increase. If the fin shape is set so as to weaken the swirl flow to suppress it, the atomization / diffusion of the urea aqueous solution becomes insufficient, and the two are in a trade-off relationship. In the conventional exhaust purification apparatus shown in FIG. 3, the pipe 33b, which originally has a small passage cross-sectional area, is further narrowed by the installation of the fin device 37, which tends to increase the exhaust pressure. On the other hand, the fin device 37 itself is small in size and shape. Because it is limited, a strong swirling flow cannot be expected, and both requirements can be met only in a low dimension.

  On the other hand, in this embodiment, since the large fin device 37 is arranged in the spray diffusion chamber 36, the passage cross-sectional area of the spray diffusion chamber 36 can be sufficiently secured even after the fin device 37 is installed, and the fin device. A strong swirling flow can be generated by increasing the size of 37 and optimizing the fin shape, and both requirements can be achieved at a high level. Accordingly, it is possible to further improve NOx purification performance by suppressing atomization / diffusion of the urea aqueous solution by a strong swirling flow while minimizing adverse effects such as fuel consumption deterioration due to increased exhaust pressure. This effect is not limited to the case where the fin device 37 is used as the stirring means. For example, even when the flow guide described in Patent Document 1 is provided as the stirring means, the flow guide is arranged in the wide spray diffusion chamber 36. Thus, the same advantages as those of the fin device 37 can be obtained.

  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the exhaust gas purification device of the diesel engine 1 provided with the SCR catalyst 40 for NOx purification is embodied. However, the present invention is not limited to this as long as the engine is provided with a reduction catalyst that requires supply of a reducing agent. . For example, a storage-type NOx catalyst that stores NOx in exhaust gas is provided in the exhaust passage, and in order to release and reduce the stored NOx from the NOx catalyst, NOx purge is periodically performed to inject fuel into the exhaust passage as a reducing agent. It may be applied to the engine that needs it. In this case, the SCR catalyst 40 in FIG. 1 is replaced with an occlusion type NOx catalyst. However, by disposing a fuel supply injection nozzle in the spray diffusion chamber 36 of the upstream casing 31, Similarly, the effect that fuel atomization / diffusion can be promoted can be obtained.

  Moreover, in the said embodiment, although the fin apparatus 37 was arrange | positioned in the upstream of the injection nozzle 38, the positional relationship of the injection nozzle 38 and the fin apparatus 37 is not limited to this, Conversely, with respect to the fin apparatus 37, an injection nozzle 38 may be arranged on the upstream side, and the fin device 37 may be omitted.

1 is an overall configuration diagram illustrating an exhaust emission control device for a diesel engine according to an embodiment. It is the figure which showed the average temperature in each position af of an exhaust gas purification apparatus corresponding to the block diagram of FIG. It is a block diagram which shows the prior art exhaust gas purification apparatus which has arrange | positioned the fin apparatus and the injection nozzle to the pipe.

Explanation of symbols

1 engine (internal combustion engine)
11 Exhaust passage 31 Upstream casing 32 Downstream casing 33b Second pipe 34 Pre-stage oxidation catalyst 35 DPF (filter)
37 Fin device (stirring means)
38 Injection nozzle (reducing agent supply means)
40 SCR catalyst (reduction catalyst)

Claims (3)

An upstream casing provided in an exhaust passage of the internal combustion engine and containing an oxidation catalyst therein;
A downstream casing disposed on the downstream side of the upstream casing of the exhaust passage, connected to the upstream casing via a conduit, and containing a reduction catalyst therein;
An exhaust gas purification apparatus for an internal combustion engine, comprising: a reducing agent supply means that is provided downstream of the oxidation catalyst in the upstream casing and supplies a reducing agent into the upstream casing.   Between the oxidation catalyst in the upstream casing and the reducing agent supply means, a wall flow type filter for collecting particulate matter in the exhaust gas is disposed in proximity to the reducing agent supply means. The exhaust emission control device for an internal combustion engine according to claim 1.   3. An exhaust emission control device for an internal combustion engine according to claim 1, wherein a stirring means for stirring the exhaust gas flowing through the upstream casing is provided at a position close to the reducing agent supply means in the upstream casing. .

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