JP7619092B2 - Engine exhaust purification device - Google Patents

Description

The present invention relates to an engine exhaust purification device.

The exhaust gas from engines used in automobiles and the like contains NOx (nitrogen oxides). As an example of a catalyst for purifying the NOx in the exhaust gas, an exhaust purification device equipped with a NOx selective reduction catalyst and a device for injecting a reducing agent upstream of the NOx catalyst is known. In automobile engines, urea water is widely used as a reducing agent. In this configuration, a reducing agent injected from a reducing agent injection device is mixed with the exhaust gas. The exhaust gas mixed with the reducing agent is supplied to the NOx catalyst for purification.

One example of such an exhaust purification device is described in Patent Document 1. In this exhaust purification device, the reducing agent is injected from a reducing agent injection device toward a reducing agent diffusion means. This reducing agent diffusion means promotes atomization, vaporization, and thermal decomposition due to evaporation of the reducing agent, and disperses the reducing agent in the exhaust gas.

Patent No. 4943499

To increase the efficiency of NOx purification, it is preferable that the concentration distribution of the reducing agent mixed into the exhaust gas be uniform. For this reason, in the configuration of Patent Document 1, the reducing agent is dispersed uniformly in the exhaust gas by promoting atomization and vaporization of the reducing agent using a reducing agent diffusion means.

By the way, the reducing agent mixed into the exhaust gas is thermally decomposed by the heat of the exhaust gas. In order to further improve the NOx purification performance of the NOx selective reduction catalyst in the exhaust gas, it is preferable to promote this thermal decomposition.

The present invention was made in consideration of these points, and its purpose is to improve the NOx purification performance of the exhaust purification device by promoting the thermal decomposition of the reducing agent mixed in the exhaust.

To achieve the above object, the present invention provides a reducing agent injection device with multiple injection ports, and the reducing agent injected from each injection port collides with different collision walls that are independent of each other, thereby atomizing the reducing agent droplets.

Specifically, the engine exhaust gas purification device disclosed herein comprises:
A NOx selective reduction catalyst that is provided in an exhaust passage of the engine and selectively reduces and purifies NOx in the exhaust gas;
a reducing agent injection device that is provided in the exhaust passage upstream of the NOx selective reduction catalyst and that injects a reducing agent into the exhaust gas,
the reducing agent injection device has a plurality of injection ports for injecting the reducing agent into the exhaust gas,
a collision wall independent of each other is provided for each injection port on the injection axis of each injection port, against which the reducing agent injected from each injection port collides;
The collision wall is arranged so that a distance between the jet nozzle and the collision wall on the jet axis differs for each jet nozzle ,
the reducing agent injection device has a first injection port, a second injection port, and a third injection port as the injection port,
the collision wall includes a first collision wall arranged on the ejection axis of the first ejection port, a second collision wall arranged on the ejection axis of the second ejection port, and a third collision wall arranged on the ejection axis of the third ejection port,
A distance from each of the jet nozzles to each of the collision walls is set so that the first collision wall is the shortest, the third collision wall is the longest, and the second collision wall is an intermediate length between them,
the first collision wall, the second collision wall, and the third collision wall protrude in the same direction from a wall surface of the exhaust passage,
The first collision wall and the second collision wall are arranged offset on both sides in a direction perpendicular to the protruding direction, and the third collision wall is arranged offset forward in the protruding direction relative to the first collision wall and the second collision wall .

According to this engine exhaust purification device, a reducing agent is mixed into the exhaust passing through the exhaust passage before it is supplied to the NOx selective reduction catalyst where NOx is reduced and purified. This reducing agent is injected from each of the multiple injection ports provided in the reducing agent injection device. The reducing agent injected from each injection port collides with a collision wall provided on the injection axis of each injection port. The reducing agent is atomized by splitting and scattering upon collision, and is diffused in the exhaust and thermally decomposed. When the reducing agent collides with the collision wall, some of the reducing agent adheres to the collision wall. The reducing agent attached to the collision wall spreads over the collision plate and is vaporized and thermally decomposed.

In this way, the reducing agent is diffused into the exhaust gas from multiple collision walls, allowing the reducing agent to be diffused evenly throughout the exhaust gas, resulting in homogeneous mixing of the exhaust gas and the reducing agent. This promotes the vaporization and thermal decomposition of the reducing agent due to the heat of the exhaust gas. In addition, the reducing agent that has been atomized by colliding with the collision walls has an increased surface area, promoting heat and mass transfer, and promoting the vaporization and thermal decomposition of the reducing agent.

In addition, if reducing agent injected from multiple injection ports is caused to collide with a single collision wall, reducing agent accumulation occurs on the collision wall, which is likely to result in undesirable deposits. In contrast, with the above configuration, reducing agent injected from each injection port collides with a different collision wall, making it difficult for reducing agent accumulation to occur, which is advantageous in suppressing the formation of undesirable deposits.

As described above, in the exhaust gas purification device for the engine,
the reducing agent injection device has a first injection port, a second injection port, and a third injection port as the injection port,
the collision wall includes a first collision wall arranged on the ejection axis of the first ejection port, a second collision wall arranged on the ejection axis of the second ejection port, and a third collision wall arranged on the ejection axis of the third ejection port,
A distance from each of the jet nozzles to each of the collision walls is set so that the first collision wall is the shortest, the third collision wall is the longest, and the second collision wall is an intermediate length between them,
the first collision wall, the second collision wall, and the third collision wall protrude in the same direction from a wall surface of the exhaust passage,
The first collision wall and the second collision wall are arranged offset on both sides in a direction perpendicular to the protruding direction, and the third collision wall is arranged offset forward in the protruding direction relative to the first collision wall and the second collision wall.

According to this configuration, the first collision wall, the second collision wall, and the third collision wall are each fixed to one mounting plate, and the mounting plate is attached to the wall surface of the exhaust passage, so that the three collision walls can be fixed to the wall surface of the exhaust passage. In this way, the collision walls can be assembled more easily than if each of the three collision walls were attached to the wall surface separately.

In the exhaust gas purification device for the engine,
a swirl portion disposed upstream of the NOx selective reduction catalyst in the exhaust passage, the swirl portion swirls the exhaust gas around an axis of the exhaust passage,
The collision wall is provided on the rotating portion,
The collision wall is formed of a flat plate,
The wall surface of the collision wall is disposed substantially perpendicular to the swirl axis of the exhaust gas.

This configuration prevents the swirling force of the exhaust gas from being hindered by the wall surface of the collision wall. This promotes mixing of the swirling flow of the exhaust gas with the reducing agent, facilitating the vaporization and thermal decomposition of the reducing agent by the heat of the exhaust gas.

In the exhaust gas purification device for the engine,
an oxidation catalyst that oxidizes HC and CO in the exhaust gas is provided upstream of the NOx selective reduction catalyst in the exhaust passage;
an exhaust passage portion connecting the oxidation catalyst and the NOx selective reduction catalyst includes a bent portion that is bent so that the flow of exhaust gas changes from a direction extending in an axial direction of the oxidation catalyst to a direction intersecting the axial direction,
The bent portion is provided with the swirl portion, and the swirl portion swirls the exhaust gas around a passage axis on the downstream side of the swirl portion extending in the intersecting direction as a swirl axis.

In this way, the exhaust gas flows from the oxidation catalyst toward the bent portion, directed toward a portion deviated to one side from the axis of the passage extending in the intersecting direction, which makes it easier to generate the above-mentioned swirling flow at the bent portion, which is advantageous for mixing the reducing agent and the exhaust gas.

In the exhaust gas purification device for the engine,
The exhaust passage is characterized in that a throttle portion having a passage diameter smaller than that of the swirl portion is provided between the swirl portion and the NOx selective reduction catalyst.

In this way, the throttling section applies resistance to the exhaust flow. This ensures that the exhaust gas remains in the swirling section, promoting mixing of the reducing agent with the exhaust gas and promoting vaporization and thermal decomposition of the reducing agent. In addition, the throttling section gradually reduces the radius of the swirling flow, increasing the angular velocity of the swirl and promoting mixing of the reducing agent with the exhaust gas.

In the exhaust gas purification device for the engine,
The throttle portion is provided with a resistance member that provides resistance to the flow of the exhaust gas.

This ensures that the exhaust gas remains in the swirl section for a sufficient amount of time. This promotes mixing of the reducing agent into the exhaust gas. In addition, liquid or undecomposed reducing agent is trapped by the resistance member, preventing it from passing through.

In the exhaust gas purification device for the engine,
The collision wall extends from a peripheral wall of the swirl portion toward the center of the swirl portion.

This prevents the collision wall from interfering with the swirling of the exhaust.

According to the present invention, the NOx purification efficiency of the NOx selective reduction catalyst can be improved by promoting the vaporization and thermal decomposition of the reducing agent mixed in the exhaust gas.

1 is a diagram showing a configuration of an exhaust gas purification device for an engine. 1 is a side view of an exhaust gas purification device for an engine. 1 is a perspective view of an exhaust gas purification device for an engine; 2 is a perspective view of the engine exhaust gas purification device excluding a first bent portion and a rotating portion. FIG. FIG. FIG. FIG. FIG. 2 is a perspective view of a reducing agent injection device and a collision wall. FIG. 2 is a perspective view of a reducing agent injection device injecting a reducing agent and a collision wall.

The following describes in detail an embodiment of the present invention with reference to the drawings. The following description of the preferred embodiment is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses.

<Configuration of Exhaust Gas Purification Device>
In the exhaust purification device for an engine (diesel engine) E shown in Fig. 1, reference numeral 1 denotes an exhaust passage through which exhaust gas discharged from the engine E passes. In this exhaust passage 1, an oxidation catalyst 2 and a filter with a urea SCR catalyst (hereinafter referred to as "SCR ON F") 3 are arranged in this order from the upstream side in the exhaust gas flow direction. The exhaust purification device is equipped with a urea injection device (injector) 4 as a reducing agent injection device that injects and supplies urea water between the oxidation catalyst 2 and the SCR ON F 3. As the urea water, one called AdBlue is used.

The oxidation catalyst 2 is a catalyst that oxidizes HC and CO in the exhaust gas, and is made by supporting a precious metal as a catalytic metal on a honeycomb-shaped carrier. In this example, Pt is used as the catalytic metal, and activated alumina is used as the support material for Pt.

SCR ON F3 is a filter that collects particulates in exhaust gas and supports a urea SCR catalyst as a NOx selective reduction catalyst that selectively reduces NOx. The filter is a wall-flow type honeycomb structure, and the urea SCR catalyst is supported on the inner wall surface of the cells and the inner pore surface of the porous wall that separates the cells. The urea SCR catalyst reduces and purifies NOx in the exhaust gas using NH ₃ generated by thermal decomposition of urea and NH ₃ generated by hydrolysis of isocyanic acid generated by the thermal decomposition as reducing agents. Cu zeolite, which is zeolite supported with Cu by ion exchange, can be preferably used as the urea SCR catalyst. CHA (chabazite) can be preferably used as the zeolite. Fe, Ti, Ce, and W can also be used as the catalyst component.

As shown in Figures 2 to 4, the oxidation catalyst 2 and the SCR ON F3 are arranged side by side so that their axial directions are approximately parallel to each other. In this embodiment, the oxidation catalyst 2 is arranged above the SCR ON F3. As shown in Figure 5, the outlet 21 through which the exhaust gas of the oxidation catalyst 2 flows out and the inlet 31 through which the exhaust gas of the SCR ON F3 flows in are open in approximately the same direction.

The exhaust passage section 10 connecting the outlet 21 of the oxidation catalyst 2 and the inlet 31 of the SCR ON F3 has a first bent section 11 that bends so that the exhaust flow changes from the axial direction of the oxidation catalyst 2 to a direction intersecting the axial direction, and a second bent section 12 that bends so that the exhaust flow changes to the axial direction of the SCR ON F3. In this embodiment, since the oxidation catalyst 2 is disposed above the SCR ON F3, the exhaust passage section 10 bends from a substantially horizontal horizontal direction to a vertical direction (up and down direction) at the first bent section 11, and bends from the vertical direction to a horizontal direction at the second bent section 12.

The first bend 11 is provided with a swirling section 112 that swirls the exhaust gas around the passage axis extending in the intersecting direction (vertical direction in this embodiment). Exhaust gas flows into this swirling section 112 from the outlet 21 of the oxidation catalyst 2. As shown in FIG. 4, the outlet 21 of the oxidation catalyst 2 is provided shifted to one side (left side in FIG. 4) from the axis of the oxidation catalyst 2. Therefore, the exhaust gas from the outlet 21 flows into the swirling section 112 in a direction deviated to one side from the passage axis extending in the intersecting direction. Therefore, the exhaust gas that flows into the swirling section 112 is swirled around the vertical direction as the axis of rotation, as shown by the arrow in FIG. 5.

The outlet 21 is also provided with a straightening member 5 that extends toward the swirl section 112. This straightening member 5 is inclined so that it leans toward the one side (the left side in FIG. 4) as it moves forward in the exhaust flow direction. By being guided by this straightening member 5, the exhaust from the outlet 21 tends to flow into the swirl section 112 along its inner circumferential wall. This strengthens the swirl of the exhaust flowing into the swirl section 112.

A throttle section 13 is provided downstream of the swirl section 112, that is, at a portion that connects the first bent section 11 and the second bent section 12 in the exhaust passage 1 and extends in the intersecting direction (vertical direction in this embodiment). The passage diameter of the throttle section 13 is smaller than the passage diameter of the swirl section 112. This throttle section 13 is provided with a resistance member 6 for providing resistance to the exhaust. This resistance member 6 is shown in FIG. 6. The resistance member 6 is circular and arranged to cross the exhaust passage. An attachment flange 61 is provided on the outer periphery of the resistance member 6. The resistance member 6 has four quarter-circular portions 62 cut and raised downstream to form openings. The quarter-circular portions 62 are cut and raised along the swirling direction of the exhaust gas so that the swirling of the exhaust gas is not hindered by the quarter-circular portions 62. As shown by the arrow in FIG. 5, the exhaust gas flowing through the swirl section 112 is resisted by the throttle section 13 and the resistance member 6, and flows downstream from the opening of the resistance member 6. In addition, the throttling section 13 gradually reduces the radius of the swirling flow, increasing the angular velocity of the swirl and promoting mixing of the reducing agent and exhaust gas.

As shown in FIG. 5, the first bend 11 is provided with a urea injector 4 that injects urea water in the intersecting direction toward the swirl 112. In this embodiment, the urea injector 4 is provided on the upper wall of the exhaust passage that forms the first bend 11, and injects urea water downward. Below the urea injector 4, a collision wall 7 formed of a flat plate that extends toward the center of the swirl 112 is provided.

In FIG. 7, the underside of the urea injector 4 is shown by a two-dot chain circle. A first injection port 41, a second injection port 42, and a third injection port 43 are provided on the underside of the urea injector 4. The first injection port 41 and the second injection port 42 are disposed on the inner circumferential wall side of the swirling portion 112, and the third injection port 43 is disposed at a position away from the inner circumferential wall.

As shown in FIG. 8, the collision wall 7 includes a first collision wall 71, a second collision wall 72, and a third collision wall 73, which correspond to each other from the top. The collision walls 71 to 73 are plate-shaped and have approximately the same width. The first collision wall 71 and the second collision wall 72 each have a notch at the tip. The third collision wall 73 has a longer length in the protruding direction than the first collision wall 71 and the second collision wall 72. The first collision wall 71, the second collision wall 72, and the third collision wall 73 are independent of each other, and each base end is fixed to the collision wall mounting plate 70. This collision wall mounting plate 70 is fixed to one location on the wall surface of the swirl section 112 by welding. The wall surfaces of the collision walls 71 to 73 fixed in this manner are approximately perpendicular to the exhaust rotation axis in the swirl section 112.

The first collision wall 71 is disposed on the injection axis of the first injection nozzle 41, the second collision wall 72 is disposed on the injection axis of the second injection nozzle 42, and the third collision wall 73 is disposed on the injection axis of the third injection nozzle 43. In other words, the distance from each injection nozzle to each collision wall 7 on the injection axis is set so that the first collision wall 71 is the shortest, the third collision wall 73 is the longest, and the second collision wall 72 is intermediate between them.

9, the urea water sprayed from each of the first injection port 41, the second injection port 42, and the third injection port 43 is shown by two-dot chain lines. The urea water sprayed from the first injection port 41 collides with the first collision wall 71, the urea water sprayed from the second injection port 42 collides with the second collision wall 72, and the urea water sprayed from the third injection port 43 collides with the third collision wall. The cutout portion of the first collision wall 71 is formed on the injection axis of the second injection port 42. The cutout portion of the second collision wall 72 is also formed on the injection axis of the first injection port 41. Furthermore, the injection axis of the third injection port 43 is directed toward the tip of the third collision wall 73 so that the first collision wall 71 and the second collision wall 72 are not located on the injection axis. In this way, the positions where the urea water collides with the first collision wall 71 and the second collision wall 72 are shifted on both sides in the direction perpendicular to the protruding direction of each collision wall. In addition, the position where the urea water collides with the third collision wall is shifted forward in the direction of protrusion of each collision wall with respect to the positions where the urea water collides with the first collision wall 71 and the second collision wall 72. On the collision walls 71 to 73 in FIG. 7, the collision center positions of the urea water sprayed from the first injection port 41, the second injection port 42, and the third injection port 43 are depicted by small circles in two-dot chain lines.

<Exhaust gas purification>
[Oxidation purification by oxidation catalyst]
The oxidation catalyst 2 oxidizes and purifies HC and CO contained in the exhaust gas.

[Inflow into turning section]
The exhaust gas purified by oxidation by the oxidation catalyst 2 is guided by the straightening member 5 and flows from the outlet 21 of the oxidation catalyst 2 into the swirling portion 112 of the first bent portion 11. At this time, the exhaust gas from the outlet 21 is directed in a direction deviated to one side from the passage axis extending in the intersecting direction, and therefore flows in along the inner peripheral wall of the swirling portion 112. Therefore, the exhaust gas swirls along the inner peripheral wall of the swirling portion 112. Furthermore, by being guided by the straightening member 5, the exhaust gas flows into the swirling portion 112 along its inner peripheral wall. This strengthens the swirling flow of the exhaust gas in the swirling portion 112. The exhaust gas swirled in this manner flows from the swirling portion 112 toward the throttling portion 13.

[Supply of reducing agent]
Urea water as a reducing agent is injected and supplied from the urea injector 4 to the swirl section 112 according to the NOx concentration value of the exhaust gas flowing into the SCR ON F3 and the temperature of the exhaust gas flowing into the SCR ON F3 (e.g., 200°C or higher). The urea water injected from the first injection port 41 collides with the first collision wall 71, the urea water injected from the second injection port 42 with the second collision wall 72, and the urea water injected from the third injection port 43 with the tip of the third collision wall 73. The urea water that collides with each collision wall 7 is atomized and diffused in the swirling exhaust gas. The urea water diffused in the exhaust gas is vaporized and thermally decomposed by the heat input from the exhaust gas to generate _NH3 and HNCO.

The urea droplets are more susceptible to heat from the exhaust gas as the exhaust gas swirls and mixes with the urea. This promotes the vaporization and thermal decomposition of the urea. In addition, the atomized urea droplets have an increased surface area, making them more susceptible to heat from the exhaust gas, which promotes vaporization and thermal decomposition.

Furthermore, the urea water is atomized and dispersed by collision from three locations, the first collision wall 71, the second collision wall 72, and the third collision wall 73, which are located at different positions in terms of the distance from the urea injection device 4, the protruding direction of the collision wall 7, and the width direction of the collision wall 7, and the atomized urea water spreads over a wide area within the swirling section 112. The atomized urea water is then caught in the swirling exhaust gas and mixed homogeneously into the exhaust gas, which facilitates the thermal decomposition of the urea water.

In addition, if urea water sprayed from multiple nozzles is caused to collide with one collision wall 7, a puddle of urea water will form on the collision wall 7, and undesirable deposits (such as biuret, cyanuric acid, and ammelide) will likely form. In contrast, in the above configuration, the urea water sprayed from each nozzle collides with a different collision wall 7, making it difficult for a puddle of urea water to form, which is advantageous in suppressing the formation of undesirable deposits.

A part of the urea water that has collided with each collision wall 7 adheres to each collision wall 7. The urea water that has adhered to the collision wall 7 is vaporized and thermally decomposed on the collision wall 7. As a result, gaseous urea, _NH3, and HNCO are generated. The generated gaseous urea and _NH3 are diffused from above the collision wall 7 into the exhaust gas.

The first collision wall 71 is provided with a notch so that the urea water sprayed from the second injection port 42 does not collide with the first collision wall 71. Also, the second collision wall 72 is provided with a notch so that the urea water sprayed from the first injection port 41 does not collide with the first collision wall 71. Therefore, the widths of the portions of the first collision wall 71 and the second collision wall 72 where no notch is provided can be widened to increase the amount of urea water that adheres to these walls. This makes it possible to increase the amount of _NH3 generated from the urea water that adheres to the collision wall 7.

[Flow into the throttle section]
The exhaust gas flowing from the swirling section 112 to the throttling section 13 is given exhaust resistance by the throttling section 13 and the resistance member 6. This lengthens the residence time of the exhaust gas in the swirling section 112. This ensures sufficient time for the exhaust gas to mix with the urea water and _NH3 in the swirling section 112. Furthermore, the swirling flow radius is gradually reduced by the throttling section 13, which increases the angular velocity of the swirl and promotes mixing of the reducing agent and the exhaust gas. Furthermore, the liquid or undecomposed urea water is trapped by the resistance member 6, which prevents it from passing through.

[NOx selective reduction by SCR ON F]
Exhaust gas is supplied to the SCR ON F3 from the opening of the resistance member 6 of the throttle section 13, through the second bent section 12 and the inlet 31. _NH3 generated by the above-mentioned thermal decomposition is adsorbed by the Cu zeolite of the SCR ON F3. HNCO is hydrolyzed in the SCR ON F3 and adsorbed by the zeolite. NOx (NO, _NO2 ) flowing into the SCR ON F3 is reduced and purified to _N2 by the _NH3 adsorbed by the Cu zeolite, and is discharged together with the _H2O generated at that time. _NH3 not adsorbed by the Cu zeolite is oxidized by an _NH3 oxidation catalyst (not shown) arranged downstream of the SCR ON F3, thereby preventing it from being discharged into the atmosphere.

<Other embodiments>
In the above embodiment, the oxidation catalyst 2 and the SCR ON F3 are arranged side by side so as to be substantially parallel to each other in their respective axial directions, and the outlet 21 of the oxidation catalyst 2 and the inlet 31 of the SCR ON F3 are oriented in substantially the same direction. However, the oxidation catalyst 2 and the SCR ON F3 may be arranged substantially parallel to each other with a gap therebetween in their respective axial directions. In this case, the outlet 21 of the oxidation catalyst 2 opens to the SCR ON F3 side in the axial direction of the oxidation catalyst 2, and the inlet 31 of the SCR ON F3 opens to the oxidation catalyst 2 side in the axial direction of the SCR ON F.

In the above embodiment, the collision wall 7 is provided on the peripheral wall of the swirl section 112 below the urea injection device 4. However, the collision wall 7 may be attached anywhere downstream of the outlet 21 of the oxidation catalyst 2 and upstream of the resistance member 6.

1 Exhaust passage
2. Oxidation catalyst
3 SCR ON F
4. Urea injection device
5. Straightening member
6 Resistance member
7. Collision wall

Claims (6)

A NOx selective reduction catalyst that is provided in an exhaust passage of the engine and selectively reduces and purifies NOx in the exhaust gas;
a reducing agent injection device that is provided in the exhaust passage upstream of the NOx selective reduction catalyst and that injects a reducing agent into the exhaust gas,
the reducing agent injection device has a plurality of injection ports for injecting the reducing agent into the exhaust gas,
a collision wall independent of each other is provided for each injection port on the injection axis of each injection port, against which the reducing agent injected from each injection port collides;
The collision wall is arranged so that a distance between the jet nozzle and the collision wall on the jet axis differs for each jet nozzle ,
the reducing agent injection device has a first injection port, a second injection port, and a third injection port as the injection port,
the collision wall includes a first collision wall arranged on the ejection axis of the first ejection port, a second collision wall arranged on the ejection axis of the second ejection port, and a third collision wall arranged on the ejection axis of the third ejection port,
A distance from each of the jet nozzles to each of the collision walls is set so that the first collision wall is the shortest, the third collision wall is the longest, and the second collision wall is an intermediate length between them,
the first collision wall, the second collision wall, and the third collision wall protrude in the same direction from a wall surface of the exhaust passage,
an exhaust gas purification device for an engine, characterized in that the first collision wall and the second collision wall are arranged offset on both sides in a direction perpendicular to the protruding direction, and the third collision wall is arranged offset forward in the protruding direction relative to the first collision wall and the second collision wall . The exhaust gas purification device for an engine according to claim 1 ,
a swirl portion disposed upstream of the NOx selective reduction catalyst in the exhaust passage, the swirl portion swirls the exhaust gas around an axis of the exhaust passage,
The collision wall is provided on the rotating portion,
The collision wall is formed of a flat plate,
An exhaust gas purification device for an engine, wherein a wall surface of the collision wall is disposed substantially perpendicular to the rotation axis of the exhaust gas. The exhaust gas purification device for an engine according to claim 2 ,
an oxidation catalyst that oxidizes HC and CO in the exhaust gas is provided upstream of the NOx selective reduction catalyst in the exhaust passage;
an exhaust passage portion connecting the oxidation catalyst and the NOx selective reduction catalyst includes a bent portion that is bent so that the flow of exhaust gas changes from a direction extending in an axial direction of the oxidation catalyst to a direction intersecting the axial direction,
an exhaust gas purifying device for an engine, characterized in that the swirl portion is provided at the bent portion, and the swirl portion swirls the exhaust gas around a passage axis on the downstream side of the swirl portion extending in the intersecting direction as a swirl axis. The exhaust gas purification device for an engine according to claim 2 or 3 ,
An exhaust gas purification device for an engine, comprising: a throttle portion, the throttle portion having a passage diameter smaller than that of the swirl portion, provided between the swirl portion and the NOx selective reduction catalyst in the exhaust passage. The exhaust gas purification device for an engine according to claim 4 ,
2. An engine exhaust gas purification device, comprising: a restrictor member provided in the restricting portion for providing resistance to the flow of the exhaust gas. The exhaust gas purification device for an engine according to any one of claims 2 to 5 ,
13. An exhaust gas purification device for an engine, comprising: a first portion having a first surface and a second surface having a second surface; a first surface having a first surface;

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