Engine exhaust purification device

Abstract

To improve the NOx eliminating performance of an exhaust emission control device by promoting the vaporization and thermal decomposition of reductant mixed in exhaust gas.SOLUTION: An exhaust emission control device for an engine includes: a NOx selective reduction catalyst which is provided in an exhaust passage of the engine, and selectively reduces and eliminates NOx in exhaust gas; and a reductant injection device which is provided on an upstream side of the NOx selective reduction catalyst in the exhaust passage, and injects reductant into the exhaust gas. The reductant injection device has a plurality of injection ports for injecting the reductant into the exhaust gas. On the injection axis of each injection port, mutually independent collision walls are each provided at each injection port, and subjected to collision of the reductant injected from the injection port. The collision walls are each arranged with a distance between the injection port and the collision wall on the injection axis, being different from one injection port to another.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an exhaust gas purification device for an engine. [Background technology]

[0002] 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 gas purification device is known that includes a NOx selective reduction catalyst and a device that injects a reducing agent upstream of the NOx catalyst. 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.

[0003] An example of such an exhaust purification device is described in Patent Document 1. In this exhaust purification device, a reducing agent is injected from a reducing agent injection device toward a reducing agent diffusing means. The reducing agent diffusing means promotes atomization, vaporization, and thermal decomposition due to evaporation of the reducing agent, and the reducing agent is dispersed in the exhaust gas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4943499 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to improve the efficiency of NOx purification, it is preferable that the concentration distribution of the reducing agent mixed in the exhaust gas is 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 diffusing means.

[0006] Incidentally, the reducing agent mixed in the exhaust gas is thermally decomposed by the heat of the exhaust gas. In order to further improve the NOx purification performance in the exhaust gas by the NOx selective reduction catalyst, it is preferable to promote this thermal decomposition.

[0007] The present invention has been made in consideration of these points, and its purpose is to improve the NOx purification performance of an exhaust purification device by promoting the thermal decomposition of a reducing agent mixed in the exhaust gas. [Means for solving the problem]

[0008] In order to achieve the above-mentioned 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.

[0009] Specifically, the engine exhaust gas purification device disclosed herein comprises: A NOx selective reduction catalyst 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 the distance between the injection port and the collision wall on the injection axis differs for each injection port. And, 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, The distance from each of the jet ports 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 to be shifted on both sides in a direction perpendicular to the protruding direction, and the third collision wall is arranged to be shifted forward in the protruding direction with respect to the first collision wall and the second collision wall. It is characterized by the fact that

[0010] 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 a plurality of nozzles provided in the reducing agent injection device. The reducing agent injected from each nozzle collides with a collision wall provided on the injection axis of each nozzle. The reducing agent is atomized by being split and scattered 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.

[0011] 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 by the heat of the exhaust gas. In addition, the reducing agent 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.

[0012] In addition, if the reducing agent injected from multiple injection ports is caused to collide with one collision wall, the reducing agent may accumulate on the collision wall, which may lead to the formation of undesirable deposits. In contrast, according to the above configuration, the reducing agent injected from each injection port collides with a different collision wall, which makes it difficult for the reducing agent to accumulate, and is advantageous in suppressing the formation of undesirable deposits.

[0013] In addition, as mentioned 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, The distance from each of the jet ports 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.

[0014] 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. This makes it easier to assemble the collision walls than to attach each of the three collision walls to the wall surface separately.

[0015] In the exhaust gas purification device for the engine, a swirl section disposed upstream of the NOx selective reduction catalyst in the exhaust passage, the swirl section 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.

[0016] This configuration can prevent the swirling force of the exhaust gas from being hindered by the wall surface of the collision wall, thereby facilitating mixing of the swirling flow of the exhaust gas with the reducing agent, and facilitating vaporization and thermal decomposition of the reducing agent by the heat of the exhaust gas.

[0017] 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.

[0018] 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 passage axis extending in the intersecting direction, so that the above-mentioned swirling flow can be easily generated at the bent portion, which is advantageous for mixing the reducing agent and the exhaust gas.

[0019] 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.

[0020] In this way, the narrowing section applies resistance to the exhaust flow. This ensures that the exhaust gas remains in the swirling section for a certain period of time, which promotes the mixing of the reducing agent and exhaust gas, and promotes the vaporization and thermal decomposition of the reducing agent. In addition, the narrowing section gradually reduces the radius of the swirling flow, which increases the angular velocity of the swirl and promotes the mixing of the reducing agent and exhaust gas.

[0021] 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.

[0022] In this way, the exhaust gas can be kept in the swirl section for a sufficient period of time, which promotes mixing of the reducing agent into the exhaust gas. Also, the reducing agent in a liquid state or not yet decomposed is trapped by the resistance member, which prevents the reducing agent from passing through.

[0023] 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.

[0024] In this way, it is possible to prevent the collision wall from interfering with the swirling of the exhaust gas. Effect of the Invention

[0025] According to the present invention, the efficiency of NOx purification by the NOx selective reduction catalyst can be improved by promoting the vaporization and thermal decomposition of the reducing agent mixed in the exhaust gas. [Brief description of the drawings]

[0026] [Figure 1] 1 is a diagram showing a configuration of an exhaust gas purification device for an engine. [Diagram 2] 1 is a side view of an exhaust gas purification device for an engine. [Diagram 3] 1 is a perspective view of an exhaust gas purification device for an engine; [Figure 4] 2 is a perspective view of the engine exhaust gas purification device excluding a first bent portion and a rotating portion. FIG. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. 2 is a perspective view of a reducing agent injection device and a collision wall. [Figure 9] FIG. 2 is a perspective view of a reducing agent injection device injecting a reducing agent and a collision wall. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following preferred embodiments are merely exemplary in nature and are not intended to limit the present invention, its applications, or its uses.

[0028] <Configuration of exhaust 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 F3. As the urea water, a substance called AdBlue is used.

[0029] The oxidation catalyst 2 is a catalyst that oxidizes HC and CO in the exhaust gas, and is formed 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 a support material for Pt.

[0030] 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 exhaust gas using NH3 generated by thermal decomposition of urea and NH3 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.

[0031] 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 Fig. 5, an outlet 21 from which the exhaust gas of the oxidation catalyst 2 flows out and an inlet 31 into which the exhaust gas of the SCR ON F3 flows are open in approximately the same direction.

[0032] The exhaust passage section 10 connecting the outlet 21 of the oxidation catalyst 2 and the inlet 31 of the SCR ON F3 includes a first bent section 11 that bends so that the flow of the exhaust gas 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 flow of the exhaust gas 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 the horizontal direction at the second bent section 12.

[0033] The first bent portion 11 is provided with a swirling portion 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 portion 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 portion 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 portion 112 is swirled around the vertical direction as the axis of rotation, as shown by the arrow in FIG. 5.

[0034] In addition, the outlet 21 is provided with a straightening member 5 extending towards the swirl section 112. This straightening member 5 is inclined so as to lean towards 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 gas from the outlet 21 tends to flow into the swirl section 112 along its inner circumferential wall. This strengthens the swirl of the exhaust gas flowing into the swirl section 112.

[0035] A throttle section 13 is provided downstream of the swirl section 112, that is, at a portion of the exhaust passage 1 that connects the first bent section 11 and the second bent section 12 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. The throttle section 13 is provided with a resistance member 6 for providing resistance to the exhaust. The resistance member 6 is shown in FIG. 6. The resistance member 6 is circular and disposed so as 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 openings of the resistance member 6. Furthermore, the swirl angular velocity increases as the radius of the swirling flow gradually decreases due to the throttle portion 13, and mixing of the reducing agent and exhaust gas is promoted.

[0036] 5, the first bent portion 11 is provided with a urea injector 4 that injects urea water in the intersecting direction toward the swirl portion 112. In this embodiment, the urea injector 4 is provided on an upper wall portion of the exhaust passage that forms the first bent portion 11, and injects urea water downward. Below the urea injector 4, a collision wall 7 formed of a flat plate extending toward the center of the swirl portion 112 is provided.

[0037] 7, the underside of the urea injector 4 is indicated 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 part 112, and the third injection port 43 is disposed at a position away from the inner circumferential wall.

[0038] 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 in this order from the top, and these collision walls 71 to 73 correspond to each other from above. The collision walls 71 to 73 are plate-shaped and have approximately the same width. In addition, a notch is provided at the tip of each of the first collision wall 71 and the second collision wall 72. The third collision wall 73 has a length in the protruding direction longer 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 place on the wall surface of the swirl part 112 by welding. The wall surfaces of the collision walls 71 to 73 fixed in this manner are approximately perpendicular to the exhaust swirl axis in the swirl part 112.

[0039] The first collision wall 71 is disposed on the jet axis of the first jet orifice 41, the second collision wall 72 is disposed on the jet axis of the second jet orifice 42, and the third collision wall 73 is disposed on the jet axis of the third jet orifice 43. In other words, the distance from each jet orifice to each collision wall 7 on the jet 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.

[0040] In FIG. 9, the urea water injected 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 injected from the first injection port 41 collides with the first collision wall 71, the urea water injected from the second injection port 42 collides with the second collision wall 72, and the urea water injected 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 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 positioned 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 to 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 protruding direction 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 injected from the first injection port 41, the second injection port 42 and the third injection port 43 are drawn by small circles in two-dot chain lines.

[0041] <Exhaust gas purification> [Oxidation purification using oxidation catalysts] The oxidation catalyst 2 oxidizes and purifies HC and CO contained in the exhaust gas.

[0042] [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, so that it 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.

[0043] [Supply of reducing agent] According to the NOx concentration value of the exhaust gas flowing into the SCR ON F3 and the exhaust gas temperature (e.g., 200°C or higher) flowing into the SCR ON F3, urea water as a reducing agent is injected and supplied from the urea injector 4 to the swirl section 112. 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.

[0044] The urea droplets are more likely to receive 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, so they are more likely to receive heat from the exhaust gas, which promotes the vaporization and thermal decomposition of the urea.

[0045] Furthermore, the urea water is atomized and diffused 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 the distance from the urea injector 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 swirl section 112. The atomized urea water is then caught in the swirl of the exhaust gas and mixed homogeneously with the exhaust gas, which facilitates the thermal decomposition of the urea water.

[0046] In addition, if the urea water sprayed from a plurality of nozzles is caused to collide with one collision wall 7, a puddle of the urea water will form on the collision wall 7, and undesirable deposits (such as biuret, cyanuric acid, and ammelide) will be easily formed. In contrast, in the above-described configuration, the urea water sprayed from each nozzle collides with a different collision wall 7, so that a puddle of the urea water is unlikely to form, which is advantageous in suppressing the formation of undesirable deposits.

[0047] A portion 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.

[0048] The first collision wall 71 is provided with a notch so that the urea water sprayed from the second nozzle 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 nozzle 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 increased 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.

[0049] [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.

[0050] [Selective NOx 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 via 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 the NH3 oxidation catalyst (not shown) arranged downstream of the SCR ON F3, thereby preventing it from being discharged into the atmosphere.

[0051] <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 the axial direction, 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 the axial direction. 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.

[0052] In the above embodiment, the collision wall 7 is provided on the peripheral wall of the swirl part 112 below the urea injector 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. [Explanation of symbols]

[0053] 1 Exhaust passage 2. Oxidation Catalyst 3 SCR ON F 4 Urea injection device 5 Straightening members 6 Resistance members 7 Collision wall

Claims

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. In the engine exhaust gas purification device according to any one of claims 2 to 5, 13. An exhaust gas purification device for an engine, comprising: a collision wall that extends from a peripheral wall of the swirl portion toward a center of the swirl portion.

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