JP2018123788A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further uniformize distribution of a reducing agent in exhaust gas.SOLUTION: An exhaust emission control device for an engine includes: an exhaust passage 4 drawn out from a combustion chamber 1 of the engine 8; an oxidation catalyst device 10 for a diesel provided on the inner side of an inner wall surface of the exhaust passage 4 and heated by passing exhaust gas; a reducing agent injector 20 provided downstream of the oxidation catalyst device 10 for the diesel and injecting urea as a reducing agent into exhaust gas; a reduction catalyst body 13 for eliminating nitrogen oxide in exhaust gas by using ammonia generated from urea; an impactor 22 for partitioning inside of the exhaust passage 4 into a first space 27 on the inner side and a second space 26 on the outer side by using a cylindrical partition wall 23; and a mixer 30 disposed between the impactor 22 and the reduction catalyst body 13 and having a projecting piece 31 projecting from the inner surface of the exhaust passage 4 toward the inner side. The injecting direction of the reducing agent by using the reducing agent injector 20 is oriented to an injection target section 28a set on the surface on the first space 27 side of the partition wall 23.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an engine exhaust gas purification device that purifies exhaust gas discharged from an engine.

  In general, as an exhaust gas purifying device in a diesel engine or the like, a diesel oxidation catalyst device (Diesel Oxidation Catalyst) for the purpose of purifying diesel exhaust particulates (PM) or nitrogen oxides (NOx) contained in exhaust gas, In addition, a diesel particulate filter or the like is used.

  In addition, for the purpose of purifying nitrogen oxide (NOx) contained in lean exhaust gas, there is a system using a nitrogen oxide trap catalyst device (NOx Trap Catalyst), a urea selective catalyst reduction device (Selective Catalytic Reduction), or the like. To do.

The urea selective catalytic reduction device injects urea aqueous solution as a reducing agent into exhaust gas through a reducing agent injector provided on the upstream side of the reduction catalyst main body, whereby the urea is decomposed by the heat of the exhaust gas and ammonia ( NH ₃ ) is used. The produced ammonia reacts with nitrogen oxides in the exhaust gas in the vicinity of the main body of the reduction catalyst to become nitrogen gas (N ₂ ) and water (H ₂ O). Thereby, nitrogen oxides in the exhaust gas are purified.

  For example, in Patent Document 1, a diesel oxidation catalyst device and a diesel particulate collection filter are sequentially arranged along the gas flow direction of the exhaust passage, and a reducing agent injector of the urea selective catalyst reduction device is disposed downstream of the diesel particulate collection filter. The reduction catalyst main body is arranged in order.

JP 2012-122469 A

  In general, a urea selective catalytic reduction device is superior in nitrogen oxide purification characteristics in a high temperature range than a nitrogen oxide trap catalyst device, but tends to have poor purification performance in a low temperature range. For this reason, in recent years, the urea selective catalytic reduction device is often arranged closer to the engine to obtain a layout that ensures a high reaction temperature.

  When the urea selective catalyst reduction device is arranged at a position close to the engine, the distance from the combustion chamber of the engine to the reduction catalyst body of the urea selective catalyst reduction device is shortened. For this reason, it is difficult to uniformly distribute the injected urea water throughout the exhaust gas until the exhaust gas flows into the reduction catalyst main body.

  If the urea water in the exhaust gas is insufficiently uniform, there is a problem that sufficient purification performance cannot be exhibited with respect to the supplied urea water amount. For this reason, a mixer for dispersing urea water in the exhaust gas is often arranged downstream of the reducing agent injector.

  The mixer is effective to some extent for dispersing urea water in the exhaust gas. However, further improvement is required in order to constantly distribute the urea water uniformly in the exhaust gas with respect to various operating conditions and temperature conditions that change every moment.

  Accordingly, an object of the present invention is to make the distribution of the reducing agent injected into the exhaust gas more uniform.

  In order to solve the above problems, the present invention provides an exhaust passage drawn from a combustion chamber of an engine, a reducing agent injector that injects a reducing agent into exhaust gas in the exhaust passage, and the reducing agent or the reducing agent. A reduction catalyst main body that purifies nitrogen oxides in the exhaust gas by a substance generated from the agent, and an impactor that divides the inside of the exhaust passage into an inner first space and an outer second space by a cylindrical partition wall; And a mixer having a protruding piece disposed between the impactor and the reduction catalyst body and protruding inward from the inner surface of the exhaust passage, and the injection direction of the reducing agent by the reducing agent injector is the partition wall The engine exhaust gas purifier directed to the injection target set on the surface of the first space is adopted.

  The protruding piece may be disposed on the entire inner circumference of the exhaust passage.

  The second space includes a slow flow rate portion where the exhaust gas flow rate is relatively slow and a rapid flow rate portion where the exhaust gas flow rate is relatively fast along the circumferential direction. The protrusion length can employ | adopt the structure set smaller than the protrusion length of the said protrusion piece in the said rapid flow-velocity part.

  At this time, the exhaust passage has a bent portion on the upstream side of the impactor, and the slow flow velocity portion has a point where the distance from the inward end portion of the bent portion in the second space is the shortest distance. In addition, the steep flow velocity portion may employ a configuration including a point in the second space where the distance from the outer end portion of the bent portion is the shortest distance.

  In each of these aspects, it is possible to adopt a configuration in which the protruding piece is inclined toward the downstream side as it goes inward from the inner surface of the exhaust passage.

  Moreover, the structure provided with the guide member which reflects the said reducing agent between the said injection target part and the said reducing agent injector, and disperse | distributes it in said 1st space is employable.

  In the present invention, an impactor having a partition wall that divides the exhaust passage into a first space and a second space is disposed, and the injection of the reducing agent by the reducing agent injector is performed on the inner surface of the partition on the first space side. Further, since the mixer is disposed between the impactor and the reduction catalyst main body so as to be directed to the target portion, the reducing agent hits the impactor whose temperature is increased by the exhaust gas, and vaporization is promoted. Further, since the exhaust gas passing through the first space containing a large amount of the reducing agent and the exhaust gas passing through the second space containing a small amount of the reducing agent are fused by the mixer, the reducing agent is not allowed to reach the reduction catalyst main body until the exhaust gas reaches the reduction catalyst body. It becomes more uniformly distributed.

1 is a schematic view of an engine exhaust gas purification device according to an embodiment of the present invention. It is a top view which shows the detail of an impactor installation part. It is a front view which shows the detail of an impactor and a mixer installation part. It is a perspective view of an impactor and a mixer installation part. It is a perspective view which shows the modification of an impactor and a mixer installation part. It is a top view which shows the modification of an impactor installation part. It is a front view which shows the modification of an impactor and a mixer installation part. It is a schematic diagram which shows other embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram conceptually showing the structure of an exhaust gas purification apparatus for an engine according to this embodiment.

  As shown in FIG. 1, an intake passage 3 and an exhaust passage 4 are connected to the combustion chamber 1 of the engine 8. Air is supplied to the combustion chamber 1 through the intake passage 3. In addition, fuel is injected into the combustion chamber 1 by a fuel injection device 2. Exhaust gas from the combustion chamber 1 is sent out through the exhaust passage 4 drawn out from the combustion chamber 1, and is discharged to the atmosphere after passing through an exhaust purification section that removes harmful substances.

  The intake passage 3 leading to the combustion chamber 1 includes an air cleaner, a throttle valve 5 for controlling the flow rate of intake air by changing the passage cross-sectional area from the upstream side to the downstream side, an air flow sensor 6 for detecting the intake air amount, and the like. It is provided in order.

  In the exhaust passage 4, from the upstream side toward the downstream side, the turbine 7 of the mechanical supercharger, the diesel oxidation catalyst device 10 as the upstream exhaust purification unit, and the reducing agent that injects the reducing agent into the exhaust gas. Injector 20 and impactor 22, a mixer 30 for dispersing the reducing agent in the exhaust gas to make it uniform, a reducing catalyst body 13 for purifying nitrogen oxides in the exhaust gas with the reducing agent or a substance generated from the reducing agent, and a silencer A muffler or the like is sequentially provided.

  The reducing agent injector 20, the impactor 22, the mixer 30, the reduction catalyst main body 13, and the like constitute a urea selective catalyst reduction device 14 as an exhaust purification section on the downstream side.

  The diesel oxidation catalyst device 10 includes therein a space having a larger cross section than the front and rear exhaust passages 4, and a honeycomb structure member is accommodated in the space. The carrier has a collection of many cells through which exhaust gas can pass. As the material, for example, crystalline ceramics (cordierite composition) having a low coefficient of thermal expansion and excellent thermal shock resistance are used. A metal for exhibiting the function of the catalyst is supported on the surface of the support. Thereby, harmful substances such as carbon monoxide and hydrocarbons contained in the passing exhaust gas can be purified to harmless substances such as water and carbon dioxide.

  The diesel oxidation catalyst device 10 constituting the upstream exhaust purification unit and the urea selective catalytic reduction device 14 serving as the downstream exhaust purification unit are both close to the combustion chamber 1 of the engine 8 and have a relatively high temperature. It is placed as a proximity catalyst in an environment where there are many opportunities to be exposed to.

  The impactor 22 has a cylindrical partition wall 23 that divides the space in the exhaust passage 4 into a first space 27 and a second space 26. The partition wall 23 has a cylindrical shape, and the second space 26 is disposed so as to surround the entire outer periphery of the first space 27 in the cylinder. In particular, in this embodiment, the exhaust pipe wall 4a constituting the inner wall of the exhaust passage 4 is circular in cross section, and the cylindrical partition wall 23 is also circular in cross section (cylindrical), and both are arranged concentrically. .

The reducing agent injector 20 injects the reducing agent toward the inner surface of the partition wall 23 of the impactor 22. Here, urea (CO (NH ₂ ) ₂ ) is employed as the reducing agent.

  The reducing agent injection direction by the reducing agent injector 20 is directed to the injection target portion 28a set on the surface of the partition wall 23 on the first space 27 side, as shown in each of FIGS. The injection target portion 28 a is an intersection of the injection center line p in the reducing agent injection direction and the inner surface of the partition wall 23.

  In this embodiment, the partition wall 23 includes a reducing agent introduction hole 23 a between the injection target portion 28 a and the reducing agent injector 20. For this reason, the injected reducing agent enters the first space 27 through the introduction hole 23a, and is hardly dispersed into the second space 26 between the introduction hole 23a and the reducing agent injector 20. It has become.

  Further, as shown in FIG. 3, the reducing agent injection center line p intersects the exhaust gas flow directions C and D between the upstream side and the downstream side of the impactor 22. Since they are orthogonal, the time required for vaporization of the reducing agent before reaching the reduction catalyst main body 13 as compared with the case where the injection direction of the reducing agent is the same direction (parallel direction) as the flow direction of the exhaust gas. It is easy to secure a relatively long time for diffusion.

  Further, since the exhaust gas passes through the partition wall 23 to the inner first space 27 and the outer second space 26, the impactor 22 constituted by the partition wall 23 and the like constitutes the inner wall of the exhaust passage 4. The temperature becomes higher than the exhaust pipe wall portion 4a. This is because the temperature of the exhaust pipe wall 4a is relatively lower than that of the impactor 22 because the outer surface of the exhaust pipe wall 4a is in contact with the outside air.

  Urea, which is a reducing agent, is injected from the reducing agent injector 20 in the form of an aqueous solution, is scattered mainly in the exhaust gas in the first space 27, and a part of the urea adheres to the impactor 22. And urea is decomposed | disassembled by the high heat | fever of the impactor 22 or exhaust gas, and produces | generates ammonia. Since urea adheres to the impactor 22 having a temperature higher than that of the exhaust pipe wall 4a, decomposition of the urea into ammonia is promoted.

  Here, the partition wall 23 is supported by a material having a lower thermal conductivity than the material of the partition wall 23 with respect to the exhaust pipe wall portion 4 a constituting the inner wall of the exhaust passage 4. The support member 25 shown by the code | symbol 25 in FIG. 2 is comprised with the raw material with this low heat conductivity. Thereby, it is suppressed that the heat of the impactor 22 is transmitted to the exhaust pipe wall 4a having a relatively low temperature, and the impactor 22 is easily maintained at a higher temperature.

  As the material having a low thermal conductivity, a material that is relatively less likely to transmit heat than the metal that is the material of the impactor 22, such as a resin or rubber, can be employed. However, it is limited to a material having heat resistance that does not deteriorate or deteriorate even at the temperature of the exhaust passage 4.

  As a method of making it difficult for the heat of the impactor 22 to be transmitted to the exhaust pipe wall portion 4a, in addition to specifying the material of the support member 25 as described above, or in addition to that, specifying the shape of the support member 25 is also possible. Is possible.

  For example, a plate-like member or a shaft-like member that connects the partition wall 23 and the inner wall of the exhaust passage 4 can be used as the support member 25. In the case of a plate-like member, the surface direction is desirably arranged in a direction connecting the partition wall 23 and the inner wall of the exhaust passage 4. In the case of the shaft-like member, it is desirable that the axial direction is arranged in a direction connecting the partition wall 23 and the inner wall of the exhaust passage 4. The plate-like member and the shaft-like member have a smaller volume than the block-like member having the same length of one side, and the end face in the plate thickness direction and the cross section in the axis crossing direction are the partition wall 23 and the exhaust passage. Since the contact area with each other can be reduced by being in contact with the inner walls of the four, heat conduction can be suppressed.

  The reducing agent injector 20 is provided in a concave offset hole 21 that opens into the exhaust passage 4. For this reason, the injection port of the reducing agent injector 20 is disposed at a position slightly behind the inner wall surface of the exhaust passage 4. For this reason, a long injection distance from the injection port to the injection target portion 28a of the impactor 22 and the guide member 24 can be secured, and the reducing agent injector 20 can be protected from the heat of the exhaust gas. Furthermore, the reducing agent injector 20 does not hinder the flow of exhaust gas.

  In the reduction catalyst main body 13 or in the vicinity thereof, ammonia generated from urea reacts with nitrogen oxides contained in the exhaust gas by the function of the catalyst provided in the reduction catalyst main body 13 to generate nitrogen gas and water. As a result, the exhaust gas is purified before being released to the atmosphere.

  Here, since the mixer 30 is provided between the impactor 22 and the reduction catalyst main body 13, the dispersion and homogenization of urea as a reducing agent in the exhaust gas is further promoted. For this reason, the generation of ammonia and the reaction between ammonia and nitrogen oxides are even better.

  In this embodiment, as shown in FIGS. 1, 3, and 4, an annular projecting piece 31 that projects from the entire inner circumference of the exhaust passage 4 toward the inner diameter side is employed as the mixer 30. The projecting length of the projecting piece 31 to the inside can be adjusted according to the flow rate of the exhaust gas passing through the second space 26.

  In FIG. 3, the flow C (O) of the exhaust gas passing through the second space 26 near the right side in the drawing, that is, the side close to the reducing agent injector 20 is near the left side in the drawing, that is, the side far from the reducing agent injector 20. Is assumed to be faster than the flow C (I) of the exhaust gas passing through the second space 26 in FIG. Such a difference in flow velocity can be caused by circumstances such as the shape of the exhaust passage 4 being bent on the upstream side, as shown in FIG. The fluid passing near the outer side 9a of the bent portion 9 tends to have a higher flow rate (see arrow O in FIG. 1), and the fluid passing closer to the inner side 9b tends to have a slower flow rate (see arrow I in FIG. 1). .

  Hereinafter, the position (orientation) where the flow C of exhaust gas passing through is the fastest is referred to as a rapid flow velocity portion, and the position (orientation) where the flow of exhaust gas C passing through is the slowest flow velocity portion. That is, the rapid flow velocity portion includes a point where the distance from the end portion closer to the outer side 9a of the bent portion 9 is the shortest distance in the annular second space 26, and the rapid flow velocity portion is the annular second space. 26 includes a point where the distance from the end portion closer to the inner side 9b of the bent portion 9 is the shortest distance.

  At this time, as shown by the reference numeral 31a in the figure, the protruding length of the protruding piece 31 located on the side where the flow velocity is fast is increased to the inner diameter side, and as shown by the reference numeral 31b in the figure, on the side where the flow speed is slow. It is desirable to shorten the protruding length of the protruding piece 31 positioned toward the inner diameter side. Moreover, the protrusion length in the intermediate part 31c between the high speed side and the low speed side is an appropriate length between the longest protrusion length corresponding to the reference numeral 31a and the shortest protrusion length corresponding to the reference numeral 31b. Can be set to length. For example, the protrusion length at the intermediate portion 31c may be an average of the longest protrusion length and the shortest protrusion length. Further, the protruding length of the protruding piece 31 is gradually and intermittently decreased between the rapid flow velocity portion set to the longest protruding length and the slow flow velocity portion set to the shortest protruding length. It can also be set as follows.

  As a result, as shown in FIG. 3, the flow speed is fast (see arrow C (O) in the figure), the slow side (see arrow C (I)), and the lateral side (arrow C (S ))), The exhaust gas flow E passing through the first space 27 containing a large amount of the reducing agent and the exhaust gas flows C and D passing through the second space 26 containing almost no reducing agent. The reducing agent can be more evenly distributed over the entire cross section of the exhaust passage 4 by collision.

  In addition, as shown in FIG. 5, you may set the protrusion piece 31 by the mortar-shaped member which inclines to a downstream side as it goes inside from the inner surface of the said exhaust passage.

  Thus, by adopting the protruding piece 31 inclined toward the downstream side, the exhaust gas passing through the second space 26 containing almost no reducing agent is changed from the arrow C to the arrow D shown in FIG. The direction is changed to a direction that forms an obtuse angle that is greater than 90 degrees with each other, and then the flow is merged with the flow E of exhaust gas that passes through the first space 27. For this reason, as shown in FIG. 4, the loss of the flow rate of the exhaust gas can be reduced as compared with the case where the change in the direction from the arrow C to the arrow D by the protruding piece 31 is a right angle. If the loss of flow velocity is small, the relative speed of exhaust gases that collide with each other can be increased, and the reducing agent can be dispersed more smoothly.

  Further, the protruding piece 31 may be provided continuously along the entire inner surface of the exhaust passage 4 as described above, or may be provided intermittently along the inner surface of the exhaust passage 4.

  Furthermore, the mixer 30 can employ various types other than the aspect configured by the protruding pieces 31 on the inner surface of the exhaust passage 4 as described above.

  For example, a directional plate that provides a swirl flow to the exhaust gas flow is provided in the exhaust passage 4, and the swirl flow causes the exhaust gas flow E that passes through the first space 27 containing a large amount of the reductant and the reductant to flow. You may make it collide with the flow C of the exhaust gas which passes the 2nd space 26 which hardly contains. At this time, the swirl flow may be applied to the exhaust gas flow E passing through the first space 27 containing a large amount of the reducing agent, or the exhaust gas flow C passing through the second space 26. You may make it provide with respect. Alternatively, a swirl flow may be applied to each of the exhaust gas flow E passing through the first space 27 and the exhaust gas flow C passing through the second space 26.

  In addition to this example, the exhaust gas flow E passing through the first space 27 containing a large amount of the reducing agent and the exhaust gas flow C passing through the second space 26 containing almost no reducing agent are caused to collide with each other. Various mixers 30 that control the flow of each exhaust gas can be employed.

  The modification of embodiment is shown in FIG.6 and FIG.7. In this modification, a guide member 24 that reflects and disperses the injected reducing agent in the first space 27 is provided between the injection target portion 28 a of the partition wall 23 and the reducing agent injector 20.

  By this guide member 24, the reducing agent is dispersed in the direction opposite to the injection direction from the reducing agent injector 20 side to the injection target portion 28a side, that is, from the injection target portion 28a side to the reducing agent injector 20 side. It spreads and spreads uniformly throughout the first space 27.

  In this embodiment, as shown in FIGS. 6 and 7, the guide member 24 is composed of a pair of reflectors 24 a and 24 a that increase in distance as they approach the injection target portion 28 a along the injection direction of the reducing agent. Has been. For this reason, the injected reducing agent hits and reflects the pair of reflecting plates 24a, 24a arranged in a V shape in plan view, and as indicated by an arrow B in FIG. And dispersed throughout the first space 27. For this reason, the uniformization of the reducing agent is smooth.

  Here, since the injection center line p of the reducing agent intersects with the ridge line portion 24c which is the connecting portion of the pair of reflectors 24a and 24a, the reducing agent is evenly distributed on both sides across the ridge line portion 24c. be able to.

  Further, the pair of reflection plates 24a includes a plurality of passage holes 24b penetrating the reducing agent injector 20 side and the injection target portion 28a side. For this reason, as shown by the arrow A in FIG. 6, the reducing agent can be smoothly dispersed in the buffer space 28 located closer to the injection target portion 28a than the guide member 24 in the first space 27. it can.

  Incidentally, the reducing agent injector 20 generally has a strong penetration force, and the injected reducing agent tends to have a strong force to go straight, particularly in the vicinity of the injection center line p.

  For this reason, as shown in FIG. 6 and FIG. 7, the total opening area per unit area increases as the passage holes 24b provided in the pair of reflecting plates 24a and 24a move away from the reducing agent injection center line p. Is set to For this reason, the ratio of the reducing agent reflected by the reflector 24a is increased near the injection center line p of the reducing agent, and the ratio of the reducing agent that goes straight is set higher near the distance from the injection center line p. The distribution of the reducing agent can be made uniform throughout the space 27.

  6 and 7, all the passage holes 24b provided in the pair of reflection plates 24a and 24a have the same shape (circular shape) and the same cross-sectional area, and the distribution number of the passage holes 24b per unit area is defined as the pair of reflection plates 24a. , 24a is gradually increased as the distance from the ridge line portion 24c is increased. For example, while the passage holes 24b provided in the pair of reflection plates 24a and 24a are all the same shape (circular), the cross-sectional area of each of the passage holes 24b is changed from the ridge portion 24c connecting the pair of reflection plates 24a and 24a. It is also possible to adopt a method of gradually increasing as the distance increases. Or you may set so that the sum total of the opening area per unit area by the passage hole 24b may increase radially, as it distances from the injection centerline p of a reducing agent.

  Note that the passage hole 24b provided in the guide member 24 can be omitted as necessary. However, the position and shape of the guiding member 24 and the position and orientation of the reducing agent injector 20 are set so that at least a part of the injected reducing agent enters the buffer space 28 on the injection target portion 28a side of the guiding member 24. It is desirable to set.

  In addition to the V-shape in a plan view, for example, a member whose surface on the reducing agent injector 20 side is curved in a cylindrical shape or a spherical shape can be adopted as the guide member 24. Here, it is desirable that the surface of the guide member 24 on the reducing agent injector 20 side has a shape that approaches the injection target portion 28a side as the distance from the injection center line p of the reducing agent increases. In addition, as long as the guide member 24 reflects the reducing agent and disperses it throughout the first space 27, not only the plate-like members such as the pair of reflectors 24a and 24a but also block-like members and fins. It can also be composed of a set of members having a shape, a mesh member, or the like.

  For example, as shown in the modification of FIG. 8, the injection center line p in the injection direction of the reducing agent injector 20 is at an angle α (0 <0) with respect to the exhaust gas flow directions C and E in the exhaust passage 4. It is good also as an opposing direction with (alpha) <90 degree | times. Also in this modification, the reducing agent is directed to the injection target portion 28a set on the inner surface of the partition wall 23 on the first space 27 side. Further, when the guide member 24 is provided on the impact 22, the reducing agent can be smoothly dispersed throughout the first space 27 by being reflected by being reflected by the guide member 24. The same is true in that the guide member 24 may be provided with a passage hole 24b. In the case of the modification of FIG. 8, the introduction hole 23a provided in the partition wall 23 can be omitted.

As shown in FIG. 1, the exhaust passage 4 includes an ammonia detection unit b that acquires information on the amount of inflow of ammonia on the upstream side (near the inlet) of the reduction catalyst main body 13. In addition, a nitrogen oxide detector c and an O ₂ sensor d for acquiring information on the amount of nitrogen oxide discharged are provided on the downstream side (near the outlet) of the reduction catalyst main body 13. Further, an exhaust gas temperature detecting means a for detecting the temperature of the exhaust gas is provided on the upstream side (near the inlet) of the oxidation catalyst device 10 for diesel.

  A vehicle equipped with the engine 8 includes an electronic control unit 40. The electronic control unit 40 controls all of the intake / exhaust valves, the fuel injection device, other devices necessary for the operation of the engine 8, various vehicle equipment, and the like. Information from various sensors is transmitted to the electronic control unit 40 through a cable.

  Based on the information on the amount of inflow of ammonia by the ammonia detector b and the information on the amount of nitrogen oxide discharged by the nitrogen oxide detector c, the electronic control unit 40 An engine control device 41 that controls the amount of intake air or controls the amount and timing of the reducing agent to be injected is provided.

  With these controls, the engine control device 41 controls the amount of ammonia generated on the upstream side of the reduction catalyst main body 13 in accordance with the operating state, thereby reducing the emission amount of nitrogen oxides.

  Moreover, although urea was employ | adopted as a reducing agent in said embodiment, this invention is applicable also when employ | adopting reducing agents other than urea. For example, ammonia may be employed as the reducing agent and an aqueous solution of the ammonia may be injected.

  Furthermore, in the above-described embodiment, the diesel oxidation catalyst device 10 that is the upstream exhaust purification unit and the urea selective catalyst reduction device 14 that is the downstream exhaust purification unit are both close proximity catalysts. The present invention can also be applied to the case where the catalyst is disposed as an underfloor catalyst located in an environment far from the combustion chamber 1 of the engine 8 and exposed to relatively high temperature exhaust gas.

  In this embodiment, the purification of exhaust gas in a diesel engine has been described. However, in addition to the diesel engine, the present invention is based on the reducing agent or a substance generated from the reducing agent by injection of the reducing agent into the exhaust gas. The engine can be used for all engines equipped with a reduction catalyst body that purifies nitrogen oxides in exhaust gas.

DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Fuel injection device 3 Intake passage 4 Exhaust passage 5 Throttle valve 6 Air flow sensor 7 Supercharger 8 Engine 10 Diesel oxidation catalyst device 13 Reduction catalyst body 14 Urea selective catalyst reduction device 20 Reducing agent injector 21 Offset hole 22 Impactor 23 partition wall 23a introduction hole 24 guide member 24b passage hole 25 support member 26 second space 27 first space 28 buffer space 28a injection target part 30 mixer 31 projecting piece 40 electronic control unit 41 engine control unit 41 exhaust gas temperature detection part Means b Ammonia detector c Nitrogen oxide detector d O ₂ sensor

Claims (6)

An exhaust passage drawn from the combustion chamber of the engine;
A reducing agent injector for injecting a reducing agent into the exhaust gas in the exhaust passage;
A reduction catalyst main body for purifying nitrogen oxides in the exhaust gas by the reducing agent or a substance generated from the reducing agent;
An impactor that separates the inside of the exhaust passage into a first inner space and a second outer space by a cylindrical partition;
A mixer that is disposed between the impactor and the reduction catalyst main body and has a protruding piece protruding inward from the inner surface of the exhaust passage;
With
An exhaust gas purifying apparatus for an engine in which an injection direction of the reducing agent by the reducing agent injector is directed to an injection target portion set on a surface of the partition on the first space side. The engine exhaust gas purification device according to claim 1, wherein the projecting piece is disposed on the entire inner surface of the exhaust passage. The second space includes a slow flow rate portion in which the flow rate of the exhaust gas is relatively slow and a rapid flow rate portion in which the flow rate of the exhaust gas is relatively fast along the circumferential direction,
The engine exhaust gas purification device according to claim 1 or 2, wherein a protruding length of the protruding piece in the slow flow velocity portion is set smaller than a protruding length of the protruding piece in the rapid flow velocity portion. The exhaust passage includes a bent portion on the upstream side of the impactor,
The slow flow rate portion includes a point where the distance from the inward end portion of the bent portion in the second space is the shortest distance,
The engine exhaust gas purification device according to claim 3, wherein the rapid flow velocity portion includes a point where a distance from an outer end portion of the bent portion is the shortest distance in the second space. The exhaust gas purification device for an engine according to any one of claims 1 to 4, wherein the protruding piece is inclined toward the downstream side from the inner surface of the exhaust passage toward the inner side. The engine exhaust gas according to any one of claims 1 to 5, further comprising a guide member that reflects and reduces the reducing agent in the first space between the injection target portion and the reducing agent injector. Purification equipment.

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