JP5224294B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust purification device for purifying engine exhaust, and more particularly, to an ammonia selective reduction type NOx catalyst that reduces NOx in exhaust using ammonia generated from urea water supplied in exhaust as a reducing agent. The present invention relates to an exhaust purification device.

  As an exhaust purification device for purifying NOx (nitrogen oxide), which is one of the pollutants contained in engine exhaust, an ammonia selective reduction type NOx catalyst is disposed in the exhaust passage of the engine, and ammonia as a reducing agent. There is known an exhaust gas purification device that purifies exhaust gas by reducing NOx by supplying NOx to an ammonia selective reduction type NOx catalyst.

  In such an exhaust purification device, in order to supply ammonia to the ammonia selective reduction type NOx catalyst, it is common to supply urea water, which is easier to handle than ammonia, into the exhaust gas. Used to inject urea water into the exhaust. The atomized urea water supplied into the exhaust gas from the urea water injector is hydrolyzed by the heat of the exhaust gas, and the resulting ammonia is supplied to the ammonia selective reduction type NOx catalyst. The NOx catalyst promotes the denitration reaction between ammonia supplied to the NOx catalyst and NOx in the exhaust, whereby NOx is reduced and exhaust purification is performed.

  At this time, a part of the urea water spray injected from the urea water injector collides with the inner wall of the exhaust passage and the like to form a liquid film and adhere to the exhaust passage, and the moisture vaporizes and solid urea crystals etc. And deposits as urea-derived deposits on the inner wall of the exhaust passage. Due to the generation of urea-derived deposits, the amount of ammonia originally required for the reduction of NOx is insufficient and the exhaust purification rate decreases, and the accumulated urea-derived deposits increase the flow resistance of the exhaust passage and exhaust gas. Cause troubles such as passage blockage. In addition, the accumulated urea-derived deposits are converted to ammonia at once when the exhaust gas temperature rises, so that more ammonia than necessary is supplied to the ammonia selective reduction catalyst, and the surplus is released into the atmosphere. The problem also arises.

  In view of such problems, as a countermeasure for preventing the urea water injected from the urea water injector from adhering to the exhaust passage to diffuse and vaporize well in the exhaust gas, for example, the technique of Patent Document 1 is proposed. ing. In Patent Document 1, an injection device is provided in an exhaust flue for circulating exhaust gas from an engine, urea water is injected from the injection device so as to cross the flow direction of exhaust gas, and ammonia generated from urea water is used. Thus, an exhaust purification device is disclosed in which nitrogen oxides in exhaust gas are reduced by a denitration catalyst on the downstream side.

  Since urea water injected from the injection device collides with and adheres to the opposing wall in the exhaust flue, a multi-stage perforated plate with a collision surface inclined to the exhaust downstream side is disposed on the urea water injection path as a countermeasure. Arranged and prevented the urea water from adhering to the opposing wall in the exhaust flue by causing the injected urea water to collide with the perforated plate, and the perforated plate by boiling the urea water colliding on the perforated plate It also prevents urea water from adhering to the water.

JP 2007-32472 A

  As shown in FIG. 4 of Patent Document 1, the film boiling of urea water assumed by the technology of Patent Document 1 is high under a condition where the temperature difference between exhaust gas and urea water is high and the spray collision density of urea water on the perforated plate is low. In other regions, film boiling changes to nucleate boiling, and the perforated plate is rapidly cooled by the colliding urea water, so that the urea water adheres to the perforated plate. Therefore, in the technique of Patent Document 1, on the premise of the temperature difference between exhaust gas and urea water, the aperture ratio of the porous plate, the distance from the injection point to the porous plate, the spray spread angle, etc. Is set.

  However, various conditions such as the exhaust temperature vary greatly depending on the operating state of the engine, and even when the spray collision density is set as described above, the film boiling of urea water can be established in all operating states. Not necessarily. Therefore, in the technique of Patent Document 1, for example, when low-load operation at a low exhaust temperature is continued, transition to nucleate boiling occurs, and urea water adheres to the cooled perforated plate, and thus deposits of urea-derived deposits. Has occurred, and the above-mentioned various troubles are caused by the accumulated urea-derived deposit.

  The present invention has been made to solve such problems, and the object of the present invention is to reliably prevent urea water from adhering to the opposing wall in the exhaust passage regardless of the exhaust temperature. An object of the present invention is to provide an exhaust emission control device for an engine that can avoid various troubles caused by urea-derived deposits.

  In order to achieve the above object, a first aspect of the present invention is a casing which is disposed in an exhaust passage of an engine and into which exhaust from the engine is introduced, and is disposed on an installation surface of the casing so as to cross the inside of the casing. And urea water injection means for injecting urea water toward the opposing wall in the casing, and ammonia for selectively reducing NOx in the exhaust gas using ammonia as a reducing agent, disposed downstream of the urea water injection means in the casing. The selective reduction type NOx catalyst, the casing is partitioned into an upstream chamber and a downstream chamber in which the ammonia selective reduction type NOx catalyst is accommodated, and the first opposing surface and the first opposing surface that oppose each other on the injection axis of the urea water injection means A partition wall that forms a diffusion chamber that communicates with the downstream chamber between the two opposing surfaces, and has a cylindrical shape with one end opened from the first facing surface of the partition wall into the diffusion chamber and the other end Predetermined Opposite the installation surface of the urea water injection means with a gap, the exhaust in the upstream chamber flows into the interior through the gap, and an exhaust air flow in substantially the same direction as the urea water injected from the urea water injection means is generated. A first guide pipe that flows into the diffusion chamber and has a cylindrical shape with one end opening from the second facing surface of the partition wall into the diffusion chamber and the other end facing the opposing wall in the casing with a predetermined gap. A second guide pipe that is opposed to each other, causes exhaust in the upstream chamber to flow into the interior through a gap, and causes an exhaust airflow in a substantially opposite direction to the urea water injected from the urea water injection means to flow into the diffusion chamber. It is equipped with.

  Accordingly, the engine exhaust flows into the first and second guide pipes through the gap from the upstream chamber in the casing, and is in the same direction as the urea water injected from the urea water injection means in the first guide pipe. An exhaust air flow is generated and flows into the diffusion chamber, and an exhaust air flow substantially opposite to the urea water is generated in the second guide pipe and flows into the diffusion chamber, and these exhaust air flows collide with each other in the diffusion chamber. Then, it is transferred to the downstream ammonia selective reduction type NOx catalyst together with the urea water spray.

  In the flow direction of the exhaust air flow, the collision point of the exhaust air flow in the diffusion chamber with respect to the first and second guide pipes corresponds to the downstream side, so the urea water spray injected from the urea water injection means After being guided to the collision point following the flow direction, the progress in the direction away from the collision point against the exhaust airflow, that is, the progress in the direction of passing through or reversing the collision point is hindered. Therefore, the urea water spray is transferred to the ammonia selective reduction type NOx catalyst without greatly deviating from the collision point.

On the other hand, the flow path when the exhaust in the upstream chamber flows into the first and second guide pipes is limited to the vicinity of the installation surface where the gap is formed and the vicinity of the opposing wall in the casing. It flows into each guide pipe with a high flow velocity along the surface and the opposing wall. Therefore, the vicinity of the urea water injection means and the facing wall of the casing are constantly exposed to the exhaust airflow having a high flow velocity.
Therefore, even if the injected urea water spray passes through the collision point of the exhaust airflow or is reversed at the collision point, these urea water sprays are blocked by the high-speed exhaust airflow, and the casing facing wall and urea water Adhesion / deposition on the injection means is prevented, and problems caused by urea-derived deposits are prevented.

  According to the engine exhaust gas purification apparatus of the first aspect of the present invention, an exhaust air flow in the same direction as the urea water injected from the urea water injection means is generated in the first guide pipe, and the second guide pipe In order to generate an exhaust airflow in the substantially opposite direction and collide with each other in the diffusion chamber, the urea water spray can be actively guided to the collision point of the exhaust airflow and transferred to the ammonia selective reduction type NOx catalyst as it is. Regardless of this, it is possible to prevent the urea water from adhering to the casing facing wall and the urea water injection means.

  In addition, since the exhaust gas flows into the first and second guide pipes through the gap, an exhaust air flow having a high flow velocity along the installation surface and the opposing wall is generated. Even if the exhaust airflow passes through or reverses at the collision point, these urea water sprays can be blocked by the high-speed exhaust airflow to prevent adhesion to the casing facing wall and urea water injection means. It is possible to more reliably prevent the urea water from adhering to the region, and to prevent problems caused by deposits.

1 is an overall configuration diagram showing a diesel engine to which an exhaust emission control device of an embodiment is applied. It is a partial expanded sectional view which shows the structure around the partition of a casing. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. FIG. 5 is a cross-sectional view taken along line VV in FIG.

Hereinafter, an embodiment of an exhaust emission control device for an engine embodying the present invention will be described.
FIG. 1 is an overall configuration diagram of a four-cylinder diesel engine (hereinafter referred to as an engine) to which the exhaust emission control device of this embodiment is applied.
The engine 1 includes a high-pressure accumulator chamber (hereinafter referred to as a common rail) 2 common to each cylinder, and high-pressure fuel supplied from a fuel injection pump (not shown) and stored in the common rail 2 is an injector 4 provided in each cylinder. The fuel is injected into each cylinder from each injector 4.

  The intake passage 6 is equipped with a turbocharger 8. The intake air drawn from an air cleaner (not shown) flows into the compressor 8a of the turbocharger 8 from the intake passage 6, and the intake air supercharged by the compressor 8a is intercooler. 10 and the intake control valve 12 are introduced into the intake manifold 14. An intake air amount sensor 16 for detecting an intake air flow rate to the engine 1 is provided upstream of the compressor 8a in the intake passage 6.

On the other hand, an exhaust port (not shown) through which exhaust is discharged from each cylinder of the engine 1 is connected to an exhaust pipe 20 (exhaust passage) via an exhaust manifold 18. An EGR passage 24 that communicates the exhaust manifold 18 and the intake manifold 14 via the EGR valve 22 is provided between the exhaust manifold 18 and the intake manifold 14.
The exhaust pipe 20 passes through the turbine 8 b of the turbocharger 8 and is connected to an exhaust aftertreatment device 28 via an exhaust throttle valve 26. The rotating shaft of the turbine 8b is connected to the rotating shaft of the compressor 8a so that the turbine 8b receives the exhaust flowing in the exhaust pipe 20 and drives the compressor 8a.

The casing 29 of the exhaust gas purification device 28 is divided forward and backward by a partition wall 30. Hereinafter, the partitioned front space is referred to as an upstream chamber 29a, and the rear space is referred to as a downstream chamber 29b. As will be described in detail later, the exhaust discharged from the engine 1 is introduced into the downstream chamber 29b through the partition wall 30 from the upstream chamber 29a.
The upstream oxidation catalyst 32 is accommodated in the upstream chamber 29 a, and a particulate filter (hereinafter referred to as a filter) 33 is accommodated downstream of the upstream oxidation catalyst 32. The filter 33 is provided to purify the exhaust of the engine 1 by collecting particulates in the exhaust.

Since the pre-stage oxidation catalyst 32 oxidizes NO (nitrogen monoxide) in the exhaust gas to generate NO ₂ (nitrogen dioxide), the pre-stage oxidation catalyst 32 and the filter 33 are arranged in this manner, so that the filter 33 captures them. The accumulated particulates react with NO ₂ supplied from the pre-stage oxidation catalyst 32 to be oxidized, and the filter 33 is continuously regenerated.

In the downstream chamber 29b, an ammonia selective reduction type NOx catalyst (hereinafter referred to as an SCR catalyst) 35 for purifying exhaust gas by selectively reducing NOx (nitrogen oxide) in exhaust gas using ammonia as a reducing agent is housed. A downstream oxidation catalyst 36 for removing ammonia flowing out from the SCR catalyst 35 is accommodated on the downstream side of the SCR catalyst 35. The post-stage oxidation catalyst 36 also has a function of oxidizing CO (carbon monoxide) generated when particulates are incinerated by forced regeneration of the filter 33 and discharging it to the atmosphere as CO ₂ (carbon dioxide). ing.

  Further, a urea water injector (urea water injection means) 38 for supplying urea water into the exhaust gas in the communication passage 32 is provided in the vicinity of the partition wall 30 corresponding to the most upstream portion in the downstream chamber 29b. Urea water is supplied from a urea water tank 39 that stores water to a urea water injector 38 via a urea water supply pump (not shown), and urea water is injected into the exhaust gas in the downstream chamber 29b in response to opening and closing of the urea water injector 38. It has come to be.

The atomized urea water injected from the urea water injector 38 is hydrolyzed by the heat of the exhaust gas to become ammonia, and is supplied to the SCR catalyst 35. The SCR catalyst 35 reduces NOx to harmless N ₂ by promoting a denitration reaction between the supplied ammonia and NOx in the exhaust.
Further, an exhaust gas temperature sensor 40 for detecting the temperature of the exhaust gas flowing in the exhaust gas aftertreatment device 28 is provided on the downstream side of the upstream oxidation catalyst 32 in the upstream chamber 29a.

The ECU (control means) 50 is a control device for performing comprehensive control including operation control of the engine 1, and includes a CPU, a memory, a timer counter, and the like, and calculates various control amounts. Various devices are controlled based on the control amount.
On the input side of the ECU 50, in order to collect information necessary for various controls, in addition to the intake air amount sensor 16 and the exhaust gas temperature sensor 40 described above, a rotational speed sensor 51 that detects the rotational speed of the engine 1 and an accelerator pedal (not shown) Various sensors such as an accelerator opening sensor 52 for detecting the depression amount of the vehicle are connected. Further, various devices such as the injector 4, the intake control valve 12, the EGR valve 22, the exhaust throttle valve 26, and the urea water injector 38 of each cylinder that are controlled based on the calculated control amount are connected to the output side of the ECU 50. Has been.

  The ECU 50 also performs calculation of the fuel supply amount to each cylinder of the engine 1 and control of fuel supply from the injector 4 based on the calculated fuel supply amount. The fuel supply amount (main injection amount) necessary for the operation of the engine 1 is preliminarily determined based on the engine speed detected by the engine speed sensor 51 and the accelerator pedal depression amount detected by the accelerator opening sensor 52. It is determined by reading from the stored map. The amount of fuel supplied to each cylinder is adjusted by the valve opening time of the injector 4, and each injector 4 is driven to open in a driving time corresponding to the determined fuel amount, and main injection is performed in each cylinder. As a result, an amount of fuel necessary for the operation of the engine 1 is supplied.

  In addition to such fuel supply control to each cylinder, the ECU 50 performs forced regeneration of the filter 33 and urea water supply control for supplying ammonia to the SCR catalyst 35. The forced regeneration of the filter 33 is already widely known and will not be described in detail here. However, the ECU 50 determines each cylinder from the injector 4 separately from the main injection based on the detection value of the exhaust temperature sensor 40. By injecting fuel into the exhaust gas, the fuel is supplied into the exhaust gas, and the temperature of the exhaust gas is raised by the oxidation reaction of the fuel in the exhaust gas in the pre-stage oxidation catalyst 32 to forcibly regenerate the filter 33.

  Further, the ECU 50 determines the engine 1 based on the main injection amount from the injector 4, the rotational speed of the engine 1 detected by the rotational speed sensor 51 and the intake air flow rate to the engine 1 detected by the intake air amount sensor 16. An exhaust emission amount and a NOx emission amount per unit time are obtained, and a target supply amount of urea water is obtained from the amount of ammonia necessary for the selective reduction of NOx by the SCR catalyst 35 with respect to the NOx emission amount. Then, the urea water injector 38 is controlled based on this target supply amount, whereby urea water is supplied from the urea water injector 38 into the exhaust gas upstream of the SCR catalyst 35.

As described above, the mist-like urea water jetted from the urea water injector 38 is hydrolyzed to ammonia by the heat of the exhaust gas, and this ammonia is supplied to the SCR catalyst 35. The SCR catalyst 35 reduces NOx to harmless N ₂ by promoting a denitration reaction between the supplied ammonia and NOx in the exhaust.
2 is a partially enlarged cross-sectional view showing a configuration around the partition wall 30 of the casing 29, FIG. 3 is a cross-sectional view taken along the line III-III of FIG. 2 when the periphery of the partition wall 30 of the casing 29 is viewed from the DPF 33 side, and FIG. 2 is a cross-sectional view taken along the line IV-IV in FIG. 2 as seen from the SCR catalyst 35 side, and FIG. 5 is a cross-sectional view taken along the line V-V in FIG.

  As shown in these drawings, the urea water injector 38 is fixed on an installation surface 61 formed as a horizontal surface in the upper part of the casing 29 and injects urea water through a through hole 61 a formed in the installation surface 61. It has become. The injection axis L of the urea water injector 38 is set to be vertical, that is, a direction orthogonal to the longitudinal direction of the casing 29. From the urea water injector 38, urea water is directed downward so as to cross the inside of the casing 29 at a right angle. Be injected.

  For this reason, as described in [Background Art], the injected urea water collides with and adheres to the opposing wall 29c in the casing 29, and deposits as urea-derived deposits due to vaporization of water, causing various troubles. There is a possibility to make it. In view of such problems, in the present embodiment, measures are taken to prevent the urea water from adhering to the opposing wall 29c in the casing 29, and the measures will be described in detail below.

  The partition wall 30 is positioned on the injection axis L of the urea water injector 38 and is opposed to the installation surface 61 of the casing 29 to which the urea water injector 38 is fixed at a predetermined distance from the horizontal upper facing surface 63 ( A first opposing surface), which is also located on the injection axis L and faces the lower opposing surface 63 at a predetermined interval below the upper opposing surface 63 (second opposing surface), the upper opposing surface 63, and The upstream surface 65 connecting the upstream end of the lower facing surface 64, the upper downstream surface 66 connecting the downstream end of the upper facing surface 63 to the downstream end of the installation surface 61, and the downstream end of the lower facing surface 64 as the downstream end of the casing 29. It is comprised from the lower downstream surface 67 connected to the opposing wall 29c.

  The partition 30 divides the casing 29 into an upstream chamber 29a and a downstream chamber 29b, and a diffusion chamber 68 communicating with the downstream chamber 29b is formed between the upper facing surface 63 and the lower facing surface 64 of the partition 30. Is formed. Further, an upper inflow chamber 69 communicating with the upstream chamber 29 a is formed between the upper facing surface 63 and the installation surface 61 of the partition wall 30, and similarly between the lower facing surface 64 and the facing wall 29 c of the casing 29. A lower inflow chamber 70 communicating with the upstream chamber 29a is formed.

An upper guide pipe 71 (first guide pipe) is disposed in the upper inflow chamber 69, and a lower end (one end) of the upper guide pipe 71 is connected to the upper facing surface 63. Similarly, a lower guide pipe 72 (second guide pipe) is disposed in the lower inflow chamber 70, and an upper end (one end) of the lower guide pipe 72 is connected to the lower facing surface 64. .
The upper guide pipe 71 and the lower guide pipe 72 have a cylindrical shape extending in the vertical direction and are arranged in series with each other with the diffusion chamber 68 interposed therebetween. The axial centers of both guide pipes 71 and 72 are injected by the urea water injector 38. It coincides with the axis L. However, the axial centers of both guide pipes 71 and 72 do not have to coincide with the injection axis L. The diameters of both guide pipes 71 and 72 may be the same or different.

  A gap 73 is formed between the upper end (the other end) of the upper guide pipe 71 and the installation surface 61, and the upper inflow chamber 69 communicates with the diffusion chamber 68 through the gap 73 and the upper guide pipe 71. Similarly, a gap 74 is formed between the lower end (the other end) of the lower guide pipe 72 and the opposing wall 29 c of the casing 29, and the lower inflow chamber 70 passes through the gap 74 and the lower guide pipe 72 and then the diffusion chamber 68. It communicates with the inside.

Next, the operation of the exhaust emission control device for the engine 1 of the present embodiment configured as described above will be described.
During the operation of the engine 1, as indicated by arrows in FIGS. 2 to 5, the exhaust of the engine 1 is collected in the upper inflow chamber 69 and the lower inflow chamber 70 after passing through the filter 33 in the upstream chamber 29 a. The Exhaust gas in the upper inflow chamber 69 flows into the inside from the entire periphery of the upper end of the upper guide pipe 71 through the gap 73 and flows downward in the upper guide pipe 71. Similarly, the exhaust gas in the lower inflow chamber 70 flows into the inside from the entire periphery of the lower end of the lower guide pipe 72 through the gap 74 and flows upward in the lower guide pipe 72.

  For this reason, in the process of flowing through the upper and lower guide pipes 71 and 72, the respective exhausts generate exhaust airflows in the same axis and in opposite directions, and along the injection axis L from the urea water injector 38 in these exhaust airflows. Then, urea water is injected downward. The upper and lower exhaust airflows flow into the diffusion chamber 68 and collide with each other and are vigorously stirred with the urea water, and the NOx is selectively reduced by the SCR catalyst 35 using ammonia generated from the urea water.

  The point where the exhaust airflow from above and below collides in the diffusion chamber 68 corresponds to the downstream side of the upper and lower guide pipes 71 and 72 in the flow direction of the exhaust airflow. Accordingly, the spray of urea water injected from the urea water injector 38 is guided to the collision point following the exhaust air flow directed downward in the upper guide pipe 71, and then proceeds in a direction away from the collision point, that is, Progressing in the direction of passing downward through the collision point or reversing upward at the collision point is hindered. Due to the action of the exhaust airflow from above and below, the urea water spray guided to the collision point of the exhaust airflow diffuses and atomizes well in the exhaust gas without greatly deviating from the collision point in the vertical direction. It is transferred to the SCR catalyst 35.

  Therefore, the urea water spray is prevented from adhering to the facing wall 29c of the casing 29 or the nozzle hole portion of the urea water injector 38. And even if the exhaust temperature fluctuates with changes in the engine operating state, the adhesion prevention action of urea water spray due to the exhaust airflow from above and below is surely obtained, so the patent for boiling the urea water on the perforated plate There is no possibility that the desired action cannot be obtained unlike the technique of Document 1, and the above-described effects can be stably obtained in a wide engine operating state.

  By the way, although the action of preventing the adhesion of urea water spray by the exhaust airflow from above and below can be obtained regardless of the engine operation region, in some cases, the collision point is not transferred from the collision point to the SCR catalyst 35 side. There is also a urea water spray that passes through or goes up from the collision point. The urea water spray passing downward through the collision point adheres to the opposing wall 29c of the casing 29, and the urea water spray reversed upward from the collision point adheres to the nozzle hole portion of the urea water injector 38. Only moisture will evaporate and solid urea will not sublimate, which may cause troubles such as deposits that hinder the flow of exhaust or hinder the injection of urea water.

Therefore, in the present embodiment, the exhaust gas in the upper and lower inflow chambers 69 and 70 is caused to flow into the corresponding guide pipes 71 and 72 through the gaps 73 and 74 in order to further enhance the adhesion prevention effect of the urea water spray. Yes.
That is, as is clear from FIG. 2 and the like, the exhaust in the upstream inflow chamber 69 is passed through the gap 73 formed between the upper end of the upstream guide pipe 71 and the installation surface 61 into the upstream guide pipe 71. Similarly, the exhaust in the downstream inflow chamber 70 is caused to flow into the downstream guide pipe 72 through a gap 74 formed between the lower end of the downstream guide pipe 72 and the opposing wall 29c of the casing 29. ing.

  Accordingly, since the flow path when the exhaust gas in the upper inflow chamber 69 flows into the upper guide pipe 71 is limited to the vicinity of the installation surface 61 in which the gap 73 is formed in the vertical direction, the exhaust gas follows the installation surface 61. Flows into the upper guide pipe 71 from the entire circumference at a high flow rate. Similarly, the flow path when the exhaust gas in the lower inflow chamber 70 flows into the lower guide pipe 72 is also limited to the vicinity of the casing facing wall 29c in which the gap 74 is formed in the vertical direction. It flows from the entire circumference into the lower guide pipe 72 at a high flow velocity along 29c.

  For this reason, the nozzle hole part of the urea water injector 38 and the opposing wall 29c of the casing 29 are always exposed to the exhaust airflow having a high flow velocity. Therefore, even if the sprayed urea water spray passes below through the collision point of the exhaust airflow, it is blocked by the high-speed exhaust airflow flowing along the casing facing wall 29c and is prevented from adhering to the facing wall 29c. . Further, even if the injected urea water spray is reversed upward from the collision point of the exhaust airflow, it is blocked by the high-speed exhaust airflow flowing along the installation surface 61 to prevent the urea water injector 38 from adhering to the nozzle hole portion. Is done.

  Moreover, even if urea water spray adheres to the casing facing wall 29c or the nozzle hole portion of the urea water injector 38 for some reason, the urea water not only evaporates water but also sublimates solid urea due to the high flow velocity of the exhaust airflow. Promoted. Therefore, the production | generation of the deposit to the casing opposing wall 29c and the nozzle hole part of the urea water injector 38 can be suppressed, and the various trouble resulting from a urea origin deposit can be prevented more reliably.

  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the exhaust purification device of the diesel engine 1 provided with the selective reduction type SCR catalyst 35 is embodied, but the application target is not limited to this. For example, a gasoline engine may be provided with the SCR catalyst 35 assuming a lean combustion operation, and may be applied to such a gasoline engine.

In the above embodiment, the urea water is injected from the urea water injector 38 along the injection axis L so as to cross the casing 29 at a right angle, while the exhaust airflow is coaxial and completely opposite to the injection axis L. Is generated by the upper and lower guide pipes 71 and 72, but the urea water does not necessarily have to be injected so as to cross the casing 29 at a right angle, and the exhaust airflow does not necessarily have to be coaxial with the injection axis L, and is completely It is not necessary to be in the opposite direction or the same direction. Therefore, these requirements may be arbitrarily changed.
The same applies to the facing surfaces 63 and 64 of the partition wall 30, and the upper facing surface 63 is not necessarily completely opposed to the installation surface 61 of the casing 29, or both the facing surfaces 63 and 64 are completely opposed. There is no need, and they may be arranged to face each other at a predetermined angle.

1 Engine 20 Exhaust pipe (exhaust passage)
29 Casing 29a Upstream chamber 29b Downstream chamber 29c Opposite wall 30 Partition 35 SCR catalyst (ammonia selective reduction type NOx catalyst)
38 Urea water injector (urea water injection means)
61 Installation surface 63 Upper facing surface (first facing surface)
64 Lower facing surface (second facing surface)
68 Diffusion chamber 71 Upper guide pipe (first guide pipe)
72 Lower guide pipe (second guide pipe)
73, 74 gap

Claims (1)

A casing disposed in the exhaust passage of the engine and into which exhaust from the engine is introduced;
Urea water injection means disposed on the installation surface of the casing and injecting urea water toward the opposing wall in the casing so as to cross the inside of the casing;
An ammonia selective reduction type NOx catalyst that is disposed downstream of the urea water injection means in the casing and selectively reduces NOx in the exhaust gas using ammonia as a reducing agent;
The casing is partitioned into an upstream chamber and a downstream chamber in which the ammonia selective reduction type NOx catalyst is accommodated, and a first opposing surface and a second opposing surface facing each other on the injection axis of the urea water injection means. A partition wall that forms a diffusion chamber communicating with the downstream chamber between the opposing surfaces;
One end is opened from the first facing surface of the partition wall into the diffusion chamber, and the other end is opposed to the installation surface of the urea water injection means with a predetermined gap, and the gap is passed through the gap. A first guide pipe that causes the exhaust in the upstream chamber to flow into the interior and causes an exhaust airflow in substantially the same direction to the urea water injected from the urea water injection means to flow into the diffusion chamber;
One end is opened from the second facing surface of the partition wall into the diffusion chamber and the other end is opposed to the facing wall in the casing with a predetermined gap, and the upstream chamber passes through the gap. And a second guide pipe for causing an exhaust air flow in a substantially opposite direction to the urea water injected from the urea water injection means to flow into the diffusion chamber. Exhaust gas purification device for the engine.

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