JP5316796B2 - Engine exhaust purification system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an engine increased in NOx elimination performance by well mixing urea water and the exhaust gas while allowing the use of an inexpensive liquid-only urea water injector. <P>SOLUTION: A liquid-only urea water injector 27 is affixed to the rear surface of a spray chamber 22 into which the exhaust gas from an engine flows. Urea water is injected into the spray chamber 22, and the exhaust gas in the spray chamber 22 is transferred to an SCR catalyst 16 on the downstream side through four conduits 24 disposed around the urea water injector 27 to secure the ventilation performance necessary for cooling the urea water injector 27. The exhaust gas flowing into the spray chamber 22 flows radially toward the conduits 24 to stir with the urea water, and the urea water is atomized in the exhaust gas while the contact area of the urea water and the exhaust gas is increased due to the hollow cone-shaped injection pattern. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

TECHNICAL FIELD The present invention relates to an engine exhaust purification device, and more specifically, urea water is injected into an exhaust passage from a urea water injector, and ammonia (NH ₃ ) generated from urea water is used as a reducing agent to downstream ammonia selective reduction type NOx. The present invention relates to an exhaust purification device that supplies a catalyst (hereinafter referred to as an SCR catalyst).

As an exhaust purification device for purifying NOx (nitrogen oxide), which is one of the pollutants contained in engine exhaust, an SCR catalyst is disposed in the exhaust passage of the engine, and ammonia is used as a reducing agent for the SCR catalyst. 2. Description of the Related Art An exhaust gas purification device that purifies exhaust gas by reducing NOx by supplying is known.
In such an exhaust purification device, in order to supply ammonia to the SCR catalyst, it is common to supply urea water, which is easier to handle than ammonia, into the exhaust. A urea water injector is used to supply the urea water, and the urea water injector is installed in the exhaust passage upstream of the SCR catalyst and pressurized urea water is supplied from the urea water tank, and is built in the urea water injector. Urea water is injected into the exhaust passage according to the opening and closing of the solenoid valve. In order for the SCR catalyst to exhibit good NOx purification performance, it is necessary to uniformly supply ammonia to each part of the SCR catalyst. To that end, the urea water injected from the urea water injector is sufficiently mixed with the exhaust gas. It is important to atomize the exhaust gas uniformly.

  By the way, as the urea water injector, a liquid-only type that injects only urea water and an air assist type that injects compressed air together with urea water have been put into practical use. Any type of urea water injector is installed on the outer surface of the exhaust passage that does not receive exhaust heat directly in order to protect the built-in solenoid valve. For example, when the SCR catalyst is arranged in series with another exhaust purification device such as a DPF (Diesel Particulate Filter) in consideration of the on-board property of the exhaust purification device, the SCR catalyst on the outer surface of the casing containing the exhaust purification device The injector body is installed at the upstream position. Although both urea water injectors are common in this respect, the position of the nozzle for injecting urea water is different due to the structure of each urea water injector.

In other words, the liquid-only type urea water injector shortens the path from the solenoid valve to the nozzle because the urea water remaining in the path to the nozzle after the solenoid valve is closed may solidify and cause clogging. The nozzle is integrated with the main body having a built-in solenoid valve. For this reason, as shown in FIG. 9, when the main body 102a is installed on the outer surface of the casing 101 that houses the exhaust gas purification device, the nozzle 102b can only be disposed near the inner surface of the casing so as to penetrate the casing wall surface and face the inside. Inevitably, the urea water is necessarily injected so as to be orthogonal to the exhaust gas flow direction in the casing 101.
On the other hand, in an air assist type urea water injector, urea water remaining in the path from the solenoid valve to the nozzle can be removed by jetting compressed air, so the nozzle is separated from the main body containing the solenoid valve and placed at an arbitrary position. It can be installed. Therefore, for example, in the technique described in Patent Document 1, as shown in FIG. 2, the casing is advantageous in that the urea water is mixed with the exhaust gas after the main body is installed on the outer surface of the casing containing the SCR catalyst. A nozzle is arranged in the vicinity of the inner axis (center), and urea water is injected toward the exhaust downstream side.

JP 2007-85247 A

In the air assist type urea water injector described in Patent Document 1 in which there is no restriction on the nozzle position, the nozzle position can be optimized to mix the urea water and the exhaust gas well, but on the other hand, compressed air is used separately from the urea water. Since it is necessary to add a configuration for injection, there is a problem that the system cost of the urea water injector is high, and as a result, the manufacturing cost of the exhaust gas purification device is increased.
On the other hand, since the liquid-only urea water injector of FIG. 9 does not have a configuration for injecting compressed air, the system cost is much lower than that of the air assist type. However, because of its structure, the nozzle 102b cannot be separated from the injector main body 102a, so the nozzle position is limited to the vicinity of the inner surface of the casing 101. Therefore, the urea water injected from the nozzle 102b diffuses while crossing the exhaust gas flowing through the casing 101, and the mixing state of the urea water with respect to the exhaust gas is greatly different between the vicinity of the nozzle and the vicinity of the opposing wall. Adhesion of urea water to the water also occurs. Therefore, the exhaust gas purification apparatus using this liquid-only type urea water injector has room for improvement in terms of promoting the mixing of exhaust gas and urea water.

  The present invention has been made in order to solve such problems. The object of the present invention is to make it possible to use a liquid-only urea water injector with a low system cost and to use an air assist type urea. Urea water and exhaust gas can be mixed well in the same way as when using a water injector, and ammonia generated from urea water is uniformly supplied to each part of the SCR catalyst to maximize the NOx purification performance. It is an object of the present invention to provide an exhaust emission control device for an engine.

  In order to achieve the above object, an invention according to claim 1 is provided with a spray chamber that is provided in an exhaust passage of an engine and into which exhaust gas from the engine flows through an inflow hole formed on the exhaust upstream side, and an outside of the spray chamber. A hollow cone-shaped spray which is arranged downstream and faces the nozzle into the spray chamber through the downstream wall surface of the spray chamber so as to substantially coincide with the axis of the inflow hole, and injects urea water from the nozzle into the spray chamber. A urea water injector that forms a downstream side of the spray chamber of the exhaust passage, an ammonia selective reduction type NOx catalyst that selectively reduces NOx in the exhaust gas using ammonia as a reducing agent, and an inlet of the ammonia selective reduction type NOx catalyst A merging chamber provided on the upstream side and facing the spraying chamber located on the upstream side at a predetermined interval, and disposed between the spraying chamber and the merging chamber so as to surround the periphery of the urea water injector. When It is obtained by a plurality of conduits for communicating the internal mutually the fluidic chamber are connected respectively.

Therefore, the exhaust gas from the engine flows into the spray chamber through the inflow hole, and flows into the pipes located on the outer peripheral side while being mixed with the urea water injected from the urea water injector. The exhaust gas passes through the pipes, joins in the junction chamber, and is then transferred to the ammonia selective reduction type NOx catalyst. Ammonia generated from the urea water in the exhaust gas is used for NOx purification of the NOx catalyst.
A urea water injector is disposed on the downstream side of the spray chamber to inject urea water into the spray chamber, while exhaust gas is guided to the merge chamber through a plurality of pipes disposed around the urea water injector. doing. Therefore, it is possible to install a so-called liquid-only urea water injector having a nozzle integrated with the main body of the urea water injector on the central axis of the exhaust flow, and the air permeability required for cooling the urea water injector. Secured.

  On the other hand, the exhaust gas flowing into the spray chamber through the inflow hole flows radially toward the outer circumferential direction, and urea water is injected from the urea water injector into this exhaust gas, so that the urea water is vigorously stirred together with the exhaust gas and is excellent Mixed. In addition, in the injection characteristics of the hollow cone type, since the spray cross-sectional area increases rapidly with respect to the urea water injection distance, the contact area between the urea water and the exhaust gas is large, and the urea water is centered on the axis. Since it is injected radially with point symmetry, it is well mixed with the exhaust gas under substantially the same conditions at any angle in the circumferential direction. Therefore, the urea water is sufficiently atomized in the exhaust gas, and the ammonia generated from the urea water is uniformly supplied to each part of the SCR catalyst.

According to an engine exhaust gas purification apparatus of a second aspect of the present invention, in the first aspect, a radial fin having a spiral shape centering on the inflow hole is disposed on the upstream wall surface of the spray chamber.
Accordingly, since the swirl flow is imparted to the exhaust gas by the radial fin, the flow state of the exhaust gas in the spray chamber becomes more intense and the mixing with the urea water is promoted.

According to the engine exhaust gas purification apparatus of the third aspect of the present invention, in the first or second aspect, the inner diameter is set so that the inflow hole opens on the inner peripheral side from the hollow cone-shaped spray region by the urea water injector. Is.
Accordingly, since the inflow hole is opened on the inner peripheral side of the spray region of the urea water injector, a situation in which the injected urea water adheres to the upstream side exhaust purification device through the inflow hole can be avoided.

According to an engine exhaust gas purification apparatus of a fourth aspect of the present invention, in the first to third aspects of the present invention, a relief recess is provided on the upstream wall surface of the merging chamber to secure a gap with the urea water injector. is there.
Therefore, the clearance between the urea water injector and the merging chamber is increased by the formation of the escape recess in the merging chamber, so that the air permeability necessary for cooling the urea water injector is further ensured.

  As described above, according to the engine exhaust gas purification apparatus of the first aspect of the present invention, the urea water injector is disposed on the downstream side outside the spray chamber into which exhaust gas from the engine flows, and urea water is injected into the spray chamber. In this way, the exhaust gas in the spray chamber is transferred to the NOx catalyst from the downstream merging chamber through a plurality of pipes arranged around the urea water injector, so that the ventilation necessary for cooling the urea water injector is achieved. A liquid-only urea water injector can be used that can be sufficiently secured, thereby reducing the system cost. On the other hand, the exhaust gas flowing into the spray chamber is caused to flow radially and stirred vigorously with the urea water, and the contact area between the urea water and the exhaust gas is increased by the injection characteristics of the hollow cone type, and the point is symmetrical about the axis. By spraying urea water radially, the urea water can be sufficiently atomized in the exhaust gas, so that ammonia generated from the urea water can be uniformly supplied to each part of the NOx catalyst to maximize NOx. Purification performance can be demonstrated.

According to the engine exhaust gas purification apparatus of the second aspect of the present invention, in addition to the first aspect, the swirl flow can be generated in the exhaust gas by the radial fins and can be further mixed with the urea water.
According to the engine exhaust gas purification apparatus of the third aspect of the invention, in addition to the first or second aspect, the urea water is prevented from adhering to the upstream side exhaust gas purification apparatus through the inflow hole, for example, exhaust gas purification. Troubles such as device deterioration can be prevented in advance.

According to the engine exhaust gas purification apparatus of the fourth aspect of the invention, in addition to the first to third aspects, the clearance between the urea water injector and the merging chamber can be secured by forming the relief recess, so that the urea water can be improved by improving the ventilation. It is possible to cool the injector more reliably and improve the heat resistance reliability .

1 is an overall configuration diagram illustrating an exhaust emission control device for a diesel engine according to an embodiment. It is sectional drawing of the nozzle casing which shows the communication state of a spray chamber and a confluence | merging chamber, and each pipe line. It is sectional drawing of the nozzle casing which similarly shows the positional relationship of each pipe line and urea water injector. It is A arrow line view of FIG. 2 which shows the radial fin provided in the front surface of the spraying chamber. It is the VV sectional view taken on the line of FIG. 2 which shows the positional relationship of each pipe line and a urea water injector. FIG. 3 is a view as viewed in the direction of arrow B in FIG. 2 showing an escape recess formed on the rear surface of the merge chamber. It is C arrow line view of FIG. 5 which shows the external appearance of a nozzle casing. It is sectional drawing which shows the spray chamber of another example. It is a figure which shows the conventional exhaust gas purification apparatus using a liquid-only type urea water injector.

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

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

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

  The exhaust passage 10 is provided with an exhaust purification device of the present invention, and the exhaust purification device is accommodated in an upstream casing 11, a downstream casing 12, and a nozzle casing 13 disposed between the casings 11, 12. . The upstream casing 11 and the downstream casing 12 have a cylindrical shape extending in the front-rear direction of the vehicle (the left-right direction in FIG. 1), and the upstream casing 11 has a pre-stage oxidation catalyst 14 and a DPF (diesel particulate filter) from the upstream side. 15 is accommodated, and an SCR catalyst (selective reduction type NOx catalyst) 16 and a post-stage oxidation catalyst 17 are accommodated in the downstream casing 12 from the upstream side.

  2 is a cross-sectional view of the nozzle casing showing the state of communication between the spray chamber and the merge chamber and each pipe, FIG. 3 is a cross-sectional view of the nozzle casing showing the positional relationship between each pipe and the urea water injector, and FIG. 2 is a view taken along the arrow A in FIG. 2 showing the radial fin provided on the front surface of the spray chamber, FIG. 5 is a sectional view taken along the line V-V in FIG. 2 showing the positional relationship between each pipe line and the urea water injector, and FIG. 2 is a view as viewed in the direction of arrow B in FIG. 2 showing the relief recess formed on the rear surface of the chamber, and FIG. 7 is a view in the direction of arrow C in FIG. 5 showing the appearance of the nozzle casing. 2 and FIG. 3 are different in cross section. FIG. 2 corresponds to a cross section taken along the line II-II shown in FIG. 5 and FIG. 3 shows the location of the urea water injector shown in FIG. This corresponds to a cross section taken along line III-III.

  In particular, as shown in FIGS. 2 and 5, the nozzle casing 13 as a whole has a shape in which a spray chamber 22 and a merge chamber 23 arranged in front and rear are connected by a conduit 24 made of four cylindrical pipe members, and each member 22 to 24 are made of steel plates and are welded to each other. The spray chamber 22 and the merge chamber 23 each have a thin rectangular parallelepiped shape in the longitudinal direction of the vehicle, the front end of the spray chamber 22 is connected to the rear end of the upstream casing 11, and the rear end of the merge chamber 23 is the front end of the downstream casing 12. It is connected to the.

  The spray chamber 22 and the merge chamber 23 are arranged to face each other at a predetermined interval in the front-rear direction, and the four corners of the spray chamber 22 and the merge chamber 23 viewed from the front of the vehicle are connected to each other by the pipe line 24. Yes. The spray chamber 22 and the merge chamber 23 are located on an axis L that connects the upstream casing 11 and the downstream casing 12, and each pipe line 24 is inevitably disposed so as to surround the axis L. The total passage cross-sectional area of the pipe line 24 is set to be substantially equal to the passage cross-sectional area of the DPF 15 and the SCR catalyst 16.

  As shown in FIG. 4, an inflow hole 25 is provided through the front surface of the spray chamber 22 around the axis L. On the front surface (upstream wall surface) of the spray chamber 22, a spiral-shaped radial fin 26 centering on the inflow hole 25 of the spray chamber 22 is fixed, and this radial fin 26 is located immediately downstream of the DPF 15 in the downstream casing 12. positioned. The rear end of the merge chamber 23 is opened rearward and communicates with the inside of the downstream casing 12. As a result, the upstream casing 11 communicates with the spray chamber 22 via the inflow hole 25, the spray chamber 22 communicates with the merge chamber 23 via each conduit 24, and the merge chamber 23 communicates with the downstream casing 12. Yes.

  A urea water injector 27 is disposed on the downstream side outside the spray chamber 22, and a main body 27 a of the urea water injector 27 is fixed to the rear surface (downstream wall surface) of the spray chamber 22. The nozzle 27 b of the urea water injector 27 faces the spray chamber 22 through the rear surface of the spray chamber 22, is located on the axis L, and is opposed to the inflow hole 25 in the spray chamber 22. As a result, the pipes 24 are distributed and positioned so as to surround the urea water injector 27 around the urea water injector 27, and a sufficient gap is formed between the pipe lines 24 and the urea water injector 27. Air permeability required for cooling the injector 27 is ensured. In addition, the front surface (upstream wall surface) of the merge chamber 23 is recessed backward with respect to the axis L (that is, toward the inside of the merge chamber 23) to form a relief recess 28, and the relief recess 28 is gentle. A gap is secured between the rear end of the urea water injector 27 and a square pyramid shape.

  The urea water injector 27 is configured as a liquid-only type with a built-in electromagnetic valve, and a predetermined pressure of urea water supplied from a urea tank (not shown) is injected into the spray chamber 22 when the electromagnetic valve is opened. The spray characteristics of the urea water injector 27 are set in a wide-angle hollow cone shape, and the urea water is sprayed in the spray chamber 22 from the nozzle 27b located on the axis L in a slightly forward-facing outer peripheral direction. The inflow hole 25 has an inner diameter set so as to open on the inner peripheral side of the hollow cone-shaped spray region centered on the axis L.

  On the other hand, the fuel injection valve 2 and the urea water injector 27 are connected to an ECU 31 (electronic control unit), and other sensors and devices are connected to the ECU 31. For example, the ECU 31 sets a fuel injection amount according to a map (not shown) from the engine rotation speed Ne and the accelerator operation amount θacc, sets a fuel injection timing according to a map (not shown) from the engine rotation speed Ne and the fuel injection amount, and these fuel injection amounts. The engine 1 is operated by drivingly controlling the fuel injection valve 2 based on the fuel injection timing. Further, the ECU 31 supplies a target amount of urea water based on an exhaust gas temperature detected by a temperature sensor (not shown) installed on one side of the spray chamber 22 in order to supply ammonia onto the SCR catalyst 16 to exert a NOx purification action. Is determined, and the solenoid valve of the urea water injector 27 is driven and controlled based on the target injection amount to inject urea water from the urea water injector 27.

  During operation of the engine 1, exhaust gas discharged from the engine 1 is introduced into the upstream casing 11 through the exhaust manifold 9 and the exhaust passage 10, and is contained when flowing through the DPF 15 through the upstream oxidation catalyst 14. (Particulate matter) is collected. Thereafter, the exhaust gas is guided by the radial fin 26 in the inner circumferential direction, is given a swirling component as indicated by a solid arrow, and then flows into the spray chamber 22 through the central inflow hole 25. In the spray chamber 22, the exhaust gas generates a strong swirling flow centered on the axis L, and spirally circulates in the outer peripheral direction as indicated by the dashed arrow, and is mixed with the urea water injected from the urea water injector 27. However, it flows into each pipe line 24 located on the outer peripheral side while flowing. Further, the exhaust gas that has circulated in the pipes 24 merges from the four corners in the merge chamber 23 and is transferred to the SCR catalyst 16. The urea water is mixed with exhaust gas and generates ammonia by exhaust heat in the process of being transferred through the nozzle casing 13, and this ammonia is used for NOx purification of the SCR catalyst 16.

  By the way, as described in [Problems to be Solved by the Invention], the liquid-only urea water injector 27 has a low system cost, but the nozzle 27b cannot be separated from the injector body 27a. There is no choice but to arrange the nozzle 27b on the inner side surface and inject urea water so as to be orthogonal to the exhaust gas flow direction in the casing, and there is room for improvement in terms of promoting mixing of the exhaust gas and urea water.

Therefore, in view of the problem of such a liquid-only urea water injector 27, the exhaust purification device of the present embodiment is provided with the nozzle casing 13, and the operation of the nozzle casing 13 will be described below.
First, there is no structural or in-vehicle demerit due to the provision of the nozzle casing 13.
That is, as is apparent from FIG. 1, the upstream casing 11, the nozzle casing 13 and the downstream casing 12 are sufficiently rigid as a structure constituting a part of the exhaust passage to be suspended in the lower part of the vehicle body, Flexural rigidity is required when both ends are suspended and supported. The upstream casing 11 and the downstream casing 12 are connected by a nozzle casing 13. Since each pipe line 24 is spaced apart to the maximum by being arranged at the four corners of the spray chamber 22 and the merge chamber 23, the spray chamber 22 and the merge chamber 23 are firmly connected by the four pipe lines 24. Sufficiently high rigidity can be secured. Therefore, sufficient rigidity can be secured as a whole of the upstream casing 11, the nozzle casing 13, and the downstream casing 12, and there is no possibility of breakage during traveling.

  Further, the spray chamber 22 and the merge chamber 23 of the nozzle casing 13 have a rectangular parallelepiped shape with respect to the cylindrical upstream and downstream casings 11 and 12, but as is apparent from FIGS. The left and right and vertical dimensions of the merge chamber 23 are substantially equal to the outer diameters of the upstream and downstream casings 11 and 12. Although the pipe lines 24 of the nozzle casing 13 are arranged to be spaced apart from each other to the maximum extent, they do not protrude greatly from the nozzle casing 13 and are within the horizontal and vertical dimensions of the spray chamber 22 and the merge chamber 23. Therefore, the occupied space when mounted on a vehicle hardly increases as compared with a general exhaust purification device using only a cylindrical casing, for example, and there is no on-vehicle demerit.

On the other hand, as apparent from FIGS. 2 and 5, the urea water injector 27 is fixed to the rear surface of the spray chamber 22 and urea water is injected into the spray chamber 22, while the exhaust gas in the spray chamber 22 is discharged from the urea water injector 27. It is configured to guide to the merge chamber 23 through four pipe lines 24 disposed around. Therefore, using the liquid-only urea water injector 27 having a structure in which the nozzle 27b is integrated with the injector body 27a, it is possible to inject the urea water into the spray chamber 22 symmetrically without any trouble.
As described above, since the exhaust gas is guided through the pipe line 24 around the urea water injector 27 and a sufficient gap is formed between each pipe line 24 and the urea water injector 27, air permeability is ensured. The urea water injector 27 is sufficiently cooled. Further, since a gap is also formed between the escape recess 28 formed in the front surface of the merge chamber 23 and the rear end of the urea water injector 27, the ventilation is further improved. Therefore, the heat resistance reliability of the urea water injector 27 can be sufficiently ensured, and the urea water injector 27 can be reliably prevented from being damaged by radiant heat from the exhaust passage portion.

In addition, due to the fact that the urea water injector 27 is arranged on the axis L as described above and the structure of the nozzle casing 13 described below, even if the liquid-only urea water injector 27 is used, the air assist is used. The urea water and the exhaust gas can be mixed well compared with the conventional exhaust gas purification apparatus that employs the type of urea water injector 27.
First, the state of mixing of urea water into the exhaust gas flowing into the spray chamber 22 will be described in detail. The exhaust gas flowing into the spray chamber 22 from the inflow hole 25 flows intensely radially from the center toward the outer periphery, In addition, since the swirl flow is preliminarily applied to the exhaust gas at this time by the radial fin 26, the flow state of the exhaust gas in the spray chamber 22 becomes even more severe than the swirl flow. And since urea water is injected in such exhaust gas, urea water is vigorously stirred with exhaust gas and mixed well.

  On the other hand, in the injection characteristic of the wide-angle hollow cone type, the spray cross-sectional area increases rapidly with respect to the urea water injection distance, so that the urea water is mixed with the exhaust gas with a sufficient contact area. In addition, the nozzle 27b of the urea water injector 27 is located on the axis L that is the center of the spray chamber 22, and the urea water is injected radially into the spray chamber 22 with point symmetry about the axis L. Any angle in the circumferential direction centered on L is well mixed with the exhaust gas under substantially the same conditions. Further, since the injected urea water diffuses slightly in the outer circumferential direction facing forward, the distance of the urea water to reach the front and side surfaces in the spray chamber 22, in other words, the mixing time with the exhaust gas is maximized. Secured. As described above, since the contact area between the urea water and the exhaust gas is large and the mixing time of the exhaust gas and the urea water is long, the urea water is sufficiently mixed in the exhaust gas while the exhaust gas flows through the spray chamber 22. The

And since the exhaust gas which passed through the spraying chamber 22 once diverts to each pipe line 24, it merges again in the confluence chamber 23, Therefore Exhaust gas is also stirred strongly also in the case of these division and confluence. Therefore, the urea water and the exhaust gas can be mixed well to sufficiently atomize the urea water in the exhaust gas, and the ammonia generated from the urea water can be uniformly supplied to each part of the SCR catalyst 16, thereby having the SCR catalyst. 16 can exhibit the maximum NOx purification performance.
Further, since the inner diameter of the inflow hole 25 is set so as to open on the inner peripheral side with respect to the hollow cone-shaped spray region centered on the axis L, the injected urea water passes through the inflow hole 25 and passes through the DPF 15. The situation of adhering to is avoided beforehand. Adhesion of urea water to the high-temperature DPF 15 can be a factor that degrades the DPF 15, but such troubles can be prevented in advance.

  In addition, since the total passage sectional area of the pipeline 24 is set so as to be substantially equal to the passage sectional area of the DPF 15 and the SCR catalyst 16, the passage sectional area is not reduced at the location of the pipeline 24. It does not cause an increase in back pressure. Further, since the above-described escape recess 28 protrudes backward in the merge chamber 23 with the axis L as an apex, the exhaust gas flowing into the merge chamber 23 from each pipe line 24 rises along the escape recess 28. The distribution direction is changed backward while being guided. Therefore, it is possible to reduce the resistance when the exhaust gas merged in the merge chamber 23 changes the flow direction rearward, thereby obtaining another advantage of preventing a decrease in engine performance due to an increase in back pressure.

Although the description of the embodiment embodying the present invention has been completed above, the configuration of the exhaust emission control device of the present invention can be arbitrarily changed without being limited to the present embodiment. For example, the configuration as in another example described below May be. In the other example, each pipe line 24 is opened in the tangential direction of the swirling flow of the exhaust gas in the spray chamber 22.
FIG. 8 is a cross-sectional view showing a spray chamber 22 of another example of the embodiment, and is a cross-section corresponding to the position of the line VIII-VIII shown in FIG. In the above embodiment, the front ends of the four pipelines 24 made of cylindrical pipe material are connected to the rear surface of the spray chamber 22. In this alternative example, the front ends of the pipelines 24 penetrate the rear surface of the spray chamber 22. The front of the spray chamber 22 is reached. In the spray chamber 22, each pipe 24 is cut off about half of the annular cross section 24 a, and roughly expressed, about half of the counterclockwise portion 24 a centering on the axis L as seen from the front of the vehicle is cut off. , About half of the clockwise direction 24b remains.

  Thereby, in the spray chamber 22, each pipe line 24 opens in the tangential direction of the swirl flow of the exhaust gas around the axis L, and the swirl flow can be generated in the spray chamber 22 by the suction effect. Mixing of urea water and exhaust gas is promoted by the swirling flow of the exhaust gas generated in the spray chamber 22, and ammonia can be uniformly supplied to each part of the SCR catalyst 16.

On the other hand, the following requirements can also be arbitrarily changed without being limited to the embodiment and other examples. For example, in the above-described embodiment, various advantages are obtained by using the liquid-only type urea water injector 27. However, the type of the urea water injector is not necessarily limited to the liquid-only type. For example, the air assist type urea is used. A water injector may be used.
In the above embodiment, the radial fin 26 is provided on the front surface of the spray chamber 22 and the escape recess 28 is formed on the rear surface of the merge chamber 23. However, the radial fin 26 and the escape recess 28 are not necessarily provided and may be omitted. .

  In the above embodiment, the four corners of the spray chamber 22 and the merge chamber 23 are connected by the four pipelines 24 to ensure the rigidity of the nozzle casing 13, but the arrangement and number of the pipelines 24 are not limited thereto. It is not limited and can be changed arbitrarily. Further, the cross-sectional shape of the conduit 24 is not limited to the embodiment, and can be changed to, for example, a rectangular tube shape.

1 Engine 16 SCR catalyst (Ammonia selective reduction type NOx catalyst)
22 spray chamber 23 merge chamber 24 pipe 25 inflow hole 26 radial fin 27 urea water injector 27b nozzle 28 escape recess L axis

Claims (4)

A spray chamber that is provided in the exhaust passage of the engine and allows exhaust gas from the engine to flow into the interior through an inflow hole formed on the exhaust upstream side;
A nozzle is provided on the downstream side of the spray chamber and faces the spray chamber through the downstream wall surface of the spray chamber so as to substantially coincide with the axis of the inflow hole. From the nozzle, urea water enters the spray chamber. A urea water injector to form a hollow cone spray by spraying
An ammonia selective reduction type NOx catalyst that is disposed downstream of the spray chamber in the exhaust passage and selectively reduces NOx in the exhaust gas using ammonia as a reducing agent;
A merging chamber provided on the inlet side of the ammonia selective reduction type NOx catalyst and facing the spray chamber located on the upstream side at a predetermined interval;
A plurality of pipes that are disposed between the spray chamber and the merge chamber so as to surround the urea water injector, and connect the spray chamber and the merge chamber to communicate with each other. An exhaust purification device for an engine characterized by that.   2. The exhaust emission control device for an engine according to claim 1, wherein a radial fin having a spiral shape with the inflow hole as a center is disposed on an upstream wall surface of the spray chamber.   3. The engine exhaust gas purification apparatus according to claim 1, wherein an inner diameter of the inflow hole is set so as to open on an inner peripheral side with respect to a hollow cone-shaped spray region formed by the urea water injector.   The engine exhaust gas purification apparatus according to any one of claims 1 to 3, wherein a relief recess for securing a gap with the urea water injector is provided in an upstream wall surface of the merge chamber.

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