JP5610120B2 - Engine exhaust purification system - Google Patents

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. In the air assist type urea water injector, the urea water remaining in the path to the nozzle after the solenoid valve is closed can be removed by the injection of compressed air, so there is a risk of clogging due to solidification of the urea water even if the path is long. In addition, the nozzle can be separated from the main body incorporating the electromagnetic valve and installed at an arbitrary position.

  On the other hand, the liquid-only urea water injector does not require a configuration for injecting compressed air, and has the advantage of reducing the system cost. However, if the path from the solenoid valve to the nozzle is long, residual urea Water can solidify and cause clogging. Therefore, in order to shorten the path from the solenoid valve to the nozzle, the nozzle is integrated with the main body incorporating the solenoid valve. For this reason, the nozzle position is limited to a position where the injector body can be installed on the exhaust passage, and the nozzle cannot always be arranged at an optimal position for promoting the mixing of urea water and exhaust gas.

  As an exhaust gas purification apparatus using this type of liquid-only urea water injector, for example, a technique described in Patent Document 1 can be cited. FIG. 6 is a view showing an installation state of the urea water injector described in Patent Document 1, and an SCR catalyst 19 is accommodated in a casing 11 into which exhaust gas from an engine is introduced via an inlet pipe 10a. A mount pipe 101 is interposed on the inlet pipe 10a, and a urea water injector 15 is installed on the mount pipe 101. Urea water is discharged from the nozzle 15b of the urea water injector 15 into the exhaust gas flowing through the inlet pipe 10a. It comes to be injected.

JP 2008-138594 A

  In the technique of Patent Document 1, since the urea water injector 15 is disposed on the inlet pipe 10a, in order to inject urea water into the exhaust gas flowing through the inlet pipe 10a, It is necessary to intersect the injection axis L of the urea water injector 15 at a predetermined angle. Naturally, as shown in FIG. 6, the mounting pipe 101 as a separate member is interposed on the inlet pipe 10 a, and not only the mounting pipe 101 itself, which is a separate part from the casing, but also the inlet pipe 101 is attached. Welding work was also necessary, and this increased the manufacturing cost due to the increased number of parts. In addition, the mount pipe 101 and the urea water injector 15 projecting obliquely laterally from the mount pipe 101 also became a factor of reducing the space efficiency around the exhaust purification device.

  Further, with the above configuration, urea water is injected from the nozzle 15b of the urea water injector 15 so as to intersect with the exhaust gas flow at a predetermined angle. For this reason, the mixing state of the urea water and the exhaust gas is greatly different between the vicinity of the nozzle immediately after the injection and the vicinity of the opposing wall in the inlet pipe 10a in which the spray is diffused to some extent, which promotes the mixing of the urea water and the exhaust gas. There was room for improvement.

  The present invention has been made to solve such problems, and the object of the present invention is to increase the manufacturing cost after enabling the use of a liquid-only urea water injector with a low system cost. An object of the present invention is to provide an engine exhaust gas purification apparatus that can avoid problems such as a decrease in space efficiency and improve the NOx purification performance by mixing urea water and exhaust gas well.

In order to achieve the above object, the invention of claim 1 has a cylindrical shape extending in the exhaust circulation direction, the downstream end of the inlet pipe is connected to the end face on the exhaust upstream side, and exhaust gas from the engine is passed through the inlet pipe to the inside. A casing to be introduced, a partition partitioning the inside of the casing into a spray chamber on the exhaust upstream side and a catalyst storage chamber on the exhaust downstream side, and being stored in the catalyst storage chamber of the casing, selectively reducing NOx in the exhaust gas using ammonia as a reducing agent The ammonia selective reduction type NOx catalyst is disposed in the casing spray chamber in a cylindrical shape, with one end directed toward the upstream end face of the casing and spaced apart from the upstream end face to form a gap and expand into a trumpet shape and, the other end is opened to the catalyst containing chamber through the partition wall, the exhaust gas flowing from the inlet pipe to the spray chamber to the catalyst storage chamber side is introduced into the interior through the gap The inner pipe is fixed to the upstream end face outside the casing, and the nozzle faces the spray chamber to be positioned in the mixing pipe, and urea water is injected from the nozzle so as to substantially follow the axis in the mixing pipe. In an exhaust emission control device for an engine provided with a urea water injector, the urea water injector is disposed closer to the center of the upstream end surface than the connection portion of the inlet pipe at the upstream end surface of the casing.

Therefore, after the exhaust gas from the engine flows into the spray chamber from the inlet pipe, the exhaust gas is introduced into the mixing pipe through a gap formed between the upstream end face of the casing and one end of the mixing pipe, and the catalyst passes through the mixing pipe. Guided toward the ammonia selective reduction type NOx catalyst housed in the housing chamber. The urea water is injected from the urea water injector into the mixing pipe, the exhaust gas is transferred to the NOx catalyst while being mixed with the urea water, and the ammonia generated from the urea water during the transfer is used for NOx purification of the NOx catalyst. . Since the urea water injector is fixed to the upstream end face of the casing and the urea water is injected from the nozzle facing the spray chamber, a liquid-only urea water injector with low system cost can be used.

And in the mixing pipe, urea water is injected to the exhaust gas flowing along the axis so as to substantially follow the axis. As a result, the flow of exhaust gas and the flow of spray of urea water are coaxial, so the urea water and the exhaust gas are almost in the same mixing state at any location in the axial direction of the mixing pipe, and both are mixed well. Promoted. The flow rate of the exhaust gas is the highest when it flows into the mixing pipe through the gap, and the urea water injector nozzle is constantly exposed to this high flow rate exhaust gas, which prevents the urea water from adhering to the nozzle. Generation of deposits is prevented.

  In addition, the urea water injector is fixed to the upstream end face of the casing together with the inlet pipe. However, the urea water injector is disposed near the center of the upstream end face in preference to the inlet pipe. Is also disposed closer to the center with respect to the inlet of the downstream NOx catalyst. As a result, ammonia generated from urea water in the process of flowing through the mixing pipe is uniformly supplied to each part of the NOx catalyst. In addition, since the urea water injected along the axis of the mixing pipe is mixed with the exhaust gas without being blocked by the casing wall surface, the generation of deposits due to collision and adhesion of urea water to the casing wall surface is prevented. Is done.

  On the other hand, in order to dispose the mixing pipe by partitioning the inside of the casing with a partition wall, for example, as in the technique of Patent Document 1, a complex-shaped mount pipe is manufactured and interposed on the inlet pipe by welding. The manufacturing cost can be reduced as compared with the case. Moreover, since the urea water injector protrudes forward from the upstream end face of the casing, it is compared with the technique of Patent Document 1 in which the urea water injector protrudes obliquely on a mount pipe that is a separate part from the casing. Thus, the space efficiency around the exhaust purification device can be improved.

As described above, according to the engine exhaust gas purification apparatus of the first aspect of the present invention, since the urea water injector is fixed to the upstream end surface of the casing and the urea water is injected into the spray chamber, the system cost is low. A liquid-only urea water injector can be used. The flow of the exhaust gas in the mixing pipe and the flow of the spray of urea water are made substantially coaxial so that the mixing state in the axial direction can be made uniform and the mixing can be promoted, and the urea water injector is given priority over the inlet pipe. Is disposed closer to the center of the upstream end face of the casing, so that ammonia from the mixing pipe can be uniformly supplied to each part of the NOx catalyst, thereby improving the NOx purification performance of the NOx catalyst. In addition, by injecting urea water into the mixing pipe, it is possible to prevent the generation of deposits due to the collision and adhesion of urea water to the casing wall, and to prevent the exhaust gas in the spray chamber from flowing between the upstream end face of the casing and the mixing pipe. By flowing into the mixing pipe through a gap formed between the one end and the pipe, it is possible to prevent the generation of deposits due to the urea water adhering to the nozzle . Furthermore, it is possible to reduce the manufacturing cost by eliminating the need to manufacture a mount pipe that is a separate component from the casing, and to prevent the urea water injector from projecting to the side, thereby improving the space efficiency around the exhaust purification device. it can.

1 is an overall configuration diagram illustrating an exhaust emission control device for a diesel engine according to an embodiment. It is a partial expanded sectional view of the casing which shows the structure around a spraying chamber. It is A arrow line view of FIG. 2 which shows the positional relationship of an inlet pipe and urea water injector. It is a partial expanded sectional view which shows another example of the mixing pipe in which the circular hole was formed. It is a partial expanded sectional view which shows another example of the mixing pipe which formed the clearance gap between the upstream end surfaces of the casing. It is sectional drawing which shows the conventional exhaust gas purification apparatus.

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 connected coaxially with the compressor 7a.

  The intake air introduced into the intake passage 5 via 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 via 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 burned near the compression top dead center. The exhaust gas after combustion passes through the exhaust manifold 9 and rotates the turbine 7b, and then passes through the exhaust passage 10. Guided.

FIG. 2 is a partially enlarged cross-sectional view of the casing showing the configuration around the spray chamber, and FIG. 3 is a view as seen from the arrow A in FIG. 2 showing the positional relationship between the inlet pipe and the urea water injector.
The exhaust passage 10 is provided with the exhaust purification device of the present invention, and the exhaust purification device is accommodated in the casing 11. The casing 11 has a cylindrical shape extending in the exhaust flow direction (the left-right direction in FIG. 1 and corresponding to the longitudinal direction of the vehicle), and the rear end of the exhaust passage 10 is connected to the upstream end surface 11a of the casing 11 as an inlet pipe 10a. Has been. The inside of the casing 11 is divided forward and backward by a partition wall 12, the exhaust upstream side is referred to as a spray chamber 13, and the exhaust downstream side is referred to as a catalyst housing chamber 14.

  A main body 15 a of a liquid-only urea water injector 15 is fixed to the upstream end surface 11 a of the casing 11. The nozzle 15b of the urea water injector 15 faces the spray chamber 13 via the upstream end face 11a, and urea water of a predetermined pressure is supplied to the main body 15a from a urea tank (not shown), and the electromagnetic valve built in the main body 15a. As the valve opens, urea water is injected into the spray chamber 13 from the nozzle 15b.

  As shown in FIG. 3, the inlet pipe 10a is positioned on the upper side with respect to the center C of the upstream end surface 11a of the casing 11, and the urea water injector 15 is aligned in a straight line in the vertical direction so as to be positioned on the lower side. . The distance C1 from the center C of the upstream end face 11a to the urea water injector 15 is set shorter than the distance C2 from the center C to the inlet pipe 10a. In other words, the urea water injector 15 is located closer to the center of the upstream end face 11a than the connection location of the inlet pipe 10a.

  As shown in FIG. 2, a mixing pipe 17 is disposed in the spray chamber 13, and the mixing pipe 17 has a cylindrical shape extending in the exhaust circulation direction. One end of the mixing pipe 17 is connected to the upstream end surface 11 a of the casing 11, and the other end is connected to the partition wall 12 and penetrates the partition wall 12 to open the inside into the catalyst housing chamber 14. The axis L of the mixing pipe 17 coincides with the injection axis of the urea water injector 15, and as a result, the nozzle 15 b of the urea water injector 15 is located at the center in the mixing pipe 17. A large number of slits 18 (holes) extending in the axis L direction are arranged in the circumferential direction on the entire outer periphery of the mixing pipe 17, and the inside and outside of the mixing pipe 17 communicate with each other through these slits 18.

  On the other hand, an SCR catalyst (selective reduction type NOx catalyst) 19 is disposed on the upstream side in the catalyst housing chamber 14, and an oxidation catalyst 20 is disposed on the downstream side. Note that a predetermined space is secured on the upstream side of the SCR catalyst 19 in the catalyst storage chamber 14, and the mixing of urea water and exhaust gas is promoted in this space, as will be described later.

  On the other hand, the fuel injection valve 2 and the urea water injector 15 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 13 in order to supply ammonia onto the SCR catalyst 19 and exert a NOx purification action. The urea water injector 15 is driven and controlled based on the target injection amount to inject urea water from the urea water injector 15.

  During operation of the engine 1, the exhaust gas discharged from the engine 1 flows into the spray chamber 13 from the inlet pipe 10 a through the exhaust manifold 9 and the exhaust passage 10. And it introduce | transduces in the mixing pipe 17 through each slit 18 of the outer periphery of the mixing pipe 17 from the inside of the spray chamber 13, and it collides with each other in the mixing pipe 17, and goes to the downstream side along the axis line L, stirring vigorously. Circulate.

  Then, urea water is injected from the nozzle 15 b of the urea water injector 15 into the exhaust gas flowing through the mixing pipe 17 in this way. The exhaust gas at this time flows along the axis L in the mixing pipe 17, and urea water is injected along the axis L. Therefore, the flow of exhaust gas and the flow of spray of urea water are coaxial. It becomes. For this reason, the urea water and the exhaust gas are in substantially the same mixed state at any location in the axis L direction of the mixing pipe 17, and the mixing of both is favorably promoted. Moreover, since the exhaust gas is vigorously stirred in the mixing pipe 17, the injected urea water is also stirred, and this factor also contributes to the promotion of mixing.

Therefore, the urea water and the exhaust gas are already sufficiently mixed in the mixing pipe 17, but in the process of being transferred from the mixing pipe 17 to the catalyst housing chamber 14, the inside of the catalyst housing chamber 14 is enlarged from the narrow mixing pipe 17. Since the exhaust gas is released into the space, the exhaust gas is rapidly diffused to further promote mixing with the urea water.
Then, ammonia generated from the urea water during the transfer is supplied to the SCR catalyst 19 and used for NOx purification. From the viewpoint of NOx purification, it is desirable to supply ammonia uniformly to each part of the SCR catalyst 19, and for this purpose, a mixing pipe 17 that serves to supply ammonia is connected to the inlet of the SCR catalyst 19 on the downstream side. It is effective to dispose as close to the center in the vertical and horizontal directions as possible.

  As described above, in the present embodiment, the urea water injector 15 is disposed closer to the center (that is, closer to the center C) in preference to the inlet pipe 10a on the limited upstream end surface 11a of the casing 11. Therefore, the mixing pipe 17 inevitably sharing the axis L with the urea water injector 15 is also arranged closer to the center with respect to the inlet of the SCR catalyst 19 on the downstream side. Therefore, ammonia generated from the urea water is uniformly supplied to each part of the SCR catalyst 19. As described above, urea water and exhaust gas can be mixed well and ammonia can be uniformly supplied to each part of the SCR catalyst 19. As a result, the NOx purification performance of the SCR catalyst 19 can be maximized. .

  In addition, since the urea water injected along the axis L of the mixing pipe 19 is mixed with the exhaust gas without being blocked by the casing wall surface, deposits are generated due to the collision and adhesion of the urea water to the wall surface of the casing 11. It can be prevented in advance.

  On the other hand, as apparent from FIG. 2, the injector body 15a is fixed to the upstream end surface 11a of the casing 11, and the urea water is injected from the nozzle 15b facing the spray chamber 13, so that the system cost is low. A liquid-only urea water injector 15 can be used without any trouble. Then, in order to divide the inside of the casing 11 by the partition wall 12 and arrange the mixing pipe 17, for example, a mount pipe 101 having a complicated shape is manufactured as in the technique of Patent Document 1 shown in FIG. The manufacturing cost can be reduced as compared with the case where the pipe 10a is interposed by welding. Moreover, since the urea water injector 15 protrudes forward from the upstream end surface 11a of the casing 11, the technique of Patent Document 1 in which the urea water injector protrudes obliquely from a mount pipe that is a separate component from the casing. In comparison, the space efficiency around the exhaust purification device can be improved.

  Although the description of the embodiment embodying the present invention has been completed above, the configuration of the exhaust purification apparatus of the present invention can be arbitrarily changed without being limited to the present embodiment. For example, the mixing pipe 17 is another example described below. You may comprise as follows.

  FIG. 4 is a partially enlarged cross-sectional view showing another example of the mixing pipe in which circular holes are formed. As shown in this figure, a large number of circular holes 41 (holes) are formed on the entire outer periphery of the mixing pipe 17 instead of the slits 18. It may be provided. Even in this case, when the exhaust gas is introduced into the mixing pipe 17 through the circular hole 41 as in the above embodiment, the mixing with the urea water can be promoted by vigorous stirring.

  Although not shown, by providing fins of a predetermined angle adjacent to each slit 18 of the mixing pipe 17 described in the above embodiment, and changing the exhaust gas flow when circulating through the slit 18 by these fins, A swirling flow may be generated in the exhaust gas in the mixing pipe 17. In this case, the exhaust gas and the urea water can be more vigorously stirred by the swirling flow and mixed well.

  FIG. 5 is a partially enlarged cross-sectional view showing another example of the mixing pipe in which a gap is formed between the upstream end face of the casing. As shown in FIG. 5, the upstream end face 11a and one end of the mixing pipe 17 are A gap 51 may be formed between them. In such a configuration, the exhaust gas flows into the mixing pipe 17 through the gap 51, and the flow rate of the exhaust gas increases most at the time of the inflow. Further, since the nozzle 15b of the urea water injector 15 is always exposed to the exhaust gas having a high flow rate, adhesion of the urea water to the nozzle 15b is prevented, and generation of deposits due to this can be prevented. Benefits are gained. Further, one end of the mixing pipe 17 may be expanded in a trumpet shape, whereby the pipe resistance of the exhaust gas when flowing into the mixing pipe 17 can be reduced.

  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 15, but 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-described embodiment, the SCR catalyst 19 and the oxidation catalyst 20 on the downstream side thereof are provided as the exhaust purification device, but the present invention is not limited to this. For example, another casing may be provided on the upstream side of the casing 11 and connected by the inlet pipe 10a, and the pre-stage oxidation catalyst and DPF (diesel particulate filter) may be accommodated in the newly provided casing. Even in this case, since the positional relationship between the inlet pipe 10a on the upstream end face 11a and the urea water injector 15 is established in the same manner as in the above-described embodiment, the same effect can be obtained.

  In the above embodiment, the inlet pipe 10a is disposed on the upper side and the urea water injector 15 is disposed on the lower side with respect to the center C of the upstream end surface 11a of the casing 11, but the urea water injector 15 is disposed on the upstream end surface with respect to the inlet pipe 10a. As long as it is positioned closer to the center of 11a, the positional relationship in the vertical and horizontal directions is not limited. Therefore, the positional relationship between the inlet pipe 10a and the urea water injector 15 on the upstream end surface 11a can be arbitrarily changed. Also good.

DESCRIPTION OF SYMBOLS 1 Engine 10a Inlet pipe 11 Casing 11a Upstream end surface 12 Bulkhead 13 Spraying chamber 14 Catalyst accommodating chamber 15 Urea water injector 15b Nozzle 17 Mixing pipe 18 Slit (hole)
19 SCR catalyst (ammonia selective reduction type NOx catalyst)
41 Circular hole (hole)
51 clearance L axis

Claims (1)

A casing extending in the exhaust gas flow direction and connected to the downstream end of the inlet pipe at the exhaust upstream side end face, and through which the exhaust gas from the engine flows into the interior through the inlet pipe;
A partition that divides the inside of the casing into a spray chamber on the exhaust upstream side and a catalyst storage chamber on the exhaust downstream side,
An ammonia selective reduction-type NOx catalyst that is housed in the catalyst housing chamber of the casing and selectively reduces NOx in exhaust gas using ammonia as a reducing agent;
A cylindrical shape is disposed in the spray chamber of the casing, with one end directed toward the upstream end surface of the casing and spaced apart from the upstream end surface to form a gap, and the other end is expanded into a trumpet shape. A mixing pipe that opens into the catalyst housing chamber through a partition wall, introduces exhaust gas flowing into the spray chamber from the inlet pipe into the inside through the gap, and guides the exhaust gas to the catalyst housing chamber side;
Urea that is fixed to the upstream end face outside the casing, is located in the mixing pipe with the nozzle facing the spray chamber, and injects urea water from the nozzle substantially along the axis in the mixing pipe In an exhaust emission control device for an engine equipped with a water injector,
The exhaust gas purifier for an engine according to claim 1, wherein the urea water injector is disposed closer to the center of the upstream end face than the connection portion of the inlet pipe at the upstream end face of the casing.

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