JP6724750B2 - Selective reduction catalyst system - Google Patents

Description

The present invention relates to a selective reduction catalyst system including a catalyst that removes nitrogen oxides (NOx) contained in engine exhaust.

BACKGROUND ART Conventionally, as an exhaust gas purification system for reducing NOx in engine exhaust, a selective reduction catalyst system provided with a reducing agent-added selective reduction catalyst (Selective Catalytic Reduction, hereinafter referred to as “catalyst”) is known. .. That is, an injector for injecting a reducing agent (for example, urea water) is provided on the exhaust gas upstream side of the catalyst, and NOx is reduced to nitrogen on the catalyst by using ammonia generated by hydrolysis of urea. In this selective reduction catalyst system, it is desirable that the concentration of ammonia gas be uniform before the catalyst. For this reason, an exhaust gas purification system has been proposed in which a stirring structure such as a mixer or a collision plate is provided in the exhaust pipe so as to make the reducing agent (ammonia gas concentration) uniform.

JP, 2011-58478, A

However, if a stirring structure such as a mixer is added to the exhaust pipe, the exhaust flow passage is narrowed, so that the pressure loss increases, which may affect the output of the engine.
The present invention has been devised in view of such problems, and an object thereof is to provide a selective reduction catalyst system that improves the dispersibility of a reducing agent without using a stirring structure. It is to be noted that the present invention is not limited to these objectives, and it is also possible to achieve operational effects that are obtained by the respective configurations shown in the modes for carrying out the invention described later and that cannot be obtained by conventional techniques. Is.

(1) The selective reduction catalyst system disclosed herein is installed in an exhaust pipe of an engine, and a catalyst for reducing nitrogen oxides in exhaust gas of the engine to nitrogen by a reducing agent; and the reducing agent in the exhaust pipe. And a plurality of injectors for injecting. The exhaust pipe has a first curved portion that is curvedly formed on the exhaust upstream side of the catalyst, and a second curved portion that is curved and formed in a direction opposite to the first curved portion immediately downstream of the first curved portion. It is S-shaped with a portion . Further, the plurality of injectors are arranged so that the injected reducing agent collides with each other at a position immediately downstream of the first bending portion and on an extension of a curve inner side region of the first bending portion , wherein the reducing agent impinges position, Ru curve outer region der of the second curved portion.

(2) two of the injector, relative to a virtual plane which divides the first curved portion in the left and right through the center axis of the exhaust pipe, it is preferably disposed plane-symmetrically.

( 3 ) In this case, it is preferable that the third injector is arranged between the two injectors.
( 4 ) It is preferable that the injector has one injection hole and injects the reducing agent in a beam shape.

According to the disclosed selective reduction catalyst system, the reducing agents injected from the injectors are made to collide with each other at a position where the flow velocity of exhaust gas is low, so that the dispersibility of the reducing agents is improved without using a stirring structure such as a mixer. be able to.

It is a schematic diagram of an engine provided with a selective reduction catalyst system concerning an embodiment. It is a typical perspective view which shows the principal part of the selective reduction catalyst system of FIG. FIG. 3 is a partially enlarged side view of FIG. 2. 4A is a top view of FIG. 3, and FIG. 4B is a cross-sectional view taken along the line BB of FIG. 4A. It is a partially expanded side view of the selective reduction catalyst system which concerns on a modification. FIG. 6 is a top view of FIG. 5.

A selective reduction catalyst system as an embodiment will be described with reference to the drawings. The embodiments described below are merely examples, and are not intended to exclude various modifications and application of techniques that are not explicitly described in the following embodiments. Each configuration of the embodiment can be variously modified and implemented without departing from the spirit thereof. In addition, they can be selected or combined as needed.

[1. overall structure]
The selective reduction catalyst system 10 of this embodiment is applied to the engine 1 shown in FIG. The engine 1 is, for example, a diesel engine that uses light oil as a fuel, and is mounted on a vehicle (not shown). The engine 1 has, for example, an exhaust gas recirculation system (not shown) that recirculates a part of the exhaust gas to the intake side, and a turbocharger 4 that is arranged across the intake passage 2 and the exhaust passage 3. Note that FIG. 1 illustrates one of a plurality of cylinders provided in the engine 1.

A pre-stage exhaust gas purification system 5 and a selective reduction catalyst system 10 are provided downstream of the turbine 4A in the exhaust passage 3 of the engine 1 as a device for purifying the exhaust gas. The pre-stage purification system 5 is provided with an oxidation catalyst 5A and a filter 5B. The oxidation catalyst 5A oxidizes nitrogen oxide (NO) in the exhaust gas to generate nitrogen dioxide (NO ₂ ) and supplies the nitrogen dioxide (NO ₂ ) to the filter 5B on the downstream side. The oxidation catalyst 5A also functions to oxidize the unburned fuel (HC) in the exhaust gas to generate heat of oxidation and raise the exhaust gas temperature.

The filter 5B is a porous body having both a function of collecting particulate matter (PM) in the exhaust gas and a function of oxidizing and removing the collected PM. The PM contained in the exhaust gas is collected by the filter 5B, and is incinerated under a predetermined temperature condition by using, for example, NO ₂ produced by the oxidation catalyst 5A as an oxidant. As a result, the PM accumulated in the filter 5B is removed, and the filter 5B is regenerated and purified.

The selective reduction catalyst system 10 is provided with a selective reduction catalyst 11 (hereinafter referred to as “catalyst 11”) that reduces NOx in exhaust gas to nitrogen with a reducing agent, and an injector 12 that supplies the reducing agent to the catalyst 11. .. The catalyst 11 of the present embodiment is a urea addition type NOx selective reduction catalyst. That is, the catalyst 11 has a function of hydrolyzing urea supplied from the upstream side of the exhaust flow into ammonia and using this ammonia to reduce NOx in the exhaust.

The injector 12 is an injection valve that is arranged upstream of the catalyst 11 in the exhaust passage 3, supplies urea water into the exhaust passage 3, and injects urea water in a mist form from the injection hole at the tip thereof. The injector 12 of this embodiment has one injection hole and injects urea water in a beam shape. The injection amount and injection timing of the urea water injected from the injector 12 are controlled by an electronic control unit (not shown) based on, for example, the operating state of the engine 1, the running state of the vehicle, the temperature of the catalyst 11, and the like.

[2. Main composition]
Next, the selective reduction catalyst system 10 of the present embodiment will be described in detail with reference to FIGS. The selective reduction catalyst system 10 of the present embodiment makes the urea water (reducing agent) injected from the plurality of injectors 12 collide with each other, thereby effectively dispersing the urea water without using a stirring structure such as a mixer or a collision plate. Let

In the following description, the direction of the selective reduction catalyst system 10 is defined by using the direction in which the engine 1 (selective reduction catalyst system 10) is mounted on the vehicle. That is, the following description will be made assuming that the traveling direction of the vehicle is the front and the opposite is the rear, the left and right are determined with the front as the reference, and the direction of gravity is the lower and the opposite is the upper.

As shown in FIG. 2, the selective reduction catalyst system 10 of the present embodiment includes a catalyst 11 provided in the exhaust passage 3 and two injectors 12 having the same configuration. In the present embodiment, the exhaust passage 3 that connects the upstream exhaust purification system 5 and the catalyst 11 is called “exhaust pipe 30”. The exhaust pipe 30 constitutes a part of the exhaust passage 3. The exhaust pipe 30 of the present embodiment is a pipe having a circular cross-section (transverse cross-section) in a direction orthogonal to the central axis O [see FIG. 4(a)], and has three curved portions 31 to 33 that are curved. Have. Hereinafter, when distinguishing these, they are referred to as a first bending portion 31, a second bending portion 32, and a third bending portion 33 in order from the upstream side.

The selective reduction catalyst system 10 of the present embodiment has a posture in which the exhaust gas flowing through the exhaust pipe 30 flows from the front and the upper side toward the rear and the lower side, and the exhaust gas flowing through the catalyst 11 flows from the front to the rear side. Installed in the vehicle. That is, the exhaust pipe 30 of the present embodiment extends in the front-rear direction, and is arranged such that the upstream side is located above and the downstream side is located below. Further, the catalyst 11 is arranged such that its axial direction is along the front-back direction.

As shown in FIGS. 2 and 3, the exhaust pipe 30 is formed in a corrugated shape in a side view (when viewed from the left and right direction) by the three curved portions 31 to 33. Specifically, the first bending portion 31 is curved downward from the upper side to the rear side, the second bending portion 32 is curved downward from the front side to the upper side, and the third bending portion 33 is bent upward from the rear side. It is convexly curved downward. That is, the second bending portion 32 is curved and formed in the direction opposite to the first bending portion 31 immediately downstream of the first bending portion 31, and the third bending portion 33 has the second bending portion immediately downstream of the second bending portion 32. It is curved and formed in the opposite direction to the portion 32 (in the same direction as the first bending portion 31). When focusing on the first bending portion 31 and the second bending portion 32, the exhaust pipe 30 in this portion has an S shape in a side view.

In the two injectors 12, the injected urea water has a position immediately downstream of the first bending portion 31 and on a position on the extension of the curve inner area 31 _IN in the first bending portion 31 (within the area K indicated by a chain double-dashed line in FIG. 3). ) Are arranged to collide with each other. It should be noted that “on extension” means a straight line when the tangent line at the curve end position of the first bending portion 31 (the boundary position with the second bending portion 32 in FIG. 3) is extended to the downstream side.

In the present embodiment, the position and the angle of the injector 12 are set so that the urea waters collide with each other in the curve outside region _32OT of the second bending portion 32. The “curve inside region” and the “curve outside region” mean that, as shown in FIG. 4B, the exhaust pipe 30 is defined by a virtual plane that extends in the left-right direction through the central axis O of the exhaust pipe 30. When divided, it means an area located inside the curve (for example, a curve inside area 32 _IN ) and an area located outside the curve (for example, a curve outside area 32 _OT ).

The reason why the urea water is made to collide in the above-mentioned region K will be described. The exhaust gas that has passed through the upstream exhaust purification system 5 flows downstream in the first curved portion 31 of the exhaust pipe 30 while changing its flow direction. At this time, in the first bending portion 31, the flow velocity of the exhaust gas flowing in the curve outer region 31 _OT is higher than that of the exhaust gas flowing in the curve inner region 31 _IN . The arrows shown by broken lines in FIGS. 2 and 3 are exhaust flows having a high flow velocity.

In other words, in the first curved portion 31, the exhaust gas flow velocity is high in the curve outer region 31 _OT , and the exhaust gas flow velocity is low in the curve inner region 31 _IN . Therefore, when the curve inner region 31 _IN of the first bending portion 31 is extended to the exhaust downstream side, a region K having a low exhaust flow velocity is formed immediately downstream of the first bending portion 31. Then, as shown in FIGS. 4A and 4B, the urea water is injected from the two injectors 12 toward the position P (hereinafter referred to as the “collision position P”) in the low flow velocity region K. , The urea waters can be made to collide with each other without losing the exhaust gas flow (hardly affected by the exhaust gas flow). In addition, the solid thick arrow in FIG. 4A indicates the trajectory of the urea water immediately after the injection, and the broken thin arrow and the trajectory of the urea water dispersed (stirred) after the collision.

That is, by disposing the two injectors 12 so that the urea waters collide with each other in the low flow velocity region K, it becomes possible to stably collide the urea waters with each other. Since the exhaust pipe 30 of the present embodiment has the second curved portion 32 that is curved in the opposite direction immediately downstream of the first curved portion 31, the low flow velocity region K has the second curved portion 32. It is formed in the curve outer region 32 _OT . Therefore, the two injectors 12 are arranged so as to cause the urea water to collide with each other at the collision position P in the curve outer region 32 _OT of the second bending portion 32.

In the selective reduction catalyst system 10 of the present embodiment, as shown in FIG. 4A, the two injectors 12 are virtual planes in which the first curved portion 31 passes through the central axis O of the exhaust pipe 30 and spreads in the vertical direction. They are arranged symmetrically with respect to (a virtual plane that divides the exhaust pipe 30 into left and right). Further, in the selective reduction catalyst system 10 of the present embodiment, the mounting seat surface 34 for mounting the injector 12 is formed on the outer peripheral surface of the second curved portion 32 on the outer side of the curve. Further, as shown in FIG. 4B, the collision position P is set vertically above the central axis O and closer to the outer peripheral surface in the curve outer region 32 _OT of the second bending portion 32.

[3. effect]
(1) In the selective reduction catalyst system 10 described above, the exhaust pipe 30 has the first curved portion 31 that is curvedly formed on the upstream side of the catalyst 11, and the two injectors 12 mutually inject the injected urea water. It is arranged to cause a collision. Furthermore, the collision position P of the urea water is set immediately downstream of the first bending portion 31 and on the extension of the curve inside region 31 _IN of the first bending portion 31. Since the flow velocity of the exhaust gas is low at the collision position P, the dispersibility of the urea water can be improved by causing the urea water injected from the injector 12 to collide with each other at this position P.

As a result, the concentration of ammonia gas can be made uniform, and the NOx reduction performance of the catalyst 11 can be improved. Further, the selective reduction catalyst system 10 described above does not require a stirring structure such as a mixer, so that pressure loss can be reduced. Furthermore, since a space for arranging a mixer or the like is not necessary, the distance between the injector 12 and the catalyst 11 can be reduced, and the selective reduction catalyst system 10 can be made compact.

(2) In the selective reduction catalyst system 10 described above, since the exhaust pipe 30 is formed in the S-shape by the first curved portion 31 and the second curved portion 32, the curve outer region 32 _OT of the second curved portion 32. A region K having a low flow velocity is formed at. Therefore, by setting the position P at which the urea water collides with the curve outer area 32 _OT of the second bending portion 32, the urea water injected from the injector 12 can be stably collided, and the urea water dispersibility can be improved. Can be improved.

(3) According to the selective reduction catalyst system 10 described above, since the two injectors 12 are arranged in plane symmetry, the urea water can be made to collide more easily, and the dispersibility of the urea water can be further improved. You can
(4) Further, since the injector 12 has one injection hole and injects the urea water in the form of a beam, the urea water is vigorously injected without losing the exhaust flow (hard to be affected by the exhaust flow). can do. As a result, the urea water injected from the injector 12 can be made to collide more stably, and the dispersibility of the urea water can be further improved.

[4. Other]
Regardless of the embodiment described above, various modifications can be implemented without departing from the spirit thereof. The configurations of the present embodiment can be selected as needed or may be appropriately combined.
In the above-described embodiment, the configuration in which the selective reduction catalyst system 10 has two injectors 12 is illustrated, but the number of injectors 12 is not limited to this. For example, the selective reduction catalyst system 10 may include the third injector 13 having the same configuration as the two injectors 12 described above.

In the example shown in FIGS. 5 and 6, the third injector 13 is arranged between the two injectors 12 described above. That is, the third injector 13 is attached to the mounting seat surface 34 formed on the outer peripheral surface of the second curved portion 32 outside the curve, and the injected urea water is the urea water injected from the two injectors 12 described above. The angle and position are set so as to collide with each other at the collision position P.

By disposing the injectors 12 and 13 so that the urea water injected from the three injectors 12 and 13 collides at the collision position P, the dispersibility of the urea water can be further improved. The number of injectors may be four or more. Further, the plurality of injectors may not have the same configuration, and the number of injection holes and the aspect of urea water injection are not limited to those described above.

Further, in the above-described embodiment, the two injectors 12 are arranged symmetrically, but the injectors 12 do not have to be symmetrically arranged. It suffices that at least the collision position P at which the reducing agent collides is set within the region S, and the plurality of injectors 12 may be attached to the first bending portion 31 or may be arranged deviated in the exhaust flow direction. May be. Further, the collision position P may be just downstream of the first bending portion 31 and on the extension of the curve inner region 31 _IN of the first bending portion 31, and the central axis O in the curve outer region 32 _OT of the second bending portion 32. It may be set closer.

In the above-described embodiment, the case where the exhaust pipe 30 has the three curved portions 31 to 33 is illustrated, but the exhaust pipe may have at least the first curved portion 31. Moreover, although urea water was mentioned as an example of the reducing agent in the above-described embodiment, the reducing agent is not limited to urea water.
The exhaust gas purification system provided in the exhaust passage 3 is not limited to the one described above, and may be any system that has at least a selective reduction catalyst system.

1 Engine 3 Exhaust Passage 10 Selective Reduction Catalyst System 11 Catalyst (Selective Reduction Catalyst)
12 injector 13 third injector 30 exhaust pipe 31 first curved portion 31 _OT curve outer region 31 _IN curve inner region 32 second curved portion 32 _OT curve outer region 32 _IN curve inner region 33 third curved portion 34 mounting seat surface K Low flow velocity region O Exhaust pipe central axis P Collision position

Claims (4)

A catalyst that is interposed in the exhaust pipe of the engine and reduces nitrogen oxides in the exhaust gas of the engine to nitrogen with a reducing agent;
A plurality of injectors for injecting the reducing agent into the exhaust pipe,
Wherein the exhaust pipe, as well as have a first curved portion which is curved in the exhaust upstream of the catalyst, the second which is curved in the first curved portion and a reverse direction immediately downstream of the first curved portion S-shaped with a curved portion ,
The plurality of injectors are arranged such that the injected reducing agent collides with each other at a position immediately downstream of the first bending portion and on an extension of a curve inner region in the first bending portion ,
The selective reduction catalyst system is characterized in that the position where the reducing agent collides is an area outside the curve of the second curved portion . Two of the injector, relative to a virtual plane which divides the first curved portion in the left and right through the center axis of the exhaust pipe, characterized in that it is arranged in plane symmetry, placing claim 1 Symbol Selective reduction catalyst system. The selective reduction catalyst system according to claim 2 , wherein the third injector is arranged between the two injectors. The injector has a single nozzle hole, characterized by injecting the reducing agent into a beam, selective catalytic reduction system as claimed in any one of claims 1-3.

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