WO2012172944A1

WO2012172944A1 - Exhaust gas after-treatment device

Info

Publication number: WO2012172944A1
Application number: PCT/JP2012/063193
Authority: WO
Inventors: 真範八田; 笹谷　亨; 昭一前田; 信太郎川崎; 敦城所; 作太郎星
Original assignee: 株式会社豊田自動織機
Priority date: 2011-06-15
Filing date: 2012-05-23
Publication date: 2012-12-20

Abstract

Upstream of an SCR catalyst (4) in an exhaust gas pipe (2) are provided a dispersion member (21) for dispersing urea water injected from an injection nozzle (5) in the exhaust gas pipe (2), and a mixer (31) for mixing the dispersed urea water into the exhaust gas. The dispersion member (21), a flat member arranged in a position facing the injection nozzle (5), extends parallel to the flow direction of the exhaust gas. Meanwhile, the mixer (31), a substantially disk-shaped member through which exhaust gas and urea water can flow, and is disposed perpendicular to the flow direction of the exhaust gas. The dispersion member (21) and the mixer (31) are adjacent, and urea water impinging on and dispersed by the dispersion member (21) is immediately supplied to the mixer (31).

Description

Exhaust gas aftertreatment device

The present invention relates to an exhaust gas aftertreatment device, and more particularly to a configuration for purifying exhaust gas from a diesel engine using a reducing agent.

An example of an exhaust gas aftertreatment device that purifies exhaust gas of a diesel engine is a urea selective reduction system (urea SCR system) that purifies nitrogen oxide (NOx) in exhaust gas using urea water as a reducing agent. For example, as described in Patent Document 1, the urea SCR system includes a reduction catalyst provided in an exhaust pipe, and a reducing agent injection device that injects urea water into the exhaust pipe upstream of the reduction catalyst. . The reduction catalyst reacts ammonia (NH ₃ ) generated from urea water injected into the exhaust pipe with NOx contained in the exhaust gas, and reduces it to harmless nitrogen (N ₂ ) and water (H ₂ O). To do. In order to perform this reduction efficiently, it is necessary to supply urea water with a uniform distribution to the reduction catalyst.

Also, the urea SCR system described in Patent Document 1 includes a mixer unit for mixing exhaust gas and urea water to make the distribution state of urea water uniform. The mixer unit is a plate-like member provided between the reducing agent injection device and the reduction catalyst, and includes a plurality of passages through which exhaust gas and urea water flow, and a plurality of passages formed on the outlet side of each passage. With fins. The reducing agent injection device injects urea water toward the mixer plate, and the urea water atomized by colliding with the mixer plate is dispersed in the exhaust pipe. The dispersed urea water passes through each passage of the mixer plate together with the exhaust gas, and then is mixed with the exhaust gas by the turbulent flow generated by each fin and then supplied to the reduction catalyst.

JP 2009-24654 A

In order to uniformly disperse urea water with a single mixer plate described in Patent Document 1, it is necessary to make urea water injected from the reducing agent injection device collide with the entire surface of the mixer unit. Here, the reducing agent injection device normally injects urea water in a conical shape. Therefore, in order for the urea water to collide with the entire surface of the mixer unit, it is necessary to provide a distance between the reducing agent injection device and the mixer unit so that the injection range of the urea water is sufficiently widened. That is, the urea SCR system described in Patent Document 1 has a problem that the exhaust pipe on the upstream side of the mixer unit cannot be shortened and it is difficult to downsize the entire apparatus.

The present invention has been made to solve such problems, and provides an exhaust gas after-treatment device that achieves downsizing while uniformly dispersing the reducing agent in the exhaust gas. Objective.

An exhaust gas aftertreatment device according to the present invention includes an exhaust pipe through which exhaust gas discharged from an internal combustion engine flows, a reducing agent supply device that injects a reducing agent into the exhaust pipe, and a downstream side of the reducing agent supply device. A reduction catalyst that purifies the exhaust gas by reacting the exhaust gas and the reducing agent, and inside the exhaust pipe, a plate-like dispersion member disposed at a portion facing the reducing agent supply means; A mixing means is provided between the dispersion member and the reduction catalyst, and a mixing means for mixing the exhaust gas and the reducing agent is provided. The dispersion member and the mixing means are arranged adjacent to each other.

Here, the term “adjacent” includes the case where the dispersing member and the mixing means are integrally formed and the case where they are arranged separately as separate parts. The range of the distance at which the dispersing member and the mixing means are separated is such that the flow of the exhaust gas does not substantially change between these members. For example, the distance is separated by a distance of 10% or less with respect to the diameter of the exhaust pipe. .

The reducing agent supply device injects the reducing agent in a direction perpendicular to the direction in which the exhaust gas flows through the exhaust pipe. Here, the vertical is not necessarily strictly vertical as long as it is less susceptible to changes in the flow of exhaust gas. As the angle deviates from the vertical, the vertical component of the penetrating force of the injected reducing agent tends to weaken. Therefore, the range of about −5 degrees to 5 degrees, which is a range in which the vertical component is less affected by the flow of exhaust gas, can be set.

Also, the dispersion member can be extended in parallel to the direction in which the exhaust gas flows through the exhaust pipe. Here, the term “parallel” does not need to be strictly parallel and includes an angle at which pressure loss can be ignored.

Note that the dispersion member can be a single member. Further, the dispersion member can have a width capable of contacting the inner peripheral surface of the exhaust pipe.

The mixing means has a plurality of first fins and a plurality of second fins which are arranged so as to be parallel to each other and which incline the flow of exhaust gas passing therethrough at a predetermined angle which is opposite to each other. The mixing means and the reduction catalyst are connected to each other through a straight piping portion that extends in a straight line and a tapered piping portion that is formed so as to widen from the upstream side to the downstream side. When the inner diameter of the piping part is D and the length of the straight piping part is L,
D / 2 × cotα ≦ L ≦ 3/2 × D × cotα
Meet.

In the mixing member, a row in which a plurality of first fins are arranged and a row in which a plurality of second fins are arranged are alternately arranged one by one. Moreover, the straight piping part can be made into a cylindrical shape. Furthermore, the gradient at which the tapered pipe portion spreads can be made smaller than the angle α, and the angle α can be set to 45 °.

According to the present invention, the exhaust gas aftertreatment device can be miniaturized while the reducing agent is uniformly dispersed in the exhaust gas.

It is the schematic which shows the structure of the exhaust-gas aftertreatment apparatus which concerns on Embodiment 1 of this invention. 1 is a cross-sectional side view schematically showing a configuration of an exhaust gas aftertreatment device according to Embodiment 1. FIG. FIG. 2 is a perspective view schematically showing a dispersion member and mixing means in the exhaust gas aftertreatment device according to Embodiment 1, wherein (a) is a perspective view seen from the downstream side in the exhaust gas flow direction, and (b) is an upstream side. It is the perspective view seen from the side. FIG. 4 is a cross-sectional view taken along IV-IV in FIG. 2. It is a cross-sectional side view which shows roughly the structure of the exhaust-gas aftertreatment apparatus which concerns on Embodiment 2 of this invention. It is a cross-sectional side view which shows roughly the structure of the exhaust-gas aftertreatment apparatus which concerns on Embodiment 3 of this invention. FIG. 6 is a schematic diagram for explaining the flow of exhaust gas generated inside a straight piping section in an exhaust gas aftertreatment device according to Embodiment 3. FIG. 9 is a schematic diagram for explaining the flow of exhaust gas generated inside a straight pipe portion and a taper pipe portion in an exhaust gas aftertreatment device according to Embodiment 3. 6 is a graph showing the transition of the CV value when the length of the straight pipe portion is changed with respect to the exhaust gas aftertreatment device according to Embodiment 3. FIG. 6 is a cross-sectional view showing a modification of the exhaust gas aftertreatment device according to Embodiment 1. FIG. 6 is a cross-sectional view showing a modification of the exhaust gas aftertreatment device according to Embodiment 1.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 schematically shows the configuration of an exhaust system of a diesel engine provided with the exhaust gas aftertreatment device according to the first embodiment. An exhaust pipe 2 is connected to the diesel engine 1 which is an internal combustion engine, and the exhaust gas discharged from the diesel engine 1 into the exhaust pipe 2 is in the direction indicated by the arrow A with the diesel engine 1 side as the upstream side. Circulate. An oxidation catalyst 3 that oxidizes carbon monoxide (CO), hydrocarbon (HC), and the like contained in the exhaust gas is provided in the middle of the exhaust pipe 2. An SCR catalyst 4 that is a reduction catalyst for purifying nitrogen oxide (NOx) contained in the exhaust gas is provided on the downstream side of the oxidation catalyst 3.

The SCR catalyst 4 is a catalyst that purifies NOx by reacting ammonia (NH ₃ ) generated from urea water, which is a reducing agent added to the exhaust gas, and the exhaust gas. Between the oxidation catalyst 3 and the SCR catalyst 4, an injection nozzle 5 is provided as a reducing agent supply device that injects urea water into the exhaust pipe 2. A urea water tank 6 that stores urea water therein and a urea water addition system 7 that supplies urea water in the urea water tank 6 to the injection nozzle 5 are connected to the injection nozzle 5 via a connection pipe 8. ing. The urea water addition system 7 is electrically connected to an ECU 9 that controls the operation of the diesel engine 1 and the exhaust gas aftertreatment device.

Further, a NOx sensor 11 and a NOx sensor 12 for detecting the amount of NOx contained in the exhaust gas are provided on the upstream side and the downstream side of the SCR catalyst 4, and these NOx sensors are electrically connected to the ECU 9. ing. The ECU 9 determines the injection amount and the injection timing of the urea water from the injection nozzle 5 based on the NOx amount detected by the

NOx sensors

11 and 12, and outputs a signal based on the injection amount to the urea water addition system 7 to thereby inject the injection nozzle. 5 controls the injection of urea water.

A filter 13 for collecting particulate matter (PM) contained in the exhaust gas is provided on the downstream side of the SCR catalyst 4. In addition, on the downstream side of the filter 13, for example, when the amount of ammonia is excessive with respect to the amount of NOx contained in the exhaust gas, the ammonia that has passed through the SCR catalyst 4 without being reacted is removed. A slip catalyst 14 is provided. A muffler (not shown) is connected to the downstream side of the slip catalyst 14, and the exhaust gas that has passed through the slip catalyst 14 is released into the atmosphere after the exhaust noise is reduced inside the muffler.

In the exhaust system of the diesel engine 1 configured as described above, urea water injected from the injection nozzle 5 is atomized and dispersed in the exhaust pipe 2 on the upstream side of the SCR catalyst 4 inside the exhaust pipe 2. There are provided a dispersion member 21 for mixing and a mixer 31 which is a mixing means for mixing the urea water dispersed by the dispersion member 21 into the exhaust gas.
Hereinafter, the configuration of the dispersion member 21 and the mixer 31 will be described in detail with reference to FIGS. For convenience of the following description, the vertical direction in the exhaust gas aftertreatment device is defined by the arrows shown in FIG.

As shown in FIG. 2, the dispersion member 21 is a flat plate-like member disposed at a portion facing the injection nozzle 5, and is provided so as to extend in parallel to the exhaust gas flow direction indicated by the arrow A. ing. The length of the dispersion member 21 in the flow direction is a length in which all urea water injected from the injection nozzle 5 collides with the dispersion member 21. On the other hand, the mixer 31 is a substantially disk-shaped member disposed adjacent to the downstream end of the dispersion member 21, and is provided so as to be perpendicular to the flow direction of the exhaust gas. In the part where the mixer 31 is located, the exhaust pipe 2 is divided into an upstream pipe 2a and a downstream pipe 2b, and the outer peripheral portion of the mixer 31 is held between them. The injection nozzle 5 injects urea water F indicated by a one-dot chain line in a direction substantially perpendicular to the flow direction of the exhaust gas, that is, in a direction substantially perpendicular to the dispersion member 21. F is directly collided with the dispersion member 21.

As shown in FIG. 3 (a), a plurality of first fins 32a and a plurality of first fins 32a and a plurality of first fins 32a are bent at portions located inside the exhaust pipe 2 in the mixer 31 by bending a trapezoidal cut that is partially connected. Two fins 32b are formed. The mixer 31 has a plurality of openings 33 formed by bending these

fins

32 a and 32 b, and exhaust gas flowing from the upstream side of the mixer 31 passes through these openings 33. Circulate downstream. Further, the mixer 31 according to the first embodiment has a rectangular pipe member 35 (see FIG. 3B) disposed on the upstream side corresponding to each opening 33, and the dispersion member 21. The exhaust gas that has passed through passes through the opening 33 as it is through the rectangular pipe member 35.

The first fin 32a and the second fin 32b are bent in directions opposite to each other, and the first fin 32a is bent so that the front end portion thereof faces obliquely upward. On the other hand, the 2nd fin 32b is bent so that the front-end | tip part may face diagonally downward. The

fins

32a and 32b are parallel to each other in a row in which a plurality of first fins 32a are arranged in the vertical direction and a row in which the plurality of second fins 32b are arranged in the vertical direction. It is arranged alternately one row at a time. That is, the mixer 31 in the present embodiment is a device that mixes the fluid that passes by changing the flow of the exhaust gas upward and downward. Further, as shown in FIG. 3B, a pair of support portions 34 projecting to the upstream side are joined to the upstream surface 31 a of the mixer 31, and both sides of the dispersion member 21 are joined by these support portions 34. The part is supported.

As shown in FIG. 4, the dispersion member 21 is disposed so as to pass through the central portion in the exhaust pipe 2 and has a width W that is substantially the same as the inner diameter of the exhaust pipe 2. Accordingly, the portion where the dispersion member 21 is disposed in the exhaust pipe 2 is in a state of being divided into a region R1 on the upper side of the dispersion member 21, that is, the region R2 on the injection nozzle 5 side, and a region R2 on the lower side. The urea water F injected from the injection nozzle 5 is dispersed in the region R1 without flowing into the region R2. Part of the exhaust gas that has passed through the oxidation catalyst 3 (see FIG. 1) flows through the region R1, and the remaining part flows through the region R2. The NOx sensor 11 provided on the upstream side of the SCR catalyst 4 (see FIG. 1) is provided so as to be positioned below the dispersion member 21 and is separated from the injection nozzle 5 by the dispersion member 21. . Moreover, as shown in FIG. 3, the upper side and the lower side divided by the dispersion member 21 correspond to the upper side and the lower side where the

fins

32a and 32b of the mixer 31 change the flow of the exhaust gas.

Here, as described above, the dispersion member 21 is disposed at a portion facing the injection nozzle 5, and the urea water F injected from the injection nozzle 5 directly collides with the dispersion member 21. The urea water thus dispersed is dispersed in the exhaust gas flowing through the region R1. Further, since the dispersion member 21 is disposed adjacent to the mixer 31, the urea water dispersed in the exhaust gas by colliding with the dispersion member 21 is immediately supplied to the mixer 31 by the flow of the exhaust gas. Is done. On the other hand, if it is intended to disperse urea water in the exhaust gas without using the dispersion member 21, for example, urea water is generally injected obliquely toward the mixer 31. In this case, in order to make the distribution of the urea water in the exhaust gas uniform, it is necessary to make the urea water collide with the entire surface of the mixer 31. Accordingly, it is necessary to provide a distance between the injection nozzle 5 and the mixer 31 so that the injection range of the urea water extends over the entire surface of the mixer 31.

That is, the exhaust gas aftertreatment device according to the present invention disperses urea water using the dispersion member 21 disposed at a portion facing the injection nozzle 5, and disposes the dispersion member 21 and the mixer 31 adjacent to each other. Thus, the distance between the injection nozzle 5 and the mixer 31 can be shortened. Accordingly, the distance between the oxidation catalyst 3 (see FIG. 1) and the SCR catalyst 4 is also shortened, so that the exhaust gas aftertreatment device can be miniaturized to improve the mountability on the vehicle. Further, since the apparatus is downsized, the temperature drop until the exhaust gas reaches the SCR catalyst 4 is suppressed, so that the NOx purification by the SCR catalyst 4 can be performed efficiently.

Next, the operation of the exhaust gas aftertreatment device according to Embodiment 1 of the present invention will be described.
As shown in FIG. 1, when the operation of the diesel engine 1 is started, the exhaust gas discharged into the exhaust pipe 2 flows in the direction indicated by the arrow A and passes through the oxidation catalyst 3. During this passage, carbon monoxide (CO), hydrocarbon (HC), etc. contained in the exhaust gas are oxidized by the oxidation catalyst 3 and at the same time, a part of nitrogen monoxide (NO) is nitrogen dioxide (NO ₂ ). It is oxidized to. Further, when the operation of the diesel engine 1 is started, the ECU 9 outputs a signal to the urea water addition system 7 and starts injection of urea water by the injection nozzle 5.

As shown in FIG. 2, part of the exhaust gas that has passed through the oxidation catalyst 3 flows through the region R1 partitioned by the dispersion member 21 on the injection nozzle 5 side (see arrow A1), and the remaining part is on the lower side. Is distributed (see arrow A2). The urea water F injected from the injection nozzle 5 is added to the exhaust gas flowing through the region R1. Since the dispersion member 21 is provided at a portion facing the injection nozzle 5, the urea water F injected from the injection nozzle 5 directly collides with the dispersion member 21, and the urea water atomized by colliding with the dispersion member 21 is formed. Dispersed in the exhaust gas flowing through the region R1. Further, since the dispersing member 21 and the mixer 31 are disposed adjacent to each other, the urea water dispersed in the region R1 is immediately supplied to the mixer 31 by the flow of the exhaust gas. The urea water dispersed in the exhaust gas is hydrolyzed by the heat of the exhaust gas in the process of flowing downstream, thereby generating ammonia. In particular, since the dispersion member 21 is disposed so as to pass through the central portion in the exhaust pipe 2, it is efficiently heated by the heat of the exhaust gas, and further promotes hydrolysis of urea water.

On the other hand, the exhaust gas flowing through the region R2 side is supplied to the mixer 31 as it is. The exhaust gas and urea water flowing from the region R1 side and the exhaust gas flowing from the region R2 side are mixed by the turbulent flow generated when they pass through the

fins

32a and 32b of the mixer 31, thereby The urea water is uniformly mixed with the exhaust gas flowing through the exhaust pipe 2. When the exhaust gas and ammonia that have passed through the mixer 31 are supplied to the SCR catalyst 4 in this way, the SCR catalyst 4 reacts with the ammonia and the exhaust gas to convert NOx contained in the exhaust gas into harmless nitrogen (N ₂ ). Reduce to water (H ₂ O). Since the dispersion member 21 is a flat plate member and is provided so as to be parallel to the exhaust gas flow direction, NOx purification can be performed without increasing the exhaust gas pressure loss. Can do.

Here, since the injection nozzle 5 injects urea water in a direction perpendicular to the direction in which the exhaust gas flows (in this embodiment, perpendicular to the dispersion member 21), urea water is injected into the exhaust gas. When water is dispersed, it is not easily affected by the flow rate of the exhaust gas. That is, as described above, when urea water is injected obliquely and the urea water is dispersed by the mixer 31 without using the dispersion member 21, the range in which the injected urea water collides with the mixer 31 has a high exhaust gas flow rate. Since it becomes narrow as it becomes, the range where urea water is disperse | distributed with it is also narrowed. On the other hand, when the urea water is injected perpendicularly to the direction in which the exhaust gas circulates, the injected urea water collides with the dispersion member 21 even when the flow rate of the exhaust gas increases, so that the urea water is reliably dispersed. It is possible. In other words, even if the flow rate of the exhaust gas changes, the dispersion characteristics hardly change.

Further, the dispersion member 21 has a width W (see FIG. 4) that is substantially the same as the inner diameter of the exhaust pipe 2, and divides the interior of the exhaust pipe 2 into a region R1 and a region R2. That is, since the urea water injected from the injection nozzle 5 is not supplied to the region R2 side, the amount of urea water adhering to the inner peripheral surface of the exhaust pipe 2 is reduced. Here, the exhaust pipe 2 is heated by the exhaust gas flowing through the inside thereof. However, since the outer peripheral surface of the exhaust pipe 2 is cooled by the outside air, for example, the exhaust immediately after the diesel engine 1 (see FIG. 1) is started. The temperature of the pipe 2 is lower than the temperature of the exhaust gas. If urea water adheres to the inner peripheral surface of the exhaust pipe 2 in such a state, hydrolysis does not occur, the water of the urea water evaporates and urea remains, and the remaining urea accumulates on the inner peripheral surface of the exhaust pipe. Sometimes. That is, since the accumulated urea does not reach the SCR catalyst 4, the amount of ammonia that is originally required is not supplied to the SCR catalyst 4, and it is necessary to increase the amount of urea water added.

However, in the exhaust gas aftertreatment device according to the present invention, the inside of the exhaust pipe 2 is partitioned into the region R1 and the region R2 by the dispersing member 21, and the amount of urea water adhering to the inner peripheral surface of the exhaust pipe 2 is reduced. Thus, most of the injected urea water can be supplied to the SCR catalyst. In addition, since the dispersion member 21 is disposed so as to pass through the central portion of the exhaust pipe 2, that is, a portion that becomes high in temperature, the dispersion member 21 is quickly heated without being influenced by the temperature of the exhaust pipe 2. Further, since the dispersion member 21 is shorter than the exhaust pipe 2 in the flow direction of the exhaust gas and has a small heat capacity, it is easily heated by the exhaust gas. Therefore, the generation of ammonia from the urea water adhering to the dispersion member 21 is not hindered due to the low temperature of the exhaust pipe 2.

Further, the NOx sensor 11 provided on the upstream side of the SCR catalyst 4 usually contains fine ceramics such as zirconia as a material. Further, since the NOx sensor 11 is exposed to the exhaust gas flowing inside the exhaust pipe 2, it operates at a high temperature of, for example, 600 ° C to 1000 ° C. When urea water adheres to the NOx sensor 11 operating at such a high temperature, a sudden temperature change occurs, so-called thermal shock is applied, and breakage such as cracking may occur.

In order to prevent such damage, the NOx sensor 11 is generally provided at a predetermined distance on the upstream side of the injection nozzle 5 so that the urea water F does not adhere. However, since the upstream NOx sensor 11 in the present invention is separated from the injection nozzle 5 by the dispersion member 21, the upstream NOx sensor 11 is not damaged due to adhesion of the urea water F, and is disposed in the vicinity of the injection nozzle 5. It is possible to do. Therefore, the distance between the oxidation catalyst 3 (see FIG. 1) and the SCR catalyst 4 can be further shortened to reduce the size of the apparatus.

Furthermore, the upper side and the lower side divided by the dispersing member 21 correspond to the upper side and the lower side where the first fin 32a and the second fin 32b of the mixer 31 change the flow of the exhaust gas. Accordingly, urea water or hydrolyzed ammonia that has collided with the dispersion member 21 disposed so as to pass through the central portion in the exhaust pipe 2 is dispersed from the mixer 31 upward and downward to be dispersed throughout. .

Referring back to FIG. 1, the exhaust gas that has passed through the SCR catalyst 4 passes through the filter 13, and particulate matter contained in the exhaust gas is removed at that time. If the exhaust gas that has passed through the filter 13 contains excess ammonia, the excess ammonia is removed by the slip catalyst 14. The exhaust gas that has passed through the slip catalyst 14 is reduced in noise inside a muffler (not shown) and released into the atmosphere. The

NOx sensors

11 and 12 detect the NOx concentration on the upstream side and the downstream side of the SCR catalyst 4 as needed, and the ECU 9 uses the injection nozzle 5 based on the NOx concentration detected by these NOx sensors. The injection amount of the urea water F is controlled.

As described above, since the plate-like dispersion member 21 is provided at the portion facing the injection nozzle 5, the urea water injected from the injection nozzle 5 directly collides with the dispersion member 21. The reducing agent that collides with the dispersing member 21 and atomized is dispersed in the exhaust pipe 2, mixed with the exhaust gas by the mixer 31, and then supplied to the SCR catalyst 4. Since the urea water is dispersed by the dispersing member 21, the distance between the injection nozzle 5 and the mixer 31 in order to widen the injection range of the urea water as in the case of injecting the urea water toward the mixer 31. There is no need to take large. Further, since the dispersion member 21 and the mixer 31 are disposed adjacent to each other, it is not necessary to lengthen the exhaust pipe in order to provide the dispersion member 21. Therefore, it is possible to reduce the size of the exhaust gas aftertreatment device while uniformly dispersing urea water in the exhaust gas.

Further, since the injection nozzle 5 injects urea water in a direction perpendicular to the direction in which the exhaust gas flows, the influence of the flow of exhaust gas until the injected urea water collides with the dispersion member 21. It becomes difficult to receive. Therefore, the urea water can be reliably collided with the dispersion member 21 and efficiently dispersed in the exhaust gas.

Further, since the dispersion member 21 is provided so as to extend in parallel to the direction in which the exhaust gas flows through the inside of the exhaust pipe 2, it is possible to supply urea water to the mixer 31 without increasing the pressure loss. Become.

Embodiment 2. FIG.
Next, an exhaust gas aftertreatment device according to Embodiment 2 of the present invention will be described.
In the exhaust gas aftertreatment device according to the second embodiment, the exhaust gas aftertreatment device according to the first embodiment includes the single dispersion member 21, whereas the first dispersion member and the plurality of the dispersion members are described below. And a second dispersion member. In each of the embodiments described below, the same reference numerals as those in FIGS. 1 to 4 are the same or similar components, and detailed description thereof will be omitted.

As shown in FIG. 5, five dispersion members 41 a to 41 e each having a flat plate shape are arranged in a state of being arranged in the vertical direction at a portion facing the injection nozzle 5 in the exhaust pipe 2. Yes. Further, a mixer 31 is provided so as to be adjacent to the downstream end portions of the dispersion members 41a to 41e. Of the dispersing members 41a to 41e, the first dispersing member 41a located on the lowermost side is a flat plate-like member similar to the dispersing member 21 in the first embodiment. On the other hand, the four second dispersion members 41b to 41e provided on the upper side of the first dispersion member 41a are flat members in which a plurality of through holes 42 are formed, and urea water injected from the injection nozzle 5 F can be sequentially passed from the upper side to the lower side.

A part of the urea water F injected to the upper surface of the uppermost second dispersion member 41e is dispersed in the exhaust gas by colliding with the second dispersion member 41e, and the remaining part is in the through hole 42. Pass through. Similarly, part of the urea water that has passed through the through hole 42 of the second dispersion member 41e is dispersed in the exhaust gas by colliding with the second dispersion member 41d, and the remaining part is dispersed in the second dispersion member 41c, It passes through 41b sequentially and finally collides with the first dispersion member 41a. Therefore, the urea water F can be widely dispersed in the exhaust pipe 2 by reducing the amount of the urea water F passing through the through holes 42 of the second dispersion members 41b to 41e by, for example, 20%. It is possible. Other configurations are the same as those in the first embodiment.

As described above, even if a plurality of dispersion members are used and the first dispersion member having no through holes and the second dispersion member having the through holes are configured, the urea water that collides with each dispersion member and is dispersed immediately To the mixer 31. Therefore, as in the first embodiment, the exhaust gas aftertreatment device can be reduced in size.

Embodiment 3 FIG.
Next, an exhaust gas aftertreatment device according to Embodiment 3 of the present invention will be described. In the exhaust gas aftertreatment device according to the third embodiment, the dimensional regulations described below are added to the exhaust pipe 2 and the mixer 31 of the exhaust gas aftertreatment device according to the first embodiment.

As shown in FIG. 6, the diameter of the SCR catalyst 4 located on the downstream side of the mixer 31 is larger than the diameter of the downstream piping part 2b, and the downstream piping part 2b and the SCR catalyst 4 are directed from the upstream side to the downstream side. Are connected via a tapered pipe portion 2c formed so as to spread in a tapered shape. That is, the mixer 31 and the SCR catalyst 4 are connected to each other via the downstream pipe portion 2b and the taper pipe portion 2c that extend linearly. Here, the downstream side piping section 2b constitutes a straight piping section of the exhaust gas aftertreatment device according to the third embodiment.

As described in the first embodiment, the bent directions of the first fin 32a and the second fin 32b are opposite to each other, but the angle is a common angle α. That is, the mixer 31 tilts the flow of exhaust gas (see arrow A) before passing through the mixer 31 by an angle α in the vertical direction opposite to each other by the first fin 32a and the second fin 32b. is there.

The angle α at which the first fin 32a and the second fin 32b are bent in the mixer 31, that is, the angle α at which the

fins

32a and 32b incline the flow of the exhaust gas is set to 45 °. Moreover, the internal diameter D of the downstream piping part 2b which connects the mixer 31 and the taper piping part 2c is set to 66 mm. In this way, in the exhaust gas aftertreatment device in which the angle α = 45 ° and the inner diameter D = 66 mm, the length L of the downstream pipe portion 2b is defined in accordance with the angle α and the inner diameter D, and the following ( 1) It is set to satisfy the equation.
D / 2 × cotα ≦ L ≦ 3/2 × D × cotα (1)
That is, when α = 45 ° and the inner diameter D = 66 mm, the range of the length L is 33 (mm) ≦ L ≦ 99 (mm).

When the angle α is 45 °, that is, when cot α = 1 in the above equation (1), the length L of the downstream pipe portion 2b eventually satisfies the following equation (2). Set to
2 / D ≦ L ≦ 3/2 × D (2)
In the exhaust gas aftertreatment device according to Embodiment 3, the length L of the downstream pipe portion 2b is set to 43 mm that satisfies the above equations (1) and (2). Note that the slope β of the taper pipe portion 2c spreading toward the downstream side, that is, the angle β at which the taper pipe portion 2c spreads with respect to the axial direction of the downstream pipe portion 2b is smaller than the angle α = 45 °. Yes. Other configurations are the same as those in the first embodiment.

In the exhaust gas aftertreatment device configured as described above, in order to efficiently reduce NOx by the SCR catalyst 4, it is necessary to supply ammonia to the entire surface of the SCR catalyst 4 in a uniform distribution state. Become. For that purpose, it is necessary to uniformly disperse ammonia in the exhaust gas and to diffuse the exhaust gas in the tapered pipe portion 2c. Here, as shown in FIG. 3 (a), the first fin 32a and the second fin 32b of the mixer 31 are bent in the vertical direction opposite to each other, and the flow of exhaust gas passing therethrough. Tilt up and down. The

fins

32a and 32b are arranged such that a plurality of first fins 32a arranged in the vertical direction and a plurality of second fins 32b arranged in the vertical direction are arranged with each other. They are arranged one by one alternately so as to be parallel.

Therefore, as shown in FIG. 7, the flow of the exhaust gas inclined upward by the row of the first fins 32a inside the downstream piping portion 2b on the downstream side of the mixer 31 (see FIG. 6). (Refer to arrow B1) and the flow of exhaust gas (see arrow B2) tilted downward by the row of the second fins 32b are alternately adjacent to each other. Moreover, since the downstream side piping part 2b is cylindrical, the flow along the circumferential direction of the downstream side piping part 2b (see arrow B3) flows in the exhaust gas that has collided with the inner peripheral surface 2d of the downstream side piping part 2b. Given. That is, out of the exhaust gas flowing through the mixer 31 and flowing into the downstream pipe portion 2b, the exhaust gas that has collided with the inner peripheral surface 2d has a cross section perpendicular to the axial direction of the downstream pipe portion 2b. A circulating flow is provided. As a result, ammonia can be efficiently dispersed in the exhaust gas flowing through the downstream side piping portion 2b.

Also, as shown in FIG. 8, the exhaust gas that has passed through the mixer 31 is given a flow inclined at an angle α in the vertical direction by the first fin 32a and the second fin 32b, as indicated by the arrow C1. In addition, the exhaust gas that has collided with the inner peripheral surface 2d of the downstream pipe portion 2b goes straight along the axial direction of the downstream pipe portion 2b. Here, the timing at which the exhaust gas that has passed through the first fin 32a and the second fin 32b collides with the inner peripheral surface 2d of the downstream pipe portion 2b varies depending on the positions of the

fins

32a and 32b. The flow of exhaust gas along the axial direction and the flow of exhaust gas inclined at an angle α coexist in the downstream side piping section 2b.

More specifically, in the case of the first fin 32a, the exhaust gas that has passed through the first fin 32a located on the uppermost side collides with the inner peripheral surface 2d at the earliest timing (see the arrow C1). As the position of the first fin 32a becomes lower, the timing of the collision is delayed (see arrow C2). Further, when the position of the first fin 32a is further on the lower side, the exhaust gas that has passed therethrough does not collide with the inner peripheral surface 2d, but flows in a direction (see arrow C3) directly flowing into the tapered pipe portion 2c. The second fin 32b is the same except that the direction is reversed. Therefore, the flow of exhaust gas (see arrows C1 and C2) along the axial direction of the downstream pipe portion 2d collides with the flow of exhaust gas inclined with respect to the axial direction (see arrow C3), and the angle of the flow α is gradually decreased (see arrow C4).

That is, the flow angle of the exhaust gas flowing through the downstream pipe portion 2b and flowing into the tapered pipe portion 2c is the angle α at which the first fin 32a and the second fin 32b tilt the flow of the exhaust gas, and the downstream side When the inner diameter D and the distance L (see FIG. 6) of the pipe portion 2b are satisfied, and these satisfy the above-described equations (1) and (2), the flow of exhaust gas along the axial direction (arrow) C1, C2) and the flow of exhaust gas inclined with respect to the axial direction (arrow C3) are balanced. In addition, since the angle β of the gradient of the tapered pipe portion 2c is smaller than the angle α, a flow substantially along the angle β is given to the exhaust gas that has passed through the downstream side pipe portion 2b. Accordingly, since the ammonia dispersed in the exhaust gas in the downstream pipe portion 2b is diffused along the gradient of the taper pipe portion 2c, the ammonia can be supplied to the SCR catalyst 4 in a uniform distribution state. It becomes.

Here, when the angle α is 45 °, the inner diameter D is 66 mm, and the length L is changed, the transition of the distribution state of ammonia supplied to the SCR catalyst 4, the transition of the so-called in-plane uniformity is measured. Is shown in FIG. The exhaust gas flow rate was 52 (g / s), and the exhaust gas temperature was 423 (° C.). In this case, according to the exhaust gas aftertreatment device according to Embodiment 3, the preferred range of the length L is
33 (mm) ≤ L ≤ 99 (mm)
In such a range, the CV value can be made less than 10%. FIG. 9 shows the CV value (variation coefficient: number obtained by dividing the standard deviation by the average × 100), which is one of the indexes indicating the in-plane uniformity, with the length L of the downstream pipe portion 2b as the horizontal axis. It is the graph which made the vertical axis | shaft. Further, the CV value becomes zero when the distribution state of ammonia supplied to the SCR catalyst 4 is uniform, and increases as the distribution state becomes non-uniform.

As shown in FIG. 9, when the length L of the downstream pipe portion 2b is less than about 30 (mm), the CV value increases rapidly. This is because the length L of the downstream pipe portion 2b is too short, so that the exhaust gas flows into the tapered pipe portion 2c before ammonia is sufficiently dispersed inside the downstream pipe portion 2b. That is, the flow of exhaust gas tilted with respect to the axial direction (arrow C3 in FIG. 8) becomes too strong, resulting in insufficient dispersion.

On the other hand, when the length L of the downstream pipe portion 2b exceeds about 50 (mm), the CV value gradually increases as the length L increases. This is because the flow in the direction along the axial direction of the downstream pipe portion 2b (see arrows C1 and C2 in FIG. 8) becomes too strong as the length L increases, so that the exhaust gas flowing into the tapered pipe portion 2c. Is not diffused along the taper shape but goes straight as it is and is supplied only to the vicinity of the center of the SCR catalyst 4. As described above, when the angle α, the inner diameter D, and the length L satisfy the above-described formulas (1) and (2), ammonia is supplied to the SCR catalyst 4 in a uniform distribution state from FIG. Can also be confirmed.

Even when the flow rate and flow rate of the exhaust gas change, the flow rate and flow rate of the flows indicated by arrows C1 to C4 shown in FIG. 8 change at the same rate, so the result is the same as that shown in FIG. It becomes a trend.

As described above, in the exhaust gas aftertreatment device in which the mixer 31 and the SCR catalyst 4 are connected to each other via the downstream pipe portion 2b and the tapered pipe portion 2c, the first fin 32a and the second fin 32a of the mixer 31 are connected. When the angle at which the flow of the exhaust gas passing through the fin 32b is inclined is α, the inner diameter of the downstream side pipe portion 13 is D, and the length is L,
D / 2 × cotα ≦ L ≦ 3/2 × D × cotα
When configured so as to satisfy the above, it is possible to cause a flow along the gradient of the tapered pipe portion 2c to the exhaust gas flowing through the downstream side pipe portion 2b and flowing into the tapered pipe portion 2c. Therefore, in addition to obtaining the same effect as in the first embodiment, ammonia can be supplied to the SCR catalyst 4 in a uniform distribution state.

Further, in the mixer 31, since the rows in which the plurality of first fins 32a are arranged and the rows in which the plurality of second fins 32b are arranged are alternately arranged one by one, in the downstream side piping section 2b, Exhaust gas flows in directions different from each other occur alternately and ammonia is efficiently dispersed in the exhaust gas. Furthermore, since the downstream side piping part 2b is cylindrical, the flow along the circumferential direction is given to the exhaust gas that has passed through the mixer 31 and collided with the inner peripheral surface 2d of the downstream side piping part 2b, so that ammonia is more efficient. It is often dispersed in exhaust gas.

In the first embodiment, the injection nozzle 5 as the reducing agent supply device is configured to inject urea water in a direction perpendicular to the dispersion member 21, but limits the direction in which urea water is injected. is not. For example, even if the spray nozzle 5 ′ and the spray nozzle 5 ″ shown in FIG. 10 are provided at an angle with respect to the dispersion member 21, the urea water directly collides with the dispersion member 21, so that the same In addition, since the injection nozzles 5 'and 5 "are injected perpendicularly to the flow direction, both of the exhaust gas is discharged until the injected reducing agent collides with the dispersion member. Less affected by flow.

Further, the dispersion member 21 in the first and third embodiments is arranged so as to be parallel to the flow direction of the exhaust gas. However, for example, like the dispersion member 51 shown in FIG. It is also possible to make an angle with respect to it. In this case, the pressure loss increases, but the dispersibility can be adjusted by adjusting the direction of the exhaust gas flowing into the mixer.

Further, the dispersion member does not directly contact the exhaust pipe 2 at the end portion, and may be separated. In this case, the dispersion member may be supported only by the mixer. In this case, the temperature of the dispersion member can be kept high because it is in contact with the outside air and separated from the exhaust pipe 2 having a relatively low temperature. Conversely, the end portion may be directly supported by the exhaust pipe 2 without being supported by the mixer.

In the first and third embodiments, the dispersion member 21 is disposed so as to pass through the central portion in the exhaust pipe 2, but the configuration is not limited thereto. What is necessary is just to oppose the injection nozzle 5 and to arrange | position adjacent to the mixer 31. As for the position of the dispersion member 21, for example, the surface on which the urea water collides may be arranged at the center of the mixer.

In the first to third embodiments, the first fins and the second fins of the mixer are arranged so as to be alternately arranged one by one, but the arrangement of these fins is not limited. The first and second fins only need to be able to change the flow angle of the exhaust gas passing therethrough. For example, the first fin row and the second fin row are alternately arranged in two rows. Other arrangements are also possible.

In the third embodiment, dimensional regulations are added to the exhaust pipe 2 and the mixer 31 of the exhaust gas aftertreatment device according to the first embodiment provided with a single dispersion member. However, the present invention is not limited to this configuration. Absent. It is also possible to add dimensions to the exhaust pipe 2 and the mixer 31 of the exhaust gas aftertreatment device according to Embodiment 2 including a plurality of second dispersion members.

Claims

An exhaust pipe through which exhaust gas discharged from the internal combustion engine flows;
A reducing agent supply device for injecting a reducing agent into the exhaust pipe;
A reduction catalyst disposed on the downstream side of the reducing agent supply device and purifying the exhaust gas by reacting the exhaust gas with the reducing agent;
In the exhaust pipe,
A plate-like dispersion member disposed at a portion facing the reducing agent supply means;
A mixing means disposed between the dispersion member and the reduction catalyst and mixing the exhaust gas and the reducing agent;
The dispersion member and the mixing means are exhaust gas aftertreatment devices that are arranged adjacent to each other.
The exhaust gas aftertreatment device according to claim 1, wherein the reducing agent supply device injects the reducing agent in a direction perpendicular to a direction in which the exhaust gas flows through the exhaust pipe.
The exhaust gas aftertreatment device according to claim 1 or 2, wherein the dispersion member extends in parallel with a direction in which the exhaust gas flows through the inside of the exhaust pipe.
The exhaust gas aftertreatment device according to any one of claims 1 to 3, wherein the dispersion member is a single member.
The mixing means includes a plurality of first fins and a plurality of second fins that are arranged so as to be parallel to each other and that incline the flow of the exhaust gas passing therethrough at a predetermined angle that is opposite to each other. And
The mixing means and the reduction catalyst are sequentially connected through a straight piping portion extending linearly and a tapered piping portion formed so as to widen from the upstream side toward the downstream side,
When the angle is α, the inner diameter of the straight pipe portion is D, and the length of the straight pipe portion is L,
D / 2 × cotα ≦ L ≦ 3/2 × D × cotα
The exhaust gas aftertreatment device according to claim 1, wherein:
6. The exhaust gas aftertreatment according to claim 5, wherein the mixing member includes a row in which a plurality of the first fins are arranged and a row in which the plurality of second fins are arranged alternately. apparatus.
The exhaust gas aftertreatment device according to claim 5 or 6, wherein the straight pipe portion is cylindrical.
The exhaust gas aftertreatment device according to any one of claims 5 to 7, wherein a gradient in which the tapered pipe portion spreads is smaller than the angle α.
The exhaust gas aftertreatment device according to any one of claims 5 to 8, wherein the angle α is 45 °.