JP2018035715A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device in which a reduction of pressure loss and a performance degradation of a catalyst due to reductant hardly occur and which can achieve space and energy saving.SOLUTION: The exhaust emission control device for purifying exhaust gas generated in an internal combustion engine of a vehicle includes an exhaust gas pipe, a reductant injection part for injecting nitrogen oxide reducing reductant inside the exhaust gas pipe, and a reduction catalyst arranged inside the exhaust gas pipe at its exhaust gas downstream side further than the reductant injection part. The exhaust gas pipe has a depression in the inner wall of the exhaust gas pipe between the reductant injection part and the reduction catalyst for storing part of the reductant injected from the reductant injection part. The inner wall face of the depression has a plurality of protrusions and/or a plurality of recesses.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an exhaust gas purification device for purifying exhaust gas generated in an internal combustion engine of a vehicle.

  Conventionally, various exhaust gas purification apparatuses for removing nitrogen oxides (generally also referred to as “NOx”) contained in exhaust gas from an internal combustion engine of a vehicle have been developed. For example, as shown in FIG. 1, an exhaust gas pipe 510 connected to an internal combustion engine (not shown), a reducing agent injection unit 530 for injecting urea water into the exhaust gas pipe 510, a reduction catalyst 520, There is known an exhaust gas purifying apparatus 500 having the above (for example, Patent Document 1). In the exhaust gas purification apparatus 500, the urea water discharged from the reducing agent injection unit 530 is warmed by the exhaust gas, vaporized, and hydrolyzed. Then, ammonia generated by the reaction reacts with nitrogen oxides in the exhaust gas in the presence of the reduction catalyst 520, and the nitrogen oxides are rendered harmless.

  However, when the temperature of the exhaust gas is low or the temperature of the exhaust gas pipe 510 is low, the temperature of the urea water is not sufficiently high, and a part of the urea water remains attached to the inner wall of the exhaust gas pipe 510, It will precipitate. Therefore, it has been proposed to provide a storage part for storing urea water or ammonia water 580 generated by hydrolysis of urea water on the inner wall of the exhaust gas pipe 510 (for example, Patent Documents 2 and 3).

JP 2000-27627 A JP-A-2005-214176 JP 2013-127228 A

  In the exhaust gas purifying apparatus as in Patent Document 1 described above, when liquid urea water adheres to the exhaust gas pipe, the urea water gathers under the exhaust gas pipe due to gravity, and protects the reduction catalyst and the reduction catalyst. Infiltrate the protective member. When the urea water is cooled, it crystallizes inside the reduction catalyst or the protection member, crushing the pores of the reduction catalyst or clogging the pores of the reduction catalyst. As a result, problems such as an increase in pressure loss of the exhaust gas purification device or a reduction in the effective volume of the reduction catalyst, making it impossible to remove nitrogen oxides sufficiently.

  Therefore, it has been studied to cover a part of the exhaust gas upstream side of the reduction catalyst with a metal plate or the like so that the liquid urea water does not penetrate into the reduction catalyst or the protection member. However, in this case, the reduction catalyst located behind the metal plate cannot be sufficiently functioned, and in this case as well, there are problems such as an increase in pressure loss of the exhaust gas purification device and a reduction in the effective volume of the catalyst. Prone to occur.

  On the other hand, as proposed in Patent Document 2 and Patent Document 3 described above, if a reservoir for removing urea water, ammonia water, or the like is provided, the penetration of urea water into the reduction catalyst or the like is suppressed. However, in these apparatuses, it is necessary to remove urea water, ammonia water, and the like accumulated in the reservoir. Therefore, in these exhaust gas purification devices, a heater for heating the inside of the storage portion is provided outside the exhaust gas pipe. However, when such a heater is provided, the exhaust gas purification device is likely to be large and energy consumption increases. There was a problem.

  The present invention has been made in view of the above problems. That is, an object of the present invention is to provide an exhaust gas purifying apparatus that can reduce the pressure loss and the catalyst performance due to the reducing agent and can save space and energy.

  The exhaust gas purifying apparatus of the present invention is an apparatus for purifying exhaust gas generated in an internal combustion engine of a vehicle. The exhaust gas purification apparatus includes an exhaust gas pipe, a reducing agent injection unit for injecting a reducing agent for nitrogen oxide reduction into the exhaust gas pipe, an inside of the exhaust gas pipe, and an exhaust gas downstream of the reducing agent injection unit. A reduction catalyst disposed on a side of the exhaust pipe, the exhaust pipe being injected from the reducing agent injection section between the reducing agent injection section and the reduction catalyst and on an inner wall of the exhaust pipe. The inner wall surface of the recess has a plurality of convex portions and / or a plurality of concave portions.

  According to the exhaust gas purification apparatus of the present invention, it is difficult for pressure loss and catalyst performance to be reduced due to the reducing agent. Furthermore, according to the gas purification apparatus, space saving and energy saving are possible.

It is a schematic sectional drawing which shows an example of the conventional exhaust gas purification apparatus. It is a front view when the exhaust gas purification apparatus which concerns on one Embodiment of this invention is observed from exhaust gas downstream. It is a schematic sectional drawing of the AA line shown in FIG. It is a schematic sectional drawing of the BB line shown in FIG.

(Configuration of exhaust gas purification device)
Hereinafter, an exhaust gas purification apparatus of the present invention will be described in detail with reference to the drawings. However, the exhaust gas purification apparatus of the present invention is not limited to the structure shown in the drawing.
FIG. 2 shows a front view of the exhaust gas purification apparatus 100 according to an embodiment of the present invention when observed from the exhaust gas downstream side, FIG. 3 shows a schematic cross-sectional view along the line AA shown in FIG. 4 is a schematic sectional view taken along line BB shown in FIG. Further, in this specification, the vertical direction in FIG. 2 coincides with the “gravity direction”. Moreover, in FIG. 3 and FIG. 4, each arrow indicates the direction in which exhaust gas flows (exhaust gas flow direction).

  As shown in FIGS. 3 and 4, the exhaust gas purification apparatus 100 of the present embodiment includes an exhaust gas pipe 110, a reducing agent injection unit 130 for injecting a reducing agent into the exhaust gas pipe 110, an interior of the exhaust gas pipe 110, In addition, a reduction catalyst (hereinafter, also referred to as “SCR” (Selective Catalytic Filter)) 120 disposed on the exhaust gas downstream side of the reducing agent injection unit 130, and an oxidation disposed inside the exhaust gas pipe 110 and on the exhaust gas downstream side of the SCR 120. Catalyst (hereinafter also referred to as “DOC” (Diesel Oxidation Catalyst)) 140.

  The exhaust gas purification apparatus 100 of the present embodiment is used by being directly or indirectly connected to a diesel engine of a vehicle. Further, a diesel particulate collection unit (hereinafter also referred to as “DPD”) having a diesel particulate collection filter (hereinafter also referred to as “DPF”) is disposed upstream or downstream of the exhaust gas from the exhaust gas purification apparatus 100 of the present embodiment. Is done. Hereinafter, although the case where DPD is arrange | positioned to the waste gas upstream of the waste gas purification apparatus 100 is demonstrated to an example, this invention is not restrict | limited to the said embodiment.

  As shown in FIG. 3, the exhaust gas pipe 110 of the present embodiment includes an exhaust gas introduction part 110 a for connecting to a member (for example, DPD) disposed on the exhaust gas upstream side of the exhaust gas purification device 100, an SCR 120 and a DOC 140 inside. It has a catalyst storage part 110c to be stored, and an exhaust gas discharge part 110e for connecting to a member (for example, a muffler) disposed on the exhaust gas downstream side of the exhaust gas purification apparatus 100. The exhaust gas introduction part 110a, the catalyst storage part 110c, and the exhaust gas discharge part 110e are all substantially cylindrical, and the diameter of the catalyst storage part 110c is set in accordance with the diameters of the SCR 120 and the DOC 140. In the present embodiment, the diameter of the catalyst housing part 110c is set larger than the diameters of the exhaust gas introduction part 110a and the exhaust gas discharge part 110e. Therefore, an enlarged diameter portion 110b whose diameter increases toward the downstream side is disposed between the exhaust gas introduction portion 110a and the catalyst housing portion 110c. Further, a reduced diameter portion 110d whose diameter decreases toward the downstream side is disposed between the catalyst housing portion 110c and the exhaust gas discharge portion 110e.

  Here, the exhaust gas pipe 110 is a part of the reducing agent 180 injected from the reducing agent injection unit 130 on the inner wall between the reducing agent injection unit 130 and the SCR 120 (in this embodiment, the inner wall of the catalyst housing unit 110c). Has a recess 111 for storing. The inner wall surface of the recess 111 has a plurality of convex portions and / or a plurality of concave portions. These convex portions and / or concave portions may be formed not only on the inner wall surface of the recess 111 but also on the outer wall surface of the recess 111 due to the relationship between the inner wall surface and the front and back surfaces. That is, the outer wall surface of the recess 111 may have a convex portion or a concave portion similar to the inner wall surface. In the present specification, “convex portion” or “concave portion” means a convex portion or a concave portion mechanically formed by various molding processes or the like.

  When the inner wall surface of the recess 111 has a recess or a protrusion, the surface area becomes larger than when the inner wall surface of the recess 111 is flat, and the contact area between the reducing agent 180 stored in the recess 111 and the recess 111 is increased. growing. In the exhaust gas purification apparatus 100 of the present embodiment, as will be described later, the reducing agent 180 stored in the dent 111 is volatilized by the heat during DPF regeneration, but when the inner wall surface of the dent 111 has a recess or a protrusion, Heat during DPF regeneration is easily transmitted to the reducing agent 180. Therefore, the reducing agent 180 stored in the recess 111 can be surely volatilized.

  Here, the shape of the recess 111 is not particularly limited as long as the reducing agent 180 can be sufficiently stored. In the present embodiment, as shown in FIGS. 2 and 3, the outer wall surface of the region corresponding to the dent 111 protrudes from the outer peripheral surface of the cylindrical exhaust pipe 110. Further, as shown in FIGS. 2 and 4, the recess 111 has a gravity direction (0 °) when the gravity direction when the exhaust pipe 110 is observed from the exhaust gas downstream side (or the exhaust gas upstream side) is 0 °. Is formed in a band shape in a range of ± 45 ° around the center.

  Here, the maximum depth of the recess 111 (the length represented by h in FIG. 3) is relative to the inner diameter (the length represented by D in FIG. 3) of the catalyst housing portion 110c of the exhaust pipe 110. The depth is preferably about 10 to 25%. If the maximum depth of the dent 111 is too deep, the exhaust gas purification apparatus 100 is likely to be enlarged. On the other hand, if the maximum depth of the recess 111 is too shallow, a sufficient amount of the reducing agent 180 cannot be stored in the recess 111, and the reducing agent 180 tends to overflow from the recess 111.

  Further, the width of the recess 111 in the flow direction of the exhaust gas (the length represented by w in FIG. 3) is substantially horizontal when the exhaust gas purification device 100 is mounted on the vehicle, compared with the SCR 120 of the catalyst housing portion 110c. It is preferable that the width is substantially equal to the width of the upstream region.

  Moreover, the inner wall surface of the dent 111 may be subjected to various treatments such as a hydrophilization treatment as necessary. When the inner wall surface of the dent 111 is hydrophilized, the contact area between the reducing agent 180 and the inner wall surface of the dent 111 increases, and heat during DPF regeneration is easily transmitted.

  On the other hand, the shape of the convex part and / or the concave part of the inner wall surface of the recess 111 is not particularly limited as long as the surface area of the recess 111 can be sufficiently increased. In this embodiment, as shown in FIG. 2 and FIG. 4, ridges and ridges having a uniform shape parallel to the flow direction of the exhaust gas are alternately arranged in the dents 111. Further, in the present embodiment, not only the inner wall surface of the recess 111 but also the outer wall surface is formed with convex portions and recesses so that the cross section of the recess 111 orthogonal to the exhaust gas flow of the exhaust gas pipe 110 has a corrugated shape. Has been. However, the shape of a convex part and a recessed part is not restrict | limited to the said embodiment, and especially the number of a convex part and / or a recessed part is not restrict | limited. Further, the shapes of the plurality of convex portions and / or the plurality of concave portions may be all the same or different. Further, the convex portion and / or the concave portion may be in the form of a stripe or an island. Further, the cross-sectional shape of the convex portion or the concave portion is not particularly limited, and may be a semicircular shape, a rectangular shape, a triangular shape, or the like.

  Here, it is preferable that the exhaust gas pipe 110 does not have a joint between the dent 111 and the other region of the exhaust gas pipe 110. If there is a seam between the dent 111 and another region, the part is easily corroded by the reducing agent.

  The method for forming the exhaust gas pipe 110 can be the same as a general method for forming the exhaust gas pipe. For example, a cylindrical tube having a groove at a desired location is formed by integral molding. Then, the groove is pressed to form desired convex portions and / or concave portions on the inner wall surface (and outer wall surface) of the groove.

  On the other hand, the reducing agent injection unit 130 included in the exhaust gas purifying apparatus 100 may be any one that is disposed on the exhaust gas upstream side of the SCR 120 and can inject the reducing agent into the exhaust gas pipe 110. The reduction injection unit 130 includes at least an injection nozzle for injecting a reducing agent, a storage unit (not shown) for storing the reducing agent, and a pipe (not shown) connecting them. The injection nozzle is normally arranged at the upper part of the exhaust gas pipe 110, and in this embodiment, it is arranged at the upper part of the exhaust gas introduction part 110a of the exhaust gas pipe 110. Here, the reducing agent injection unit 130 injects the reducing agent and compressed air from the injection nozzle into the exhaust gas pipe 110 as necessary. The injection amount and the injection timing of the reducing agent depend on the rotational speed of the internal combustion engine, It is controlled according to the fuel injection amount and the like.

  The type of the reducing agent 180 injected by the reducing agent injection unit 130 is not particularly limited as long as it is a compound capable of reacting with nitrogen oxides in exhaust gas and detoxifying the nitrogen oxides (for example, ammonia) or a precursor thereof. . However, urea water that can generate ammonia by hydrolysis is usually used as a reducing agent.

  Further, the SCR 120 is disposed in the catalyst housing part 110 c of the exhaust gas pipe 110. The SCR 120 only needs to be capable of adsorbing the reducing agent 180 or the like (in this embodiment, ammonia) and reacting the nitrogen oxide with the reducing agent or the like inside the SCR 120. The SCR 120 can be a member in which, for example, a zeolite is supported on a porous ceramic carrier.

  On the other hand, the DOC 140 is disposed in the catalyst housing part 110c of the exhaust gas pipe 110 downstream of the SCR. The DOC 140 only needs to be capable of oxidizing and detoxifying ammonia that has passed (slipped) downstream from the SCR 120, and is a member in which platinum, rhodium, cerium oxide, or the like is supported on a porous ceramic carrier. be able to.

  Here, the SCR 120 and the DOC 140 are fixed to the exhaust gas pipe 110 via protective members 121 and 141. When the SCR 120 and the DOC 140 are fixed via the protective members 121 and 141, they are less likely to be affected by external impacts and vibrations. The protection members 121 and 141 may be mats made of ceramic or metal fiber, for example.

(Function)
Hereinafter, the operation of the exhaust gas purifying apparatus 100 of the present embodiment will be described by taking a case where the reducing agent 180 is urea water as an example. In the exhaust gas purification apparatus 100 of the present embodiment, urea water is injected from the reducing agent injection unit 130 when the exhaust gas passes through the exhaust gas pipe 110. Most of the urea water injected into the exhaust gas pipe 110 is warmed by the exhaust gas heat, vaporizes, and is hydrolyzed. Ammonia gas generated by the reaction moves to the SCR 120 side together with the exhaust gas. The nitrogen oxides and ammonia in the exhaust gas react in the SCR 120, whereby the nitrogen oxides are decomposed into nitrogen and water. Subsequently, the exhaust gas moves into the DOC 140. Inside the DOC 140, ammonia (ammonia slipped from the SCR 120) contained in the exhaust gas is oxidized and rendered harmless. Thereafter, the exhaust gas is discharged to the outside of the exhaust gas purification apparatus 100, and is released into the atmosphere via, for example, a muffler (not shown) connected to the exhaust gas purification apparatus 100.

  On the other hand, the exhaust gas purification apparatus 100 of the present embodiment is used in connection with the DPD as described above. In DPD, diesel particulates (hereinafter, also referred to as “PM”) in exhaust gas are collected by DPF, and PM accumulated on DPF is removed and DPF is regenerated in response to an instruction from a user. At the time of regeneration of the DPF, post injection is performed by fuel injection control in the cylinder of the internal combustion engine, or fuel is supplied to the exhaust gas, and the fuel is oxidized by an oxidation catalyst. As a result, the temperature of the exhaust gas temporarily rises, and the PM deposited on the DPF is burned and removed.

  Here, in the exhaust gas purification apparatus 100 of the present embodiment, when the temperature of the exhaust gas is low or when the temperature of the exhaust gas pipe 110 is low, a part of the urea water injected from the reducing agent injection unit 130 is not vaporized, It remains in a liquid state and adheres to the exhaust gas pipe 110. The liquid urea water 180 adhering to the exhaust gas pipe 110 gathers under the exhaust gas pipe 110 due to gravity and moves to the SCR 120 side together with the exhaust gas. The urea water 180 is stored in a recess 111 disposed on the inner wall of the exhaust gas pipe 110. Thereafter, when the above-described DPF regeneration is performed, high-temperature exhaust gas is also supplied into the exhaust gas purification apparatus 100. Thereby, the temperature of the exhaust gas pipe 110 rises, and the temperature of the dent 111 also rises. As a result, the temperature of the urea water 180 stored in the recess 111 rises and volatilizes.

(effect)
As described above, according to the exhaust gas purifying apparatus of the present embodiment, the SCR deformation and the holding member deformation due to crystallization of urea water do not occur as in the conventional case. That is, according to the exhaust gas purifying apparatus of the present embodiment, it is difficult for pressure loss and catalyst performance to be reduced due to the reducing agent. Moreover, according to the exhaust gas purification apparatus of this embodiment, it is possible to remove the reducing agent (urea water) stored in the recess without separately providing a heater outside the exhaust gas pipe. Therefore, it is possible to reduce the size of the exhaust gas purification device and save energy.

  According to the exhaust gas purification apparatus of the present invention, it is difficult for pressure loss and catalyst performance to be reduced due to the reducing agent. Furthermore, according to the exhaust gas purification apparatus, space saving and energy saving are possible. Therefore, it is suitable for passenger cars and commercial vehicles equipped with diesel engines.

100, 500 Exhaust gas purification device 110, 510 Exhaust gas pipe 111 Recess 120, 520 Reduction catalyst (SCR)
121, 141 Protective member 130, 530 Reducing agent injection part 140 Oxidation catalyst (DOC)
180 Reducing agent

Claims (4)

An exhaust gas purification device for purifying exhaust gas generated in an internal combustion engine of a vehicle,
An exhaust pipe,
A reducing agent injection unit for injecting a reducing agent for nitrogen oxide reduction into the exhaust gas pipe;
A reduction catalyst disposed in the exhaust gas pipe and on the exhaust gas downstream side of the reducing agent injection unit;
Including
The exhaust gas pipe has a recess for storing a part of the reducing agent injected from the reducing agent injection part between the reducing agent injection part and the reduction catalyst and on an inner wall of the exhaust gas pipe. ,
The inner wall surface of the recess has a plurality of convex portions and / or a plurality of concave portions,
Exhaust gas purification device. Further comprising an oxidation catalyst disposed inside the exhaust gas pipe and on the exhaust gas downstream side of the reduction catalyst,
The exhaust gas purification apparatus according to claim 1. The inner wall surface of the dent alternately has ridges and ridges parallel to the flow direction of the exhaust gas in the exhaust pipe,
The exhaust gas purification apparatus according to claim 1 or 2. The cross section of the dent perpendicular to the exhaust gas flow of the exhaust pipe is corrugated.
The exhaust gas purification apparatus according to any one of claims 1 to 3.

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