JP2021055634A - Exhaust system structure - Google Patents

Abstract

To bring a wall surface temperature of an inner pipe, into which a reducing agent is sprayed, into a high temperature state as a whole.SOLUTION: An exhaust system structure includes an outer pipe 57 into which exhaust gas is introduced from a predetermined direction, an inner pipe 63 arranged inside the outer pipe, and an injector 35 for injecting a reducing agent into the inner pipe 63. The exhaust system structure includes: a first inflow port 64 that is opened to a peripheral surface of the inner pipe 63 to face the predetermined direction and that allows the exhaust gas introduced into the outer pipe 57 to flow into the inner pipe 63; a second inflow port 65 that is opened to the peripheral surface of the inner pipe 63 adjacent to the first inflow port 64 in the circumferential direction; and a circumferential flow path 70 that is partitioned by the inner peripheral surface of the outer pipe 57 and the outer peripheral surface of the inner pipe 63, and that allows the exhaust gas introduced into the outer pipe 57 to flow from one end of the first inflow port 64 on the side opposite to the second inflow port 65 toward the second inflow port 65 along the outer peripheral surface of the inner pipe 63 and to flow into the second inflow port 65.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to an exhaust system structure, and more particularly to a technique relating to a structure of a mixer chamber that agitates and mixes exhaust gas discharged from an internal combustion engine and a reducing agent supplied to a reducing catalyst.

Conventionally, as an exhaust aftertreatment device for an internal combustion engine, nitrogen oxidation contained in exhaust gas uses ammonia produced by hydrolyzing urea water injected from a urea water injector by exhaust heat or steam in the exhaust gas as a reducing agent. Those provided with a selective catalytic reduction (hereinafter, SCR catalyst) for reducing and purifying a substance (hereinafter, NOx) are known.

For example, Patent Document 1 includes an inner pipe in which urea water is injected from a urea water injector and an outer pipe that covers the outer periphery of the inner pipe, and the exhaust introduced into the outer pipe from the exhaust upstream side is provided as an inner pipe. A structure is disclosed in which a swirling flow is generated in the inner pipe by flowing into the inner pipe from the tangential direction through the opening of the inner pipe.

Japanese Unexamined Patent Publication No. 2008-215286

By the way, the urea water injected from the urea water injector into the inner pipe is struck and adhered to the inner peripheral surface of the inner pipe by the swirling flow of the exhaust gas. In the structure described in the above document, the first inflow port and the second inflow port, which allow exhaust gas to flow from the outer pipe into the inner pipe, are opened facing each other in the radial direction, and the space between the outer pipe and the inner pipe is widened. The flowing exhaust gas is introduced into the inner pipe from the second inflow port without flowing through the entire outer peripheral surface of the inner pipe. For this reason, there is a possibility that the wall surface temperature of the portion of the inner peripheral surface of the inner pipe where the exhaust gas does not flow along the outer peripheral surface may decrease, and there is room for improvement in promoting the hydrolysis of the urea water adhering to the portion. It can be said that there is.

An object of the present disclosure technique is to raise the wall surface temperature of the inner pipe into which the reducing agent is sprayed to a high temperature as a whole in the exhaust system structure including the inner pipe and the outer pipe.

In the technique of the present disclosure, an outer pipe into which the exhaust discharged from the internal combustion engine is introduced from a predetermined direction and an outer pipe are arranged inside the outer pipe at intervals from the outer pipe, and a reduction catalyst is arranged on the downstream side thereof. An exhaust system structure including an inner pipe provided with an inner pipe and an injector for injecting a reducing agent into the inner pipe, which is opened in the peripheral surface of the inner pipe facing the predetermined direction, and the outer pipe is opened. A first inflow port that allows the exhaust introduced into the inner pipe to flow into the inner pipe, a second inflow port that opens adjacent to the first inflow port in the circumferential direction on the peripheral surface of the inner pipe, and the outer pipe. The exhaust is partitioned by an inner peripheral surface and an outer peripheral surface of the inner pipe, and the exhaust introduced into the outer pipe is directed from one end of the first inflow port on the opposite side of the second inflow port to the second. It is characterized by including a circumferential flow path that flows along the outer peripheral surface of the inner pipe toward the inflow port and flows into the second inflow port.

Further, the flow of the exhaust gas which is connected to the outer peripheral surface of the inner pipe adjacent to the one end portion of the first inflow port and is introduced into the outer pipe is referred to the first inflow port and the circumferential flow path. It is connected to the outer peripheral surface of the inner pipe between the first inflow port and the second inflow port, and closes the terminal side of the circumferential flow path in the exhaust flow direction. It is preferable to further include a second partition plate to be provided.

Further, it is preferable that at least one of the first partition plate and the second partition plate is connected to the inner pipe from the tangential direction of the inner pipe.

Further, the injector is a urea water injector that injects urea water into the inner tube, and the reduction catalyst reduces and purifies nitrogen oxides in exhaust gas using ammonia generated from the urea water as a reducing agent. It may be a selective reduction catalyst.

According to the technique of the present disclosure, in the exhaust system structure including the inner pipe and the outer pipe, the wall surface temperature of the inner pipe on which the reducing agent is injected can be set to a high temperature as a whole.

It is a schematic overall block diagram which shows the exhaust system of the engine provided with the exhaust system structure which concerns on this embodiment. It is a schematic perspective view which shows the exhaust aftertreatment device which concerns on this embodiment. It is a schematic cross-sectional view which shows the inside of the mixer chamber which concerns on this embodiment.

Hereinafter, the exhaust system structure according to the present embodiment will be described with reference to the attached drawings. The same parts have the same reference numerals, and their names and functions are also the same. Therefore, detailed explanations about them will not be repeated.

[overall structure]
FIG. 1 is a schematic overall configuration diagram showing an exhaust system of an engine 10 including an exhaust system structure according to the present embodiment.

As shown in FIG. 1, the engine 10 (internal combustion engine) includes an engine main body 11 including a cylinder head, a cylinder block in which a plurality of cylinders are formed, and the like. The cylinder head of the engine body 11 is provided with an exhaust manifold 12 that collects the exhaust gas discharged from each cylinder. An upstream exhaust pipe 13, an exhaust aftertreatment device 20, a downstream exhaust pipe 15, a silencer (not shown), and the like are connected to the exhaust manifold 12 in this order from the exhaust upstream side.

The exhaust aftertreatment device 20 includes a front casing 21, a mixer chamber 50, a urea water injection device 30, a connection exhaust pipe 60, and a rear casing 41 in this order from the exhaust upstream side.

Inside the front casing 21, the oxidation catalyst 22 and the filter 23 are housed in this order from the upstream side of the exhaust gas.

The oxidation catalyst 22 is formed by supporting a catalyst component or the like on the surface of a ceramic carrier such as a cordierite honeycomb structure. When unburned fuel (hydrocarbon: HC) is supplied by the post-injection of the engine 10 or the exhaust pipe injection of an exhaust pipe injector (not shown), the oxidation catalyst 22 oxidizes the unburned fuel (hydrocarbon: HC) to raise the exhaust temperature.

The filter 23 is formed, for example, by arranging a large number of cells partitioned by a porous partition wall along the flow direction of exhaust gas, and alternately sealing the upstream side and the downstream side of these cells. .. The filter 23 collects particulate matter (PM) in the exhaust gas in the pores and surface of the partition wall, and when the PM deposition amount reaches a predetermined amount, it burns and removes the particulate matter (PM). Is carried out.

The upstream end of the mixer chamber 50 is connected to the downstream end of the front casing 21. Further, the mixer chamber 50 is provided with a urea water injector 35 of the urea water injection device 30, and the injected urea water is agitated and mixed with the exhaust gas.

The urea water injection device 30 supplies the urea water tank 31 that stores the urea water, the strainer 32 that is immersed in the urea water in the urea water tank 31 to remove foreign matter, and the supply pipe 33 that is connected to the strainer 32. A urea water pump 34 provided in the pipe 33 to pump urea water from the urea water tank 31 and a urea water injector 35 for injecting the urea water supplied from the supply pipe 33 into the mixer chamber 50 (connection exhaust pipe 60). I have. The urea water injected from the urea water injector 35 is hydrolyzed by exhaust heat and water vapor in the exhaust to produce ammonia (NH3), which is supplied to the SCR catalyst 48 on the downstream side as a reducing agent.

The connection exhaust pipe 60 is formed in a substantially cylindrical shape, and connects the mixer chamber 50 and the upstream end of the rear casing 41. The upstream end of the connection exhaust pipe 60 is inserted into the inside of the mixer chamber 50, and urea water is axially injected into the inside from the urea water injector 35.

An SCR catalyst 48 (an example of the reduction catalyst of the present disclosure) is housed inside the rear casing 41. The SCR catalyst 48 is formed by supporting zeolite or the like on a porous ceramic carrier, for example. The SCR catalyst 48 adsorbs ammonia supplied as a reducing agent from the urea water injector 35, and selectively reduces and purifies NOx from the exhaust gas passing by the adsorbed ammonia.

[Exhaust aftertreatment device]
FIG. 2 is a perspective view showing an exhaust aftertreatment device 20 according to the present embodiment.

As shown in FIG. 2, the front casing 21 and the rear casing 41 are cylindrical, their axes are parallel to each other, and they are connected by a connecting exhaust pipe 60 arranged between them. .. The connection exhaust pipe 60 includes a cylindrical first connection exhaust pipe 61, and is arranged so that the axes of the connection exhaust pipe 61 are parallel to the axes of the front casing 21 and the rear casing 41.

The mixer chamber 50 includes a first chamber 51 having an arc-shaped side surface arranged at the exhaust downstream end of the front casing 21, and a second chamber 52 having an arc-shaped side surface extending from the side surface of the first chamber 51 toward the rear casing 41. I have. The first chamber 51 is arranged coaxially with the front casing 21. Further, the diameter of the second chamber 52 is smaller than the diameter of the first chamber 51, and the boundary between the two is curved in an arc shape. An annular flange is provided between the exhaust downstream end of the front casing 21 and the exhaust upstream end of the first chamber 51, and both flanges are fastened with bolts and nuts.

The connection exhaust pipe 60 is a second connection exhaust pipe 62 that connects a cylindrical first connection exhaust pipe 61 connected to the second chamber 52, the first connection exhaust pipe 61, and an exhaust upstream end of the rear casing 41. And have. The upstream end side of the first connection exhaust pipe 61 is inserted into the second chamber 52, and is arranged coaxially with the injection shaft of the urea water injector 35.

The second connection exhaust pipe 62 is an elbow pipe, and the downstream end of the exhaust is formed in a disk shape. The straight portion of the second connection exhaust pipe 62 is arranged coaxially with the first connection exhaust pipe 61, and an annular flange is formed between the exhaust downstream end of the first connection exhaust pipe 61 and the exhaust upstream end of the second connection exhaust pipe 62. Is provided, and both flanges are fastened with bolts and nuts. Further, an annular flange is provided at the exhaust downstream end of the second connection exhaust pipe 62 and the exhaust upstream end of the rear casing 41, and both flanges are fastened with bolts and nuts.

The urea water injector 35 is provided in the second chamber 52. The injection shaft of the urea water injector 35 is aligned with the axis of the first connection exhaust pipe 61, and urea water is injected (sprayed) from the urea water injector 35 into the inside of the first connection exhaust pipe 61.

In the first connection exhaust pipe 61, the urea water injected from the urea water injector 35 and the exhaust flowing from the mixer chamber 50 to the subsequent casing 41 are mixed, and the urea water is hydrolyzed by the exhaust heat to produce ammonia (NH3). Is generated. The generated ammonia is supplied to the SCR catalyst 48 on the downstream side of the exhaust gas by the flow of the exhaust gas.

[Mixer chamber]
FIG. 3 is a schematic cross-sectional view showing the inside of the mixer chamber 50 according to the present embodiment.

As shown in FIG. 3, the upstream end of the first connection exhaust pipe 61 is inserted and arranged in the second chamber 52 of the mixer chamber 50, and the inner pipe of the present disclosure is arranged by the upstream end of the first connection exhaust pipe 61. 63 is configured. The second chamber 52 is provided so as to cover the outer peripheral surface of the inner pipe 63 at a predetermined interval, and the outer pipe 57 of the present disclosure is formed by the arc side wall of the second chamber 52.

The first chamber 51 has an arc side wall 54 having substantially the same diameter as the front casing 21 (see FIG. 2 for details) that houses the filter 23. The first chamber 51 and the second chamber 52 are connected to each other via a communication portion 53. The communication portion 53 has a substantially linear first communication side wall 55 facing each other at intervals, and a semicircular second communication side wall 56.

Specifically, the arc side wall 54 of the first chamber 51 and the outer pipe 57 of the second chamber 52 open wall surfaces facing each other. One end of the opening of the arc side wall 54 and one end of the opening of the outer pipe 57 are connected to each other by a substantially linear first communication side wall 55, and the other end of the opening of the arc side wall 54 and the other end of the opening of the outer pipe 57. Are connected to each other by a second communication side wall 56 having a substantially semicircular arc shape. That is, the exhaust gas that has passed through the filter 23 and flows into the first chamber 51 is introduced into the outer pipe 57 of the second chamber 52 via the communication portion 53 from the radial direction (predetermined direction of the present disclosure). It is configured.

A first inflow port portion 64 that opens facing the communication portion 53 side is provided on the peripheral surface of the inner pipe 63. Further, between the inner pipe 63 and the outer pipe 57, a circumferential flow path 70 is formed in which exhaust gas is circulated along the outer peripheral surface of the inner pipe 63 by these facing spaces.

The communication portion 53 is provided with a first partition plate 71 extending substantially parallel to the first communication side wall 55 at intervals. The first partition plate 71 divides the exhaust gas flowing from the first chamber 51 into the communication portion 53 into an exhaust gas E1 introduced into the first inflow port portion 64 and an exhaust gas E2 introduced into the circumferential flow path 70. The first partition plate 64 is preferably connected to the opening end of the first inflow port portion 64 on the side of the first communication side wall 55 from the tangential direction of the inner pipe 63, and is inside from the first inflow port portion 64. A swirling flow is generated in the exhaust E1 flowing into the pipe 63.

Further, on the peripheral surface of the inner pipe 63, the second communication side wall 56 side of the first inflow port portion 64 is not confronted with the first inflow port portion 64 in the radial direction, but is peripheral to the first inflow inlet portion 64. A second inflow port 65 that opens adjacent to the direction is provided. A second partition plate 72 that closes the end of the circumferential flow path 70 in the exhaust flow direction is connected between the first inflow port portion 64 and the second inflow port portion 65.

Specifically, one end side of the second partition plate 72 is connected to the inner wall surface of the second communication side wall 56, and the other end side is between the first inflow port portion 64 and the second inflow port portion 65. It is connected to the outer peripheral surface of the inner pipe 63. In this way, by providing the second partition plate 72 on the terminal side adjacent to the first inflow port portion 64 of the circumferential flow path 70, the exhaust E2 directed to the circumferential flow path 70 by the first partition plate 71 can be generated. , After flowing along substantially the entire outer peripheral surface excluding the second inflow port portion 64 and the second inflow inlet portion 65 of the inner pipe 63, the second inflow inlet portion 65 is introduced into the inner pipe 63. Become.

The second partition plate 72 is preferably connected to the inner pipe 17 between the first inflow port portion 64 and the second inflow port portion 65 from the tangential direction of the inner pipe 63, and is a circumferential flow path. A swirling flow is generated in the exhaust E2 flowing from the 70 into the inner pipe 63 via the second inflow inlet portion 65. That is, the exhaust E1 guided from the first inflow port portion 64 into the inner pipe 63 by the first partition plate 71, and the exhaust E2 led from the second inflow inlet portion 65 into the inner pipe 63 by the second partition plate 72. By generating each swirling flow, the swirling flow can be effectively secured in the exhaust of the inner pipe 63.

Here, the urea water injector 35 injects urea water into the inner pipe 63. At least a part of the jetted (sprayed) urea water adheres to the inner peripheral surface of the inner pipe 63 by the exhaust swirling flow in the inner pipe 63. In the present embodiment, the exhaust E2 directed to the circumferential flow path 70 by the first partition plate 71 is flown in the circumferential flow path 70 over a wide area along the outer peripheral surface of the inner pipe 63, and then the first 2 It is introduced into the inner pipe 63 from the inflow port portion 65. That is, the exhaust gas E2 flowing in the circumferential flow path 70 along the outer peripheral surface of the inner pipe 63 is configured so that the wall surface temperature of the inner pipe 63 can be maintained in a high temperature state as a whole. As a result, it becomes possible to effectively prevent a decrease in the wall surface temperature of the inner pipe 63 to which the urea water adheres, and it is possible to effectively improve the hydrolysis efficiency of the urea water.

[Other]
The present disclosure is not limited to the above-described embodiment, and can be appropriately modified and implemented without departing from the spirit of the present disclosure.

For example, the reduction catalyst housed in the subsequent casing 41 is not limited to the SCR catalyst 48 using ammonia generated from urea water as a reducing agent, and may be a reduction catalyst using another reducing agent.

10 engine (internal combustion engine)
20 Exhaust aftertreatment device 21 First stage casing 22 Oxidation catalyst 23 Filter 30 Urea water injection device 35 Urea water injector 41 Second stage casing 48 SCR catalyst (reduction catalyst)
50 Mixer chamber 51 1st chamber 52 2nd chamber 53 Communication part 60 Connection exhaust pipe 63 Inner pipe 64 1st inflow inlet 65 2nd inflow inlet 57 Outer pipe 70 Circumferential flow path 71 1st partition plate 72 2nd partition Board

Claims (4)

An outer pipe in which the exhaust gas discharged from the internal combustion engine is introduced from a predetermined direction,
An inner tube which is arranged inside the outer tube at a distance from the outer tube and a reduction catalyst is provided on the downstream side thereof.
An exhaust system structure including an injector for injecting a reducing agent into the inner pipe.
A first inflow port that opens in the peripheral surface of the inner pipe in the predetermined direction and allows the exhaust gas introduced into the outer pipe to flow into the inner pipe.
A second inflow port that opens adjacent to the first inflow port in the circumferential direction on the peripheral surface of the inner pipe,
It is partitioned by the inner peripheral surface of the outer pipe and the outer peripheral surface of the inner pipe, and the exhaust gas introduced into the outer pipe is one end of the first inflow port on the opposite side of the second inflow port. An exhaust system structure comprising: a circumferential flow path that circulates from the second inflow port toward the second inflow port along the outer peripheral surface of the inner pipe and flows into the second inflow port. The exhaust flow, which is connected to the outer peripheral surface of the inner pipe adjacent to the one end of the first inflow port and is introduced into the outer pipe, is divided into the first inflow port and the circumferential flow path. The first partition plate to be used
Further, a second partition plate which is connected to the outer peripheral surface of the inner pipe between the first inflow port and the second inflow port and closes the terminal side in the exhaust flow direction of the circumferential flow path. The exhaust system structure according to claim 1. The exhaust system structure according to claim 2, wherein the first partition plate and at least one of the second partition plates are connected to the inner pipe from the tangential direction of the inner pipe. The injector is a urea water injector that injects urea water into the inner pipe.
The exhaust system structure according to any one of claims 1 to 3, wherein the reduction catalyst is a selective reduction type catalyst that reduces and purifies nitrogen oxides in the exhaust using ammonia generated from the urea water as a reducing agent. ..

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