JP7791052B2 - Exhaust gas purification equipment - Google Patents

Description

This disclosure relates to an exhaust gas purification device configured to purify exhaust gas using an SCR catalyst.

As disclosed in Patent Document 1 below, a configuration is known in which an exhaust gas purification device injects a reducing agent such as urea water from an injector, and the injected reducing agent is agitated by an agitator and supplied to an SCR catalyst.

Japanese Patent Application Laid-Open No. 2021-156226

In an exhaust gas purification device, there is a demand for a state in which the reducing agent and the exhaust gas are more appropriately mixed.
One aspect of the present disclosure provides a configuration that allows a reducing agent and exhaust gas to be mixed more appropriately in an exhaust gas purification device configured to purify exhaust gas using an SCR catalyst.

One aspect of the present disclosure is an exhaust gas purification device configured to purify exhaust gas using an SCR catalyst. The exhaust gas purification device includes an exhaust pipe, an injector, and an agitator. The downstream side of the exhaust pipe in the exhaust gas flow direction is connected to a member that houses the SCR catalyst. The injector injects a reducing agent into the exhaust pipe along the exhaust gas flow direction. The agitator is positioned in the exhaust pipe downstream of the injector in the exhaust gas flow direction and has a protrusion that protrudes toward the injector.

With this configuration, the reducing agent is injected along the flow of the exhaust gas, so it is supplied toward the stirring member at high speed. The stirring member is also configured with protrusions to increase its surface area. This configuration allows the reducing agent to be well stirred by the stirring member and heated by the high-temperature exhaust gas, allowing the reducing agent and exhaust gas to be well mixed and supplied to the SCR catalyst.

In one aspect of the present disclosure, the exhaust pipe may include a curved pipe and an upstream pipe. The curved pipe is a section in which an agitator is disposed and which curves away from the injector. The upstream pipe is disposed upstream of the curved pipe in the flow direction. The agitator has a cross section perpendicular to the flow direction within the curved pipe that is flat, arc-shaped, or annular, and has a main body extending downstream in the flow direction. The flow direction in the upstream pipe and the extension direction of the main body of the agitator may be configured to be parallel. Note that "parallel" includes "approximately parallel," which indicates that the flow direction is substantially parallel. "Substantially parallel" indicates that there is not much difference in action and effect between when the flow direction is not parallel and when the flow direction is parallel. The same applies to "substantially coincident," which will be described later.

This configuration allows the agitator member to collide with the flow direction of the exhaust gas within the curved pipe at a predetermined angle. This allows the agitator member to have a longer length in the extension direction within the curved pipe. This increases the contact area between the exhaust gas from the upstream side and the agitator member, increasing the opportunities for contact between the exhaust gas and the reducing agent.

In one aspect of the present disclosure, the injector and the stirring member may be disposed opposite each other across the central axis of the upstream pipe.
According to this configuration, the distance that the reducing agent must travel to reach the stirring member can be secured, so that the reducing agent can be sufficiently diffused and accelerated before reaching the stirring member.

In one aspect of the present disclosure, the central axis of the exhaust pipe at the portion between the injector and the agitator may coincide with the central axis of the injection range of the injector. Note that "coincidence" includes "approximately coincidence," which indicates that the axis substantially coincides.
According to this configuration, the reducing agent can be easily supplied to the center of the exhaust gas flowing through the exhaust pipe, which makes it easier to mix the reducing agent and the exhaust gas well.

In one aspect of the present disclosure, the stirring member may constitute a collision portion onto which the reducing agent is directly injected.
According to this configuration, the reducing agent is injected directly onto the stirring member, so that the reducing agent and exhaust gas can be supplied to the catalyst in a more favorable mixed state.

In one aspect of the present disclosure, the stirring member may have a plurality of through holes.
This configuration can suppress pressure loss around the agitator, allowing the reducing agent and exhaust gas to flow more easily downstream of the agitator. Furthermore, if the agitator is flat and not curved, for example, if the agitator is flat and perpendicular to the exhaust gas flow direction, exhaust gas stagnation tends to occur upstream of the agitator. However, with the agitator of this embodiment, exhaust gas stagnation is less likely to occur. This is because the curved shape of the agitator and the multiple through holes allow the exhaust gas to flow more easily.

1 is a perspective view showing an exhaust gas purification device according to a first embodiment. 1 is a central cross-sectional view showing an exhaust gas purification device according to a first embodiment. 3 is a cross-sectional view taken along line III-III in FIG. 2, illustrating the flow of exhaust gas. FIG. 4 is a perspective view showing an exhaust gas purification device according to a second embodiment. FIG. 4 is a cross-sectional view showing an exhaust gas purification device according to a second embodiment.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.
1. First embodiment
[1-1. Configuration]
The exhaust gas purification device 1 shown in Figures 1 and 2 is a device that purifies exhaust gas from an internal combustion engine using an SCR (Selective Catalytic Reduction) catalyst 17. The exhaust gas purification device 1 includes an exhaust pipe 10. The exhaust pipe 10 forms an exhaust gas flow path for discharging exhaust gas generated in an internal combustion engine (not shown). The exhaust pipe 10 may include an introduction portion 11 and a connection portion 13, for example, as shown in Figure 1.

The exhaust pipe 10 is connected downstream in the exhaust gas flow direction to a catalyst holding section 12 equipped with an SCR catalyst 17. The inlet section 11, catalyst holding section 12, and connecting section 13 form an exhaust gas flow path. The exhaust gas purification device 1 is equipped with an injector 14, a stirring member 16, and an SCR catalyst 17, which together perform the function of purifying exhaust gas.

Note that in the following explanation, up, down, left, and right directions may be described based on Figure 2, but this is merely for the convenience of explanation and does not in any way limit the shape or actual usage of the exhaust gas purification device 1.

<Exhaust gas flow path>
1 and the following figures, arrows in the exhaust gas flow path indicate the direction in which at least a portion of the exhaust gas flows. The inlet portion 11 has an upstream pipe 21, a reducing agent inlet pipe 22, and a curved pipe 23.

The upstream pipe 21 is a straight pipe that introduces exhaust gas flowing from the internal combustion engine into the exhaust gas purification device 1. The upstream pipe 21 is located upstream of the curved pipe 23 in the flow direction (i.e., on the left side in Figure 2). The reducing agent introduction pipe 22 protrudes from the upstream pipe 21 on the side opposite the agitator when viewed from the central axis of the upstream pipe 21. The injector 14 is located at the upper left end of the reducing agent introduction pipe 22.

The curved pipe 23 is located downstream of the upstream pipe 21 and the reducing agent introduction pipe 22 in the introduction section 11, and curves away from the injector 14 as it moves away from the upstream pipe 21. On the upstream pipe 21 side, the curved pipe 23 curves downward from a horizontal state as it moves away from the upstream pipe 21, and then curves back to a horizontal state as it approaches the connecting section 13.

The width of the curved pipe 23 is approximately the same as that of the upstream pipe 21. The width direction is a direction perpendicular to the vertical direction in Figure 2 and perpendicular to the left-right direction, and is perpendicular to the plane of the paper in Figure 2. The stirring member 16, which will be described later, is disposed in the curved pipe 23.

The catalyst holding unit 12 is a cylindrical member that houses the SCR catalyst 17 and has a larger diameter than the upstream pipe 21 and the curved pipe 23. The SCR catalyst 17 is held by the catalyst holding unit 12 via a mat (e.g., an elastic member) (not shown). While Figures 1 and 2 show the portion that holds the SCR catalyst 17 as the catalyst holding unit 12, a pipe (not shown) is connected downstream of this for directing exhaust gas further downstream.

The connecting portion 13 connects the downstream end of the curved pipe 23 to the upstream end of the catalyst holding portion 12. The connecting portion 13 has a tapered shape with a diameter that increases toward the downstream side. The connecting portion 13 is welded to the curved pipe 23 and the catalyst holding portion 12, thereby fixing the introduction portion 11, catalyst holding portion 12, and connecting portion 13 together.

The upstream pipe 21 is disposed upstream of the agitator 16. As shown in FIG. 2, the first central axis 21a of the upstream pipe 21 and the second central axis 17a, which is the central axis of the SCR catalyst 17, are approximately parallel. "Approximately parallel" here means "substantially parallel." For example, the axes may be inclined so that when they intersect without changing their angles, the angle they form is 5° or less. The second central axis 17a coincides with the central axis of the catalyst holding unit 12. Furthermore, there is a gap between the second central axis 17a and the first central axis 21a in the intersecting direction (the vertical direction in FIG. 2) that intersects with the second central axis 17a. In other words, the upstream pipe 21 and the catalyst holding unit 12 are parallel pipes.

<Functional parts>
The injector 14 is connected to a reducing agent tank (not shown) and injects the reducing agent within the exhaust pipe 10 along the flow direction of the exhaust gas, for example, within a predetermined radial injection range. "Along the flow direction of the exhaust gas within the exhaust pipe 10" means that the flow direction of the exhaust gas downstream of the injector 14 (for example, a part of the center line 23a of the pipe) and the direction of the injection axis 22a of the injector 14 are approximately aligned. The injection axis 22a is the central axis of the injection range when the injector 14 injects the reducing agent, and in this embodiment, it is aligned with the central axis of the injector 14 itself. The injector 14 injects the reducing agent within a predetermined angular range centered on the injection axis 22a. The reducing agent is, for example, urea water.

At this time, the injector 14 injects the reducing agent along the flow direction of the exhaust gas within the curved pipe 23 (for example, along the center line 23a that continuously connects the central axes of the curved pipes 23). Furthermore, the center line 23a of the curved pipe 23 and the injection axis 22a of the injector 14 are positioned so that they are substantially aligned when viewed from above.

The injection axis 22a passes near the center line 23a of the curved pipe 23 and is directed toward the agitator 16. In particular, the injection axis 22a is directed toward the surface of the agitator 16 facing the protruding portion 16b. In the direction in which the reducing agent is injected from the injection axis 22a, the object closest to the injector 14 is the agitator 16. In other words, there are no other components between the injector 14 and the agitator 16 that would significantly change the flow of exhaust gas. Therefore, the injected reducing agent passes through the reducing agent introduction pipe 22 and enters the curved pipe 23, and most of the reducing agent strikes the agitator 16. Thus, the portion of the agitator 16 from which the reducing agent is directly injected when it first strikes the agitator 16 without coming into contact with other components constitutes the collision portion. The collision portion is primarily the surface of the agitator 16 facing the injector 14. Specifically, the collision portion corresponds to the area surrounding the multiple through holes 16h, which will be described later, and the protruding portion 16b. Furthermore, some of the reducing agent flows circumferentially along the surface of the stirring member 16 and toward the lower side of the stirring member 16.

The agitator 16 is positioned inside the curved pipe 23, downstream of the injector 14 and upstream of the SCR catalyst 17. The agitator 16 is joined near the downstream end of the curved pipe 23 at the connection 16a and extends upstream from the connection 16a. The extension direction of the agitator 16 is configured to be approximately parallel to the flow direction of exhaust gas in the upstream pipe 21 and catalyst holding section 12. The agitator 16 extends linearly from near the upper end of the curved pipe 23 to near the lower end of the curved pipe 23. Because the agitator 16 is positioned in the curved pipe 23, which is the curved portion of the exhaust pipe 10, a longer member can be positioned in a more linear manner.

The agitator 16 has a main body 16c that extends downstream in the flow direction when the cross section of the agitator 16 is positioned within the curved pipe 23 so that it coincides with a cross section perpendicular to the flow direction. The main body 16c has a protruding portion 16b that protrudes upstream in the flow direction, in other words, toward the injector 14. The protruding portion 16b is a portion that protrudes in one direction beyond the periphery, for example, a portion where the central portion of the main body 16c protrudes beyond the ends in the shorter direction. The agitator 16 is formed into a semi-cylindrical shape by bending a plate-like member, for example, and the region including the circumferential center of the semi-cylindrical portion is the protruding portion 16b. The cross section of the main body 16c perpendicular to the flow direction within the curved pipe 23 may be flat, arc-shaped, or annular.

The stirring member 16 has both ends curved away from the injector 14, with the protrusion 16b as the center. Note that the semi-cylinder is a shape similar to a cylinder cut along a plane extending in the axial direction. The semi-cylinder is not limited to a cross section that is an arc that forms part of a perfect circle, as long as the cross section is roughly arc-shaped.

The agitator 16 is positioned so that the extension direction of the agitator 16, in other words, the central axis direction of the semi-cylinder, intersects at a certain angle with the flow direction of the exhaust gas in the curved pipe 23. Therefore, the agitator 16 is positioned so that it crosses part of the exhaust gas flow path within the exhaust pipe 10.

The central axis here refers to the central axis of the aforementioned imaginary cylinder of which the semi-cylinder is a part. In this configuration, the exhaust gas collides with the surface of the agitator 16 on the side of the protruding portion 16b.
The stirring member 16 (i.e., the main body 16c) has a plurality of through holes 16h. The plurality of through holes 16h may be circular, elongated holes such as oval holes, burring holes, or the like.

<Flow of exhaust gas>
2, the exhaust gas introduced from the upstream pipe 21 of the introduction section 11 flows into the curved pipe 23. The curved pipe 23 constitutes a part of the exhaust gas flow path extending from the first central axis 21a side toward the second central axis 17a side.

The agitator 16 is positioned so that exhaust gas passing through the curved pipe 23 from the first central axis 21a toward the second central axis 17a strikes the protruding portion 16b of the agitator 16. In other words, the agitator 16 is positioned so that the outer peripheral surface of the semi-cylinder faces the injector 14. The outer peripheral surface here refers to the portion that corresponds to the outer surface of the peripheral wall that constitutes the cylinder, assuming that the agitator 16 is part of the cylinder.

As the exhaust gas and reducing agent pass around the agitator 16, as shown in Figure 3, some of the exhaust gas can pass through the interior of the multiple through-holes 16h. In other words, the multiple through-holes 16h function to facilitate diffusion of the exhaust gas and reducing agent. Furthermore, if the agitator 16 were flat and not curved or bent, exhaust gas would likely stagnate on the upstream side of the agitator 16 where the reducing agent hits (i.e., the upper side in Figure 3). However, with the agitator 16 of this embodiment, exhaust gas stagnation is less likely to occur. This is because the curved shape of the agitator 16 and the multiple through-holes 16h allow the exhaust gas to flow more easily.

The multiple through holes 16h also contribute to reducing pressure loss in the exhaust gas flow path. In this manner, in the configuration of this embodiment, the curved shape of the stirring member 16 and the multiple through holes 16h disperse the flow of exhaust gas, making it easier for the exhaust gas and reducing agent to mix.

Exhaust gas passes around the agitator 16 and is guided through the curved pipe 23 to the connecting portion 13, where it is introduced into the SCR catalyst 17. The SCR catalyst 17 has many holes (not shown) that are parallel to the second central axis 17a. The exhaust gas flows into these holes, where nitrogen oxides are purified by a reduction reaction.

[1-2. Effects]
According to the first embodiment described above in detail, the following effects are achieved.
(1a) One aspect of the present disclosure is an exhaust gas purification device 1 configured to purify exhaust gas using an SCR catalyst 17. The exhaust gas purification device 1 includes an exhaust pipe 10, an injector 14, and an agitator 16. The downstream side of the exhaust pipe 10 in the exhaust gas flow direction is connected to a member that houses the SCR catalyst 17. The injector 14 injects a reducing agent along the exhaust gas flow direction within the exhaust pipe 10. The agitator 16 is disposed downstream of the injector 14 in the exhaust gas flow direction within the exhaust pipe 10, and has a protrusion 16b that protrudes toward the injector 14.

With this configuration, the reducing agent is injected along the flow of the exhaust gas, so that the reducing agent is supplied toward the agitator 16 at high speed. The agitator 16 is also configured with a protrusion 16b, which increases its surface area. This configuration allows the reducing agent to be well agitated by the agitator 16 and heated by the high-temperature exhaust gas, allowing the reducing agent and exhaust gas to be well mixed and supplied to the SCR catalyst 17.

(1b) In one aspect of the present disclosure, the exhaust pipe 10 may include a curved pipe 23 and an upstream pipe 21. The curved pipe 23 is a section in which the agitator 16 is disposed and which curves away from the injector 14. The upstream pipe 21 is disposed upstream of the curved pipe 23 in the flow direction. The agitator 16 has a cross section perpendicular to the flow direction within the curved pipe 23 that is flat, arc-shaped, or annular, and has a main body portion 16c extending downstream in the flow direction, with the flow direction in the upstream pipe 21 and the extension direction of the main body portion 16c of the agitator 16 configured to be approximately parallel.

This configuration allows the agitator 16 to have a longer length in the extension direction within the curved pipe 23. This increases the contact area between the exhaust gas from the upstream side and the agitator 16, increasing the opportunities for contact between the exhaust gas and the reducing agent.

(1c) In one aspect of the present disclosure, the injector 14 and the stirring member 16 may be disposed opposite each other across the central axis of the exhaust pipe 10 .
According to this configuration, the reducing agent can be configured to reach the agitator 16 after passing through the central axis of the exhaust pipe 10, so that the reducing agent can reach the agitator 16 at a higher speed.

(1d) In one aspect of the present disclosure, the central axis of the exhaust pipe 10 downstream of the injector 14 in the flow direction (part of the curved portion) may be approximately aligned with the center line 23a of the exhaust pipe 10 between the injector 14 and the agitator 16, which is the central axis of the injection range of the injector 14.

This configuration makes it easier for the reducing agent to be supplied to the center of the exhaust gas flowing through the exhaust pipe 10, making it easier for the reducing agent and exhaust gas to mix well.

(1e) In one aspect of the present disclosure, the stirring member 16 may constitute a collision portion onto which the reducing agent is directly injected.
According to this configuration, the reducing agent is injected directly onto the stirring member 16, so that the reducing agent and exhaust gas can be supplied to the SCR catalyst 17 in a more favorably mixed state.

(1f) In one aspect of the present disclosure, the stirring member 16 may have a plurality of through holes 16h.
This configuration can suppress pressure loss around the agitator 16, making it easier for the reducing agent and exhaust gas to flow downstream of the agitator 16. Furthermore, if the agitator 16 is flat and not curved or bent, for example, if the agitator 16 is flat and perpendicular to the flow direction of the exhaust gas, exhaust gas stagnation is likely to occur upstream of the agitator 16. However, with the agitator 16 of this embodiment, exhaust gas stagnation is less likely to occur. This is because the curved shape of the agitator 16 and the multiple through holes 16h make it easier for the exhaust gas to flow.

[2. Second embodiment]
[2-1. Differences from the first embodiment]
The second embodiment has the same basic configuration as the first embodiment, and therefore differences will be described below. Note that the same reference numerals as those in the first embodiment indicate the same configuration, and the preceding description will be referred to.

In the first embodiment of the exhaust gas purification device 1 described above, the agitator 16 extends upstream along the flow of exhaust gas, and its direction coincides with the second central axis 17a of the SCR catalyst 17. In contrast, the exhaust gas purification device 2 of the second embodiment differs from the first embodiment in that the agitator 16 is oriented in a different direction.

[2-2. Configuration]
The exhaust gas purification device 2 of the second embodiment is configured as shown in Figures 4 and 5. That is, the curved pipe 23 includes a central portion 231, a first curved portion 232, and a second curved portion 233. The central portion 231 is configured as a straight pipe. The first curved portion 232 is configured to curve toward the upstream pipe 210 on the upstream side of the central portion 231. The reducing agent introduction pipe 22 is disposed so as to protrude from the first curved portion 232 toward the outside of the curve. An injector 14 is disposed in the reducing agent introduction pipe 22.

The second curved portion 233 is configured to curve vertically downward downstream of the central portion 231. The stirring member 16 is disposed in the downstream portion of the second curved portion 233, extending vertically from the lower side to the upper side.

A catalyst holding section 12 including an SCR catalyst 17 is disposed vertically below the curved pipe 23 .
The injector 14 is configured such that the injection axis 22a coincides with the central axis of the central portion 231. The injection axis 22a is disposed so as to face the protruding portion 16b of the stirring member 16, similar to the injection axis 22a of the first embodiment.

[2-3. Effects]
According to the second embodiment described above in detail, the effect (1a) of the first embodiment described above is achieved.
3. Other Embodiments
Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modifications.

(3a) In the above embodiment, the agitator 16 is provided with a semi-cylindrical shape having a plurality of through holes 16h, but the configuration of the agitator 16 is not limited to this. The agitator 16 may have any configuration as long as it can effectively mix the exhaust gas and the reducing agent. For example, the agitator 16 does not need to have a plurality of through holes 16h.
The stirring member 16 may also be a flat plate, a combination of flat plates, a combination of a flat plate and a curved plate, or a bent flat plate. In this case, the protruding portion 16b of the stirring member 16 may be formed from such a flat plate or curved plate.

(3b) Multiple functions possessed by one component in the above embodiments may be realized by multiple components, or one function possessed by one component may be realized by multiple components. Also, multiple functions possessed by multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Also, part of the configuration of the above embodiments may be omitted. Also, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

(3c) In addition to the exhaust gas purification devices 1 and 2 described above, the present disclosure can also be realized in various forms, such as a system including the exhaust gas purification devices 1 and 2 as components, and a method of purifying exhaust gas using the exhaust gas purification devices 1 and 2.

[Technical idea disclosed in this specification]
[Item 1]
An exhaust gas purification device configured to purify exhaust gas using an SCR catalyst,
an exhaust pipe whose downstream side in the flow direction of exhaust gas is connected to a member accommodating an SCR catalyst;
an injector that injects a reducing agent along the flow direction within the exhaust pipe;
an agitator disposed in the exhaust pipe downstream of the injector in the flow direction, the agitator having a protruding portion protruding toward the injector;
An exhaust gas purification device comprising:

[Item 2]
Item 1 is an exhaust gas purification device according to item 1,
The exhaust pipe is
a curved pipe in which the stirring member is disposed and which is curved so as to move away from the injector;
an upstream pipe disposed upstream of the curved pipe in the flow direction;
Equipped with
the stirring member has a main body portion whose cross section perpendicular to the flow direction in the curved pipe is flat, arc-shaped, or annular, and extends downstream in the flow direction;
The exhaust gas purification device is configured so that a flow direction in the upstream pipe and an extension direction of the main body portion of the stirring member are parallel to each other.

[Item 3]
Item 2: The exhaust gas purification device according to item 2,
The exhaust gas purification device, wherein the injector and the stirring member are arranged to face each other across the central axis of the upstream pipe.

[Item 4]
The exhaust gas purification device according to any one of items 1 to 3,
An exhaust gas purification device configured so that a central axis of the exhaust pipe at a portion between the injector and the stirring member coincides with a central axis of the injection range of the injector.

1, 2...exhaust gas purification device, 10...exhaust pipe, 11...inlet portion, 12...catalyst holding portion, 13...connecting portion, 14...injector, 16...agitating member, 16a...connecting portion, 16b...protruding portion, 16c...main body portion, 16h...through hole, 17...SCR catalyst, 17a...second central axis, 21, 210...upstream pipe, 21a...first central axis, 22...reducing agent introduction pipe, 22a...injection axis, 23...curved pipe, 23a...center line, 23b...flow path, 231...central portion, 232...first curved portion, 233...second curved portion.

Claims (4)

An exhaust gas purification device configured to purify exhaust gas using an SCR catalyst,
an exhaust pipe whose downstream side in the flow direction of exhaust gas is connected to a member accommodating an SCR catalyst;
an injector that injects a reducing agent along the flow direction within the exhaust pipe;
an agitator disposed in the exhaust pipe downstream of the injector in the flow direction, the agitator having a protruding portion protruding toward the injector;
Equipped with
The exhaust pipe is
a curved pipe in which the stirring member is disposed and which is curved so as to move away from the injector;
an upstream pipe disposed upstream of the curved pipe in the flow direction;
Equipped with
the stirring member has a main body portion whose cross section perpendicular to the flow direction in the curved pipe is flat, arc-shaped, or annular, and extends downstream in the flow direction;
The exhaust gas purification device is configured so that a flow direction in the upstream pipe and an extension direction of the main body portion of the stirring member are parallel to each other. The exhaust gas purification device according to claim 1,
The exhaust gas purification device, wherein the injector and the stirring member are arranged to face each other across the central axis of the upstream pipe. The exhaust gas purification device according to claim 1,
the stirring member is a plate-shaped member that faces the injector and is disposed so as to block a portion of the exhaust pipe,
The exhaust gas purification device, wherein the stirring member has a plurality of through holes formed therein. The exhaust gas purification device according to any one of claims 1 to 3,
An exhaust gas purification device configured so that a central axis of the exhaust pipe at a portion between the injector and the stirring member coincides with a central axis of the injection range of the injector.