EXHAUST GAS PURIFYING DEVICE FOR INTERNAL COMBUSTION ENGINE, AND SWIRL GENERATING DEVICE

Abstract

An exhaust gas purifying device for an internal combustion engine, provided with a swirl generating means for generating a swirl which has a strong swirl force and applying reduced resistance to the swirl. A swirl generating device for generating a swirl which has a strong swirl force and applying reduced resistance to the swirl is also provided. An exhaust gas purifying device (100) for an internal combustion engine is provided with an exhaust pipe (1), a reduction catalyst (2), a reducing agent supply means (3), and a swirl generating means (40). The swirl generating means (40) has two blades (410, 420) formed by dividing a substantially elliptic plate into two in the direction of the major axis thereof. The two blades (410, 420) are integrated together such that the two blades are rotated relative to each other about the minor axis of the plate so as to cross each other, and the two blades are mounted such that the direction of the major axis is parallel to the direction of flow of exhaust gas.

Description

TECHNICAL FIELD

The present invention relates to an exhaust gas purifying device for an internal combustion engine and a swirl generating device.

BACKGROUND ART

An exhaust gas purifying device for an internal combustion engine is a device for purifying exhaust gas exhausted from the internal combustion engine. A known device of this type includes an exhaust pipe through which exhaust gas exhausted from the internal combustion engine flows, a reduction catalyst provided in the exhaust pipe and reducing and purifying oxynitride contained in the exhaust gas, reducing agent supply means for supplying a reducing agent by injecting it into the exhaust gas flowing upstream of the reduction catalyst, and swirl generating means provided upstream of the reduction catalyst in the exhaust pipe and generating a swirl in the exhaust gas (see Japanese Patent Laid-Open No. 2006-29233, for example).

FIG. 8 shows an exemplary exhaust gas purifying device for an internal combustion engine according to the related art. FIG. 8(a) is a schematic view of the exhaust gas purifying device, and FIG. 8(b) is an enlarged perspective view of a key portion V shown in FIG. 8(a).

As shown in FIG. 8(a), an exhaust gas purifying device 10 for an internal combustion engine includes an exhaust pipe 1, a reduction catalyst 2, a reducing agent injection nozzle 3 that supplies a reducing agent (such as urea solution) by injecting it into exhaust gas flowing upstream of the reduction catalyst 2, and swirl generating means 4 for generating a swirl in the exhaust gas and provided upstream of the reduction catalyst 2 in the exhaust pipe 1 (specifically, upstream of a location where the reducing agent is sprayed into the exhaust gas through the reducing agent injection nozzle 3 (see “reducing agent sprayed portion” in FIG. 8(a)). As shown in FIG. 8(b), the swirl generating means 4 is a finned structure including columns 41 and blades 42 and generating turbulence or swirl in the exhaust gas to facilitate diffusion of the reducing agent in the exhaust gas.

In the thus configured exhaust gas purifying device 10 for an internal combustion engine, the swirl generating means 4 generates turbulence or swirl in the exhaust gas to facilitate diffusion of the reducing agent in the exhaust gas. As a result, the reducing agent can be uniformly supplied to the reduction catalyst 2, whereby exhaust gas purifying performance can be ensured at a certain level or higher.

SUMMARY OF INVENTION

Technical Problem

If a swirl force created by the swirl generating means 4 can be increased, the reducing agent can be more uniformly supplied to the reduction catalyst, whereby the exhaust gas purifying performance can be improved. The swirl force created by the swirl generating means 4 is therefore desirably improved.

On the other hand, when the exhaust gas passes through the swirl generating means 4, it produces large resistance. The swirl generating means 4 therefore needs to have a certain magnitude of strength. If the resistance produced by the swirl generating means 4 can be reduced, not only can the strength required for the swirl generating means 4 be reduced, but also the fuel consumption of the internal combustion engine can be improved. The resistance produced by the swirl generating means 4 is therefore desirably reduced.

If the swirl force created by the swirl generating means 4 is attempted to be increased, however, the resistance produced by the swirl generating means 4 tends to increase, whereas if the resistance produced by the swirl generating means 4 is attempted to be reduced, the swirl force created by the swirl generating means 4 tends to decrease. This is a reason why in related art increase in the swirl force created by the swirl generating means 4 and reduction in the resistance produced by the swirl generating means 4 cannot be simultaneously achieved.

It has therefore been desired to develop an exhaust gas purifying device for an internal combustion engine including swirl generating means that creates a strong swirl force and applies reduced resistance. In addition to the development of such an exhaust gas purifying device for an internal combustion engine, it has also been desired to develop swirl generating means itself that can be disposed in a typical exhaust pipe, produce a strong swirl force, and apply reduced resistance.

An object of the present invention is to provide an exhaust gas purifying device for an internal combustion engine including swirl generating means that creates a strong swirl force and applies reduced resistance. Another object of the present invention is to provide swirl generating means that creates a strong swirl force and applies reduced resistance.

SOLUTION TO PROBLEM

To achieve the objects described above, the present invention provides an exhaust gas purifying device for an internal combustion engine including an exhaust pipe through which exhaust gas exhausted from the internal combustion engine flows, a reduction catalyst provided in the exhaust pipe and reducing and purifying an oxynitride contained in the exhaust gas, reducing agent supply means for supplying a reducing agent by injecting the reducing agent into the exhaust gas flowing upstream of the reduction catalyst, and swirl generating means provided upstream of the reduction catalyst in the exhaust pipe and generating a swirl in the exhaust gas. The swirl generating means has two blades formed by halving a substantially elliptic plate along the direction of a major axis thereof. The two blades are so integrated together that the blades are rotated relative to each other about a minor axis of the plate so as to cross each other. (Let θ be a crossing angle between the two blades integrated as described above, and an angle expressed by 90-θ×1/2 is called a fin angle.) The two blades are so mounted that the direction of the major axis is parallel to the direction in which the exhaust gas flows.

The present invention further provides swirl generating means provided in an exhaust pipe having two blades formed by halving a substantially elliptic plate along the direction of a major axis thereof. The two blades are so integrated together that the blades are rotated relative to each other about a minor axis of the plate so as to cross each other, and the two blades are so mounted that the direction of the major axis is parallel to the direction in which the exhaust gas flows.

At least one of the two blades described above is desirably so configured that an arcuate portion of an outer edge of the blade is in contact with an inner wall of the exhaust pipe. In particular, both the two blades are more desirably so configured that the arcuate portions of the outer edges of the blades are in contact with the inner wall of the exhaust pipe.

At least one of the two blades is desirably so configured that both ends thereof in the direction of the major axis are cut in the direction parallel to the minor axis. In particular, both the two blades are desirably so configured that both ends thereof in the direction of the major axis are cut in the direction parallel to the minor axis.

It is desirable that the two blades are so configured that both ends thereof in the direction of the major axis are integrated together by connecting portions, and that one of the connecting portions, the connecting portion disposed on the upstream side in the exhaust pipe, is configured to connect upstream ends of the two blades with each other.

CROSS REFERENCE TO RELATED DOCUMENTS

The present application claims the priority of Japanese Patent Application No. 2008-241382 filed on Sep. 19, 2008, and the disclosure of which is incorporated herein by reference.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] FIG. 1 shows a key portion of an exhaust gas purifying device for an internal combustion engine according to an embodiment of the present invention.

[FIG. 2] FIG. 2 shows swirl generating means viewed from several directions (A to D) shown in FIG. 1.

[FIG. 3] FIG. 3 is a table showing comparison between the swirl generating means of the present invention and swirl generating means of related art in terms of the magnitudes of swirl force and resistance for fin specifications (I to III).

[FIG. 4] FIG. 4 shows a flow analysis result (flow line) for the fin specifications.

[FIG. 5] FIG. 5 shows a flow analysis result (swirl force) for the fin specifications.

[FIG. 6] FIG. 6 shows a flow analysis result (resistance) for the fin specifications.

[FIG. 7] FIG. 7 shows a flow analysis result (flow speed) for the fin specifications.

[FIG. 8] FIG. 8 shows an exemplary exhaust gas purifying device for internal combustion engine according to related art.

[FIG. 9] FIGS. 9(a) and 9(b) show swirl generating means 50 disposed in an exhaust pipe 1 and viewed from various angles.

[FIG. 10] FIGS. 10(a) to 10(c) show the swirl generating means 50 viewed from directions E to G shown in FIG. 9.

[FIG. 11] FIG. 11 shows exhaust gas flowing through the exhaust pipe 1 in which the swirl generating means 50 is disposed, the exhaust gas monitored with “EFD V5”.

[FIG. 12] FIGS. 12(a) and 12(b) show swirl generating means 60 disposed in the exhaust pipe 1 and viewed from various angles.

[FIG. 13] FIGS. 13(a) to 13(c) show the swirl generating means 60 viewed from directions H to J shown in FIG. 12.

[FIG. 14] FIG. 14 shows exhaust gas flowing through the exhaust pipe 1 in which the swirl generating means 60 is disposed, the exhaust gas monitored with “EFD V5”.

[FIG. 15] FIG. 15 shows the relationship between a fin angle and a swirl force.

[FIG. 16] FIG. 16 shows the relationship between the fin angle and pressure loss.

DESCRIPTION OF EMBODIMENTS

The best mode for carrying out the present invention will be described below.

FIG. 1 shows a key portion of an exhaust gas purifying device for an internal combustion engine according to an embodiment of the present invention. FIG. 2 shows swirl generating means 40 viewed from several directions (A to D) shown in FIG. 1. FIGS. 2(A) to 2(D) correspond to those of the swirl generating means 40 viewed from the directions A to D shown in FIG. 1, respectively. In FIGS. 1 and 2, the same portions as those in FIG. 8 have the same reference characters.

As shown in FIG. 1, an exhaust gas purifying device 100 for an internal combustion engine includes the swirl generating means 40 in an exhaust pipe 1. As shown in FIG. 2, the swirl generating means 40 has two blades 410 and 420 formed by halving a substantially elliptic plate along the direction of the major axis thereof. The two blades 410 and 420 are so integrated together via connecting portions 431 and 432 that the two blades are rotated relative to each other about the minor axis (hereinafter also referred to as a central axis) of the plate so as to cross each other, and the two blades 410 and 420 are so mounted that the direction of the major axis is parallel to the direction in which the exhaust gas flows. The blades 410 and 420 are so configured that arcuate portions 410a and 420a of outer edges of the blades are in contact with the inner wall of the exhaust pipe 1.

In the thus configured exhaust gas purifying device 100 for an internal combustion engine, the two blades 410 and 420, which form the swirl generating means 40, produce a double spiral swirl in the exhaust gas flowing through the exhaust pipe 1. As a result, the exhaust gas purifying device 100 for an internal combustion engine can create a strong swirl force. Further, since the blades 410 and 420 have a structure to which the exhaust gas applies less resistance, the double spiral swirl flows smoothly along the wall surfaces of the blades 410 and 420. As a result, the resistance produced in the exhaust gas purifying device 100 for an internal combustion engine decreases.

In FIG. 1, the swirl generating means 40 is disposed upstream of a reducing agent sprayed portion (see FIG. 8). The present invention is, however, not limited to the embodiment shown in FIG. 1, and the swirl generating means 40 may be disposed downstream of the reducing agent sprayed portion as long as being disposed upstream of the reduction catalyst 2.

Differences between the swirl generating means of the present invention and the swirl generating means of the related art will next be described with reference to FIGS. 3 to 7.

FIG. 3 is a table showing comparison between the swirl generating means of the present invention (see “inventive proposal” in FIG. 3) and the swirl generating means of the related art (see “related art structures 1 and 2” in FIG. 3) in terms of the magnitudes of the swirl force and the resistance for fin specifications (I to III). FIGS. 4 to 7 show flow analysis results for the fin specifications shown in FIG. 3. FIG. 4 shows flow lines. FIG. 5 shows the swirl force. FIG. 6 shows the resistance. FIG. 7 shows the flow speed. It is noted that FIG. 6 shows flow analysis results (resistance) only for the fin specifications I and II out of the fin specifications I to III shown in FIG. 3 but does not shows a flow analysis result (resistance) for the fin specification III.

First, as shown in FIG. 3, the inventive proposal shows a large swirl force of 2.2 revolutions and a low resistance of 3.2 kPa. In contrast, the related art structure 1 shows a large swirl force of 2.1 revolutions, which is similar to the magnitude of the swirl force provided in the inventive proposal, but a significantly high resistance of 65.1 kPa. On the other hand, the related art structure 2 shows a low resistance of 3.2 kPa, which is the same as the magnitude of the resistance provided in the inventive proposal, but a significantly small swirl force of 0.5 revolutions. Further, the flow analysis results shown in FIGS. 4 to 7 indicate that the inventive proposal achieves a large swirl force and low resistance at the same time unlike the related art structures 1 and 2.

As described above, the exhaust gas purifying device 100 for an internal combustion engine according to the embodiment of the present invention (see FIG. 1) advantageously provides a stronger swirl force and lower resistance than the exhaust gas purifying device 10 for an internal combustion engine of the related art (see FIG. 8).

Other Embodiments

The above description is provided by way of example for easier understanding of the present invention but does not intend to limit the present invention. The present invention can, of course, be changed or improved without departing from the substance and purpose thereof and encompasses equivalents thereof.

For example, the above description has been made with reference to the swirl generating means 40 as the swirl generating means, but instead of or in addition to the swirl generating means 40, swirl generating means 50 shown in FIGS. 9 to 11 or swirl generating means 60 shown in FIGS. 12 to 14 may be used.

The swirl generating means 50 and the swirl generating means 60 will be described below.

<Swirl generating means 50>

The swirl generating means 50 will first be described in detail with reference to FIGS. 9 to 11. FIG. 11 shows the exhaust gas flowing through the exhaust pipe 1 in which the swirl generating means 50 is disposed, the exhaust gas monitored with “EFD V5” (manufactured by “KOZO KEIKAKU ENGINEERING Inc.”).

As shown in FIGS. 9 and 10, the swirl generating means 50 has two blades 510 and 520 formed by halving a substantially elliptic plate along the direction of the major axis thereof. The two blades 510 and 520 are so integrated together that they are rotated relative to each other about the minor axis (hereinafter also referred to as a central axis) of the plate so as to cross each other, and the two blades 510 and 520 are so mounted in the exhaust pipe 1 that the direction of the major axis is parallel to the direction in which the exhaust gas flows.

The blades 510 and 520 are so configured that arcuate portions 510a and 520a of outer edges of the blades are in contact with the inner wall of the exhaust pipe 1. The two blades 510 and 520 are also so configured that both ends thereof in the direction of the major axis (specifically, an upstream end 510b of the blade 510, a downstream end 510c of the blade 510, an upstream end 520b of the blade 520, and a downstream end 520c of the blade 520) are cut in the direction parallel to the minor axis. The two blades 510 and 520 are so integrated together on both sides thereof in the direction of the major axis by connecting portions 531 and 532.

One of the connecting portions 531 and 532, the connecting portion 531 disposed on the downstream side in the exhaust pipe 1, is configured to connect downstream portions of the two blades 510 and 520. More specifically, the connecting portion 531 is configured to connect downstream portions of the two blades 510 and 520 with each other in a region upstream of the downstream ends 510c and 520c of the two blades 510 and 520 (that is, a region between the downstream ends 510c, 520c and the central axis described above). On the other hand, the connecting portion 532 disposed on the upstream side in the exhaust pipe 1 is configured to connect upstream portions of the two blades 510 and 520. More specifically, the connecting portion 532 is configured to connect the upstream ends 510b and 520b of the two blades 510 and 520 with each other. The connecting portion 532 has a larger width in the direction in which the exhaust gas flows than that of the connecting portion 531.

As shown in FIG. 11, when the swirl generating means 50 is disposed in the exhaust pipe 1, the swirl force of the exhaust gas becomes strong. In FIG. 11, the flow rate of the exhaust gas was 1200 kg/h; the temperature of the exhaust gas was 520° C.; and the fin angle was 52.5°. The pressure loss under these conditions was 12.998 kPa. As described above, when the swirl generating means 50 is disposed in the exhaust pipe 1, the resistance applied to the exhaust gas also decreases.

<Swirl generating means 60>

The swirl generating means 60 will next be described in detail with reference to FIGS. 12 to 14. FIG. 14 shows the exhaust gas flowing through the exhaust pipe 1 in which the swirl generating means 60 is disposed, the exhaust gas monitored with “EFD V5” (manufactured by “KOZO KEIKAKU ENGINEERING Inc.”).

As shown in FIGS. 12 and 13, the swirl generating means 60 has substantially the same configuration as that of the swirl generating means 50. Specifically, the swirl generating means 60 has two blades 610 and 620 formed by halving a substantially elliptic plate along the direction of the major axis thereof. The two blades 610 and 620 are so integrated together that the they are rotated relative to each other about the minor axis (hereinafter also referred to as a central axis) of the plate so as to cross each other, and the two blades are so mounted in the exhaust pipe 1 that the direction of the major axis is parallel to the direction in which the exhaust gas flows. The two blades 610 and 620 are so configured that arcuate portions 610a and 620a of outer edges of the blades are in contact with the inner wall of the exhaust pipe 1, as in the case of the two blades 510 and 520. The swirl generating means 60 is, as in substantially the same manner as the swirl generating means 50, further so configured that both ends thereof in the direction of the major axis (specifically, an upstream end 610b of the blade 610, a downstream end 610c of the blade 610, an upstream end 620b of the blade 620, and a downstream end 620c of the blade 620) are cut in the direction parallel to the minor axis. The two blades 610 and 620 are so integrated together on both sides thereof in the direction of the major axis by connecting portions 631 and 632.

The swirl generating means 60, however, has a configuration different from that of the swirl generating means 50. Specifically, both ends of the swirl generating means 60 are cut by a greater amount than the amount by which both ends of the swirl generating means 50 are cut.

As shown in FIG. 14, when the swirl generating means 60 is disposed in the exhaust pipe 1, the swirl force of the exhaust gas becomes strong, as in the case where the swirl generating means 50 is disposed in the exhaust pipe 1. In FIG. 14 as well, the flow rate of the exhaust gas was 1200 kg/h; the temperature of the exhaust gas was 520° C.; and the fin angle was 52.5°. The pressure loss under these conditions was, however, 10.209 kPa. As described above, when the swirl generating means 60 is disposed in the exhaust pipe 1, the resistance applied to the exhaust gas decreases as well.

In particular, both ends of the swirl generating means 60 are cut by a greater amount than the amount by which both ends of the swirl generating means 50 are cut. Therefore, when the swirl generating means 60 is disposed in the exhaust pipe 1, the gap (that is, exhaust gas flow path) formed between the inner wall of the exhaust pipe 1 and both ends of the swirl generating means 60 is larger than that in the case where the swirl generating means 50 is disposed in the exhaust pipe 1. As a result, the resistance applied to the exhaust gas decreases. Since the swirl generating means 60 is smaller than the swirl generating means 50, the structure in which the swirl generating means 60 is disposed in the exhaust pipe 1 can be lighter and more compact than the structure in which the swirl generating means 50 is disposed in the exhaust pipe 1.

===Confirmation Test===

To confirm the advantageous effect of the present invention (that is, the advantageous effect of a stronger swirl force of the exhaust gas and lower resistance applied thereto provided when any of the swirl generating means of the present invention is used), the following confirmation test was conducted. That is, the relationship between the fin angle and the swirl force (see the flow line diagram of FIG. 15) and the relationship between the fin angle and the pressure loss (see the graph in FIG. 16) were studied in the confirmation test by using two types of fin shown in FIG. 15, specifically, a new fin (an example of the swirl generating means of the present invention) and a conventional fin (an example of the swirl generating means of the related art).

As shown in FIG. 15, the swirl force created when the fin angle of the new fin is 65° is substantially equal to or as strong as the swirl force created when the fin angle of the conventional fin is 45°. On the other hand, as shown in FIG. 16, the pressure loss was approximately 27 kPa when the fin angle of the new fin is 65°, whereas the pressure loss was approximately 44 kPa when the fin angle of the conventional fin is 45°.

The findings described above indicate that using the new fin and adjusting the fin angle as appropriate not only allow substantially the same magnitude of swirl force as that created when the conventional fin is used to be obtained but also allow the resistance applied to the exhaust gas to be reduced and hence the pressure loss to be lowered as compared to the case where the conventional fin is used.

INDUSTRIAL APPLICABILITY

The present invention can provide an exhaust gas purifying device for an internal combustion engine including swirl generating means that creates a strong swirl force and applies reduced resistance. The present invention can further provide a swirl generating device that creates a strong swirl force and applies reduced resistance.

REFERENCE SIGNS LIST

• 1 exhaust pipe
• 2 reduction catalyst
• 3 reducing agent injection nozzle
• 40, 50, 60 swirl generating means
• 410, 420, 510, 520, 610, 620 blade
• 410 a, 420 a, 510 a, 520 a, 610 a, 620 a arcuate portion
• 510 b, 520 b, 610 b, 620 b upstream end
• 510 c, 520 c, 610 c, 620 c downstream end
• 431, 432, 531, 532, 631, 632 connecting portion

Claims

1. An exhaust gas purifying device for an internal combustion engine, the exhaust gas purifying device comprising: an exhaust pipe through which exhaust gas exhausted from the internal combustion engine flows;a reduction catalyst provided in the exhaust pipe and reducing and purifying an oxynitride contained in the exhaust gas;reducing agent supply means for supplying a reducing agent by injecting the reducing agent into the exhaust gas flowing upstream of the reduction catalyst; andswirl generating means provided upstream of the reduction catalyst in the exhaust pipe and generating a swirl in the exhaust gas,wherein the swirl generating means has two blades formed by halving a substantially elliptic plate along the direction of a major axis thereof, the two blades so integrated together that the blades are rotated relative to each other about a minor axis of the plate so as to cross each other, the two blades so mounted that the direction of the major axis is parallel to the direction in which the exhaust gas flows.

2. The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the two blades are so configured that arcuate portions of outer edges of the blades are in contact with an inner wall of the exhaust pipe.

3. The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the two blades are so configured that both ends thereof in the direction of the major axis are cut in the direction parallel to the minor axis.

4. The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the two blades are so configured that both ends thereof in the direction of the major axis are integrated together by connecting portions, andone of the connecting portions, the connecting portion disposed on the upstream side in the exhaust pipe, is configured to connect upstream ends of the two blades with each other.

5. Swirl generating means provided in an exhaust pipe, the swirl generating means comprising: two blades formed by halving a substantially elliptic plate along the direction of a major axis thereof, the two blades so integrated together that the blades are rotated relative to each other about a minor axis of the plate so as to cross each other, the two blades so mounted that the direction of the major axis is parallel to the direction in which the exhaust gas flows.

6. The swirl generating means according to claim 5, wherein the two blades are so configured that arcuate portions of outer edges of the blades are in contact with an inner wall of the exhaust pipe.

7. The swirl generating means according to claim 5, wherein the two blades are so configured that both ends thereof in the direction of the major axis are cut in the direction parallel to the minor axis.

8. The swirl generating means according to claim 5, wherein the two blades are so configured that both ends thereof in the direction of the major axis are integrated together by connecting portions, andone of the connecting portions, the connecting portion disposed on the upstream side in the exhaust pipe, is configured to connect upstream ends of the two blades with each other.

9. The exhaust gas purifying device for an internal combustion engine according to claim 2, wherein the two blades are so configured that both ends thereof in the direction of the major axis are cut in the direction parallel to the minor axis.

10. The exhaust gas purifying device for an internal combustion engine according to claim 2, wherein the two blades are so configured that both ends thereof in the direction of the major axis are integrated together by connecting portions, andone of the connecting portions, the connecting portion disposed on the upstream side in the exhaust pipe, is configured to connect upstream ends of the two blades with each other.

11. The exhaust gas purifying device for an internal combustion engine according to claim 3, wherein the two blades are so configured that both ends thereof in the direction of the major axis are integrated together by connecting portions, andone of the connecting portions, the connecting portion disposed on the upstream side in the exhaust pipe, is configured to connect upstream ends of the two blades with each other.

12. The swirl generating means according to claim 6, wherein the two blades are so configured that both ends thereof in the direction of the major axis are cut in the direction parallel to the minor axis.

13. The swirl generating means according to claim 6, wherein the two blades are so configured that both ends thereof in the direction of the major axis are integrated together by connecting portions, andone of the connecting portions, the connecting portion disposed on the upstream side in the exhaust pipe, is configured to connect upstream ends of the two blades with each other.

14. The swirl generating means according to claim 7, wherein the two blades are so configured that both ends thereof in the direction of the major axis are integrated together by connecting portions, andone of the connecting portions, the connecting portion disposed on the upstream side in the exhaust pipe, is configured to connect upstream ends of the two blades with each other.