JP5239764B2 - Engine exhaust system structure - Google Patents

Description

  The present invention relates to an exhaust system structure of an engine.

Conventionally, by removing harmful substances contained in exhaust gas from diesel engines such as nitrogen oxide (NOx), carbon monoxide (CO), and particulate matter (hereinafter simply referred to as PM), exhaust gas is reduced. Various technologies for purification have been developed.
As an example, Patent Document 1 below includes a technique for injecting fuel from a nozzle (2) into an exhaust passage (7) as shown in FIG.

In the technique of this patent document 1, as disclosed in FIG. 2 of the document, the bulging portion (1) is formed in the exhaust passage (7). And this nozzle (2) is provided in the central part vicinity of the bulging part (1).
Further, as disclosed in FIG. 3 of the same document, the fuel injection direction from the nozzle (2) is the inner periphery of the bulging portion (1) as shown by an arrow (C) in FIGS. It is set so as to be directed to the exhaust flow (B) generated along the surface (1a).
JP 2007-247591 A

However, in the technique of Patent Document 1, although the fuel injected from the nozzle (2) is injected toward the exhaust flow (B), it can adhere to the inner peripheral surface (1a) of the bulging portion (1). There is a possibility that the exhaust gas performance cannot be sufficiently improved.
Of course, even with the technique of Patent Document 1, it is possible to obtain the effect of purifying exhaust gas, but in recent years, further improvement in exhaust gas performance has been strongly demanded from the viewpoint of environmental protection.

On the other hand, FIG. 3 shows a structure (prototype structure) created in the process of creating the exhaust system structure of the engine of the present invention. The structure shown in FIG. 3 is hereinafter referred to as a prototype structure 100.
In this prototype structure 100, an exhaust connection pipe 101 formed in a substantially Y shape is provided.
An exhaust outlet (not shown) of a turbocharger (not shown) provided in an engine (not shown) is connected to one inlet 102 in the exhaust connection pipe 101.

An injector 104 that injects fuel into the exhaust connection pipe 101 is provided at the other inlet 103 of the exhaust connection pipe 101.
An exhaust passage 106 is connected to an outlet 105 in the exhaust connection pipe 101.
An oxidation catalyst 107 is provided in the exhaust passage 106, and a NOx trap catalyst 108 is disposed below the oxidation catalyst 107.

  Then, by injecting fuel from the injector 104 into the exhaust connection pipe 106, exhaust gas containing a relatively large amount of fuel components can be flowed into the oxidation catalyst 107 and the NOx trap catalyst 108. . Thus, the oxidation in the oxidation catalyst 107 is promoted, and the NOx component occluded in the NOx trap catalyst 108 is released from the oxidation catalyst 107 and the NOx trap catalyst 108 (so-called NOx purge is executed). It can be done.

Here, it is preferable that the fuel injected from the injector 104 does not adhere to the wall surface of the exhaust connection pipe 101. For this reason, the injector 104 is set to a penetrating force that does not adhere to the wall surface in the process in which the spray of injected fuel is diffused.
However, if the penetration force of the injected fuel is ensured, the fuel and exhaust gas injected from the injector 104 are not sufficiently stirred in the exhaust connection pipe 106 and directly flow into a part of the oxidation catalyst 107 and the NOx trap catalyst 108. A situation will occur.

In other words, the fuel injected from the injector 104 is not sufficiently diffused and cannot pass through the oxidation catalyst 107 and the entire NOx trap catalyst 108 in a balanced manner. For this reason, the exhaust catalyst cannot be efficiently purified as a whole of the oxidation catalyst 107 and the NOx trap catalyst 108.
Further, the fuel that has flowed directly into a part of the oxidation catalyst 107 is vaporized in the oxidation catalyst 107 thereafter. At this time, the temperature of the oxidation catalyst 107 is partially lowered due to the heat of vaporization of the fuel, and the purification efficiency of the exhaust gas further decreases.

  On the other hand, an exhaust gas containing a high concentration fuel component, that is, a region where exhaust gas in a very rich atmosphere flows (see symbol Fa in FIG. 3) or a fuel that has not been vaporized, is part of the oxidation catalyst 107 and the NOx trap catalyst 108 In the region where the liquid flows as it is (refer to the reference numeral Fa in FIG. 3), a severe chemical reaction partially occurs, and the temperature distribution of the oxidation catalyst 107 and the NOx trap catalyst 108 becomes uneven.

This point will be described again with reference to FIGS. 4 and 5A to 5C.
Here, FIG. 4 shows a case where the horizontal cross section of the oxidation catalyst 107 or the NOx trap catalyst 108 (see symbols CS1, CS2, and CS3 in FIG. 3) is viewed from above. In FIG. 4, it is assumed that the exhaust gas in an extremely rich atmosphere flows in the portions P1 and P2 among the portions indicated by P1 to P5, or the fuel that has not been vaporized flows in the liquid state.

5A shows the temperature at the first horizontal section CS1 of the oxidation catalyst 107 shown in FIG. 3, and FIG. 5B shows the temperature at the second horizontal section CS2 of the oxidation catalyst 107 shown in FIG. 5C shows the temperature at the third horizontal section CS3 of the NOx trap catalyst 108 shown in FIG.
As shown in FIG. 5A, the portion P1 (see the alternate long and short dash line) and the portion P2 (see the alternate long and two short dashes line) in the first horizontal section CS1 of the oxidation catalyst 107 are caused by the heat of vaporization of the fuel adhering to the oxidation catalyst 107. It can be seen that it is locally cooled.

On the other hand, as shown in FIG. 5B and FIG. 5C, in the second horizontal cross section CS2 of the oxidation catalyst 107 and the third horizontal cross section CS3 of the NOx trap catalyst 108, the portion P1 (refer to the dashed line) ) And the portion P2 (refer to the two-dot chain line) are locally heated by heat (reaction heat) generated by oxidation of the fuel component.
As described above, the uneven temperature distribution in the oxidation catalyst 107 and the NOx trap catalyst 108 is caused by the fact that the exhaust gas in the rich atmosphere is not supplied in a well-balanced manner to the entire oxidation catalyst 107 and the NOx trap catalyst 108. For this reason, the exhaust gas purification efficiency by the oxidation catalyst 107 and the NOx trap catalyst 108 is lowered, and it becomes difficult to improve the exhaust gas performance.

  The present invention has been devised in view of such problems, and an object of the present invention is to provide an engine exhaust system structure that can further improve exhaust gas performance and contribute to environmental protection.

To achieve the above object, an exhaust system structure for an engine of the present invention (Claim 1) includes a fuel injection device for injecting fuel into the exhaust pipe connected to an engine, between the engine and the exhaust pipe A turbocharger provided, an inner pipe provided in the vicinity of the turbocharger , having an inner diameter smaller than the inner diameter of the exhaust pipe and provided in the exhaust pipe, the inner pipe and the exhaust pipe, A support member that supports the inner pipe with respect to the exhaust pipe while forming a gap through which exhaust gas flows, and fuel injected from the fuel injection device that is drilled in the inner pipe. A fuel introduction hole to be introduced into the peripheral surface, and the support member is located on the inner peripheral surface of the inner pipe with respect to the exhaust pipe while avoiding a portion to be injected through which the fuel introduced through the fuel introduction hole is injected. The inner pipe is supported, the fuel injection direction by the fuel injection device and the inner pipe The center by a predetermined distance offset, and the injected fuel characterized in that is set so as to pivot the inner tube in the same direction as the swirling flow generated by the turbocharger.

The exhaust system structure of the engine of the present invention according to claim 2 is the content of claim 1, wherein the exhaust pipe downstream of the inner pipe is provided with an exhaust catalyst for purifying exhaust gas from the engine. It is characterized by being .

According to the exhaust system structure of the engine of the present invention, it is possible to prevent a situation in which exhaust gas containing a relatively large amount of fuel is biased to a part of the exhaust pipe, thereby improving exhaust gas performance and protecting the environment. Can contribute. In addition, there is a gap between the inner pipe and the exhaust pipe, and the support member supports the inner pipe while avoiding the fuel injected from the fuel injection device. It can be difficult to reach itself. Further, it is possible to easily generate a swirling flow of fuel on the inner peripheral surface of the inner pipe, and the fuel is well agitated with the exhaust gas. (Claim 1)
Further, the swirling flow of the exhaust gas generated on the downstream side of the turbocharger and the swirling flow of the fuel generated on the inner peripheral surface of the inner pipe are made in the same direction, thereby further promoting the stirring of the exhaust gas and the fuel. I can do it. (Claim 1)
Further, even when a catalyst is provided on the downstream side of the exhaust pipe, it is possible to prevent a situation where a relatively large amount of fuel flows in a part of the catalyst. (Claim 2 )

Hereinafter, an engine exhaust system structure according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an overall configuration thereof, and FIG. 2 is a schematic diagram showing an essential configuration thereof. The II-II arrow cross section of is shown.
As shown in FIGS. 1 and 2, a diesel engine (engine) 11 mounted on a vehicle 10 is provided with a turbocharger 12.

In addition, an inlet 15 of a first exhaust pipe (exhaust pipe) 14 is connected to the outlet 13 of the turbocharger 12. Hereinafter, expressions such as “upstream” or “downstream” are used, but these are based on the flow of exhaust gas discharged from the diesel engine 11.
The turbocharger 12 has a turbine-compressor (not shown), and can rotate the turbine-compressor with exhaust gas discharged from the diesel engine 11 to perform intake air supercharging of the diesel engine 11. .

The first exhaust pipe 14 is a cylindrical part formed in a substantially L shape, and an inlet 18 of a second exhaust pipe (exhaust passage) 17 is connected to the outlet 16 of the first exhaust pipe 14.
Further, a punching metal 19 is provided at the outlet 16 of the first exhaust pipe 14. The punching metal 19 is a metal plate in which a plurality of holes are formed, and the exhaust gas can be disturbed when the exhaust gas passes through these holes.

The first exhaust pipe 14 is formed so that the inner diameter D3 near the outlet 18 is larger than the inner diameter D1 near the inlet 15. That is, the exhaust gas passage area in the first exhaust pipe 14 is set to gradually increase between the inlet inner diameter D1 and the outlet inner diameter 18.
The second exhaust pipe 17 is provided with an oxidation catalyst (exhaust catalyst) 21, and a NOx trap catalyst (exhaust catalyst) 22 is provided downstream of the oxidation catalyst 21 and below the oxidation catalyst 21. .

Among these, the oxidation catalyst 21 is provided close to the diesel engine 11 so that the exhaust gas discharged from the diesel engine 11 can flow into the oxidation catalyst 21 at a relatively high temperature. Further, the oxidation catalyst 21 contains noble metals such as platinum (Pt) and rhodium (Rh), and these noble metals oxidize carbon oxide (CO) and hydrocarbons (HC) contained in the exhaust gas to produce carbon dioxide. by chemically changing to carbon and (CO2) and water (H 2 _O), so that the exhaust gas can be purified.

  The NOx trap catalyst 22 contains an alkali metal (for example, barium (Ba)) as a NOx occlusion material, so that NOx in the exhaust gas can be occluded. Further, the NOx occlusion material can occlude NOx components in the exhaust gas when the exhaust gas is in a lean atmosphere, and can release the stored NOx into the exhaust gas when the exhaust gas is in a rich atmosphere. ing.

  In addition, the NOx occlusion material of the NOx trap catalyst 22 may occlude sulfur oxide (SOx), which is a reaction product of the sulfur component contained in the fuel and oxygen, instead of NOx. In order to release the SOx occluded in the NOx trap catalyst 22 from the NOx trap catalyst 22, the exhaust gas may be made rich as in the case of NOx.

The control for releasing NOx stored in the NOx trap catalyst 22 from the NOx trap catalyst 22 is referred to as NOx purge, and the control for releasing SOx stored in the NOx trap catalyst 22 from the NOx trap catalyst 22 is referred to as S purge.
An inner pipe 23 is provided in the vicinity of the inlet 15 of the first exhaust pipe 14 .
The inner pipe 23 is formed to have an inner diameter D2 that is smaller than the inlet inner diameter D1 of the first exhaust pipe 14.

Further, as shown in FIG. 2, the inner pipe 23 is supported on the inner peripheral surface 14 </ b> A of the first exhaust pipe 14 through four support members 24. These support members 24 are metal parts, and are interposed between the inner pipe 23 and the first exhaust pipe 14. One end of the support member 24 is welded to the outer peripheral surface 23 </ b> A of the inner pipe 23, and the other end is welded to the inner peripheral surface 14 </ b> A of the first exhaust pipe 14. As a result, a gap G can be formed between the outer peripheral surface 23A of the inner pipe 23 and the inner peripheral surface 14A of the first exhaust pipe 14.

A part of the main flow A1 of the exhaust gas discharged from the turbocharger 12 provided in the diesel engine 11 can flow into the gap G as a side flow A2.
Further, a fuel introduction hole 25 is formed in the inner tube 23. The fuel introduction hole 25 allows the fuel (see symbol F in FIG. 1) injected from an injector (fuel injection device) 26 provided in the vicinity of the inlet 15 of the first exhaust pipe 14 to the inner peripheral surface of the inner pipe 23. 23B is a hole to be introduced.

A fuel passage 27 is connected to the fuel introduction hole 25. The fuel passage 27 is a cylindrical part extending in the same direction as the jetting direction C ₂₆ of the fuel by the injector 26. A flange 28 is formed at the upper end of the fuel passage 27.
Further, the above-described support members 24 are provided on the inner peripheral surface (inner tube inner peripheral surface) 23B of the inner tube 23 so as to avoid the injected portion Pf. Here, the portion Pf to be injected on the inner peripheral surface 23B of the inner pipe is a portion to which the fuel introduced through the fuel passage 27 and the fuel introduction hole 25 (see symbol F in FIG. 1 ) hits. That is, the fuel injected from the injector 26 first collides with the injected portion Pf on the inner peripheral surface 23B of the inner pipe 23.

However, since the support member 24 is provided so as to avoid the injected portion Pf, even if the inner tube 23 is cooled by the heat of vaporization of the fuel adhering to the inner peripheral surface 23B of the inner tube, the cooling effect thereof is achieved. However, it is possible to make it difficult to reach the outer pipe, that is, the first exhaust pipe 14 itself.
Further, as shown in FIG. 2, the fuel injection direction _{C 26} by the injector 26, and the center _{C 23} of the inner tube 23 is set to a predetermined distance _{L 1} offset. As a result, the fuel injected by the injector 26 generally flows along the inner peripheral surface 23B of the inner pipe 23, and the swirling flow of fuel on the inner peripheral surface 23B of the inner pipe 23 (see arrow Fr in FIG. 2). ) Can be easily generated. The offset direction is set so that the swirl flow of the fuel is the same direction as the swirl flow generated in the turbocharger 12.

Since the exhaust system structure of an engine according to an embodiment of the present invention is configured as described above, the following operations and effects are achieved.
When the injector 26 injects fuel into the first exhaust pipe 14, this fuel is introduced into the inner peripheral surface 23 </ b> B of the inner pipe 23 through the fuel passage 27 and the fuel introduction hole 25.
The fuel introduced into the inner pipe 23 forms a swirling flow along the inner peripheral surface 23B of the inner pipe 23. At this time, the exhaust gas discharged from the turbocharger 12 of the diesel engine 11 is well stirred. Is done.

  Further, a gap G is formed by the support member 24 between the inner pipe 23 and the first exhaust pipe 14. Therefore, even if the inner pipe 23 is cooled when the fuel adhering to the inner pipe 23 is vaporized, it is possible to prevent the first exhaust pipe 14 itself from being directly cooled. For this reason, not only the 1st exhaust pipe 14 but the temperature of the 2nd exhaust pipe 17 connected with this 1st exhaust pipe 14 can also be suppressed.

Further, the stirring of the exhaust gas and the fuel is performed inside the inner pipe 23 having an inner diameter D2 smaller than the inlet inner diameter D1 of the first exhaust pipe 14. That is, by providing the inner pipe 23 in the first exhaust pipe 14, the exhaust gas and the fuel can be agitated in a portion where the exhaust gas passage area in the first exhaust pipe 14 is narrowed. ing.
Further, since the exhaust gas flow passage area in the first exhaust pipe 14 is set to gradually increase between the inlet inner diameter D1 and the outlet inner diameter 18, the fuel and exhaust gas are diffused and stirred. (See arrows A4 and A5 in FIG. 1).

Therefore, it is possible to prevent a situation in which exhaust gas containing a relatively large amount of fuel flows in a part in the first exhaust pipe 14 and the second exhaust pipe 17, thereby improving exhaust gas performance and protecting the environment. Can contribute.
In addition, the oxidation catalyst 21 and the NOx trap catalyst 22 are provided on the downstream side of the inner pipe 23 because the fuel and the exhaust gas are well agitated in the inner pipe 23. However, the oxidation catalyst 21 and the NOx trap are provided. It is possible to prevent a situation in which a relatively large amount of fuel flows in a part of the catalyst 22.

Thereby, it is possible to prevent a part of the oxidation catalyst 21 and the NOx trap catalyst 22 from reacting locally, and to efficiently perform exhaust gas purification using the entire oxidation catalyst 21 and the NOx trap catalyst 22 efficiently.
In other words, the exhaust gas and the fuel are agitated satisfactorily, thereby reducing the fuel injection amount to the minimum necessary and maintaining the balance of the exhaust gas air-fuel ratio and enriching the oxidation catalyst 21 and the NOx trap catalyst 22 as a whole. Exhausted exhaust gas can be introduced. Therefore, when NOx purge or S purge is executed, NOx or SOx can be efficiently purged from the NOx trap catalyst 22.

Further, as shown in FIG. 2, the support member 24 supports the inner pipe 23 with respect to the first exhaust pipe 14 at a position avoiding the injected portion Pf. Thereby, the cooling effect of the inner pipe 23 by the heat of vaporization of the fuel adhering to the inner peripheral surface 23B of the inner pipe 23 extends to the first exhaust pipe 14 and the second exhaust pipe 17 connected to the first exhaust pipe 14. Can be difficult.
Thereby, it is possible to suppress the temperature of the exhaust gas flowing into the oxidation catalyst 21 and the NOx trap catalyst 22 from being lowered, and to activate the oxidation catalyst 21 and the NOx trap catalyst 22 at an early stage. Therefore, even when the temperature of the diesel engine 11 is low (for example, at the time of cold start), exhaust gas purification by the oxidation catalyst 21 and the NOx trap catalyst 22 can be quickly started.

Further, as shown in FIG. 2, and the center C ₂₃ of the fuel injection direction C ₂₆ and the inner tube 23 by the injector 26 is set to a predetermined distance L ₁ offset. As a result, the fuel injected from the injector 26 can easily generate a swirling flow (see arrow Fr in FIG. 2) on the inner peripheral surface 23B of the inner pipe 23.
Further, as shown in FIG. 1, a turbocharger 12 is provided between the diesel engine 11 and the first exhaust pipe 14. The inner pipe 23 is provided in the first exhaust pipe 14 so as to be close to the turbocharger 12.

  As a result, the swirl flow of exhaust gas generated on the downstream side of the turbocharger 12 (see arrow A3 in FIG. 1) generated by the operation of the turbine-compressor (not shown) of the turbocharger 12, and the inner pipe 23 By making the swirl flow of fuel generated on the inner peripheral surface 23B (see arrow Fr in FIG. 2) the same direction, the injected fuel is uniformly supplied to the oxidation catalyst 21 without being biased.

As shown in FIG. 1, a punching metal (turbulent flow generation means) 19 is provided at the outlet 16 of the first exhaust pipe 14. Then, when the exhaust gas passes through the hole of the punching metal 19, the flow of the exhaust gas can be disturbed, and the stirring of the exhaust gas and the fuel can be further promoted.
Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and various modifications can be made without departing from the spirit of the present invention. An example is shown below.

  In the above-described embodiment, the case where the oxidation catalyst 21 and the NOx trap catalyst 22 are used as the exhaust catalyst has been described. However, the present invention is not limited to this. For example, not only the oxidation catalyst 21 and the NOx trap catalyst 22, but also an SCR (Selective Catalytic Reduction) catalyst, an HC trap catalyst, or the like may be used in combination with various variations.

In the above-described embodiment, the case where the two exhaust catalysts of the oxidation catalyst 21 and the NOx trap catalyst 22 are used has been described as an example. However, the present invention is not limited to this, and the number of exhaust catalysts is not limited. .
Moreover, in the above-mentioned embodiment, although the case where the punching metal 19 was provided in the exit 16 of the 1st exhaust pipe 14 was demonstrated, it is not limited to this. For example, instead of the punching metal 19, a protrusion (not shown) may be formed on the inner peripheral surface 14A of the first exhaust pipe 14. That is, the projection (turbulent flow generation means) can disturb the flow of the exhaust gas, and can further promote the stirring of the exhaust gas and the fuel.

Moreover, in the above-mentioned embodiment, although the diesel engine 11 was demonstrated as an example, it is not limited to this. For example, a gasoline engine may be used instead of the diesel engine 11.
In the above-described embodiment, the case where one end of the support member 24 is welded to the outer peripheral surface 23A of the inner pipe 23 and the other end is welded to the inner peripheral surface 14A of the first exhaust pipe 14 has been described. However, the present invention is not limited to this. For example, a technique such as press fitting may be employed instead of welding.

It is a mimetic diagram showing the whole exhaust system structure of an engine concerning one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a main part configuration of an exhaust system structure of an engine according to an embodiment of the present invention, and schematically shows a cross-section taken along line II-II in FIG. 1. It is a mimetic diagram showing the structure (trial structure) created in the process of creating the engine exhaust system structure concerning one embodiment of the present invention. (A) is a schematic horizontal cross-sectional view corresponding to the location indicated by reference character CS1 in FIG. 3, and (B) is a schematic horizontal cross-sectional view corresponding to the location indicated by reference character CS2 in FIG. ) Is a schematic horizontal sectional view corresponding to a portion indicated by reference numeral CS3 in FIG. (A) is a graph schematically showing the temperature at the location indicated by reference character CS1 in FIG. 3, (B) is a graph schematically showing the temperature at the location indicated by reference character CS2 in FIG. 3, (C) is It is a graph which shows typically the temperature in the location shown by code | symbol CS3 in FIG.

Explanation of symbols

11 Diesel engine (engine)
12 Turbocharger (supercharger)
14 First exhaust pipe (exhaust pipe)
17 Second exhaust pipe (exhaust pipe)
21 Oxidation catalyst (exhaust catalyst)
22 NOx trap catalyst (exhaust catalyst)
23 inner pipe 24 support member 25 fuel introduction hole 26 exhaust injector (fuel injection device)
D1 Inner diameter (exhaust pipe inner diameter)
D2 Inner diameter of inner tube C ₂₃ Center of inner tube
G Gap Pf Injected part L ₁ Offset distance

Claims (2)

A fuel injection device for injecting fuel into an exhaust pipe connected to the engine;
A turbocharger provided between the engine and the exhaust pipe;
An inner pipe provided in the vicinity of the turbocharger , having an inner diameter smaller than the inner diameter of the exhaust pipe and provided in the exhaust pipe;
A support member that supports the inner pipe with respect to the exhaust pipe while forming a gap through which the exhaust gas flows between the inner pipe and the exhaust pipe;
A fuel introduction hole for introducing the fuel injected from the fuel injection device into the inner pipe into the inner peripheral surface of the inner pipe;
The support member supports the inner pipe with respect to the exhaust pipe while avoiding an injected portion to which the fuel introduced through the fuel introduction hole is injected on the inner peripheral surface of the inner pipe,
The fuel injection direction by the fuel injection device and the center of the inner pipe are offset by a predetermined distance, and the injected fuel is set to swirl in the inner pipe in the same direction as the swirling flow generated in the turbocharger. The engine exhaust system structure. 2. An exhaust system structure for an engine according to claim 1, wherein an exhaust catalyst for purifying exhaust gas from the engine is provided in the exhaust pipe downstream of the inner pipe .

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