JP4136411B2 - Exhaust system of multi-cylinder internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust system of a multi-cylinder internal combustion engine to which a reducing agent injector for injecting and supplying a reducing agent to a NOx purification catalyst device is attached.
[0002]
[Prior art]
Conventionally, various techniques for reducing nitrogen oxide (NOx) in exhaust gas discharged from an internal combustion engine have been proposed. For example, in Japanese Patent Laid-Open No. 2001-65333, a NOx purification catalyst device for reducing and purifying NOx in exhaust gas is provided in an exhaust system, and a reducing agent such as fuel is separately supplied to the catalyst device. There has been proposed an exhaust emission control device. By supplying the reducing agent to the catalyst device in this manner, for example, hydrocarbon (HC), carbon monoxide (CO), etc. remaining in the exhaust, such as a diesel engine or a gasoline engine that performs combustion under a lean air-fuel ratio, etc. Even in a relatively small number of internal combustion engines, the NOx purification function of the catalyst device can be ensured.
[0003]
[Problems to be solved by the invention]
By the way, as described in the above publication, for example, such a reducing agent is supplied by injecting a reducing agent such as fuel from the injection port of a reducing agent injector attached to the exhaust system into the exhaust system. It has been broken. Thus, by using the injector when supplying the reducing agent, the reducing agent is atomized and injected from the nozzle, and the metering operation of the reducing agent is relatively easy. The reduction action in the catalyst device is more suitably performed.
[0004]
However, such a reducing agent injector is attached to an exhaust system such as an exhaust port so that its nozzle hole is exposed, and the nozzle is always in contact with the exhaust during engine operation. Therefore, the following problems cannot be ignored.
[0005]
That is, when the exhaust gas comes into contact with the injection port of the reducing agent injector, soot contained in the exhaust gas adheres to the periphery of the injection port, and this is denatured and solidified by exhaust heat or the like. The solidified soot becomes a so-called deposit and accumulates in the vicinity of the nozzle hole, resulting in a reduction in the opening area of the nozzle hole. When the opening area of the nozzle hole is reduced in this way, it becomes difficult to supply a sufficient amount of the reducing agent to the catalyst device, and the NOx purification function of the catalyst device may be lowered.
[0006]
The present invention has been made in view of such conventional circumstances, and an object of the present invention is to provide an exhaust system of a multi-cylinder internal combustion engine that can suppress deposit accumulation in the vicinity of the injection port of the reducing agent injector. is there.
[0007]
[Means for Solving the Problems]
Means for solving the above-described problems and their effects are described below.
According to the first aspect of the present invention, a branch portion connected to each cylinder of the multi-cylinder internal combustion engine, a collecting portion connected to the downstream side of each branch portion, and a downstream side of the collecting portion are connected. Multi-cylinder internal combustion engine equipped with a reducing agent injector for injecting a reducing agent into a specific branch portion of the branching portion and supplying the same to the catalytic device In the exhaust system of the engine, an internal wall that suppresses exhaust pressure pulsation propagating from another branch portion extends from the inner wall of the collective portion toward the inside of the specific branch portion.
[0008]
When intermittent explosion occurs in each cylinder of the internal combustion engine, exhaust pressure pulsation is generated in the exhaust system due to the explosion. When such exhaust pressure pulsation occurs, pulsation also occurs in the exhaust flow. For this reason, when the exhaust pressure pulsation propagates to the vicinity of the attachment position of the reducing agent injector, the exhaust flow repeatedly collides with the nozzle of the reducing agent injector in accordance with the period of the exhaust pressure pulsation. As a result, soot gradually adheres to the injection port of the reducing agent injector due to the collision of the exhaust flow, and deposits are deposited.
[0009]
According to the above configuration, the exhaust pressure pulsation propagates from the other branch part toward the specific branch part to which the reducing agent injector is attached by the inner wall extending from the inner wall of the collecting part toward the inside. To be suppressed. Accordingly, it is possible to suppress the soot adhesion accompanying the propagation of the exhaust pressure pulsation, and the deposit accumulation caused by the soot, and the change in the injection characteristics of the reducing agent injector due to the deposit accumulation, and the NOx of the catalyst device. It becomes possible to suitably suppress the purification function deterioration.
[0010]
In order to more suitably suppress the propagation of the exhaust pressure pulsation, as described in claim 2, the inner wall is located between the specific branch portion and the branch portion adjacent thereto. It is desirable to adopt a configuration that extends from the inner wall of the gathering portion.
[0011]
Further, according to a third aspect of the invention, the inner walls are extended along the flow direction of the exhaust gas flowing into the collecting portion from the specific branch portion, thereby collecting the inner walls. An increase in exhaust resistance due to the formation inside the portion can be suppressed as much as possible.
[0012]
Further, the present inventors have confirmed through various experiments that there is a suitable range for effectively suppressing the propagation of the exhaust pressure pulsation with respect to the length of the inner wall in the extending direction.
[0013]
That is, according to the invention described in claim 4, the length L in the extending direction of the inner wall extends from the connection position between the specific branch portion and the corresponding cylinder to the NOx purification catalyst device. The distance Lc in the exhaust flow direction is preferably formed so as to satisfy the relationship L ≧ 0.10 Lc. Thus, by suitably defining the minimum value of the length in the extending direction of the inner wall, the effect of suppressing the propagation of the exhaust pressure pulsation can be more suitably achieved.
[0014]
Here, when the length in the extending direction of the inner wall is gradually increased, the specific branch portion to which the reducing agent injector is attached is gradually isolated from the other branch portions by the extension of the inner wall. As a result, an exhaust passage independent of them is formed. Therefore, from the viewpoint of suppressing exhaust pressure pulsation that circulates from another branch portion, such extension of the inner wall can be suitably suppressed. However, on the other hand, the exhaust pressure pulsation generated in the cylinder corresponding to the specific branching portion is a space isolated by the inner wall by extension of the inner wall, in other words, a specific branching portion or a set connected to the same. It becomes difficult to leak from the inside of the part to the outside. Therefore, the exhaust pressure pulsation generated in a specific branch portion to which the reducing material injector is attached is repeatedly reflected between the cylinder and the NOx purification catalyst device, and the degree of attenuation is naturally small. For this reason, under the influence of the exhaust pressure pulsation generated by the combustion explosion in the cylinder corresponding to the specific branch portion, the soot adhering to the injection port of the reducing agent injector increases. Therefore, if the inner wall is gradually extended, the exhaust pressure pulsation from other branch portions is suppressed, but the exhaust pressure pulsation generated in a specific branch portion to which the reducing agent injector is attached is suppressed. The effect of is not negligible.
[0015]
Therefore, according to the invention described in claim 5, it is desirable that the inner wall is formed so that the length L further satisfies the relationship L ≦ 0.32Lc with respect to the distance Lc. In this way, by suitably defining the maximum value of the length in the extending direction of the inner wall, in addition to the exhaust pressure pulsation propagating from other branch parts other than the specific branch part, as described above, An adverse effect of exhaust pressure pulsation generated in a cylinder corresponding to a specific branch portion can be suppressed as much as possible.
[0016]
In such an exhaust system, a supercharger may be provided between the collecting portion and the NOx purification catalyst device. In this case, for example, according to the invention described in claim 6, the supercharger has a length L in the extending direction of the inner wall from the connection position between the specific branch portion and the corresponding cylinder. It is desirable to adopt a configuration in which the distance Lt in the exhaust gas flow direction is formed so as to satisfy the relationship of L ≧ 0.10 Lt.
[0017]
According to this configuration, similarly to the operational effect of the invention described in claim 4, the effect of suppressing the propagation of the exhaust pressure pulsation by suitably defining the minimum value of the length in the extending direction of the inner wall. Can be more suitably achieved.
[0018]
Still further, according to the invention as set forth in claim 7, it is desirable that the inner wall is formed so that the length L further satisfies the relationship L ≦ 0.32Lt with respect to the distance Lt.
[0019]
According to this configuration, similarly to the invention according to claim 5, by suitably defining the maximum value of the length in the extending direction of the inner wall, the other branch portions other than the specific branch portion are defined. In addition to the propagating exhaust pressure pulsation, the adverse effect of the exhaust pressure pulsation generated at the specific branch portion can be suppressed as much as possible.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which an exhaust system of a multi-cylinder internal combustion engine according to the present invention is applied to an exhaust system of a common rail type four-cylinder diesel engine (hereinafter simply referred to as “engine”) will be described in detail with reference to FIGS. To do.
[0021]
FIG. 1 is a schematic configuration diagram illustrating a configuration of an exhaust system according to the present embodiment and an engine 1 to which the exhaust system is applied.
As shown in FIG. 1, a plurality of fuel injectors 3 a to 3 d are attached to the cylinder head 2 of the engine 1 corresponding to the cylinders # 1 to # 4 of the engine 1. In the cylinder head 2, intake ports (not shown) that communicate with the cylinders # 1 to # 4 when the intake valves (not shown) are opened are individually formed corresponding to the cylinders # 1 to # 4. . Intake manifolds 5 are connected to these intake ports, and the intake manifold 5 is connected to a supercharger 9 via an intake pipe 7. An intercooler 10 for reducing the temperature of the intake air is provided in the middle of the intake pipe 7.
[0022]
The fuel injectors 3a to 3d are connected to a common rail 14 for accumulating high-pressure fuel, respectively. The common rail 14 is connected to a supply pump 15, and fuel in a fuel tank (not shown) is pumped from the supply pump 15 to the common rail 14. When the fuel injectors 3a to 3d are opened, the high-pressure fuel in the common rail 14 is injected into the corresponding cylinders # 1 to # 4 from the injection ports (not shown) of the fuel injectors 3a to 3d.
[0023]
On the other hand, as shown in FIG. 2, the cylinder head 2 has an exhaust port 8 (exhaust gas connected to the fourth cylinder # 4 in FIG. 2) communicating with the cylinders # 1 to # 4 when the exhaust valve 4 is opened. Only ports are shown). The exhaust port 8 is connected to a supercharger 9 via an exhaust manifold 20. The exhaust manifold 20 corresponds to the exhaust ports 8 of the cylinders # 1 to # 4 and is connected to the four branch pipes 22a to 22d, and the collecting pipe to which the downstream sides of the branch pipes 22a to 22d are connected. 23. In the present embodiment, the exhaust port 8 and the branch pipes 22a to 22d connected to the exhaust port 8 constitute a branch part, and the collecting pipe 23 of the exhaust manifold 20 is provided downstream of the branch part. It constitutes a collective part connected to the side.
[0024]
In the exhaust system, a NOx purification catalyst device 13 (hereinafter simply referred to as “catalyst device”) is provided downstream of the supercharger 9. When the air-fuel ratio of the exhaust gas is lean, the catalyst device 13 stores NOx in the exhaust gas, and when the air-fuel ratio becomes rich or when a reducing agent is supplied, the stored NOx is reduced and the NOx is reduced. This is a so-called NOx occlusion reduction type catalyst device having a function of decomposing.
[0025]
In a diesel engine, engine combustion is performed in an oxygen-excess atmosphere, so that HC and CO contained in the exhaust gas are relatively small, and therefore, there is very little opportunity for the air-fuel ratio to become rich. For this reason, in a NOx occlusion reduction type catalyst device mounted on a diesel engine, it is difficult to obtain a sufficient amount of reducing agent from exhaust gas for reducing NOx. Therefore, in the present embodiment, a reducing agent injector 16 for supplying a reducing agent to the catalyst device 13 is provided separately from the fuel injectors 3a to 3d. The reducing agent injector 16 is connected to a supply pump 15, and fuel is supplied from the pump 15.
[0026]
As shown in FIG. 2, the reducing agent injector 16 is attached to the cylinder head 2 in a state where the injection port 17 is exposed in the exhaust port 8 corresponding to the fourth cylinder # 4. The fuel injected from the nozzle 17 into the exhaust port 8 along with the opening of the reducing agent injector 16 flows to the downstream side of the exhaust port 8 together with the exhaust discharged from the fourth cylinder # 4. Supplied as a reducing agent. By supplying such a reducing agent at a predetermined timing, the NOx purification function of the catalyst device 13 is maintained for a long period of time.
[0027]
Furthermore, the exhaust system according to the present embodiment includes a mechanism for suppressing a change in the injection characteristic of the reducing agent injector 16 and maintaining the NOx purification function of the catalyst device 13 for a long period of time. That is, in this embodiment, the inner wall 30 for suppressing the exhaust pressure pulsation from propagating from the other cylinders # 1 to # 3 into the exhaust port 8 of the fourth cylinder # 4 to which the reducing agent injector 16 is attached. Is formed inside the collecting pipe 23.
[0028]
As shown in FIG. 1, the inner wall 30 is an inner wall of the collecting pipe 23 located between the branch pipes 22c and 22d of the third and fourth cylinders # 3 and # 4, in other words, each of these branch pipes. A portion where the inner walls of 22c and 22d are connected is a starting point, and extends from the starting point toward the inside of the collecting pipe 23. The extending direction of the internal wall 30 is set so as to substantially coincide with the flow direction A of the exhaust gas flowing into the collecting pipe 23 from the branch pipe 22d corresponding to the exhaust port 8 connected to the fourth cylinder # 4. ing.
[0029]
In the present embodiment, since such an inner wall 30 is provided inside the collecting pipe 23, the other cylinders # are directed toward the exhaust port 8 of the fourth cylinder # 4 to which the reducing agent injector 16 is attached. Exhaust pressure pulsations (see broken lines in FIG. 3A) that are to propagate from 1 to # 3 are suppressed. As a result, soot adhesion due to the propagation of the exhaust pressure pulsation and further deposit deposition caused thereby are suitably suppressed.
[0030]
Further, since the inner wall 30 is located between the fourth cylinder # 4 to which the reducing agent injector 16 is attached and the third cylinder # 3 adjacent to the fourth cylinder # 4, the inner wall 30 is influenced by the proximity. Propagation of the exhaust pressure pulsation of the third cylinder # 3, which is easy, is more effectively suppressed.
[0031]
In addition, since the internal wall 30 is extended along the flow direction of the exhaust gas from the fourth cylinder # 4 to the collecting pipe 23 through the exhaust port 8 and the branch pipe 22d, the inner wall 30 is connected to the collecting pipe 23. The increase in exhaust resistance due to the formation inside is suppressed as much as possible.
[0032]
Furthermore, the present inventors conducted the following experiment in order to define the optimum range of the length L in the extending direction of the inner wall 30. First, as shown in FIG. 2, the length of the inner wall 30 in the extending direction is defined as “inner wall length L”. Further, as shown in FIG. 2, the exhaust port 8 of the fourth cylinder # 4 is located closest to the exhaust valve 4 (position where the valve 4 is seated), in other words, the exhaust port 8 of the fourth cylinder # 4. And the connection position of the fourth cylinder # 4 as a starting point, and the distance in the exhaust flow direction from the starting point to the connection position of the supercharger 9 is defined as “pipe length Lt”. Then, the flow rate reduction rate K of the reducing agent injector 16 when the ratio L / Lt of the inner wall length L to the pipe length Lt was variously changed under the constant pipe length Lt was examined. The flow rate reduction rate K is determined by the actual maximum injection amount Q that can be actually injected from the reducing agent injector 16 under a constant pressure, and the maximum injection amount QMAX at the start of use of the injector 16 (or The nominal maximum injection amount of the reducing agent injector 16) is defined by the following relational expression.
[0033]
K = (QMAX−Q / QMAX) × 100
As is apparent from this equation, when the amount of reducing agent (fuel) that can be injected from the reducing agent injector 16 is reduced due to deposit accumulation or the like, the flow rate reduction rate K increases.
[0034]
FIG. 4 is an experimental result showing the relationship between the flow rate reduction rate K and the ratio L / Lt after the engine 1 has been operated for a predetermined period.
As shown in the figure, when the ratio L / Lt is small, that is, when the inner wall length L is set relatively short with respect to the pipe length Lt (L <0.10 Lt), the flow rate The decrease rate K increases rapidly as the ratio L / Lt decreases. When the inner wall length L becomes shorter in this way, as shown by a solid line in FIG. 3B, the branch pipe 22c of the third cylinder # 3, etc., the other branch pipes 22a, 22b, 22c to the fourth cylinder # The exhaust pressure pulsation that propagates around the inner wall 30 to the fourth branch pipe 22d cannot be avoided. As a result, an increase in the amount of soot attached to the nozzle hole 17 and, in turn, an increase in the amount of deposited deposits are caused, and the flow rate reduction rate K also increases greatly.
[0035]
On the other hand, when the ratio L / Lt is large, that is, when the inner wall length L is set to be relatively long with respect to the pipe length Lt (L> 0.32), the flow rate decrease rate K is It increases rapidly as L / Lt increases.
[0036]
FIG. 5 shows the results of an experiment conducted to confirm this reason. FIG. 5 shows the temporal transition of the exhaust pressure P measured in the vicinity of the attachment position of the reducing agent injector 16. Here, FIG. 5 (a) shows the time transition of the exhaust pressure P when the inner wall 30 is omitted, as shown in FIG. 3 (b), and FIG. 5 (b) shows FIG. 3 (c). As shown, the time transition of the exhaust pressure P when the inner wall 30 is extended to the position of the catalyst device 13 is shown. In FIG. 5, the timings t1, t2,..., T5 when the peak of the exhaust pressure P is observed are the second cylinder # 2, the first cylinder # 1, the third cylinder # 3, and the fourth cylinder, respectively. This corresponds to the combustion explosion timing in # 4 and the second cylinder # 2. In FIGS. 5A and 5B, “PL1” indicates the exhaust pressure P at the same level.
[0037]
As shown in FIGS. 5A and 5B, when the inner wall 30 is set to be very long and extended to the position of the supercharger 9, the exhaust pressure P seen at timings t1 to t3 and t5. All of the peaks are below the predetermined level PL1. That is, it can be seen that the exhaust pressure pulsation propagating due to the combustion explosion in the cylinders # 1 to # 3 other than the fourth cylinder # 4 is reduced as compared with the case where the inner wall 30 is omitted. On the other hand, regarding the combustion explosion (timing t4) of the fourth cylinder # 4, it can be seen that the exhaust pressure pulsation propagating thereby increases compared to the case where the inner wall 30 is omitted. From the above points, the reason why the flow rate decrease rate K increases when the inner wall 30 is set to be extremely long can be explained as follows.
[0038]
That is, when the inner wall length L becomes longer in this way, the branch pipe 22d connected to the fourth cylinder # 4 is connected to the other cylinders # 1 to # 3 by the inner wall 30 as shown in FIG. They are isolated from the branch pipes 22a to 22c and become substantially independent from them. Therefore, the exhaust pressure pulsation propagating due to the combustion explosion in the first to third cylinders # 1 to # 3 other than the fourth cylinder # 4 is reduced. However, the exhaust pressure pulsation propagating due to the combustion explosion in the fourth cylinder # 4 is unlikely to leak to the outside from the space isolated by the inner wall 30 as shown by a one-dot chain line in FIG. The reflection is repeated between the exhaust port 8 connected to the fourth cylinder # 4 and the supercharger 9. Therefore, the exhaust pressure pulsation generated by the combustion explosion in the fourth cylinder # 4 is smaller in attenuation than the exhaust pressure pulsation generated by the combustion explosion of the other cylinders # 1 to # 3. As a result, the nozzle 17 of the reducing agent injector 16 attached to the exhaust port 8 of the fourth cylinder # 4 is affected by the exhaust pressure pulsation caused by the combustion explosion in the fourth cylinder # 4. Soot tends to adhere, and therefore an increase in the flow rate reduction rate K is unavoidable.
[0039]
FIG. 6 shows the magnitude of the exhaust pressure pulsation generated near the attachment position of the reducing agent injector 16 due to the combustion explosion of the fourth cylinder # 4 and the exhaust generated by the combustion explosion of the third cylinder # 3 adjacent thereto. It is the experimental result which changed the internal wall length L variously about the magnitude | size of atmospheric pressure pulsation.
[0040]
As is apparent from FIG. 6, the exhaust pressure pulsation generated in the vicinity of the attachment position of the reducing agent injector 16 by the combustion explosion of the fourth cylinder # 4 tends to increase as the internal wall length L increases. Therefore, in this case, the soot adhesion gradually increases due to the propagation of the exhaust pressure pulsation caused by the combustion explosion of the fourth cylinder # 4. On the other hand, the exhaust pressure pulsation generated by the combustion explosion of the third cylinder # 3 shows the opposite tendency, and gradually decreases as the internal wall length L increases. Therefore, in this case, the soot adherence is caused by the influence of the exhaust pressure pulsation caused by the combustion explosion of the third cylinder # 3, that is, the propagation of the exhaust pressure pulsation coming from the cylinders other than the fourth cylinder # 4. It will gradually increase.
[0041]
From these experimental results, it can be seen that there is an optimum setting range for the inner wall length L in order to suppress deposit accumulation in the vicinity of the injection hole 17 of the reducing agent injector 16. In the present embodiment, the optimum setting range of the internal wall length L is based on the experimental results of FIGS. 5 and 6 in addition to the relationship between the flow rate decrease rate K and the ratio L / LC shown in FIG.
Condition (1): L ≧ 0.10 Lt
Condition (2): L ≦ 0.32Lt
It is set to satisfy both of the above conditions.
[0042]
Here, when the inner wall length L is set so as to satisfy the condition (1), other branches connected to cylinders other than the fourth cylinder # 4, such as the branch pipe 22c of the third cylinder # 3. Exhaust pressure pulsation that circulates from the pipes 22a, 22b, and 22c to the branch pipe 22d of the fourth cylinder # 4 is effectively suppressed. As a result, it is possible to suppress the soot adhesion and the deposit accumulation due to the wraparound of the exhaust pressure pulsation.
[0043]
Further, when the inner wall length L is set so that the condition (2) is satisfied, the exhaust pressure pulsation generated in the fourth cylinder # 4 is reflected on the supercharger 9 and the injection port of the reducing agent injector 16 Propagation to 17 is effectively suppressed. As a result, the soot adhesion due to the reflection of the exhaust pressure pulsation, and hence the deposit accumulation, are suppressed.
[0044]
Therefore, according to the present embodiment in which the inner wall length L is set so as to satisfy both of these conditions (1) and (2), these functions and effects can be achieved together.
[0045]
According to this embodiment described above, the following effects can be obtained.
An internal wall 30 that suppresses exhaust pressure pulsation propagating from the branch pipes 22a to 22c of the other cylinders # 1 to # 3 in the branch pipe 22d of the fourth cylinder # 4 to which the reducing agent injector 16 is attached is a collecting pipe 23 It extended from the inner wall to the inside. As a result, it is possible to suppress the soot adhesion to the injection nozzle 17 of the reducing agent injector 16 due to the exhaust pressure pulsation, and hence the deposition of deposits in the vicinity of the injection nozzle 17, and the injection characteristics of the reducing agent injector 16 can be improved over a long period. Can be maintained over.
[0046]
The inner wall 30 is provided between the fourth cylinder # 4 to which the reducing agent injector 16 is attached and the third cylinder # 3 adjacent thereto. Therefore, the propagation of the exhaust pressure pulsation of the third cylinder # 3, which is easily affected by the position closest to the fourth cylinder # 4 to which the reducing agent injector 16 is attached, is more effectively suppressed. Will be able to.
[0047]
Also, the extending direction of the inner wall 30 is set in the direction along the flow direction of the exhaust from the fourth cylinder # 4 to the collecting pipe 23 through the exhaust port 8 and the branch pipe 22d. By forming such an inner wall 30 inside the collecting pipe 23, an increase in exhaust resistance can be suppressed as much as possible.
[0048]
In the relationship between the inner wall length L and the pipe line length Lt, the inner wall length L is set so that the conditional expression (1) shown above is satisfied, so the other cylinders # 1 to # 3 It is possible to effectively suppress the exhaust pressure pulsation that wraps around, and to suppress the soot adhesion caused by the wraparound of the exhaust pressure pulsation, and thus the deposit accumulation.
[0049]
Furthermore, the inner wall length L is set so that the condition (2) described above is further satisfied in the relationship between the inner wall length L and the pipe line length Lt. For this reason, it is possible to effectively suppress the exhaust pressure pulsation generated in the fourth cylinder # 4 from being reflected on the supercharger 9 and propagating to the injection port 17 of the reducing agent injector 16, and soot adhesion resulting therefrom. As a result, deposit accumulation can be suppressed.
[0050]
In addition, the said embodiment can also be changed and implemented as follows. In the above embodiment, the exhaust system provided with the supercharger 9 is shown as an example, but the exhaust system not provided with the supercharger 9, that is, the downstream side of the exhaust manifold 20 is directly connected to the catalyst device 13. The present invention can be applied even if it is. In this case, the previous conditions (1) and (2) are as follows.
[0051]
Condition (3): L ≧ 0.10 Lc
Condition (4): L ≦ 0.32Lc
Here, “Lc” is a substitute for the previous pipe length Lt, and the position closest to the exhaust valve 4 in the exhaust port 8 of the fourth cylinder # 4, in other words, the exhaust port of the fourth cylinder # 4. A connection position between the cylinder 8 and the fourth cylinder # 4 is a starting point, and a distance in the exhaust flow direction from the starting point to the connection position of the catalytic device 13 is defined as a “pipe length Lc”. Even if the configuration is changed in this way, the effects according to the above-described embodiment can be obtained.
[0052]
In the above modified example and the previous embodiment, both the conditions (1) and (2) or the conditions (3) and (4) are satisfied as the conditions regarding the inner wall length L. For example, the condition (1) It is also possible to set the length of the inner wall length L so that only the above is satisfied.
[0053]
In the above embodiment, the reducing agent injector 16 is attached to the exhaust port 8 connected to the fourth cylinder # 4, but is connected to other cylinders # 1 to # 3, for example, the third cylinder # 3. The reducing agent injector 16 may be attached to the exhaust port.
[0054]
FIG. 7 shows a configuration example of the inner wall when the reducing agent injector 16 is attached to the exhaust port of the third cylinder # 3 in this way. As shown in the figure, in this case, the inner wall 31 is the inner wall of the collecting pipe 23 positioned between the branch pipes 22c and 22d of the third and fourth cylinders # 3 and # 4, in other words, these. A portion where the inner walls of the branch pipes 22c and 22d are connected is a starting point, and extends from the starting point toward the inside of the collecting pipe 23. Further, an inner wall 32 different from the inner wall 31 is used as an inner wall of the collecting pipe 23 located between the branch pipes 22b and 22c of the second and third cylinders # 2 and # 3, in other words, each of these branches. A portion where the inner walls of the pipes 22c and 22d are connected is a starting point, and extends from the starting point toward the inside of the collecting pipe 23.
[0055]
Further, the extending directions of these inner walls 31 and 32 are substantially the same as the flow direction B of the exhaust gas flowing into the collecting pipe 23 from the branch pipe 22c corresponding to the exhaust port connected to the third cylinder # 3. Is set. Furthermore, the length L1 in the extending direction of the inner wall 31 and the length L2 in the extending direction of the other inner wall 32 are set so as to satisfy the following conditions.
[0056]
Condition (5): L1, L2 ≧ 0.10 Lb
Condition (6): L1, L2 ≦ 0.32Lb
Here, “Lb” is synonymous with “pipe length Lt” or “pipe length Lc” shown in the previous embodiment or its modification. That is, when a turbocharger is connected to the exhaust manifold, the position closest to the exhaust valve in the exhaust port of the third cylinder # 3, in other words, the exhaust port of the third cylinder # 3 and the third cylinder # 3 This is the distance in the exhaust flow direction from the starting point to the connecting position of the turbocharger. Further, when the catalyst device is connected to the exhaust manifold, it means the distance in the exhaust flow direction from the start point to the connection position of the catalyst device. Even if such a configuration is adopted, the operational effects according to the previous embodiment can be obtained.
[0057]
Further, in the above modification, the inner walls are provided between the branch pipe 22d of the fourth cylinder # 4 and the branch pipe 22c of the third cylinder # 3, and the branch pipe 22c and the second cylinder # 2 of the third cylinder # 3. Although the inner walls 31 and 32 are provided between the inner wall 31 and the branch pipe 22b, only one of the inner walls 31 and 32 may be provided.
[0058]
-Furthermore, in the above modification, the lengths L1, L2 in the extending direction of the inner walls 31, 32 are set so that both of the conditions (5), (6) are satisfied. For example, it can also be configured such that only condition (5) is satisfied for these lengths L1, L2.
[0059]
In the above embodiment, the reducing agent injector 16 is attached to the exhaust port. However, for example, it can be attached to the branch pipes 22a to 22d.
[0060]
In the above embodiment, the fuel to be used for engine combustion as the reducing agent is injected from the reducing agent injector 16. Examples of the reducing agent include urea, ammonia compound, cyanuric acid, dimethyl ether, and methyl ether. Those having other reducing actions may be used.
[0061]
In the above embodiment, the present invention is embodied in an exhaust system of a diesel engine. However, the present invention can also be applied to an exhaust system of another internal combustion engine such as a gasoline engine that performs lean combustion.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an exhaust system of an engine and its peripheral configuration.
FIG. 2 is a cross-sectional view showing an attachment mode of a reducing agent injector.
FIG. 3 is a schematic view showing a propagation mode of exhaust pulsation in the exhaust manifold.
FIG. 4 is a graph showing the relationship between the internal wall length and the flow rate reduction rate of the reducing agent injector.
FIG. 5 is a graph showing the transition of exhaust pressure pulsation due to the difference in internal wall length.
FIG. 6 is a graph showing the relationship between the inner wall length and the exhaust pressure pulsation amount.
FIG. 7 is a schematic configuration diagram showing a modified example related to the attachment position of the reducing agent injector.
[Explanation of symbols]
# 1 to # 4 ... Cylinder, 1 ... Engine, 2 ... Cylinder head, 3a-3d ... Fuel injector, 4 ... Exhaust valve, 5 ... Intake manifold, 7 ... Intake pipe, 8 ... Exhaust port, 9 ... Supercharger DESCRIPTION OF SYMBOLS 10 ... Intercooler, 13 ... NOx purification catalyst apparatus, 14 ... Common rail, 15 ... Supply pump, 16 ... Reducing agent injector, 17 ... Injection hole, 20 ... Exhaust manifold, 22a-22d ... Branch pipe, 23 ... Collecting pipe 30 to 32 ... inner wall, L ... inner wall length, Lt, Lc, Lb ... pipe length.

Claims (7)

A branch portion connected to each cylinder of the multi-cylinder internal combustion engine, a collecting portion connected to the downstream side of each branch portion, and a NOx purification catalyst device connected to the downstream side of the collecting portion In an exhaust system of a multi-cylinder internal combustion engine to which a reducing agent injector for injecting a reducing agent into a specific branching portion of the branching portion and supplying the reducing agent to the NOx purification catalyst device is attached.
An exhaust system for a multi-cylinder internal combustion engine, characterized in that an inner wall for suppressing exhaust pressure pulsation propagating from another branch portion extends from the inner wall of the collective portion toward the inside of the specific branch portion. The exhaust system of a multi-cylinder internal combustion engine according to claim 1, wherein the inner wall extends from an inner wall of the collective portion located between the specific branch portion and a branch portion adjacent to the specific branch portion. 3. The exhaust system of a multi-cylinder internal combustion engine according to claim 2, wherein the inner wall extends along a flow direction of exhaust gas flowing from the specific branch portion into the collecting portion. The length L in the extending direction of the inner wall is L ≧ 0.10 Lc with respect to a distance Lc in the exhaust flow direction from the connection position between the specific branch portion and the corresponding cylinder to the NOx purification catalyst device. The exhaust system of a multi-cylinder internal combustion engine according to claim 3, which is formed so as to satisfy the relationship. The exhaust system of a multi-cylinder internal combustion engine according to claim 4, wherein the inner wall is formed so that the length L further satisfies a relationship of L≤0.32Lc with respect to the distance Lc. In the exhaust system, a supercharger is provided between the collecting portion and the NOx purification catalyst device, and the length L in the extending direction of the inner wall corresponds to the specific branch portion. The exhaust system of a multi-cylinder internal combustion engine according to claim 3, wherein the exhaust system is formed so as to satisfy a relationship of L≥0.10Lt with respect to a distance Lt in the exhaust flow direction from a connection position with a cylinder to be operated to the supercharger. The exhaust system of a multi-cylinder internal combustion engine according to claim 6, wherein the inner wall is formed so that the length L further satisfies the relationship L ≦ 0.32Lt with respect to the distance Lt.

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