DE102006049392B4 - Exhaust emission control system for an internal combustion engine - Google Patents

Abstract

An exhaust emission control system for an internal combustion engine (1) comprising: a turbocharger (4) having a turbine (4b), a turbine rotor (46) thereof being driven by exhaust gas produced by the internal combustion engine (1) having a plurality of cylinders , is ejected; a first exhaust duct (5, 7) extending from a first group of cylinders of the internal combustion engine (1); a second exhaust duct (6, 8) extending from a second group of cylinders of the internal combustion engine (1); a third exhaust duct (9) extending downstream from the turbine (4b); an exhaust emission control catalyst (10) disposed in the third exhaust passage; a reducing agent adding device (14) for adding a reducing agent to the exhaust gas; and an EGR system (11) for supplying part of the exhaust gas as EGR gas to an air intake system (2), characterized in that: the reducing agent adding means is arranged in the first exhaust passage; an EGR gas outlet (13) of the EGR system (11) is arranged in the second exhaust passage; and most of it ...

Description

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to an exhaust emission control system for an internal combustion engine provided with an exhaust gas recirculation (EGR) system.

2. Description of the Related Art

A technology is known in which by arranging a reductant addition valve in a first exhaust manifold connected to a group of cylinders of a multi-cylinder internal combustion engine and providing an EGR gas outlet of an EGR system in a second exhaust manifold is connected to the other cylinder group, it is prevented that a reducing agent, which is added by the reducing agent addition valve, enters the EGR system (see, for example, Japanese Patent Laid-Open No. JP 2004-76 595 A ).

However, with a view to those disclosed in Japanese Patent Laid-Open Publication No. 2-220117 JP 2004-76 595 A technology, the first exhaust manifold in which the reductant addition valve is disposed, and the second exhaust manifold in which the EGR gas outlet is provided are connected to each other in front of a turbine of a downstream turbocharger. Accordingly, it is possible that the reducing agent added via the reducing agent adding valve passes through the connecting portion in front of the turbine into the second exhaust manifold and thus into the EGR system.

Furthermore, the teaches DE 10 2005 008 650 A1 an internal combustion engine in which the valve timing of the intake valves and / or the exhaust valves of the individual cylinders of the brake engine are provided differently. In this case, the cylinders which supply the exhaust gas recirculation device have no or shorter valve overlap times than the cylinders which do not supply the exhaust gas recirculation device.

The DE 28 55 687 further discloses an internal combustion engine having a turbine and compressor unit, comprising a suction line and an exhaust line, wherein the outlet of the compressor is connected by a line to the suction line. The exhaust pipe is divided into two sections and each section is connected to receive the exhaust gases of a group of cylinders. The turbine is composed of two parts, and each turbine part, the exhaust gases are supplied via the associated section of the exhaust pipe. An exhaust gas recirculation line exhaust gases are supplied from one of the two cylinder groups, so they get to the intake. The cylinders of one group change according to the firing order with the cylinders of the other group. In the turbine part, which is connected to the relevant section of the exhaust pipe and the Abgasrückumwälzleitung, the passage cross section is restricted, whereby the pressure in this section of the Agasleitung is increased to a value which is higher than the pressure in the intake manifold.

From the DE 198 57 234 A1 Finally, a device for exhaust gas recirculation for a supercharged internal combustion engine with an exhaust gas turbocharger with an exhaust turbine and a compressor, an exhaust pipe, a charge air line and an exhaust gas recirculation line connecting the exhaust pipe before the exhaust gas turbine with the charge air line to the compressor known. The exhaust gas turbine is designed as a double-flow turbine. The channels of the two floods are asymmetrical, with a smaller and a larger channel. The exhaust gas turbine has a variable geometry for changing the exhaust gas flow rate. By a control device, the pressure in the exhaust gas recirculation line is controlled so that it is higher adjustable than the pressure in the charge air line to the compressor.

SUMMARY OF THE INVENTION

An object of the present invention is to propose a technology which makes it possible to prevent penetration of a reducing agent added to an exhaust gas into an EGR system.

A first aspect of the present invention uses the following construction. More specifically, the first aspect of the present invention relates to an exhaust emission control system for an internal combustion engine comprising: a turbocharger having a turbine, a turbine rotor thereof being exhausted by exhaust gas discharged from the internal combustion engine including a plurality of cylinders; is driven; a first exhaust passage extending from a first cylinder group of the internal combustion engine; a second exhaust passage extending from a second cylinder group of the internal combustion engine; a third exhaust passage extending downstream of the turbine; an exhaust emission control catalyst disposed in the third exhaust passage; a reducing agent adding means for adding a reducing agent to the exhaust gas; and an EGR system for supplying a part of the exhaust gas as EGR gas into the air intake system. In this exhaust emission control system, the reducing agent adding means is provided in the first exhaust passage; and an EGR Gas outlet of the EGR system is provided in the second exhaust passage, whereby most of the exhaust gases discharged from the first and second exhaust passages separately flow into the turbine rotor without being mixed, and the exhaust gas passing through the first exhaust passage into the turbine has flowed through a region of relatively high temperature in the turbine can flow.

According to the first aspect of the present invention, most of the exhaust gases discharged from the first and second exhaust passages respectively remain separated without being mixed with each other until the gases reach the turbine rotor of the turbine which is located downstream of the first and second exhaust passages. Therefore, the exhaust gas discharged from the first exhaust passage is less likely to enter the second exhaust passage and is prevented from reaching the EGR gas outlet in the second exhaust passage. Accordingly, even if the addition of the reducing agent is carried out while EGR gas is supplied to the air intake system, it is possible to further prevent the added reducing agent from flowing into the EGR system through the EGR gas outlet.

The reducing agent added to the exhaust gas in the first exhaust passage, which has flowed into the turbine, tends to adhere to the inside of the turbine when the ambient temperature decreases. If the reducing agent adheres to the inside of the turbine, the reducing agent acts as a binder so that the particulates in the exhaust gas tend to accumulate in the turbine. The exhaust gas that has flowed into the turbine through the first exhaust passage flows through the relatively high temperature region in the turbine so that the exhaust gas with the reducing agent flows through the relatively high temperature region in the turbine. Therefore, it is possible to prevent the reducing agent from adhering to the inside of the turbine. In addition, it is possible to prevent the particles from accumulating in the turbine due to the attached reducing agent.

The exhaust emission control system may further include intake air amount regulating means for making the amount of intake air introduced into the cylinders of the first group smaller than the amount of intake air introduced into the cylinders of the second group.

By reducing the amount of intake air introduced into a cylinder, it is possible to increase the temperature of the exhaust gas discharged from the cylinder. Therefore, it is possible to make the temperature of the exhaust gas discharged from the first exhaust passage higher than the temperature of the exhaust gas discharged from the second exhaust passage. In this way, it is possible to prevent the reducing agent from adhering to the inside of the first exhaust passage or the turbine. In addition, since it is possible to accelerate the evaporation of the reducing agent, it is possible to increase the temperature of the exhaust emission control catalyst more efficiently, and more efficiently perform purification of the exhaust gas in the exhaust emission control catalyst.

The exhaust emission control system may further include a swirl control means for making the swirl of the intake air introduced into the cylinders of the first group more intense than the swirling of the intake air placed in the cylinders of the second group.

If the amount of intake air introduced into the cylinders of the first group is reduced, the air-fuel ratio in the cylinders of the first group decreases, which facilitates smoke generation. However, with the invention described above, it is possible to make the air-fuel ratio distribution in the cylinders more uniform by enhancing the swirling of the intake air into the cylinders of the first group. In this way it is possible to avoid the formation of smoke.

With the present invention, it is possible to further prevent the reducing agent, which is added to the exhaust gas, from entering the EGR gas outlet. Accordingly, it also becomes possible to prevent the reducing agent mixed with the exhaust gas from flowing into the EGR system.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following description of preferred embodiments with reference to the accompanying drawings, in which like reference numerals are used to designate like elements; showing:

1 FIG. 12 is a diagram showing a schematic arrangement of an internal combustion engine to which an exhaust emission control system according to a first embodiment is applied, and an intake and exhaust system thereof; FIG.

2 FIG. 12 is a diagram illustrating a schematic configuration of a turbine according to the first embodiment; FIG.

3 is a diagram showing a schematic configuration of an internal combustion engine, in which an exhaust emission control system according to a second embodiment is used, as well as an inlet and outlet system thereof;

4 FIG. 12 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust emission control system according to a third embodiment is applied, and an intake and exhaust system thereof.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

1 11 is a diagram showing a schematic arrangement of an internal combustion engine to which an exhaust emission control system according to a first embodiment of the present invention is applied, and an intake and exhaust system thereof.

The combustion engine 1 , in the 1 is a water-cooled four-cylinder four-cylinder diesel engine, first to fourth cylinders # 1 to # 4.

At the combustion engine 1 is an intake manifold 2 connected to inlet ports of the cylinders on an upstream side. An inlet pipe or intake pipe 3 is with the intake manifold or intake manifold 2 connected at the upstream side. A compressor 4a a turbocharger 4 is in the intake pipe 3 arranged.

An exhaust manifold is connected to the internal combustion engine 1 connected via exhaust ports of the cylinders on the downstream side. In the first embodiment, the exhaust manifold is divided into two manifolds. A first exhaust manifold 5 is connected to the first and fourth cylinders # 1 and # 4, and a second exhaust manifold 6 is connected to the second and third cylinders # 2 and # 3. A first exhaust pipe or exhaust pipe 7 is with the first Abgaskrummer 5 connected on the downstream side. A second exhaust pipe or exhaust pipe 8th is with the second exhaust manifold 6 connected on the downstream side. The first exhaust manifold 5 and the first exhaust pipe 7 may be interpreted as a first exhaust passage of the present invention. The second exhaust manifold 6 and the second exhaust pipe 8th may be interpreted as a second exhaust passage of the present invention.

The downstream ends of the first and second exhaust pipes 7 and 8th are with a turbine 4b of the turbocharger 4 connected. In the turbocharger 4 rotates a turbine rotor 46 the turbine 4b by receiving exhaust gas from the first and second exhaust pipes 7 and 8th is discharged, causing the compressor 4a , which with the turbine 4b is brought to rotate to charge the engine with the intake air. The turbocharger 4 is a variable geometry turbocharger (variable nozzle turbocharger) and has a variable nozzle 41 in the turbine 4b ,

As in 2 As shown, there are two separate inlet ports of the turbine 4b with which the first and second exhaust pipes 7 and 8th are connected. The first and second exhaust pipes 7 and 8th are each with the first and second inlet port 42 and 43 connected.

A twin-screw turbocharger or twin-scroll turbo is called a turbocharger 4 which has two separate inner conduits extending from the two inlet ports, the first and second inlet ports 42 and 43 , extend. A first scroll line or screw line 44 and a second scroll line 45 each extend from the first and second inlet ports 42 and 43 , The first and second scroll lines or screw lines 44 and 45 run spirally and allow the exhaust, to the variable nozzle 41 to stream. This exhaust gas turns the turbine rotor 46 ,

The turbine 4b is with a bearing housing 47 near the turbine rotor 46 provided. The bearing housing 47 is supplied with lubricating oil and cooling water. For this reason, the temperature of the turbine 4b on the side of the bearing housing 47 lower than on the opposite side, the exhaust outlet side. In the turbine 4b is the second inlet port 43 on the side of the bearing housing 47 arranged, and the first inlet port 42 is on the exhaust outlet side away from the bearing housing 47 arranged.

A third exhaust pipe 9 is with the turbine 4b of the turbocharger 4 connected at the downstream side. A filter 10 that carries a NOx storage reduction catalyst as the exhaust gas control catalyst is in the third exhaust pipe 9 arranged. A silencer (not shown) is downstream of the filter 10 arranged, and the exhaust gas is discharged via the silencer to the environment.

On the other hand, there is an exhaust gas recirculation (EGR) system. 11 in the combustion engine 1 Installed. The EGR system 11 Reduces the NOx contained in the exhaust gas by lowering the combustion temperature in the internal combustion engine 1 by returning a portion of the exhaust gas as EGR gas into the intake manifold 2 the combustion engine 1 ,

The EGR system 11 has an EGR pipe 12 of which one end is connected to the second exhaust pipe 8th is connected, and the other end to the intake manifold 2 connected is. An EGR gas outlet 13 for introducing the EGR gas from the second exhaust pipe 8th into the EGR pipe 12 is in the second exhaust pipe 8th provided.

A reductant addition nozzle 14 as the reducing agent adding means is at the first exhaust manifold 5 the combustion engine 1 appropriate. The reductant addition nozzle 14 adds fuel as a reducing agent to the exhaust. The reductant addition nozzle 14 is immediately downstream of cylinder # 1 in the first exhaust manifold 5 arranged.

The combustion engine 1 with the construction described above is also equipped with an electronic control unit (ECU) 15 for controlling the internal combustion engine 1 provided. The ECU 15 is a control computer made up of a CPU, ROM, RAM, backup RAM etc.

The ECU 15 works according to the program stored in the ROM and realizes the EGR operation using the EGR system 11 and / or the addition of the reducing agent using the reducing agent addition nozzle 14 ,

The EGR operation means the operation in which, in order to prevent the generation of the NOx by lowering the exhaust gas temperature in the internal combustion engine, a part of the exhaust gas into the intake manifold 2 over the EGR pipe 12 is introduced when the internal combustion engine 1 is operated at a certain operating condition in which the exhaust gas pressure is higher than the inlet pressure.

The addition of the reducing agent means the act of adding the fuel via the reducing agent addition nozzle 14 , This will be at the time of treatment of the filter 10 , such as NOx reduction treatment, SOx poisoning treatment and / or PM removal oxidation treatment.

The NOx reduction treatment is the treatment in which the air-fuel ratio of the exhaust gas flowing into the NOx catalyst of the filter by adding fuel which is the reducing agent to the exhaust gas via the reducing agent addition nozzle 14 is enriched or enriched, whereby the NOx applied in the NOx catalyst is dissolved and reduced. The SOx poisoning treatment is the treatment in which the air-fuel ratio of the exhaust gas that enters the NOx catalyst of the filter 10 flows through the reductant addition nozzle by adding fuel, which is a reducing agent, to the exhaust gas 14 is enriched or enriched when the catalyst temperature is between 600 ° C and 800 ° C, whereby the SOx applied in the NOx catalyst is dissolved and reduced. The PM removal-oxidation treatment is the treatment in which fuel is added to the exhaust gas via the reducing agent addition nozzle 14 is added to the unburned fuel in the NOx catalyst of the filter 10 to oxidize, and the temperature of the filter 10 is increased by the heat generated during the oxidation, resulting in the filter 10 accumulated PM (solids or particles) are removed.

In this embodiment, the first exhaust manifold 5 with the reducing agent addition nozzle 14 provided, and the second exhaust pipe 8th is with the EGR gas outlet 13 of the EGR system 11 provided. The first and second exhaust pipes 7 and 8th are each with two separate first and second inlets 42 and 43 the turbine 4b of the turbocharger 4 which is a twin scroll turbo connected.

In particular, in the first embodiment, that of the first exhaust manifold remains 5 and first exhaust pipe 7 as well as from the second exhaust manifold 6 and second exhaust pipe 8th discharged exhaust gas in the downstream of the first and second exhaust pipe 7 and 8th arranged turbine 4b separated, and a majority of the exhaust gas flows separately to the turbine rotor 46 without being mixed. That of the first exhaust manifold and the first exhaust pipe 7 discharged exhaust tends less to enter the second exhaust pipe through the turbine 4b is prevented from obtaining the EGR gas outlet 13 in the second exhaust pipe 8th to reach. Therefore, it is possible even if fuel via the reducing agent addition nozzle 14 during EGR operation is added to prevent added fuel from entering the EGR gas outlet 13 arrives. Accordingly, it is possible to prevent the reducing agent mixed with the exhaust gas from entering the EGR system 11 flows.

In this way, it is possible to reduce the torque fluctuation and the deterioration of the exhaust emission due to the penetration of the fuel, which is a reducing agent, into the air intake system. In addition, the addition of the reducing agent is efficient, with as little fuel as possible feasible.

In addition, the turbocharger 4 a twin scroll turbo or twin-screw turbocharger, and the first and second scroll ducts 44 and 45 extend from the first and second inlet ports 42 and 43 so that the first and second exhaust pipes 7 and 8th discharged exhaust even in the turbine 4b are separated. That from the first exhaust manifold 5 and the first exhaust pipe 7 discharged exhaust tends less to, in the second exhaust pipe 8th through the turbine 4b is prevented from obtaining the EGR gas outlet 13 in the second exhaust pipe 8th to reach.

As in 2 shown, is the first inlet port 42 arranged such that from the first exhaust pipe 7 discharged exhaust gas through the first screw passage 44 , which is arranged on the exhaust gas outlet side, flows, which is a section of the turbine 4b of the turbocharger 4 which is a Twin Scroll Turbo, with relatively high temperature.

The exhaust gas in the first exhaust manifold 5 admixed fuel which enters the turbine 4b has flowed, tends to be on the inside of the turbine 4b stick when the ambient temperature decreases. If the fuel is on the inside of the turbine 4b adheres, the fuel serves as a binder, so that the particles in the exhaust gas tend to accumulate in the turbine. If the first inlet port 42 as in 2 is arranged, the exhaust gas flows from the first exhaust manifold 5 which the fuel via the reducing agent addition nozzle 14 was added through the first snail passage 44 , which is arranged on the exhaust gas outlet side, which is a section of the turbine 4b with a relatively high temperature. Therefore, it is possible to prevent fuel, which is a reducing agent, from being inside the turbine 4b adheres. In addition, it is possible to prevent particles between the variable nozzle 41 and the first snail passage 44 in the turbine 4b for example due to stuck fuel.

In addition, when the EGR gas outlet 13 in the second exhaust pipe 8th downstream from the second Abgaskrummer 6 is arranged, the flow of the EGR gas smoothed, and it is possible to reduce the pressure loss and to keep the fuel consumption low.

3 11 is a diagram showing a schematic arrangement of an internal combustion engine to which an exhaust emission control system according to a second embodiment of the present invention is applied, and an intake and exhaust system thereof. In the description of the second embodiment, only the different points between this embodiment and the first embodiment will be described.

The combustion engine 1 The second embodiment comprises a variable valve train 16 for controlling the valve timing of the intake valves of the cylinders. The variable valve train 16 is electric with the ECU 15 ally.

The amount of in the first and fourth cylinders # 1 and # 4, which with the first exhaust manifold 5 are introduced intake air is when using the variable valve train 16 lower than the amount of intake air introduced into the second and third cylinders # 2 and # 3 with the second exhaust manifold 6 are connected.

Specifically, the intake valve closing timing of the first and fourth cylinders # 1 and # 4 is delayed relative to the intake valve closing timing of the second and third cylinders # 2 and # 3. The variable valve train 16 and the ECU 15 that performs this control may be interpreted as intake air amount regulating means. continue here

When the amount of intake air introduced into the first and fourth cylinders # 1 and # 4 is reduced in this manner, it is possible to increase the temperature of the exhaust gas discharged from the first and fourth cylinders # 1 and # 4, the amount of intake air thereof is low. Therefore, it is possible to change the temperature of the first exhaust manifold 5 and the first exhaust pipe 7 ejected exhaust gas to make higher than the temperature of the second exhaust manifold 6 and of the second exhaust pipe 8th discharged exhaust gas. Accordingly, in the high-temperature exhaust gas, the less fuel tends to be on the inside of the first exhaust manifold 5 and the exhaust pipe 7 or the turbine 4b even if fuel, which is a reducing agent, from the first exhaust manifold 5 discharged exhaust gas via the reducing agent addition nozzle 14 and much less likely to act as a binder causing accumulation of the particles due to the adhesion of the fuel.

If the temperature of the first exhaust manifold 5 and the first exhaust pipe 7 discharged exhaust gas is increased in this way, it is possible to accelerate the evaporation of the fuel, which is a reducing agent, in the high-temperature exhaust gas. Because of this it is possible to change the temperature of the filter 10 to increase efficiency and purify the exhaust gas in the filter 10 perform more efficiently.

4 FIG. 12 is a diagram showing a schematic configuration of an internal combustion engine using an exhaust emission control system according to a third embodiment of the present invention, and an intake and exhaust system thereof. FIG. In the description of the third embodiment, only the different points between this embodiment and the first embodiment will be described.

The combustion engine 1 the third embodiment is with swirl control valves (SCV) 17 equipped at the inlet ports of the cylinders. The swirl control valves 17 are electric with the ECU 15 connected. The swirl control valves 17 can be individually controlled on a cylinder-by-cylinder basis. The ECU 15 controls the intensity of the swirling flow generated in each cylinder by controlling the opening / closing of each swirl control valve 17 the corresponding cylinder.

The turbulence of the intake air or intake air, which in the first and fourth cylinders # 1 and # 4, with the first exhaust manifold 5 is introduced is using the swirl control valves 17 carried out more intensively than the swirling of the intake air, which is introduced into the second and third cylinders # 2 and # 3, which with the second exhaust manifold 6 are connected. In particular, the swirl control valves 17 of the second and third cylinders # 2 and # 3 are opened relatively wide, so that the intake air amount is increased. On the other hand, the swirl control valves of the first and fourth cylinders # 1 and # 4 are opened relatively little, so that the intake air amount is reduced, and the swirling flow generated in the first and fourth cylinders # 1 and # 4 becomes intensified (turbulence reinforcement).

If the swirl in the first and fourth cylinders # 1 and # 4 is increased and the amount of intake air introduced into the first cylinders # 1 and # 4 is decreased, it is possible to control the temperature of the first and fourth cylinders # 1 and # 4 discharged exhaust gas whose intake air amount is low, increase. Therefore, it is possible to change the temperature of the first exhaust manifold 5 and the first exhaust pipe 7 discharged exhaust gas to make higher than the temperature of the exhaust gas, which from the second exhaust manifold 6 and the second exhaust pipe 8th is delivered. Accordingly, the fuel tends less to the inside of the first exhaust manifold 5 and the first exhaust pipe 7 , or the turbine 4b even if fuel, which is a reducing agent, is added to the exhaust gas from the first exhaust manifold 6 via the reducing agent addition nozzle 14 is ejected, and in the high-temperature exhaust gas, it is much less likely to serve as a binder, causing the particles to accumulate due to the adhesion of the fuel.

If the temperature of the first exhaust manifold 5 and first exhaust pipe 7 discharged exhaust gas is increased in this way, it is possible to accelerate the evaporation of the fuel, which is a reducing agent, in the high-temperature exhaust gas. For this reason, it is possible to change the temperature of the filter 10 to increase efficiency and purify the exhaust gas in the filter 10 perform more efficiently.

If the intake air amount introduced into the first and fourth cylinders # 1 and # 4 is decreased, the air-fuel ratio in the first and fourth cylinders # 1 and # 4 decreases, facilitating smoke generation. However, it is possible to improve the distribution of the air-fuel ratio in the cylinders by intensifying the swirling of the intake air in the first and fourth cylinders # 1 and # 4 by the swirl control valves 17 to make it more uniform. In this way it is possible to prevent smoke formation.

Although the invention has been described above with reference to what is to be understood as the preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or arrangements. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while different elements of the disclosed invention are pointed out in various combinations and arrangements, which are merely exemplary in nature, other combinations and arrangements including more or less or merely a single part are also within the scope of the appended claims.

Claims (6)

Exhaust emission control system for an internal combustion engine ( 1 ), comprising: a turbocharger ( 4 ) with a turbine ( 4b ), wherein a turbine rotor ( 46 ) thereof is driven by exhaust gas emitted by the internal combustion engine ( 1 ) having a plurality of cylinders is ejected; a first exhaust duct ( 5 . 7 ) extending from a first group of cylinders of the internal combustion engine ( 1 ) extends; a second exhaust duct ( 6 . 8th ) extending from a second group of cylinders of the internal combustion engine ( 1 ) extends; a third exhaust duct ( 9 ) extending from the turbine ( 4b extending downstream; an exhaust emission control catalyst ( 10 ) disposed in the third exhaust passage; a reducing agent adding device ( 14 ) for adding a reducing agent to the exhaust gas; and an EGR system ( 11 ) for supplying a portion of the exhaust gas as EGR gas to an air intake system ( 2 ), characterized in that: the reducing agent adding means is disposed in the first exhaust passage; an EGR gas outlet ( 13 ) of the EGR system ( 11 ) is disposed in the second exhaust passage; and most of the exhaust gases discharged from the first and second exhaust passages separate from each other Turbine rotor ( 46 ) flows without being mixed, whereby the exhaust gas which flows into the turbine ( 4b ) has passed through the first exhaust passage, through a relatively high temperature region in the turbine ( 4b ) flows. Exhaust emission control system for an internal combustion engine ( 1 ) according to claim 1, characterized in that: the first and second exhaust ducts with the turbocharger ( 4 ) are connected. Exhaust emission control system for an internal combustion engine ( 1 ) according to claim 1 or 2, characterized in that the turbocharger ( 4 ) two separate first and second inlet ports ( 42 . 43 ) and first and second screw ducts ( 44 . 45 ) connected respectively to the first and second inlet ports ( 42 . 43 ) are connected; and the exhaust gases discharged from the first and second exhaust passages respectively through the first and second scroll ducts (FIG. 44 . 45 ) to the turbine rotor ( 46 ) stream. Exhaust emission control system for an internal combustion engine ( 1 ) according to claim 3, characterized in that: the turbocharger ( 4 ) is a variable geometry turbocharger having a variable nozzle ( 41 ) Has; and the first and second screw ducts ( 44 . 45 ) extend spirally and the exhaust gas flow to the variable nozzle ( 41 ) allow. Exhaust emission control system for an internal combustion engine ( 1 ) according to any one of claims 1 to 4, characterized in that it further comprises: an intake air quantity regulating means for making an intake air amount introduced into the cylinders of the first group smaller than an intake air amount flowing into the cylinders of the second group is introduced. Exhaust emission control system for an internal combustion engine ( 1 ) according to one of claims 1 to 5, characterized in that it further comprises: a swirling control means for making turbulence of the intake air, which is introduced into the cylinders of the first group, more intense than a swirling of the intake air entering the Cylinder of the second group is introduced.

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