WO2010052055A1

WO2010052055A1 - Internal combustion engine with turbocharger and oxidation catalyst

Info

Publication number: WO2010052055A1
Application number: PCT/EP2009/061842
Authority: WO
Inventors: Thorsten Raatz; Roderich Otte
Original assignee: Robert Bosch Gmbh
Priority date: 2008-11-05
Filing date: 2009-09-14
Publication date: 2010-05-14
Also published as: DE102008043487A1

Abstract

The invention relates to an internal combustion engine (1) of a motor vehicle with an exhaust system (2), which has at least one first turbine (5) of at least one turbocharger for charging the internal combustion engine and at least one first oxidation catalyst (21). According to the invention, the first oxidation catalyst (21) is situated upstream of the turbine (5) with regard to the flow and the exhaust system (2) has at least one denitrification apparatus (23) which is situated downstream of the first oxidation catalyst (21). Furthermore, the invention relates to a corresponding method.

Description

description

title

Internal combustion engine with turbocharger and oxidation catalyst

The invention relates to an internal combustion engine of a motor vehicle with a

Exhaust system having at least one first turbine of at least one turbocharger for charging the internal combustion engine and at least one, first oxidation catalyst.

State of the art

Internal combustion engines achieve their maximum efficiency in an operation with an excess of air in a fuel-air mixture at an air ratio λ> 1. In this case, a special exhaust aftertreatment system is required to reduce a nitrogen oxide content with exhaust gas of the internal combustion engine. A nitrogen oxide reduction (NO _x reduction) can only be carried out in the case of excess fuel, ie for λ <1 or in a catalytic manner with a stoichiometric mixture, that is to say for λ = 1. For this reason, both in a diesel internal combustion engine and in an Otto internal combustion engine, nitrogen oxide storage catalysts are used. These internal combustion engines also use selective catalytic reduction (SCR). Furthermore, an after-combustion of partially oxidized or unburned hydrocarbons additionally usually requires an oxidation catalyst and possibly a particle filter for particle reduction.

A nitrogen oxide storage catalyst stores nitrogen oxides during lean operation, that is, for λ> 1, and is regularly regenerated in the presence of fuel surplus to always ensure a sufficient storage capacity. During regeneration, nitrogen oxides are released, which react with unburned fuel or carbon monoxide to form nitrogen, carbon dioxide and / or water. If the storage capacity is exceeded, the nitrogen oxides pass the nitrogen oxide storage catalyst and are expelled from the vehicle as pollutants. The nitrogen oxide storage catalytic converters operate in a temperature range of the exhaust gases from approximately 250 to 500 ⁰ C. The fact that motor efficiency continued to improve and temperatures ren of the exhaust gas to be reduced further and further, a low-temperature activity of the nitrogen oxide storage catalytic converters is very relevant.

If a motor vehicle is operated with sulfur-containing fuel, sulfates can form and store in the nitrogen oxide storage catalyst, which leads to a loss of storage capacity in the nitrogen oxide catalyst. To ensure the

Storage capability of the nitrogen oxide storage catalyst must be occasionally desulfated. For this purpose, temperatures of the exhaust gas of at least 650 ⁰ C must be present in the nitrogen oxide storage catalyst.

Denitration of exhaust gas by means of a system based on selective catalytic reduction requires the addition of ammonia (NH ₃ ) or precursors for the formation of ammonia, which are introduced into the exhaust gas. In the catalytic reduction catalyst (SCR catalyst), the ammonia reacts via different reaction paths with the nitrogen oxides. It can come to the standard reaction with nitrogen monoxide and oxygen, a slow reaction with nitrogen dioxide or for rapid reaction with nitrogen monoxide and nitrogen dioxide. Such SCR catalysts generally operate in a temperature range of about 230 to 450 ° C. Especially nitrogen dioxide can be reacted even at temperatures below 230 ⁰ C. If the SCR catalyst is preceded by an oxidation catalyst, a proportion of nitrogen dioxide in the inlet of the SCR catalyst increases, which increases the low-temperature activity of the SCR catalyst.

Basically, the effectiveness of the mentioned denitrification processes are influenced by the temperature of the exhaust gas. In particular, during a warm-up phase of the internal combustion engine after a cold start, a denitrification device (DeNO _x system) as well as the oxidation catalyst, must be brought quickly to an operating temperature so that in a short driving cycle, such as a short certification driving cycle (new European driving cycle NEDC) sufficient Gesamtkonvertierungsphasen Denitrification can be achieved. The temperature of the exhaust gas at the denitrification device depends mainly on the type of internal combustion engine and on a structural design of the exhaust system. Charging systems, such as two-stage turbochargers, allow high engine specific engine performance, but elude the engine

Exhaust usually has more heat than, for example, a single-stage turbocharger. As a result, on the one hand, the heat flow required for heating the exhaust aftertreatment system in the warm-up phase is reduced, and on the other hand, the inlet temperatures for the exhaust gas aftertreatment are reduced.

What is needed is a device which achieves an increase in exhaust gas temperatures in the exhaust aftertreatment and thus an improvement of pollutant conversion rates.

Disclosure of the invention

According to the invention, provision is made for the first oxidation catalytic converter to be arranged upstream of the turbine and for the exhaust gas system to have at least one denitrification device, which is arranged in terms of flow after the first oxidation catalytic converter. By this arrangement of

Oxidation catalyst is achieved that this is located near the combustion chambers - cylinder - the internal combustion engine is placed and is supplied with exhaust gas, which has a high exhaust gas temperature, whereby the oxidation catalyst is heated very quickly to its operating temperature. Thus, it is achieved that an exhaust gas aftertreatment by the oxidation catalyst is carried out very quickly effectively and is very effective even at low load and / or speed of the internal combustion engine and / or despite high engine efficiencies. The use of the denitrification device (DeNOx system) in the exhaust system means that nitrogen oxides in the exhaust gas are reduced by denitrification. The application of the first oxidation catalyst before the denitrification device further leads to the advantage that a nitrogen dioxide concentration within the exhaust gas is increased towards the denitrification device, which improves denitrification during a part-load operation of the internal combustion engine. According to a development of the invention, it is provided that the denitrification device is arranged in terms of flow before or after the turbine. Due to its mass, the turbine acts as a heat sink, which reduces the exhaust gas temperature. This is the case in particular in the instationary mode of the internal combustion engine. By arranging the denitrification device in front of the turbine, it is achieved that the denitrification device is exposed to a high exhaust gas temperature in the same way as the first oxidation catalyst and thereby reaches its operating temperature very rapidly, whereby emissions of the internal combustion engine can be effectively reduced rapidly. Further, urea evaporation for ammonia generation in the denitrification apparatus is enhanced by higher exhaust gas temperatures (eg, Ad Blue evaporation). Particularly advantageous is the arrangement of the denitrification between the first oxidation catalyst and the turbine, since the Denitrifikationsvorrichtung earlier reaches its operating temperature at a cold start of the engine and also in an operation of the internal combustion engine at low loads a very good exhaust aftertreatment takes place. An arrangement of the denitrification device downstream of the turbine results in the denitrification device being heated more slowly, thus counteracting aging of the denitrification device.

According to a development of the invention, a second oxidation catalyst is provided. The second oxidation catalyst is preferably arranged after the first oxidation catalyst and leads to a particularly good exhaust aftertreatment, which is characterized by low emissions when the exhaust gas is discharged. Depending on the design of the first Oxidationskatalysa- sector, that is, depending on the dimensions, cell density and / or type of noble metal coating, the second oxidation catalyst is required to achieve as complete as possible a hydrocarbon hydrocarbon monoxide oxidation.

According to a development of the invention, provision is made for the second oxidation catalytic converter to be arranged downstream of the turbine. Due to this arrangement, the second oxidation catalyst is protected from rapid aging. According to a development of the invention, it is provided that the second oxidation catalyst is arranged in terms of flow before or after the denitrification device. In particular, the arrangement according to the denitrification device is advantageous, since a possible ammonia slip, that is to say ammonia, which emerges from the denitrification device can be reacted at the second oxidation catalyst.

According to a development of the invention, it is provided that the first and / or second oxidation catalyst is a three-way catalyst. This is advantageous in particular when the otherwise lean-running internal combustion engine is operated with a higher fuel content, stoichiometric. This stoichiometric operation is characterized by an air ratio λ = 1. In this case, the use of the three-way catalyst leads to an exhaust aftertreatment, which can implement both nitrogen oxides and hydrocarbons and carbon monoxide.

According to a development of the invention, it is provided that the exhaust system has a particle filter which, in terms of flow technology, is arranged as the last member within the exhaust system. In the context of this application, "components" are understood to mean particulate filters, denitrification devices, oxidation catalysts and turbines. Structural elements do not refer to exhaust-gas-conducting systems such as exhaust pipes and exhaust gas heads. The use of the particulate filter is preferably provided in diesel internal combustion engines.

According to a development of the invention, a bypass is provided. The bypass allows exhaust gas to bypass at least one of the members. As a result, the corresponding members are loaded less and thus aging of the members is prevented. Furthermore, by the bypass on the bypassed members a pressure within the exhaust system can be reduced.

According to a development of the invention it is provided that the bypass is fluidically connected in parallel to the first oxidation catalyst. Thus, it is achieved that the first oxidation catalyst is acted upon with a smaller amount of exhaust gas, whereby the above-described

Benefits arise. According to a development of the invention it is provided that the bypass is fluidically connected in parallel to the series connection of oxidation catalyst and denitrification device. Thus, it is achieved that the oxidation catalytic converter, and the denitrification device are subjected to less exhaust gas, resulting in the advantages described above.

According to a development of the invention, it is provided that the bypass has a controllable valve. This ensures that the amount of exhaust gas passed can be controlled. The controllable valve is preferably designed so that it can be at least partially opened and partially closed depending on the need. By controlling the valve, preferably by controlling the exhaust gas flow controlled by the valve, by means of the valve is made possible to keep pressure losses in the exhaust system at a rated power and / or a temperature load of the members low. This is especially the case when the particulate filter is present and this is to be regenerated. In this way it is achieved that the aging of the members is further reduced and thus there is a component protection for the members. In particular, it is provided to completely open the bypass during a full-load operation of the internal combustion engine in order to prevent aging of the structural members and to effect component protection.

According to a development of the invention, it is provided that the turbocharger is a two-stage turbocharger with the first turbine and a second turbine. By using the two-stage turbocharger, additional heat is extracted from the exhaust gas in the second turbine, which further reduces the exhaust gas temperature. Therefore, an arrangement of the oxidation catalyst and preferably also the denitrification device before the turbine is particularly useful. In this way, they can still be brought very quickly to an operating temperature, resulting in the advantages described above.

According to a development of the invention, it is provided that the second turbine of the first turbine is downstream of flow.

According to a development of the invention, it is provided that the first turbine is a high-pressure turbine and the second turbine is a low-pressure turbine. According to a development of the invention it is provided that the bypass is fluidically connected in parallel to the series connection of oxidation catalyst, denitrification device and the first turbine. In this way it is achieved that exhaust gas with a high exhaust gas temperature can be forwarded to the turbine downstream components, if necessary, while maintaining at least part of the power of the turbocharger. This procedure is particularly advantageous for regeneration of the particulate filter. If it is provided that the Denitrifikationsvorrichtung is arranged fluidically after the high-pressure turbine and behind the bypass line can through

Change in exhaust flow within the bypass of a nitrogen dioxide to nitrogen monoxide ratio controlled and / or regulated. If the denitrification device is arranged fluidically parallel to the bypass, for example, the regeneration of the particulate filter can take place without undesired temperature drop at the denitrification device.

Furthermore, the invention relates to a method for operating an internal combustion engine of a motor vehicle, in particular according to the preceding description, with an exhaust system for guiding exhaust gas having at least a first turbine at least one turbocharger for charging the internal combustion engine and at least one first oxidation catalyst, wherein the exhaust first flows through the oxidation catalyst and then the first turbine and a denitrification device. By flowing through the oxidation catalytic converter upstream of the turbine and the denitrification device, it is achieved that the oxidation catalytic converter is brought to an operating temperature very rapidly, since the exhaust gas temperature upstream of the turbine and the denitrification device is higher than after the turbine and the denitrification device. This leads to a very good exhaust gas aftertreatment, in that the oxidation catalytic converter can treat emissions very effectively after commissioning, such as, for example, starting the internal combustion engine.

According to a development of the method according to the invention, it is provided that at high load, in particular full load of the internal combustion engine, at least a portion of the exhaust gas of the internal combustion engine at least on Oxidationskataly- or on the oxidation catalyst and the denitrification or oxidation catalyst, a denitrification and at the first Turbine is bypassed. By passing the exhaust gas past the members ensures that the members are protected from aging and excessive stress. Depending on which components the exhaust gas is conducted past, downstream components can be exposed to high exhaust gas temperatures, for example, to perform regenerations without burdening the members.

According to a development of the invention, it is provided that a nitrogen oxide conversion in the de-nitrification device, a nitrogen dioxide to nitrogen monoxide ratio in the exhaust gas, is achieved by at least partial bypassing of the exhaust gas

Denitrification, a temperature of Denitrifikationsvorrichtung and / or a temperature of the oxidation catalyst is / are regulated. The possibility of which of the variables mentioned is regulated depends on which components of the exhaust system the exhaust gas is conducted past. Furthermore, a corresponding sensing is necessary for a control and the control can be advantageously carried out by a control unit, in particular engine control unit.

The drawings illustrate the invention by means of exemplary embodiments, in which:

1 shows an internal combustion engine with an exhaust system in a first embodiment,

2 shows an internal combustion engine with an exhaust system in a second embodiment, and

3 shows an internal combustion engine with an exhaust system in a third embodiment.

1 shows an internal combustion engine 1 of a motor vehicle, not shown, with an exhaust system 2 in a first embodiment 3, which has a turbocharger 4 with a turbine 5. Furthermore, the internal combustion engine 1 has an air intake system 6. The air intake system 6 has an air intake 7, which via a pipe 8 air to a first compressor 9 of the

Turbocharger 4 leads, the compressor 9 via a shaft 9 'with the turbine fifth connected is. The air is further brought via a pipe 10 in air ducts 1 1. The air ducts 1 1 lead to cylinders 12 of the internal combustion engine 1, from which exhaust gas is passed into the exhaust manifold 13 and thus into the exhaust system 2. Starting from the manifolds 13, there is additionally an exhaust gas recirculation 14, which leads exhaust gas from the exhaust manifolds 13 via a pipeline 15 to a cooling element 16 and further via a pipeline 17 to a recirculation valve 18. After the return valve 18 recirculated exhaust gas is brought via a pipe 19 into the pipe 10. The exhaust gas recirculation 14 serves to introduce exhaust gas into the air of the pipeline 10 in order to influence the combustion process and thus to reduce the nitrogen oxide emissions. Starting from the

Exhaust manifolds 13 extends a pipeline 20 to a first Oxidationskata- ysator 21st From the first oxidation catalytic converter 21, a pipeline 22 extends to a denitrification device 23, which is fluidically connected to the turbine 5 via a pipeline 24. Via a pipe 25, the exhaust gas from the turbine 5 is passed to a second oxidation catalyst 26, which is connected via a further pipe 27 with a particulate filter 28. The particulate filter 28 discharges the exhaust gas via a pipe 29 and an exhaust gas outlet 30. At the pipeline 20, a bypass 31 begins, which opens into the pipe 24. The bypass 31 has a controllable valve 32, which can change an exhaust gas quantity passed through the bypass 31. As structural members 33, the first oxidation catalytic converter 21, the denitrification device 23, the first turbine 5, the second oxidation catalytic converter 26 and the particle filter 28 are considered here.

The illustrated in Figure 1 first embodiment 3 of the exhaust system 2 makes it possible, at least partially pass the exhaust gas to the first oxidation catalyst 21 and the denitrification device 23 via the bypass 31. This allows the particulate filter 28 to be exposed to very high exhaust gas temperatures without unnecessarily heating the first oxidation catalyst 21 and the denitrification device 23. Thus, aging of the first oxidation catalyst 21 and the denitrification device 23 is prevented. It is envisaged that in a full load operation of the internal combustion engine 1, the valve 32 is fully opened so that as much exhaust gas as possible is conducted past the first oxidation catalyst 21 and the denitrification device 23 in order to obtain component protection by avoiding unnecessary aging of the relevant members 33 becomes. In the illustrated Regulation shows that the exhaust gas near the engine, that is in the vicinity of the cylinder 12 enters the first oxidation catalyst 21 with a high exhaust gas temperature and this heated very quickly to its operating temperature. With the remaining exhaust gas temperature present after the first oxidation catalytic converter 21, the denitrification device 23 then rapidly changes to its

Operating temperature heated. Thus, it is achieved that the two relevant members 33 are taken very quickly after a start of the internal combustion engine 1 in operation and perform an optimal exhaust aftertreatment.

FIG. 2 shows the internal combustion engine 1 of FIG. 1 with all its features.

FIG. 2 differs from FIG. 1 in that the exhaust system 2 is present in a second embodiment 34. In the second embodiment 34 of the exhaust system 2, the denitrification device 23 is arranged downstream of the turbine 5. Thus, it follows that the first oxidation catalyst 21 is connected directly to the pipeline 24, whereas the pipeline 25 leads into the denitrification device 23, which is connected to the second oxidation catalyst 26 via an additional pipeline 35. The pipe 22 is completely eliminated with respect to FIG. In the illustrated second embodiment 34 of the exhaust system 2, the bypass 31 also extends from the pipe 20 to the pipe 24, whereby the exhaust gas at the first

Oxidation catalyst 21 is bypassed. The amount of bypassed exhaust gas is controlled or regulated via the valve 32.

Due to the second embodiment 34 of the exhaust system 2, the already mentioned advantages with respect to rapid heating and the component protection against aging for the oxidation catalyst 21 result. In addition, a nitrogen dioxide to nitrogen monoxide ratio in the exhaust gas can be controlled by, as continuously as possible, exhaust gas is bypassed via the bypass 31 to the oxidation catalyst 21. In this way, it is possible to optimize a nitrogen oxide (NO _x ) conversion in the denitrification device 23.

FIG. 3 shows the internal combustion engine 1 with the exhaust system 2 in a third embodiment 35. The internal combustion engine 1 in FIG. 3 has all the features of FIG. In contrast to Figure 1, the turbocharger 4, the first

Turbine 5 and a second turbine 36. The first turbine 5 is used as a high- pressure turbine 37 formed, whereas the second turbine 36 is formed as a low-pressure turbine 38. Further differences arise as follows. The pipeline 8 extends to a compressor 39 of the second turbine 36, which leads compressed air via a pipeline 40 to the compressor 9 of the turbocharger 4. Thus, the turbocharger 4 is formed as a two-stage turbocharger 40. Of the

Compressor 9 is operatively connected to the turbine 5 via the shaft 9 ', and the compressor 39 is connected to the turbine 36 via a shaft 43. The third embodiment 35 of the exhaust system 2 starts with the exhaust manifolds 13 and passes via the pipe 20 to the first oxidation catalyst 21 and on via the pipe 22 to the denitrification device 23. From the denitrification device 23 extends a pipe 44, which leads to the first turbine 5. The first turbine 5 is connected via a pipe 45 to the second turbine 36, which is followed by the pipe 25. The further course of the third embodiment 35 of the exhaust system 2 to the exhaust outlet 30 corresponds to that of Figure 1. The bypass 31 begins in the pipe 20 and opens into the pipe 45, so that the exhaust gas to the oxidation catalyst 21, the denitrification 43 and the first turbine 5 can be passed around. Via the valve 32 it is possible to set the amount of exhaust gas which is to be bypassed.

The third embodiment 35 of the exhaust system 2 shown makes it possible to bypass the first turbine 5, the high-pressure turbine 37, in addition to the already mentioned advantages with respect to rapid achievement of the operating temperatures and component protection against aging. This is advantageous when high loads are present on the internal combustion engine 1, so that the high-pressure turbine 5 of the turbocharger

4 can be spared if possible. Embodiment 35 allows the particulate filter 28 to be subjected to high exhaust gas temperatures for regeneration without exposing the denitrification device 23 to thermal stresses.

In a further embodiment, not shown, of the exhaust system 2, it is conceivable, starting from the embodiment 35, to arrange the denitrification device 23 after the first turbine 5 and after the bypass 31. This embodiment makes it possible to control the nitrogen dioxide to nitric oxide ratio via the valve 32. Furthermore, in all embodiments 3, 24 and 35, it is conceivable that the oxidation catalysts 21 and / or 26 are designed as three-way catalysts. This is advantageous when the internal combustion engine 1 is at least temporarily operated in a stoichiometric operation with an air ratio λ = 1.

Claims

claims

1. internal combustion engine (1) of a motor vehicle, comprising an exhaust system (2) having at least one first turbine (5) at least one turbocharger (4) for charging the internal combustion engine (1) and at least one first oxidation catalyst (21) characterized in that the first oxidation catalyst

(21) is arranged upstream of the turbine (5) and that the exhaust system (2) has at least one denitrification device (23), which is arranged downstream of the first oxidation catalyst (21).

2. Internal combustion engine (1) according to claim 1, characterized in that the

Denitrification device (23) fluidly before or after the turbine (5) is arranged.

3. Internal combustion engine (1) according to one of the preceding claims, characterized by a second oxidation catalyst (26).

4. internal combustion engine (1) according to any one of the preceding claims, characterized in that the second oxidation catalyst (26) is arranged fluidically after the turbine (5).

5. Internal combustion engine (1) according to one of the preceding claims, characterized in that the second oxidation catalyst (26) is arranged in terms of flow before or after the denitrification device (23).

6. Internal combustion engine (1) according to any one of the preceding claims, characterized in that the first and / or second oxidation catalyst (21, 26) is a three-way catalyst.

7. Internal combustion engine (1) according to any one of the preceding claims, character- ized in that the exhaust system (2) has a particulate filter (28), the - seen fluidically - is arranged as the last member (33) within the exhaust system (2).

8. Internal combustion engine (1) according to one of the preceding claims, characterized by a by-pass (31).

9. Internal combustion engine (1) according to one of the preceding claims, characterized in that the bypass (31) is fluidically connected in parallel to the first oxidation catalyst (21).

10. Internal combustion engine (1) according to one of the preceding claims, characterized in that the bypass (31) is fluidically connected in parallel to the series connection of oxidation catalyst (21) and denitrification device (23).

1 1. Internal combustion engine (1) according to one of the preceding claims, characterized in that the bypass (31) has a controllable valve (32).

12. Internal combustion engine (1) according to any one of the preceding claims, character- ized in that the turbocharger (4) is a two-stage turbocharger (40) with the first turbine (5) and a second turbine (36).

13. Internal combustion engine (1) according to one of the preceding claims, characterized in that the second turbine (36) of the first turbine (5) is downstream of fluidic.

14. Internal combustion engine (1) according to one of the preceding claims, characterized in that the first turbine (5) is a high-pressure turbine (37) and the second turbine (36) is a low-pressure turbine (38).

15. Internal combustion engine (1) according to one of the preceding claims, characterized in that the bypass (31) is fluidically connected in parallel to the series connection of oxidation catalyst (21), denitrification device (23) and the first turbine (5).

16. A method for operating an internal combustion engine (1) of a motor vehicle, in particular according to one or more of the preceding claims, with an exhaust system (2) for guiding exhaust gas, the at least one first turbine (5) at least one turbocharger (4) for charging the Internal combustion engine (1) and at least one first oxidation catalyst (21), characterized in that the exhaust gas flows through first the oxidation catalyst (21) and then the first turbine (5) and a denitrification device (23).

17. The method according to claim 15, characterized in that at high load, in particular full load of the internal combustion engine (1), at least a portion of the exhaust gas of the internal combustion engine (1) at least on the oxidation catalyst (21) or on the oxidation catalyst (21) and on the Denitrification device (23) or on the oxidation catalyst (21), the denitrification device (23) and the first turbine (5) is passed.

18. Method according to claim 1, characterized in that by at least partial bypassing of the exhaust gas a nitrogen oxide conversion in the denitrification device (23), a nitrogen dioxide to nitrogen monoxide ratio in the denitrification device (23), a temperature of the denitrification device (23) and / or a temperature of the oxidation catalyst (21, 26) is / are regulated.