DE102010029989A1 - Exhaust gas after-treatment system for use in internal combustion engine, has heat exchanger exchanging heat between feed line and discharging unit, and exhaust treatment element provided with feed line - Google Patents

Abstract

The system has an exhaust treatment element (40) provided with a feed line (71). A discharging unit (72) discharges gas e.g. nitrogen oxide gas, from the exhaust after-treatment element, which is arranged on a turbine (22) of a turbocharger. A heat exchanger (60) exchanges heat between the feed line and the discharging unit. The exhaust treatment element and the heat exchanger are integrated into a housing. The exhaust treatment element is selected from one of a reduction catalyst, a particulate filter, and an oxidation catalyst converter. An independent claim is also included for a device comprising a combustion engine.

Description

Technical area

The invention relates to the field of supercharged by exhaust gas turbochargers internal combustion engines.

It relates to an exhaust aftertreatment system with one or more exhaust aftertreatment elements, as well as a device having an internal combustion engine supercharged by an exhaust gas turbocharger and an exhaust gas aftertreatment system arranged in the exhaust gas line between the internal combustion engine and the turbine of the exhaust gas turbocharger.

State of the art

In recent years, the legal requirements regarding exhaust emissions from large diesel engines have sharply worsened worldwide. In the field of marine diesel engines, the requirements are mainly focused on the limitation of nitrogen oxides (NOx) and sulfur oxides (SOx).

Since the introduction of "IMO Tier I", the first stage of the so-called "IMO MARPOL 73/78 Annex VI" emission regulations for marine diesel engines from the year 2000, the proportion of NOx-optimized engines is constantly increasing. The next tier "Tier II" of the aforementioned IMO target will enter into force in 2011 and calls for a further 20% reduction in NOx emissions compared to "IMO Tier I". The third stage of the IMO Tier III IMO emissions regulation is scheduled for 2016 and provides for a further reduction of NOx emissions in certain Emission Control Areas to the level of 80% under Tier I. From today's point of view, these requirements are so strict that completely new measures and technical solutions will be required based on the engine systems used today. In view of the stringent emission regulations, reducing exhaust emissions in the foreseeable future will thus be the predominant topic in research and development in the field of large diesel engines. In this case, exhaust aftertreatment elements, which are arranged in the exhaust system after exiting the cylinders of the engine and the exhaust gas tank (exhaust receiver), play a crucial role.

Already today, SCR catalysts (Selective Catalytic Reaction) are increasingly being used as exhaust aftertreatment elements in order to reduce nitrogen oxide emissions to a lower level. The chemical reaction generated in the SCR catalyst is selective, that is, it is preferred that the nitrogen oxides are reduced, while undesirable side reactions are largely suppressed, for example, the oxidation of sulfur dioxide to sulfur dioxide.

SCR catalysts have a considerable heat capacity. In practice, it has been found that this can lead to unstable engine operation when the SCR catalyst is arranged in the exhaust line in front of the turbine of an exhaust gas turbocharger used for the charging of the engine, especially in stationary operation and load shedding (see curve (2) in the diagram in 2 ).

When taking loads on engines with SCR catalysts, it may also happen that the engine is operated at or above the thermal load limit. These phenomena occur more frequently in the two-stroke range and are mitigated until now with active control mechanisms, which are however throughout complicated, costly and error-prone.

In both cases, the thermal inertia of the catalyst is the cause of the problem. The energy required at the turbine comes in the case without catalyst directly from the cylinder in the form of heat of the exhaust gas. In operation with catalysts before turbine, the energy content of the exhaust gas is given by the thermal inertia of the catalyst delayed to the turbine.

With a load bearing, the pressure in the receiver and the mass air flow must increase, to enable this, the turbine needs more energy, which is emitted by the engine in the form of higher exhaust gas temperature. However, the catalyst is colder than the exhaust gas flowing out of the cylinder due to the operation of the original load point. The catalyst thus removes heat energy from the exhaust gas, which is then available to the turbine with a delay. Because of the resulting lack of air, the temperature in and after the cylinder continues to increase, which can lead to thermal overloading of the engine.

Temperature oscillations occur when the temperature in front of the catalytic converter continues to heat up until the energy requirement of the turbine is exceeded. In return, the exhaust gas temperature after the cylinder decreases again until the required energy demand is reached. At certain operating points and load jumps, the system dampens these temperature oscillations, in others this must be done by an active control.

Problems similar to those described with reference to the SCR catalyst may also be encountered when using other exhaust aftertreatment elements, such as particulate filters or oxidation Catalysts occur, especially if they are located in the exhaust line in front of the turbine.

Brief description of the invention

The object of the invention is therefore to reduce in a supercharged internal combustion engine with an exhaust aftertreatment element in the exhaust line in front of the turbine of the exhaust gas turbocharger, a possible delay in the delivery of the exhaust gas energy to the turbine.

According to the invention, this is achieved by providing a heat exchanger for heat exchange between these two exhaust gas lines between the section of the exhaust line between the cylinders of the internal combustion engine and the exhaust aftertreatment element and the portion of the exhaust line between the exhaust aftertreatment element and the turbine.

Since, in the case of temperature oscillations, the temperatures in the respective exhaust gas line before and after the exhaust gas aftertreatment element can be different and are out of phase up to half a wavelength, a heat exchanger is a suitable means for damping this thermal oscillation.

A thermal overload of the internal combustion engine can be averted, since the high proportion of energy is passed before the exhaust aftertreatment element via heat exchanger of the turbine and thus ensures a permissible and safe load change.

The heat exchanger itself is usually a passive element and therefore requires no control. Optionally, the heat exchanger can be connected to an external energy source and has an active control, so that the energy input into the respective exhaust pipe to be heated can be further increased if necessary.

Certain exhaust aftertreatment elements are not flowed through at low load, for which a bypass valve is provided, with which the exhaust gas flow can be passed directly to the turbine of the exhaust gas turbocharger. In the inventive installation of a heat exchanger, the same bypass valve can be used to flow around the system heat exchanger and exhaust aftertreatment element.

Optionally, the heat exchanger and exhaust aftertreatment element are combined in one element, whereby the pressure loss in the exhaust system but also the space required by the additional elements between engine and exhaust gas turbocharger can be reduced.

The inventive expansion of the exhaust system by means of heat exchangers can be carried out with different exhaust aftertreatment elements, such as an SCR catalyst, a particulate filter or an oxidation catalyst.

Further advantages emerge from the dependent claims.

Brief description of the drawings

The device with an according to the invention with a heat exchanger in the exhaust line in front of the turbine of the exhaust gas turbocharger equipped internal combustion engine is described with reference to the drawings. This shows

1 a schematic representation of the inventive arrangement of the heat exchanger in the region of the exhaust aftertreatment element in the exhaust line in front of the turbine of the exhaust gas turbocharger,

2 a diagram of a simulation of the temperature profile in the exhaust system immediately after the combustion chambers of the internal combustion engine after a load shedding, the three curves the temperature curves in an internal combustion engine without exhaust aftertreatment element (SCR catalyst), in an internal combustion engine with exhaust aftertreatment element and in an inventive equipped with a heat exchanger internal combustion engine with Exhaust aftertreatment element show, and

3 a schematic representation of the inventive arrangement of the heat exchanger in the region of the exhaust aftertreatment element in the exhaust line in front of the turbines of two exhaust gas turbochargers of a two-stage supercharging system.

Way to carry out the invention

In the 1 illustrated internal combustion engine, for example, a marine diesel engine, comprises a plurality of cylinders 13 (Combustion chambers) in which a mixture of fuel and air is converted by combustion into mechanical energy. The air needed for combustion is passed through the compressor 21 an exhaust gas turbocharger 20 into an air receiver upstream of the cylinder 11 guided. Between the compressor 21 and the air tank 11 In general, some of the heat is removed from the air, which is in the process of compressing the compressor 21 the exhaust gas turbocharger 20 originated. This is in the intake manifold a charge air cooler 30 arranged. After the combustion process that is pulsating from the cylinders 13 expelled exhaust gas in an exhaust gas tank 12 (exhaust receiver) collected before passing over the exhaust line of the turbine 22 the exhaust gas turbocharger 20 and then the exhaust system is supplied. The turbine 22 the exhaust gas turbocharger 20 drives the compressor connected to the turbine via an exhaust gas turbocharger shaft 21 of the exhaust gas turbocharger.

Further, in the schematic representation in the exhaust line between the combustion chambers of the internal combustion engine and the turbine of the exhaust gas turbocharger an exhaust aftertreatment system with an exhaust aftertreatment element 40 For example, SCR catalyst, oxidation catalyst, or particulate filter provided. Although in the following only one exhaust gas aftertreatment element is mentioned, several exhaust gas aftertreatment elements can of course be arranged in the exhaust gas system. In this case, the formulation 'an exhaust aftertreatment element' may also include a plurality of exhaust aftertreatment elements. A supply line 71 the exhaust gas from the combustion chambers of the internal combustion engine leads to the exhaust gas aftertreatment element 40 , A derivative 72 then leads the exhaust gas from the exhaust aftertreatment element 40 to the turbine of the exhaust gas turbocharger.

In addition to the exhaust aftertreatment element 40 the exhaust aftertreatment system according to the invention comprises a heat exchanger 60 , The heat exchanger couples the supply line thermally 71 to the exhaust aftertreatment element 40 and the derivative 72 from the exhaust aftertreatment element 40 in such a way that a heat exchange takes place between the two exhaust pipes. Lies in the supply line 71 Exhaust gas at a higher temperature than in the discharge 72 , then the heat exchanger heats the exhaust gas in the drain 72 on, wherein the heat exchanger as a passive element, the necessary energy from the hot exhaust gas in the supply line 71 refers. In this way, according to the invention, a thermal overloading of the internal combustion engine can be averted, since the high proportion of energy in the hot exhaust gas of the supply line 71 before the exhaust aftertreatment element 40 via heat exchanger 60 the derivative leading to the turbine is transferred. Thereby, the adverse effect of the heat capacity of the exhaust aftertreatment element is reduced to the dynamic behavior of the internal combustion engine, thus ensuring a permissible and safe load change.

Accordingly, energy flows in the opposite direction, if in the derivative 72 a higher temperature prevails than in the supply line 71 ,

In the case of temperature oscillations, the temperatures in the respective line before and after the exhaust gas aftertreatment element may be different in phase and up to half a wavelength in phase. In this case, a heat exchanger is a suitable means to damp this thermal vibration.

Between the supply line 71 and the derivative 72 is optional a bypass line 73 arranged, in which a bypass valve 50 is arranged. For example, at low load, can by means of bypass valve 50 the exhaust gas are passed directly from the engine to the turbine of the exhaust gas turbocharger.

Optionally, the heat exchanger and the exhaust aftertreatment element may be formed as a component. This facilitates the assembly and allows a space saving in the region of the exhaust line of the internal combustion engine. Optionally, the blow-by line and the blow-by valve can also be integrated as part of this one component. Thus, then the entire exhaust aftertreatment system is designed as a component which can be switched directly into the exhaust system between the engine and turbine of the exhaust gas turbocharger. Alternatively, only blow-by valve and heat exchanger can be realized as an integrated component, which can be connected in parallel to the exhaust aftertreatment element in the exhaust system.

In the case of a two-stage or multi-stage supercharging of an internal combustion engine, the exhaust-gas aftertreatment system according to the invention can be arranged in front of one of the several turbines, not necessarily before the first high-pressure turbine connected directly to the internal combustion engine. Optionally, two or more of the exhaust aftertreatment systems according to the invention may also be provided in the case of a two-stage or multi-stage supercharging.

It can be before each turbine, so in a two-stage charging, as in 3 shown, before the directly downstream of the engine high-pressure turbine 22H as well as the subsequent low-pressure turbine 22L , according to the invention with a heat exchanger 60 equipped exhaust aftertreatment system may be arranged. In the case of multi-part charging stages, it is also possible to arrange exhaust-gas aftertreatment systems according to the invention only in front of part of the turbines.

Based on the in 2 the diagram shown, the effect of the inventively arranged in the exhaust aftertreatment system heat exchanger is shown to the temperature at the outlet of an internal combustion engine.

The diagram shows a simulation of the temperature curve over time immediately after a load shedding. The solid curve (1) shows as a reference curve the course of the temperature in an internal combustion engine without exhaust aftertreatment element, in this particular case of simulation, without an SCR catalyst. After the load shedding, the temperature drops briefly, but immediately catches again and then remains constant at a level which is slightly lower than the starting temperature before load shedding.

The second curve (2), shown in dashed lines, shows the temperature profile in an internal combustion engine with an SCR catalytic converter as the exhaust gas aftertreatment element, wherein the SCR catalytic converter is unregulated. After the load has been released and the temperature has dropped for the first time, a very strong, almost uncontrolled fluctuation of the temperature sets in, which is inadmissible for the operation of a motor.

The third curve (3), shown by dashed lines with dots, shows the temperature profile of the exhaust gas aftertreatment system according to the invention, equipped with a heat exchanger. Although, after the temperature drops immediately after load shedding, a slight oscillation also sets in, but this assumes a clearly controlled course. The self-adjusting, constant temperature after load shedding is slightly higher than the final temperature of the reference system.

LIST OF REFERENCE NUMBERS

10

Internal combustion engine, internal combustion engine

11

Charge air receiver (air receiver)

12

Exhaust receiver

13

Combustion chambers, cylinders

20

turbocharger

20 _{H / L}

High / low pressure exhaust gas turbocharger

21

compressor

22

turbine

22 _{H / L}

High / low pressure turbine

30

Intercooler

40

exhaust aftertreatment element

50

Bypass valve

60

heat exchangers

71

supply

72

derivation

73

Bypass line

Claims (8)

Exhaust after-treatment system comprising at least one exhaust aftertreatment element ( 40 ), a supply line ( 71 ) for supplying exhaust gas of an internal combustion engine to the exhaust gas aftertreatment element ( 40 ), as well as a derivation ( 72 ) for removing exhaust gas from the exhaust aftertreatment element ( 40 ) on the turbine of an exhaust gas turbocharger, characterized in that a heat exchanger ( 60 ) is provided for heat exchange between the supply line and the discharge. Exhaust after-treatment system according to claim 1, wherein the exhaust aftertreatment element ( 40 ) and the heat exchanger ( 60 ) are integrated in a housing and formed as a component. Exhaust after-treatment system according to one of claims 1 or 2, wherein. between the supply line ( 71 ) and the derivative ( 72 ) a bypass line ( 73 ) arranged on the exhaust gas aftertreatment element ( 40 ) and the heat exchanger ( 60 ) and in which a bypass valve ( 50 ) is arranged, by means of which the bypass line ( 73 ) can be opened or closed. An exhaust after-treatment system according to claim 3, wherein the heat exchanger ( 60 ) and the bypass valve ( 50 ) or the heat exchanger ( 60 ), the bypass valve ( 50 ) and the exhaust aftertreatment element ( 40 ) are integrated in a housing and formed as a component Exhaust after-treatment system according to one of claims 1 to 4, wherein the exhaust aftertreatment element ( 40 ) is an SCR catalyst, an oxidation catalyst, or a particulate filter. Device comprising an internal combustion engine ( 10 ), an exhaust gas turbocharger ( 20 ) for charging the internal combustion engine ( 10 ), as well as in the exhaust line between the internal combustion engine ( 10 ) and the turbine ( 22 ) of the exhaust gas turbocharger ( 20 ) arranged exhaust gas aftertreatment system according to one of claims 1 to 5, wherein the heat exchange between the supply line ( 71 ) between the internal combustion engine ( 10 ) and the exhaust aftertreatment element ( 40 ) and the derivative ( 71 ) between the exhaust aftertreatment element ( 40 ) and the turbine ( 22 ) of the exhaust gas turbocharger ( 20 ) he follows. Device comprising an internal combustion engine ( 10 ), two or more turbochargers ( 20 ) a two-stage or multi-stage charging device for charging the internal combustion engine ( 10 ), as well as in the exhaust line between the internal combustion engine ( 10 ) and the turbine ( 22H ) of a directly downstream of the engine exhaust gas turbocharger ( 20H ) or in the exhaust line between the turbine ( 22H ) of a first exhaust gas turbocharger ( 20H ) and the turbine ( 22L ) of a second exhaust gas turbocharger ( 20L ) arranged exhaust aftertreatment system according to one of claims 1 to 5. Apparatus according to claim 7, wherein at least a second exhaust gas aftertreatment system according to any one of claims 1 to 5 is provided, so that in the exhaust line in front of at least two turbines ( 22H . 22L ) of the two or more exhaust gas turbochargers ( 20H . 20L ) is arranged in each case an exhaust aftertreatment system.

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