DE102020100465A1 - Process for exhaust aftertreatment of an internal combustion engine and exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine (10) with at least one combustion chamber (12). The outlet (16) of the internal combustion engine (10) is connected to an exhaust system (20) in which, in the flow direction of an exhaust gas flow through the exhaust system (20), an electrically heatable catalytic converter (36) and, downstream of the electrically heatable catalytic converter (36), a particle filter ( 30). It is provided that the electrically heatable catalytic converter (36) is heated to a temperature (TB) above an oxidation temperature (TOX) for soot particles when the internal combustion engine (10) is in operation and to this when the internal combustion engine (10) is in operation Temperature (TB) is maintained so that the soot particles on the surface of the electrically heatable catalytic converter (36) are continuously oxidized. The invention also relates to an exhaust gas aftertreatment system for an internal combustion engine (10) for carrying out such a method.

Description

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine and an exhaust gas aftertreatment system for carrying out such a method according to the preamble of the independent claims.

The current exhaust gas legislation, and one that will become ever more stringent in the future, place high demands on the engine-related raw emissions and the exhaust gas aftertreatment of internal combustion engines. The demands for a further decrease in consumption and the further tightening of the exhaust gas standards with regard to the permissible nitrogen oxide emissions represent a challenge for the engine developers. Upstream and downstream catalytic converters. Exhaust aftertreatment systems are currently used in diesel engines which have an oxidation catalytic converter or a NO _x storage catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for separating soot particles and, if necessary, further catalytic converters. In order to meet the high requirements for minimal nitrogen oxide emissions, exhaust gas aftertreatment systems are known which have two SCR catalytic converters connected in series, each of the SCR catalytic converters being preceded by a metering element for metering in a reducing agent. A synthetic, aqueous urea solution is preferably used as the reducing agent, which is mixed with the hot exhaust gas flow in a mixing device upstream of the SCR catalytic converter. As a result of this mixing, the aqueous urea solution is heated, the aqueous urea solution releasing ammonia in the exhaust gas duct. A commercially available, aqueous urea solution generally consists of 32.5% urea and 67.5% water.

An exhaust gas aftertreatment system for a diesel engine for exhaust gas aftertreatment of the diesel engine at low exhaust gas temperatures is known from WO 2009/014 275 A1. The exhaust aftertreatment system comprises an oxidation catalytic converter for the oxidation of unburned hydrocarbons and nitrogen monoxide as well as a catalytic filter for continuous soot combustion. A fuel injector is arranged on the exhaust system, which is followed by an electrically heatable catalytic converter, in such a way that the metered fuel is converted exothermically with the oxygen on the electrically heatable catalytic converter and thus heats the exhaust gas flow from the diesel engine.

The DE 10 2010 064 020 B4 discloses a method for heating a particle filter in an exhaust system of an internal combustion engine, in which fuel is introduced into an exhaust gas flow transported in the exhaust system in order to form an exhaust gas / fuel mixture. A partial flow of the exhaust gas / fuel mixture is converted in an electrically heatable catalytic converter to form a catalytic converter exhaust gas, a further partial flow of the exhaust gas / fuel mixture being fed to the catalytic converter exhaust gas in order to form a catalytic converter exhaust gas / exhaust gas / fuel mixture. This catalytic converter exhaust gas / exhaust gas / fuel mixture is converted in an additional oxidation catalytic converter in order to form a further catalytic converter exhaust gas, the further catalytic converter exhaust gas being mixed with the residual flow of the exhaust gas / fuel mixture in order to form a catalytic converter exhaust gas / exhaust gas / fuel mixture. This catalytic converter exhaust gas / exhaust gas / fuel mixture is converted in a main oxidation catalytic converter in order to form a catalytic converter exhaust gas for heating the particle filter.

From the DE 10 2017 010 267 A1 is an exhaust aftertreatment system for a diesel engine with an exhaust pipe in which an electrically heatable catalyst, an oxidation catalyst, another oxidation catalyst and a diesel particle filter with a coating for the selective, catalytic reduction of nitrogen oxides are arranged in the flow direction of an exhaust gas of the diesel engine. A fuel injector is arranged on the exhaust line, with which additional fuel can be introduced into the exhaust line, which fuel is converted exothermically by one of the oxidation catalysts in order to heat the diesel particulate filter to its regeneration temperature.

The invention is now based on the object of minimizing the particle emissions in an internal combustion engine and, in particular, of resolving the conflict of objectives between low particle emissions and low nitrogen oxide emissions.

According to the invention, this object is achieved by a method for exhaust gas aftertreatment of an internal combustion engine with at least one combustion chamber. The outlet of the internal combustion engine is connected to an exhaust system in which an electrically heatable catalytic converter is arranged in the flow direction of an exhaust gas flow through the exhaust system and a particle filter is arranged downstream of the electrically heatable catalytic converter. According to the invention, it is provided that the electrically heatable catalyst is heated to a temperature above an oxidation temperature for soot particles when the internal combustion engine is operating and is kept at this temperature when the internal combustion engine is in operation, so that the soot particles on the surface of the electrically heatable catalyst are continuously oxidized. As a result, the soot particles can be converted continuously, so that loading of the particle filter arranged downstream of the electrically heatable catalytic converter is significantly slowed down. The regeneration intervals of the particulate filter can thus be extended or the internal combustion engine can be operated with higher particulate emissions with the same tailpipe emissions, as a result of which the NOx raw emissions can be reduced.

The features listed in the dependent claims allow advantageous improvements and non-trivial further developments of the method for exhaust gas aftertreatment of an internal combustion engine mentioned in the independent claim.

In a preferred embodiment of the invention it is provided that the electrically heatable catalytic converter is kept at a temperature of at least 600 ° C., preferably of at least 700 ° C., particularly preferably of at least 800 ° C., when the internal combustion engine is operating. This makes it possible to ensure that the soot particles contained in the exhaust gas flow of the internal combustion engine are oxidized with the residual oxygen contained in the exhaust gas flow of the internal combustion engine when they strike a surface of the electrically heatable catalytic converter.

In an advantageous embodiment of the method it is provided that the electrically heatable catalytic converter is activated in map areas of the internal combustion engine with increased raw particle emissions. Due to the continuous oxidation of the soot particles, a second exhaust gas aftertreatment component is created in addition to the particle filter to reduce the soot particles. In this way, higher particulate emissions can also be reduced by exhaust gas aftertreatment, so that an increase in particulate emissions does not lead to an inadmissible increase in tailpipe emissions or an inadmissibly high load on the particulate filter.

In a further preferred embodiment of the invention it is provided that the electrically heatable catalytic converter is activated when a conversion of the nitrogen oxide emissions in the exhaust gas flow of the internal combustion engine is restricted or impossible. In principle, when designing a diesel combustion process, there is a conflict of objectives between low nitrogen oxide emissions and low particle emissions (NOx particle trade-off). If an efficient exhaust gas aftertreatment of the nitrogen oxide emissions cannot be guaranteed, the combustion process can be designed with regard to low NOx raw emissions and increased particulate raw emissions. These increased raw particle emissions can be reduced by the continuous oxidation of the soot on the surface of the electrically heated catalytic converter, so that minimal tailpipe emissions with regard to nitrogen oxides and particles can be achieved.

It is particularly preferred that the injection quantity and / or the injection time of the fuel into the combustion chambers of the internal combustion engine is selected in such a way that the raw nitrogen oxide emissions are reduced and the raw particle emissions are increased. Further preferred embodiments of the invention emerge from the other features mentioned in the subclaims.

Another aspect of the invention relates to an exhaust gas aftertreatment system for an internal combustion engine with an exhaust system in which an electrically heatable catalytic converter and a particle filter are arranged downstream of the electrically heatable catalytic converter in the flow direction, as well as with a control unit which is set up to carry out a method according to the invention for exhaust gas aftertreatment when a machine-readable program code is executed by the control unit. As a result, the soot particles can be converted continuously, so that loading of the particle filter arranged downstream of the electrically heatable catalytic converter is significantly slowed down. The regeneration intervals of the particulate filter can thus be extended or the internal combustion engine can be operated with higher particulate emissions with the same tailpipe emissions, as a result of which the NOx raw emissions can be reduced.

In an advantageous embodiment of the exhaust gas aftertreatment system, it is provided that the electrically heatable catalyst is arranged downstream of an outlet of the internal combustion engine, preferably downstream of a turbine of an exhaust gas turbocharger of the internal combustion engine, and upstream of an oxidation catalyst or a NOx storage catalyst. This makes it possible for the soot particles to bond with unburned hydrocarbons in the exhaust gas flow of the internal combustion engine, which increases the mass of the particles and thus the mass inertia. This increases the likelihood that a soot particle will hit a hot catalytic converter wall when flowing through the electrically heatable catalytic converter and be oxidized on it.

In a further improvement of the exhaust gas aftertreatment system it is provided that the electrically heatable catalytic converter is preceded by an element for influencing the flow, with which a cross flow is impressed on the exhaust gas flow of the internal combustion engine before it enters the electrically heatable catalytic converter. A cross flow can increase the likelihood of a Soot particles hitting a wall of the electrically heatable catalyst are increased. The conversion performance of the electrically heatable catalytic converter with regard to a continuous oxidation of the soot particles can thus be increased. As a result, more soot particles can already be converted on the electrically heated catalytic converter and the loading of the particle filter is slowed down with the same raw particle emissions. The flow can be influenced in such a way that the flow is preferably impressed with a swirl flow or turbulence.

Alternatively or additionally, it is advantageously provided that the electrically heatable catalytic converter is preceded by a screen or a flow guide plate which at least partially covers the inlet openings of the electrically heatable catalytic converter so that the exhaust gas flow is deflected before it enters the electrically heatable catalytic converter. A diaphragm or a flow guide plate can also increase the probability that a soot particle will hit a hot catalytic converter wall of the electrically heatable catalytic converter and be oxidized on this wall with the residual oxygen in the exhaust gas flow. The screen and the honeycomb of the electrically heatable catalytic converter are spaced from one another and block the cross section of the exhaust gas duct in the flow direction, so that a soot particle almost inevitably hits the screen or the honeycomb of the electrically heated catalytic converter. This makes it possible to achieve a particularly high probability that a soot particle will at least hit a wall which has a temperature above the oxidation temperature of the soot particle. Due to the inertia, larger and heavier soot particles, in particular, are unable to follow a flow deflection between the diaphragm and the electrically heatable catalytic converter and strike the hot wall of the electrically heatable catalytic converter.

Due to the thermal radiation of the electrically heatable catalytic converter, the diaphragm or the flow guide plate itself can be heated up considerably and thus reach a temperature which is above the oxidation temperature of the soot particles. Thus, the surface for the oxidation of the soot particles can be increased.

In addition, a further diaphragm or a further flow guide plate can be provided downstream of the electrically heatable catalytic converter in order to enlarge the effective area and thus to increase the conversion performance of the electrically heatable catalytic converter.

In a further improvement of the exhaust gas aftertreatment system, it is provided that the electrically heated catalyst is installed at an angle of at least 10 °, preferably of at least 20 °, particularly preferably of at least 30 ° to the direction of flow, so that the frontal area of the electrically heated catalyst is increased and thus the Impact probability of the soot particles on the hot surface is also increased.

In a further improvement of the exhaust gas aftertreatment system, it is provided that the element for influencing the flow, the diaphragm, the flow guide plate, or the electrically heated catalyst are provided with a catalytically active coating which lowers the oxidation temperature of the soot particles. As a result, soot particles can already be oxidized at lower temperatures, in particular from a temperature range of 400 ° C., whereby the electrical heating output can be minimized.

The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless stated otherwise in the individual case.

• 1 ein Ausführungsbeispiel für ein erfindungsgemäßes Abgasnachbehandlungssystem für einen Verbrennungsmotor;
• 2 ein erstes Ausführungsbeispiel eines elektrisch beheizbaren Katalysators zur kontinuierlichen Rußoxidation;
• 3 ein weiteres Ausführungsbeispiel eines elektrisch beheizbaren Katalysators zur kontinuierlichen Rußoxidation; und
• 4 ein weiteres Ausführungsbeispiel eines elektrisch beheizbaren Katalysators zur kontinuierlichen Rußoxidation.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Show it:

• 1 an embodiment of an exhaust gas aftertreatment system according to the invention for an internal combustion engine;
• 2 a first embodiment of an electrically heatable catalyst for continuous soot oxidation;
• 3 a further embodiment of an electrically heatable catalyst for continuous soot oxidation; and
• 4th Another embodiment of an electrically heatable catalyst for continuous soot oxidation.

1 shows an internal combustion engine 10 , which with its outlet 16 with an exhaust system 20th connected is. The internal combustion engine 10 has a plurality of combustion chambers 12th on each of which a fuel injector 14th for injecting a combustible fuel into the respective combustion chamber 12th of the internal combustion engine 10 is arranged. The outlet 16 of the internal combustion engine 10 includes an exhaust manifold 18th in which the exhaust gases from the combustion chambers 12th of the internal combustion engine 10 collected and a common exhaust duct 22nd of the exhaust system 20th are fed.

In the exhaust system 20th are in the flow direction of an exhaust gas flow of the internal combustion engine 10 downstream of a turbine of an exhaust gas turbocharger 48 a first catalyst 24 , preferably an oxidation catalyst 26th or a NOx storage catalytic converter 28, an electrically heatable catalytic converter 36 and a particulate filter 30th arranged. The particle filter 30th preferably has a catalytic coating 32 , especially a coating 34 for the selective, catalytic reduction of nitrogen oxides. Alternatively, the particle filter 30th can also be made uncoated. The electrically heated catalytic converter 36 includes an electrical heating element 38 , in particular an electric heating disk. The electrically heated catalytic converter 36 can, as in 3 or 4th shown a flow element 70 , 72 , 74 be connected upstream to the probability of the impact of a soot particle from the exhaust gas flow of the internal combustion engine 10 on a wall of the electrically heatable catalytic converter 36 to increase. Downstream of the first catalyst 24 and upstream of the particulate filter 30th with the SCR coating 34 is a first metering valve 40 for the introduction of a reducing agent 62 in the exhaust duct 22nd arranged. The first metering valve 40 is a first exhaust mixer 42 downstream to ensure homogeneous mixing of the reducing agent 62 with the exhaust gas flow of the internal combustion engine 10 to enable.

Downstream of the particulate filter 30th is a branch 44 formed on which an exhaust gas recirculation duct of a low-pressure exhaust gas recirculation 46 from the exhaust duct 22nd the exhaust system 20th branches off. Downstream of the branch 44 is another SCR catalytic converter 54 arranged. The other SCR catalytic converter 54 is preferably an ammonia barrier catalyst 56 downstream in order to avoid uncontrolled leakage of ammonia and the associated odor nuisance. Downstream of the branch 44 and upstream of the further SCR catalytic converter 54 is a second metering valve 50 for the introduction of a reducing agent 62 in the exhaust duct 22nd of the internal combustion engine 10 arranged. The second metering valve 50 is another exhaust mixer 52 downstream to the mixing of the exhaust gas flow with the reducing agent 62 before entering the further SCR catalytic converter 54 to improve. The first metering valve 40 and the second metering valve 50 are each via a reducing agent line 64 , 66 with a storage container 68 connected in which the reducing agent 62 , in particular aqueous urea solution, is stored.

The internal combustion engine 10 is a control device 60 assigned, via which the fuel injection by the injectors 14th into the combustion chambers 12th of the internal combustion engine 10 is controlled. The control unit also controls 60 the dosing of the reducing agent 62 through the two metering valves 40 , 50 and the heating power of the electrically heatable catalytic converter 36 .

During the operation of the internal combustion engine 10 becomes the electrically heated catalytic converter 36 heated to a temperature of at least 600 ° C., preferably of at least 700 ° C., particularly preferably of at least 800 ° C., at which soot particles can be oxidized with the residual oxygen in the exhaust gas stream. This can reduce the load on the particle filter 30th can be reduced, whereby the period between two necessary regenerations of the particulate filter 30th can be extended. Furthermore, the conflict of objectives between low NOx raw emissions and low soot raw emissions can be resolved in the direction of stronger soot raw emissions, since the electrically heated catalytic converter 36 an additional oxidation of soot particles takes place. The electrically heated catalytic converter 36 can be provided with a catalytic coating in order to reduce the temperature necessary for the oxidation of the soot particles.

Alternatively, it is advantageously provided that the electrically heatable catalyst 36 as the first component of the exhaust gas aftertreatment immediately downstream of the turbine of the exhaust gas turbocharger 48 and upstream of the oxidation catalyst 26th or the NOx storage catalytic converter 28 is arranged. As a result, the soot particles can be bonded to the unburned hydrocarbons in the exhaust gas flow, which increases the mass of the soot particles and thus their inertia. This increases the likelihood that a soot particle will hit a hot wall of the electrically heated catalytic converter 36 hits and is oxidized there.

In 2 is a first embodiment of an electrically heatable catalytic converter 36 shown. The electrically heated catalytic converter 36 has a plurality of honeycombs which are perpendicular to the flow direction of an exhaust gas flow of the internal combustion engine 10 through the exhaust duct 22nd are aligned and thus a flow grid 58 form. The advantage of this embodiment is a relatively low flow resistance, but this alignment of the honeycomb has a relatively low probability of a soot particle striking a wall of the electrically heatable catalytic converter 36 connected. This is the conversion performance of the electrically heated catalytic converter 36 comparatively low with regard to the oxidation of soot particles.

In 3 is a further embodiment of an electrically heatable catalytic converter 36 for continuous soot oxidation in an exhaust gas stream of the internal combustion engine 10 shown. In this variant, the electrically heated catalytic converter 36 an element to influence the flow 70 , in particular a swirl element connected upstream, which the exhaust gas flow before entry into the electrically heatable catalytic converter 36 a twist imposes. The element for influencing the flow 70 has several wings 72 on, which preferably evenly over the circumference of the element for influencing the flow 70 are arranged and thus ensure a swirl flow formed uniformly over the cross section of the exhaust gas duct. This reduces the likelihood of a soot particle hitting a hot wall of the electrically heated catalytic converter 36 elevated. At the same time, the element influences the flow 70 to a slight increase in the exhaust back pressure. The element for influencing the flow 70 can through the thermal radiation of the electrically heated catalytic converter 36 _{even be heated to a temperature T OX} necessary for the oxidation of the soot particles, which increases the effective area. Furthermore, the element can be used to influence the flow 70 be provided with a catalytically active coating to prevent the oxidation of the soot particles on the element for influencing the flow 70 to favor.

In 4th is a further embodiment of an electrically heatable catalyst 36 for continuous soot oxidation in an exhaust gas stream of the internal combustion engine 10 shown. In this variant, the electrically heated catalytic converter 36 an aperture 74 or a flow guide plate 76 upstream, which the openings of the electrically heated catalyst 36 at least substantially block in the direction of flow. In addition, the electrically heated catalytic converter 36 be designed as a flow guide plate, whereby a very high probability of a soot particle hitting a hot wall of the electrically heatable catalytic converter 36 results. The soot particles are on the hot wall of the electrically heated catalytic converter 36 with the residual oxygen in the exhaust gas flow of the internal combustion engine 10 oxidized. As a result, a high conversion rate can be achieved, so that the particle filter is not loaded 30th is significantly reduced and the regeneration cycles of the particle filter 30th can be extended significantly.

In addition, a further sheet metal can be placed downstream of the electrically heatable catalytic converter 36 be provided around the soot-oxidizing surface in the exhaust duct 22nd to enlarge further. Alternatively, the honeycomb structure of the electrically heatable catalytic converter 36 also be designed in such a way that a straight flow through the electrically heatable catalyst 36 is impossible and the exhaust gas flow inevitably in the electrically heated catalytic converter 36 is diverted.

List of reference symbols

10

Internal combustion engine

12th

Combustion chamber

14th

Fuel injector

16

Outlet

18th

Exhaust manifold

20th

Exhaust system

22nd

Exhaust duct

24

first catalyst

26th

Oxidation catalyst

28

NOx storage catalytic converter

30th

Particle filter

32

catalytic coating

34

SCR coating

36

electrically heated catalytic converter

38

electric heating element

40

first metering valve

42

first exhaust mixer

44

branch

46

Low pressure exhaust gas recirculation

48

Exhaust gas turbocharger

50

second metering valve

52

second exhaust mixer

54

SCR catalytic converter

56

Ammonia barrier catalyst

58

Flow grid

60

Control unit

62

Reducing agent

64

first reducing agent line

66

second reducing agent line

68

Storage container

70

Element for influencing the flow

72

wing

74

cover

76

Flow guide plate

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102010064020 B4 [0004]
• DE 102017010267 A1 [0005]

Claims (10)

Method for exhaust gas aftertreatment of an internal combustion engine (10) with at least one combustion chamber (12), the outlet (16) of which is connected to an exhaust system (20) in which an electrically heatable catalytic converter (36) and, downstream of the electrically heatable catalytic converter (36), a particle filter (30) are arranged, characterized in that the electrically heatable catalytic converter (36) is heated to a temperature (T _B ) above an oxidation _{temperature (T OX} ) for soot particles during operation of the internal combustion engine (10) and to this temperature (T _B ) is held so that the soot particles are continuously oxidized on a surface of the electrically heatable catalytic converter (36) when the internal combustion engine (10) is in operation. Procedure according to Claim 1 , characterized in that the electrically heatable catalytic converter (36) is kept at a temperature of at least 600 ° C when the internal combustion engine (10) is in operation. Procedure according to Claim 1 or 2 , characterized in that the electrically heatable catalytic converter (36) is activated in map areas of the internal combustion engine (10) with increased raw particle emissions. Method according to one of the Claims 1 to 3 , characterized in that the electrically heatable catalytic converter (36) is activated when a conversion of the nitrogen oxide emissions in the exhaust gas flow of the internal combustion engine (10) is restricted or impossible. Procedure according to Claim 4 , characterized in that the combustion process is influenced in such a way that the raw NOx emissions are reduced and the raw particulate emissions are increased at the same time. Exhaust gas aftertreatment system for an internal combustion engine (10) with an exhaust system (20) in which an electrically heatable catalytic converter (36) and a particle filter (30) are arranged downstream of an electrically heatable catalytic converter (36) in the flow direction, as well as with a control unit (60), which is set up to use a method according to one of the Claims 1 to 5 execute when a machine-readable program code is executed by the control device (60). Exhaust aftertreatment system after Claim 6 , characterized in that the electrically heatable catalytic converter (36) is preceded by an element for influencing the flow (70) with which a cross flow is impressed on the exhaust gas flow of the internal combustion engine (10) before it enters the electrically heatable catalytic converter (36). Exhaust aftertreatment system after Claim 6 or 7th , characterized in that the electrically heatable catalyst (36) is preceded by a screen (74) or a flow guide plate (76) which at least partially cover the inlet openings of the electrically heatable catalyst (36) so that a flow deflection of the exhaust gas flow before it enters the electrically heatable catalyst (36) is achieved. Exhaust aftertreatment system after Claim 6 to 8th , characterized in that the electrically heatable catalytic converter (36) is rotated at an angle of at least 10 ° to the direction of flow, so that a flow deflection of the exhaust gas flow in the electrically heatable catalytic converter (36) is achieved. Exhaust aftertreatment system after Claim 7 to 9 , characterized in that the element for influencing the flow (70), the diaphragm (74), the flow guide plate (76), or the electrically heated catalyst (36) are provided with a catalytically active coating which lowers the oxidation temperature of the soot particles.

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