DE102018127643A1 - Exhaust aftertreatment system and method for exhaust aftertreatment of an internal combustion engine - Google Patents

Abstract

The invention relates to an exhaust gas aftertreatment system for an internal combustion engine (10), comprising an exhaust gas system (20) with an exhaust gas duct (22), in which an oxidation catalyst (26) downstream of the exhaust gas duct of the internal combustion engine (10) through the exhaust gas duct (22) Oxidation catalyst (26), a metering module (30) for metering a reducing agent (28) into the exhaust gas duct (22) and further downstream an exhaust gas aftertreatment component (34, 36, 38) for the selective, catalytic reduction of nitrogen oxides. It is provided that an electrically heatable exhaust gas mixer (40) is arranged downstream of the metering module (30) and upstream of the exhaust gas aftertreatment component (32, 34, 36) for the selective, catalytic reduction of nitrogen oxides, an injection nozzle (38) of the metering module (30) The invention further relates to a method for exhaust gas aftertreatment of an internal combustion engine (10) with such an exhaust gas aftertreatment system, the exhaust gas mixer (40) being electrically heated after a cold start of the internal combustion engine.

Description

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

The current exhaust gas legislation, which will become increasingly stringent in the future, places high demands on raw engine emissions and 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 engine developers. In gasoline engines, exhaust gas cleaning is carried out in a known manner using a three-way catalytic converter and the three-way Catalyst upstream and downstream further catalysts. Exhaust gas aftertreatment systems are currently used in diesel engines, which have an oxidation catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for the separation of soot particles and, if appropriate, further catalytic converters. Ammonia is preferably used as the reducing agent. Because the use of pure ammonia is complex, a synthetic, aqueous urea solution is usually used in vehicles, which is mixed with the hot exhaust gas stream in a mixing device upstream of the SCR catalytic converter. This mixing heats the aqueous urea solution, 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.

In order to achieve the best possible mixing of the exhaust gas flow with the reducing agent before entering the catalytic converter for the selective catalytic reduction of nitrogen oxides (hereinafter referred to as SCR catalytic converter), exhaust gas mixers are known which include the evaporation of a liquid reducing agent and the mixing of this reducing agent promote the exhaust gas flow.

From the DE 10 2012 006 365 A1 An exhaust gas aftertreatment system for a diesel engine is known in which a metering module for introducing an aqueous urea solution and an SCR catalytic converter arranged in the flow direction of an exhaust gas through the exhaust system downstream of the metering module are provided in the exhaust system. An exhaust gas mixer is positioned downstream of the metering module and upstream of the SCR catalytic converter in order to improve the mixing of the aqueous urea solution with the exhaust gas stream before it enters the SCR catalytic converter. The exhaust gas mixer is arranged such that it is preferably conductively heated via a hot component in the exhaust system, in particular the exhaust manifold.

From the EP 894 523 A1 An exhaust gas aftertreatment system with a metering element for metering a reducing agent into the exhaust system and a catalyst downstream of the metering element for selective, catalytic reduction of nitrogen oxides is known, a heatable exhaust mixer being integrated into the housing of the SCR catalytic converter and connected upstream of the SCR catalytic converter.

The invention is based on the object of improving the extraction of ammonia from aqueous urea solution at cold exhaust gas temperatures and thus optimizing the reduction of nitrogen oxides in the cold start phase of the internal combustion engine.

According to the invention, this object is achieved by an exhaust gas aftertreatment system for an internal combustion engine with an exhaust gas system, in which an oxidation catalyst, a metering module for a reducing agent arranged in the flow direction of an exhaust gas of the internal combustion engine downstream of the oxidation catalyst, and an exhaust gas aftertreatment component arranged downstream of the metering module for the selective, catalytic reduction of nitrogen oxides. It is provided that an electrically heatable exhaust gas mixer is arranged downstream of the dosing module and upstream of the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides, an injection nozzle of the dosing module being arranged such that the liquid drops of the reducing agent hit the electrically heatable exhaust gas mixer. Through the heatable exhaust gas mixer and the direct impact of the reducing agent on the heatable exhaust gas mixer, the atomization can be improved and the evaporation of the reducing agent can be improved. In addition, the exhaust gas duct downstream of the electrically heatable exhaust gas mixer is heated, whereby the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides reaches its operating temperature more quickly.

In addition, pollutant emissions can be minimized, since good conversion rates for the limited exhaust gas components are achieved shortly after the cold start. The proposed exhaust gas aftertreatment system is particularly effective in terms of nitrogen oxide emissions, since the ratio of nitrogen monoxide NO to nitrogen dioxide NO _{2 is} improved by heating the oxidation catalyst and by heating the exhaust system downstream of the Oxidation catalyst faster an operating temperature of the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides is reached. The reducing agent, in particular an aqueous urea solution, can thus be metered in sooner after the cold start, as a result of which the efficiency in the conversion of nitrogen oxides can be increased. The oxidation catalytic converter can have a storage component for the storage of nitrogen oxides, at least for a limited time, in order to minimize nitrogen oxide emissions, in particular in the cold start phase, in which the light-off temperature has not yet been reached.

The features listed in the dependent claims enable advantageous improvements and non-trivial further developments of the exhaust gas aftertreatment system listed in the independent claim.

In a preferred embodiment of the invention it is provided that the electrically heatable exhaust gas mixer comprises an electrical heating element, in particular an electrical heating resistor, which is electrically connected to a battery, in particular the starter battery of a motor vehicle.

In a preferred embodiment of the invention, it is provided that both the oxidation catalyst and the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides are arranged in a position in the exhaust system close to the engine. In this context, a position close to the engine is understood to mean a position in which the inlet-side end face of the exhaust gas aftertreatment component is arranged less than 80 cm, preferably less than 60 cm, from an outlet of the internal combustion engine. Due to the position close to the engine, heating of the exhaust gas aftertreatment components is favored, since the waste heat losses via the wall of the exhaust gas duct are reduced. As a result, the exhaust gas mixer and the exhaust gas aftertreatment components can be heated to their operating temperature more quickly, which improves the efficiency of the exhaust gas aftertreatment. Furthermore, the risk of cooling below the light-off temperature of the exhaust gas aftertreatment components in a low-load phase or in an overrun mode is reduced, since even in low-load operation there is still sufficient heat input into the exhaust gas aftertreatment component to keep the temperature above the respective light-off temperature .

In a preferred embodiment of the exhaust gas aftertreatment system, it is provided that the exhaust gas aftertreatment component for selective, catalytic reduction of nitrogen oxides is a particle filter with a coating for selective, catalytic reduction (SCR coating). A coated particle filter combines the functionality of an SCR catalytic converter with a particle filter. For this purpose, this exhaust gas aftertreatment component can advantageously be arranged close to the engine, so that both heating up after a cold start and heating up for regeneration of the particle filter are facilitated by the lower heat losses through the wall of the exhaust gas duct. In addition, a further SCR catalytic converter can be arranged downstream of the particle filter with the SCR coating, in particular in an underbody position of a motor vehicle. A further metering element is then preferably connected upstream of this further SCR catalytic converter in order to provide two exhaust gas aftertreatment components which can be operated essentially independently of one another for the selective, catalytic reduction of nitrogen oxides. In addition to redundancy of the SCR systems and / or an increase in the catalyst volume for the selective, catalytic reduction of nitrogen oxides, this also enables efficient use of the reducing agent and an expansion of the operating range in which at least one of the exhaust gas treatment components for the selective, catalytic reduction of nitrogen oxides in one particularly efficient temperature range can be operated.

Alternatively, it is advantageously provided that the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides is an SCR catalytic converter. An SCR catalytic converter also enables an efficient reduction of nitrogen oxides. An SCR catalytic converter is less expensive than a particle filter with an SCR coating, which means that the costs for the exhaust gas aftertreatment system can be reduced.

It is particularly preferred if a particle filter is arranged downstream of the SCR catalytic converter, in particular in an underbody position of a motor vehicle. This gives the designers of the exhaust system additional degrees of freedom, which makes it easier to arrange the exhaust gas aftertreatment components, especially in tightly packed engine compartments.

In a preferred embodiment of the invention it is provided that the exhaust duct of the exhaust system downstream of the oxidation catalytic converter and upstream of the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides has at least one deflection element, the injection nozzle of the metering module being arranged in the region of the deflection element.

• - Ermitteln einer Temperatur in der Abgasanlage des Verbrennungsmotors,
• - Vergleichen der ermittelten Temperatur in der Abgasanlage mit einer Schwellentem peratur,
• - Elektrisches Beheizen des Abgasmischers, wenn die ermittelte Temperatur in der Abgasanlage unterhalb der Schwellentemperatur liegt,
• - Eindosieren von Reduktionsmittel in die Abgasanlage, wobei das Reduktionsmittel an der Oberfläche des elektrisch beheizbaren Abgasmischers verdampft.

The invention relates to a method for exhaust gas aftertreatment of an internal combustion engine with an inventive one Proposed exhaust gas aftertreatment system, which comprises the following steps:

• Determining a temperature in the exhaust system of the internal combustion engine,
• - comparing the temperature determined in the exhaust system with a threshold temperature,
• - electrical heating of the exhaust gas mixer if the temperature determined in the exhaust system is below the threshold temperature,
• - Dosing of reducing agent into the exhaust system, the reducing agent evaporating on the surface of the electrically heated exhaust mixer.

A method according to the invention can shorten the time interval in which an efficient conversion of the pollutants is not possible after a cold start of an internal combustion engine. By heating the exhaust gas mixer and injecting the reducing agent directly onto the heated exhaust gas mixer, the evaporation of the reducing agent is supported, as a result of which the mixing of the reducing agent and the exhaust gas flow of the internal combustion engine is improved. After the oxidation catalytic converter has reached its light-off temperature, the ratio of nitrogen monoxide to nitrogen dioxide is also improved, so that the conversion rate for the selective, catalytic reduction can be increased. In addition, the electrically heatable exhaust gas mixer also heats the exhaust gas flow downstream of the exhaust gas mixer, as a result of which the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides reaches its operating temperature faster, from which an efficient reduction of nitrogen oxides is possible.

An improvement of the method provides that the reducing agent is an aqueous urea solution, ammonia being obtained from the aqueous urea solution by means of thermolysis and hydrolysis for the selective, catalytic reduction of nitrogen oxides. Aqueous urea solution is a well-known and widely used reducing agent for the selective, catalytic reduction of nitrogen oxides. In order to be able to use this urea solution for the catalytic process, the urea solution must be evaporated and ammonia released from the urea solution. This is done by means of thermolysis and hydrolysis.

Another improvement of the method provides that the metering in of the reducing agent is only activated when the electrically heatable exhaust gas mixer has reached a threshold temperature. If the temperature is below this threshold temperature, no significant conversion rates can yet be generated in the exhaust gas aftertreatment component for the selective, catalytic reduction of nitrogen oxides. This would lead to increased ammonia emissions if the reducing agent flows unused through the corresponding exhaust gas aftertreatment component. The metering should therefore only begin when both the evaporation of the urea solution and a corresponding temperature of the exhaust gas aftertreatment component for selective, catalytic reduction of nitrogen oxides has been reached.

It is particularly preferred if the threshold temperature of the exhaust gas mixer is in the range from 150 ° C. to 250 ° C., preferably in the range between 180 ° C. and 220 ° C.

In a preferred embodiment variant of the method it is provided that the electrical heating of the exhaust gas mixer is switched off when the exhaust gas temperature or the output of the internal combustion engine exceed a threshold value. If the exhaust gas temperature exceeds a critical temperature of approximately 450 ° C., the ammonia obtained from the aqueous urea solution is thermally decomposed. This reduces the conversion rates and the effectiveness of the selective, catalytic reduction is limited. It is therefore expedient to set the electric heating of the exhaust gas mixer at high exhaust gas temperatures or high outputs of the internal combustion engine, which lead to high exhaust gas temperatures, in order not to further promote this process. In addition, in the case of a combustion engine that is at operating temperature, the aqueous urea solution is adequately prepared for entry into the exhaust gas aftertreatment component for selective, catalytic reduction of nitrogen oxides even without additional heating of the exhaust gas mixer, so that electric heating does not provide any additional benefit and reduces the energy efficiency of the internal combustion engine.
The various embodiments of the invention mentioned in this application can be combined with one another, if not specified otherwise in the individual case.

• 1 ein Ausführungsbeispiel für einen Verbrennungsmotor mit einem erfindungsgemäßen Abgasnachbehandlungssystem; und
• 2 ein Ablaufdiagramm zur Durchführung eines erfindungsgemäßen Verfahrens zur Abgasnachbehandlung eines Verbrennungsmotors mit einem solchen Abgasnachbehandlungssystem.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. The same components or components with the same function are identified in the different figures with the same reference numbers. Show it:

• 1 an embodiment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention; and
• 2nd a flowchart for performing an inventive method for exhaust aftertreatment of an internal combustion engine with such an exhaust aftertreatment system.

1 shows the schematic representation of an internal combustion engine 10th which with its outlet 16 with an exhaust system 20th connected is. The internal combustion engine 10th is a direct injection diesel engine in this embodiment and has several combustion chambers 12th on. At the combustion chambers 12th is a fuel injector 14 for injecting a fuel into the respective combustion chamber 12th arranged. The internal combustion engine 10th may further comprise a high-pressure exhaust gas recirculation, via which an exhaust gas of the internal combustion engine 10th from the outlet 16 to an inlet of the internal combustion engine 10th can be traced back. At the combustion chambers 12th Inlet valves and outlet valves are arranged, with which a fluid connection from the intake tract to the combustion chambers 12th or from the combustion chambers 12th to the exhaust system 20th can be opened or closed.

The exhaust system 20th includes an exhaust duct 22 , in which in the flow direction of an exhaust gas of the internal combustion engine 10th through the exhaust duct 22 a turbine 24th of an exhaust gas turbocharger 18th and downstream of the turbine 24th an oxidation catalytic converter as the first component of exhaust gas aftertreatment 26 are arranged. The exhaust gas turbocharger 18th is preferably used as an exhaust gas turbocharger 18th designed with variable turbine geometry. For this are a turbine wheel of the turbine 24th adjustable guide vanes upstream, through which the flow of the exhaust gas onto the blades of the turbine 24th can be varied. Downstream of the oxidation catalyst 26 is a particle filter 32 with a coating 34 arranged for the selective catalytic reduction of nitrogen oxides. Alternatively, you can also use a particle filter 32 and an SCR catalyst 36 be provided as two separate components. Downstream of the oxidation catalyst 26 and upstream of the particulate filter 32 points the exhaust duct 22 a first deflecting element 52 and a second deflecting element 54 with which the exhaust gas flow is deflected by about 90 °. In the area of the deflection elements 52 , 54 is an injector 38 a dosing module 30th for introducing a reducing agent 28 , especially of aqueous urea solution, in the exhaust duct 22 intended. Downstream of the dosing module 30th and upstream of the exhaust aftertreatment component 32 , 34 , 36 An electrically heatable exhaust gas mixer is used for the selective, catalytic reduction of nitrogen oxides 40 in the exhaust duct 22 arranged. The exhaust mixer 40 is via appropriate fasteners on the exhaust duct wall 56 of the exhaust duct 22 fixed. The electrically heated exhaust mixer 40 has an electric heating element 42 , in particular an electrical heating resistor, which is connected to a battery via corresponding power lines 58 , in particular the starter battery of a motor vehicle, is connected.

Downstream of the particle filter 32 with the SCR coating 34 can be a NOx sensor 46 be provided with which the effectiveness of the SCR coating 34 of the particle filter 32 can be checked as part of an on-board diagnosis. Furthermore, by the NOx sensor 46 the amount of the reducing agent metered in 28 be regulated to overdose or underdose of reducing agent 28 to avoid and further improve the efficiency of the use of reducing agents. Also on the particle filter 32 a differential pressure sensor 48 provided with which the soot loading of the particle filter 32 is monitored and if a loading threshold is exceeded, regeneration of the particle filter 32 is initiated. Furthermore, in the exhaust duct 22 a temperature sensor 44 be provided to the temperature of the exhaust aftertreatment components 26 , 32 , 36 monitor and combustion of the internal combustion engine 10th and the metering of reducing agents 28 to control the exhaust aftertreatment components 26 , 32 , 36 be operated in the most efficient temperature range possible.

In 2nd FIG. 10 is a flowchart for a method for exhaust gas aftertreatment of an internal combustion engine 10th represented with such an exhaust gas aftertreatment system. In a first step <100> becomes a temperature T _ES in the exhaust system 20th of the internal combustion engine 10th determined. This can be the exhaust gas temperature in particular T _EG or the temperature of one of the exhaust aftertreatment components 26 , 32 , 36 or the exhaust mixer 40 be. In a second step <110> becomes the determined temperature T _ES in the exhaust system 20th with a first threshold temperature T _S1 compared. Is the temperature T _ES below this threshold temperature T _S1 , takes place in one process step <120> activation of the electric heating element 42 in the exhaust mixer 40 , wherein the exhaust gas mixer is heated to an operating temperature of at least 150 ° C, preferably at least 200 ° C. Do the oxidation catalyst 26 , the exhaust mixer 40 and the exhaust aftertreatment component 32 , 34 , 36 For selective, catalytic reduction, their operating temperature, from which an efficient conversion of the nitrogen oxides can be expected, is reached in one process step <130> the reducing agent 28 in the exhaust duct 22 injected, the reducing agent 28 on the surface of the electrically heated exhaust mixer 40 evaporates. The reducing agent is preferably metered in only when the electrically heatable exhaust gas mixer 40 and the exhaust gas aftertreatment components for the selective, catalytic reduction of nitrogen oxides have each reached their operating temperature in order to avoid an increase in ammonia emissions. If the internal combustion engine has reached a certain operating temperature, which is characterized in particular by an essentially constant coolant temperature of approximately 90-100 ° C., the electrical heating element can 42 in the exhaust mixer 40 in one process step <140> be deactivated again. Alternatively, deactivation can take place when the exhaust gas aftertreatment components 26 , 32 , 36 have exceeded certain threshold temperatures.

Have all components for exhaust gas aftertreatment 26 , 32 , 36 and the exhaust mixer 40 their operating temperature has been reached, the primary goal is to maintain this temperature level through suitable measures. As measures for maintaining the temperature level, in particular an internal exhaust gas recirculation or the further use of the exhaust gas energy by an exhaust gas heat coupling can be initiated. Alternatively or additionally, it is possible to raise the temperature in the fresh air in the intake tract downstream of an intercooler.

In the event of the exhaust gas mixer cooling down 40 can the electric heating element 42 can be reactivated to the evaporation and treatment of the reducing agent 28 to improve.

Reference list

10th

Internal combustion engine

12th

Combustion chamber

14

Fuel injector

16

Outlet

18th

Exhaust gas turbocharger

20th

Exhaust system

22

Exhaust duct

24th

turbine

26

Oxidation catalyst

28

Reducing agent

30th

Dosing module

32

Particle filter

34

SCR coating

36

SCR catalytic converter

38

Injector

40

Exhaust mixer

42

electric heating element

44

Temperature sensor

46

NOx sensor

48

Differential pressure sensor

50

Engine control unit

52

first deflecting element

54

second deflecting element

56

Exhaust duct wall

58

battery

T

temperature

T _EG

Exhaust gas temperature

T _ES

Temperature in the exhaust system

T _LO

Light-off temperature of the oxidation catalytic converter

T _M

Exhaust mixer temperature

T _S1

Threshold temperature

T _S2

second threshold temperature

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for better information for 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 102012006365 A1 [0004]
• EP 894523 A1 [0005]

Claims (10)

Exhaust gas aftertreatment system for an internal combustion engine (10), with an exhaust system (20) in which an oxidation catalyst (26), a metering module (30) for a reducing agent (28) arranged downstream of the oxidation catalyst (26) in the flow direction of an exhaust gas of the internal combustion engine (26) and downstream of the metering module (30) there are an exhaust gas aftertreatment component (32, 34, 36) for the selective, catalytic reduction of nitrogen oxides, characterized in that downstream of the metering module (30) and upstream of the exhaust gas aftertreatment component (32, 34, 36) for selective, an electrically heatable exhaust gas mixer (40) is arranged catalytically reducing nitrogen oxides (32, 34, 36), an injection nozzle (38) of the metering module (30) being arranged such that the liquid drops of the reducing agent (28) onto the electrically heatable exhaust gas mixer ( 40) hit. Exhaust aftertreatment system after Claim 1 , characterized in that the electrically heatable exhaust gas mixer (40) comprises an electrical heating element (42) which is electrically connected to a battery (58). Exhaust aftertreatment system after Claim 1 or 2nd , characterized in that the oxidation catalyst (26) and the exhaust gas aftertreatment component (32, 34, 36) for selective, catalytic reduction are arranged in a position close to the engine in the exhaust system (20). Exhaust aftertreatment system according to one of the Claims 1 to 3rd , characterized in that the exhaust gas aftertreatment component (32, 34, 36) for the selective, catalytic reduction of nitrogen oxides is a particle filter (32) with a coating (34) for the selective, catalytic reduction or an SCR catalytic converter (36). Exhaust aftertreatment system according to one of the Claims 1 to 3rd , characterized in that the exhaust duct (22) of the exhaust system (20) downstream of the oxidation catalyst (26) and upstream of the exhaust gas aftertreatment component (32, 34, 36) for the selective, catalytic reduction of nitrogen oxides has at least one deflection element (52, 54), wherein the injection nozzle of the metering module (30) is arranged in the region of the deflecting element (52, 54). Method for exhaust gas aftertreatment of an internal combustion engine (10), with an exhaust gas aftertreatment system according to one of the Claims 1 to 5 , comprising the following steps: - determining a temperature (T _ES ) in the exhaust system (20) of the internal combustion engine (10), - comparing the determined temperature (T _ES ) in the exhaust system (20) with a threshold temperature (T _S1 ), - electrical Heating the exhaust gas mixer (40) when the temperature determined in the exhaust gas system (T _ES ) is below the threshold temperature (T _S1 ), - reducing agent (28) is metered in, the reducing agent (28) being on the surface of the electrically heatable exhaust gas mixer (40 ) evaporates. Exhaust gas aftertreatment process after Claim 6 , characterized in that the reducing agent (28) is an aqueous urea solution, ammonia being obtained from the aqueous urea solution by means of thermolysis and hydrolysis for the selective, catalytic reduction of nitrogen oxides. Exhaust gas aftertreatment process after Claim 5 or 6 , characterized in that the metering of the reducing agent (28) is only activated when the electrically heatable exhaust gas mixer (40) has reached a threshold temperature (T _S2 ). Procedure according to Claim 8 , characterized in that the threshold temperature (T _S2 ) is in the range from 150 ° C to 250 ° C. Procedure according to one of the Claims 6 to 9 , characterized in that the electrical heating of the exhaust gas mixer (40) is switched off when the exhaust gas temperature (T _EG ) or the output of the internal combustion engine (10) exceeds a threshold value.

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