Exhaust aftertreatment system for an internal combustion engine

Abstract

Exhaust aftertreatment system for an internal combustion engine (10), comprising a first three-way catalyst (22) and a second three-way catalyst (24) arranged downstream of the first catalyst (22), wherein a heating device (32) is arranged downstream of the first three-way catalyst (22) and upstream of the second three-way catalyst (24), with which an exhaust gas stream of the internal combustion engine (10) can be heated essentially independently of the operating state of the internal combustion engine (10), characterized in that the first three-way catalyst (22) has a NOx storage component (48).

Description

[0001] The invention relates to an exhaust gas aftertreatment system for an internal combustion engine and a method for exhaust gas aftertreatment of an internal combustion engine with such an exhaust gas aftertreatment system according to the preamble of the independent patent claims.

[0002] In view of further tightening emissions standards, for example, with the introduction of the EU7 standard, it is necessary to significantly reduce cold-start emissions, which account for a large portion of total emissions. During cold-start operation, i.e., immediately after starting the combustion engine, the exhaust aftertreatment components are generally not sufficiently warmed up to enable conversion of the raw emissions generated during fuel combustion. This leads, in particular, to increased nitrogen oxide emissions during the cold-start phase, which, even with complete conversion after the cold-start phase, means that the limit values ​​are no longer met.

[0003] To comply with the EU6 emissions standard for gasoline engines, exhaust aftertreatment systems comprising one or more three-way catalysts and a particulate filter have become widespread. It is also known to heat the three-way catalyst with an external heating medium, such as an electric heating element or an exhaust gas burner, so that the catalyst reaches its light-off temperature more quickly and is available for effective conversion of limited emissions more quickly after a cold start.

[0004] However, a disadvantage of the exhaust aftertreatment systems known from the state of the art is that even with engine-external heating means there is a short period of time during which the exhaust aftertreatment components have not yet reached their light-off temperature and the raw emissions are emitted unconverted into the environment.

[0005] The object of the invention is to further reduce cold start emissions and to overcome the disadvantages known from the prior art.

[0006] US 2019 / 0376424 A1 discloses an internal combustion engine and an exhaust aftertreatment system for this internal combustion engine. The exhaust aftertreatment system comprises a nitrogen oxide storage catalyst and two SCR catalysts connected in series in the direction of flow of an exhaust gas through the exhaust system of the internal combustion engine. One of the SCR catalysts may have an electric heating element for heating the SCR catalyst.

[0007] From US 2015 / 0158023 A1, an exhaust gas aftertreatment system for an internal combustion engine with a cold-start catalyst is known, which can store unburned hydrocarbons and nitrogen oxides during a cold-start phase of the internal combustion engine.

[0008] US 2013 / 0312392 A1 discloses an exhaust aftertreatment system for an internal combustion engine with a NOx storage catalyst, an HC storage catalyst and an SCR catalyst.

[0009] DE 10 2017 118 215 A1 discloses an exhaust aftertreatment system for a spark-ignition internal combustion engine. A particulate filter and a first three-way catalyst are arranged close to the engine in an exhaust system connected to an exhaust of the internal combustion engine. A further three-way catalyst is arranged downstream of the first three-way catalyst in the underbody position of the motor vehicle. It is provided that an exhaust gas burner is activated from the moment the engine is started, with which hot exhaust gas is introduced into the exhaust system downstream of the particulate filter in order to heat at least one of the three-way catalysts to a light-off temperature as quickly as possible after a cold start, thus enabling efficient exhaust aftertreatment.

[0010] DE 10 2015 212 846 A1 discloses a device and method for exhaust gas aftertreatment of an internal combustion engine. The exhaust of the internal combustion engine is connected to an exhaust system with an exhaust duct. Arranged in the exhaust system in the flow direction of an exhaust gas flow from the internal combustion engine through the exhaust system are a three-way catalyst, a secondary air line inlet downstream of the three-way catalyst (14), and further downstream are a NOx storage catalyst and a particulate filter.

[0011] DE 10 2014 017 303 A1 describes a method for operating a drive device for a motor vehicle, in which the introduction of fuel into at least one cylinder of an internal combustion engine of the motor vehicle is prevented. A fluid from the at least one cylinder is introduced into an exhaust system coupled to the internal combustion engine. At least a portion of the fluid flows through a nitrogen oxide storage catalyst arranged in the exhaust system. A temperature of the nitrogen oxide storage catalyst is determined. The introduction of fuel into the at least one cylinder is prevented if the temperature of the nitrogen oxide storage catalyst is greater than a predetermined threshold value.

[0012] Furthermore, an exhaust gas aftertreatment system for an internal combustion engine is known from DE 10 2020 105 330 A1. The exhaust gas aftertreatment system comprises an exhaust system with an exhaust duct in which, in the flow direction of an exhaust gas flow of the internal combustion engine, a turbine of an exhaust gas turbocharger, a first three-way catalyst downstream of the turbine, a second three-way catalyst downstream of the first three-way catalyst, and a particulate filter further downstream are arranged.

[0013] The invention is based on the object of further reducing cold start emissions in a spark-ignition combustion engine and thus meeting even stricter exhaust emission limits.

[0014] This object is achieved by an exhaust gas aftertreatment system for an internal combustion engine, which comprises a first three-way catalyst and a second three-way catalyst arranged downstream of the first three-way catalyst. A heating device is arranged downstream of the first three-way catalyst and upstream of the second three-way catalyst, with which an exhaust gas flow of the internal combustion engine can be heated essentially independently of the operating state of the internal combustion engine. According to the invention, the first three-way catalyst has a NOx storage component.

[0015] The NOx storage component of the first three-way catalyst allows nitrogen oxides to be stored during a cold-start phase, in which the three-way catalysts have not yet reached a sufficient temperature to efficiently convert the pollutants in the exhaust stream of the combustion engine, and only released again when the second three-way catalyst, heated by the heater, has reached its light-off temperature. This allows emissions during the cold start phase, especially nitrogen oxide emissions, to be significantly reduced compared to the solutions used in spark-ignition gasoline engines.

[0016] The additional features listed in the dependent claims enable advantageous improvements and further developments of the exhaust gas aftertreatment system.

[0017] In a preferred embodiment of the invention, the NOx storage component comprises a system of palladium and a cerium oxide. A system of palladium and a cerium oxide makes it possible to store nitrogen oxides even at low temperatures, starting at approximately 60°C, and only release them again when the first catalyst temperature exceeds 250°C. Thus, the nitrogen oxides can be stored during the heat-up phase of the exhaust gas aftertreatment system and converted into unlimited exhaust gas components during subsequent normal operation.

[0018] It is particularly preferred if the NOx storage component of the first three-way catalyst is designed as a palladium cerium oxide coating or a palladium-doped zeolite coating. Such a coating enables improved storage capacity and higher temperature stability during the storage of nitrogen oxides compared to known aluminum oxide coatings (Al2O3 coatings).

[0019] In an advantageous embodiment of the exhaust gas aftertreatment system, the exhaust gas aftertreatment system additionally comprises a particulate filter, preferably an uncoated particulate filter. A particulate filter makes it possible to filter out not only the gaseous emissions but also the particulates from the exhaust stream of the combustion engine. Since further tightening of exhaust gas standards is expected to lead to stricter limits for emitted particulates, such a particulate filter may be necessary to meet the more stringent emission standards. In addition to accelerating the heating of the second three-way catalytic converter, the heating device also assists in heating the particulate filter, so that it can be regenerated more easily during a low-load phase of the combustion engine and reliably reaches its regeneration temperature even at low load.

[0020] According to a preferred embodiment of the exhaust gas aftertreatment system, the heating device is designed as an electric heating element. An electric heating element enables a particularly simple and compact design of the exhaust gas aftertreatment system. Furthermore, the heating output of an electric heating element can be controlled particularly easily and precisely, ensuring efficient heating of the exhaust gas aftertreatment components while avoiding wasted energy.

[0021] It is particularly preferred if the electric heating element is an electric heating disc connected to the outlet-side end face of the first three-way catalytic converter or the inlet-side end face of the second three-way catalytic converter. This allows for particularly simple and secure attachment of the electric heating disc.

[0022] In a further preferred embodiment of the invention, the heating device comprises an exhaust gas burner, wherein the exhaust gas burner has a combustion chamber on which an ignition device is arranged, wherein the combustion chamber has an air connection and a fuel connection for supplying a fuel-air mixture to the combustion chamber, and wherein the ignition device is designed to ignite this fuel-air mixture in the combustion chamber. An exhaust gas burner can provide a particularly high energy input into the exhaust system because the maximum output of the exhaust gas burner is not limited by the voltage of the on-board electrical system and the current intensity. A disadvantage of an exhaust gas burner, however, is the comparatively high cost.

[0023] In an advantageous embodiment of the exhaust aftertreatment system, the first three-way catalyst, the heating device, and the second three-way catalyst are arranged in a catalyst unit. Such an assembly can be preassembled accordingly, allowing the complete catalyst unit to be used during assembly of the exhaust system, thus reducing assembly effort.

[0024] It is particularly preferred if the first three-way catalyst, the heating device, and the second three-way catalyst are arranged in a common housing. This allows for particularly simple assembly of the catalyst unit.

[0025] In an advantageous embodiment of the exhaust gas aftertreatment system, the particulate filter is arranged downstream of the second three-way catalyst. The heat introduced into the exhaust system by the heating device can be additionally used to heat the particulate filter to its regeneration temperature during idle or low-load operation.

[0026] In a preferred embodiment of the invention, the first three-way catalytic converter is arranged in an exhaust system of the internal combustion engine in the flow direction of an exhaust gas flow through the exhaust system as the first emission-reducing exhaust gas aftertreatment component in a position close to the engine. In this context, a position close to the engine means that a front-end inlet of the first three-way catalytic converter has an exhaust gas flow length of less than 80 cm, preferably less than 60 cm, particularly preferably less than 40 cm from an outlet of the internal combustion engine. This position close to the engine enables particularly efficient heating of the first three-way catalytic converter by the exhaust gas flow of the internal combustion engine, since the short exhaust gas flow length minimizes heat losses.

[0027] Alternatively, the first three-way catalytic converter and the second three-way catalytic converter can also be arranged under the body of a motor vehicle. In this case, it is advantageous if a third three-way catalytic converter is arranged close to the engine and a particulate filter is arranged immediately downstream of the third three-way catalytic converter. The second three-way catalytic converter is heated comparatively quickly by the heating device, and the third three-way catalytic converter is heated comparatively quickly by the exhaust gas flow in conjunction with the short exhaust gas path length, while the first three-way catalytic converter heats up comparatively slowly and can thus store the nitrogen oxides for a comparatively long time. This ensures that the nitrogen oxides are only released when efficient conversion of the gaseous exhaust gas components by the second and third three-way catalytic converter is possible.

[0028] A further aspect of the invention relates to a method for exhaust gas aftertreatment of an internal combustion engine with such an exhaust gas aftertreatment system, which comprises the following steps: - Starting the combustion engine, whereby the nitrogen oxides produced during a cold start phase of the combustion engine are stored in the NOx storage component of the first three-way catalyst, - Heating of the second three-way catalyst by the heating device, - Release of stored nitrogen oxides when the second three-way catalyst has reached its light-off temperature, - Conversion of the released nitrogen oxides through the second three-way catalyst.

[0029] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0030] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show: Fig. 1 shows an internal combustion engine which is connected on the exhaust side to a preferred embodiment of an exhaust gas aftertreatment system according to the invention; Fig. 2 shows a further embodiment of an exhaust gas aftertreatment system according to the invention; Fig. 3 a third embodiment of an exhaust gas aftertreatment system according to the invention for an internal combustion engine.

[0031] Fig. Figure 1 shows an internal combustion engine 10 with four combustion chambers 12, which is designed as a spark-ignition internal combustion engine 10 based on the Otto cycle principle. A fuel injector 14 and a spark plug 16 for igniting a combustible fuel-air mixture are arranged at each of the combustion chambers 12.

[0032] The exhaust 18 of the internal combustion engine 10 is connected to an exhaust system 20, in which a turbine 56 of an exhaust gas turbocharger 54 is arranged in the flow direction of an exhaust gas flow of the internal combustion engine 10 through the exhaust system, and a first three-way catalyst 22 is arranged downstream of the turbine 56 as the first emission-reducing exhaust gas aftertreatment component. The first three-way catalyst 22 has a NOx storage component 48 in order to be able to store nitrogen oxides during a cold start phase of the internal combustion engine 10 and to release them later at higher exhaust gas temperatures. The nitrogen oxides can be stored starting at an exhaust gas temperature of approximately 60°C and are released again at exhaust gas temperatures of approximately 250°C. The NOx storage component is designed as a coating of the first three-way catalyst 22 and comprises palladium and cerium oxide.

[0033] Immediately downstream of the first three-way catalytic converter 22 is a heating device 32, which in this exemplary embodiment is designed as an electric heating element 34 in the form of an electric heating disk 36. Immediately downstream of the heating device 32, a second three-way catalytic converter 24 is arranged in the exhaust system.

[0034] The first three-way catalyst 22, the electric heating element 34 and the second three-way catalyst 24 can be designed as a catalyst unit 30 with a common housing 68 in order to enable a particularly compact design of the catalyst unit 30 and to facilitate the assembly of the exhaust system 20.

[0035] Further downstream in the exhaust system, a particulate filter 26 can be arranged to filter out particulates from the exhaust stream of the internal combustion engine in addition to the gaseous emissions. The first three-way catalyst 22, the electric heating element 34, and the second three-way catalyst 24 are arranged in a position close to the engine in the exhaust system 20 to enable the catalysts 22, 24 to be heated as efficiently as possible by the exhaust stream of the internal combustion engine 10 and to minimize waste heat losses.

[0036] The internal combustion engine 10 is operatively connected to a control unit 60, which has a memory unit 62 and a computing unit 64. A machine-readable program code 66 is stored in the memory unit 62, which controls the fuel injection quantity by the fuel injectors 14, the ignition timing of the spark plugs 16, and the activation of the electric heating element 34 when the machine-readable program code is executed by the computing unit 64 of the control unit 60.

[0037] During a cold start phase of the internal combustion engine 10, the nitrogen oxide emissions cannot yet be efficiently converted due to the low exhaust gas temperatures and the low component temperatures of the three-way catalysts 22, 24. Therefore, in this operating state of the internal combustion engine 10, the nitrogen oxide emissions are initially stored in the NOx storage component 48 of the first three-way catalyst 22. To accelerate the heating of the exhaust gas aftertreatment components, they are heated not only by the exhaust gas flow during the cold start phase, but also by the electric heating element 34. Due to convection, the second three-way catalyst 24 reaches its light-off temperature before the first three-way catalyst 22.Since the heating of the first three-way catalyst 22, which is heated primarily by the exhaust gas flow of the internal combustion engine 10, is delayed compared to the second three-way catalyst 24, which is heated by the exhaust gas flow and the electric heating element, the nitrogen oxides can be stored in the NOx storage component 48 of the first three-way catalyst 22 until the second three-way catalyst 24 reaches its light-off temperature, thus enabling efficient conversion of the nitrogen oxides. At the same time, the accelerated heating of the second three-way catalyst 24 also enables faster conversion of other limited exhaust components such as carbon monoxide and unburned hydrocarbons.

[0038] In Fig. 2 shows a further exemplary embodiment of an exhaust gas aftertreatment system according to the invention. In this exemplary embodiment, the heating device 32 is designed as an exhaust gas burner 38. The exhaust gas burner 38 has an air connection 44 for supplying air and a fuel connection 42 for supplying fuel to a combustion chamber 40 of the exhaust gas burner 38. An ignition element 58 is arranged on the combustion chamber 40 in order to ignite a fuel-air mixture in the combustion chamber 40 and to introduce the combusted fuel-air mixture at an inlet point 46 into the exhaust gas duct 52 of the exhaust system 20 in order to heat the exhaust gas aftertreatment components 24, 26 downstream of the inlet point in the flow direction of an exhaust gas flow through the exhaust system 20, in particular a second three-way catalytic converter and a particulate filter 26 downstream of the second three-way catalytic converter.

[0039] The exhaust gas aftertreatment system has, as the first emission-reducing exhaust gas aftertreatment component, a first three-way catalyst 22 close to the engine, which has a NOx storage component 48. The first three-way catalyst 22 close to the engine is arranged upstream of the inlet point 46 of the exhaust gas burner 38 in order to be able to store the nitrogen oxides produced during a cold start phase until the second three-way catalyst 24 is heated to its light-off temperature by the exhaust gas burner 38 and can efficiently convert the nitrogen oxides into molecular nitrogen and carbon dioxide using a reducing agent, in particular unburned hydrocarbons. A decoupling element 50 can be arranged downstream of the first catalyst 22 and upstream of the inlet point 46.

[0040] In Fig.Figure 3 shows a further exemplary embodiment of an exhaust gas aftertreatment system according to the invention for an internal combustion engine 10. In this exemplary embodiment, a third three-way catalyst 28 is arranged as the first exhaust gas aftertreatment component close to the engine. This third three-way catalyst 28 is followed, in the flow direction of an exhaust gas flow through the exhaust system 20, by a particulate filter 26 and, further downstream, by a first three-way catalyst 22, an electric heating element 34, and a second three-way catalyst 24.

[0041] In this exemplary embodiment, the third three-way catalyst 28 and the particulate filter 26 are arranged in a position close to the engine, while the catalyst unit 30 with the first three-way catalyst 22, the NOx storage component 48, the electric heating element 34, and the second three-way catalyst 24 are arranged in an underbody position of a motor vehicle. A decoupling element 50 is arranged in the exhaust duct 52 of the exhaust system 20, downstream of the particulate filter 26 and upstream of the first three-way catalyst 22. List of reference symbols 10 Combustion engine 12 combustion chamber 14 Fuel injector 16 Spark plug 18 Outlet 20 Exhaust system 22 first three-way catalyst 24 second three-way catalyst 26 particle filters 28 third three-way catalyst 30 Catalyst unit 32 Heating device 34 electric heating element 36 heating disc 38 exhaust gas burners 40 combustion chamber 42 Fuel connection 44 Air connection 46 Discharge point 48 NOx storage component 50 decoupling element 52 exhaust duct 54 exhaust gas turbochargers 56 turbines 58 Ignition element 60 control unit 62 storage unit 64 computing unit 66 Program code 68 housings

Claims

[1] Exhaust gas aftertreatment system for an internal combustion engine (10), comprising a first three-way catalyst (22) and a second three-way catalyst (24) arranged downstream of the first catalyst (22), wherein a heating device (32) is arranged downstream of the first three-way catalyst (22) and upstream of the second three-way catalyst (24), with which an exhaust gas flow of the internal combustion engine (10) can be heated substantially independently of the operating state of the internal combustion engine (10), characterized by that the first three-way catalyst (22) has a NOx storage component (48). [2] Exhaust aftertreatment system according to claim 1, characterized by that the NOx storage component (48) comprises a system of palladium and a cerium oxide. [3] Exhaust aftertreatment system according to claim 2, characterized bythat the NOx storage component (48) of the first three-way catalyst (22) is designed as a palladium cerium oxide coating or a palladium-doped zeolite coating. [4] Exhaust gas aftertreatment system according to one of claims 1 to 3, characterized by that the exhaust gas aftertreatment system additionally comprises a particle filter (26). [5] Exhaust gas aftertreatment system according to one of claims 1 to 4, characterized by that the heating device (32) is designed as an electrical heating element (34). [6] Exhaust gas aftertreatment system according to one of claims 1 to 5, characterized byin that the heating device (32) comprises an exhaust gas burner (38), wherein the exhaust gas burner (38) has a combustion chamber (40) on which an ignition device (58) is arranged, wherein the combustion chamber (40) has an air connection (44) and a fuel connection (42) in order to supply a fuel-air mixture to the combustion chamber (40), and wherein the ignition device (58) is designed to ignite this fuel-air mixture in the combustion chamber (40). [7] Exhaust gas aftertreatment system according to one of claims 1 to 6, characterized by that the first three-way catalyst (22), the heating device (32) and the second three-way catalyst (24) are arranged in a catalyst unit (30), in particular in a common housing (68). [8] Exhaust gas aftertreatment system according to claim 4, characterized by that the particulate filter (26) is arranged downstream of the second three-way catalyst (24). [9] Exhaust gas aftertreatment system according to one of claims 1 to 8, characterized by that the first three-way catalyst (22) is arranged in an exhaust system (20) of the internal combustion engine (10) in the flow direction of an exhaust gas flow through the exhaust system (20) as the first emission-reducing exhaust gas aftertreatment component and in a position close to the engine. [10] Method for exhaust gas aftertreatment of an internal combustion engine (10) with an exhaust gas aftertreatment system according to one of claims 1 to 9, comprising the following steps: - starting the internal combustion engine (10), whereby the nitrogen oxides produced in the cold start phase of the internal combustion engine (10) are stored in the NOx storage component (48) of the first three-way catalyst (22), - heating the second three-way catalyst (24) by the heating device (32), - release of the stored nitrogen oxides when the second three-way catalyst (24) has reached its light-off temperature, - Converting the released nitrogen oxides through the second three-way catalyst (24).

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