DE102021203097A1 - Exhaust aftertreatment method and exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a method for treating the exhaust gas of an internal combustion engine, the exhaust gas flowing through at least one exhaust gas cleaning device (10) close to the engine, the exhaust gas cleaning device (10) close to the engine having at least one first three-way catalytic converter (12), the exhaust gas flowing downstream of the exhaust gas cleaning device (1) close to the engine 10) flows through at least one second three-way catalytic converter (14) and at least one heating device (16) is provided for heating the second three-way catalytic converter (14).
In a method for exhaust gas aftertreatment, in which all components of the exhaust gas aftertreatment can be brought to their operating temperature as quickly as possible in order to reduce cold start emissions as effectively as possible, it is provided that at least one engine and/or extra-engine measure for heating up the exhaust gas cleaning device (10) close to the engine is carried out.

Description

The invention relates to a method for the aftertreatment of exhaust gas from an internal combustion engine, the exhaust gas flowing through at least one exhaust gas purification device close to the engine, the exhaust gas purification device close to the engine having at least one first three-way catalytic converter, the exhaust gas flowing through at least one second three-way catalytic converter downstream of the exhaust gas purification device close to the engine and at least one preferably thermal heating device being provided for heating up the second three-way catalytic converter.

In addition, the invention relates to an exhaust gas aftertreatment system for an internal combustion engine, with an inlet for receiving the exhaust gas of the internal combustion engine, with at least one exhaust gas duct, with an exhaust gas purification device close to the engine being arranged downstream of the inlet in the exhaust gas duct, the exhaust gas purification device close to the engine comprising at least one first three-way catalytic converter At least one second three-way catalytic converter is arranged downstream of the close-coupled first three-way catalytic converter in the exhaust gas duct and at least one preferably thermal heating device is provided for heating the second three-way catalytic converter.

Due to the development of exhaust gas legislation, vehicle manufacturers are faced with the challenge of reducing engine raw emissions and purifying the exhaust gas that is still produced by means of appropriate exhaust gas aftertreatment. Legislative stage EU7 makes it necessary for gasoline engines to frequently require a particle filter in order not to exceed the specified permissible number of particles in emissions. Such an Otto particle filter is loaded with soot when driving. So that the exhaust back pressure does not increase too much, this Otto particle filter must be regenerated continuously or periodically. The increase in exhaust gas back pressure can lead to increased consumption by the combustion engine, loss of performance and an impairment of smooth running up to misfiring.

Especially in the cold start phase, gasoline engines emit significant amounts of gaseous pollutants. These include nitrogen oxides (NOx), hydrocarbons (HC) and carbon monoxide (CO). According to the state of the art, these pollutants are converted via coated catalysts. These systems require a minimum temperature to be operational. Against the background of the threatened shortening of the urban part within the framework of the EU7 legislation and a further tightening of limit values in other parts of the world, for example the USA, compliance with the limit values using known technologies is critical. Thermally heated three-way catalytic converters (preferably via a burner system) can be heated to the minimum temperature quickly because of the very high burner output.

the WO 99/34902 A1 shows, for example, an arrangement for cleaning an exhaust gas stream of an internal combustion engine with an electrically heatable honeycomb body for heating a honeycomb body, which is equipped with a catalytically active coating.

For such heating, however, an optimal mixture composition is required for the highest conversion rates. In underbody arrangements, the underbody system with burner-typical 15 - 25 kW heat output is warmed up faster than the upstream components of the exhaust gas cleaning system, i.e. catalytic converters and lambda sensors. The minimum temperature of the underbody system can thus be reached faster than the operational readiness of the lambda probe before the close-coupled three-way catalytic converter and in particular the step response probe after the close-coupled three-way catalytic converter.

The invention is therefore based on the object of specifying a method for exhaust gas aftertreatment and an exhaust gas aftertreatment system in which all components of the exhaust gas aftertreatment can be brought to their operating temperature as quickly as possible in order to reduce cold start emissions as effectively as possible.

This object is achieved in the present invention by the features of the characterizing part of patent claim 1 in that at least one engine and/or extra-engine measure for heating the exhaust gas purification device close to the engine is carried out in addition to the heating measures on the underbody exhaust gas purification.

In this context, a position close to the engine is a position in the exhaust gas aftertreatment system with an exhaust gas flow length from a front inlet of the three-way catalytic converter of less than 80 cm, preferably less than 50 cm, from an outlet of the internal combustion engine.

In the context of this application, a three-way catalytic converter is to be understood as a material that is able to at least partially convert carbon monoxide (CO), nitrogen oxides (NOx) and unburned hydrocarbons (HC) to form carbon dioxide (CO ₂ ), nitrogen (N ₂ ) and water (H ₂ O).

An engine-related measure for heating up the exhaust gas cleaning device close to the engine is to be understood as meaning a method which, as a result of adjustments made to the internal combustion engine, leads to the exhaust gas cleaning device close to the engine being heated up. A measure outside of the engine for heating the exhaust gas cleaning device close to the engine is to be understood as a method in which external influences outside of the internal combustion engine are used or used in a targeted manner in order to heat up the exhaust gas cleaning device close to the engine.

The heating device for the second three-way catalytic converter can preferably be a burner arranged in full flow or, more favorably, in side flow, with 10 to 60 kW, preferably 15 to 25 kW, thermal heating output at the burner outlet. Alternatively, it can be a flow-through, electric heating disk, which is arranged in the exhaust gas duct. The heating disc can bear against a three-way catalytic converter with a first contact surface in order to optimize the heating of the catalytic converter.

A first advantage of the method according to the invention is that the combination of different measures for heating up different catalysts in an exhaust gas aftertreatment system significantly reduces the time it takes to heat up all the catalysts and measuring probes during a cold start, thereby significantly reducing the pollutants emitted during a cold start.

Further preferred configurations of the invention result from the remaining features mentioned in the dependent claims.

In a first embodiment of the method according to the invention, provision is made for a motor measure to be implemented by means of a torque reserve. In a modern motor vehicle whose internal combustion engine is controlled by an electronic engine management system, a so-called torque reserve is used when the internal combustion engine is idling. Thanks to the torque reserve, speed fluctuations in the internal combustion engine can be avoided. RPM fluctuations can be caused, for example, when the load is applied, which are caused, for example, by an air conditioning system, the steering and/or by the operation of a window lifter.

In addition, it is also possible to avoid quasi-steady-state fluctuations in the rotational speed, which are associated with the development of noise. The torque reserve is realized by the stationary injection of an increased combustion air mass in connection with a neutralization of the additional torque through delayed ignition angles that degrade efficiency. Although this increases the fuel consumption of the internal combustion engine, it is also possible to heat up the three-way catalytic converter close to the engine.

In an alternative or additional embodiment of the method according to the invention, it is provided that an engine-based measure is implemented by means of a combination of secondary air injection, engine-based rich operation and an ignition angle retardation. Secondary air in the engine's exhaust pipe reduces the content of carbon monoxide and hydrocarbons through post-combustion. Post combustion temperatures range from about 500°C to 700°C. Afterburning produces water and carbon dioxide. Due to the chemical reactions, the exhaust gas temperature is also increased simultaneously. The increased exhaust gas temperature contributes to the fact that the catalytic converter is heated up correspondingly faster when starting a petrol engine and reaches its optimum operating temperature more quickly

With a stoichiometric fuel ratio, there is exactly the amount of air that is theoretically needed to completely burn the fuel. This is denoted as λ=1. In this context, rich engine operation means that more fuel is available in relation to the stoichiometric fuel ratio. In the case of rich engine operation, the exhaust gas temperature is actually reduced. Additional injection of secondary air restores the ideal stoichiometric ratio and increases the total amount to be burned. In this way, the exhaust gas cleaning device close to the engine can be heated up more quickly. Alternatively, the secondary air injection can be dimensioned in such a way that an over-stoichiometric air ratio is set, e.g. B. Lambda = 1.01 - 1.1.

Additionally or alternatively, it can also be provided that an extra-engine measure is implemented by an electrical heating device in front of the close-coupled three-way catalytic converter. As with the optional electrical heating device for the second three-way catalytic converter, the electrical heating device in front of the close-coupled three-way catalytic converter can also be an electric heating disc through which flow can take place, which is arranged in the exhaust gas duct. The heating disc can bear against a three-way catalytic converter with a first contact surface in order to optimize the heating of the catalytic converter. A compact design can thus be implemented.

For an optimal use of the electrical heating device is in a further embodiment the invention provides that the electric heater is arranged in the direction of flow before or in the first three-way catalytic converter.

In a further advantageous embodiment of the method according to the invention, provision is made for cylinder-specific lambda control to be carried out.

The aforementioned object is also achieved by an aforementioned exhaust gas aftertreatment system for an internal combustion engine, with an inlet for receiving the exhaust gas of the internal combustion engine, with at least one exhaust gas duct, an exhaust gas purification device close to the engine being arranged downstream of the inlet, the exhaust gas purification device close to the engine having at least one first three -Way catalytic converter, wherein at least one second three-way catalytic converter is arranged downstream of the close-coupled first three-way catalytic converter in the exhaust gas duct and at least one heating device, preferably a thermal heating device, is provided for heating the second three-way catalytic converter. Provision is made for the exhaust gas aftertreatment system to be designed to carry out a method according to one of Claims 1 to 6. The above statements on the method according to the invention also apply correspondingly to the exhaust gas aftertreatment system according to the invention.

The exhaust aftertreatment system is connectable to the inlet with an outlet of an internal combustion engine such that exhaust gases emitted by the engine are directed into the exhaust aftertreatment system. The exhaust gas duct is preferably designed as a pipeline through which the exhaust gas can flow. The various internals, such as the first three-way catalytic converter and the second three-way catalytic converter, can be arranged in the pipeline or themselves be part of the pipeline.

The underbody arrangement for the thermal heating device is preferred for the positioning of the exhaust gas aftertreatment system, since arrangements of the burner close to the engine can have significant installation space problems, particularly in the case of transversely installed engines.

In a first embodiment of the exhaust gas aftertreatment system according to the invention, it is provided that the exhaust gas cleaning device close to the engine comprises at least one particle filter. The particle filter can be designed as an Otto particle filter in which a highly porous, heat-resistant cordierite ceramic is used. The soot particles contained in the exhaust gas stick to the rough ceramic surface.

In order to further improve the functioning of the exhaust gas aftertreatment system according to the invention, a further embodiment provides for a first lambda probe to be installed upstream of the first three-way catalytic converter, a second lambda probe downstream of the first three-way catalytic converter and additionally downstream of the second three-way catalytic converter. Catalyst is arranged a third lambda probe and that the first lambda probe and / or the second lambda probe is designed as a dew point end-free probe. A lambda sensor is designed to compare the residual oxygen content in the exhaust gas with a reference oxygen content. The oxygen content of the current atmospheric air is usually used as the reference oxygen content. With knowledge of the residual oxygen content, the combustion air ratio Ä can be determined and adjusted accordingly.

With a dew point end-free probe, operation is not only possible with a warm engine. The probe can also be operated when the exhaust gas is cold, i.e. before the so-called end of the dew point is reached, at which point the exhaust gas contains water droplets that would destroy an exhaust gas sensor heated to operating temperature or would have a significantly negative effect on the measurement result of these sensors. The lambda probe upstream and downstream of the first three-way catalytic converter is preferably configured as a probe without a dew point end. The disadvantage of this probe design is that the surrounding protective cover is intended to prevent liquid water from penetrating into the probe body in order to protect the measuring body in the probe. For this purpose, the gas supply to the measuring body is routed via deflections and the flow through the probe is reduced compared to designs without a dew point end. The quick readiness for operation of the dew point-free probe is therefore accompanied by poorer measurement dynamics during operation.

In a further embodiment of the exhaust gas aftertreatment system according to the invention, it is advantageously provided that at least one turbine is arranged in the exhaust gas duct between the inlet and the first three-way catalytic converter. The turbine can be part of a turbocharger, for example. A turbocharger is a component for generating engine supercharging. It increases engine performance and the efficiency of the combustion engine. It works by harnessing some of the energy in the engine exhaust via the turbine inside the exhaust system to drive a compressor.

The various embodiments of the invention mentioned in this application are, Unless stated otherwise in individual cases, they can be advantageously combined with one another.

• 1 ein bevorzugtes Ausführungsbeispiel für ein erfindungsgemäßes Abgasnachbehandlungssystem für einen Verbrennungsmotor zur Durchführung eines erfindungsgemäßen Verfahrens in einer schematischen Darstellung.

The invention is explained below in an exemplary embodiment with reference to the associated drawing. It shows:

• 1 a preferred exemplary embodiment of an exhaust gas aftertreatment system according to the invention for an internal combustion engine for carrying out a method according to the invention in a schematic representation.

1 shows a schematic implementation of a method for exhaust gas aftertreatment of an internal combustion engine M. After the exhaust gas leaves the internal combustion engine M, it is first conducted into an exhaust gas purification device 10 close to the engine. The exhaust gas cleaning device 10 close to the engine comprises a first three-way catalytic converter 12. A second three-way catalytic converter 14 is arranged downstream of the exhaust gas cleaning device 10 close to the engine.

The second three-way catalyst 14 has a catalytic layer. Upon contact with the exhaust gas, the catalytic layer is able to convert at least some of the carbon monoxide (CO), nitrogen oxides (NOx) and unburned hydrocarbons (HC) contained in the exhaust gas into carbon dioxide (CO ₂ ), nitrogen (N ₂ ) and water (H ₂ O) to convert.

So that the second three-way catalytic converter 14 can optimally develop its catalytic effect, it must be brought to its optimum operating temperature. Especially in the cold start phase, gasoline engines emit significant amounts of gaseous pollutants. It is therefore necessary for the second three-way catalytic converter 14 to be brought to the appropriate operating temperature as quickly as possible. Although the three-way catalytic converters 12, 14 are heated up by the hot exhaust gas, among other things, a heating device, preferably a thermal heating device 16, is also provided upstream of the second three-way catalytic converter 14.

Overall, an exhaust gas aftertreatment system 18 is formed by the close-coupled exhaust gas cleaning device 10 and the second three-way catalytic converter 14 as well as the thermal heating device 16 . The exhaust gas aftertreatment system 18 has an inlet 20 for receiving the exhaust gases of the internal combustion engine M, which are routed via an exhaust gas duct 22 to the individual components of the exhaust gas aftertreatment system 18 .

The exhaust gas cleaning device 10 close to the engine can additionally have a particle filter 24 which is arranged downstream of the first three-way catalytic converter 12 . In this exemplary embodiment, the particle filter 24 is an Otto particle filter. The particle filter 24 can have a catalytically active coating, so that the particle filter 24 can be configured as a four-way catalytic converter. In this way, the functionality of a three-way catalytic converter and the gasoline particulate filter are combined in one component.

A first lambda probe 26 is arranged upstream of the first three-way catalytic converter 12 . The first lambda probe 26 is designed as a broadband probe. A second lambda probe 27 is arranged downstream of the first three-way catalytic converter 12 . The second lambda probe 27 is designed as a step response probe. A third lambda probe 28 is arranged downstream of the second three-way catalytic converter 14 . The third lambda probe 28 is designed as a jump probe. Lambda sensors 26, 27, 28 are designed to compare the residual oxygen content in the exhaust gas with a reference oxygen content. In the present exemplary embodiment, the oxygen content of the current atmospheric air is used as the reference oxygen content. With knowledge of the residual oxygen content, the combustion air ratio Ä is determined and adjusted accordingly.

The exhaust gas cleaning device 10 close to the engine is firstly heated by the exhaust gas. In addition, in this exemplary embodiment, engine-related measures are also provided in order to accelerate the heating of the exhaust gas cleaning device 10 close to the engine, i.e. in particular the three-way catalytic converter 12, so that the first three-way catalytic converter 12 can reach its operating temperature quickly and the operational readiness of the Lambda sensors 26, 27 is reached early.

In this exemplary embodiment, two motor measures are provided, which can be set and controlled via a motor controller 30 . A first measure consists in heating up the first three-way catalytic converter 12 by means of a torque reserve.

Internal combustion engine M, which is controlled by engine controller 30, has a torque reserve when internal combustion engine M is idling. Speed fluctuations of the internal combustion engine M can be avoided by the torque reserve. RPM fluctuations can be caused, for example, when the load is applied, which are caused, for example, by an air conditioning system, the steering and/or by the operation of a window lifter.

The torque reserve is achieved by stationary injection of an increased combustion air mass in conjunction with neutralization of the additional torque through delayed ignition angles that degrade efficiency. Although this increases the fuel consumption of the internal combustion engine M, it is also possible to heat up the three-way catalytic converter 12 close to the engine.

A further engine measure for heating the first three-way catalytic converter 12 consists in a combination of secondary air injection and engine rich operation. Secondary air in the exhaust pipe of the internal combustion engine M reduces the carbon monoxide and hydrocarbon content through post-combustion. Post combustion temperatures range from about 500°C to 700°C. Afterburning produces water and carbon dioxide. Due to the chemical reactions, the exhaust gas temperature is also increased simultaneously. The increased exhaust gas temperature contributes to the fact that the first three-way catalytic converter 12 is heated up correspondingly more quickly when an Otto engine is started and that it reaches its optimal operating temperature more quickly

Because the operating temperature is quickly reached in the exhaust gas cleaning device 10 close to the engine as a result of the engine measures described above, the lambda probes 26, 27 can preferably be designed as probes that do not have a dew point end. The disadvantage of later operational readiness compared to dew-point end-free probes is minimized by the motor measures and the advantages of the better control dynamics can be used in the operating-warm condition.

Reference List

10

Exhaust gas purification device close to the engine

12

First three-way catalytic converter

14

Second three-way catalyst

16

Electric heater

18

exhaust aftertreatment system

20

inlet

22

exhaust duct

24

particle filter

26

First lambda probe

27

Second lambda probe

28

Third lambda probe

30

engine control

M

combustion engine

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited 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

• WO 9934902 A1 [0005]

Claims (10)

Method for the exhaust aftertreatment of an internal combustion engine, wherein the exhaust gas flows through at least one exhaust gas cleaning device (10) close to the engine, the exhaust gas cleaning device (10) close to the engine has at least one first three-way catalytic converter (12), the exhaust gas downstream of the exhaust gas cleaning device (10) close to the engine has at least a second three -way catalytic converter (14) and at least one heating device (16) for heating up the second three-way catalytic converter (14) is provided, characterized in that in addition at least one engine and/or extra-engine measure for heating up the exhaust gas cleaning device ( 10) is carried out. procedure after claim 1 , characterized in that a motor measure is implemented by means of torque reserve. procedure after claim 1 or 2 , characterized in that an engine measure is implemented by means of a combination of secondary air injection, engine rich operation and ignition angle retardation. Procedure according to one of Claims 1 until 3 , characterized in that an extra-engine measure is implemented by an electrical heating device before or in the first three-way catalytic converter (12). procedure after claim 1 , characterized in that the heating device (16) is designed as a burner with a maximum thermal heating capacity at the burner outlet of 10 to 60 kW, preferably 15 to 25 kW. Procedure according to one of Claims 1 until 5 , characterized in that a cylinder-specific Lambda control is carried out. Exhaust gas aftertreatment system (18) for an internal combustion engine, with an inlet (20) for receiving the exhaust gas of the internal combustion engine, with at least one exhaust gas duct (22), with an exhaust gas purification device (10) close to the engine being arranged downstream of the inlet (20) in the exhaust gas duct (22), the close-coupled exhaust gas cleaning device (10) comprises at least one first three-way catalytic converter (12), downstream of the close-coupled first three-way catalytic converter (12) in the exhaust gas duct (22) at least one second three-way catalytic converter (14) is arranged and wherein at least one heating device (16) for heating the second three-way catalytic converter (14) is provided, characterized in that the exhaust gas aftertreatment system (18) is designed to use a method according to one of Claims 1 until 6 to perform. Exhaust aftertreatment system (18) after claim 7 , characterized in that the close-coupled exhaust gas cleaning device (10) comprises at least one particle filter (24). Exhaust aftertreatment system (18) after claim 7 or 8th , characterized in that upstream of the first three-way catalytic converter (12) a first lambda probe (26) and downstream of the first three-way catalytic converter (12) a second lambda probe (27) is arranged and that the first lambda probe (26) and/or the second lambda probe (27) is designed as a probe that does not have a dew point end. Exhaust aftertreatment system (18) according to one of Claims 7 until 9 , characterized in that at least one turbine is arranged in the exhaust gas duct between the inlet (20) and the first three-way catalytic converter (12).

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