DE102021117847A1 - Process for exhaust aftertreatment of a vehicle - Google Patents

Abstract

The invention relates to a method for exhaust gas aftertreatment of a vehicle, comprising an internal combustion engine 1, a fresh air line 11 for supplying the internal combustion engine 1 with combustion air 9, an exhaust line 13 and an exhaust gas recirculation system 2 with an exhaust gas recirculation line 21, which branches off from the exhaust line 13 and is upstream of the internal combustion engine 1 in the fresh air line 11 opens. A burner 4 that can be operated with fuel is arranged in/on the exhaust gas line 13 upstream of the exhaust gas recirculation line 21 or in/on the exhaust gas recirculation line 21 . First, an oxygen concentration in an exhaust gas 5 downstream of the internal combustion engine 1 is determined. If the oxygen concentration exceeds a predetermined threshold value, the burner 4 is operated to burn a mixture 6 of exhaust gas 5 from the internal combustion engine 1 and fuel supplied to the burner 4, converting the oxygen contained in the exhaust gas 5 and generating a burner exhaust gas 7. The burner exhaust gas 7 produced is then fed via the exhaust gas recirculation line 21 into the fresh air line 11 to reduce the oxygen concentration in the combustion air 9 of the internal combustion engine 1. Furthermore, an exhaust gas aftertreatment system 100 for carrying out the method and a vehicle with such an exhaust gas aftertreatment system 100 are already provided.

Description

The invention relates to a method for exhaust gas aftertreatment of a vehicle, which comprises an internal combustion engine, a fresh air line for supplying the internal combustion engine with combustion air, an exhaust line and an exhaust gas recirculation system with an exhaust gas recirculation line, which branches off from the exhaust line and opens into the fresh air line upstream of the internal combustion engine. The invention also relates to an exhaust gas aftertreatment system for a vehicle, which is set up for carrying out the method for exhaust gas aftertreatment of the internal combustion engine, and to a vehicle having such an exhaust gas aftertreatment system.

The current exhaust gas legislation and one that will become increasingly strict in the future places high demands on engine raw emissions and the exhaust gas aftertreatment of combustion engines. During the combustion of the air-fuel mixture, the main by-products are the pollutants NOx, CO and HC. In Otto engines, the exhaust gas is cleaned in a known manner via a three-way catalytic converter and further catalytic converters connected upstream and downstream of the three-way catalytic converter. 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) or a NOx storage catalytic converter as well as a particle filter for separating soot particles and, if necessary, further catalytic converters.

Exhaust gas cleaning measures such as three-way catalytic converters are intended to reduce the pollutants in the exhaust gas by accelerating the degrading chemical reactions. However, this only works when a catalytic converter has reached its light-off temperature of several hundred degrees Celsius. Catalytic converters are therefore largely ineffective in the critical phase directly after starting the engine, where the composition of the exhaust gas is still particularly unfavorable. Furthermore, the cold start emissions are particularly influenced by the engine load. Especially in the case of exhaust gas treatment measures that are not yet active, tailpipe emissions also increase.

Exhaust gas recirculation systems are used to reduce the generation of raw emissions, especially nitrogen oxides, during combustion in diesel or petrol engines. In the case of exhaust gas recirculation (EGR), part of the exhaust gas flow is usually fed to the fresh air (combustion air) to be supplied to the combustion unit. The recirculation of the exhaust gas to the internal combustion engine leads to a reduction in the combustion temperature and thus to a reduction in the engine's raw NOx emissions. The background here is the formation mechanism of thermal NOx formation. Here, atmospheric nitrogen is converted into nitrogen oxide. In principle, it can be deduced from the Zeldovich mechanism that thermal NOx formation can be reduced by reducing the local concentrations of oxygen and nitrogen and by reducing the local temperature. The recirculated exhaust gas, which is an inert gas, lowers the oxygen concentration on the one hand and reduces the combustion temperature on the other. As a result, there is a reduction in pollutant emissions, in particular nitrogen oxides, and possibly a reduction in the fuel requirement and in the engine's tendency to knock. Due to legal limit values for emissions from internal combustion engines, in particular with regard to the group of nitrogen oxides, the use of exhaust gas recirculation systems and the rates of exhaust gas discharged are increasing sharply. Exhaust gas recirculation supplements the exhaust gas cleaning measures, since the strict requirements for emission values can only be met in combination. In addition, the exhaust gas recirculation serves to dethrottle the engine at certain operating points.

A further operating mode to be taken into account in addition to the cold start with regard to the raw emissions caused is the overrun mode (also known as overrun mode) of a vehicle clutch not depressed) the engine is dragged through the vehicle, i.e. kept rotating. In modern vehicles, an overrun cut-off interrupts the fuel supply during overrun operation. Overrun fuel cut-off is an intentional, temporary interruption of the fuel supply in an internal combustion engine when the engine is not supposed to deliver power but is being dragged by the vehicle mass while it is in motion. Thus, it is not necessary to supply fuel to the engine. Instead, the engine's motion is sustained by the rotation imposed by the drive train. During overrun operation, the engine is throughput with combustion air, which flows through the engine without combustion taking place. If a load is applied to the engine after overrun has been stopped and overrun cutoff has been deactivated, fuel is supplied to the combustion air, ie to the mixture of recirculated exhaust gas and fresh air. However, the recirculated exhaust gas initially corresponds approximately the fresh air, since no combustion took place during overrun. Thus, the recirculated exhaust gas has a high oxygen concentration. As a result, a high oxygen concentration occurs in the intake manifold of the engine, which exceeds the desired oxygen concentration necessary for combustion. However, if the oxygen concentration is too high, increased amounts of nitrogen oxides are released as a result of combustion. These have a significant influence on the lower nitrogen oxide concentrations in the exhaust gas during normal operation.

The described operating states of cold start or a weak load and the change from overrun have a correspondingly significant effect on raw engine emissions in connection with an exhaust gas recirculation system and as a result of the increased oxygen concentrations caused by these operating states.

JP 2020-51302 A relates to a device for heating recirculated exhaust gas from an internal combustion engine. The device is arranged in the exhaust gas recirculation line and includes a heat storage material. The exhaust gas exiting the internal combustion engine is fed to a portion of the exhaust gas recirculation and heated during a cold start to reduce condensation of water in the exhaust gas within the device. This is done by adding water to the thermal storage material, causing a hydration reaction that releases heat and heats the recirculated exhaust gas.

CN 205841043 U describes an internal combustion engine and downstream exhaust gas recirculation. The exhaust gas recirculation has a heating device that heats the recirculated exhaust gas before it is fed to a cooling device. This is intended to reduce condensation in the cooling device and in an exhaust gas recirculation valve arranged downstream of the cooling device.

U.S. 10,808,633 B2 relates to a hybrid vehicle that includes an internal combustion engine with a turbocharger and an exhaust gas catalyst. The catalytic converter has an electric heater. The vehicle also has exhaust gas recirculation. The heating device is designed to heat up the exhaust gas catalytic converter as required.

The invention is now based on the object of providing a method and a corresponding exhaust gas aftertreatment system and a corresponding vehicle which at least partially overcome the stated disadvantages of the prior art and enable emissions to be reduced.

This object is achieved by a method and an exhaust gas aftertreatment system and a vehicle having the features of the independent claim. Advantageous developments of the invention are defined in the dependent claims.

According to the invention, a method for exhaust gas aftertreatment of a vehicle is provided, which comprises an internal combustion engine, a fresh air line for supplying the internal combustion engine with combustion air, an exhaust line and an exhaust gas recirculation system with an exhaust gas recirculation line, which branches off from the exhaust line and upstream of the internal combustion engine opens into the fresh air line. In this case, a burner that can be operated with fuel is arranged in/on the exhaust gas line upstream of the exhaust gas recirculation line or in/on the exhaust gas recirculation line. First, an oxygen concentration in an exhaust gas is determined downstream of the internal combustion engine. If the oxygen concentration exceeds a predetermined threshold value, the burner is operated to burn a mixture of exhaust gas from the internal combustion engine and fuel supplied to the burner, converting the oxygen contained in the exhaust gas and producing a burner exhaust gas. The burner exhaust gas produced is then fed via the exhaust gas recirculation line into the fresh air line to reduce the oxygen concentration in the combustion air of the internal combustion engine.

The method makes it possible to reduce the oxygen concentration of the combustion air that is supplied to the internal combustion engine during every operating state of the vehicle. This also includes all operating states during which exhaust gas from the internal combustion engine is recirculated due to the exhaust gas recirculation system. As mentioned at the beginning, the oxygen concentration in the combustion air influences the nitrogen oxide emissions that leave the internal combustion engine in the form of raw emissions. Due to different operating states, the exhaust gas of the internal combustion engine has different residual oxygen concentrations, which are caused on the one hand by incomplete combustion and on the other hand by the mode of operation. A recirculation of exhaust gas and mixing of the recirculated exhaust gas with fresh air without prior measures can then result in combustion air that has too high an oxygen concentration. As a result, nitrogen oxide emissions increase during the combustion process. The method according to the invention counteracts this by first determining whether the Exhaust gas contains oxygen or how high the oxygen concentration in the exhaust gas is downstream of the internal combustion engine. If the oxygen concentration exceeds a predetermined threshold, then the burner is operated. This means that a mixture of exhaust gas from the internal combustion engine and fuel supplied to the burner is formed and burned to convert the oxygen contained in the exhaust gas and to produce a burner exhaust gas. The threshold can be statically or dynamically predetermined. Furthermore, the burner can be operated in a controlled or regulated manner. A simple exemplary control provides, for example, that the threshold value is considered to have been exceeded after overrun operation. However, the regulation or control is by no means limited to this variant. What is achieved by this process is that the oxygen concentration of the recirculated exhaust gas is reduced. After combustion, the burner exhaust gas produced is fed via the exhaust gas recirculation line into the fresh air line to reduce the oxygen concentration in the combustion air of the internal combustion engine. The combustion air also has a certain oxygen concentration. By precombusting the exhaust gas, the oxygen concentration of the exhaust gas is selectively reduced to a value of zero over a continuous range. The reduction in the oxygen concentration in the recirculated exhaust gas means that the oxygen concentration in the combustion air also assumes lower values than would be the case without the procedure according to the invention. Among other things, this can preferably be achieved by the quantity of fuel injected into the combustion chamber. The more the oxygen concentration of the exhaust gas is to be reduced in order to ensure a reduction in the oxygen concentration of the combustion air, the greater the necessary amount of fuel that is injected into the combustion chamber. This makes it possible to ensure a reduced oxygen concentration in the combustion air in every operating state of the vehicle.

At the same time, other components that are used within an exhaust aftertreatment system can be heated up by the combustion within the burner. These are, in particular, exhaust gas catalytic converters, which the vehicle preferably includes or which can preferably be the subject of the method. These have a catalytic coating. For example, they can be pure exhaust gas catalytic converters, for example three-way catalytic converters, oxidation catalytic converters, NOx storage catalytic converters or SCR catalytic converters. In addition, catalytically coated particle filters (especially in the first position) are possible, ie particle filters that are equipped with one of the catalyst coatings mentioned above. In the case of a particle filter equipped with a three-way catalytic coating, one also speaks of a four-way catalytic converter. The efficiency of the catalytic converters depends, among other things, on their temperature. The implementation or conversion rate of pollutant emissions increases with higher temperatures. The heating of these components can thus be promoted by the combustion of the exhaust gas. Thus, on the one hand, the amount of raw emissions is reduced by the combustion and reduction in the oxygen concentration of exhaust gas and combustion air, and on the other hand, the conversion of the pollutants that are nevertheless formed by the exhaust gas catalytic converters, which are heated up more quickly, is promoted.

In addition, higher oxygen concentrations often occur in the exhaust gas, particularly when the vehicle is cold-starting, in a low-load condition, or changing from overrun mode. As explained above, the exhaust gas has a high oxygen concentration, particularly after overrun, since the combustion air flows through the internal combustion engine without combustion. In this case, recirculation of the exhaust gas leads to an oxygen concentration in the combustion air that assumes high values after the end of the overrun operation. Furthermore, the temperatures of the components are also low during a cold start. The temperatures of the catalytic converters also drop when the engine is overrun and under low load, so that their conversion rates also drop. Thus, under normal circumstances, two mechanisms adversely affecting emissions would occur simultaneously. Due to high oxygen concentrations in the recirculated exhaust gas, the (nitrogen oxide) raw emissions increase and at the same time there are low conversion rates of the exhaust gas catalytic converters. This state is largely prevented by the method according to the invention, since the oxygen concentration in the exhaust gas is reduced, so that the combustion air has more advantageous values for the oxygen concentration of the combustion air. In addition, the energy released by combustion in the burner can be used to heat up the catalytic converters. This increases their conversion rate at the same time.

The oxygen concentration of the exhaust gas is determined, for example, by measuring the exhaust gas composition or using a model. Sensors for determining the exhaust gas composition are usually arranged in the exhaust gas system of internal combustion engines. These include lambda probes or NOx sensors, which each record the oxygen concentration. The modeling is usually done using a map that the Sauer substance concentration of the engine as a function of its operating point (load, speed).

Exhaust gas recirculation is controlled by an EGR valve. This has the task of metering the amount of recirculated exhaust gas. It is installed either on the exhaust manifold or on the intake tract. In some engines, it sits in a heat-resistant exhaust pipe that connects the exhaust manifold to the intake tract. EGR valves in diesel vehicles have large opening cross sections due to the high recirculation rates.

The burner is arranged in/on the exhaust gas line upstream of the exhaust gas recirculation line or in/on the exhaust gas recirculation line. With the first-mentioned arrangement, the entire exhaust gas of the internal combustion engine flows through the burner, since the splitting of the exhaust gas, which results from the recirculation of part of the exhaust gas, takes place only after the exhaust gas has left the burner. Consequently, the entire exhaust gas mass flow is exposed to combustion in the burner. If the mixture of exhaust gas from the internal combustion engine and the fuel supplied to the burner is burned to reduce the oxygen concentration in the combustion air, the entire exhaust gas is heated by the combustion. Thus, on the one hand, a reduced oxygen concentration in the combustion air is achieved and, on the other hand, heating of other components that are used within an exhaust gas aftertreatment system is ensured. This can be controlled, among other things, by the amount of fuel supplied to the burner. In the second arrangement, only the mass flow of exhaust gas from the internal combustion engine flows through the burner, which is taken from the entire exhaust gas mass flow during exhaust gas recirculation and fed to the fresh air line via the exhaust gas recirculation line. The advantage of this arrangement is that the burner can be made smaller and has a more compact design. This provides a space-saving alternative for integrating the burner into the vehicle. The heating has a particular effect on the exhaust gas recirculation system. This particularly counteracts the problem of exhaust gases falling below the dew point, which can cause condensate to form. This often represents a major problem, especially after the engine has been started, which is largely solved by arranging the burner in/on the exhaust gas recirculation line, in addition to reducing the oxygen concentration in the combustion air. Furthermore, due to the increased speed of combustion due to lower mass flows, earlier use of exhaust gas recirculation is made possible.

The exhaust gas recirculation system is preferably a low-pressure exhaust gas recirculation system. In this case, the exhaust gas is extracted downstream of the turbine of an exhaust gas turbocharger and introduced into the fresh air line upstream of the turbocompressor. A problem that has to be solved technically in low-pressure exhaust gas recirculation systems is that when the exhaust gases fall below the dew point, condensate can form and cause corrosion, especially on the compressor. In connection with the method according to the invention, falling below the dew point can be avoided here, since the combustion by the burner raises the temperature of the exhaust gas.

According to a preferred embodiment of the invention, the burner is operated in such a way that a predetermined oxygen concentration of the combustion air supplied to the internal combustion engine is set, in particular controlled or regulated. Accordingly, the mixture of exhaust gas from the internal combustion engine and fuel supplied to the burner is burned to set a predetermined oxygen concentration in the combustion air of the internal combustion engine. As a result, the quantity of pollutants escaping from the internal combustion engine can be influenced in a targeted manner, and these can be reduced in a particularly optimized manner.

The predetermined oxygen concentration of the combustion air supplied to the internal combustion engine is preferably predetermined as a function of an operation-dependent combustion air ratio λ. The combustion air ratio λ indicates the mass ratio of air to fuel relative to the stoichiometrically ideal ratio for a theoretically complete combustion process. The operation-dependent combustion air ratio λ depends on a desired combustion process, temperatures, the formation of pollutants and an efficiency. On the basis of a combustion calculation or a modeling of a characteristics map, a combustion air ratio is determined, for example by an engine control device, which represents a particularly suitable combustion air ratio with regard to the aforementioned criteria for various operating states. The operating state of the internal combustion engine is influenced by its operating point (load, speed). As a result, on the one hand, the oxygen concentration in an exhaust gas and consequently also the oxygen concentration in the combustion air is reduced by the combustion. In addition, a value is guaranteed for the oxygen concentration of the combustion air, which has a reducing effect on the pollutant emissions, in particular nitrogen oxide, and/or at the same time fulfills other criteria. By depending on the predetermined Sauer substance concentration from an operation-dependent combustion air ratio λ, a value that is particularly suitable for the currently prevailing operating conditions is determined for the predetermined oxygen concentration of the combustion air. The predetermined oxygen concentration of the combustion air preferably includes a tolerance range within which the actual oxygen concentration of the combustion air should lie. This increases flexibility in operating the burner to meet various criteria that are also important.

According to an advantageous embodiment, the burner is arranged in the exhaust pipe and the output of the burner, which is arranged upstream of the exhaust gas recirculation pipe, is at least 10 kW, preferably at least 15 kW and particularly preferably between 15 kW and 20 kW. Providing a burner of this size ensures that complete combustion is possible with the exhaust gas mass flows that usually occur for internal combustion engines in a vehicle. Furthermore, due to this dimensioning, a suitable amount of energy is available, which ensures rapid heating of components of the exhaust gas aftertreatment system arranged downstream of the burner by the heated exhaust gas.

According to an advantageous embodiment, the burner is arranged in the exhaust gas recirculation line and the output of the burner is at least 3 kW, preferably at least 10 kW and particularly preferably between 10 kW and 15 kW. Providing a burner of this size ensures that complete combustion is possible with the recirculated exhaust gas mass flows that usually occur for internal combustion engines in a vehicle. In the case of this arrangement, a more compact arrangement is possible, with this dimensioning providing a suitable amount of energy that ensures rapid heating of the exhaust gas recirculation system.

In a preferred embodiment of the invention, at least one first exhaust gas catalytic converter is arranged in the exhaust pipe and a fuel quantity supplied to the burner is predetermined as a function of the oxygen concentration in the exhaust gas and a conversion rate of the at least one first exhaust gas catalytic converter. This supplements the strategy by taking into account the conversion rate of one or more catalytic converters. The conversion rate of an exhaust gas catalytic converter can be used to assess how effectively and to what extent it converts or stores the pollutants. The conversion rate can be determined in a known manner. For example, this can be done using temperature measurements of the exhaust gas catalytic converter or the exhaust gas downstream of the exhaust gas catalytic converter or by modeling them. Alternatively, the conversion is determined directly by measuring or modeling the pollutants upstream and downstream of the catalytic converter. For example, if the temperature of the catalytic converter is above the light-off temperature, then the catalytic converter is within its active range and is converting the pollutants. Consequently, this knowledge can be used in a complementary manner to control fuel delivery into the combustion chamber. For example, if there are high oxygen concentrations in the exhaust gas, these are reduced by combustion in the burner so that both a reduced oxygen concentration in the exhaust gas and in the combustion air is achieved. In the case of an active, operational catalytic converter that successfully reduces nitrogen oxide emissions in particular, a higher oxygen concentration in the exhaust gas and a higher oxygen concentration in the combustion air can be tolerated than in the case that the catalytic converters are below their light-off temperature and only one make a small contribution to the reduction of pollutants. Then the goal is increasingly to reduce raw emissions until the catalytic converters can be operated effectively enough. In this case, therefore, there must be a lower oxygen concentration in the exhaust gas and a lower oxygen concentration in the combustion air, and a higher quantity of fuel is supplied to the burner, which in turn also results in faster heating of the still inactive exhaust gas catalytic converters.

Provision can advantageously be made for at least one first exhaust gas catalytic converter to be arranged in the exhaust pipe and for a predetermined oxygen concentration of the combustion air fed to the internal combustion engine to be determined as a function of the oxygen concentration in the exhaust gas and a conversion rate of the at least one first exhaust gas catalytic converter and/or the temperature of the at least one first exhaust gas catalytic converter and/or the temperature of the exhaust gas is determined downstream of the at least one first exhaust gas catalytic converter. A predetermined oxygen concentration in the combustion air is thus determined as precisely as possible using characteristic diagrams or models, through which synergies between the reduction of raw emissions by reducing the oxygen concentration in the combustion air and rapid heating of one or more exhaust gas catalytic converters are as large as possible, while at the same time excessive combustion is avoided. The predetermined oxygen concentration of the combustion air thus enables a scenario that enables particularly efficient operation of the burner light. By considering the amount of raw emissions and the ability of the catalytic converters to convert them, both mechanisms are adequately factored into determining the predetermined oxygen concentration of the combustion air.

Provision is advantageously made for the method to be carried out after overrun operation or in lower part-load operation of the vehicle. With regard to pollutant emissions, these operating modes represent operating areas that are particularly relevant to emissions. They contribute a significant proportion of the total emissions. In other operating ranges, the emissions can already be kept at a low level, so that the potential for reducing emissions after overrun or when the vehicle is operated under partial load is particularly large. By focusing the method on the operating modes mentioned, the overall emissions can be greatly influenced, while the method can be adjusted during other operating states in order not to unnecessarily consume fuel, electrical energy for the operation of actuators or the computing power of the engine control unit and still guarantee excellent emission values. In addition, this protects the service life of the parts and components required by the process.

According to a preferred embodiment of the method, the threshold value of the oxygen concentration in the exhaust gas is determined as a function of an operating state of the internal combustion engine. The operating state of the internal combustion engine is influenced by its operating point (especially load and speed). In particular, operating states such as a cold start or changing from overrun are relevant here. The threshold oxygen concentration thus varies. Consequently, for example after overrun, it is taken into account that the exhaust gas of the internal combustion engine has high oxygen concentrations, while any exhaust gas catalytic converters that may be used have cooled down and have lower conversion rates. In this scenario, the pre-determination of the threshold value provides a lower value, since the conversion of pollutants takes place below an effective catalyst behavior. For normal nominal operation, on the other hand, the threshold value is higher because the exhaust gas catalytic converters convert the pollutants to the greatest possible extent. The threshold value of the oxygen concentration in the exhaust gas is determined, for example, from a model, a map, or experimental investigations in a test bench as a function of an operating state of the internal combustion engine.

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

• 1 einen Systemaufbau eines erfindungsgemäßen Abgasnachbehandlungssystems in einer ersten Ausführung der Erfindung;
• 2 einen Systemaufbau eines erfindungsgemäßen Abgasnachbehandlungssystems in einer zweiten Ausführung der Erfindung;
• 3 einen Ablaufplan eines Verfahrens zum Betreiben einer Verbrennungskraftmaschine gemäß einer Ausgestaltung der Erfindung.

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

• 1 a system structure of an exhaust gas aftertreatment system according to the invention in a first embodiment of the invention;
• 2 a system structure of an exhaust gas aftertreatment system according to the invention in a second embodiment of the invention;
• 3 a flowchart of a method for operating an internal combustion engine according to an embodiment of the invention.

The invention is embodied below according to a first and a second embodiment of the present invention, taking its application to a vehicle as an example. However, the method is in no way limited to these applications.

In 1 an exhaust gas aftertreatment system 100 according to a first embodiment of the invention is shown, which is arranged downstream of an internal combustion engine 1 of a vehicle which is otherwise not shown in any more detail. The internal combustion engine is connected upstream via a fresh air line 11 to an air supply for supplying the internal combustion engine 1 with combustion air 9 and downstream to an exhaust gas line 13 . Depending on the exhaust gas recirculation system, the combustion air 9 can only consist of pure fresh air 8 or of a mixture of fresh air 8 and recirculated exhaust gas 22 . An exhaust gas catalytic converter, which is designed as a three-way catalytic converter 3 in this example, is arranged in the exhaust pipe 13 downstream of the internal combustion engine 1 . In addition, the exhaust gas aftertreatment system 100 includes a temperature sensor 31. This is located downstream of the three-way catalytic converter 3 and measures the temperature of the exhaust gas 5 exiting the three-way catalytic converter 3. Alternatively, the temperature sensor 31 can also be arranged directly on or in the three-way catalytic converter 3 in order to measure the catalytic converter temperature measure up.

Furthermore, an exhaust gas recirculation system 2 is arranged downstream of the three-way catalytic converter 3 . This includes an exhaust gas recirculation line 21, which branches off from the exhaust line 13 downstream of the three-way catalytic converter 3 and downstream of a turbine, not shown, of an exhaust gas turbocharger and upstream of a compressor, not shown, of the exhaust gas turbocharger opens into the fresh air line 11 upstream of the internal combustion engine 1 . The exhaust gas recirculation system 2 has a burner 4 which is integrated into the exhaust gas recirculation line 21 . A part of the exhaust gas 5, which is consequently recirculated exhaust gas 22, flows through it. The burner 4 has a fuel supply 41 and a combustion chamber 42 . Accordingly, a mixture 6 of the recirculated exhaust gas 22 and fuel is formed within the combustion chamber 42 through which the recirculated exhaust gas 22 flows, which mixture is optionally burned there.

The vehicle also includes an engine control unit or an on-board computer 12. It is used, among other things, for processing and evaluating the signals which originate from the temperature sensor 31, among other things. In addition, it controls the fuel supply 41, which is connected to the on-board computer 12 in a signal-conducting manner, as well as the EGR valve, which is not shown. The fuel supply 41 receives a signal from the onboard computer 12 that includes the amount of fuel to be supplied to the combustion chamber 42 .

In 2 An exhaust aftertreatment system 100 according to a second embodiment of the invention is shown. In the following, only the differences compared to the first embodiment are described, with the rest of the structure being the same as in 1 structure shown is the same.

According to the second embodiment of the invention, the burner 4 is now not arranged in the exhaust gas recirculation line 21 but downstream of the internal combustion engine 1 and upstream of the three-way catalytic converter 3 in the exhaust gas line 13 and connected to it in a fluid-conducting manner. Thus, the exhaust gas 5 originating from the internal combustion engine 1 flows through at least a partial flow first through the burner 4 before it reaches the three-way catalytic converter 3, the exhaust gas recirculation line 21 and other components arranged downstream.

The following is based on 3 the method according to the invention using the example of the exhaust gas aftertreatment system in a first and second embodiment 1 and 2 explained.

The method starts in block 1. It starts with the internal combustion engine 1 being in operation. This can involve, among other things, starting the internal combustion engine 1 , operation with a low load or, in particular, changing operation from the overrun mode by reconnecting a load to the internal combustion engine 1 . Essentially, these are operating states that are associated with an increased oxygen concentration in the exhaust gas 5 .

Furthermore, as shown in block 2, a partial flow 22 of the exhaust gas 5 or of the burner exhaust gas 7 is recirculated into the fresh air line 11 and into the combustion cycle by means of the exhaust gas recirculation system 2 . For this purpose, the exhaust gas recirculation system 2, controlled by the EGR valve, removes a partial flow 22 of the exhaust gas 5 or the burner exhaust gas 7 from the exhaust gas line 13 and mixes this recirculated exhaust gas 22 with the fresh air 8 in the fresh air line 11 upstream of the internal combustion engine 1.

According to a preferred embodiment of the method, the threshold value of the oxygen concentration in the exhaust gas 5 is now predetermined in block 3 as a function of an operating state of the internal combustion engine 1 . The threshold value of the oxygen concentration varies during operation depending on the operating state of internal combustion engine 1. The threshold value of oxygen concentration in exhaust gas 5 comes, for example, from a model, a map or experimental investigations on a test bench. For example, it takes into account the change from overrun to normal operation, so that a low threshold value is determined. Since in such an operating state it is crucial for reducing the pollutants by avoiding the formation of raw emissions to operate the burner 4, the oxygen concentration in the combustion air 9 must be as low as possible, which is reflected in the determination of the threshold value.

In block 4, the oxygen concentration in the exhaust gas 5, ie the oxygen concentration of the internal combustion engine exhaust gas that leaves the internal combustion engine 1, is determined. This is preferably done by means of sensors that are usually present, not shown here, such as lambda probes or NOx sensors, or by map-supported modeling of the oxygen concentration as a function of the operating point of internal combustion engine 1.

In the subsequent step according to block 5, the on-board computer 12 checks, for example, whether the determined oxygen concentration in the exhaust gas 5 exceeds the predetermined threshold value. If the exhaust gas 5 has an oxygen concentration that is too high and the threshold value is exceeded, the method is continued in block 6 and the burner is operated. Otherwise, the method goes back to block 3 and the determination of the threshold value of the oxygen concentration in the exhaust gas 5, shown in block 3, shown in block 4 Determination of the oxygen concentration in the exhaust gas 5 and the subsequent comparison with the threshold value in block 5 are repeated.

According to the 3 Furthermore, in block 6 an oxygen concentration of the combustion air 9 of the internal combustion engine 1 is predetermined. The combustion air 9 is the gas mixture that finally enters the internal combustion engine 1 and runs through the combustion process there together with the supplied fuel. The predetermined oxygen concentration of the combustion air is also determined using a characteristic map or model or a combustion calculation. The predetermined oxygen concentration represents the desired threshold value of the oxygen concentration of the combustion air 9 from the point of view of required performance, efficiency and low pollutant emissions. The model therefore takes into account in particular a dependency of the predetermined oxygen concentration on the actual oxygen concentration in the exhaust gas 5, 22 and a conversion rate of the exhaust gas catalytic converter 3. The conversion rate allows statements to be made about the effectiveness with which the three-way catalytic converter 3 removes pollutants from the exhaust gas. It can be determined directly in particular by comparing the pollutant concentrations upstream and downstream of the three-way catalytic converter 3 . Alternatively, the conversion rate can be calculated based on the temperature of the exhaust gas catalytic converter 3 or the temperature of the exhaust gas 5 downstream of the exhaust gas catalytic converter 3 . By considering the oxygen concentration in the exhaust gas 5 and the conversion rate, information about the exhaust gas aftertreatment system 100 is available that enables the predetermined oxygen concentration of the oxygen concentration in the combustion air 9 to be determined very precisely, which takes into account the various criteria listed above.

On the basis of the predetermined oxygen concentration of the oxygen concentration of the combustion air 9, the on-board computer 12 in connection with the mass flows of the fresh air 8 and the recirculated exhaust gas 22 as well as other models relevant to the combustion determine a suitable quantity of fuel, which the fuel supply 41 supplies to the combustion chamber 42 of the burner 4. As a result, a mixture 6 of at least part of the exhaust gas 5 or of recirculated exhaust gas 22 from the internal combustion engine 1 and the fuel fed to the burner 4 is produced in block 7 . Here, the mixture comprises 6 according to 1 only part of the exhaust gas 5, the recirculated exhaust gas 22, since the burner 4 is arranged in the exhaust gas recirculation line 21. According to 2 on the other hand, the burner 4 is arranged upstream of the exhaust gas recirculation line 21 in the exhaust gas line 13, so that the mixture 6 in this case includes the entire exhaust gas 5 or at least a partial flow thereof as well as fuel.

After this has taken place, the mixture 6 can be burned in the burner 4 according to block 8 .

Then, in block 9, the burner exhaust gas 7 produced is supplied to the fresh air 8 via the exhaust gas recirculation line 21, which opens into the fresh air line 11, and is mixed with it. According to the second embodiment 2 the burner exhaust gas 7 first flows through the three-way catalytic converter 3 before part of the burner exhaust gas 7 is recirculated through the EGR valve via the exhaust gas recirculation line 21 and takes the path described in block 9 into the fresh air line 11 .

The mixture then forms in block 10 the combustion air 9, the oxygen concentration of which is reduced compared to pure fresh air 8 and corresponds to the predetermined oxygen concentration.

reference list

100

exhaust aftertreatment system

1

internal combustion engine

11

fresh air line

12

Engine control unit/board computer

13

exhaust pipe

2

exhaust gas recirculation system

21

exhaust gas recirculation line

22

Part of the flue gas / recirculated flue gas

3

catalytic converter

31

temperature sensor

4

burner

41

fuel delivery

42

combustion chamber

5

exhaust

6

mixture

7

burnt mixture

8th

fresh air

9

combustion air

QUOTES INCLUDED IN DESCRIPTION

This list of the 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

• JP 202051302 A [0007]
• CN 205841043 U [0008]
• US 10808633 B2 [0009]

Claims (10)

Method for exhaust gas aftertreatment of a vehicle, which has an internal combustion engine (1), a fresh air line (11) for supplying the internal combustion engine (1) with combustion air (9), an exhaust line (13) and an exhaust gas recirculation system (2) with an exhaust gas recirculation line (21), which branches off from the exhaust gas line (13) and opens into the fresh air line (11) upstream of the internal combustion engine, with a burner that can be operated with fuel in/on the exhaust gas line (13) upstream of the exhaust gas recirculation line (21) or in/on the exhaust gas recirculation line (21). (4) is arranged, comprising the following steps: Determining an oxygen concentration in an exhaust gas (5, 22) downstream of the internal combustion engine (1), when the oxygen concentration exceeds a predetermined threshold value, the burner (4) is operated to burn a mixture (6) of exhaust gas (5, 22) from the internal combustion engine (1) and fuel supplied to the burner, converting the oxygen contained in the exhaust gas and generating a burner exhaust gas (7), and Supplying the burner exhaust gas (7) produced via the exhaust gas recirculation line (21) into the fresh air line (11) to reduce the oxygen concentration in the combustion air (9) of the internal combustion engine (1). procedure after claim 1 , wherein the burner (4) is operated in such a way that a predetermined oxygen concentration of the combustion air (9) supplied to the internal combustion engine (1) is set, in particular controlled or regulated. procedure after claim 2 , wherein the predetermined oxygen concentration of the combustion air (9) is predetermined as a function of an operation-dependent combustion air ratio λ. Procedure according to one of Claims 1 until 3 , wherein the burner (4) is arranged in the exhaust pipe (13) and the output of the burner (4) is at least 10 kW, preferably at least 15 kW and particularly preferably between 15 kW and 20 kW. Procedure according to one of Claims 1 until 3 , wherein the burner (4) is arranged in the exhaust gas recirculation line (21) and the output of the burner (4) is at least 3 kW, preferably at least 10 kW and particularly preferably between 10 kW and 15 kW. Method according to one of the preceding claims, wherein at least one first exhaust gas catalytic converter (3) is arranged in the exhaust pipe (13) and a fuel quantity supplied to the burner (4) depends on the oxygen concentration in the exhaust gas (5, 22) and a conversion rate of the at least one first Exhaust catalyst (3) is predetermined. procedure after claim 2 , wherein at least one first exhaust gas catalytic converter (3) is arranged in the exhaust pipe (13) and the predetermined oxygen concentration of the combustion air (9) fed to the internal combustion engine (1) depends on the oxygen concentration in the exhaust gas (5, 22) and a conversion rate of the at least one first Exhaust gas catalytic converter (3) and/or the temperature of the at least one first exhaust gas catalytic converter (3) and/or the temperature of the exhaust gas (5) downstream of the at least one first exhaust gas catalytic converter (3) is determined. Method according to one of the preceding claims, wherein the method is carried out after overrun operation or in lower part-load operation of the vehicle. Exhaust aftertreatment system (100) for a vehicle, set up to carry out the method according to one of Claims 1 until 8th . Vehicle, an exhaust aftertreatment system (100). claim 9 having.

Images