Method for operating an exhaust system and exhaust system

Abstract

Method for operating an exhaust system (1) arranged downstream of an internal combustion engine (2), wherein - the exhaust gas of the internal combustion engine (2), which is operated with a combustion air ratio λ = 1, is fed into the exhaust system (1), - a defined quantity of fuel is injected into an exhaust pipe section (4) of the exhaust system (1) in the vicinity of an ignition device, so that a local air-fuel mixture with a combustion air ratio λ < 1 results, - an air quantity corresponding to this injected fuel quantity is introduced into the exhaust pipe section (4), so that the total result is again a stoichiometric exhaust gas which has an air-fuel mixture with a combustion air ratio λ = 1, - the air-fuel mixture is ignited by means of the ignition device.

Description

[0001] The present invention relates to a method for operating an exhaust system. Furthermore, the present invention relates to an exhaust system.

[0002] An exhaust system is located downstream of an internal combustion engine and serves to remove the exhaust gas produced during the combustion of an air-fuel mixture and clean it using one or more exhaust treatment devices. These exhaust treatment devices include, for example, catalytic converters and particulate filters. Currently, so-called three-way catalytic converters are commonly used in motor vehicles. These are capable of converting pollutants produced during the combustion process, such as nitrogen oxides, carbon monoxide, and unburned hydrocarbons, into carbon dioxide, nitrogen, and water in a catalytic process. Particulate filters serve the purpose of filtering out soot particles contained in the exhaust gas of the internal combustion engine.If the functions of the three-way catalyst and the particulate filter are implemented in a single catalyst, it is often referred to as a four-way catalyst.

[0003] With increasing demands for compliance with legally prescribed emission limits, such as those planned for the future Euro 7 standard for gasoline engines, the volumes of catalytic converters and particulate filters will most likely also increase. This means that in some vehicle types, the pre-catalytic converters of the exhaust system will likely require the entire near-engine area as installation space. An additional catalytic converter, a particulate filter, or a four-way catalytic converter will then be installed in a first position in the underbody of the vehicle. This creates the need to actively heat the catalytic converters or particulate filters, especially in vehicles with low driving resistance and powerful engines.

[0004] In motor vehicles with a so-called sailing function and in hybrid vehicles, which have an electric motor as a drive device in addition to an internal combustion engine, the effect of the exhaust system cooling down during driving is further increased by longer downtimes of the internal combustion engine in purely electric motor mode.

[0005] On the other hand, the exhaust aftertreatment system must be capable of converting the exhaust gases within a very short time. This means that a temperature must be reached at which the catalysts become active (the so-called "light-off temperature") in order to comply with the strict emissions regulations under all real-world driving conditions.

[0006] Heating the exhaust system components can be achieved in a variety of ways and depends, for example, on the size of the internal combustion engine and the driving resistance of the vehicle. Relatively small internal combustion engines, such as four-cylinder in-line engines (R4 engines), in larger vehicles, can achieve this, for example, through conventional heating of the catalytic converter with a secondary air system. Medium-weight vehicles with medium-sized internal combustion engines, such as V6 engines, can supply this energy directly to the exhaust system via electric heating catalysts. Relevant examples of this are provided by DE 10 2009 052 008 A1, EP 0 783 621 B1, DE 10 2014 115 923 A1, and US Pat. No. 9 060 387 B2.

[0007] For internal combustion engines operating in smaller vehicles with low loads and thus low exhaust temperatures, a burner system may be necessary to provide the high energy required by burning fuel, similar to a supplementary heater system for a parking heater or for a motor vehicle's interior heater. Examples of this are EP 0 590 699 B1, EP 0 238 916 A1, and EP 1 807 612 B1.

[0008] However, if these systems are operated autonomously or in a partial flow, they are very complex to control and can only be monitored with considerable additional effort in the on-board diagnostics of the vehicle (see DE 41 04 165 A1).

[0009] DE 39 20 159 A1 discloses a method for utilizing the energy released during a catalytic conversion of a reaction mixture of air with fuel and / or exhaust gas containing convertible components for heating purposes in motor vehicles. This method allows the thermal energy released in an exhaust gas catalyst to be specifically influenced and utilized for heating purposes. This opens up potential applications, for example, as an auxiliary heater or as auxiliary heating during the cold start phase of the internal combustion engine.

[0010] DE 196 17 190 A1 discloses a method for exhaust gas detoxification by means of which the heating phase of an exhaust gas catalyst is shortened or the pollutant emissions occurring during this time are reduced.

[0011] If the internal combustion engine is designed as a Otto engine, an air mass of 14.7 kg is required for the ideal combustion of 1 kg of gasoline. The mass ratio of air mass to gasoline is then 14.7:1 (stoichiometric ratio). The so-called combustion air ratio λ indicates in a combustion process how the air-fuel mixture actually supplied to the combustion process deviates from the mass ratio theoretically required for stoichiometrically complete combustion. If the air mass actually supplied to the combustion process corresponds to the air mass theoretically required for complete combustion, the combustion air ratio λ = 1 applies. With a combustion air ratio λ < 1 there is a lack of air. In this context it is often referred to as a rich mixture. With a combustion air ratio λ > 1 there is an excess of air, resulting in a lean mixture.

[0012] The Euro 7 emissions standard mentioned above, which will apply in the future, will likely require the combustion process of a gasoline engine to always operate with a combustion air ratio of λ = 1 (stoichiometric ratio) throughout its entire operating range. The combustion air ratio cannot therefore be varied in such a way that the gasoline engine temporarily operates with a combustion air ratio of λ < 1 or with a combustion air ratio of λ > 1.

[0013] The present invention has for its object to provide a method for operating an exhaust system and an exhaust system for carrying out such a method, which enables operation of an internal combustion engine in a stoichiometric ratio.

[0014] This object is achieved by a method for operating an exhaust system having the features of claim 1. With regard to the exhaust system, this object is achieved by an exhaust system having the features of claim 5. The subclaims relate to advantageous developments of the invention.

[0015] In a method according to the invention for operating an exhaust system arranged downstream of an internal combustion engine, it is provided that - the exhaust gas of the internal combustion engine, which is operated with a combustion air ratio λ = 1, is fed to the exhaust system, - a defined quantity of fuel is injected into an exhaust pipe section of the exhaust system near an ignition device, such as an electrical ignition or heating device, so that an air-fuel mixture with a combustion air ratio λ < 1 is produced locally, - an amount of air matching the injected fuel quantity is introduced into the exhaust pipe section, so that in total a stoichiometric exhaust gas is again produced, which has an air-fuel mixture with a combustion air ratio λ = 1, - the air-fuel mixture is ignited by means of the ignition device.

[0016] The method according to the invention enables heating of parts of the exhaust system, in particular catalytic converters and / or particulate filters, in such a way that a first part of the temperature increase is supplied directly via electrical energy to operate the ignition device, and a second part of the temperature increase is added via the exothermic combustion of the air-fuel mixture. This ensures that none of the energy paths that can be used to heat parts of the exhaust system is overloaded. The internal combustion engine can always be operated with a combustion air ratio of λ = 1. The exhaust gas also has a global air ratio of λ = 1. This allows compliance with future legal standards.Further advantages include, for example, a smaller installation space requirement and lower costs compared to a stand-alone burner system, which can be provided in a secondary flow of the exhaust system to heat up parts of the exhaust system.

[0017] In a preferred embodiment, it is proposed that the ignition of the air-fuel mixture takes place by means of the ignition device within a first catalyst of the exhaust system. From a functional perspective, the first catalyst forms a heating catalyst.

[0018] In an advantageous embodiment, it is proposed that an electric heating device is used as an ignition device for the air-fuel mixture.

[0019] In an alternative embodiment, it may be provided that a glow device or a glow plug is used as the ignition device for the air-fuel mixture.

[0020] Alternatively, it may be provided that a heated spark plug is used as an ignition device for the air-fuel mixture.

[0021] An exhaust system according to the invention, which is suitable for carrying out a method according to one of claims 1 to 4, is arranged downstream of an internal combustion engine and has an exhaust pipe section and an electrical ignition device along a flow direction of an exhaust gas of the internal combustion engine, wherein the exhaust pipe section comprises at least one fuel injector, by means of which fuel can be injected into the exhaust pipe section, and at least one air inlet, by means of which air can be introduced into the exhaust pipe section, wherein - the fuel injector is designed to inject a defined amount of fuel into the exhaust pipe, so that the exhaust gas of the internal combustion engine within the exhaust pipe section locally has an air-fuel mixture with a combustion air ratio λ < 1, - an air quantity matching the injected fuel quantity can be introduced into the exhaust pipe section via the air inlet, so that in total a stoichiometric exhaust gas is again produced which has an air-fuel mixture with a combustion air ratio λ = 1, and - the electrical ignition device is designed to ignite the air-fuel mixture.

[0022] By means of the exhaust system according to the invention, parts of the exhaust system are heated with the advantages already mentioned above in such a way that a first part of the temperature increase is supplied directly via electrical energy to operate the electrical ignition device, and a second part of the temperature increase is added via the exothermic combustion of the air-fuel mixture. The internal combustion engine can always be operated in a stoichiometric ratio with a combustion air ratio of λ = 1.

[0023] In a preferred embodiment, it is proposed that the exhaust system has a first catalyst which is arranged downstream of the exhaust pipe section.

[0024] In a particularly preferred embodiment, it is possible for the ignition device to be housed within the first catalyst. From a functional perspective, the first catalyst then forms a heating catalyst.

[0025] In an advantageous embodiment, it can be provided that the ignition device is designed as an electrical heating device, in particular as a heating disc.

[0026] In an alternative embodiment, it is possible for the ignition device to be designed as a glow device or glow plug.

[0027] In a further alternative embodiment, it is possible for the ignition device to be designed as a heated spark plug.

[0028] In an advantageous embodiment, the exhaust system can be provided with a second catalyst located downstream of the first catalyst. This second catalyst can be designed, for example, as a three-way catalyst, which can be preceded by a particulate filter, or as a four-way catalyst with an integrated particulate filter. In an advantageous further development, the exhaust gas aftertreatment functions of the second catalyst and / or a particulate filter can also be integrated into the first catalyst.

[0029] Further features and advantages of the present invention will become clear from the following description of a preferred embodiment with reference to the enclosed Fig.1, which shows a highly simplified schematic view of an exhaust system 1 arranged downstream of an internal combustion engine 2 of a motor vehicle. The internal combustion engine 2 is a gasoline engine.

[0030] The exhaust system 1 is connected on the intake side in a conventional manner to an exhaust manifold of the internal combustion engine 2 (not further described here). This exhaust manifold is designed to collect the exhaust gas emitted by the cylinders of the internal combustion engine 2 during the combustion process of an air-fuel mixture and to feed it to the exhaust system 1 located downstream of the exhaust manifold for the purpose of exhaust gas aftertreatment. In this exemplary embodiment, the exhaust system 1 has at least one pre-catalyst 3 in an area adjacent to the internal combustion engine 1.

[0031] In this exemplary embodiment, the exhaust system 1 further comprises an exhaust pipe section 4, which is connected on the inlet side to an outlet of the pre-catalytic converter 3, and a first catalytic converter 5, which is connected on the inlet side to an outlet of the exhaust pipe section 4. Furthermore, the exhaust system 1 in this exemplary embodiment comprises a particulate filter 6, which is arranged downstream of the first catalytic converter 5, and a second catalytic converter 7, which is arranged downstream of the particulate filter 6. The first catalytic converter 5, the particulate filter 6, and the second catalytic converter 7 are arranged in an underbody of the motor vehicle.

[0032] The second catalytic converter 7 can be designed, for example, as a three-way catalytic converter. Alternatively, the second catalytic converter 7 can also be a four-way catalytic converter, in which the function of the particulate filter 6 is integrated into the second catalytic converter 7. Depending on the design, the particulate filter 6 can also be arranged at a different location in the exhaust system 1. For example, the particulate filter 6 can be arranged downstream of the pre-catalytic converter 3 or integrated into the first catalytic converter 5.

[0033] Particularly in motor vehicles with low driving resistance and powerful internal combustion engines, it is necessary to actively heat parts of the exhaust system 1, in particular the catalytic converters 5, 7 located in the underbody and the particulate filter 6. This is because the exhaust gas aftertreatment system must be capable of conversion within a very short time. This means that a temperature must be reached at which the catalytic converters 5, 6 become active (so-called "light-off temperature") in order to comply with the strict emissions regulations under all driving conditions. In motor vehicles with a so-called coasting function and in hybrid vehicles that have an electric motor as a drive device in addition to an internal combustion engine, the effect of the exhaust system 1 cooling down during driving is further increased by longer downtimes of the internal combustion engine when driving purely under electric motor.

[0034] The following explains how parts of the exhaust system 1 can be heated up quickly.

[0035] The exhaust system 1 has at least one fuel injector 8, which opens into the exhaust pipe section 4 upstream of the first catalyst 5 in the direction of exhaust gas flow and can inject fuel into this area during operation. The exhaust pipe section 4 also has an air inlet 40, by means of which air can be supplied to the exhaust pipe section 4.

[0036] In a method according to the invention for operating the exhaust system 1, the exhaust gas of the internal combustion engine 2, which is operated in stoichiometric mode with a combustion air ratio λ = 1, is fed to the exhaust system 1. After flowing through the pre-catalyst 3, the exhaust gas is fed via the exhaust line section 4 to the first catalyst 5, the particulate filter 6, and the second catalyst 7 for exhaust gas treatment.

[0037] The first catalyst 5 is embodied here as a heating catalyst and comprises an electric heating device 50 with an electrical connection 51. Preferably, the first catalyst 5 has the same diameter as the second catalyst 7. Alternatively, the first catalyst 5 can have a slightly larger diameter than the second catalyst 7.

[0038] From a functional perspective, the electric heating device 50 forms an electrical ignition source in the main exhaust gas flow of the exhaust system 1 and can be designed, for example, as a heating disk. In the present case, the electric heating device 50 is integrated into the first catalytic converter 5, so that from a functional perspective, the latter forms a heating catalytic converter. The electric heating device 50, designed in particular as a heating disk, can alternatively also be arranged outside the first catalytic converter 5, in front of the latter. Alternatively, an electric glow device or glow plug, for example, can also be used as the electrical ignition source.

[0039] By means of the fuel injector 8, a defined fuel injection can take place during operation into the exhaust line section 4 near an inlet of the first catalytic converter 5. This ensures that the air-fuel mixture in this area becomes locally rich, so that the following applies locally to the combustion air ratio: λ < 1. Furthermore, a stoichiometric amount of air matching this supplied amount of fuel is supplied via the air inlet 40, so that overall a stoichiometric exhaust gas with a combustion air ratio λ = 1 is again produced. After the appropriate mixture preparation, the air-fuel mixture supplied to the first catalytic converter 5 is ignited / combusted in an ignition area 9 by means of the electric heating device 50 within the first catalytic converter 5.

[0040] With the aid of the method presented here, parts of the exhaust system 1 are heated in such a way that a first part of the temperature increase is supplied directly via the electrical energy to operate the electrical heating device 50 of the first catalyst 5, and a second part of the temperature increase is added via the exothermic combustion of the air-fuel mixture within the first catalyst 5. The internal combustion engine 2 is constantly operated with a combustion air ratio λ = 1 (stoichiometric ratio).

[0041] An advantage of the method described here is that rapid heating of parts of the exhaust system 1 can be achieved without overloading any of the available energy supply paths. Overall, the air-fuel mixture remains at a global stoichiometric ratio (combustion air ratio λ = 1), as is considered necessary for future exhaust emission standards.

[0042] An on-board diagnosis of the method described here can preferably be carried out using existing sensor means with new functionalities, but without additional sensors.

[0043] Further advantages include, for example, a smaller installation space requirement and lower costs compared to a stand-alone burner system in a secondary flow of the exhaust system 1 for heating.

Claims

[1] Method for operating an exhaust system (1) arranged downstream of an internal combustion engine (2), wherein - the exhaust gas of the internal combustion engine (2), which is operated with a combustion air ratio λ = 1, is fed to the exhaust system (1), - a defined quantity of fuel is injected into an exhaust pipe section (4) of the exhaust system (1) in the vicinity of an ignition device, so that an air-fuel mixture with a combustion air ratio λ < 1 is produced locally, - an amount of air matching the injected fuel quantity is introduced into the exhaust pipe section (4), so that in total a stoichiometric exhaust gas is again produced which has an air-fuel mixture with a combustion air ratio λ = 1, - the air-fuel mixture is ignited by means of the ignition device. [2] Method according to claim 1, characterized bythat the ignition of the air-fuel mixture takes place by means of the ignition device within a first catalyst (5) of the exhaust system (1). [3] Method according to one of claims 1 or 2, characterized by that an electric heating device (50) is used as an ignition device for the air-fuel mixture. [4] Method according to one of claims 1 or 2, characterized by that a glow device or a glow plug is used as an ignition device for the air-fuel mixture. [5] Method according to one of claims 1 or 2, characterized by that a heated spark plug is used as an ignition device for the air-fuel mixture. [6] Exhaust system (1) for carrying out a method according to one of claims 1 to 4, wherein the exhaust system (1) is arranged downstream of an internal combustion engine (2) and has an exhaust pipe section (4) and an ignition device along a flow direction of an exhaust gas of the internal combustion engine (2), wherein the exhaust pipe section (4) comprises at least one fuel injector (8), by means of which fuel can be injected into the exhaust pipe section (4), and at least one air inlet (40), by means of which air can be introduced into the exhaust pipe section (4), wherein - the fuel injector (8) is designed to inject a defined amount of fuel into the exhaust pipe (4) so ​​that the exhaust gas of the internal combustion engine (2) within the exhaust pipe section (4) locally has an air-fuel mixture with a combustion air ratio λ < 1, - an air quantity matching the injected fuel quantity can be introduced into the exhaust pipe section (4) via the air inlet (40), so that in total a stoichiometric exhaust gas is again produced which has an air-fuel mixture with a combustion air ratio λ = 1, and - the ignition device is designed to ignite the air-fuel mixture. [7] Exhaust system (1) according to claim 6, characterized by that the exhaust system (1) has a first catalyst (5) which is arranged downstream of the exhaust pipe section (4). [8] Exhaust system (1) according to claim 7, characterized by that the ignition device is accommodated within the first catalyst (5). [9] Exhaust system (1) according to one of claims 6 to 8, characterized by that the ignition device is designed as an electrical heating device (50). [10] Exhaust system (1) according to one of claims 6 to 8, characterized bythat the ignition device is designed as a glow device or glow plug. [11] Exhaust system (1) according to one of claims 6 to 8, characterized by that the ignition device is designed as a heated spark plug. [12] Exhaust system (1) according to one of claims 7 to 11, characterized by that the exhaust system (1) has a second catalyst (7) and / or a particle filter (6) which is arranged downstream of the first catalyst (5).

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