Method for operating an internal combustion engine with an exhaust system and internal combustion engine with such an exhaust system

Abstract

The invention relates to a method for operating an internal combustion engine (10) with an exhaust system (20) in which an exhaust gas burner (50) is arranged. The exhaust gas burner (50) is connected via a burner channel (66) to an inlet point (68) at which hot burner exhaust gas from the exhaust gas burner (50) can be introduced upstream of at least one exhaust gas aftertreatment component (28, 32, 38) arranged in the exhaust system (20), wherein an exhaust gas flap (46, 69) is arranged downstream of a combustion chamber (52) of the exhaust gas burner (50).The method comprises the following steps: - Closing the exhaust flap (46, 69) to increase the pressure in the combustion chamber (52) of the exhaust burner (50), - Starting the exhaust burner (50), wherein air is supplied to the combustion chamber (52) of the exhaust burner (50) via an air supply (62) and fuel via a fuel supply (54), whereby - an ignitable fuel-air mixture is formed in the combustion chamber (52) of the exhaust burner (50) and ignited by an ignition device (78), - Opening the exhaust flap (46, 69) when stable combustion of the fuel (96) supplied to the combustion chamber (52) of the exhaust burner (50) via the fuel supply (54) is ensured. The invention further relates to an internal combustion engine (10) for carrying out such a method.

Description

The invention relates to a method for operating an internal combustion engine having an exhaust system on which an exhaust gas burner is arranged, and to an internal combustion engine and an exhaust system having an exhaust gas burner of this type for carrying out a method of this type according to the preamble of the independent patent claims.Current exhaust gas legislation, and exhaust gas legislation which becomes ever more stringent in the future, place high demands on the raw engine emissions and the exhaust gas after-treatment of internal combustion engines. The requirements for a further decreasing consumption and the further strengthening of the exhaust gas standards with regard to the permissible nitrogen oxide emissions constitute a challenge for the engine designers. In spark ignition engines, the exhaust gas purification takes place in a known manner via a three-way catalytic converter, as well as further catalytic converters connected upstream and downstream of the three-way catalytic converter. In diesel engines, exhaust gas aftertreatment systems are currently being used which have an oxidation catalyst, a catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst) and a particle filter for the separation of soot particles and optionally further catalysts. Ammonia is preferably used as reducing agent. Because the handling of pure ammonia is complicated and hazardous, vehicles usually use a synthetic, aqueous urea solution which is mixed with the hot exhaust gas stream of the internal combustion engine. The aqueous urea solution is heated by this mixing, wherein the aqueous urea solution releases ammonia in the exhaust gas duct. A commercial aqueous urea solution is generally composed of 32.5% urea and 67.5% water.At low external temperatures, in particular at temperatures below -7° C., in particular below -10° C., the urea-water solution can freeze as a function of the urea content of the urea-water solution. In order to make it possible to meter in the reducing agent, electrical heating elements are known which heat at least a part of the storage container in which the urea-water solution is stored, in order to liquify at least a portion of the urea-water solution and to be able to meter it into the exhaust system.Furthermore, particularly at low external temperatures, there is the challenge of heating the exhaust gas aftertreatment components, in particular a catalyst for selective, catalytic reduction of nitrogen oxides, to a light-off temperature as close as possible to a so-called light-off temperature immediately after a start of the internal combustion engine, in order to enable efficient conversion of the pollutants in the exhaust gas stream of the internal combustion engine. In order to speed up the heating of the exhaust gas aftertreatment components, exhaust gas burners are known which introduce a hot burner exhaust gas into the exhaust system in order to speed up the heating of the exhaust gas aftertreatment components.In solutions known from the prior art, there is the problem that the time period from activation of the exhaust gas burner to ignition of the first fuel in the exhaust gas burner is too long and the time period for heating the exhaust gas after-treatment is extended by this time period for the burner start.It has also been found that exhaust gas burners are susceptible to unfavourable boundary conditions for initial ignition during a cold start of the internal combustion engine. This can lead to an increase in emissions, in particular of unburned hydrocarbons, if the fuel injected into the combustion chamber of the exhaust gas burner cannot be ignited or cannot be completely ignited and the fuel reaches the exhaust system of the internal combustion engine without being burnt.DE 10 2008 032 604 A1 discloses a method for setting a state of an exhaust gas flow of an internal combustion engine of a motor vehicle. The internal combustion engine is coupled to an exhaust system, on which an exhaust gas burner is arranged, via which additional fuel can be burned and the hot exhaust gas of the exhaust gas burner can be introduced into the exhaust system of the internal combustion engine at a junction point. In order to make possible an improved setting of the state, a branch-off of a secondary air mass flow at a branch-off point downstream of the compressed air source into the burner for supplying the burner with combustion air and a raising or setting of a pressure gradient from the branch-off point to the junction point are provided.DE 10 2018 009 400 A1 describes an internal combustion engine for a motor vehicle having an exhaust tract through which exhaust gas from the internal combustion engine can flow, and having a burner which is arranged in the exhaust tract and has a combustion chamber in which a fuel is burned by means of the burner in order to heat the exhaust gas, forming an open flame. The exhaust tract has an exhaust pipe through which the exhaust gas can flow, in which the combustion chamber through which the exhaust gas flowing through the exhaust pipe can flow is arranged. The exhaust tract further has a flap, by means of which a first quantity of exhaust gas flowing through the exhaust pipe and a second quantity of exhaust gas bypassing the combustion chamber can be adjusted as a function of a load and a rotational speed of the internal combustion engine.DE 10 2020 126 714 A1 discloses an exhaust gas aftertreatment system for an internal combustion engine, which comprises an exhaust system having an exhaust gas duct in which a turbine of an exhaust gas turbocharger is arranged in the flow direction of an exhaust gas flow of the internal combustion engine through the exhaust gas system, a first exhaust gas aftertreatment component is arranged downstream of the turbine and at least one further exhaust gas aftertreatment component is arranged downstream of the first exhaust gas aftertreatment component. It is provided that downstream of the first exhaust gas aftertreatment component and upstream of at least one further exhaust gas aftertreatment component, a first exhaust gas recirculation line of a low-pressure exhaust gas recirculation branches off from the exhaust gas channel. In this first exhaust gas recirculation line, an exhaust gas burner is arranged in the flow direction of a recirculated exhaust gas flow of the internal combustion engine, and a heat exchanger is arranged downstream of the exhaust gas burner. A coolant circuit of the internal combustion engine is fluidically connected to the heat exchanger.DE 10 2019 108 008 A1 discloses an exhaust gas aftertreatment system for an internal combustion engine, which exhaust gas aftertreatment system is connected by its outlet to an exhaust system of the exhaust gas aftertreatment system. The exhaust system comprises an exhaust gas duct in which a turbine of an exhaust gas turbocharger and downstream of the turbine an oxidation catalytic converter or a NOx storage catalytic converter are arranged. Downstream of the oxidation catalytic converter or the NOx storage catalytic converter, a particle filter with a coating for the selective, catalytic reduction of nitrogen oxides is arranged. A second SCR catalyst is arranged downstream of the particle filter. In this case, the exhaust system has a branch downstream of the particle filter, at which branch a low-pressure exhaust gas recirculation branch off from the exhaust gas duct.The object of the invention is to improve the starting behavior of an exhaust gas burner on an exhaust system of an internal combustion engine and at least partially overcome the disadvantages known from the prior art.The object is achieved by a method for operating an internal combustion engine having an exhaust system on which an exhaust gas burner is arranged. In this case, the exhaust gas burner is connected via a burner duct to an introduction point at which a hot burner exhaust gas of the exhaust gas burner can be introduced into the exhaust system upstream of at least one exhaust gas aftertreatment component arranged in the exhaust system, wherein an exhaust flap is arranged downstream of a combustion chamber of the exhaust gas burner. The method comprises the following steps:closing the exhaust flap in order to increase a pressure in the combustion chamber of the exhaust gas burner,starting the exhaust gas burner, wherein air is supplied to the combustion chamber of the exhaust gas burner by an air supply and fuel is supplied by a fuel supply, whereinan ignitable fuel-air mixture is formed in the combustion chamber of the exhaust gas burner and ignited by an ignition device,opening the exhaust flap when stable combustion of the fuel supplied by the fuel supply to the combustion chamber of the exhaust burner is ensured.In this context, an internal combustion engine is understood to mean an engine which, by combustion of a fuel, converts the chemical energy of the fuel at least proportionally into kinematic energy, which can be used in particular for driving a motor vehicle or a working machine. An exhaust system is understood to mean a system which conducts the exhaust gases of the internal combustion engine which are produced during the combustion of the fuel, preferably by post-treatment of the exhaust gases in the exhaust system from an outlet of the internal combustion engine to a final pipe at which the (purified) exhaust gas is emitted to the environment. An exhaust gas burner is understood to mean a device which, independently of the internal combustion engine, is configured by combustion of a fuel to supply a hot burner exhaust gas to the exhaust system in order to enable heating of the exhaust gas aftertreatment components in the exhaust system independently of heating by the exhaust gas flow of the internal combustion engine. An exhaust gas aftertreatment component is understood to mean a component in the exhaust system which stores harmful, limited exhaust gas components and / or converts them into unlimited, harmless or at least less harmful exhaust gas components. In particular, but not in conclusion, the exhaust gas aftertreatment component can be an oxidation catalytic converter, a storage catalytic converter, in particular a NO x- storage catalytic converter, a three-way catalytic converter, a particle filter, a SCR catalytic converter, an ammonia blocking catalytic converter or a NO x- adsorber.A burner duct is understood to mean a duct which connects a combustion chamber of the exhaust gas burner to the exhaust gas duct of the internal combustion engine and introduces the exhaust gases of the exhaust gas burner into the exhaust gas duct of the internal combustion engine at an introduction point. An exhaust flap is to be understood as a flap arranged in the exhaust system and / or in the burner channel, with which flap the free cross section of the exhaust gas channel and / or of the burner channel can be blocked at least partially in order to increase the exhaust gas back pressure and in particular to return a partial flow of the exhaust gas via exhaust gas recirculation into an intake tract of the internal combustion engine.An air supply is understood to mean a system which supplies fresh air to the combustion chamber of the exhaust gas burner. Such an air supply can comprise in particular a blower, also referred to as secondary air blower. As an alternative to a blower, other delivery elements, in particular pumps, are also known, which supply the combustion chamber with fresh air. A fuel supply is understood to mean a system which delivers fuel to the combustion chamber of the exhaust gas burner and injects it into the air supply of the exhaust gas burner or preferably directly into the combustion chamber of the exhaust gas burner.Stable combustion in this context is understood to mean combustion which is substantially insensitive to disturbance variables, in particular to pressure fluctuations or fluctuations in the flow speed of the exhaust gas flow in the exhaust system and is not endangered by these in such a way that there is a risk of undesired extinction of the exhaust gas burner. In this context, a fuel is understood to mean a liquid or gaseous fuel, the combustion of which converts chemical energy into heat. Such a fuel can be, in particular, diesel, gasoline, oil, ethanol, natural gas, biogas, hydrogen or a synthetic fuel.By closing the exhaust flap, the pressure and flow conditions in the combustion chamber of the exhaust gas burner can be influenced, which has proven particularly favorable, in particular at a start of the burner, in order to prevent misfires and an associated entry of unburned fuel into the exhaust system. The aim of the method is to influence the pressure conditions in the combustion chamber of the exhaust gas burner in a targeted manner and thus to improve the start of the burner. An increased pressure in the combustion chamber of the exhaust gas burner also improves the mixture preparation during the injection of fuel into the combustion chamber, as a result of which ignition of the fuel-air mixture is facilitated.By subsequently opening the exhaust flap, the flow conditions in the combustion chamber, the burner duct and / or the exhaust tract can be improved in order to achieve the best possible mixing of the hot burner exhaust gases with the exhaust gas flow of the internal combustion engine and / or the most uniform possible inflow of the exhaust gas aftertreatment components with the hot burner exhaust gas of the exhaust gas burner. Furthermore, by closing the exhaust flap, the air-fuel ratio in the combustion chamber can be influenced in a targeted manner and without manipulation of the injection device. Furthermore, the increased pressure enables a larger fuel quantity to be injected without critical side effects such as wall wetting of the combustion chamber of the exhaust gas burner, as a result of which a problem with the smallest quantity capability of the injection system for the exhaust gas burner is solved or at least significantly alleviated.The features listed in the dependent claims allow advantageous improvements and further developments of the method for operating an internal combustion engine specified in the independent claim.In a preferred embodiment of the method, it is provided that the opening of the exhaust flap takes place in order to generate a relief effect and / or turbulence effect in the combustion chamber of the exhaust gas burner, in the burner channel and / or in the exhaust gas channel, and in order to achieve uniform impingement of the hot burner exhaust gas of the exhaust gas burner on the exhaust gas aftertreatment component(s) arranged downstream of the introduction point.In this context, a "relief effect" is understood to mean a local, possibly only brief, reduction in the pressure or a local pressure drop in the exhaust system, as a result of which a volume flow is forced locally. This facilitates the vaporization of the fuel and the break-up of fuel droplets in the combustion chamber of the exhaust gas burner. The pressure drop generates an increased flow velocity in the exhaust system, which suitably leads to turbulence.A turbulence effect is to be understood as meaning the introduction of (local) turbulences and, associated therewith, kinetic energy of the turbulence (TKE) in the exhaust system and / or the combustion chamber of the exhaust gas burner. This turbulence helps the fuel break-up, the fuel evaporation and the mixing of the hot burner exhaust gases with the exhaust gas flow of the internal combustion engine and thus an equal distribution of the heat introduced by the hot burner exhaust gas of the exhaust gas burner over the cross section of the exhaust system, in particular over a cross section of an exhaust gas aftertreatment component arranged in the exhaust system.In a further preferred embodiment of the method, it is provided that a further closing of the exhaust flap is provided after the opening of the exhaust flap in order to raise the pressure in the combustion chamber of the exhaust burner again. By means of the renewed closure, the pressure in the combustion chamber can be raised again, whereby in particular the atomization of the fuel injected into the combustion chamber and, connected therewith, the mixture formation of an ignitable fuel-air mixture in the combustion chamber is improved.In an advantageous embodiment of the method, it is provided that a position of the exhaust flap is dynamically changed during the method in order to control the pressure in the combustion chamber and / or the flow conditions in the combustion chamber. As a result, the control possibilities are further improved, so that the method can be adapted with regard to the optimum flow and pressure conditions at the current time. This allows a reliable burner start and heating of the exhaust gas aftertreatment components to be further improved.In a further advantageous embodiment of the method, it is provided that a position of the exhaust flap is transferred after closing into a defined opened position and this position is held statically. This embodiment of the method enables a further improvement of the flow conditions with minimal effort for the actuation of the exhaust flap.According to a preferred embodiment of the method, it is provided that a position of the exhaust flap is changed depending on an ambient pressure. By detecting the ambient pressure, an additional influence on the pressure in the combustion chamber of the exhaust gas burner can be detected and the method can be adapted to this additional parameter. In this case, in particular a reduction in the air pressure, which is dependent on the geodetic height, can be compensated at least partially by closing the exhaust flap.Alternatively or additionally, it is advantageously provided that a position of the exhaust flap is changed depending on an ambient temperature. As the ambient temperature rises, the vaporization of the fuel into the combustion chamber is facilitated, so that less additional pressure is required in order to achieve a sufficient mixture preparation in the combustion chamber.In addition, a fuel quality of the fuel injected into the combustion chamber of the exhaust burner may be analyzed and taken into account as an additional parameter in the position of the exhaust flap. This can be effected in particular with regard to an evaporation temperature of the fuel, but also with regard to other fuel parameters of the fuel.In an advantageous embodiment of the method, it is provided that a position of the exhaust flap is changed for initiating a shut-off process of the exhaust burner. In this case, the exhaust flap can be used to ensure substantially complete combustion of the fuel located in the combustion chamber of the exhaust burner when the burner is shut down, in particular when the fuel supply to the burner is shut down, and thus to prevent an increase in unburned hydrocarbons in the exhaust system of the internal combustion engine.A further partial aspect of the invention relates to an internal combustion engine having an exhaust system on which an exhaust gas burner is arranged. In this case, the exhaust gas burner is connected via a burner duct to an introduction point on an exhaust gas duct of the exhaust system, at which point a hot burner exhaust gas of the exhaust gas burner can be introduced into the exhaust system upstream of at least one exhaust gas aftertreatment component arranged in the exhaust system. An exhaust flap is arranged downstream of a combustion chamber of the exhaust gas burner. The internal combustion engine comprises a control unit which is configured to execute a method for operating the internal combustion engine described in the preceding paragraphs, in particular if a computer program code stored in the control unit is executed by a computing unit of the control unit.In such an internal combustion engine, the exhaust gas burner can be started, in particular in the event of a cold start of the internal combustion engine, without additional measures and additional internals in the exhaust gas burner and / or in the exhaust system. In particular, an already present exhaust flap can be used for the method according to the invention for controlling low-pressure exhaust gas recirculation, so that the starting process of an exhaust gas burner can be stabilized and improved without cost-intensive multipartys.In a preferred embodiment of the invention, it is provided that the exhaust flap is arranged in the exhaust system in order to control an exhaust gas recirculation via an exhaust gas recirculation channel, in particular an exhaust gas recirculation channel of a low-pressure exhaust gas recirculation of the internal combustion engine. Such an exhaust flap which is already present in any case can be used to carry out a method according to the invention, as a result of which the method can be realized only by increased outlay in terms of the control of the exhaust flap and does not require additional components.Alternatively or additionally, an exhaust flap is provided, which is arranged in the burner duct, which connects the combustion chamber of the exhaust burner to the introduction point on the exhaust duct of the exhaust system. By means of a flap in the burner channel, efficient stabilization of the exhaust gas burner in the starting phase can likewise take place. Furthermore, a shorter control path can provide a more rapid control of the pressure in the combustion chamber of the exhaust gas burner. However, this requires the installation of an additional exhaust flap, which is associated with additional costs and additional assembly effort.The various embodiments of the invention mentioned in this application can be combined with one another with advantage unless stated otherwise in the individual case.The invention is explained below in exemplary embodiments with reference to the associated drawings. The following are shown: FIG. 1 shows a preferred exemplary embodiment of an internal combustion engine with an exhaust system on which an exhaust gas burner is arranged, FIG. 2 shows a further exemplary embodiment of an internal combustion engine having an exhaust system on which an exhaust gas burner is arranged, FIG. 3 shows a further exemplary embodiment of an internal combustion engine having an exhaust system on which an exhaust gas burner is arranged, and FIG. 4 shows a flow chart for a method according to the invention for operating an internal combustion engine having an exhaust system.FIG. 1 shows an internal combustion engine 10 having a plurality of combustion chambers 12, wherein a fuel injector 14 for injecting fuel 96 into the respective combustion chamber 12 is arranged on each combustion chamber 12. The internal combustion engine 10 has an inlet 16, by means of which the internal combustion engine 10 can be connected to an air supply system, not shown. The internal combustion engine 10 further has an outlet 18, by means of which the internal combustion engine 10 can be connected to an exhaust system 20. The internal combustion engine 10 includes an engine block and at least one cylinder head.For the fuel supply of the fuel injectors 14, a high-pressure fuel pump and a high-pressure fuel accumulator are provided, which is supplied with fuel 96 by the high-pressure fuel pump.The exhaust system 20 comprises an exhaust manifold, which supplies the exhaust gases of a plurality of combustion chambers 12 to a common exhaust gas duct 22. In the exhaust gas duct 22, downstream of the exhaust manifold, a turbine 26 of an exhaust gas turbocharger 24, downstream of the turbine 26 of the exhaust gas turbocharger 24, a first exhaust gas aftertreatment component 28, in particular an oxidation catalytic converter 30, and downstream of the first exhaust gas aftertreatment component 28, at least one further exhaust gas aftertreatment component 32, 38 are arranged. In the exemplary embodiment shown in FIG. 1, a second exhaust gas aftertreatment component 32 for selective, catalytic reduction of nitrogen oxides in the form of a particle filter 34 having an SCR coating 36 for selective catalytic reduction of nitrogen oxides (SCR) is arranged downstream of the oxidation catalytic converter 30, and a third exhaust gas aftertreatment component 38 in the form of an SCR catalytic converter 40 is arranged downstream of the particle filter 34. Downstream of the oxidation catalytic converter 30 and upstream of the particle filter 34 with the SCR coating 36, a first metering element 42 is arranged for metering in a reducing agent, in particular aqueous urea solution. Downstream of the particulate filter 34 and upstream of the SCR catalytic converter 40, a second metering element 44 is arranged.Downstream of the particulate filter 34 with the SCR coating 36 and upstream of the SCR catalytic converter 40, a branch 48 is provided, at which a EGR duct 72 of a low-pressure EGR 70 branches off from the exhaust duct 22 of the exhaust system 20 and connects the exhaust duct 22 to an intake tract, not shown, of the internal combustion engine 10. The low-pressure exhaust gas recirculation 70 further comprises an exhaust gas recirculation cooler 76 arranged in the exhaust gas recirculation channel 72 and an exhaust gas recirculation valve 74.In the exhaust system 20, an exhaust flap 46 is arranged downstream of the branch 48 of the exhaust gas recirculation duct 72, with which exhaust flap a cross section of the exhaust gas duct 22 can be reduced and therefore a dynamic pressure can be generated in order to direct the exhaust gas flow at least partially through the low-pressure exhaust gas recirculation 70 back into the intake tract of the internal combustion engine 10. The exhaust flap 46 may be actuated by an actuator 94 that adjusts the exhaust flap 46 in discrete steps or continuously and allows dynamic or static adjustment.Furthermore, an exhaust gas burner 50 having a combustion chamber 52, a fuel supply 54 and an air supply 62 is arranged in the exhaust system 20 upstream of at least one of the exhaust gas aftertreatment components 28, 32, 38 in order to be able to heat the exhaust gas aftertreatment components 28, 32, 38 substantially independently of the operation of the internal combustion engine 10. The combustion chamber 52 of the exhaust gas burner 50 is connected via a burner duct 66 to an introduction point 68 on the exhaust gas duct 22 of the exhaust gas system 20. An injection nozzle 56 is provided on the combustion chamber 52, which permits injection of a fuel supplied by the fuel supply 54 into the combustion chamber 52 of the exhaust gas burner 50. The injector 56 may be supported by a nozzle holder 58 to ideally position the injector relative to the combustion chamber 52 of the exhaust burner 50.The exhaust gas burner 50 further comprises an air supply 62 which supplies fresh air to the combustion chamber 52 via an air supply duct 64. Furthermore, an ignition device 78 is provided in the combustion chamber 52 in order to ignite an ignitable fuel-air mixture in the combustion chamber 52 of the exhaust gas burner 50. Additionally, a swirl or turbulence generator 60 may be provided in or on the combustion chamber 52 to influence the flow conditions of the fresh air supplied to the combustion chamber 52 or of the hot exhaust gas stream exiting the combustion chamber 52.Furthermore, various sensors 90, 92, in particular a pressure sensor 90 and a temperature sensor 92, are arranged on the exhaust system 20 in order to detect an exhaust gas temperature and a pressure in the exhaust gas duct 22 of the exhaust system 20. Furthermore, a further pressure sensor 90 and a further temperature sensor 92 can be provided in order to detect an ambient temperature and / or an ambient pressure of the internal combustion engine 10.The internal combustion engine 10 is operatively connected to a control unit 80 which is configured to control the internal combustion engine 10 and the components of the exhaust system 20 and the exhaust gas burner 50. The control device 80 comprises a storage unit 82 and a computing unit 84. Stored in the storage unit 82 is a computer program code 86, which, when executed by the computing unit 84, executes a method according to the invention for operating an internal combustion engine 10.FIG. 2 shows an alternative exemplary embodiment of an internal combustion engine 10 having an exhaust system 20. With substantially the same construction as embodied in FIG. 1, in this exemplary embodiment an exhaust flap 69 is alternatively arranged in the burner duct 66, which connects the combustion chamber 52 of the exhaust burner 50 to the introduction point 68 for the hot burner exhaust gas into the exhaust duct 22 of the exhaust system. Such an embodiment is suitable in particular for internal combustion engines 10 which have no exhaust gas recirculation or at least no low-pressure exhaust gas recirculation 70 and therefore have no exhaust flap 46 in the exhaust gas duct 22 of the exhaust system 20.FIG. 3 shows a further alternative exemplary embodiment of an internal combustion engine 10 having an exhaust system 20. With a substantially identical construction as embodied in FIG. 1, two exhaust flaps 46, 69 are provided in this exemplary embodiment, namely a first exhaust flap 46 in the exhaust gas duct 22 downstream of the branch 48 of the exhaust gas recirculation duct 72 and a second exhaust flap 69 in the burner duct 66, which connects the combustion chamber 52 of the exhaust gas burner 50 to the introduction point 68 for the hot burner exhaust gas into the exhaust gas duct 22 of the exhaust gas system 20. The two exhaust flaps 46, 69 are actuated by two actuators 94 and can thus be adjusted independently of one another in order to enable even better control of the pressure and flow conditions in the combustion chamber 52 of the exhaust gas burner 50.FIG. 4 shows a flow diagram for a method according to the invention for operating an internal combustion engine 10 having an exhaust system 20 and an exhaust gas burner 50 arranged on the exhaust system 20. In a first method step <100>, an exhaust flap 46, 69 is closed downstream of the combustion chamber 52 of the exhaust burner 50.In a subsequent method step <110>, an air supply 62 to combustion chamber 52 and a fuel supply 54 to combustion chamber 52 are activated and air and fuel 96 are accordingly supplied to combustion chamber 52 in order to produce an ignitable fuel-air mixture in combustion chamber 52.In a method step <120>, this fuel-air mixture is ignited and thus the exhaust gas burner 50 is started.In a method step <130>, the exhaust flap 46, 69 is opened again, as a result of which the exhaust gas back pressure in the exhaust system 20 is lowered. Furthermore, by opening the exhaust flap 46, 69, a positive effect can be achieved by generating a turbulence which ensures improved mixing of the hot exhaust gas flow of the exhaust gas burner 50 and / or a more uniform inflow of the hot burner exhaust gas onto an exhaust gas aftertreatment component 28, 32, 38 arranged in the exhaust system 20.In a further method step <140>, a further starting sequence of the exhaust gas burner 50 can be initiated, wherein the exhaust flap 46, 69 is closed again in order to increase the pressure in the combustion chamber 52 of the exhaust gas burner 50.In a method step <150>, the actual burner operation of the exhaust gas burner 50 then takes place, wherein a hot burner exhaust gas of the exhaust gas burner 50 is introduced into the exhaust gas duct 22 of the exhaust system 20 at an introduction point 68, in order to heat up the exhaust gas aftertreatment components 28, 32, 38 in addition to the exhaust gas flow of the internal combustion engine 10 and thus more quickly to reach an operating temperature of the exhaust gas aftertreatment component 28, 32, 38 at which an efficient exhaust gas aftertreatment of the exhaust gases of the internal combustion engine 10 is possible.In a method step <160>, the exhaust gas burner 50 is switched off when all the exhaust gas aftertreatment components 28, 32, 38 have reached their operating temperature and an efficient conversion of the limited exhaust gas component into harmless and / or unlimited exhaust gas components is ensured. In this case, the exhaust flap 46, 69 can be actuated again by the actuator 94 in order to shut off the exhaust burner 50, in order to assist the shut-off process.List of reference characters10 Internal combustion engine 12 combustion chamber 14 fuel injector 16 inlet 18 outlet 20 exhaust system 22 exhaust gas duct 24 exhaust gas turbocharger 26 turbine 28 first exhaust gas aftertreatment component 30 oxidation catalytic converter 32 second exhaust gas aftertreatment component 34 particle filter 36 SCR coating 38 third exhaust gas aftertreatment component 40 SCR catalytic converter 42 first metering element 44 second metering element 46 exhaust flap 48 branch 50 exhaust gas burner 52 combustion chamber 54 fuel supply 56 injection nozzle 58 nozzle holder 60 swirl or turbulence generator 62 air supply 64 air supply duct 66 burner duct 68 introduction point 69 exhaust flap 70 low-pressure exhaust gas recirculation 72 exhaust gas recirculation duct 74 exhaust gas recirculation valve 76 exhaust gas recirculation cooler 78 ignition device 80 control device 82 storage unit 84 arithmetic unit 86 computer program code 90 pressure sensor 92 temperature sensor 94 actuator 96 fuel

Claims

Method for operating an internal combustion engine (10) having an exhaust system (20) on which an exhaust gas burner (50) is arranged, wherein the exhaust gas burner (50) is connected via a burner duct (66) to an introduction point (68) at which a hot burner exhaust gas of the exhaust gas burner (50) can be introduced into the exhaust system (20) upstream of at least one exhaust gas aftertreatment component (28, 32, 38) arranged in the exhaust system (20), wherein an exhaust flap (46, 69) is arranged downstream of a combustion chamber (52) of the exhaust gas burner (50), comprising the following steps: - closing the exhaust flap (46, 69) in order to increase a pressure in the combustion chamber (52) of the exhaust gas burner (50), - starting the exhaust gas burner (50), wherein air is supplied to the combustion chamber (52) of the exhaust gas burner (50) by an air supply (62) and fuel is supplied by a fuel supply (54), wherein - an ignitable fuel-air mixture is formed in the combustion chamber (52) of the exhaust gas burner (50) and ignited by an ignition device (78), - opening the exhaust flap (46, 69) if stable combustion of the fuel (96) supplied by the fuel supply (54) to the combustion chamber (52) of the exhaust gas burner (50) is ensured.Method according to claim 1, wherein the opening of the exhaust flap (46, 69) takes place in order to generate a relief effect and / or a turbulence effect in the combustion chamber (52) of the exhaust burner (50), in the burner duct (66) and / or in the exhaust duct (22) in order to achieve uniform impingement of the hot burner exhaust gas of the exhaust burner (50) on the exhaust gas aftertreatment components (28, 32, 38) arranged downstream of the introduction point (68).The method of claim 1 or 2, wherein the method comprises further closing the exhaust flap (46, 69) after opening the exhaust flap (46, 69) to again raise the pressure in the combustion chamber (52).Method according to one of claims 1 to 3, wherein a position of the exhaust flap (46, 69) is dynamically changed during the method in order to control the pressure in the combustion chamber (52) of the exhaust burner (50) and / or the flow conditions in the combustion chamber (52) of the exhaust burner (50).Method according to one of Claims 1 to 4, wherein a position of the exhaust flap (46, 69) is transferred to a definedly open position after closing.Method according to one of Claims 1 to 5, wherein a position of the exhaust flap (46, 69) is changed as a function of an ambient pressure and / or an ambient temperature.Method according to one of Claims 1 to 6, wherein a position of the exhaust flap (46, 69) is changed in order to initiate a switching-off operation of the exhaust burner (50).Internal combustion engine (10) having an exhaust system (20) on which an exhaust gas burner (50) is arranged, wherein the exhaust gas burner (50) is connected via a burner duct (66) to an introduction point (68) at which a hot burner exhaust gas of the exhaust gas burner (50) can be introduced into the exhaust system (20) upstream of at least one exhaust gas aftertreatment component (28, 32, 38) arranged in the exhaust system (20), wherein an exhaust flap (46, 69) is arranged downstream of a combustion chamber (52) of the exhaust gas burner (50), and having a control unit (80) which is configured to carry out a method according to one of Claims 1 to 7.The internal combustion engine (10) of claim 8, wherein the exhaust flap (46) is disposed in the exhaust system (20) to control exhaust gas recirculation via an exhaust gas recirculation passage (72).Internal combustion engine (10) according to Claim 8 or 9, wherein the exhaust flap (69) is arranged in the burner duct (66) which connects the combustion chamber (52) of the exhaust burner (50) to the introduction point (68).

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