Exhaust system for an internal combustion engine of a motor vehicle as well as motor vehicle

Abstract

The invention relates to an exhaust system (10) for an internal combustion engine (12) of a motor vehicle, comprising a burner (48) supplied with air and fuel, by means of which a mixture comprising air and fuel is to be combusted, an air duct (58) through which air flows, and an air pump (56) arranged in the air duct (58), by means of which the air can be conveyed through the air duct (58) and conveyed to the burner (48) in order to supply the burner (48) with air. A recirculating air duct (68) is provided, which is fluidically connected to the air duct (58) at a first connection point (V2) arranged downstream of the air pump (56) and at a second connection point (V3) arranged upstream of the air pump (56).

Description

The invention relates to an exhaust system for an internal combustion engine of a motor vehicle according to the preamble of claim 1. Furthermore, the invention relates to a motor vehicle, in particular a motor car. DE 10 2019 008 965 A1 discloses an exhaust system for an internal combustion engine, comprising a nitrogen oxide storage catalyst through which exhaust gas from the internal combustion engine flows, and a burner supplied with air and fuel, by means of which a fuel-air mixture containing the fuel and air is to be combusted. Furthermore, DE 10 2021 001 580 A1 discloses a burner for an exhaust tract through which exhaust gas from an internal combustion engine of a motor vehicle flows. DE 10 2010 037 538 A1 discloses a device for supplying air to a burner with a compressor driven by an electric motor, the burner having its outlet facing an exhaust system of an internal combustion engine in the direction of exhaust gas flow upstream of a cleaning unit switched on in the exhaust system. The object of the present invention is to create an exhaust system for an internal combustion engine of a motor vehicle and a motor vehicle with such an exhaust system, so that a burner of the exhaust system can be operated particularly advantageously. This problem is solved by an exhaust system with the features of claim 1 and by a motor vehicle with the features of claim 7. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims. A first aspect of the invention relates to an exhaust system for an internal combustion engine, also referred to as a motor or combustion engine, and designed, for example, as a reciprocating engine, i.e., a piston engine, of a motor vehicle, also simply referred to as a vehicle. This means that the motor vehicle, in its fully manufactured state, has the internal combustion engine and can be driven by means of the internal combustion engine. The internal combustion engine, in the fully manufactured state of the motor vehicle, includes the exhaust system. The exhaust system is permeable to exhaust gases from the internal combustion engine. The motor vehicle is designed, for example, as a car, in particular as a passenger car, or as a commercial vehicle.During operation of the internal combustion engine, combustion processes take place within the engine, particularly in at least one or more combustion chambers, resulting in the exhaust gas, also known as engine exhaust. The engine exhaust can flow out of the respective combustion chamber and into the exhaust system, also called the exhaust tract, and through it. The exhaust system includes a burner, which can be supplied with fuel, particularly liquid fuel, and with air, also known as burner air. Unless otherwise specified, the term "air" refers to burner air. For example, the exhaust system includes at least one additional component besides the burner, such as an exhaust aftertreatment element, for treating the exhaust gas.The exhaust aftertreatment element is or includes, for example, a catalyst, in particular an SCR catalyst, wherein, for example, selective catalytic reduction (SCR) can be catalytically supported and / or effected by means of the SCR catalyst, so that, for example, the SCR catalyst is catalytically active for the SCR process. In selective catalytic reduction, any nitrogen oxides contained in the engine exhaust are at least partially removed from the engine exhaust by reacting the nitrogen oxides with ammonia to form nitrogen and water. The ammonia is provided, for example, by a reducing agent, which is particularly liquid and could, for example, be an aqueous urea solution. Furthermore, it is conceivable that the exhaust aftertreatment element is or includes a particulate filter. In particular, the particulate filter is a diesel particulate filter (DPF).The particulate filter can be used to filter out any particles, especially soot particles, that may be contained in the exhaust gas. A burner is used to combust a mixture, also known as a burner mixture, which comprises the burner air and the fuel. For this purpose, the burner has, for example, a combustion chamber, also referred to as the main combustion chamber, in which the burner mixture can be combusted, in particular ignited and burned. The combustion chamber is specifically bounded by a chamber element, particularly a solid body, and especially by an inner circumferential surface of the chamber element. The combustion of the burner mixture, which takes place particularly in the combustion chamber, produces burner exhaust gas, also known as burner exhaust gas.The burner exhaust gas can, for example, flow out of the burner, particularly from the combustion chamber, and into an exhaust duct of the exhaust system through which the engine exhaust gas flows, especially at an inlet point that is located, for example, upstream of the aforementioned component in the direction of flow of the engine exhaust gas through the exhaust system, i.e., the exhaust duct. Thus, the component is permeable to the burner exhaust gas. For example, the burner exhaust gas mixes with the engine exhaust gas. Consequently, the burner exhaust gas, especially the burner exhaust gas mixed with the engine exhaust gas, can flow through the component, thereby heating it up.In particular, it is conceivable that the burner exhaust gas can flow out of the combustion chamber and into the exhaust duct, thereby mixing with the engine exhaust gas and / or gas flowing through the exhaust duct, thus heating the engine exhaust gas or the gas. In other words, this can, for example, result in a particularly high temperature of the engine exhaust gas or the gas, also known as the exhaust gas temperature.In particular, the gas can be, for example, air flowing through the exhaust duct, especially while the internal combustion engine is being towed, i.e., when the engine is not firing and therefore not producing exhaust gas. In this case, the gas, especially the air, is forced through the exhaust duct, particularly by the internal combustion engine. The high exhaust gas temperature can heat and / or keep the component warm, as the burner exhaust and, for example, the engine exhaust or the gas flow through the component. Thus, for example, the burner exhaust from the combustion chamber is introduced into the exhaust duct at the aforementioned injection point, and consequently into the engine exhaust or gas flowing through the exhaust duct. The exhaust system includes a supply line through which the combustion air flows to supply the burner. This supply line is also referred to as an air line. The exhaust system also includes an air pump, typically located in addition to the burner and the internal combustion engine. This pump forces the combustion air through the supply line to the burner, thus supplying it with combustion air. For example, the air pump may be an electric pump, which is electrically operated to supply the burner with combustion air, specifically to force the combustion air through the supply line to the burner. To achieve particularly advantageous burner operation, the invention provides that the exhaust system includes a recirculating air line, in particular in addition to the supply line, which is fluidically connected to the supply line at a first connection point and at a second connection point. In the direction of flow of the burner air flowing through the supply line, which flows through the supply line during operation of the air pump and, in particular, also of the burner, the first connection point is arranged downstream of the air pump and preferably upstream of the burner.In the direction of flow of the burner air through the supply line, the second connection point is located upstream of the air pump and thus upstream of the burner, so that the second connection point is located upstream of the first connection point in the direction of flow of the burner air through the supply line. Thus, the connection points are spaced apart from each other in the direction of flow of the burner air through the supply line. Furthermore, in the direction of flow of the burner air through the supply line, the air pump is located between the connection points, that is, upstream of the first connection point and downstream of the second connection point. For example, the air pump is designed to pump the burner air through the supply line and compress it in the process, so that the air pump is also referred to as a compressor or is designed as a compressor.Via the recirculation line, at least a portion of the air flowing through the supply line can be returned from the first connection point to the second connection point, bypassing the air pump. Specifically, at the first connection point, at least a portion of the burner air flowing through the supply line can be diverted from the supply line and introduced into the recirculation line. The portion of burner air diverted from the supply line at the first connection point and introduced into the recirculation line can then flow through the recirculation line and be routed from the first connection point to the second connection point, bypassing the air pump. At the second connection point, the diverted air flowing through the recirculation line can, in particular, flow back into the supply line, bypassing the air pump. The characteristic that the air flowing through the recirculation line can be returned to the second connection point without passing through the air pump, and can then be introduced into the supply line at the second connection point without passing through the air pump, means that the recirculation line and the air flowing through it bypass the air pump. This means that the air flowing through the recirculation line does not pass through the air pump on its way from the first connection point to the second connection point and into the supply line. At the second connection point, the air flowing through the recirculation line can exit the recirculation line and (re)enter the supply line, and then, for example, pass through the air pump again. Because the air flowing through the recirculation line bypasses the air pump, the recirculation line is also referred to as a bypass line. Furthermore, according to the invention, a valve element is provided by means of which the quantity, i.e., in particular a volume and / or mass flow rate, of the air (burner air) flowing through the recirculation line and thus bypassing the air pump can be adjusted. This means, in particular, that the quantity of air flowing through the recirculation line can be set to several different values ​​by means of the valve element, wherein, for example, at least or exactly one of the values ​​is 0, so that the recirculation line is fluidically blocked or can be blocked by means of the valve element. At least or exactly one second value is a value other than zero (0) whose absolute value is greater than 0. Most preferably, several second values ​​are values ​​other than 0, each with an absolute value greater than 0, wherein, in particular, the several second values ​​differ from each other in pairs.This allows the amount of air flowing through the recirculation line to be adjusted, and in particular regulated, to meet specific requirements by means of the valve element, so that a particularly advantageous supply of air to the burner and consequently a particularly advantageous operation of the burner can be achieved. The invention is based in particular on the following findings and considerations: To operate the burner, for example, a control system can be provided, which is implemented, for example, by means of an electronic computing device, also referred to as a control unit, in order to regulate the burner and thus operate it in a controlled manner. Typically, the burner control system is divided into a so-called fuel path and a so-called air path. The fuel path receives quantity information from a lambda signal, which is generated, for example, from an air mass. The quantity information is, or characterizes, for example, the quantity of fuel with which the burner is or has been supplied.The air mass is or characterizes the mass of the burner air with which the burner is or was supplied, whereby the air mass is measured, for example, by means of an air mass meter, in particular a hot-film air mass meter (HFM). The lambda signal is or characterizes, for example, an oxygen content, in particular residual oxygen content, in the burner exhaust gas, whereby the oxygen content is measured, for example, by means of a lambda probe, which can, for example, provide the lambda signal. From the quantity information, an injection rate can then be derived, which is, for example, a quantity of fuel that is used to form the burner mixture or, for example, is introduced into the combustion chamber.In the air path, a requirement, particularly regarding the quantity of burner air, is derived from numerous measured variables, such as pressure and temperature, especially of the burner air, measured by sensors. From these parameters, the quantity of burner air, expressed as a volume or mass flow rate, with which the burner is supplied or to be supplied is determined, or in particular calculated. The quantity of burner air with which the burner is supplied or to be supplied is used, for example, as a control variable for the air pump, i.e., for operating the air pump and, in particular, its electrical power, speed, and control. Thus, the determined quantity of burner air with which the burner is to be supplied is used, for example, to operate the air pump, in particular to regulate or control it. The aforementioned fuel is introduced into the combustion chamber, for example, via an injection valve, to form the burner mixture. The fuel path is highly dynamic and can be operated dynamically. For instance, a control frequency at which the injection valve can be actuated to introduce the fuel into the combustion chamber, and an opening duration of the injection valve, which remains open continuously during this time, allow for advantageous adjustment or setting—that is, variation of the fuel quantity—even under extreme fluctuations and ramps. This can be ensured, for example, by means of a learning function, even over a long service life and operating time of the burner. However, the air path typically behaves differently.The amount of burner air supplied to the burner, also referred to as or designed as air mass flow, depends strongly on the back pressure in the exhaust duct, which is characterized by high momentum dynamics and steep ramps. Furthermore, the characteristic curve of the air pump, such as that of a compressor wheel used to compress the burner air, exhibits extreme nonlinearity when external conditions create an unfavorable relationship between mass flow and back pressure. This forces the efficiency of the air pump to decrease, particularly at the corners of its characteristic curve, making it difficult to operate, and especially to control, the air pump efficiently.If the mass flow rate no longer matches the air pump's rotational speed due to backpressure dynamics, the air pump's operating point shifts to the left of its characteristic curve, and the air mass flow rate abruptly drops to zero. This extreme control challenge can severely limit the reliable operation of the air pump and thus the burner, especially with significant backpressure in the exhaust duct, high dynamic vehicle operation, or operation at high, higher, and extremely high temperatures, where air density and absolute pressure decrease. The aforementioned problems and disadvantages can now be avoided by the invention. Compared to conventional solutions, the invention provides a recirculation line and a valve element, also referred to as a recirculation valve or designed as a recirculation valve. The recirculation line is or comprises a recirculation channel through which air flows, whereby the air flowing through the recirculation channel bypasses the air pump and thus does not flow through it. The recirculation line enables particularly advantageous operation, especially particularly advantageous control, of the air pump and thus of the burner. Flow separation in the air pump, also referred to as stalling or, for example, compressor stall, and especially at the impeller of the air pump, as well as the probability of the air pump falling outside its operating range, can be avoided or significantly minimized.Excessive sensitivity of the air pump or burner operation to altitude and temperature can be avoided, as can excessive sensitivity of the air pump or burner operation to back pressure in the exhaust duct. By using the recirculation line and the valve element, a similarly rapid control dynamic can be achieved for the air path as for the fuel path.The recirculating air line can ensure a stable supply of burner air to the burner with the available volume or mass flow of air and a pressure level on the air pump outlet side, whereby a particularly robust supply of burner air to the burner can be achieved in particular through a storage effect of flow energy in the recirculating air duct or in the air flowing through the recirculating air line, especially with regard to and also in the case of pressure peaks and disturbances in or from the overall system. By means of the valve element, also referred to as or designed as a recirculation valve, the quantity of air flowing through the recirculation line, as well as the pressure, particularly of the air, at an outlet side of the air pump, can be advantageously set, particularly in combination with the rotational speed of the air pump, i.e., the impeller of the air pump. This is defined, for example, as a volume and / or mass flow rate, and can be controlled, particularly independently of the actual quantity of burner air currently required by the burner, defined, for example, as a volume and / or mass flow rate. Thus, burner output control does not require a change in efficiency or the rotational speed of the air pump, but can be set, particularly solely, by a corresponding switching state or position of the valve element. The air pump is a turbomachine, which is typically a very sluggish system. Experience has shown that this sluggishness either leads to drastic operating limits and restrictions in dynamics and power spreads, or the turbomachine must be intelligently augmented with additional components to enable safe operation, particularly control, and an extension of the operating map. The invention makes the latter possible, thus enabling particularly robust and therefore safe operation of the burner. The burner, for example, has at least one channel through which the burner air flows, which is arranged, for instance, upstream of the combustion chamber in the direction of flow of the burner air through the channel. The combustion chamber can be supplied with the burner air flowing through the channel. For example, a swirling flow of the burner air flowing through the channel can be created by means of the channel, so that the burner air exhibits a swirling flow, at least within the combustion chamber. This allows the burner air to be mixed particularly effectively with the fuel, resulting in a particularly advantageous formation of the burner mixture, also referred to as mixture formation or mixture preparation.The channel has, for example, at least or exactly, an outlet opening through which the burner air can flow, and through which the burner air, in particular from the channel, can be discharged and introduced into the combustion chamber. The burner has, for example, a closure element, designed, for example, as a closing flap, which is movable, in particular pivotable, between a closed position and at least one open position, particularly relative to the chamber element and / or relative to the channel and / or relative to the outlet opening. In the closed position, the outlet opening and thus the channel are fluidically separated from the combustion chamber by means of the closure element. In the open position, the closure element releases the outlet opening and the channel, so that in the open position the outlet opening and the channel, i.e., the channel via the outlet opening, are fluidically connected to the combustion chamber.In the closed position, the sealing element prevents engine exhaust from flowing from the exhaust duct through the combustion chamber into the outlet opening and the duct, for example, when the burner is deactivated and therefore not producing any burner exhaust gas, and the sealing element is in the closed position. This prevents components such as soot and / or particles contained in the engine exhaust gas from accumulating or settling in unwanted areas of the burner and thus clogging the outlet opening or the duct excessively. When the burner is started, that is, when it is switched from its deactivated state to its activated state, the locking element is opened, thus moving from the closed position to the open position. In order to be able to adjust the amount of burner air flowing through the recirculation line, and thus the amount of burner air flowing through the recirculation line, particularly advantageously, in one embodiment of the invention it is provided that the valve element is arranged in the recirculation line. Another embodiment is characterized by the fact that the valve element is electrically controllable in order to adjust the amount of air flowing through the recirculation duct. This allows the amount of burner air flowing through the recirculation duct to be adjusted particularly precisely and according to demand, thus enabling particularly advantageous burner operation. Another embodiment is characterized by an electronic computing device, also referred to as a control unit or designed as such, by means of which the valve element can be electrically controlled. The electronic computing device is specifically designed to provide an electrical signal by means of which the valve element can be controlled. The valve element can, for example, receive the electrical signal, thereby enabling it to be electrically controlled. This allows the valve element to be operated, and in particular regulated, as required, so that, for example, the amount of burner air flowing through the recirculating air duct can be adjusted, and in particular regulated, as required. In a further, particularly advantageous embodiment of the invention, the valve element is switchable between a closed state that fluidly blocks the recirculation line and at least one open state that releases the recirculation line. This means that in the closed state, the recirculation line is fluidly blocked by the valve element, so that no air can flow through the recirculation line. In this state, the amount of burner air flowing through the recirculation line is zero, as mentioned above. In the open state, air can flow through the recirculation line, so that in the open state, the amount of air flowing through the recirculation line, or its value, is different from zero, and in particular is greater than zero. To achieve particularly advantageous operation, and especially particularly advantageous control, of the burner, a further embodiment of the invention provides that the valve element is switchable between the closed state and several open states that release the recirculating air duct. These open states are the aforementioned open state as the first open state and several further open states, each differing from the others with respect to the quantity of burner air flowing through the recirculating air duct. This means that the valve element releases the recirculating air duct in the open states, but it is provided that the valve element releases the recirculating air duct to varying degrees or extents in the open states, particularly when considered in pairs.This allows the amount of burner air flowing through the recirculating air duct to be adjusted, and in particular regulated, with particular precision and according to demand, thus enabling particularly advantageous burner operation. A second aspect of the invention relates to a motor vehicle, also referred to simply as a vehicle, preferably a motor car, in particular a passenger car or a commercial vehicle, which has an internal combustion engine by means of which the motor vehicle can be propelled. Furthermore, the motor vehicle, and in particular the internal combustion engine, has an exhaust system through which exhaust gas from the internal combustion engine flows, according to the first aspect of the invention. Advantages and advantageous embodiments of the first aspect of the invention are to be regarded as advantages and advantageous embodiments of the second aspect of the invention, and vice versa. Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and / or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. The drawing shows in: Fig. 1 a schematic representation of an exhaust system for an internal combustion engine of a motor vehicle; Fig. 2 a partial further schematic representation of the exhaust system; and Fig. 3 a schematic sectional view of a burner of the exhaust system. In the figures, identical or functionally equivalent elements are provided with the same reference symbols. Fig. 1 shows a schematic representation of an exhaust system 10 for an internal combustion engine 12, also referred to as a motor, internal combustion engine, or combustion power unit, of a motor vehicle, preferably a car, which is also referred to as a vehicle. This means that the motor vehicle, in its fully manufactured state, has the internal combustion engine 12 and can be driven by means of the internal combustion engine 12. For example, the internal combustion engine 12 is designed as a diesel engine. A tank 14, also referred to as a fuel tank, is associated with the internal combustion engine, in which a fuel, in particular a liquid fuel, is stored or held for operating the internal combustion engine 12 during its combustion operation. The fuel is, for example, diesel fuel, which is also simply referred to as diesel.A low-pressure pump 16 transfers fuel from tank 14 to a high-pressure pump 18. The high-pressure pump 18 pressurizes the fuel and delivers it to injectors 20. Specifically, the high-pressure pump 18 delivers the fuel to a common fuel distribution element, also known as a rail, which is shared by the injectors 20. The high-pressure fuel can be temporarily stored in the fuel distribution element. The high-pressure fuel stored in the fuel distribution element is then distributed to the injectors 20, allowing it to be injected directly into the respective combustion chambers and thus into the respective cylinders 22 of the internal combustion engine 12.Each cylinder 22 partially limits the respective combustion chamber of the internal combustion engine 12. The internal combustion engine 12 has an intake tract 24, also referred to as the intake tract, through which air flows. The air flowing through the intake tract 24 is also called fresh air or combustion air. The fresh air flowing through the intake tract 24 is directed to and into the combustion chambers and thus to the cylinders 22. A fuel-air mixture is thus formed from the fuel and the fresh air, which is ignited in the respective combustion chamber and thus in the respective cylinder 22, in particular by auto-ignition, and subsequently burned. This results in exhaust gas from the internal combustion engine 12, also referred to as engine exhaust. The internal combustion engine 12 has an exhaust tract 26 through which the engine exhaust gas from the combustion chambers flows, which is, for example, a component of the exhaust system 10.The exhaust system 10 is permeable to the engine exhaust gas from the combustion chambers. The respective fuel-air mixture comprises fresh air and fuel. The internal combustion engine 12 also includes a charging device 28, which has at least one exhaust gas turbocharger 30. The exhaust gas turbocharger 30 comprises a compressor 32 arranged in the intake tract 24, by means of which the fresh air flowing through the intake tract 24 can be compressed. The exhaust gas turbocharger 30 also comprises a turbine 34 arranged in the exhaust tract 26 and driven by the engine exhaust gas, by means of which the compressor 32 can be driven, in particular via a shaft of the exhaust gas turbocharger 30. The exhaust system 10 has an exhaust aftertreatment device 36, which may, for example, comprise a nitrogen oxide storage catalyst 38, a particulate filter 40, and an SCR catalyst 42.The nitrogen oxide storage catalyst 38, also referred to as a storage catalyst, storage catalytic converter, or NOx storage catalyst, is designed to capture, retain, and, in particular, store any nitrogen oxides (NOx) contained in the engine exhaust gas. The nitrogen oxide storage catalyst 38, the particulate filter 40, and the SCR catalyst 42 are components of the exhaust system 10. These components are arranged sequentially in the direction of flow of the engine exhaust gas through the exhaust system 10, i.e., in series with one another. The engine exhaust gas can flow through the components. In this context, the components are exhaust aftertreatment elements by means of which the engine exhaust gas is or can be treated. The storage catalyst is arranged upstream of the particulate filter 40 in the direction of flow of the engine exhaust gas through the exhaust system 10, which in turn is arranged upstream of the SCR catalyst 42.The particulate filter 40 is designed, for example, to filter out any particles contained in the exhaust gas, especially soot particles, from the engine exhaust. In particular, if the internal combustion engine 12 is a diesel engine, the particulate filter 40 is designed, for example, as a diesel particulate filter. Furthermore, a metering device 44 is provided, by means of which a reducing agent, in particular a liquid, such as an aqueous urea solution, can be introduced or is introduced into the exhaust gas flowing through the exhaust system 10 at a point S1, also referred to as the injection point. The exhaust system 10 has at least one exhaust channel through which the engine exhaust gas flows, and the reducing agent can be introduced, in particular injected, into the exhaust channel and thus into the engine exhaust gas flowing through the exhaust channel, particularly at point S1, for example, by means of the metering device 44. In the present case, the exhaust system 10 has a mixing chamber 46, which is arranged downstream of point S1 and upstream of the SCR catalyst 42.In the mixing chamber 46, for example, the reducing agent introduced into the exhaust duct and thus into the engine exhaust can mix with the exhaust gas (engine exhaust) flowing through the exhaust system 10 or the exhaust duct. The exhaust system 10 also has a burner 48. The burner 48 can be supplied with a fuel, in particular a liquid, and with air, which is also referred to as burner air. For example, the fuel mentioned above is referred to as the fuel. By means of the burner 48, a mixture, also referred to as a burner mixture, can be formed from the burner air, with which the burner 48 can be supplied, is supplied, or was supplied, and from the fuel, with which the burner 48 can be supplied, was supplied, or is supplied. By means of the burner 48, the burner mixture can be combusted, in particular by forming a flame 50.This results, for example, in the exhaust gas from burner 48, also referred to as burner exhaust. It is evident that the burner mixture comprises the burner air and the fuel by which burner 48 can be supplied, is supplied, or was supplied. In particular, the burner exhaust gas can flow out of burner 48 and into the exhaust duct, subsequently flowing through the exhaust duct, i.e., the exhaust system 10. It is evident that the burner exhaust gas can flow through the respective component, so that, for example, at least one of the components can be heated and / or kept warm by means of the burner exhaust gas.It is evident that the burner 48, in particular an inlet point where the burner exhaust gas and, for example, the flame 50 can be introduced into the exhaust duct and thus into the engine exhaust flowing through the exhaust duct, is arranged upstream of the nitrogen oxide storage catalyst 38 and / or upstream of the particulate filter 40 and / or upstream of the SCR catalyst 42. This allows, for example, the nitrogen oxide storage catalyst 38 and / or the particulate filter 40 and / or the SCR catalyst 42 to be heated and / or kept warm. To supply the burner 48 with fuel, a fuel line 52 is provided. The fuel line 52 is fluidically connected at a first connection point V1 to a supply line 54, through which the fuel can be conveyed from the tank 14 to the injectors 20 or to the fuel distribution element. The connection point V1 is arranged downstream of the low-pressure pump 16 and upstream of the high-pressure pump 18 in the direction of fuel flow through the supply line 54. At least a portion of the fuel flowing through the supply line 54 can be diverted from the supply line 54 and introduced into the fuel line 52.The fuel diverted from the supply line 54 via the fuel line 52 can flow through the fuel line 52 and is conveyed as fuel via the fuel line 52 to the burner 48, thus supplying the burner 48 with the fuel flowing through the fuel line 52. In this way, the burner 48 is supplied with fuel from the tank 14, with the fuel being used as the fuel. Furthermore, the burner 48 is equipped with its own air pump 56, which is electrically operated and independent of the internal combustion engine 12. This air pump is provided in addition to the internal combustion engine 12 and thus in addition to the charging device 28. An air line 58, designated as the supply line, is also provided, in which the air pump is located.The air pump 56 allows the burner 48 to be supplied with air, as burner air, independently of the internal combustion engine 12 and thus independently of the charging device 28. In other words, air can flow through the air line 58, so that the burner 48 can be supplied with the air flowing through the air line 58, which serves as burner air. The air pump 56 can pump the air flowing through the air line 58. Thus, the air pump 56 can pump the burner air through the air line 58 and deliver it to the burner 48, thereby supplying the burner 48 with burner air. A valve element 60 is arranged in the fuel line 52, by means of which the quantity of fuel with which the burner 48 can be supplied or is supplied is adjustable, in particular controllable. A valve element 62 is arranged in the air line 58, in particular downstream of the air pump 56, by means of which the quantity of air with which the burner 48 can be supplied or is supplied is adjustable, in particular controllable. For example, an electronic computing device, also referred to as a control unit 64, is provided, specifically assigned to the burner 48. The control unit 64 is designed, for example, to actuate, in particular to control or regulate, the valve element 60. This allows, for example, the amount of fuel supplied to the burner 48 to be adjusted, in particular to be regulated or controlled, by the control unit 64 through actuation of the valve element 60. Alternatively or additionally, the control unit 64 can actuate, in particular to control or regulate, the valve element 62. Thus, the control unit 64 can, for example, adjust, in particular to control or regulate, the amount of air flowing through the air line 58 to supply the burner 48 by actuation, in particular to control or regulate, the valve element 62.In particular, this allows the ratio of burner air to fuel, also known as the combustion air ratio, to be adjusted to meet specific requirements. To achieve particularly advantageous operation of the burner 48, the exhaust system 10 has a recirculating air duct 68, which is provided in addition to the air duct 58 and is at least partially separated from it. The recirculating air duct 68 is or comprises a recirculating air channel, which will be explained in more detail below. The recirculating air duct 68 is fluidically connected to the air duct 58 at both a connection point V2 and a connection point V3. Figure 1 shows that, in the direction of flow of the air flowing through the air duct 58, also referred to as burner air, connection point V2 is located downstream of the air pump 56 and upstream of the burner 48, specifically upstream of the valve element 62. In the direction of flow of the air flowing through the air duct 58, connection point V3 is located upstream of the air pump 56 and thus upstream of connection point V2.At connection point V2, at least a portion of the air flowing through air duct 58 and supplied by air pump 56, particularly during its operation, can be diverted from air duct 58 and introduced into recirculating air duct 68. The air diverted from air duct 58 and introduced into recirculating air duct 68 can flow through recirculating air duct 68 and is or is routed from connection point V2, bypassing air pump 56, to connection point V3, in particular, returned or recirculated. At connection point V3, the air flowing through recirculating air duct 68 and thus bypassing air pump 56 can or is routed out of recirculating air duct 68, bypassing air pump 56, and (re)introduced into air duct 58. It can be seen that the air pump 56 is to be bypassed or is bypassed by the air flowing through the recirculation line 68.This means that the air flowing through the recirculating air line 68 bypasses the air pump 56 on its way from the connection point V2 to the connection point V3 and into the air line 58, and therefore does not flow through the air pump 56. The exhaust system 10 also includes a valve element 70, by means of which the quantity of air flowing through the recirculation line 68 and thus bypassing the air pump 56, for example as a volume flow and / or mass flow, can be adjusted, in particular regulated. In the embodiment shown in Fig. 1, the valve element 70 is arranged in the recirculation line 68, downstream of connection point V3 and upstream of connection point V2. The valve element 70 is preferably electrically controllable in order to adjust the amount of air flowing through the recirculation line 68. For this purpose, the exhaust system 10 includes, for example, the control unit 64 by means of which the valve element 70 can be controlled. The valve element 70 is preferably switchable between, in particular, a closed state that fluidly blocks the recirculation duct 68 and several open states that each release the recirculation duct 68. By switching the valve element 70 to the respective open state, a different value than zero can be set for the quantity of air flowing through the recirculation duct 68, wherein the values ​​greater than zero differ from each other, in particular in pairs. Since the recirculation duct 68 is fluidly blocked by the valve element 70 in the closed state, the value of the quantity of air flowing through the recirculation duct 68 is, so to speak, zero. Fig. 2 shows that the valve element 70, for example, has a valve part 74 which is movable between at least one closed position and a respective open position, particularly translationally and / or rotationally, especially relative to the recirculating air line 68 and / or relative to the air line 58. In Fig. 2, an arrow 76 illustrates the flow of air towards the burner 48, particularly downstream of connection point V2 and downstream of the air pump 56. Furthermore, Fig. 2 shows that, for example, an air filter 72 is arranged in the air line 58 for filtering the air flowing through it. In the embodiment shown in Fig. 2, the air filter 72 is arranged upstream of the air pump 56 and upstream of connection point V3. Finally, Fig. 3 shows a schematic longitudinal sectional view of the burner 48. As can be seen from Fig. 3, the burner 48 has a combustion chamber 78 in which the burner mixture, comprising the combustion air supplied to the burner 48 and the fuel supplied to the burner 48 (preferably liquid), is to be ignited and thereby combusted, i.e., ignited and thereby combusted during operation of the burner 48. The combustion chamber 78 is bounded, in particular directly, by a chamber element 80, which in this case is designed as a solid body, and in particular by an inner circumferential surface 82 of the chamber element 80. The burner 48 has an ignition device 84, which is designed in particular as a spark plug, glow plug, or glow pin, and is in particular electrically operated, by means of which the burner mixture, in particular in the combustion chamber 78, can be ignited.By means of the ignition device 84, in particular by using electrical energy by which the ignition device 84 can be supplied or is supplied, at least one ignition spark can be generated at at least or exactly one ignition point Z, by means of which the burner mixture in the combustion chamber 78 can be ignited and subsequently combusted, in particular by providing the burner exhaust gas and / or by providing the flame 50. It is evident that the ignition point Z is arranged in the combustion chamber 78. The chamber element 80 has at least one or, in this case, several flow openings 86 through which the burner exhaust gas from the combustion chamber 78 can flow. Thus, the burner exhaust gas can be discharged from the combustion chamber 78 via the flow openings 86 and introduced into the exhaust gas duct. In the embodiment shown in Fig. 3, the burner 48 has a first channel 88 with a first swirl chamber 90, which is also referred to as the inner swirl chamber. A first portion of the burner air can flow through the first channel 88 and thus the first swirl chamber 90. A first swirl flow of the first portion of the burner air can be effected by means of the first swirl chamber 90. When air is mentioned below, unless otherwise specified, this refers to the burner air. The feature that the first swirl flow of the first portion of the air can be effected by means of the first swirl chamber 90 means, in particular, that the first portion of the air flows in a swirl pattern through at least a first sub-region of the swirl chamber 90 and / or flows out of the swirl chamber 90 in a swirl pattern and / or flows in a swirl pattern into and thus into the combustion chamber 78.The first channel 88 and, in this case, the first swirl chamber 90, each have, in particular, a first outlet opening 92, through which the first portion of air can flow in a first direction of passage of the outlet opening 92 and thus in a first direction of flow that coincides with the first direction of passage, or through which the first portion of air flows during operation of the burner 48. The burner 48 also has an injection element 94 by means of which the fuel can be introduced, at least indirectly, and in particular directly, into the channel 88 and thus, in this case, into the swirl chamber 90, and in particular injected. The injection element 94 is also referred to as an injection valve.The channel 88, and thus the swirl chamber 90, is therefore permeable to both the first portion of air and the fuel injected from the injection element 94, so that the outlet opening 92 is permeable to both the first portion of air and the fuel from the injection element 94. The first portion of air, and thus the fuel, can flow through the channel 88, and thus the swirl chamber 90 and the outlet opening 92, in the first flow direction, which is illustrated by arrow 96. The injection element 94 has, for example, at least or exactly one outlet opening, also referred to as an injection opening, or at least or exactly three outlet openings, also referred to as injection openings, wherein the respective outlet opening is permeable to the fuel supplied to the injection element 94.The injection element 94 can eject the fuel from its respective outlet opening and, in particular, introduce it at least indirectly, and especially directly, into the channel 88 and thus into the swirl chamber 90, forming a steel structure created by the fuel. In particular, the injection element 94 can introduce the fuel into the channel 88, bypassing the combustion chamber 78. In the embodiment shown in Fig. 3, the burner 48 further comprises a second channel 98 with a second swirl chamber 100. The second swirl chamber 100 is an outer swirl chamber which surrounds at least a length of the first channel 88 and thus the first swirl chamber 90, and in particular completely, in a circumferential direction around the first flow direction, and in this case also the first outlet opening 92. The first flow direction, in which the first part of the air and in this case also the fuel can flow through the first outlet opening 92, runs in the axial direction of the swirl chamber 90 or coincides with the axial direction of the swirl chamber 90. The circumferential direction of the inner swirl chamber (swirl chamber 90) runs around the axial direction of the inner swirl chamber (swirl chamber 90).The second channel 98, and thus the outer, second swirl chamber 100, whose axial direction coincides with that of the first swirl chamber 90, is designed to allow a second portion of the burner air to flow through it in a second direction and is configured to generate a second swirl flow of this second portion of air. The second flow direction and the first flow direction point in the same direction, so the second flow direction is also illustrated by arrow 96. The feature that the outer, second swirl chamber 100 is configured to generate the second swirl flow means that the second portion of air flows through the swirl chamber 100 in a swirl pattern and / or flows out of the swirl chamber 100 in a swirl pattern and / or flows into and thus into the combustion chamber 78 in a swirl pattern.In particular, it is provided that the second part of the burner air flows in a swirling motion through at least a second sub-area of ​​the swirl chamber 100 and / or flows out of the swirl chamber 100 in a swirling motion and / or flows in a swirling motion into and thus into the combustion chamber 78. The second channel 98, and thus the outer, second swirl chamber 100, whose radial direction is perpendicular to the axial direction of the swirl chamber 100, has, in particular, a second outlet opening 102 through which the second portion of air flowing through the channel 98, and thus the swirl chamber 100, can flow in the second flow direction, and whose second direction of passage coincides with the second flow direction. The outlet opening 102 can be passed through in the second direction of passage, and thus in the second flow direction, by the second portion of air flowing through the channel 98, and thus the swirl chamber 100. The second flow direction, and thus the second direction of passage, coincides with the axial direction of the swirl chamber 100, and thus with the axial direction of the swirl chamber 90, whose radial direction is perpendicular to the axial direction of the swirl chamber 90 and, in this case, coincides with the radial direction of the swirl chamber 100.It can be seen that the outlet opening 102 is arranged downstream of the outlet opening 92 in the direction of airflow of the respective portion of the air and thus also in the direction of fuel flow, so that the outlet opening 102 can be permeated by the second portion of the air, the first portion of the air, and, in this case, also by the fuel. In the direction of airflow through channels 88 and 98 and thus through swirl chambers 90 and 100, the second outlet opening 102 is arranged downstream of the first outlet opening 92 and is connected in series with the first outlet opening 92, so that the second outlet opening 102 can be permeated by the second portion of the air, the first portion of the air, and, in this case, also by the fuel from channel 88 or swirl chamber 100. The channel 88 is, for example, directly bounded by a solid component 104 of the burner 48. In this case, the channel 88 is directly bounded by an inner circumferential surface 106 of the component 104. In particular, the inner circumferential surface 106 directly forms or bounds a flow cross-section of the channel 88, the flow cross-section of which, in the first flow direction (arrow 96), is permeable to the first portion of the air and, in this case, also to the fuel. In this case, the channel 88 is designed as a nozzle, at least in a length L of the channel 88, such that the flow cross-section tapers in the first flow direction. The channel 88 has an end E facing the combustion chamber 78, at which the channel 88 terminates in the first flow direction.The outlet opening 92 is located at end E, so that, viewed in the first flow direction, the channel 88 and, in this case, also the swirl chamber 90 terminate at end E and thus at the outlet opening 92. Therefore, the first part of the air, and in this case also the fuel, can flow out of the channel 88 at and via end E and subsequently be fed into the combustion chamber 78. The burner 48 has a closing element 108 which, particularly relative to the chamber element 80, is movable, in particular pivotable, between at least one locking position shown in Fig. 3 and at least one release position not shown. In the locking position, the outlet opening 92 is closed by the closing element 108 and thus fluidically separated from the combustion chamber 78. In the release position, the closing element 108 releases the outlet opening 92, so that the outlet opening 92 and, via the outlet opening 92, the channel 88 are fluidically connected to the combustion chamber 78. Reference symbol list 10 Exhaust system 12 Internal combustion engine 14 Tank 16 Low-pressure pump 18 High-pressure pump 20 Injector 22 Cylinder 24 Intake manifold 26 Exhaust manifold 28 Charging device 30 Exhaust turbocharger 32 Compressor 34 Turbine 36 Exhaust aftertreatment device 38 Nitrogen oxide storage catalyst 40 Particulate filter 42 SCR catalyst 44 Metering device 46 Mixing chamber 48 Burner 50 Flame 52 Fuel line 54 Supply line 56 Air pump 58 Air line 60 Valve element 62 Valve element 64 Control unit 68 Recirculation line 70 Valve element 72 Air filter 74 Valve part 76 Arrow 78 Combustion chamber 80 Chamber element 82 Inner circumferential surface 84 Ignition device 86 Flow opening 88 First channel 90 First swirl chamber 92 First outlet opening 94 Inlet element 96 Arrow 98 second channel 100 second swirl chamber 102 second outlet opening 104 component 106 inner circumferential surface E end L length range S1 position V1 connection point V2 connection point V3 connection point Z ignition point

Claims

Exhaust system (10) for an internal combustion engine (12) of a motor vehicle, with a burner (48) supplied with air and fuel, by means of which a mixture comprising air and fuel is to be burned, with an air duct (58) through which air can flow, and with an air pump (56) arranged in the air duct (58), by means of which the air can be conveyed through the air duct (58) and conveyed to the burner (48) in order to supply the burner (48) with air, characterized by: - ​​a recirculation line (68) fluidically connected to the air duct (58) at a first connection point (V2) arranged downstream of the air pump (56) and at a second connection point (V3) arranged upstream of the air pump (56),via which at least a portion of the air flowing through the air line (58) can be returned from the first connection point (V2) to the second connection point (V3), bypassing the air pump; and a valve element (70) by means of which the quantity of air flowing through the recirculation line (68) and thereby bypassing the air pump (56) can be adjusted. Exhaust system (10) according to claim 1, characterized in that the valve element (70) is arranged in the recirculation line (68). Exhaust system (10) according to claim 1 or 2, characterized in that the valve element (70) is electrically controllable in order to adjust the amount of air flowing through the recirculation line (68). Exhaust system (10) according to claim 3, characterized by an electronic computing device (64) by means of which the valve element (70) can be electrically controlled. Exhaust system (10) according to one of the preceding claims, characterized in that the valve element (70) is switchable between a closed state which fluidly blocks the recirculation line (68) and at least one open state which releases the recirculation line (68). Exhaust system (10) according to claim 5, characterized in that the valve element (70) is switchable between the closed state and several open states releasing the recirculated air line (68), namely the open state as the first open state and several further open states, wherein the open states differ from each other with respect to a respective value of the quantity. Motor vehicle, with an internal combustion engine (12) by means of which the motor vehicle can be driven, and with an exhaust system (10) through which exhaust gas of the internal combustion engine (12) flows according to one of the preceding claims.

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