Burner for an exhaust tract through which exhaust gas from an internal combustion engine of a motor vehicle can flow

Abstract

The invention relates to a burner (10) for an exhaust tract (25) through which exhaust gas (36) from an internal combustion engine of a motor vehicle flows, comprising a combustion chamber (12) in which a mixture comprising air and a fuel is to be ignited and thereby burned, comprising at least one housing element (18) which at least partially delimits the combustion chamber (12), and comprising at least one outlet element (20) which has at least one through-opening (22) via which burner exhaust gas (34) produced by the combustion of the mixture can be discharged from the combustion chamber (12) for heating the exhaust tract (25) of the internal combustion engine.The invention is characterized in that the through-opening (22) has at least one first longitudinal region (26) through which the burner exhaust gas (34) can flow, which has a first cross-section with a convergent course, and at least one second longitudinal region (28) through which the burner exhaust gas (34) can flow, which second cross-section with a divergent course.

Description

[0001] The invention relates to a burner for an exhaust tract through which exhaust gas from an internal combustion engine of a motor vehicle can flow, according to the preamble of patent claim 1, an internal combustion engine with a burner for a motor vehicle and a method for operating such a burner.

[0002] Motor vehicles with internal combustion engines and exhaust systems, also known as exhaust tracts, are known from series vehicle construction. Exhaust gas from the respective internal combustion engine, also known as an internal combustion engine, can flow through each exhaust tract. The exhaust gas can also be referred to as engine exhaust and can arise during combustion processes in which a fuel-air mixture is to be burned or is burned. The internal combustion engine preferably has at least one combustion chamber in which the combustion processes take place. The combustion chamber is designed, for example, as a cylinder. The combustion chamber is separate from the burner. In particular, the combustion chamber and the burner are spaced apart from one another.In some operating states or operating situations of the respective internal combustion engine, a high exhaust gas temperature may be desirable, for example in order to be able to quickly heat up and / or keep warm an exhaust gas aftertreatment device arranged in the exhaust tract, although in these operating states or operating situations the temperature of the exhaust gas of the internal combustion engine is only insufficiently high. To heat the exhaust tract, the exhaust tract has a burner. The burner can have at least one combustion chamber in which a mixture comprising air and a fuel, in particular a liquid fuel, is to be ignited and thereby burned. In addition, the burner has at least one housing element, which can be referred to in particular as a combustion chamber housing or burner housing or combustion chamber housing.The housing element delimits the combustion chamber at least partially, in particular predominantly or completely, for example in the radial direction of the combustion chamber and / or in the axial direction of the combustion chamber. Furthermore, the burner has at least one outlet element, in particular delimiting the combustion chamber at least partially, for example in the axial direction of the combustion chamber. The outlet element has at least one through-opening through which burner exhaust gas generated by the combustion of the mixture can be discharged from the combustion chamber for heating the exhaust tract of the internal combustion engine, in particular for heating the exhaust gas aftertreatment device arranged in the exhaust tract of the internal combustion engine, and in particular can be introduced into the exhaust tract or at least a longitudinal region of the exhaust tract.In particular, the outlet element is arranged on an outlet side of the combustion chamber, wherein the outlet side is, for example, an axial end face of the combustion chamber or the housing element. The outlet side can in particular be referred to as the gas outlet side.

[0003] DE 10 2021 001 581 A1 discloses a burner for an exhaust tract through which exhaust gas from an internal combustion engine of a motor vehicle flows, comprising a combustion chamber in which a mixture comprising air and a fuel is to be ignited and thereby burned. The burner has at least one housing element which at least partially delimits the combustion chamber and at least one outlet element which has at least one through-opening. Furthermore, DE 10 2004 034 868 A1 and DE 39 01 126 A1 each disclose a burner with a combustion chamber in which a mixture comprising air and a fuel is to be ignited and thereby burned. The burners have at least one housing element which at least partially delimits the combustion chamber and at least one outlet element which has at least one through-opening.

[0004] Such a known through-hole can have a cross-section or cross-sectional profile that widens or diverges in the direction of flow, i.e., from the combustion chamber through the outlet element to the gas outlet side. A through-hole with only one diverging cross-section can also be referred to as a diffuser. This can have the disadvantage that a wall area of the outlet element around an inlet opening into the through-hole heats up particularly strongly when hot burner exhaust gas flows through it. This particularly high local heating can cause thermal stresses and / or expansions, which can lead to cracks in the outlet element.The inlet opening can refer to the cross-section through which the flow or the burner exhaust gas coming from the combustion chamber enters the through-opening, flows through it, and exits the through-opening on the gas outlet side. The object of the present invention is to provide a burner for an exhaust tract through which exhaust gas from an internal combustion engine of a motor vehicle flows, an internal combustion engine for a motor vehicle, and a method for operating such a burner, so that the thermal load capacity of the burner can be particularly increased.

[0005] This object is achieved according to the invention by a burner for an exhaust tract through which exhaust gas from an internal combustion engine of a motor vehicle flows, having the features of patent claim 1, by an internal combustion engine having the features of patent claim 10, and by a method having the features of patent claim 11. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0006] A first aspect of the invention relates to a burner for an exhaust tract through which exhaust gas from an internal combustion engine of a motor vehicle flows, comprising a combustion chamber in which a mixture comprising air and a fuel is to be ignited and thereby combusted, at least one housing element that at least partially delimits the combustion chamber, and at least one outlet element that has at least one through-opening through which burner exhaust gas generated by the combustion of the mixture can be discharged from the combustion chamber to heat the exhaust tract of the internal combustion engine. The motor vehicle is designed, for example, as a motor vehicle, in particular as a passenger car or as a commercial vehicle.

[0007] In order to be able to particularly increase the thermal load capacity of the burner, in particular of the outlet element, it is provided according to the invention that the through-opening has at least one first longitudinal region through which the burner exhaust gas can flow, which has a first cross section with a convergent course, and at least one second longitudinal region through which the burner exhaust gas can flow, which has a second cross section with a divergent course.

[0008] This results in the advantage that heat input from the hot burner exhaust gas into the outlet element can be reduced, compared to a through-hole with, for example, a constant or only divergent cross-sectional profile. Another advantage is that the temperature can be evenly distributed within the outlet element. This can prevent stress cracks due to thermal stresses and / or expansion, particularly during heating and / or cooling of the outlet element. Stresses here refer in particular to tensile stresses and / or compressive stresses.

[0009] During operation of the burner, the combustion chamber can heat up particularly strongly, for example to up to 1150 °C, for example on an outlet side, which may have the outlet element. A possible temperature difference, which may be particularly high and amount to almost 1200 K, for example, can lead to very high, in particular thermal, stresses on a perforated outlet surface in the form of the outlet element having the at least one through-opening, which stresses can lead to cracks. The housing element can delimit the combustion chamber at least partially, in particular predominantly or completely, for example in the radial direction of the combustion chamber and / or in the axial direction of the combustion chamber. Furthermore, the burner can have at least one outlet element, in particular delimiting the combustion chamber at least partially, for example in the axial direction of the combustion chamber.The outlet element can have at least one through-opening through which burner exhaust gas generated by the combustion of the mixture can be discharged from the combustion chamber for heating the exhaust tract of the internal combustion engine, in particular for heating the exhaust aftertreatment device arranged in the exhaust tract of the internal combustion engine, and in particular can be introduced into the exhaust tract or at least a longitudinal region of the exhaust tract. In particular, the outlet element can be arranged on an outlet side of the combustion chamber, wherein the outlet side can be, for example, an axial end face of the combustion chamber or of the housing element. The outlet side can in particular be referred to as the gas outlet side.

[0010] The term "convergent" refers in particular to a cross-sectional shape that narrows in the flow direction of the burner exhaust gas being discharged or removed from the combustion chamber via the through-opening. This means that the cross-sectional area through which the flow passes becomes narrower along a flow or in the flow direction or downstream of an inlet opening, which can also be referred to as the inflow cross-section, i.e. it is narrower downstream than upstream or has a smaller cross-sectional area. "Divergent" means in particular that the cross-sectional area through which the flow passes widens in the flow direction of the burner exhaust gas being discharged or removed from the combustion chamber via the through-opening, i.e. the cross-sectional area through which the flow passes is larger downstream than upstream. The cross-sectional area here refers to the area through which the flow passes that is perpendicular to a mean flow direction.Thus, the respective cross-sectional profiles, i.e., the convergent cross-sectional profile and the divergent cross-sectional profile, refer to a cross-sectional profile extending in the direction of flow. "Permeable" here means that the through-opening can be flowed through by the burner exhaust gas and / or a flame, or is flowed through during burner operation. "Flame" here can refer to exhaust gas that is not yet fully combusted or is in the process of being combusted. The outlet element can have a wall region that contains the through-opening.

[0011] The invention is based in particular on the following considerations and findings: In order to make the burner, in particular the outlet element, particularly thermally resilient, an attempt should be made to minimize heat input into a wall area around the through-opening, or into the wall area containing the through-opening. The heat input, which can also be referred to as heat flux density, refers here to the amount of heat energy that is introduced into or transferred from the flow into or onto the wall area per time and per area of the wall area.The heat input from a flow into a wall region that at least partially bounds or guides the flow depends not only on the temperature difference between the flow temperature and the wall temperature, in particular the static temperature, but also on the (thermal) boundary layer thickness, the flow path length, the flow velocity, and the static pressure distribution along the flow. Likewise, or alternatively, on the Reynolds number, which describes the ratio of inertial forces to viscous forces of the flow or along the flow.According to the Bernoulli equation, which assumes a constant total pressure, which describes the sum of static pressure and dynamic pressure in loss-free flow and when height differences are neglected, in conjunction with an incompressible flowing fluid and the conservation of mass, a convergent cross-sectional profile leads to an acceleration of the flow, accompanied by a drop in the static pressure in the flow. As the flow accelerates, the boundary layer thickness decreases, which increases the heat transfer from the flow to the wall region. Along a divergent cross-sectional profile, i.e. a cross-sectional profile along which the cross-section widens, the static pressure along the flow increases, which increases the boundary layer thickness and decreases the heat transfer from the flow to the wall region.If the cross-section continues to widen, causing the static pressure or backpressure to continue to increase, the boundary layer separates from the wall region starting at a so-called separation point. Further downstream of the separation point, a turbulent backflow region forms between the flow and the wall region. Turbulent flows are characterized by the fact that, in addition to the movement of fluid particles in the direction of flow or the main flow direction, the fluid particles also move perpendicularly or transversely to the main flow direction or flow direction. Turbulent flows are therefore particularly well suited to the mixing of fluids and / or different thermal zones of fluids. A further finding underlying the invention is that, for the heating of a wall region, the heat conduction from the wall region into which heat is introduced into the material surrounding this wall region must be taken into account.This means that particularly thin wall areas overheat more quickly than thicker wall areas, since the heat introduced here can only be dissipated into the surrounding material via a small amount of available material.

[0012] The invention also includes further developments which result in additional advantages.

[0013] According to a further development of the burner, the first length region is arranged upstream of the second length region, in particular in the flow direction of the exhaust gas flowing through the passage opening.

[0014] The first longitudinal section, along which the hot burner exhaust gas flows into the through-hole, has a convergent cross-sectional profile, although the heat input may increase due to a resulting increase in flow velocity. Due to the convergent cross-sectional profile, an obtuse angle, i.e., greater than 90 degrees, exists between the wall region adjacent to the flow, which encompasses the first longitudinal section, and a wall region perpendicular to the inflow direction into the first longitudinal section, particularly in an inlet or inflow region or around the inlet opening, viewed in a section perpendicular to the inlet opening through the through-hole, for example.In contrast to a divergent cross-sectional profile, the heat introduced, for example, at the apex of the angle, has more material available to spread from the inflow area into the surrounding wall material than with a divergent cross-sectional profile directly or immediately in the flow direction away from the inflow area. In other words, with a convergent inflow area, the heat introduced here can be more effectively dissipated into the surrounding material via thermal conduction. This results in the advantage that more heat can be introduced until a material-specific failure limit is reached, compared to a cross-sectional profile that only diverges in the flow direction.In order to reduce the overall heat input from the flow into the wall area surrounding the passage opening, the second length area, which adjoins the first length area downstream, has a divergent cross-sectional profile.

[0015] This results in the advantage that the heat input or a quantity of heat introduced into a wall region in the inflow region of the first longitudinal region of the through-opening can be dissipated particularly well by heat conduction, even though the heat input here may be increased by the convergent cross-sectional profile. In the second longitudinal region, the heat input from the flow into the wall region surrounding or encompassing the second longitudinal region can be reduced by a deceleration of the flow and an increase in the boundary layer thickness as a result of the static pressure increase along the flow. The burner exhaust gas is given a flow direction through the at least one through-opening from the combustion chamber into the exhaust tract, wherein the first longitudinal region is arranged upstream of the second longitudinal region in the flow direction and can be flowed through and / or is arranged upstream of the divergent cross-sectional profile.When the burner is in operation, the burner exhaust gas first flows through the first longitudinal section and immediately afterwards through the second longitudinal section. The first longitudinal section being positioned upstream of the second longitudinal section in the flow direction can result in the advantage that flow losses are lower when flowing through the entire through-opening than if the through-opening were designed only as a diffuser. A reduction in flow losses can mean that more burner exhaust gas or a larger mass flow of burner exhaust gas can be or is discharged from the combustion chamber into the exhaust tract when the burner is in operation than with higher flow losses.

[0016] According to a further development of the burner, the second longitudinal section has an opening angle greater than 8 arc degrees, in particular greater than 30 arc degrees and / or less than 100 arc degrees. In other words, the opening angle of the second longitudinal section, which has the divergent cross-sectional profile, should be so large that the flow separates when flowing through the divergent cross-sectional profile. Separation of the flow when flowing through the second longitudinal section has the advantage that the heat input from the flow in the region of the separated flow, i.e. between a backflow or a dead water region and the wall region along the second longitudinal section, is lower than if the flow were present there.In other words, a main flow is surrounded or enveloped by the backflow region, so that the backflow is located or formed between the main flow in a center or central region of the second longitudinal section and the wall region around this longitudinal section. The backflow can thus thermally insulate the wall region from the main flow. This embodiment is based on the knowledge that such separation can be expected from an opening angle of 8 arc degrees. However, it has been shown that separation behaves particularly favorably from an opening angle of 30 arc degrees, especially when the opening angle is less than 100 arc degrees.Another advantage is that the separation increases the turbulence in the flow after it exits the second longitudinal section or the through-opening, and in particular into the exhaust tract, compared to a flow that is present and exits over the entire second longitudinal section. The increased turbulence of the return flow exiting on the gas outlet side together with the main flow can achieve better mixing of the burner exhaust gas with, for example, cooler engine exhaust gas. The improved mixing can reduce local temperature differences in the flow flowing through the exhaust tract downstream of the burner, or it can homogenize a heat profile or heat distribution in the flow in the exhaust tract downstream of the burner.This prevents localized overheating of the exhaust gas aftertreatment system when the flow impinges, which may represent a mixture of burner exhaust gas and engine exhaust gas. The exhaust gas aftertreatment system can, in particular, be a catalytic converter.

[0017] According to a further development of the burner, the through-opening has a third longitudinal region, particularly downstream of the first longitudinal region in the flow direction of the burner exhaust gas flowing through the through-opening, and a third longitudinal region, particularly upstream of the second longitudinal region in the flow direction of the burner exhaust gas flowing through the through-opening, which third longitudinal region has a third cross-section with a constant profile. In other words, viewed in the flow direction, when flowing through the through-opening, a third longitudinal region is to be arranged between the first longitudinal region and the second longitudinal region, which has a cross-section with a constant profile. In particular, the third longitudinal section can be arranged upstream of the second longitudinal region and downstream of the first longitudinal region in the flow direction of the burner exhaust gas flowing through the through-opening.The third longitudinal region can thus directly adjoin the first longitudinal region along the through-opening, and the second longitudinal region can directly adjoin the third longitudinal region. The third longitudinal region through which flow occurs and having a constant cross-sectional profile can, in particular, have a cross-section that corresponds to the narrowest or smallest cross-section of the first longitudinal region with the convergent cross-sectional profile and the narrowest or smallest cross-section of the second longitudinal region with the divergent cross-sectional profile. Thus, according to this refinement, the through-opening has at least one convergent and at least one divergent region, and at least one flow-through region with a constant cross-section between them.

[0018] This has the advantage that, after possible separation after exiting the first length range before entering the second length range, the flow can attach itself again to a wall of this third length range when flowing through the third length range, which wall may surround, enclose or encompass it. This makes it possible to avoid or reduce local temperature or heat input peaks in the second length range. When selecting or designing the third cross-section, which may in particular be the narrowest cross-section of the through-opening or when flowing through the through-opening, it must be taken into account that, depending on a combustion chamber pressure in the combustion chamber of the burner and a pressure on the gas outlet side, the speed of sound or a Mach number of 1 can be reached in the flow in this narrowest cross-section.The through-hole can be in the form of a convergent-divergent nozzle, also called a Laval nozzle, which closes the nozzle when the speed of sound is reached. Closing the nozzle means that the mass flow cannot be further increased by lowering the pressure on the gas outlet side. However, according to the invention, it can be provided that the speed of sound is reached precisely in this narrowest cross-section, since this allows the maximum flow velocity to be achieved at a given combustion chamber pressure and pressure on the gas outlet side, thus maximizing the mass flow.

[0019] According to a further development of the burner, the outlet element has a plurality of through-openings through which the burner exhaust gas can be discharged from the combustion chamber to heat the exhaust tract of the internal combustion engine. In particular, the outlet element is provided with a plurality of identically constructed through-openings. The plurality of through-openings provides the advantage of increasing the mass flow of burner exhaust gas, which can be fed into the engine exhaust gas or can be discharged into the exhaust tract.

[0020] According to a further development of the burner, the burner exhaust gas can be mixed with an engine exhaust gas flowing through the exhaust tract as it is discharged from the outlet element. In other words, the burner exhaust gas exiting or being discharged from the outlet element should mix with the engine exhaust gas flowing through the exhaust tract, which engine exhaust gas can be discharged or discharged from at least one combustion chamber of the internal combustion engine that is separate and / or spaced from the burner. In particular, the increased turbulence of the burner exhaust gas flowing out of the burner on the gas outlet side should promote or assist mixing of the burner exhaust gas with the engine exhaust gas. Mixing the burner exhaust gas with the engine exhaust gas offers the advantage that the temperature and / or the gas mixture flowing through the exhaust tract downstream of the outlet element can be changed or increased.In addition, mixing offers the advantage that the temperature of this gas mixture can be evenly distributed, particularly across a cross-section of the exhaust tract, i.e., across the gas mixture flowing through this cross-section. "Even distribution" here means that no temperature differences greater than 50 Kelvin (K) develop within a flow cross-section.

[0021] According to a further development of the burner, the outlet element is arranged upstream of an exhaust gas aftertreatment device arranged in the exhaust gas tract, relative to the flow direction of the exhaust gas tract. In other words, a mixture or gas mixture of the burner exhaust gas and the engine exhaust gas can be supplied to the exhaust gas aftertreatment device. This results in the advantage that the temperature of the exhaust gas mixture supplied to the exhaust gas aftertreatment device can be increased or decreased by supplying the burner exhaust gas, compared to an inflow of pure, unmixed engine exhaust gas.

[0022] According to a further development of the burner, the outlet element has at least one curvature. In other words, the outlet element, which has the one or more through-openings, is curved, bulged, and / or bent, i.e., the outlet element is not designed as a flat or planar plate. In particular, the outlet element can be curved outward from the combustion chamber or the housing element or into the exhaust tract.

[0023] This offers the advantage of a larger surface area, due to the curvature, over which thermal stresses can be distributed compared to a flat plate. This reduces stress peaks caused by thermal loads on the outlet element, for example, by hot burner exhaust gas flowing through the through-holes.

[0024] The thermal load capacity of the burner according to the invention, in particular of the outlet element and / or the housing element, can be particularly increased. This can be achieved in particular by designing the outlet element in a convex and / or curved manner, whereby an expansion direction can be predetermined for the outlet element under thermal stress, in particular to contract and / or expand. A predetermined convexity or curvature of the outlet element allows thermal expansion between the outlet element and the burner or the combustion chamber housing or the combustion chamber to occur evenly in the region of the convexity, thereby preventing thermal stresses and cracks.

[0025] A second aspect of the invention relates to an internal combustion engine for a motor vehicle with a burner, in particular according to the first aspect of the invention. Advantages and advantageous developments of the first aspect of the invention are to be regarded as advantages and advantageous developments of the second aspect of the invention, and vice versa.

[0026] The internal combustion engine is preferably designed to drive the motor vehicle. The internal combustion engine may comprise an exhaust tract and the burner according to the first aspect of the invention. Furthermore, the internal combustion engine may also comprise the exhaust gas aftertreatment device.

[0027] For example, the internal combustion engine, particularly in its fully manufactured state, has the burner, wherein the burner is preferably arrangeable or can be arranged in the exhaust tract of the internal combustion engine. The internal combustion engine preferably has at least one combustion chamber in which combustion processes take place, in which a fuel-air mixture is to be burned or is burned. The combustion chamber is designed, for example, as a cylinder. The combustion chamber is designed separately from the burner. In particular, the combustion chamber and the burner are spaced apart from one another. The internal combustion engine preferably has at least one intake tract through which air can flow and via which air can be supplied to the combustion chamber. The exhaust gas of the internal combustion engine generated from the combustion of the fuel-air mixture in the combustion chamber can be discharged from the combustion chamber via the exhaust tract.

[0028] A third aspect of the invention relates to a method for operating a burner, in particular according to the first aspect of the invention. Advantages and advantageous developments of the first aspect of the invention are to be regarded as advantages and advantageous developments of the third aspect of the invention, and vice versa.

[0029] During operation of the burner, a mixture comprising air and fuel is ignited and burned in its combustion chamber. The resulting burner exhaust gas and / or flame flows through one or more through-openings in the outlet element into the exhaust system, where it mixes with engine exhaust gas discharged from the combustion chamber of the internal combustion engine. Downstream of the burner, a gas mixture of burner exhaust gas and engine exhaust gas can flow to an exhaust aftertreatment device, in particular a catalytic converter, located in the exhaust system.

[0030] A further aspect relates to a motor vehicle with an internal combustion engine, in particular according to the second aspect of the invention. Advantages and advantageous developments of the first, second, and third aspects of the invention are to be regarded as advantages and advantageous developments of the further aspect, and vice versa.

[0031] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective specified combinations, but also in other combinations or on their own, without departing from the scope of the invention.

[0032] Showing: Fig. 1 is a schematic sectional view of a burner according to the invention; and Fig. 2 a schematic detailed sectional view of an outlet element of the burner with through openings; and Fig. 3 a schematic sectional view of a flow-through diffuser; and Fig. 4 a schematic sectional view of a passage opening with three length regions, each with a cross-sectional profile.

[0033] In the figures, identical or functionally identical elements are provided with the same reference symbols.

[0034] Fig. Figure 1 shows a schematic sectional view of a burner 10 for an exhaust tract through which exhaust gas 36 from an internal combustion engine of a motor vehicle flows. The motor vehicle is designed, for example, as a motor vehicle, in particular as a passenger car or a commercial vehicle. The motor vehicle is preferably driven by the internal combustion engine.

[0035] The exhaust tract can be understood, in particular, to mean an exhaust system of the internal combustion engine. In some operating states or operating situations of the internal combustion engine, a high temperature of the exhaust gas 36 can be desirable, for example in order to be able to quickly heat up and / or keep warm an exhaust gas aftertreatment device 40 arranged in the exhaust tract. However, in these operating states or operating situations, the temperature of the exhaust gas of the internal combustion engine is only insufficiently high. The exhaust tract, and in particular the exhaust gas aftertreatment device 40, can be heated up and / or kept warm by means of the burner 10. This means that the exhaust tract, in particular the exhaust gas aftertreatment device 40, can be heated up and / or kept warm by means of the burner 10, for example in addition to being heated up and / or kept warm by means of the exhaust gas 36.This exhaust gas 36 can be understood, in particular, as an exhaust gas 36 generated from a fuel-air mixture in a combustion chamber of the internal combustion engine. The combustion chamber, which is designed, for example, as a cylinder, is formed separately from the burner 10.

[0036] The internal combustion engine is designed, for example, as a diesel engine. The exhaust gas aftertreatment device 40 comprises, for example, at least one catalytic converter or is designed as a catalytic converter. The exhaust gas aftertreatment device 40 or the catalytic converter is designed, for example, as an oxidation catalyst, in particular a diesel oxidation catalyst, a nitrogen oxide storage catalyst, an SCR catalyst, or as a particulate filter, in particular a diesel particulate filter. The exhaust gas 36 of the internal combustion engine can be cleaned by means of the exhaust gas aftertreatment device 40. The burner 10 has at least one combustion chamber 12 in which a mixture comprising air and a, in particular liquid, fuel is to be ignited and thereby burned. This means that the burner 10 can ignite and combust the mixture in the combustion chamber 12, in particular to form a flame and in particular to provide a burner exhaust gas 34.

[0037] For example, the fuel is the fuel that is also burned in the combustion chamber, which is configured, for example, as a cylinder, of the internal combustion engine. Thus, the fuel can be used as the fuel. However, the burner exhaust gas 34 is not the exhaust gas 36 or engine exhaust generated in the combustion chamber of the internal combustion engine.

[0038] In the exemplary embodiment, the burner 10 has a burner housing 13 in which an introduction element 14 is provided, by means of which or via which the fuel, in particular for forming the mixture, can be introduced, in particular directly, into the combustion chamber 12. The introduction element 14 is designed, for example, as an injection valve.

[0039] Furthermore, the burner 10 has an air supply 15 in the combustion housing 13, through which the air can be introduced into the combustion chamber 12 to form a mixture. The introduction element 14 preferably injects the fuel into the air in the air supply 15, after which the air is mixed with the injected fuel already in the air supply 15 and passes directly into the combustion chamber 12.

[0040] The air supply 15 can be fluidically separated from the combustion chamber 12 by a flap 16. For this purpose, the flap 16 is pivotably mounted on the burner housing 13 in the combustion chamber 12. By pivoting the flap 16, the air supply 15, which is separated from the combustion chamber 12, can be reconnected to the combustion chamber 12, so that air and fuel can be introduced from the air supply 15 into the combustion chamber 12.

[0041] Furthermore, the burner 10 has at least one ignition device, provided in particular in the burner housing 13 and extending into the combustion chamber 12, by means of which the mixture comprising the air and fuel is to be ignited and thereby burned. The ignition device is designed, for example, as a spark plug, glow plug, or glow element. The ignition device is arranged, for example, in an installation position designated by the reference numeral 17. The burner 10 has at least one housing element 18, which can in particular be referred to as a combustion chamber housing. The housing element 18 is attached to the burner housing 13. The housing element 18 and the burner housing 13 delimit the combustion chamber 12. In the exemplary embodiment, the combustion chamber 12 or the housing element 18 is at least substantially cylindrical. Furthermore, the housing element 18 in the exemplary embodiment can at least partially, in particular predominantly or completely, delimit the combustion chamber 12 in its radial direction 19. Furthermore, the housing element 18 has, for example, at least one outlet element 20, which at least partially delimits the combustion chamber 12 in its axial direction 21, in particular at one end or in the axial direction 21 adjoining the combustion chamber 12 or the housing element 18. The outlet element 19 and the housing element 19 can preferably be formed together in one piece.

[0042] Fig. 2 shows a schematic detailed sectional view of the outlet element 19 of the burner 10 with a plurality of preferably identical through-openings 22. The outlet element 20 can have one or more, in particular identical through-openings 22. In the exemplary embodiment, the outlet element 20 comprises a plurality of through-openings 22. The housing element 18, the combustion chamber 12 and / or the outlet element 20 can be designed rotationally symmetrically about a central axis. The central axis can extend in particular in the axial direction of the combustion chamber 12. The outlet element 20 can have an inflow side pointing or facing the combustion chamber 12 and an outer gas outlet side 24 pointing or facing the exhaust tract. Fig. 1, a flow direction 32 can be predetermined for the through-openings 22. The burner exhaust gas 34 or the flame coming from the combustion chamber 12 or from the inflow side should enter the through-opening or through-openings 22, flow through the through-openings 22, and flow out or out on the gas outlet side 24 or flow into the exhaust tract.

[0043] In the exemplary embodiment, the outlet element 20 can be curved. Preferably, the outlet element 20 is curved, pointing away from the combustion chamber 12 outwards towards the exhaust tract. The through-openings 22 can be evenly distributed on a circular path around the central axis or axis of rotational symmetry of the housing element 18 and / or the combustion chamber 12 and / or the outlet element 20, i.e., arranged at the same distance from one another in the circumferential direction on a circular path. The respective flow directions 32 for each through-opening 22 can be different, but each flow direction 32 is perpendicular to an inflow side or inlet side or inlet plane of a respective through-opening 22. The different flow directions 32 for each through-opening 22 can be due to or caused by the curvature of the outlet element 20.The through-openings 22 can have a circular or rotationally symmetrical cross-section. The outlet element 20, which is curved in the exemplary embodiment, can be integrally connected to the housing element 18 and thus directly adjoin the combustion chamber 12 or the housing element 18. As shown in FIG. Fig. 2 using a sectioned through-opening 22, each through-opening 22 can be chamfered at least on the inflow side 23 and / or on the gas outlet side 24. Thus, it can have at least one or more, in particular two, variable cross-sectional profiles along the flow direction 32. Coming from the inflow side 23, the flow can, for example, first flow through a first longitudinal section 26 with a convergent cross-sectional profile, which can be referred to as nozzle-shaped. The flow can then flow through a second longitudinal section 28, which widens toward the gas outlet side 24 and can be referred to as a diffuser.

[0044] Fig. 3 shows a schematic sectional view of a diffuser D through which air flows. Fig. 3 illustrates the basic flow phenomena of a diffuser flow. The diffuser D in Fig. 3 has three different cross-sectional shapes. The diffuser D in Fig. 3 can be rotationally symmetrical about a central axis or axis of symmetry (not shown). In the flow direction 32, the flow can first flow through a first region B1 with a constant cross-section, immediately followed in the flow direction 32 by a second region B2 with a divergent cross-sectional profile, which can represent the actual diffuser D. Directly adjacent to the second region B2 in the flow direction 32 can be a third region B3 with a constant cross-sectional profile, which can have a larger cross-sectional area than the first region B1. Along one or the flow directions 32, the flow can enter the diffuser D or the second region B2 with a velocity profile 48, which can develop in or along the first region B1 depending on the Reynolds number and the flow length. As in Fig. 3, the velocity profile 48 of the flow may not be homogeneous or evenly distributed over the cross section, because the velocity in the flow or in a flow cross section may increase away from a wall or a wall area towards the center of the flow.

[0045] The area in the flow where the velocity increases away from the wall can also be referred to as the boundary layer. Directly at the wall, the flow has no velocity or a velocity of zero due to the adhesion condition. The diffuser D, i.e. the second length range B2, can have an opening angle of 42. The diffuser D in Fig. 3 is characterized by the fact that it has a divergent cross-sectional shape along the flow or in the flow direction 32. The Fig. The diffuser D shown in Figure 3 can be designed to be rotationally symmetrical to a central axis (not shown). If the flow flows through the widening cross-sectional area or second area B2, the static pressure in the flow can increase along the flow, i.e. in the flow direction 32, according to the Bernoulli equation. Since the flow velocity in a region close to the wall or within the boundary layer can be lower than in the center of the flow, the kinetic energy of the flow in the region close to the wall may not be sufficient to counteract the increasing static pressure when flowing through the widening area or along the divergent cross-sectional profile. As a result, the boundary layer of the flow can detach from the wall, whereby a backflow region 44 can form.When a backflow region 44 is formed, the flow in the second region B2 can be divided into two regions, namely the backflow region 44 or the backflow region and a main flow region, which can be enclosed by the backflow region 44 in the case of a rotationally symmetrical diffuser D. In . Fig. 3 shows a third region B3 with a constant cross-sectional profile adjacent to the second region B2 with the widening cross-sectional profile. If the flow detaches from the wall in the diffuser D, it can attach itself to the wall again along the flow after entering the third region B3 with a constant cross-sectional profile, wherein the attachment can specify an attachment point or attachment region which, viewed in the flow direction 32, limits or ends the return flow region 44. The point or, in the example, annular region, at which the flow detaches from the wall can be referred to as the separation point, or in this case as the separation region. The return flow region 44 can thermally insulate a diffuser wall or the wall region surrounding the main flow or the flow from, for example, a hot flow.This means that heat input or heat flow from the flow into the wall region can be reduced or inhibited. The separation point or separation region depends essentially on the opening angle 42 of the diffuser D, and not significantly on an inlet length, which determines the height of the boundary layer, and / or on a flow velocity or the flow velocity profile 48, and thus on the Reynolds number. A region as shown in [figure omitted] can be connected to the second region B2, which has a divergent cross-sectional profile. Fig. 3 shown length range with a constant cross-section in the direction of flow. Thus, the second length range 28 ( Fig. 4) have a flow pattern as shown in the Fig. 3. This means that, in addition to the main flow, the backflow region 44 can also exit from a respective through-opening 22 on the gas outlet side 24. The backflow region 44 has the property that it exhibits a particularly high degree of turbulence compared to the main flow. Turbulence means that fluid particles move not only in the main flow direction but also in directions perpendicular to it. Turbulent flows therefore have the ability to mix particularly well with other flows or fluids.

[0046] Fig. Figure 4 shows a schematic sectional view of a through-opening 22 with three length regions, each with a cross-sectional profile. These three length regions are different from those previously described in connection with the description of Fig. 3 introduced areas B1, B2 and B3 and refer in the following only to the Fig. 4 described embodiment. In the flow direction 32, i.e. coming from the combustion chamber 12, in the embodiment, a first longitudinal region 26 can be flowed through first in the flow direction 32. This longitudinal region can have a convergent cross-sectional profile. As in Fig. 4, this can mean that the cross section narrows or becomes narrower in the flow direction or is nozzle-shaped. According to the Bernoulli equation, a nozzle flow has the property that the flow is accelerated, whereby the static pressure in the flow decreases along the flow as it flows through the convergent cross-sectional profile. The acceleration ensures or can ensure that the flow adheres to the wall or a wall region, whereby the boundary layer thickness decreases or increases more slowly with the flow length along the flow direction, compared to a diffuser flow. This can increase heat transfer from the flow into the wall region surrounding the flow. The first longitudinal region 26 and the entire through-opening 22 can have a rotationally symmetrical cross-sectional profile around a Fig. 4 not shown central axis. The cross-sectional profile of the first longitudinal section 26 can be as shown in Fig. 4 can be linear. However, the cross-sectional shape can also be quadratic or parabolic. As shown in Fig. As shown in Figure 4, an obtuse angle, i.e. an angle greater than 90 degrees, can form between an inflow side 23, from which the fluid flows into the through-opening 22, and the first longitudinal region 26. This results in better heat conduction or heat transfer from the wall region surrounding the first longitudinal region 26 into the surrounding material, which can be encompassed by the outlet element 20, compared to an acute angle, which would form, for example, if a divergent cross-sectional profile were to arise or exist directly from the inflow side. A third longitudinal region 30 can adjoin the first longitudinal region 26 in the flow direction. This third longitudinal region 30 can be designed as shown in Fig. 4, have a constant cross-sectional profile. This can have the advantage that a flow that separates at the transition between the first longitudinal region 26 and the third longitudinal region 30 can attach again before the second longitudinal region 28, which directly adjoins it in the flow direction, is flowed through. The narrowest cross section of the third longitudinal region 30 can be equal to the narrowest cross section or cross-sectional area or, in the case of a rotationally symmetrical through-opening 22, the narrowest or smallest diameter of each of the first longitudinal region 26 and the second longitudinal region 28. The second longitudinal region 28, which can have a cross-sectional profile that diverges in the flow direction, can have an opening angle 42 of at least 8° arc degrees, a maximum of 100° arc degrees, in particular an opening angle 42 of 40 arc degrees.Along a flow through the second longitudinal region 28, the flow can separate, whereby a turbulent backflow region 44 can form. Because, as in . Fig.3, the divergent cross-sectional profile is followed by an area with a constant cross-sectional profile, this turbulent backflow region 44 can exit from the through-opening 22 on the gas outlet side 24 with a main flow. Exhaust gas 36 or engine exhaust gas discharged from a combustion chamber of the internal combustion engine can flow around the gas outlet side 24. The burner exhaust gas 34 can mix particularly well with this exhaust gas 36 after exiting the through-opening 22 due to the high turbulence of the flow caused by the backflow region 44. As a result, a temperature distribution in a mixed exhaust gas 38, i.e. a mixture of exhaust gas 36 and burner exhaust gas 34, can be particularly homogeneous, viewed or measured in a flow cross-section. This can be particularly advantageous when flowing towards an exhaust aftertreatment device 40, which can be located downstream of the through-opening 22 in the exhaust tract.At the same time, the mixed exhaust gas 38 can have a higher temperature than the exhaust gas 36. As a result, the exhaust gas aftertreatment device 40, which can preferably be a catalyst, can be brought to a required operating or working temperature or maintained at this temperature.

[0047] A particularly preferred embodiment is described below.

[0048] A sharp edge at the inlet or at the inlet opening of the diffuser, which the second longitudinal section 28 may have, can tend to cause overheating. Therefore, a chamfer, which the first longitudinal section 26 may have, is also applied to an inner side of the combustion chamber 12. This geometric change also reduces flow losses of the exhaust gas 36 that can flow into the diffuser.

[0049] The diffuser reduces the flow velocity of the exhaust gas 36 and increases the gas pressure or static pressure in the flow. Reducing the gas velocity or flow velocity reduces the heat transfer or heat input into the combustion chamber wall, which may be present in the housing element (the Reynolds number decreases), and thus reduces thermal stresses that can lead to component failure (in this case, cracks). A further advantage of turbulence is the even distribution of the hot exhaust gas 36 into the catalytic converter, which may represent the exhaust aftertreatment element 40. If the exhaust gas 36 flows directly onto the catalytic converter surface, local overheating could lead to stress cracks.The turbulent and thus well-mixed exhaust gas, which can also be referred to as mixed exhaust gas 38, from the burner 10 (very hot, approximately 1200°C) and the combustion engine exhaust gas, which can also be referred to as exhaust gas 36 (cooler, approximately 500°C), heats the catalyst more evenly. Since the angle of the diffuser, which can be exhibited by the second length region 28, is 40 degrees (30 degrees to 100 degrees) and thus significantly above the critical 8 degrees limit for separation, turbulence, dead space areas, and friction losses can occur.

[0050] The following technical problem can be solved. Crack formation due to local component overheating at the combustion chamber outlet, which the outlet element 16 can have, and at the catalyst can be avoided. Diffuser flows are known in aircraft engines or power plant combustion chambers. Due to the diffuser-shaped design of the through-opening 22, which can be provided by the outlet element 20, the flow velocity and thus also the heat transfer or heat input of the burner gas or burner exhaust gas 34 to a wall of the combustion chamber 12, which can be provided by the housing element 18, can be reduced. At the same time, the resulting turbulence flows can force optimized mixing and even distribution of the burner exhaust gas 34 with the engine exhaust gas or exhaust gas 36. Crack formation due to thermal component stresses at the combustion chamber outlet opening and the catalyst can advantageously be avoided. List of reference symbols 10 burners 12 Combustion chamber 13 Burner housing 14 Insertion element 15 Air supply 16 flap 17 Installation position of an ignition device 18 Housing element 19 radial direction of the combustion chamber 20 Exit element 21 axial direction of the combustion chamber 22 passage opening 23 Inlet side 24 Gas outlet side 26 first length range 28 second length range 30 third length range 32 Flow direction 34 Burner exhaust gas 36 exhaust 38 mixed exhaust gas 40 exhaust aftertreatment system 42 opening angle 44 Backflow area 46 Parting line 48 Speed profile B1 first area B2 second area B3 third area D diffuser

Claims

[1] Burner (10) for an exhaust tract through which exhaust gas (36) of an internal combustion engine of a motor vehicle can flow, comprising a combustion chamber (12) in which a mixture comprising air and a fuel is to be ignited and thereby burned, with at least one housing element (18) which at least partially delimits the combustion chamber (12), and with at least one outlet element (20) which has at least one through-opening (22) via which burner exhaust gas (34) produced by the combustion of the mixture can be discharged from the combustion chamber (12) for heating the exhaust tract of the internal combustion engine, characterized bythat the passage opening (22) has at least one first longitudinal region (26) through which the burner exhaust gas (34) can flow, which has a first cross section with a convergent course, and at least one second longitudinal region (28) through which the burner exhaust gas (34) can flow, which second cross section with a divergent course. [2] Burner (10) according to claim 1, characterized by that the first length region (26) is arranged upstream of the second length region (28). [3] Burner (10) according to one of the preceding claims, characterized by that the second length range (28) has an opening angle greater than 8 arc degrees and / or less than 100 arc degrees. [4] Burner (10) according to one of claims 1 or 2, characterized by that the second length range (28) has an opening angle greater than 30 arc degrees, and / or less than 100 arc degrees. [5] Burner (10) according to one of the preceding claims, characterized by that the through-opening (22) has a third longitudinal region (30) downstream of the first longitudinal region (26) and upstream of the second longitudinal region (28), which has a third cross-section with a constant profile. [6] Burner (10) according to one of the preceding claims, characterized by that the outlet element (20) has a plurality of through openings (22) through which the burner exhaust gas (34) can be discharged from the combustion chamber (12) for heating the exhaust tract of the internal combustion engine. [7] Burner (10) according to one of the preceding claims, characterized by that the burner exhaust gas (34) can be mixed with an exhaust gas (36) flowing through the exhaust tract when being discharged from the outlet element (20). [8] Burner (10) according to one of the preceding claims, characterized bythat the outlet element (20) is arranged upstream of an exhaust gas aftertreatment device (40) arranged in the exhaust gas tract with respect to a flow direction of the exhaust gas tract. [9] Burner (10) according to one of the preceding claims, characterized by that the outlet element (20) has at least one curvature. [10] Internal combustion engine for a motor vehicle with a burner (10) according to one of the preceding claims. [11] Method for operating a burner (10) according to one of claims 1 to 9.

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