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, at least one housing element (17) which at least partially delimits the combustion chamber (12), and at least one outlet element (18) which has at least one through-opening (19) via which burner exhaust gas (34) produced by the combustion of the mixture can be discharged from the combustion chamber (12) to heat the exhaust tract (25) of the internal combustion engine. The burner (10) is characterized in that the outlet element (18) has at least one curvature (20).

Description

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, and to an internal combustion engine having a burner for a motor vehicle.Such a burner is known from DE 10 2021 001 580 A1. The burner has at least one combustion chamber in which an air and a mixture, in particular a liquid mixture, comprising fuel is to be ignited and thereby burned. In addition, the burner has at least one housing element. 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 an outlet element which delimits the combustion chamber at least partially, for example in the axial direction of the combustion chamber. The outlet element has at least one passage opening, via which burner exhaust gas generated by the burning of the mixture can be discharged from the combustion chamber for heating the exhaust tract of the internal combustion engine, in particular for heating at least one component arranged in the exhaust tract of the internal combustion engine, and can be introduced in particular into the exhaust tract or at least one 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 side of the combustion chamber or of the housing element. The outlet side can be referred to in particular as the gas outlet side.It is an object of the present invention to provide a burner for an exhaust tract through which exhaust gas from an internal combustion engine of a motor vehicle can flow, and an internal combustion engine having a burner for a motor vehicle, such that a thermal load capacity of the burner can be particularly increased.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 can flow, having the features of patent claim 1, and by an internal combustion engine having the features of patent claim 10. Advantageous embodiments with expedient developments of the invention are specified in the other claims.A first aspect of the invention relates to a burner for an exhaust tract through which exhaust gas of an internal combustion engine of a motor vehicle can flow, having a combustion chamber in which a mixture comprising air and a fuel can be ignited and thereby burned, having at least one housing element which at least partially delimits the combustion chamber, and having at least one outlet element which has at least one through opening via which burner exhaust gas generated by the burning of the mixture can be discharged from the combustion chamber for heating 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 motor vehicle. In order to create a burner of the stated type, so that a thermal load capacity of the burner, in particular of the outlet element and / or of the housing element, can be particularly increased, it is provided that the outlet element has at least one curvature.In other words, the outlet element should not be designed as a planar surface. The outlet element can be curved, curved and / or bulbous. The outlet element can be connected to the housing element in a form-fitting and / or materially bonded and / or force-fitting manner or can in particular be formed integrally with the housing element. The curved shape, i.e. the fact that the outlet element has at least one curved surface or is designed as a curved element or curved surface, results in the advantage that more surface or surface or volume is available for expansion or contraction, correspondingly when the outlet element is heated or cooled. As a result, a larger surface or surface or volume is available for distributing, for example, thermal stresses and / or expansions, as a result of which stress peaks and / or expansion peaks can be avoided or reduced. At the same time, the shape of the curvature can be used to define an extension direction for the outlet element, in particular in the direction of the curvature, that is to say that the curvature increases during an extension or the curved surface increases. The at least one surface of the outlet element can be designed as a partial surface of a hyperboloid. The housing element and / or the outlet element can be manufactured from metal, a metal alloy, in particular from a steel. 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 an outlet element which delimits the combustion chamber at least partially, for example in the axial direction of the combustion chamber. The outlet element can have at least one passage opening, via which burner exhaust gas generated by the burning 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, or is discharged during operation of the burner, and can be introduced or is introduced in particular into the exhaust tract or at least a length 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 side of the combustion chamber or of the housing element. The outlet side can be referred to in particular as the gas outlet side. The exhaust gas aftertreatment device can be, in particular, a catalytic converter.The invention is based in particular on the following findings and considerations: during operation of the burner, the combustion chamber can heat up particularly strongly, for example to up to 1150° C. As a result of a possible temperature difference, which can be particularly high and is, for example, almost 1,200 K, very high, in particular thermal, stresses can occur at a perforated outlet surface in the form of the outlet element having the at least one passage opening, which stresses can lead to cracks. A conventional burner can have a gas outlet with a flat and / or planar outlet element connected to the burner or the housing element. This means that in the conventional burner no curved or curved outlet element can be provided. Thus, in the conventional burner, for example, during cooling, there may be a risk of cracking. Thermal stress cracks can therefore occur in the conventional burner.In contrast, by means of the burner according to the invention, the thermal load capacity of the burner, in particular of the outlet element and / or of the housing element, can be particularly increased. This can be achieved in particular by the outlet element being curved and / or curved, as a result of which an expansion direction can be predefined for the outlet element under thermal load, in particular in order to contract and / or expand., that is to say the outlet element is in particular not designed as a planar or flat plate. By means of a predefined curvature or curvature of the outlet element, thermal expansions between the outlet element and the burner or the combustion chamber housing or the housing element or the combustion chamber can take place uniformly in the region of the curvature, as a result of which thermal stresses and cracks can be avoided. In particular, crack formation, for example in the outlet element, as a result of excessively high tensile stresses and / or excessively high compressive stresses can be prevented, above all during cooling of the combustion chamber. Overall, it can be seen that a burner with a curved gas outlet side can be realized. By increasing the thermal load capacity of the burner, safety against damage to the burner can be particularly increased. In particular, a service life of the burner can be particularly increased.The invention also includes developments by means of which additional advantages are obtained.According to a development of the burner, the curvature has a shape of at least part of a spherical surface. The shape here means at least one surface of the outlet element, i.e. a side pointing towards the combustion chamber or closest to the combustion chamber and facing and / or a side facing the exhaust tract.In other words, the outlet element or the curvature should have the shape of an imaginary spherical surface. In particular, the ball surface should be designed such that it can be represented as part of a ball surface with only one opening. The opening can be such that it comes to a plane in the case of an imaginary section or section of the ball, which is in particular an imaginary ball. The at least one part can be one of the imaginary two parts of the ball, in particular of the ball surface, which are produced by the cut. The at least one part is formed as a surface which is not completely closed by the opening. The ball whose part or partial surface is intended to represent the curvature after the cut can be in particular an imaginary or fictitious ball. In particular, the curvature should not represent the shape of a strip element of the surface of the imaginary sphere, wherein such a strip would have at least two openings and would come about by a section of the imaginary sphere having at least two imaginary planes.According to a further development of the burner, the part is a first, smaller of two parts which are produced in the case of a decentral intersection of a sphere with a plane.In other words, the shape of the curvature is to be defined or determined by cutting, in particular completely intersecting, an imaginary sphere from an imaginary plane. Decentral means here that this plane runs outside a center point of the sphere when the sphere is notionally cut, as a result of which two imaginary hemispheres of different sizes are produced, as a result of which a first, smaller part is given. In particular, the curvature should have the shape of the part which is the smaller of the two imaginary parts in the imaginary section of the ball with the plane. The uniform shape of the curvature when it is formed as part of the imaginary sphere results in the advantage that, under a thermal load, the outlet element can deform or expand or contract uniformly, as a result of which stress peaks, for example as a result of an irregular geometry of the curvature, can be avoided.According to a development of the burner, the through-opening has at least one first longitudinal region through which the burner exhaust gas can flow, which first longitudinal region 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 second longitudinal region has a second cross section with a divergent course.This results in the advantage that a heat input from the hot burner exhaust gas into the outlet element can be reduced compared to a through-opening with, for example, a constant or only divergent cross-sectional profile. In addition, there is an advantage that a temperature in the outlet element can be uniformly distributed. As a result, stress cracks as a result of thermal stresses and / or expansions can be prevented, in particular during heating and / or cooling of the outlet element. Stresses are understood here to mean tensile stresses and / or compressive stresses.The convergent course is understood here in particular to mean a cross-sectional course which narrows in the flow direction of the burner exhaust gas discharged or to be discharged from the combustion chamber via the passage opening. This means that the cross-sectional area through which flow can pass 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, that is to say is narrower downstream than upstream or has a smaller cross-sectional area. Divergent means in particular that the cross-sectional area through which flow can pass widens in the flow direction of the burner exhaust gas which is discharged or is to be discharged from the combustion chamber via the passage opening, that is to say that the cross-section through which flow can pass is greater downstream than upstream. The cross-sectional area here denotes the flow-through area which is perpendicular to a middle flow direction. Thus, the respective cross-sectional profiles, i.e. the convergent cross-sectional profile and the divergent cross-sectional profile, mean a cross-sectional profile which extends in each case in the flow direction. Flow-through means here that the burner exhaust gas and / or a flame can flow through the passage opening or is flowed through during operation of the burner. The flame may be used here to mean exhaust gas which has not yet been completely burnt or burnt. The outlet element can have a wall region which has the through opening.In particular, the first longitudinal region, in particular in the flow direction of the exhaust gas flowing through the passage opening, should be arranged upstream of the second longitudinal region.The first longitudinal region, along which the hot burner exhaust gas flows into the passage opening, has a convergent cross-sectional profile, although the heat input can increase as a result of a flow speed which is increased as a result. As a result of the convergent cross-sectional profile, an obtuse angle, that is to say greater than 90 degrees of arc, is provided between the wall region adjoining the flow and comprising the first longitudinal section and a wall region perpendicular to the inflow direction into the first longitudinal region, precisely in an inflow region or inflow region or around the inlet opening, as viewed in a section, for example perpendicular to the inlet opening through the passage opening. In contrast to a divergent cross-sectional profile, more material is available to the introduced heat, which is introduced, for example, at the apex of the angle, via which material it can be distributed away from the inflow region into surrounding wall material than in the case of a divergent cross-sectional profile directly or directly away from the inflow region in the direction of flow. In other words, in the case of a convergent inflow region, the heat introduced here can be dissipated better via heat conduction into the surrounding material. This results in the advantage that more heat can be introduced until a material-specific failure limit is reached, compared to an only divergent cross-sectional profile in the flow direction. In order to reduce the heat input from the flow into the wall region surrounding the through-opening overall, the second length region, which adjoins the first length region downstream, has a divergent cross-sectional profile. The heat input or a quantity of heat introduced into a wall region can be dissipated particularly well by heat conduction in the inflow region of the first longitudinal region of the passage opening, although here the heat input can be increased by the convergent cross-sectional profile. In the second longitudinal region, the heat input from the flow into the wall region which surrounds or comprises the second longitudinal region can be reduced by a delay in the flow and an increase in the boundary layer thickness as a result of the static increase in pressure along the flow. A flow direction through the at least one through opening from the combustion chamber into the exhaust tract is predefined for the burner exhaust gas, wherein the first longitudinal region is arranged in front of the second longitudinal region in the flow direction and can be flown through and / or is arranged upstream of the divergent cross-sectional profile. During operation of the burner, the burner exhaust gas thus flows first through the first longitudinal section and immediately subsequently through the second longitudinal section. The first longitudinal section upstream of the second longitudinal section in the flow direction can result in the advantage that flow losses when flowing through the entire through-opening are lower than if the through-opening is configured only as a diffuser. A reduction in flow losses can mean that more burner exhaust gas or a greater mass flow of burner exhaust gas can be discharged from the combustion chamber into the exhaust tract or is discharged from the combustion chamber during operation of the burner than in the case of higher flow losses.According to a development of the burner, the through opening, in particular in the flow direction of the burner exhaust gas flowing through the through opening, has, downstream of the first longitudinal region and, in particular in the flow direction of the burner exhaust gas flowing through the through opening, upstream of the second longitudinal region, a third longitudinal region which has a third cross section with a constant profile.In other words, when viewed in the flow direction, a third length region is arranged between the first length region and the second length region when flowing through the through opening, said third length region having a cross section with a constant profile. In particular, the third longitudinal section is 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 length region can thus directly adjoin the first length region along the through-opening and the second length region can directly adjoin the third length region. The third length region with the constant cross-sectional profile, through which flow can pass, can have in particular a cross section which corresponds to the narrowest or smallest cross section of the first length region with the convergent cross-sectional profile and the narrowest or smallest cross section of the second length 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, in between, at least one region with a constant cross section through which flow can take place.This results in the advantage that after a possible separation after an exit from the first length region before entering the second length region, the flow can again be applied to a wall of this third length region when flowing through the third length region, which wall can surround or enclose or encompass it. As a result, local temperature or heat input peaks in the second length range can be avoided or reduced. When selecting or configuring the third cross section, which can be in particular the narrowest cross section of the through-opening or when flowing through the through-opening.In particular, it can be provided that the through opening or each through opening is configured rotationally symmetrically about a central axis which is configured perpendicular to a or a respective inlet opening or on a or respective inlet cross section through which the flow can flow when it flows through the through opening.The housing element and / or the combustion chamber and / or the outlet element can be designed to be rotationally symmetrical about a further central axis and / or tubular. The further central axis may coincide with the or a central axis of the through-openings.According to a development of the burner, the at least one through-opening is arranged in a region of the outlet element which has the curvature.In other words, the outlet element has the at least one through-opening in the region of the curvature or in a curved region.The through-opening extends through the curvature, that is to say through the outlet element in a region of the curvature. When hot burner exhaust gas flows through the through-opening, a heat input in a region or wall region around the through-opening can be particularly high compared to a wall region which does not have a through-opening. In particular, the heat input can be greater here than in the housing element. Because this wall region around the passage opening into which a high heat input can take place lies in the region of the curvature, an expansion of the outlet element can take place in a particularly low-stress manner, since the passage opening is located in the region of the curvature.According to a further development of the burner, the outlet element has a plurality of passage openings via which the burner exhaust gas can be discharged from the combustion chamber for heating the exhaust tract of the internal combustion engine.In particular, it is provided that the outlet element has a plurality of structurally identical passage openings. The plurality of through openings results in the advantage that a mass flow of burner exhaust gas, which can be supplied to the engine exhaust gas or can be discharged into the exhaust tract, can be increased.In this case, it can be provided that the plurality of passage openings, in particular all passage openings, are arranged in a region of the outlet element which has the curvature. In other words, all through-openings should extend through the curvature in each case. In this case, the through openings can each be spaced apart from one another. This results in the advantage that the quantity of burner exhaust gas, in particular a mass flow of burner exhaust gas which is to be supplied to the exhaust gas or engine exhaust gas from the combustion chamber of the internal combustion engine, can be increased by a plurality of passage openings.According to a development of the burner, the passage openings are arranged evenly distributed in the circumferential direction of the outlet element.This results in the advantage that, due to an equally distributed arrangement of the passage openings, heat input as a result of hot burner exhaust gas flowing through the respective passage openings is also introduced symmetrically or uniformly into the outlet element. As a result, local stress peaks in or on or on the outlet element can be prevented or avoided or reduced.The through openings can be arranged in the circumferential direction of the combustion chamber in an equally distributed manner, in particular if the combustion chamber or the housing element at least partially enclosing the combustion chamber is formed rotationally symmetrically about a central axis. In this case, the through openings are arranged in particular along an, in particular imaginary, circle, the center point of which is arranged on the central axis.According to a further development of the burner, the curvature is curved outwards with respect to the combustion chamber. In other words, the outlet element should be curved outwards away from the combustion chamber or the housing element or into the exhaust tractThis results in the advantage that an outflow from the combustion chamber takes place in a particularly fluidically favorable and / or low-resistance manner, because burner exhaust gas, which is still located in the combustion chamber, can collect before the passage openings before an outflow from the burner through the passage openings in the curvature, which is curved outwards.A second aspect of the invention relates to an internal combustion engine for a motor vehicle having a burner, in particular according to the first aspect of the invention. Advantages and advantageous refinements of the first aspect of the invention are to be regarded as advantages and advantageous refinements of the second aspect of the invention and vice versa.The internal combustion engine is preferably designed for driving the motor vehicle. The internal combustion engine can comprise an exhaust tract and the burner according to the invention according to the first aspect of the invention. In addition, the internal combustion engine can also comprise the exhaust gas aftertreatment device.For example, the internal combustion engine, in particular in its completely produced state, has the burner, wherein the burner is preferably arrangeable or 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 formed 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, via which intake tract 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. An exhaust gas aftertreatment device for aftertreatment of the exhaust gas can be arranged in the exhaust tract. By means of the burner, in particular by means of the burner exhaust gas generated in the combustion chamber of the burner, the exhaust gas aftertreatment device can thus be heated. The exhaust gas aftertreatment device, which is arranged in particular in the exhaust tract of the internal combustion engine, is preferably at least one catalytic converter.A further aspect relates to a motor vehicle having an internal combustion engine, in particular according to the second aspect of the invention. Advantages and advantageous refinements of the first, the second and the third aspect of the invention are to be regarded as advantages and advantageous refinements of the further aspect and vice versa.Further advantages, features and details of the invention are evident from the following description of preferred exemplary embodiments and on the basis of the drawings. The features and combinations of features mentioned above in the description and 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 respectively specified combination but also in other combinations or alone without departing from the scope of the invention.The following are shown: FIG. 1 is a schematic sectional view of a burner according to the invention; and FIG. 2 shows a schematic detailed sectional view of an outlet element of the burner with passage openings, and FIG. 3 shows a schematic plan view of a rotationally symmetrical outlet element with passage openings, viewed from outside a combustion chamber.In the figures, identical or functionally identical elements are provided with identical reference symbols.FIG. 1 shows a schematic sectional view of a burner 10 for an exhaust tract 25 through which exhaust gas from an internal combustion engine of a motor vehicle can flow. The motor vehicle can preferably be driven by means of the internal combustion engine.The exhaust tract 25 can be understood in particular as 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 may be desirable in order to be able to quickly heat up and / or keep warm an exhaust gas aftertreatment device arranged in the exhaust tract 25, for example, wherein, however, the temperature of the exhaust gas is only insufficiently high in these operating states or operating situations. By means of the burner 10, the exhaust tract 25, and in particular the exhaust gas aftertreatment device, can be heated and / or kept warm. This means that the exhaust tract 25, in particular the exhaust gas aftertreatment device, can be heated and / or kept warm by means of the burner 10, for example in addition to heating and / or keeping warm by means of the exhaust gas. This exhaust gas can be understood to mean, in particular, an exhaust gas generated from a fuel-air mixture in a combustion chamber of the internal combustion engine. The combustion chamber, which is designed as a cylinder, for example, is designed separately from the burner 10.The internal combustion engine is designed, for example, as a diesel engine. The exhaust gas aftertreatment device comprises, for example, at least one catalytic converter or is designed as a catalytic converter. The exhaust gas aftertreatment device or the catalytic converter is designed, for example, as an oxidation catalytic converter, in particular a diesel oxidation catalytic converter, a nitrogen oxide storage catalytic converter, an SCR catalytic converter as a particle filter, in particular a diesel particle filter. The exhaust gas of the internal combustion engine can be purified by means of the exhaust gas aftertreatment device.The burner 10 has a burner housing 11 and a combustion chamber 12 provided on the burner housing, in which a mixture comprising air and a fuel, 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 with the formation of a flame and in particular with the provision of a burner exhaust gas.For example, the fuel is the fuel which is also burned in the combustion chamber, which is designed as a cylinder, for example, of the internal combustion engine. Thus, the fuel may be used as the fuel. However, the burner exhaust gas is not the exhaust gas or engine exhaust gas generated in the combustion chamber of the internal combustion engine.In the exemplary embodiment, the burner 10 furthermore has an air feed 13 in the burner housing 11, by means of which or via which the air, in particular for forming the mixture, can be introduced into the combustion chamber 12, in particular directly. Furthermore, the air feed 13 can be closed by a flap 14 pivotably attached to the burner housing 11, in particular can be closed by the flap 14 with respect to the combustion chamber 12, so that, for example, no soot from the exhaust gas of the internal combustion engine can be deposited on and in the air feed 13, as a result of which a trouble-free function of the air feed 13 and of the burner 10 can be at least extended overall.In the exemplary embodiment, the burner 10 furthermore has an introduction element 15, by means of which or via which the fuel, in particular for forming the mixture, can be introduced into the combustion chamber 12. The introduction element 15 is designed, for example, as an injection valve. The introducing element 15 initially injects the fuel into the air supply 13, after which the fuel is introduced together with the air from the air supply 13 directly into the combustion chamber 12.For example, the burner 10 has at least one ignition device, in particular arranged in the combustion chamber 12, by means of which the mixture comprising the air and the fuel is to be ignited and thereby burned. The ignition device is designed, for example, as a spark plug, glow plug or glow plug. The ignition device is arranged, for example, in an installation position 16 in the burner housing 11 provided with the reference numeral 16.The burner 10 has at least one housing element 17, which can be referred to in particular as a combustion chamber housing. The housing element 17 delimits the combustion chamber 12 at least partially, in particular predominantly. In the exemplary embodiment, the combustion chamber 12 or the housing element 17 is at least substantially cylindrical. Furthermore, in the exemplary embodiment, the housing element 17 can delimit the combustion chamber 12 at least partially, in particular predominantly or completely, in its radial direction 24. Furthermore, the housing element 17 has, for example, at least one outlet element 18 which at least partially delimits the combustion chamber 12 in its axial direction 23, in particular at one end or in the axial direction 23, adjoining the combustion chamber 12 or the housing element 17. The combustion chamber 12 is delimited by the burner housing 11 opposite the outlet element 18 in the axial direction 23. Overall, the combustion chamber 12 is delimited and formed, starting from the burner housing 11, the housing element 17 and the outlet element 18, as seen in the axial direction 23. The outlet element 18 and the housing element 17 are preferably formed together in one piece or formed separately from one another. The outlet element 18 can be curved as shown in FIG. 1, i.e. it cannot be formed as a flat plate extending in the radial direction 24, which flat plate closes the combustion chamber 12. The outlet element 18 can bulge or expand away from the combustion chamber 12 and thus into the exhaust tract 25. As shown in FIG. 1, the outlet element 18 can have at least one, in particular a plurality of, passage openings 19.FIG. 2 shows a schematic detailed sectional view of the outlet element 18 of the burner 10 with a plurality of preferably identically constructed through-openings 19. This can mean that the through-openings 19 extend through the outlet element 18. In the exemplary embodiment, the outlet element 18 comprises a plurality of through-openings 19. The central axis can extend in particular in the axial direction 23 of the combustion chamber 12. The burner exhaust gas or a flame in the combustion chamber 12 enters the through-opening or through-openings 19 from the combustion chamber 12, flows through the through-openings 19 and flows from the through-opening or through-openings 19 into the exhaust tract 25.In the exemplary embodiment, the outlet element 18 can be curved, that is to say can have a curvature 20 and / or can be completely curved. Preferably, the outlet element 18 is arched pointing outward away from the combustion chamber 12 toward the exhaust tract 25. In this case, respective flow directions of the burner exhaust gas per passage opening 19 can be different. The different flow directions per through-opening 19 can be caused or caused by the curvature 20 of the outlet element 18. However, the outlet element 18 can have only a single through opening 19 arranged, for example, centrally or symmetrically about the central axis or axis of rotation. The one or each through-opening 19 can have a circular or rotationally symmetrical cross section. The outlet element 18 which is curved in the exemplary embodiment can be connected integrally to the housing element 17 and thus directly adjoin the combustion chamber 12 or the housing element 17. As shown in FIG. 2 by means of a cut through-opening 19, each through-opening 19 can be beveled at least toward the combustion chamber 12 and / or toward the exhaust tract 25.As described in the exemplary embodiment, the outlet element 18 can be formed as a partial surface or outer surface of an imaginary and not illustrated ball which is cut or cut through by an imaginary and not illustrated plane. As can be seen from the cross section along the axial direction 23 of the outlet element 18, the outlet element 18 can have the shape of a smaller ball half which is produced during the section with the imaginary ball having the imaginary plane. In this case, the ball can be cut off in a decentralized manner, that is to say outside its center point, with the result that no two equally sized ball halves are produced. In a further exemplary embodiment, a connecting element 21 can be arranged directly between the housing element 17 and the outlet element 18 in the axial direction 23. This connecting element 21 can have a different curvature or curvature than the outlet element 18. Additionally or alternatively, the connecting element 21 can be formed integrally with the outlet element 18 and / or with the housing element 17.FIG. 3 shows a schematic plan view of a rotationally symmetrical outlet element 18 with passage openings 19 as viewed from outside a combustion chamber 12, The passage openings 19 can be arranged on a circular path around the central axis or rotational symmetry axis of the housing element 17 and / or the combustion chamber 12 and / or the outlet element 18 in a uniformly distributed manner, that is to say at an identical distance from one another in the circumferential direction 22 on a circular path. The through-openings 19 can be arranged only on the outlet element 18 or extend only through it. As shown in FIG. 3, the outlet element 18 and the combustion chamber 12 or the housing element 17 enclosing the combustion chamber 12 in the radial direction 24 can be formed rotationally symmetrically about a central axis, wherein the central axis can be parallel or coincident with the radial direction 24.A particularly preferred exemplary embodiment is described below.The following technical problem can be solved. During operation of the burner 10, the combustion chamber 12 heats up to 1150° C. on the outlet side, which can also be referred to as outlet element 18. Due to the possible temperature difference of almost 1200 Kelvin, very high stresses occur at the perforated outlet surface, which can be formed by the outlet element 18, which can lead to cracks. These stress cracks are to be prevented by the solution described. Exit elements with planar surfaces are known in this case. Their disadvantage can be that high stresses arise or can occur during cooling, as a result of which a risk of cracking can exist. One possible solution may be as follows: Due to the curved geometry of the curvature 20, the area in which the stresses occur can increase. This larger area can be more elastic and can thus also be suitable for minimizing tensile and compressive stresses. Curved technical systems, for example pressure accumulators, with σ=F / A (sigma: stress, F: force, A: surface) projected, are suitable for reducing stresses, since the projected surface area becomes larger in the case of a curved plate. Advantageously, crack formation as a result of excessively high tensile and compressive stresses can be prevented, especially during cooling of the combustion chamber 12.List of reference characters10 Burner 11 Burner housing 12 Combustion chamber 13 Air feed 14 Flap 15 Introduction element 16 Ignition device 17 Housing element 18 Outlet element 19 Passage openings 20 Curvature 21 Connecting element 22 Circumferential direction 23 Axial direction of the combustion chamber 24 Radial direction of the combustion chamber 25 Exhaust tractReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2021 001 580 A1

[0002]

Claims

Burner (10) for an exhaust tract (25) through which exhaust gas (36) of an internal combustion engine of a motor vehicle can flow, having a combustion chamber (12) in which a mixture comprising air and a fuel can be ignited and thereby burned, having at least one housing element (17) which at least partially delimits the combustion chamber (12), and having at least one outlet element (18) which has at least one through opening (19) via which burner exhaust gas (34), which is generated by the burning of the mixture, can be discharged from the combustion chamber (12) for heating the exhaust tract (25) of the internal combustion engine, characterized in that the outlet element (18) has at least one curvature (20).Burner (10) according to claim 1, characterized in that the bulge (20) has a shape of at least a part of a spherical surface.Burner (10) according to claim 2 characterized in that said part is a first, smaller one of two parts formed by a decentral intersection of a sphere with a plane.Burner (10) according to one of the preceding claims, characterized in that the passage opening (19) has at least one first longitudinal region through which the burner exhaust gas (34) can flow, which first longitudinal region has a first cross section with a convergent course, and at least one second longitudinal region through which the burner exhaust gas (34) can flow, which second longitudinal region has a second cross section with a divergent course.Burner (10) according to claim 4, characterised in that the through-opening (19) has, downstream of the first length region and upstream of the second length region, a third length region which has a third cross-section with a constant course.Burner (10) according to one of the preceding claims, characterized in that the at least one through-opening (19) is arranged in a region of the outlet element (18) which has the curvature (20).Burner (10) according to one of the preceding claims, characterized in that the outlet element (18) has a plurality of passage openings (19), via which the burner exhaust gas (34) can be discharged from the combustion chamber (12) in order to heat the exhaust tract (25) of the internal combustion engine.Burner (10) according to Claim 7, characterized in that the passage openings (19) are arranged in a uniformly distributed manner in a circumferential direction (22) of the outlet element (18).Burner (10) according to one of the preceding claims, characterized in that the curvature (20) is curved outwards with respect to the combustion chamber (12).Internal combustion engine for a motor vehicle having a burner (10) according to one of the preceding claims.

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