DE102011081309B3 - Method for operating burner in exhaust system of internal combustion engine of motor vehicle, involves setting smaller burner power in region at which air-fuel ratio is greater than one so as to reduce thermal load of burner - Google Patents

Abstract

The method involves heating an oxidation catalyst (8) depending on a burner power. Burner (10) arranged in the component (7) of an exhaust system (4) is operated by varying supplied air volume and fuel quantity. Thermal load of the burner and the exhaust system is reduced by setting smaller burner power in the region at which air-fuel ratio is greater than 1, and by setting greater burner power in the region at which air-fuel ratio is less than 1. An independent claim is included for exhaust system of internal combustion.

Description

The present invention relates to a method for operating a burner which is arranged in an exhaust system of an internal combustion engine, in particular of a motor vehicle, in particular upstream of an oxidation catalytic converter. The invention also relates to an exhaust system equipped with such a burner.

Modern exhaust systems of internal combustion engines include efficient exhaust gas treatment devices, such as SCR systems, _NOx storage and particulate filter. So that certain exhaust treatment facilities, such. As catalysts can work optimally, they must have a predetermined minimum operating temperature. Furthermore, it is for regenerating certain exhaust treatment devices, such. As particulate filter, often required to heat them to a regeneration temperature. In order to be able to achieve these temperature levels independently of the operating state of the respective internal combustion engine and to shorten a cold start phase of the internal combustion engine, it is possible to equip the exhaust system additionally with an oxidation catalyst, which is arranged upstream with respect to the components to be heated. It is basically possible to integrate the respective oxidation catalyst in the form of a catalytically active coating in the respective component to be heated. Upstream of this oxidation catalytic converter can then be arranged a separate fuel supply, with the aid of which a fuel, so-called secondary fuel, is introduced into the exhaust gas flow. This fuel can then be reacted in the oxidation catalyst, whereby the exhaust gas flow heats up strongly. The hot exhaust gas can then be used to heat the subsequent components.

Alternatively, it is also possible, upstream of the components to be heated to connect a burner to the exhaust system, which has its own fuel supply (secondary fuel) and its own air supply (secondary air). In the burner fuel can then also be reacted with air depending on demand to produce hot burner exhaust gases, which are added to the motor exhaust gases coming from the engine, so as to produce a hot exhaust gas flow, with the aid of which the respective exhaust gas treatment component can be heated.

From the DE 10 2008 063 990 A1 Such an exhaust system is known, which is equipped with such a burner for heating the exhaust gas flow.

The present invention is concerned with the problem of providing for an exhaust system with burner or for an associated operating method, an improved embodiment, which is characterized in particular by the fact that the thermal stability and durability of the burner or the exhaust system is increased.

According to the invention, this problem is solved by the subject matters of the independent claims. Advantageous embodiments are the subject of the dependent claims.

The invention is based on the fundamental idea of reducing the local combustion temperature. As a result, on the one hand, the peak temperature is reduced, which at the same time improves the temperature uniform distribution. According to the invention, the lowering of the combustion temperature is achieved, depending on the required burner output, either by an overstoichiometric operation, ie by operation with excess air (λ> 1) or by substoichiometric operation, ie by operation with excess fuel (λ <1). In this case, an air-fuel ratio (λ) greater than 1 is preferably set in a range of smaller burner powers. In superstoichiometric operation, the excess air serves as a cooling inert gas, so that the combustion temperature can be reduced. In contrast, an air-fuel ratio (λ) is set smaller than 1 in a range of larger burner powers. In such substoichiometric combustion, the excess vaporized fuel serves as an inert gas. At the same time, the heat required for the evaporation of the liquid supplied fuel causes a lowering of the combustion temperature. After mixing the burner exhaust gas with the engine exhaust gas, the excess fuel can be reacted with the excess air which is contained in the engine exhaust, which is usually lean, that is to say an excess of air. Due to the high temperatures, this can already be done from the mixing of the burner exhaust gas to the engine exhaust gas in the respective exhaust gas line. However, the exhaust system preferably contains an oxidation catalytic converter downstream of the burner or downstream of the connection point of the burner to the exhaust system. At the latest in this oxidation catalyst, the reaction of the excess fuel of the burner exhaust gas with the excess air of the engine exhaust gas then takes place.

According to a preferred embodiment, the control of the burner power takes place in the range of smaller burner powers by varying the amount of air and varying the amount of fuel. With increasing burner power, the amount of air and the amount of fuel is increased until a maximum supply of air is reached. The range of smaller burner power is thus by the maximum supply air and the condition that the air-fuel ratio should be greater than a minimum value limited. This minimum value may preferably be 1.

According to an advantageous development, the amount of fuel can now be further increased in the range of smaller burner powers with increasing burner power when the maximum air quantity is reached, while the air quantity remains set to the maximum value. As a result, as the burner power increases, that is, as the fuel quantity increases, the air-fuel ratio in the direction 1 decreases, that is, approaches the value 1 from above. Appropriately it can now be provided that at a first switching value of the air-fuel ratio, which is greater than 1, the transition from the range of smaller burner power to the region of greater burner power takes place. Advantageously, this transition is realized in that with increasing burner power, the air quantity is suddenly set to a reduced value, such that the air-fuel ratio also decreases abruptly to a second switching value, which is smaller than 1. In this way, an air-fuel ratio value range containing 1 (λ = 1) is skipped. In other words, the change from the operating mode (λ> 1) assigned to the range of smaller burner powers to the operating mode associated with the range of larger burner powers (λ <1) occurs abruptly and virtually without transition.

Advantageously, the burner output can now be regulated by varying the amount of air and varying the amount of fuel in the range of larger burner powers, wherein in the range of larger burner performance, the condition is met that the air-fuel ratio is less than 1.

In a subsequent to the transition from the range of smaller burner powers in the range of larger burner power range of greater burner power, it is expedient to increase the burner with increasing burner power, while the amount of air set on the transition set below the maximum air volume constant value remains held. This ensures that the air-fuel ratio continues to decrease, that is, downwards from the value 1.

Particularly advantageously, it can now be provided that with further increasing burner power at a third switching value of the air-fuel ratio, which is smaller than 1, the amount of air is increased again, thereby increasing the burner power. The increase in the amount of air is carried out again until reaching the maximum adjustable air volume. The increase in the amount of air can be carried out continuously or in steps or in individual stages or steps. In any case, the air-fuel ratio, once the maximum amount of air is reached, reaches a fourth switching value, which is less than 1.

If the burner output is to be increased further, only the fuel quantity is increased while the air quantity remains set to the maximum value.

Preferably, the aforementioned second shift value and the aforementioned fourth shift value may be equal.

Alternatively, it is also possible, starting from the second shift value, to increase the amount of fuel and the amount of air so that the air-fuel ratio remains substantially constant at the second shift value. If one works with a constant air-fuel ratio, the above-mentioned third shift value can be ignored and directly the fourth shift value can be achieved, which then differs from the second shift value only in that the maximum amount of air is reached in the fourth shift value.

To reduce the burner power, the operation is reversed accordingly to be able to skip the range of the stoichiometric air-fuel ratio here. Thus, in the range of larger burner powers, with decreasing burner output, first the air quantity is kept constant at its maximum value, while only the fuel quantity is reduced. Once the fourth air-fuel ratio shift value is reached, the amount of air is reduced until the third air-fuel ratio shift value is reached. The reduction in the amount of air can be performed suddenly, stepped or continuously, continuously. As the burner output continues to decrease, only the fuel quantity is reduced, while the air quantity is kept constant at the value set below the maximum air volume. When the second switching value is reached, the air quantity is then suddenly increased to its maximum value. In this case, the air-fuel ratio again skips the value range which contains the value 1. Thus, this corresponds to the sudden transition from the range of larger burner power to the range of smaller burner power. With further decreasing burner output, the air quantity can now be kept constant at its maximum value, while only the fuel quantity is reduced. As a result, the air-fuel ratio increases, so that its value moves upwards from the value of 1. As the burner output continues to decrease, both the amount of fuel and the amount of air can be reduced.

Alternatively, it is also possible to reduce the amount of air and fuel quantity from the fourth shift value so that the air-fuel ratio remains constant, that is substantially at the fourth shift value. Thus, the third switching value can be bypassed. The second shift value then differs from the fourth shift value only by a predetermined, compared to the maximum air volume reduced air quantity.

Alternatively, the procedure described above can be described by the fact that starting from a minimum burner power with increasing burner power, the air flow is increased until reaching a maximum air flow, to further increase the burner power only the amount of fuel is increased while the amount of air, eg. B. is kept constant at its maximum value, so that the air-fuel ratio decreases, to skip a value range containing the value 1 of the air-fuel ratio, the amount of air is suddenly reduced and only at further increasing burner power back to the maximum Air quantity, in particular jump-like, is increased, however, so that the air-fuel ratio remains smaller than 1. To further increase the burner power then only the amount of fuel is increased again, while the amount of air is kept constant at its maximum value.

In addition, for reducing the burner power, the above-described procedure can also be described such that, starting from a maximum burner power with decreasing burner power, the fuel quantity is reduced while the air quantity remains constant at a maximum air quantity, so that the air-fuel ratio increases in which upon reaching a predetermined switching value of the air-fuel ratio, the air quantity, in particular abruptly, is reduced, wherein the fuel quantity is further reduced to reduce the burner power, wherein to skip a value range of the air-fuel ratio containing the value 1, the amount of air jumpy, z. B. to the maximum amount of air is increased, with further decreasing burner power, the amount of air is kept constant at the maximum air flow, while the fuel quantity is reduced, with further decreasing burner power, the amount of air and the amount of fuel can be reduced.

Particularly useful is an embodiment in which in a lower portion of the range of smaller burner power, the burner output is adjusted by the amount of air and fuel quantity are varied, wherein in an upper portion of the range of smaller burner power, the burner power is adjusted by the amount of fuel is varied while the amount of air is kept constant, and in the range of larger burner powers, the burner power is adjusted by the amount of fuel is varied while the amount of air is kept constant.

According to another expedient embodiment, it can be provided that when changing between the area with a larger burner power and the area with a smaller burner power for traversing a value of 1 containing area of the air-fuel ratio, the air quantity is suddenly reduced with increasing burner power and decreasing burner power is increased suddenly. In other words, with increasing burner power, the amount of air should be suddenly reduced in a change from the range with a smaller burner power to the area with a larger burner power to skip a value range of the air-fuel ratio 1, wherein it may be provided that with increasing Burner capacity, the amount of air before the sudden reduction is constant and in particular maximum and / or after the sudden reduction, z. B. to the maximum value, increased and with further increasing burner power constant, z. B. is held at the maximum value. In contrast to this, with decreasing burner output at a change from the area with larger burner power to the area with smaller burner power for skipping a value 1 containing range of the air-fuel ratio, the amount of air jump, z. B. can be increased to a maximum, in which it can be provided in particular that with decreasing burner power, the amount of air is reduced before the sudden increase, in particular starting from a maximum, and / or after the sudden increase to the increased value, for. B. maximum, is kept constant and is reduced only at further decreasing burner output.

An exhaust system according to the invention comprises at least one oxidation catalyst, which may be realized in the form of a separate component or in that it is structurally integrated into an exhaust gas treatment device of the exhaust system, for example in the form of a catalyst element or in the form of a catalytically active coating. The exhaust system further includes at least one downstream of the oxidation catalyst disposed component having a varying heating demand. As already mentioned, the oxidation catalyst can already be structurally integrated into this component, for example as a catalyst element or as a catalytically active coating. Furthermore, the exhaust system upstream of the oxidation catalyst includes a burner, for a fuel supply device for supplying fuel to the burner, and a Air supply means are provided for supplying air to the burner. Furthermore, a control for actuating the fuel supply device and the air supply device is provided as a function of the heating requirement of the at least one component. Said control is now suitably designed and / or programmed so that it can operate the burner according to the above-described method during operation of the exhaust system.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

It show, each schematically

1 a greatly simplified schematic diagram of an exhaust system,

2 a diagrammatic diagram illustrating an operating method.

Corresponding 1 includes an internal combustion engine 1 an engine block 2 with combustion chambers, not shown, a fresh air system 3 for supplying fresh air to the combustion chambers of the engine block 2 as well as an exhaust system 4 for discharging exhaust gas from the combustion chambers of the engine block 2 , A fresh air flow is through an arrow 5 indicated. An engine exhaust flow is indicated by an arrow 6 indicated.

The exhaust system 4 contains at least one exhaust gas purification device 7 which may be, for example, a particulate filter or an SCR catalyst or an NO _x storage catalyst or the like. The exhaust system 4 contains upstream of the exhaust treatment device 7 an oxidation catalyst 8th , which also represents an exhaust treatment device and is designed to be in an indicated by an arrow exhaust stream 9 entrained unburned fuel residues also in the exhaust stream 9 catalytically react entrained oxygen.

At the in 1 embodiment shown are the oxidation catalyst 8th and the at least one further exhaust treatment device 7 represented as two separate components. However, it is clear that the oxidation catalyst 8th For example, in the form of a catalyst element or in the form of a catalytically active coating structurally in the exhaust gas treatment device 7 can be integrated, such that the exhaust gas flow 9 first the oxidation catalyst 8th applied.

Furthermore, the exhaust system 4 with a burner 10 equipped upstream of the oxidation catalyst 8th in an exhaust system 11 the exhaust system 4 is arranged or upstream of the oxidation catalyst 8th to the exhaust system 11 connected. The burner 10 generates a burner exhaust gas during operation, which is the engine exhaust gas 6 is mixed. A corresponding burner exhaust stream 12 is indicated by an arrow. In the operation of the burner 10 is the exhaust gas flow 9 through a mixture of engine exhaust 6 and burner exhaust 12 educated. When the burner is off 10 corresponds to the exhaust gas flow 9 the engine exhaust 6 ,

To supply the burner 10 with fuel is a fuel supply 13 provided, for example, a fuel conveyor 14 contains, whose capacity is the burner 10 supplied amount of fuel determined. Furthermore, to supply the burner 10 with air an air supply 15 intended. This includes, for example, an air conveyor 16 , with the help of which the burner 10 supplied amount of air can be adjusted. Furthermore, owns the exhaust system 4 or the internal combustion engine 1 a controller 17 , with the help of which the fuel supply 13 and the air supply device 15 can be operated. For example, corresponding control lines can be used for this purpose 18 to the respective conveyor 14 respectively. 16 be connected. Furthermore, a signal line 19 be provided to the controller 17 with the burner 10 , For example, with a temperature sensor or with an igniter of the burner 10 to pair.

In the diagram of 2 are on the abscissa an air-fuel ratio λ and plotted on the ordinate a burner power P. In particular, the ordinate shows a normalized burner power P, wherein the burner output P used for normalization is that of the burner 10 in stoichiometric operation, ie at λ = 1 would have. This results in the diagram a straight line for a heating demand H, which corresponds to the desired burner power P. The heating demand H is shown with a broken line. With dash-dotted line required to cover the respective heating demand H fuel amount K is entered. A solid line represents the amount of air required for the realization of the respective heating demand H L. In the diagram of 2 a region B for air-fuel ratios is marked which contains the value λ = 1. Area boundaries b1 and b2 are spaced apart on both sides of the stoichiometric value λ = 1.

The area B separates in the diagram of the 2 also a range I of smaller burner powers P from a range II of larger burner powers P. The control 17 is programmed or configured so that it sets the air-fuel ratio λ> 1 in the region I smaller burner power P, while the air-fuel ratio λ <1 is set for the range II larger burner power P.

Starting from a minimum burner power P _min , the air quantity L and the fuel quantity K are increased in the region I of smaller burner powers P with increasing burner power P until a maximum deliverable air quantity Lmax is reached. This state is achieved, for example, at an air-fuel ratio λ5. If now the burner power P is to be further increased, the fuel quantity K increases with increasing burner power P, while the air quantity L is kept constant at its maximum value Lmax. With further increasing burner power P, a first switching value λ1 is achieved for the air-fuel ratio λ. At this first switching value λ1, the transition from region I of smaller burner powers P to region II of larger burner powers P takes place. This transition is realized with increasing burner power P by setting the air quantity L abruptly from its maximum value Lmax to a reduced value Lred. This reduced air volume value Lred is dimensioned such that the air-fuel ratio λ suddenly reaches a second switching value λ2, which is smaller than 1, while the first switching value λ1 was still greater than 1. Thus, the value λ = 1 or the value range B is skipped.

After this transition to region II of larger burner powers P, initially only the fuel quantity K is increased with increasing burner power P, while the air quantity L remains constant at the reduced value Lred. As a result, the air-fuel ratio λ can be further reduced. Now reaches the air-fuel ratio λ at further increasing burner power P a third switching value λ3, which is smaller than the second switching value λ2 and less than 1, with increasing burner power P now the air flow L can be increased again. This is shown in the example of 2 preferably performed abruptly, so that the air-fuel ratio λ reaches a value λ4, which is still less than 1, but greater than λ3. Suitably, the second switching value λ2 and the fourth switching value λ4 can be the same size. In that regard, the representation of the amount of air L in the diagram of 2 with respect to the abscissa independently to better explain the operation method for skipping the area B can.

If, starting from the fourth switching value λ4, the burner power P continues to increase, only the fuel quantity K is increased as a result, while the air quantity L remains constant at its maximum value Lmax.

The reduction of the burner power P is then reversed in a corresponding manner, at least in such a way that the area B can again be skipped to λ 2 from the region II larger burner power P with stoichiometric operation λ <1 in the range I smaller burner power P with superstoichiometric operation λ> 1 to be able to change suddenly.

In particular, starting from a maximum burner output Pmax with decreasing heating demand H, the fuel quantity K is reduced, while the air quantity L is kept constant at its maximum value Lmax, so that the air-fuel ratio λ gradually increases. Achieved hereby the air-fuel ratio λ the fourth switching value λ4, the supplied amount of air L is reduced, preferably abruptly, to the value Lred. With further decreasing heating demand H, the fuel quantity K is further reduced, while the air quantity L can remain constant at the reduced value Lred. When heating demand H continues to fall, the air-fuel ratio λ reaches the second switching value λ2, which triggers a sudden increase in the amount of air L to the maximum value Lmax. In this case, the air-fuel ratio λ skips the region B and reaches the first switching value λ1.

In an alternative solution, it may be provided for the decreasing burner power B that, when the fourth shift value λ4 is reached, the air quantity L and the fuel quantity K are reduced such that the air-fuel ratio λ remains constant, namely remains at the fourth shift value λ4. As soon as the air quantity L reaches the predetermined reduced air quantity Lred, the air quantity L can be suddenly increased to its maximum value Lmax, which then transitions directly from the fourth switching value λ4 to the first switching value λ1. For the reverse case of the power increase, this means that upon reaching the first switching value λ1, the air quantity L is suddenly reduced from the maximum value Lmax to the reduced value Lred in order to achieve the second switching value λ2. Then, with further increasing burner power P, the air-fuel ratio λ at this second switching value λ2 be kept constant by the air quantity L and the fuel quantity K are increased accordingly. As soon as the air quantity L reaches its maximum value Lmax, the fourth shift value λ4 is directly present, from which only the fuel quantity K is then increased, while the air quantity L is kept constant at its maximum value Lmax.

The control 17 causes at the in 2 shown in a lower portion Iu of the range I smaller burner power P adjusting the burner power P by both the amount of air L and the amount of fuel K are varied accordingly. In an upper portion Io of the region I of the smaller burner powers P, however, the setting of the burner power P takes place in that only the fuel quantity K is varied while the air quantity L is kept constant, in particular at its maximum value Lmax. In an upper portion IIo of the range II larger burner power P, the setting of the burner power P takes place in that only the amount of fuel K is varied while the amount of air L remains constant, in particular their maximum value Lmax occupies. In a lower portion IIu of the range II larger burner power P setting the burner power P is appropriate so that only the amount of fuel K is varied, while the air amount L is kept constant at a reduced value Lred. Alternatively, in this lower portion IIu, it is also possible to vary the burner power P by varying both the air amount L and the fuel amount K, but then keeping the air-fuel ratio λ substantially constant.

Claims (14)

Method for operating a burner ( 10 ) located in an exhaust system ( 4 ) an internal combustion engine ( 1 ), in particular a vehicle, in particular upstream of an oxidation catalytic converter ( 8th ), - in which a burner power (P) depends on a heating demand (H) of the oxidation catalyst ( 8th ) and / or at least one downstream of the burner ( 10 ) arranged component ( 7 ) of the exhaust system ( 4 ) by varying a burner ( 10 ) supplied amount of air (L) and / or a burner ( 10 adjusted fuel quantity (K) is set, - in which in a region (I) of smaller burner powers (P) an air-fuel ratio (λ) is set greater than 1, - in which in a range (II) larger burner power ( P) an air-fuel ratio (λ) is set smaller than 1. A method according to claim 1, characterized in that in the region (I) of smaller burner power (P) with increasing burner power (P), the amount of air (L) and the fuel quantity (K) are increased until a maximum supply air quantity (Lmax) is reached. A method according to claim 2, characterized in that in the region (I) of smaller burner powers (P) with increasing burner power (P) at maximum air volume reached (Lmax), the fuel quantity (K) is further increased, while the amount of air (L) to the maximum value (Lmax) remains set. A method according to claim 3, characterized in that at a (first) switching value (λ1) of the air-fuel ratio (λ) which is greater than 1, the transition from the region (I) of smaller burner powers (P) to the region (II ) of greater burner power (P) is achieved in that with increasing burner power (P), the air quantity (L) is suddenly set to a reduced value (Lred), such that the air-fuel ratio (λ) to a (second) switching value (λ2) is set smaller than 1. A method according to claim 4, characterized in that in the region (II) of larger burner powers (P) from the transition with increasing burner power (P) the fuel quantity (K) is increased, while the amount of air (L) on the below the maximum air flow (Lmax Reduced value (Lred) is kept constant, wherein it can be provided in particular that with increasing burner power (P) at a (third) switching value (λ3) of the air-fuel ratios (λ), which is smaller than 1, the amount of air (L), in particular abruptly, to the maximum amount of air (Lmax) is increased, such that the air-fuel ratio (λ) assumes a (fourth) switching value (λ4) is less than 1. A method according to claim 4, characterized in that in the region (II) of larger burner powers (P) from the transition with increasing burner power (P), the fuel quantity (K) and the amount of air (L) are increased, such that the air-fuel Ratio (λ) remains constant at the (second) switching value (λ2), wherein it can be provided in particular that with increasing burner power (P) from reaching the maximum air flow (Lmax) only the fuel quantity (K) is further increased. A method according to claim 5 or 6, characterized in that in the region (II) of larger burner power (P) with further increasing burner power (P), the fuel quantity (K) is increased while the amount of air (L) is set to the maximum value (Lmax) , Method according to one of claims 5 to 7, characterized in that the second switching value (λ2) and the fourth switching value (λ4) are equal. Method according to one of claims 1 to 8, characterized in that - starting from a minimum burner power (Pmin) with increasing burner power (P), the air quantity (L) is increased until a maximum air quantity (Lmax) is reached, it being possible in particular to provide that for further increasing the burner power (P) only the amount of fuel (K) is increased, so that the air-fuel ratio (λ) decreases, - that to skip a value range containing the value 1 (B) of the air-fuel Ratio the amount of air (L) is suddenly reduced and only at further increasing burner power (P) again, in particular abruptly increased, but in particular to the maximum amount of air (Lmax) but such that the air-fuel ratio (λ) is less than 1 remains. Method according to one of claims 1 to 9, characterized, - That starting from a maximum burner power (Pmax) with decreasing burner power (P), the fuel quantity (K) is reduced, while the amount of air (L) is set constant, in particular to a maximum air flow (Lmax), so that the air-fuel Ratio (λ) increases, it being possible in particular for the air quantity (L), in particular abruptly, to be reduced when a predetermined switching value (λ4) of the air-fuel ratio (λ) is reached, In that, in order to skip over a value range (B) of the air-fuel ratio (λ) containing the value 1, the air quantity (L) is suddenly increased to the maximum air quantity (Lmax), it being possible in particular to provide that as the burner output continues to decrease ( P) the amount of air (L) is kept constant at the maximum air quantity (Lmax) while the fuel quantity (K) is reduced, and with decreasing burner power (P) the air quantity (L) and the fuel quantity (K) are reduced. Method according to one of claims 1 to 10, characterized, That in a lower portion (Iu) of the region (I) smaller burner powers (P), the burner power (P) is adjusted by the amount of air (L) and the fuel quantity (K) are varied, That in an upper portion (Io) of the region (I) of smaller burner powers (P), the burner output (P) is adjusted by varying the fuel quantity (K) while keeping the amount of air (L) constant, - That at least in an upper portion (IIo) of the range (II) of greater burner power (P), the burner power (P) is adjusted by the amount of fuel (K) is varied while the amount of air (L) is kept constant. Method according to one of claims 1 to 11, characterized in that when changing from region (I) with smaller burner powers (P) to region (II) with larger burner powers (P) for skipping a value range (B) of value 1 containing Air-fuel ratio (λ), the amount of air (L) is suddenly reduced, it being particularly provided that with increasing burner power (P), the amount of air (L) before the sudden reduction is constant and preferably maximum and / or after the sudden Reduction, z. B. to the maximum value (Lmax), increased and with further increasing burner power (P) constant, z. B. at the maximum value (Lmax), is held. Method according to one of claims 1 to 12, characterized in that when changing from the region (II) with larger burner powers (P) to the region (I) with smaller burner powers (P) for skipping a region containing the value 1 (B) of Air-fuel ratio (λ) the amount of air (L) abruptly, z. B. to a maximum (Lmax), is increased, wherein in particular may be provided that with decreasing burner power (P), the amount of air (L) is reduced before the sudden increase, in particular starting from its maximum (Lmax), and / or after the jump-like increase, z. B. at the maximum (Lmax), is kept constant and only at further decreasing burner power (P) is reduced. Exhaust system for an internal combustion engine, in particular a vehicle, - with an oxidation catalyst ( 8th ), - with at least one downstream of the oxidation catalyst ( 8th ) arranged component ( 7 ), which has a varying heating requirement, - with an upstream of the oxidation catalyst ( 8th ) arranged burner ( 10 ), - with a fuel supply device ( 13 ), the burner ( 10 ) Supplies fuel, - with an air supply device ( 15 ), the burner ( 10 ) Supplies air, - with a control ( 17 ) for actuating the fuel supply device ( 13 ) and the air supply device ( 15 ) depending on the heating requirement (H) of the at least one component ( 7 ), - whereby the controller ( 17 ) is designed and / or programmed so that during operation of the exhaust system ( 4 ) the burner ( 10 ) according to the method of any one of claims 1 to 13 operates.

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