DE102024201151A1 - Exhaust gas burner and method for operating an exhaust gas burner - Google Patents

Abstract

The invention relates to an exhaust gas burner (50) for an exhaust gas aftertreatment system of an internal combustion engine (10), which comprises a combustion chamber (52) for combusting a fuel-air mixture, a fuel supply (54) for supplying fuel (48) to the combustion chamber (52), and an air supply (62) for supplying fresh air to the combustion chamber (52). The exhaust gas burner (50) further comprises a flame-starting plug (66) for heating the fuel (48) supplied to the combustion chamber (52), wherein the flame-starting plug (66) has at least a first heating zone (68) and a second heating zone (70) different from the first heating zone (68). The temperatures in the two heating zones (68, 70) can be adjusted essentially independently of one another.
The invention further relates to an internal combustion engine (10) with an exhaust gas aftertreatment system in which such an exhaust gas burner (50) is arranged, and to a method for controlling such an exhaust gas burner (50).

Description

The invention relates to an exhaust gas burner for an exhaust gas aftertreatment system of an internal combustion engine, an internal combustion engine with such an exhaust gas aftertreatment system and a method for operating such an exhaust gas burner according to the preamble of the independent patent claims.

Current emissions legislation, which will become increasingly stringent in the future, places high demands on raw engine emissions and exhaust aftertreatment in internal combustion engines. The demands for further reduced fuel consumption and the further tightening of emissions standards regarding permissible nitrogen oxide emissions pose a challenge for engine developers. In gasoline engines, exhaust gas purification is achieved in the usual way via a three-way catalyst, as well as additional catalysts upstream and downstream of the three-way catalyst. Diesel engines currently use exhaust aftertreatment systems that include an oxidation catalyst, a catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst), a particulate filter for the separation of soot particles, and possibly additional catalysts. Ammonia is the preferred reducing agent. Because handling pure ammonia is complex and hazardous, vehicles typically use a synthetic, aqueous urea solution, which is mixed with the hot exhaust stream of the combustion engine. This mixing heats the aqueous urea solution, releasing ammonia into the exhaust duct. A commercially available aqueous urea solution generally consists of 32.5% urea and 67.5% water.

At low outside temperatures, especially at temperatures below -7 °C, especially below -10 °C, the urea-water solution can freeze depending on the urea content of the urea-water solution. To enable the metered addition of the reducing agent, electrical heating elements are known that heat at least a portion of the storage container containing the urea-water solution in order to liquefy at least a portion of the urea-water solution and meter it into the exhaust system.

Furthermore, especially at low outside temperatures, there is the challenge of heating the exhaust aftertreatment components, in particular a catalyst for the selective, catalytic reduction of nitrogen oxides, to a so-called light-off temperature as quickly as possible after the combustion engine starts in order to enable efficient conversion of the pollutants in the exhaust stream of the combustion engine. To accelerate the heating of the exhaust aftertreatment components, exhaust gas burners are known. These introduce hot burner exhaust gas into the exhaust system to accelerate the heating of the exhaust aftertreatment components.

The problem with solutions known from the state of the art is that the period from the activation of the exhaust gas burner to the ignition of the first fuel in the exhaust gas burner is too long and the period for heating up the exhaust gas aftertreatment is extended by this period for the burner start.

The DE 42 43 964 A1 discloses a flame glow plug with a housing having a connection nipple with a fuel metering device. A heating rod is arranged coaxially in the housing, and a protective tube surrounds the part of the heating rod protruding from the housing. The protective tube is closed at the heating rod end and provided with at least one air inlet opening and one lateral opening, which are arranged axially spaced from one another.

From the DE 21 15 620 A1 A flame glow plug is known for starting diesel engines. The flame glow plug is installed in the intake manifold of the diesel engine and is equipped with a fuel connection and a glow plug with a helically wound heating coil inside. Such flame glow plugs are used to preheat the combustion air supplied to the cylinders of the diesel engine. Typically, emphasis is placed on reaching the vaporization and ignition temperature of the fuel as quickly as possible.

DE 195 04 183 A1 describes an exhaust gas burner for the thermal regeneration of a particulate filter in an exhaust aftertreatment system of an internal combustion engine, in particular a diesel engine. The burner is arranged fully within the exhaust pipe, in particular in an extended, straight, coaxial exhaust pipe section. This allows axial flow to the particulate filter, resulting in a simplified design and good temperature distribution. The exhaust gas burner is preheated during the start-up phase by the heat of the engine exhaust. During the burner's operating phase, the engine exhaust cools the burner surface, preventing thermal overload.

Furthermore, the DE 10 2011 008 748 A1 a regeneration device for a diesel part The regeneration device comprises a burner that can be connected to the measuring port of the diesel particulate filter housing. A control system regulates the regeneration of the filter module located in the diesel particulate filter housing.

The invention is based on the object of enabling the exhaust gas burner to start as quickly and as low-emission as possible in an exhaust gas aftertreatment system with an exhaust gas burner and thus to heat the exhaust gas aftertreatment components of the exhaust gas aftertreatment system to the operating temperature as quickly as possible after starting the internal combustion engine, at which an efficient conversion of the limited exhaust gas components contained in the exhaust gas flow of the internal combustion engine is possible.

The problem is solved by an exhaust gas burner for an exhaust gas aftertreatment system of an internal combustion engine, which comprises a combustion chamber for combusting a fuel-air mixture, a fuel supply for supplying fuel to the combustion chamber, and an air supply for supplying fresh air to the combustion chamber. The exhaust gas burner further comprises a flame starter plug for heating the fuel supplied to the combustion chamber, wherein the flame starter plug has at least a first heating zone and a second heating zone different from the first heating zone. The temperatures in the two heating zones can be adjusted essentially independently of one another. In this context, a flame starter plug is understood to be a glow plug that heats both the air supplied to the combustion chamber of the exhaust gas burner and the fuel supplied to the combustion chamber, thereby enabling ignition of the fuel in the combustion chamber. Such a flame starter plug is necessary to start the exhaust gas burner and thus heat the exhaust gas aftertreatment components in the exhaust system of the internal combustion engine. In this context, a heating zone is understood to be a section of the flame starter plug that heats the respective section of the flame starter plug through an electrical heating resistor. Essentially independent heating of the two heating zones means that the heating zones can be controlled independently of one another, although a certain amount of heat transfer, particularly through conduction and/or radiation, between the two heating zones cannot be ruled out.

The independent heating of the first heating zone, which primarily serves to vaporize the fuel, and the second heating zone, which primarily serves to ignite the fuel, enables a particularly fast and low-emission start of the exhaust gas burner. In particular, the flame start plug improves fuel vaporization in the combustion chamber of the exhaust gas burner while simultaneously heating the air in the combustion chamber to achieve targeted ignition of the fuel-air mixture at a glow rod tip of the flame start plug facing the combustion chamber.

The additional features listed in the dependent claims enable advantageous further developments and improvements of the exhaust gas burner specified in the independent claim.

In a preferred embodiment of the invention, the first heating zone has a first heating resistor and the second heating zone has a second heating resistor, wherein the two heating resistors can be controlled independently of one another. By means of two differently controllable heating resistors, the two heating zones of the flame starter plug can be separated in a simple and effective manner. In particular, by controlling the two heating resistors differently, independent temperature control for the two heating zones of the flame starter plug can be achieved. This makes it possible to only introduce energy into the flame starter plug, so that after ignition of the fuel-air mixture in the combustion chamber, evaporation of the fuel and ignition of the fuel-air mixture are ensured. The energy consumption of the flame starter plug can thus be reduced compared to a flame starter plug with only one heating zone.

In an advantageous embodiment of the exhaust gas burner, the second heating zone is formed at an end of the flame starter plug facing the combustion chamber. This allows the second heating zone to be designed for the ignition or igniting of the fuel-air mixture in the combustion chamber, so that this heating zone can be deactivated, particularly at a sufficiently high temperature in the combustion chamber, when the existing flame front is sufficient to vaporize newly injected fuel into the combustion chamber or sufficient vaporization of the fuel is achieved by the first heating zone.

In a further advantageous embodiment of the exhaust gas burner, the first heating zone is formed in the area of a fuel connection of the flame starter plug. This allows for particularly efficient evaporation of the fuel or parts of the fuel. so that an ignitable fuel-air mixture is present at the glow rod tip.

In a further advantageous embodiment of the exhaust gas burner, the first heating zone comprises an evaporator screen, an evaporator network, and/or an evaporator tube for evaporating the fuel supplied to the flame starter plug. An evaporator screen and/or an evaporator tube can increase the surface area over which the fuel is heated, thereby improving heat transfer and thus facilitating fuel evaporation. Furthermore, an evaporator screen can prevent solid fuel components, particularly paraffin deposits, which evaporate only slowly and insufficiently for ignition, from being retained and only being fed to the first heating zone of the flame starter plug once the solid fuel components have sufficiently liquefied. Furthermore, the proportion of unevaporated, liquid fuel components decreases because sufficient time is provided for evaporation.

According to an advantageous embodiment of the exhaust gas burner, the first heating zone extends from an insulation in the area of electrical contact of the flame starter plug to a protective tube opening in a protective tube of the flame starter plug. This makes the largest possible area of the flame starter plug, or the largest possible surface, usable for heating the fuel, allowing the largest possible amount of fuel to evaporate. This can improve the ignitability of the fuel-air mixture in the combustion chamber of the exhaust gas burner.

According to a further advantageous embodiment of the exhaust gas burner, the second heating zone extends from a protective tube opening in a protective tube of the flame starter plug to a glow rod tip of the flame starter plug facing the combustion chamber. This zone can be used to create a defined ignition point in the combustion chamber, at which the fuel-air mixture can be reliably ignited. The second heating zone can be designed to be correspondingly small and compact compared to the first heating zone, thereby minimizing energy consumption for the second heating zone, as long as a hot spot is present at which the fuel ignites.

In an advantageous embodiment of the exhaust gas burner, an unheated third zone is formed between the first heating zone and the second heating zone. This allows for a simple separation of the two heating zones, minimizing heat transfer from one heating zone to the other. This simplifies temperature control in the heating zones and improves the accuracy of temperature control in the heating zones.

An advantageous further development of the exhaust gas burner provides for a temperature sensor to be arranged in the first heating zone and/or the second heating zone. A temperature sensor allows the temperature in the respective heating zone to be easily determined. This simplifies temperature control for the respective heating zone. Temperature measurement eliminates the need for a model-based temperature calculation, thus reducing the computing power of a control unit for the exhaust gas burner.

Alternatively, a resistance of the respective heating element can also be determined, since the heating resistance in the relevant temperature range changes in a strictly monotonically increasing manner, preferably essentially proportional to the temperature of the respective heating zone, and the temperature in the respective heating zone can be deduced from the electrical resistance of the heating resistance.

A further aspect of the invention relates to an internal combustion engine with an exhaust aftertreatment system, wherein the exhaust aftertreatment system comprises such an exhaust gas burner for heating at least one exhaust aftertreatment component of the exhaust aftertreatment system. In such an internal combustion engine, in particular a diesel engine with an exhaust aftertreatment system comprising at least one SCR catalyst, the disadvantages of a slower burner start or higher emissions from the exhaust gas burner can be reduced by reducing the coking of the exhaust gas burner's injection nozzle. This results in fewer emissions being released unconverted into the environment during the heat-up phase of the exhaust aftertreatment system.

• - Aktivierung des Abgasbrenners, wobei die erste Heizzone und die zweite Heizzone der Flammstartkerze aktiviert werden,
• - Aktivieren der Kraftstoffversorgung des Abgasbrenners, wenn beide Heizzonen der Flammstartkerze ihre für einen Brennerstart des Abgasbrenners vorgegebene Zieltemperatur erreicht haben, wobei
• - über die erste Heizzone eine Kraftstofftemperatur des zu verdampfenden Kraftstoffs eingeregelt wird, und wobei
• - über die zweite Heizzone eine Temperatur an der Glühstabspitze der Flammkerze eingeregelt wird, um eine Entflammung des Kraftstoff-Luft-Gemischs in der Brennkammer sicherzustellen.

A further aspect of the invention relates to a method for operating an exhaust gas burner on an exhaust gas aftertreatment system of an internal combustion engine, which comprises the following steps:

• - Activation of the exhaust gas burner, whereby the first heating zone and the second heating zone of the flame starter candle are activated,
• - Activating the fuel supply of the exhaust gas burner when both heating zones of the flame starter candle has reached its target temperature specified for a burner start of the exhaust gas burner, whereby
• - a fuel temperature of the fuel to be evaporated is regulated via the first heating zone, and wherein
• - a temperature at the glow rod tip of the flame plug is regulated via the second heating zone in order to ensure ignition of the fuel-air mixture in the combustion chamber.

Such a process enables the exhaust gas burner to be operated in a way that allows for the fastest and lowest-emissions start-up possible. This allows the exhaust aftertreatment components in the combustion engine's exhaust system to be heated to their operating temperature as quickly as possible, thereby reducing cold-start emissions in particular.

In an advantageous embodiment of the method, once the target temperature has been reached, the temperature in the first heating zone is regulated independently of the temperature in the second heating zone. This allows optimal temperatures for evaporating the fuel or igniting the fuel-air mixture to be set individually for each heating zone, thereby achieving particularly low-emission and clean combustion. Furthermore, the energy requirement of the flame starter plug can be minimized, since only as much energy needs to be introduced into the respective heating zone to fulfill its respective function. For example, the second heating zone can be deactivated when a stable operating point of the exhaust gas burner is reached.

According to a further advantageous embodiment of the method, when the exhaust gas burner is shut down, the fuel supply is shut off and, in parallel, the air supply to the combustion chamber is reduced to slow the cooling rate of the combustion chamber. The residual fuel in the flame starter plug is released into the combustion chamber and ignited by the second heating zone. This minimizes secondary emissions from the exhaust gas burner, particularly emissions of unburned hydrocarbons, caused by fuel emitted from the exhaust gas burner. Once all residual fuel has been combusted, the air supply to the exhaust gas burner is also shut off.

In an advantageous embodiment of the method, a temperature is determined in the region of the second heating zone, and the air supply is maintained after the combustion of the residual fuel from the flame starter plug has been completed in order to prevent thermal overload of the flame starter plug as long as the temperature in the second heating zone remains above a threshold temperature. The remaining air flow can cool the flame starter plug or other components in the combustion chamber of the exhaust gas burner, thereby preventing thermal overload. Alternatively, the air supply can also be switched off when the exhaust gas burner is deactivated in order to minimize energy consumption.

In an advantageous further development of the method, the heating rate and/or cooling rate of the heating zones are stored in a model in a control unit of the exhaust gas burner. To analyze the functionality of the flame starter plug, a temperature profile determined when the corresponding heating zone is energized is compared with a temperature profile expected for the respective heating zone according to the model. This enables on-board diagnostics regarding the function of the individual heating zones of the flame starter plug.

In particular, it is intended that the determined heating and cooling rates of the heating zones are compared with the values stored in the model, whereby an ambient temperature and/or a temperature in the combustion chamber of the exhaust gas burner are taken into account. The heating zones can preferably be tested after the exhaust gas burner has been shut down by first energizing the heating resistor in one of the two heating zones and measuring the temperatures in both heating zones. Subsequently, the heating resistor in the other heating zone is energized and the temperature is measured in both heating zones. From the measured values, heating curves, steady-state temperatures and/or cooling curves of the respective heating zone can be determined. These curves can be compared with the values stored in the model, whereby a deviation beyond a limit value can be concluded that the flame starter plug is malfunctioning. The control values of the flame starter plug are initially adapted to compensate for the deviations. If the deviations continue to increase or can no longer be compensated by adaptation, an error message is issued as part of an on-board diagnosis, which requests the replacement of the flame starter plug.

The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

• 1 einen Verbrennungsmotors mit einem Abgasnachbehandlungssystem, in welchem ein erfindungsgemäßer Abgasbrenner angeordnet ist,
• 2 einen erfindungsgemäßen Abgasbrenner in einer schematischen Darstellung,
• 3 eine Flammstartkerze für einen erfindungsgemäßen Abgasbrenner in einer schematischen Darstellung, und
• 4 ein Ablaufdiagramm zur Durchführung eines erfindungsgemäßen Verfahrens zum Betreiben eines Abgasbrenners.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show:

• 1 an internal combustion engine with an exhaust gas aftertreatment system in which an exhaust gas burner according to the invention is arranged,
• 2 an exhaust gas burner according to the invention in a schematic representation,
• 3 a flame starter plug for an exhaust gas burner according to the invention in a schematic representation, and
• 4 a flow chart for carrying out a method according to the invention for operating an exhaust gas burner.

1 shows an internal combustion engine 10 with multiple combustion chambers 12, wherein a fuel injector 14 is arranged at each combustion chamber 12 for injecting fuel into the respective combustion chamber 12. The internal combustion engine 10 has an inlet 16, with which the internal combustion engine 10 can be connected to an air supply system (not shown). The internal combustion engine 10 further has an outlet 18, with which the internal combustion engine 10 can be connected to an exhaust system 20. The internal combustion engine 10 has an engine block and at least one cylinder head.

To supply fuel to the fuel injectors 14, a high-pressure fuel pump and a high-pressure fuel reservoir are provided, which is supplied with fuel by the high-pressure fuel pump.

The exhaust system 20 comprises an exhaust manifold which feeds the exhaust gases of a plurality of combustion chambers 12 to a common exhaust duct 22. In the exhaust duct 22, a turbine 26 of an exhaust gas turbocharger 24 is arranged downstream of the exhaust manifold, a first exhaust gas aftertreatment component 28, in particular an oxidation catalyst 30, is arranged downstream of the turbine 26 of the exhaust gas turbocharger 24, and at least one further exhaust gas aftertreatment component 32, 38 is arranged downstream of the first exhaust gas aftertreatment component 28. 1 In the exemplary embodiment shown, a second exhaust gas aftertreatment component 32 for the selective, catalytic reduction of nitrogen oxides in the form of a particulate filter 34 with a coating 36 for the selective, catalytic reduction of nitrogen oxides is arranged downstream of the oxidation catalyst 30, and a third exhaust gas aftertreatment component 38 in the form of an SCR catalyst 40 is arranged downstream of the particulate filter 34. Downstream of the oxidation catalyst 30 and upstream of the particulate filter 34 with the SCR coating 36, a first metering element 42 for metering in a reducing agent, in particular an aqueous urea solution, is arranged. Downstream of the particulate filter 34 and upstream of the SCR catalyst 40, a second metering element 44 is arranged.

Furthermore, an exhaust gas burner 50 with a combustion chamber 52, a fuel supply 54 and an air supply 62 is arranged in the exhaust system 20 upstream of at least one of the exhaust gas aftertreatment components 28, 32, 38 in order to be able to heat the exhaust gas aftertreatment components 28, 32, 38 essentially independently of the operation of the internal combustion engine 10. The exhaust gas burner 50 has a flame starter plug 66 in order to enable the exhaust gas burner 50 to start as quickly and as low in emissions as possible. The inlet point for the exhaust gas burner is preferably as shown in 1 As shown, the inlet point 54 is arranged downstream of the turbine 26 of the exhaust gas turbocharger 24 and upstream of the oxidation catalyst 30. Alternatively, the inlet point can also be arranged downstream of the oxidation catalyst 30 and upstream of the particulate filter 34. The fuel supply 54 is controlled by a metering device 55 or shut-off device 55, which controls the supply of fuel to the exhaust gas burner 50 or the flame starter plug 66.

The internal combustion engine 10 is operatively connected to a control unit 99, which includes a memory unit and a computing unit. A computer program code is stored in the memory unit, which controls the fuel injection into the combustion chambers 12 of the internal combustion engine 10 and into the combustion chamber 52 of the exhaust gas burner 50, as well as the heating of the flame starter plug 66, when the computer program code is executed by the computing unit of the control unit 99.

2 shows an exhaust gas burner 50 according to the invention with a combustion chamber 52 for combusting a fuel-air mixture, a fuel supply 54 for supplying fuel to the combustion chamber 52, an air supply 62 for supplying fresh air to the combustion chamber, and a flame starter plug 66 for heating the fuel supplied to the combustion chamber. The flame starter plug 66 has a first heating zone 68 and a second heating zone 70 different from the first heating zone 68, wherein the temperatures of the two heating zones 68, 70 can be adjusted essentially independently of one another. For this purpose, the first heating zone 68 has a first heating resistor 96 and the second heating zone 70 has a second heating resistor 98. An unheated zone 69 can be formed between the first heating zone 68 and the second heating zone, which unheated zone separates the two heating zones 68, 70 from one another.

The exhaust burner 50 comprises a swirl or turbulence generator 60 with an air supply duct 64 connected to the air supply 62. The exhaust burner 50 may further include an injection nozzle 56 and a nozzle holder 58 in which the injection nozzle 56 is integrated. The injection nozzle 56 may also be omitted in the proposed solution or integrated into the flame-starting plug 66. In addition to the flame-starting plug 66, the exhaust burner 50 may have an additional ignition source 94 to ensure ignition of an ignitable fuel-air mixture in the combustion chamber 50 and, in particular, to facilitate starting the exhaust burner 50.

In 3 A preferred embodiment of a flame-starting plug 66 for an exhaust gas burner 50 according to the invention is shown. The flame-starting plug 66 comprises a plug housing 76 in which a glow rod 82 is arranged. The glow rod 82 is connected to a power supply via an electrical contact 72 at an end facing away from the combustion chamber 52 when installed. An insulation 74 is provided between the electrical contact 72 and the plug housing 76. The glow rod 82 has a glow rod tip 88 at its end opposite the electrical contact 72, which glow rod tip faces the combustion chamber 52 when installed in the exhaust gas burner 50.

The flame starter plug 66 further comprises a fuel connection 78, via which a fuel 48 for operating the exhaust gas burner 50 can be supplied to the flame starter plug 66. The flame starter plug 66 has an evaporator tube 80 to at least partially evaporate the fuel and supply it to the combustion chamber 52 of the exhaust gas burner 50. To increase the area for evaporating the fuel, the flame starter plug 66 can have an evaporator mesh 81 in addition to the evaporator tube 80. The flame starter plug 66 can further comprise a protective screen 46 to prevent solid fuel components or contaminants from entering the evaporator tube 80. The evaporator tube 80 is encased in a protective tube 84, which has protective tube openings 85 in the region of the glow rod tip 88, through which the evaporated fuel 48 can pass into the combustion chamber 52 of the exhaust gas burner 50. Furthermore, the flame-starting plug 66 has a flame sleeve 86 to limit the ignition area at the glow rod tip 88 and create optimal ignition conditions for the fuel-air mixture. The flame sleeve 86 prevents an already ignited flame from being extinguished at the tip of the flame-starting plug 66.

The flame starter plug 66 has a first heating zone 68 with a first heating resistor 96 and a second heating zone 70 with a second heating resistor 98, which can be controlled independently of one another via two electrical contacts 72. The first heating zone 68 extends from the insulation 74 to the protective tube openings 85 of the flame starter plug 66 and primarily serves to vaporize the fuel 48. The second heating zone 70 extends from the protective tube openings 85 to the glow rod tip 88 and primarily serves to ignite the fuel-air mixture in the combustion chamber 52. An unheated third zone 69 can be located between the first heating zone 68 and the second heating zone 70, which spatially separates the first heating zone 68 from the second heating zone 70. In both heating zones 68, 70, the temperature of the respective heating zone can be determined via the resistance of the respective heating element 96, 98, since the resistance of the heating resistors exhibits a strictly monotonic function that changes continuously with temperature in the relevant temperature range. Alternatively or additionally, a temperature sensor 90, 92 can be arranged in each of the heating zones 68, 70 to determine the temperature in the respective heating zone 68, 70.

4 shows a flowchart for a method according to the invention for operating an exhaust gas burner 50. When a start is requested for the exhaust gas burner 50, both heating zones 68, 70 of the flame glow plug 66 are first energized in a method step <100>. The energization is carried out with the maximum possible intensity in order to have an ignitable fuel-air mixture present in the combustion chamber 52 of the exhaust gas burner 50 as quickly as possible. The energization at maximum intensity occurs until both heating zones 68, 70 have reached their respective target temperatures. Subsequently, in a method step <110>, the temperature in the respective heating zone 68, 70 is individually regulated to the desired level. The regulation can be carried out, for example, by pulsed energization, by pulse width modulation (PWM) of the current, or by a current source with a variable voltage.

The first heating zone 68 is adjusted to a temperature which is higher than the initial boiling point of the fuel 48. Preferably, at least 10 volume percent, preferably at least 20 volume percent, particularly preferably at least 30 volume percent of the fuel supplied to the flame starter plug is evaporated in the first heating zone 68. The second heating zone 70 is first heated to a temperature which is above the auto-ignition temperature of the fuel 48. The second heating zone 70 is preferably heated to a temperature of at least 600°C. If the exhaust gas burner 50 has an additional ignition source 94 in the combustion chamber 52 in addition to the flame glow plug 66, The second heating zone 70 can be used to set an optimal temperature for the post-evaporation of the fuel 48 in the combustion chamber 52. The temperature of the additional ignition source 94 is preferably below the temperature of the second heating zone 70 of the flame glow plug 66, in particular in the range of 300°C - 500°C. The additional ignition source 94 can, in particular, be a spark igniter, in particular a spark plug, a thermal igniter, or a second flame starter plug.

Once both heating zones 68, 70 of the flame glow plug 66 have reached their target temperature, the fuel supply 54 for the exhaust gas burner 50 is activated in a method step <120>. At least a portion of the fuel 48 supplied to the flame glow plug 66 is vaporized. The vaporized fuel 48 is ignited via the second heating zone 70 and/or the additional ignition source 94.

By independently controlling the temperatures in the two heating zones 68, 70 of the flame glow plug 66, sufficient vaporization and ignition of the fuel 48 can be ensured during operation of the exhaust gas burner 50. Once the vaporized fuel 48 has ignited reliably, the temperature in the second heating zone 70 can be reduced or the second heating zone 70 can be completely deactivated, thereby reducing the power consumption of the flame glow plug 66. This is achieved, in particular, by reducing the heating power in the first heating zone 68.

During operation, the exhaust gas burner 50 is operated in a process step <130> with a fuel-to-air ratio favorable for the respective operating point, with the amount of fuel and air supplied to the combustion chamber 52 being adjusted accordingly. Dead times of the flame starter plug 66 and the air supply 62 system can be taken into account accordingly. In particular, the output of the heating zones 68, 70 can be adjusted within the framework of a pre-control before the amount of fuel supplied to the combustion chamber 52 changes in order to compensate for the thermal inertia of the system.

When the exhaust gas burner 50 is shut down, the fuel supply 54 is first shut off in a method step <140>. Furthermore, in a method step <150>, the air volume supplied to the combustion chamber 52 is reduced in order to slow the cooling rate of the combustion chamber 52, whereby the residual fuel in the flame glow plug 66 can be burned with low emissions. A minimum air flow is required to expel residual fuel 48 from the flame glow plug 66, regardless of whether purging of the flame glow plug 66 is necessary for thermal component protection.

The first heating zone 68 is heated to a temperature above the boiling point of the fuel 48, while the second heating zone 70 is heated to a temperature above the autoignition temperature of the fuel 48, thereby combusting the remaining fuel 48 present in the flame glow plug 66 at the time of shutdown. This minimizes emissions of unburned hydrocarbons.

Once the fuel 48 has been completely combusted, the air supply 62 for the exhaust gas burner 50 can be shut off in a process step <160>. However, if necessary for component protection reasons, the air supply can also be maintained to introduce a cooling air flow into the combustion chamber 52. In this case, the first heating zone 68 and the second heating zone 70 are deactivated. In particular, a temperature measurement can be performed in the second heating zone 70, and the air supply can be shut off if the temperature falls below a threshold.

Fuel residues still present in the evaporator tube 80 can alternatively be removed by heating the first heating zone 68 during pyrolysis. Any remaining ash is removed during the next start-up. Such pyrolysis does not have to be performed every time the exhaust gas burner 50 is deactivated, but can be performed at specific intervals, for example, depending on the amount of fuel passed through the flame glow plug 66, the operating time of the flame glow plug 66, the number of start-ups of the exhaust gas burner 50, in a time-controlled manner, or by monitoring the changes in the heating and cooling curves of the flame glow plug 66.

To diagnose the flame glow plug 66, the heating and cooling rates of the heating zones 68, 70 of the flame glow plug 66 can be measured and compared with values stored in the control unit 99, whereby other factors such as the outside temperature or the temperature of the combustion chamber 52 can be taken into account in order to increase the accuracy of the diagnostic procedure. The heating zones 68, 70 of the flame glow plug 66 can be checked against each other, in particular after the exhaust gas burner 50 has been switched off. First, one of the heating zones 68, 70 is energized, and the temperature in both heating zones 68, 70 is measured, preferably using the temperature sensors 90, 92. Subsequently, the other heating zone 68, 70 is energized, and the temperature in both heating zones 68, 70 is determined again. The heating rates ven, the steady-state temperatures or the cooling curves are determined, whereby the temperature curve in both heating zones 68, 70 is evaluated.

Furthermore, in an exhaust gas burner 50 which has an additional ignition source 94 in the combustion chamber 52, the second heating zone 70 can be used to post-evaporate the fuel 48, while the actual ignition occurs via the additional ignition source 94. The temperatures in the first heating zone 68 and in the second heating zone 70 can be coordinated to one another in such a way that optimal vaporization of the fuel 48 is achieved. During normal operation of the exhaust gas burner 50, the fuel 48 is therefore not ignited at the glow rod tip 88, but rather by the additional ignition source 94. However, the glow rod tip 88 can be heated as an additional ignition source by the second heating zone 70 if there is a malfunction of the additional ignition source 94 or if the ignitability of the fuel-air mixture is to be increased during a start-up phase of the exhaust gas burner 50.

List of reference symbols

10

combustion engine

12

combustion chamber

14

fuel injector

16

inlet

18

Outlet

20

exhaust system

22

exhaust duct

24

exhaust gas turbocharger

26

turbine

28

first exhaust aftertreatment component

30

Oxidation catalyst

32

second exhaust aftertreatment component

34

Particle filter

36

SCR coating

38

third exhaust aftertreatment component

40

SCR catalyst

42

first dosing element

44

second dosing element

46

Protective sieve / evaporator sieve

48

fuel

50

Exhaust gas burner

52

combustion chamber

54

Fuel supply

55

Shut-off device / dosing device

56

Injector

58

nozzle holder

60

Swirl or turbulence generators

62

Air supply

64

Air supply duct

66

Flame starter candle

68

first heating zone

69

unheated zone

70

second heating zone

72

electrical contact

74

insulation

76

candle housing

78

Fuel connection

80

evaporator tube

81

Evaporator network

82

Glow rod

84

protective tube

85

Protective tube opening

86

Flame sleeve

88

Glow rod tip

90

first temperature sensor

92

second temperature sensor

94

additional ignition source

96

first heating resistor

98

second heating resistor

99

control unit

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 42 43 964 A1 [0006]
• DE 21 15 620 A1 [0007]
• DE 195 04 183 A1 [0008]
• DE 10 2011 008 748 A1 [0009]

Claims (15)

An exhaust gas burner (50) for an exhaust gas aftertreatment system of an internal combustion engine (10), comprising: - a combustion chamber (52) for combusting a fuel-air mixture, - a fuel supply (54) for supplying fuel (48) to the combustion chamber (52), - an air supply (62) for supplying fresh air to the combustion chamber (52), and - a flame-starting plug (66) for heating the fuel (48) supplied to the combustion chamber (52), wherein the flame-starting plug (66) has at least a first heating zone (68) and a second heating zone (70) different from the first heating zone (68), wherein the temperatures in the two heating zones (68, 70) can be adjusted substantially independently of one another. Exhaust gas burner (50) according to Claim 1 , wherein the first heating zone (68) has a first heating resistor (96) and the second heating zone (70) has a second heating resistor (98), wherein the two heating resistors (96, 98) can be controlled independently of one another. Exhaust gas burner (50) according to Claim 1 or 2 , wherein the second heating zone (70) is formed at an end of the flame starter candle (66) facing the combustion chamber (52). Exhaust gas burner (50) according to one of the Claims 1 until 3 , wherein the first heating zone (68) is formed in the region of a fuel connection (78) of the flame starter plug (66). Exhaust gas burner (50) according to one of the Claims 1 until 4 , wherein the first heating zone (68) has an evaporator screen (46), an evaporator network (81) and/or an evaporator tube (80) for evaporating the fuel (48) supplied to the flame starter plug (66). Exhaust gas burner (50) according to one of the Claims 1 until 5 , wherein the first heating zone (68) extends from an insulation (74) in the region of an electrical contact (72) of the flame starter candle (66) to a protective tube opening (85) in a protective tube (84) of the flame starter candle (66). Exhaust gas burner (50) according to one of the Claims 1 until 6 , wherein the second heating zone (70) extends from a protective tube opening (85) in a protective tube (84) of the flame starter candle (66) to a glow rod tip (88) of the flame starter candle (66) facing the combustion chamber (52). Exhaust gas burner (50) according to one of the Claims 1 until 7 , wherein an unheated third zone (69) is formed between the first heating zone (68) and the second heating zone (70). Exhaust gas burner (50) according to one of the Claims 1 until 8 , wherein a temperature sensor (90, 92) is arranged in the first heating zone (68) and/or in the second heating zone (70). Internal combustion engine (10) with an exhaust gas aftertreatment system, wherein the exhaust gas aftertreatment system comprises an exhaust gas burner (50) according to one of the Claims 1 until 9 has. A method for operating an exhaust gas burner (50) in an exhaust gas aftertreatment system of an internal combustion engine (10), comprising the following steps: - activating the exhaust gas burner (50), wherein the first heating zone (68) and the second heating zone (70) of the flame-starting plug (66) are activated, - activating the fuel supply (54) for the exhaust gas burner (50) when both heating zones (68, 70) of the flame-starting plug (66) have reached their target temperature intended for starting the exhaust gas burner (50), - wherein a fuel temperature of the fuel (48) to be vaporized is regulated via the first heating zone (68), and - wherein a temperature at the glow rod tip (88) of the flame plug (66) is regulated via the second heating zone (70) in order to ensure ignition of the fuel-air mixture in the combustion chamber (52). Procedure according to Claim 11 , wherein after reaching the target temperature, the temperature in the first heating zone (68) is controlled independently of the temperature in the second heating zone (70). Procedure according to Claim 11 or 12 , wherein when the exhaust gas burner (50) is switched off, the fuel supply (54) is switched off and, in parallel, the air supply (62) into the combustion chamber (52) is reduced in order to slow down the cooling rate of the combustion chamber (52), wherein the residual fuel located in the flame starter plug (66) is released into the combustion chamber (52) and ignited by the second heating zone (70). Procedure according to Claim 13 , wherein a temperature in the region of the second heating zone (70) is determined and the air supply is maintained after completion of the combustion of the residual fuel from the flame starter plug (66) in order to prevent thermal overload of the flame starter plug (66) as long as the temperature in the second heating zone (70) is above a threshold temperature. Method according to one of the Claims 11 until 14 , wherein the heating and/or cooling speed of the heating zones (68, 70) are stored in a model in a control unit (99) of the exhaust gas burner and, in order to analyse the functionality of the flame starter plug (66), a temperature profile determined when the corresponding heating zone (68, 70) is energised is compared with a temperature profile to be expected for the respective heating zone (66, 70) according to the model.