Internal combustion engine with burner integrated into an exhaust system

Abstract

An internal combustion engine comprises an internal combustion engine (1) and an exhaust system (5) in which a burner (6) is integrated. The burner (6) includes a fuel injector (14) with a fuel channel connecting a fuel inlet (15) to a fuel outlet (19), the fuel outlet (19) being closable by means of a valve body. The fuel channel is further connected or connectable to a fuel outlet (20). The internal combustion engine further comprises a fuel tank (8). The fuel tank (8) is connected to the fuel inlet (15) of the fuel injector (14), with a fuel pump and a heating device (16) being integrated into this connection.In operation of the burner (6), fuel is supplied to the fuel inlet (15) of the fuel injector (14) by means of the fuel pump, whereby this fuel is heated by the heating device (16) during a warm-up phase and completely discharged again via the fuel outlet (20). During a combustion phase, however, the supplied fuel is introduced at least partially into a combustion chamber (18) via the fuel outlet (19) and burned there.

Description

The invention relates to an internal combustion engine having a burner which is integrated into an exhaust system of the internal combustion engine. The invention also relates to a method for operating such an internal combustion engine.The exhaust limits applicable to internal combustion engines are increasingly exacerbated. This applies in particular to internal combustion engines which are provided for driving motor vehicles. In order to be able to meet these exhaust gas limit values, it is necessary that the conversion capability of exhaust gas aftertreatment devices which are integrated into the exhaust lines of these internal combustion engines exists as quickly as possible after an engine start in the cold state (cold start). This means that the exhaust gas aftertreatment devices reach their light-off temperatures (also called light-off temperatures) as quickly as possible after a cold start, from which temperatures sufficient effectiveness for the exhaust gas aftertreatment can be assumed.It is known to temporarily selectively heat exhaust gas aftertreatment devices. This can be implemented both by engine measures which aim at an internal combustion engine discharging exhaust gas with a relatively high exhaust gas temperature and by active heating measures, for example by means of electrical heating devices or by means of burners. Such a burner can use, in particular, the fuel that is also provided for operating the internal combustion engine as fuel (cf. DE 10 2013 013 663 B4 and DE 10 2009 053 379 B4). In this case, the fuel is usually supplied to the burner at a relatively low pressure of significantly below 10 bar.At relatively low temperatures of the fuel due to correspondingly low ambient temperatures, operation and in particular ignition of the burner may be problematic. This applies in particular when using diesel fuel as fuel for the burner.DE 42 42 091 A1 discloses a regeneration burner of a particle filter system which has a heating device. This can comprise a glow plug integrated into an atomizer nozzle housing or a heating coil surrounding the atomizer nozzle housing.EP 2 617 957 A1 discloses a method for preheating a burner which is integrated into an exhaust system of an internal combustion engine. For this purpose, an electromagnetic injection valve of the burner is supplied with electrical voltage without the burner being opened. The electrical voltage causes the injection valve and the fuel contained therein to be heated via the electrical resistance, as a result of which its viscosity is reduced and therefore its sputterability is improved.DE 10 2021 001 584 A1 discloses a burner for an exhaust system of an internal combustion engine, in which a fuel injector is surrounded by a cooling jacket, which is provided for a coolant to flow through.DE 10 2008 055 056 A1, DE 11 2007 000 787 T5 and DE 10 2010 030 343 A1 each disclose fuel injectors for introducing fuel into an exhaust system of an internal combustion engine, wherein the fuel injectors can each also be cooled by means of the fuel and have a fuel return for this purpose.US 2010 / 0 212 641 A1 discloses a fuel injector for introducing fuel into an exhaust system of an internal combustion engine, wherein the fuel injector comprises a plurality of valves, one of which is connected to a fuel return.The invention is based on the object of improving the operation and in particular an ignition of a burner which is integrated into an exhaust system of an internal combustion engine, in particular at relatively low temperatures of the fuel used for its operation.This object is achieved by the subject matters of the patent claims.The invention relates to a fuel injector for a burner. A "burner" is basically a device that burns fuel with oxygen, in particular as a component of air, and thereby generates a hot gas that can be used for direct heating of a component. The burner is used in an exhaust system of an internal combustion engine according to the invention and can be assigned in particular to at least one exhaust gas aftertreatment device, so that its operation is provided for heating the exhaust gas aftertreatment device in a targeted manner and as required. Such heating can be provided in particular before or immediately after a cold start of the internal combustion engine if the exhaust gas aftertreatment device has a temperature which is below its starting temperature, from which sufficient effectiveness for the provided exhaust gas aftertreatment can be assumed. Such heating can, however, also be provided for the realization of a temporarily particularly high temperature of the exhaust gas aftertreatment device with the aim of regenerating the exhaust gas aftertreatment device.The exhaust system serves for discharging exhaust gas originating from at least one combustion chamber of an internal combustion engine of the internal combustion engine. The exhaust gas is discharged by means of the exhaust line at least partially into the environment.The fuel injector comprises a fuel channel which connects a fuel inlet to a fuel outlet, wherein the fuel outlet can be closed by means of a valve body. By means of the closable fuel outlet, fuel can be introduced, if necessary, in metered fashion into a combustion chamber of the burner. The fuel outlet of the fuel injector leads to the combustion chamber for this purpose. The burner furthermore also comprises an oxygen supply to the combustion chamber in order to supply the combustion chamber with the oxygen necessary for burning the fuel, in particular as a constituent of air or a mixture of air and further gases, in particular exhaust gas from an exhaust gas recirculation system. According to the invention, the fuel channel of the fuel injector is furthermore connected or connectable to a fuel outlet of the fuel injector.Such a fuel injector may advantageously be flowed through by fuel which is not provided for introduction into the combustion chamber. This makes it possible, on the one hand, to discharge relatively cold fuel which is present within the fuel injector and to replace it with heated fuel, with the result that the fuel which is to be introduced into the combustion chamber for a combustion operation of the burner directly has a relatively low viscosity, as a result of which the atomization thereof is positively influenced, which in turn can lead to good ignition behavior of the fuel in the combustion chamber. In addition, a flow of heated fuel through the fuel injector may lead to preheating of the fuel injector, which may likewise have an advantageous effect with regard to operation of the burner.In order to heat (directly or indirectly) the fuel which is supplied to the fuel injector, an internal combustion engine according to the invention comprises a heating device which is integrated into a fuel-conducting connection of a fuel tank of a fuel supply system of the internal combustion engine to the fuel inlet of the fuel injector of the burner. The heating device can also be part of the burner and in particular of the fuel injector thereof. The maximum heating power of the heating device can be between 200 W and 250 W, for example.A "heating device" is understood in principle to mean a device which is provided primarily or exclusively for releasing thermal energy in a controlled manner as required. Such a heating device can be designed electrically in particular and can accordingly be based on a conversion from electrical energy into thermal energy. Such an electrical heating device can be designed in particular as a resistance heating device, wherein alternative configurations for the (electrical) heating device, for example in the form of a piezoelectric heating device or a PTC heating device, can also be advantageously provided. The heating device of an internal combustion engine according to the invention can preferably be designed to be controllable or regulable with regard to the heating power. A control or regulation can preferably be carried out electronically. However, simple mechanical control by means of, for example, a Bi-metal switch is also possible.A "fuel-conducting" is understood to mean a connection between two components which is configured to conduct fuel at least temporarily from the first-mentioned component to the second-mentioned component. Preferably, the connection may be arranged such that this fuel can lead solely from the first-mentioned component to the second-mentioned component (and not in the opposite direction). For this purpose, a suitably configured check valve and / or differential pressure valve can be integrated into such a connection, for example.The details according to which a fuel-conducting connection is provided between two components or sides of components are to be understood in such a way that corresponding fuel lines are provided, which are integrated into the fuel supply system in such a way that such pressures of the fuel prevail at the ends thereof that are assigned to the components or the sides of these components.Furthermore, a fuel pump is integrated into the connection of the fuel tank to the fuel inlet of the burner of an internal combustion engine according to the invention in order to ensure delivery of the fuel. This fuel pump can be driven in particular by electric motor in order to allow operation of the burner even independently of operation of the internal combustion engine of the internal combustion engine.A method according to the invention for operating the burner of an internal combustion engine according to the invention provides that fuel is supplied to the fuel inlet of the fuel injector by means of the fuel pressure pump, wherein this fuel is heated by means of the heating device during a heating phase and is discharged again completely via the fuel outlet. During a combustion phase following the warming-up phase (preferably directly), on the other hand, the supplied fuel is introduced at least partially, optionally completely, into the combustion chamber via the fuel outlet and is burned there with oxygen which has been supplied via the oxygen supply.The heating of the fuel by means of the heating device at least during the heating phase serves to improve the atomization of the fuel to be introduced into the combustion chamber, which is of importance in particular when a temperature of the fuel was previously relatively low or is still relatively low in the non-heated part of the fuel. Accordingly, according to one embodiment of a method according to the invention, it can be provided that the warming phase is carried out only when this temperature of the fuel (at the beginning of the warming phase) is less than a defined first limit value, which can be 20° C., for example.An operation of the heating device can also be provided during the combustion phase. This applies in particular to a first time section of the combustion phase in order to ensure safe combustion operation of the burner until sufficient heating of the burner and in particular of the fuel injector thereof has taken place by the combustion operation.The warming phase can preferably be ended when a defined period of time has elapsed and / or a temperature of the fuel which is or has been discharged via the fuel outlet of the fuel injector is greater than a defined second limit value, which can be 20° C., for example, when a temperature is determined downstream of the fuel outlet of the fuel injector. It can then be assumed that a reliable ignition of the fuel introduced into the combustion chamber and thus a reliable combustion operation of the burner can then take place.The fuel pump is preferably a low-pressure pump which can provide a delivery pressure of at most 20 bar or at most 10 bar or at most 6 bar. Such a fuel pump can be distinguished by a correspondingly low power requirement and relatively low production costs and a relatively small installation space requirement.According to the invention, values for the pressure represent an overpressure to the ambient pressure.The fuel pump can furthermore preferably be a so-called prefeed pump, which also supplies fuel to a high-pressure pump of the internal combustion engine. A "high-pressure pump" is understood here to mean a pump which can generate a pressure of the fuel of at least 100 bar, preferably of at least 1000 bar, or which generates it at least temporarily during operation. By means of the high-pressure pump, which is preferably directly drivable by means of the internal combustion engine, the fuel can then be supplied at a high pressure of, for example, 2000 bar (e.g. in the case of a diesel engine) to at least one combustion chamber injector which is assigned to the at least one combustion chamber of the internal combustion engine in order to supply this fuel at least partially to the at least one combustion chamber. Accordingly, it may be provided that the fuel tank of an internal combustion engine according to the invention is also connected to a suction side of such a high-pressure pump in a fuel-conducting manner, and a pressure side of the high-pressure pump is connected to the at least combustion chamber injector in a fuel-conducting manner. For operation of the burner, a fuel pump can consequently be used which usually has an internal combustion engine anyway, because a high-pressure pump is often not sufficiently effective in a suction-conducting manner and therefore requires a prefeed pump.It may preferably be provided that the internal combustion engine has a plurality of combustion chambers, each of which is assigned a combustion chamber injector.The possibility according to the invention of also letting fuel flow through the fuel injector, which is not provided for introduction into the combustion chamber, can also be used to cool the fuel injector at least temporarily during the combustion phase, in particular during a second section of this combustion phase, in which the heating device is not (any longer) operated. Accordingly, one embodiment of a method according to the invention provides that the fuel is partially discharged again via the fuel outlet during the combustion phase at least temporarily. As a result, thermal overloading of the fuel injector during continuous operation of the burner can be avoided in an advantageous manner, it being possible to dispense with supplementary measures for cooling the fuel injector. For a constructionally as simple as possible implementation of such a functionality of the fuel injector, it may preferably be provided that it comprises a valve that can be adjusted into a first switching position in which the fuel inlet is connected to the fuel outlet (and not to the fuel outlet) in a guiding manner, and at least into a second switching position in which the fuel inlet is connected to the fuel outlet as well as to the fuel outlet in a guiding manner.Cooling the fuel injector may also be useful after termination of the combustion operation of the burner in order to avoid thermal overloading as a result of a build-up of heat. Accordingly, according to one embodiment of a method according to the invention, it can be provided that the supplied fuel is discharged again completely via the fuel outlet during a cooling phase following the combustion phase (preferably directly) in order to effect cooling of the fuel injector by this fuel. This cooling phase can be provided for a defined period of time, for example, and / or be controlled, in particular also ended, as a function of a temperature of the burner, which can be measured and / or modeled.According to a configuration of the fuel injector of an internal combustion engine according to the invention which is advantageous from a structural point of view, it can be provided that the fuel duct is formed in an inner housing and the fuel outlet is formed in an outer housing, wherein a fuel guide space is formed between the inner housing and the outer housing, which is part of the connection of the fuel duct to the fuel outlet. The fuel guidance chamber can preferably surround the inner housing over its entire circumference in at least one section, as a result of which a transition of thermal energy, which is as large as possible, between the fuel, which flows through the fuel injector, on the one hand, and the inner housing and the outer housing, on the other hand, can be realized, which can have an advantageous effect with regard to a desired temperature control (heating or cooling) of the fuel injector or of the fuel (effect as a heating or cooling jacket).The fuel outlet of the fuel injector of an internal combustion engine according to the invention can preferably be connected to the fuel tank in a fuel-conducting manner in order to return fuel discharged from the fuel outlet of the fuel injector into the fuel tank. In this connection of the fuel outlet of the fuel injector to the fuel tank, a throttle valve and / or a shut-off valve may furthermore preferably be integrated. By means of such a throttle valve, the pressure of the fuel in the fuel injector and thus in particular also an introduction of the fuel via the fuel outlet into the combustion chamber of the burner can be specifically influenced. The throttle valve may preferably be designed to be controllable with respect to the throttle effect in order to control the pressure of the fuel in the fuel injector as required. By means of such a shut-off valve, a fuel flow through the fuel injector can be prevented as required. The throttle valve and the shut-off valve may preferably be functionally combined into one valve. By means of a defined timing of the switching state changes (on / on) of a shut-off valve, a controllable throttle effect can be achieved. The throttle valve and / or the shut-off valve may also be integrated into the burner and in particular into the fuel injector thereof.The internal combustion engine of an internal combustion engine according to the invention can be, in particular, a (self-igniting and quality-controlled) diesel engine, because relatively low temperatures, in particular in the case of diesel fuel, can have a negative effect on its properties, in particular with regard to the sprayability. However, it is also possible for the internal combustion engine to be a (spark-ignited and quantity-controlled) spark-ignition engine or a functional combination of diesel and spark-ignition engines, for example an internal combustion engine with homogeneous-charge compression ignition. The internal combustion engine can be operated in particular with liquid fuel (i.e. diesel or gasoline fuel).The invention also relates to a motor vehicle, in particular a land vehicle, particularly preferably a wheel-based and non-rail-bound motor vehicle (preferably a passenger car or a truck), having an internal combustion engine according to the invention. In this case, the internal combustion engine of the internal combustion engine can be provided in particular for (directly or indirectly) providing the driving power for the motor vehicle.The invention is explained in more detail below with reference to exemplary embodiments shown in the drawings. The drawings show, in each case in a simplified illustration: FIG. 1 : an internal combustion engine according to the invention, FIG. 2 : a section of a burner for an internal combustion engine according to the invention according to a first embodiment, and FIG. 3 : a section of a burner for an internal combustion engine according to the invention according to a second embodiment.The internal combustion engine shown in FIG. 1 comprises an internal combustion engine 1, which is only schematically shown and which, for example, forms four combustion chambers 2, each of which is assigned a combustion chamber injector 3 of a fuel supply system of the internal combustion engine. The fuel injectors 2 are integrated into the internal combustion engine 1 in such a way that fuel can be introduced directly into the combustion chambers 2 by means of said fuel.The internal combustion engine further comprises a fresh gas line 4, which is likewise only schematically illustrated, for supplying fresh gas, which at least partially comprises ambient air, to the combustion chambers 2, and an exhaust gas line 5 for removing exhaust gas which originates from the combustion chambers 2. A burner 6 is integrated into this exhaust line 5. This burner 6 is provided for generating hot gas as required, by means of which at least one exhaust gas aftertreatment device 7, which is integrated into the exhaust line 5 downstream of the burner 6, is heated.The fuel supply system of the internal combustion engine further comprises a fuel tank 8 for receiving fuel, which is provided primarily for the operation of the internal combustion engine 1. Within the fuel tank 8 there is arranged a low-pressure pump 9 which can be driven by an electric motor and which can be actuated by means of a control device 10 of the internal combustion engine. The low-pressure pump 9 is connected via fuel lines to a suction side of a high-pressure pump 11 in a manner conducting fuel, wherein a fuel filter 12 is integrated into this connection. The high-pressure pump 11 is driven by means of the internal combustion engine 1 by a mechanical coupling with an output shaft (not shown) of the internal combustion engine 1.The pressure side of the high-pressure pump 1 is connected to a fuel distributor 13 in a fuel-conducting manner, separate connections to all of the combustion chamber injectors 2 extending from this fuel distributor 13, so that the pressure side of the high-pressure pump 8 is connected to the combustion chamber injectors 2 in a fuel-conducting manner via the fuel distributor 13. A leakage oil line 41 leads away from the separate connections to a return line 42, via which excess fuel, which was made available by the low-pressure pump 9 of the high-pressure pump 11, can be returned to the fuel tank 8.The fuel supply system further comprises a fuel-carrying connection from the fuel distributor 13 to the fuel tank 8, via which connection surplus fuel can be returned from the fuel distributor 13 into the fuel tank 8.The fuel supply system further comprises a fuel-conducting connection from the fuel tank 8 to a fuel inlet 15 of a fuel injector 14 of the burner 6, this connection being formed in a first section integrally with the connection of the fuel tank 8 to the suction side of the high-pressure pump 11. Integrated into this integral section are the low-pressure pump 9, the fuel filter 12 and a third sensor device 43 downstream of the fuel filter. A heating device 16 and, between the heating device 16 and the fuel inlet 15 of the fuel injector 14, a first sensor device 17 for local measurement of a first pressure and a first temperature of the fuel are integrated into a second section of the connection from the fuel tank 8 to the fuel inlet 15 of the fuel injector 14.The fuel injector 14 furthermore comprises a fuel outlet 19 which opens into a combustion chamber 18 of the burner 6 and a fuel outlet 20, and a flow of fuel in the fuel injector 14 can be controlled by means of a valve 21, which is designed as a simple 3 / 2-way valve. In a first switching position of this valve 21, the fuel inlet 15 is connected to the fuel outlet 20 only for guiding fuel, while in a second switching position (cf. FIG. 1 ) the fuel inlet 15 is connected to both the fuel outlet 19 and the fuel outlet 20 for guiding fuel. In the first switching position of the valve 21, fuel, delivered by means of the low-pressure pump 9, flows through the fuel injector 14 without being introduced into the combustion chamber 18. The fuel discharged via the fuel outlet 20 is returned to the fuel tank 8 via a fuel-conveying connection of the fuel outlet 20 to the fuel tank 8. Integrated in a first section of this connection is a second sensor device 22 for the local determination of a second pressure and a second temperature of the fuel and, downstream thereof, a throttle and shut-off valve 23 in an embodiment as a 2 / 2-way valve. This throttle and shut-off valve 23, which can likewise be controlled by means of the control device 10, can serve for controlled throttling of the pressure of the fuel and thus for adjustability of the pressure of the fuel in the fuel injector 14. For a controlled throttling of the pressure of the fuel, the throttle valve, which is designed as a 2 / 2-way valve, can be switched between the two switching positions (enabling a fuel flow and blocking a fuel flow) by means of a defined timing. The flow cross section opened by the throttle and shut-off valve 23 can be so small that the delivery pressure provided by the low-pressure pump 9 in the fuel injector 14 is not influenced to a relevant extent. In order to damp severe fluctuations in the pressure of the fuel in the connection of the fuel outlet 20 to the fuel tank 8 upstream of the throttle and shut-off valve 23 as a result of a clocked changeover of the throttle and shut-off valve 23, it can be provided that the fuel line is designed to be correspondingly stretchable, in particular radially stretchable, in this section of the connection. Alternatively, a relatively large damping volume can also be provided in this section of the connection.Before, immediately with or shortly after the internal combustion engine 1 is put into operation in a cold state of the internal combustion engine and thus also of the exhaust gas aftertreatment device 7 (cold start), the burner 6 should be put into operation in order to bring about the fastest possible action of the exhaust gas aftertreatment device 7. Depending on the ambient temperature, the fuel contained (everywhere) in the fuel supply system may have a relatively low temperature, whereby a safe ignition of the fuel as well as an advantageous burning of the fuel in the combustion chamber 18 cannot be easily ensured.According to the invention, it is therefore provided that when the temperature of the fuel is less than a first limit value (e.g. 20° C.), a warm-up phase is carried out during operation of the burner 6. During this warm-up phase, fuel, delivered by the low-pressure pump 9, is heated by means of the heating device 16 and supplied to the fuel inlet 15 of the fuel injector 14. The heating device 16 can heat the fuel, for example, to a temperature between 50° C. and 80° C., measured by means of the first sensor device 17. During the warm-up phase, the valve 21 of the fuel injector 14 is in the first switching position, so that the heated fuel supplied via the fuel inlet 15 is discharged again completely via the fuel outlet 20 and thereby displaces the still cold fuel contained previously in the fuel injector 14 from the fuel injector 14. The heated fuel flowing through the fuel injector 14 additionally leads to preheating of the fuel injector 14 and ensures that the fuel introduced into the combustion chamber 18 at the beginning of a combustion phase during operation of the burner 6 already has a relatively high temperature, which has an advantageous effect with regard to the atomization of the fuel and thus the ignition capability and the combustion behavior. Preheating both the fuel and the fuel injector 14 leads to good mixture formation already with the first fuel injection by means of the fuel injector 14.The fuel in the combustion chamber 18 is burned in conjunction with oxygen which branches off from the fresh gas line 4 of the internal combustion engine downstream (with respect to the flow direction of fresh gas in the fresh gas line 4 in the direction of the internal combustion engine 1) of an air filter 25 to the combustion chamber 18 via an oxygen feed 24, which leads to a gas delivery device 37, preferably in a configuration as a blower, and a shut-off valve 38 are integrated into said gas delivery device.A transition from the warming-up phase to the combustion phase takes place when the temperature of the fuel determined by means of the second sensor device 22 has exceeded a defined second limit value of 20° C., for example. The valve 21 of the fuel injector 14 is then placed in the second switching position and thereby an introduction of fuel into the combustion chamber 18 is enabled. The heating device 16 can be operated even further at least during a first section of the combustion phase in order to further ensure good atomization of the fuel introduced into the combustion chamber 18. However, operation of the heating device 16 can be ended if the fuel injector 14 has been heated to such an extent that sufficiently good atomization of the fuel to be introduced into the combustion chamber 18 is ensured even without heating of the fuel by means of the heating device 16 on account of the combustion operation and by a fundamental heating of the internal combustion engine and by a supply of heated fuel which has been heated via a return line 39 which leads from a pressure regulating valve 40 of the fuel distributor 13 into the fuel supply line upstream of the fuel filter 12.During the combustion phase, according to the second switching position of the valve 21 of the fuel injector 14, a portion of the fuel supplied via the fuel inlet 15 is also discharged via the fuel outlet 20. As a result, cooling of the fuel injector 14 can be effected by dissipating thermal energy by the fuel leaving the fuel injector 14 via the fuel outlet 20, which can avoid thermal overloading of the fuel injector 14 at least after a relatively long-lasting burning operation of the burner 6.The combustion operation of the burner 6 can be ended as soon as the exhaust gas aftertreatment device 7 has reached its light-off temperature or a regeneration measure for the exhaust gas aftertreatment device 7 is concluded. For this purpose, the valve 21 of the fuel injector 14 is again placed in the first switching position. A cooling phase can then follow during operation of the burner 6, in which no fuel is likewise introduced into the combustion chamber 18. During the cooling phase, fuel, delivered by means of the low-pressure pump 9, is once again delivered through the fuel injector 14 and discharged via the fuel outlet 20, as a result of which this fuel discharges thermal energy from the fuel injector 14. The throttle and shut-off valve 23 is open in this case. The cooling phase can be provided until the temperature of the fuel, measured by means of the second sensor device 22, has fallen below a third limit value of 20° C., for example. This third limit value should preferably always be greater than the ambient temperature.As soon as the cooling phase has ended or whenever no use of the burner 6 is provided, the throttle and shut-off valve 23 is permanently switched into its shut-off valve position and as a result prevents a partial flow of fuel, which is conveyed by means of the low-pressure pump 9 to the high-pressure pump 11 during operation of the internal combustion engine 1, being conveyed back into the fuel tank 8 through the fuel injector 14 as the leakage flow bypassing the high-pressure pump 11.FIGS. 2 and 3 each show an embodiment of a fuel injector 14 for an internal combustion engine according to the invention according to FIG. 1, for example. The fuel injectors 14 each comprise an outer housing 26 and an inner housing 27 which is arranged within the outer housing 26. The inner housing 27 rotationally symmetrical with respect to a longitudinal axis 28 of the respective fuel injector 14 forms an annular fuel channel 29 which is connected at an inlet end, not shown, to the fuel inlet 15 of the fuel injector 14. In the region of an outlet end of the fuel duct 29, the inner housing 27 forms one or, as illustrated, a plurality of passage openings 30, which are likewise connected to the fuel duct 29 and which serve as a fuel outlet 19 of the fuel injector 14. The through-openings 30 can, as illustrated, be oriented parallel or at least partially at an angle (oblique) to the longitudinal axis 28. The through openings 30 and thus the fuel outlet 19 of the fuel injector 14 can be closed or released depending on the position of a valve body 31, which is arranged inside the fuel channel 29 so as to be displaceable by means of an actuator, not shown (e.g. electromagnetically or piezo-actuated), of a valve 21 of the fuel injector 14.As close as possible in the region of the outlet end, one or, as illustrated, a plurality of annularly distributed first passage openings 32 are formed in the wall of the inner housing 27 delimiting the fuel duct 29, as a result of which the fuel duct 29 is connected to a fuel guide space 33 which surrounds a section of the inner housing 27 in a closed, annularly shaped manner. The first passage openings 32 can be designed radially with respect to the longitudinal axis 28 or at an angle to the radial alignment, in particular inclined in the circumferential direction, in order to achieve a rotation of the flow of the fuel in the fuel guide space 33 about the longitudinal axis 28. Likewise, the first passage openings 32 can be inclined with respect to the longitudinal axis 28, in particular in the direction of the combustion chamber 18, in order to achieve increased cooling of the components which are subject to particularly thermal loads. The distance between the passage openings 32 and the end face of the fuel injector 14 with the fuel outlet 19 formed therein can preferably be as large as possible. In the fuel injector 14 according to FIG. 2, the fuel guidance space 33 is delimited by portions of the outer side of the inner housing 27 and by inner sides of an annular insert 34. In the fuel injector 14 according to FIG. 3, the fuel guidance chamber 33, on the other hand, is bounded by a section of the inner housing 27 and the outer housing 26 and by sealing elements 35. Corresponding sealing elements 35 are also provided in the fuel injector 14 according to FIG. 2 ; however, these are arranged outside the fuel guidance chamber 33. The sealing elements 35 prevent an undesired escape of fuel via gaps which are formed between the inner housing 27 and the outer housing 26 of the respective fuel injector 14.The sealing elements 35 can preferably be configured as conventional sealing rings made of an elastomer ("O-rings") or at least partially, in particular in the region of the outlet end of the fuel channel and thus in the vicinity of the combustion chamber 18 (cf. FIG. 3 ), of an alternative material, for example modified / filled PTFE, which is distinguished by a relatively good temperature resistance and / or a relatively good thermal conductivity, and / or as an annular element with rectangular cross-sectional areas.In the fuel injector 14 according to FIG. 2, which serves to secure the position of the sealing element 35 arranged in the region of the outlet end, the annular insert 34 forms a second through opening 36, which is arranged so as to overlap with the fuel outlet 20, which is formed in the outer housing 26, or with a channel of the outer housing 26 leading to the fuel outlet 20. Alternatively, the annular insert 34 can also have a plurality of second through-openings 36 distributed over its circumference, wherein a second fuel guidance chamber should then be provided on the outside of the circumferential section of the insert. This second fuel guidance chamber can be formed, for example, by an annular depression in the outer side of the insert 34, into which the through-openings 36 open. In the fuel injector 14 according to FIG. 3, the fuel outlet 20 or the channel leading to it opens directly into the fuel guide chamber 33.In a first valve position of the valve body 31 of each of the fuel injectors according to FIGS. 2 and 3, in which the valve body 31 covers the through openings 30, fuel which enters the fuel duct 29 via the fuel inlet 15 is discharged again completely via the through openings 30, 36, the fuel guidance space 33 and the fuel outlet 20. This enables a discharge of relatively cold fuel, which is located inside the fuel injector 14 at the beginning of an operation of the respective burner 6, and a preheating of this fuel injector 14 by heated fuel, as has already been described with reference to FIG. 1.In a second valve position of the respective valve body 31, in which the latter releases the through openings 30, on the other hand, a first part of the fuel supplied via the fuel inlet 15 is introduced via the fuel outlet 19 into the combustion chamber 18 of the burner 6, as a result of which a burning operation of the burner 6 is made possible, while a second part of the supplied fuel is discharged again via the fuel outlet 20. This second part of the fuel can serve to cool the fuel injector 14 during a continuous combustion operation of the burner 6 and / or after a combustion operation, as has likewise already been described with reference to FIG. 1.List of reference characters1 Internal combustion engine 2 combustion chamber 3 combustion chamber injector 4 fresh gas line 5 exhaust line 6 burner 7 exhaust gas aftertreatment device 8 fuel tank 9 low-pressure pump 10 control device 11 high-pressure pump 12 fuel filter 13 fuel distributor 14 fuel injector 15 fuel inlet of the fuel injector 16 heating device 17 first sensor device 18 combustion chamber 19 fuel outlet of the fuel injector 20 fuel outlet of the fuel injector 21 valve of the fuel injector 22 second sensor device 23 throttle and shut-off valve 24 oxygen supply 25 air filter 26 outer housing of the fuel injector 27 inner housing of the fuel injector 28 longitudinal axis of the fuel injector 29 fuel channel 30 through-opening 31 valve body 32 first through-opening 33 fuel guidance chamber 34 insert 35 sealing element 36 second through-opening 37 gas delivery device 38 shut-off valve 39 return line 40 pressure control valve of the fuel distributor 41 leak oil line 42 return line 43 third sensor device

Claims

Internal combustion engine having • an internal combustion engine (1) which forms at least one combustion chamber (2), • an exhaust line (5) for discharging exhaust gas which originates from the at least one combustion chamber (2), wherein a burner (6) is integrated into the exhaust line (5), wherein the burner (6) • has a fuel injector (14) having a fuel duct (29) via which a fuel inlet (15) is connected or can be connected to a fuel outlet (19) in a conducting manner, wherein the fuel outlet (19) can be closed by means of a valve body (31), characterized in that the fuel duct (29) is furthermore connected or can be connected to a fuel outlet (20) in a conducting manner, • a combustion chamber (18) into which the fuel outlet (19) opens, and • an oxygen feed (24) to the combustion chamber (18), and • a fuel supply system having a fuel tank (8), a fuel-conducting connection of the fuel tank (8) to the fuel inlet (15) of the fuel injector (14) of the burner (6), wherein a fuel pump and a heating device (16) are integrated into this connection.Internal combustion engine according to Claim 1, characterized in that the heating device (16) is part of the fuel injector (14).Internal combustion engine according to Claim 1 or 2, characterized bya valve (21) of the fuel injector (14) having a first switching position in which the fuel inlet (15) is connected to the fuel outlet (20) in a fuel-conducting manner only, and having a second switching position in which the fuel inlet (15) is connected to the fuel outlet (19) and to the fuel outlet (20) in a fuel-conducting manner.Internal combustion engine according to one of the preceding claims, characterized in that the fuel duct (29) is formed in an inner housing (27) and the fuel outlet (20) is formed in an outer housing (26), wherein a fuel guidance space (33), which is part of the connection of the fuel duct (29) to the fuel outlet (20), is arranged between the inner housing (27) and the outer housing (26).Internal combustion engine according to Claim 4, characterized in that the fuel-conducting space (33) surrounds the inner housing (27) over its entire circumference in at least one section.Internal combustion engine according to one of the preceding claims, characterized in that the fuel tank (8) is connected to a suction side of a high-pressure pump (11) so as to conduct fuel, and a pressure side of the high-pressure pump (11) is connected to at least one combustion chamber injector (3) of the internal combustion engine (1) which is assigned to the combustion chamber (2) so as to conduct fuel.Internal combustion engine according to one of the preceding claims, characterized bya fuel-conducting connection of the fuel outlet (20) of the fuel injector (14) to the fuel tank (8).Internal combustion engine according to Claim 7, characterized in that a throttle valve (23) and / or a shut-off valve (23) is / are integrated into the connection of the fuel outlet (20) of the fuel injector (14) to the fuel tank (8).Method for operating the burner (6) of an internal combustion engine according to one of the preceding claims, characterized in that fuel is supplied by means of the fuel pump to the fuel inlet (15) of the fuel injector (14), wherein this fuel • is heated by means of the heating device (16) during a warm-up phase and is discharged again completely via the fuel outlet (20), and • is introduced at least partially into the combustion chamber (18) via the fuel outlet (19) during a combustion phase following the warm-up phase and is burned there with oxygen which has been supplied via the oxygen supply (24).Method according to Claim 9, characterized in that the warming-up phase is carried out only if a temperature of the fuel is less than a first limit value.Method according to Claim 9 or 10, characterized in that during the combustion phase the fuel is partly discharged via the fuel outlet (20).Method according to one of Claims 9 to 11, characterized in that the warming-up phase is ended if a defined period of time has elapsed or a temperature of the fuel which is or has been discharged via the fuel outlet (20) is greater than a second limit value.Method according to one of Claims 9 to 12, characterized in that the fuel is discharged completely via the fuel outlet (20) during a cooling phase which follows the combustion phase.

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