Method for the exhaust aftertreatment of an internal combustion engine and exhaust aftertreatment system

Abstract

The invention relates to a method for the exhaust aftertreatment of an internal combustion engine, which on the outlet side is connected to an exhaust gas system. Provided in the exhaust gas system is at least one exhaust aftertreatment component with which, upon reaching the light-off temperature of this exhaust aftertreatment component, the gaseous limited exhaust gas components may be converted into unlimited exhaust gas components. An introduction point is provided at an exhaust duct of the exhaust gas system, at which a hot gas, in particular an exhaust gas of an exhaust gas burner, is introduced into the exhaust duct. The hot gas mixes with the exhaust gas of the internal combustion engine in such a way that a hot mixed gas results in which the unburned exhaust gas components are oxidized to unlimited exhaust gas components, without a catalytically active surface. It is provided that the introduction of the hot gas is set as soon as the exhaust gas components of the exhaust aftertreatment system have reached their respective light-off temperature.

Claims

1. A method for exhaust aftertreatment of an internal combustion engine, which on the outlet side is connected to an exhaust gas system, wherein at least a first exhaust aftertreatment component and a second exhaust aftertreatment component are situated in the exhaust gas system, wherein an introduction point for introducing a hot gas is formed at an exhaust duct of the exhaust gas system downstream of the first exhaust aftertreatment component and upstream of the second exhaust aftertreatment component, and wherein the internal combustion engine is connected to a control unit, the method comprising the following steps: the control unit operating the internal combustion engine with an under-stochiometric fuel-air mixture, introducing the exhaust gases of the internal combustion engine into the exhaust duct, introducing an over-stochiometric hot gas of an exhaust burner into the exhaust duct at an introduction point, wherein the hot gas mixes with the exhaust gas of the internal combustion engine in a mixing zone, so that a stoichiometric or overstoichiometric exhaust gas results downstream from the mixing zone, and oxidizing the unburned exhaust gas components of the exhaust gas of the internal combustion engine in a reaction zone downstream from the mixing zone, wherein the unburned exhaust gas components are reacted with the residual oxygen in the mixed gas, wherein the under-stochiometric fuel-air mixture of the combustion engine is used to regenerate the first exhaust aftertreatment component upstream of the introduction point.

2. The method for exhaust aftertreatment according to claim 1, further comprising the control unit causing adjustment of the understoichiometric combustion fuel-air mixture during an enrichment in an acceleration phase or full load phase of the internal combustion engine.

3. The method for exhaust aftertreatment according to claim 1, further comprising the control unit selecting to operate the internal combustion engine with the under-stochiometric fuel-air mixture for protection of a component of the internal combustion engine and/or of the exhaust gas system.

4. The method for exhaust aftertreatment according to claim 1, wherein the method is carried out in a cold start phase of the internal combustion engine in which a catalytic converter situated in the exhaust gas system has not yet reached its light-off temperature.

5. The method for exhaust aftertreatment according to claim 4, further comprising the control unit deactivating the introduction of the hot gas as soon as an exhaust aftertreatment by means of the exhaust aftertreatment components is possible.

6. The method for exhaust aftertreatment according to claim 1, further comprising the control unit selecting a mixing ratio of hot gas to exhaust gas of the internal combustion engine for which a temperature of at least 650 C. develops in the reaction zone.

7. An exhaust aftertreatment system for an internal combustion engine having an exhaust gas system, wherein at least a first exhaust aftertreatment component and a second exhaust aftertreatment component are situated in the exhaust gas system, and wherein an introduction point for introducing a hot gas is formed at an exhaust duct of the exhaust gas system downstream of the first exhaust aftertreatment component and upstream of the second exhaust aftertreatment component, the exhaust aftertreatment system comprising: a control unit, wherein the control unit is configured for carrying out a method according to claim 1 when a machine-readable program code is executed by the control unit.

8. The exhaust aftertreatment system according to claim 7, wherein the hot gas is generated by an exhaust gas burner.

9. The exhaust aftertreatment system according to claim 7, further comprising a mixing element situated in the mixing zone.

10. The exhaust aftertreatment system according to claim 7, further comprising an element for reducing the flow speed of the mixed gas situated in the mixing zone and/or in the reaction zone.

11. The exhaust aftertreatment system according to claim 10, wherein the exhaust duct has a cross-sectional expansion in the area of the reaction zone.

12. The exhaust aftertreatment system according to claim 7, wherein the first exhaust aftertreatment component is a first three-way catalytic converter and the second exhaust aftertreatment component has three-way catalytic activity.

13. The exhaust aftertreatment system according to claim 12, wherein the second exhaust aftertreatment component is either a second three-way catalytic converter or a four-way catalytic converter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained below in exemplary embodiments, with reference to the associated drawings. Identical components or components having the same function are denoted by the same reference numerals in the various figures. In the figures:

(2) FIG. 1 shows an internal combustion engine with an exhaust aftertreatment system according to the invention;

(3) FIG. 2 shows a detail of the exhaust duct of an exhaust aftertreatment system according to the invention; and

(4) FIG. 3 shows a flow chart for carrying out a method according to the invention for the exhaust aftertreatment of an internal combustion engine.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows an internal combustion engine 10 having an exhaust aftertreatment system according to the invention, in a schematic illustration. The internal combustion engine 10 has a plurality of combustion chambers 12 at which at least one intake valve 14 and one exhaust valve 16 is situated in each case. The internal combustion engine 10 has an intake via which the internal combustion engine 10 is connectable to an air supply system, not illustrated for reasons of clarity. The internal combustion engine 10 also has an exhaust gas aspirator 18 via which the internal combustion engine 10 is connected to an exhaust gas system 20 in such a way that an exhaust gas may be conducted from the combustion chambers 12 of the internal combustion engine 10 into the exhaust gas system 20 when the exhaust valves 16 are open. The exhaust gas system 20 includes an exhaust duct 22 in which a turbine 26 of an exhaust gas turbocharger 24, a three-way catalytic converter 28 downstream from the turbine 26, and a particulate filter 62 or a four-way catalytic converter 32 downstream from the three-way catalytic converter 28 are situated in the flow direction of an exhaust gas 52 of the internal combustion engine 10 through the exhaust duct 22. Optionally, a NOx storage catalytic converter 30 may be additionally situated downstream from the three-way catalytic converter 28 and upstream from the particulate filter 62 or the four-way catalytic converter 32. Alternatively, the order of the exhaust aftertreatment components 28, 30, 32 may be interchanged. In addition, in a simplified design of the exhaust aftertreatment system the particulate filter 62 or the four-way catalytic converter 32 may be omitted. The three-way catalytic converter 28, as the first component of the exhaust aftertreatment, is preferably situated in a position in the exhaust gas system 20 close to the engine. In this context, a position close to the engine is understood to mean a position with an exhaust gas running length of less than 80 cm, preferably less than 50 cm, beginning at the exhaust gas aspirator 18 of the internal combustion engine 10. The particulate filter 62 or the four-way catalytic converter 32 is preferably situated in an underbody position of a motor vehicle. In addition, an electric heating element may be provided, with which at least one of the catalytic converters 28, 30, 32 or the particulate filter 62 is electrically heatable.

(6) A first lambda sensor 34 is situated in the exhaust duct 22, downstream from the turbine 26 of the exhaust gas turbocharger 24 and upstream from the three-way catalytic converter 28. The first lambda sensor 34 is preferably designed as a broadband sensor, and thus allows a quantitative assessment of the combustion air ratio upstream from the three-way catalytic converter 28. A second lambda sensor 36, which is preferably designed as a jump sensor, is provided in the exhaust duct 22, downstream from the three-way catalytic converter 28 and upstream from the second catalytic converter 30. The combustion air ratio of the internal combustion engine 10 is controllable via the two lambda sensors 34, 36. In addition, at least one introduction point 44 for introducing a hot gas 54 into the exhaust duct 22 is provided at the exhaust duct 22. FIG. 1 shows several possible introduction points, wherein the invention is not limited to the positions illustrated. The introduction point 44 is particularly preferably situated downstream from the first three-way catalytic converter 28 and upstream from the four-way catalytic converter 32 or a further three-way catalytic converter. The first three-way catalytic converter 28 close to the engine may be heated by engine-internal heating measures, and the four-way catalytic converter 32 or the further three-way catalytic converter may be heated with the hot gas 54 from an exhaust gas burner 42. The hot gas 54 is preferably introduced upstream from a particulate filter 62 to allow additional use to be made of the hot gas for heating the particulate filter 62 during a particulate filter regeneration.

(7) FIG. 2 illustrates a section of the exhaust duct 22 with an introduction point 44 for introducing a hot gas into the exhaust duct 22. The hot gas 54 is generated by a hot gas generator 40, preferably an exhaust gas burner 42 illustrated in FIG. 2, by combustion of an fuel-air mixture. Provided in the exhaust duct 22 is a mixing zone 46 in which the hot gas from the hot gas generator 40 mixes with the exhaust gas 52 of the internal combustion engine 10. To improve the mixing of the hot gas 54 and the exhaust gas 52, a mixing element 56 may be provided in the mixing zone which deflects and/or swirls the flow in the exhaust duct 22 in such a way that the mixing of the exhaust gas 52 and the hot gas 54 to form a mixed gas 58 is facilitated. Downstream from the mixing zone 46, a reaction zone 48 is situated in the exhaust duct 22, in which the unburned exhaust gas components react with the residual oxygen from the mixed gas 58 and are thus oxidized into unlimited exhaust gas components. The hot gas generator 40 and the mixing zone 46 in the exhaust duct 22 are designed in such a way that afterburning of the oxidizable exhaust gas components, in particular carbon monoxide, unburned hydrocarbons, methane, or hydrogen, is possible, even without a catalytic surface. The objective of the mixing zone 46 is to uniformly mix the exhaust gas 52 with the hot gas 54, so that the best possible oxidation of these exhaust gas components can take place in the subsequent reaction zone 48. In the exhaust duct 22, an element 64 for reducing the flow speed may be situated in the mixing zone 46 and/or in the reaction zone 48. In one very simple embodiment, a cross-sectional expansion 60 of the exhaust duct 22 in the reaction zone 48 is provided in order to reduce the flow speed in this zone 48.

(8) The reaction zone 48 is to be designed in such a way that a sufficient residence time of the mixed gas 58 is ensured for substantial oxidation of the unburned exhaust gas components. The quantity and the temperature of the hot gas 54 are selected in such a way that a temperature above 650 results for the mixed gas 58 in the reaction zone 48. The air ratio of the mixed gas 58 is preferably rich in oxygen (i.e., overstoichiometric), so that a stoichiometric or overstoichiometric mixed gas results in the reaction zone 48, even with an understoichiometric combustion air ratio in the combustion chambers 12 of the internal combustion engine 10.

(9) FIG. 3 illustrates a flow chart of a method according to the invention for the exhaust aftertreatment of an internal combustion engine 10. An exhaust aftertreatment system (e.g., exhaust aftertreatment system in FIG. 1) having a control unit 50 may be configured to carry out the method according to the invention. The control unit 50 operates the internal combustion engine 10 with a fuel-air mixture, and the internal combustion engine 10 introduces exhaust gas 52 into the exhaust duct 22 of the exhaust gas system 20, in a first method step <100>. The operating conditions of the internal combustion engine 10 as well as the temperature of the exhaust aftertreatment components 28, 30, 32, 62 are determined by the control unit 50 in a second method step <110>. If the temperature of the exhaust aftertreatment components 28, 30, 32, 62, in particular the temperature of the three-way catalytic converter 28 or the four-way catalytic converter 32, is below their light-off temperature, or if a complete conversion of the unburned exhaust gas components by the catalytic converters 28, 32 is not possible for other reasons, the control unit 50 causes the hot gas generator 40 to generate and introduce hot gas 54 into the exhaust duct 22 at the introduction point 44 in a method step <120>. In a method step <130>, the control unit 50 causes the mixing element 56, in the mixing zone 46, to mix the hot gas 54 with the exhaust gas 52 of the internal combustion engine 10 to form a mixed gas 58. In the reaction zone 48, the unburned exhaust gas components HC, CO, CH.sub.4, H.sub.2 are exothermically reacted with the residual oxygen from the mixed gas 58 in a method step <140>. As soon as the exhaust aftertreatment components 28, 30, 32, 62 have reached their light-off temperature, in a method step <150> the control unit 50 deactivates the introduction of the hot gas 54, and exhaust aftertreatment takes place using conventional methods known from the prior art.

(10) In addition to a cold start of the internal combustion engine 10, in which the catalytic converters 28, 30, 32, 62 have not yet reached their light-off temperature, the proposed method may take place in particular with enrichment of the fuel-air mixture in the combustion chambers 12 of the internal combustion engine 10 during an acceleration or in full load operation of the internal combustion engine 10. In addition, a method according to the invention may take place with enrichment for protection of a component of the internal combustion engine 10, in particular for protection of the exhaust valves 16 or of an exhaust aftertreatment component, in particular the turbine 26, the three-way catalytic converter 28, the four-way catalytic converter 32, or the particulate filter 62. Furthermore, enrichment of the fuel-air mixture is provided for regeneration of an exhaust aftertreatment component, in particular for regeneration or desulfurization of a NOx storage catalytic converter 30 or for suppression of an undesirable regeneration of the particulate filter 62 or the four-way catalytic converter 32. In these operating situations, the unburned exhaust gas components may be oxidized by the method according to the invention without the need for a catalytically active surface of one of the catalytic converters 28, 30, 32.

LIST OF REFERENCE NUMERALS

(11) 10 internal combustion engine 12 combustion chamber 14 intake valves 16 exhaust valves 18 exhaust gas aspirator 20 exhaust gas system 22 exhaust duct 24 exhaust gas turbocharger 26 turbine 28 three-way catalytic converter 30 NOx storage catalytic converter 32 four-way catalytic converter 34 first lambda sensor 36 second lambda sensor 40 hot gas generator 42 exhaust gas burner 44 introduction point 46 mixing zone 48 reaction zone 50 control unit 52 exhaust gas 54 hot gas 56 mixing element 58 mixed gas 60 cross-sectional expansion 62 particulate filter 64 element for reducing the flow speed