REGENERATION APPARATUS

Abstract

A regeneration apparatus for a particulate filter of an exhaust gas system is provided which includes an exhaust gas duct and a catalyst which is integrated into the exhaust gas duct upstream of the particle filter. The exhaust gas system or the combustion engine includes an injection apparatus which is in communication with a fuel reservoir and is able to input fuel, in particular fuel containing hydrocarbons, into the exhaust gas flow. The regeneration apparatus includes a burner and at least one switching device. The burner is able to heat the catalyst to a reaction temperature at which an exothermic reaction of the fuel takes place. The switching device is able to activate and deactivate the burner and/or the injection apparatus selectively in dependence on an operating state of the exhaust gas system. An exhaust gas system for a combustion engine and a method for the regeneration of a particulate filter of an exhaust gas system are also provided.

Description

FIELD OF THE INVENTION

The present invention relates to a regeneration apparatus for a particulate filter of an exhaust gas system which includes an exhaust gas duct for the conducting of a hot exhaust gas flow away from a combustion engine, in particular from a diesel engine, and a catalyst, in particular an oxidation catalyst, which is integrated into the exhaust gas duct upstream of the particulate filter, wherein the exhaust gas system or the combustion engine includes an injection apparatus which is in communication with a fuel reservoir and is able to input fuel, in particular fuel containing hydrocarbons, into the exhaust gas flow.

BACKGROUND OF THE INVENTION

Combustion engines emit an exhaust gas flow containing different kinds of pollutants into the atmosphere. Various apparatus for exhaust gas post-treatment have been developed to reduce the emission of pollutants. For example, catalysts are used for the conversion of harmful gaseous substances into harmless components and particulate filters are used for the capturing of unwanted solid particles. The exhaust tract of a diesel engine can e.g. be provided with a diesel oxidation catalyst and a particulate filter arranged downstream thereof. Sooty particles, which are located in the exhaust gas flow are captured by the particulate filter and are stored in it. From a specific quantity onward, the collected soot has to be removed from the particulate filter so that the emission of exhaust gas is not impeded in too unacceptable a manner. This procedure is called regeneration. A common process for the regeneration of a particulate filter is to heat the particulate filter to a specific temperature in order thus to burn the deposited soot. This can in principle take place by any desired heating apparatus. However, such a heating apparatus has to have a relatively high performance to heat the particulate filter to the ignition temperature of the soot, which has the consequence of an increased requirement for energy and installation space.

Other processes have therefore been developed which are based on the principle of secondary fuel injection (HC dosing). In this respect, the fact is utilized that fuel, in particular in the form of unburned hydrocarbons, can cause a reaction in the catalyst and can thereby heat it. From a specific temperature onward, which is generally called the light-off temperature, an exothermic reaction of the fuel takes place, i.e. the reaction continues to run independently after the ignition while continuing to release heat. The catalyst can be heated sufficiently by the exothermic reaction to heat the particulate filter arranged downstream to the required temperature for the burning off of the deposited soot. No separate heating apparatus is required in this case. The injection of fuel into the exhaust gas flow usually takes place using an injection apparatus which is arranged in direct proximity to the catalyst. Alternatively, the injection of the fuel into the exhaust gas flow can also take place within the engine, for example by a subsequent injection of fuel into the combustion space.

However, at catalyst temperatures below the light-off temperature, no exothermic reaction takes place so that a particulate filter regeneration by fuel injection is only possible at specific operating states of the combustion engine. There is moreover the problem of an increased fuel consumption.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to make the regeneration of particulate filters more flexible, more reliable and more fuel-saving. This object is satisfied by a regeneration apparatus having the features of as described hereinafter.

In accordance with the invention, the regeneration apparatus additionally includes a burner, which is able to heat the catalyst to a reaction temperature at which an exothermic reaction of the injected fuel takes place, and at least one switching device which is able to activate and deactivate the burner and/or the injection apparatus selectively in dependence on an operating state of the exhaust gas system and/or of the combustion engine.

The catalyst can be heated to the light-off temperature at any time using the burner and the regeneration can be carried out independently of the operating state of the combustion engine. In this respect, the burner can be designed substantially smaller and more energy-saving than a burner for the direct heating of the particulate filter since in accordance with the invention, the burner only has to be able to heat the catalyst to the reaction temperature. Since this is usually substantially lower than the burn-off temperature for deposited sooty particles, significant potential for savings results. In dependence on the operating state of the exhaust gas system and/or of the combustion engine, the switching device can select and activate the respective suitable apparatus or both and can thus optimize the operation of the regeneration apparatus overall.

The invention further relates to a method for the regeneration of a particulate filter of an exhaust gas system which includes an exhaust gas duct for the conducting of a hot exhaust gas flow away from a combustion engine, in particular from a diesel engine, and a catalyst, in particular an oxidation catalyst which is integrated into the exhaust gas duct upstream of the particulate filter, wherein the exhaust gas system or the combustion engine includes an injection apparatus which is in communication with a fuel reservoir and is able to input fuel, in particular fuel containing hydrocarbons, into the exhaust gas flow.

The method in accordance with the invention additionally comprises the steps of providing a burner which is able to heat the catalyst to a reaction temperature at which an exothermic reaction of the fuel takes place, of determining an operating state of the exhaust gas system and/or of the combustion engine, and of activating the burner and/or the injection apparatus in dependence on the determined operating state of the burner and/or of the injection device in the case of a regeneration of the particulate filter.

Possible further developments of the invention are set forth in the dependent claims, in the description and in the drawing.

The switching device is preferably made to activate the burner and, where necessary, the injection apparatus when the temperature of the catalyst is below the reaction temperature and a regeneration of the particulate filter should be carried out. if therefore, for example, the charge of the particulate filter with deposited sooty particles has reached a degree which requires a regeneration, but, on the other hand, the temperature of the catalyst is too low for an exothermic reaction since, for example, the combustion engine has just been started, the switching device can activate the burner and thus provided an efficient and fast heating of the catalyst to the temperature required for a secondary fuel injection. In addition, the injection apparatus is activated unless sufficient non-consumed fuel is already contained in the exhaust gas flow.

The switching device is preferably made only to activate the injection apparatus when the temperature of the catalyst is above the reaction temperature and a regeneration of the particulate filter should be carried out. In this manner, a superfluous operation of the burner is avoided and the regeneration of the particulate filter can take place in an efficient manner via the secondary fuel injection whenever it is possible.

The switching device can also be made to deactivate the burner again when the temperature of the catalyst has risen above the reaction temperature. A switchover to the more effective heating principle is therefore made directly as soon as the catalyst has reached the required temperature. Depending on the application, it may be desirable also to operate the burner simultaneously with the injection apparatus for a specific time period after reaching the reaction temperature or up to the reaching of a specific threshold temperature.

The regeneration apparatus can be made as a modular unit, with the injection apparatus being integrated into the modular unit. This allows an installation of the regeneration apparatus into the exhaust tract of different types of combustion engines and brings along advantages with respect to production and maintenance.

The burner and the injection apparatus can in particular be realized by a common component which can easily be integrated into a plurality of different exhaust gas systems.

The object underlying the invention is furthermore satisfied by an exhaust gas system having the features described hereinafter.

In the regeneration method in accordance with the invention, a temperature of the catalyst can be determined for the determination of the operating state of the exhaust gas system, for example by a temperature sensor attached thereto. Alternatively, an operating parameter of the combustion engine can also be determined, for example its temperature or speed.

The burner is preferably activated when the temperature of the catalyst is below the reaction temperature and a regeneration of the particulate filter should be carried out. If, in contrast, the temperature of the catalyst is above the regeneration temperature and if a regeneration should be carried out, preferably only the injection apparatus is activated. The burner can be deactivated again if the temperature of the catalyst has risen above the reaction temperature.

The invention will be described in the following by way of example with reference to the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a part of an exhaust gas system which comprises a particulate filter and an oxidation catalyst as well as a regeneration apparatus in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The exhaust gas duct 13 shown in the Figure receives the hot exhaust gas flow from a combustion engine (not shown) at an end disposed upstream and conducts it on up to an exhaust tailpipe (not shown) through which the exhaust gases are emitted into the atmosphere. Before escaping into the atmosphere, the exhaust gas flow, represented by an arrow, passes through a catalyst 15 and a particulate filter 11 for emission control. The catalyst 15 can be a common oxidation catalyst such as a diesel oxidation catalyst. The particulate filter 11 is a sooty particle filter which filters sooty particles contained in the exhaust gas flow from the exhaust gas flow and stores it in its interior. A regeneration apparatus is arranged upstream of the catalyst 15 and is made here as a modular device or as a regeneration module 23. The regeneration module 23 includes both an injection apparatus 17 and a burner 19 which are both in communication with the exhaust gas duct 13. The injection apparatus 17 is furthermore in communication with a fuel reservoir (not shown). The communication between the regeneration module 23 and the exhaust gas duct 13 is such that, on the one hand, the injection apparatus 17 opens into the exhaust gas duct 13 and, on the other hand, the burner 19 has sufficient thermal communication with the catalyst 15.

The regeneration module 23 can adopt four different operating states. In accordance with a first operating state, both the injection apparatus 17 and the burner 19 are deactivated, i.e. there is neither an injection of fuel into the exhaust gas flow nor a heating of the exhaust gas flow by the burner 19. In accordance with a second operating state, the injection apparatus 17 is deactivated and the burner 19 is activated, i.e. there is a heating of the exhaust gas flow by the burner 19, but no injection of fuel. In accordance with a third operating state, the injection apparatus 17 is activated and the burner 19 is deactivated, i.e. the injection apparatus 17 inputs fuel into the exhaust gas flow, but there is no heating of the exhaust gas flow by the burner 19. In accordance with a fourth operating state, both the injection apparatus 17 and the burner 19 are activated, i.e. there is simultaneously an injection of fuel into the exhaust gas flow and a heating of the exhaust gas flow by the burner 19.

The control of the individual operating states of the regeneration module 23 takes place by means of a switching apparatus 21 to which the regeneration module 23 is connected. The switching device 21 can be a simple electrical switching arrangement which, for example, uses a bimetallic strip for the temperature determination. Alternatively, the switching device 21 can also include a complex integrated circuit. In the embodiment shown, the switching device 21 is made as a separate control device which is arranged remote from the regeneration module 23 and is connected thereto via an electrical cable. Alternatively, the switching device 21 can also be made directly as an additional component which is positioned directly at or in the regeneration module 23. In accordance with another embodiment, the switching device 21 can also be integrated into a control device of the combustion engine.

The switching device 21 receives different input signals and on this basis controls the operation of the regeneration module 23. The switching device 21 in particular receives a catalyst temperature signal 25 and a particulate filter charge signal 27. However, a variety of other input signals are conceivable by means of which a decision can be made whether a regeneration of the particulate filter 11 should take place, whether the temperature of the catalyst 15 is above the light-off temperature and whether a fuel injection is required.

If the particulate filter charge signal 27 indicates that a regeneration of the particulate filter 11 should be carried out, the switching device 21 checks, with reference to the catalyst temperature signal 25, whether the temperature of the catalyst 15 is below the reaction temperature at which an exothermic reaction of the injected fuel takes place. If this is the case, the burner 19 is activated to heat the exhaust gas duct 13 as well as the catalyst 15. The switching device 21 then continuously checks as required the catalyst temperature with reference to the catalyst temperature signal 25. As soon as the catalyst temperature has risen above the reaction temperature, the switching device 21 activates the injection apparatus 17 as required to thereby input unburned liquid hydrocarbons into the exhaust gas flow. They react exothermically in the catalyst 15, whereby heat is released and the catalyst temperature increases. The heating of the catalyst 15 by the burner 19 as well as the injection of fuel by the injection apparatus 17 run after reaching the reaction temperature up to the reaching of a defined threshold temperature. After reaching the threshold temperature, the burner 19 is deactivated again by the switching device 21. The catalyst 15 as well as the particulate filter 11 arranged in direct proximity are heated by the exothermic reaction of the injected fuel up to a temperature which is sufficient to achieve a burning of the sooty particles in the particulate filter 11 and consequently a regeneration of the particulate filter 11.

In the embodiment shown, the regeneration apparatus is made as a modular unit which comprises an injection apparatus 17 and equally a burner 19. Alternatively, the injection apparatus 17 and the burner 19 can be realized in a single common component. Depending on the application, however, it can also be expedient to make the injection apparatus 17 and the burner 19 as independent, separate apparatus and to arrange them separately from one another. For example, the injection apparatus 17 can be realized by a fuel injection apparatus provided for the operation of the combustion engine. In this variant, fuel is introduced into the fuel chamber with a time delay during the expansion cycle and thus reaches the exhaust gas flow at least partly unburned. The fuel injection therefore takes place here inside the engine so that the provision of a separate injection apparatus 17 is omitted.

It is possible by the regeneration module 23 described above to carry out regeneration of the particulate filter 11 at any times and during any operating states of the exhaust gas system or of the combustion engine, that is e.g., also directly after the start of the combustion engine. A costly and space-consuming heating apparatus is nevertheless not required for the direct heating of the particulate filter 11 to the soot burn-off temperature. Furthermore, an increased fuel consumption is avoided since a fuel injection only takes place when it also leads to the desired result, that is if the temperature of the catalyst 15 has risen above the light-off temperature. The regeneration concept in accordance with the invention can be used in a number of different types of combustion engine in industrial plant and in the automotive sector.

Claims

1. A regeneration apparatus for a particulate filter of an exhaust gas system which includes an exhaust gas duct for the conducting of a hot exhaust gas flow away from a combustion engine, in particular from a diesel engine, and a catalyst, in particular an oxidation catalyst which is integrated into the exhaust gas duct upstream of the particulate filter, wherein the exhaust gas system or the combustion engine includes an injection apparatus which is in communication with a fuel reservoir and which is able to input fuel, in particular fuel containing hydrocarbons, into the exhaust gas flow; characterized in that the regeneration apparatus comprises:

a burner which is able to heat the catalyst to a reaction temperature at which an exothermic reaction of the fuel takes place; and

at least one switching device which is able to activate and deactivate the burner and/or the injection apparatus selectively in dependence on an operating state of the exhaust gas system and/or of the combustion engine.

2. A regeneration apparatus in accordance with claim 1, characterized in that the switching device is made to activate the burner and, as required, the injection apparatus, when the temperature of the catalyst is below the reaction temperature and a regeneration of the particulate filter should be carried out.

3. A regeneration apparatus in accordance with claim 1, characterized in that the switching device is made only to activate the injection apparatus when the temperature of the catalyst is above the reaction temperature and a regeneration of the particulate filter should be carried out.

4. A regeneration apparatus in accordance with claim 1, characterized in that the switching device is made to deactivate the burner again when the temperature of the catalyst has risen above the reaction temperature.

5. A regeneration apparatus in accordance with claim 1, characterized in that it is made as a modular unit.

6. A regeneration apparatus in accordance with claim 5, characterized in that the injection apparatus is integrated into the modular unit.

7. A regeneration apparatus in accordance with claim 1, characterized in that the burner and the injection apparatus are realized by a common component.

8. An exhaust gas system for a combustion engine, in particular for a diesel engine, comprising:

an exhaust gas duct for the conducting of a hot exhaust gas flow away from the combustion engine;

a particulate filter; and

a catalyst, in particular an oxidation catalyst which is integrated into the exhaust gas duct upstream of the particulate filter;

wherein the exhaust gas system or the combustion engine includes an injection apparatus which is in communication with a fuel reservoir and is able to input fuel, in particular fuel containing hydrocarbons, into the exhaust gas flow;

characterized in that the exhaust gas system furthermore comprises a regeneration apparatus in accordance with any one of the preceding claims.

9. A method for the regeneration of a particulate filter of an exhaust gas system which includes an exhaust gas duct for the conducting of a hot exhaust gas flow away from a combustion engine, in particular from a diesel engine, and a catalyst, in particular an oxidation catalyst which is integrated into the exhaust gas duct upstream of the particulate filter, wherein the exhaust gas system or the combustion engine includes an injection apparatus which is in communication with a fuel reservoir and which is able to input fuel, in particular fuel containing hydrocarbons, into the exhaust gas flow,

characterized by the following steps: providing a burner which is able to heat the catalyst to a reaction temperature at which an exothermic reaction of the fuel takes place; determining an operating state of the exhaust gas system and/or of the combustion engine; and activating the burner and/or the injection apparatus in dependence on the determined operating state in the case of a regeneration of the particulate filter.

10. A method in accordance with claim 9, characterized in that a temperature of the catalyst is determined for the determination of the operating state of the exhaust gas system.

11. A method in accordance with claim 9, characterized in that the burner and, as necessary, the injection apparatus are activated when the temperature of the catalyst is below the reaction temperature and a regeneration of the particulate filter should be carried out.

12. A method in accordance with claim 9, characterized in that only the injection apparatus is activated when the temperature of the catalyst is above the reaction temperature and a regeneration should be carried out.

13. A method in accordance with claim 9, characterized in that the burner is deactivated again when the temperature of the catalyst has risen above the reaction temperature.