Device and method for regenerating a particulate filter arranged in the exhaust section of an internal combustion engine

Abstract

A device and a method for regenerating a particulate filter that is arranged in the exhaust tract of an internal combustion engine. There is disposed at least one NO oxidation catalytic converter upstream of the particulate filter for the oxidation of NO, and in particular to form NO.sub.2. At least one heating device is also provided upstream of the particulate filter, by way of which an exhaust-gas flow that is conducted towards the particulate filter can be heated to a defined temperature in accordance with defined regeneration parameters, in particular in accordance with a degree of loading of the particulate filter and/or in accordance with an efficiency of an NO.sub.2-based regeneration of the particulate filter by way of an NO.sub.2 quantity formed in the at least one NO oxidation catalytic converter.

Claims

1. A method for regenerating a particle filter arranged in an exhaust tract, which method comprises: conducting an exhaust-gas flow through at least one NO oxidation catalytic converter for the oxidation of NO upstream of the particle filter; conducting an exhaust-gas flow through at least one heating device and to the particle filter, and heating the exhaust-gas flow to a defined temperature in dependence on defined regeneration parameters; providing the heating device in parallel, in terms of flow, with the NO oxidation catalytic converter, splitting the exhaust gas flow into a first exhaust-gas flow and a second exhaust gas flow and conducting the first exhaust-gas flow through the NO oxidation catalytic converter and the second exhaust-gas flow through or over the heating device, and merging the first and second exhaust-gas flows downstream of the NO oxidation catalytic converter and the heating device and upstream of the particle filter; at least during a regeneration phase causing a defined increase in an exhaust-gas temperature upstream of the particle filter and setting a mass ratio between carbon and nitrogen dioxide contained in the exhaust gas to at least 1:4; and supplying a predefined quantity of a charge-air-side fresh-air flow and/or a predefined quantity of a charge-air flow branched off downstream of the opening point of an exhaust-gas recirculation line into a charge-air line to the exhaust-gas flow upstream of the heating device when a predefined lambda value is undershot and/or when a predefined oxygen value is undershot.

2. The method according to claim 1, which comprises heating the exhaust gas for active and passive particle filter regeneration which are combined at least at times.

3. The method according to claim 1, wherein one of the regeneration parameters is an efficiency of an NO2-based regeneration of the particle filter by means of an NO.sub.2 quantity formed on the at least one NO oxidation catalytic converter.

4. The method according to claim 1, wherein the mass ratio of carbon to nitrogen dioxide is 1:8, at least during the regeneration phase.

5. The method according to claim 1, which comprises heating the exhaust-gas flow conducted to the particle filter with the at least one heating device to a temperature below a regeneration temperature of a pure active particle filter regeneration by way of metering hydrocarbons into the exhaust-gas flow.

6. The method according to claim 5, which comprises heating the exhaust-gas flow to a temperature below 600 C.

7. The method according to claim 6, which comprises heating the exhaust-gas flow to a temperature of less or equal to approximately 550 C., with a temperature window extending from approximately 300 C. to no more than 550 C.

8. The method according to claim 6, which comprises heating the exhaust-gas flow to a temperature of less or equal to approximately 450 C., with a temperature window extending from approximately 350 C. to no more than 450 C.

9. The method according to claim 1, which comprises providing an open-loop or closed-loop control device for predefining the temperature of the exhaust-gas flow conducted to the particle filter in a defined region of at least one exhaust-gas flow as a function of an NO2 concentration and/or the loading of the particle filter and/or the regeneration capability of the particle filter.

10. The method according to claim 1, which comprises, during a regeneration of the particle filter, varying at least one of an NOx untreated emissions of the internal combustion engine or an oxidation capability of the NO oxidation catalytic converter by adjusting defined operating parameters.

11. The method according to claim 10, wherein the varying step comprises increasing at least one operating parameter selected from the group consisting of a fuel injection pressure, a start of injection, an exhaust-gas recirculation rate, and a number of injections.

12. The method according to claim 1, wherein one of the defined regeneration parameters is a degree of loading of the particle filter.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 schematically shows a diagram which shows by way of example the improvement in soot oxidation as a result of the increase in temperature;

(2) FIG. 2 schematically shows a diagram illustrating the improvement in soot oxidation as a result of an increase in NO.sub.2 availability and temperature;

(3) FIG. 3 shows a first embodiment of a parallel arrangement of an NO oxidation catalytic converter and of a heating catalytic converter, designed as an HC oxidation catalytic converter, upstream of a particle filter;

(4) FIG. 4 schematically shows an alternative embodiment of a parallel arrangement of an NO oxidation catalytic converter and of a heating catalytic converter, designed as an HC oxidation catalytic converter, upstream of a particle filter;

(5) FIG. 5 schematically shows a further alternative refinement of a device according to the invention for regenerating a particle filter arranged in the exhaust tract of an internal combustion engine, with a serial arrangement of an NO oxidation catalytic converter and an HC oxidation catalytic converter upstream of a particle filter; and

(6) FIG. 6 schematically shows an alternative embodiment to FIG. 5, in which a burner is used instead of a heating catalytic converter.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 3 shows a first exemplary embodiment according to the invention, in which, in the exhaust tract 1 of an internal combustion engine not illustrated here, in particular of a diesel internal combustion engine, an exhaust-gas flow 2 is conducted by means of a supply line 3 to an NO oxidation catalytic converter 4. A discharge line 5 leads from said NO oxidation catalytic converter 4 to a particle filter 6.

(8) Upstream of the NO oxidation catalytic converter 4, a branch line 7 branches off from the supply line 3 and opens into the discharge line 5 downstream of the NO oxidation catalytic converter 4.

(9) An HC oxidation catalytic converter 8 as a heating device is arranged in said branch line 7. Furthermore, a nozzle 9 is arranged in the branch line 7 upstream of the HC oxidation catalytic converter 8, by means of which nozzle 9 fuel 10 as reducing agent can be injected into the branch line 7 upstream of the HC oxidation catalytic converter 8.

(10) For this reason, the nozzle 9 is a constituent part of a dosing device 11 which, aside from the nozzle 9, also has a fuel tank 12 and a control and/or regulating device 13 which controls and/or regulates the dosing.

(11) A shut-off element 14 is optionally arranged in the branch line 7 upstream of the nozzle 9, which shut-off element 14 may likewise be coupled to an electronic monitoring unit, which is however not illustrated here, in order to branch off a defined exhaust-gas quantity from the exhaust-gas flow 2 at predefined times, such that a first exhaust-gas flow 2 flows through the NO oxidation catalytic converter 4 and a second exhaust-gas flow 2 flows through the branch line 7. Said two exhaust-gas flows are then merged again downstream of the NO oxidation catalytic converter 4 and downstream of the HC oxidation catalytic converter 8, and supplied as exhaust-gas flow 2 to the particle filter 6.

(12) As is illustrated merely schematically in FIG. 3, the NO oxidation catalytic converter 4 is designed and dimensioned to be significantly larger than the HC oxidation catalytic converter 8, the reason for this being that the particle filter regeneration should be carried out substantially as NO.sub.2-based particle filter regeneration, that is to say by means of the NO.sub.2 formed in the NO oxidation catalytic converter 4. Only in the event that the regeneration work of the NO.sub.2 formed in or on the NO oxidation catalytic converter 4 is not sufficient is fuel 10 dosed into the branch line 7 via the nozzle 9 in a manner correspondingly controlled or regulated by means of the control and/or regulating device 13. At the same time, by means of corresponding activation of the shut-off element 14, a corresponding exhaust-gas mass flow as a second exhaust-gas flow 2 is conducted via the branch line 7 in order to supply an exhaust-gas flow enriched with hydrocarbons to the HC oxidation catalytic converter 8, as a result of which an exothermic reaction takes place in the HC oxidation catalytic converter, which exothermic reaction generates a hot second exhaust-gas flow 2 which is mixed with the first exhaust-gas flow 2 downstream of the NO oxidation catalytic converter 4, such that said first exhaust-gas flow 2, which as before is enriched with NO.sub.2, is raised to a higher temperature level, as a result of which the NO.sub.2-based soot oxidation in the particle filter 6 takes place in an optimized manner, as schematically illustrated in FIG. 1. In said figure, 15 denotes the ideal line which represents 100% conversion; specifically, here, 0.13 g of carbon is oxidized per gram of NO.sub.2 supplied. If it is now detected by the electronic monitoring unit that the NO.sub.2 regeneration work in the lower temperature range 16 no longer provides satisfactory regeneration results and/or the degree of loading of the particle filter has risen above a predefined limit, then by means of the measures specified above, the temperature level is raised to the upper temperature range 17 in order to make more effective, and optimize, the soot burn-off. Here, on account of the combination according to the invention of possible active and passive regeneration, it is for example sufficient for the exhaust-gas flow conducted to the particle filter 6 to be raised to a temperature level which lies preferably in the range from 370 C. to 400 C. As a result of the additional increase in the NO.sub.2 level shown in FIG. 2 by means of the increase, already described above, of the NO.sub.x untreated emissions and/or the improvement in the NO oxidation activity of the NO oxidation catalytic converter by means of changed operating parameters of the internal combustion engine and/or of the NO oxidation catalytic converters, the regeneration capability can be additionally improved in relation to the pure increase in exhaust-gas temperature.

(13) The determination of the NO.sub.2 quantity and/or of the regeneration capability and/or of the degree of loading of the particle filter may be carried out for example by means of mathematical models and/or characteristic maps and/or by means of exhaust-gas sensors, in particular pressure sensors, NO.sub.2 sensors, NO.sub.x sensors, temperature sensors and/or sensors for determining the particle or soot quantity.

(14) That which has been stated above applies analogously to the alternative refinement according to FIG. 4, in which, in contrast to the refinement according to FIG. 3, the NO oxidation catalytic converter 4 and HC oxidation catalytic converter 8 have been connected in parallel in such a way that the HC oxidation catalytic converter 8, which forms the heating catalytic converter or the heating device, is surrounded here at least in regions by the NO oxidation catalytic converter. In this way, the cooling of the HC oxidation catalytic converter 8 is more effectively prevented than is the case with a separate arrangement of an HC oxidation catalytic converter 8. Here, similarly to the embodiment according to FIG. 3, the fuel 10 is dosed only to the HC oxidation catalytic converter 8. For the division of the exhaust-gas flows through the NO oxidation catalytic converter 4 on the one hand and through the HC oxidation catalytic converter 8 on the other hand, it is possible here, too, for flow guiding elements to be provided, for example a guide element 18 illustrated merely schematically in FIG. 3. Furthermore, a shut-off element may also be provided in the region of said guide element 18, which shut-off element controls and/or regulates the quantity or generally the inflow of an exhaust-gas flow to the HC oxidation catalytic converter 8, as has already been described above in conjunction with the shut-off element 14 and the branch line 7.

(15) Through the use of a guide element, it is also made possible for the NO oxidation catalytic converter 4 and the HC oxidation catalytic converter 8 to be applied to a common catalytic converter substrate. Here, those regions which, during the regeneration, are impinged on by hydrocarbons from the supply unit, designed in this case for example as a nozzle 9, are formed, in particular coated, as an HC oxidation catalytic converter 8, whereas the remaining regions are formed, in particular coated, as NO oxidation catalytic converters 4. The different regions usually vary over the cross section, that is to say perpendicular to the flow direction.

(16) FIG. 4 also shows merely schematically a NO.sub.X reduction catalytic converter 21 which is likewise arranged in the exhaust tract 1 and which is designed for example as a NO.sub.X storage catalytic converter or SCR catalytic converter.

(17) The mode of operation and method implementation otherwise correspond to those already described in conjunction with FIGS. 1 to 3.

(18) Finally, FIG. 5 shows an embodiment in which the NO oxidation catalytic converter 4 and the HC oxidation catalytic converter 8 are not connected in parallel but rather are arranged in series. In physical terms, this means that the HC oxidation catalytic converter 8 is arranged downstream of the NO oxidation catalytic converter 4 and also upstream of the particle filter 6. The dosing of the fuel 10 as reducing agent then takes place here likewise such that said fuel cannot pass into the NO oxidation catalytic converter 4, by virtue of the dosing taking place downstream of the NO oxidation catalytic converter 4 and upstream of the HC oxidation catalytic converter 8. The method implementation and the mode of operation otherwise correspond to those already explained in more detail above in conjunction with FIGS. 1 to 4. The significant difference here therefore consists in that, in contrast to the refinements of FIGS. 3 and 4, the exhaust-gas flow 2 is not branched or divided, but rather the entire exhaust-gas flow 2 flows firstly through the NO oxidation catalytic converter 4, subsequently through the HC oxidation catalytic converter 8 and subsequently further through the particle filter 6.

(19) FIG. 6 finally shows an alternative embodiment to that shown in FIG. 5, in which, instead of an HC oxidation catalytic converter 8 as a heating device, use is made of a burner 19 operated with fuel. The use of such a burner is always possible in particular also in connection with the embodiments mentioned above, in particular in connection with the embodiment according to FIG. 3. The design of FIG. 6 otherwise corresponds to that of FIG. 5, such that in order to avoid repetitions, reference is made to the statements made above.

(20) In all the embodiments, therefore, the exhaust-gas flow or a partial exhaust-gas flow is conducted over a heating device. The heating power to be attained in this way is however limited, as already described above, by the available oxygen quantity. To avoid this, it is optionally possible for fresh air, for example a fresh-air flow branched off at the charge-air side, to be supplied to the exhaust-gas flow to be heated after a predefined temperature and/or a predefined time is reached and/or when a predefined lambda or oxygen value is undershot. The fresh air supply 20 and a shut-off valve 20 are illustrated merely highly schematically in FIGS. 3, 5 and 6.