EXHAUST GAS SYSTEM

Abstract

An exhaust system for the aftertreatment of exhaust gases of an internal combustion engine, having, in series as viewed in a flow direction of the exhaust gas, a catalyst for the oxidation of the exhaust gas and/or a catalyst for storing nitrogen oxides, having an introduction point for the feed of a reducing agent, having an SCR catalyst for the selective catalytic reduction of nitrogen oxides, and having a particle filter, wherein the particle filter is arranged downstream of the SCR catalyst in the flow direction, and a second SCR catalyst and/or an ammonia slippage catalyst is arranged downstream of the particle filter in the flow direction.

Claims

1. An exhaust system for the aftertreatment of exhaust gases of an internal combustion engine, comprising: a catalyst for the oxidation of the exhaust gas and/or a catalyst for storing nitrogen oxides, having an introduction point for the feed of a reducing agent; a first SCR catalyst for the selective catalytic reduction of nitrogen oxides, the SCR catalyst arranged downstream of the catalyst in a flow direction of the exhaust gas; a particle filter arranged downstream of the SCR catalyst in the flow direction; and a second catalyst arranged downstream of the particle filter in the flow direction.

2. The exhaust system of claim 1, wherein the first SCR catalyst, which is arranged upstream of the particle filter in the flow direction, is electrically heatable.

3. The exhaust system of claim 1, wherein the first SCR catalyst in the flow direction has an extent of at most 80 mm along the flow direction, the first SCR catalyst preferably has an extent of less than 50 mm, and the first SCR catalyst particularly preferably has an extent of less than 40 mm.

4. The exhaust system of claim 1, wherein the first SCR catalyst in the flow direction is arranged with a spacing to the particle filter along the flow direction of at most 20 mm.

5. The exhaust system of claim 1, wherein the first SCR catalyst in the flow direction is arranged with a spacing to the particle filter along the flow direction of less than 10 mm.

6. The exhaust system of claim 1, wherein the first SCR catalyst in the flow direction is arranged with a spacing to the particle filter along the flow direction of less than 5 mm.

7. The exhaust system of claim 1, wherein the first SCR catalyst in the flow direction and the second catalyst in the flow direction are formed as a modular unit with the particle filter.

8. The exhaust system of claim 1, wherein the first SCR catalyst, the second catalyst, and the particle filter are formed by a common honeycomb body.

9. The exhaust system of claim 8, wherein the honeycomb body of the particle filter has a cell geometry which differs from that of the honeycomb body of the first SCR catalyst in the flow direction and from that of the honeycomb body of the second catalyst in the flow direction.

10. The exhaust system of claim 9, wherein at least one of the cell geometry or the chemically active coating of the honeycomb body or the amount of coating of the honeycomb body of the first SCR catalyst in the flow direction differs from at least one of the cell geometry or the cell density or the chemically active coating of the honeycomb body of the second catalyst in the flow direction.

11. The exhaust system of claim 8, wherein the honeycomb body of the particle filter has a cell density which differs from that of the honeycomb body of the first SCR catalyst in the flow direction and from that of the honeycomb body of the second catalyst in the flow direction.

12. The exhaust system of claim 11, wherein at least one of the cell density or the chemically active coating of the honeycomb body or the amount of coating of the honeycomb body of the first SCR catalyst in the flow direction differs from at least one of the cell geometry or the cell density or the chemically active coating of the honeycomb body of the second catalyst in the flow direction.

13. The exhaust system of claim 8, wherein the honeycomb body of the particle filter has a cell geometry and cell density which differs from that of the honeycomb body of the first SCR catalyst in the flow direction and from that of the honeycomb body of the second catalyst in the flow direction.

14. The exhaust system of claim 13, wherein at least one of the cell geometry or the cell density or the chemically active coating of the honeycomb body or the amount of coating of the honeycomb body of the first SCR catalyst in the flow direction differs from at least one of the cell geometry or the cell density or the chemically active coating of the honeycomb body of the second catalyst in the flow direction.

15. The exhaust system of claim 1, the second catalyst further comprising a second SCR catalyst.

16. The exhaust system of claim 15, further comprising an ammonia slippage catalyst arranged downstream of the second SCR catalyst.

17. The exhaust system of claim 1, the second catalyst further comprising an ammonia slippage catalyst.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will be discussed in detail below on the basis of an exemplary embodiment and with reference to the drawing. In the drawing:

[0024] FIG. 1 shows a sectional view through an exemplary exhaust tract with a multiplicity of catalysts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0026] FIG. 1 shows a sectional view through an exhaust tract of an exhaust system 1. The exhaust system 1 has a multiplicity of catalysts, which are arranged in casings and which are connected to one another by pipelines such that exhaust gas flows through the catalysts.

[0027] In the exemplary embodiment of FIG. 1, a catalyst 3 for the oxidation of the exhaust gas is arranged first in the flow direction 2 of the exhaust gas. Provided downstream of this is an introduction point 4 through which a reducing agent, such as for example an aqueous urea solution, is introduced into the exhaust tract. Arranged immediately adjacent to this introduction point 4 is an evaporation element 5, on which the reducing agent is evaporated in order to subsequently react, as ammonia, with the nitrogen oxides in the exhaust gas.

[0028] This is followed, downstream, by a first SCR catalyst 6, in which the nitrogen oxides in the exhaust gas react with the ammonia and the chemically active coating of the SCR catalyst 6 and thus form nitrogen and water.

[0029] Positioned downstream of the first SCR catalyst 6 is a particle filter 7, which serves for filtering the exhaust gas and which filters in particular soot particles out of the exhaust gas.

[0030] The particle filter 7 is followed by a second SCR catalyst 8. In terms of chemistry, the same reaction takes place in the second SCR catalyst as in the first SCR catalyst 6.

[0031] The advantage of such a construction lies in the fact that a reduction of the nitrogen oxides in the exhaust gas takes place already before the exhaust gas flows into the particle filter. The exhaust gas flowing into the first SCR catalyst is therefore still at a particularly high temperature, and also the exhaust-gas distribution over the cross section of the flow path has not yet been adversely affected by the particle filter. In this way, a particularly effective conversion of the nitrogen oxides in the exhaust gas may take place. Owing to the particle filter, which normally has a large volume, the temperature of the exhaust gas decreases considerably, as a result of which the chemical reaction in the downstream SCR catalyst normally does not take place optimally. The second SCR catalyst serves substantially for reducing that nitrogen oxide fraction which has not yet been reduced in the first SCR catalyst.

[0032] Instead of or in addition to the second SCR catalyst, an ammonia slippage catalyst may also be installed, which may bind excess ammonia (NH.sub.3) that has not been converted during the reduction of the nitrogen oxides in the exhaust gas. In this way, it is for example possible to prevent a breakthrough of ammonia into the exhaust tailpipe, which could result in ammonia escaping into the surroundings and lead to an unpleasant smell or to contamination of the environment.

[0033] The exemplary embodiment in FIG. 1 is in particular not of a limiting nature, and serves for illustrating the concept of the invention.

[0034] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.