DE202006011281U1 - Exhaust gas purifying unit for vehicle internal combustion (IC) engine e.g. diesel engine, has concentric outer and inner emission control stages, respectively provided with particle filter and SCR catalyst - Google Patents

Abstract

The unit (1) has concentric outer and inner emission control stages (2,3), respectively provided with a sintered metal particle filter (8) and a selective catalytic reduction (SCR) catalyst (11). In operation, the exhaust gas flowing in from an exhaust pipe (4) circulates through the outer emission control stage, injected with emission reducing agent from a reducing agent supply (12), and passed through the inner emission control stage leading to the return pipe (5). Both pipes lie on one side of the unit.

Description

The invention relates to an exhaust gas purification system for purifying the exhaust gas flow of an internal combustion engine, in particular a diesel engine, comprising a first exhaust gas purification stage with a particulate filter and a second exhaust gas purification stage with a catalyst for NO _x reduction by catalytic reduction (SCR stage).

Diesel engines generate soot particles and nitrogen oxides (NO _x ) during the combustion process. In order for diesel engines to comply with the applicable emission standards, which stipulate both the maximum permissible particulate matter and NO _x emissions, different methods are used to meet these requirements. A particularly effective emission control method is in EP 1 054 722 B1 described. With the method described in this document, without having to interfere in a special way in the engine management, it is possible to reduce both the particulate emission and the NO _x emission to a level that even meets the exhaust emission standards that are valid in a few years. The emission control system described in this document has a two-stage design. The first exhaust gas purification stage comprises a particle filter for removing particles entrained in the exhaust gas flow, these being, in particular, soot particles. The exhaust gas stream purified by this exhaust gas purification stage is subsequently fed to a second exhaust gas purification stage. This second exhaust gas purification stage is used for denitrification (reduction of the NO _x content) of the exhaust gas by means of a selective catalytic reduction on a catalyst. So that the desired decomposition of the NO _x contained in the exhaust gas flow to harmless nitrogen and water takes place, a reducing agent is needed. Used as a reducing agent ammonia, which is viewed in the flow direction of the exhaust gas injected into the exhaust line before the SCR catalyst. The reducing agent ammonia used for this catalysis is usually carried in the motor vehicle in the form of a so-called ammonia precursor, from which the ammonia is split off. Different ammonia precursors have become known, for example ammonium carbamate ( DE 197 20 209 A1 ), the use of an aqueous urea solution or solid urea. When an aqueous urea solution is used, the temperature of the exhaust gas stream is generally used in order to bring about the necessary decomposition. This presupposes that there is a sufficient flow path between the location of the injection and the SCR catalytic converter so that the decomposition of the aqueous urea solution can be carried out to liberate the desired ammonia and the ammonia can then be distributed as evenly as possible in the exhaust gas flow.

During operation of the diesel engine, the particles emerging from the combustion chambers, in particular soot particles, accumulate successively on the upstream surface of the particle filter. It is therefore necessary to clean the particulate filter from time to time. This takes place during operation of the internal combustion engine by active or passive triggering of a soot oxidation (Rußabbrand). In order to trigger and carry out soot combustion at lower temperatures, the fuel is admixed with an additive which reduces the soot ignition temperature and / or an oxidation catalytic converter for generating NO _{2 is connected} upstream of the particulate filter in the exhaust gas flow. A Rußabbrand takes place regularly when the temperature of the exhaust gas exceeds the Rußzündtemperatur. In addition to these passive regeneration methods, active regeneration methods have become known in which a particulate filter regeneration is actively triggered in the presence of certain conditions. For this purpose, inter alia, thermoelectric heaters are used with which the filter body is heated locally above the Rußzündtemperatur, which then triggers the Rußabbrand. Active regeneration can also be triggered by supplying hydrocarbons (HC) into the exhaust gas flow either through late injection of fuel into the cylinder of the internal combustion engine or through a hydrocarbon feed located behind the cylinder outlet.

Also if, as a result, with this prior art technology a Sufficient requirements Cleaning of the exhaust gas flow possible is to be noted that for a fitting of such Emission control system required Room not inconsiderable is. This is due to the series connection of the two emission control stages and when using a watery urea solution as a reducing agent necessary mixing distance between the two Emission levels.

Furthermore would it be desirable if the arranged with not insignificant distance from the engine SCR catalyst after an engine start faster reaches its operating temperature. The SCR catalyst works within a certain temperature window. If the SCR catalyst is at a temperature level is below its operating temperature, the desired denitrification takes place not or is only inadequate. The SCR catalyst is through the entrained in the exhaust stream Temperature warmed up. Therefore, the second emission control stage works only after a certain Running time of the diesel engine.

Based on this discussed prior art, the present invention is therefore based on the object of further developing an aforementioned exhaust gas purification system of the type described above. that not only does it build more compact, but that the SCR catalyst also reaches its operating temperature faster.

Is solved this task according to the invention by an aforementioned emission control system, in which the two Exhaust gas purification stages concentric with each other in a single unit are arranged in a group and the particle filter of the first Emission control stage the SCR catalyst the second emission control stage at least partially enclosing is arranged.

at This emission control system is the two emission control stages arranged concentrically to one another, in one unit summarized. It is provided that the particle filter of first purification stage the SCR catalyst of the second purification stage at least partially encloses, thus ring surrounding it. The concentric arrangement of the two emission control stages to each other As a result, the exhaust gas flow, after this one purification step flows through has, re its flow direction must be diverted to the opposite direction of flow to be able to flow through the other exhaust gas purification stage. As a result of the diversion exists in this emission control system, the possibility of the supply line and the discharge to one and the same side of the emission control system to be able to order. The deflection also has the advantage that this not insignificant Turbulence generated within the exhaust stream, which are used can, to a fed Reduce reducing agent in the exhaust stream and this effectively in the exhaust stream to be able to distribute. By enclosing the SCR catalyst through the particulate filter, forms the Particle filter quasi a thermal jacket for the SCR catalyst. This As a result, the SCR catalyst due to the lower heat radiation not only heated faster will, but also longer remains at its operating temperature, even if the diesel engine is off. Especially with vehicles that are in the inner city Traffic used, this brings for the intended functioning the SCR catalyst significant advantages.

The Emission control system can basically be in both directions flows through be, with the supplied Unpurified exhaust either first through the SCR catalyst second emission control stage and then through the particulate filter of the first cleaning stage or vice versa. Is preferred however, that embodiment in which the unpurified waste gas stream first passed through the exhaust gas purification stage comprising the particulate filter and then over the SCR catalyst the second emission control stage. In this mode of operation of the exhaust gas purification system results Another advantage of the concentric described above Arrangement. There is then the possibility the heat released in a regeneration of the particulate filter for heating the SCR catalyst should not use this on his Operating temperature are located. A Rußabbrand can already at temperatures of 250 ° C ignited become. The regeneration reaction is exothermic. The at the soot combustion released heat heated the annular of the particle filter enclosed SCR catalyst. In this way, in particular with an active filter regeneration control the time of such a filter regeneration at a time in which a Rußabbrand possible and the SCR catalyst is not yet at its operating temperature has reached. In a preferred embodiment, the inner borders lateral surface of the particulate filter directly to the outer surface of the SCR catalyst.

The concentric arrangement of the two emission control stages, wherein the SCR catalyst enclosing first emission control stage with their particle filter thus is responsible that the SCR catalyst especially at a intermittent operation of the diesel engine based on the operating times the diesel engine over much longer Periods is at its operating temperature. The compact Construction of the emission control system allows it in such To install motor vehicles in which only a limited installation space to accommodate such an emission control system is available.

For deflecting the exhaust gas stream, after it has passed through a first exhaust gas purification stage, and for supplying this exhaust gas stream to the second exhaust gas purification stage, a collector connected to the concentric arrangement of the two exhaust gas purification stages is expediently used. In the above-described preferred mode of operation of the exhaust gas purification system, this collector serves not only to divert the exhaust gas stream discharged from the first exhaust gas purification stage in an annular stream and initially carried in the exhaust stream, but also as a mixing chamber for supplying and mixing a reductant such as aqueous urea solution. Such a reducing agent supply comprises a feed nozzle or injection nozzle, which is expediently arranged centrally on the rear wall of the collector. According to a preferred embodiment, the injection nozzle is concentrically surrounded by a guide cone. This favors the deflection of the emerging from the first emission control stage ring stream. The deflection of the ring stream to the input side of the second emission control stage due to a not inconsiderable turbulence and a bestimmungsge moderate homogeneous distribution of the same within the exhaust stream and a splitting of a injected ammonia precursor. For this reason, the collector does not need to have a very long longitudinal extent, which contributes to the compactness of the exhaust gas purification system. Instead of a centrally arranged reducing agent supply, it is also possible to provide an annular supply, wherein the ring formed by the injectors is arranged concentrically to the longitudinal axis of the emission control system. In the collector, the exhaust gas flow directing internals may be arranged, through which the turbulence of the exhaust stream can be increased within the collector. This serves the purpose of supporting the distribution of the supplied reducing agent so that it enters the SCR catalyst as homogeneously as possible with the exhaust gas flow. Such installations can be designed, for example, like a shovel.

The for removing the entrained in the exhaust stream particles, in particular the soot particles, serving exhaust purification stage includes a particulate filter. Basically it does not matter what material the particle filter made is. However, an embodiment is preferred in which the particle filter a metal filter is. For this purpose, for example, metal foams are suitable. According to one preferred embodiment, the annular particle filter is a sintered metal filter, from a variety alternately upstream and downstream open filter bags is formed. From such individual filter bags, as described for example in WO 02/102494 A1 of the applicant are, can be annular Form particle filter easily. The of the particle filter enclosed SCR catalyst can also be made of different materials. Consists this made of metal and is the particle filter around a metal filter, for example a sintered metal filter as described above, are due to an equal or approximately equal thermal expansion coefficient the requirements for concentric storage of these two components low. in principle There is no need for both purification stages from each other in longitudinal axial Direction to avoid thermal stresses against each other are decoupled. This supports the heat transfer or the heat transfer from the particulate filter to the SCR catalyst.

following the invention with reference to an embodiment with reference on the attached Figures described. Show it:

1 : A schematic sectional view of an emission control system with two emission control stages and

2 : A plan view of the connection side of the emission control system of 1 ,

An emission control system 1 includes two emission control stages 2 . 3 which are arranged concentrically with each other. The emission control system 1 is to the exhaust system 4 a diesel engine connected; Consequently, it is about the exhaust system 4 the cleaning system 1 supplied to the exhaust gas to be cleaned, as in 1 through the block arrow in the exhaust line 4 is indicated. The purified exhaust gas passes through a pipe 5 from the emission control system 1 out. The exhaust gas supplying the unpurified exhaust gas 4 flows into an intake collector 6 , wherein the inlet of the exhaust line 4 , like out 2 seen, eccentric to the longitudinal axis of the emission control system 1 is arranged. The pipe exhausting the purified exhaust gas 5 is in contrast in the illustrated embodiment in an axial arrangement. In the inlet collector 6 are not shown in the figure internals for evenly distributing the over the exhaust line 4 supplied exhaust gas within the annular inlet collector, so that this evenly distributed as the first emission control stage 2 flows against. The first emission control stage 2 includes in the illustrated embodiment, an oxidation catalyst 7 which a sintered metal particle filter 8th is downstream. The oxidation catalyst 7 and the sintered metal particle filter 8th form an annular body. With regard to the configuration of the above-described first exhaust gas purification stage 2 this may also have a different configuration. For example, the oxidation catalyst may be arranged at a distance from the particle filter. Likewise, it is possible to use a catalytically coated particulate filter or to combine the aforementioned measures.

In another embodiment, not shown in the figures, the oxidation catalyst is not within the actual emission control system, but this is upstream in the flow direction of the exhaust gas, for example in the in 1 with the reference number 4 designated exhaust system.

At the in 1 Shown embodiment, the first emission control stage 2 cleaned with an active regeneration strategy. For this purpose, the inlet collector comprises 6 an HC supply, not shown in the figure, via the fuel in the intake manifold 6 is injected, if a filter regeneration is to take place by Rußabbrand. Alternatively, an active regeneration of the particulate filter can also be provided thermoelectrically.

After the exhaust gas flow the first emission control stage 2 flowed through, this enters a collector 9 one. The collector 9 is formed by the rear housing closure 10 the emission control system 1 , The collector 9 or the rear housing closure 10 serve to divert the from the first emission control stage 2 in the form of a ring stream exiting exhaust gas stream, so this then the second emission control stage 3 is supplied. In the second emission stage 3 it is an SCR catalyst 11 for Entsticken the exhaust gas. In the collector 9 an overall ends with the reference numeral 12 characterized reducing agent supply, the output of an injection nozzle 13 having. At the injector 13 it is in the illustrated embodiment, an atomizer. The reducing agent supply 12 is connected to a container containing the reducing agent. As a reducing agent, ammonia is used in the illustrated embodiment, which is in the form of a precursor, namely as an aqueous urea solution. From the precursor, the reducing agent required for the SCR catalysis - ammonia - within the collector 9 as a result of the temperatures prevailing therein is split off. The injector 13 is concentrically surrounded by a Leitkonus 14 with curved top, through which the diversion of the first exhaust gas purification stage 2 emerging ring current is favored. The concentric enclosure of the injector 13 through the Leitkonus 14 also serves the purpose of supporting the mixing process of the injected ammonia precursor. When deflecting the ring stream for supplying the same to the second exhaust gas purification stage, the previously external flow regions are brought together. This requires a not inconsiderable turbulence within the collector 9 whereby the mixing process of the injected reducing agent within the exhaust gas stream is assisted. After denitrification on the SCR catalyst 11 the second emission control stage 3 the purified exhaust gas passes over the pipe 5 from the emission control system 1 out.

To support the deflection of the exhaust stream in the collector 9 and / or to assist in the mixing process may be in the collector 9 be arranged corresponding fittings. In the figures, such installations are not shown for the sake of clarity.

The description of the embodiment makes it clear that through the first exhaust gas purification stage 2 with her particle filter 8th the SCR catalyst 11 the second emission control stage 3 ring-shaped framed in the manner of a coat. The through the exhaust stream of the emission control system 1 supplied heat first heats the oxidation catalyst 7 and then the sintered metal particle filter 8th , The heat received is due to the good thermal conductivity and the immediate juxtaposition of the inside of the sintered metal particulate filter 8th to the outside of the SCR catalyst 11 directly to the SCR catalyst 11 transferred so that this not only by the exhaust gas flow itself, after this in the collector 9 is deflected, but at the same time by heat conduction and / or thermal radiation through the SCR catalyst 11 annular enclosing, made of oxidation catalyst 7 and sintered metal particle filters 8th formed first emission control stage 2 , Due to its mass, the sintered metal particulate filter 8th as it were a heat storage. In consequence of the described arrangement of the sintered metal particle filter 8th to the SCR catalyst 11 the SCR catalyst remains 11 After it has reached its operating temperature, even after switching off the diesel engine over a longer period at its operating temperature. Consequently, the SCR catalyst is located 11 after restarting the diesel engine either still at its operating temperature or reached this already after a short period of operation of the diesel engine.

In an embodiment not shown in the figures, the emission control system is basically constructed as the emission control system 1 , In contrast to this, however, it is flowed through in such a way that the exhaust gas to be purified flows via the centric tube into the exhaust gas purification system and is first passed over the SCR catalyst. The injection of the reducing agent can then be located within the exhaust gas line transporting the exhaust gas to be cleaned upstream of the exhaust gas purification system. In such a case, it will be appropriate to use the in 1 the guide cone described in the illustrated embodiment form completely with a tip and to draw the tip as far as possible to the output of the SCR catalyst out.

1

emission control system

2

waste gas cleaning stage

3

waste gas cleaning stage

4

exhaust gas line

5

pipe

6

intake manifold

7

oxidation catalyst

8th

Sintered metal particulate filter

9

collector

10

body seat

11

SCR catalyst

12

Agent supplying

13

injection

14

guide cone

Claims (13)

Exhaust gas purification system for purifying the exhaust gas flow of an internal combustion engine, in particular of a diesel engine, comprising a first exhaust gas purification stage ( 2 ) with a particle filter ( 8th ) and a second emission control stage ( 3 ) with a catalyst ( 11 ) for NO _x reduction by catalytic reduction (SCR stage), characterized in that the two emission control stages ( 2 . 3 ) concentric with each other in a structural unit ( 1 ) and the particle filter ( 8th ) of the first emission control stage ( 2 ) the SCR catalyst ( 11 ) of the second emission control stage ( 3 ) is arranged at least partially enclosing. Emission control system according to claim 1, characterized in that the emission control system ( 1 ) is designed so that the exhaust gas stream to be cleaned first the first emission control stage ( 2 ) flows through and is then deflected with respect to its flow direction, so that the exhaust gas flow in the opposite direction of flow, the second emission control stage ( 3 ) flows through. Exhaust gas purification system according to claim 2, characterized in that the emission control system ( 1 ) one in the flow direction of the first emission control stage ( 2 ) downstream collector ( 9 ) for merging the from the first emission control stage ( 2 ) Exiting annular exhaust gas stream and for deflecting the same, wherein the collector ( 9 ) a reducing agent supply ( 12 ) is assigned for supplying required for the selective catalytic reduction reducing agent. Exhaust gas purification system according to claim 3, characterized in that the reducing agent supply ( 12 ) one at one the collector ( 9 ) rear wall defining in the region of the center of the same arranged injection nozzle ( 13 ). Exhaust gas purification system according to claim 4, characterized in that the injection nozzle ( 13 ) concentric with a guide cone ( 14 ) is surrounded. Emission control system according to one of claims 1 to 5, characterized in that the particulate filter ( 8th ) is a sintered metal particle filter formed from a plurality of alternately upstream and downstream open filter pockets. Emission control system according to one of claims 1 to 6, characterized in that the particle filter on the inflow side carries a catalytic coating. Emission control system according to one of claims 1 to 7, characterized in that the particulate filter ( 8th ) an oxidation catalyst ( 7 ) is connected upstream. Emission control system according to one of claims 1 to 8, characterized in that the emission control system ( 1 ) an inlet collector ( 6 ) for distributing the incoming exhaust gas flow to the upstream filter surface of the particulate filter ( 8th ) having. Exhaust gas purification system according to claim 9, characterized that the inlet collector internals for distributing the incoming Exhaust gas flow to the upstream side filter area of the particulate filter. Emission control system according to claim 9 or 10, characterized in that the exhaust gas flow eccentrically relative to the longitudinal axis of the exhaust gas purification system ( 1 ) in the inlet collector ( 6 ) entry. Emission control system according to one of claims 9 to 11, characterized in that associated with the inlet header HC supply is. Emission control system according to one of claims 1 to 12, characterized in that the particulate filter ( 8th ) is associated with a thermo-electric heater for triggering a regeneration process.