DE102005058858A1 - Method for exhaust gas aftertreatment in internal combustion engines, and apparatus for carrying out this method - Google Patents

Abstract

The The present invention relates to a method for exhaust aftertreatment in internal combustion engines, in which the exhaust gas by a in the exhaust system arranged NOx trap catalyst assembly is entstickt. It is provided, the exhaust gas in two successive stages in a first, close to the engine arranged NOx storage catalyst and then in a second, remote from the engine NOx storage catalyst denitrinating. In cold-start and partial-load operation, the engine is working close to the engine NOx storage catalyst in a favorable working window and takes over the larger share the denitrification. In full-load operation, the engine remote works NOx storage catalyst in a favorable working window, so that he takes over the larger proportion of denitrification in this mode of operation. In this way, the working window of the overall arrangement is opposite to individual NOx storage catalysts significantly increased.

Description

The The present invention relates to a method for exhaust aftertreatment in internal combustion engines, in which the exhaust gas by a in the exhaust system arranged NOx catalyst arrangement nitrogen oxides be withdrawn, according to the preamble of claim 1, as well as a Apparatus for carrying out This method according to the preamble of claim 6.

To de-nitrogen the exhaust gases modern NOx storage catalysts are used, which collect the nitrogen oxides contained in the driving, in which the NOx storage catalyst flowing exhaust gas contained, which then chemically harmless, for example, after reaching a predetermined filling state of the NOx storage catalyst by means of suitable reducing agents Nitrogen and water are reduced. Such NOx storage systems and their regeneration, for example, in the DE 195 22 165 A1 described.

A Another active exhaust aftertreatment measure is the filtering out of solid combustion residues in so-called particulate filters, which is especially true of diesel engines is important.

It It is generally known that NOx storage catalysts only in one certain exhaust gas temperature range have satisfactory conversion rates, i.e. the efficiency of the NOx storage catalyst depends i.a. also from where it is located in the exhaust system. A close to the engine Arrangement has the advantage that the NOx storage catalyst already at cold start or in partial load a satisfactory conversion rate Has. In the high-load range of the internal combustion engine is the exhaust gas temperature but then generally outside of for the operation of the NOx storage catalytic most favorable exhaust gas temperature window.

For this Operating condition is therefore a remote engine arrangement of the NOx storage catalyst advantageous because this due to the strong temperature drop of Exhaust gases in the exhaust system is also effective in the high load range.

From the DE 10 2004 029 2002 A1 an exhaust gas purification system for a lean-running internal combustion engine is known which a main and a secondary storage device for nitrogen oxides known, the main storage device for nitrogen oxides arranged close to the engine and the secondary storage device is arranged in the exhaust gas flow direction to the main memory.

It The object of the present invention is a generic method and a generic device of the type mentioned above, in which an improved NOx conversion achieved throughout the engine map area.

These Task is by a method for exhaust aftertreatment with the Features of claim 1 and by an apparatus for exhaust aftertreatment solved with the features of claim 6. Preferred embodiments The invention are the subject of the dependent claims.

According to the invention Exhaust gas in two consecutive stages in a first, close to the engine arranged NOx storage catalyst and then in entstickt a second, remote from the engine NOx storage catalyst. The NOx conversion is therefore divided into two components, the their best efficiency in different engine map areas to have. Due to the close-coupled arrangement of the first NOx storage catalyst is the working window of the NOx storage catalytic converter in the cold start quickly reached and not fallen below in the lower load range of the engine. The engine-remote NOx catalyst has due to the sharp drop in temperature of the exhaust gases in the exhaust system even in the high load range of the internal combustion engine a good Efficiency. Thus, in the entire engine map area a high NOx conversion achieved. This arrangement becomes an extension the working window of the NOx storage catalyst arrangement in comparison achieved to a single component with the same total volume and with the same NOx storage catalytic converter area. The distance between both components and the achieved thereby Temperature difference is an optimization parameter for the working window. In this case, the exhaust gas in one of the two stages in a catalyst / particulate filter assembly at the same time i.e. one of the two stages is for example as a particle filter with a NOx storage coating educated. becomes.

at the internal combustion engines are either lean-running gasoline engines or to diesel engines.

The decommissioning of the exhaust gas in the catalyst / particulate filter assembly is preferably carried out in the first stage, ie in a close-coupled assembly. As stated above, the NOx storage catalyst coating of the engine-mounted assembly is preferably effective in the cold start and in the lower load range of the engine. The close-coupled arrangement of the particulate filter has the advantage that a thermal regeneration of the accumulated soot without additional measures such as fuel additive or external post-injection is possible. In addition, the coating of the particulate filter can assist in filtering erosion. The engine-remote NOx storage catalyst is, as just if already explained, preferably effective in the high load range of the internal combustion engine.

According to one However, in another embodiment of the invention, the exhaust gas is in the second stage, i.e. in a remotely located catalyst / particulate filter assembly. This arrangement may arise when for package reasons a close to the engine Arrangement of the particulate filter is not possible, especially in terms the largest possible maintenance interval and thus an enlargement of the Component. In this case, the regeneration of the engine-remote particulate filter also over additional Regenerative aids, e.g. an external post-injection or the Addition of fuel additives done. This additional External post-injection can also be used in the desulfurization of the second stage the emission control system are used, as this temperatures of 600-750 ° C are required, which are difficult to produce in the second component, without the first cleaning stage must be much hotter.

The inventive method is preferably used in conjunction with a low-pressure exhaust gas recirculation, wherein after the particulate filter stage of the exhaust aftertreatment Branched off the exhaust gas from the exhaust line and into the intake tract, optionally, preferably before a compressor of an exhaust gas turbocharger is returned. In this method with low-pressure exhaust gas recirculation with an exhaust gas removal After particulate filter, the engine raw emissions, depending on the exhaust gas recirculation rate, and thus the total emissions of the vehicle compared to one usual High pressure exhaust gas recirculation reduced, in the known although the nitrogen oxide formation lowered, the pollutant emissions however are increased.

According to one Another embodiment of the method according to the invention is this Used in conjunction with a partially homogeneous diesel combustion process. Especially in engine map areas with low exhaust gas temperatures, where the activity of the NOx catalyst limited This can be achieved by the very low NOx emissions at a partially homogeneous operation can be compensated. The NOx storage capacity is longer with low raw emissions of the internal combustion engine, so that the risk of NOx slippage can be reduced. Besides, they are at low raw emissions, the time intervals between two NOx regeneration phases greater. The Height of Fuel consumption is thereby reduced. Also, the burden of the NOx storage catalyst reduced by the lower number of regeneration processes.

Analogous to the method described above, an apparatus for exhaust aftertreatment is included Internal combustion engines with an arranged in the exhaust line NOx storage catalyst arrangement for Denitrification of the exhaust gas configured such that the NOx catalyst assembly is two-stage, with a first, close-coupled NOx storage catalytic converter preferably for the cold start and part load operation and with a downstream thereof arranged engine-removed NOx storage catalyst, preferably for full-load operation, wherein one of the two NOx storage catalytic converters with a particle filter is combined into a structural unit.

there can either the first NOx storage catalyst with a particulate filter be combined, which has the advantage that a thermal regeneration of accumulated soot without additional measures as fuel additives or external Nacheineinspritzung is possible. In another embodiment, the second NOx storage catalyst combined with a particulate filter, wherein the particulate filter of Outside one for whose regeneration required energy can be supplied, should motor activities not used or not sufficient. This energy can for example, by a microwave device or another be supplied with electrical heating device; preferably however, before the particulate filter, a regeneration agent, for example Fuel injected.

Around to perform the low-pressure exhaust gas recirculation described above, is according to a preferred embodiment of the invention according to the NOx storage catalyst, which is combined with a particulate filter, from the exhaust system a portion of the exhaust branched off and via a corresponding return line returned to the intake. These Arrangement must be complied with because of the fact, because only fairly clean exhaust gas can be recycled in the low pressure EGR may, as this is due to strong cooling otherwise it would spoil very fast.

Several embodiments The invention are illustrated in the drawings and described in more detail below. Show it:

1 schematically a motor vehicle, in the exhaust system, a close-coupled catalyst / particulate filter assembly and a motor remote NOx storage catalyst are arranged;

2 a diagram of an exhaust gas measurement cycle, wherein the NOx concentration is shown above the exhaust path;

3 in a similar representation, a diagram of another exhaust gas measuring cycle;

4 a representation similar to the 1 . wherein, however, a close-coupled NOx storage catalyst and a remote engine catalyst / particulate filter assembly are arranged in the exhaust system.

That in the 1 schematically illustrated motor vehicle 2 is powered by an internal combustion engine 4 , powered by a diesel engine in this embodiment. As also shown schematically, the internal combustion engine 4 with an exhaust gas turbocharger 6 equipped, which in a known manner the exhaust gases of the internal combustion engine 4 uses to charge this.

The exhaust gases of the internal combustion engine 4 be through with one as a whole 8th designated exhaust system discharged into the environment. In this exhaust system is directly behind the internal combustion engine 4 a NOx storage catalyst / particulate filter assembly 10 arranged in which the exhaust gases nitrogen oxides and soot particles are removed. This catalyst / particulate filter assembly is designed as a particulate filter with a NOx storage catalyst coating.

The catalyst part of the unit 10 Due to its near-motor arrangement is acted upon by relatively hot exhaust gases. This exhaust gas temperature is especially in the cold start and during partial load operation in the effective working window of the NOx catalyst, so that it makes the majority of the denitrification of the exhaust gases in this operating range.

Another NOx storage catalyst 12 is downstream of the unit 10 in the exhaust system 8th arranged in a remote motor position. In cold start and part load operation, the temperature of the exhaust gases at this point has fallen so far that it is below the effective working window of this catalyst, so that it has a smaller share in the denitrification in this operating range.

In full-load operation, however, the engine-remote NOx storage catalyst works 12 in the favorable working window, while the close-coupled catalyst part of the unit 10 works outside of this window and has only a small share of the denitrification at these operating points.

2 shows a diagram of a typical driving cycle for diesel cars in the exhaust test. It is a test in which full-load driving conditions predominate. As the diagram shows, the exhaust gases are at the entrance to the unit 10 a temperature of about 450 ° C, at the entrance of the NOx storage catalyst 12 then a temperature of 350 ° C. From the purely qualitative diagram of 2 shows that the NOx concentration in the engine-near assembly 10 , whose catalyst part already works outside its most favorable working window, reduced by 30%. Starting from this value, the NOx concentration in the engine-remote NOx storage catalyst 12 , which works in the cheap working window, reduced by 85% to its final value.

3 shows a diagram similar to the 2 However, this diagram is based on a part-load operation At the entrance of the unit 10 the exhaust gas has a temperature of 250 ° C, and at the entrance of the NOx storage catalyst 12 the exhaust gas temperature is equal to 150 ° C. As the qualitative diagram shows, the NOx concentration in the engine-near assembly 10 , whose catalyst part works in a favorable working window, reduced by 85%; starting from the achieved value is in the engine-remote NOx storage catalyst 12 working outside the cheap work window, reduced by a further 15% to its final value.

4 shows a representation similar to the 1 , with a motor vehicle 2 , an internal combustion engine 4 , an exhaust gas turbocharger 6 and an exhaust system 8th ,

In contrast to the motor vehicle of the 1 is the NOx storage catalyst 12 ' immediately behind the combustion engine 4 , ie, arranged close to the engine, while the NOx storage catalyst / particulate filter assembly 10 ' downstream thereof, that is arranged remotely. Such an arrangement may be required if for package reasons, a close-coupled arrangement of the unit 10 ' not possible. In this case, the regeneration of the motor remote particle filter part of the assembly 10 ' If additional regeneration aids are used, eg an external post-injection or the addition of fuel additive, the use of engine measures should not be desired or ineffective. In the in 4 illustrated embodiment, a fuel post-injection is provided. For this purpose, the fuel tank 14 taken from the vehicle fuel and a Nacheinspritzleitung 16 in front of the unit 10 in the exhaust system 8th injected (HCI = HC injection).

As already stated above, the method according to the invention is preferably used in conjunction with a low-pressure exhaust gas recirculation, in which the exhaust gas removal preferably takes place after the structural unit 10 and the introduction of the exhaust gas takes place in front of the compressor of the turbocharger. 1 schematically shows an exhaust gas recirculation line 18 , via which an exhaust gas component from the exhaust gas system 8th branched off and into the intake tract 20 In this system with an exhaust gas removal after the coated particle filter and the concentration of NOx, CO and HC of the recirculated exhaust gas is significantly reduced. In this way, depending on the exhaust gas recirculation rate, the Motorrohemissionen and thus the total emission of the vehicle compared to a high-pressure exhaust gas recirculation can be reduced.

2

motor vehicle

4

internal combustion engine

6

turbocharger

8th

exhaust gas line

10

NOx storage catalytic converter / particulate filter assembly

10 '

NOx storage catalytic converter / particulate filter assembly

12

NOx catalyst

12 '

NOx catalyst

14

Fuel tank

16

Nacheinspritzleitung

18

Exhaust gas recirculation line

20

intake system

Claims (11)

A method for exhaust gas aftertreatment in internal combustion engines, in which the exhaust gas is de-nitrogen by an arranged in the exhaust line NOx catalyst arrangement, wherein the NOx catalyst arrangement is formed in two stages with two consecutive NOx storage catalysts, characterized in that the first NOx storage catalyst close to the engine and the second NOx Storage catalytic converter are arranged remote from the engine, wherein one of the two NOx storage catalysts as a catalyst / particulate filter assembly ( 10 . 10 ' ) is trained. Method according to claim 1, characterized in that that the exhaust gas is discharged in the first stage. A method according to claim 1, characterized in that the exhaust gas is discharged in the second stage, wherein the catalyst / particulate filter assembly ( 10 ' ) is supplied from the outside a required for the regeneration of the particulate filter energy. Method according to one of claims 1 to 3, characterized in that it is used in conjunction with a low-pressure exhaust gas recirculation, wherein after the particulate filter, a portion of the exhaust gas from the exhaust line ( 8th ) and into the intake tract ( 20 ) is returned. Method according to one of claims 1 to 4, characterized that it is in conjunction with a semi-homogeneous diesel combustion process is used. Apparatus for exhaust gas aftertreatment in internal combustion engines, comprising an arranged in the exhaust line NOx storage catalytic converter for denitrification of the exhaust gas, wherein the NOx storage catalytic converter is formed in two stages with a first NOx catalyst and downstream arranged second NOx storage catalytic converter, characterized in that one of the two NOx Storage catalytic converter with a particle filter to a structural unit ( 10 ) is combined. Apparatus according to claim 6, characterized in that the first NOx storage catalytic converter with a particle filter to a structural unit ( 10 ) is combined. Apparatus according to claim 6, characterized in that the second NOx storage catalytic converter with a particle filter to a structural unit ( 10 ' ) is combined, and that the particulate filter is supplied from the outside an energy required for its regeneration. Device according to claim 8, characterized in that that for the regeneration of the particulate filter externally supplied energy also for used the desulfation of the engine-removed NOx storage catalyst component becomes. Device according to one of claims 8 and 9, characterized that fuel is injected into the exhaust line before the particulate filter becomes. Device according to one of claims 6 to 10, characterized in that after the first NOx storage catalyst, which is combined with a particulate filter to form a structural unit, from the exhaust gas line ( 8th ) branched off a part of the exhaust gas and into the intake tract ( 20 ) is returned.