DE102014215269B3 - Exhaust gas aftertreatment with bypass for regeneration - Google Patents

Abstract

The invention introduces an exhaust aftertreatment device (5) for an internal combustion engine (3) which is equipped with a sulfur storage (8), a nitrogen oxide storage catalyst (9) arranged downstream of the sulfur storage (8) and an SCR catalyst (10) downstream of the nitrogen oxide storage catalyst (9) ) Is provided. According to the invention, furthermore, a first bypass line (11) has an inlet arranged upstream of the sulfur store (8) and an outlet arranged between the sulfur store (8) and the nitrogen oxide storage catalytic converter (9), and a second bypass line (12) which interposes one between the two Disposal of the first bypass line (11) and the nitrogen oxide storage catalyst (9) arranged inlet and a downstream of the nitrogen oxide storage catalyst (9) arranged outlet provided. A second aspect of the invention relates to a motor vehicle (1) equipped with such an exhaust aftertreatment device (5).

Description

The invention relates to an exhaust aftertreatment device for an internal combustion engine and a motor vehicle with an internal combustion engine and an exhaust aftertreatment device connected to the internal combustion engine.

Due to steadily increasing demands on the exhaust gas purity of motor vehicles is trying to prevent or reduce the formation of pollutants in the combustion of the fuel in the internal combustion engine and chemically or physically reduce the resulting pollutants in the exhaust. In particular, a reduction in the emission of nitrogen oxides, NOx for short, is aimed for.

To meet the requirements, modern motor vehicles have exhaust aftertreatment devices that reduce the pollutant content in the exhaust by converting the pollutants into less harmful gases. Examples of such exhaust aftertreatment devices that are particularly common with diesel engines are Diesel Particulate Filter (DPF), Diesel Oxidation Catalyst (DOC), or Lean NOx Trap (LNT) catalysts.

The various exhaust aftertreatment units usually perform their best function in certain temperature windows. Below a minimum temperature is often a catalytic effect too low, above a maximum temperature there is a risk of damage to the substrate of the exhaust aftertreatment unit. In addition, some exhaust aftertreatment units may be operated in different operating modes, which also have different temperature requirements. For example, for regeneration of a catalyst or soot filter, a temporarily determined exhaust gas composition (eg, substoichiometric) and / or elevated temperature may be provided to dissolve or burn off an adsorbed or stored pollutant. In addition, reducing agents can be used to aid regeneration or catalytic reactions.

US 2007/0 271 908 A1 shows an exhaust aftertreatment device with a NOx storage catalyst and an SCR catalyst, in which via a valve located upstream of the storage catalytic converter and a bypass line exhaust gas can be passed around the storage catalyst directly to the SCR catalyst.

US 2013/0 167 510 A1 discloses a method for operating an exhaust aftertreatment device in which a NOx storage catalyst is purged by passing a portion of the incoming exhaust gas around the storage catalyst while increasing the injection of ammonia solution and recombining the exhaust substreams upstream of an SCR catalyst.

DE 103 46 345 A1 proposes an exhaust aftertreatment device having a plurality of catalysts with respective operating temperature ranges and a respective bypass line. Depending on its temperature, the exhaust gas is directed to the catalyst or catalysts in whose working temperature range the exhaust gas temperature falls.

In order to achieve the lowest possible pollutant emissions and at the same time to achieve mutual compatibility of the various provided in an exhaust line of an internal combustion engine exhaust aftertreatment units, therefore, some effort is necessary.

The invention therefore has for its object to introduce an improved exhaust aftertreatment device, which allows a particularly effective exhaust aftertreatment.

A first aspect of the invention therefore introduces an exhaust aftertreatment device for an internal combustion engine equipped with a sulfur reservoir, a nitrogen oxide storage catalyst disposed downstream of the sulfur reservoir, and a selective catalytic reduction (SCR) catalyst downstream of the nitrogen oxide storage catalyst. According to the invention, a first bypass line, which has an input disposed upstream of the sulfur reservoir and an outlet arranged between the sulfur storage and the nitrogen oxide storage catalyst, and a second bypass line, which arranged an input disposed between the junction of the first bypass line and the nitrogen oxide storage catalyst and a downstream of the nitrogen oxide storage catalyst Output has provided.

The sulfur storage can adsorb sulfur compounds, usually sulfur oxide, and thus extract the exhaust gas. The sulfur affects the performance of other exhaust aftertreatment units and may even damage them. Since the absorption capacity of the sulfur storage is naturally limited, the sulfur storage must be regenerated, the adsorbed sulfur is released under increasing the temperature of the sulfur storage under stoichiometric conditions from the sulfur storage. The dissolved sulfur can now be using the second bypass line to the Nitrogen oxide storage catalyst and optionally bypassed the SCR catalyst, so that the dissolved sulfur is not taken up again by its or its substrates. It is also possible to dissolve any sulfur that has passed through the sulfur reservoir to the nitrogen oxide storage catalyst and adsorbs it undesirably from the nitrogen oxide storage catalyst. In many modes of operation of the internal combustion engine, for example, at low engine power, the exhaust gas temperature of the already exhausted through the sulfur storage exhaust gas is not sufficient to perform such a regeneration or desulfurization of the nitrogen oxide storage catalyst. For this purpose, it is known to increase the exhaust gas temperature by injection of fuel, for example, by late post-injection in the internal combustion engine, but this leads to an undesirable increase in fuel consumption. The invention makes it possible to reduce this disadvantage by the exhaust gas of the internal combustion engine for desulfurization of the nitrogen oxide storage catalyst and possibly the SCR catalyst is bypassed via the first bypass line to the sulfur reservoir and thus reaches the exhaust gas after-treatment units to be desulfurized at a higher temperature.

In this case, depending on the respective exhaust gas temperatures and required substrate temperatures, a mixing ratio of passed through the bypass line exhaust gas on the one hand and passed through the sulfur storage exhaust gas on the other hand freely to set the desired exhaust gas temperature at the entrance of the nitrogen oxide storage catalyst or the SCR catalyst.

The invention thereby enables the desulfurization or regeneration of the exhaust aftertreatment units with reduced use of fuel for these purposes. However, an injection of reducing agents or fuel may be provided, for example, upstream of the nitrogen oxide storage catalyst and / or upstream of the sulfur reservoir.

The sulfur reservoir can also be, for example, a diesel oxidation catalyst or a NOx-storing catalyst. Such exhaust aftertreatment units can adsorb sulfur.

The selective catalytic reduction catalyst can also be designed, for example, as a soot filter with an SCR catalytic coating.

The nitrogen oxide storage catalyst may in particular be an LNT with active regeneration (eg substoichiometric) or a passive nitrogen oxide adsorber (PNA). However, the nitrogen oxide storage catalyst may also be embodied as a soot particle filter with a nitrogen oxide storage coating.

The exhaust aftertreatment device may include a third bypass line having an inlet disposed between the nitrogen oxide storage catalyst and the selective catalytic reduction catalyst and an exit located downstream of the selective catalytic reduction catalyst. The third bypass line can be used to also lead the dissolved sulfur compounds on the SCR catalyst in the case of desulfurization of the sulfur reservoir, if this is not arranged upstream of the output of the second bypass line. In particular, however, the third bypass line can also be used in embodiments of the exhaust gas aftertreatment device according to the invention, in which the nitrogen oxide storage catalytic converter is designed as a soot particle filter with a nitrogen oxide storage coating. In this case, the third bypass line can be used to pass the high exhaust-gas temperatures arising during a burning-off process of the soot stored in the soot particle filter with catalytic coating into the SCR catalytic converter, thereby protecting it from damage.

The output of the second bypass line may be located either downstream or upstream of the selective catalytic reduction catalyst. An arrangement downstream of the SCR catalyst is useful in embodiments without the mentioned third bypass line, since the SCR catalyst can be protected by the second bypass line from the sulfur released during desulfurization of the sulfur reservoir. Overheating damage to the SCR catalyst is not to be feared in this arrangement since the SCR catalyst is usually not exposed to high temperatures due to its location behind the nitrogen oxide storage catalyst and thus relatively far downstream. Conversely, if the second bypass line ends upstream of the SCR catalytic converter, a third bypass line is recommended for the reasons mentioned above.

The exhaust aftertreatment device may include a passive selective catalytic reduction catalyst disposed downstream of the selective catalytic reduction catalyst. Such a passive SCR catalyst can do without urea injection and can utilize, for example, ammonia for the reduction of nitrogen oxides produced by the sulfur storage and / or the nitrogen oxide storage catalyst during a regeneration with fuel injection or a rich exhaust gas mixture. In addition, an SCR catalyst is relatively sulfur tolerant, which is why he downstream of the existing bypass lines may be arranged. Thus, it is advantageously possible to divide the task of selective catalytic reaction to two exhaust aftertreatment units, one of which is also available when the exhaust gas is temporarily bypassed all or part of the nitrogen oxide storage catalyst through the second bypass line.

The exhaust aftertreatment device may be provided with a valve assembly configured to variably set respective proportions of a total flow rate of exhaust gas in the exhaust aftertreatment device in the bypass lines. The exhaust aftertreatment device may in particular have a control unit connected to the valve arrangement, which is designed to control the valve arrangement and thereby reduce a flow rate of exhaust gas through the nitrogen oxide storage catalyst during a desulfurization process of the sulfur storage and during a regeneration of the nitrogen oxide storage catalyst, a flow rate of exhaust gas through the sulfur storage to reduce.

A second aspect of the invention relates to a motor vehicle having an internal combustion engine and an exhaust gas aftertreatment device connected to the internal combustion engine according to the first aspect of the invention.

The invention will be explained in more detail with reference to figures. Show it:

1 a motor vehicle with an exhaust aftertreatment device according to the invention;

2 a first embodiment of the exhaust aftertreatment device according to the invention;

3 A second embodiment of the exhaust aftertreatment device according to the invention; and

4 A third embodiment of the exhaust aftertreatment device according to the invention.

1 shows a motor vehicle 1 with an exhaust aftertreatment device according to the invention 5 , The car 1 has a plurality of wheels 2 and an internal combustion engine 3 for the drive of the motor vehicle 1 , That of the internal combustion engine 3 exhaust produced in operation flows through an exhaust manifold 4 to the exhaust aftertreatment device according to the invention 5 in which the exhaust gas pollutants are removed and converted into harmless exhaust gases. Downstream of the exhaust aftertreatment device 5 Optionally, further exhaust aftertreatment units may be provided, for example an SCR catalyst. In addition, conventional measures such as an exhaust gas recirculation or an exhaust gas turbine can be combined with the exhaust aftertreatment device of the invention. The exhaust gas purified by the exhaust aftertreatment is finally via an exhaust system 7 released to the environment.

2 shows a first embodiment of the exhaust aftertreatment device according to the invention 5 , The exhaust aftertreatment device 5 has a sulfur storage 8th which besides a pure sulfur adsorber can also be a Diesel Oxidation Catalyst (DOC) or a NOx Storage Catalyst (LNT). Downstream of the sulfur storage 8th is also a nitric oxide storage catalyst 9 provided, for example, as a NOx storage catalyst (LNT), as a soot filter with nitrogen oxide storage coating or as a passive nitrogen oxide (PNA) may be performed. In addition, in the first embodiment of the invention, a downstream of the nitrogen oxide storage catalyst 9 arranged SCR catalyst 10 intended.

According to the invention, the exhaust aftertreatment device has a first bypass line 11 on top of that by a valve 14 a valve assembly upstream of the sulfur reservoir 8th branching off around the sulfur reservoir 8th around so that the exhaust gas flowing along the direction of the arrow in the figures through the exhaust aftertreatment device wholly or in some embodiments optionally only partially around the sulfur reservoir 8th can be diverted. The first bypass line 11 opens upstream of the nitrogen oxide storage catalyst 9 in the main exhaust line, wherein it is preferably provided, a reflux of the before the nitrogen oxide storage catalyst 9 possibly stagnant exhaust gas through the first bypass line 11 to be prevented by appropriate measures such as valves.

The exhaust aftertreatment device of the invention also has a second bypass line 12 on top of one between the sulfur storage 8th and the nitrogen oxide storage catalyst 9 arranged another valve 14 branches off and downstream of the nitrogen oxide storage catalyst 9 empties. Again, it can be provided to prevent backflow of exhaust gases against the main flow direction of the exhaust gas by appropriate measures. This may be necessary in particular when downstream of the mouth of the second bypass line 12 further exhaust aftertreatment units follow. In the embodiment of the invention shown here opens the second bypass line 12 downstream of the SCR catalyst 10 , whereby the entire exhaust gas or - again depending on the exact implementation - even a selectable part of the exhaust gas at the same time also around the SCR catalyst 10 can be diverted. This is especially true in a desulfurization of sulfur storage 8th advantageous.

3 shows a second embodiment of the exhaust aftertreatment device according to the invention 5 , The exhaust aftertreatment device of 3 essentially corresponds to that of the first embodiment, which is why what is said there also applies to the second embodiment, unless expressly stated otherwise. The exhaust aftertreatment device 5 of the second embodiment is with a third bypass line 13 equipped by another valve 14 a valve assembly which is between the nitrogen oxide storage catalyst 9 and the SCR catalyst 10 is located, branches off and downstream of the SCR catalyst 10 empties. In turn, measures can be taken to a backflow of exhaust gas through the third bypass line 13 to suppress against the main flow direction. In the example of 3 opens the second bypass line 12 upstream of the SCR catalyst 10 , but it can also, as in the third embodiment of 4 , which also has a third bypass line 13 has, be provided, the second bypass line 12 downstream of the SCR catalyst 10 to be ignited. In this case, the second and the third bypass line 12 and 13 be realized along a leg through the same line section. For example, the third bypass line 13 from the associated valve 14 branch off and after a short distance in the second bypass line 12 which, in turn, are downstream of the SCR catalyst 10 opens and on this line section the bypassed exhaust gas streams both the second bypass line 12 as well as the third bypass line 13 transported.

The third bypass line 13 is particularly advantageous when the nitrogen oxide storage catalyst 9 as explained above, because the SCR catalyst through the third bypass line 13 can be protected from the resulting during a burning of the collected in such a soot particle filter soot in the course of a regeneration of the particulate filter high temperatures.

For the in 4 shown third embodiment of the exhaust aftertreatment device according to the invention 5 Otherwise, what has been said above for the further exemplary embodiments applies.

Although the invention has been further illustrated and described in detail by way of embodiments of preferred embodiments, the invention is not limited by the disclosed examples. Variations of the invention may be derived by those skilled in the art from the illustrated embodiments without departing from the scope of the invention as defined in the claims.

LIST OF REFERENCE NUMBERS

1

 motor vehicle

2

 wheel

3

 Internal combustion engine

4

 exhaust manifold

5

 exhaust aftertreatment device

6

 exhaust gas treatment unit

7

 Exhaust

8th

 sulfur storage

9

 Nitrogen oxide storage catalyst

10

 SCR catalyst

11

 first bypass line

12

 second bypass line

13

 third bypass line

14

 Valve

Claims (11)

Exhaust aftertreatment device ( 5 ) for an internal combustion engine ( 3 ) and with a sulfur storage ( 8th ), one downstream of the sulfur reservoir ( 8th ) arranged nitrogen oxide storage catalyst ( 9 ) and a downstream of the nitrogen oxide storage catalyst ( 9 ) selective catalytic reduction catalyst ( 10 ), characterized by a first bypass line ( 11 ), one upstream of the sulfur reservoir ( 8th ) and one between the sulfur storage ( 8th ) and the nitrogen oxide storage catalyst ( 9 ) arranged output, and by a second bypass line ( 12 ), one between the junction of the first bypass line ( 11 ) and the nitrogen oxide storage catalyst ( 9 ) and a downstream of the nitrogen oxide storage catalyst ( 9 ) arranged output. Exhaust aftertreatment device ( 5 ) according to claim 1, wherein the sulfur reservoir ( 8th ) is a diesel oxidation catalyst or a NOx-storing catalyst. Exhaust aftertreatment device ( 5 ) according to any one of the preceding claims, wherein the selective catalytic reduction catalyst ( 10 ) is designed as a soot filter with an SCR catalytic coating. Exhaust aftertreatment device ( 5 ) according to any one of the preceding claims, wherein the nitrogen oxide storage catalyst ( 9 ) an active NOx storing catalyst or a passive one Nitrogen adsorber is or is designed as a soot particle filter with a nitrogen oxide storage coating. Exhaust aftertreatment device ( 5 ) according to one of the preceding claims, with a third bypass line ( 13 ), one between the nitrogen oxide storage catalyst ( 9 ) and the selective catalytic reduction catalyst ( 10 ) and downstream of the selective catalytic reduction catalyst ( 10 ) arranged output. Exhaust aftertreatment device ( 5 ) according to one of the preceding claims, in which the output of the second bypass line ( 12 ) downstream of the selective catalytic reduction catalyst ( 10 ) is arranged. Exhaust aftertreatment device ( 5 ) according to one of claims 1 to 5, in which the output of the second bypass line ( 12 ) upstream of the selective catalytic reduction catalyst ( 10 ) is arranged. Exhaust aftertreatment device ( 5 ) according to one of the preceding claims, with a downstream of the selective catalytic reduction catalyst ( 10 ) passive selective catalytic reduction catalyst ( 6 ). Exhaust aftertreatment device ( 5 ) according to one of the preceding claims, with a valve arrangement ( 14 ), which is formed, respective proportions of a total flow rate of exhaust gas in the exhaust gas aftertreatment device ( 5 ) in the bypass lines ( 11 . 12 . 13 ) variable. Exhaust aftertreatment device ( 5 ) according to claim 9, with one with the valve arrangement ( 14 ) connected control unit, which is designed, the valve assembly ( 14 ) during a desulfurization process of the sulfur reservoir ( 8th ) a flow rate of exhaust gas through the nitrogen oxide storage catalyst ( 9 ) and during a regeneration of the nitrogen oxide storage catalyst ( 9 ) a flow rate of exhaust gas through the sulfur storage ( 8th ) to reduce. Motor vehicle ( 1 ) with an internal combustion engine ( 3 ) and one with the internal combustion engine ( 3 ) connected exhaust gas aftertreatment device ( 5 ) according to one of the preceding claims.

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