DE102015200023A1 - Use of an electric heater arranged upstream of a nitrogen oxide storage catalyst - Google Patents

Abstract

The invention relates to an exhaust aftertreatment device (1) for after-treatment of an exhaust gas flow (5) flowing through the exhaust aftertreatment device (1). The exhaust aftertreatment device (1) has a nitrogen oxide storage catalyst (2) and an SCR catalyst (4) arranged downstream of the nitrogen oxide storage catalyst (2). Also, a first electric heater (3) arranged upstream of the nitrogen oxide storage catalyst (2) and configured to heat the exhaust gas flow (5) and a diesel particulate filter (6) downstream of the nitrogen oxide storage catalyst (2) and downstream of the SCR catalyst (4) ) intended.
Further aspects of the invention relate to a motor vehicle equipped with such an exhaust gas after-treatment device (1) and to a method for operating such a motor vehicle.

Description

The invention relates to an exhaust aftertreatment device, a motor vehicle having such an exhaust aftertreatment device and a method for operating such a motor vehicle.

The emissions of motor vehicles are subject to legal provisions with the aim of reducing the environmental impact of motor vehicle traffic. This applies in particular to the emission of environmental toxins such as nitrogen oxides. Here, it is known to provide a nitrogen oxide storage catalyst which adsorbs nitrogen oxides contained in an exhaust gas stream of an internal combustion engine of the motor vehicle on its surface and thus stores. Such nitrogen oxide storage catalysts are also called lean NOx traps (LNT) or lean nitrogen oxide traps. Since the capacity of the nitrogen oxide storage catalyst is limited, the nitrogen oxide storage catalyst can be regenerated. For this purpose, a rich fuel mixture for the internal combustion engine can be generated. It is also possible to add unburned fuel to the exhaust gas stream by late post-injection. In both cases, the hydrocarbons contained in the rich exhaust gas flow react with the nitrogen oxides stored in the nitrogen oxide storage catalyst and decompose them in this way.

The object of the invention is to improve the efficiency of the exhaust aftertreatment.

The invention therefore introduces an exhaust aftertreatment device for after-treatment of an exhaust gas flow passing through the exhaust aftertreatment device. The exhaust aftertreatment device has a nitrogen oxide storage catalyst and an SCR (SCR) catalyst downstream of the nitrogen oxide storage catalyst (SCR). Also provided is a first electric heater disposed upstream of the nitrogen oxide storage catalyst and configured to heat the exhaust stream and a diesel particulate filter disposed downstream of the nitrogen oxide storage catalyst and downstream of the SCR catalyst.

The first electrical heating device has the advantage that the exhaust gas flow can be heated before it enters the nitrogen oxide storage catalytic converter. The electrical power used for this purpose can be provided via a so-called alternator or in the course of a braking force recuperation, wherein in the latter case advantageously no increased fuel consumption is to be expected. The heated exhaust gas stream also indirectly heats the nitrogen oxide storage catalyst. The heating of the nitrogen oxide storage catalyst has the effect of increasing an intake capacity of the nitrogen oxide storage catalyst after a cold start, so that even in the first time after the cold start, the emission of nitrogen oxides can be reduced by activating the first electric heater at the cold start or shortly thereafter , In addition, by heating, the purging of the nitrogen oxide storage catalyst with rich exhaust gas mixture can be made more efficient, so that the regeneration of the nitrogen oxide storage catalyst can be done in a shorter time, which saves fuel. Further, since an SCR catalyst is disposed downstream of the nitrogen oxide storage catalyst, heating of the nitrogen oxide storage catalyst may be used to thermally desorb the nitrogen oxides adsorbed in the nitrogen oxide storage catalyst and catalytically convert them from the downstream SCR catalyst into harmless ones. Further, the heating of the nitrogen oxide storage catalyst may be performed to promote desulfurization of the nitrogen oxide storage catalyst or regeneration of a diesel particulate filter located downstream of the nitrogen oxide storage catalyst. The heating of the exhaust gas flow by the first electrical heating device can be advantageously used to support a regeneration of the diesel particulate filter, in which the particles deposited in the diesel particulate filter are removed by oxidation.

Preferably, the first electrical heating device is arranged immediately upstream of the nitrogen oxide storage catalytic converter, whereby the fastest possible heating of the nitrogen oxide storage catalytic converter after activation of the first heating device is achieved.

The first electric heater may be, for example, a heater grid. Heaters are reliable and inexpensive to manufacture.

The exhaust aftertreatment device may be equipped with a second electric heater located downstream of the nitrogen oxide storage catalyst and upstream of the SCR catalyst. For example, the second electric heater may be advantageously used to heat the SCR catalyst independently of the nitrogen oxide storage catalyst. As a result, the optimum temperatures for both catalysts can be set largely independently.

It may also be provided to provide upstream of the SCR catalyst a urea injector configured to inject urea solution into the exhaust gas stream. The urea solution may be chemically active in the catalytic decomposition of nitrogen oxides.

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

Another aspect of the invention relates to a method for operating such a motor vehicle, in which an exhaust gas of the internal combustion engine of the motor vehicle is passed through the exhaust gas aftertreatment device. It is provided that a desorption of the nitrogen oxide storage catalyst is performed by the exhaust gas flow is heated by the first electric heater.

The desorption process can be a DeNOx process. The desorbed nitrogen oxides are reduced by the SCR catalyst. Alternatively, the desorption process may be a DeSOx process, ie, desulfurization, in which the engine is operated so that the exhaust gas flow is rich.

The invention will be explained in more detail with reference to illustrations of exemplary embodiments. Show it:

1 a detail of a first embodiment of an exhaust aftertreatment device according to the invention; and

2 A second embodiment of an exhaust aftertreatment device according to the invention.

1 shows a section of a first embodiment of an exhaust aftertreatment device according to the invention 1 that of an exhaust gas flow 5 is flowed through. The exhaust gas flow 5 is through a first electric heater 3 heated as needed and enters a nitrogen oxide storage catalyst 2 one, the exhaust gas flow 5 Extracts nitrogen oxides by adsorbing them on its surface. The first electric heater 3 For example, it may be activated after a cold start or in operating conditions in which an exhaust gas flow with a low exhaust gas temperature is generated in order to increase the exhaust gas temperature. The exhaust temperature desired by the heating may vary as required, for example, a different exhaust gas temperature may be set for a DeNOx operation than for an improvement in the adsorption properties of the nitrogen oxide storage catalyst 2 after a cold start.

Downstream of the nitrogen oxide storage catalyst 2 is an SCR catalyst 4 provided, which in the course of a DeNOx process of the nitrogen oxide storage catalyst 2 desorbed nitrogen oxides catalytically converts. The first electric heater 3 can also be used to charge the SCR catalyst via the exhaust stream 5 to heat to a desired suitable temperature. The SCR catalyst 4 may be immediately downstream of the nitrogen oxide storage catalyst 2 and in particular also together with the nitrogen oxide storage catalyst 2 be arranged in a housing. Also provided is a diesel particulate filter 6 (not shown) downstream of the SCR catalyst 4 is arranged.

2 shows a second embodiment of an exhaust aftertreatment device according to the invention 1 , wherein the same reference numerals designate identical or functionally corresponding objects. For a new repetition is omitted for reasons of clarity, it applies to the second embodiment, the first to the extent, unless expressly stated otherwise.

The exhaust aftertreatment device 1 of the second embodiment has a second electric heater 7 upstream of the SCR catalyst 4 is arranged and can be used to control the exhaust flow 5 regardless of the first heater 3 to a desired, for the operation of the SCR catalyst 4 to bring suitable temperature.

It is also downstream of the SCR catalyst 4 a diesel particulate filter 6 provided, which in the exhaust gas stream 5 contained particles from the exhaust stream 5 filters out and deposits in itself. Upstream of the SCR catalyst 4 can be a urea injector 8th be provided, which is designed to inject urea solution into the exhaust stream. Such urea solution is available, for example, under the name "AdBlue" and may be in a motor vehicle in one with the urea injection device 8th connected reservoir 9 be carried along. The urea solution carries in the SCR catalyst 4 for the chemical decomposition of nitrogen oxides.

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

 exhaust aftertreatment device

2

 Nitrogen oxide storage catalyst

3

 first electric heater

4

 SCR catalyst

5

 exhaust gas flow

6

 diesel particulate Filter

7

 second electric heater

8th

 Urea injector

9

 reservoir

Claims (9)

An exhaust aftertreatment device ( 1 ) for aftertreatment by the exhaust aftertreatment device ( 1 ) flowing exhaust gas stream ( 5 ) and with a nitrogen oxide storage catalyst ( 2 ), downstream of the nitrogen oxide storage catalyst ( 2 ) arranged SCR catalyst ( 4 ), one upstream of the nitrogen oxide storage catalyst ( 2 ) arranged first electrical heating device ( 3 ), which is formed, the exhaust gas flow ( 5 ) and one downstream of the nitrogen oxide storage catalyst ( 2 ) and downstream of the SCR catalyst ( 4 ) arranged diesel particulate filter ( 6 ). The exhaust aftertreatment device ( 1 ) of the preceding claim, wherein the first electric heating device ( 3 ) immediately upstream of the nitrogen oxide storage catalyst ( 2 ) is arranged. The exhaust aftertreatment device ( 1 ) of one of the preceding claims, wherein the first electrical heating device ( 3 ) is a heating grid. The exhaust aftertreatment device ( 1 ) of one of the preceding claims, with a second electrical heating device ( 7 ) downstream of the nitrogen oxide storage catalyst ( 2 ) and upstream of the SCR catalyst ( 4 ) is arranged. The exhaust aftertreatment device ( 1 ) of one of the preceding claims, with an upstream of the SCR catalyst ( 4 ) arranged urea injection device ( 8th ), which is formed, urea solution in the exhaust gas stream ( 5 ). A motor vehicle having an internal combustion engine and an exhaust aftertreatment device ( 1 ) according to one of the preceding claims. A method of operating a motor vehicle according to the preceding claim, wherein an exhaust gas of the internal combustion engine of the motor vehicle by the exhaust aftertreatment device ( 1 ), characterized in that a desorption process of the nitrogen oxide storage catalyst ( 2 ) is carried out by the exhaust gas flow ( 5 ) by the first electric heater ( 3 ) is heated. The method of the preceding claim, wherein the desorption process is a DeNOx process, wherein the desorbed nitrogen oxides are passed through the SCR catalyst ( 4 ) are reduced. The method of claim 7, wherein the desorbing operation is a DeSOx operation, wherein the internal combustion engine is operated so that the exhaust gas flow ( 5 ) is fat.

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