DE102004049289B4 - Exhaust after-treatment system and exhaust aftertreatment method for an internal combustion engine - Google Patents

Abstract

An exhaust gas aftertreatment system (20) of an internal combustion engine (10) comprising at least one SCR catalytic converter section (22) and an oxidation catalytic converter section (24), which form a structural unit, and a device (28) for supplying a first auxiliary material ( 30) and a second auxiliary substance (32) for supporting the exhaust after-treatment, wherein the device (28) has one or more metering cross sections (34, 36) for metering the first adjuvant (30) and the second adjuvant (32), characterized that, viewed in the flow direction of the exhaust gas, after the oxidation catalyst section (24) is provided a particle filter section (26) which is contained in the structural unit forming the exhaust aftertreatment system (20) and in that both the feed line (38) for the first auxiliary (30) and the feed line (40) for the second auxiliary (32) in a same, in the flow direction of the exhaust gas before the SCR- Catalyst section (22) lying partial volume (42) of the exhaust aftertreatment system (20) open.

Description

State of the art

The invention relates to an exhaust aftertreatment system of an internal combustion engine having at least one SCR catalyst section, an oxidation catalyst section, a particulate filter section and a device for supplying a first adjuvant and a second adjuvant to assist exhaust aftertreatment, the device having one or more metering cross sections for metering the first adjuvant and the second excipient. Furthermore, the invention relates to a method for the aftertreatment of the exhaust gas of an internal combustion engine with such an exhaust aftertreatment system.

Such an exhaust aftertreatment system and method are known per se. The SCR catalyst section is used for the selective catalytic reduction of nitrogen oxides in the exhaust gas with the aid of a reducing agent to form molecular nitrogen. The reducing agent is ammonia. To generate the ammonia, a urea-water solution is fed to the exhaust gas before the SCR catalyst as the first auxiliary. In the SCR catalyst or in an upstream hydrolysis catalyst, the urea supplied decomposes into ammonia and carbon dioxide by reaction with the water of the solution.

The particle filter section serves, as the name implies, to reduce particulate emissions. Particle filters are usually realized as porous structures, which are traversed by the exhaust gas and thereby retain the particles contained in the exhaust gas in the porous structures. In order to maintain the functionality of such a particulate filter for extended periods of time, the retained particles must be removed from the filter from time to time. Such a regeneration of the filter is usually carried out by a thermal oxidation of the embedded particles.

For the thermal oxidation, oxygen-rich, hot exhaust gas is generated by a regeneration unit upstream of the particle filter. As regeneration units burners, electric heaters or oxidation catalysts in connection with a supply of hydrocarbons in front of the oxidation catalyst are known. To heat a downstream particulate filter before an oxidation catalyst in the exhaust stream dosed hydrocarbons thus provide an example of a second excipient to support the exhaust aftertreatment.

In the known exhaust aftertreatment system, the catalyst sections mentioned are separated from one another and from the particle filter section by partial volumes of the exhaust aftertreatment system lying between them. The supply of the first auxiliary substance takes place in the part volume lying in front of the SCR catalyst section and the supply of the second auxiliary substance takes place in the partial volume of the exhaust gas aftertreatment system upstream of the particle filter. The problem with such a known exhaust aftertreatment system is the large installation space required, resulting from the installation space requirement of the individual exhaust aftertreatment components and the said sub-volumes of the exhaust aftertreatment system.

The subvolumes mentioned can not be arbitrarily reduced because, for example, the formation of ammonia from a hydrolysis of a urea-water solution requires a non-negligible volume of exhaust gas and thus a certain length. Similarly, when dosing hydrocarbons in front of an oxidation catalyst, removal to the oxidation catalyst is necessary to achieve good mixing and treatment of the hydrocarbons in the exhaust gas prior to entry into the oxidation catalyst.

The publication DE 103 01 605 A1 describes an exhaust aftertreatment system of an internal combustion engine having an SCR catalyst and another catalyst which can form a structural unit with the SCR catalyst. The supply of two acting as a reagent excipients is provided. According to a first embodiment, both adjuvants are mixed in a mixing device and metered via a common supply line upstream of the SCR catalyst. According to another embodiment, a first acting as a reagent adjuvant upstream of the SCR catalyst and a second, also acting as a reagent adjuvant, upstream of the other catalyst is metered, with separate supply lines are provided.

In the published patent application DE 102 43 270 A1 an emission control system is described, which, viewed in the flow direction of the exhaust gas, oxidation catalyst and an SCR catalyst. The dosing of a reagent acting as a reagent is provided, wherein the excipient is metered via separate supply lines both upstream of the oxidation catalyst and upstream of the SCR catalyst.

Advantages of the invention

Against this background, the object of the invention is to specify an exhaust aftertreatment system with which both the nitrogen oxide emissions and the particle emissions of Internal combustion engines can be reduced and which has a reduced compared to the known exhaust aftertreatment system space requirement and in particular a reduced length.

Furthermore, the object of the invention is to specify an exhaust gas aftertreatment process with which a reduced installation space requirement and a shorter structural length of such an exhaust gas aftertreatment system can be realized.

This object is achieved in the exhaust aftertreatment system according to the invention, which provides an assembly which, viewed in the flow direction of the exhaust gas, an SCR catalyst section, an oxidation catalyst section and a particulate filter section, solved in that supply lines for both the supply of the first excipient and for Supply of the second excipient in the same, before the SCR catalyst section lying partial volume of the exhaust aftertreatment system open. Both auxiliaries are thus metered upstream of the SCR catalyst, with both auxiliaries being led via separate feed lines to the subvolume of the exhaust gas aftertreatment device located upstream of the SCR catalyst section.

Advantageous embodiments and further developments of the exhaust aftertreatment system according to the invention are objects in each case of dependent device claims.

The inventive device enables a compact construction of the exhaust aftertreatment device, wherein due to the separate supply lines for the two auxiliaries a flexible dosing concept of the two auxiliaries can be realized, which forms in each case objects of the method claims.

Due to these features, the mixing of the two auxiliaries with the exhaust gas takes place in the same subvolume of the exhaust aftertreatment system. The sequence of the arrangement of the individual exhaust aftertreatment components results in the heating of the particulate filter for regeneration purposes, no heating or overheating of the upstream SCR catalyst. The arrangement of the SCR catalyst in front of the particulate filter is also favorable for a rapid onset of the selective catalytic reaction after a start of the internal combustion engine.

The inventive method for operating the device is characterized in that at the dosage of the first adjuvant and the second adjuvant at least one first operating mode is distinguished from a second operating mode of the exhaust aftertreatment system, wherein in the first operating mode, only a dosage of the first excipient takes place and wherein in the second mode of operation only one dosage of the second excipient takes place.

During the supply of the first auxiliary substance, the nitrogen oxides contained in the raw exhaust gas of the internal combustion engine are reduced to molecular nitrogen with the aid of the SCR catalytic converter, while the particles are deposited in the particle filter section. In the second operating mode, the supplied second auxiliary substance passes through the SCR catalytic converter and is oxidized exothermically on the oxidation catalytic converter. The released heat, together with an excess of oxygen in the exhaust gas, serves to regenerate the particle filter section by thermal oxidation of the particles stored there. During the regeneration of the particulate filter there is no reduction of the nitrogen oxides in the exhaust gas.

It is also preferred that when dosing the first adjuvant and the second adjuvant at least one first operating mode of a third operating mode of the exhaust aftertreatment system is distinguished, wherein in the first operating mode only a dosage of the first excipient takes place and wherein in the second operating mode both a dosage of first adjuvant and a dosage of the second excipient.

This refinement has the advantage that the reduction of the nitrogen oxides in the exhaust gas, which presupposes a supply of the first auxiliary substance, does not have to be interrupted when the particle filter section is reduced.

Furthermore, it is preferred that within the first operating mode, a loading state of the particulate filter is determined and compared with a predetermined threshold value and that exceeding the threshold triggers a changeover to the second operating mode.

As a consequence, the regeneration of the particulate filter associated with undesirable consumption of the second adjuvant per se can be triggered as needed, so that a good filtering effect with a low consumption of second reducing agent is achieved.

A further preferred embodiment provides that within the second operating mode, a measure for a discharge of the particulate filter is formed and compared with a predetermined threshold value and that exceeding the threshold triggers a changeover to the first operating mode.

As a result of this embodiment, the consumption of the second reducing agent is likewise reduced and, in addition, any interruption of the reduction of the nitrogen oxides, which may possibly take place, is minimized.

It is also preferred that the supply of the first adjuvant and / or of the second adjuvant takes place at least temporarily together with a supply of air to the partial volume.

This refinement has the advantage that nitrogen oxides are further reduced even during regeneration of the particle filter section.

Further advantages will become apparent from the description and the accompanying figures.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

drawings

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it:

1 schematically an embodiment of an exhaust aftertreatment system according to the invention together with its technical environment, and

2 An embodiment of inventive method.

1 shows an internal combustion engine 10 that's from a suction pipe 12 supplied air with fuel burns. The fuel is via a fuel metering device 14 to combustion chambers of the internal combustion engine 10 dosed. The fuel metering device 14 is usually realized as an arrangement of fuel injection valves, wherein for each combustion chamber of the internal combustion engine 10 an injection valve is present. It is made from a first storage tank 16 fueled and from a control unit 18 driven.

Exhaust gases resulting from combustion are passed through an exhaust aftertreatment system 20 in which pollutants such as nitrogen oxides and particles are largely converted to molecular nitrogen, CO ₂ and water. For this purpose, the exhaust aftertreatment system 20 in particular an SCR catalyst section 22 , an oxidation catalyst section 24 and a particulate filter section 26 which are traversed by the exhaust gas in this order. In addition, the exhaust aftertreatment system has 20 a device 28 for supplying a first excipient 30 and a second excipient 32 to the exhaust aftertreatment system 20 on. The device 28 has one or more dosing sections 34 and 36 for dosing the first excipient 30 and the second excipient 32 , The metering cross sections 34 and 36 are at the exhaust end of supply lines 38 . 40 for the first excipient 30 and the second excipient 32 arranged, with the supply lines 38 and 40 in the same, in the flow direction of the exhaust gases before the SCR catalyst section 22 lying partial volume 42 the exhaust aftertreatment system 20 lead. Optionally, in the flow direction of the exhaust gases upstream of the metering cross sections 34 and 36 an additional oxidation stage, for example, be arranged an oxidation catalyst. Such an oxidation state oxidizes NO to NO ₂ , which favorably influences the following SCR process.

For the first auxiliary 30 it is preferably a reducing agent such as ammonia or a reducing agent precursor for the selective catalytic reduction of nitrogen oxides in the SCR catalyst section 22 , For example, a urea-water solution is a reductant precursor that provides ammonia as a reductant. For the controlled dosage of the first excipient 30 is in the associated supply line 38 a metering valve 44 arranged by the control unit 18 is pressed. Analog has the supply line 40 of the second excipient 32 a metering valve 46 on, also from the control unit 18 is pressed. As second adjuvant 32 be hydrocarbons, preferably the operation of the internal combustion engine 10 Serving fuel from the first storage tank 16 used. In contrast, the first excipient 30 in a separate storage tank 48 carried.

Preferably, the leads open 38 and 40 via a multi-fluid nozzle 50 in the subvolume 42 one. It is understood that the multi-fluid nozzle 50 together with the dosing valves 44 and 46 can be realized as a structural unit. Optionally, the device 28 another secondary air blower 52 also from the control unit 18 is controlled and optionally air over a junction 53 in the subvolume 42 blows. Also the junction 53 of the secondary air blower 52 can in the multi-material nozzle 50 be integrated.

With the help of the secondary air blower 52 may be the atomization of the first excipient 30 and the second excipient 32 be improved. In addition, the injected secondary air for cooling the multi-component nozzle 50 be used. Another advantage of the secondary air supply via a secondary air blower 52 is that the oxygen needed for an exothermic regeneration of the particulate filter section 26 is required, regardless of the proportion of air to combustion chamber fillings of the internal combustion engine 10 in the exhaust aftertreatment system 20 can be introduced. For controlling the internal combustion engine 10 and the exhaust aftertreatment system 20 processes the controller 18 Signals from sensors, the operating parameters of the internal combustion engine 10 and / or the exhaust aftertreatment system 20 to capture. For example, signals of an air mass meter 54 and / or a driver desire 55 , a speed sensor 56 and an exhaust gas sensor 58 processed from one or more exhaust gas sensors. It is understood that this list has only exemplary character and that alternatively and / or additionally signals from other sensors such as pressure sensors and temperature sensors can be processed.

The following is with reference to the 2 An embodiment of a method according to the invention for the aftertreatment of the exhaust gas of the internal combustion engine 10 with an exhaust aftertreatment system 20 explained.

The step represents 60 a first operating mode BM_1 of the internal combustion engine 10 and the exhaust aftertreatment system 20 , In the first operating mode BM_1, the dosing cross section is used 34 only the first auxiliary 30 dosed to the exhaust gas. The metering takes place by opening the metering valve 44 , From the knowledge of the intake air mass and / or via the fuel metering device to the combustion chambers of the internal combustion engine 10 metered fuel mass closes the controller 18 on the nitrogen mass in the exhaust and fits the metering of the first excipient 30 by varying the activation of the metering valve 44 to the need.

The first auxiliary 30 can alone or optionally with simultaneous over the secondary air blower 52 successful supply of secondary air to be supplied. The in the partial volume 42 metered first excipient reacts in the SCR catalyst section 22 with the nitrogen oxides contained in the exhaust gas, wherein the nitrogen oxides are reduced to molecular nitrogen. By contrast, the carbon particles (soot) contained in the exhaust gas pass through the SCR catalyst and accumulate in the particle filter section 26 from. The amount of soot in the exhaust gas depends on operating parameters of the internal combustion engine. From these in the control unit 18 known operating parameters forms the control unit 18 a measure B for the loading of the particle filter section 26 with soot. Of course, the loading of the particulate filter section 26 with soot can also be determined by sensors.

In one step 62 a comparison of the in step 60 formed measure B with a threshold B_S. As long as the threshold B_S is not exceeded, the process returns to the step 60 in which the first operating mode BM_1 is performed. The loop from the steps 60 and 62 is passed through until the measure B exceeds the threshold B_S. This excess triggers regeneration of the particulate filter section 26 by setting a second operating mode BM_2 in one step 64 out.

In the second operating mode BM_2, the supply of the first auxiliary substance 30 it stops with the supply of the second excipient 32 began. The supply of the second adjuvant 32 can be done with or without supply of secondary air. The supplied second auxiliary passes through the SCR catalyst section 22 and is at the oxidation catalyst section 24 between the SCR catalyst section 22 and the particulate filter section 26 is oxidized with excess oxygen from the exhaust gas or optionally supplied secondary air with the release of heat.

The amount of the second adjuvant 32 is controlled or regulated so that the heat generated is sufficient to those in the particle filter section 26 thermally oxidize accumulated particles. During the regeneration of the particulate filter section due to the thermal oxidation 26 becomes a measure E of the resulting discharge of the particulate filter section 26 formed and in one step 66 compared with a threshold E_S.

As soon as the discharge E exceeds the threshold value E_S, which is due to a particle filter section which is largely discharged and thus ready to receive again 26 becomes the inquiry step 66 back in the step 60 branches, in which the already described operating mode BM_1 is performed. As long as the threshold E_S in step 66 on the other hand, the program branches again into the step 64 so that the loop out of the steps 64 and 66 as long as the particle filter section 26 is sufficiently regenerated.

During the regeneration of the particle filter section in the second operating mode BM_2 there is no reduction of the nitrogen oxides contained in the raw exhaust gas.

As an alternative to carrying out a second operating mode BM_2, a third operating mode BM_3 can also be carried out. This is in the 3 through the step 68 represents the alternative to the step 64 out 2 between the steps 62 and 66 out 2 lies. In the third operating mode BM_3, the second auxiliary substance 32 simultaneously with the first excipient 30 supplied, wherein the supply can also be done here with and without secondary air. This operating mode BM_3 thus represents a combination of the first two described operating modes BM_1 and BM_2 and allows a reduction of nitrogen oxides by the SCR catalyst section 22 also during a regeneration of the particle filter section 26 ,

The second operating mode BM_2 or the third operating mode BM_3 are rare compared to the first operating mode BM_1. Usually, the first operating mode BM_1 is maintained over several hundred kilometers, while the other two operating modes BM_2 or BM_3 are performed only for a few kilometers each.

As already mentioned, an advantage of the series arrangement is that it is in the regeneration of the particle filter section 26 not to a temperature increase at the SCR catalyst section 22 which could be associated with a loss of ammonia storage capacity and thus result in undesirable ammonia breakthrough. If, for some reason, it falls into one of the three modes of ammonia breakthrough operation behind the SCR catalyst section 22 should come, then the downstream of the SCR catalyst section oxidation catalyst section 24 eliminate the breakthrough ammonia to form nitrogen oxides. Although this would worsen the total sales of nitrogen oxides, but certainly prevents an ammonia breakthrough.

Claims (8)

Exhaust aftertreatment system ( 20 ) of an internal combustion engine ( 10 ), which at least one, viewed in the flow direction of the exhaust gas, SCR catalyst section ( 22 ) and an oxidation catalyst section ( 24 ), which form a structural unit, and a device ( 28 ) for supplying a first excipient ( 30 ) and a second excipient ( 32 ) in support of the exhaust aftertreatment, wherein the device ( 28 ) one or more metering cross sections ( 34 . 36 ) for the dosage of the first excipient ( 30 ) and the second excipient ( 32 ), characterized in that, viewed in the flow direction of the exhaust gas, after the oxidation catalyst section ( 24 ) a particle filter section ( 26 ) provided in the exhaust aftertreatment system ( 20 ) and that both the supply line ( 38 ) for the first excipient ( 30 ) as well as the supply line ( 40 ) for the second excipient ( 32 ) in a same, in the flow direction of the exhaust gas before the SCR catalyst section ( 22 ) lying partial volume ( 42 ) of the exhaust aftertreatment system ( 20 ). Exhaust aftertreatment system ( 20 ) according to claim 1, characterized in that the supply lines ( 38 . 40 ) via a multi-fluid nozzle ( 50 ) into the partial volume ( 42 ), whereby the via the first supply line ( 38 ) supply of the first excipient ( 30 ) separated from that via the second supply line ( 40 ) supply of the second excipient ( 32 ) is controllable. Exhaust aftertreatment system ( 20 ) according to claim 1 or 2, characterized in that a device ( 52 ) for the supply of air to the partial volume ( 42 ) is provided. Method for operating the device according to one of the preceding claims, characterized in that during the dosing of the first auxiliary substance ( 30 ) and the second excipient ( 32 ) at least one first operating mode (BM_1) of a second operating mode (BM_2) of the exhaust gas aftertreatment system (BM_2) 20 ), wherein in the first operating mode (BM_1) only one dosage of the first excipient ( 30 ) and wherein in the second operating mode (BM_2) only one dosage of the second excipient ( 32 ) he follows. A method according to claim 4, characterized in that in the dosage of the first excipient ( 30 ) and the second excipient ( 32 ) at least one first operating mode (BM_1) of a third operating mode (BM_3) of the exhaust aftertreatment system ( 20 ), wherein in the first operating mode (BM_1) only one dosage of the first excipient takes place and wherein in the third operating mode (BM_3) both a dosage of the first excipient ( 30 ) as well as a dosage of the second excipient ( 32 ) he follows. A method according to claim 5, characterized in that within the first operating mode (BM_1) a loading state of the particulate filter section ( 26 ) and compared with a predetermined threshold value (B_S) and that exceeding the threshold value (B_S) initiates a changeover to the second operating mode (BM_2) or the third operating mode (BM_3). Method according to at least one of claims 5 to 6, characterized in that within the second and the third operating mode (BM_2; BM_3) a measure (E) for a discharge of the particle filter section (FIG. 26 ) is formed and compared with a predetermined threshold value (E_S) and that exceeding the threshold value (E_S) initiates a changeover to the first operating mode (BM_1). Method according to at least one of claims 4 to 7, characterized in that the supply of the first auxiliary substance ( 30 ) and / or the second Excipient ( 32 ) at least temporarily together with a supply of air to the partial volume ( 42 ) he follows.

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