DE102004049289A1 - Exhaust after-treatment system and exhaust aftertreatment method for an internal combustion engine - Google Patents

Abstract

Presented becomes an exhaust aftertreatment system (20) of an internal combustion engine (10), the at least one SCR catalyst section (22), a Oxidation catalyst section (24), a particle filter section (26) and a device (28) for supplying a first excipient (30) and a second excipient (32) in support of the Having exhaust aftertreatment, wherein the device (28) one or a plurality of flow cross-sections (34, 36) for metering the first excipient (30) and the second auxiliary (32). The exhaust aftertreatment system (20) is characterized by the fact that supply lines for both the first Excipient as well the second excipient in a same, in the flow direction of the exhaust gases before the partial volume (42) of the SCR catalyst section (22) Exhaust aftertreatment system (20) open. Further, an exhaust aftertreatment process presented.

Description

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

One such exhaust aftertreatment system and method each 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 the molecular nitrogen. The reducing agent is ammonia. For the production of ammonia becomes the exhaust gas before the SCR catalyst as the first auxiliary one Urea-water solution fed. In the SCR catalyst or in an upstream hydrolysis catalyst decomposes the supplied Urea due to a reaction with the water of the solution too Ammonia and carbon dioxide.

Of the Particle filter section serves, as the name implies, to reduce the particle emissions. Particulate filters are usually called porous structures realized, which are flowed through by the exhaust gas while the in Retain exhaust gas particles in the porous structures. To the functionality such a particle filter over longer Periods of time to receive the withheld Particles are removed from the filter from time to time. Such Regeneration of the filter is usually done by a thermal Oxidation of the embedded particles.

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

at the known exhaust aftertreatment system are the catalyst sections mentioned from each other and from the particulate filter section through between them lying partial volumes of the exhaust aftertreatment system separated. The supply of the first excipient takes place in the before SCR catalyst section lying partial volume and the supply of the second excipient takes place in the upstream of the particulate filter Partial volume of the exhaust aftertreatment system. Problematic with a Such known exhaust aftertreatment system is the large installation space requirement, arising from the installation space requirement of the individual exhaust aftertreatment components and the said sub-volumes of the exhaust aftertreatment system.

The Partial volumes mentioned can not be arbitrarily reduced, because for example, ammonia formation from hydrolysis of a urea-water solution not negligible Exhaust gas volume and thus a certain length needed. Similar is the dosage of hydrocarbons in front of an oxidation catalyst for removal to the oxidation catalyst necessary to good mixing and Treatment of hydrocarbons in the exhaust gas before entry to reach the oxidation catalyst.

Advantages of invention

In front In this background, the object of the invention in the specification an exhaust aftertreatment system, with which both the nitrogen oxide emissions and reduces the particulate emissions of internal combustion engines can be and the one compared to the known exhaust aftertreatment system reduced installation space requirement and in particular a reduced Length.

Further the object of the invention is to specify an exhaust gas aftertreatment process, with a reduced space requirement and a shorter overall length of a realize such exhaust aftertreatment system.

These Task is in an exhaust aftertreatment system of the aforementioned Sort of solved by that leads for both the supply of the first excipient and for the supply of the second excipient in the same, lying in front of the SCR catalyst section partial volume of the exhaust aftertreatment system open.

Further This object is achieved in a method of the type mentioned solved by that the supply of the first excipient in the same, in the flow direction the exhaust gases before the SCR catalyst section lying partial volume the exhaust aftertreatment system takes place.

By these characteristics, the mixing of both auxiliaries with the Exhaust gas in the same sub-volume of the exhaust aftertreatment system. In contrast to the known exhaust aftertreatment system in which between the individual exhaust aftertreatment components (SCR catalyst section, Regeneration unit, particle filter section) each have a separate Partial volume had to be present, these sub-volumes can in extreme cases, namely in a summary of the SCR catalyst section, the oxidation catalyst section and the particulate filter to a structural unit, completely eliminated. Even otherwise, their length can at least be reduced.

in the Within the scope of an embodiment of the exhaust gas aftertreatment system, it is preferable that the SCR catalyst section in the flow direction the exhaust gases before the oxidation catalyst section and this before the particle filter section is arranged.

By this order of arrangement of the individual exhaust aftertreatment components results in the heating of the particulate filter for regeneration purposes no warming or overheating the upstream SCR catalyst. The arrangement of the SCR catalyst before the particulate filter is beyond for a rapid onset of selective catalytic reaction after one Start of the engine cheap.

A Another preferred embodiment is characterized in that the supply lines over one multicomponent nozzle lead into the subvolume, being the over a first feed supply of the first excipient takes place separately from the over a second feed delivery of the second adjuvant is controllable.

there is under a multi-fluid nozzle every structural unit understood, over the two separate ones inflows lead into the same subvolume. The control of the feed over Both supply lines can be integrated into the multi-fluid nozzle or detached from the multi-substance nozzle in one to the multi-component nozzle leading Feed line section done. Unlike a supply line over two separate Leaves valves a designed as a structural unit Mehrstoffdüse especially realize compact and stable. In addition, the installation effort reduced in the production of the exhaust aftertreatment system. By the separate controllability, the supply of both auxiliaries individually the needs of the exhaust aftertreatment system done coordinated. For example, the supply of a urea-water solution as first adjuvant must be continuously required while the Dosing of hydrocarbons as a second excipient only periodically at intervals of several operating hours of the exhaust aftertreatment system must be done.

Prefers is also that the exhaust aftertreatment system a device for Supply of air to the partial volume has.

there For example, the supply of air can take place via the multi-substance nozzle, so that the advantage of cooling the multi-substance nozzle results. About that addition, the supply of air can serve to atomize the Improve excipients in their supply to the sub-volume.

With View of embodiments of the method is preferred that at the dosage of the first excipient and the second excipient at least a first operating mode of a second operating mode the exhaust aftertreatment system is distinguished, wherein in the first mode only one dosage of the first excipient takes place and wherein in the second mode of operation only one dosage the second excipient takes place.

During the Supply of the first auxiliary substance are contained in the raw exhaust gas of the internal combustion engine Nitrogen oxides with the help of the SCR catalyst to molecular nitrogen reduced while down deposit the particles in the particle filter section. In the second operating mode happens the supplied second Excipient the SCR catalyst and is oxidized exothermically on the oxidation catalyst. The released Heat serves together with an excess of oxygen in the exhaust gas for regeneration of the particulate filter section by a thermal oxidation of the particles stored there. During the Regeneration of the particulate filter is no reduction of nitrogen oxides in the exhaust.

Prefers is also that in the dosage of the first excipient and the second auxiliary at least a first operating mode of a distinguished a third mode of operation of the exhaust aftertreatment system is, wherein in the first mode of operation only a dosage of the first Auxiliary material takes place and wherein in the second operating mode both a dosage of the first adjuvant as well as a dosage of the second excipient takes place.

These Design has the advantage that the reduction of nitrogen oxides in the exhaust gas, which requires a supply of the first auxiliary, at a reduction of the particle filter section is not interrupted must become.

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

When Consequence can be the one with an undesirable consumption of the second Adjuvant associated regeneration of the particulate filter are triggered as needed, allowing a good filtering effect with a low consumption second reducing agent is achieved.

A Another preferred embodiment provides that within the second Operating mode is a measure of a discharge of the particulate filter and at a predetermined threshold is compared and that an overrun the threshold value, a changeover to the first operating mode triggers.

By This embodiment is also the consumption of the second reducing agent reduced and as well will be an eventual interruption of the reduction minimizes the nitrogen oxides.

Prefers is also that the supply of the first adjuvant and / or the second Excipient at least temporarily together with a supply of air partial volume.

These Design has the advantage that even during a regeneration of Particle filter section further nitrogen oxides are reduced.

Further Advantages will be apparent from the description and the attached figures.

It it is understood that the above and the following yet to be explained features not only in the specified combination, but also in other combinations or alone, without to leave the scope of the present invention.

drawings

embodiments The invention are illustrated in the drawings and in the following description explained. 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 to together with the metering 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 that is 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 ,

Of the second operating mode BM_2 or the third operating mode BM_3 come rarely available in comparison to the first operating mode BM_1. Usually becomes the first operating mode BM_1 over several hundred kilometers maintain while the other two operating modes BM_2 or BM_3 only during each of a few less kilometers become.

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 (10)

Exhaust aftertreatment system ( 20 ) of an internal combustion engine ( 10 ), the at least one SCR catalyst section ( 22 ), an oxidation catalyst section ( 24 ), a particle filter section ( 26 ) 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 supply lines ( 38 . 40 ) for both the first excipient ( 30 ) as well as the second excipient ( 32 ) in a same, in the flow direction of the exhaust gases 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, in each case in the flow direction of the exhaust gases, the SCR catalyst section ( 22 ) before the oxidation catalyst section ( 24 ) and this before the particle filter section ( 26 ) is arranged. Exhaust aftertreatment system ( 20 ) according to claim 1 or 2, characterized in that the supply lines ( 38 . 40 ) via a multi-fluid nozzle ( 50 ) into the partial volume ( 42 ), whereby the via a first supply line ( 38 ) supply of the first excipient ( 30 ) separated from that via a second supply line ( 40 ) supply of the second excipient ( 32 ) is controllable. Exhaust aftertreatment system ( 20 ) according to at least one of claims 1 to 3, characterized by a device ( 52 ) for the supply of air to the partial volume ( 42 ). Process for aftertreatment of the exhaust gas of an internal combustion engine ( 10 ) with an exhaust aftertreatment system ( 20 ), the at least one SCR catalyst section ( 22 ), an oxidation catalyst section ( 24 ), a particle filter section ( 26 ) and a device ( 28 ) for supplying a first excipient ( 30 ) and a second excipient ( 32 ) in support of the exhaust aftertreatment, characterized in that the supply of the first excipient ( 32 ) in a same, in the flow direction of the exhaust gases before the SCR catalyst section ( 22 ) lying partial volume ( 42 ) of the exhaust aftertreatment system ( 20 ) he follows. A method according to claim 5, 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 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 5, 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 systems ( 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. Method according to at least one of claims 5 and 6, characterized in that within the first operating mode (BM_1) a loading state of the particle filter section ( 26 ) is determined and compared with a predetermined threshold value (E_S) and that exceeding the threshold value (E_S) triggers 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 7, 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 ( 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 5 to 9, characterized in that the supply of the first excipient ( 30 ) and / or the second excipient ( 32 ) at least temporarily together with a supply of air to the partial volume ( 42 ) he follows.