DE102010005813A1 - Exhaust system for diesel engine of low-load passenger car, has supercharger arranged in exhaust line, and exhaust-gas recycling plants including passive storage properties for nitrogen oxides and/or hydrocarbons - Google Patents

Abstract

The system (1) has an exhaust gas manifold (3) gas-conductively connected with an exhaust line (4). A supercharger (5) is arranged in the line. Another supercharger (16) is arranged behind the former supercharger in direction of flow of exhaust gas. An exhaust-gas recycling plant (8) is arranged behind the latter supercharger. A selective catalytic reduction (SCR) catalytic converter (10) is arranged behind the plant. Another exhaust-gas recycling plant (6) is arranged between the superchargers in the line. The plants include passive storage properties for nitrogen oxides and/or hydrocarbons.

Description

The invention relates to an exhaust system for an internal combustion engine with the features of the preamble of patent claim 1.

It is based on the not yet published German disclosure DE 10 2008 057 572.0 out. For this purpose, a generic exhaust system for an internal combustion engine is known. This consists at least of an exhaust manifold, which is connected exhaust gas leading to an exhaust line, in which an exhaust gas of the internal combustion engine durchflutbarer exhaust gas turbocharger is arranged. In this case, the exhaust gas first flows through the exhaust manifold and then through the exhaust gas turbocharger, wherein a first exhaust gas purification system is arranged in the exhaust gas line in front of the exhaust gas turbocharger. A flow cross section of the first exhaust gas purification system is in the region of the first exhaust gas purification system a partial flow cross section of the exhaust gas line. In this case, the partial flow cross section of the exhaust gas line and the flow cross section of the first exhaust gas purification system can be closed alternately by a closing element. Behind the exhaust gas turbocharger is a particulate filter and behind the particulate filter another emission control system, an SCR catalyst, arranged in the exhaust system. In a further embodiment, a second exhaust gas turbocharger is arranged in the flow direction of the exhaust gas behind the first exhaust gas turbocharger. By using the generic exhaust system, the hydrocarbon (HC) and carbon monoxide (CO) emissions can be significantly reduced. When the exhaust system is new, it is thus able to fall below the legal emission limit values with a sufficient safety margin and to pass the type test positively.

A disadvantage of this prior art, however, is that after a cold start of the internal combustion engine, the SCR catalyst to reduce the nitrogen oxides (NO _x ) downstream of the particulate filter reaches its operating temperature only very slowly and in some operating cycles only towards the end. The released from the internal combustion engine nitrogen oxides can be converted very late and cause relatively high emissions of nitrogen oxides of the vehicle.

Object of the present invention is to avoid the above-mentioned disadvantages.

This object is solved by the features in the characterizing part of patent claim 1.

What is new is that the catalytic components with the previously known oxidation function are replaced by catalytic components with completely new functionality. Instead of the oxidation catalysts, catalysts with passive storage properties for NO _x and / or HC are used. In contrast to the NO _x storage catalytic converter (NSC), these do not require a rich exhaust gas (stoichiometric mixture composition) for their regeneration. The removal of pollutants depends essentially on the parameters of exhaust gas temperature and exhaust gas mass flow rate. The previously known oxidation function is essentially retained. This results in a new emission control system with completely new properties. During the warm-up phase of the internal combustion engine, the nitrogen oxide and / or HC emissions are cached by the catalysts with passive storage characteristics until the downstream SCR system has reached its operating temperature downstream of the particulate filter. Thereafter, the cached emission components are accumulated as described above and converted from the downstream components (nitrogen oxides are reacted by the SCR catalyst, HC emissions from the coated diesel particulate filter). The withdrawal is controlled by raising the exhaust gas temperature and / or the exhaust gas mass flow. This can be implemented either by an increased load of the internal combustion engine due to the driving profile or by internal combustion engine intervention.

Further advantageous developments of the invention can be found in the dependent claims.

In a further variant, either only the first emission control system with passive NO _x / HC storage properties and the second emission control system can be equipped with a known oxidation coating or vice versa.

In yet another variant, the coating with passive NO _x / HC storage properties can be integrated into the particulate filter.

In a further variant, the SCR catalyst arranged downstream of the particulate filter can also be integrated into the coating of the particulate filter and does not necessarily have to be applied to a separate catalyst support. In this case, the reducing agent introduction point is located in front of the particle filter.

In a further variant, the operation of the system can be configured such that the removal of pollutants from the first emission control system with passive NO _x / HC storage properties by temporarily opening the bypass valve in operating conditions of the internal combustion engine with sufficiently high exhaust gas temperatures.

In a further variant, the operation of the system can be configured such that immediately after the cold start of the internal combustion engine and operating conditions with low NO _x emission (low-load operating points, close to idling or quasi-stationary operation, ....) with conventional engine NO _x and HC emissions are buffered in the NO _x / HC passive gas emission control systems and are switched to stoichiometric operation in high NO _x emission states and converted by 3-way catalysis.

With the proposed inventive design of the exhaust system for an internal combustion engine thus the above-mentioned functional disadvantages of the known prior art can be completely bypassed.

• 1. NO_x-Speicherkatalysator (NSC) und
• 2. SCR-System (selective catalytic reduction).

So far, according to the known state of the art, two technologies are available to reduce nitrogen oxides in the lean exhaust gas, for example in the case of the diesel engine:

• 1. NO _x storage catalytic converter (NSC) and
• 2. SCR system (selective catalytic reduction).

Both systems have so far had fundamental disadvantages: The NO _x storage catalytic converter only works in a very limited operating range of the internal combustion engine, is very complicated to apply and has an increased consumption.

The SCR system operates in a much wider operating range, but so far has been reluctant to reach operating temperature and will not convert nitrogen oxides during warm-up.

• – Leichte Fahrzeuge
• – NO_x-unkritische aber HC/CO-kritische Fahrzeug/Brennkraftmaschinenkombinationen
• – Testzyklen mit niedriger Dynamik, moderaten Lasten bzw. NO_x-Grenzwerten.

The invention provides the following advantages over the prior art:
With the present invention, a system is described which is particularly suitable for low-load car applications, such. B .:

• - Light vehicles
• - NO _x -uncritical but HC / CO-critical vehicle / engine combinations
• - Test cycles with low dynamics, moderate loads or NO _x limits.

• – Stickoxidemissionen unmittelbar nach dem Brennkraftmaschinenstart zwischenspeichert und konvertiert;
• – sehr strenge Emissionsgesetze (EU6 und ff., US-SULEV, ...) schafft;
• – im gesamten Betriebsbereich der Brennkraftmaschine funktioniert;
• – ohne zusätzlichen Kraftstoffmehrverbrauch auskommt;
• – die Dynamik des Fahrzeuges nicht einschränkt;
• – alterungsstabil ist;
• – aufgrund der kleinen Abmessungen geringe Zusatzkosten verursacht und
• – mit überschaubaren Änderungen in ein bestehendes Package unterzubringen ist.

Thus, according to the invention, a system is available which:

• Nitrogen emissions cached and converted immediately after the engine start;
• - creates very strict emission laws (EU6 and ff., US-SULEV, ...);
• - works in the entire operating range of the internal combustion engine;
• - manages without additional fuel consumption;
• - does not restrict the dynamics of the vehicle;
• - aging stable;
• - caused small additional costs due to the small dimensions and
• - is to accommodate with manageable changes in an existing package.

In the following the invention with reference to a preferred embodiment is explained in more detail in two figures.

1 schematically shows a first embodiment of an exhaust system according to the invention for an internal combustion engine.

2 shows a diagram of a pollutant emissions of an internal combustion engine with an exhaust system according to the invention.

1 schematically shows an exhaust system according to the invention 1 for an internal combustion engine 2 , The internal combustion engine 2 has in this embodiment 6 Cylinder on, which are represented symbolically by circles with injectors. To the internal combustion engine 2 is an exhaust manifold 3 arranged for the discharge of exhaust gases. To the exhaust manifold 3 is an exhaust system 4 Flanged, in which a first exhaust gas turbocharger 5 is arranged, wherein an unspecified figured turbine housing is flowed through by the exhaust gas.

In the flow direction of the exhaust gas after the first exhaust gas turbocharger 5 is a first emission control system according to the invention 6 in the exhaust system 4 having passive storage properties for NO _x and / or HC (nitrogen oxides and / or hydrocarbons). Further in the flow direction are a second exhaust gas turbocharger 16 and a second emission control system 8th as well as a particle filter 11 in the exhaust system 4 arranged. Downstream of the particulate filter 11 is a reductant delivery point 9 for a reducing agent, such as. B. aqueous urea solution, which is for an SCR catalyst 10 in the flow direction of the exhaust gas behind the reducing agent introduction point 9 is provided arranged.

Next has a turbine of the first exhaust gas turbocharger 5 over a first bypass 17 with a first throttle element 18 and a turbine of the second exhaust gas turbocharger 16 via a second bypass 19 with a second throttle element 20 ,

The intake side, the first and the second exhaust gas turbocharger 5 . 16 in each case an unnumbered compressor housing, which with an intake air line 13 Gas leading are connected. The compressors are driven by the turbines during operation of the internal combustion engine and first convey an intake air into an intercooler 14 and then further into an intake air collector 15 , From there, the intake air enters the cylinder mentioned above. Next, the intake air line 13 an actuator 21 on, with which the airway in response to an operating condition of the internal combustion engine is variable.

According to the invention, the first and / or the second emission control system 6 . 8th passive storage properties for NO _x and / or HC (nitrogen oxides and / or hydrocarbons).

A passive NOx storage catalyst is also referred to as an "oxidation catalyst with passive NO _x and / or HC storage properties".

• – Passive Speichereigenschaften für NO_x- und/oder HC. Diese erfordern im Gegensatz zum NO_x-Speicherkat (NSC) kein fettes Abgas zu deren Regeneration; die Ausspeicherung ist im Wesentlichen von den Parametern Abgastemperatur und -massendurchsatz abhängig.
• – Die bekannten Oxidationseigenschaften bleiben im Wesentlichen erhalten.
• – Optional können Drei-Wege-Konvertierungseigenschaften integriert werden. Dabei werden in einem engen Lambda-Fenster und bei ausreichend hoher Abgastemperatur HC und CO oxidiert und gleichzeitig die Stickoxide reduziert.

The properties of "oxidation catalysts with passive NO _x and / or HC storage properties" are:

• - Passive storage properties for NO _x - and / or HC. In contrast to the NO _x storage catalytic converter (NSC), these require no rich exhaust gas for their regeneration; The withdrawal is essentially dependent on the parameters of exhaust gas temperature and mass flow rate.
• - The known oxidation properties are essentially retained.
• - Optionally, three-way conversion features can be integrated. In this case, HC and CO are oxidized in a narrow lambda window and at a sufficiently high exhaust gas temperature and at the same time the nitrogen oxides are reduced.

• – DOC: Diesel-Oxidation-Catalyst (oxidiert HC- + CO-Emissionen)
• – DOAC: Diesel-Oxidation-Advanced-Catalyst (oxidiert wie DOC auch HC + CO, ist aber um die Funktionalität der passiven NO_x- und/oder HC-Einspeicherung erweitert = Advanced; optional können auch Drei-Wege-Konvertierungseigenschaften integriert werden = Advanced)

The development patterns currently under investigation are supplied, for example, by Umicore AG and are traded under the name "DOAC". Even the name of this technology shows the extended functionality compared to the classic "DOC":

• - DOC: Diesel Oxidation Catalyst (oxidizes HC + CO emissions)
• - DOAC: Diesel Oxidation Advanced Catalyst (oxidized as DOC also HC + CO, but is extended to the functionality of passive NO _x and / or HC injection = Advanced; optionally, three-way conversion properties can also be integrated = advanced)

• 1) Weil die Ausspeicherung von NO_x und/oder HC keine aktiven, zyklisch wiederholten Eingriffe in das Brennkraftmaschinenmanagement erfordern, um die Abgaszusammensetzung zu verändern (beim NSC muss alle paar Minuten ein „Fettpuls” erzeugt werden, d. h. von normal mager = Lambda > 1 muss alle paar Minuten auf fettes Abgas = Lambda < 1 für die Dauer von ca. 10 sec. umgeschaltet werden).
• 2) Die Ausspeicherung erfolgt rein passiv, d. h. indem die Abgastemperatur oder der Abgasmassenstrom im Laufe des Brennkraftmaschinenbetriebs ansteigt. Ab einer gewissen Temperatur kann das angelagerte NO_x bzw. HC nicht mehr gehalten werden und wird wieder ausgespeichert bzw. wird bei erhöhtem Abgasmassenstrom wieder ausgeblasen.
• 3) Um eine eindeutige Abgrenzung zum NO_x-Speicherkat (NSC) zu haben.

The term "passive NO _x and / or HC storage properties" has been chosen for the following reasons:

• 1) Because the removal of NO _x and / or HC does not require active, cyclic interventions in the engine management to change the exhaust gas composition (in the NSC, a "fat pulse" must be generated every few minutes, ie of normal lean = lambda> 1) must be switched every few minutes to rich exhaust gas = lambda <1 for a period of about 10 sec.).
• 2) The withdrawal is purely passive, ie by the exhaust gas temperature or the exhaust gas mass flow increases in the course of internal combustion engine operation. From a certain temperature, the accumulated NO _x or HC can no longer be kept and is again stored out or is blown out at increased exhaust gas mass flow again.
• 3) To have a clear demarcation to the NO _x storage cat (NSC).

2 shows a diagram of a pollutant emissions of an internal combustion engine with an exhaust system according to the invention 1 , A X-axis the time is shown in [s], via a Y-axis provides a measure of NO _x upstream of the catalyst (Cat), NO _x on the catalyst, HC before catalyst, HC on the catalyst, exhaust gas temperature before the catalyst and the lambda upstream of the catalyst shown. Time phases are designated phase 1, 2, 3, 4, 5 and 6.

NO _x : In phase 1, "Loaded tank", the measured variable "NO _x after cat" initially shows a lower value than "NO _x before cat", ie a part of the raw emission is stored and only a remainder is slipped. This is the case until either the NO _x storage tank is full or, as shown, the exhaust gas temperature / exhaust gas mass flow is increased, see Phase 3 "Draining the storage tank". In this phase, the stored NO _{x is} expelled and converted by a downstream SCR system, which in the meantime is at operating temperature. Thus, the storage can start again, z. B. Phase 4.

HC: In the example shown, only a very small part of HC is stored in phase 1 ("HC after Cat" is only slightly lower than "HC before Cat"). However, due to its oxidation function, the catalyst almost completely converts HC emission once it has reached its HC light-off temperature (50% conversion), see Phase 2 "Achieving Light-Off Temperature for" HC "). If the catalyst is exposed to an exhaust gas temperature below the light-off temperature, then the catalyst cools again (phase 4 "load tank") and HC will slip again.

TWC function: in stage 5 "Emptying storage by stoichiometric operation" the reaction of the catalyst is shown, which optionally has a three-way conversion characteristic (TWC) integrated. If this catalyst is charged with stoichiometric exhaust gas (lambda = 1), then it works as a three-way catalyst and converts not only CO but also HC and NO _x .

• – Stickoxidemissionen unmittelbar nach dem Brennkraftmaschinenstart zwischenspeichert und konvertiert;
• – sehr strenge Emissionsgesetze (EU6 und ff. US-SULEV (super ultra low emissions vehicle, .....) schafft;
• – im gesamten Betriebsbereich der Brennkraftmaschine funktioniert;
• – ohne zusätzlichen Kraftstoffmehrverbrauch auskommt;
• – die Dynamik des Fahrzeuges nicht einschränkt;
• – alterungsstabil ist;
• – aufgrund der kleinen Abmessungen geringe Zusatzkosten verursacht und
• – mit überschaubaren Änderungen in ein bestehendes Package unterzubringen ist.

Thus, according to the invention, a system is available which:

• Nitrogen emissions cached and converted immediately after the engine start;
• - creates very stringent emissions legislation (EU6 and ff. US SULEV (super ultra low emission vehicle, .....);
• - works in the entire operating range of the internal combustion engine;
• - manages without additional fuel consumption;
• - does not restrict the dynamics of the vehicle;
• - aging stable;
• - caused small additional costs due to the small dimensions and
• - is to accommodate with manageable changes in an existing package.

LIST OF REFERENCE NUMBERS

1

exhaust system

2

Internal combustion engine

3

exhaust manifold

4

exhaust gas line

5

turbocharger

6

first emission control system

8th

second emission control system

9

Reduktionsmitteleinbringstelle

10

SCR catalyst

11

particulate Filter

13

intake air line

14

Intercooler

15

plenum chamber

16

second exhaust gas turbocharger

17

first bypass

18

first throttle element

19

second bypass

20

second throttle element

21

actuator

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008057572 A [0002]

Claims (5)

Exhaust system ( 1 ) for an internal combustion engine ( 2 ), consisting at least of an exhaust manifold ( 3 ), the gas-conducting with an exhaust line ( 4 ) in which one of an exhaust gas of the internal combustion engine ( 2 ) flooded first exhaust gas turbocharger ( 5 ) and in the flow direction of the exhaust gas behind a second exhaust gas turbocharger ( 16 ), wherein behind the second exhaust gas turbocharger ( 16 ) a second emission control system ( 8th ) and behind this a SCR (Selective Catalytic Reduction) catalyst ( 10 ) is arranged, characterized in that in the exhaust line ( 4 ) between the exhaust gas turbocharger ( 5 ) and the second exhaust gas turbocharger ( 16 ) a first emission control system ( 6 ) is arranged and the first and / or second emission control system ( 6 . 8th ) has passive storage properties for NO and / or HC (nitrogen oxides and / or hydrocarbons). Exhaust system according to claim 1, characterized in that in the flow direction of the exhaust gas behind the second emission control system ( 8th ) a reducing agent introduction site ( 9 ) is provided. Exhaust system according to claim 1 or 2, characterized in that between the second emission control system ( 8th ) and the reducing agent introduction site ( 9 ) a particle filter ( 11 ) in the exhaust system ( 1 ) is arranged. Exhaust system according to one of the claims 1 to 3, characterized in that the first and / or the second emission control system ( 6 . 8th ) has an oxidation property. Exhaust system according to one of the claims 1 to 4, characterized in that the first and / or the second emission control system ( 6 . 8th ) has a three-way conversion property.

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