EP1882090B1 - Exhaust system with two exhaust treatment units - Google Patents

Abstract

The inventive exhaust system (1) of an internal combustion engine (2) comprises a first exhaust treatment unit (3) with a first back pressure and comprises a second exhaust treatment unit (4) with a second back pressure, the first back pressure being less than the second back pressure. The inventive exhaust system (1) advantageously enables the formation of systems having two exhaust treatment units (3, 4) that are arranged one behind the other in the direction of flow. The first (3) and/or the second exhaust treatment unit (4) can be provided with a smaller design due to the homogenization of flow. This applies, for example, when an oxidation-type catalytic converter is provided as a first exhaust treatment unit (3) and when a particulate filter is provided as a second exhaust treatment unit (4). The homogenization of flow in first exhaust treatment unit (3) increases the conversion rate so that the first (3) and/or second exhaust treatment unit (4) can be provided with a smaller design. This saves considerable costs when designed systems of this type.

Description

The subject matter of the present invention is an exhaust system for internal combustion engines with two exhaust gas treatment units.

In many countries exhaust emission limits are specified, which must be observed by motor vehicles or stationary internal combustion engines. Often these are relatively complex threshold systems, where, for example, not only one limit for one size but rather several limits must be met simultaneously. In order to comply with these limits, relatively complex exhaust gas reclamation operations are often required which require multiple combined exhaust gas purification components.

For example, particulate filters require regeneration in which the soot particles collected by the filter are burned. This takes place for example in the form of a continuous regeneration (CRT, continuous regeneration trap) with nitrogen dioxide (NO ₂ ). Since there is often insufficient nitrogen dioxide in the exhaust gas flowing into the filter, it is known to provide an oxidation catalyst upstream of the particulate filter, with which nitrogen monoxide (NO) is oxidized to nitrogen dioxide (NO ₂ ).

Another example is Selective Catalytic Reduction (SCR) of Nitric Oxide (NO _X ), which requires the introduction of reductant such as urea. This urea must be hydrolyzed, so that often in the flow direction upstream of an SCR catalyst, a hydrolysis catalyst is formed.

Thus, there are a variety of examples of systems that require two or more different exhaust treatment units that work together. All of these systems therefore have first and second exhaust gas treatment units lying one behind the other in the flow direction.

In all these cases, the highest possible reaction rate in the second exhaust gas treatment component as a rule requires most efficient conversion in the first, first exhaust gas treatment component lying in the flow direction before the second exhaust gas treatment component.

The DE 40 24 942 A1 discloses a monolithic honeycomb body which has consecutively different cell densities in the flow direction, so that the light-off behavior and the thermal aging can be influenced.

Based on this, the object of the invention is to propose an exhaust system with a first and a second exhaust treatment unit, in which the highest possible reaction rate in the second exhaust treatment component is achieved and at the same time the smallest possible volume of the exhaust gas treatment components is made possible.

This object is achieved by an exhaust system with the features of claim 1. Advantageous developments are the subject of the dependent claims.

The exhaust system according to the invention of an internal combustion engine, comprising a first exhaust treatment unit with a first dynamic pressure and a second exhaust treatment unit with a second dynamic pressure, wherein the first back pressure is smaller than the second back pressure, characterized in that the first exhaust treatment unit in such a first distance in the flow direction is formed before the second exhaust treatment unit, that during operation of a entering into the first exhaust gas treatment unit gas flow is made uniform. This means, in particular, that the back pressure in the flow direction before the exhaust gas treatment unit is influenced by the first dynamic pressure of the heat exchanger.

In the exhaust system according to the invention, the first distance between the first exhaust treatment unit and the second exhaust treatment unit is less than 15 mm, preferably less than 10 mm, more preferably less than 5 mm, so that the effect of the first stall pressure of the first exhaust treatment unit and the second back pressure of accumulate second exhaust treatment unit, so that the exhaust gas flowing into the first exhaust treatment unit, must overcome a back pressure, which is coarser than the first back pressure of the first exhaust treatment unit alone.

The internal combustion engine is in particular a diesel or gasoline engine, for example a diesel or gasoline engine of a motor vehicle (eg a passenger car, a truck, a motorized two-wheeler, boat or aircraft) or a stationary or diesel diesel engine.

In particular, honeycomb bodies, for example ceramic or metallic honeycomb bodies, or else wire knit bodies, bodies made of metal foam or the like are suitable as exhaust gas treatment units. Metallic honeycomb bodies may in particular be constructed from at least one at least partially structured metallic layer and optionally at least one substantially smooth layer, which are wound or stacked together and wound. The twisted or wound layers form permeable cavities, which are bounded by the layers. The layers are in particular made of a high temperature corrosion resistant material, such as Al or Cr steel. The layers may be interconnected, in particular cohesively, such as by a Hochtemperaturlötverfahren. Both the essentially smooth layers and the at least partially structured layers can have microstructures, guide surfaces, perforations and / or perforations, at least in some areas, which serve for even better mixing of the gas flow. Under an exhaust gas treatment unit is understood in particular no heat exchanger. The exhaust treatment units may also be formed in an exhaust gas recirculation line.

The equalization of the gas flow before entering the first exhaust gas treatment unit is advantageously carried out by forming the first exhaust gas treatment unit relatively close to the second exhaust gas treatment unit. This leads to an equalization of the gas flow already in the first exhaust gas treatment unit, so that here the conversion rate is improved because the cross section of the first exhaust gas treatment unit is more uniformly exposed to exhaust gas. Thus, the volume of the first exhaust treatment unit can be reduced in comparison to a conventional structure at the same rate of conversion of the pollutants in the exhaust gas. Due to the much more efficient implementation rate of Pollutants also improves the conversion rate of the second exhaust gas purification unit, so that it may be smaller in size compared to conventional second exhaust gas purification units.

In order to form an exhaust gas treatment unit which has only a low dynamic pressure, it is possible to use a honeycomb body which has a relatively low cell density, for example less than 200 cpsi (cells per square inch), preferably less than 150 cpsi 100 cpsi and less. For example, an exhaust treatment unit having a relatively high back pressure may be a high cell honeycomb body having, for example, a cell density of about 800 cpsi, 1000 cpsi or more. Furthermore, the length of the cavities in a honeycomb body has an influence on the dynamic pressure, so that an exhaust gas treatment unit having a relatively small back pressure can be formed by a short honeycomb body and an exhaust gas treatment unit having a relatively large back pressure by a long honeycomb body.

According to an advantageous embodiment of the exhaust system according to the invention, the first distance is selected such that the effect of the first dynamic pressure and the second dynamic pressure accumulate.

Cumulating means here in particular that the dynamic pressure present in front of the first exhaust gas treatment unit is greater than the first back pressure that the first exhaust gas treatment unit has as such, which therefore exists when only the first exhaust gas treatment unit is flown, without a second exhaust gas treatment unit being formed , The cumulation of the dynamic pressures advantageously leads to the exhaust gas, before it flows into the first exhaust gas treatment unit, having to overcome a dynamic pressure which is greater than the first back pressure of the first exhaust gas treatment unit. Depending on the design of the first and the second exhaust gas treatment unit, the dynamic pressure is even significantly greater than the first dynamic pressure. The increase of the dynamic pressure causes a Vergleichmä-ßigung the flow of the first exhaust gas treatment unit and thus the gas flow through the first exhaust gas treatment unit and the second exhaust gas treatment unit.

According to a further advantageous embodiment, a second distance of a gas inlet-side end face of the first exhaust gas treatment unit from a gas inlet-side end face of the second exhaust gas treatment unit is less than 60 mm, preferably less than 45 mm, particularly preferably less than 30 mm.

These values have proven to be particularly advantageous. In particular, it comes under normal operating conditions to cumulate the effects of the first and the second dynamic pressure come.

According to a further advantageous embodiment of the exhaust system according to the invention, the expansion of the first exhaust treatment unit in the flow direction is less than 45 mm, preferably less than 35 mm, particularly preferably 25 mm or less.

Due to the very uniform and effective implementation of the corresponding substances in the exhaust gas relatively small first exhaust gas treatment units can be used. In the second exhaust treatment unit can also be chosen a smaller volume, for example, in the case that as the second exhaust treatment unit is a particulate filter and the first exhaust treatment unit formed an oxidation catalyst, the more uniform flow of the first exhaust treatment unit causes an improved supply of nitrogen dioxide and thus a more uniform regeneration so that a smaller particulate filter volume is sufficient.

According to a further advantageous embodiment of the exhaust system according to the invention, the first and / or the second exhaust gas treatment unit comprise at least one honeycomb body.

With a honeycomb body, a first and / or second exhaust treatment unit can be created, whose properties such as surface, pressure, etc., can be very accurately predetermined. As honeycomb body are particularly suitable metallic or ceramic honeycomb. Also particulate filter can be formed as a honeycomb body with at least partially porous channel walls and optionally channel terminations or corresponding baffles and openings.

In particular, it is also advantageous to provide both exhaust gas treatment units in a common housing. Here, the exhaust gas treatment units may be held in corresponding beads of the housing by means of a flanging or the like. It is also possible to fit the second exhaust gas treatment unit flush on a front side of the heat exchanger. It may be advantageous, in particular in the last region of the first exhaust gas treatment unit, to allow the exhaust gas to flow crosswise. In the case of honeycomb bodies, this can be achieved by providing perforations in the walls of the cavities in the last region, for example in the last 20% or 10% of the length of the first exhaust gas treatment unit. This is particularly advantageous if the second exhaust gas treatment unit comprises a particle filter with alternately closed channels. In particular, it is also possible to allow the duct walls to end at different points in the area of the gas outlet-side end face of the first exhaust treatment unit or the gas inlet-side end face of the second exhaust treatment unit, so that no smooth end face, but a rugged face of the first and / or the second exhaust treatment unit arises, which can also lead to cross flows in particular between adjacent channels.

According to a further advantageous embodiment of the exhaust system according to the invention, at least the first exhaust gas treatment unit comprises a catalytically active coating.

The catalytically active coating comprises, for example, a ceramic washcoat which contains materials which catalyze the desired reactions, ie in particular reduce the reaction temperature of these reactions to such an extent that they run to a considerable extent at the temperatures in the exhaust gas recirculation line. Suitable catalysts are in particular noble metals such as platinum, rhodium or the like. An oxidation catalyst coating catalyzes in particular the oxidation of hydrocarbons (HC) or nitrogen oxides (NO _X ). Furthermore, it is likewise possible according to the invention that, alternatively or cumulatively, the second exhaust gas treatment unit has a catalytically active coating. For example, the first exhaust treatment unit may comprise a hydrolysis catalyst, while the second exhaust treatment unit comprises an SCR catalyst.

According to a further advantageous embodiment of the exhaust system according to the invention, the ratio of the first dynamic pressure to the second dynamic pressure is greater than 2, preferably greater than 10.

Particularly in the case of these dynamic pressure conditions, ie if the dynamic pressure of the second exhaust gas treatment unit is greater than the dynamic pressure of the first exhaust gas treatment unit by more than a factor of 2 or even 10, the effects of the first dynamic pressure of the heat exchanger and the second dynamic pressure of the exhaust gas treatment unit accumulate in a particularly advantageous manner first distances of 15 mm or less.

1. (a) offener Partikelfilter;
2. (b) geschlossener Partikelfilter; und
3. (c) SCR-Katalysator.

According to a further advantageous embodiment of the exhaust system according to the invention, the second exhaust gas treatment unit comprises at least one of the following components:

1. (a) open particulate filter;
2. (b) closed particulate filter; and
3. (c) SCR catalyst.

All of these three possible second exhaust treatment units (a), (b) and (c) are components with a relatively high dynamic pressure.

An open particle filter should be characterized in that a particle, in particular a soot particle, can pass through it without being caught by a channel wall. In a closed particulate filter, this is not possible, as this regularly alternately closed channels, so that in a subset channels the exhaust gas can only flow in, but not through a regular channel opening can leave the channel, but rather that the exhaust gas through the porous Walls of the filter must flow, whereby it enters another subset of channels, which in turn have no input-side free flow cross-section, but only an output-side free flow cross-section. In the case of closed particulate filters, in principle, it is not possible to break through a relatively large particle through the filter if it is intact, since the particle gets caught in the porous channel wall. In an open filter system this is possible in principle. An open particle filter has porous regions at least in part of its walls.

For example, it is possible to provide an open or closed particulate filter as a second exhaust treatment unit, which is preceded by an oxidation catalyst as the first exhaust treatment unit, so that the particulate filter is continuously regenerated, is oxidized in the oxidation catalyst Nitrogen in oxide to nitrogen dioxide, which can be used for combustion of the soot particles is. According to the invention, the oxidation catalyst can be made smaller than when the distance between the two exhaust gas treatment units is not selected according to the invention. In particular, if a closed particulate filter, for example a diesel particulate filter of a known type, is designed as the second exhaust gas treatment unit and a honeycomb body as the first exhaust gas treatment unit and the distance as small as possible, possibly even close to zero by applying the end face of the honeycomb body to the corresponding end face of the particulate filter, is selected, it is advantageous to provide in the end region of the channel walls of the first exhaust treatment unit perforations and / or optionally baffles, which favor further mixing of the exhaust gas.

Another example is a high cell SCR coating honeycomb body second exhaust treatment unit, preceded by a low cell honeycomb body with a urea hydrolysis promoting coating.

Fig. 1

schematisch ein Ausführungsbeispiel einer erfindungsgemäßen Abgasanlage;

Fig. 2

schematisch einen Ausschnitt des Ausführungsbeispiels einer erfindungsgemäßen Abgasanlage;

Fig. 3

schematisch im Querschnitt einen Wabenkörper; und

Fig.4

schematisch Wahrscheinlichkeitsverteilungen von Strömungsgeschwindigkeiten.

It is to be expressly understood that these are only examples of high backpressure systems and the invention is not limited to these examples. The present invention will be further explained with reference to the accompanying figures, without being limited to the embodiments and advantages shown and described there. Show it:

Fig. 1

schematically an embodiment of an exhaust system according to the invention;

Fig. 2

schematically a section of the embodiment of an exhaust system according to the invention;

Fig. 3

schematically in cross section a honeycomb body; and

Figure 4

schematically probability distributions of flow velocities.

Fig. 1 1 schematically shows an exemplary embodiment of an exhaust system 1 according to the invention of an internal combustion engine 2, which comprises a first exhaust gas treatment unit 3 and a second exhaust gas treatment unit 4. The first exhaust treatment unit 3 is designed as a closed particle filter with mutually closed channels, while the second exhaust treatment unit 4 is formed as a honeycomb body with a catalytically active coating, which catalyzes the conversion of nitrogen monoxide to nitrogen dioxide, without the invention being limited thereto. The particle filter may be formed as a ceramic solid extrudate or according to metallic layers. The first exhaust gas treatment unit 3 has a first hydrodynamic dynamic pressure, while the second exhaust gas treatment unit 4 has a second dynamic pressure, which is greater than the first dynamic pressure.

According to the invention, the first exhaust gas treatment unit 3 is formed in such a first distance 5 upstream of the second exhaust gas treatment unit 4, so that during operation, a gas flow 6 symbolized by an arrow is homogenized in the first exhaust gas treatment unit 3. The first distance 5 is here in particular less than 15 mm, preferably less than 10 mm, particularly preferably less than 5 mm. The first 3 and second exhaust treatment unit 4 are designed so that at this first distance 5 to accumulate the effects of the first back pressure and the second back pressure, so that the flowing into the first exhaust treatment unit 3 exhaust gas must overcome a dynamic pressure which is greater than that first back pressure of the first exhaust treatment unit 3 as such. As explained above, this leads to an equalization of the gas flow 6, which flows into the first exhaust gas treatment unit 3.

Fig. 2 schematically shows the section of the exhaust system 1, which comprises the first 3 and the second exhaust treatment unit 4. A second distance 7 between a gas inlet-side end face 8 of the first exhaust gas treatment unit 3 and a gas inlet-side end face 9 of the second exhaust treatment unit 4 is selected according to the invention so that it comes to a homogenization of the flow in the first exhaust gas treatment unit 3. In particular, the second distance 7 is less than 60 mm, preferably less than 45 mm, particularly preferably less than 30 mm. In particular, short honeycomb bodies can be used as the first exhaust gas treatment unit 4, in particular an extension 10 in the flow direction of approximately 20 to approximately 40 mm. The first distance 5 is for example less than 15 mm, or even 5 mm or less. In particular, the first distance 5 is selected so that the effect of the first dynamic pressure of the first exhaust treatment unit 3 and the second dynamic pressure of the second exhaust treatment unit 4 accumulate, so that the exhaust gas flowing into the first exhaust treatment unit 3 has to overcome a dynamic pressure that is larger , Preferably significantly greater than the first back pressure of the first exhaust treatment unit 3 alone

Fig. 3 schematically shows an example of a honeycomb body 11 in cross-section, which may be formed as a first 3 and / or second exhaust treatment unit 4. This honeycomb body 11 comprises a honeycomb structure 12 in a jacket tube 13. The honeycomb structure 12 has cavities 14 which can be wetted or even flowed through, which are formed by substantially smooth layers 15 and at least partially structured layers 16. At least one at least partially structured layer 16 and optionally at least one substantially smooth layer 15 are wound up or stacked and wound one or more stacks in the same direction or in opposite directions. Substantially smooth layers 15 may have microstructures whose amplitude is smaller than the patterning amplitude of the at least partially structured layer 16. Layers 15, 16 are preferably metallic layers, in particular sheet metal layers and / or metallic fiber layers, in particular of high-temperature resistant and corrosion-resistant material such as Al or Cr steels can be made. The layers 15, 16 may have microstructures, perforations, apertures and / or baffles.

Fig. 4 schematically shows a first probability distribution 17 of the velocity v and a second probability distribution 18 of the velocity v. The first probability distribution 17 results if only the first exhaust gas treatment unit 3 is flowed with gas, ie without a second exhaust gas treatment unit 4 being formed behind it in the flow direction. Plotted for both distributions, the probability that a certain speed is present in the gas. Both the probability and the speed are given in relative units. The second probability distribution 18 is the probability distribution in a system according to the invention. It therefore relates to an exhaust system 1 of a first exhaust treatment unit 3 and a second exhaust treatment unit 4. The second probability distribution 18 is wider, in particular has a greater width at half maximum height (full width half maximum) than the first probability distribution 17. This is based on the invention Equalization of the flow.

The exhaust system 1 according to the invention advantageously allows the formation of systems with two exhaust treatment units 3, 4, which are arranged one behind the other in the flow direction. Due to the flow equalization, the first 3 and / or the second exhaust treatment unit 4 can be made smaller. This applies, for example, if the first exhaust gas treatment unit 3 is an oxidation catalytic converter and a second exhaust gas treatment unit 4 is a particle filter. By equalizing the flow in the first exhaust gas treatment unit 3, the conversion rate is increased, so that first 3 and / or second exhaust treatment unit 4 can be made smaller. This saves considerable costs in the design of such systems.

LIST OF REFERENCE NUMBERS

1

exhaust system

2

internal combustion engine

3

first exhaust treatment unit

4

second exhaust treatment unit

5

first distance

6

gas flow

7

second distance

8th

Gas inlet side end face of the first exhaust gas treatment unit

9

Gas inlet side end side of the second exhaust treatment unit

10

expansion

11

honeycombs

12

honeycomb structure

13

casing pipe

14

cavity

15

essentially smooth position

16

at least partially structured situation

Claims (7)

1. An exhaust system (1) for an internal combustion engine (2), comprising a first exhaust gas treatment unit (3) with a first back pressure and a second exhaust gas treatment unit (4) with a second back pressure, wherein the first back pressure is less than the second back pressure, characterized in that the first exhaust gas treatment unit (3) is constructed at a first distance (5) upstream of the second exhaust gas treatment unit (4) in the direction of flow such that during operation a gas flow (6) which enters the first exhaust gas treatment unit (3) is homogenized, in which the first distance (5) between the first exhaust gas treatment unit (3) and the second exhaust gas treatment unit (4) is less than 15 mm, so that the effect of the first back pressure and of the second back pressure accumulate and so that the exhaust gas, before flowing into the first exhaust gas treatment unit (3), has to overcome a back pressure which is higher than the first back pressure of the first exhaust gas treatment unit (3) alone.
2. The exhaust system (1) as claimed in claim 1, in which a second distance (7) of a gas inlet end (8) of the first exhaust gas treatment unit (3) from a gas inlet end (9) of the second exhaust gas treatment unit (4) is less than 60 mm, preferably less than 45 mm, particularly preferably less than 30 mm.
3. The exhaust system (1) as claimed in one of the preceding claims, in which the extent (10) of the first exhaust gas treatment unit (3) in the direction of flow is less than 45 mm, preferably less than 35 mm, particularly preferably 25 mm or less.
4. The exhaust system (1) as claimed in one of the preceding claims, in which the first exhaust gas treatment unit (3) and/or the second exhaust gas treatment unit (4) comprise at least one honeycomb body (11).
5. The exhaust system (1) as claimed in one of the preceding claims, in which at least the first exhaust gas treatment unit (3) comprises a catalytically active coating.
6. The exhaust system (1) as claimed in one of the preceding claims, in which the ratio of the first back pressure to the second back pressure is greater than 2, preferably greater than 10.
7. The exhaust system (1) as claimed in one of the preceding claims, in which the second exhaust gas treatment unit (4) comprises at least one of the following components:

   (a) an open particle filter;

   (b) a closed particle filter; and

   (c) an SCR catalytic converter.

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