JP2002256852A - Device for processing exhaust gas of internal combustion engine and vehicle mounted with the device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for processing the exhaust gas of an internal combustion engine having a supplying unit for continuously supplying a carrier element and a reducing agent. SOLUTION: In the device for processing the exhaust gas of an internal combustion engine equipped with a supplying unit supplying the carrier element containing a catalyst activity substance for oxidizing and/or reducing several components of the exhaust gas, in particular, a ceramic carrier element and reducing agent, the separate region having the reducing condition and the oxidizing condition is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a supply unit for continuously supplying a carrier element, in particular a ceramic carrier element, and a reducing agent containing a catalytically active substance for oxidizing and / or reducing different components of the exhaust gas. And a device for treating exhaust gas from an internal combustion engine.

[0002]

2. Description of the Related Art As the level of knowledge progresses,
For the protection of health and the environment, legal standards regulating the emission of motor vehicle emissions are constantly becoming more stringent. To meet this criterion, for example, EP 0 864 1
According to the description of the specification, a lean exhaust gas of an internal combustion engine, that is to say an exhaust gas catalyst having an air ratio λ> 1, is used, which comprises a separate supply of hydrocarbons on the back side of the catalytically active layer. Has a tube.

[0003] When the internal combustion engine is operated at lean correspondingly, only carbon monoxide emissions and fuel emissions but are slightly, but, NO _X emissions is relatively high, the exhaust gas in this case , Especially nitrogen oxides (NO), which cannot be catalytically reduced in lean exhaust gases or can be reduced only at low reaction rates. Separate feeds of hydrocarbons allow for the formation of a reduction ratio, thereby reducing the emission of NO _X , in which case nitrogen (N ₂ ) or carbon dioxide (CO ₂ ) and inter alia Water (H ₂ O) is formed.

However, in the case of the exhaust gas catalysts described in EP 08 264 411, it is clear that the reduction ratio can be maintained merely by supplying a relatively large amount of hydrocarbons.
It is a disadvantage. This is because oxygen can diffuse through the catalytically active layer from the side facing the exhaust gas. N
O transfer of emission of _X is significantly impaired thereby. In addition, the large supply of hydrocarbons has a detrimental effect on the concept of lean-burn engines.

[0005]

The object of the present invention, on the other hand, is to provide an apparatus for treating exhaust gas of an internal combustion engine, comprising a carrier element and a supply unit for continuously supplying a reducing agent. It is a proposal, in this case, that the device improves the transfer of the NO _X emissions of the lean exhaust gas of the internal combustion engine, and the amount of reducing agent that can be supplied at the same time is significantly reduced.

[0006]

This object is achieved by starting from the device described at the outset and by the characterizing features of claim 1.

[0007] The preferred embodiments and other forms of the invention are made possible by the methods recited in the dependent claims.

Accordingly, the device according to the invention for treating the exhaust gas of an internal combustion engine is provided with separate zones with reducing and oxidizing conditions, preferably with a lean air ratio (λ> 1). Is shown.

[0009] By using such a device, the conversion of exhaust gas components of the NO _X is guaranteed to be advantageously possible in reducing the area. In particular, in this case, the strong reduction conditions which can be adjusted according to the invention in a correspondingly large scalable region result in an essentially good transfer of the NO _X emissions.

As a result, the amount of hydrocarbons that can be supplied can be significantly reduced, especially in the form of fuel for the internal combustion engine, which leads to a substantial reduction in fuel consumption and thus economics. An improvement in the power and environmental protection can be guided correspondingly to the engine to be operated. According to the invention, the device can be used, for example, for Otto engines as well as for diesel engines.

In this case, the separate regions may be formed in various ways or may be formed. In this way, a large number of separate zones with, for example, reducing and / or oxidizing conditions can be realized. Preferably, a region formed in a layer having a reduction condition is provided. Thereby, it is possible that the advantageously formed interface can be transformed for the separation of various regions. For this purpose, a separating layer may in principle also be provided. This separation layer is, for example, a membrane,
It can be realized as a filter layer or the like.

[0012] Also, the interface can be realized by forming regions having different structures and / or material compositions. Preferably, materials for storing for forming nitrates and / or NO _X is provided, thus advantageously NO _X exhaust gas components are converted to nitrate. In this way, a separation of nitrogen transport, in particular by solid surface diffusion and / or solid bulk diffusion of nitrates, and in particular oxygen transport carried out by gas phase diffusion can be realized.

In this case, the transport of NO _X is impeded in the gas phase as well as the transport of oxygen, but the transport of solids independent of the gas phase of nitrogen using substances is as advantageous as possible. Some or essentially advantageous. The nitrogen oxides absorbed as nitrates reach, inter alia, in regions having reducing conditions by solid state diffusion, in which case the nitrates can be reacted with a continuously supplied reducing agent, whereby (N ₂ ).

For similar gas diffusion coefficients, for example,
NO by simple oxygen diffusion limitation _XTransport is disturbed
And thus a portion of the exhaust gas is simply
To reach the area where_XRelease of
Only a portion could be converted. However, in the present invention
According to the use of substances, by the formation of nitrates
Oxygen transport is suppressed, while nitrogen transport is promoted,
This results in additional improvements in the formation of separate areas
You.

[0015] Preferably, as a substance for storing for forming nitrates and / or NO _X, alkaline earth metal oxides, in particular barium oxide, strontium oxide and / or calcium oxide and / or alkali metal oxides Alternatively, a mixed oxide of the described oxides and one or more components of aluminum oxide, zirconium oxide, lanthanum oxide and / or cerium oxide are provided.

[0016] In another special form of the present invention, at least one catalytically active material comprises a material for storing for forming nitrates and / or NO _X. This makes it possible to convert the layered regions which advantageously have reducing conditions and, in the case of producing the device according to the invention, to form nitrates and / or N 2
Materials for accumulating O _X are in particular for the reduction for and inter alia NO _X in the oxidation of hydrocarbons and carbon monoxide, the catalytic active material, such as platinum, ruthenium, palladium or corresponding combination of metal Can be added.

In particular, a pore size of about 0.1 to 5 μm, in this case a length of pores of about 20 to 500 μm, is provided, in particular to advantageously control the pore size and porosity of the catalytically active substance. By doing so, it is possible to limit the diffusion of oxygen, in which case the removal of products of nitrate reduction, such as CO ₂ and H ₂ O, from the reaction zone is blocked to a considerable extent. .

In a preferred embodiment of the invention, the catalytically active substances are arranged in layers at least on the side of the carrier facing the exhaust gas. Thereby, preferably the production of the carrier element and the continuous supply of the reducing agent, as well as the formation of the lamellar region with the reducing conditions, can be modified.

It also has a supply line for the ammonia accumulator and the oxidizing agent, using a corresponding substance for forming ammonia and / or for accumulating ammonia, selectively with respect to the substances described above. The reducing agent accumulator may be provided from a side remote from the exhaust gas.

Advantageously, an exhaust gas distributor is provided for the distribution of the exhaust gas stream. This ensures that a favorable distribution of the exhaust gas stream is feasible, for example, for different work-up of the individual exhaust gas streams.

In another particular embodiment of the invention, at least one mixing device is provided for the mixing of the reducing agent with the offgas stream, so that the offgas stream has a fat-to-air ratio (λ). <1), preferably 0.6-0.
And has an air ratio of 7. This makes it possible for the preferably waste gas stream containing fat to be supplied to the carrier element by the supply unit, in particular on the side remote from the exhaust gas.

It is preferred that the mixing of the reducing agent and the offgas stream before entry into the catalyst prevents the formation of carbon black and thus the blockage of the pores of the support element. According to the prior art in the case of exhaust gas catalysts, the formation of cracks and the obstruction of the pores are, according to the state of the art, provided by pure hydrocarbon feeds.
At normal catalyst temperatures of ° C. this can be expected, which results in a strong disturbance of the transport of the reducing agent and thus a shift in the emission of NO _X.

Preferably, the offgas stream mixed with the reducing agent comprises only a fraction of the total offgas stream and is therefore relatively low in order to produce reducing conditions, ie a fat-containing air ratio (λ <1). Must be supplied.

In particular, the control unit is provided for controlling the supply of the reducing agent. This ensures that the supply of the reducing agent, preferably at different operating conditions of the internal combustion engine, can be adapted to the operating conditions. This is particularly advantageous in the case of internal combustion engines for vehicles or the like.

In another particular embodiment of the invention, the control unit includes at least one sensor for measuring the air ratio λ, so that even in different operating conditions of the internal combustion engine, the control unit includes The air ratio λ can be adjusted to a constant value.

Preferably, a tubular carrier element is provided which has a number of passages and at least one exhaust gas guiding element for supplying a split stream of exhaust gas to different parts of the carrier element, all parts comprising: Includes multiple passages.
This makes it possible to vary the supply of the preferred offgas stream to the carrier element.

[0027] Thereby, the interface for simultaneously forming a separate region with reducing conditions and a lean air ratio may advantageously be enlarged. Essentially enlarging the interface between the discrete areas according to the invention essentially
preferable. This makes it possible to improve the transport of the reaction starting materials as well as the reaction product, in particular the material flow.

For example, the formation of a circular, linear and / or complex zone in the radial direction by means of a corresponding exhaust gas guiding element can be envisaged, inter alia, in combination with a corresponding supply unit. The tubular carrier element is circular,
It can have an elliptical, angular or comparable cross-section, in which case a large number of passages are arranged in a slit and / or row.

[0029] The supply unit is preferably arranged in the central zone of the carrier element, in which case an overflow passage is provided for distributing the exhaust gas divergence in a slit-like or row-like manner. This ensures that, for example, the rows and / or the slits can advantageously alternately flow through different exhaust gas branches.

If appropriate, a compounding device is provided as an exhaust gas guiding element, for example a partition plate with or without corresponding overflow passages, corresponding plugs or the like for individual or multiple passages of the carrier element. Have been. In this case, a correspondingly arranged overflow channel can provide, for example, a distribution of the exhaust gas stream to a partitioned or plugged channel.

By arranging the supply unit in the central zone of the carrier element, a relatively flow-favorable distribution of the offgas stream can be achieved. For example, an exhaust gas divergence having a fat-containing air ratio flows into the outer region of the carrier element via an overflow channel. In some cases, the two exhaust gas streams with lean air ratios flow into the central region of the carrier element by means of corresponding overflow channels, wherein the exhaust gas stream advantageously separates the carrier element into slits or rows. Flow through.

One embodiment of the present invention is shown in the drawings and will now be described in detail with reference to the drawings.

[0033]

FIG. 1 schematically shows a porous, gas-permeable supporting ceramic, not shown in detail, and a ceramic-supported catalyst 1 having a catalytically active layer, wherein the catalytically active layer comprises nitrate. using the formation and / or material for of the NO _X storage containing catalytically active material for the oxidation and reduction of the different components of the exhaust gas from the well-known exhaust gas catalyst technology. A split stream 3 is supplied to the ceramic supported catalyst 1 via a supply pipe 4 at the center of a vertical row of passages. Shunt 3
Has a portion of the exhaust gas stream 5, for example less than 5% of the total exhaust gas stream. According to FIG. 4, the branch stream 3 is supplied with a reducing agent 7 by means of an injection device 8, which preferably corresponds to the fuel of the internal combustion engine.

According to FIG. 1, the ceramic supported catalyst 1
It has a large number of small passages, in which case the number of passages is essentially smaller than for a real catalyst, for the sake of clarity. A plug 2 can be seen from the part shown in detail in FIG. 1, which plug closes the end of the passage.
The plug 3 contains fat, that is, a fat-containing air ratio (λ <
1), a diverted stream 3, preferably having an air ratio of 0.6 to 0.7, is supplied at the center of the ceramic carrier by means of a supply pipe 4 and flows according to FIG. It is arranged to be able to.

According to FIG. 1, the exhaust gas stream 5 flows into a passage which is open at the top and at the bottom of the ceramic carrier 1 and has a corresponding overflow opening 9 in the central part of the ceramic body 1 of the corresponding slit. Flows into. Correspondingly, the passage with the exhaust gas having a lean, ie lean, air ratio (λ> 1) is closed tightly in the central part with the plug 2 and has a slit with a fat-containing air ratio (λ <1). The passage is tightly closed at the top as well as at the bottom of the ceramic carrier 1.

FIG. 2 shows a line "2"-"described in FIG.
2 "is schematically shown in this case.
In addition, the arrangement of the overflow opening 9 becomes clear. In the case of the exemplary slit shown in FIG.
Flows into the entire passage of the slit and, according to the description in FIG. 3, flows through the pores of the porous supporting ceramic onto the back surface of the catalyst layer of the ceramic carrier 1. In particular, the substances added to the catalyst layer for the formation of silicates and / or for the accumulation of NOx result in the formation of fat-containing exhaust gas regions and stoichiometric exhaust gas regions, whereby nitrogen is converted at a relatively high conversion rate. It is guaranteed that it can be reduced.

Additionally, the narrow pores of the catalyst layer and the flow of reaction products and residual nitrogen prevent oxygen diffusion,
Improves the formation of stoichiometric and fat-containing reaction zones. The supply of nitrogen in the gas phase into the catalyst layer is likewise prevented. However, this material guarantees the transport of the nitrogen oxides independently of the gas phase in the form of solid-bound nitrate diffusion. Supported without a corresponding solid,
Nitrogen transport is combined with suppression of oxygen transport and complete N
O _X conversion can not be guaranteed.

FIG. 4 shows a supply pipe 4 having an exhaust gas distributor 10 for generating a split stream 3 having a fat-containing air ratio (λ <1). The supply tube 4 is mounted such that the supply tube is placed almost tightly on the ceramic carrier 1. In this case, a small leak does not impair the function of the device. This is because, for the above-mentioned air ratio of the split stream 3, this split stream remains fat-containing with little leakage, while the exhaust gas stream 5 remains lean even with a corresponding leak. Because there is. The simply increased HC content of the lean exhaust gas stream 5 is fully oxidized by the catalyst.

FIG. 4 also shows an injection device 8 in which the fuel 7 to be sprayed comprises two mixing plates 11,
12 is mixed almost completely with the offgas stream 3.
For example, a sensor 13 embodied as a commercially available λ sonde of the type LSU, ie a λ Sonde-Universal, measures the air ratio λ downstream towards the mixing plates 11, 12. If a control unit not shown in detail is used, for example,
Is controlled. In this case, for example, a pump (not shown in detail) is operated, which pumps the fuel from the fuel tank to a spray device 8, which is formed, for example, as a spray nozzle. According to the invention, further suitable spraying and mixing devices are also possible.

FIG. 5 shows the supply pipe 4 having the exhaust gas distributor 10 and the mixing plate 12 in a perspective view for explanation. FIG. 5 also shows the arrangement of the two guide plates 14 and the exhaust pipe 15. Illustratively, the entire device is welded to the exhaust pipe of the internal combustion engine by a guide plate 14.

FIG. 6 shows FIG. 5 for easy understanding.
Are additionally shown in a front view.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a ceramic supported catalyst according to the present invention, including parts shown in detail.

FIG. 2 is a schematic sectional view showing the ceramic supported catalyst according to the present invention along the line “2”-“2” described in FIG. 1;

FIG. 3 is a schematic sectional view showing the ceramic supported catalyst according to the present invention along the line “3”-“3” described in FIG. 1;

FIG. 4 is a schematic sectional view showing an apparatus according to the present invention.

FIG. 5 is a schematic perspective view showing an exhaust gas distributor.

FIG. 6 is a schematic perspective view showing an exhaust gas distributor.

[Explanation of symbols]

1 ceramic supported catalyst, 2 stoppers, 3 branch flow, 4
Supply pipe, 5 exhaust gas flow, 6 casing, 7
Fuel, 8 atomizing device, 9 overflow opening, 10 exhaust gas distributor, 11 mixing plate, 12 mixing plate, 13
Sensor, 14 guide plate, 15 exhaust pipe

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Bernd Schumann Luthesheim Daimlerstrasse 23 F-term (reference) 3G091 AA17 AA18 AA28 AB06 AB09 BA14 CA16 CA27 DB10 EA34 FB10 FB12 GA06 GA10 GA24 GB01X GB01Y GB03Y GB04Y GB10X GB GB17X HA36 4D048 AA06 AB02 AC02 BB02 CC23 CC47 DA02 DA20

Claims (12)

[Claims] 1. A carrier element comprising a catalytically active substance for oxidizing and / or reducing different components of an exhaust gas (5),
In particular, in a device for treating the exhaust gas of an internal combustion engine, which comprises a ceramic carrier element and a supply unit (4) for continuously supplying a reducing agent (7), separate devices having reducing and oxidizing conditions are provided. Device for treating exhaust gas of an internal combustion engine, characterized in that it has an area. 2. The apparatus according to claim 1, wherein a layered region having a reducing condition is provided. 3. The device according to claim 1, wherein a substance for forming nitrates and / or accumulating NO _X is provided. 4. The device according to claim 1, wherein the at least one catalytically active substance comprises a substance for forming nitrates and / or for accumulating NO _X. 5. The device as claimed in claim 1, wherein the catalytically active substance is arranged in a layer at least on the side of the carrier element facing the exhaust gas. 6. The exhaust gas distributor (10) comprises an exhaust gas stream (3,
6. The device according to claim 1, which is provided for the distribution of 5). 7. At least one mixing device (11, 1).
2) is provided for mixing the reducing agent (7) with the exhaust gas divergence (3), so that this exhaust gas shunt (3)
Has an air ratio λ <1. 7. 8. The method according to claim 1, wherein the control unit is provided for controlling the supply amount of the reducing agent.
The device according to item. 9. The device according to claim 1, wherein the control unit includes at least one sensor for measuring the air ratio λ. 10. A tubular carrier element having a number of passages and having at least one exhaust gas guiding element (2) for supplying an exhaust gas split stream (3, 5) to different parts of the carrier element is provided. 10. The device according to any one of the preceding claims, wherein all parts here comprise a number of passages. 11. The supply unit (4) is arranged in the central part of the carrier element, wherein the upper flow passage (9) distributes the exhaust gas divergence (3, 5) between the slits or in a line. Claims 1 to 10 provided for
The apparatus according to any one of the preceding claims. 12. A vehicle provided with the device according to claim 1. Description: