DE102007021470A1 - Ceramic honeycomb body for use in emission control systems - Google Patents

Abstract

A ceramic honeycomb body (118) is proposed for use in emission control systems. The ceramic honeycomb body (118) has an input side (122) and an output side (124) and includes a plurality of dummy channels (126). The blind channels (126) in turn comprise a multiplicity of outlet channels (130) sealed on the input side and a large number of inlet channels (128) closed on the output side. The ratio eta of the proportion of the inlet channels (128) on a cross-sectional area unit to the proportion of the outlet channels (130) on a cross-sectional area unit varies over the total cross-sectional area of the honeycomb body (118).

Description

State of the art

The The invention is based on known emission control systems, for example Catalysts or filters, which are usually in the exhaust system used by internal combustion engines. Such emission control systems in many cases comprise ceramic substrates, which, for example, as a carrier for catalytic active materials or as porous filter materials, used.

In many cases are ceramic honeycomb body used as a carrier. Such ceramic honeycomb body are made of ceramic materials such as silicon carbide, Aluminum titanate or cordierite or other ceramic materials manufactured. The production takes place for example by means of an extrusion process.

there The ceramic honeycomb bodies usually comprise a plurality of blind channels with any (for example round, rectangular, square or hexagonal) cross section, wherein mutually inlet channels are provided, which on the (seen in the flow direction) output side of the Honeycomb body are closed, and outlet channels, which are closed on the input side. This ensures that that is to be cleaned exhaust gas stream, which the honeycomb body flows through, at least once the wall of the honeycomb body must penetrate.

Especially in diesel particulate filters, which are used to filter soot particles used from the diesel exhaust, plays the removal of particles from the honeycomb filter a crucial role. The accumulated in the filter Soot must be in regular due to the increasing exhaust back pressure Intervals can be removed by burning (regeneration). Will the Regeneration initiated when the soot load is too high, so threatens a thermo-mechanical damage to the filter.

Out US 4,276,071 is a cleanable by burn, monolithic ceramic filter element known. In this case, a number of channel geometries are disclosed, including geometries with asymmetrical channels, in which the inlet channels account for a larger proportion of the total cross-section than the outlet channels. This reduces the increase in backpressure caused by the filter as the load increases. There are constructions of an asymmetry known in which the different area ratios by different channel size and / or by a different number of inlet and outlet channels.

While the regeneration becomes the filter through the exhaust, its temperature is increased by motor action, convective heated. The edge areas of the filter thereby reach due to the heat dissipation through the insulation to the housing and due to the poorer flow in the wall boundary layer only a lower temperature than the radially further inward Area of the filter. After comparing higher temperatures there a part of the soot has been burned off, diminishes the flow resistance caused by the soot layer, and a larger proportion of the hot exhaust gas flows through the radially inner area.

By this asymmetrical flow with predominant Proportion of the flow of hot exhaust gases through the radially inward area worsens the already bad Heating the exterior of the filter. As a result, can in this area of the filter, the temperature necessary for regeneration not or not always be achieved, and there actually existing filter surface remains unused. Furthermore go with one exclusively in the radially inner area regeneration of the filter, large radial temperature gradients accompanied by thermal stresses to the failure of the filter can lead to cracking.

Of Further, a non-regenerated soot layer may pass through further accumulation (albeit diminished in speed) of soot in an ultimately more successful regeneration lead to critical peak temperatures.

Disclosure of the invention

It Accordingly, a ceramic honeycomb body for the use in emission control systems of the type described above and a diesel particulate filter with an inventive ceramic honeycomb body proposed which are those listed above Disadvantages of ceramic honeycomb body or diesel particulate filters with such honeycomb bodies avoid at least largely. In addition to use in diesel particulate filters, the ceramic Honeycomb body according to the invention also advantageous be used in other emission control systems, because the advantages mutatis mutandis transferred to other such systems such as other types of filters or catalysts.

A basic idea of the present invention is to make the temperature field over the cross-section of the ceramic honeycomb body more uniform during regeneration. This homogenization of the temperature field is inventively increased by an Deposition of soot in the areas in which compared to conventional honeycomb bodies, the temperature is to be increased reached. In particular, the temperature can be selectively increased in the radially outer regions of the honeycomb body by there is an elevated position of soot and thus increased burnup during regeneration.

It Accordingly, a ceramic honeycomb body with a Suggested input side and an output side, which, for example, from can be made of the above-mentioned ceramic materials. The ceramic honeycomb body may, for example, in total be cylindrical and a body axis exhibit. The ceramic honeycomb body has an input side and an exit side, which extends through the flow direction define the exhaust gas flowing through the honeycomb body.

Farther includes, as in the prior art, the ceramic honeycomb body a plurality of blind channels having a plurality of input side sealed outlet channels and a variety of output side closed inlet channels. It can in particular the number of inlet channels of the number of outlet channels However, different numbers of admission and outlet channels are possible.

As well as in US 4,276,071 disclosed, the inlet channels and the outlet channels have different area ratios to the total cross-section.

The Ratio of the proportion of inlet channels to one Cross-sectional area unit to the proportion of the outlet channels on a cross-sectional surface unit is in the following denoted by η. For example, a cross-sectional area unit be chosen perpendicular to the body axis, which at least one inlet channel and at least one outlet channel includes. This cross-sectional area unit may preferably be chosen such that this one in the overall cross-section of the honeycomb body repeating unit (which is also called "cell") could be designated). Preferably, this is Cross sectional area unit small compared to the Total cross section of the ceramic honeycomb body.

Around Thus, the calculation of the ratio η becomes first the opening area of the inlet channels determined within this cross-sectional area unit, then the opening area of the outlet channels in this cross-sectional area unit, and then the quotient formed from these opening areas.

One The basic idea of the present invention is to provide this area ratio η between Inlet and outlet channels over the cross section of the ceramic honeycomb body such time to adjust that thereby the temperature more uniform is designed. In particular, as described above, in the Edge regions of the ceramic honeycomb body according to the State of the art to low temperatures occur, it is special preferred if η increases from the inside to the outside.

Accordingly is η in the region of the body axis preferably smaller than in more distant from the body axis Areas of the honeycomb body. In particular, η of the body axis outwards substantially continuously increase (where "essentially" also jumps in the ratio are possible, especially due to the non-continuous surface design with inlet and outlet channels). In particular, η can be linear or increase quadratically towards the outside.

As As described above, it is known in the art that the inlet channels larger from their cross section are as the outlet channels, or that the cross-sectional area proportion the inlet channels is larger than the Cross-sectional area of the outlet channels, since in this way, the soot build-up in the inlet channels can be compensated.

in the Frame of the present invention, in which a targeted setting the ratio η across the cross section of the honeycomb body, this ratio can but even be reversed, so that ratios η smaller 1 can occur. For example, an embodiment be advantageous in which η in the region of the body axis smaller than 1 and larger at the edge of the honeycomb body is considered 1. In this way, the temperature uniformity be achieved.

Especially however, it is preferred if η despite the described Variation, larger in the entire area of the honeycomb body is as 1. For example, ratios have the same 1,1 proven in the body axis, which up to the edge of the honeycomb body towards preferably equal to η 1.5 increase. Deviations from the stated values are, however, also possible. The proportion of the wall surface between the Blind channels on the entire cross-sectional area is usually between 20% and 60%, preferably about 40%.

The inventive design of the ceramic honeycomb body, in which the area ratio η is used for homogenization of the temperatures, in particular in the filter regeneration, has compared to conventional honeycomb and diesel particulate filters offer a number of key benefits. Since a soot layer of approximately uniform thickness is formed on the entire filter surface after a certain loading, as a consequence of the uneven distribution of η over the cross section of the ceramic honeycomb body in areas with smaller η, a smaller amount of soot is incorporated than in areas with a larger η , In this way, since the soot is the "fuel" for the burn-up, the temperature in certain areas of the ceramic honeycomb body can be adjusted specifically.

So may be in the peripheral areas where due to the above Effects low temperatures occur as in the filter interior, by Providing a larger area ratio η the lower Heat release due to the lower specific burn rate Partially compensated according to the invention be that a larger soot mass stored becomes. The heat release is more uniform in this case and the resulting radial temperature gradients are lower.

All in all can be characterized by use of the ceramic honeycomb body Use filters with higher reliability, which lower tendency to thermal stress and failure of the Show filters by cracking. Also be targeted by the Setting the temperature distribution created opportunities to avoid reaching critical peak temperatures.

Farther Overall, the maximum soot loading can be by the inventive design of the ceramic Increase honeycomb body, so that overall longer Intervals between two regenerations can be set.

These Improvement of filter characteristics and improvement of filter regeneration also leads to lower fuel consumption, especially since the filter regeneration extremely energy-consuming is. An oil dilution can be through Reduce the use of the ceramic honeycomb body.

Brief description of the drawings

embodiments The invention is illustrated in the drawings and in the following Description explained in more detail.

It demonstrate:

1 a schematic representation of an internal combustion engine with a diesel particulate filter according to the invention;

2 a honeycomb body according to the invention in longitudinal section; and

3 a schematic representation of a plan view of a honeycomb body according to the invention.

In the 1 and 2 are schematic representations of the prior art corresponding exhaust aftertreatment systems shown. It shows 1 a schematic representation of an internal combustion engine 110 to which an exhaust system 112 followed. In the following it is assumed that it is the internal combustion engine 110 is a diesel engine, being in the exhaust system 112 a diesel particulate filter 114 is provided. Through this diesel particulate filter 114 Soot particles can be removed from the exhaust gas stream.

The diesel particulate filter 114 includes a cylindrical housing 116 , in which a in the present embodiment, rotationally symmetrical, a total of also cylindrical honeycomb body 118 is arranged.

In 2 is a honeycomb body corresponding to the prior art 118 in a longitudinal section parallel to the body axis 120 shown. The honeycomb body 118 is in this embodiment as extruded molded body made of a ceramic material, for example magnesium-aluminum silicate, preferably cordierite. The honeycomb body 118 will be in the direction of the arrows 121 flows through exhaust gas.

The exhaust gas occurs at an input side 122 in the honeycomb body 118 and leaves this at a home page 124 ,

Parallel to the body axis 120 runs a variety of blind channels 126 , These blind channels 126 include a plurality of inlet channels 128 and a variety of Auslasska channels 130 , The inlet channels 128 are at the exit side 124 locked. In the embodiment shown here are sealing plugs for this purpose 132 intended. Instead of the closure plugs 132 However, it is also possible that the inlet channels 128 to the exit side 124 taper down until the walls of the inlet channels 128 touch and the inlet channels 128 be closed in this way. In this case, the inlet channel 128 in the direction parallel to the body axis 120 a triangular-shaped cross-section.

Accordingly, the outlet channels 130 at the exit side 124 open and are in the area of the entrance side 122 locked.

The flow path of the uncleaned Abga This therefore leads to one of the inlet channels 128 and from there through a filter wall 134 into one of the outlet channels 130 , This is exemplified by the arrows 136 shown.

In the schematic representation according to 2 have the inlet channels 128 and the outlet channels 130 essentially the same opening cross-sections.

In 3 In contrast, an inventive embodiment of a honeycomb body 118 shown schematically. Here is a plan view of the input side 122 shown, with view parallel to the body axis 120 in 2 , To simplify the illustration, only a few blind channels 126 in the area of the body axis 120 and some blind channels near the outer periphery of the honeycomb body 118 shown. The size of the cross sections of the blind channels 126 is in 3 greatly exaggerated. During typical diameter of the honeycomb body 118 lie at about 15 cm, are typical diameter or edge lengths of openings or the cross sections of the blind channels 126 in the range of 1 mm.

In the in 3 shown, non-limiting embodiment is in each case an inlet channel 128 an outlet channel 130 assigned. As described above, however, a plurality of inlet channels can also be assigned to an outlet channel, for example.

3 shows a plan view of the input side 122 of the honeycomb body 118 , Accordingly, the outlet channels 130 hidden and in 3 only shown in dashed lines, whereas the inlet channels 128 are visible.

The inlet and outlet channels have a square cross-section in the illustrated embodiment. In this case, the inlet channels 128 an edge length of the openings a, the outlet channels 130 however, an edge length b. Typically, this edge length lie in the range between 0.9 and 1.3 mm. Alternatively or in addition to the square cross section, other cross-sectional shapes may also be used, for example round cross sections, rectangular cross sections, triangular cross sections, generally polygonal (eg hexagonal) cross sections or mixtures of different cross sections.

At the in 3 illustrated embodiment, the arrangement of the blind channels 126 regularly in such a way that each two outlet channels 130 and two inlet channels 128 along with the intervening walls of the honeycomb body 118 Forming cells, which are arranged in a row recurring. Apart from that over the cross section of the honeycomb body 118 changing area ratio between inlet channels 128 and outlet channels 130 These cells form the smallest recurring units. These cells also have a square cross section with a "pitch" which is in 3 is denoted by A.

As stated above, according to the invention over the cross section of the honeycomb body 118 the ratio η of the proportion of inlet channels 128 at a cross-sectional area unit to the portion of the outlet channels 130 on the cross-sectional area unit over the entire cross section of the honeycomb body 118 varied.

With the in 3 As shown, this ratio yields η to:

In the area of the center of the honeycomb body 118 , ie in the area of the body axis 120 , is at the in 3 illustrated embodiment, the cross section of the outlet channels 130 only slightly smaller than the cross section of the inlet channels 128 , Thus, the ratio η in this range is only just above 1. As described above, however, values below 1 are also conceivable.

In the edge region of the honeycomb body 118 however, as in 3 to recognize the cross sections of the outlet channels 130 significantly smaller than the cross sections of the inlet channels 128 , Thus, here is a ratio η, which is well above 1. the value of η thus increases from the inside to the outside. For example, the ratio η may be from a value of 1.1 in the center of the honeycomb body 118 to a value 1.5 at the edge of the honeycomb body 118 increase.

Finally, it should be mentioned that typically the openings of the inlet channels 128 and the outlet channels 130 in total only about 50% to 70% of the total area of the honeycomb body 118 turn off. The remaining portion is wall portion of the honeycomb body 118 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 4276071 [0005, 0013]

Claims (10)

Ceramic honeycomb body ( 118 ) for use in emission control systems, with an input side ( 122 ) and an output side ( 124 ), comprising a plurality of dummy channels ( 126 ), where the blind channels ( 126 ) a plurality of input-side sealed outlet channels ( 130 ) and a plurality of outlet-side closed inlet channels ( 128 ), characterized in that the ratio η of the portion of the inlet channels ( 128 ) at a cross-sectional area unit to the proportion of the outlet channels ( 130 ) at a cross-sectional area unit over the total cross-sectional area of the honeycomb body ( 118 ) varies. Ceramic honeycomb body ( 118 ) according to the preceding claim, wherein η in the region of a body axis ( 120 ) of the honeycomb body ( 118 ) is smaller than in further from the body axis ( 120 ) areas of the honeycomb body ( 118 ). Ceramic honeycomb body ( 118 ) according to the preceding claim, wherein η is from the body axis ( 120 ) increases outwardly substantially continuously. Ceramic honeycomb body ( 118 ) according to the preceding claim, wherein η increases linearly or quadratically. Ceramic honeycomb body ( 118 ) according to one of the preceding claims, wherein η in the region of a body axis ( 120 ) of the honeycomb body ( 118 ) is between 0.5 and 1.3, and preferably 1.1. Ceramic honeycomb body ( 118 ) according to one of the preceding claims, wherein η at the edge of the honeycomb body ( 118 ) is between 1.3 and 1.7, and preferably 1.5. Ceramic honeycomb body ( 118 ) according to one of the preceding claims, wherein η in the region of a body axis ( 120 ) of the honeycomb body ( 118 ) is smaller than 1 and at the edge of the honeycomb body ( 118 ) is greater than 1. Ceramic honeycomb body ( 118 ) according to any one of claims 1-6, wherein η in the entire honeycomb body ( 118 ) is greater than 1. Ceramic honeycomb body ( 118 ) according to one of the preceding claims, wherein the proportion of the wall surface between the blind channels ( 126 ) is between 20% and 60% of the total area, preferably 40%. Diesel particulate filter ( 114 ) for cleaning exhaust gases of a diesel engine, comprising a ceramic honeycomb body ( 118 ) according to one of the preceding claims.