WO1995006803A1

WO1995006803A1 - Particulate exhaust filter for diesel engines

Info

Publication number: WO1995006803A1
Application number: PCT/DE1994/001013
Authority: WO
Inventors: Friedrich Sperling; Reinhardt Schuster
Original assignee: Friedrich Sperling; Reinhardt Schuster
Priority date: 1993-09-02
Filing date: 1994-09-02
Publication date: 1995-03-09
Also published as: DE4329558A1

Abstract

The invention pertains to a diesel particulate exhaust filter having at least one inorganic filter body mounted in a housing through which flows exhaust gas from the diesel engine and having a device (electrically operated heating element) for combustion (oxidation) of the filtered exhaust particles, characterized in that the filter body is made of a low temperature age hardening material produced from a flowable organic molding material consisting of an oxide mixture including amorphous SiO2 and Al2O3 and/or electrostatic filter ash from high-temperature coal-fired power stations and/or calcined ground bauxite and an alkali silicate solution.

Description

Soot filter for diesel engines

State of the art

The invention is based on a soot filter for diesel internal combustion engines according to the type of the main claim.

The filtering out of soot particles from the exhaust gases of a diesel engine is preferably carried out by oxidizing d. H . Burn these particles, for which a wide variety of methods are known (DE OS 4012719). After the exhaust gases have been cleaned of the soot particles and possibly the latter have been oxidized, the exhaust gases usually flow through a catalyst, through which, on the one hand, a reduction in nitrogen oxide compounds in the exhaust gas and, on the other hand, an oxidation of still unburned hydrocarbons in the exhaust gas can take place. Such a catalytic treatment may also be necessary for the soot particles burned in the soot filter. As is known, the combustion of the soot particles requires a minimum ignition temperature of the exhaust gases, which, as is known, can be achieved in various ways, including by means of electrical heating walls, by means of additional fuels introduced and, as a result, by additional combustion, and by catalytic influence if the temperature of the exhaust gas is not sufficient for soot combustion. Accordingly, the quality of the carrier of such a filter is of particular importance.

In a known soot filter, the carrier body is made of ceramic material and has the shape of a honeycomb body, the longitudinal channels of this honeycomb body being mutually closed and the intermediate walls between the individual longitudinal channels consisting of finely porous, temperature change-resistant ceramic material. In addition to the fact that the production of such a filter body from gas-permeable material is very complex due to the mutually closed channels, it is also expensive to burn the soot once collected in the channels, after which this oxidizes CO to CO 2, penetrate the fine porous walls of the filter In order to burn off the filter body is drum-shaped, a segment of this drum is separated from the exhaust gas stream in order to burn the filter cake accumulated in this segment. By rotating the drum further, this segment is then again exposed to the exhaust gas flow, while another segment can be fired accordingly. Such a system is not only very expensive but also prone to failure.

According to another known method (DE-OS 36 22 623), the excess electrical energy which is present anyway in the diesel vehicle is used for burning off the soot particles by placing a heating coil around a ceramic alternating filter around which accumulates on the outer surface of the wound filter Burn off soot. Naturally, the effective filter area of such filter bodies is very small, so that a relatively very large filter body is required and, accordingly, a relatively long heating coil with the correspondingly high energy consumption. Apart from that, the efficiency of the heating coil is very poor due to the design, since a substantial part of the energy is transmitted to the outer exhaust shell as radiation energy. In addition, the combustion quality is very different, since there is a certain amount of overheating during combustion in the vicinity of the heating wire in order to maintain the sufficient combustion temperature in the area between two courses of the heating coil. In any case, this temperature is above 450 ° C. At full load of the internal combustion engine, the exhaust gases can reach temperatures of up to 600 ° C, but not at idle partial load or when the internal combustion engine is started, so that a relatively difficult temperature control is also required is.

It is therefore not possible to incorporate the electrical heating elements into the ceramic filter body itself, since these heating elements would be destroyed at the high temperatures required in the ceramic firing process. In contrast, during the operation of a soot filter, even with the known soot burning methods, the working temperature remains below 1000 ° C. Another disadvantage of the exposed heating elements is that they are quickly destroyed in the service life of the engine and the acidic atmosphere of the exhaust gases, ie they only have a short lifespan. With filter bodies made of metal, the use of electronically safe heating means would lead to problems of electrical insulation.

Advantages of the invention

The soot filter according to the invention with the characterizing features of the main claim has the advantage, inter alia, that the electrical metallic heating elements can also be incorporated into the filter body before it hardens. The curing temperature is below 550 ° C. copper has, for example, a heat resistance of over 1000 ° C, which cannot be achieved with soot gasification or combustion. In contrast to ceramics, no eutectic can be created with the metallic heating elements. In addition, since the filter body material according to the invention is electrically non-conductive, it is inherently a type of electrical insulator, for example, to a sheet metal housing surrounding the filter. On the other hand, since such a material has a not inconsiderable heat storage capacity, a soot combustion temperature can be changed relatively easily by the electrical heating element, for example 450 ° C can be set, so that with short changes from full load to partial load or idling, heating is not necessary, but the pent-up heat causes the combustion, which in turn generates additional heat in the manner of a chain reaction.

According to an advantageous embodiment of the invention, the filter body consists of a mixture of the flowable inorganic molding compound with catalyst material made of noble metals or of metals based on oxides and sulfides, such as vanadium, molybdenum, tungsten, copper, nickel, cobalt, iron, titanium, Zircon, cerium or rare earth metals and mixtures of these. This gives the filter body the additional effect of a catalyst body. Of course, the wall of the channels can also be coated with a catalyst material such as platinum when using a honeycomb body with alternately closed channels.

According to a further advantageous embodiment of the invention, the flowable inorganic molding compound can be shaped into a filter body provided with thin walls or into a large-area open-pored foam body, through which, in particular, depending on the pore size, targeted accumulation of the exhaust gases can be achieved, or the filter body is formed by sintering still moist Material. Through the filter body can Correspondingly strong turbulence takes place with a particularly good combustion of the soot particles, quite apart from the beneficial effect for the reduction or oxidation catalysis of the 7_b gases.

According to the invention, the soot filter and catalytic converter, also partially made of the same material, can be arranged as separate blocks in series or in parallel in the exhaust. It is also conceivable according to the invention that foamed, sintered or honeycomb-shaped bodies are arranged in such blocks one behind the other or next to one another, also with switchover, with storage spaces in between for gas distribution or swirling.

According to a further advantageous embodiment of the invention, the combustion device works in particular with electrical or catalytic means. While the arrangement and effect of the electrical means has already been described above, the advantage of using catalytic means which can be cold-molded and thus take over or promote part of the oxidation may be mentioned here. Such a catalyst material which promotes the special oxidation of soot can be incorporated into the support material in a pulverized or slurry-like state before it hardens. In this way, not only is there an oxidation of the carbon monoxide on the surface, but the soot particles are oxidized in a possibly viscous gaseous state in the carrier material after their decomposition largely taking place on the surface of the filter.

According to a further advantageous embodiment of the invention, in addition to the combustion device, further control and transmitter elements such as temperature probe and / or oxygen probe can be molded into the filter body before drying out. Thus, a temperature probe can be provided upstream of the heating element which controls the heating operation, that is to say that when the temperature of the Exhaust gas or in the filter body for the combustion of the soot is not sufficient, the heating element switches on and vice versa switches off again at sufficient temperatures. Of course, such a heating element can be designed as a grating that penetrates the filter body or as a heating spiral, possibly also as a heating coil. The natural electrical conductivity of the carbon black can also be used here.

According to a further advantageous embodiment of the invention, the filter body is provided with a jacket (housing) of the same material, which either serves to isolate it from a sheet metal housing or itself serves as a housing. Such a housing can be integrated into the exhaust system of the internal combustion engine. By mixing in metals or inorganic fibers or reinforcing powders such as talc and mica, a significant improvement in the mechanical strength of this jacket can be achieved. Last but not least, an intermediate layer of the same material, which serves only as a connecting element or for the insulation, can be provided between a sleeve and the filter body, in order to counteract above all problems with thermal expansion. The material of the flowable organic molding compound also has the advantage that, despite "cold curing", it has an extraordinarily high mechanical strength, so that connecting elements for the further exhaust system, such as flanges, bolts or screws, can be incorporated into such a jacket.

All of the features shown in the description and the following claims can be essential to the invention both individually and in any combination with one another.

Claims

Soot filter for diesel internal combustion engines with at least one inorganic filter body, which is arranged in a housing through which the exhaust gas of the diesel internal combustion engine flows, and a device (electrically operated heating element) which serves for the combustion (oxidation) of the filtered out soot particles, characterized in that the filter body consists of a material which can be hardened at low temperatures as a product of a flowable organic molding compound made from an oxide mixture with contents of amorphous Si02 and A1203 and / or electrofilter ash

High temperature hard coal power plants and / or calcined ground bauxite and an alkali silicate solution.

Soot filter according to claim 1, characterized in that the flowable inorganic molding compound is coated and / or mixed with catalyst material made of noble metals or from metals based on oxides and sulfides such as vanadium, molybdenum, tungsten, copper, nickel, cobalt, iron, titanium, zirconium, cerium or rare earth metals and mixtures of these.

3. soot filter according to claim 1 or 2, characterized in that the flowable inorganic molding compound is formed into a filter body provided with thin walls (honeycomb body with mutually closed longitudinal channels) or is processed into an open-cell foam body as a filter body or by sintering of still moist material Filter body is processed.

4. soot filter according to one of the preceding claims, characterized in that the combustion device, in particular works with electrical or catalytic means.

5. soot filter according to one of the preceding claims, characterized in that in addition to the combustion device other devices such as sensors (temperature sensors), oxygen probe and the like. be molded into the filter body before curing.

6. soot filter, in particular according to one of the preceding claims, characterized in that the housing of the filter body is made of the same flowable organic molding compound as the filter body.

7. A soot filter according to claim 6, characterized in that the jacket material is reinforced by woven fabrics made of metals or inorganic fibers or from fiber hexels or from reinforcing powders such as talc and mica. Soot filter according to claim 6 or 7, characterized in that a thin closed-pore insulating layer made of the same flowable organic molding compound is arranged between the filter body and the housing.