DE3139565A1 - "METHOD FOR TREATING A HOT EXHAUST FLOW FROM AN INTERNAL COMBUSTION ENGINE" - Google Patents

Description

Process for the treatment of a hot exhaust gas stream an internal combustion engine

In any internal combustion engine, a treatment of the exhaust gases is desirable so that they can easily be in the ambient atmosphere can be discharged. With some machines, especially with the diesel engines, however, one of the main operational problems is that there is still (combustible) Particles are included, which are primarily carbon from an incomplete Combustion of the hydrocarbon fuel under certain operating conditions of the machine results. The amount of carbon produced is also dependent on the operational efficiency the machine.

The presence of a relatively large amount of carbon Particles in the exhaust gas flow of an internal combustion engine can be recognized by a dark smoke. Not only is this smoke extremely undesirable to the eye, it can also be unhealthy in large quantities be. Precautions have therefore already been taken to remove such particles from the exhaust gas flow to be eliminated or to limit their content to a minimum, for example using suitable filters but for which it was found that they were the result of an excessive collection of the particles over time

■ * ■ have become saturated and / or unusable.

It is known that the entire hot exhaust gas stream of an internal combustion engine can be treated by passing the exhaust gases through a filter containing a catalyst which promotes combustion of the trapped particulates. It can be assumed as known that in a diesel engine the production of carbon particles takes place under all operating conditions, whereby it generally applies to every internal combustion engine that the amount and the composition of the exhaust gas flow depends on these operating conditions and changes with them. Thus, the temperature of the exhaust gas stream can change and a diesel engine between slightly above ambient temperature a little over 670 ⁰ C. When the exhaust gas stream is hot enough, the carbon particles retained in a filter are burned off. However, this refreshing or recovery of the filter is not

^ O always under the operating conditions for the diesel engine of a passenger vehicle.

When an internal combustion engine is continuously operated under such conditions that the (contaminating) particles are continuously generated and collected in the filter, then the particles must restrained filter bed can be refreshed with a certain consistency. When the exhaust gas flow is sufficient is hot, then this refreshment is only

borrowed in the introduction of sufficient oxygen-containing hot exhaust gas stream into the filter bed, whereby the carbon particles retained in this as As a result of contact with the exhaust gas flow, they are burned. The combustion of any major accumulation of carbon particles however, it generates temperatures higher than that of the exhaust gas flow. From such excessive temperatures the filter bed can experience thermal shock, damage, or warping.

To get a satisfactory or controlled rate of removal of carbon from an exhaust gas stream without damaging the filter is achieved according to the present invention essentially provides a reaction chamber or filter bed, which is partially consists of a catalytic segment through which at least a portion of the exhaust gas flow passes flows. This catalyst surface can be uniformly incorporated into the bed retaining the particles, or it can be placed only at the upstream end of the bed. So that the main filter bed or several beds can remain functional for the machine despite the operating conditions, the exhaust gas flow or at least a partial amount are preheated. An initial preheating can also take place within the catalytic Segments are achieved through which the exhaust gas flow is passed.

The initial heating of the exhaust gas flow to a temperature which corresponds to at least the "lightoff" temperature of the catalytic converter, can on can be achieved in different ways. After the "Ablicht" temperature of the catalyst is reached, additional Fuel supplied. As soon as the oxidation of the additional fuel begins, preheating can take place of the exhaust gas flow can be weakened or interrupted without the oxidation being quenched.

According to the invention, therefore, the main filter bed

cleaned or refreshed regularly and at periodic intervals. If this treatment is too predetermined Repeated times, this prevents carbon build-up that would otherwise occur in the case of a Failing to remove them to thermal stresses in the filter bed or to its damage to the. Point in time at which such an accumulation would be burned.

According to the invention, a filter of the aforementioned type is thus provided, which is in an exhaust gas flow an internal combustion engine can retain combustible particles contained and by burning this particle is periodically recovered or refreshed. The periodic recovery or refreshment of the The filter element is linked to the distance such solid elements from the exhaust gas flow through the Feeding additional fuel into the filter bed during operation of the machine under such conditions, that the exhaust gas temperatures are not sufficient for the combustion of the additional fuel initiate. The removal of the particles from the exhaust gas flow takes place without endangering the integrity of the filter bed subject to thermal shock or other damage.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing. It shows: 20th

Figure 1 is a schematic representation of a diesel engine that is used to treat an exhaust gas flow has the filter system according to the invention,

Figure 2 is an enlarged view in cross section of the

filter element used in the diesel engine according to FIG. 1,

FIG. 3 shows a graphic representation to illustrate the treatment of the exhaust gas flow in the

Diesel engine according to Figure 1 and

FIG. 4 shows a view corresponding to FIG Filterelomen ta, where I still have /.usüL/..l one electric heater is used.

For the description of the exemplary embodiment, a diesel engine 10 is used as the source of a hot exhaust gas flow an internal combustion engine taken into account. In the case of a diesel engine, the air is passed through an air filter 11 as well a manifold 12 distributed to the individual combustion chambers. The diesel fuel is then controlled in Amount is injected into each one of these combustion chambers by a fuel pump 13, its Flow rate regulated by means of an actuation linkage 14 will.

The hot exhaust gas flow is diverted via the exhaust manifold 16 and a smoke filter 17 through an exhaust pipe 18 fed. Although a muffler could also be used as a silencer in the exhaust pipe such an element is not absolutely necessary and in no way essential to the present process of the Treatment of the hot exhaust gas flow and those to be observed Operating conditions.

When the exhaust gas flow leaves the exhaust manifold 16, it usually has a temperature of about 95 to 650 ^° C. The exact temperature depends on the operating conditions of the engine. When the engine is idling and under a low load, the exhaust gases are still relatively cold or only moderately heated. The particles contained in the exhaust gas stream are consequently retained by the filter bed 19 of the filter 17 along numerous different passages when the exhaust gas stream containing these particles is fed to the filter 17. Although the exhaust gases from an internal combustion engine are primarily composed of multiple gases, they usually contain a sufficient amount of oxygen to sustain at least limited combustion within the flow of the exhaust gases.

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In the embodiment according to FIG. 2, the filter 17 consists of an elongated metallic housing 21, which is provided with opposing walls 22 and 23 and defines an inner reaction chamber 24. the Reaction chamber 24 is mainly filled with at least one filter bed 19 made of a material exists, which is particularly suitable for providing a large number of irregular flow channels. The filter bed 19 or the like, for arrangement in the The beds provided in the reaction chamber 24 provide a series of channels along which the exhaust gas flows. While the flow through these channels, the particulate matter contained in the exhaust gas flow to the individual Canal walls held back.

The filter bed 19 can preferably be made of a metallic, Mesh-like mass, such as steel wool, metal fibers or the like. Are made for an essential Filling the reaction chamber 24 is arranged and shaped. The filter bed 19 can be upstream at both of them and downstream ends by perforated panels 26 and 27 or other similarly rigid transverse walls be supported. The panels 26, 27 are on the wall of the housing 21 to support the filter bed 19 or more such beds are arranged if the filter bed or beds experience a weakening when heated.

The upstream wall 22 of the filter 17 is provided with a Inlet port 28 or an inlet channel provided over which the exhaust gases from the upstream side of the filter bed 19 can be forwarded. Similarly, on the downstream wall 23 of the filter 17 is an outlet channel connected, via which the particle-free exhaust gases are then derived from the filter bed 19. To the filter The best way to reach the exhaust gases is through the filter bed 19 from a suitable gas-permeable medium or a Matrix exist, which are contained in the exhaust gas stream

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Retains solid particles. In order to facilitate or promote the combustion of the retained particles, the exhaust gases fed into the filter bed are initially the segment of the filter bed containing the catalyst warm by touch. As soon as the catalyst is warmed up to the "Ablichf" temperature, additional Fuel fed.

The catalyst bed then has a temperature of about 230 to 290 ^° C. when the injection of the additional fuel begins. The fuel mixture, either liquid or gaseous, is ignited by contact with the catalytic surface, its subsequent combustion being supported by the oxygen contained in the exhaust gas flow. As soon as this combustion of the fuel mixture begins, the catalyst bed does not require any further warm-up energy. As a result of the continued combustion of the fuel mixture, the temperature of the bed rises gradually to about 570 to 925 ^° C. When the exhaust gas flow from the catalyst segment enters the main filter bed 19, it has approximately the same temperature as the catalyst bed. At this increased temperature of the exhaust gas flow, the solid particles retained in the main filter bed are burned, so that the filter bed 19 then essentially no longer contains any solid particles.

A filter with the front or upstream end can be used to perform the method of the filter bed 19 has a catalyst segment or a catalyst bed 21. Such a catalyst segment or the catalyst bed comprises a matrix or filter medium with a thin layer of an oxidizing agent Catalyst material attached to a surface of the matrix. This layer causes oxidation of the additional fuel when it is mixed with

promoted the exhaust gas. This preheating segment or chambers 31 of the filter physically forms preferably part of the bed 19, wherein it preferably fills less than half the volume.

As an alternative, it can also be a segment that is separate from the bed.

The preheating segment 31 is in the front or upstream Part of the housing 21 is arranged and extends transversely to this so that the entire brought up The exhaust gas flow is immediately touched when it enters the reaction chambers 24. To a controlled A fuel injection system is used to preheat the exhaust gas stream provided, primarily a source 32 of additional fuel and equipment comprises a measured amount of the additional fuel in the preheating segment 31 of the Filter bed 19 can be introduced. The fuel source can either use the additional fuel as fine contain atomized liquid or gas to achieve the desired preheating. It can turn out to be act once to a supply of diesel fuel that is used to drive the diesel engine 10. Age-, native it can also be a compressed hydrocarbon gas, such as propane, hydrogen or the like., act that is carried on the motor vehicle, in order to be injected periodically into the preheating segment 31 will. The additional fuel can generally be any volatile substance as well as carbon

° 0 hydrogen, kerosene or various alcohols, but it should be assumed that the fuel used in each case can react within the catalyst chambers 31 in order to achieve the desired combustion.

According to one embodiment, there is the injection system for the additional fuel from a pump, 36 or other suitable metering device, whose

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Inlet side 37 connected to fuel source 32 is. The pump 36 is connected to an injection nozzle 38 which has one or more atomizer nozzles 39 may have. The atomizing nozzles 39 are arranged so that the fuel is upstream in the exhaust gas stream is injected from the preheating chambers 31 containing the catalyst.

If the pump 36 is actuated periodically by a control device 41, then a measured amount of the combustible, fluidized fuel through the nozzles directly into the heated exhaust gas flow when it enters inserted into the chambers 31. The additional fuel is then oxidized by the oxidizing catalyst. However, the supply of additional fuel is only maintained over a period of time that sufficient to remove the carbon contained in the filter bed 19 to burn particles. Then the injection of the fuel is ended, so that then again normal flow of exhaust gases through the filter bed can take place. Before oxidation of additional fuel takes place, however, the catalyst segment 31, in which the exhaust gases are first taken up, on brought to such a high temperature that the oxidation on contact with the additional fuel is initiated with the catalytic surface. The catalytic surface is at least on the "Ablicht" temperature brought so that the additional fuel within the segment 31 is not unburned remain.

The segment 31 can be heated to the desired "light-off" temperature in various ways. A method is preferred in which the exhaust gas temperatures of the exhaust gases which are sufficiently high ^{as a result of 3t> certain operating conditions are used for this preheating.} In normal operation of the machine, however, such high exhaust gas temperatures are rarely reached,

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so that an additional heat source is required.

Such an additional heat source may be, for example, an electrical heating element 42 which is shown as shown in FIG 4 is arranged on the upstream side of the filter bed 19. The heating element 42 is included aligned transversely to housing 21 at the inlet end of the filter. Instead, it can be applied to each other be arranged any point upstream of the filter bed 19.

The heating element 42 can be connected directly to the electrical system of the machine, such as a battery or similar power source, be connected. Its periodic activation can be provided by a timer 43 or some other electrical device Switching device are controlled, which is arranged between the heating element and the battery.

In the graphic representation according to FIG. 3, the temperatures are shown which prevail within a filter body at two different points. These temperature test points are upstream of and within filter bed 19 where oxidation of the injected additional gas is most prevalent. The point A shows the temperature within the front inlet opening 28 of the filter, which is about 205 ⁰ C to the catalytic segment to raise 31 initially to the desired "downlight" temperature of about 260 ⁰ C, the operation of the machine is initially changed by opening the air flap of the carburetor, whereby the temperature of the exhaust gases at point B is increased to about 270 ^° C. This initial heating of the catalytic segment by the exhaust gases can alternatively be achieved by using an electric heater or by increasing the injection of fuel or by throttling the air intake through the carburetor.

After this initial preheating, lasting for about 20 s, at which the temperature within segment 31 reaches a value of about 270 ^° C., the introduction of propane into segment 31 is started. As soon as the propane contacts the heated catalytic surface within the segment 31, the temperature within the filter bed 19 will rise relatively quickly. This segment of the graph not only illustrates the combustion of the additional propane along the curve between points C and D, it also illustrates the combustion of the carbon particles that have been retained on the walls of the filter bed 19. At a maximum temperature of approximately 965 ^° C., which is maintained for approximately 1 minute, the supply of propane is interrupted. The temperature in the filter bed 19 then falls very rapidly in accordance with the course of the curve between points D and E, because then neither additional fuel is fed in nor any carbon particles

more to be burned. The temperature of the filter bed 19 then stabilizes at about 205 ° C, what the Corresponds to the temperature of the exhaust gases.

The periodic heating of the filter bed 19, which precedes the heating of the catalytic segment 31, is carried out on a schedule. This preheating can also be ended by monitoring the Temperature within the filter bed 19 by means of a

Thermostats or the like. can be achieved. A sol-30

rather thermostat either for a control of the electric Heater 42 can be used within the filter bed 19 or using other means to regulate the temperature of the exhaust gases on

upstream end of the filter bed. 35

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Claims (13)

Claims j 1.! Process for the treatment of a hot exhaust gas stream an internal combustion engine, .the a carbon-hydrogen fuel burns, the exhaust gas flow from the engine carrying combustible particles with it and passed through a filter bed made up of a matrix having at least one segment consists of a catalytic material and which is permeable to the exhaust gas flow, while in the Particles contained in the exhaust gas flow are retained by the filter bed, characterized in that that the filter bed is periodically cleaned of the particles retained in it, that first at least a portion of the exhaust gas stream is preheated to a temperature at which additional Fuel oxidizes on contact with the catalytic material, that is then additional Fuel in the preheated catalytic Segment to initiate combustion of the additional fuel and the retained particles is fed in the filter bed, and that while maintaining the feed of the fuel the initial preheating of the partial amount of the exhaust gas flow is interrupted for the catalytic segment is to maintain the oxidation until the filter bed is free of the retained particles is. 2. The method according to claim 1, characterized in that that the catalytic material is arranged in substantially the entire filter bed. 3. The method according to claim 1, characterized in-35 indicates that the catalytic segment is only at the upstream end of the filter bed for contact is arranged with the exhaust gas stream before its entry into the filter bed. 4. The method according to claim 1, characterized in that that the catalytic material is attached to the matrix as a thin coating. 5. The method according to claim 1, characterized in that the segment of the filter bed containing a catalytic material makes up less than about half the volume of the filter bed retaining the particles.
10 6. The method according to any one of claims 1 to 5, characterized characterized in that the additional fuel is fed into the catalytic segment in liquid form. 7. The method according to any one of claims 1 to 5 ", d adurch characterized in that the additional fuel is fed into the catalytic segment in gaseous form will. 8. The method according to any one of claims 1 to 7, characterized in that the additional fuel diesel fuel, Contains or consists of kerosene or alcohol. 9. The method according to any one of claims 1 to 7, characterized in that the additional fuel Contains or consists of hydrogen or propane. ^ov 10. The method according to any one of claims 1 to 9, characterized in that the catalytic material contains an oxidation catalyst or consists of it. 11. The method according to any one of claims 1 to 10, characterized characterized in that the filter bed during operation of the internal combustion engine of the retained particles is cleaned periodically as a function of time. 12. The method according to any one of claims 1 to 11, characterized in that the supply line of the additional fuel in the catalytic segment to regulate the temperature inside the filter bed is regulated. 13. The method according to any one of claims 1 to 12, characterized in that the temperature monitored within the filter bed and the supply of additional fuel to the catalytic Segment is regulated depending on the temperature of the filter bed.