WO1988009865A1

WO1988009865A1 - Exhaust gas cleaning device for diesel engines

Info

Publication number: WO1988009865A1
Application number: PCT/DE1987/000270
Authority: WO
Inventors: Siegfried Wörner; Peter Reiser; Peter Prinz
Original assignee: Firma J. Eberspächer
Priority date: 1985-12-20
Filing date: 1987-06-12
Publication date: 1988-12-15
Also published as: DE3545437C2; DE3545437A1; UA12339A; EP0357595A1; EP0357595B1; RU2009335C1; DE3776353D1

Abstract

An exhaust gas cleaning device for diesel engines has an exhaust gas soot filter (2) with a filter body (6) supported in a housing (4). The filter body (6) is regenerated by combustion of the soot when its temperature rises above the middle operating exhaust gas temperature range. Also provided is a burner (26) with a combustion air fan (28) whose hot gas side is connected with the flow through the exhaust gas soot filter (2). The filter (6) is supported in the housing in such a manner that at least a large part of its outer surface is heated externally during operation of the burner (26).

Description

Exhaust gas cleaning device for diesel engines

The invention relates to an exhaust gas cleaning device for diesel engines, which has an exhaust soot filter with a filter body supported in a housing, which regenerates itself through soot combustion when its temperature rises above the mean operating exhaust gas temperature range.

In the exhaust gas of diesel engines, soot particles are found in a more or less high concentration, which are polluted with the environment and are even considered to be potentially hazardous to health if they are present in higher concentrations in the breathing air. For this reason, efforts have been underway for some time to detoxify the exhaust gases of diesel engines by at least largely removing the soot particles. Exhaust soot filters have been considered as the most technically promising measure for this, their porosity being so matched that they largely retain the soot particles from the exhaust gas flowing through. However, these soot filters, which are often made of ceramic material because of the required 'temperature resistance to the usual exhaust gas temperatures of diesel engines, have the tendency to become clogged with increasing service life. It had been hoped that the soot particles trapped in the soot filter would burn away to the same extent as new soot particles accumulate, especially when the corresponding diesel engine was in a higher power state. However, it has been shown that this hope is not fulfilled, at least in the case of a large number of diesel engines, in particular those which are not operated or are operated too rarely in operating states with relatively high exhaust gas temperatures. Rather, there is an increasing accumulation of - -

Soot particles in the soot filter, which increasingly comes into the state of undesirably high exhaust gas flow resistance.

The invention has for its object to provide a generic exhaust gas purification device with more effective regeneration, ie more effective soot reduction, of the exhaust soot filter.

To solve this problem, Invention is provided that a burner with combustion air blower is provided, the hot gas side of which is in flow connection with the exhaust gas soot filter, and that the filter body is supported in its housing in such a way that at least a large part of its outer surface during operation of the burner is heated from the outside.

According to the invention, care is therefore taken to ensure that, for the regeneration of the soot filter, temperatures exceeding the normal exhaust gas temperatures prevail, which allow soot combustion, and that the peripheral areas of the soot filter, which are particularly critical with regard to regeneration, are (additionally) heated from its outer surface.

The average or normal exhaust gas temperature range of diesel engines is in the region of 200 to 400 ° C, whereby temperature peaks during operation in the area of maximum performance are not taken into account. The "outer surface" is the area of the outer surface of the soot filter that is not the exhaust gas inlet side or the exhaust gas outlet side. It can be provided that by means of the filter body support according to the invention almost this entire outer surface of the filter body is heated from the outside. The external heating usually takes place indirectly through a filter body casing there. The burner is usually in flow connection with the inflow side of the exhaust soot filter. The inventive design of the exhaust gas soot filter makes it possible to make available a unit which acts in combination as a silencer and soot filter.

Exhaust soot filters often have an essentially prismatic shape with one exhaust gas inlet side and one. Exhaust gas outlet side and a cross section given transversely to the exhaust gas flow direction with circular shape, elliptical shape, oval shape, rectangular shape, square shape or the like. The expression "prismatic shape" is also intended to cover geometries in which the exhaust gas inlet side and / or the exhaust gas outlet side are not at right angles to the flow direction of the soot filter and / or in which the outer (circumferential) surface of the soot filter progresses within certain limits in the direction of its flow varies.

To support the filter body in the housing of the exhaust soot filter, there are, in particular in the case of the geometries mentioned above, a whole series of possibilities which, according to the invention, allow the outer surface or the outer circumference to be heated, but care must be taken to ensure that an outer Flowing the exhaust gases past the filter body is at least preferably to be avoided in order to ensure the effective separation of the soot particles from the entire exhaust gas stream. For example, the filter body could be Support parts in its housing with a circumferential distance and provide a flow-preventing barrier at one point in the annular gap between the filter body and the housing. It is particularly preferred to support the filter body by means of a plurality of ring-like holders which are spaced apart in the direction of flow and which have openings of such a number and size that gas can flow through them, but one of which is closed in order to prevent the above-mentioned free flow of the To prevent annular gaps with exhaust gas. It is pointed out that the terms "ring-like" and "ring-gap" do not mean "circular-shaped", but are meant in a comprehensive sense and also include in particular oval, elliptical and angular, overall closed configurations.

The exhaust gas purification device according to the invention preferably has, as a filter body, a ceramic monolith with non-continuous flow channels, as is known per se. The most common configuration is that the flow channels running essentially in the overall flow direction of the filter body are alternately closed on the inlet side of the filter body and on the outlet side of the filter body, so that the exhaust gas flowing into a flow channel on the inlet side is imperative through the porous Wall of the flow channel in question must pass into one or more adjacent flow channels in order to be able to exit the filter body again on the flow exit side.

The burner is preferably a burner constructed on the principle of an evaporation burner. According to a particularly preferred embodiment of the invention, the burner is provided for regeneration operation during breaks in operation of the diesel engine, in each case after a longer diesel engine operating phase. According to this embodiment, the burner is not allowed to run continuously in order to sufficiently increase the exhaust gas temperature at the inlet into the filter body, but an intermittent operation is preferred in which the soot filter regenerates within a very short time during a standstill phase of the diesel engine becomes. It is advantageous to operate the burner with excess air in order to have oxygen in the soot filter for burning off the soot deposited there. The design mentioned makes the soot burning particularly effective since the hot gases of the burner do not mix with the colder diesel engine exhaust.

Preferably, the exhaust gas purification device has a control device of the burner, which switches on the combustion air blower and a glow plug to ignite the fuel for the burner at the start of the regeneration operation, switches on a fuel pump of the burner with a time delay, after igniting the burner, the glow plug switches off because the burner now turns off continues to burn without glow plug support, and after a certain time the fuel pump has stopped and the combustion air fan continues to run for a short or a long time. This control device preferably controls the aforementioned phases of the regeneration operation automatically. A sensor is preferably provided which directly or indirectly detects the extent of the filter body becoming clogged with soot and either provides a signal that a new regeneration is necessary and / or triggers a regeneration in a suitable manner, preferably when the diesel engine comes to a standstill again. The sensor can, for example, respond to the pressure increase upstream of the soot filter caused by increasing clogging of the filter body, work on the basis of the measurement of gas flow velocities or the like. It is also possible to work with a device for recording the operating time of the diesel engine since the last regeneration.

The separator is preferably designed such that it brings the filter body to a regeneration temperature of more than 550 ° C., most preferably more than 600 ° C. or even more than 700 ° C. The burner does not have to be in operation for the entire regeneration time, since the soot once set on fire burns to the end even without burner support and heat is released in the process. The burner is also preferably designed so that a relatively short regeneration time of, depending on the size of the filter body, from a few minutes to about thirty minutes. Temperatures in the region of 850 ° C can occur during the burning of the soot.

A burner and a combustion air blower are preferably used for the burner, as are already commercially available, in particular from motor vehicle-independent motor vehicle heaters. A particularly preferred area of application of the exhaust gas purification device according to the invention is vehicles, in particular forklifts, which are used in at least largely closed buildings, for example production halls, warehouses or the like. Soot emissions are particularly troublesome under these operating conditions, and regeneration can be carried out conveniently at the end of each shift, for example.

The features of some subclaims, in particular of claim 6, also have an inventive meaning without the relevant claim back-reference or in combination with only a part of the features of superordinate claims.

The invention and further developments of the invention are explained in more detail below with reference to a preferred exemplary embodiment shown in the drawing. The only drawing shows a longitudinal section of an exhaust soot filter and a connected burner.

The exhaust soot filter 2 shown consists essentially of a housing 4 made of sheet steel with a ceramic, monolithic filter body 6 supported therein. The housing 4 is cylindrical in the central region and tapers conically on the left and right to the diameter of an exhaust gas line 8 Exhaust gas flow direction through the soot filter 2 is in the drawing from right to left in accordance with the arrow P, the exhaust pipe section feeding from the right coming from a diesel engine and the exhaust pipe section going to the left leading to the end of the exhaust tract. The filter body 6 is also cylindrical and has only schematically indicated flow channels 10 which run essentially parallel to the common longitudinal axis 12 of the filter body 6 and the housing 4 and are alternately closed on the right and left.

One can also see an intermediate support 14 made of sheet steel, which is essentially cylindrical with flange portions 16 drawn inwards at the left and right ends. The filter body 6 is held axially between the two flange regions 16 by means of resilient intermediate rings 18 made of sufficiently temperature-resistant material. For reasons of thermal expansion, there is a narrow gap in the radial direction between the filter body 6 and the intermediate carrier 14. The intermediate carrier 14 is on the one hand with the aid of two annular holders 20 internally welded to the cylindrical area of the housing 4 so that there is an annular annular gap 22 between the filter body 6 or the intermediate carrier 14 and the housing 4, which is 5 to 20 mm wide radially. The two holders 20 are spaced apart in the axial direction and are each closer to an axial end of the intermediate carrier 14 than to the center thereof.

The holder 20 on the left in the drawing, that is to say downstream, is provided with, for example, circular openings or openings 24 over its entire circumference. These openings could instead be provided in the right holder 20 in the drawing. It would also be possible to provide large and numerous openings 24 in the left holder, while only few and small openings are provided in the right holder 20, or vice versa, so that a very small amount of exhaust gas can flow through the annular gap 22 from front to back. The annular gap 22 axially between the two holders 20 can also be filled with a sufficiently temperature-resistant, flow-through insulating material, for example basalt wool. The soot filter 2 shown and described so far also serves as an exhaust silencer, with the annular space 22 representing a resonance space.

A burner 26 with combustion air blower 28 is connected to the conical, that is to say the inflow-side region of the housing 4 in the drawing. A fuel pump 30 for the fuel of the burner 26, for example diesel oil, and a glow plug 32 for igniting the fuel-air mixture formed in the burner can also be seen. Finally, one can see a control unit 34 for the burner 26 or that of the burner 26 and the combustion air blower 28 existing unit.

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If the soot filter 6 is clogged to a considerable extent with soot particles after the diesel engine has been in operation for several hours, the filter body 6 is regenerated, preferably during a break in operation of the diesel engine. For this purpose, the combustion air blower 28 and the glow plug 32 are first switched on by means of the control unit 34. After about 30 to 60 s, the fuel metering pump 30 is switched on, which pumps fuel into the combustion chamber of the burner 26. If the combustion has started properly there, which can be determined by flame monitoring, the glow plug 32 is switched off; the combustion air blower 28 continues to run. This combustion operation of the burner runs, depending on the size of the soot filter 2, for about 2 to 10 minutes and in the course of this “activation time” a temperature in the order of 600 to 750 ° C. is reached on the filter body 6. Then the burner 26 can be switched off, since at this temperature the burning of the soot on the filter body 6 has started and continues even without burner support. The oxygen required for this can either be taken from the exhaust tract (which still contains residual oxygen in diesel engines) or can be drawn in through the combustion air blower 28 and the burner 26; however, the combustion air blower 28 can also be allowed to continue to run, for example at a lower level. Depending on the size of the soot filter 2, this soot burning-off takes about 5 to 30 minutes, during which time the temperature on the filter body 6 still slightly increases due to the soot combustion or remains approximately the same or slightly can sink. After the burner 26 has been switched off as described by switching off the fuel metering pump 30, the combustion air blower 28 is in any case left to run for a certain time, for example 2 to 4 minutes, in order to no longer ignite a combustible fuel-air mixture in the burner 26 to have.

34 denotes a pressure probe in the space in front of the filter body 6, which responds to increased pressure due to the increasing clogging of the filter body 6 and indicates the need for a new regeneration and / or this, preferably in a subsequent break in operation of the diesel engine, via the Control unit 34 triggers automatically.

Due to the openings 24 in the left holder 20 ', the hot gases of the burner 26 can flow into the annular gap 22 after flowing through the filter body 6 and from there ^' also heat the filter body 6 from its outer surface or its outer circumference. This heating has an effect through the intermediate carrier 14. This external heating is essential in order to bring the peripheral parts of the filter body 6 which are difficult to heat up without the described measure to a sufficiently high temperature. If more than two spaced holders 20 are provided, all or all but one of them are provided with openings 24.

The output of the burner is in the region of 2 to 15 kW, depending on the size of the soot filter 2.

The soot filter 2 can also have a plurality of filter bodies 6 axially one behind the other, it being sufficient if one I Δ -

wants to preclude an external flow of exhaust gas past all filter bodies - to provide a surrounding exhaust gas flow barrier at only one of the filter bodies.

Claims

Expectations

1. Exhaust gas purification device for diesel engines, with a soot filter unit (2) provided in the diesel engine exhaust line (8), which has a filter body (6) supported in a housing (4) and regenerable by soot burnup, with an exhaust gas inlet side, an exhaust gas outlet side and has an outer surface therebetween, with a space (22) between the housing (4) and the outer surface of the filter body (6), and with a burner (26) with a combustion air blower (28), the hot gas side of which has the spacer (22) ^¬ compound in flow so that the filter body (6) Center for Regene¬ of at least a large part of its outer surface is ago heatable, characterized in that the soot filter unit at the same time constructed as a sound absorber with the Abstandsrauiri as a resonance chamber (22) (2); and that the burner (26) is connected upstream before the filter body (6) so that the hot gas according to the Abgasströ ung to a ^¬ inlet side during operation of the burner (26) of the filter body (6) and flows to the resonance chamber ^{^(22).}

That a Ummanteiung (1) is provided on the outer surface of the filter body (6) 2. Abgasreinigungεvorrichtung according to claim 1, characterized in that said resonance is ^¬ space (22) formed between the housing (4) and the Ummanteiung (14).

3. Exhaust gas purification device according to claim 1 or 2, characterized by gas-permeable insulating material in the resonance chamber (22).

4. Exhaust gas purification device according to one of claims 1 to 3, characterized in that a plurality of spaced, ring-like holders (20) are provided for supporting the filter body (6) in the housing (4); and that, with the exception of a closed holder (20), the other holder (s) (20) have flow openings (24).

5. Exhaust gas purification device according to one of claims 1 to 4, characterized in that the filter body (6) is a ceramic monolith with non-continuous flow channels (10).

6. Exhaust gas purification device according to one of claims 1 to 5, characterized in that the filter body (6) has a substantially prismatic shape with a circular or non-circular cross section.

7. Exhaust gas purification device according to one of claims 1 to 6, characterized in that the burner (26) is an evaporation burner.

8. Exhaust gas purification device according to one of claims 1 to 7, characterized in that the burner (26) is provided for regeneration operation in breaks in operation of the diesel engine after several hours of diesel engine operation.

9. Exhaust gas purification device according to one of claims 1 to 8, characterized by a control device (34) of the burner (26) which switches on the combustion air blower (28) and a glow plug (32) at the start of the regeneration operation, a fuel pump with a time delay (30) turns on the burner (26), turns off the glow plug (32) after igniting the burner (26), and after a certain time turns off the fuel pump (30) and the combustion air blower (28) for a short or a long time runs long.

10. Exhaust gas purification device according to one of claims 1 to 9, characterized in that the burner (26) is designed such that it brings the filter body (6) to a regeneration temperature of more than 550 ° C.

11. Exhaust gas purification device according to one of claims 1 to 10, characterized in that a sensor (36) is provided which detects the extent of clogging of the filter body (6) with soot and supplies a regeneration signal and / or triggers the regeneration .

12. Use of the exhaust gas purification device according to one of claims 1 to 11 in a vehicle intended for use in at least largely closed buildings, preferably a forklift.