EP0212396A2 - Apparatus for eliminating the soot or the like from the exhaust gases of an internal-combustion engine - Google Patents

Abstract

1. Apparatus for eliminating soot or the like from the exhaust gases of an internal combustion engine, more particular a diesel engine, comprising a micro-wave source (18), a cavity resonator (1) constituting an intermediate member coupled to the exhaust-gas pipe (15) and containing a metal grating (14) in each of its two exhaust-gas openings (6, 8) disposed in the end faces (2, 3), and a tubular soot filter (20) made of dielectric material and disposed in the region of maximum energy density of the electromagnetic field in the flow path of the exhaust gases in the cavity resonator (1), one exhaust-gas opening (6) being situated radially inside the filter cross-section, characterised in that the tubular soot filter (20) extends from one end wall (2) to the other end wall (3) of the cavity resonator (1), the other exhaust-gas opening (8) is situated radially outside the filter cross-section, and the metal gratings (14) are honeycomb gratings and extend from the exhaust-gas openings (6, 8) for a preset axial minimum length into the exhaust-gas pipe (15).

Description

The invention relates to an apparatus and a method for removing soot or the like. from the exhaust gases of an internal combustion engine, in particular a diesel internal combustion engine, with a microwave source which is coupled to an intermediate piece of the exhaust pipe and excites an electromagnetic field there, and with a soot filter made of dielectric material in the intermediate piece in the flow path of the exhaust gases.

From DE-PS 30 24 539 such a device is known in which the soot filter is held by a metal body in the intermediate piece of the exhaust pipe and is flowed through essentially radially by the exhaust gases. The soot filter serves to retain soot particles suspended in the exhaust gases. If the soot deposits exceed a predetermined level, an electromagnetic field is excited in the intermediate piece, whereby the soot is to be burned on the soot filter.

A disadvantage of the arrangement known from DE-PS 30 24 539 is that the soot filter is held by a metallic support body which projects coaxially into the intermediate piece and ends a short distance in front of the end wall of the intermediate piece. The electromagnetic field therefore forms essentially between the end wall of the carrier body and the end wall of the intermediate piece. On the cylindrical peripheral surface of the support body on which the filter on the other hand, very few electrical field lines end. The energy density of the electromagnetic field is therefore negligibly low in the area of the filter mat, the intended combustion of the soot particles deposited on the soot filter cannot be realized for this reason. In contrast, in the area of high energy density, namely on the front wall of the support body, there is no filter mat.

It is also disadvantageous that the exhaust gases flowing into the intermediate piece - due to the support body directed towards the exhaust gas inlet - are directed into the area of low energy density in the intermediate piece, and that smaller soot particles not retained by the filter mat after passing through the filter into a field-free zone , namely the interior of the metallic carrier body and can then flow out undisturbed.

In contrast, the object of the invention is to further develop the device and the method of the type mentioned at the outset in such a way that the soot can be effectively removed in a simple manner.

This object is achieved according to the invention in that the intermediate piece is designed as a cavity resonator and contains a metal grille at each of its two exhaust gas openings, and in that the soot filter is arranged in the cavity resonator in a region of relatively high energy density of the electromagnetic field.

The advantages of the invention are, in particular, that the intermediate piece is designed as a cavity resonator in which an electromagnetic field of high energy density can be generated, and that the soot filter is arranged in the region of relatively high energy density, so that the soot particles separated on the soot filter are constantly or during predetermined intervals are burned by the sufficiently strongly excited electromagnetic field. Due to the attachment of the soot filter in the area of high energy density, the flow lines of the exhaust gases inevitably also run through this area and are therefore - with sufficient amplitude of the excited electromagnetic field - partially burned during the approach to the soot filter, so that the filter only with part of the soot particles entering the resonator are acted upon. The amount of soot deposited on the soot filter is therefore small per unit of time; In order to fall below a certain soot concentration in the exhaust gases flowing off, a filter with lower efficiency or lower flow resistance may be sufficient.

The soot filter can be designed either entirely or in sections in a self-supporting construction. An embodiment of such a self-supporting soot filter has several axially aligned channels. Adjacent channels are closed on opposite end sides, so that the exhaust gases entering the open channels at the end flow through the partition walls made of filter material and on the other end side - in the adjacent channels - emerge from the soot filter. Such an arrangement has the advantage of not requiring a separate support body. If such a self-supporting soot filter is inserted axially into the flow path of the exhaust gases, a particularly homogeneous guidance of the exhaust gases in the resonator and thus also in the resonator area of high energy density is ensured, whereby the soot particles both during their flow movement and during or after deposition on the filter be burned effectively.

In order to achieve a relatively low flow resistance, in a preferred embodiment of the invention the soot filter is designed as a filter mat or filter layer which is arranged on a sufficiently gas-permeable dielectric carrier body. The filter-coated carrier body has the shape of a tube, which extends essentially from the first exhaust opening to the second exhaust opening. According to the invention, one exhaust gas opening of the resonator lies within the filter cross section, and the other exhaust gas opening lies outside the filter cross section, so that the exhaust gases also have to flow through the filter mat and the carrier body when flowing through the cavity resonator. If the exhaust gases are introduced within the filter cross-section, they flow through the filter mat provided with an axial and a radial component and then emerge from the resonator in a flow with, for example, an annular cross section through the other exhaust gas opening lying in a ring around the support body and the filter mat . Alternatively, the exhaust gases can flow through the resonator in the opposite direction, they then pass through an annular exhaust gas opening which surrounds the carrier body and the filters is arranged around, into the resonator and out of the resonator through a circular exhaust gas opening within the filter cross section.

The filter unit consisting of carrier body and filter mat can be provided at the upstream or downstream end with a conical flow divider, which preferably projects into the adjoining exhaust pipe and forms the central core of the annular exhaust opening.

The nominal width of the carrier body is particularly preferably equal to the nominal width of the exhaust gas line adjoining the first end wall, and the exhaust gas opening in this end wall likewise has this nominal width. The exhaust opening on the opposite second end wall is then annular and surrounds the flow divider projecting through this exhaust opening. In this way, unnecessary jumps in diameter between the exhaust pipe and the filter unit are prevented and additional flow resistance is avoided.

According to a preferred embodiment of the invention, a dielectric, gas-tight insert is arranged as a tube with a nominal width that is larger than the diameter of the soot filter and the support body and the exhaust pipe and is arranged concentrically to the soot filter and forms the outer wall of the exhaust gas duct in the region of the resonator. In addition, the end walls of the resonator can be provided with gas-tight dielectric inserts at a predetermined distance. In this way, the hot exhaust gases are kept away from the walls of the resonator, which is therefore less thermally stressed and is subject to less thermal expansion. These inserts are also suitable to direct the gas flow in the resonator through the areas of relatively high energy density.

The resonator is particularly preferably designed and operated as an E _01n resonator, with n = 0, 1, 2 ... Alternatively, however, the resonator can also be designed and operated as an H _01m resonator, m = 1, 2, 3 .. ., although other suitable resonator shapes and operating modes are also possible. In the aforementioned forms of resonator design, the greatest energy density of the excited electromagnetic field is either concentrically formed on the inside or outside around the tubular support body / filter mat, so that the flow of the exhaust gases through the resonator runs before and after flowing through the soot filter in the area of high energy density which can also directly burn the suspended moving soot particles.

The metal grids on the two exhaust gas openings of the resonator ensure that there is sufficient metallic limitation for the microwave field in the area of the exhaust gas openings, as a result of which the high quality of the resonator required to achieve high energy densities and a homogeneous field profile is achieved and the radiation of microwave energy by the exhaust pipe is effectively suppressed. This creates the prerequisite for being able to generate the high energy density required to burn the suspended or deposited soot particles on the soot filter.

The metal grids are advantageously designed as honeycomb grids with a predetermined axial minimum length and extend from the exhaust gas openings into the exhaust gas line. This will change the field configuration in the cavity resonates as little as possible, the areas of high energy density can be specified in the resonator in the known manner.

If a low load on the soot filter is desired, or if filters with different properties are to be used in succession, it is also preferable to insert several resonators with the same or different soot filters into the exhaust line, all resonators being able to be fed by a microwave source. If, on the other hand, the flow resistance is to be reduced further, it may alternatively be desirable to use several resonators in parallel in the exhaust line. The resonators can be coupled by means of coupling elements which couple the microwave energy from one resonator to the adjacent resonator.

So that the resonator and / or the microwave source do not have to be detuned in frequency if possible during operation, the resonator and the microwave source are preferably decoupled thermally from the exhaust gas line as effectively as possible. In addition, it may be necessary to cool the resonator (s) by means of a cooling system. The cooling water system of the internal combustion engine, which allows its cooling water to flow through an outer cooling jacket of the resonator, is particularly advantageous for this purpose. In addition, the resonator is expediently made of a metal with a low thermal expansion value.

In the method according to the invention, the exhaust gases from an internal combustion engine, in particular a diesel internal combustion engine, are continuously or during predetermined Operating intervals passed through a soot filter which is arranged in an electromagnetic microwave field of high energy density in order to burn the soot particles suspended in the exhaust gas stream and deposited on the soot filter.

Advantageous developments of the invention are characterized by the features of the subclaims.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawing.

• Fig. 1 einen Längsschnitt durch eine erste Aus­führungsform der erfindungsgemässen Vor­richtung;
• Fig. 2 einen Längsschnitt durch eine zweite Aus­führungsform der Vorrichtung; und
• Fig. 3 einen Längsschnitt durch eine dritte Aus­führungsform der Vorrichtung.

Show it:

• 1 shows a longitudinal section through a first embodiment of the device according to the invention.
• 2 shows a longitudinal section through a second embodiment of the device; and
• Fig. 3 shows a longitudinal section through a third embodiment of the device.

1 and 2 show a longitudinal section through a first and second embodiment of the device according to the invention. A microwave cavity resonator 1 is inserted as an intermediate piece in an exhaust pipe 15 of a diesel internal combustion engine (not shown). The cavity resonator 1 has a first end wall 2, at a predetermined axial distance from it a second end wall 3 and a peripheral wall 4, which in the example shown forms a circular cylinder and connects the end walls 2 and 3 to one another. The exhaust pipe 15 opens out via a first Ab gas opening 6 in the first end wall 2, and via a second exhaust opening 8 in the second end wall 3 into the cavity resonator 1. The exhaust line 15 either passes in one piece or via flange connections into the end walls 2 and 3 or corresponding inlet or outlet connections. The resonator consists of a metal with a low thermal expansion value, for example stainless steel, and may be coated on its inner surface with an electrically highly conductive layer.

Via a waveguide 12, which ends on the peripheral wall 4 of the resonator 1 and contains a coupling hole 10 opening into the interior of the resonator, microwave energy is fed into the resonator 1 at a frequency of a suitable type from a microwave source 18 with a frequency such that the electromagnetic Field with a desired vibration mode, e.g. an E₀₁₀ mode, which has a decreasing electric field and a decreasing electrical energy density with increasing distance from the axis of the resonator.

The two exhaust openings 6, 8 are each provided with a metal grille 14, which e.g. is formed from a thin metal sheet as a honeycomb grid and a predetermined minimum axial length protrudes into the exhaust line 15 in order to generate a sufficient metallic limitation of the resonator volume for the electromagnetic field and nevertheless to be able to pass the exhaust gases through the resonator 1 without greater flow resistance.

In the resonator 1, a soot filter 20 is arranged coaxially with the exhaust pipe 15, which extends from the first end wall 2 to the second end wall 3. The soot Filter 20 contains a filter mat 22, which is arranged on a gas-permeable, tubular support body 24 made of dielectric material on the inside or outside surface and completely covers this area.

According to the embodiment according to FIG. 1, the nominal width of the first exhaust opening 6 and the nominal width of the carrier body 24 are equal to the nominal width of the exhaust pipe 15 adjoining the first end wall 2. The opposite second end wall 3 closes the tubular support body 24 with a central section at this end 3a, which forms a conical flow divider 13 protruding into the adjoining exhaust pipe 15. Around this central section 3a of the second end wall 3, the second exhaust opening 8 is designed in a ring shape, and the end wall 3 merges into the exhaust line 15 with a conical line section 16. The nominal width of the second exhaust opening is larger than the nominal width of the carrier body 24 and the filter mat 22, so that exhaust gases entering through the first exhaust opening 6 pass through the carrier body 24 and the filter mat 22 with a radial movement component when flowing through the resonator 1 and then through the ring-shaped one second exhaust opening 8 leave the resonator 1 again. The frequency of the electromagnetic field fed by the microwave source 18 through the waveguide 12 and the coupling hole 10 is matched to the dimensions of the resonator 1 in such a way that the resonator 1 resonates with a specific vibration mode, for example the H _01m mode with m = 1 , 2, 3 .., or is operated with the E _01n mode, with n = 0, 1, 2. The index n or m is a measure of the relative axial length L of the resonator, measured in whole multiples of half the resonance wavelength. The generated electromagnetic field burns the soot particles deposited on the filter mat 22, and it can also burn soot particles contained in the exhaust gases if such a vibration mode is used that the energy density in the central area of the resonator increases accordingly.

The structure of the device according to FIG. 2 essentially corresponds to that of FIG. 1 with the exception that the exhaust gases enter the resonator through the annular second exhaust opening 8 and then from the outside with a radial component through the filter mat 22 and the support body 24 in the Enter the central interior of the soot filter and then leave the resonator 1 through the first exhaust opening 6. In order to keep the flow resistance of the device low, the nominal width of the support body 24 is also equal to the nominal width of the first exhaust gas opening 6, which is equal to the nominal width of the exhaust gas line 15 downstream.

The resonator 1 of the device according to FIG. 2 additionally contains a gas-tight dielectric insert 7 which is designed as a tube and has a nominal diameter which corresponds to the nominal diameter of the second exhaust gas opening 8. The insert 7 is arranged over the entire axial length of the resonator 1 from the end wall 2 to the end wall 3. While the insert 7 influences the electromagnetic field in the resonator 1 only insignificantly, it forms an outer boundary wall for the exhaust gas flow, which prevents the exhaust gases from coming into contact with the peripheral wall 4 of the resonator and undesirably heating the resonator.

In the embodiment according to FIG. 2, the resonator can preferably be operated as a H₀₁₀ resonator which receives microwave energy through the waveguide 12 and the coupling hole 10 from the microwave source 18 to excite a H₀₁₀ mode. In this vibration mode, the area of high energy density is in the form of a ring zone, so that the tubular soot filter 20 lies in this excellent high-energy area. The soot particles deposited on the filter mat 22 are therefore burned particularly effectively, and the flow resistance is only slightly increased by the filter.

3 shows a third embodiment of the device according to the invention. The resonator 1 is provided on its two end walls 2 and 3 with equal-sized exhaust gas openings 6, 8, which have the nominal size of the exhaust pipe 15 adjoining on both sides. A metal grid 14 is inserted in each of the two exhaust gas openings 6, 8, which is designed as a honeycomb grid and protrudes into the exhaust pipe 15.

Between the two end walls 2 and 3, a self-supporting soot filter 20 is inserted coaxially with the exhaust line 15, the outer diameter of which is slightly larger than the nominal width of the exhaust line 15 and has a gas-tight outer wall. The self-supporting soot filter 20 contains a plurality of axially aligned channels 21, the intermediate walls of which are made of filter material. Adjacent channels are closed on opposite end sides, so that the exhaust gases entering the channels 21 pass through the intermediate walls and exit at the downstream end in the adjacent channels from the resonator 1 into the exhaust line 15.

Via a coupling device 10, 12 which e.g. consists of a waveguide 12 with a coupling hole 10, the microwave source 18 excites an electromagnetic field in the resonator with a suitable vibration mode, which has the maximum energy density in the area of the soot filter 20 and therefore burns the soot particles deposited on the soot filter.

Due to the inevitable heating of the resonator and due to possible deposition of combustible / non-combustible particles on the resonator walls or on the soot filter 20, detuning of the resonators cannot be prevented during operation. In order to constantly maintain the resonance conditions in the resonators, a tuning device (not shown) is present in each resonator 1, which ensures compliance with the resonance conditions, for example by an automatic mechanical change in the resonator cavity. Alternatively, the corresponding change in the resonance frequency is also possible.

1, instead of the filter mat 22 and its gas-permeable carrier body 24, an inherently rigid ring body made of dielectric, ceramic foam can be provided in the exemplary embodiment according to FIG. 1. This embodiment is advantageous if a large filter with a relatively low flow resistance can be implemented in a relatively small resonator volume.

2, the filter mat 22 and its gas-permeable support body 24 can be replaced by a soot filter 20 with axially aligned channels 21 according to the example of FIG. 3, this soot filter 20 in the gas-tight dielectric Insert 7 is arranged.

Claims (23)

1. Device for removing soot or the like. from the exhaust gases of an internal combustion engine, in particular a diesel internal combustion engine
- With a microwave source (18),
- which is coupled to an intermediate piece of the exhaust pipe (15) and excites an electromagnetic field there,
and with a soot filter made of dielectric material in the intermediate piece in the flow path of the exhaust gases,
characterized,
- The intermediate piece is designed as a cavity resonator (1) and contains a metal grille (14) at each of its two exhaust gas openings (6, 8),
- And that the soot filter (20) in the cavity (1) is arranged in a region of relatively high energy density of the electromagnetic field. 2. Device according to claim 1,
characterized,
- That the soot filter (20) is fully or partially self-supporting. 3. Device according to claim 2,
characterized,
- That the self-supporting soot filter (20) contains several axially aligned channels with partitions made of filter material,
- And that adjacent channels are closed on opposite end sides. 4. The device according to claim 1,
characterized,
- That the soot filter (20) forms a filter mat (22) which surrounds a gas-permeable carrier body (24) made of dielectric material on at least one surface. 5. The device according to claim 4,
characterized,
- The filter-coated carrier body (24) is designed as a tube and extends essentially from the end wall (2) to the end wall (3) of the cavity resonator (1).
- That the first exhaust opening (6) on the first end wall (2) of the resonator (1) within the filter cross section,
- And the second exhaust opening (8) is outside the filter cross section. 6. The device according to claim 5,
characterized,
- That the second exhaust opening (8) on the second end wall (3) of the resonator (1) concentrically surrounds the filter-coated carrier body (24). 7. The device according to claim 6,
characterized,
- That the section (3a) of the second end wall (3) surrounded by the second exhaust opening (8) has a conical flow distributor (13) projecting into the adjoining exhaust line. 8. Device according to one of claims 5 to 7,
characterized,
- That the first exhaust opening (6) is equal to the nominal size of the connecting exhaust pipe (15). 9. Device according to one of claims 5 to 8,
characterized,
- That the nominal width of the carrier body (24) is equal to the nominal width of the exhaust pipe connected to the first end wall (2). 10. The device according to one of claims 4 to 9,
characterized,
- That the soot filter (20) has self-supporting volume areas. 11. The device according to one of the preceding claims,
characterized,
- That a dielectric gas-tight insert (7) as a tube with a compared to the diameter of the soot Filters (20) or the support body (24) and the exhaust pipe (15) enlarged nominal size is arranged concentrically to the soot filter (20)
- And forms the outer wall (4) of the resonator (1) for the exhaust duct. 12. The device according to claim 11,
characterized,
- That the nominal width of the gas-tight insert (7) is equal to the width of the second exhaust opening (8). 13. Device according to one of the preceding claims,
characterized,
- That the resonator (1) is designed and excited as an E _01n resonator, with n = 0, 1, 2 .... 14. The device according to one of claims 1 to 12,
characterized,
- That the resonator (1) is designed and excited as an H _01m resonator, with m = 1, 2, 3 .... 15. Device according to one of the preceding claims,
characterized,
- That the metal grid (14) are designed as a honeycomb grid with a predetermined axial minimum length. 16. The apparatus of claim 15,
characterized,
- That the metal grille (14) extend from the exhaust openings (6, 8) a predetermined axial minimum length into the exhaust pipe (15). 17. Device according to one of the preceding claims,
characterized,
- That several resonators (1), each with a soot filter (20) are inserted in series in the exhaust pipe (15). 18. Device according to one of claims 1 to 16,
characterized,
- That several resonators (1), each with a soot filter (20) are inserted parallel to each other in the exhaust pipe (15). 19. Device according to one of claims 17 or 18,
characterized,
- That the several resonators (1) for microwave coupling have a feed coupling (10, 12) and each have a coupling element in common walls of the resonators. 20. Device according to one of the preceding claims,
characterized,
- That the / the resonators (1) are thermally decoupled from the exhaust pipe (15). 21. Device according to one of the preceding claims,
characterized,
- That the coupling line (12) leading to the microwave source (18) is thermally decoupled from the microwave source (18). 22. Device according to one of the preceding claims,
characterized,
- That the / the resonators (1) can be cooled with the cooling water system of the internal combustion engine. 23. A method for removing soot or the like. from the exhaust gases of an internal combustion engine, in particular a diesel internal combustion engine, in which the soot particles of the exhaust gases are filtered out,
characterized,
that the exhaust gases are passed through an electromagnetic microwave field of high energy density and filtered there,
- Which burns the soot particles suspended in the exhaust gas stream and the soot particles deposited on the soot filter.

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