EP0191437B1 - Device and process for removing soot or the like from the exhaust gases of an internal-combustion engine - Google Patents

Abstract

PCT No. PCT/EP86/00066 Sec. 371 Date Dec. 4, 1986 Sec. 102(e) Date Dec. 4, 1986 PCT Filed Feb. 7, 1986 PCT Pub. No. WO86/04640 PCT Pub. Date Aug. 14, 1986.A device and method for separating soot or other impurities from the exhaust gases of an internal-combustion engine, particularly a diesel internal-combustion engine, comprises a microwave source that is coupled to the intermediate section of the exhaust pipe that is constructed for the development of an electromagnetic field, an effective burning of the soot with a low flow resistance, the intermediate section being developed as a cavity resonator and at its exhaust gas inlet and exhaust gas outlet, is equipped with a metal grid, and an insert made of a dielectric material in the cavity resonator concentrates the exhaust gas flow in the area of high energy density of the electromagnetic field.

Description

The invention relates to a device for removing soot from the exhaust gases of an internal combustion engine, with a microwave source, a cavity resonator which is coupled as an intermediate piece to the exhaust pipe of the internal combustion engine and an exhaust gas inlet in an end wall and an exhaust gas outlet on an opposite end wall has, and each with a metal grid in the exhaust gas inlet and the exhaust gas outlet.

Such a device is known from DE-A-3 024 539 in which the intermediate piece contains a soot filter made of dielectric material in the flow path of the exhaust gases, through which the exhaust gases flow essentially radially and which retains soot from the exhaust gases. If the soot deposits on the soot filter exceed a predetermined level, an electromagnetic microwave field is excited in the intermediate piece, whereby the soot is to be burned. It is disadvantageous that the soot particles on the soot filter impair the flow resistance, even if the soot particles deposited there are burnt off from time to time. In addition, since the cavity resonator is provided at its inlet and outlet with simple metal grids, which have a relatively small hole area for sufficient metallic limitation of the microwave field in the cavity resonator, the flow resistance for the exhaust gases is additionally increased by this metal grille, which leads to a loss in performance of the Internal combustion engine leads.

From US-A-3 461 261 a device is known in which a cavity resonator is provided with a tubular ceramic insert, through which filamentary or particulate material or fluids are passed and subjected to a heat treatment there. If the ceramic insert - in one embodiment of the known device - remains open at its inlet and its outlet, the relatively large radiation losses of the microwave field make resonance operation and thus an effective high-temperature treatment in the ceramic insert impossible. However, if - in another embodiment of this known device - an iris diaphragm is attached to the inlet and outlet of the ceramic insert, a homogeneous and efficient flow of fluids through the ceramic insert is made impossible.

In contrast, the object of the invention is to develop a device according to the preamble of the main claim in such a way that an effective combustion of the soot particles floating freely in the exhaust gases takes place with low flow resistance.

This object is achieved in the device of the type mentioned in that the cavity resonator contains a first gas-tight ceramic insert, which is designed as a tube and axially aligned with the exhaust pipe from the exhaust gas inlet to the exhaust outlet, and that the metal grille to achieve a low Exhaust gas flow resistance are designed as honeycomb grids which extend into the exhaust gas line with a predetermined minimum axial length in order to limit the microwave field in the cavity resonator sufficiently.

The advantages of the invention are, in particular, that the exhaust gas flow in the tubular ceramic insert is passed homogeneously through that region of the resonator in which the greatest energy density of the electromagnetic field is present. Due to the design of the metal grille as a honeycomb grille, the exhaust gases can flow through the cavity resonator without greater flow resistance. In addition, since the honeycomb grids protrude into the exhaust pipe over a predetermined minimum axial length, a sufficient metallic limitation for the microwave field generated in the cavity resonator is realized at the same time, so that high energy densities and homogeneous field profiles of the excited electromagnetic waves arise within the ceramic insert, which are necessary to burn the soot particles contained in the homogeneous exhaust gas flow during their flight through the ceramic insert.

The invention thus realizes a device which is simple in terms of construction, in which built-in elements in the exhaust gas line or in the cavity resonator which form flow resistances are avoided and, moreover, the maintenance work required for a soot retention device is dispensed with.

The device is preferably switched on continuously or at predetermined intervals during the operating time of the internal combustion engine in order to continuously burn the soot particles flowing into the resonator.

According to a particularly preferred embodiment of the invention, the exhaust gas inlet and the exhaust gas outlet are arranged opposite one another on the two end walls of the resonator and have essentially the same nominal width as the exhaust gas line. The two end walls are connected by a peripheral wall, preferably with a circular cross section, the nominal width of which is determined by the resonance frequency with which the resonator and the microwave source are operated. Due to the operating frequencies approved by the postal authorities, the nominal size of the resonator must be chosen larger than that of the exhaust pipe.

The resonator is particularly preferably designed as a cylindrical E _oio resonator and operated with the vibration mode E _olo , and the flue gas pipe is preferably _flange- mounted centrally on the end face. The electric field lines have their maximum and in the center of the resonator decrease steadily towards the outside, in the central area there is a high energy density. In this embodiment of the invention, the ceramic insert is designed as a tube with the nominal size of the exhaust pipe and runs in alignment with the exhaust pipe from the inlet to the outlet of the resonator. In this embodiment, the insert guides the exhaust gas flow homogeneously through the resonator and thereby prevents the exhaust gases from coming into contact with the metallic walls of the resonator, as a result of which undesirable heating of the resonator, which leads to a change in the resonance frequency, is counteracted. For this purpose, the application is chosen so that on the one hand it influences the electromagnetic field as little as possible, that is, it should consist of a material with a low dielectric constant and a low loss factor, which moreover provides the best possible thermal insulation. For this reason, glass or a loss-free ceramic material are particularly suitable.

Alternatively, the resonator can be designed and operated as a Ho11 or as an E ₀₂₀ resonator, it also being possible, of course, to design and operate in other suitable vibration modes.

If the resonator is designed and operated as a H _o11 or E _o2o resonator, the area of high energy density coincides with a ring zone around the axis of rotation of the resonator. A second ceramic insert in the form of a hollow or solid cylinder with a reduced nominal width, which is closed at the end, is then preferably inserted centrally and axially into the resonator, which guides the exhaust gas flow into an annular channel between the first and second ceramic insert through the resonator.

The second ceramic insert tapers preferably conically at its ends and protrudes with the end cones into slightly conical connecting sections of the exhaust pipe, which are also again, for. B. in the range of the nominal size, which contains honeycomb-shaped metal grid.

In general, all E _01n resonators or Holm resonators are suitable, n = 0, 1, 2, 3 ... or m = 1, 2, 3 ..., which are operated accordingly. 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 λ _0/2 . Longer structural lengths, ie vibration modes / resonators with a higher index n or m can be advantageous in particular if the residence time of the soot particles has to be increased for sufficient combustion.

Should it - e.g. B. because of a very high exhaust gas speed or too low power output of the microwave source - prove necessary to increase the length of stay in the combustion zone, it is also preferable to insert several resonators in series into the exhaust line. Adjacent resonators can then be arranged adjacent to one another and have between them a common end wall with an exhaust gas opening, each of which carries a honeycomb grid. This arrangement requires only one coupling of the microwave source, which is preferably carried out via a waveguide and a coupling hole if coupling elements, for. B. coupling holes or coupling loops are incorporated.

If, on the other hand, it proves necessary to further reduce the low flow resistance caused by the honeycomb grid and the resonator in order to achieve better engine performance, then according to the invention several resonators can also be used in parallel in the exhaust pipe.

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 thermally decoupled 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 is particularly advantageously suitable for cooling the cavity resonator (s). For this purpose, the cavity resonator can be provided with a cooling jacket and constantly charged with cooling liquid between the resonator wall and the cooling jacket. In addition, the resonator is expediently made of a metal with a low thermal expansion value.

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 erfindungsgemässe Vorrichtung ;
• Fig. 2 einen Querschnitt durch die Vorrichtung der Fig. 1 längs der Linie 11-11 ;
• Fig. 3 einen Längsschnitt durch eine zweite Ausführungsform der Vorrichtung ;
• Fig. 4 einen Querschnitt längs der Linie A-B der Fig. 3 ;
• Fig. 5 einen Längsschnitt durch eine dritte Ausführungsform der Vorrichtung ; und
• Fig. 6 einen Längsschnitt durch eine vierte Ausführungsform der Vorrichtung.

Show it :

• 1 shows a longitudinal section through an inventive device.
• FIG. 2 shows a cross section through the device of FIG. 1 along the line 11-11;
• 3 shows a longitudinal section through a second embodiment of the device;
• 4 shows a cross section along the line AB of FIG. 3.
• 5 shows a longitudinal section through a third embodiment of the device; and
• Fig. 6 shows a longitudinal section through a fourth embodiment of the device.

1 and 2 show a first embodiment of the device in longitudinal and cross section. 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 here a second end wall 3 and a circular cylindrical peripheral wall 4, which connects the outer circumference of the end walls 2 and 3 to one another. The end walls 2 and 3 have concentrically to the axis of rotation an exhaust gas inlet 6 or an exhaust gas outlet 8 with approximately the nominal size of the exhaust pipe 15. The exhaust pipe 15 goes in one piece at the inlet 6 and at the outlet 8 or via a flange connection into the forehead walls 2, 3 or a corresponding inlet or outlet connection. The resonator consists of a metal with a low thermal expansion value, e.g. B. made of 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 cavity resonator, microwave energy 18 of a suitable type is fed into the resonator 1 at a frequency such that the resonator the electromagnetic field with a desired shrinkage mode, e.g. B. forms an E _oio resonance, which has a decreasing electric field and a decreasing electrical energy density with increasing distance from the axis of rotation.

The exhaust gas inlet 6 and the exhaust gas outlet 8 are each provided with a honeycomb-shaped metal grille 14, which is formed from thin metal sheet and protrudes a predetermined minimum length into the exhaust gas line 15 in order to generate a sufficient metallic limitation of the resonator volume for the electromagnetic field and nevertheless the exhaust gases without to be able to conduct greater flow resistance through the resonator.

In the resonator 1, a first tubular ceramic insert 5 is attached - from end wall to end wall - the nominal width of which is equal to that of the exhaust pipe 15. The insert 5 is arranged centrally and axially between the exhaust gas inlet 6 and the outlet 8 in alignment with the exhaust gas line 15 and conducts the exhaust gases through the resonator region of high energy density without changing the cross section. Since the nominal width or the diameter of the resonator 1 is substantially larger than the nominal width of the exhaust pipe 15 and is determined by the resonance frequency with which the device - according to the postal regulations - may be operated, the exhaust gas flow through the insert 5 is at a greater distance from of the resonator wall, which thereby remains relatively cold and experiences little or no thermal expansion.

3 and 4 show a structure corresponding to FIG. 1, in which an H _o , _o resonator with spaced end walls 2, 3 and the intermediate peripheral wall 4 and the exhaust gas inlet 6 and outlet 8 is inserted into the exhaust line 15, which receives microwave energy to excite the H _o , _a oscillation through a waveguide 12 and the coupling hole 10. In this mode of vibration, the area of high energy density is in the form of a ring zone. Therefore, in order to guide the exhaust gases as they pass through the resonator 1 in this ring zone, a cylindrical second ceramic insert 7, which tapers conically at its ends, is inserted axially and centrally in the resonator 1, the end cones of the second ceramic insert 7 being passed through the inlet 6 and the outlet 8 protrude into the exhaust pipe 15, which has correspondingly conical sections 17.

In the embodiment shown, the honeycomb-shaped metal grid 14 is mounted concentrically around the end cone of the second ceramic insert 7 in the region of the inlet 6 and the outlet 8. In order to also delimit the ring zone from the outside, the first ceramic insert 5 in the form of a tube is also inserted concentrically with the second ceramic insert 7 in the resonator.

In FIG. 5, several e _oio resonators, all of which are constructed in accordance with FIG. 1, are inserted in series into an exhaust gas line 15. Adjacent resonators 1 are arranged adjacent to one another and have a common end wall 3 which, like the outer end walls 2, contains a central exhaust opening 9 which has the nominal width of the exhaust line 15 and each carries a honeycomb-shaped metal grille 14 for the electromagnetic delimitation of the resonator interior. Between the inlet 6 of the first resonator 1, the exhaust openings 9 and the outlet 8 of the last resonator 1, tubular ceramic inserts 5 with the nominal size of the exhaust line 15 are inserted, which guide the exhaust gas flow centrally. One of the resonators 1 is connected to the microwave source 18 via a hollow line 12. The common end walls 3 also each have a coupling member 20, for. B. a coupling loop or a coupling opening to feed the subsequent resonators with microwave energy.

According to FIG. 6, an e _oio resonator according to FIG. 1 and a H _on resonator according to FIG. 3 are inserted in series into the exhaust line 15. Both resonators are fed via a separate hollow line 12 from the microwave source 18.

The individual or the several resonators connected in series or in parallel can be thermally decoupled from the exhaust pipe in order to achieve the highest possible frequency constancy (not shown). The individual resonator 1 can also be thermally decoupled from the microwave source 18 (not shown). In addition, the resonators can be cooled by means of cooling systems which, for. B. can be integrated into the cooling systems of the internal combustion engines.

Claims (14)

1. Apparatus for the elimination of soot from the exhaust gases of an internal combustion engine, comprising a microwave source (18), a cavity resonator (1) which, as an intermediate component, is coupled to the exhaust gas pipe (15) of the internal combustion engine and has an exhaust gas inlet in one end wall (2) and an exhaust gas outlet (8) at an opposite end wall (3), and a respective metal grid (14) in the exhaust gas inlet (6) and in the exhaust gas outlet (8), characterised in that the cavity resonator (1) contains a first gas-tight ceramic insert (5) which is constructed as a tube and extends axially in alignment with the exhaust gas pipe (15) from the exhaust gas inlet (6) to the exhaust gas outlet (8), and that the metal grids (14) are constructed as honeycomb grids to achieve a slight exhaust gas flow resistance and extend by a predetermined minimum axial length into the exhaust gas pipe (15) for sufficient metallic limitation of the microwave field in the cavity resonator (1).

2. Apparatus according to Claim 1, characterised in that the exhaust gas inlet (6) and the exhaust gas outlet (8) have substantially the same nominal diameter as the exhaust gas pipe (15), and that the circumferential wall (4) between the end walls (2, 3) of the cavity resonator (1) has a circular cross-section of greater nominal diameter than the exhaust gas pipe (15).

3. Apparatus according to Claim 1 or 2, characterised in that the cavity resonator (1) is constructed and excited as an E_ol,-resonator, in which n = 0, 1, 2..., and that the first ceramic insert (5) is constructed as a tube having the nominal diameter of the exhaust gas pipe (15).

4. Apparatus according to Claim 1 or 2, characterised in that the cavity resonator (1) is constructed and excited as an H_o,_m resonator, in which m = 1, 2, 3..., and that a second ceramic insert (7) is constructed as a cylinder of reduced nominal diameter which is closed at the front end and which is inserted centrally and axially into the cavity resonator (1) to produce a flow channel of annular cross-section.

5. Apparatus according to Claim 4, characterised in that the second ceramic insert (7) narrows in a tapered shape at its ends.

6. Apparatus according to any one of the preceding claims, characterised in that a plurality of cavity resonators (1), each with at least one gas-tight ceramic insert (5), are fitted in series in the exhaust gas pipe (15).

7. Apparatus according to Claim 6, characterised in that adjacent cavity resonators (1) are arranged to adjoin each other and in each case have a common end wall (3) with an exhaust gas opening (9) carrying the metal grid (14).

8. Apparatus according to Claim 7, characterised in that, for microwave coupling, the plurality of cavity resonators (1) have a supply coupling (10, 12) and in each case a coupling member (20) in the common end walls (3).

9. Apparatus according to any one of Claims 1 to 5, characterised in that a plurality of cavity resonators (1) are fitted parallel to each other in the exhaust gas pipe (15).

10. Apparatus according to any one of the preceding claims, characterised in that the resonator(s) (1) is/are thermally uncoupled from the exhaust gas pipe (15).

11. Apparatus according to any one of the preceding claims, characterised in that the coupling line (12), leading to the microwave source (18), is thermally uncoupled from the microwave source.

12. Apparatus according to any one of the preceding claims, characterised in that the resonators(s) (1) is/are able to be cooled by a cooling system.

13. Apparatus according to Claim 12, characterised in that the cooling system communicates with the cooling water system of the internal combustion engine.

14. Apparatus according to any one of the preceding claims, characterised in that the resonator (1) is made of a metallic material with a low thermal expansion value.

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