GB2080140A

GB2080140A - Apparatus for removing soot from exhaust gases

Info

Publication number: GB2080140A
Application number: GB8111313A
Authority: GB
Original assignee: Filterwerk Mann and Hummel GmbH
Current assignee: Mann and Hummel GmbH
Priority date: 1980-06-28
Filing date: 1981-04-10
Publication date: 1982-02-03
Also published as: FR2485623A1; SE450027B; DE3024539C2; DE3024539A1; SE8102424L

Abstract

Apparatus for removing carbon or soot from the exhaust gases of an internal combustion engine comprises a metal filter housing enclosing a filter insert (11) made of ceramic fibres, accumulated soot being periodically burnt off the insert (11) by heating it by means of microwaves from a generator (20) which is connected to the unfiltered gas chamber (15). Perforate metal walls (12, 27, 29) block the passage of the microwaves to the inlet and outlet openings of the housing, and a further filter insert (30) excludes soot from the generator. The generator may by controlled by a timer or pressure switch responding to clogging of insert (11). <IMAGE>

Description

SPECIFICATION Apparatus for removing soot from the exhaust gases of an internal combustion engine The present invention relates to an apparatus for removing soot from the exhaust gases of an internal combustion engine and especially a diesel engine.

The temperatures of exhaust gases of internal combustion engines vary in dependence upon the state of loading. If it is intended with soot particles deposited in filters traversed by exhaust gases to burn such carbon particles into carbon dioxide, then, besides the presence of oxygen, there are required temperatures which the exhaust gases during idling or part load generally do not possess and which can only be obtained by supplying extraneous energy.

In DE-OS 27 56 570 there is proposed a heatable exhaust gas filter for an internal combustion engine in which for burning-up soot particles deposited on a filter bed of metal fibres an electric heating element arranged upstream can be caused to assume sufficiently high temperatures. Because the exhaust gases flow through the heated filter bed and thereby dissipate heat, a relatively high energy requirement is necessary for the heating element.

In DE-OS 27 50 960 there is disclosed a soot filter in the exhaust gas flow of compression combustion engines in which the soot deposited on ceramics fibres should burn off automatically. As stated above, this is not always successful in every case.

It is an object of the invention to provide known soot filters with simple means so that deposited soot can be burnt off at any operational state of the internal combustion engine with a minimum supply of electric energy.

According to the present invention there is provided apparatus for removing carbon or soot from the exhaust gases of an internal combustion engine, comprising a metal filter housing and a filter insert which in the filter housing separates an unfiltered gas chamber from a filtered gas chamber provided with a filtered gas outlet opening, and with said filter insert having a highly temperature-resistant, filter means having "depth effect," for filtering out soot; and an electrically operated device for the controlled burning-off of the soot deposited on the filter means, characterised by the feature that the apparatus includes a microwave generator for emitting microwaves for heating the soot deposited on the non-metal filter means and wich is connected to the unfiltered gas chamber, and that gas-permeable walls blocking the passage of the generated microwaves are arranged in the filter housing between the microwave outlet opening of the generator and the unfiltered gas inlet opening and also downstream of the filter means.

The advantage of the microwave generator is that as such it only heats up the soot and causes it to combust by means of the internal heat so obtained. Undesirable dissipation of heat to any substantial extent does not occur.

The energy required is so small that the internal combustion engine can produce such itself without difficulties. The relatively small overall volume of the generator also permits its accommodation with internal combustion engines of vehicles, for example, lorries.

To prevent the contamination of the microwave generator, a development of the invention provides for the microwave outlet opening of the generator to be covered by a non-metallic highly temperature resistant filter means. The microwave generator is preferably adapted to be switched-on and -off in adjustable time intervals by an electric switching device. Variable time intervals for operating make it readily possible to select the correct time and duration of use of the microwave generator in adaptation to the operational employment of the internal combustion engine.

Another proposal according to the invention provides an electric switching device by means of which upon exceeding a predetermined flow resistance through the filter insert the generator may be switched on and, after a predetermined time interval, may be switched off. In this development, the flow resistance signals the nature and quantity of the soot deposited in the filter insert, so that, with changing operational conditions of the internal combustion engine, the soot may be automatically burnt-off at the correct time.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an axial section of an embodiment of an apparatus for removing carbon or soot; and Figure 2 is a section taken qn the line 2-2 of Fig. 1.

A filter housing 1 has a housing jacket 2 which at the end face is closed by bases or end plates 3 and 4. An unfiltered gas inlet pipe 5 which defines unfiltered gas inlet opening 6 leads into the base plate 3. Leading from the plate 4 is the filtered gas outlet pipe 7 which defines filtered gas inlet opening 9.

The housing jacket 2, plates 3 and 4 and unfiltered gas inlet pipe 5 and filtered gas outlet pipe 7 are made of steel sheet.

An annular filter insert 10 has a tubular, highly temperature resistant filter means or medium 11 having "depth effect", which in the embodiment is made of silicon dioxide fibres, also of a non-metallic material. By the tem "depth effect" is to be understood that the filter means 10 separates solid impurities, particularly carbon soot, from the exhaust gases not only at the outer circumference but also over a considerable radial depth. The filter medium 11 encloses a metal wall 1 2 of perforated sheet formed as a support tube which at one end face is welded to a metal disc 1 3 and at the other end face is welded to a metal ring flange 14 hermetically secured to the housing jacket 2.The filter insert 10 separates an unfiltered gas chamber 1 5 provided with an unfiltered gas inlet opening 6 from a filtered gas chamber 1 6 provided with a filtered gas outlet opening 9.

An electrically operated device for controlled burning of the soot or carbon deposited on the filter means 11 comprises a microwave generator 20, which by means of parts 21, 22 and flanges 23, 24 adapted as a hollow conductor 25, is connected to the filter housing 1 and in the switched-on, operational state the generator 20 transmits microwaves into the filter housing 1 to bring the particles of soot deposited on the filter means to temperatures at which they are burnt and oxidised to carbon dioxide.

To prevent the transmitted microwaves from accidentally leaving the filter housing 1 through the unfiltered gas inlet opening 6 or the filtered gas outlet opening 9, walls 1 2 and 27 made of perforated metal sheet are located in the filter housing 1 between the outlet opening 26 of the microwave generator 20 and the unfiltered gas inlet opening 6 and downstream of the filter medium. These walls of which the wall 1 2 as stated above is formed as a support tube, are permeable to the exhaust gases but block the passage of the generated microwaves.

If a filter medium is used which has sufficient ridigity as such and therefore does not require any support, it is possible as with wall 27 and base 3 to locate a further gas-permeable wall 29 close to the base 4 barring the passage to microwaves.

A non-metallic, highly temperature resistant non-metallic filter means or medium 30 of silicon dioxide fibres is located at right angles in the part 21 of the hollow conductor 25 and thus covers the microwave outlet opening 26 of the generator 20, to prevent soot or carbon from entering the generator 20.

An electric switching device formed as a time switch and connected via electric leads 37, 39 to a correspondingly dimensioned electric generator (not shown) of the internal combustion engine acts via electric leads 41, 42 on the microwave generator 20 and switches it on and off in adjustable time intervals.

In practical operation, the apparatus for removing soot or carbon, is traversed flowed through by exhaust gases of a Diesel compression combustion engine-in the direction of the arrows. The unfiltered gases enter via the unfiltered gas pipe 5 and the unfiltered gas inlet opening 6 into the unfiltered gas chamber 15, traverse the wall 27 and pass through the filter medium 11 and the wall 1 2 radially inwards and so arrive in the filtered gas chamber 1 6. From there they leave the filter housing 1 through the filtered gas outlet opening 9 and the filtered gas outlet pipe 7.

On switching-on of the microwave generator 20 by the electric switching device 40 the particles of soot deposited on the filter means 11 are heated to such an extent that they are converted into carbon dioxide. After a sufficiently long period of time, which is adjustable by means of the electric switching device and hence can be adapted to practical requirements, the microwave generator 20 is shut off. A new cycle commences in which particles of soot are deposited on the filter means 11. The time period to the switching-on of the microwave generator 20 may also be varied and hence adapted to the requirements.

The electric switching device 40 may, for example, be formed as a differential pressure switch connected to the unfiltered gas outlet pipe 5 and the filtered gas outlet pipe 7 or as a pressure switch connected only to the unfiltered gas inlet pipe 5, in such a manner that it does not switch on the microwave generator until exceeding a predetermined flow resistance in the filter insert 10 and switches off again via an incorporated delay action after a predetermined time interval. Operation is then fully automatic and requires no adjustment by the operator.

Claims

1. Apparatus for removing carbon or soot from the exhaust gases of an internal combustion engine, comprising a metal filter housing and a filter insert which in the filter housing separates an unfiltered gas chamber from a filtered gas chamber provided with a filtered gas outlet opening, and with said filter insert having a highly temperature-resistant, filter means having "depth effect", for filtering out soot; and an electrically operated device for the controlled burning-off of the soot deposited on the filter means, characterised by the feature that the apparatus includes a microwave generator for emitting microwaves for heating the soot deposited on the non-metal filter means and which is connected to the unfiltered gas chamber, and that gas-permeable walls blocking the passage of the generated microwaves are arranged in the filter housing between the microwave outlet opening of the generator and the unfiltered gas inlet opening and also downstream of the filter means.

2. Apparatus as claimed in claim 1, in which the microwave outlet opening of the generator is covered by a non-metallic, highly temperature resistant filter means.

3. Apparatus as claimed in claim 1 or 2, in which the microwave generator is adapted to be switched on and off at ajustable time intervals by means of an electric switching device.

4. Apparatus as claimed in claim 1 or 2, in which an electric switching device is provided by means of which the microwave generator may be switched on and on exceeding a predetermined filter insert flow resistance and which may be switched off again after a predetermined time interval.

5. Apparatus for removing soot from the exhaust gases of an internal combustion engine, substantially as herein described, with reference to and as illustrated in the accompanying drawings.