Soot filter process and soot filter device for a diesel engine.

The invention relates to a soot filter device for a diesel engine according to the preamble of claim 1.

Diesel engines produce at certain load cases soot which should be filtered out of the exhaust gases. In testing are ceramic particulate filter, which can accommodate the soot from 5 to 8 hours driving. Thereafter, the filter must be regenerated. The regeneration is carried out by combustion of the soot particles at high exhaust gas temperatures of at least 600 ° C. Such high exhaust temperatures in diesel engines not available due to the high excess air. Currently, methods are being tested, in which the filter device has a separate burner. Because of these burners can not work against the pulsating exhaust pressure of the diesel engine, are devices in testing, in which the filter is bridged via an additional silencer during regeneration.

The invention has for its object to provide a device of the soot filter specified in the preamble of claim 1 type in which the regeneration of the filter can be carried out during operation of the diesel engine without passing the engine exhaust gases.

This object is inventively with the features specified in the characterizing portion of claim 1.

When soot filter device of the invention in the main combustion chamber of the burner is only partial combustion of the supplied fuel with the aid of forced into a certain flow rate of air fed, but without soot formation. The unburned part of fuel is supplied together with the combustion gases of the secondary combustion chamber, where it burns by the oxygen contained in the engine exhaust. The first part of the combustion is performed with supplied external air, and only the post-combustion engine exhaust gases can be used. Since compressed air is supplied only for the main combustion in a substoichiometric amount of air required is relatively small.

The atomizing nozzle of the burner is preferably provided with a swirl elements ring nozzle. This annular nozzle has an annular Zerstäuberzunge, on the inner fuel along sweeps which is feinzerstäubt from the rotating air stream to form a flow cone. A reliable, stable combustion is achieved despite a pulsating counterpressure and despite lack of air by using such "air atomizing nozzle". If all of the air for the main combustion is supplied with a differential pressure of at least 10 mbar is obtained immediately after the die an intimate mixture of a fine mist of fuel with the combustion air. Together with the caused by the swirl elements of the atomizer Heißgasrezirkulation this leads to a body independent of the pressure pulsations combustion.

The supplied to the burner compressed air can be taken from the compressed air system of the vehicle and fed via a powered with supercritical pressure ratio nozzle of the atomiser nozzle. Supercritical pressure ratio means that the air in the narrowest nozzle cross-section flows at least at sonic velocity. Thus, independent of the pressure pulsations of the engine exhaust gas output of the burner to be driven.

Alternatively, the combustion air can be promoted by a positive displacement. Here, too, the air mass flow from the backpressure of the diesel exhaust gas stream is not or only slightly affected, and there is a burner operation with the unaffected by pulsating engine compressed air flow rate and thus uninfluenced burner performance guarantees. If one couples the air compressor with the speed of the diesel engine and the fuel also promotes a positive displacement pump, obtaining a speed-proportional amount of mixture control. A change the speed of the diesel engine, so the burner output adapts the modified exhaust gas mass flow. Thereby, the temperature can be optimally met at the filter during regeneration.

The burner is so small that it can easily be incorporated into the filter housing and cooled by a heat exchanger with the engine exhaust.

In the following the invention will be explained in more detail with reference to the drawings of exemplary embodiments.

Show it:<ul><li>Fig. 1 shows a schematic longitudinal section of the filter device,</li><li>Fig. 2 is a detailed longitudinal section through the atomizer nozzle,</li><li>Fig. 3 is a section along the line III-III of Fig. 2, and</li><li>Fig. 4 shows another example of the air supply to the atomizing nozzle.</li></ul>

The filter device shown in Fig. 1 comprises a cylindrical housing 10. The housing 10 has at one end a radial or tangential inlet 11 for the engine exhaust, and contains a total housing section engaging ceramic filter 12. At the other end of the housing 10 is the outlet 13, through which the engine exhaust and combustion gases emerging from the housing.

The exhaust gas inlet 11 leads into an annular manifold chamber 14 surrounding the main combustion chamber 15 of the burner sixteenth The atomizing nozzle 17 is attached to the lid wall 18 of the nozzle housing 19th This top panel 18 is flanged to the end wall of the housing 10 and limits the main combustion chamber 15. The fuel line 20 leads into the nozzle housing 19 and is directly connected to the atomizer 17th The nozzle housing 19 also has an air inlet 21, is hineingepreßt through the compressed air into the interior of the nozzle housing. As shown in FIG. 2, the fuel line 20 leads 17a through the interior of the nozzle body through and emerges at its end face. To the Ausstrittsrohr 20a around, on the flange-like end wall 22 of the nozzle body numerous air conducting swirl elements 23 are arranged in the form of wings. This swirl elements 23 are inclined as shown in FIG. 3 in the circumferential direction and taper towards the inner end. The swirl elements 23 define channels 24 through which the radially inflowing air has a circumferential component. Each of the channels 24 is reduced down in cross-section to its inner end so that in each channel 24, the air is accelerated increasingly.

The swirl elements 23 are arranged between the end wall 22 and a parallel to this end wall extending plate 25th The swirl elements 23 facing away from the end wall of the plate 25 forms the boundary wall of another nozzle chamber, which is also equipped with swirl elements 26, which are attached to the front side of a further board 27th The plate 27 is parallel to the plate 25 and swirl elements 26 are formed in the same way and arranged like the swirl elements 23 of the plate 22nd

The laterally flowing in through the air inlet 21 into the nozzle housing 19 air is distributed inside the nozzle housing and flows radially into the channels 24 between the swirl elements 23 and in the corresponding channels between the swirl elements 26th By swirl elements the air is given a twist, ie a circular movement.

The plate 25 is ring-shaped and its inner edge is bent in the form of a flow direction axially projecting, annular, conically tapering towards the end edge 29. The inner edge of the annular plate 27 axially in the flow direction and forms a conical ring 30 which surrounds the cutting edge 29 at a radial distance.

The emerging from the tubular liquid fuel 20a is detected by the rotating air current and sprayed onto the inside of the cutting 29th The cutting edge 29 is on both sides flows around rotating and axially moving air currents, who demolished the fuel from the circular sharp tip of the cutting edge 29 and distribute it finely and uniformly in the form of droplets. The fuel droplets mix it with the combustion air and come together with this one in the tubular main combustor 15th As a result of the swirl injection under high pressure arising in the main combustion chamber 15 annular flow rollers, in which a part of the mixture stream is recycled, and which rotate about the longitudinal axis. To ignite the mixture in the main combustion chamber 15, an electrode 31 is arranged.

The main combustion chamber 15 is provided at the end facing away from the atomizer nozzle 17 defined by an annular wall 32 forming an opening 33 for the exit of the combustion gases. At a distance behind the annular wall 32 is an end wall 34 which delimits the main combustion chamber 15 located behind the space 35th extend to the peripheral wall of the outer side of the main combustion chamber 15 heat exchanger fins 36 which extend up to the end wall 34th Between these heat exchanger fins 36, the combustion gases flow radially out of the space 35 out into the secondary combustion chamber 37, which is bounded at one end by the filter 12th

From the distribution chamber 14 provides an annular passage 38 to the heat exchanger fins 36. The engine exhaust gases flow through the passage 38 therethrough, the heat exchange fins 36 along, and are then mixed with the combustion gases to flow together with these in the post-combustion chamber 37th From here the hot gas mixture passes through the filter 12 to the outlet connection. 13

The chamber 35 forms at its periphery a cross-flow mixer 39, in the intensive mixing of the gas streams takes place.

The compressed air inlet 21 includes a critically traversed nozzle 40, which is connected via a switching valve 41 to the pressure plenum 42 of the diesel engine DM. The output shaft of the diesel engine drives (directly or via a reduction), a blower 43, which feeds the compressed air collector 42nd

When the valve 41 is opened and fuel is pumped into the fuel line 20, fuel and air enter the atomizing nozzle 17. The atomizing nozzle 17 impressed in the swirl stabilized flame and burns soot in spite of the stoichiometric quantity of air. The exhaust gas of the engine passes via the inlet 11 and the distribution chamber 14 between the heat exchanger fins 36 to cool the wall 15 of the main combustion chamber. After mixing engine exhaust gas and combustion gas in cross flow mixer 39, the burnout of the flame with the aid of the residual oxygen contained in exhaust gas in the combustion chamber takes place by 37. The thus-heated gas passes through the ceramic filter 12 and burns off the carbon black.

Fig. 4 shows an embodiment in which the atomizer nozzle 17 of the supplied compressed air is generated by a volumetric pump or positive displacement pump 45th The positive displacement pump 45 is coupled via a coupling 46, to the output shaft 47 of the diesel engine DM (direct or via a gear). The fuel is the fuel line 20 is also fed via a positive displacement pump 48 which is driven by the output shaft 47 of the diesel motor. Since both the quantities of compressed air and fuel vary depending on the engine speed, but their mutual relationship remains constant, there is a speed-proportional amount of mixture control. As a result, the burner power always fits with varying speed of the diesel engine to the modified exhaust gas stream. Characterized the temperature can be kept substantially constant on the filter during regeneration.