WO1991004394A1

WO1991004394A1 - Process and device for cleaning a soot filter

Info

Publication number: WO1991004394A1
Application number: PCT/EP1990/001455
Authority: WO
Inventors: Peter Kugland; Alois Ullmer; Enrique Santiago
Original assignee: Zeuna-Stärker GmbH & Co. KG
Priority date: 1989-09-12
Filing date: 1990-08-31
Publication date: 1991-04-04
Also published as: DE59004756D1; EP0417383B1; EP0417383A3; EP0417383A2; KR0145522B1; KR920701619A

Abstract

In a process for cleaning a soot filter (4) in the exhaust pipe (2) of a diesel engine (3), the flow of exhaust gas (5) is directed through a burner (1). When the load on the soot filter (4) reaches a certain level, the burner (1) is ignited by injection of fuel into the burner (1). The soot that has collected in the soot filter (4) is burned by the hot combustion gas. This regeneration of the soot filter (4) is initiated, however, only when the instantaneous operating point of the engine (3) lies within a predetermined ignition characteristic field (Z). The fuel injection stops as soon as the motor reaches an operating point which lies outside a predetermined combustion characteristic field (B) that is greater than the ignition characteristic field (Z).

Description

Method and device for cleaning a Russian filter

description

The present invention relates to a method for cleaning a soot filter in the exhaust line of a diesel engine under load, the total exhaust gas stream being divided into a partial exhaust gas stream and a main exhaust gas stream, the partial exhaust gas flow being passed into a combustion chamber in which a fuel nozzle and a this associated electrical ignition device is installed, the partial exhaust gas flow is ignited in the combustion chamber with fuel injected there, a heating gas being produced and the heating gas leaving the combustion chamber being combined with the main exhaust gas flow bypassing the combustion chamber and the resulting fuel gas being fed to the soot filter, where it initiates the combustion of the soot collected there. In the same way, the invention relates to a device for carrying out the method.

A method of the type mentioned is known from DE-OS 3720829. The necessity to use a burner for the regeneration of a soot filter arises from the fact that the soot accumulated on the soot filter only burns at temperatures above approx. 550 ° C., which, however, cannot be achieved in inner city operation. The The known method works without secondary air supply, ie the burner burns part of the residual oxygen present in the engine exhaust gas, while a further part of this residual oxygen is used for the regeneration of the filter, ie the combustion of the soot that has accumulated.

It has been shown that the known method cannot achieve a uniform and stable mode of operation in the entire operating range of the engine.

Accordingly, the present invention has for its object to provide a method of the type mentioned, in which the regeneration of the soot filter takes place reliably and takes place under optimal conditions with minimal pollutant emissions.

This object is achieved according to the proposal of the invention in a generic method in that the regeneration is only initiated when the soot filter is loaded when the engine operating point within

of a predefined ignition map (Z), the fuel injection into the combustion chamber is interrupted if the engine operating point lies outside a predefined combustion map (B) and that the combustion map is larger than the ignition map.

The invention makes use of the knowledge that the reliable initiation of the combustion necessary for the regeneration of the soot filter requires the existence of certain conditions with regard to the state of the exhaust gas (in particular excess air); it is provided according to the invention that after the burner has been ignited, the load on the engine can be increased beyond the ignition range defined by the ignition map without the burner going out. The combustion area thus includes the ignition area, but is larger than this. Only when the operating point of the engine shifts so much due to a change in load that it lies outside the combustion map is the fuel injection into the combustion chamber interrupted, because otherwise the combustion of the soot collected in the soot filter would not proceed satisfactorily. Because the residual oxygen content in the exhaust gas of the diesel engine decreases with increasing load, the optimal combustion required for the regeneration of the soot filter cannot take place in the entire map area of the engine. By switching off the fuel supply to the fuel nozzle according to the invention when the instantaneous operating point of the engine is outside a predetermined combustion map, increased emission values are not to be feared.

The load information for determining the current engine operating point is particularly preferably taken directly from the injection pump of the engine or from the accelerator pedal or its control rod; this prevents the flame from going out due to inaccurate or delayed load information before the burner is specifically switched off.

The control of the method is preferably carried out in such a way that the temperature of the fuel gas is measured upstream of the soot filter and used as a control variable for the amount of fuel injected. The higher the measured temperature, the more

less fuel is supplied. In this way, despite possibly considerably fluctuating values for the quantity and the temperature of the exhaust gas flow introduced into the burner - these values change depending on the respective engine operating point - optimal conditions for the regeneration of the soot filter are always maintained. By regulating the temperature upstream of the soot filter via the injected fuel quantity to a predetermined value, on the one hand the regeneration can take place in short operating phases, which are non-critical for the filter service life, on the other hand preventing the filter from overheating during regeneration .

To detect the filter loading state, the pressure in the exhaust system is preferably measured in front of the filter. The measured instantaneous system pressure is constantly compared with a pressure map in an electronic control. In this pressure characteristic field it is taken into account that the system pressure depends on the engine speed, the load and the temperature. This ensures that the regeneration is actually only initiated when the filter is loaded with soot. According to a preferred embodiment of the invention, however, the regeneration is only initiated if the engine operating point lies within the ignition map for longer than a minimum period, ie the initiation of regeneration is suppressed if the engine operation point is only briefly, for example, less than 2 seconds in the ignition map. This measure increases the reliability of the ignition. The ignition electrodes are preferably heated before the burner is switched on. This promotes detachment of the soot deposited on the ignition electrodes or their insulators and reduces the risk of short circuits or leakage currents. The corresponding heating device is preferably designed as a resistance heater.

Purge air flows through the fuel nozzle preferably during two regeneration phases. This flow, for example with an air volume of 80 liters per hour, ensures that the injection nozzle is not contaminated, so that great long-term stability of the fuel injection into the burner is ensured. A check valve interrupts the burner operation Air supply to the injector. In a preferred embodiment of the method according to the invention, the burner temperature is measured over a predetermined period of time, for example 4 seconds, after the start of fuel injection, in order to check whether the ignition of the injected fuel has actually taken place and the combustion takes place without problems; the measured temperature profile is compared with a target profile, and any deviations that may occur may indicate improper combustion. In this case, the fuel injection can be switched off safely.

The regeneration control is thus preferably carried out in the following manner: To detect the filter loading condition, the pressure in the exhaust system is measured in front of the filter; the current system pressure is constantly compared in the electronic control with a pressure map (speed, load and temperature dependent). When the filter is loaded, which requires regeneration, the ignition electrodes are activated first

heated, preferably 2 to 15 min; a heating time of 8 minutes is generally appropriate. A computer checks whether the engine is in the ignition map area via the speed signal and the load information, which is taken, for example, from a control sensor on the engine's injection pump, and conducts it after the heating phase if necessary, i.e. depending on the loading of the soot filter and If the ignition conditions exist, the burner ignition. During the burner operation, these signals also determine whether the engine is moving in the combustion area of the map; the fuel supply is stopped at an engine operating point outside the combustion map. The temperature in front of the soot filter is used to regulate the temperature in front of the soot filter to a predetermined value, for example 700 ° C., in order to carry out regenerations in short time intervals which are non-critical for the filter life and on the other hand to overheat of the filter during regeneration. Depending on the temperature after the soot filter, a signal about the completed regeneration

of the soot filter to the control unit, which leads to the burner being switched off. In order to maintain optimal burner operation in different driving conditions, the temperature in the burner is also constantly measured.

The range of engine characteristics in which burner operation is possible can be enlarged by means of two further features in one embodiment of the method according to the invention. By passing the heating gas over a flame-retaining insert, which forms a hot (glow) point, it is possible to increase the stability of the combustion; by generating a swirl of the partial exhaust gas stream entering the combustion chamber, the heating gas is mixed particularly well and its contact with the flame-retaining insert is intensified, whereby the risk of streak formation, ie the formation of cold zones of the heating gas, is considerably reduced. The improved contact between the heating gas and the flame-retaining insert means that the latter can be made particularly small, ie in particular with a smaller surface; this allows the reduce the flow resistance caused by the flame-retaining insert, which also promotes combustion. The combustion chamber can thus be of compact construction, ie long mixing distances which have hitherto been used to make the combustion more uniform are unnecessary.

The main exhaust gas stream is preferably combined with the heating gas in several stages. As a result, the temperature distribution within the fuel gas supplied to the soot filter can be further evened out. The main exhaust gas stream preferably flows around the combustion chamber, i.e. an annular space is formed between the combustion chamber and the burner housing surrounding it, which serves as a bypass line for the main exhaust gas flow. The main exhaust gas stream is hereby preheated before it is combined with the heating gas at the combustion chamber, which also promotes combustion; at the same time, the annulus serves as insulation against heat loss and to ensure a low temperature of the burner housing.

The heating gas preferably has a fuel excess, ie more fuel is injected into the partial exhaust gas flow than can burn. Hereby When the heating gas is combined with the main exhaust gas stream, afterburning takes place, which also favors the stability of the combustion.

The device for carrying out the method according to the invention is characterized by a swirl plate arranged at the entrance to the combustion chamber and a flame-retaining insert arranged on the outlet side in the combustion chamber, the ignition device and fuel nozzle being arranged between the swirl plate and the insert. It is preferably provided that the ignition device comprises one or more ignition electrodes, which are each arranged close to the mouth of the fuel nozzle, and that the spray device of the fuel nozzle runs transversely to the flow direction of the combustion chamber. The result is reliable ignition in all engine operating conditions, which are intended for the soot combustion.

To control the method according to the invention, the above-mentioned device comprises an electronic control unit which determines the respective engine operating point with a predetermined ignition map and a combustion engine. The map compares and only initiates regeneration when the engine operating point lies within the ignition map, and the fuel injection is interrupted when the engine operating point lies outside the combustion map. The maps are areas in the speed / load diagram. The map data stored in the electronic control unit are matched to the respective engine type or the particular engine. These data are used to compare the measured values for speed and load supplied to the control unit, by which the engine operating point is characterized.

The fuel nozzle is preferably assigned a proportional valve for regulating the amount of fuel injected. Such a proportional valve allows the exact amount of fuel injected to be adjusted to the respective engine operating point; As already explained, the uncleaned exhaust gas leaving the engine has a certain temperature at every engine operating point, so that depending on this temperature and the amount of exhaust gas, a certain amount of fuel is required to keep the fuel gas supplied to the soot filter at the desired temperature (eg 700 °) C) keep. In the burner housing upstream of the combustion chamber, baffles are expediently provided to even out the flow. This is particularly advantageous if the exhaust gas does not flow into the burner housing axially but in the transverse direction. This results in a uniform flow distribution over the cross section of the combustion chamber.

The advantages that can be achieved with the method and the device according to the invention relate not only to the homogenization of the flame during the regeneration operation. Even during normal engine operation without regeneration, the built-in combustion chamber results in an even distribution of the exhaust gas flow and thus the soot deposition over the filter surface. When the accumulated soot burns off, tensions and cracks in the filter material caused by temperature fluctuations are largely avoided.

Embodiments of the invention are explained in more detail below with reference to the drawing. It shows

1 schematically shows an overall arrangement consisting of a diesel engine, particle filter and burner arranged in between,

2 shows the perspective view of an embodiment of a burner in a partially broken open representation,

3 shows a qualitative representation of the ignition map and the combustion map in the load / speed diagram for a burner according to FIGS. 2 and

Fig. 4 is a flow chart for a control of the method according to the invention.

The burner 1 is arranged in the exhaust line 2 of a diesel engine 3 in the flow direction of the exhaust gas in front of a soot filter 4 for depositing soot particles. The unpurified total exhaust gas stream S1 is fed to the burner 1; The cleaned exhaust gas stream S2 emerges from the soot filter 4.

In order to burn the soot accumulated in the soot filter 4 during engine operation and the filter

to regenerate, fuel is injected into the burner 1 by means of a fuel nozzle 5, which is ignited at ignition electrodes 6. For this purpose, the fuel nozzle 5 is supplied with fuel by a pump 7 via a fuel line 8; the pump 7 is in turn connected to the fuel tank 10 of the vehicle via a fuel line 9.

An electronic control unit 11 is provided to control the regeneration of the soot filter 4. The electronic control unit controls the pump 7, a proportional valve 12 arranged between the pump 7 and the fuel nozzle 5 and the ignition electrodes 6. For an optimal control of the regeneration process, the electronic control unit 11 processes the following input signals: The temperature T1 before burner 1, pressure Pl before burner 1, temperature T2 in burner 1, temperature T3 before soot filter 4 and temperature T4 after soot filter 4. In addition, electronic control unit 11 receives information about loads L and the speed N of the engine 3, whereby its operating point is fixed. Finally, the electronic control unit 11 also has via an energy supply E, which also serves to cover the ignition energy Z to be supplied to the ignition electrodes 6.

The structure of an exemplary embodiment of a burner for use in connection with the method according to the invention is shown in FIG. 2. The burner 1 is made of a cylindrical burner housing

13 and a combustion chamber arranged in this

14 constructed, which is also cylindrical. The burner housing 13 surrounds the combustion chamber 14 at a radial distance, which creates an annular space 15. The through the pipe socket 16 in the burner housing

13 incoming exhaust gas stream S1 is thereby divided into an exhaust gas 1 stream AT which is in the combustion chamber

14 enters and a main exhaust gas flow AH, which enters the annular space 15 between the combustion chamber 14 and the burner housing 13 and thus flows around the combustion chamber 14. At the inlet end of the combustion chamber 14, a swirl plate 17 is provided, which has radially extending twisted blades 18. The exhaust gas stream AT entering the combustion chamber 14 is given a swirl by the blades 18 with respect to the longitudinal axis of the burner 1.

The two ignition electrodes 6 and the fuel nozzle 5, which are arranged on a common mounting plate 19, open into the combustion chamber 14. The mounting plate 19 is fastened on a flange 20 which is firmly connected to the burner housing 13. The porcelain body surrounding the ignition electrodes 6 as an insulator can be heated by means of a resistance heater installed therein before the burner is switched on. The ignition electrodes 6 are connected to the ignition cables Z via suitable plugs 21. The proportional valve 12, into which the fuel line 8 opens, is arranged on the fuel nozzle 5. A control line 22 is connected to the proportional valve 12 and is used to transmit the signals of the electronic control unit 11 used to control the proportional valve 12.

An air supply 23 is also connected to the fuel nozzle 5, through which air is blown through the fuel nozzle 5 between two regeneration phases in order to prevent it from becoming dirty.

At the outlet end of the combustion chamber 14, a flame-retaining insert 25 consisting of four radial webs is supported on the combustion chamber wall by means of the webs; it has a centrally located conical incandescent body 24.

In the area of the entry of the exhaust gas flow into the burner 1, two angled baffles 26 are arranged, through which the exhaust gas entering radially into the burner housing 13 is deflected in such a way that it flows axially against the combustion chamber 14 and the annular gap 15. On the output side, the burner housing 13 has a connecting flange 27, to which a corresponding connecting flange 28 of a transition cone 29 is screwed. The transition cone 29 is firmly connected to the cylindrical housing 30 of the soot filter 4.

FIG. 3 shows the map data stored in the electronic control unit 11 (according to FIG. 1). They form the basis for the comparison with the respective engine operating point. It is clear that the combustion map B is considerably larger than

the ignition map Z, i.e. after the burner has been ignited, the load L of the engine can be increased beyond the ignition map without the burner going out. This is also a consequence of the flame-stabilizing measures, namely the use of the swirl plate 17 at the inlet and the glowing insert 25 at the outlet of the combustion chamber 14.

FIG. 4 shows a flow diagram for an advantageous control of the device according to FIGS. 1 and 2. When the soot filter is loaded, the burner 1 is only ignited when the operating point of the engine 3 lies within the ignition map Z. Likewise, in order to prevent undesired emissions, the burner 1 is switched off when the engine operating point shifts so much that it lies outside the combustion characteristic field B. The end of the regeneration can equally be determined by the elapse of a maximum time t or by reaching a maximum temperature TX.

Claims

1. A method for cleaning a soot filter (4) in the exhaust pipe (2) of a diesel engine (3) under load, wherein

the total exhaust gas stream (Sl) is divided into an exhaust gas stream (AT) and a main exhaust gas stream (AH),

the exhaust gas flow (AT) is passed into a combustion chamber (14) in which a fuel nozzle (5) and an electrical ignition device assigned to it are installed,

- the exhaust gas flow (AT) in the combustion chamber

(14) is ignited with fuel injected there, producing a heating gas and

- The heating gas leaving the combustion chamber (14) combines with the main exhaust gas stream (AH) directed past the combustion chamber and the resulting fuel gas is fed to the soot filter (4), where it initiates the combustion of the soot accumulated there, characterized in that

- That the regeneration when the soot filter (4) is only initiated when the engine operating point within a predetermined ignition map

(Z) lies,

- That the fuel injection into the combustion chamber is interrupted when the engine operating point outside a predetermined combustion map

(B) lies and

- That the combustion map (B) is larger than the ignition map (Z).

2. The method according to claim 1, characterized in that the temperature (T3) of the fuel gas upstream of the soot filter (4) is measured and used as a control variable for the amount of fuel injected.

3. The method according to claim 1, characterized in that to determine the filter loading, a Druck¬ measurement in front of the soot filter (4) and that the instantaneous pressure in front of the soot filter (4) is compared with a pressure map, which shows a dependence of the pressure on the Engine load, speed and exhaust gas temperature are taken into account.

4. The method according to claim 1, characterized in that the initiation of regeneration is suppressed when the engine operating point is only briefly within the ignition map (Z).

5. The method according to claim 1, characterized in that the fuel nozzle (5) is flushed with air between the regeneration phases.

6. The method according to claim 1, characterized in that after the start of fuel injection, the temperature (T2) in the burner (1) is measured over a predetermined period and its increase is used to check the success of the initiated combustion.

7. The method according to claim 1, characterized in that the exhaust gas flow (AT) of the combustion chamber (14) is supplied with a swirl.

8. The method according to claim 1, characterized in that the heating gas is passed through a flame-retaining insert (25).

9. The method according to claim 1, characterized in that the main exhaust gas stream (AH) flows around the combustion chamber (14).

10. Device for cleaning a soot filter (4) in the exhaust pipe (2) of a diesel engine

(3) under load, with one in front of the soot filter

(4) arranged combustion chamber (14) in which a fuel nozzle (5) and an electrical ignition device assigned to it are installed, and with a bypass line that bypasses the combustion chamber (14), characterized by a at the entrance to the combustion chamber (14) arranged swirl plate (17) and a flame-retaining insert (25) arranged on the outlet side in the combustion chamber (14), the ignition device and fuel nozzle (5) being arranged between the swirl plate (17) and the insert (25).

11. The device according to claim 10, characterized in that the ignition device comprises one or more Zünd¬ electrodes (6) which are each arranged close to the mouth of the fuel nozzle (5) and that the spray direction of the fuel nozzle (5) transversely Flow direction of the combustion chamber (14).

12. The apparatus according to claim 11, characterized in that the fuel nozzle (5) and the ignition electrodes (6) are arranged on a common mounting plate (19).

13. The apparatus according to claim 10, characterized in that the flame-retaining insert (25) comprises an incandescent body (24).

14. The apparatus according to claim 10, characterized in that the swirl plate (17) is designed as a disc with twisted radially projecting blades (18).

15. The apparatus according to claim 10, characterized in that the combustion chamber (14) from a Brennerge¬ housing (13) is encased, such that a serving as a bypass line for the main exhaust gas stream (AH) annular space (15) between the Brenner¬ housing (13) and the combustion chamber wall is formed.

16. The apparatus according to claim 15, characterized in that in the burner housing (13) in the direction of flow in front of the combustion chamber (14) baffles (26) are provided for equalizing the flow.

17. The apparatus according to claim 10, characterized in that the fuel nozzle (5) has a connection for an air feed (23) and a proportional valve (12) for regulating the amount of fuel injected.