DE4307525A1 - Method and device for the treatment of exhaust gases from an internal combustion engine - Google Patents

Abstract

In a method for the treatment of exhaust gases from a diesel internal combustion engine by means of a burner with a combustion chamber, an ignitable mixture of fuel and air is produced, the said mixture fed to the combustion chamber and burnt therein and the entire flow of exhaust gas led through the combustion chamber. As a result the greater proportion of the soot particles contained in the exhaust gases can be directly burnt so that a downstream catalytic converter filter is only slightly burdened and is moreover rapidly regenerated by the exhaust gases heated by the combustion gases.

Description

The invention relates to a method for aftertreatment of the Exhaust gases from an internal combustion engine, in particular a diesel engine Internal combustion engine, using a burner with a burner chamber, and on a device for performing the Ver driving.

There are a number of suggestions for procedures and proposals directions for the aftertreatment of the exhaust gases of a diesel burner engine to the soot particles contained in the exhaust gases to eliminate. The best known is the arrangement of a soot fil ters in the exhaust pipe. Because such a soot filter but relatively quickly clogged, measures to Regenerate the same can be taken. It is known to for this purpose to provide a burner, the combustion chamber in which one is charged with diesel fuel Fuel nozzle and a burner connected to an air pump air line opens. The force generated in the combustion chamber Material-air mixture is ignited by an ignition device and the hot fuel gases are mixed with the exhaust gases and lift the exhaust gas temperature so far that the in the soot filter oxidize collected soot particles. With spark ignited Engines are such burners for quick opening heat a catalyst arranged in the exhaust pipe used.  

The burners proposed for this purpose are fan burners ner with pressure atomizer nozzle, which can be found in modern heating systems have proven themselves many times and are highly efficient. However, they have for use as afterburner in exhaust system suffers from a number of disadvantages. For afterburning Burner capacities of significantly less than 10 kW are required. At these low powers, the nozzle opening becomes the Fuel nozzle so small that after a relatively short period of operation tends to coke, especially when the Burner is operated intermittently and during rest times the nozzle is heated up by the hot exhaust gases. Another disadvantage of such atomizing burners is in that the flame is unstable when the back pressure increases gets high and / or pulsates. However, they are always in the exhaust pipe Pulsations are present. The instability with pressure fluctuations in the exhaust pipe stems among other things from the fact that in such Atomizing burners with a low combustion air supply Pressure of about 40 to 100 mm WS takes place.

The object of the invention is a method for aftertreatment the exhaust gases of an internal combustion engine, in particular one To create a diesel internal combustion engine with which the externally ignited internal combustion engines safely heats up the catalytic converter tors and with diesel internal combustion engines the elimination of Soot particles more effective and reliable than before follows and may be dispensed with a soot filter can.

This object is achieved in that a creates an ignitable mixture of fuel and air, this Mixture fed to the combustion chamber and this is burned and the hot gases are mixed with the exhaust gas stream.

In the proposal according to the invention, the flammable becomes Mixture not only in the combustion chamber, but outside of it  Combustion chamber generated and it thus enters from the burner nozzle flammable aerosol, the flame of which is increased and changing back pressure and pulsations in the exhaust pipe remains stable. The fact that the burner nozzle is not only power material, but a fuel-air mixture can be supplied ver the nozzle opening even with small burner capacities be executed relatively large, so that the risk of a Coking is largely eliminated.

In diesel engines, the entire exhaust gas flow passed through the combustion chamber. This has the consequence that a Most of the soot particles in the area of hot fuel gases reaches and with the help of the air contained in the exhaust gases shot is burned, so that, if any, only one small amount of soot particles in a downstream soot fil ter must be caught. This soot filter is however through the exhaust gases brought to high temperature by the fuel gases regenerated immediately.

The amount of soot particles in the exhaust gas of a diesel internal combustion engine The machine is speed and load dependent, although at high loads a lot of soot and a large amount of exhaust gas at high speed. To safely remove the soot particles or at least It is therefore expedient to reach a large part of the same ßig, the amount of fuel fed to the combustion chamber Air mixture depending on the speed and the load to control the internal combustion engine. Because modern diesel fuel engines already electronic, map-controlled Have fuel injectors, the in this map stored parameters for controlling the Burner fed mixture amount can be used.

Especially when in the exhaust pipe behind the burner Catalyst is provided, it may be appropriate to the amount of the fuel-air mixture supplied to the combustion chamber (also) depending on the temperature of the exhaust gases behind  to control the combustion chamber to prevent the catalytic converter from overheating to avoid torsion or a corresponding heating of the same to reach.

The proposed method is reliable ensures the fuel-air mixture, since this Mixture, as mentioned, not in the combustion chamber, but except half of the same is generated so that it is ensured that an ignitable mixture with an air ratio of about 1.0 to 1.3 is present. To make sure that these ratios too when starting the engine, it is appropriate moderate, the burner before or at the latest with the start of the Switching on the internal combustion engine and thereby avoiding that exhaust gas can get into the combustion chamber before the burner starts what the ignition of the burner nozzle could affect the mixture.

The invention also relates to a device for carrying it out of the method according to the invention, characterized in that is that the combustion chamber closed at one end in the Exhaust pipe of the internal combustion engine is arranged and with this forms an annular space through openings in the wall the combustion chamber with the interior of which is connected an exhaust pipe at the open end of the combustion chamber concludes that the annulus is delimited by a transverse wall, which forces the entire exhaust gas flow through from the annular chamber the openings in the combustion chamber and from there into the exhaust pipe to flow, and that at the closed end of the combustion chamber a burning nozzle is arranged, the one with the ignitable Fuel-air mixture generating device is connected and through which the mixture is introduced into the combustion chamber. It is useful to achieve soot-free combustion moderate if the combustion chamber is funnel-shaped from the nozzle expanded, preferably according to the spray cone of the nozzle.

The device generating the fuel-air mixture has  preferably an air pump and a fuel pump that jointly, preferably driven by an electric motor are, the delivery line of the fuel pump in the An suction line of the air pump opens and the delivery line of the Air pump is connected to the burner nozzle, and being the Flow rates of the air pump and the fuel pump match other are coordinated that produces an ignitable mixture becomes. The ignition takes place, as usual with burners, by close electrodes arranged at the outlet opening of the burner nozzle. By introducing the fuel into the intake line of the Air pump, the fuel in the air pump becomes very intense mixed with the air so that a homogeneous fuel Air mixture forms. The delivery rate of the facility can be through Change in the speed of the electric motor can be varied in order the amount of that put into the combustion chamber and there burned fuel-air mixture the exhaust gas volume and the Soot number, i.e. the amount of soot particles per unit volume, adapt. If an electric motor is used to drive, so this can be map-controlled, with a map is used in which the soot number depending on the Speed and the load of the internal combustion engine is stored. Be The soot number is known to increase with increasing load and the exhaust gas volume with increasing speed, so that at full load and maximum speed the greatest amount of soot particles is obtained. The speed of the electric motor can be continuously adjusted be, however, it may also be sufficient if the speed can only be changed in two or three stages. Alternatively, you can the drive from the engine take place, then a flow control valve is provided in the aerosol line.

With the device according to the invention, it can be done practically table all soot particles contained in the exhaust gas in the combustion chamber to burn. For security reasons and to be expected However, it is appropriate to comply with stricter emissions regulations moderate, a soot filter in the exhaust pipe behind the combustion chamber to arrange the few unburned soot particles  catches and that through the increased temperature of the Fuel gases heated exhaust gases is regenerated very quickly.

The exhaust gases from diesel internal combustion engines also contain Soot particles include hydrocarbons and minor ones Amount of carbon oxide in an oxidation catalyst be made harmful. In the Vorrich invention would such a catalyst in the exhaust pipe ter the combustion chamber and usually arranged with the soot filter can be combined by the inner surface of the soot filter provided with an appropriate catalytic coating becomes. To prevent the catalyst from overheating or in the event of a cold start, the catalyst heats up quickly reach, it is appropriate to increase the amount of fuel air mix depending on the temperature of the exhaust gases behind to control the combustion chamber.

If the burner is not operated continuously what? with regard to the fact that when operating a diesel burner soot constantly, although in different menus is appropriate, the fuel Air mixture leading delivery line an electrically operated bar shut-off valve, which prevents that after switching off fuel oil still present in the compressor can get into the combustion chamber via the burner nozzle.

An embodiment of a device for performing the Process according to the invention for the aftertreatment of the exhaust gases a diesel engine is referred to below described on the drawing.

In the drawing, 1 denotes a section of an exhaust pipe of a diesel engine, into which the exhaust gases flow from the left in accordance with the arrows. In the exhaust line 1 , a combustion chamber 2 of a generally 3 be marked aerosol burner is arranged, the device with the exhaust line forms an annular space 4 . The combustion chamber 2 is closed at its left end in the drawing and open at its right end in the drawing. At the open end of the Brennkam mer 2 , an exhaust pipe 5 connects. The right end of the combustion chamber 2 is bent outwards in the exemplary embodiment and fastened between the end flanges of the exhaust pipe 1 and the exhaust pipe 5 . This bent end forms a wall 6 which separates the annular space 4 from the exhaust pipe 5 . A multiplicity of openings 7 are provided in the wall of the combustion chamber 2 . The exhaust gases entering the exhaust pipe 1 are therefore forced to flow through the openings 7 into the combustion chamber 2 and from there into the exhaust pipe 5 .

Before the closed left end of the combustion chamber 2 , a burner nozzle 8 is arranged concentrically to the longitudinal central axis of the Brennkam mer 2 . The combustion chamber 2 has a section 9 which widens from the burner nozzle 8 and is adjoined by a cylindrical section 10 containing the openings 7 .

The burner nozzle 8 is supplied by a device 11 with an ignitable fuel-air mixture. The device 11 has an air pump 12 and a fuel pump 13 , which in the exemplary embodiment have a common drive shaft 14 which is driven by a controllable electric motor 15 . The suction line 16 of the fuel pump 13 is connected to the fuel tank of the internal combustion engine, not shown, containing diesel fuel. Your delivery line 17 opens into the suction line 18 of the air pump 12 , for example, a vane pump. The fuel is intimately mixed with the intake air in the air pump 12 and the resulting aerosol is supplied to the air pump 12 of the burner nozzle 8 through the delivery line 19 . The entering into the Brennkam mer 2 fuel-air mixture is ignited in the usual way by ignition electrodes 20 . The hot fuel gases mix with the exhaust gases entering through the openings 7 into the combustion chamber 2 and, due to their high temperature, burn the soot particles contained in the exhaust gases. The relatively few, not burned soot particles are collected in a combined with an oxidation catalyst Rußfil ter 21 , which is connected to the exhaust pipe 5 . Since a large part of the soot particles are oxidized in the combustion chamber, the loading of the soot filter is only slight, and there is always very rapid regeneration by the exhaust gases brought to high temperature by the combustion gases.

In order to adapt the burner output of the aerosol burner 3 to the accumulation of soot particles in the exhaust gases, the speed of the electric motor 15 and thus the amount of the fuel nozzle supplied to the combustion air / fuel mixture is preferably regulated by means of an electronic control unit 22 over the entire operating range of the internal combustion engine. The control unit 22 contains a soot map in which the soot number is stored as a function of the speed and the load of the internal combustion engine. The control unit 22 thus receives the speed n and the load p _{e of} the internal combustion engine corresponding signals and controls the speed of the electric motor either stepwise or continuously by simple voltage regulation or by pulse width modulation of the supply voltage according to the stored characteristic diagram. The variation in the speed of the unit 11 does not change the ignitable ratio of the fuel and the air, since the delivery rates of the air pump 12 and the fuel pump 3 are matched to one another in such a way that an ignitable mixture with a lambda of approximately 1.0 to 1, 3 is generated.

The control unit 22 also receives a temperature signal t from a temperature sensor 23 in the exhaust pipe 5 downstream of the combustion chamber 2nd So that the speed of the electric motor 15 and thus the flow rate of the unit 11 can be controlled temperature-dependent such that, on the one hand, a rapid heating of the catalyst filter 21 is achieved during a cold start, but on the other hand, overheating is prevented.

If the unit 11 is not operated continuously but intermittently, it is expedient to provide an electromagnetic shut-off valve 24 in the delivery line 19 of the air pump 12 , which shuts off the delivery line 19 when the burner 3 is switched off, thereby preventing the air pump from being released pe 12 still existing fuel oil can get into the burner nozzle 8 and coke there.

The aerosol burner 3 is preferably switched on before or at the latest when the diesel engine is started, in order to ensure that exhaust gases are not already present in the combustion chamber 2 at the moment the burner 3 is started, which could make ignition of the air / fuel mixture difficult In operation, the exhaust gases flowing into the combustion chamber 2 are kept away from the burner nozzle 8 by the flame.

As mentioned, the entire exhaust gas flow passes through the openings 7 into the combustion chamber 2 . It flows beforehand along the wall of the combustion chamber 2 , in particular along the funnel-shaped section 9 , which is red-hot during operation of the burner 3 . So there is already a preheating of the gas stream from before it reaches the combustion chamber 2 , in which the largely complete combustion of the soot particles in the exhaust gas now takes place, since the temperature of the fuel gases in the combustion chamber 2 is approximately 1500 ° C., while the ignition temperature is Soot particles are around 500 ° C. Even if the temperature of the combustion gas 2 is considerably reduced by admixing the exhaust gas flow, which is much larger in volume, the temperature in the combustion chamber 2 is still far above the ignition temperature of the soot particles.

Claims (12)

1. A method for aftertreatment of the exhaust gases of an internal combustion engine, in particular a diesel internal combustion engine, with the aid of a burner with a combustion chamber, characterized in that an ignitable mixture of fuel and air is generated, this mixture is fed to the combustion chamber and burned in this ver and that Hot gas is mixed with the exhaust gas stream. 2. The method according to claim 1 for the after-treatment of the exhaust gases ner diesel internal combustion engine, characterized in that the entire exhaust gas flow is passed through the combustion chamber. 3. The method according to claim 2, characterized in that the Amount of fuel-air mixture supplied to the combustion chamber depending on operating parameters (speed and Load) of the internal combustion engine is controlled. 4. The method according to claim 1, characterized in that the Burner before or at the latest when the internal combustion engine is started machine is switched on. 5. The method according to any one of claims 1 to 4, characterized records that the amount of that supplied to the combustion chamber Air-fuel mixture depending on the temperature the exhaust gases are controlled behind the combustion chamber. 6. Apparatus for carrying out the method according to claims 1 and 2, characterized in that the combustion chamber ( 2 ) which is closed at one end is arranged in the exhaust line ( 1 ) of the internal combustion engine and forms an annular space ( 4 ) with it through openings ( 7 ) in the wall of the combustion chamber ( 2 ) is connected to the interior thereof, that an exhaust pipe ( 5 ) connects to the open end of the combustion chamber ( 2 ), that the annular space ( 4 ) from a transverse wall ( 6 ) is limited, which forces the entire exhaust gas flow to flow from the annular space ( 4 ) through the openings ( 7 ) into the combustion chamber ( 2 ) and from there into the exhaust pipe ( 5 ), and that at the other end of the combustion chamber ( 2 ) one Nozzle ( 8 ) is arranged, which is connected to a device ( 11 ) producing the ignitable fuel-air mixture and through which the mixture is introduced into the combustion chamber ( 2 ). 7. The device according to claim 6, characterized in that the combustion chamber ( 2 ) from the nozzle ( 8 ) widens out in a funnel shape. 8. The device according to claim 6, characterized in that the fuel-air mixture generating device ( 11 ) has an air pump ( 12 ) and a fuel pump ( 13 ), which are preferably driven by an electric motor ( 15 ), that the Delivery line ( 17 ) of the fuel pump ( 13 ) opens into the intake line ( 18 ) of the air pump ( 12 ) and the delivery line ( 19 ) of the air pump ( 12 ) is connected to the nozzle ( 8 ), and that the delivery rates of the air pump and the fuel pump are coordinated so that an ignitable mixture is generated. 9. The device according to claim 8, characterized in that the speed of the electric motor ( 15 ) is multi-stage or continuously adjustable. 10. The device according to claim 8, characterized in that in the delivery line ( 19 ) of the air pump ( 12 ) a shut-off valve ( 24 ) is provided which is closed when the burner ( 3 ) is switched off. 11. The device according to claim 6, characterized in that a soot filter ( 21 ) is arranged in the exhaust pipe ( 5 ). 12. The apparatus according to claim 6, characterized in that in the exhaust pipe ( 5 ) an oxidation catalyst ( 21 ) is angeord net.