DE19835565A1 - Vehicle exhaust gas treatment unit with reversible gas flow-path controlled temperature profile, for reduction and degradation of nitrogen oxides, hydrocarbons, and sulfur dioxide - Google Patents

Abstract

A monolithic body (4) contains channels (3) and an end section enclosed by a dome (13) which allow two-pass flow of exhaust gas through the body via inlet and outlet sections in the end face (2). The body contains a filter disk (6), and parts (T2) of the flow channels (3) may be internally coated or contain catalytic reductants/ oxidants for nitrogen oxides, hydrocarbons, and /or carbon monoxide. The flow channel section, and preferably the whole body (4), is rotatable about its central axis by a drive unit (9), so that flow channel sections B1 and B2 are alternatively connected to the inlet and outlet ports (1,8). The rotation speed is adjusted to ensure that the filter (6) remains the hottest part of the unit, and is typically 0.3-10 rpm. The processes of continuous soot retention and after-burning in a unit of this type, and also of desulfurization are CLAIMED. For desulfurization a temperature of approximately 650 deg C, and a reducing atmosphere, is produced in the device by controlling the rotation and injecting fuel into the engine exhaust manifold. Nitrogen oxide catalysts may be platinum type, and the storage catalyst may be zeolite based.

Description

The invention relates to a device and a method for aftertreatment of the Engine exhaust gases from an internal combustion engine, and particularly relates to a device and a Process for the aftertreatment of soot particles and nitrogen oxides.

Known NOx catalysts absorb that during the lean operation of an engine generated nitrogen oxides and reduce the stored NOx during a rich operation of the Motors, the known methods are discontinuous and the storage and Reduction of nitrogen oxides occurs in different phases. To such a thing To be able to carry out procedures, the memory has to wait for a certain time its finite absorption capacity can be emptied. This happens either after expiration a predetermined time or the degree of filling of the catalyst must be determined become. If the memory is regenerated after a fixed predetermined time, this has the disadvantage that the storage capacity of the catalyst is not full for safety reasons is exploited so that no optimal engine operation in terms of consumption and exhaust gas behavior is possible. Is the memory regenerated when a certain filling level of the Memory is reached, this has the disadvantage that an additional device is required is determined, the degree of filling of the NOx storage catalyst. The exact one Determination of the degree of filling of the memory difficult, so that here too on the brisk nerative operation is switched when the memory is not completely filled. Ultimately, this also leads to less than optimal operation of the engine. Furthermore applies to both methods that during the rich operation of the engine no optimal exhaust behavior achieved and a complicated motor control is required for cyclic motor operation.

The invention is therefore based on the object of a device and a method for Treatment of the exhaust gas flow of an internal combustion engine to develop a  enable optimal engine operation. Furthermore, in the case of a NOx storage reduction catalyst a simple process for desulfating can be created.

The invention is solved by the features of claims 1, 18 and 21. Preferred Embodiments of the invention are the subject of the dependent claims.

The device according to the invention for the aftertreatment of the engine exhaust gases Internal combustion engine has a body or monolith with Ka through which the exhaust gas flows channels, which is rotatably arranged in the exhaust gas flow. Monolith is a body here understood that in one piece from ceramic, from metallic carrier materials or from ke ramischen or metallic segments, which are arranged in a receiving structure, can exist.

Preferably, the device comprises a filter which can be rotatably arranged, wherein the filter can rotate especially with the monolith.

Furthermore, the device has an inflow channel which is connected to a part (B1) of the channels of the Body is in fluid communication. A flow connection is also provided, that on the output side with the part B1 of the channels flowed against by the inflow channel Connection is established and connects this in terms of flow to part B2 of the channels, which is not in flow connection with the inflow channel.

Preferably, the body or monolith is divided into two areas B1, B2, the exhaust gas entering the first area B1 on the front face of the body, exiting on the rear face of the first area B1, passing through the filter attached there, into one End face of the second area B2 enters and leaves the second area B2 on the other end face 2 , the body 4 rotating during the flow around an axis parallel to the flow direction of the exhaust gas stream. Furthermore, the exhaust gas flow after exiting the rear end face of the first region and passing through the filter can undergo a 180 ° turn and enter the rear end face of the body in the second region B2 through the filter.

The subdivision of the storage catalytic converter or of the monolith into the first and the second area B1, B2 is effected by a wall that the incoming Exhaust gas flows into the first area B1 of the monolith.

Furthermore, the internal combustion engine can directly inject fuel into the combustion chamber have and / or be a diesel fuel machine.

The filter preferably has a heating element, for example after a filter Bring cold start to the necessary temperature. After reaching the required The temperature can be switched off at a temperature of approx. 200 ° C. Basically is Additional heating is only provided if the engine conditions (Exhaust gas temperature) do not lead to soot burn-off. In particular, the required Alternative or supportive temperature for the conversion of pollutants also suitable selected engine parameters (injection quantity, injection process, post-injection) quickly be achieved, again the motor parameters are based on their normal conditions returned when the desired temperature is reached.

The device also has a fixed housing in which the body ( 4 ) rotating about its longitudinal axis is arranged. The rotation of the body can be brought about by a drive unit, wherein an electric motor can be used as the drive unit. The rotational speed of the body is preferably approximately 0.3 to 10 rpm. However, it is also possible to rotate the body or the monolith in the manner of a turbine by means of the gas pressure of the inflowing exhaust gas.

The body for reducing pollutants, in particular for reducing NOx, HC and / or CO, is preferably at least partially catalytically coated, the body being made of metal or ceramic. The body ( 4 ) is preferably a monolith.

The method according to the invention for the continuous afterburning of the soot particles in the exhaust gas stream of a diesel engine, wherein a body is arranged in the exhaust gas stream, which has channels in the exhaust gas flow direction and is divided into two areas B1, B2, has the following steps:
Directing the exhaust gas flow into the front end face of the first area B1,
Directing the exhaust gas flow on the rear end face of the first area B1 into an end face 5 of the second area B2 and exiting the exhaust gas flow on the other end face of the second area B2, and
Rotating the body about an axis during operation so that the channels change from the first area B1 to the second area B2.

The body is preferably rotated about its axis at such a speed that that heating of the second region B2 by the exhaust gas flow leads to heating of the exhaust gas flow through the first area.

Furthermore, a retention or retention of the soot particles of the exhaust gas flow on one Filter that acts between the rear face of the first area B1 and Exhaust gas inlet end face of the second region B2 is arranged, and the Rotation speed is chosen so that the maximum of the temperature front is in is located on the filter.

In the inventive method for desulfating a device for Aftertreatment of the exhaust gases of an internal combustion engine begins at the beginning of the desulfation ver rotation of the body while increasing the amount of pollutants in the exhaust gas slow or exposed until an emerging temperature maximum in or through the second area B2, in particular near the exhaust gas outlet-side end face of the second Area B2 has migrated, the body is rotated until the second area B2 the place of occupies the first area at least predominantly, so that the temperature maximum above lies primarily in the first range, and the rotation is suspended until the temperature measure ximum has at least reached the second area B2, and the post-injection will take place below and the body turned again.

The slowdown of the rotation or the stop of the body can be repeated several times until essentially all areas have been desulfurized.

Continuous rotation of the body resumes when the tem temperature maximum is approximately at the interface of the two areas B1, B2.  

In summary, the device according to the invention and the corresponding method have the following advantages:
Due to the good heat recovery due to the rotation of the monolith and the flow reversal of the exhaust gas, continuous soot afterburning is achieved, which offers energetic advantages.

Continuous soot combustion is much easier and more effective than dis continuous process.

There is no dangerous spontaneous ignition of accumulated soot.

The system has a lower pressure drop than systems with one-sided locking channels.

The monolith used for the soot filter as a heat exchanger is replaced by a Appropriate coating used as NOx storage.

Due to the increase in exhaust gas temperature, the catalytic converter achieves greater effectiveness.

Desulfation of the NOx storage catalytic converter is possible.

A preferred embodiment of the invention is described below with reference to the drawings explained.

Fig. 1a shows a cross section through an inventive NOx catalyst,

FIG. 1b shows a view of the catalyst of Fig. 1b from below,

Fig. 2 shows temperature profiles of the rotating monoliths for three different channels,

Fig. 3 shows the migration of the temperature front at the start of desulfation,

Fig. 4 shows the migration of the temperature front during desulfation, and

Fig. 5 shows the migration of the temperature front at the decay of the desulfation.

FIGS. 1a and 1b show a cross section and a bottom view of a preferred embodiment of the device for exhaust gas treatment.

The exhaust gas coming from an engine (not shown) is applied to the first half of the front end face 2 of a monolith 4 with channels 3 via an inflow channel 1 . The engine exhaust flows in this area, hereinafter called the first area B1, the monolith 4 from the front to the rear. On the rear side of the monolith 4 , the exhaust gas enters through the first half of the rear end face 5 into a filter mat 6 and is deflected by 180 ° after passing through the filter mat 6 (deflection 7 ) and enters through the second half of the rear end face 5 in the second half of the monolith 4 , hereinafter referred to as the second region B2, flows through it from the rear to the front and then enters the outflow channel 8 through the second half of the front end face 2 for forwarding to the muffler (not shown). During the flow, the monolith 4 rotates in the circumferential direction, ie around an axis parallel to the flow direction of the exhaust gas. Furthermore, the monolith 4 is provided with an inert surface or coating in its lower part T1, while it is provided with a catalytic coating in its upper and generally larger part T2 and therefore acts as a NOx storage catalytic converter. The catalytic coating can also extend over the entire monolith 4 .

The rotation of the monolith 4 is realized by a suitable electric drive 9 . For this purpose, the monolith 4 is mounted on a rotatably mounted shaft 10 , which is set in rotation by the above-mentioned drive 9 . When using an electric motor, the rotational speed can be adapted to the operating state of the vehicle engine using suitable information from the engine control unit. In addition, targeted regeneration measures can be initiated by freely regulating the rotation, which will be explained in more detail below.

A cover 11 serves to protect the drive unit 9 and likewise prevents exhaust gases from escaping in the event of gas leakage at the shaft bushing.

Furthermore, the monolith 4 is arranged in a fixed housing 12 , the housing 12 having a dome 13 which causes the gas flow to be deflected 7 .

The method on which the device is based is a continuous afterburning of the soot particles in the filter mat 6 . This post-combustion takes place in an oxygen-rich atmosphere at temperatures between 500 ° C (catalytically supported) and 600 ° C (not catalytically supported). The engine exhaust and the filter mat 6 must be heated to this temperature.

The soot particles are caught in the filter mat 6 and have enough time to be completely oxidized there. By turning filter mat 6 further, excessive accumulation of particles in area B1 is avoided.

The exhaust gas temperature of the diesel engine is too low at low and medium loads to reach a sufficiently high temperature in the system for the soot particles to burn up. In the event of a cold start of the vehicle, that is to say a completely cooled exhaust system, the filter mat 6 is heated by an additional heat source (not shown). For this purpose, an electrical heater (not shown) integrated in the filter mat 6 is provided, which can be switched off after the required temperature of approximately 200 ° C. has been reached. Heating is only necessary if the motor conditions do not lead to soot burn-off. In addition, the use of so-called flame candles, such as those used in diesel-powered car parking heaters, can be considered.

If engine exhaust gas now flows through the heated filter mat 6 , part of this heat is transported into the upper part of the catalytic converter (monolith 4 ). The filter mat 6 is not heated until the working temperature of 600 ° C. is reached, but only until the upper part of the monolith 4 is at the ignition temperature. The ignition temperature (approx. 200 ° C) is the temperature at which the catalytic conversion of the incomplete combustion products (CO, HC, H ₂ ) in the exhaust gas begins. The further increase in temperature then takes place due to the heat of reaction released during the implementation of the exhaust gas components mentioned. This measure is energetically much more effective than complete electrical heating.

The filter mat 6 must be such that the soot particles can be retained in the filter mat 6 until the combustion temperature is reached. So no soot particles get into the environment even when the device is started up.

Furthermore, the heating of the system above the ignition temperature after a cold start, as well as the heat required during operation to keep the system at the required level Maintain temperature level through the catalytic conversion of products incomplete combustion reached. The concentrations required for this are in the However, rule over those that are released during regular engine running. By The use of a common rail injection system will result in targeted post-injection required concentrations reached. The system has a corresponding one for this Control.

The front part T1 of the monolith 4 of FIG. 1a is only used for heat exchange and is not catalytically active. The middle and rear part T2 of the monolith 4 is generally in a temperature range of 250-500 ° C. and is used as a catalyst for removing the nitrogen oxides by means of a corresponding catalytic coating. Both continuously acting catalysts based on platinum or zeolite are possible, as are storage catalysts.

A reducing atmosphere must prevail for the regeneration of the storage catalyst loaded with nitrogen oxides (monolith 4 with appropriate coating). This exhaust gas composition with an air ratio of λ <1 is also achieved by post-injection using common rail at selected operating points of the engine or, in the case of non-common rail engines, is generated by suitably selected engine parameters.

FIG. 1b shows a bottom view of the device according to Fig. 1a, in which the front end face 2 is visible to the channels 3 of the monolith 4 in the housing 12. The subdivision of the monolith into a first region B1 and a second region B2 is brought about by a wall 14 which guides the exhaust gas flow supplied in the first region B1 of the monolith 4 . This wall 14 is formed by a corresponding shape from the hood 11 . The exhaust gas flow direction in this view is represented by arrows 15 and the direction of rotation of the monolith 4 around the shaft 10 by an arrow 16 . Furthermore, the locations of three channels K1, K2 and K3 are shown, which will later be required to explain the temperature fronts in the monolith 4 .

Fig. 2 shows temperature profiles of three different channels K1, K2, K3 of the monolith. The model calculations assume an exhaust gas temperature of approx. 100 ° C.

In order to afterburn the soot particles stored in the filter mat, the engine exhaust gas and filter mat must be heated to 500-600 ° C. A very high degree of heat recovery is required for energy-efficient operation of the system. This effect can be achieved by rotating a heat-storing medium, here the monolith, in connection with the flow reversal (regenerator principle). There are temperature profiles for different channels of the monolith as shown in FIG. 2. To understand this figure, imagine the area B1, the filter mat and the area B2 connected in series. When flowing through the system, the gas flows through the individual areas in this order. Without rotation, the temperature front would be driven out of the system. By turning the monolith, the temperature font is driven back into the system again and again. On average, a periodically stationary profile is created, the maximum of which lies in the area of the filter mat.

In FIG. 2, the temperature T [° C] with respect to the coordinate x [m] is applied a channel of the monolith. Here, a channel of the monolith under consideration is formed by, as already described, the area B2 of the monolith being mentally folded up, that is to say the first area B1, the filter mat and the second area B2 are arranged one behind the other so that the flow through them Gas gives a "straight" channel. It is consequently assumed for the purpose of explanation and calculation that a channel of the area B1 would be connected to its channel of the area B2 arranged symmetrically with respect to the axis of rotation.

The curve at time t0 in FIG. 2 shows the temperature profile of a channel K1, which was just turned into area B1 coming from area B2 and is now subjected to exhaust gas (see FIG. 1b). The exhaust gas temperature of 100 ° C assumed to simplify the calculation is then colder than the temperature of channel K1, which previously had a temperature of approx. 200 ° C at its exit in area B2 due to the catalytic conversion of HC, CO, H ₂ . It can be seen that the maximum temperature of the channel K1 is in front of the dashed interface (180 ° reversal area 7 ) of the areas B1 and B2, which is located at the location x = 0.2 in the figures.

A further rotation of the monolith by 90 ° leads to channel K2. Due to the cooling The front face of area B1 of the monolith is the temperature at the beginning of the Channel fell and the maximum of the temperature front has moved towards the middle, i.e. H. the area the filter mat.

A further turning of the monolith by approximately 90 ° leads to a channel K3 which is just in area B1 and shortly before moving to area B2 stands. The entrance of channel K3 has now reached the exhaust gas temperature of 100 ° C, but the maximum of the temperature front is already in the second area B2 of the monolith. Would the channel K3 not change to the second area B2, for example if If no rotation were carried out, the temperature front would be made from the monolith wander out. The change of the channel K3 into the second area B2 means that the end of channel K3 moves into area B1 and becomes an entrance. With others Words, the process begins again with channel K1, which is currently in area B1 has changed. In this way, the temperature front through the rotation in the Monoliths held and on the average is the maximum of the temperature front in the Area of the exhaust gas deflection by 180 ° in which the filter mat is located.

FIGS. 3-5 based on temperature profiles of a channel of a cascaded considered areas B1 and B2 of the monolith the course of desulfation of a designed as a NOx storage catalytic converter monolith.

When using sulfur-containing fuel, the catalyst must be desulfated from time to time. This takes place thermally at temperatures above 650 ° C in a slightly reducing atmosphere (λ = 0.98-0.95). As already mentioned above, an almost arbitrary increase in temperature can be achieved by post-injection. By suitably controlling rotation and post-injection, a temperature front can be driven over the monolith in such a way that each area can be kept at the required high temperatures for the required time of approximately 20 to 300 seconds. This is shown in Figs. 3-5.

FIG. 3 shows the beginning of desulfation using the example of a channel, for example channel K1 of FIG. 2, based on the temporal development of the temperature front in this channel. The local course of the temperature front is shown, the location x = 0.2 representing the interface of the areas B1 and B2, ie the location of the filter mat. At the beginning of the desulfation, shown by the curve at time t0, the rotation is suspended while increasing the post-injection until the temperature front has moved from approx. 700 ° C in the area B2 to just before the outflow channel (times t1-t4). The following generally applies to the representation in FIGS. 3-5: t0 <t1 <. . .t20.

At time t4, the monolith is rotated by 180 ° and the development of the temperature front over time is shown in FIG. 4 for times t5 to t14. Now the high temperatures are in the B1 range. The rotation is again suspended until the temperature front has passed through areas B1 and B2. Now every area of the monolith was exposed to the high temperatures required. The post-injection is reduced again.

Now the monolith is rotated again by 180 ° and the temperature profiles for the times t15 to t20 are shown in FIG. 5. When the maximum of the temperature front has returned to the location of the filter element (x = 0.2) at time t20, the desulfation has ended and the process of continuous rotation is started again.

The energy expenditure for desulfation is compared to conventional systems much lower.

Should the period of time in which the catalytically coated part of the body on the Desulfation temperature has not been sufficient for complete desulfation the entire process can be repeated a corresponding number of times.  

Reference list

1

Inflow channel

2nd

front face

3rd

channels

4th

monolith

5

rear face

6

Filter mat

7

Redirection

8th

Outlet channel

9

drive

10th

wave

11

Cover

12th

casing

13

dome

14

wall

15

Exhaust gas flow direction

16

Direction of rotation monolith
B1 first area
B2 second area
T1 inert part of the monolith
T2 catalytically active part of the monolith
K1 first channel
K2 second channel
K3 third channel
t0-t20 times
T temperature
x location

Claims (23)

1. Device for the aftertreatment of the engine exhaust gases of an internal combustion engine, characterized in that the device has a body ( 4 ) with channels ( 3 ) through which the exhaust gas flows, which is rotatably arranged in the exhaust gas flow. 2. Device according to claim 1, characterized in that the device has a filter ( 6 ). 3. Device according to claim 2, characterized in that the filter ( 6 ) is rotatably arranged, in particular together with the body ( 4 ). 4. Device according to one of the preceding claims, characterized in that an inflow channel ( 1 ) is provided which is in flow connection with a part (B1) of the channels ( 3 ) of the body ( 4 ). 5. The device according to claim 4, characterized in that a flow connection ( 7 , 13 ) is provided, which is connected to the flow side of the inflow channel ( 1 ) part (B1) of the channels ( 3 ) and these flow with a Part (B2) of the channels connects that is not in flow connection with the inflow channel ( 1 ). 6. Device according to one of the preceding claims, characterized in that the body ( 4 ) is divided into two areas (B1, B2), the exhaust gas entering the first area (B1) at the front face ( 2 ) of the body , at the rear end face ( 5 ) of the first area (B1), through the filter ( 6 ) attached there, into an end face ( 5 ) of the second area (B2) and the second area (B2) at the other end face ( 2 ) leaves, the body ( 4 ) rotating during the flow around an axis parallel to the flow direction of the exhaust gas stream. 7. The device according to claim 6, characterized in that the exhaust gas flow after exiting the rear end face of the first region (B1) and passing through the filter ( 6 ) undergoes a 180 ° turn ( 5 ) and through the filter back into the rear face ( 5 ) of the body ( 4 ) enters the second area (B2). 8. The device according to claim 5-7, characterized in that the subdivision of the storage catalytic converter into the first and the second region (B1, B2) is effected by a wall ( 14 ) which the incoming exhaust gas flow in the first region (B1) of Body ( 4 ) conducts. 9. Device according to one of the preceding claims, characterized in that that the internal combustion engine has a direct fuel injection into the combustion chamber points and / or is a diesel fuel machine. 10. Device according to one of the preceding claims, characterized in that the filter ( 6 ) has a heating element. 11. Device according to one of the preceding claims, characterized in that the device has a fixed housing ( 12 ) in which the body ( 4 ) rotating about its longitudinal axis is arranged. 12. Device according to one of the preceding claims, characterized in that the body ( 4 ) for pollutant reduction, in particular for the reduction of NOx, HC and / or CO, is at least partially catalytically coated. 13. Device according to one of the preceding claims, characterized in that the body ( 4 ) is rotated by a drive unit ( 9 ). 14. The apparatus according to claim 13, characterized in that the drive unit ( 9 ) is formed by an electric motor. 15. Device according to one of the preceding claims, characterized in that the rotational speed of the body ( 4 ) is approximately 0.3 to 10 U / min. 16. Device according to one of the preceding claims, characterized in that the body ( 4 ) is made of metal or ceramic. 17. Device according to one of the preceding claims, characterized in that the body ( 4 ) is a monolith. 18. A method for the continuous afterburning of the soot particles in the exhaust gas flow of an internal combustion engine, characterized in that a body ( 4 ) is arranged in the exhaust gas flow, which is traversed in the exhaust gas flow direction with channels ( 3 ) and is divided into two areas (B1, B2), the exhaust gas flow is directed into the front end face ( 2 ) of the first area (B1), the exhaust gas flow at the rear end face ( 5 ) of the first area (B1) is led into an end face ( 5 ) of the second area (B2) and at the other end face ( 2 ) of the second area (B2) emerges, and the body ( 4 ) is rotated about an axis during operation, so that the channels ( 3 ) change from the first area (B1) to the second area (B2). 19. The method according to claim 18, characterized in that the body ( 4 ) is rotated about its axis at such a speed that heating of the second region (B2) by the exhaust gas flow leads to heating of the exhaust gas flow through the first region. 20. The method according to any one of claims 18 or 19, characterized in that a retention of the soot particles of the exhaust gas flow is effected on a filter ( 6 ) between the rear end face ( 5 ) of the first region (B1) and the exhaust gas inlet side end face ( 5 ) of the second region (B2) is arranged, and the rotational speed is chosen so that the maximum of the temperature front is approximately on the filter ( 6 ). 21. A method for desulfating a device for the aftertreatment of the exhaust gases of an internal combustion engine according to one of the preceding claims, characterized in that at the beginning of the desulfation, the rotation of the body ( 4 ) is slowed down or suspended while increasing the amount of pollutants in the exhaust gas until a temperature maximum occurring in or through the second area (B2), in particular near the exhaust gas outlet-side end face ( 2 ) of the second area (B2), the body ( 4 ) is rotated until the second area (B2) at least predominantly takes the place of the first area takes so that the temperature maximum is predominantly in the first area, and the rotation is suspended until the temperature maximum has at least reached the second area (B2), the post-injection is reduced and the body ( 4 ) is rotated again. 22. The method according to claim 21, characterized in that the slowdown of the Rotation or stop is repeated several times until essentially all areas are desulfurized. 23. The method according to claim 21 or 22, characterized in that the continuous rotation of the body ( 4 ) is resumed when the temperature maximum is approximately at the interface of the two areas (B1, B2).