EP1212522A1

EP1212522A1 - Method and device for treating exhaust gases produced by an internal combustion engine

Info

Publication number: EP1212522A1
Application number: EP00969193A
Authority: EP
Inventors: Nikolaus Benninger; Horst Harndorf
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-08-21
Filing date: 2000-08-18
Publication date: 2002-06-12
Also published as: JP2003507631A; DE19939807A1; DE19939807C2; WO2001014697A1; US6810657B1

Abstract

The invention relates to a method and a device for the post-treatment of exhaust gases from an internal combustion engine (1), especially in a motor vehicle. The invention is characterized in that the following devices are provided: a hydrolysis unit (10) and a dosage device (15) connected to said hydrolysis unit via a hydrogen line (17) for the dosed introduction of hydrogen to the crude exhaust gas (A) and/or to exhaust gas treated by an oxidation catalyst (3), in addition to a control/regulating unit (18) which is functionally connected to the hydrolysis unit (10) and the dosing device (15) in order to control or regulate hydrogen generation in the hydrolysis unit (10) and the dosing device (15) independently from the operational state of the internal combustion engine (1) and detected parameters of the exhaust gas system parameters.

Description

METHOD AND DEVICE FOR EXHAUST GAS TREATMENT OF THE EXHAUST GENERATED BY AN INTERNAL COMBUSTION ENGINE

State of the art

The invention relates to a method and a device for exhaust gas aftertreatment, in particular for lean-burn engines in motor vehicles, for. B. directly injecting diesel engines and gasoline engines as well as maintaining the functionality of NO _x storage catalysts in gasoline and diesel engines and particle filters in diesel engines.

In the case of the oxidation catalytic converter sitting in the exhaust pipe of a modern gasoline or diesel engine with direct injection, SO _x deposits in the oxidation catalytic converter deteriorate the desired N0 ₂ formation up to the inactivity of the catalytic converter system. N0 ₂ becomes at NO _x -

Storage catalysts required for the storage process. For particle filters that use the CRT process

(CRT: Continuously Regeneration Trap), N0 _{2 is} required for the continuous oxidation-regeneration process of the soot particles. In the case of sulfur contamination of the NO _x storage catalytic converter, the desired NO ₂ storage is reduced due to the SO _x deposits in the NO _x adsorber which arise from the fuel sulfur until the system is completely inactive. The breakdown of this sulfur compound regeneration of the storage catalytic converter is possible by briefly applying increased exhaust gas temperatures (a temperature greater than 650 ° C is used in gasoline direct injection engines). The realization of such exhaust gas temperatures in diesel engines is not considered promising in the prior art. Particulate filters that use the CRT process mentioned above require exhaust gas temperatures that exceed 230 ° C for the continuous regeneration process. These conditions cannot always be met with the direct-injection diesel engine. As a result, a critical filter loading can occur, which may lead to the destruction of the particle filter.

For the regeneration process of NO _x storage catalysts, C0, which comes from the fuel hydrocarbon, must be added and at the same time a rich exhaust gas composition (λ <l) must be generated. The provision of the hydrocarbons (HC) required for regeneration in diesel engines is, however, inherently atypical and extremely critical in diesel engines, and is also associated with high consumption losses. In contrast to the petrol engine, the process gas throughputs in the diesel engine are much higher, which means that the temperatures required for regeneration cannot be reached at all operating points. The post-engine provision of a "rich" exhaust gas composition in the diesel engine is also problematic, since an oxidation catalytic converter is necessary for the formation of CO, an exhaust gas temperature profile is sometimes inadequate, and cycles with rich exhaust gas can only be achieved via a bypass system.

Object and advantages of the invention

The object of the invention is to avoid the above-mentioned difficulties in exhaust gas aftertreatment in modern lean-burn engines, in particular gasoline and diesel engines with direct injection in motor vehicles, and to provide a method and a device for exhaust gas aftertreatment of the exhaust gas generated by an internal combustion engine so that if necessary the Exhaust gas temperature increases, overall exhaust gas quality and especially under certain operating conditions of the internal combustion engine improved, at the same time the engine acoustics do not deteriorate and regeneration of a storage catalytic converter and / or a particle filter at regular intervals and / or after sulfur poisoning at the oxidation levels of a NO _x storage catalyst and particle filter are made possible.

This task is solved according to the requirements. According to an essential aspect, in the method for exhaust gas aftertreatment according to the invention, a hydrolysis unit for the production of hydrogen is provided, which is connected on the one hand to a water reservoir and on the other hand to a metering device for metering in the amount of hydrogen supplied to the raw exhaust gas and / or the exhaust gas treated by an oxidation catalyst Dependency on a requirement for hydrogen occurring in certain operating states and / or catalyst functions is set up.

In one embodiment of the method, the amount of hydrogen required in each case can be d. H. discontinuously generated in the hydrolysis unit and then made available directly for metering.

In an alternative embodiment of the method, a hydrogen reservoir can be provided, which temporarily stores a certain amount of the hydrogen generated by the hydrolysis unit.

The size of the hydrogen reservoir and thus the amount of temporarily stored hydrogen can be dimensioned such that it is sufficient to heat and regenerate a NO _x storage catalytic converter.

With appropriate design of the connecting pipes between the metering device and the hydrolysis unit the reservoir can be represented by the inner lumen of the pipeline.

For the metering of the hydrogen to be supplied, the temperature of the raw exhaust gas, the λ value and also certain operating states of the catalyst system are preferably recorded.

In the case of a diesel engine, in particular with direct injection, the addition of hydrogen to the exhaust gas is activated when hydrocarbon production within the engine is not possible.

In the case of a gasoline engine, in particular one with direct injection, the addition of hydrogen to the exhaust gas is activated if the current engine operating point does not allow an internal engine hydrocarbon supply at a sufficient temperature.

The method according to the invention can be used to restore a sufficient conversion rate after sulfur poisoning at the oxidation levels of a NO _x storage catalytic converter or a particle filter by regenerating the oxidation levels of the storage catalytic converter or the particle filter by means of hydrogen reduction. The regeneration by adding hydrogen can be activated whenever a decrease in the conversion rate of the NO _x storage catalytic converter or the particulate filter is detected. In temperature-critical low-load operation of an internal combustion engine, the exhaust gas temperature can be raised by the addition of hydrogen according to the invention, in order to ensure the regeneration conditions in the low-load range during operation of a particle filter.

In a device for aftertreatment of the exhaust gas of an internal combustion engine, in particular in a motor vehicle, which solves the above object, there is a hydrolysis unit and a metering device connected to it via a hydrogen line for metered addition of the hydrogen to the raw exhaust gas and / or to the exhaust gas treated by an oxidation catalyst and a control and regulating unit is provided which is functionally connected to the hydrolysis unit and the metering device in order to control or regulate the generation of hydrogen in the hydrolysis unit and the metering device depending on specific operating states of the internal combustion engine and on detected parameters of the exhaust system.

The metering device is preferably a metering and shut-off valve.

The control unit preferably has a catalyst monitoring function that is functionally connected to an exhaust gas sensor system.

The above and further advantageous features of the method according to the invention and of the invention Devices are explained in the following description of preferred exemplary embodiments of the method according to the invention and the device according to the invention with reference to the drawing figures.

drawing

Figure 1 shows schematically in the form of functional blocks, a first embodiment in which the inventive method for exhaust aftertreatment is used in an internal combustion engine equipped with NO _x storage catalyst in the exhaust system.

FIG. 2 also shows schematically, in the form of a functional block diagram, a second exemplary embodiment in which the inventive method for exhaust gas aftertreatment is used in an internal combustion engine equipped with a CRT particle filter in the exhaust system.

embodiments

FIG. 1 schematically shows blocks which illustrate the essential functions and elements of a first exemplary embodiment of the method according to the invention. From water removed from a water tank 19, a hydrolysis unit 10 generates hydrogen (H ₂ ) in a certain amount on request, which is passed through a hydrogen line 17 via a pressure reducing valve 14 to a metering and Shut-off valve 15 and from there the raw exhaust gas is mixed at a point β and / or the exhaust gas treated by an oxidation catalytic converter 3 is added at a point 7 in an exhaust pipe 2 leading from an internal combustion engine 1. The arrow A indicates the direction of flow of the exhaust gas. A NO _x storage catalytic converter 4 is located in the exhaust pipe 2, downstream of the oxidation catalytic converter 3.

The H ₂ gas which is generated by the hydrolysis unit 10 can either be generated in the amount required in each case on request, or a hydrogen reservoir 11 can be connected between the hydrolysis unit 10 and the pressure reducing valve 14, from which a condensate return RK via Shut-off valve 16 leads to water tank 19. A pressure sensor 13 is connected to the hydrogen reservoir 11 serving as an intermediate store. Furthermore, a safety valve 12 is attached to the hydrogen reservoir 11. Optionally, the hydrogen reservoir 11 can also be represented by the inner lumen of the H _{2 line} 17.

The metering and shut-off valve can be designed such that, if required, the hydrogen flowing to point 6, ie the hydrogen portion added to the raw exhaust gas and the hydrogen portion added to the exhaust gas after the oxidation catalyst 3 (at point 7), can be metered separately. FIG. 1 also shows that a control unit 18 has an interface which is connected to the hydrolysis unit 10, the pressure sensor 13 of the hydrogen reservoir 11, the metering and shut-off valve 15, the shut-off valve 16 and a temperature sensor 5 measuring the exhaust gas temperature T _A stands. The control unit 18 is set up to control and regulate the generation of hydrogen in the hydrolysis unit 10 and the metering device 15 as a function of certain operating states of the internal combustion engine 1 and of detected parameters of the exhaust system, which includes the exhaust gas temperature T _A.

If the equipped with the device for aftertreatment of the exhaust gas according to the invention internal combustion engine 1 z. B. is a direct injection gasoline engine, the inventive method can be applied in various ways:

1. Add H ₂ to the raw exhaust gas (at point 6) to show the regeneration phases of the NO _x storage catalytic converter 4 (spacing approx. 1 x per minute), if the current engine operating point does not allow HC to be provided on the engine at a sufficient temperature. The regeneration is controlled by the control unit 18 in analogy to the NO _x catalyst control in the gasoline direct injection engine.

2. Restoration of a sufficient conversion rate after sulfur poisoning at the oxidation stages of the NO _x storage catalytic converter 4. This is, e.g. B. after a few hours of operation, depending on the sulfur content of the fuel. The regeneration is controlled by the control unit 18 after the decrease in the conversion rate has been detected. For this purpose, the control unit 18, which is connected to a corresponding catalyst sensor system, has a catalyst monitoring function.

Figure 2 shows a second embodiment in which the inventive method in a motor vehicle engine equipped with a CRT particle filter, for. B. a diesel engine with direct injection is used for exhaust gas aftertreatment. Such a particle filter 8, as shown in FIG. 2, is contained in the exhaust pipe 2 of the direct-injection diesel engine 1. An oxidation catalytic converter 3 is connected upstream of the CRT particle filter 8. The hydrogen generated by the hydrolysis unit 10 and dosed in an appropriate amount by the metering and shut-off valve 15 is mixed at point 6 with the raw exhaust gas which flows through the exhaust pipe 2 (arrow A). All other apparatus details of the device shown in FIG. 2 are identical to those of the device described above and shown in FIG. 1.

There are several different uses here:

1. In the diesel engine, H _{2 is added to} the raw exhaust gas to represent the regeneration phases of the particle filter 8, if an internal engine HC generation not possible. The regeneration is controlled in analogy to the NO _x catalyst control in gasoline direct injection engines.

2. In the diesel engine, the method according to the invention can be used to restore a sufficient conversion rate after sulfur poisoning of the particle filter 8 by the method according to the invention. This is e.g. B. required after a few hours of operation depending on the sulfur content of the fuel. The control of the regeneration of the particle filter 8 can start after a recognized decrease in the conversion rate, for which purpose a catalyst monitoring function is integrated in the control unit 18.

3. The exhaust gas temperature can be raised by the introduction of hydrogen according to the invention to ensure the regeneration conditions during operation of the particle filter 8 in temperature-critical low-load areas.

It also applies in FIG. 2 that the H ₂ reservoir 11 is only optionally available, and instead an H ₂ tube with sufficient inner lumen can replace the H ₂ reservoir 11 serving as a buffer.

Taken together, the method according to the invention for the aftertreatment of the exhaust gas of an internal combustion engine, in particular in a motor vehicle, serves to increase the exhaust gas and catalyst temperature, which is particularly the case with Cold start and in low load operation is required. Furthermore, with the method according to the invention, hydrogen can be generated “on-board” and in transient operation and, depending on the need and application, can be added to the catalyst or particle filter via the metering and shutoff valve 15. In contrast to the internal engine HC generation, which requires a "common rail" injection system, the exhaust gas quality, in particular the particle rate, and the engine acoustics are not additionally deteriorated. In addition, the response behavior of the systems is much faster when hydrogen is added.

1. A method for exhaust gas aftertreatment of the exhaust gas generated by an internal combustion engine (1), in particular in a motor vehicle, characterized by

Providing a hydrolysis unit (10) connected to a water reservoir (19) for the production of hydrogen, and

Metering of the amount of hydrogen supplied to the raw exhaust gas (A) and / or the exhaust gas treated by an oxidation catalytic converter (3) depends on a need for hydrogen occurring in certain operating states and / or catalytic converter functions.

2. The method according to claim 1, characterized in that the required amount of hydrogen is generated on request in the hydrolysis unit (10) and is made available directly for metering.

3. The method according to claim 1, characterized by the

Provision of a hydrogen reservoir (11) which stores a certain amount of the hydrogen generated by the hydrolysis unit (10).

4. The method according to claim 3, characterized in that the amount of hydrogen in the reservoir (11) is dimensioned such that it is sufficient for heating and regeneration of a NO _x storage catalyst (4). 5. The method according to any one of the preceding claims, characterized in that the temperature (T _A ) of the raw exhaust gas (A) and certain operating states of the catalyst system (3, 4) are detected.

6. Use of the method according to any one of claims 1 to 5 for the representation of regeneration phases in a NO _x storage catalyst, wherein hydrogen is added to the raw exhaust gas in certain time intervals and in each required amount.

7. Use according to claim 6, characterized in that in the case of a diesel engine the addition of hydrogen to the exhaust gas is activated when an internal engine hydrocarbon production is not possible.

8. Use according to claim 6, characterized in that in the case of a gasoline engine, the addition of hydrogen to the exhaust gas is activated if the current engine operating point does not allow an internal engine hydrocarbon supply at a sufficient temperature.

9. Use of the method according to one of claims 1 to 5 for restoring a sufficient conversion rate after sulfur poisoning at the oxidation stages of a NO _x storage catalyst (4) or a particle filter (8) by regeneration of the Oxidation levels of the storage catalytic converter (4) or of the particle filter (8) by means of hydrogen reduction.

10. Use according to claim 9, characterized in that the regeneration is activated after detection of the decrease in the conversion rate of the NO _x storage catalytic converter (4) or of the particle filter (8).

11. Use of the method according to one of claims 1 to 5 for raising the exhaust gas temperature (T _Ä ) to the

To ensure regeneration conditions when operating a particle filter (8) in temperature-critical low-load operation.

12. Device for aftertreatment of the exhaust gas of an internal combustion engine (1), in particular in a motor vehicle, characterized in that a hydrolysis unit (10) and a metering device (15) connected to it via a hydrogen line (17) for metered addition of hydrogen to the raw exhaust gas ( A) and / or to the exhaust gas treated by an oxidation catalyst (3) and a control / regulating unit (18) are provided, which is in functional connection with the hydrolysis unit (10) and the metering device (15) in order to generate hydrogen in to control or regulate the hydrolysis unit (10) and the metering device (15) depending on specific operating states of the internal combustion engine (1) and on detected parameters of the exhaust system. 13. The apparatus according to claim 12, characterized in that the metering device (15) is a metering and shut-off valve.

14. The apparatus according to claim 12 or 13, characterized in that the hydrolysis unit (10) is followed by a hydrogen intermediate store (11) in order to store a certain amount of hydrogen.

15. Device according to one of claims 12 to 14, characterized in that the control / regulating unit (18) has a catalyst monitoring function which is in functional connection with an exhaust gas sensor system (5).