WO2000032914A1

WO2000032914A1 - Device for secondary treatment of exhaust gases from an internal combustion engine

Info

Publication number: WO2000032914A1
Application number: PCT/DE1999/003107
Authority: WO
Inventors: Hermann Grieshaber
Original assignee: Robert Bosch Gmbh
Priority date: 1998-12-01
Filing date: 1999-09-28
Publication date: 2000-06-08
Also published as: DE19855385A1

Abstract

A device for secondary treatment of exhaust gases from an internal combustion engine, consisting of a reduction catalyst (18) that is used to reduce the NOx components of said exhaust gases and an exhaust pipe (2) leading thereto. The inventive device also comprises a supply (4) of reducing agent, a dosing device for said reducing agent (6, 10, 12) and a vaporization device (6) for said reducing agent, whereby the reducing agent is dosed (6, 10, 12) and at least partially vaporized by means of at least one nozzle (6) that is provided on the exhaust pipe (2). A heating element (8) can be associated with the nozzle (6). The nozzle (6) can also be embodied as a heater nozzle.

Description

Device for the aftertreatment of exhaust gases from an internal combustion engine

The present invention relates to a device ^'for the aftertreatment of exhaust gases of an internal combustion engine, with a reduction of NOx constituents of the exhaust gases serving reduction catalyst, in particular, but not exclusively for self-igniting internal combustion engines or diesel engines.

After the pollutant limits have been set ever lower in recent years, various devices for the after-treatment of exhaust gases from internal combustion engines have been developed in recent years. A very efficient way to treat exhaust gases are

Catalyst systems that use urea and / or ammonia as reducing agents for NOx conversion. This solution, although very effective, is relatively complex since the reducing agent has to be carried along with the fuel. Furthermore one should

Infrastructure to fill up with urea. Therefore, catalysts have been used in recent years developed, which are based on a NOX storage reduction process and which use the hydrocarbons of the fuel carried on board as a reducing agent. Various materials, such as alkali metals, are used in these processes to store nitrogen oxides. The conventional three-way catalytic converter technology is still used to convert the nitrogen oxides. This conversion takes place during the regeneration of the memory, ie in a phase during which the engine is briefly operated at λ <1.0, so that the conversion of NOX can take place. In other words, "lean exhaust" takes place at the NO x storage by NO is oxidized at a Edeϊmetallkatalysator to N0 _2, which is N0 ₂ adsorbed at the NO x storage member to nitrate formation. When the exhaust gas as the "fat", is detected or is adjusted a nitrate decomposition takes place so that N0 _{2 is} released, a reduction of NOX taking place on the noble metal catalyst. The effectiveness of the catalytic NOX reduction essentially depends on the treatment of the reducing agent at the catalyst inlet.

From DE-A-44 441 261 a device for the aftertreatment of exhaust gases from an internal combustion engine is known, in which the performance of the catalyst is to be improved via a metering device. The metering device is designed as a small-volume metering displacement pump, which has a thread in the form of a groove on a cylindrical rotating body, with the

Rotating body is driven at variable speed. In addition to the metering of the reducing agent, its condition when entering the catalyst is an extremely important treatment criterion. From DE-A-19 625 447 a device for aftertreatment of exhaust gases from an internal combustion engine with a reduction catalytic converter is known according to the preamble of claim 1. This generic device comprises a reduction catalyst serving to reduce NOX components of the exhaust gases, to which an exhaust pipe leads. The reducing agent is supplied via a reducing agent supply and metered in via a controllable valve. The metered amount of reducing agent is fed to a tube evaporator with a glow plug, which acts as a reducing agent evaporation device. ^'However, this known system does not guarantee any reducing agents -

Uniform distribution at the catalyst inlet. The cavity provided in the evaporation device also creates a certain dead volume, which prevents precise control of the processing of reducing agent and thus the entire aftertreatment.

It is accordingly an object of the present invention to develop a generic device for the aftertreatment of exhaust gases in such a way that an improved cleaning function is achieved.

According to the invention, this object is achieved by a device having the feature of claim 1.

Preferred embodiments are defined in the dependent claims. In particular, in the solution according to the invention, an improved uniform distribution of reducing agent is achieved in that the reducing agent is introduced by means of a nozzle provided on the exhaust pipe. The direct injection of the reducing agent directly upstream of the reduction catalytic converter also enables more precise control, both with regard to the amount of reducing agent and the preparation of the reducing agent.

The atomization or evaporation of the reducing agent is advantageously supported in that the nozzle has a heating device or is a so-called heating nozzle, a heating nozzle with self-regulating PTC heating elements being preferred in particular. In a particularly preferred embodiment, the reducing agent is largely evaporated and dispensed at temperatures of approximately 300 ° C. to 360 ° C. Heating nozzles with self-regulating thermistor heating elements are particularly preferred because only short-term regeneration phases are required and because with high efficiency an exact adjustment by means of a suitable selection of materials and thus resistance-temperature characteristics is possible.

Since the nozzle is provided directly on the exhaust pipe and may itself be heated as a heating nozzle, the nozzle should advantageously be formed from temperature-resistant materials. In addition and / or alternatively, individual heat decoupling elements, such as, for example, insulating bushes or the like, can also be provided in order to protect individual, thermally not so resistant components from the temperatures of up to 360 ° C. In a preferred embodiment, the nozzle is arranged on the exhaust pipe in such a way that it introduces the reducing agent into the exhaust pipe substantially perpendicular to the direction of movement of the exhaust gas. This arrangement enables a very high degree of uniformity of mixing with the exhaust gas at the catalyst inlet to be achieved. Furthermore, for improved mixing, the reducing agent can be introduced slightly off-center, for example, so that an exhaust gas swirl or rotation movement is caused.

The nozzle is advantageously arranged on the exhaust pipe in such a way that it is essentially flush with the inside of the exhaust pipe. This arrangement does not change the cross-sectional area of the exhaust pipe, so that the flow processes prevailing therein are easy to master.

An application device is preferably assigned to the nozzle, e.g. in the form of a gear pump with pressure regulator or the like. By applying the reducing agent, depending on e.g. the exhaust gas velocity in the exhaust pipe or other

Operating parameters of the engine, the speed of the introduced reducing agent and thus the even distribution can be controlled. Furthermore, the configuration with the application device enables an optimized injection, in which the

Evaporation effect can take place by means of relaxation, atomization and heating. In order to achieve an even better mixing of the exhaust gas with the reducing agent, in a preferred embodiment, a device is provided on or in the exhaust pipe that can influence the exhaust gas flow. This device can be provided, for example, in the form of simple baffle plates or more complex systems in order to give the exhaust gas flow a certain flow profile before and / or after introduction of the reducing agent, for example in order to achieve a swirl action on the exhaust gas or to generate a turbulent flow .

In addition to the reduction catalytic converter, the device advantageously comprises an oxidation catalytic converter connected upstream of this, which may be necessary for implementing the three-way catalytic converter principle for NOx conversion. In this embodiment, the nozzles or heating nozzles should be arranged upstream of the oxidation catalytic converter so that it converts hydrocarbons and thus consumes oxygen.

In a particularly advantageous embodiment, a plurality of nozzles are arranged on the exhaust pipe, these being particularly preferably arranged regularly. An arrangement that is constant in the radial direction is preferred as a regular arrangement. If, for example, three nozzles are used, they should preferably be arranged at 120 ° apart on a tube with a circular cross section. However, it should be understood that the arrangement of several nozzles does not necessarily have to be in one plane, but rather that there is a certain spacing in the axial direction Direction can be advantageous. Finally, it is also possible to provide a plurality of reducing agent supply nozzles spaced apart from one another at a radial position in order to utilize a flow profile present in the exhaust pipe for uniform distribution.

Finally, it is preferred that if more than one nozzle is provided, it can be controlled via an independent control. This control should include both the discharge rate, the nozzle opening degree, the

Atomization function and possibly control the heating elements.

Further advantages and features of the invention will become apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings, in which:

Figure 1 shows a schematic diagram of a device according to a preferred embodiment of the invention.

FIG. 2 shows a sectional view through part of the device shown schematically in FIG. 1.

FIG. 3 shows a sectional view through a heating nozzle which can be used in the device according to the invention.

In the schematic representation of FIG. 1, a system for the aftertreatment of exhaust gases is not shown

Internal combustion engine shown as a preferred embodiment of the device according to the invention. The exhaust gases from the In the embodiment shown, the internal combustion engine is guided via an exhaust pipe to an oxidation catalytic converter 18, which is optional and forms part of a three-way catalytic converter system. After the oxidation catalytic converter, the exhaust gases enter a reduction catalytic converter 1.

The reduction catalyst 1 can be operated essentially in two different modes, namely a so-called lean mode, during which NO oxidation takes place on a noble metal of the catalyst to NO ₂ , which NO ₂ can be adsorbed via nitrate formation, so that the reduction catalyst as NOX storage is used. The second mode is ^" the so-called rich mode, ie the oxidation catalytic converter is charged with a" rich exhaust gas ". In this mode, the NOXs stored in the reducing agent catalyst 1 are released. In particular, the adsorbed nitrates are decomposed to N0 ₂ , with a reduction of NOX taking place on a noble metal of the catalyst. The selection of the

Mode can take place depending on the operating states of the engine, the engine controller possibly also being able to control the engine for a short time in such a way that one or the other mode is executed, depending on whether regeneration of the storage catalytic converter 1 is required or not. To assess whether a regeneration phase is required, sensors, for example nitrogen oxide and / or pressure sensors 14, 15 can be provided in the exhaust pipe before and after the catalytic converter. According to the invention, however, the “exhaust gas rich” mode is supported or provided overall by introducing a reducing agent into the exhaust line 2 upstream of the reduction catalytic converter 1 For this purpose, in the embodiment shown, a nozzle 6 is arranged upstream of the reduction catalytic converter 1 on the exhaust pipe 2.

The nozzle 6 is supplied by a pump 10, which is connected, for example, to the fuel reservoir of the internal combustion engine. A control device 12 controls the delivery rate of the pump 10 and the throughput volume and the atomization phase or injection rate of the nozzle 6, depending on the supply

Internal combustion engine parameters, possibly taking into account the exhaust gas values detected by sensors 14, 15. In order to better process the reducing agent which is introduced into the exhaust pipe 2 via the nozzle 6, a heating device 8 is assigned to the nozzle 6, which can also be controlled via the control device 12. In the preferred embodiment, the heating device 8 is a self-regulating PTC thermistor. In a particularly simple embodiment, the nozzle 6 and the heating device 8 are provided as a prefabricated element, namely a so-called heating nozzle.

As shown, the nozzle 6 is provided substantially flush with the inside of the exhaust pipe 2, so that the exhaust gas flow in the exhaust pipe 2 is not influenced by the nozzle itself. The exhaust gas flowing in the exhaust pipe 2 can thus mix in a particularly efficient manner with the reducing agent emerging from the nozzle 6, so that a practically homogeneous mixture is present at the catalyst inlet. Mixing is further increased by the essentially vertical injection of the reducing agent. In order to make the mixture of reducing agent, here diesel fuel, and exhaust gas even more homogeneous, a controllable exhaust gas deflection device 20 is provided in the embodiment shown, which can act on the exhaust gas flow in the exhaust pipe 2 in a swirling manner or make it turbulent. The deflection device 20 is controlled by a control device 22. It should be noted that both the controller 12 and the

Control device 22 can be part of the engine control for the internal combustion engine, as well as devices that are present separately in this regard.

FIG. 2 shows an arrangement of a heating nozzle 6, 8 on an exhaust pipe 2 as part of a preferred embodiment of the invention. The exhaust pipe 2 tapers in a funnel shape after the reducing agent has been fed in via the nozzle 6 and opens into the reduction catalytic converter 1. The funnel-shaped tapering forms a

Device 20 influencing exhaust gas flow, which supports homogenization of the mixture of reducing agent and exhaust gas.

In the embodiment shown in FIG. 2 it can be clearly seen that the nozzle 6 is practically aligned with the inner wall of the exhaust pipe 2 and the reducing agent is introduced into the exhaust pipe 2 essentially perpendicular to the exhaust gas flow. The introduced reducing agent is deflected by the exhaust gas flow, whereby a corresponding advantageous blending can be achieved. Finally, FIG. 3 shows a heating nozzle in a detailed sectional view, which can be used in the solution according to the invention. The heating nozzle shown comprises a valve support 31 which is provided at its right end with a reducing agent connecting device which opens into a filter element 38. The reducing agent is guided past the PTC thermistor heating elements 8 by the filter element 38 and released from the nozzle at the left end by means of expansion. To relax the reducing agent, the nozzle comprises a valve group 6, which will not be discussed in further detail, since this is familiar to the person skilled in the art. The heating elements 8 can be fed via a contact pin 37, for example via a battery. The insulating bushes 32 and 33 are to be regarded as an important component of the heating nozzle, by means of which the heating nozzles can be adapted to the high thermal stresses in the exhaust gas environment.

In summary, it can be stated that the solution according to the invention specifies a reducing agent metering and preparation which can be optimized depending on the parameters with regard to the number of introduction points, the arrangement with optimized

Temperature control and optimized switching time. With regard to the catalyst cross-section, a distribution of the predominantly or overall gaseous reducing agent that is as uniform as possible and thus a high NOx conversion rate can thus be achieved. With high NOX

Conversion becomes a low-consumption and low-particle basic adaptation of the internal combustion engine and in particular the Injection system ensures that an earlier, consumption-optimized start of injection and a high injection pressure for the internal combustion engine can be realized, so that the proposed system also proves to be particularly efficient for the aftertreatment of exhaust gases from a diesel engine.

Although the invention has been fully described in terms of some preferred embodiments, those skilled in the art should understand that various changes and

Modifications are possible within the scope of the claims. By way of example, a plurality of nozzles can be arranged on the exhaust pipe, at a distance in the axial direction and / or radial direction, it being known to the person skilled in the art that these several nozzles can be controlled together in groups or individually. Finally, the function of an exhaust gas flow influencing device can also be fulfilled by the arrangement of the one or more nozzles, for example by the exhaust gas flow is swirled by the injected or introduced reducing agent, is set in rotation or is made turbulent.

Claims

Expectations

1. Device for the aftertreatment of exhaust gases from an internal combustion engine, with a reduction catalyst (1) serving to reduce NOX components of the exhaust gases, to which an exhaust pipe (2) leads, a reducing agent supply (4), a reducing agent metering device (6, 10, 12) and a reducing agent evaporation device (6, 8, 10, 12), characterized in that the reducing agent metering and the at least partial evaporation takes place by means of at least one nozzle (6) provided on the exhaust pipe (2).

2nd Apparatus according to claim 1, characterized in that the nozzle (6, 8) comprises a heating device, in particular a heating nozzle (6, 8) with self-regulating thermistor heating elements (8).

3. Apparatus according to claim 1 or 2, characterized in that the nozzle (6, 8) is formed from temperature-resistant materials.

4. Device according to one of the preceding claims, characterized in that the nozzle (6, 8) Introduces reducing agent into the exhaust pipe (2) essentially perpendicular to the exhaust gas movement direction.

5. Device according to one of the preceding claims, characterized in that the nozzle (6, 8) is substantially aligned with the inside of the exhaust pipe (2).

6. Device according to one of the preceding claims, characterized in that the nozzle (6, 8) is assigned an application device (10, 12).

7. Device according to one of the preceding claims, characterized in that a device influencing the exhaust gas flow (20, 22) is provided in the exhaust pipe (2).

8. Device according to one of the preceding claims, characterized in that the reduction catalyst (1) is preceded by an oxidation catalyst (18).

9. Device according to one of the preceding claims, characterized in that with more than one nozzle (6, 8) these are arranged regularly, in particular at least equidistant in the radial direction.

10. Device according to one of the preceding claims, characterized in that with more than one nozzle (6, 8) a respective independent control (12) is provided.