WO2019137689A1

WO2019137689A1 - Exhaust gas aftertreatment system

Info

Publication number: WO2019137689A1
Application number: PCT/EP2018/083085
Authority: WO
Inventors: Bjoern Damson
Original assignee: Robert Bosch Gmbh
Priority date: 2018-01-11
Filing date: 2018-11-30
Publication date: 2019-07-18
Also published as: DE102018200326A1

Abstract

The invention relates to an exhaust train (12) of an exhaust gas aftertreatment system (10) for compression ignition engines. The exhaust train (12) comprises an exhaust pipe (6) which includes an SCR catalyst (14) and into which dosed amounts of an operating/auxiliary medium (76) are admixed. The exhaust pipe (60) includes an electrically heated wall surface (68) in the region (80) in which the operating/auxiliary medium (76) is admixed.

Description

description

Abaasnachbehandlunassystem

Technical area

The invention relates to an exhaust system of a

Exhaust after-treatment system for self-igniting

Internal combustion engines, a method for operating an exhaust system of an exhaust aftertreatment system and to a use of the

Exhaust line.

State of the art

The selective catalytic reduction (SCR) of nitrogen oxides in the exhaust gas

auto-ignition engines is state of the art. In this case, at low temperatures in the exhaust system problems due to incomplete evaporation of the operating / auxiliary substance occur, which among other things have the formation of deposits result, to the blocking of the exhaust system and corrosion of components of the exhaust system. Furthermore, the minimum temperature of the exhaust gas of about 200 ° C required for evaporation of the operating / auxiliary substance prevents the use of an SCR catalytic converter at low exhaust gas temperatures, which in particular directly after the start of the

auto-igniting internal combustion engine occur, as well

possibly also at their low engine load points or ranges. As a result, there are difficulties to comply with the limit values that can be specified with future emissions legislation.

A well-known remedy against low exhaust gas temperatures is the use of an electrically heated catalyst, the exhaust over heats up its entire cross section. Disadvantage of this procedure is the very high electrical power required, the occurrence of very high

Production costs and the limited life of the catalyst.

In a further development of the heated S CR catalyst only a partial flow of the exhaust gas is directed through the catalyst and heated, so that no longer the entire exhaust gas flow must be heated. As a result, the need for electrical power is reduced, and a reduction in the size of the catalyst can be achieved, which can also have a positive effect on costs and service life. On the other hand, the removal and

Re-introduction of the partial flow of the exhaust gas very expensive and calls for additional measures.

Presentation of the invention

According to the invention, an exhaust gas line of an exhaust aftertreatment system for internal combustion engines with an exhaust pipe, which comprises an SCR catalyst and in which by means of a dosing an operating / auxiliary substance is metered, proposed, wherein the exhaust pipe a in the

Includes metering of the operating / auxiliary material arranged electrically heated wall surface.

Compared to exhaust aftertreatment systems that have a heated

Catalyst use, can be realized by the present invention proposed on the exhaust pipe in the dosing of the operating / auxiliary electrically heated wall surface, which serves as an evaporator, a significantly lower electrical energy consumption, since a relatively low heating of the exhaust gas flow is realized. As a result of a small heated surface of the construction effort is relatively low and a direct integration of the proposed solution according to the invention in the

Exhaust after-treatment system of a self-igniting

Internal combustion engine possible. The above problems with durability and corrosion can be avoided. In an advantageous development of the solution proposed according to the invention, the electrically heated wall surface lies in a region of a pipe wall of the exhaust pipe in the exhaust gas line, which is embodied in a reduced wall thickness. This allows the fastest possible heating to be achieved, with a preferred value such as the reduced wall thickness between 0.3 mm and 1 mm, preferably about 0.5 mm. Since this relatively thin wall thickness is possible only on a limited area of the pipe wall, the mechanical stability of the exhaust pipe can be taken over by the areas outside the electrically heated area acting as evaporator. In the area of the electrically heated wall surface, thermal insulation with integrated mechanical protection against damage from the outside is very advantageous.

In particular, it is proposed to heat the electrically heated wall surface from the outside of the pipe wall of the exhaust pipe. As a result, the actual heating in the form of an electric heater is separated by the pipe wall of the exhaust pipe. This eliminates the need for one

Current passage through the pipe wall of the exhaust pipe, on the other hand, the heating element, which tempered the electrically heated wall surface, protected against corrosion.

In an advantageous manner, at least one electrical heating conductor runs on the outer side of the tube wall in the electrically heated wall surface in such a way that it runs substantially meander-shaped and thus reduces in size

Wall thickness executed electrically heated wall surface of the pipe wall of the exhaust pipe heated extremely effectively.

In a further development of the solution proposed according to the invention, the electrically heated wall surface in the pipe wall of the exhaust pipe is such that it covers an angle range between 0 ° and 180 °. The size of the wall surface is oriented at the impact area of the spray from the metering module, in particular its injector. The application of

The proposed solution according to the invention is also possible in systems in which the injection of the operating / auxiliary substance takes place in a region of the exhaust system which deviates significantly from the shape of a pipe, for example in the thickening of an exhaust pipe in the form of a mixing chamber. Moreover, the invention relates to a method for operating a

Exhaust line of an exhaust aftertreatment system with the following process steps: a) Measurement of the temperature of the electrically heated as an evaporator

Wall surface by means of a temperature sensor or by evaluation of the electrical resistance of the heating conductor,

b) adjusting the temperature of the electrically heated wall surface to a temperature between 200 ° C and 280 ° C, preferably 250 ° C, to a

Transfer maximum heat to the operating / auxiliary substance, or

c) setting the temperature of the electrically heated wall surface at a temperature above 250 ° C in order to achieve a secondary atomization of the operating / auxiliary substance in the flow cross-section of the exhaust pipe.

It is advantageous to limit the temperature of the electrically heated surface acting as evaporator, for example, to 250 ° C, so that the electrically generated heating power can be effectively transferred to the drops of the operating / auxiliary substance. Thus, the Leidenfrost effect can be counteracted, according to which at high temperatures between the droplets of the operating / auxiliary substance and acting as an evaporator electrically heated wall surface of the exhaust pipe forms a vapor cushion, so that the drops of the operating / auxiliary material bounce off a large part and only little energy is transferred from the acting as an evaporator electrically heated surface on the drops of the operating / auxiliary material.

On the other hand, it is possible to proceed according to process step c) and to bring the acting as an evaporator electrically heated wall surface at relatively high temperatures in order to achieve a good secondary atomization of the droplets of the operating / auxiliary material acting on the evaporator heated surface, for example to achieve a possible uniform distribution of the operating / auxiliary material over the flow cross-section of the exhaust pipe. In a further development of the method proposed according to the invention, the temperature in process step c) is in a temperature range between 320 ° C. and 370 ° C. In addition to influencing the temperature of the acting as an evaporator electrically heated wall surface, it may also be useful to influence the speed of the droplets of the operating / auxiliary material from the dosing into the flow cross section of the exhaust pipe.

Influencing the speed can be achieved by pressure variation at the

Dosing occur, at an increased pressure in the metering module, the exit velocity of the operating / auxiliary substance is increased, resulting in improved atomization of the operating / auxiliary material. For example, with the supply units currently available on the market, the upper limits for the pressure are 5 bar or 9 bar, and in the future may be too

Supply parts with a higher maximum pressure of up to 25 bar and more can be available.

In addition, the method proposed according to the invention further includes the possibility of reducing the exit velocity of the droplets of the operating / auxiliary substance from the dosing module by a low pressure on the dosing module, whereby the evaporation of the operating / auxiliary substance is favored. A lower limit for the pressure is for example 1.5 bar. Overall, the largest possible area for printing should be sought.

Finally, the present invention relates to the use of the exhaust line in an exhaust aftertreatment system for a self-igniting internal combustion engine.

Advantages of the invention

The advantages of the present invention are mainly to be seen in that compared to an exhaust aftertreatment system without heating catalyst evaporation of the operating / auxiliary material takes place at low exhaust gas temperatures, which in turn avoids the formation of deposits and corrosion occurring in the area serving as an evaporator electrically heated wall surface. Thus, the reduction of NOx even at low Exhaust gas temperatures are ensured. Compared to

Exhaust aftertreatment systems, in which the S CR catalyst is heated, can be achieved by the proposed solution according to the invention a significantly reduced electrical energy consumption, since the exhaust gas flow is relatively low heated in the exhaust pipe. It can be a much lower construction costs due to achieve a smaller designed electrically heated area, so that a direct integration of the proposed invention solution in an exhaust aftertreatment system is possible. Furthermore, the problems encountered in the solution according to the prior art can be avoided in that the durability is improved and corrosion does not occur at all.

Due to the fact that the electrically heated wall surface is heated from the outside of the exhaust pipe forth, eliminates the need for a current feed through the pipe wall of the exhaust pipe, so that the arranged on the electrically heated wall heating element is permanently protected from corrosion.

With regard to the temperature measurement of the electrically heated wall surface of the exhaust pipe is to mention as an advantage that a temperature measurement is not carried out by a separate, a discrete component performing temperature sensor, but that can be evaluated to save this temperature sensor, the electrical resistance of the heating, since this is generally temperature-dependent is, wherein the evaluation is made so that the resistance of the applied voltage and the current is determined.

Alternatively, the heating power can be controlled without temperature signal due to maps, for example, depending on

Exhaust gas temperature, engine air, mass flow and currently set

Dosing quantity of the operating / auxiliary substance.

Short description of the drawing

With reference to the drawing, the invention will be discussed in more detail below

described. It shows:

Figure 1 shows the components of an exhaust aftertreatment system a

self-igniting internal combustion engine and

Figure 2 shows a detailed view of the exhaust pipe of the exhaust line of a

Exhaust after-treatment system with an electrically heated wall surface indicated by way of example.

variants

FIG. 1 shows an exhaust aftertreatment system 10 for a self-igniting internal combustion engine.

The exhaust aftertreatment system 10 includes an exhaust line 12 in which an SCR catalyst 14 is contained. The SCR catalyst operates according to the principle of selective catalytic reduction (SCR process). In an exhaust gas flow 16, which flows through the exhaust gas line 12, an operating / auxiliary substance is metered in via a metering module 18, preferably in the manner of a fine droplet contained spray introduced into this. The operating / auxiliary substance is, in particular, a urea-water solution freezing below -11 ° C. outside temperature, which is known under the trade name AdBlue®.

As can be seen from FIG. 1, for example, the dosing module 18 is tempered via a cooling fluid circuit 20 of the internal combustion engine. The

Einosierungsstelle the operating / auxiliary material through the dosing 18, a first temperature sensor 22 is connected upstream. Via a pressure line 24, which is heated by a generally electrically running heater 26, the dosing module 18 from the supply part 28 with the operating / auxiliary material for

Metering supplied.

The exhaust aftertreatment system 10 further includes a controller 30. As is further apparent from Figure 1, the supply part 28 is connected via a return line 32 with a storage tank 36 in connection. In the storage tank 36 the freezer is stored. The liquid level within the storage tank 36 is determined by a level sensor 38.

In the bottom of the reservoir 36 branches a suction line 34, which as well as the return line 32 by a preferably designed as an electric heater 26 heating with heating air from. The temperature of the stored in the storage tank 36 operating / auxiliary substance is detected by a temperature sensor 40. The storage tank 36 is heated via a heating line 42, so that the consumed in this operating / auxiliary material does not freeze.

The control unit 30 of the exhaust aftertreatment system 10 comprises a number of sensor terminals 44, as well as a number of actuator terminals 46. Via the sensor terminals 44 and the actuator 46, the individual components, such as the dosing module 18 are controlled and detects levels or temperatures. The control unit 30 communicates with the internal combustion engine via a first CAN bus 48 and uses a second CAN bus 50 for diagnostic purposes.

From the illustration according to FIG. 1, it is also apparent that downstream of the SCR catalytic converter 14, a second temperature sensor 52, which in turn is followed by a NO.sub.c sensor 54, is arranged in the exhaust gas train 12 of the internal combustion engine.

FIG. 2 shows the illustration of an electrically heated surface acting as an evaporator in the pipe wall 64 of an exhaust pipe 60.

The illustration according to FIG. 2 shows that an exhaust gas pipe 60 is contained in the exhaust gas train 12 of the exhaust aftertreatment system 10. The

Exhaust pipe 60 is formed symmetrically to its axis of symmetry 74 and defines a flow cross-section 62. The exhaust pipe 60 is formed by a pipe wall 64 and is passed from the exhaust gas stream 16 in the flow direction 66. In the tube wall 64 of the exhaust pipe 60 acting as an evaporator electrically heatable wall surface 68 is formed. This extends in the circumferential direction 72 along the tube wall 64. The indicated in Figure 2, according to the curvature of the tube wall 64 of the exhaust pipe 60 curved electrically heated wall surface 68 extends in the illustrated in Figure 2 Variant from 0 ° to slightly more than 90 °, ie corresponding to a quarter circular arc, with areas up to about half a circular arc of about 180 ° can occur.

FIG. 2 reveals that a heating conductor is located on an outer side 82 of the tube wall 64 on the electrically heated wall surface 68. This is formed, for example, in the form of a meander describing several arcs, so that the electrically heated wall surface 68 can be heated as fully as possible from the outside 82. In an advantageous manner and to allow the fastest possible heating, it is useful to make the tube wall 64 of the exhaust pipe 60 particularly thin in the region in which the electrically heated wall surface 68 is formed. The wall thickness of the tube wall 64 of the exhaust pipe 60 is in the region in which the electrically heated wall surface 68 is formed, a wall thickness between 0.3 mm and 1 mm, preferably 0.5 mm. Since this thin wall thickness of the tube wall 64 is required only from a limited area, the mechanical stability of the exhaust pipe 60 can be taken over at the areas outside of the electrically heated wall surface 68 serving as evaporator. In the area of the electrically heated wall surface 68, which serves as an evaporator, insulation with integrated mechanical protection against damage from the outside 82 is particularly advantageous.

The representation according to FIG. 2 furthermore shows that the operating / auxiliary substance 76 in the form of spray jets 78, which are directed onto the electrically heated wall surface 68, is metered from the metering module 18 arranged above the exhaust pipe 60 within a metering region 80.

The inventively proposed exhaust line 12 and acting in this evaporator as electrically heated wall surface 68 is operated according to the following process steps: a) Measurement of the temperature of the electrically heated as an evaporator

Wall surface 68 by means of a temperature sensor or by evaluation of the electrical resistance of the heating conductor 70, b) adjusting the temperature of the electrically heated wall surface 68 to a temperature between 200 ° C and 280 ° C, preferably 250 ° C, to transfer a maximum of heat to the operating / excipient 76, or

c) adjusting the temperature of serving as an evaporator electrically

heated wall surface 68 to a temperature above 250 ° C to a secondary atomization of the operating / excipient 76 in

To achieve flow cross section 62 of the exhaust pipe.

In the method step c) proposed according to the invention, it is advantageous to restrict the temperature of the electrically heated wall surface 68 serving as evaporator from the example 250 ° C. so that the generated heating power is effectively transferred to the droplets in the spray jets 78 of the operating / auxiliary substance 76 can. By this temperature limitation, the Leidenfrost effect can be taken into account, according to which at high temperatures between the droplets of the operating / excipient 76 and as

Evaporator serving electrically heated wall surface 68 forms a vapor cushion, so that the droplets of the operating / auxiliary largely bounce and only little energy is transmitted from the serving as an evaporator electrically heated wall surface 68 to the droplets.

Alternatively, it may be useful, according to step c), to bring the electrically heated wall surface 68 serving as an evaporator to high temperatures, from about 320 ° C. to 370 ° C., to ensure good secondary atomization of the droplets of the operating / auxiliary substance 76 from the To achieve that serves as an evaporator electrically heated wall surface, so that, for example, a uniform distribution of the operating / auxiliary material in the flow cross-section 62 of the exhaust pipe 60 can be achieved.

The supplement for adjusting the temperature according to method steps b) and alternatively c), may be useful to influence the exit velocity of the droplets of the excipient 76 in the spray jets 78. For this purpose, a pressure change on the dosing module 18 offers. At high pressures on the metering module 18, the droplets of the operating / auxiliary substance 76 in the spray jet 78 get higher speeds, resulting in a larger proportion rebounding droplets of the operational / Hilfsstoffes 76 leads, thus a better atomization thereof in the flow cross-section 62 allows. In contrast, a low pressure on the dosing module 18 in the dosing range 80 leads to low speeds of the droplets of the operating / auxiliary substance 76 contained in spray jets 78 and thus to increased heat transfer from the as

Evaporator serving electrically heated wall surface 68, which in turn leads to improved evaporation.

For measuring the temperature of the electrically heated wall surface 68 serving as evaporator, a temperature sensor can be used. When saving just those sensors but also the electrical resistance of the at least one heat conductor 70, the electrically heated wall surface 68 of the

Outside 82 are evaluated by the exhaust pipe 60 heated ago. The electrical resistance is generally temperature dependent and evaluable in that the resistance is based on applied voltage and

Amperage can be determined. Alternatively, the heating power can be controlled without temperature signal due to maps. For this purpose, for example, maps of exhaust gas temperature, engine air, mass flow and current metering amount of the operating / auxiliary substance 76, which is metered into the exhaust pipe 60 in the metering region 80, offer.

The invention is not limited to the embodiments described herein and the aspects highlighted therein. Rather, within the scope given by the claims a variety of modifications are possible, which are within the scope of expert action.

Claims

claims

1. exhaust line (12) of an exhaust aftertreatment system (10) for

self-igniting internal combustion engines with an exhaust pipe (60), which comprises an SCR catalyst (14) and in which by means of a metering module (18) an operating / auxiliary material (76) is metered, characterized in that the exhaust pipe (60) one in a

Dosing range (80) of the operating / auxiliary material (76) arranged, electrically heated wall surface (68).

Second exhaust line (12) according to claim 1, characterized in that the electrically heated wall surface (68) in a region of a pipe wall (64) of the exhaust pipe (60), which is designed in reduced wall thickness.

3. exhaust line (12) according to claim 2, characterized in that the reduced wall thickness of the tube wall (64) between 0.3 mm and 1.0 mm, preferably 0.5 mm.

4. exhaust line (12) according to claim 1, characterized in that the electrically heated wall surface (68) from the outside (82) of the tube wall (64) is heated from.

5. exhaust line (12) according to claim 4, characterized in that on the outer side (82) of the tube wall (64), a at least one electrical heating conductor (70) is arranged, which extends substantially meandering.

6. exhaust system (12) according to claim 1, characterized in that the electrically heated wall surface (68) in the circumferential direction (72) of the tube wall (64) covers an angle range from 0 ° to 180 °.

7. A method for operating an exhaust line (12) according to one of the preceding claims with the following method steps: a) measuring the temperature of serving as an evaporator electrically heated wall surface (68) by means of a temperature sensor or by evaluating the electrical resistance of at least one heat conductor (70),

b) adjusting the temperature of the electrically heated wall surface (68) to a temperature between 200 ° C and 280 ° C, preferably 250 ° C, in order to transfer a maximum of heat to the operating / auxiliary substance (76),

or

c) Setting the temperature of serving as evaporator

electrically heated wall surface (68) to a temperature above 250 ° C in order to achieve a secondary atomization of the operating / auxiliary substance (76) in the flow cross-section (62) of the exhaust pipe.

8. The method according to claim 7, characterized in that the

Temperature according to process step c) is in a temperature range between 320 ° C and 370 ° C.

9. The method according to claim 7, characterized in that a

Exit speed of the operating / auxiliary material (76) from the

Dosing module (18) in the flow cross section (62) of the exhaust pipe (60) is influenced.

10. The method according to claim 9, characterized in that at

increased pressure, preferably at least 5 bar to 9 bar in the dosing module (18), the exit velocity of the operating / auxiliary substance (76) is increased, resulting in improved atomization of the operating / auxiliary substance (76).

11. The method according to claim 9, characterized in that at a low pressure of about 1.5 bar on the metering module (18) the

Exit rate of the operating / Hilfsstoffes (76) is reduced, whereby the evaporation of the operating / Hilfsstoffes (76) is favored.