DE102018200326A1 - aftertreatment system - Google Patents

Abstract

The invention relates to an exhaust gas line (12) of an exhaust aftertreatment system (10) for self-igniting internal combustion engines. The exhaust gas line (12) comprises an exhaust pipe (60) which comprises an SCR catalytic converter (14) and into which an operating / auxiliary substance (76) is metered in by means of a metering module (18). The exhaust pipe (60) comprises an electrically heated wall surface (68) arranged in the metering region (80) of the operating / auxiliary substance (76).

Description

Technical area

The invention relates to an exhaust system of an exhaust aftertreatment system for self-igniting internal combustion engines, to a method for operating an exhaust system of an exhaust aftertreatment system and to a use of the exhaust system.

State of the art

The selective catalytic reduction (SCR) of the nitrogen oxides in the exhaust gas of self-igniting 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 evaporating the operating / auxiliary substance prevents the use of an SCR catalytic converter at low exhaust gas temperatures, which occur in particular directly after the start of the self-igniting internal combustion engine, and 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 known remedy against low exhaust gas temperatures is the use of an electrically heated catalyst which heats the exhaust gas over 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 SCR 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. By contrast, the removal and re-introduction of the partial flow of the exhaust gas is very expensive and requires additional measures.

Presentation of the invention

According to the invention, an exhaust system 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 / excipient is metered proposed, wherein the exhaust pipe comprises a arranged in the dosing of the operating / auxiliary electrically heated wall surface ,

Compared to exhaust aftertreatment systems that use a heated catalyst, can be realized by the present invention proposed on the exhaust pipe in the dosing of the operating / excipient electrically heated wall surface, which serves as an evaporator, a significantly lower electrical energy consumption, since a relatively low heating the exhaust gas flow is realized. As a result of a small heated surface, the structural complexity is relatively low and a direct integration of the proposed solution according to the invention in the exhaust aftertreatment 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 one hand, the need for a current feedthrough 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 outside of the tube wall in the electrically heated wall surface in such a way that it substantially meandering and thereby extremely effectively heats the electrically heated wall surface of the tube wall of the waste gas pipe which is designed in reduced wall thickness.

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.

• a) Messung der Temperatur der als Verdampfer elektrisch beheizten Wandfläche mittels eines Temperatursensors oder durch Auswertung des elektrischen Widerstandes des Heizleiters,
• b) Einstellung der Temperatur der elektrisch beheizten Wandfläche auf eine Temperatur zwischen 200°C und 280°C, bevorzugt 250°C, um ein Maximum an Wärme an den Betriebs-/Hilfsstoff zu übertragen, oder
• c) Einstellung der Temperatur der elektrisch beheizten Wandfläche auf einer Temperatur oberhalb von 250°C, um eine Sekundärzerstäubung des Betriebs-/Hilfsstoffes im Strömungsquerschnitt des Abgasrohres zu erreichen.

In addition, the invention relates to a method for operating an exhaust system of an exhaust aftertreatment system with the following method steps:

• a) measurement of the temperature of the electrically heated as evaporator wall surface by means of a temperature sensor or by evaluation of the electrical resistance of the heating element,
• b) setting the temperature of the electrically heated wall surface to a temperature between 200 ° C and 280 ° C, preferably 250 ° C, to transfer a maximum of 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 forms at high temperatures between the droplets of the operating / auxiliary material and acting as an evaporator electrically heated wall surface of the exhaust pipe, a vapor cushion, so that the drops of the operating / auxiliary material bounce to a large extent 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 metering module, wherein at an increased pressure in the metering module, the exit speed of the operating / auxiliary substance is increased, which leads to an improved atomization of the operating / auxiliary substance. In the case of the supply parts currently available on the market, the upper limits for the pressure are, for example, 5 bar or 9 bar, although in the future supply parts with a higher maximum pressure of up to 25 bar and more may also be available.

In addition, the method proposed according to the invention further comprises 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 can be ensured even at low exhaust gas temperatures. Compared to exhaust aftertreatment systems, in which the SCR catalyst is heated, a significantly reduced electrical energy consumption can be achieved by the proposed solution according to the invention, since the exhaust gas flow in the exhaust pipe is heated relatively low. It can be a significantly lower construction costs due to a achieve 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 the exhaust gas temperature, engine air, mass flow and currently set dosing of the operating / auxiliary material.

list of figures

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

• 1 die Komponenten eines Abgasnachbehandlungssystems einer selbstzündenden Verbrennungskraftmaschine und
• 2 eine Detaildarstellung des Abgasrohres des Abgasstranges eines Abgasnachbehandlungssystems mit einer exemplarisch angedeuteten elektrisch beheizten Wandfläche.

It shows:

• 1 the components of an exhaust aftertreatment system of a self-igniting internal combustion engine and
• 2 a detailed representation of the exhaust pipe of the exhaust line of an exhaust aftertreatment system with an exemplified electrically heated wall surface.

variants

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

The exhaust aftertreatment system 10 includes an exhaust system 12 in which an SCR catalyst 14 is included. The SCR catalyst operates according to the principle of selective catalytic reduction (SCR process). In an exhaust gas flow 16 that the exhaust tract 12 flows through, is via a dosing 18 an operating / excipient metered, preferably introduced in the manner of a fine droplets contained spray 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®.

How out 1 shows, for example, the dosing 18 via a cooling fluid circuit 20 the internal combustion engine tempered. The dosing point of the operating / auxiliary substance through the dosing module 18 is a first temperature sensor 22 upstream. Via a pressure line 24 by a generally electrically running heater 26 is heated, the dosing is 18 from the supply part 28 supplied with the operating / auxiliary substance for metering.

The exhaust aftertreatment system 10 also includes a controller 30 , How out 1 continues to show, is the supply part 28 via a return line 32 with a storage tank 36 in connection. In the storage tank 36 the freezer is stored. The fluid level inside the storage tank 36 is through a level sensor 38 determined. In the bottom of the storage tank 36 branches a suction line 34 as well as the return line 32 by a preferred as an electric heater 26 trained heating with heating air, from. The temperature of the storage tank 36 stocked operational / Hilfsstoffes is by a temperature sensor 40 detected. The storage tank 36 is via a heating cable 42 heated, so that in this recorded operating / auxiliary material does not freeze.

The control unit 30 the exhaust aftertreatment system 10 includes a number of sensor ports 44 as well as a number of actuator connections 46 , About the sensor connections 44 or the actuator connections 46 become the individual components, so for example the dosing module 18 controlled and detected levels or temperatures. The control unit 30 communicates via a first CAN bus 48 with the internal combustion engine and uses a second CAN bus 50 for diagnostic purposes.

From the illustration according to 1 further notes that downstream of the SCR catalyst 14 in the exhaust system 12 the internal combustion engine, a second temperature sensor 52 is arranged, in turn, a NOx sensor 54 is connected downstream.

2 shows the representation of acting as an evaporator electrically heated surface in the pipe wall 64 an exhaust pipe 60 ,

The representation according to 2 can be seen that in the exhaust system 12 the exhaust aftertreatment system 10 an exhaust pipe 60 is included. The exhaust pipe 60 is symmetrical to its axis of symmetry 74 designed and limits a flow cross-section 62 , The exhaust pipe 60 is through a pipe wall 64 is formed and is from the exhaust stream 16 in the flow direction 66 happens. In the pipe wall 64 of the exhaust pipe 60 is an electrically heatable wall surface acting as an evaporator 68 educated. This extends in the circumferential direction 72 along the pipe wall 64 , In the 2 indicated, according to the curvature of the pipe wall 64 of the exhaust pipe 60 curved electrically heated wall surface 68 extends into the in 2 illustrated embodiment of 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.

2 it can be seen that on an outside 82 the pipe wall 64 on the electrically heated wall surface 68 a heating conductor is located. This is designed, for example, in the form of a meander describing a plurality of bows, so that the electrically heated wall surface 68 as completely as possible from the outside 82 is heated ago. In an advantageous manner and to allow the fastest possible heating, it is useful to the pipe wall 64 of the exhaust pipe 60 in the area where the electrically heated wall surface 68 is designed to be particularly thin. The wall thickness of the pipe wall 64 of the exhaust pipe 60 is in the range in which the electrically heated wall surface 68 is formed, a wall thickness between 0.3 mm and 1 mm, preferably 0.5 mm. Because this thin wall thickness of the pipe wall 64 Only from a limited area is necessary, the mechanical stability of the exhaust pipe 60 at the areas outside of serving as an evaporator electrically heated wall surface 68 be taken over. In the area of serving as an evaporator electrically heated wall surface 68 is an insulation with integrated mechanical protection against damage from the outside 82 ago particularly advantageous.

The representation according to 2 In addition, it can be seen that from above the exhaust pipe 60 arranged metering module 18 within a metering area 80 the operating / auxiliary material 76 in the form of sprays 78 on the electrically heated wall surface 68 are directed, is metered.

• a) Messung der Temperatur der als Verdampfer elektrisch beheizten Wandfläche 68 mittels eines Temperatursensors oder durch Auswertung des elektrischen Widerstandes des Heizleiters 70,
• b) Einstellung der Temperatur der elektrisch beheizten Wandfläche 68 auf eine Temperatur zwischen 200°C und 280°C, bevorzugt 250°C, um ein Maximum an Wärme an den Betriebs-/Hilfsstoff 76 zu übertragen, oder
• c) Einstellung der Temperatur der als Verdampfer dienenden elektrisch beheizten Wandfläche 68 auf eine Temperatur oberhalb von 250°C, um eine Sekundärzerstäubung des Betriebs-/Hilfsstoffes 76 im Strömungsquerschnitt 62 des Abgasrohres zu erreichen.

The inventively proposed exhaust system 12 or in this acting as an evaporator 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) Setting the temperature of the electrically heated wall surface 68 to a temperature between 200 ° C and 280 ° C, preferably 250 ° C, to a maximum of heat to the operating / auxiliary material 76 to transfer, or
• c) adjustment of 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 / auxiliary substance 76 in the flow cross-section 62 to reach the exhaust pipe.

In the method step c) proposed according to the invention, the temperature of the electrically heated wall surface serving as evaporator is advantageous 68 from the example 250 ° C to restrict, so that the generated heat output effectively on the drops in the spray jets 78 of the operating / auxiliary substance 76 can be transferred. This temperature limitation allows the Leidenfrost effect to be taken into account, according to which at high temperatures between the droplets of the operating / auxiliary substance 76 and serving as an evaporator electrically heated wall surface 68 forms a vapor cushion, so that the droplets of the operating / auxiliary bounce mostly and little energy from serving as an evaporator electrically heated wall surface 68 is transferred to the droplets.

Alternatively, it may be useful, in accordance with process step c), to use the electrically heated wall surface serving as evaporator 68 to bring high temperatures, from about 320 ° C to 370 ° C, to a good secondary atomization of the droplets of the excipient 76 to reach from serving as an evaporator electrically heated wall surface, so for example the most uniform distribution of the operating / auxiliary substance in the flow cross-section 62 of the exhaust pipe 60 can be reached.

The supplement for adjusting the temperature according to the process steps b) and alternatively c), may be useful, the exit velocity of the droplets of the operating / auxiliary material 76 in the sprays 78 to influence. In addition a pressure change offers itself at the metering module 18 on. At high pressures on the dosing module 18 get the droplets of the operating / auxiliary material 76 in the spray 78 higher speeds, resulting in a larger proportion of rebounding droplets of the operating / auxiliary material 76 leads, therefore, a better atomization of the same in the flow cross-section 62 allows. On the other hand, a low pressure leads to the dosing module 18 in the dosing area 80 at low speeds than in spray jets 78 contained droplets of the operating / auxiliary substance 76 and thus to increased heat transfer from serving as an evaporator electrically heated wall surface 68 , which in turn leads to improved evaporation.

For measuring the temperature of serving as an evaporator electrically heated wall surface 68 a temperature sensor can be used. When saving just those sensors but can also be the electrical resistance of the at least one heat conductor 70 holding the electrically heated wall surface 68 from the outside 82 through the exhaust pipe 60 heated to be evaluated. The electrical resistance is generally temperature dependent and evaluable in that the resistance can be determined on the applied voltage and resulting current. Alternatively, the heating power can be controlled without temperature signal due to maps. This can be done, for example, maps of exhaust gas temperature, engine air, mass flow and current dosing amount of the operating / auxiliary material 76 in the exhaust pipe 60 in the dosing area 80 is metered on.

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 (11)

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) comprises an electrically heated wall surface (68) arranged in a metering region (80) of the operating / auxiliary substance (76). Exhaust line (12) according to Claim 1 , characterized in that the electrically heated wall surface (68) is located in a region of a pipe wall (64) of the exhaust pipe (60), which is designed in reduced wall thickness. Exhaust line (12) according to Claim 2 , characterized in that the reduced wall thickness of the tube wall (64) is between 0.3 mm and 1.0 mm, preferably 0.5 mm. 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. 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. Exhaust line (12) according to Claim 1 , characterized in that the electrically heated wall surface (68) in the circumferential direction (72) of the tube wall (64) sweeps over an angle range of 0 ° to 180 °. Method for operating an exhaust gas line (12) according to one of the preceding claims with the following method steps: a) measuring the temperature of the electrically heated wall surface (68) serving as evaporator by means of a temperature sensor or by evaluating the electrical resistance of at least one 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, in order to transfer a maximum of heat to the operating / auxiliary substance (76), or c) setting the temperature of serving as an evaporator electrically heated wall surface (68) to a temperature above 250 ° C, to achieve a secondary atomization of the operating / auxiliary substance (76) in the flow cross-section (62) of the exhaust pipe. 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. Method according to Claim 7 , characterized in that an exit speed of the operating / auxiliary substance (76) from the metering module (18) in the flow cross section (62) of the exhaust pipe (60) is influenced. Method according to Claim 9 , characterized in that at elevated pressure, preferably at least 5 bar to 9 bar in the dosing (18), the exit velocity of the operating / auxiliary substance (76) is increased, resulting in improved atomization of the operating / auxiliary substance (76). Method according to Claim 9 , characterized in that at a low pressure of about 1.5 bar on the metering module (18), the exit velocity of the operating / auxiliary substance (76) is reduced, whereby the evaporation of the operating / Hilfsstoffes (76) is favored.

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