CN110578586A

CN110578586A - Exhaust system with thermoelectric device, motor vehicle and method for treating exhaust gases produced by an internal combustion engine

Info

Publication number: CN110578586A
Application number: CN201910485669.7A
Authority: CN
Inventors: J·哈姆森; R·乌克罗派克; M·巴莱诺维奇; M·艾米托; C·内德洛夫
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2018-06-07
Filing date: 2019-06-05
Publication date: 2019-12-17
Also published as: DE102018208995B4; DE102018208995A1

Abstract

the invention relates to an exhaust system with a thermoelectric device, a motor vehicle and a method for treating exhaust gases produced by an internal combustion engine. An exhaust system 1 for receiving exhaust gas 3 generated by an internal combustion engine 2 is stated, comprising an LNT catalytic converter 4, a lambda sensor 5 arranged downstream of the LNT catalytic converter 4, a temperature sensor 6 arranged downstream of the LNT catalytic converter 4, one or more thermoelectric devices 7 arranged downstream of the lambda sensor 5 and downstream of the temperature sensor 6 and designed for converting thermal energy into electrical energy, and an SCR catalytic converter 8 arranged downstream of the thermoelectric devices 7. In addition, a motor vehicle with an internal combustion engine 2 and such an exhaust system 1 and a method for treating exhaust gases 3 produced by the internal combustion engine 2 are stated.

Description

exhaust system with thermoelectric device, motor vehicle and method for treating exhaust gases produced by an internal combustion engine

Technical Field

The present invention relates to an exhaust system for receiving exhaust gases produced by an internal combustion engine, a motor vehicle having an internal combustion engine and such an exhaust system, and a method for treating exhaust gases produced by an internal combustion engine.

Background

in an environment generally considered to be oxidizing, in lean engines (i.e. with combustion air ratio lambda)>1 lean air-fuel mixture operated internal combustion engine) of a diesel engine_x) Constitutes a major challenge in different operating conditions.

Nitrogen oxide storage catalytic converter (also called NSR catalytic converter (NO)_xStorage and reduction catalyst) or LNT catalytic converter (lean NO)_xTraps)) constitute one of the two major technologies for the catalytic conversion of nitrogen oxides. The alternative main technique is based on Selective Catalytic Reduction (SCR) of nitrogen oxides with nitrogenous reductants such as, for example, ammonia, which can be extracted from the supplied urea solution. For this purpose, so-called SCR catalytic converters are used.

LNT catalytic converters have been able to store nitrogen oxides at low temperatures and the storage efficiency has increased to temperatures of about 200 to 250 ℃. As the LNT catalytic converter is flushed with rich exhaust gas (λ <1) at higher temperatures, the adsorbed (i.e., stored) nitrogen oxides may then be reduced to nitrogen. In this case, components such as, for example, hydrocarbons, carbon monoxide and/or hydrogen contained in the rich exhaust gas are used as the reducing agent.

In contrast, SCR technology generally does not provide high reaction rates for the reduction of nitrogen oxides at low temperatures. However, once the temperature exceeds 200 ℃, the SCR catalytic converter exhibits excellent performance in terms of nitrogen oxide conversion.

In order to cope with increasingly stringent emission instructions, a combination of these two main technologies has become attractive and is described in e.g. DE 102015208093 a 1. In this way, nitrogen oxides may be efficiently converted over a much larger temperature range.

However, combining an LNT catalytic converter with an SCR catalytic converter also creates problems. While SCR catalytic converters are designed for use with lean exhaust (i.e., excess oxygen), LNT catalytic converters at least sometimes require rich exhaust for their regeneration, i.e., for reducing stored nitrogen oxides and discharging the reduced compounds into the exhaust stream in order to restore nitrogen oxide storage capacity.

however, occasional operation with rich exhaust gas may result in reductant slip. In other words, rich exhaust gas also reaches the SCR catalytic converter disposed downstream of the LNT catalytic converter. The components with a reducing action contained in the rich exhaust gas can have a negative effect on the efficiency of the SCR catalytic converter, in particular at high temperatures, for example during desulphurisation (sox). This impairment of the efficiency of the SCR catalytic converter is permanent and is based on deactivation of the catalyst material, for example, on the sintering process and/or on the reduction of copper in the SCR catalytic converter.

Furthermore, such impairment of the efficiency of the SCR catalytic converter is difficult to predict and can therefore only be inadequately taken into account when predicting the optimum amount of urea solution to be supplied. However, when the efficiency of the SCR catalytic converter decreases at high temperatures due to contact with rich exhaust gas mixtures and continues to supply the same amount of urea solution, an undesirable ammonia release occurs.

Disclosure of Invention

it is therefore an object of the present invention to reduce or avoid the adverse effect of rich exhaust gases, such as rich exhaust gases for regeneration of e.g. an LNT catalytic converter, on an SCR catalytic converter at high temperatures.

This object is solved by the subject matter of the independent claims. Advantageous further developments of the invention are set out in the dependent claims.

The basic idea of the invention is to protect the SCR catalytic converter from contact with rich exhaust gases at high temperatures, since a thermoelectric device is arranged upstream of the SCR catalytic converter, which cools the exhaust gases reaching the SCR catalytic converter when required to such an extent that the rich constituents contained in the exhaust gases can no longer have a negative effect on the efficiency of the SCR catalytic converter. Irreversible damage, i.e. ageing of the SCR catalytic converter, can thereby be avoided.

Thus, the LNT and the SCR catalytic converter may be permanently used together for catalytic treatment of the exhaust gas. This makes it possible to perform effective catalytic treatment of exhaust gas over a wide temperature range, so that nitrogen oxides contained in exhaust gas can be largely removed and emission instructions can be maintained.

An exhaust system for receiving exhaust gas produced by an internal combustion engine according to the present invention includes an LNT catalytic converter, a lambda (lambda) sensor disposed downstream of the LNT catalytic converter, a temperature sensor disposed downstream of the LNT catalytic converter, one or more thermoelectric devices disposed downstream of the lambda sensor and downstream of the temperature sensor and designed to convert thermal energy into electrical energy, and an SCR catalytic converter disposed downstream of the thermoelectric devices.

Internal combustion engines refer to combustion engines for converting chemical energy contained in a fuel into mechanical work. The internal combustion engine may be designed, for example, as a self-ignition or spark-ignition internal combustion engine. For example, gasoline or diesel may be used as the fuel. The flow direction refers to a flow direction of exhaust gas of the internal combustion engine in an exhaust gas direction.

The exhaust system is formed by an exhaust line through which the exhaust gas flows and in which a catalytic converter and a sensor are arranged, so that the exhaust gas can likewise flow through the catalytic converter and the properties of the exhaust gas (for example its composition, temperature, etc.) can be determined by the sensor. For the respective definitions and functions of LNT and SCR catalytic converters reference is made to the explanations at the outset.

A lambda sensor is disposed downstream of the LNT catalytic converter. Lambda sensor means a sensor which supplies a measurement signal from which the combustion air ratio lambda, i.e. the ratio of the air mass actually available for combustion to the at least necessary stoichiometric air mass required for complete combustion, is determined. The lambda sensor can be designed, for example, as a lambda probe, which compares the residual oxygen content in the exhaust gas with the oxygen content of the atmospheric air at the same time, from which the combustion air ratio can be determined. The lambda sensor can also be designed as a nox sensor, since such a nox sensor can also output the combustion air ratio in addition to determining the nox proportion.

With the help of the lambda sensor, the combustion air ratio downstream of the LNT catalytic converter can be determined, i.e. it can be determined whether the exhaust gas that has flowed through the LNT catalytic converter is a rich exhaust gas mixture (lambda <1), a stoichiometric exhaust gas mixture (lambda ═ 1) or a lean exhaust gas mixture (lambda > 1). When a rich exhaust mixture is being supplied to the LNT catalytic converter for regeneration, the time at which regeneration of the LNT catalytic converter can take place can be determined by the lambda sensor, since rich exhaust is also detected downstream at this time. This time is also referred to as λ breakthrough.

Downstream of the LNT catalytic converter, a temperature sensor is additionally arranged, with which the temperature of the exhaust gas can be determined. The temperature sensor may be disposed upstream or downstream of the lambda sensor, or at the same position based on the flow path of the exhaust gas. By means of the temperature sensor it can be determined, for example, whether the temperature of the exhaust gas exceeds a maximum temperature, for example a maximum temperature of 500 c.

Furthermore, the exhaust system comprises one or more thermoelectric devices designed for converting thermal energy into electrical energy. By means of the thermoelectric device, thermal energy can be extracted from the exhaust gas. In other words, the exhaust gas may be cooled as it flows through the thermoelectric device.

The thermoelectric device can be designed as a so-called thermoelectric generator, which can generate an electric current in the presence of a temperature difference using the seebeck effect. The thermoelectric device may include one or more thermoelectric elements arranged in a manner such that thermal energy of the exhaust gas may be converted into electrical energy. The thermoelectric elements can be connected to one another electrically and thermally in such a way that the maximum possible electrical energy can be generated. The exhaust gas can be cooled by extracting energy from the exhaust gas by means of a thermoelectric element.

the thermoelectric device is arranged downstream of the lambda sensor and the temperature sensor and upstream of the SCR catalytic converter, so that the temperature of the exhaust gas reaching the SCR catalytic converter can be influenced. When it is detected that, for example, the exhaust gas downstream of the LNT catalytic converter is rich and, at the same time, the temperature of the exhaust gas exceeds the maximum temperature, the exhaust gas may be cooled by the thermoelectric device, preferably to a temperature lower than the maximum temperature. In this way, rich exhaust gas having a temperature higher than the maximum temperature can be prevented from reaching the SCR catalytic converter disposed downstream of the thermoelectric device.

By contacting with rich exhaust gas at high temperatures, a permanent deterioration of the catalyst activity of the SCR catalytic converter can be avoided. The efficiency of the SCR catalytic converter during the removal of nitrogen oxides from the exhaust gas may be maintained for an extended period of time. In addition to this, the SCR catalytic converter can be monitored more accurately, for example, in order to determine the correct amount of ammonia forming composition to be supplied, and to prevent an undesired excess ammonia output, since restrictions on the catalyst activity are avoided (since contact with rich exhaust gases at high temperatures, which otherwise has to be taken into account). In other words, the prediction of the desired amount of ammonia-forming composition better corresponds to the amount actually required.

Alternatively, a further exhaust gas aftertreatment device, for example a particulate filter or a further catalytic converter, may be arranged in the exhaust system. In one embodiment variant, the exhaust system comprises only the above-mentioned components or the components described above and specifically named below.

According to various embodiments, a particulate filter may be disposed downstream of the thermoelectric device and upstream of the SCR catalytic converter. The particulate filter may have an SCR coating so that catalytic reduction may be performed in addition to the filtration of particulates. Particulate filters with SCR coatings are also known as SDPF.

When the particulate filter is arranged downstream of the thermoelectric device and in the case of an SCR coating of the particulate filter, irreversible damage to the SCR coating by the action of the rich exhaust gas at temperatures above the maximum temperature can likewise be avoided.

According to further embodiment variations, the exhaust system may include a particulate filter disposed downstream of the LNT catalytic converter and upstream of the thermoelectric device. Preferably, in this case, the particulate filter may be arranged downstream of the λ sensor and the temperature sensor. The particulate filter may also have an SCR coating. The arrangement of the particulate filter contributes to improvement of exhaust gas purification. Higher nitrogen oxide conversion rates can be achieved. Furthermore, by using the SCR and the particulate filter functions in combination, the required installation space can be reduced.

According to further embodiment variants, the exhaust system upstream of the SCR catalytic converter may comprise a supply device for supplying the exhaust gas with an ammonia forming composition, for example an aqueous urea solution.

The supply device is used for supplying ammonia to the SCR catalytic converter and may perform or improve a catalytic reduction of nitrogen oxides in the SCR catalytic converter. When a particulate filter with an SCR coating is present in addition to the SCR catalytic converter, the supply device can preferably be arranged upstream of the particulate filter with an SCR coating. In this way, the SCR coating may also benefit from the provision of the ammonia-forming composition.

According to a further embodiment variant, the exhaust system may comprise a control unit which is equipped and designed for outputting a control signal for controlling the thermoelectric device as a function of the sensor signals of the lambda sensor and the temperature sensor.

The control unit receives signals from the lambda sensor and the temperature sensor, processes these signals based on instructions or code programmed in the control unit corresponding to one or more programs, and sends control signals to the thermoelectric device to activate or deactivate exhaust cooling.

The control unit may be implemented as hardware and/or software and may be physically designed in one or more components. In particular, the control unit may be part of or integrated in the engine control device. In a typical configuration, an engine control device of a motor vehicle serves as a control unit.

thus, the exhaust gas may advantageously be automatically cooled by the control unit, since the thermoelectric device is activated as soon as certain conditions occur (i.e. for example, rich exhaust gas is present and the maximum temperature is exceeded). The cooling can likewise be terminated automatically when the condition no longer exists. Undesirable cooling of the exhaust gas can be avoided.

According to further embodiment variations, the exhaust system may include a rechargeable battery that is conductively connected to the thermoelectric device.

Thus, the electrical energy generated during exhaust cooling can be advantageously stored and reused. The total energy balance can be improved.

The motor vehicle according to the invention comprises an internal combustion engine and an exhaust system according to the above description. By motor vehicle is meant a vehicle such as a land vehicle, an aircraft or a watercraft driven by an internal combustion engine. In this respect, the above description of the exhaust system according to the invention is also used to describe the motor vehicle according to the invention. The advantages of the motor vehicle according to the invention correspond to the advantages of the exhaust system according to the invention and its embodiment variants.

The method according to the invention for treating exhaust gases produced by an internal combustion engine comprises the following steps: the method includes directing exhaust gas through an LNT catalytic converter, determining a combustion air ratio, lambda, and a temperature of the exhaust gas downstream of the LNT catalytic converter and upstream of one or more thermoelectric devices, contacting the exhaust gas with the thermoelectric devices, and directing the exhaust gas through an SCR catalytic converter disposed downstream of the thermoelectric devices.

Bringing the exhaust gas into contact with the thermoelectric device means that the exhaust gas is connected to the thermoelectric device in a thermally conductive manner, so that the exhaust gas can be cooled by the thermoelectric device.

The method according to the invention can be implemented, for example, with the aid of the exhaust system according to the invention described above. In this respect, the above description of the exhaust system according to the invention is also used to describe the method according to the invention. The advantages of the method according to the invention correspond to the advantages of the exhaust system according to the invention and its embodiment variants.

According to different embodiment variants, the method may comprise comparing the determined temperature with the maximum temperature. In the case where the combustion air ratio is λ <1 and the maximum temperature is exceeded, the thermoelectric device is activated to convert thermal energy into electric energy or the thermoelectric device is maintained in an activated state in order to cool the exhaust gas.

If the comparison of the determined temperature to the maximum temperature indicates that the maximum temperature has not been reached or has only been reached, and/or the combustion air ratio is λ ≧ 1, the thermoelectric device can be deactivated or remain in a deactivated state. Cooling of the exhaust gas does not occur or terminate. The temperature required for optimum catalytic activity of the SCR catalytic converter can be reached, i.e. excessive cooling of the exhaust gas is avoided.

According to different embodiment variants, storage of the electrical energy generated during the cooling of the exhaust gases may be provided. This storage may be performed, for example, in a rechargeable battery.

Drawings

further advantages of the invention will be apparent from the following description and the accompanying drawings. Wherein:

FIG. 1 illustrates a schematic diagram of an exemplary exhaust system;

FIG. 2 illustrates a schematic diagram of another exemplary exhaust system;

FIG. 3 illustrates a flow chart of an exemplary method for treating an exhaust gas stream.

Detailed Description

Fig. 1 schematically shows an internal combustion engine 2 and an exhaust system 1 attached to the internal combustion engine 2 in an embodiment variation. The internal combustion engine 2 may be designed as a self-igniting engine and may be operated, for example, with diesel fuel. The internal combustion engine produces exhaust gas 3 which is received by the exhaust system 1. Described in the flow direction of the exhaust gas 3, the exhaust system 1 comprises an LNT catalytic converter 4, a lambda sensor 5, a temperature sensor 6, a thermoelectric device 7, a particulate filter 9 (which can optionally comprise an SCR coating), and an SCR catalytic converter 8. The thermoelectric device 7, the particulate filter 9 and the SCR catalytic converter 8 may form a joint assembly.

optionally, a supply device 10 for supplying an ammonia forming composition (e.g. a urea solution) may be provided between the lambda sensor 5 and the temperature sensor 6. The lambda sensor 5 is designed as a lambda probe and is used to determine the combustion air ratio lambda. By means of the temperature sensor 6, the temperature of the exhaust gas 3 is determined.

The lambda sensor 5 and the temperature sensor 6 are in signal connection with a control unit 11. The control unit 11 therefore receives and processes the sensor signals 14a, 14b of the lambda sensor 5 and the temperature sensor 6. Depending on the result of this signal processing, the control signal 13 may then be output to the thermoelectric device 7. The control signal 13 is used to activate or deactivate the thermoelectric device 7. When the thermoelectric device 7 is activated, the exhaust gas 3 is cooled. In contrast, when the thermoelectric device is deactivated, cooling of the exhaust gas 3 does not occur.

it can be provided that the determination of the combustion air ratio λ is carried out continuously, whereas the determination of the temperature T of the exhaust gas by means of the temperature sensor 6 is carried out only if it is determined that rich exhaust gas 3 is present (λ < 1).

The thermoelectric device 7 is electrically conductively connected to a rechargeable battery 12, which rechargeable battery 12 may be, for example, a vehicle battery of a motor vehicle equipped with the exhaust system 1. By means of the rechargeable battery 12, the electrical energy generated during the cooling of the exhaust gas 3 can be stored.

Fig. 2 schematically shows an internal combustion engine 2 and an exhaust system 1 attached to the internal combustion engine 2 in another embodiment variant.

In contrast to fig. 1, the particulate filter 9 is arranged separately from the thermoelectric device 7 and the SCR catalytic converter 8 upstream of the thermoelectric device 7 and downstream of the temperature sensor 6. The thermoelectric device 7 together with the SCR catalytic converter 8 may constitute a joint assembly. As for the rest, reference is made to the description relating to fig. 1.

FIG. 3 shows a flowchart of an exemplary method for treating exhaust gas produced by internal combustion engine 2. For carrying out the method, an exhaust system 1 as shown in fig. 1 or fig. 2 can be used, for example.

First, the internal combustion engine 1 is started and the formed exhaust gas is introduced into the exhaust system 1, wherein the exhaust gas 3 and the like flow through the LNT catalytic converter 4. The combustion air ratio λ is determined immediately downstream of the LNT catalytic converter 4. When λ ≧ 1 applies, i.e., when stoichiometric or lean exhaust gas 3 is present, there is no risk of damage to the downstream SCR catalytic converter 8, and the thermoelectric device 7 can remain deactivated or be deactivated.

Conversely, when λ <1 applies, i.e. when rich exhaust gas 3 is present, the SCR catalytic converter 8 may be damaged by rich components of the exhaust gas 3, depending on the temperature. For this purpose, in a next step the temperature T of the exhaust gas 3 upstream of the SCR catalytic converter 8 and the thermoelectric device 7 is determined.

When T is less than or equal to T_maxwhen applicable, i.e. when the maximum temperature T is not exceeded_maxThere is also no risk of damage to the downstream SCR catalytic converter 8, and the thermoelectric device 7 can remain deactivated or be deactivated. Maximum temperature T in the exemplary embodiment_maxUp to 500 c, but the maximum temperature T deviating from this temperature can also be determined_max。

In contrast, when T>T_maxwhen applicable, i.e. when the maximum temperature T is exceeded_maxwhen this occurs, the SCR catalytic converter 8 may be damaged by the rich components of the exhaust gas 3. To prevent damage, the thermoelectric device 7 is activated such that the exhaust gas 3 is cooled during contact with the thermoelectric device 7. Alternatively, the electrical energy generated during cooling may be stored in a rechargeable battery 12, which rechargeable battery 12 is electrically conductively connected to the thermoelectric device 7.

Preferably, cooling is performed at the highest temperature T upstream of the SCR catalytic converter 8_maxNo longer exceeded. The exhaust gas 3 can now be led through the SCR catalytic converter 8 arranged downstream of the thermoelectric device 7 without fear of damage due to the influence of rich components of the exhaust gas 3 at high temperatures.

In the following, the combustion air ratio λ is again determined directly downstream of the LNT catalytic converter 4, and the presence of conditions requiring cooling of the exhaust gas 3, i.e. rich exhaust gas 3 and above the maximum temperature T, is again checked_maxIs present. The method ends with the internal combustion engine 2 being switched off.

Destruction of the SCR catalytic converter 8 by the action of rich components of the exhaust gas 3 at high temperatures can be avoided, thereby extending the life of the SCR catalytic converter 8. In addition, the electrical energy generated during the cooling of the exhaust gas 3 can be stored and reused, so that the cooling of the exhaust gas 3 also has a positive effect on the energy balance.

List of reference numerals

1 exhaust system

2 internal combustion engine

3 exhausting gas

4 LNT catalytic converter

5 lambda sensor

6 temperature sensor

7 thermoelectric device

8 SCR catalytic converter

9 particle filter

10 supply device

11 control unit

12 rechargeable battery

13 control signal

14a, 14b sensor signal

Lambda combustion air ratio

T temperature

T_maxMaximum temperature

Claims

1. An exhaust system (1) for receiving exhaust gas (3) produced by an internal combustion engine (2), comprising:

-an LNT catalytic converter (4),

-a lambda sensor (5) arranged downstream of the LNT catalytic converter (4),

-a temperature sensor (6) arranged downstream of the LNT catalytic converter (4),

-one or more thermoelectric devices (7) arranged downstream of said lambda sensor (5) and downstream of said temperature sensor (6) designed for converting thermal energy into electrical energy, and

-an SCR catalytic converter (8) arranged downstream of the thermoelectric device (7).

2. The exhaust system (1) according to claim 1, comprising:

-a particulate filter (9) arranged downstream of the thermoelectric device (7) and upstream of the SCR catalytic converter (8).

3. The exhaust system (1) according to any one of the preceding claims, comprising:

-a particulate filter (9) arranged downstream of the LNT catalytic converter (4) and upstream of the thermoelectric device (7).

4. The exhaust system (1) according to claim 2 or 3, wherein the particulate filter (9) has an SCR coating.

5. The exhaust system (1) according to any one of the preceding claims, comprising:

-a supply device (10) arranged upstream of the SCR catalytic converter (8) for supplying the exhaust gas (3) with an ammonia-forming composition.

6. The exhaust system (1) according to any one of the preceding claims, comprising:

-a control unit (11) equipped and designed for outputting a control signal (13), the control signal (13) being used for controlling the thermoelectric device (7) in dependence of sensor signals (14a, 14b) of the lambda sensor (5) and the temperature sensor (6).

7. The exhaust system (1) according to any one of the preceding claims, comprising:

-a rechargeable battery (12) electrically conductively connected to the thermoelectric device (7).

8. A motor vehicle having an internal combustion engine (2) and an exhaust system (1) according to any one of the preceding claims.

9. A method of treating exhaust gas (3) produced by an internal combustion engine (2), comprising the steps of:

-leading the exhaust gas (3) through an LNT catalytic converter (4),

-determining a combustion air ratio lambda and a temperature T of the exhaust gas (3) downstream of the LNT catalytic converter (4) and upstream of one or more thermoelectric devices (7),

-contacting the exhaust gas (3) with the thermoelectric device (7) and-guiding the exhaust gas (3) through an SCR catalytic converter (8) arranged downstream of the thermoelectric device (7).

10. The method of claim 9, comprising:

-comparing the determined temperature T with the maximum temperature T_maxMake a comparison and

-at said combustion air ratio λ<1 and above said maximum temperature T_maxIn the case of (2), activating the thermoelectric device (7) for cooling the exhaust gas (3) to convert thermal energy into electrical energy.

11. the method according to claim 9 or 10, comprising:

-comparing said determined temperature T with said maximum temperature T_maxMake a comparison and

-at said combustion air ratio λ ≧ 1 and/or said maximum temperature T is not reached or reached_maxIn the case of (2), deactivating the thermoelectric device (7).

12. The method of claim 10, comprising:

-storing the generated electrical energy.