DE102020130839A1 - Method for operating an internal combustion engine with substoichiometric combustion and an exhaust gas aftertreatment device assigned to the internal combustion engine, exhaust gas aftertreatment device, internal combustion engine with an exhaust gas aftertreatment device and motor vehicle - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (10) and an exhaust gas aftertreatment device (20) assigned to the internal combustion engine (10), in which the internal combustion engine (10) is operated with substoichiometric combustion of a fuel-air mixture and exhaust gas ( 12) a first catalytic converter (30) of the exhaust gas aftertreatment device (20), by means of which nitrogen oxides contained at least in the exhaust gas (12) are reduced, and fresh air is fed to the exhaust gas (12) downstream of the first catalytic converter (30) via a feed device (40). (14) is supplied, whereby a hyper-stoichiometric exhaust gas/fresh air mixture (16) is formed, which is fed to a second catalytic converter (50) of the exhaust gas aftertreatment device (20), by means of which carbon monoxide contained at least in the exhaust gas/fresh air mixture (16) is removed and ammonia are reduced. Further aspects of the invention relate to an exhaust gas treatment device (20), an internal combustion engine (10) and a motor vehicle (K).

Description

The invention relates to a method for operating an internal combustion engine and an exhaust gas aftertreatment device assigned to the internal combustion engine. Further aspects of the invention relate to an exhaust gas aftertreatment device for an internal combustion engine, an internal combustion engine with an exhaust gas aftertreatment device and a motor vehicle with an internal combustion engine.

Various operating strategies for internal combustion engines operated by Otto engines or diesel engines, ie Otto engines or diesel engines, are known from the prior art. Some of these operating strategies are aimed at heating up the respective catalytic converters of the exhaust gas aftertreatment devices assigned to the internal combustion engines as quickly as possible. Gasoline engines are usually (but not exclusively) operated stoichiometrically and thus with a combustion air ratio of λ = 1. Modern diesel engines, on the other hand, are over-stoichiometric and are therefore operated lean, so to speak, i.e. with a combustion air ratio of λ > 1. The latter is not least due to the soot emissions from diesel engines, which would be unacceptably high if diesel engines were operated stoichiometrically or even sub-stoichiometrically (λ < 1). In order to comply with ever more stringent emission standards, a great deal of effort is sometimes expended, in that several catalytic converters with different functions are often connected in series. However, the use of fuels with fluctuating fuel quality or a series distribution of internal combustion engines and/or exhaust gas aftertreatment devices can be problematic for the reliable exhaust gas aftertreatment.

The object of the present invention is to provide a method, an exhaust gas aftertreatment device, an internal combustion engine and a motor vehicle of the type mentioned at the outset, through which reliable exhaust gas aftertreatment can take place.

This object is achieved by a method having the features of patent claim 1, by an exhaust gas aftertreatment device having the features of patent claim 8, by an internal combustion engine having the features of patent claim 9 and by a motor vehicle having the features of patent claim 10. Advantageous configurations with expedient developments of the invention are specified in the dependent claims.

A first aspect of the invention relates to a method for operating an internal combustion engine and an exhaust gas aftertreatment device assigned to the internal combustion engine. In this method, the internal combustion engine is operated with substoichiometric combustion of a fuel-air mixture, and exhaust gas formed during substoichiometric combustion, in particular rich exhaust gas, is supplied to a first catalytic converter of the exhaust gas aftertreatment device. At least nitrogen oxides contained in the exhaust gas are reduced by means of the first catalytic converter. In addition, in the method, fresh air is supplied to the exhaust gas downstream of the first catalytic converter via a feed device, as a result of which a super-stoichiometric mixture of exhaust gas and fresh air is formed. The super-stoichiometric mixture of exhaust gas and fresh air is fed to a second catalytic converter of the exhaust gas aftertreatment device, by means of which the carbon monoxide and ammonia contained at least in the mixture of exhaust gas and fresh air are reduced. A major advantage of this method is that the internal combustion engine, which is preferably operated as a gasoline engine, does not have to be operated in a narrow range around the stoichiometric combustion air ratio in order to ensure effective exhaust gas aftertreatment, for example using a three-way catalytic converter, but that the method can also be used in transient operating states , Allows for example in an acceleration operation or even full load operation of the internal combustion engine, an effective reduction in emissions.

The invention is based on the knowledge that the combustion air ratio must be regulated very precisely in conventional operating methods of an internal combustion engine so that the catalytic converter connected downstream of the internal combustion engine can efficiently convert the pollutants. Even the smallest deviations from a target value for the combustion air ratio lead to increased exhaust gas emissions. This can occur as a result of an inexactly fitting pilot control due to a series scatter, due to changing boundary conditions and due to future fuel diversity, in particular fluctuating quality of the fuel and fluctuating physical properties of the fuel. When controlling the internal combustion engine, the error that has occurred must first be corrected. During this time, the catalytic converter does not convert properly and an impermissibly high amount of pollutants is released into the environment. Another problem are dynamic driving maneuvers and changes in load and speed of the combustion engine. In this case, the combustion air ratio range required for the conversion cannot be maintained. The proposed method for operating the internal combustion engine and the Exhaust gas after-treatment device, which is assigned to the internal combustion engine, the problems described in relation to the exhaust gas after-treatment can be avoided.

In the proposed method, two catalytic converters, namely the first catalytic converter and the second catalytic converter, are switched in succession, the first catalytic converter being operated rich and the second catalytic converter lean. In other words, the first catalytic converter is subjected to the exhaust gas formed by under-stoichiometric combustion and is therefore “rich”, whereas the second catalytic converter is exposed to the over-stoichiometric and therefore “lean” exhaust gas/fresh air mixture. The internal combustion engine can be operated so richly that a rich mixture can arrive at the first catalytic converter in any case. After the first catalytic converter, i.e. downstream of the first catalytic converter and before the second catalytic converter, i.e. upstream of the second catalytic converter, so much fresh air can be fed in using the feed device that the exhaust gas/fresh air mixture can arrive at the second catalytic converter as a lean mixture in any case. As little fresh air as necessary can be mixed with the exhaust gas using the feed device, i.e. fed in. While the first catalytic converter can reduce NOx emissions, i.e. nitrogen oxide emissions, the second catalytic converter makes it possible to reduce CO emissions, also known as carbon monoxide emissions, and NH3 emissions, also known as ammonia emissions.

In an advantageous development of the invention, hydrocarbons contained in the exhaust gas are reduced by means of the first catalytic converter. This is advantageous because it allows a particularly comprehensive and effective exhaust gas aftertreatment using the first catalytic converter.

In a further advantageous development of the invention, hydrocarbons contained in the mixture of exhaust gas and fresh air are reduced by means of the second catalytic converter. This is advantageous since any escape of hydrocarbons into the environment can be particularly effectively prevented by means of the second catalytic converter.

In a further advantageous development of the invention, the fresh air is supplied to the exhaust gas using a jet pump of the feed device. The advantage here is that the jet pump has a simple structure and is therefore particularly robust. A further advantage is that the exhaust gas that can be fed to the jet pump can serve as a driving medium and a quantity of fresh air supplied by the jet pump can be set with little effort by the quantity of exhaust gas and thus, so to speak, automatically as a function of this quantity.

In a further advantageous development of the invention, a diffuser of the feed device is arranged downstream of the jet pump, through which diffuser the exhaust gas/fresh air mixture is guided. This diffuser can bring about a further increase in the pressure of the exhaust gas/fresh air mixture and also lead to improved mixing of the exhaust gas/fresh air mixture.

In a further advantageous development of the invention, the internal combustion engine is operated in an operating state that differs from cold-start operation with substoichiometric combustion of the fuel-air mixture. As a result, the exhaust gas aftertreatment is advantageously ensured in a particularly large operating range, in particular the map range, of the internal combustion engine.

In a further advantageous development of the invention, the internal combustion engine is operated in an operating state that differs from full-load operation and/or acceleration operation with substoichiometric combustion of the fuel-air mixture. Accelerated operation corresponds to an operating state in which acceleration enrichment and thus combustion of a rich (sub-stoichiometric) fuel-air mixture can take place to accelerate a crankshaft of the internal combustion engine. This expands the effectiveness of the exhaust gas aftertreatment in an advantageous manner to a particularly large operating range, in particular the map range, of the internal combustion engine.

A second aspect of the invention relates to an exhaust gas aftertreatment device for an internal combustion engine, having a first catalytic converter which is designed to reduce at least the nitrogen oxides contained in exhaust gas formed by the internal combustion engine when it is operated with substoichiometric combustion of a fuel-air mixture. The exhaust gas aftertreatment device also includes a feed device, which is designed to supply fresh air to the exhaust gas downstream of the first catalytic converter and thereby to form a super-stoichiometric mixture of exhaust gas and fresh air. A second catalytic converter of the exhaust gas aftertreatment device is designed to reduce at least the carbon monoxide and ammonia contained in the exhaust gas/fresh air mixture. A particularly reliable exhaust gas aftertreatment can take place with this exhaust gas aftertreatment device.

A third aspect of the invention relates to an internal combustion engine with an exhaust gas aftertreatment device according to the second aspect of the invention. This combination of internal combustion engine and exhaust gas aftertreatment device enables particularly reliable exhaust gas aftertreatment.

A fourth aspect of the invention relates to a motor vehicle with an internal combustion engine according to the third aspect of the invention. This motor vehicle emits exhaust gases with a particularly low proportion of pollutants.

The preferred embodiments presented in relation to one of the aspects and their advantages apply correspondingly to the respective other aspects of the invention and vice versa.

The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and/or shown alone in the figures can be used not only in the combination specified in each case, but also in other combinations or on their own, without going beyond the scope of the leave invention.

Further advantages, features and details of the invention result from the claims, the following description of preferred embodiments and with reference to the drawings.

The invention is explained again below using a specific exemplary embodiment. For this shows the only 1 a schematic representation of an internal combustion engine with an exhaust gas aftertreatment device, which are associated with a highly abstract motor vehicle shown.

The only 1 shows a highly abstract representation of a motor vehicle K with an internal combustion engine 10. The internal combustion engine 10 includes an exhaust gas aftertreatment device 20 with a first catalytic converter 30, which is designed to be formed at least in the internal combustion engine 10 during its operation with substoichiometric combustion of a fuel-air mixture To reduce exhaust gas 12 contained nitrogen oxides. Provided between the first catalytic converter 30 and the internal combustion engine 10 is an exhaust gas turbocharger 18 assigned to the internal combustion engine, of which only a turbine is shown schematically in the present case. The turbine is coupled to a not shown compressor of the exhaust gas turbocharger. Using the compressor, the internal combustion engine 10 can be supplied with compressed air, which is used to burn fuel to form the exhaust gas 12 . During the operation of internal combustion engine 10 , exhaust gas 12 is applied to the turbine before the exhaust gas reaches first catalytic converter 30 . Hydrocarbons contained in the exhaust gas 12 can also be reduced by means of the first catalytic converter 30 .

The exhaust gas aftertreatment device 20 also includes a feed device 40 which is designed to supply fresh air 14 to the exhaust gas 12 downstream of the first catalytic converter 30 and thereby to form a super-stoichiometric exhaust gas/fresh air mixture 16 . The fresh air 14 can be fed to the exhaust gas 12 using a jet pump 42 of the feed device 40 . For this purpose, the jet pump 42 can draw in the fresh air 14 and feed it to the exhaust gas 12 .

In addition, the exhaust gas aftertreatment device 20 includes a second catalytic converter 50 which is designed to reduce at least the carbon monoxide and ammonia contained in the exhaust gas/fresh air mixture 16 . Hydrocarbons contained in the exhaust gas/fresh air mixture 16 can also be reduced by means of the second catalytic converter 50 .

The jet pump 42 is arranged downstream of the first catalytic converter 30 and upstream of the second catalytic converter 50 . A diffuser 44 of the feed device 40 is arranged downstream of the jet pump 42 and upstream of the second catalytic converter 50 , through which the exhaust gas/fresh air mixture 16 is guided before it reaches the second catalytic converter 50 .

A particularly low-emission, and thus cleaned, exhaust gas/fresh air mixture 13 exits the second catalytic converter 50 and is released into the environment.

The sub-stoichiometric operation of internal combustion engine 10 and exhaust gas aftertreatment device 20 ensures that even during transient, and thus dynamic operation of internal combustion engine 10 and when using fuel that is subject to (future) fuel diversity, the pollutants are effectively removed from exhaust gas 12 and the exhaust gas-fresh air mixture 16 are removed.

The internal combustion engine 10 can generally be operated in an operating state that differs from cold-start operation with substoichiometric combustion of the fuel-air mixture. In addition, the internal combustion engine 10 can differ from full-load operation and/or acceleration operation which are operated with substoichiometric combustion of the fuel-air mixture.

It is therefore conceivable to operate the internal combustion engine exclusively rich, ie with substoichiometric combustion of the fuel-air mixture.

Reference List

10

internal combustion engine

12

exhaust

13

cleaned exhaust gas/fresh air mixture

14

fresh air

16

exhaust gas/fresh air mixture

18

exhaust gas turbocharger

20

exhaust aftertreatment device

30

first catalyst

40

feeding device

42

jet pump

44

diffuser

50

second catalyst

K

motor vehicle

Claims (10)

Method for operating an internal combustion engine (10) and an exhaust gas aftertreatment device (20) assigned to the internal combustion engine (10), in which - the internal combustion engine (10) is operated with substoichiometric combustion of a fuel-air mixture and exhaust gas (12) formed during the substoichiometric combustion is fed to a first catalytic converter (30) of the exhaust gas aftertreatment device (20), by means of which at least one contained in the exhaust gas (12). Nitrogen oxides are reduced, and - Fresh air (14) is fed to the exhaust gas (12) downstream of the first catalytic converter (30) via a feed device (40), whereby a more than stoichiometric exhaust gas/fresh air mixture (16) is formed, which is fed to a second catalytic converter (50) of the exhaust gas aftertreatment device ( 20) is supplied, by means of which carbon monoxide and ammonia contained at least in the exhaust gas/fresh air mixture (16) are reduced. procedure after claim 1 , characterized in that hydrocarbons contained in the exhaust gas (12) are reduced by means of the first catalytic converter (30). procedure after claim 1 or 2 , characterized in that hydrocarbons contained in the exhaust gas/fresh air mixture (16) are reduced by means of the second catalytic converter (50). Method according to one of the preceding claims, characterized in that the fresh air (14) is supplied to the exhaust gas (12) by means of a jet pump (42) of the feed device (40). procedure after claim 4 , characterized in that downstream of the jet pump (42) a diffuser (44) of the feed device (40) is arranged, through which the exhaust gas-fresh air mixture (16) is guided. Method according to one of the preceding claims, characterized in that the internal combustion engine (10) is operated in an operating state which differs from cold-start operation with substoichiometric combustion of the fuel-air mixture. Method according to one of the preceding claims, characterized in that the internal combustion engine (10) is operated in an operating state other than full-load operation and/or acceleration operation with substoichiometric combustion of the fuel-air mixture. Exhaust gas aftertreatment device (20) for an internal combustion engine (10), with a first catalytic converter (30) which is designed to contain at least the exhaust gas (12) formed by the internal combustion engine (10) during its operation with substoichiometric combustion of a fuel-air mixture to reduce nitrogen oxides, with a feed device (40) which is designed to supply fresh air (14) to the exhaust gas (12) downstream of the first catalytic converter (30) and thereby to form a super-stoichiometric exhaust gas/fresh air mixture (16), and with a second catalytic converter (50) which is designed to reduce carbon monoxide and ammonia contained at least in the exhaust gas/fresh air mixture (16). Internal combustion engine (10) with an exhaust gas aftertreatment device (20). claim 8 . Motor vehicle (K) with an internal combustion engine (10). claim 9 .

Images