DE102021204501A1 - Operation of an internal combustion engine depending on water in the exhaust system - Google Patents

Abstract

A method for operating an internal combustion engine, which includes an internal combustion engine (1) and an exhaust system (8), provides that it is determined whether an accumulation of water in the exhaust system (8) is present, and then when a water amount is above a limit value Amount of water is determined, a filling of at least one combustion chamber (4) of the internal combustion engine (1) is limited.

Description

The invention relates to a method for operating an internal combustion engine, which includes an internal combustion engine and an exhaust system.

Exhaust gas that is generated by the internal combustion engine during operation of such an internal combustion engine and is transferred to the exhaust line includes relevant amounts of water. When it is discharged from the internal combustion engine, this water is essentially completely in vapor form, but it can condense out in the exhaust system and collect there, in particular in exhaust gas aftertreatment components that are integrated into the exhaust system. In the following, liquid water is simply referred to as water and vaporous water as water vapor. Condensation of water from the exhaust gas occurs more frequently when the exhaust gas itself already has a relatively low temperature when it is discharged from the internal combustion engine and/or when this is relatively largely due to heat transfer to the exhaust line and in particular to those integrated therein when flowing through the exhaust line Components of an exhaust aftertreatment device is cooled. Consequently, relevant amounts of water can accumulate in the exhaust system of an internal combustion engine in particular when the internal combustion engine is started relatively frequently from cold and/or is operated at a relatively low load over a longer period of time.

Water that has accumulated in the exhaust line evaporates and is thereby discharged from the exhaust line when sufficient thermal energy is supplied to it via the exhaust gas. When evaporating, water expands to a significant extent. This can lead to a temporary increase in the pressure of the exhaust gas in the exhaust system and thus in the back pressure that has to be overcome in order to eject exhaust gas from the internal combustion engine. This can have a negative effect on the operating behavior of the internal combustion engine. In particular, increased exhaust gas back pressure can prevent adequate residual gas scavenging from the combustion chambers of the internal combustion engine, which in extreme cases can lead to misfires due to excessive amounts of inert residual gas in the combustion chambers.

It is possible to detect excessive exhaust gas pressure in the exhaust line and/or misfiring in order to then initiate countermeasures, which would, however, be a relatively late reaction to the problem described.

the DE 10 2016 100 878 A1 discloses a method for operating an internal combustion engine with a particle filter integrated into an exhaust line, in which an amount of water accumulated in a particle filter is estimated and a decision is made based thereon whether the particle filter is regenerated.

the DE 10 2017 211 024 A1 discloses suspending monitoring of a particle filter with regard to a necessary regeneration after a cold start of an internal combustion engine until water that has collected in the particle filter has evaporated. This is to avoid an error in the regeneration monitoring caused by the presence of water.

the DE 101 10 340 A1 describes a method for controlling an internal combustion engine, in particular a diesel internal combustion engine, which includes an exhaust gas aftertreatment system, the amount of air that is supplied to the internal combustion engine being controlled as a function of a variable that characterizes the exhaust gas aftertreatment system. In particular, this variable can be the differential pressure across the exhaust gas aftertreatment system or the pressure before the exhaust gas aftertreatment system or a loading of a particle filter of the exhaust gas aftertreatment system with soot.

The invention was based on the object of demonstrating a possibility of reacting as quickly as possible to an increased exhaust gas pressure which is caused by water evaporating in the exhaust line.

This object is solved by a method according to patent claim 1 . Advantageous embodiments of this method are the subject matter of the further patent claims and/or result from the following description of the invention.

According to the invention, a method for operating an internal combustion engine, which includes an internal combustion engine and an exhaust line, is provided, it being determined whether there is an accumulation of (liquid) water in the exhaust line. If this determination shows that the amount of water in the exhaust system is above a water quantity limit value, filling of at least one combustion chamber of the internal combustion engine, preferably all combustion chambers if there are several combustion chambers in the internal combustion engine, is limited. The "filling" of a combustion chamber is the mass of the gas or the gas-fuel mixture that can be introduced into a combustion chamber under the given operating parameters of the combustion engine per working cycle. The aim of limiting the filling is to limit the filling of the at least one combustion chamber to a value below a maximum value the charge that can be achieved during operation of the internal combustion engine under the given operating parameters of the internal combustion engine. This value can be defined as absolute or relative, ie as a percentage of the maximum value, for example.

By limiting the filling of the combustion chamber or combustion chambers as required, it is possible to avoid the combustion engine being operated in load ranges that lead to combustion misfires (i.e. that in the combustion chamber or The fuel-containing mixture present in the combustion chambers does not ignite or does not ignite to a sufficient extent). Limiting the filling of the combustion chambers counteracts this because the volume flow of exhaust gas that flows into the exhaust system is correspondingly limited, which can have an increasing effect on the scavenging gradient over the combustion engine. As a result, an excessive residual gas content in the combustion chamber or combustion chambers, which can lead to misfires, can be avoided.

In principle, the water quantity limit value can be zero, so that a limitation can always be provided if an accumulation of water in the exhaust line is determined. However, it is preferably provided that the water quantity limit value is greater than zero, so that it is ensured that the limitation of the filling, which can also have a negative effect on the operating behavior of the internal combustion engine, is only carried out when there is so much water in the exhaust line that that its evaporation can actually lead to a problematically high exhaust gas pressure.

Provision can also be made for the filling of the at least one combustion chamber to be limited only when a temperature of the exhaust gas and/or the exhaust line is above (in each case) a temperature limit value. As a result, an (unnecessary) limitation can be avoided if or as long as there is no risk of a problematic exhaust gas pressure being reached due to evaporation of the water, despite a possible accumulation of a relevant amount of water in the exhaust gas system, because the temperature of the exhaust gas and/or the exhaust gas system is too low is to evaporate a relatively large amount of water in a relatively short time.

In order to avoid as far as possible a limitation of the filling and thus the resulting disadvantages in terms of the operating behavior of the internal combustion engine, it can also preferably be provided that the (initially implemented) limitation is canceled if the amount of water is again below a/the water quantity limit value is determined and/or when the temperature of the exhaust gas and/or the exhaust line is again below a/the temperature limit value. The water quantity limit value and/or the temperature limit value can in each case correspond to that from which a limitation of the filling is provided. However, the respective (water quantity or temperature) limit value for the removal of the limitation is preferably below the respective (water quantity or temperature) limit value for the limitation, whereby in the manner of a two-point control or a control-related hysteresis, a relatively short time multiple switching between limitation and non-limitation when the accumulated water quantity is in the range of a (single) water quantity limit value and/or when the temperature of the exhaust gas and/or the exhaust system is in the range of a (single) temperature limit value can be avoided . Against this background, it should also be provided that if the respective (water quantity and/or temperature) limit values for limitation and non-limitation differ, the distance between these limit values should be large enough to allow multiple switching in a relatively short time Time to avoid due to a slight fluctuation in the determined amount of water and / or the temperature of the exhaust and / or the exhaust line. At the same time, however, the distance between the limit values should not be too large, so that the filling of the combustion chamber or combustion chambers is only limited if this is necessary due to a correspondingly large amount of water and/or due to a correspondingly high temperature of the exhaust gas and/or the Exhaust system is required.

Provision can also preferably be made for the filling of the at least one combustion chamber to be variably limited as a function of the amount of water and/or the temperature of the exhaust gas and/or the exhaust line, with the limit being selected to be greater the greater the amount of water and/or the temperature of the exhaust gas and/or the exhaust line. Consequently, the limitation can be selected to be greater as required, the greater the potentially evaporating quantity of water and thus the greater the resulting exhaust gas pressure can be. As a result, the limitation is only implemented to the extent that it makes sense to actually avoid the disadvantages that could result from excessive exhaust gas pressure.

Water can collect in particular in the area of an exhaust gas afterbe integrated into the exhaust system treatment device, in particular in an exhaust gas catalytic converter and/or in a particle filter of the exhaust gas aftertreatment device, because the exhaust gas in these exhaust gas aftertreatment components is at times cooled to a particularly high degree. In addition, the flow velocity in these exhaust gas aftertreatment components can be relatively low, which can also increase water condensing out of the exhaust gas. And finally, such exhaust gas aftertreatment components usually have larger flow cross sections than exhaust gas pipes of the exhaust system that serve as inlet and outlet lines to these exhaust gas aftertreatment components, which means that sinks can be formed in which relatively large amounts of water that has condensed out can collect. Against this background, it can be advantageous for the accumulation of water to be determined at least within the exhaust gas aftertreatment device and in particular in the exhaust gas catalytic converter and/or the particle filter thereof.

In principle, there is the possibility of measuring an accumulation of water in the exhaust system using a suitable sensor. However, it may be necessary to position a large number of corresponding sensors within the exhaust line in order to be able to reliably determine all larger accumulations of water. For example, it could be necessary to position at least one sensor at a point that is as low as possible in the direction of gravity in each of the possible multiple exhaust gas catalytic converters and/or particle filters. This can be associated with a considerable design effort and thus correspondingly high costs. Advantageously, therefore, a determination with regard to an accumulation of water can be based on a model, so that, based on the operating parameters of the internal combustion engine, for example the ambient temperature, the course of a temperature of the internal combustion engine, the operating load and the operating speed of the internal combustion engine, etc., conclusions can be drawn as to whether and how much water has condensed out in the exhaust system and has accumulated therein. Such a model-based determination can, in particular, also take into account all operating cycles (between starting and stopping the internal combustion engine) and the times between each two such operating cycles.

In the same way, the temperature of the exhaust gas and/or the exhaust line can advantageously be determined on the basis of a model, with a measurement of at least one temperature also being possible in this regard and possibly also being advantageous.

The filling of the at least one combustion chamber can be limited in particular by adapting and in particular limiting the charging pressure, which is generated by means of a fresh-gas compressor integrated into a fresh-gas line of the internal combustion engine, because this represents the fastest and simplest possible way of limiting the filling. However, this requires a corresponding configuration of the internal combustion engine operated according to the invention that is supercharged by means of the fresh-gas compressor. In addition or as an alternative, the valve position of a throttle valve integrated into the fresh-gas line and/or the actuation of intake valves of a variable valve train of the internal combustion engine, in particular with regard to the size of the respective opening lift and/or the length of the opening duration and/or the control times (i.e. the opening of the intake valves in relation to a position of a piston that variably delimits the respective combustion chamber).

The internal combustion engine of an internal combustion engine operated according to the invention can preferably be spark-ignited at least at times, in particular spark-ignited and quantity-controlled (i.e. a spark-ignition engine). However, there is also the possibility that the internal combustion engine is a (self-igniting and quality-controlled) diesel engine or a functional combination of a gasoline engine and a diesel engine, e.g. an internal combustion engine with homogeneous compression ignition. The internal combustion engine can be operated with both liquid fuel (i.e. diesel or petrol) and gaseous fuel (especially natural gas, LNG or LPG).

The invention also relates to a motor vehicle, in particular a wheel-based and non-rail-bound motor vehicle (preferably a car or a truck), with an internal combustion engine operated according to the invention or a method for operating such a motor vehicle. The internal combustion engine of the internal combustion engine can be provided in particular for the (direct or indirect) provision of the driving power for the motor vehicle.

• 1: eine für die Durchführung eines erfindungsgemäßen Verfahrens geeignete Brennkraftmaschine in vereinfachter Darstellung.

The invention is explained in more detail below with reference to an exemplary embodiment illustrated in the drawings. In the drawings shows:

• 1 : an internal combustion engine suitable for carrying out a method according to the invention in a simplified representation.

the 1 shows an internal combustion engine for a motor vehicle that is suitable for carrying out a method according to the invention. This includes an internal combustion engine 1, the example is designed in the form of a reciprocating engine with four cylinder ports 2 arranged in series. The cylinder openings 2 delimit a combustion chamber 4 with reciprocating pistons 3 and a cylinder head movably guided therein. During operation of the internal combustion engine 1 and thus the internal combustion engine, fresh gas is supplied to these combustion chambers 4 via a fresh gas line 5, with the fresh gas being supplied by means of inlet valves 6, which are connected to the individual Combustion chambers 4 are assigned, is controlled. The fresh gas is exclusively or predominantly air that is sucked in from the environment. Exhaust gas that is produced during the combustion of mixture quantities, which consists of the fresh gas and fuel injected directly into the combustion chambers 4 via fuel injectors 7, is discharged via an exhaust system 8 of the internal combustion engine, with the exhaust gas being discharged by means of outlet valves 9, which are assigned to the individual Combustion chambers 4 are assigned, is controlled. The quantities of mixture in the combustion chambers 4 are ignited by means of electrical ignition devices 10 which, for example, generate ignition sparks (spark plugs). The exhaust gas flows through an exhaust gas after-treatment device 11, which is intended to remove components of the exhaust gas that are regarded as pollutants from the exhaust gas or to convert them into harmless components.

The internal combustion engine is supercharged, for which purpose a fresh-gas compressor 12 is integrated into the fresh-gas line 5 . The fresh gas compressor 12 is part of an exhaust gas turbocharger, which also includes an exhaust gas turbine 13 which is integrated into the exhaust line 8 . Exhaust gas that flows through the exhaust gas turbine 13 leads to a rotating drive of a turbine impeller, which is connected via a shaft 14 in a rotationally driving manner to a compressor impeller of the fresh gas compressor 12, so that the result is that the fresh gas compressor 12 is driven by the exhaust gas turbine 13.

The exhaust gas aftertreatment device 11 comprises at least one exhaust gas catalytic converter 15 and a particle filter 16. The exhaust gas catalytic converter 15 can be designed in particular as a three-way catalytic converter and can therefore at least convert carbon monoxide (CO), nitrogen oxides (NOx) and unburned hydrocarbons (HC) to carbon dioxide (CO ₂ ), Support nitrogen (N ₂ ) and water (H ₂ O) catalytically. The exhaust gas catalytic converter 15 and the particle filter 16 can also be configured integrally, for which purpose in particular a filter body of the particle filter 16 can be provided with a coating which is active catalytically and in particular as a three-way catalytic converter.

During operation of the internal combustion engine 1, the fresh gas to be supplied to it and the quantities of fuel to be introduced into the individual combustion chambers 4 by means of the fuel injectors 7 per working cycle are targeted as a function of the specific operating state of the internal combustion engine 1, which is defined in particular by the required load and the operating speed set. For this purpose, with regard to the fresh gas, the operating position of a throttle valve 17 integrated into the fresh gas line 5 and/or a variable valve train 18, by means of which the inlet valves 6 can be variably actuated, can be changed in a targeted manner.

Exhaust gas that is generated by the internal combustion engine 1 during operation of the internal combustion engine and is transferred to the exhaust system 8 includes relevant amounts of water vapor. This water vapor can condense out as water in the exhaust line 8 and collect therein, in particular in exhaust gas aftertreatment components of the exhaust aftertreatment device 11 . Condensation of water from the exhaust gas occurs more frequently if the exhaust gas itself is already at a relatively low temperature when it is discharged from the internal combustion engine 1 and/or if this is relatively strongly caused by expansion by means of the exhaust gas turbine 13 and by a Transfer of thermal energy to the exhaust line 8 and in particular to the components of the exhaust gas treatment device 11 comprised by this is cooled. Consequently, relevant amounts of water can collect in the exhaust line 8 in particular when the internal combustion engine 1 is started cold relatively frequently and/or is operated at low load over a longer period of time and/or is only operated briefly after frequent cold starts.

Water that has accumulated in the exhaust line 8 evaporates and is thereby discharged from the exhaust line 8 when a corresponding amount of thermal energy is supplied to it via the exhaust gas. When evaporating, the water expands to a considerable extent, as a result of which the pressure in the exhaust line 8 and thus the back pressure that has to be overcome in order to eject exhaust gas from the internal combustion engine 1 temporarily increases significantly. Furthermore, water that has condensed in the exhaust system can temporarily close the pores in a filter body of the particle filter 16, which thus reduces the flow cross section. This temporarily increases the back pressure until the water has evaporated. This can have a negative effect on the operating behavior of the internal combustion engine. In particular, an increased exhaust gas back pressure can prevent adequate residual gas scavenging from the combustion chambers 4 of the internal combustion engine 1, which in extreme cases can lead to combustion misfires.

In order to avoid this, it is provided that a model-based determination is made as to whether and to what extent water has accumulated in the exhaust line 8 . If this determination shows that there is a quantity of water in the exhaust line 8 that is above a water quantity limit value, filling of the combustion chambers 4 during operation of the internal combustion engine 1 is limited. This can prevent the internal combustion engine 1 from being operated in load ranges that can lead to combustion misfires when the exhaust gas pressure is too high, which can result from evaporation of the water.

In order to limit the filling of the combustion chambers 4 during operation of the internal combustion engine 1, provision can be made in particular to adapt and in particular to reduce the charging pressure or the compression of the fresh gas to be supplied to the internal combustion engine 1, which is effected by means of the fresh gas compressor 12. For this purpose it can be provided that the exhaust gas turbine has a variable turbine geometry (VTG). In order to implement such a variable turbine geometry, the exhaust gas turbine can have a device 19 in a known manner, by means of which a flow cross section, via which the exhaust gas can be routed to a turbine impeller of the exhaust gas turbine 13, can be changed, at least in terms of effectiveness, for which purpose in particular the size of the free flow cross section and /or the angle of the inflow of blades of the turbine wheel can be changeable. A variable turbine geometry can consequently be used to influence the extent to which exhaust gas enthalpy is used to generate drive power for the fresh-gas compressor 12, so that the boost pressure generated by the fresh-gas compressor 12 can be adjusted via a corresponding setting of the variable turbine geometry.

Alternatively or additionally, the filling of the combustion chambers 4 can also be achieved by closing the throttle valve 17 to a relatively large extent, which leads to an increased throttling of the flow of fresh gas to be supplied to the internal combustion engine 1, and/or by a corresponding adaptation of the actuation of the intake valves 6 by means of the variable valve train 18 be limited.

The filling is limited when an accumulation of a quantity of water in the exhaust line 8 is determined that is above a water quantity limit value, and also when both the temperature of the exhaust gas and a temperature of the exhaust line 8, in particular a temperature of the exhaust gas catalytic converter 15 and/or the particle filter 16, is above a respective temperature limit value, because then there is a real risk that relevant amounts of water will evaporate relatively quickly and the exhaust gas pressure can therefore temporarily increase so much that this has a negative effect on the operating behavior of the internal combustion engine. As soon as this danger no longer exists, the limitation is lifted again in order to avoid an unnecessarily long limitation.

Reference List

1

combustion engine

2

cylinder opening

3

reciprocating

4

combustion chamber

5

fresh gas line

6

intake valve

7

fuel injector

8th

exhaust line

9

outlet valve

10

ignition device

11

exhaust aftertreatment device

12

fresh gas compressor

13

exhaust turbine

14

Wave

15

catalytic converter

16

particle filter

17

throttle valve

18

valve train

19

Device for realizing a variable turbine geometry of the exhaust gas turbine

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102016100878 A1 [0005]
• DE 102017211024 A1 [0006]
• DE 10110340 A1 [0007]

Claims (10)

Method for operating an internal combustion engine, which comprises an internal combustion engine (1) and an exhaust system (8), it being determined whether there is an accumulation of water in the exhaust system (8), characterized in that when an amount above a water quantity limit value water is determined, a filling of at least one combustion chamber (4) of the internal combustion engine (1) is limited. procedure according to claim 1 , characterized in that the water quantity limit is greater than zero. procedure according to claim 1 or 2 , characterized in that the filling of the at least one combustion chamber (4) is only limited when a temperature of the exhaust gas line (8) flowing through exhaust gas and / or a temperature of the exhaust gas line (8) is above a temperature limit. Method according to one of the preceding claims, characterized in that the limitation is lifted if a quantity of water below a/the water quantity limit value is determined and/or when the temperature of the exhaust gas and/or the exhaust line (8) falls below a/the temperature limit value lies. Method according to one of the preceding claims, characterized in that the filling of the at least one combustion chamber (4) is variably limited depending on the amount of water and / or the temperature of the exhaust gas and / or the exhaust line (8), the limitation is selected the greater, the greater the amount of water and / or the temperature of the exhaust gas and / or the exhaust line (8). Method according to one of the preceding claims, characterized in that the accumulation of water in an exhaust gas treatment device (11) integrated in the exhaust line (8) is determined. procedure according to claim 6 , characterized in that the accumulation of water in an exhaust gas catalytic converter (15) and/or in a particle filter (16) of the exhaust gas aftertreatment device (11) is determined. Method according to one of the preceding claims, characterized in that the accumulation of water and/or the temperature of the exhaust gas and/or the exhaust line (8) is determined on the basis of a model. Method according to one of the preceding claims, characterized in that the filling of the at least one combustion chamber (4) by adjusting • the charge pressure, which is generated by means of a fresh-gas compressor (12) integrated in a fresh-gas line (5) of the internal combustion engine and/or • the valve position of a throttle valve (17) integrated in the fresh-gas line (5) and/or the actuation of intake valves (6) by means of a variable valve drive (18) of the internal combustion engine (1). Method according to one of the preceding claims, characterized in that the internal combustion engine (1) is operated with spark ignition.

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