WO2016074879A1

WO2016074879A1 - Method for operating an internal combustion engine comprising a lean nox trap

Info

Publication number: WO2016074879A1
Application number: PCT/EP2015/073945
Authority: WO
Inventors: Thorsten Schnorbus
Original assignee: Fev Gmbh
Priority date: 2014-11-10
Filing date: 2015-10-15
Publication date: 2016-05-19
Also published as: DE112015005082A5

Abstract

Disclosed is a method for operating an internal combustion engine comprising a lean NOx trap. In said method, the raw NOx emission level in the exhaust gas of the internal combustion engine is set to a reference variable at which the fuel consumption is minimal, wherein a first portion of fuel consumption (7) resulting from the combustion is taken into account in accordance with the raw NOx emission level, and a second portion of fuel consumption (8) resulting from the regeneration of the lean NOx trap at intervals is taken into account in accordance with the raw NOx emission level.

Description

Method for operating an internal combustion engine with a

NOx storage catalytic converter

description

The invention relates to a method for operating an internal combustion engine with a NOx storage catalytic converter.

An important aspect in the design of methods for operating an internal combustion engine is the reduction of fuel consumption in compliance with the emission limits required by law. Particularly in the case of lean-burn internal combustion engines, such as diesel engines, nowadays turbocharging takes place, by means of which, in addition to an increase in the boost pressure, an essentially free adjustability of the desired boost pressure is made possible. In conjunction with an adjustable exhaust gas recirculation rate, an optimum fuel consumption setpoint for the boost pressure can be set in compliance with all emission limits required by law. The change in boost pressure and EGR rate also affects a level of particulate emissions and raw emissions of nitric oxide through the associated change in air-fuel ratio.

A boost pressure control method for an exhaust gas turbocharger with adjustable turbine blades is described in the document DE 199 05 420 A1. The boost pressure is regulated by means of at least one regulator acting on an adjusting device to a supercharging pressure desired value, the regulator parameters being set via characteristic curves or characteristic diagrams as a function of operating parameters. A priority consideration of a fuel consumption optimal setting has the disadvantage that an additional consumption of additive for the selective catalytic reduction of nitrogen oxides in the exhaust aftertreatment device is disregarded. From DE 10 2012 108 237 A1 a method for operating an internal combustion engine using two resources is known. As the first resource, a fuel is used for combustion. The internal combustion engine has a device for exhaust gas aftertreatment in the form of a nitrogen oxide catalyst for the selective catalytic reduction of nitrogen oxides. In exhaust aftertreatment, an additive is used as a second resource. A resource consumption of the internal combustion engine is optimized taking into account a consumption of the first resource and taking into account a consumption of the second resource. As a result, an economical operation of the internal combustion engine is made possible because not only the fuel consumption alone, but also the additive consumption is included in the optimization. Since the fuel consumption of an internal combustion engine as a whole is significantly higher than the additive consumption, a weighting ratio of the consumption of the first operating means to the consumption of the second operating medium is predetermined, which is selected in particular from an economic point of view. In particular, the weighting ratio is based on the current market value of the operating materials.

DE 10 2010 060 992 A1 describes a method for controlling a boost pressure of an internal combustion engine with a device for exhaust gas treatment, in which the boost pressure is regulated to a boost pressure setpoint, wherein the boost pressure setpoint is set depending on operating parameters. The control of the boost pressure via a turbocharger, which compresses the intake air and possibly recirculated exhaust gas to increase the boost pressure prior to feeding to the internal combustion engine. The device for exhaust gas treatment comprises a particle filter and / or a nitrogen oxide catalyst.

A change in the air-fuel ratio by a change in the boost pressure has an influence on the fuel consumption by the combustion process in the internal combustion engine. On the one hand, this influences a process efficiency of the high-pressure process, on the other hand, an increase in the boost pressure leads to changed conditions during the charge cycle of the engine, so that the low-pressure process of the internal combustion engine is also influenced. The above influences on the high pressure process and the low pressure process with a direct relationship between boost pressure and fuel consumption.

It is determined a first value for a fuel consumption minimizing boost pressure, taking into account a direct influence of the boost pressure on a fuel consumption of the internal combustion engine. Under the influence on the fuel consumption of the internal combustion engine, the influences described above are summarized on the efficiency in the high-pressure process and on the charge cycle in the low-pressure process. Preferably, therefore, a first value is determined for a fuel consumption minimizing boost pressure, taking into account a direct influence of the boost pressure on an efficiency in the high-pressure process and on a charge change in the low-pressure process of the internal combustion engine. It is further provided that a second value for a boost pressure minimizing the fuel consumption is determined under consideration of an indirect influence of the boost pressure on an interval regeneration of the device for exhaust gas treatment. A change in the charge pressure influences the particle emission by the internal combustion engine, wherein the particle emission is crucial for a regeneration frequency and length of the particulate filter. Thus, the charge pressure setpoint also influences the length of the regeneration interval. The length of the regeneration interval in turn has an influence on the fuel consumption, since for each particulate filter regeneration a certain amount of additional fuel is consumed. As parameters for the determination of the second value of the engine speed, the injection quantity and the boost pressure are used, so that advantageously no additional sensors are needed.

Taking into account the first value and the second value, an optimized charge pressure setpoint is still set. The setting of the boost pressure setpoint includes, in particular, the determination of the value. The charge pressure desired value is preferably optimized while maintaining emission limit values with regard to minimum fuel consumption.

DE 199 26 148 A1 describes a method for compensation of aging or Damage to NOx storage catalytic converters by deliberately increasing the NOx conversion rate while maintaining a certain excess consumption threshold. In the method, the following measures are taken individually or in combination, depending on the detected extent of damage to the NOx storage catalytic converter, in order to be able to operate the NOx storage catalytic converter for a longer time without replacement: Change in the lean or rich operating time up to Initiation or termination of NOx regeneration or de-sulfation; - Constant o- the time-varying off-set to the lambda specification of a fresh NOx storage catalyst during the performance of a NOx regeneration or a desulfation; - Changing the exhaust gas recirculation rate, the ignition timing, the injection start, the injection duration, Tumbleklappenstellung, valve timing, compression and / or boost to reduce the lean NOx raw emissions under certain conditions for the exhaust gas temperature, the exhaust gas mass flow and the HC or CO emission rate; and - extension of the operating mode with Lambda = 1 in map areas in which a lean operation is possible with an undamaged NOx storage catalytic converter.

The extent to which the abovementioned measures are taken depends essentially on the related calculated additional fuel consumption and drivability. If a certain excess consumption threshold value is exceeded within a certain period of time, a detected catalyst damage is signaled since an indication of the catalyst damage appears more appropriate than a further efficiency-reduced operation. The object of the present invention is to optimize the fuel consumption of an internal combustion engine with a NOx storage catalytic converter.

The object is solved by the subject matter of patent claim 1. In the dependent claims preferred embodiments and advantageous developments are given.

In the method according to the invention for operating an internal combustion engine with a NOx storage catalytic converter, the NOx raw emission level in the exhaust gas of the internal combustion engine is regulated to a reference variable in which a minimum fuel consumption sets. Here, a first fuel consumption component is taken into account as a function of the NOx raw emission level that results from the combustion. In addition, a second fuel consumption component is taken into account as a function of the NOx raw emission level, which results from an intervalwise regeneration of the NOx storage catalytic converter.

During normal driving, the internal combustion engine is as a rule operated overstoichiometrically, i. in lean operation with excess air. For the regeneration of the NOx storage catalyst is, in a known manner, a substoichiometric operation, i. a rich operation with excess fuel required. This leads to an increased fuel consumption compared to the normal driving operation.

An advantage of the method according to the invention is that an optimized NOx raw emission level can be set in normal driving, taking into account the fuel consumption in normal driving, which results exclusively from the combustion of the fuel, as well as the fuel consumption through the intervals Regeneration of the NOx storage catalyst results. As a rule, the course of the NOx raw emission level behaves inversely to the fuel consumption, i. the lower the fuel consumption, the higher the NOx raw emission level. At a high NOx raw emission level, therefore, the fuel consumption tends to be low, but the NOx storage catalyst needs to be regenerated more frequently due to the higher NOx raw emission level, which in turn results in an increase in total fuel consumption. Therefore, according to the invention, on the one hand, a first fuel consumption component as a function of the NOx raw emission level which results from the combustion is taken into account. On the other hand, a second fuel consumption component is additionally taken into account as a function of the NOx raw emission level in the normal driving operation, which results from an interval regeneration of the NOx storage catalytic converter, which is required due to the NOx emissions.

Preferably, the NOx raw emission level in the exhaust gas should be controlled in compliance with emission limits. For this purpose, the control can be given a limit value for the NOx raw emission level. It may also be provided that a limit value for the NOx emission level (so-called tailpipe emissions) downstream of the NOx storage catalytic converter, preferably downstream of all existing exhaust gas aftertreatment devices.

The NOx raw emission level in the exhaust may be determined via a model, e.g. via one or more virtual NOx sensors. Of course, one or more real NOx sensor may alternatively or additionally be provided.

For good after-treatment efficiency, heating measures are required to increase the exhaust gas temperature. High exhaust gas temperatures, however, lead in the long term to a deterioration in the efficiency of the NOx storage catalytic converter. To counter this, it may be provided that the efficiency of the NOx storage catalytic converter is taken into account during regeneration. For this purpose, the efficiency of the NOx storage catalyst can be determined by a model. The NOx raw emission level in the exhaust gas may be regulated by, for example, a change in the exhaust gas recirculation rate, the ignition timing, the start of injection, the injection duration, the valve timing, the compression, and / or the boost pressure. The invention will be explained in more detail with reference to the figures. Hereby shows:

Figure 1 is a schematic representation of an embodiment of the method according to the invention, Figure 2 is a diagram for illustrating the individual fuel consumption components, which are due to influences of various parameters, and

Figure 3 is a diagram for illustrating the total fuel consumption. When reducing fuel consumption, among other things, the NOx raw emissions during normal driving operation must be taken into account in compliance with the emission limit values required by law, whereby when using a NOx storage catalytic converter the fuel consumption due to the fuel consumption has to be considered interval regeneration of the NOx storage catalytic converter sets. According to the invention, therefore, the NOx raw emission level is set when exiting the cylinders of the internal combustion engine, with the NOx emission level downstream of all exhaust aftertreatment devices, in particular downstream of the NOx storage catalytic converter, being taken into account with regard to the statutory emission limit values.

Figure 1 shows schematically a corresponding inventive method. In a first process section 1, a first fuel consumption fraction 7 is determined, which results at a specific NOx raw emission level due to the combustion during normal driving operation. In a second process step 2, a second fuel consumption fraction 8 is determined, which results from an intervalwise regeneration of the NOx storage catalytic converter. In this case, the course of the NOx raw emission level during normal driving since the last regeneration is taken into account and a loading of the NOx storage catalytic converter is estimated so as to be able to predict the interval frequency for the regeneration and possibly also the regeneration period.

The results of these two process steps 1, 2, that is to say the first fuel consumption proportion 7 and the second fuel consumption proportion 8, are supplied in a third process step 3 to a calculation of an optimum NOx raw emission level during normal driving. The optimum for the NOx raw emission level is where the gradient of the specific fuel consumption, taking into account the fuel consumption due to the combustion and the fuel consumption due to the regeneration of the NOx storage catalytic converter is zero: d (FuelTotal) / _ <^ ( ^ e) / d (FuelLNT rain) ι _ _n

'dNOx ^~ ' dNOx ⁺ 'dNOx ^{~ υ} ' where FuelTotal is the total fuel consumption, bed is the specific fuel consumption due to combustion, FuelLNTRegen is the specific additional fuel consumption due to the regeneration of the NOx storage catalyst and NOx is the raw NOx emission. In addition, a model 4 may additionally be provided for determining the efficiency of the NOx storage catalytic converter. The model 4, the exhaust gas temperature 9 and the exhaust gas volumetric flow 10 are supplied, from which the efficiency 1 1 of the NOx storage catalyst is determined. Based on a fourth process section 5, the legal limits for the NOx emission of the entire system are taken into account and from this a maximum NOx raw emission level 12 before the exhaust aftertreatment devices, ie at the exit from the cylinders determined.

In a fifth process section 6, a target value 14 for the raw NOx emission level is formed from the optimum NOx raw emission level 13 and the maximum NOx raw emission level 12.

To illustrate the effects of the various power consumption components on the total fuel consumption, a diagram is shown in Figure 2, in which the first fuel consumption portion 7 and the second fuel consumption portion 8 are shown on the NOx raw emission level. On the abscissa, therefore, the NOx raw emission level is plotted and on the ordinate the fuel consumption. It can be seen that as the NOx raw emission level increases, the first fuel consumption fraction 7 decreases, the first fuel consumption fraction 7, as explained above, being due to the combustion of the fuel alone. The second fuel consumption fraction 8 increases with increasing NOx raw emission level. As explained above, the second fuel consumption component 8 reflects the fuel consumption due to the required regenerations of the NOx storage catalytic converter and thus increases with increasing NOx raw emission level.

From the two fuel consumption shares 7, 8 results in a total fuel consumption 15 according to Figure 3, which has a minimum 15, which is set as a target value 14 for the NOx raw emission level. LIST OF REFERENCE NUMBERS

1 first process section

2 second process section

3 third process section

4 model

5 fourth process section

6 fifth process section

7 first fuel consumption share

8 second fuel consumption share

9 exhaust gas temperature

10 exhaust gas volume flow

1 1 efficiency

12 maximum NOx raw emission level

13 optimal NOx raw emission level

14 setpoint

15 minimum

Claims

claims

1 . Method for operating an internal combustion engine with a NOx storage catalytic converter,

in which the NOx raw emission level in the exhaust gas of the internal combustion engine is regulated to a reference value at which a minimum fuel consumption occurs,

wherein a first fuel consumption fraction (7) is taken into account as a function of the NOx crude emission level resulting from the combustion, and

wherein a second fuel consumption component (8) is taken into account as a function of the NOx crude emission level that results from an intervalwise regeneration of the NOx storage catalytic converter.

2. The method according to claim 1, characterized in that the NOx raw emission level in the exhaust gas is controlled in compliance with emission limits.

3. The method according to claim 2, characterized in that a limit value for the NOx raw emission level is specified.

4. The method according to any one of claims 2 or 3, characterized in that a limit value for the NOx emission level downstream of the NOx storage catalyst, preferably downstream of any existing exhaust aftertreatment devices, is specified.

5. The method according to any one of the preceding claims, characterized in that the NOx raw emission level in the exhaust gas is determined by a model.

6. The method according to any one of the preceding claims, characterized in that the efficiency of the NOx storage catalyst is taken into account in a regeneration.

7. The method according to claim 6, characterized in that the efficiency of the NOx storage catalyst via a model (4) is determined.

8. The method according to any one of the preceding claims, characterized the NOx raw emission level in the exhaust gas is influenced by regulation of an air path.

9. The method according to claim 8, characterized in that the NOx raw emission level in the exhaust gas is controlled by a change in the exhaust gas recirculation rate, the ignition timing, the start of injection, the injection duration, the valve timing, the compression and / or the boost pressure.