DE102011075875A1 - Method for calculating nitrogen oxide exhaust emission before catalytic converter phase of exhaust system for e.g. diesel engine of car, involves performing correcting function dependent on calculated exhaust emission by boost pressure - Google Patents

Abstract

The method involves determining oxygen concentration in a suction tube (20) as an operating parameter, and performing calculation of nitrogen oxide-exhaust emission before a catalytic converter phase as a function of the determined oxygen concentration. A correcting function is performed dependent on the calculated nitrogen oxide exhaust emission by boost pressure before catalytic converter phase. The nitrogen oxide exhaust emission before catalytic converter phase is calculated from the corrected nitrogen oxide concentration. Independent claims are also included for the following: (1) a computer program having a set of instructions to perform a method for calculating nitrogen oxide exhaust emission before catalytic converter phase in an internal combustion engine (2) a control and/or regulating device for an internal combustion engine.

Description

State of the art

The present invention relates to a method for calculating a raw NOx emission of an internal combustion engine according to the preamble of claim 1. Furthermore, the invention relates to a computer program according to the preamble of claim 7 and a control device according to the preamble of claim 8.

Exhaust gas aftertreatment of diesel engines and gasoline direct injection engines often uses selective catalytic reduction (SCR) to reduce nitrogen oxide (NO _x ) emissions. In this case, a reducing agent, usually ammonia (NH ₃ ), must be added to the exhaust gas stream. The amount of the reducing agent added depends essentially on the amount of NO _x emitted. If the amount of reducing agent is too small, too little NO _{x is} converted in the SCR catalytic converter. If, on the other hand, too much reducing agent is added, this is also emitted and thus represents an environmental burden which must be avoided. Usually, the current NO _x emissions are detected by means of a sensor.

As long as the sensor is not ready for operation after a cold start of the internal combustion engine, the reducing agent metering is based on NO _x raw emission values, which are calculated by means of models. The NO _x sensor is also calibrated with calculated values for on-board diagnostic monitoring. In recent applications, the sensor is even completely replaced by a calculation model for cost reasons.

The described applications require a high accuracy of the modeling of the NO _x raw emission values. From the DE 10 2009 05 50585 For example, a NO _x raw emission model is assumed to be known which deposits a relationship between the NO _x raw emissions and the oxygen concentration in the intake manifold of the internal combustion engine as a function of the operating point of the internal combustion engine and the current injection pattern or operating mode in maps. Wherein the operating point is characterized essentially by the speed and the load of the internal combustion engine. Environmental influences, such as pressure and temperature, are taken into account by correction factors that are applied to the base values stored in the maps.

However, the known model does not take into account deviations of the charge pressure from the design value. Charge pressure deviations occur, for example, in highly dynamic driving, when due to the relatively sluggish air system, the actual boost pressure runs after the setpoint. Or if the charging system reaches its physical limits and the required setpoint can not be adjusted.

Disclosure of the invention

The invention represents a significant improvement of the already known method for calculating NO _x raw emissions in the exhaust tract of an internal combustion engine. An essential idea is to improve the accuracy of the known method in real vehicle operation by the influence of the boost pressure after the intercooler, or in the intake manifold of the internal combustion engine, is taken into account on the NO _x -Rohemissions.

It has been shown that a boost pressure has an effect on the NO _x raw emissions. This is due to two mechanisms: On the one hand, an increased charge pressure leads to an increase in the cylinder charge. Air mass control also increases the exhaust gas recirculation rate (EGR). Because there is more recirculated exhaust gas in the combustion chamber, the proportion of fresh air and thus the oxygen content is lower. A lower oxygen content caused by the known Zeldovich reaction lower NO _x emissions. This first mechanism takes into account the known model, since it calculates the NO _x emission as a function of the oxygen concentration in the intake manifold.

The second mechanism, even at constant oxygen concentration in the intake manifold via an increased boost pressure to a lower combustion temperature and thus to a reduction of the NO _x -Rohemissions. The lower combustion temperature with increased boost pressure is due to the fact that at higher boost pressure a larger mass of the combustion chamber charge, consisting of recirculated exhaust gas sucked fresh air, must be heated with an approximately equal amount of fuel. The so-called Zeldovich reaction leads to the formation of oxygen radicals and subsequent oxidation of atmospheric nitrogen at high combustion temperatures Nitric oxide. This nitrogen radicals are generated, which in turn react with oxygen molecules to nitrogen monoxide and oxygen radicals. As the combustion temperature decreases, the velocity coefficient of the Zeldovich reaction becomes smaller, that is, less NO _{x is} formed. This mechanism is not depicted by the already known NO _x calculation model. By applying the known NO _x calculation model, however, this second mechanism can be clearly separated from the first.

According to the invention, it is now provided to determine the pressure influence of the Zeldovich reaction in an operation without exhaust gas recirculation (that is, at a constant oxygen concentration in the intake manifold) on the NO _x emission. This pressure influence can be easily transferred to the operation of the internal combustion engine with exhaust gas recirculation. Subsequently, the influence of the oxygen concentration is taken into account by applying the known NO _x calculation model. Thus, the correction function according to the invention allows a more accurate modeling and thus contributes in combination with the already known calculation model to an improvement of the modeling in real vehicle operation.

Another significant advantage is that output values of already known correction functions are used as the input value of the correction function according to the invention. By appropriate arrangement of the correction functions in the model kernel, or in the main program, interactions of the correction functions are avoided with each other. It is thus possible according to the invention to apply the correction function according to the invention independently of other correction functions. Overall, the accuracy of the modeling result in real operation is improved by the method according to the invention.

Another advantage results from the fact that the correction function is very easy to use. The reason for this is the simple separability of the influence of the oxygen concentration on the NO _x formation without exhaust gas recirculation from the influence of the boost pressure change. This considerably reduces the application effort compared with other known models.

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable. All of the features disclosed in the drawing, the description and the claims can be essential to the invention both individually and in any combination with one another.

Show it:

1 the technical environment of the invention;

2a measured relationship between NO _x raw emissions and boost pressure;

2 B modeled relationship between NO _x raw emissions and boost pressure;

3 a first embodiment of the invention in a functional block diagram;

4 a second embodiment in a functional block diagram;

5 a third embodiment in a functional block diagram

6 Integration of the method according to the invention into a known NO _x crude emission model in functional block representation.

1 shows an internal combustion engine 10 , which is used in particular for driving a motor vehicle. The illustrated internal combustion engine 10 works with a direct injection of fuel via injectors 12 in combustion chambers 14 the internal combustion engine 10 after the Otto combustion process, the diesel combustion process or another combustion process, for example, a CAI combustion process (CAI = Controlled Auto Ignition). In the Otto combustion process, spark ignition of the combustion chamber filling from air and injected fuel takes place with a spark plug 16 , Every combustion chamber 14 is from a piston 18 movably sealed and via a suction pipe 20 filled with air. Upstream of the suction pipe 20 is a charge air cooler 22 arranged the air before entering the suction pipe 20 cools. Not shown is an upstream of the intercooler 22 arranged turbocharger. Between intercooler 22 and combustion chamber 14 is a pressure sensor 24 arranged, the pressure of the air after exiting the intercooler 22 or before entering the intake manifold 20 and thus before entering the combustion chamber 14 determined. That in the combustion chamber 14 burned fuel-air mixture is in an exhaust system 26 ejected. The change of the combustion chamber filling (gas exchange) becomes by gas exchange valves 28 . 30 controlled in synchronism with the movement of the piston 18 be operated. About an exhaust gas recirculation 32 is when the exhaust gas recirculation valve is open 34 Exhaust gas in the combustion chamber 14 returned to reduce the NO _x -remission of the internal combustion engine.

The exhaust system also has exhaust aftertreatment components, not shown, such as particulate filters, catalysts, dosing systems for reducing agents, exhaust gas sensors 36 etc. on.

The internal combustion engine 10 is from a control unit 38 controlled, including signals from the exhaust gas sensor 36 , a speed sensor 40 , the pressure sensor 24 and other sensors for further operating parameters. Such further operating parameters are, for example, the accelerator pedal position or the mass of the intake fresh air. The control unit forms from these signals 38 Control signals for injectors 12 , for any existing spark plugs 16 , for exhaust gas recirculation 34 and possibly further control signals for not shown in the figure actuators, in modern internal combustion engines 10 present and therefore the expert is familiar.

Incidentally, the controller 38 set up, in particular programmed to perform the method according to the invention or one of its embodiments. The control unit 38 is particularly adapted to the NO _x raw emissions as a function of the oxygen concentration in the intake manifold 20 to model. The value of the oxygen concentration in the intake manifold 20 is in known control devices 38 of internal combustion engines 10 calculated anyway or is located in the control units 38 in front. Essential input variables for this are the aspirated fresh air mass, the exhaust gas recirculation rate, as intermediate size, the injected fuel quantity and a modeled, or with the exhaust gas sensor 36 measured oxygen concentration in the exhaust gas.

An essential prerequisite for a concrete modeling of the NO _x crude emissions as a function of the oxygen concentration or of the boost pressure p ₂ is the knowledge of the quantitative relationships.

2a shows such metrologically determined relationships. Here, the NO _x concentration in ppm in the raw emissions of the internal combustion engine 10 in each case via the volume fraction of oxygen in% in the intake manifold 20 plotted shown. Both the oxygen concentration and the NO _x concentration are plotted logarithmically.

An evaluation of the metrologically obtained data shows that an increase of the boost pressure p ₂ to an increased capacity in the combustion chamber 14 leads. Consequently, because a larger mass is heated with approximately the same amount of fuel, the combustion temperature decreases, thus leading, according to Zeldovich, to a reduction in NO _x raw emissions.

2 B shows the relationship between nitrogen oxide concentration NOx in ppm, logarithmically plotted on the ordinate and the oxygen concentration in mass percent, also plotted logarithmically on the abscissa. Measurements were made for different pressures after the intercooler or in the intake manifold 20 parallel straight lines 45a . 45b and 45c whose slope is not affected by a change in pressure.

darstellen lässt.An evaluation of the empirically obtained data has shown that this relationship with the formula

let represent.

NO _{x therein, Cor,} the corrected NO _x concentration, which depending on the current pressure p _{2, act} after the charge air cooler 22 and the concentration of NO _{x, Bas determined} under reference conditions. NO _{x, Bas} is the NO _x raw emission resulting at a reference pressure p _{2, ref} after the intercooler 22 , sets. As a reference state, the state without exhaust gas recirculation offers, since here the oxygen concentration in the intake manifold 20 is constant.

As a result, both the corrected NO _x concentration NO _{x, Cor} and the detected concentration NO _{x, Bas} relate to the oxygen concentration of 23.15 mass%. So on an operation of the internal combustion engine 10 without exhaust gas recirculation.

The parameter C can, depending on the internal combustion engine 10 and from the operating point, assume both positive and negative values. This is due to two different mechanisms of action, which have the opposite effect on NO _x formation.

A first mechanism of action causes the parameter C to assume negative values. This increases, as already explained above, by increasing charge pressure p ₂ at an operating point, the filling of the combustion chamber 14 , and is heated with the same or approximately the same amount of fuel. This leads to a lower maximum combustion temperature and thus corresponding to the Zeldovich reaction to lower _NOx formation. That is, outweighs the first mechanism of action, so is to be expected with increasing boost pressure p ₂ with decreasing NO _x emissions and the parameter C assumes a negative value.

A second mechanism of action is based on the fact that with increased boost pressure p _2, a larger air to fuel ratio (λ) sets. As a result, the oxygen content of the combustion chamber filling and thus increases according to the Zeldovich reaction, the NO _x formation. If this second mechanism of action is dominant, C assumes positive values, and increasing NO _x emissions are to be expected with increasing boost pressure p ₂ .

3 shows a functional block diagram of a first embodiment of the method according to the invention, wherein the parameter C in dependence on a boost pressure difference (p _{2, Akt} - p _{2, Ref} ) is determined.

The block 46 symbolizes the formation of one, the load L of the internal combustion engine 10 representing size. The load L may be a fuel metering signal or one from the controller 38 anyway calculated value of the internal torque of the internal combustion engine 10 , The methods customary for determining both variables are known to the person skilled in the art.

In block 48 there is a calculation of the rotational speed n of the internal combustion engine 10 from signals of the speed sensor 40 ,

In block 50 a calculation of the current boost pressure p _{2, act} after the intercooler 22 or in the intake manifold 20 the internal combustion engine 10 from the signals of the pressure sensor arranged there 24 ,

In a map 52 Reference values NO _{x, Bas} , which are determined in reference states, are stored in dependence on load and speed as a function of NO _x raw emissions.

A map 54 contains load and speed-dependent stored values of the respectively associated boost pressure p _{2, ref} . In a functional block 56 is calculated from the current, measured boost pressure p _{2, Akt} and the reference boost pressure p _{2, Ref} a boost pressure difference Δp ₂ . In the function block 58 is the value of the parameter C depending on the boost pressure difference Ap ₂ deposited. The blocks 46 to 58 thus supply all the quantities required for the application of Equation 1 to the block 60 representing the calculation of the corrected nitrogen oxide concentration NO _{x, Cor} according to equation 1. This inventively determined corrected NO _x concentration is passed to the emission calculation model.

The function block 60 Also includes a switch that disables the correction function when the boost pressure control is not active. It then applies: NO _{x, Cor} = NO _{x, Bas}

However, in principle an application of the correction function according to the invention even with a supercharging pressure control is applicable, the reference boost pressure p _{2, ref} is taken from comparative maps.

4 shows a further embodiment in the case of a load and / or speed-dependent parameter C. The sequence of the method according to the invention is carried out according to the basis of 3 previously described embodiment. With the difference that as input values for the function block 56 the load L and the rotational speed n are used instead of the boost pressure difference Δp ₂ . In the function block 56 are the load- and / or speed-dependent values for C stored in a map.

5 shows a functional block diagram of a third embodiment of the method according to the invention, wherein the parameter C as a constant to the function block 56 is removed.

The correction function according to the invention 3 . 4 or 5 will, as in below 6 shown implements the known overall function of the NO _x model.

The known total function calculates the NO _x raw emissions according to the following equation 2:

Therein, NO _{x, AKT is} the current NO _x concentration in ppm, which can be calculated as a function of the current oxygen concentration O _{2, AKT} in percent by mass and the concentrations NO _{x, REF} and O _{2, REF} detected under reference conditions. The exponent α is in each case of the rotational speed and the load of the internal combustion engine 10 dependent and to a first approximation on the current O ₂ concentration independently. The reference concentrations NO _{x, REF} and O _{2, REF} are each dependent on the speed and the load. Embodiments of the known overall function also provide load- and speed-dependent correction functions for α and O _{2, REF} .

According to the invention, in equation 2 explained above, instead of NO _{x, REF,} the result from equation 1, that is to say NO _{x, Cor is} used.

6 shows a functional block diagram of the known overall function with implemented inventive correction function. The block 46 As in previous figures, the formation of one, the load L of the internal combustion engine 10 representing size. In the block 48 there is a calculation of the rotational speed n of the internal combustion engine 10 from the signals of the sensor 40 ,

In the block 62 a calculation of the oxygen concentration O _{2, akt takes place} in the intake manifold 20 the internal combustion engine 10 , The oxygen concentration results essentially as a quotient with the oxygen flow into the intake manifold 20 in the meter and the filling mass flow (fresh air and recirculated exhaust gas) into the combustion chambers 14 the internal combustion engine 10 in the denominator.

The filling mass flow results from the general gas equation as a function of the known intake manifold volume, the measured intake manifold pressure, the measured temperature and the general gas constant.

The oxygen flow into the intake manifold 20 is the sum of the fresh air mass flow weighted with the known oxygen concentration of the fresh air (23.15 mass%), which is measured and the mass flow of the recirculated exhaust gas weighted with the oxygen concentration in the exhaust gas. In this case, the oxygen concentration in the exhaust gas from the signal of the exhaust gas sensor 36 certainly. The mass flow of the recirculated exhaust gas is obtained by subtracting the measured fresh air mass flow from the filling mass flow calculated from the general gas equation.

The oxygen concentration in the exhaust gas is lower than the oxygen concentration of the fresh air, so that the resulting oxygen concentration in the intake manifold results as the average value of the oxygen concentrations in the exhaust gas and in the fresh air, which are weighted with the fresh air and exhaust masses involved. Such calculations are carried out by modern control units anyway and are familiar to the expert.

A map 64 load- and speed-dependent contains stored values of the respectively associated oxygen concentration O _{2, REF.} In the map 66 are values of the exponent α also load- and speed-dependent stored. In block 66 becomes, as with the previous one 3 . 4 and 5 explains the corrected nitrogen oxide concentration NO _{x, Cor} calculated. The blocks 62 to 68 thus supply all the quantities required for the application of Equation 1 to the block 70 representing the calculation of the current NO _x concentration NO _{x, AKT} by the equation 1.

In the known overall function, the relationship between NO _x raw emissions and oxygen concentration in the intake manifold 20 in maps depending on the operating point, the operating mode and the injection profile of the internal combustion engine 10 deposited. Depending on the currently prevailing Ambient conditions (ambient pressure and temperature) are then, not explicitly shown in the figure, carried out for the actual values taken from the maps from the maps.

6 shows an embodiment of the known correction function for the slope of the line 45 in 2 B , modeled by Equation 2. As previously explained, the slope of the line becomes 45 by changing the boost pressure in the intake manifold 20 is not changed, so that the correction function according to the invention (equation 1) is advantageously applied to the NO _x raw emission without exhaust gas recirculation. And then the corrected with the inventive correction function nitrogen oxide NO _{x, Cor} as the output value for the known overall function (equation 2), ie for operation with exhaust gas recirculation serve. That is, in Equation 2, NO _{x, REF is} replaced by NO _{x, Cor} . By applying Equation 2 to the output value of Equation 1, both equations and the associated corrections in the modeling of the NO _x raw emissions can be applied independently of one another.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 1020090550585 [0004]

Claims (10)

Method for calculating the NO _x raw emissions (NO _{x, AKT} ) of an internal combustion engine ( 10 ) from operating parameters of the internal combustion engine ( 10 ), wherein as an essential operating parameter an oxygen concentration (O _{2, AKT} ) in a suction tube ( 20 ) is determined and the calculation of the NO _x raw emission (NO _{x, AKT} ) as a function of the determined oxygen concentration (O _{2, AKT} ), characterized in that a correction function a dependency of the raw NOx emission (NO _{x, AKT} ) of considered a boost pressure (p _{2, Akt} ). Method according to Claim 1, characterized in that the correction function satisfies the following equation:

wherein NO _{x, Cor} , the corrected NO _x concentration, which can be calculated in dependence on a current boost pressure p _{2, Akt} and the detected under reference conditions concentration NO _{x, base of} the NO _x raw emission at a boost pressure p _{2, Ref} and C is a parameter dependent on a boost pressure difference Δp ₂ = (p _{2, Akt} -p _{2, Ref} ). A method according to claim 1 or 2, characterized in that from the corrected NO _x concentration (NO _{x, Cor} ), the NO _x raw emission (NO _{x, AKT} ) is calculated. Method according to one of the preceding claims, characterized in that the parameter C is a load and / or speed-dependent variable. Method according to one of the preceding claims, characterized in that the parameter C assumes positive and negative values. Method according to one of the preceding claims, characterized in that the parameter C is a constant. Method according to one of the preceding claims, characterized in that the parameter C determined by a map access or during operation of the internal combustion engine ( 10 ) is calculated. Method according to one of the preceding claims, characterized in that the correction function can be switched off. Computer program, characterized in that it is programmed for use in a method according to one of the preceding claims. Control and / or regulating device for an internal combustion engine ( 10 ), characterized in that it is programmed for use in a method according to one of claims 1 to 8.

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