FR2850132A1 - Injecting metered amount of reactant into exhaust system of automobile engine comprises determining the amount from the nitrogen oxide concentration in the exhaust gas - Google Patents

Abstract

Injecting a metered amount of a reactant (200) into the exhaust system (20) of an automobile engine (3) comprising one or more catalysts for purifying the engine's exhaust gas comprises determining the amount from the nitrogen oxide concentration in the exhaust gas. An Independent claim is also included for apparatus for the above purpose, comprising a metering unit (50) and a control unit (90) that injects a metered amount of the reactant as a function of a detected nitrogen oxide concentration in the exhaust gas.

Description

Field of the invention

  The present invention relates to a method for dosing at least one reactive agent in the exhaust gases of a combustion installation comprising at least one catalyst installed in an exhaust gas line), in particular the combination of a RCS selective catalytic reduction catalyst and an oxidation catalyst (of a heat engine of a motor vehicle, for cleaning exhaust gases, in particular for reducing nitrogen oxides (NO.), according to which in the exhaust gas is added by metering an amount of at least one reactant, in particular of a reducing agent depending on at least one operating parameter of at least one catalyst and / or at least one quantity of operation of the combustion plant for exhaust gases.

  The invention also relates to a metering device. 15 State of the art In order to reduce the emission of pollutants contained in the exhaust gases of combustion plants, in particular in an internal combustion engine of a motor vehicle, catalysts are provided in the gas pipes of 'exhaust.

  Catalysts, for example, largely burn the hydrocarbons and carbon monoxide contained in the exhaust gases. However, nitrogen oxides, pollutants, remain in the exhaust gases which arrive in the environment.

  According to document EP 1 024 254 A2, a method 25 and a device for controlling an exhaust gas treatment system are known, according to which a reducing agent is added upstream of the catalyst and depending on the amplitude of the load and at least one operating parameter a quantity is predefined determining the quantity of reaction agent to be supplied. This quantity is corrected according to at least one other operating parameter. The correction is made on the basis of characteristic fields and a large number of characteristic fields are used for this purpose in order to allow correction as precise as possible. The characteristic fields are for example recorded on a test bench. Each field of characteristics thus increases the application work to be carried out, in particular the time required. This is particularly troublesome if it is necessary to replace the catalyst and / or the combustion installation, for example the heat engine of a motor vehicle.

  OBJECT OF THE INVENTION The object of the present invention is to develop a method for dosing at least one reagent in the exhaust gas pipe as well as a device for carrying out this method applied to a combustion installation comprising a catalyst. of the type defined above by making it possible to establish fields of characteristics used to correct the quantity of at least one reagent, with an implementation of reduced means of application, in particular a reduced working time and making it possible to modify the fields of characteristics with the use of 10 reduced technical means when replacing the catalyst and / or the combustion plant.

  The quantity of a reagent, in particular of a reducing agent, must be dosed at least according to an operating parameter of the catalyst or of the combustion installation in order to be added to the exhaust gas; for each operating state or parameter of the catalyst, for example different temperatures, and / or the combustion plant in internal combustion engines, by different speeds, or different amounts of fuel to be injected or the like, always have an optimum dosage of at least one reagent.

  Disclosure and advantages of the invention To this end, the invention relates to a process of the type defined above, characterized in that from a concentration of nitrogen dioxide contained in the exhaust gases, in particular in downstream of the oxidation catalyst ca25 11, when looking in the direction of passage of the exhaust gases, the quantity of at least one reactive agent is determined from at least one concentration of nitrogen dioxide contained in the exhaust gas.

  The invention also relates to a device for carrying out this method, this device being characterized by a control unit which doses at least one reagent from a concentration of nitrogen dioxide contained in the gaseous gases. exhaust, in particular downstream of the oxidation catalyst considered in the direction of passage of the exhaust gases.

  The method according to the invention provides for determining the quantity of at least one reactant from the concentration of nitrogen dioxide in the exhaust gases, in particular in the exhaust gas line downstream of the oxidation catalyst. . The use of the mass flow of nitrogen dioxide as a guide quantity has the advantage of allowing a significant improvement in the accuracy of the metering because the concentration of nitrogen dioxide downstream of the oxidation catalyst according to the direction of passage of the gases. exhaust is decisive for defining the quantity of reducing agent and not the overall concentration of nitrogen oxides contained in the exhaust gases. In particular for low temperature exhaust gases, the amount of nitrogen dioxide is decisive for their conversion and thus for the demand for reducing agent.

  According to an advantageous embodiment, the nitrogen dioxide concentration is determined from at least one operating parameter of the catalyst and / or at least one operating parameter of the combustion plant.

  According to another very advantageous embodiment, the concentration of nitrogen dioxide is determined from a field of nitrogen dioxide characteristics by using at least one operating parameter of the catalyst and / or from at least one minus an operating parameter of the combustion plant.

  It is advantageous that a characteristic field, i.e. the nitrogen dioxide characteristic field, is sufficient in that the amount of nitrogen dioxide downstream of the oxidation catalyst is taken into account. passage of the exhaust gases as a function of the operating parameters of the catalyst, in particular of the temperature of the exhaust gases and / or of the operating parameters of the combustion plant, in particular as a function of the engine speed, of a fuel injection installation of a heat engine.

  Advantageously, the field of characteristics of nitrogen dioxide is determined from a field of characteristics of nitrogen dioxide from the combustion plant and a field of conversion of the oxidation catalyst. The nitrogen dioxide characteristic field or the conversion field are characteristics of each combustion plant or of each oxidation catalyst and for example for manufacturing these fields can be determined separately on any bench. test so that if the combustion plant and / or the oxidation catalyst are replaced, it is sufficient to re-register the corresponding characteristic field of the components replaced. The means to be implemented for the application are thus significantly reduced, that is to say the measurements on a test bench.

  To further improve the accuracy of the quantity dosed, an advantageous development of the method provides for correcting the quantity of at least one reagent with at least one of the following operating parameters: the temperature of at least one catalyst, l air humidity, ambient speed (volume flow) of exhaust gases, in particular in at least one catalyst, the efficiency of at least one catalyst for an operating state characterized by io at least one operating parameter of the combustion plant, the quantitative ratio of nitrogen oxides NO to N02 in the exhaust gas, of an amount of at least one reagent stored in the catalyst and / or a correction value resulting from the comparison and in particular of the difference between the stationary temperature of the exhaust gases upstream and downstream of at least one catalyst according to the direction of passage of the exhaust gases for a functional state the combustion plant and the temperature of at least one catalyst.

  The reactive agent used in particular is an ammonia-releasing substance or a mixture, preferably directly of ammonia. The amount of ammonia required (NH3) is calculated stoichiometrically by applying the following formula: NO2 + NO + 2 NH3 <--> 2 N2 + 3 H20 The device according to the invention has the advantage of allowing with reduced technical means by using existing components anyway, for example by simply replacing a reduced number of components and / or by programming for example of a control unit, to allow the use of a concentration of nitrogen dioxide and / or an exhaust gas composition as a guide quantity for determining the amount of reactive agent.

  Drawings The present invention will be described below in more detail with the aid of exemplary embodiments represented schematically in the appended drawings in which: FIG. 1 schematically shows a device for operating a metering unit in conjunction with a combination of an RCS catalyst and an oxidation catalyst according to the invention, - Figure 2 schematically shows a diagram to describe a process according to the invention for determining the amount of active agent from of a field of characteristics of nitrogen dioxide, - Figure 3 schematically shows a diagram used to describe a second embodiment of a method according to the invention according to which the field of characteristics of nitrogen dioxide is determined at 10 starting from a field of characteristics of nitrogen oxides, FIG. 4 schematically shows a diagram for describing a third exemplary embodiment of a method according to which el a certain quantity of reactive agent is corrected using a field of correction characteristics and a characteristic quantity of correction. 15 Description of preferred embodiments An RCS 10 catalyst (selective catalytic reduction catalyst) according to FIG. 1 and an oxidation catalyst 11 upstream thereof but constituting with it an assembly are connected by a gas pipe. exhaust 20 to a heat engine or internal combustion engine 3. The oxidation catalyst ll is installed as close as possible to the heat engine 3. During the operation of the heat engine 3, uncleaned exhaust gases are emitted by the engine 3 and circulate in the direction of arrow 25 (direction of circulation of the exhaust gases) to arrive in the oxidation catalyst ll and the catalytic converter RCS 1 0. The oxidation catalyst ll and the catalyst RCS 10 clean in a manner known per se the raw exhaust gases. The cleaned exhaust gases escape to the environment in the direction of arrow 35 downstream of the RCS catalyst 10 through an exhaust gas line 10 in the direction of passage of the exhaust gases.

  The method and the device described below are not limited to the application to a heat engine 3. They can also be used in combination with any combustion installation, for example a heating installation or an installation of this type.

  With the aid of a metering line 40, the reagent, for example ammonia (NH3) 200, is supplied as reducing agent by the metering unit 50 to the exhaust gas in the zone between the RCS catalyst. 10 and the oxidation catalyst II to achieve in a manner known per se the reduction of the nitrogen oxides contained in the raw exhaust gas.

  Strictly speaking, one can provide another oxidation catalyst, not shown, to avoid NH3 drift.

  Instead of ammonia 200, any other reducing agent releasing ammonia or a mixture of reducing agents can be used, for example a urea-water solution (S-U / E).

  The metering unit 50 receives ammonia 200 via an ammonia line 205 coming from a tank see 206. Instead of the tank 206, strictly in terms of the principle, it is also possible to provide another installation for supplying ammonia 200, for example a preparation unit releasing ammonia 200 for example using an existing fuel on site.

  The metering unit 50 is controlled by a control unit 90 via a control line 110. The control unit 90 makes it possible to determine, in particular to calculate the quantity of ammonia 200.

  To calculate the amount of ammonia 200, a temperature sensor 60 detects the temperature 230 of the exhaust gases as will be described with reference to Figure 2; the exhaust gases concerned are those downstream of the RCS 10 catalyst. This temperature is an operating parameter of the RCS 10 catalyst and of the oxidation catalyst i1; the information is transmitted by the control unit 90 via a first data line 165. In addition, the engine speed 210 is defined, as will be described below in connection with FIG. 2 and the quantity of fuel to be injected 220 as operating parameters of the heat engine 3 using a sensor unit 150 in the known manner; the corresponding information is transmitted by a second data line 155 to the control unit 90. To simplify each time, only a temperature sensor 160 and a sensor unit 150 and a data transmission line 155, 165 respectively. However, in principle, a large number of different sensors can be used to determine various operating parameters of the RCS catalyst 10 and / or 35 of the oxidation catalyst 11 as well as of the heat engine 3. The output signals of these sensors are transmitted by corresponding lines to the control unit 90.

  According to a first diagram of execution of the exemplary embodiment of the method of the invention shown in FIG. 2, the speed 210, the quantity of fuel to be injected 220 and the temperature 230 of the exhaust gases downstream of the RCS 10 catalyst according to the direction of passage of the exhaust gases to a field of characteristics of nitrogen dioxide 250. According to the above operating parameters, the field of characteristics of nitrogen dioxide 250 provides a quantity of dioxide of nitrogen 260 existing downstream of the oxidation catalyst 10 in the direction of passage of the exhaust gases. The quantity of nitrogen dioxide 260 is transmitted to a calculating unit 270 which, starting from this quantity, supplies the quantity of ammonia 280.

  The calculation of the quantity of ammonia 280 applies the following formula: (1) NO2 + NO + 2 NH3 - 2 N2 + 3 H20.

  Numerous tests have shown that an NO / NO2 ratio equal to 1/1 gives an optimal reduction of nitrogen oxides.

  In a second embodiment shown in FIG. 3, the same references have been used as in the first embodiment in FIG. 2 to designate the same elements, the description of which will not be repeated here. This exemplary embodiment differs from the first example in that it is not provided directly to the field of characteristics of nitrogen dioxide 250, the engine speed 210, the quantity of fuel to be injected 220 and the temperature 230 of the gases d exhaust downstream of the RCS 10 catalyst in the direction of passage of the exhaust gases. Instead there is a field of characteristics of nitrogen oxides 210 of the heat engine 3 and a field of characteristics of conversion 320 of the oxidation catalyst 11 described in conjunction with FIG. 1. This field of characteristics of nitrogen oxides is plugged in intermediate. An output quantity from the conversion characteristics field 320 is transmitted to the nitrogen dioxide characteristics field 250. The engine speed 210 and the quantity of fuel to be injected 220 are supplied at the start to the oxide characteristics field 35 of nitrogen 310 which thus determines the quantity 315 of nitrogen dioxide. The quantity 315 of nitrogen oxides and the temperature 230 of the exhaust gases downstream of the RCS 10 catalyst according to the direction of the flow are then transmitted to the conversion field 320.

  In a third embodiment shown in Figure 4 we used the same references for the elements corresponding to the first and second embodiment (Figures 2 and 3) whose description will not be repeated. In the third exemplary embodiment according to FIG. 4, the quantity of ammonia 280 is corrected using another field of characteristics 410 predetermined for example by the manufacturer.

  For this, we transmit to the correction characteristics field 410 other variables characteristic of state 460, 470, produced as input quantities and from the output quantity of the correction field 410 the quantity of ammonia is corrected. 280 which gives a first quantity of corrected ammonia 430. For this, the quantity of ammonia 280 is multiplied, for example in the event of a deviation between the quantity of ammonia 280 and a predetermined set value, for example by the manufacturer, with a value taken from the correction characteristic field 410 which in the meantime is between 0 and 1.

  For another correction of the quantity of ammonia 430 already corrected for the first time, the temperature 420 of the RCS 10 catalyst is then used as the characteristic quantity of correction. If the temperature 420 of the RCS catalyst 10 deviates from another predefined setpoint, for example by manufacturing, a correction value dependent on the first deviation from the first quantity of ammonia is added or subtracted. corrected 430. The result is transmitted as the second quantity of ammonia to be assayed 440, and which is corrected to the metering unit 50.

  Strictly speaking, as a variant or in addition to the temperature 420 of the RCS 10 catalyst, it is possible to use at least one of the following correction quantities which is also used as a state characteristic quantity 460, 410: the temperature oxidation catalyst 11; the humidity of the air, the ambient speed of the exhaust gases in particular of an RCS 10 catalyst and / or of an oxidation catalyst, the efficiency of the RCS 10 catalyst and / or of the oxidation catalyst 11 for an operating state of the heat engine 3, the amount of nitrogen monoxide / nitrogen dioxide contained in the exhaust gases, an amount of ammonia 200 stored in the RCS 10 catalyst and / or in the catalyst 35 of oxidation and / or a correction comparison value, in particular the difference between the stationary temperature of the exhaust gases upstream and in val of the RCS 10 catalyst according to the direction of circulation of the fluids, for an operating state of the heat engine 3 and the temperature 420 of the RCS 10 catalyst or of the oxidation catalyst 1 1.

  Instead of the two state parameters 460, 470, it is also possible to provide a number of state parameters equal to or greater than two.

  According to an advantageous characteristic, on the basis of at least one operating parameter of at least one catalyst 10, 11 and / or of at least one operating parameter of the combustion installation 3, the concentration of dioxides d is determined. 'nitrogen.

  According to another advantageous characteristic of the invention, the field of characteristics of nitrogen dioxide 250 is determined from a field of characteristics of nitrogen oxides 310 from the combustion plant 3 and from a field of conversion characteristics 320 of the oxidation catalyst 1. 15

Claims (10)

  10) Method for dosing at least one reactive agent (200) in the exhaust gases of a combustion installation (3) comprising at least one catalyst (10, 11) installed in an exhaust gas line 5 (20), in particular the combination of an RCS selective catalytic reduction catalyst (10) and an oxidation catalyst (11), of a heat engine of a motor vehicle, for cleaning the exhaust gases, in particular to reduce nitrogen oxides (NO.), according to which in the exhaust gas is added by metering, an amount of at least one reagent 10 (200), in particular of a reducing agent dependent on at least one operating parameter of at least one catalyst (10, 11) and / or at least one operating quantity of the combustion installation (3), characterized in that from a concentration of nitrogen dioxide contained in the exhaust gases, in particular downstream of the oxidation catalyst i1, when looking in the ns of passage of the exhaust gases, the quantity of at least one reactive agent (200) is determined from at least one concentration of nitrogen dioxide contained in the exhaust gases.   2) Method according to claim 1, characterized in that from at least one operating parameter of at least one catalyst (10, 11) and / or at least one operating parameter of the installation of combustion (3) the concentration of nitrogen dioxides is determined.   30) Method according to claim 1, characterized in that starting from at least one operating parameter of at least one catalyzer 30 (10, 11) and / or at least one operating parameter of the combustion installation (3), the nitrogen dioxide concentration is determined from a field of nitrogen dioxide characteristics (250).   4) Method according to claim 3, characterized in that the field of characteristics of nitrogen dioxide (250) is determined from a field of characteristics of nitrogen oxides (310) of the installation ------   combustion (3) and a field of conversion characteristics (320) of the oxidation catalyst (11).   50) Method according to claim 1, characterized in that the reactive agent (200) is a substance or a mixture releasing ammonia.   60) Method according to claim 1, 10 characterized in that the reactive agent (200) is ammonia (NH3).   70) Method according to claim 1, characterized in that the amount of at least one reactive agent (200) is calculated stoichiometrically.   8) Method according to claim 5 or 6, characterized in that the calculation of the amount of ammonia (NH3) is done by applying the following reaction equation: NO2 + NO + 2 NH3 -> 2 N2 + 3 H2O.   9) Method according to claim 1, characterized in that one determines the amount of at least one reactive agent (200) starting in particular from a gas composition, downstream of the oxidation catalyst (11) when considers it in the direction of passage of the exhaust gases. 100) Method according to claim 1, characterized in that the quantity of at least one reactive agent (200) is corrected with at least one of the following correction parameters: a) the temperature of at least one catalyst (10, 1 1), b) the humidity of the air, c) the ambient speed of the exhaust gases, in particular in at least one of the catalysts (10, 1 1), c) the ambient speed exhaust gases, in particular in at least one of the catalysts (10, 11), d) the efficiency of at least one catalyst (10, 11) for an operating state of the combustion plant (3 ) characterizing at least one operating parameter, e) the quantitative ratio of NO / NO2 contained in the exhaust gases, t) an amount of at least one reagent (200) accumulated in a catalyst (10, 11) and / or 0o g) a correction value determined from a comparison, in particular the difference between the stationary temperature of the exhaust gases in the control installation exhaust gas line considered upstream and downstream of at least one catalyst (10, 11) for a certain operating state of the combustion plant (3) and of the temperature of at least one catalyst ( 10, 11).   110) Device for metering at least one reagent (200) in an exhaust gas combustion installation (3) having at least one catalyst (10, 11) installed in an exhaust gas line (20), in particular a combination of an RCS catalyst (10) and an oxidation catalyst (11) of a heat engine of a motor vehicle, for cleaning the exhaust gases, in particular for reducing emissions nitrogen oxides (NO.) with a metering unit (50) for metering at least one reactive agent (200) in the exhaust gas line (20), device characterized by a control unit (90) which dose at least one reagent (200) from a seizure of nitrogen dioxide contained in the exhaust gases, in particular downstream of the oxidation catalyst (11) considered in the direction of passage of the exhaust gases exhaust. 30