Method for estimating the quantity of polluting species in the exhaust gases of a compression ignition engine equipped with at least one selective catalytic reduction catalyst for nitrogen oxides

Abstract

Method for estimating the quantity of pollutants in the exhaust gases of a motor vehicle equipped with a compression- ignition engine and at least one selective reduction catalyst for nitrogen oxides, the estimation process for estimating the quantity of pollutants in the exhaust gases, in particular before a possible concentration sensor is hot enough to carry out measurements, comprising the following stages: a. identifying (1) the chemical reactions in the at least one selective reduction catalyst having the pollutants as a reactant or product, b. determining (2) the reaction rates of each identified chemical reaction, c. carrying out (3) a mass balance in the at least one selective reduction catalyst of nitrogen oxides considered as an open system, for each pollutant, and d. determining (4) the amount of polluting species in the exhaust gas according to the mass balance.

Description

[0001]DESCRIPTION: Method for estimating the quantity of polluting species in the exhaust gases of a compression ignition engine equipped with at least oneselective catalytic reduction catalyst for nitrogen oxides.Technical field The invention relates to the technical field of estimating pollutantsproduced by a compression-ignition engine, and more precisely, thepollutants produced by a compression-ignition engine equipped with at leastone catalyst for the selective reduction of nitrogen oxides (also known asSCR, from the acronym in English for: “Selective Catalytic Reduction”).Prior arts The new Euro 7 / VII standard, which will come into force from 2025,requires a reduction in pollutant emissions, compared to the current standard (Euro 6e), for vehicles marketed in Europe. Among the polluting emissions, the Euro7 / VII standard is particularlystrict with regard to emissions of nitrogen oxides ^^^ and ammonia ^^^.Among these gases, we note the particularities of the ^^^and of the^^^. Nitrogen dioxide ^^^ is a toxic gas that produces inflammation of therespiratory tract and contributes to the formation of acid rain. Ammonia ^^^contributes to the formation of secondary particles, associated withcardiovascular and respiratory diseases, and is harmful to aquaticenvironments.The Euro 7 / VII standard comprises an OBM (English acronym for“On-Board Monitoring”) on-board diagnostic obligation. It will bemandatory to monitor, on each journey made by the vehicle, the amount of nitrogen oxides ^^^(mainly nitrogen monoxide ^^ and nitrogen dioxide^^^)and the amount of ammonia ^^^ emitted at the exhaust . The vehicle will haveto transmit these values not only via the OBD (On-Board Diagnostic) socket but also via OTA (Over the Air) wireless communication to a dedicated platform. If the emissions of nitrogen oxides ^^^or ammonia ^^^exceed apredefined limit, built by multiplying the regulatory threshold of the speciesconsidered by a predetermined factor greater than 1, called conformity factor CF, then the vehicle must alert the driver by lights on the dashboard and impose the repair of the vehicle via engine torque and vehicle speedlimitat ions, or even by the prohibition of starting.In other words, if the emissions are greater than, for example, 1.5 or2 times more than predetermined thresholds, generally obtained during theapproval of the vehicle, calculated on a number of valid journeys, the alertmust be given. In order to determine these values, a concentration sensor todetermine the concentration of these pollutants in the exhaust gases must beprovided in vehicles seeking vehicle approval. An on-board sensor diagnosticsystem is also required.However, existing types of sensors are not capable of carrying out ameasurement as long as their sensitive element has not yet reached athreshold temperature, called the operating temperature. The temperature riseof the sensor can last up to 900 seconds from the start of driving forcompression-ignition (diesel) vehicles.It thus appears that it is not possible to meet the Euro 7 standard withthe only existing sensors because of the absence of measurement until 900 seconds after the start of driving. There is a need for a determination of the emissions of nitrogenoxides and ammonia at the exhaust outlet of a compression-ignition engine,before the operating temperature is reached by the sensor for measuring thesepollutants.In the prior art, many documents deal with estimating the amount ofnitrogen oxides. Mention may be made in particular of documents US8225595, US20170044962, US9771846, US9304061, EP2832965, EP2910758 and EP3819483 dealing with the specific case of diesel engines, which does not apply to the present problem. Mention may also be made of documents US11028753, JP2009287410, US2008 / 108212 and WO2016 / 159019A1 describing modelsfor determining the amount of nitrogen oxides but only at the engine outlet,and not at the exhaust outlet after the after treatment device(s).Documents EP3736418 and EP3956549 disclose models for estimating these emissions according to the measurement of sensors. Thesedocuments are inapplicable here due to the impossibil ity of taking ameasurement until the sensor has reached its operating temperature.The technical problem is therefore not solved by the prior art .Explanation of the invention The subject of the invention is a method for estimating the amount of polluting species in the exhaust gases of a motor vehicle equipped with acompression-ignition engine, and with at least a first selective catalyticreduction catalyst for nitrogen oxides, the method for estimating making itpossible to estimate the amount of polluting species in the exhaust gases, inparticular before a possible concentration sensor is hot enough to carry outmeasurements, the method comprising the following stages:identifying the chemical reactions involved in the first selectivereduction catalyst for nitrogen oxides, having as reagent or product thepolluting species whose amount in the exhaust gases must be estimated, determining the reaction rates of each identified chemical reaction,carrying out a mass balance in the first nitrogen oxide selectivereduction catalyst, considered as an open system, for each of the pollutantswhose quantity is to be determined, and determining the amount of polluting species in the exhaust gasaccording to the mass balance.The polluting species may be nitric oxide and ammonia, the methodfor estimating may then comprise the following stages:determining the temperature in the first selective nitrogen oxidereduction catalyst , the flow rate in the first selective nitrogen oxide reductioncatalyst, the quantity of ammonia entering the first selective nitrogen oxidereduction catalyst, the speed and torque of the compression-ignition engine,determining the molar fraction of nitrogen oxide in the gasesexiting the compression-ignition engine by applying a first mapping as afunction of the estimated torque of the engine, determining the molar fraction of nitrogen oxides in the gasesexiting the first ni trogen oxides selective reduction catalyst, locateddownstream of the compression-ignition engine, as a function of the molar fraction of nitrogen oxides produced by the engine and the flow rate in thefirst nitrogen oxides selective reduction catalyst , and as well as a second 1Dmapping dependent on the temperature in the first selective catalyticreduction catalyst for nitrogen oxides and a third 1D mapping dependent on the flow rate in the first selective catalytic reduction catalyst for nitrogenoxides,determining also the molar fraction of ammonia in the gasesleaving the first selective catalytic reduction (SCR) catalyst , according to afourth 1D mapping dependent on the temperature in the first selectivecatalytic reduction (SCR) catalyst and the molar fraction of nitrogen oxidesin the gases emitted by the compression-ignition engine.When, as is frequently the case, the motor vehicle is equipped with a second selective reduction catalyst for nitrogen oxides downstream of the first selective reduction catalyst for nitrogen oxides, the process maycomprise the following stages:determining the molar fraction of ammonia in the gases leaving the second selective nitrogen oxide reduction catalyst according to a fifth 1D mapping dependent on the temperature in the second selective nitrogen oxidereduction catalyst and according to the value of the number of ammoniaadsorption sites,determining the molar fraction of nitrogen monoxide in the gases leaving the second selective reduction catalyst for nitrogen oxides accordingto the molar fraction of nitrogen monoxide in the gases leaving the firstselective reduction catalyst for nitrogen oxides, and the flow rate in thesecond selective reduction catalyst for nitrogen oxides, as well as a sixth 1Dmapping dependent on the temperature in the second selective reduction catalyst for nitrogen oxides and a seventh 1D mapping dependent on the flowrate in the second selective reduction catalyst for nitrogen oxides.The mappings can be calibrated according to measurements madeduring tests.Polluting species can be carbon dioxide, carbon monoxide,hydrocarbons, ammonia, nitric oxide, nitrogen dioxide or nitrous oxide.The invention also relates to a motor vehicle provided with an estimation system configured so as to carry out the method for estimating asdescribed above, in particular within an on-board diagnosis.The motor vehicle may further comprise a partial exhaust gasrecirculation circuit at the intake.Brief description of the drawings Other aims, characteristics and advantages of the invention willbecome apparent on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which: - figure [Fig 1] illustrates the main stages of a method for estimatingthe amount of polluting species in the exhaust gases.Detailed descriptionThe following concepts specific to the determination of reaction rates in general in a given system, which can be open or closed, are recalled. Thefollowing generic chemical reaction is applied:^^ + ^^ → ^^ + ^^with a,b,c,d: stoichiometric coefficientsA,B: reagents from the reaction C,D: products of the reaction. The rate v of this chemical reaction is defined in moles per unit time:[Eq. 1] v= Vol ∙ f^T^ ∙ ^A^^^B^!With:Vol: The volume of the system,"^#^: a function of the system temperature T,[A], [B]: the volume concentrations of reagents A and B respectively, Α, β : the powers applied to these concentrations.The function f is often modelled by an Arrhenius law:[Eq. 2] f^T^ = ke&'(+ )*where:k: a pre-exponential factor of the reactionEa: the activation energy of the reaction A: the universal constant of the ideal gases (~8.3145 J / K)T: the reaction temperature, in KelvinHowever, this expression only provides two degrees of freedom, thepre-exponential factor k and the activation energy Ea, to adjust it .Experimentally, the dependence of the reaction rate on temperature can have a more complex form. In the rest of the present description, the more genericform "^#^ will therefore be used.If the system is open, as is the case with a selective reduction catalyst(SCR) fitted to the exhaust of a compression-ignit ion engine, the function fmay also have a dependency on the axial velocity of the gases, obtained asthe volume flow rate of the gases divided by the cross-sectional area of thesystem. For a constant cross-section, equation [Eq. 1] can be rewritten:[Eq. 3] ,= -. / ∙ "^#, 1^ ∙ ^^^^^^^2For an open system, the mass balance for a species A, in moles, iswrit ten:[Eq. 4] With:: Change per unit time in the number of moles of species A in thesystem 167 : Molar flow of gases entering the system849: : Molar fraction of species A in the gases entering the system1<=> : Molar flow of gases exiting the system84?@A : Molar fraction of species A in the gases leaving the system∑6 CD<E 4 ,46 : Number of moles of species A generated per second byreactions where species A is a product ∑6 F<7G 4 ,46 : Number of moles of species A consumed per second byreactions where species A is a reagent It should be noted that an SCR fitted to the exhaust of a compression-ignition engine is a gas post-treatment device that aims to reduce the nitrogenoxides contained in the exhaust gases received from the engine into harmless molecules through the action of ammonia present in the SCR and coming from a urea-based solution (Adblue®) that is injected upstream of saidcatalyst.In an SCR, particularly a first SCR, the main reactions involving nitric oxide NO and ammonia ^^^are as follows: Ammonia adsorption reaction in an ammonia ^^^adsorption site noted as Ammonia desorption reaction from an ammonia ^^^adsorption site noted as Reduction of nitric oxide by adsorbed ammonia NH3_as Reduction of nitric oxide NO and nitrogen dioxide NO2by adsorbed ammonia NH3_as 1 ^^^_^J + 2^^ +1 2^^,Q^ → ^^ + 3 / 2 ^^^ + ^J Reduction of nitrogen dioxide NO2 by adsorbed ammonia NH3_as Oxidation of ammonia adsorbed ^^^_^J in dinitrogen ^^ In this set of reactions, the reagents NO, ^^^, ^^^ and ^^ are in agaseous state.With:v ^mol / s^ = Vol ∙ f ^T, 1^ ∙ ^^^ ^^K ! KK K ^ ^as^v ^mol / s^ = Vol ∙ f ^T, 1^ ∙ ^^^ _ ^^^ ^ ^ as^v ^mol / s^ = Vol ∙ f ^T, 1^ ∙ ^^^ _ ^^ !^^ ^ ^ as^ ^^^\^v ^mol / s^ = Vol ∙ f ^T, 1 ^Q !QQ Q ^ ∙ ^^^^_as^ ^^^\^v ^mol / s^ = Vol ^S !SS ∙ fS^T, 1^ ∙ ^^^^_as^ ^^^\^v ^mol / ^W !WW s^ = Vol ∙ fW^T, 1^ ∙ ^^^^_as^ ^^^^And: The internal temperature of the catalyst T and the exhaust gas flow rate Q through the catalyst are determined, i .e. either measured using sensorsor estimated by an electronic control unit of the motor vehicle, and aresubsequently considered as input data.In a theoretical approach such as presented above, it is necessary tocalibrate as many two-dimensional functions,"6^#, 1^,s,as there are reactionsconsidered. In the case presented above, six two-dimensional functions are to be calibrated for the reactions affecting nitric oxide NO and ammonia alone ^^^.It is also necessary to estimate, in addition, the concentrations of therest of the reagents involved in each of the reactions identified above (here the oxygen^^) which will in turn be determined via new reaction schemes. Inaddition, the parameters must be determined for each of these newreactions.It thus appears that the determination and calibration of an exactmodel taking into account all the reactions affecting the concentration ofnitric oxide NO and ammonia ^^^becomes very complex. Indeed, there are many more functions to calibrate than observedphenomena (i .e. the quantities of nitric oxide NO and ammonia^^^ leavingthe SCR in the system considered here) and different solutions would bepossible, all correctly adjusting the experimental results , but without thecertainty that one of them correctly describes the physical and chemicalphenomena involved. Moreover, the very high dynamic nature of the reactions would makeit necessary to choose very small sampling stages (due to the stabil ity of thecalculations), which would make it difficult to integrate this solution into a computer, which would be overloaded. In the process detailed below, a number of assumptions will be madein order to solve these two problems and to arrive at a solution that is, at thesame time, easy to calibrate and to embed in a computer.The following assumptions and considerations apply identicallyregardless of the type of issue to be determined. In the present case, they willbe described for a system comprising the compression-ignition engine and atleast one SCR, and for which it is sought to estimate emitted quantit ies ofnitric oxide NO and ammonia ^^^.The system is considered homogeneous in space, i .e. the temperatureand concentrations are the same at all points of the considered system. Inother words, the model is a 0D model. The molar fractions inside and at theoutlet of the system are identical and it is therefore possible to write:[Eq. 5] The system is considered quasi-stationary. The variat ions in thenumber of moles of the gaseous species are instantaneous. In addit ion, theflow rate at the inlet is very close to that at the outlet :[Eq. 6] 167 ≈ 1<=> ≈ 1Based on these assumptions, the following equations are formulated:For a species A such as, for example, nitric oxide NO, the variation in the number of moles in the system being considered instantaneous, thedifferential term cancels out:[Eq. 7] 0= Q ∙ 849: − Q ∙ 8a + ∑6 CD<E 4 ,46 − ∑6 F<7G 4 ,46 (Gaseous species A)For a non-gaseous species A such as ammonia NH3stored in the SCR, the differential term is taken into account: gaseous species A)The dynamics of gas-phase species have been removed, which has the effect of transforming the differential equations into algebraic equations.By definition, the concentration of species A is written:[Eq. 9] With: XA is the molar fraction of species A in all species present in the catalyst, and n is the total amount of species in the catalyst, in molesFor species in the gas phase, the ideal gas law is applied.[Eq. 10] e. -. / = 3g#We can then reformulate the equation [Eq. 9] as follows: [Eq. 11] ^^^ = 84 e / ^g. #^Neglecting the effect of pressure variations in reaction rates (i.e.considering P substantial ly constant) in a new generic functionh^#, 1^, thefollowing equations can be written:[Eq. 12] v^mol / s^ = Vol ∙ g^T, Q^ ∙ X ^ !a Xkwith v: the reaction rate for a two-reagent gas reaction [Eq. 13] v^mol / s^ = Vol with v: the reaction rate for a reaction comprising a single reactantas a gas.For each reaction rate, only the dependence on a single gaseousreagent is retained, the one considered to be limiting. The other reagent isnot taken into account if i t is also in the gaseous state or if it is consideredto be in excess. We then reformulate the equations [Eq. 12] and [Eq. 13] asfollows: [Eq. 14] v^mol / s^ = Vol ∙ g^T, Q^ ∙ X ^awith v: the reaction rate for a two-reagent gas reaction [Eq. 15] v^mol / s^ = Vol with v: the reaction rate for a reaction comprising a single reactantas a gas.For the sake of simplicity, we assume ] = ` = 1.We therefore obtain:,^o. / / J^ = -. / ∙ h^#, 1^ ∙ 84 , A limiting gaseous reagent,^o. / / J^ = h^#, 1^ ∙ 84 ∙ 3p, A limiting gaseous reactant, B non-gaseous,^o. / / J^ = h^#, 1^ ∙ 3p, B non-gaseous reagentThe NOx (gaseous) will be consumed by the reactions with the NH3 stored inthe SCR: [Eq. 16] NH3(gaseous) can be adsorbed or desorbed: [Eq. 17] Ammonia adsorbed NH3_as can vary due to adsorption / desorption phenomenaand can be consumed by reactions with NOx and by oxidation with O2 : The combination of the equations obtained with the assumptions makesit possible to write the balance equations in a linear form with regard to themolar fractions X, which can be obtained explici tly, and therefore without theneed for an iterative calculation, making i t possible to use a calculation step of100 to 1000 times greater in iterative simulations by exact model, with anegligible loss in precision. The molar fractions 8qr and 8qtu can be isolated from the first twoequations and obtained explicitly.Adsorption phenomena are considered immediate: any species Aentering or produced in the system is stored instantaneously. Instead ofcalibrating an adsorption rate and a desorption rate, only the desorption rate istaken into account.[Eq. 19] and therefore:[Eq. 20]− hF_qtu_vG^#, 1^ ∙ 3qtu_vGThe system is thus reduced to three functions to be calibrated, notedhF_qrs , hF_qtu_vGhE_qtu.The following assumptions apply, in the particular case of NO andammonia emissions ^^^. The choice of these hypotheses was made bymeeting purely empirical or simplification criteria.The molar fractions of nitrogen oxide NO and ammonia ^^^can bewrit ten as follows:[Eq. 23] This simplification is based on experience, since the functions of hF_qrs_|^1^ and hF_qtu_vG_|^1^ act by modulating the functions of functionsofhF_qrs_*^#^ and hF_qtu_vG_*^#^ respectively. Thus, for low flow rates, hF_qr^_|^1^and hF_qtu_vG_|^1^ are equal to unity, but their value decreases as the flow rateincreases.This transforms a two-dimensional function into two one-dimensional functions, easier to calibrate and with less risk of extrapolation. Empirically, we ask:[Eq. 28] hE_qtu^#, 1^ ≈ 1 ∙ hE_qtu_*^#^Indeed, experimentally, at iso-temperature, a variation in the functionhE_qtuproportional to the flow rate through the SCR is observed. Equations [Eq. 23] and [Eq. 25] can then be rewritten as follows: [Eq. 29] At this stage, we thus have the set of equations [Eq. 29] [Eq. 30] and[Eq. 31] in order to determine the quanti ty of nitric oxide NO and ammonia^^^leaving each SCR. The ease of calibration (over a few dynamic cycles carried out on a test bench) as well as the ease of integration into a computer due to thelimited resources required, make this method an ideal candidate forapplication in the context of OBM on-board monitoring in a Euro 7 / VII standardised vehicle.The physical approach used in this invention is advantageous over other statistical or machine learning approaches because of i ts explainabilityand the need for less testing (as a rule quite expensive) for i ts calibration.Indeed, the contribution of theory to the model makes i t possible to betterpredict the response of the system in areas where there would be less training data. The area of use of the system is better covered.Finally, the simplifications made to the model facilitate the calibration task with negligible loss of accuracy. The stages of the method for estimating are notably executed by a calculation means, included in the on-board electronic computer of thevehicle or in a specific computer. The computer comprises in all cases atleast one processor, a memory and means of communication with the rest of the vehicle and in part icular the sensors and estimation means, via a wirednetwork, in particular of the can type or a wireless network. Nitrogen oxides ^^^and ammonia NH3 leaving each SCR are admitted to the downstream SCR. In particular, when the engine is equipped with two SCRs in series, nitrogen oxides NOxand ammonia NH3from the first SCR are admitted to the input of the second SCR. The method for estimating illustrated by Figure [Fig 1] comprises four main stages.A first measurement and estimation stage 1.A second stage 2 of est imating the emissions leaving thecompression-ignition engine.A third stage 3 for est imating emissions leaving at least one first SCR.A fourth stage 4 for estimating emissions leaving a second SCR. Nitrogen oxides are ^^^formed at very high temperatures in the combustion chamber, when the dioxygen in^^ the ambient air is able to reactwith dinitrogen ^^. For a compression-ignition engine, it is mainly theformation of nitric oxide NO, but this can then be transformed into nitrogendioxide ^^^ with the ozone ^^ in the ambient air.Ammonia ^^^is not formed in the engine but in the SCR, as a by-product, from other combustion products such as nitric oxide NO anddihydrogen ^^. It will therefore not be estimated in this stage.Determining the nitrogen oxide concentration ^^^at the engine output (in ppm) as a function of the engine speed and the torque estimatedby the control unit . This function can be given in the form of 2D mappings.A 2D mapping can be provided for each combustion mode of the engine, in particular a specific mapping can be provided during the regeneration phases of the post-treatment system or a specific mappingduring the heating phases.Indeed, an SCR must be heated to reach a threshold temperature fromwhich it has a predetermined minimum treatment efficiency. Thistemperature is generally reached by degrading the combustion efficiency of the engine through, for example, delayed fuel injection. It is therefore not compulsory to take into account other variables,such as the EGR (Exhaust Gas Recirculation) partial exhaust gasrecirculation rate or the richness λ , which are taken into account in part viathe engine operating point (rotational speed / load), the combustion mode (fora given engine setting) or the characterist ics of their regulation.In the case of application described here, a 1D mapping depending on the estimated torque is preferred. Indeed, such a 1D mapping is simpler tocalibrate, reduces the risk of extrapolation of the model and makes it possibleto maintain sufficient accuracy on the cycle.Nitrogen oxides ^^^generated by the compression-ignition engine are admitted into the first SCR in order to reduce them. The reduction achieved is not total, and nitrogen oxides ^^^ are st illpresent leaving the first SCR. The residual nitrogen oxides ^^^ are thenoptionally admitted into a second SCR. This second SCR then reduces the^^^ residual nitrogen oxides.The method for est imating the quantities of nitric oxide^^ andammonia ^^^in the polluting emissions of a vehicle equipped with a compression-ignition engine and an exhaust line with at least a first SCR according to the invention comprises the stages presented below. In a particular case, the compression-ignition engine may also haveother features, in particular an exhaust gas recirculation circuit at the EGRintake.The method for estimating the amount of nitric oxide and ammonia inthe exhaust gases of a motor vehicle equipped with at least one first SCR isillustrated in Figure [Fig. 1] and comprises the following stages:In a first stage 1, measuring or estimating the temperature in the first SCR, the flow in the first SCR, and the speed and torque of the compression-ignition engine.In a second stage 2, determining the molar fraction of nitric oxide inthe gases leaving the compression-ignition engine by applying a mapping as a function of the estimated torque of the engine forming a first mapping. In a third stage 3, determining the molar fraction of nitric oxide in the gases leaving the first SCR, arranged downstream of the compression-ignition engine, by applying the equation [Eq. 29], dependent on the molarfraction of nitric oxide produced by the engine and on the flow rate in thefirst SCR, as well as a 1D mapping dependent on the temperaturein the first SCR forming a second mapping, and a 1D mapping dependent on the flow rate in the first SCR forming a third mapping. Themolar fraction of ammonia in the gases leaving the first SCR is alsodetermined by applying equation [Eq.30], a function of a temperature- dependent mapping (hEwxu^#^) in the first compression-ignition SCR. The said mapping (hE_qtu) forms a fourth mapping. When the motor vehicle is provided with a second SCR downstreamof the first SCR, the process continues with a fourth stage 4.During this fourth stage 4, determining the molar fraction of ammonia in the gases leaving the second SCR by applying the same equation [Eq. 30] applied for the first SCR, depending on the mapping (hE_qtu) dependent on the temperature and flow rate in the second SCR. Determining the molar fraction of nitric oxide in the gases leavingthe second SCR by applying the equation [Eq. 29], dependent on the molarfraction of nitric oxide in the gases leaving the first SCR, the flow rate and volume of the second SCR, as well as a temperature-dependent 1D mapping (hF_qrs_^_*) in the second SCR forming a sixth mapping and a flow-dependent 1D mapping (hF_qrs_^_|) in the second SCR forming a seventh mapping. The model ([Eq. 29], [Eq. 30] and [Eq. 31]) makes it possible todescribe in a simplified but reliable manner the generation and catalysis of pollutant emissions in a motor vehicle equipped with a compression-ignitionengine and at least a first SCR, and if necessary (frequently) equipped witha second SCR. In order to be able to use this model, the following functions must becalibrated:- 2D mapping according to the engine speed and estimated torque,giving the molar fraction of ^^^the leaving the engine, by combustion modeand by fuel type,- the functions involved in determining the molar fraction of ^^^leaving each SCR ([Eq. 29]),- the functions involved in determining the number of moles ofadsorbed NH3 ([Eq. 31]),- the functions involved in determining the molar fraction of the ^^^leaving an SCR ([Eq. 30]).In other words, a (2D) mapping is to be calibrated for the engineoutput emissions in addition to the mappings used to determine the emissionsfrom ^^^ and the ^^^ leaving the SCRs (hF_qrs_*, hF_qrs_| , hC7_qtu andhE_qtu_*).To carry out this calibration, dynamic tests are carried out sweepingthe combustion modes, the engine field (rotational speed / torque), the flowrates and the temperatures in the at least one SCR, likely to be observedduring road use by the end customer.To carry out such a calibration, the following acquisitions are carriedout, in particular at an acquisit ion frequency of 10 Hz:Engine Output Emissions: ^^^ Emissions downstream of the first SCR: ^^^Exhaust output emissions: ^^^, ^^^Internal temperatures in each SCR Estimated speed and torque NH3 flow rate injected into each SCR (by Adblue® injection) Combustion mode information Flow rate through each SCR. The model is calibrated for a given technical definition, SCR ageingstatus, ECU calibration, as well as ambient conditions (temperature,pressure, humidity).Based on the acquisi tions made, the calibration is broken down intothree stages:Calibration of the quantity of nitrogen oxides ^^^leaving theengine,Calibration of the amount of nitrogen oxides ^^^and the amountof ammonia ^^^ leaving the first SCR, andCalibration of the quantity of nitrogen oxides ^^^and the amountof ammonia ^^^ leaving the second SCR (if present).As discussed above, the amount of nitrogen oxides ^^^generated bythe engine can be determined based on a two-dimensional mapping dependenton the estimated torque and the rotational speed of the engine.According to the embodiments, 2D mapping is provided for eachcombustion mode of the engine.To construct each map, determining the quantity of nitrogen oxides[ppm] by measurement ^^^ according to a function of the inputs, i .e., in thecase of application as an example, the indicated engine torque. The cuttingof this mapping is quite fine, particularly with a pitch of 10 Nm for torquein 2D mapping. Several methods are possible to determine to complete the values ofthe mapping around the measured values. Mention may be made in part icularof the use of a neural network or a Gaussian process model, for which alearning method is carried out on the measurements of the mapping.This is a static model calibrated on dynamic cycles, accordingly themeasurement of nitrogen oxides at the engine output must be wellsynchronized beforehand with respect to the engine events used.^^^The expression obtained ([Eq. 29]) to calculate the molar fraction ofnitric oxide NO leaving the SCR is applied indifferently to each SCR present.Only the origin and quantity of the pollutants received at the inlet , the flowrate, the temperature and the volume change depending on whether i t is thefirst or the second SCR. When equation [Eq. 29] is applied to the first SCR, the value corresponds to the molar fraction of ^^^in the gases leaving the engine and calculated in the first stage of the process and 8qrsis the molar fraction of^^^ in the gases leaving the first SCR.In the present case, Q denotes the flow rate passing through the firstSCR(including the low-pressure EGR if necessary), T the internaltemperature of the first SCR (homogeneous if a 0D model has beenenvisaged).The hF_qrs_*^#^and functions then take the form of 1Dmappings.hF_qrs_|^1^ During calibration, these functions are adjusted ordetermined, in particular through mathematical modelling based on a sample of values obtained during bench tests. The function hF_qrs_*^#^ can be adjusted independently of the function hF_qrs_|^1^ for small flows, the function hF_qrs_|^1^ taking a value equal to 1 in such cases. For high flow rates, the function hF_qrs_|^1^ takes values below 1, in order to account for the efficiency losses in the treatment of nitrogen oxides^^^.The molar fraction of ammonia ^^^at the outlet of the first SCR is given by the equation [Eq. 30] and equation [Eq. 31] wherein 8qr9:representsthe molar fraction of nitrogen oxides ^^^ leaving the engine, calculated inthe first stage and 8qtu_Krepresents the molar fraction of ammonia ^^^leaving the first SCR.Determining the function hE_qtu_* by bench measurements.The molar fraction of nitric oxide NO at the outlet of the second SCRis calculated with an expression similar to that used for the first SCR ([Eq.29]) modified to account for gases from the first SCR: [Eq. 32] The variables are:8qr_^9: : molar fraction of nitrogen oxides ^^^ leaving the first SCRQ_2: Flow rate through second catalyst SCRT_2: internal temperature of the second SCR 8qrs_^ : molar fraction of nitrogen oxides at ^^^ leaving the secondSCR The method for calibrating the functions hF_qrs_^_*^#_2^ andhF_qrs_^_|^1_2^ for the second SCR is identical to that used for calibrating thefunctions hF_qrs_*^#^and hF_qrs_|^1^for the first SCR. Ammonia production ^^^in the second SCR only takes into account adsorption and desorption phenomena, described by the equation [Eq. 33] below, adapted from equation [Eq. 29]) to account for admitted gases comingfrom the first SCR:[Eq. 33] Where:8qtu9: : molar fraction of ^^^ leaving the first SCR and calculated inthe previous stage.3qtu_vG : number of moles of ^^^ stored in the second SCR.8qtu_^ : molar fraction of the ^^^ output of the second SCR.Determining the function hE_qtu_*from values measured on a bench. It has a zero value as long as the temperature does not reach a predeterminedvalue accounting for the storage by adsorption of ammonia^^^, then anincrease accounting for the release by desorption of the ^^^stored ammonia. The invention has been described above in the context of estimatingthe quantities of nitrogen oxides ^^^ and ammonia produced^^^.Nevertheless, the invention can be adapted to reactions involving otherspecies as products and reagents, in particular carbon dioxide^^^^^, carbonmonoxide, HC hydrocarbons, nitrogen dioxide ^^^ or nitrous oxide ^^^.

Claims

CLAIMS1. Method for estimating the amount of polluting species in the exhaust gas ofa motor vehicle equipped with an internal combustion engine and at least afirst catalytic converter for the selective reduction of nitrogen oxides, themethod for estimating making it possible to estimate the amount of pollutingspecies in the exhaust gas, in part icular before a possible concentrationsensor is hot enough to carry out measurements, the method comprising the following stages: a. identifying the chemical reactions involved in the firstselective reduction catalyst for nitrogen oxides, having as reagent orproduct the polluting species whose amount in the exhaust gases mustbe est imated,b. determining the reaction rates of each identified chemicalreaction, c. carrying out a mass balance in the first nitrogen oxideselective reduction catalyst , considered as an open system, for each ofthe pollutants whose quantity is to be determined, and d. determining the amount of polluting species in the exhaustgas according to the mass balance.

2. Method for estimating according to claim 1, wherein the polluting speciesare nitric oxide and ammonia, the method for estimating comprising the following stages:a. determining the temperature in the first selective nitrogenoxide reduction catalyst, the flow rate in the first selective nitrogen oxide reduction catalyst, the quantity of ammonia entering the firstselective nitrogen oxide reduction catalyst, the speed and torque of the compression-ignition engine,b. determining the molar fraction of nitric oxide in the gasesleaving the internal combustion engine by compressing, by applying a first mapping as a function of the estimated torque of the engine,c. determining the molar fraction of nitrogen oxides in thegases leaving the first catalyst , arranged downstream of the internalcombustion engine, according to a function of the molar fraction of nitric oxide produced by the engine, the flow rate in the first catalystand the volume of the first catalyst, as well as a second 1D mappingdependent on the temperature in the first catalyst and a third 1D mapping dependent on the flow rate in the first catalyst,d. determining also the molar fraction of ammonia in the gasesleaving the first selective catalytic reduction (SCR) catalyst , accordingto a fourth 1D mapping dependent on the temperature in the first selective catalytic reduction (SCR) catalyst and the molar fraction of nitrogen oxides in the gases emitted by the compression-ignition engine.

3. Method for estimating according to claim 2, wherein, when the motor vehicleis equipped with a second selective reduction catalyst for nitrogen oxides downstream of the first selective reduction catalyst for nitrogen oxides, themethod comprises the following stages:a. determining the molar fraction of ammonia in the gasesleaving a second selective nitrogen oxide reduction catalyst according to a fifth 1D mapping dependent on the temperature in the second selective nitrogen oxide reduction catalyst and according to the value of the number of ammonia adsorption sites,b. determining the molar fraction of nitrogen monoxide in thegases leaving the second selective reduction catalyst for nitrogen oxides according to the molar fraction of nitrogen monoxide in the gases leaving the first selective reduction catalyst for nitrogen oxides,and the flow rate in the second selective reduction catalyst for nitrogenoxides, as well as a sixth 1D mapping dependent on the temperature inthe second selective reduction catalyst for nitrogen oxides and aseventh 1D mapping dependent on the flow rate in the second selective reduction catalyst for nitrogen oxides.

4. Method for estimating according to claim 2 or 3, wherein the mappings arecalibrated according to measurements made during tests.

5. Method for estimating according to claim 1, wherein the polluting speciesare carbon dioxide ^^^, carbon monoxide CO, hydrocarbons HC,ammonia^^^, nitric oxide NO, nitrogen dioxide ^^^ or nitrous oxide ^^^.

6. Motor vehicle equipped with an est imation system configured so as to carryout the method for estimating according to any one of claims 1 to 5, inparticular within an on-board diagnosis.

7. Motor vehicle according to claim 6, further comprising a partial exhaust gasrecirculation circuit at the intake.

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