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

Abstract

A method for estimating the quantity of polluting species in the exhaust gases of a motor vehicle equipped with a compression-ignition engine and at least one selective nitrogen oxide reduction catalyst, the estimation method for estimating the quantity of polluting species in the exhaust gases, in particular before any concentration sensor has become sufficiently hot to perform measurements, comprising the following steps: a. identifying (1) the chemical reactions in the at least one selective nitrogen oxide reduction catalyst having the polluting species as reactant or product, b. determining (2) the reaction rates of each identified chemical reaction, c. performing (3) a mass balance in the at least one selective nitrogen oxide reduction catalyst considered as an open system, for each polluting species, and d.(4) The quantity of polluting species in the exhaust gases is determined as a function of the mass balance. Figure for the abbreviation: [Fig 1].

Description

Title of the invention: Method for estimating the quantity of polluting species in the exhaust gases of a compression-ignition engine equipped with at least one catalyst for the selective reduction of nitrogen oxides. Technical field

[0001] The invention has as its technical field the estimation of polluting species produced by a compression ignition engine, and more specifically, of polluting species produced by a compression ignition engine equipped with at least one selective reduction catalyst for nitrogen oxides (also called SCR, from the English acronym for: "Selective Catalytic Reduction"). Previous techniques

[0002] 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.

[0003] Among pollutant emissions, the Euro7 / VII standard is particularly strict with regard to emissions of nitrogen oxides NOX and ammonia Ml;.

[0004] Among these gases, the particularities of NO2 and nitrogen dioxide (NO2) should be noted. NO2 is a toxic gas that causes inflammation of the respiratory tract and contributes to the formation of acid rain. Ammonia (NH3) contributes to the formation of secondary particles, associated with cardiovascular and respiratory diseases, and is harmful to aquatic environments.

[0005] The Euro 7 / VII standard includes a requirement for on-board diagnostics (OBM). It will be mandatory to monitor, on every journey the vehicle makes, the amount of nitrogen oxides (NOx) (primarily nitrogen monoxide NO and nitrogen dioxide NO2) and the amount of ammonia NH3 emitted from the exhaust. The vehicle must transmit these values ​​not only via the on-board diagnostic port (OBD) but also via over-the-air (OTA) wireless communication to a dedicated platform.

[0006] If emissions of nitrogen oxides NOX or ammonia NH3 exceed a predefined limit, constructed by multiplying the regulatory threshold of the species concerned by a predetermined factor greater than 1, called the conformity factor CF, then the vehicle must alert the driver by means of warning lights on the dashboard and require the vehicle to be repaired by means of limitations on engine torque and vehicle speed, or even by prohibiting the vehicle from starting.

[0007] In other words, if emissions are higher than, for example, 1.5 or 2 times predetermined thresholds, generally obtained during vehicle type approval, calculated over a number of valid journeys, the alert must be given.

[0008] In order to determine these values, a concentration sensor enabling the determination of the concentration of these pollutants in the exhaust gases must be provided in vehicles intended to obtain vehicle type approval. An on-board diagnostic system for the sensor is also required.

[0009] However, existing types of sensors are not capable of taking a measurement until their sensing element has reached a threshold temperature, known as the operating temperature. The sensor's temperature rise can take up to 900 seconds from the start of driving for compression-ignition vehicles (such as diesel engines).

[0010] It thus appears that it is not possible to meet the Euro 7 standard with the existing sensors alone due to the absence of measurement up to 900 seconds after the start of driving.

[0011] There is a need for a determination of the emissions of nitrogen oxides and ammonia at the exhaust outlet of a compression-ignition engine, before reaching the operating temperature by the sensor measuring these pollutants.

[0012] In the prior art, many documents deal with the estimation of the quantity of nitrogen oxides.

[0013] In particular, we can cite 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.

[0014] We can also cite the documents US 11028753, JP2009287410, US2008 / 108212 and W02016 / 159019Al describing models for determining the quantity of nitrogen oxides but only at the engine outlet, and not at the exhaust outlet after the after-treatment device(s).

[0015] Documents EP3736418 and EP3956549 disclose models for estimating these emissions based on sensor measurements. These documents are inapplicable here because it is impossible to perform a measurement until the sensor has reached its operating temperature.

[0016] The technical problem is therefore not solved by the prior art. Description of the invention

[0017] The invention relates to a method for estimating the quantity of polluting species in the exhaust gases of a motor vehicle equipped with a compression-ignition engine and at least one first selective reduction catalyst. nitrogen oxides, the estimation method for estimating the quantity of polluting species in exhaust gases, particularly before a potential concentration sensor is sufficiently hot to perform measurements, the method comprising the following steps:

[0018] the chemical reactions involved in the first catalyst for the selective reduction of nitrogen oxides are identified, having as reactant or as product the polluting species whose quantity in the exhaust gases must be estimated,

[0019] the reaction rates of each identified chemical reaction are determined,

[0020] a mass balance is performed in the first selective reduction catalyst for nitrogen oxides, considered as an open system, for each of the polluting species whose quantity must be determined, and

[0021] The quantity of polluting species in the exhaust gases is determined as a function of the mass balance.

[0022] The polluting species may be nitrogen monoxide and ammonia; the estimation process may then include the following steps:

[0023] the temperature in the first selective nitrogen oxide reduction catalyst, the flow rate in the first selective nitrogen oxide reduction catalyst, the quantity of ammonia entering the first selective nitrogen oxide reduction catalyst, and the speed and torque of the compression-ignition engine are determined.

[0024] The mole fraction of nitrogen oxide in the exhaust gases of the compression-ignition engine is determined by applying a first map based on the engine speed and estimated torque.

[0025] The mole fraction of nitrogen oxides in the gases exiting the first selective nitrogen oxide reduction catalyst, located downstream of the compression-ignition engine, is determined as a function of the mole fraction of nitrogen oxides produced by the engine, and the flow rate in the first selective nitrogen oxide reduction catalyst, and also of a second 1D temperature-dependent map in the first selective nitrogen oxide reduction catalyst and a third 1D flow-dependent map in the first selective nitrogen oxide reduction catalyst,

[0026] The mole fraction of ammonia in the gases exiting the first selective nitrogen oxide reduction catalyst is also determined as a function of a fourth 1D temperature-dependent map in the first selective nitrogen oxide reduction catalyst and the mole fraction of nitrogen oxides in the gases emitted by the compression-ignition engine.

[0027] When, as is frequently the case, the motor vehicle is equipped with a second selective nitrogen oxide reduction catalyst downstream of the first For the selective reduction catalyst of nitrogen oxides, the process may include the following steps:

[0028] The mole fraction of ammonia in the gases exiting the second selective nitrogen oxide reduction catalyst is determined as a function of a fifth 1D temperature-dependent map in the second selective nitrogen oxide reduction catalyst and as a function of the number of ammonia adsorption sites.

[0029] The mole fraction of nitrogen monoxide in the gases exiting the second selective reduction catalyst of nitrogen oxides is determined as a function of the mole fraction of nitrogen monoxide in the gases exiting the first selective reduction catalyst of nitrogen oxides, and the flow rate in the second selective reduction catalyst of nitrogen oxides, as well as a sixth 1D temperature-dependent map in the second selective reduction catalyst of nitrogen oxides and a seventh 1D flow-dependent map in the second selective reduction catalyst of nitrogen oxides.

[0030] The maps can be calibrated according to measurements taken during tests.

[0031] The polluting species may be carbon dioxide, carbon monoxide, hydrocarbons, ammonia, nitrogen monoxide, nitrogen dioxide or nitrous oxide.

[0032] The invention also relates to a motor vehicle equipped with an estimation system configured to perform the estimation process as described above, in particular within an on-board diagnostic.

[0033] The motor vehicle may further include a partial exhaust gas recirculation circuit at the intake. Brief description of the drawings

[0034] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which:

[0035] - Figure [Fig. 1] illustrates the main steps of a method for estimating the quantity of polluting species in exhaust gases. Detailed description

[0036] The following concepts specific to the determination of reaction rates in general in a given system, which may be open or closed, are recalled. The following generic chemical reaction is considered:

[0037] aA + bB cC + dD

[0038] with

[0039] a, b, c, d: stoichiometric coefficients

[0040] A, B: reactants of the reaction

[0041] C,D: products of the reaction.

[0042] The rate v of this chemical reaction is defined in moles per unit time:

[0043] [Eq. 1]

[0044] v = Vobf(T) • [Af[B]p

[0045] With:

[0046] Volume: the system volume,

[0047] / (jj : a function of the temperature T of the system,

[0048] [A], [B]: the volume concentrations of reactants A and B respectively,

[0049] A, [3 : the powers applied to these concentrations.

[0050] The function f is often modeled by an Arrhenius law:

[0051] [Eq. 2]

[0052] f(T) =keEaAr

[0053] where:

[0054] k: a pre-exponential factor of the reaction

[0055] Ea: the activation energy of the reaction

[0056] R: the universal gas constant (-8.3145 J / K)

[0057] T: the reaction temperature, in Kelvin

[0058] However, this expression only provides two degrees of freedom, the pre-exponential factor k and the activation energy Ea, for fitting it. Experimentally, the temperature dependence of the reaction rate can take a more complex form. In the remainder of this description, the more generic form / (T) will therefore be used.

[0059] If the system is open, as is the case with a selective catalytic reduction (SCR) catalyst mounted in the exhaust of a compression-ignition engine, the function f can also depend on the axial velocity of the gases, obtained as the volumetric flow rate of the gases divided by the cross-sectional area of ​​the system. For a constant cross-section, equation [Eq. 1] can be rewritten as follows:

[0060] [Eq. 3]

[0061] v^Vol-f(T,QY[A}a[B]p

[0062] For an open system, the mass balance for a species A, in moles, is written:

[0063] [Eq. 4]

[0064] x x yy dt An ^out Axit prod A Aj cons AA

[0065] With:

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085] dnA: Change per unit time of the number of moles of species A in the dt system Q: Molar flow rate of gases entering the system : Mole fraction of species A in the gases entering the system Q: Molar flow rate of gases exiting the system : Mole fraction of species A in the gases exiting the system l Number of moles of species A generated per second by reactions where species A is a product V v: Number of moles of species A consumed per second by the AN cons reactions where species A is a reactant It is recalled that an SCR mounted on the exhaust of a compression ignition engine is a gas aftertreatment device which aims to reduce the nitrogen oxides contained in the exhaust gases received from the engine into harmless molecules under the action of ammonia present in the SCR and coming from a urea-based solution (Adblue®) which is injected upstream of said catalyst. In an SCR, particularly a first SCR, the main reactions involving nitric oxide NO and ammonia NH3 are as follows: Adsorption reaction of ammonia NH3 in an ammonia adsorption site denoted as V, NH3 + as _^NH3_as Desorption reaction of ammonia NH3 from an ammonia adsorption site denoted as V2 NH3~as _^NH3 + as- Reduction of nitric oxide by adsorbed ammonia NH3_as NH3_as + NO + jO2 N2 + ^H2O + as Reduction of nitric oxide (NO) and nitrogen dioxide (NO2) by adsorbed ammonia (NH3). I 1 ^4 / NH3_as +jNO + lNO2 2 N2 + 3j 2 H2O + as Reduction of nitrogen dioxide NO2 by adsorbed ammonia NH3_as NH3_as + ^NO2 ^N2 + 3 / 2^0 +as Oxidation of adsorbed ammonia NH3_as into dinitrogen N2

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101] V6 / NH3_as + % O2 ¥2 N2 + 3 / 2 H2O + as In this set of reactions, the reactants NO, NO2, NH3 and O2 are in a gaseous state. With : v^mol / s] = vjmol / s] = Vol • f2(T, Q) • [VH3_asJz2 vjmol / s] = Vobf / T,e)^ff3_asrWxf3 \Jmol / s] = Vol • f 4(T, Q) • [NH3~ asfW / vjmol / s] = Vol<5(T,2)-[VH3_asrW^ vjmol / s] = Vol • f6(T, g)• And : "v, "io and Pp, : coefficients" The internal temperature of the catalyst T and the exhaust gas flow rate Q through The catalysts are determined, that is to say, either measured using sensors, or estimated by an electronic control unit of the motor vehicle, and are subsequently considered as input data. In a theoretical approach such as the one presented above, it is necessary to to calibrate as many two-dimensional functions as possible, , what a range of reactions to consider. In the case presented above, six two-dimensional functions need to be calibrated for the reactions affecting nitrogen monoxide NO and ammonia only. It is also necessary to estimate the concentrations of the remaining reactants involved in each of the reactions identified above (here, dioxygen O2), which will in turn be determined using new reaction schemes. Furthermore, the parameters üp P must be determined for each of these new reactions. It thus appears that the determination and calibration of an exact model taking into account all the reactions affecting the concentration of nitrogen monoxide NO and ammonia NH3 becomes very complex. Indeed, there are many more functions to calibrate than observed phenomena (i.e., the quantities of nitrogen monoxide NO and ammonia NH3 at the outlet of the SCR in the system considered here) and different solutions would be possible, all fitting the experimental results correctly, but without the certainty that one of them correctly describes the physical and chemical phenomena involved.

[0102] Moreover, the very high dynamic nature of the reactions would require choosing very small sampling steps (due to the stability of the calculations), which would make it difficult to integrate this solution into a computer, which would be overloaded.

[0103] In the detailed process below, a number of assumptions will be made in order to solve these two problems and to arrive at a solution that is both easy to calibrate and to integrate into a computer.

[0104] The following assumptions and considerations apply identically regardless of the type of emission to be determined. In the present case, they will be described for a system comprising the compression-ignition engine and at least one SCR, and for which the quantities emitted of nitrogen monoxide NO and ammonia NH3 are to be estimated.

[0105] The system is considered homogeneous in space, that is, the temperature and concentrations are the same at all points of the system considered. In other words, the model is a 0D model. The mole fractions inside and outside the system are identical, and it is therefore possible to write:

[0106] [Eq. 5]

[0107] _ nvn ,v .y V ^in ^out A prod AA^ cons A \

[0108] The system is considered quasi-stationary. The variations in the number of moles of the gaseous species are instantaneous. Furthermore, the inlet flow rate is very close to the outlet flow rate:

[0109] [Eq.6BV Q^Q

[0110] Based on these assumptions, the following equations are set forth:

[0111] For a species A such as nitrogen monoxide NO, the variation in the number of moles in the system being considered instantaneous, the differential term is zero:

[0112] [Eq. 7]

[0113] o = Q • Xy - Q • XA + R , Âv - E (Gaseous Species A) A proa A Aj cous y

[0114] For a non-gaseous species A such as ammonia NH3 stored in the SCR, the differential term is taken into account:

[0115] [Eq. 8]

[0116] nY Y (Non-gaseous Species A) dt Am A prod AA^ cons A

[0117] The dynamics of species in the gas phase has been removed, which has the effect of transforming the differential equations into algebraic equations.

[0118] By definition, the concentration of species A is written:

[0119] [Eq. 9]

[0133]

[0120] । Â -, _ [ÆJ - vd - vd

[0121] With: XA the mole fraction of species A in all species present in the SCR, and n the total quantity of species in the catalyst, in moles.

[0122] For species in the gaseous phase, the ideal gas law is applied.

[0123] [Eq. 10]

[0124] PVol = nRT

[0125] Equation [Eq. 9] can then be reformulated as follows:

[0126] [Eq. 11]

[0127] [A]-XaP!(RT)

[0128] By neglecting the effect of pressure variations on the reaction rates (i.e., by considering P to be substantially constant) in a new generic function Q, we can write the following equations:

[0129] [Eq. 12] [OBO] y[me / s] = flight ■ g(T, Q) • X / x /

[0131] with v: the reaction rate for a reaction with two reactants in gaseous form

[0132] [Eq. 13] mol / s] = Vol • g^T, çj ■

[0134] with v: the reaction rate for a reaction comprising a single reactant in gaseous form.

[0135] For each reaction rate, only the dependence on a single gaseous reactant is considered, the one deemed to be limiting. The other reactant is not taken into account if it is also in the gaseous state or if it is considered to be in excess. Equations [Eq. 12] and [Eq. 13] are then reformulated as follows:

[0136] [Eq. 14] [0B7] ^molI s] = Vol. g(T> q) . X /

[0138] with v: the reaction rate for a reaction with two reactants in gaseous form

[0139] [Eq. 15] 101401 v[mol / s] = Vol^T.Qj.X / t-^)'

[0141] with v: the reaction rate for a reaction comprising a single reactant in gaseous form.

[0142] For simplification, we set a — fi = L

[0143] We therefore obtain: [°144] ^nwi 1^ = yoi. g(T, q) . xA , A limiting gaseous reactant [014-5] ^moljs] = g{T,Q)-XA. n^, A limiting gaseous reactant, B non-gaseous

[0346] ^molfs] = ^r, Q) • B non-azous reagent

[0147]

[0148] The NOx (gaseous) will be consumed by reactions with the NH3 stored in the SCR:

[0149] [Eq. 16]

[0150] 0 = Q ■ Xnox - Q ■ XNO - gNO (T, Q) ■ X^o • as

[0151] NH3 (gaseous) can be adsorbed or desorbed:

[0152] [Eq. XNH3.nQ-XNh3 +gdNH( T, Q) n^H^as-Vol -ga nh^T,Q) XNh3

[0153] Adsorbed ammonia NH3_as can vary due to adsorption / desorption phenomena and can be consumed by reactions with NOx and by oxidation with O2:

[0154] [Eq. 18]

[0155] = Vol-gaJllh(T,Q)- Xm,-g^^ (T,Q)- nm3jl-(T,Q)-

[0156] The combination of the equations obtained with the assumptions made above allows the balance equations to be written in a linear form with respect to the mole fractions X, which can be obtained explicitly, and therefore without the need for an iterative calculation, allowing the use of a calculation step of 100 to 1000 times larger in iterative simulations by exact model, with a negligible loss in precision.

[0157] The mole fractions XN0 and Xnh3 can be isolated from the first two equations and obtained explicitly.

[0158] Adsorption phenomena are considered immediate: any species A entering or produced in the system is stored instantaneously. Instead of calibrating an adsorption rate and a desorption rate, only the desorption rate is taken into account.

[0159] [Eq. 19]

[0160] Vol • ga NH3(T,Q)-XNh3=Q ■ Xnh3.k

[0161] and therefore:

[0162] [Eq. 20]

[0163] 0 = Q • Xnox.k - Q • XNOx - gcNO^ (T,Q) • XNOx ■

[0164] [Eq. 21]

[0165] 0 = - Q • XNh3 + gd NH (T,Q) • nNH^as

[0166] [Eq. 22]

[0167] = q. - gd NHi (T, Q) • nNH3as - gcjm< (T, Q)X NOT • nNH^ - geJVHiJa (T,Q) • nNH^s

[0168] The system is thus reduced to three functions to be calibrated, denoted ^c_NO^ agg^NHv

[0169] The following assumptions apply to the specific case of nitrogen monoxide (NO) and ammonia (NH3) emissions. These assumptions were chosen based on purely empirical or simplification criteria.

[0170] The mole fractions of nitrogen oxide NO and ammonia NH3 can be written as follows:

[0171] [Eq. 23]

[0172] A NOX Q+gc ^T.Qyn^H.^

[0173] [Eq. 24]

[0174] v gd_NH.(T,Q)nNH^ ANHj~ q

[0175] [Eq. 25]

[0176] =q,Xnh -gd H (T,Q) -XNOx-nNH3n^

[0177] Empirically, we posit:

[0178] [Eq. 26]

[0179] ge XOx(T, Q) Kgc NOx T(T) gc NOx_q(Q)

[0180] [Eq. 27]

[0181] nh^os^ Ô) as q(Q)

[0182] This simplification is based on experience, indeed the functions gc and act by modulating the functions gc NO^T( T) and gc NH as t^T) respectively. Thus, for low flow rates, gc Xqx^(Q) and gc NH as are equal to one, but their value decreases as the flow rate increases.

[0183] This transforms a two-dimensional function into two one-dimensional functions, which are easier to calibrate and have less risk of extrapolation.

[0184] Empirically, we posit:

[0185] [Eq. 28]

[0186] ■ T, Q) “Q • gd T)

[0187] Indeed, experimentally, at iso-temperature, a variation of the function gd_NH3 proportional to the flow rate through the SCR is observed.

[0188] Equations [Eq. 23] and [Eq. 25] can then be rewritten as follows:

[0189] [Eq. 29]

[0190] Y__________

[0191] [Eq. 30]

[0192] %NH3~ gj NH M-NH^as

[0193] [Eq. 31]

[0194] <ü " 0                    ' anltno, ’ sc         '^nor’                     ^e-nli^us^

[0195] At this stage, we have the set of equations [Eq. 29] [Eq. 30] and [Eq. 31] to determine the quantity of nitrogen monoxide NO and ammonia NH3 at the outlet of each SCR.

[0196] The ease of calibration (on a few dynamic cycles carried out on a test bench) as well as the ease of integration into a computer due to the few resources required, make this process an ideal candidate for application in the context of on-board OBM monitoring in a Euro 7 / VII standardized vehicle.

[0197] The physical approach used in this invention is advantageous compared to other statistical or machine learning approaches because of its explainability and the need for fewer (generally quite costly) calibration trials. Indeed, incorporating theory into the model allows for better prediction of the system's response in areas where training data is less abundant. The system's range of applications is thus better covered.

[0198] Finally, the simplifications made to the model facilitate the calibration task with a negligible loss of accuracy.

[0199] The steps of the estimation process are notably executed by a computing means, included in the vehicle's on-board electronic control unit or in a specific control unit. The control unit includes in all cases at least a processor, memory, and means of communication with the rest of the vehicle, and in particular the sensors and estimation means, via a wired network, in particular of the CAN type, or a wireless network.

[0200] The nitrogen oxides NOx and ammonia NH3 exiting each SCR are admitted into the inlet of the downstream SCR. In particular, when the engine is equipped with two SCRs in series, the nitrogen oxides NOx and ammonia NH3 from the first SCR are admitted into the inlet of the second SCR.

[0201] The estimation process illustrated in Figure [Fig. 1] comprises four main steps.

[0202] A first step 1 of measurement and estimation.

[0203] A second step 2 of estimating the emissions at the output of the compression-ignition engine.

[0204] A third step 3 of estimating emissions at the output of at least a first SCR.

[0205] A fourth step 4 of estimating emissions at the output of a second SCR.

[0206] Nitrogen oxides NOx are formed at very high temperatures in the combustion chamber, when oxygen O2 from the ambient air is able to react with nitrogen N2. For a compression-ignition engine, this mainly involves the formation of nitrogen monoxide NO, which can then be transformed into nitrogen dioxide NO2 with ozone O from the ambient air.

[0207] Ammonia NH3 is not formed in the engine but in the SCR, as a by-product, from other combustion products such as nitrogen monoxide NO and dihydrogen H2. It will therefore not be estimated in this step.

[0208] The concentration of nitrogen oxides (NOx) at the engine outlet (in ppm) is determined as a function of the engine speed and the torque estimated by the computer. This function can be given in the form of 2D maps.

[0209] A 2D map can be provided for each engine combustion mode, in particular a specific map can be provided during the regeneration phases of the after-treatment system or a specific map during the heating phases.

[0210] Indeed, an SCR must be heated to reach a threshold temperature from which it exhibits a predetermined minimum treatment efficiency. This temperature is generally reached by degrading the engine's combustion efficiency, for example through delayed fuel injection.

[0211] Taking into account other variables, such as the partial recirculation rate of exhaust gases EGR (English acronym for "Exhaust Gas Recirculation") or the X richness, which are taken into account in part via the engine operating point (rotational speed / load), the combustion mode (for a given engine setting) or the characteristics of their regulation, is therefore not mandatory.

[0212] In the application described here, a 1D mapping dependent on the estimated torque is preferred. Indeed, such a 1D mapping is simpler to calibrate, reduces the risk of model extrapolation, and allows for sufficient cycle accuracy.

[0213] The nitrogen oxides NOX generated by the compression-ignition engine are admitted into the first SCR in order to reduce them.

[0214] The reduction achieved is not complete, and nitrogen oxides (NOx) are still present at the outlet of the first SCR. The residual nitrogen oxides (NOx) are then possibly admitted into a second SCR. This second SCR then performs a reduction of the residual nitrogen oxides (NOx).

[0215] The method for estimating the quantities of nitrogen monoxide NO and ammonia NH3 in the pollutant emissions of a vehicle equipped with an ignition engine by compression and of an exhaust line with at least one first SCR according to the invention includes the steps presented further below.

[0216] In a particular case, the compression-ignition engine may also have other features, including a partial exhaust gas recirculation circuit at the intake EGR.

[0217] The method for estimating the quantity of nitrogen monoxide and ammonia in the exhaust gases of a motor vehicle equipped with at least one first SCR is illustrated by Figure [Fig. 1] and comprises the following steps:

[0218] In a first step 1, the temperature in the first SCR, the flow rate in the first SCR, the speed and torque of the compression-ignition engine are measured or estimated.

[0219] In a second step 2, the mole fraction of nitrogen monoxide in the gases exiting the compression-ignition engine is determined by applying a map based on the engine speed and estimated torque, forming a first map.

[0220] In a third step 3, the mole fraction of nitrogen monoxide in the gases exiting the first SCR, located downstream of the compression-ignition engine, is determined by applying equation [Eq. 29], which depends on the mole fraction of nitrogen monoxide produced by the engine and the flow rate in the first SCR, as well as a 1D (gc y) temperature-dependent map in the first SCR forming a second map, and a 1D (gc Q) flow-dependent map in the first SCR forming a third map. The mole fraction of ammonia in the gases exiting the first SCR is also determined by applying equation [Eq. 30], which is a function of a map ( / \) depending on the temperature in the first compression-ignition SCR. This map (gdNH^) forms a fourth map.

[0221] When the motor vehicle is equipped with a second SCR downstream of the first SCR, the process continues with a fourth step 4.

[0222] During this fourth step 4, the mole fraction of ammonia in the gases at the outlet of the second SCR is determined by applying the same equation [Eq. 30] applied for the first SCR, a function of the mapping (¾ dependent on the temperature and flow rate in the second SCR.

[0223] The mole fraction of nitrogen monoxide in the gases exiting the second SCR is determined by applying equation [Eq. 29], which depends on the mole fraction of nitrogen monoxide in the gases exiting the first SCR, the flow rate and volume of the second SCR, and a 1D map (§c_NOx_2_t) depending on of the temperature in the second SCR forming a sixth map and a 1D map (Sc nox2 q) dependent on the flow rate in the second SCR forming a seventh map.

[0224] The model ([Eq. 29], [Eq. 30] and [Eq. 31]) allows for a simplified but reliable description of the generation and catalysis of pollutant emissions in a motor vehicle equipped with a compression-ignition engine and at least one first SCR, and where applicable (frequent) equipped with a second SCR.

[0225] In order to use this model, the following functions must be calibrated:

[0226] - the 2D mapping as a function of the engine speed and estimated torque, giving the Mole fraction of NOx at engine outlet, by combustion mode and by fuel type.

[0227] - the functions involved in determining the mole fraction of NOx in output of each SCR ([Eq. 29]),

[0228] - the functions involved in determining the number of moles of NH3 adsorbed ([Eq. 31]),

[0229] - the functions involved in determining the mole fraction of NH3 in output of an SCR ([Eq. 30]).

[0230] In other words, a (2D) map must be calibrated for NOX emissions at the engine outlet in addition to the maps used to determine NOX and NH3 emissions at the SCR outlet (Scj^qx and Sd-NH^T)-

[0231] To achieve this calibration, dynamic tests are carried out sweeping the combustion modes, the engine field (rotational speed / torque), the flow rates and the temperatures in at least one SCR, likely to be observed during road use by the end customer.

[0232] To perform such a calibration, the following acquisitions are carried out, in particular at an acquisition frequency of 10 Hz:

[0233] Engine output emissions: NOx

[0234] Emissions downstream of first SCR: NOX

[0235] Exhaust emissions: NOx, NH3

[0236] Internal temperatures in each SCR

[0237] Diet and estimated couple

[0238] Flow rate of NH3 injected into each SCR (by injection of Adblue®)

[0239] Combustion mode information

[0240] Flow rate through each SCR.

[0241] The model is calibrated for a technical definition, an SCR aging state, an ECU calibration, and given ambient conditions (temperature, pressure, humidity).

[0242] Based on the data acquired, the calibration is broken down into three steps:

[0243] Calibration of the quantity of nitrogen oxides NOx at the engine outlet,

[0244] Calibration of the quantity of nitrogen oxides NOx and the quantity of ammonia NH3 at the output of the first SCR, and

[0245] Calibration of the quantity of nitrogen oxides NOX and the quantity of ammonia NH3 at the outlet of the second SCR (if present).

[0246] As we have seen earlier, the quantity of nitrogen oxides NOX generated by the engine can be determined according to a two-dimensional map dependent on the estimated torque and the rotational speed of the engine.

[0247] According to the embodiments, a 2D map is provided for each combustion mode of the engine.

[0248] To construct each map, the quantity of nitrogen oxides (NOx) [ppm] is determined by measurement as a function of the inputs, i.e., in the example application, the specified engine torque. The segmentation of this map is quite fine, notably with a step of 10 Nm for the torque in a 2D map.

[0249] Several methods are possible for determining and completing the mapping values ​​around the measured values. These include the use of a neural network or a Gaussian process model, in which a learning process is performed on the mapping measurements.

[0250] This is a static model calibrated on dynamic cycles, therefore the measurement of nitrogen oxides NOX at engine output must be properly synchronized beforehand with the engine events used.

[0251] The expression obtained ([Eq. 29]) for calculating the mole fraction of nitrogen monoxide NO at the outlet of the SCR is applied indifferently to each SCR present. Only the origin and quantity of the pollutants received at the inlet, the flow rate, the temperature and the volume change depending on whether it is the first or the second SCR.

[0252] When equation [Eq. 29] is applied to the first SCR, the value Xnos corresponds to the mole fraction of NOX in the gases exiting the engine and calculated in the first step of the process and X^q is the mole fraction of NOX in the gases exiting the first SCR.

[0253] In the present case, Q designates the flow rate through the first SCR (including the low pressure EGR if necessary) and T the internal temperature of the first SCR (homogeneous if a 0D model has been envisaged).

[0254] The functions ge NO etgc yo are then presented in the form of 1D maps. During calibration, these functions are adjusted or determined, in particular through mathematical modeling based on a sample of values ​​obtained during bench tests.

[0255] The function g^ w T) can be adjusted independently of the function gc NO for small flow rates, the function gc NO g( Ô) taking a value equal to 1 in such cases.

[0256] For large flow rates, the function g^ Q) takes values ​​less than 1, in order to account for the losses in efficiency in the treatment of nitrogen oxides NOX.

[0257] The mole fraction of ammonia NH3 at the outlet of the first SCR is given by equation [Eq. 30] and equation [Eq. 31] in which %NOin represents the mole fraction of nitrogen oxides NOX exiting the engine, calculated in the first step and represents the mole fraction of ammonia NH3 at the outlet of the first SCR.

[0258] The function determined by bench measurements.

[0259] The mole fraction of nitrogen monoxide NO at the outlet of the second SCR is calculated using an expression similar to that used for the first SCR ([Eq. 29]) modified to take into account the gases from the first SCR:

[0260] [Eq. 32]

[0261] v Q_2+gc ^2 ^^ge ^

[0262] The variables are:

[0263] : mole fraction of nitrogen oxides NOx exiting the first SCR

[0264] Q_2: flow rate through the second SCR

[0265] T_2: Internal temperature of the second SCR

[0266] -Vvo, 2: mole fraction of nitrogen oxides NOx at the outlet of the second SCR

[0267] The method for calibrating the functions gc No t(T and Q_2) for the second SCR is identical to that used to calibrate the functions and S^no^q(Q) For the first SCR.

[0268] The production of ammonia NH3 in the second SCR only takes into account the adsorption and desorption phenomena, described by equation [Eq. 33] below, adapted from equation [Eq. 29] to take into account the admitted gases from the first SCR:

[0269] [Eq. 33]

[0270] XnhJI Sj NH ' ^NHy_as

[0271] [Eq. 34]

[0273] Where:

[0274] : mole fraction of NH3 exiting the first SCR and calculated in the step previous.

[0275] HNH^as ; number of moles of NH3 stored in the second SCR.

[0276] 2: mole fraction of NH3 at the outlet of the second SCR.

[0277] The function £d nh , t is determined from values ​​measured on a bench. It has a zero value until the temperature reaches a predetermined value accounting for the storage by adsorption of ammonia NH3, then an increase accounting for the release by desorption of the stored ammonia NH3.

[0278] The invention has been described above in the context of estimating the quantities produced of nitrogen oxides NOx and ammonia NH3. However, the invention can be adapted to reactions involving other species as products and as reactants, in particular carbon dioxide CO2, carbon monoxide CO, hydrocarbons HC, nitrogen dioxide NO2 or nitrous oxide N2O,

Claims

Demands

1. A method for estimating the quantity of polluting species in the exhaust gases of a motor vehicle equipped with a compression-ignition engine and at least one first catalyst for the selective reduction of nitrogen oxides, the estimation method enabling the estimation of the quantity of polluting species in the exhaust gases, in particular before a possible concentration sensor is sufficiently hot to perform measurements, the method comprising the following steps: a. We identify the chemical reactions involved in the first catalyst for the selective reduction of nitrogen oxides, where the polluting species, whose quantity in the exhaust gases must be estimated, are used as reactants or products. b. We determine the reaction rates of each identified chemical reaction, c. A mass balance is performed in the first selective nitrogen oxide reduction catalyst, considered as an open system, for each of the polluting species whose quantity must be determined, and d. The quantity of polluting species in the exhaust gases is determined as a function of the mass balance.

2. Estimation method according to claim 1, wherein the polluting species are nitrogen monoxide and ammonia, the estimation method comprising the following steps: a. The temperature in the first selective nitrogen oxide reduction catalyst, the flow rate in the first selective nitrogen oxide reduction catalyst, the quantity of ammonia entering the first selective nitrogen oxide reduction catalyst, and the engine speed and torque of the compression-ignition engine are determined. b. The mole fraction of nitrogen monoxide in the exhaust gases of the compression-ignition engine is determined by applying a first map based on the estimated engine speed and torque.

3. c. The mole fraction of nitrogen oxides in the gases exiting the first selective nitrogen oxide reduction catalyst, located downstream of the compression-ignition engine, is determined as a function of the mole fraction of nitrogen monoxide produced by the engine and the flow rate in the first selective nitrogen oxide reduction catalyst, as well as a second 1D temperature-dependent map in the first selective nitrogen oxide reduction catalyst and a third 1D flow-dependent map in the first selective nitrogen oxide reduction catalyst. d. We also determine the mole fraction of ammonia in the gases exiting the first selective reduction catalyst of nitrogen oxides, as a function of a fourth 1D temperature-dependent map in the first selective reduction catalyst of nitrogen oxides and the mole fraction of nitrogen oxides in the gases emitted by the compression-ignition engine. Estimation method according to claim 2, wherein, when the motor vehicle is equipped with a second selective nitrogen oxide reduction catalyst downstream of the first selective nitrogen oxide reduction catalyst, the method comprises the following steps: a. The mole fraction of ammonia in the gases exiting a second selective nitrogen oxide reduction catalyst is determined as a function of a fifth 1D temperature-dependent map in the second selective nitrogen oxide reduction catalyst and as a function of the number of ammonia adsorption sites. b. The mole fraction of nitrogen monoxide in the gases exiting the second selective nitrogen oxide reduction catalyst is determined as a function of the mole fraction of nitrogen monoxide in the gases exiting the first selective nitrogen oxide reduction catalyst, and the flow rate in the second selective nitrogen oxide reduction catalyst, as well as a sixth 1D temperature-dependent mapping in the second selective nitrogen oxide reduction catalyst and a seventh 1D flow-dependent mapping in the second selective nitrogen oxide reduction catalyst.

4. Estimation method according to claim 2 or 3, wherein the maps are calibrated based on measurements taken during tests.

5. Estimation method according to claim 1, wherein the polluting species are carbon dioxide CO₂, carbon monoxide CO, hydrocarbons HC, ammonia, nitrogen monoxide NO, nitrogen dioxide or nitrous oxide N₂O,

6. Motor vehicle equipped with an estimation system configured to perform the estimation process according to any one of claims 1 to 5, in particular within an on-board diagnostic.

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