Method for estimating the quantity of polluting species in the exhaust gases of an internal combustion engine, equipped with at least one three-way catalyst.

Abstract

Method for estimating the quantity of polluting species in the exhaust gases of a motor vehicle equipped with an internal combustion engine and at least one three-way catalyst, the estimation method making it possible to estimate the quantity of polluting species in the exhaust gases, in particular before a possible concentration sensor is hot enough to carry out measurements, comprising the following steps: a. identifying (1) the chemical reactions in the at least one three-way catalyst having the polluting species as 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 catalyst considered as an open system, for each polluting species, and d. determining (4) the quantity of polluting species in the exhaust gases as a function of the mass balance. Figure for abstract: No figure

Description

Title of the invention: Method for estimating the quantity of polluting species in the exhaust gases of an internal combustion engine, equipped with at least one three-way catalyst. Technical field

[0001] The technical field of the invention is the estimation of the polluting species produced by an internal combustion engine, and more precisely, of the polluting species produced by an internal combustion engine equipped with at least one catalyst. Prior techniques

[0002] The new Euro 7 standard, which will come into force from 2025, requires a reduction in polluting emissions, compared to the current standard (Euro 6e), for vehicles sold in Europe.

[0003] Among the polluting emissions, the Euro7 standard is particularly strict with regard to emissions of nitrogen oxides NOX and ammonia NH3.

[0004] Among these gases, the particularities of NO2 and NH3 should be noted. Nitrogen dioxide NO, is a toxic gas that produces 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 standard includes an obligation for on-board diagnostics OBM (acronym for "On-Board Monitoring"). It will be mandatory to monitor, on each journey made by the vehicle, the quantity of nitrogen oxides NOX (essentially nitrogen monoxide NO and nitrogen dioxide NO 2) and the quantity of ammonia NH3 emitted from the exhaust. The vehicle will have to transmit these values ​​not only via the on-board diagnostics OBD (acronym for "On-Board Diagnostic") socket but also via wireless communication OTA (acronym for "over the air") to a dedicated platform.

[0006] If the emissions of nitrogen oxides NOX or ammonia NH3 exceed a predefined limit, constructed by multiplying the regulatory threshold of the species considered 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 via engine torque and vehicle speed limitations, or even by prohibiting starting.

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

[0008] In order to determine these values, a concentration sensor for determining the concentration of these pollutants in the exhaust gases must be provided in vehicles aiming to obtain Euro 7 approval. An on-board diagnostic system for the sensor is also required.

[0009] However, existing types of sensors are not capable of making a measurement until their sensitive element has reached a threshold temperature, known as the operating temperature. The temperature rise of the sensor can last up to 90 seconds from the start of driving for spark ignition vehicles.

[0010] It thus appears that it is not possible to satisfy the Euro 7 standard with the existing sensors alone due to the absence of measurement up to 90 seconds after the start of driving.

[0011] There is a need for determining the emissions of nitrogen oxides and ammonia at the exhaust outlet of a controlled internal combustion engine, before the operating temperature is reached by the sensor for measuring these pollutants.

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

[0013] We can cite in particular 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 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 post-treatment device(s).

[0015] Documents EP3736418 and EP3956549 disclose models for estimating these emissions based on the measurement of sensors. These documents are inapplicable here due to the impossibility of carrying out a measurement until the sensor has reached its operating temperature.

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

[0017] The subject of the invention is a method for estimating the quantity of polluting species in the exhaust gases of a motor vehicle equipped with an internal combustion engine and at least one first three-way catalyst, the estimation method making it possible to estimate the quantity of polluting species in the exhaust gases, in particular before a possible concentration sensor is sufficiently hot to carry out measurements, the method comprising the following steps:

[0018] the chemical reactions involved in the first three-way catalyst having as reactant or product the polluting species whose quantity in the exhaust gases must be estimated are identified,

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

[0020] a mass balance is carried out in the first catalyst 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 based on the mass balance.

[0022] The polluting species can be nitrogen monoxide and ammonia, the estimation method can then comprise the following steps:

[0023] the temperature in the first catalyst, the flow rate in the first catalyst, and the torque of the internal combustion engine are determined,

[0024] the molar fraction of nitrogen oxide in the gases leaving the internal combustion engine is determined by applying a first map which is a function of the estimated torque of the engine,

[0025] the molar fraction of nitrogen oxides in the gases leaving the first catalyst, arranged downstream of the internal combustion engine, is determined as a function of the molar fraction of nitrogen oxides produced by the engine, of the flow rate in the first catalyst and of the volume of the first catalyst, as well as of a second 1D map dependent on the temperature in the first catalyst and of a third 1D map dependent on the flow rate in the first catalyst,

[0026] the molar fraction of ammonia in the gases leaving the first catalyst is also determined, as a function of a fourth 1D map dependent on the temperature in the first catalyst and the molar fraction of nitrogen oxides in the gases emitted by the internal combustion engine.

[0027] When, as is frequently the case, the motor vehicle is equipped with a second three-way catalyst upstream of the first three-way catalyst, the method may comprise the following steps:

[0028] the molar fraction of ammonia in the gases leaving the second catalyst is determined, as a function of a fifth 1D map dependent on the temperature in the second catalyst and as a function of the value of the number of ammonia adsorption sites,

[0029] the molar fraction of nitrogen monoxide in the gases leaving the second catalyst is determined as a function of the molar fraction of nitrogen monoxide in the gases leaving the first catalyst, of the flow rate in the second catalyst and of the volume of the second catalyst, as well as of a sixth 1D map dependent on the temperature in the second catalyst and of a seventh 1D map dependent on the flow rate in the second catalyst.

[0030] The maps can be calibrated based on measurements made during tests.

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

[0032] The invention also relates to a motor vehicle equipped with an estimation system configured so as to carry out the estimation method as described above, in particular within an on-board diagnosis.

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

[0034] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which:

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

[0036] We recall the following notions specific to the determination of reaction rates in general in a given system, which can be open or closed. We assume the following generic chemical reaction:

[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] We define the speed v of this chemical reaction in moles per unit of time:

[0043] [Eq. 1]

[0044] v= vol-f(T) ■

[0045] With:

[0046] Vol: the system volume

[0047] f(T): 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] ke-1^

[0053] where:

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

[0055] Ea: the activation energy of the reaction

[0056] R: the universal constant of ideal gases (-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, to adjust it. Experimentally, the dependence of the reaction rate on temperature can have 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 for a catalyst mounted in the exhaust of an internal combustion engine, the function f can also have a dependence on the axial velocity of the gases, obtained as the volume flow rate of the gases divided by the cross-sectional area of ​​the system. For a constant cross-section, the equation [Eq. 1] can be rewritten:

[0060] [Eq. 3]

[0061] VOl-f{T,Q)-[A]a[BŸ

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

[0063] [Eq. 4] 100641 % = eto • - e„„ ■ x^.+e, AvAl - E, „„„ AvAl

[0065] With:

[0066] dnA: Variation per unit of time of the number of moles of species A in the dt system

[0067] Q: Molar flow rate of gases entering the system

[0068] : Molar fraction of species A in the gases entering the system

[0069] Q: Molar flow rate of gases leaving the system

[0070] ^-a„U!: Molar fraction of species A in the gases leaving the system

[0071] V y: Number of moles of species A generated per second by the reactions '—'i prml A* A^ where species A is a product

[0072] V y: Number of moles of species A consumed per second by the cons A Aj reactions where species A is a reactant

[0073] It is recalled that the estimation method presented here aims to estimate the production of nitrogen oxides N Ox and ammonia NH3 between the start of rolling and the achievement of the operating temperature at a possible measuring sensor. For this purpose, the species for which the above mass balance is applied are nitrogen monoxide NO, and ammonia NH3. In the example considered here (spark ignition engine) the nitrogen oxides NOX present in engine or catalyst output are considered to be only nitrogen monoxide NO.

[0074] In a catalyst, in particular a three-way catalyst, the main reactions involving nitrogen monoxide NO and ammonia NH3 are as follows:

[0075] Reduction reaction of NO by CO

[0076] NQ + CQ}^CO2 + % N2

[0077] Reduction of NO by hydrocarbons

[0078] NQ + 2^4+r) CHr ^2^4+rj CO2 + + + V2 N2

[0079] Reduction of NO by Ce2O3

[0080] NQ + c>2q3 CeÛ2 + / / 2

[0081] Formation of ammonia NH3 and reduction of nitrogen monoxide NO by di- hydrogen H2

[0082] NO + 5^2 H2 ^NH3 + H2O

[0083] Formation of ammonia NH3 and reduction of nitrogen monoxide NO by dihydrogen H 2 and carbon dioxide CO

[0084] NO + 2CO + H2O + 1 / 2H2 +2 CO2

[0085] Oxidation of ammonia NH3 to dinitrogen N2

[0086] NH3 + 3 / 4 v^i^N2 + 3 / 2 H2O

[0087] Oxidation of ammonia NH3 to nitrous oxide N2O

[0088] NH3 + v2j / 2 N2O + 3 / 2 H2O

[0089] Oxidation of ammonia NH3 to nitrogen oxide NO

[0090] NH^ + 514 V^N() + 3^ HO

[0091] Adsorption reaction of ammonia NH3 in an ammonia adsorption site noted as

[0092] NH^ + as ^NH3_as

[0093] Desorption reaction of ammoniaNH3 from an ammonia adsorption site noted as

[0094] NH3_as V^NH3 + as

[0095] In this set of reactions the reactants NO, CO, CHr, H2 and O2 are in the gaseous state.

[0096] A mole balance is then carried out in the catalyst for nitrogen oxide NO, ammonia NH3 and adsorbed ammonia NH3_as by considering their rates of

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] [OUI]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117] formation ou de consommation : [Eq. 5] = Qin • XNO„, - Qmü • XNOmu - Vi - v2 " " v4 - v5 + V8 [Eq. 6] = Qin ' " Qout • Xnh\,u, + V4 + v5 - V6 - ' 7 ’ E8 - V9 + vio [Eq. 7] d7~ - V9~ V10 Avec : v^mol / s] = Vol-f^, Qj-[NOrtCO v^mol / s] = Vol ■ f2(T, Q) • [VOrtCH / 2 v (mol / s] = Vol • f3(T, Q) • [NO[%:e2o / ' vjmol / s] = Vol - f4(T, Q) - [NOrtH^ v(mol / s] = Vol • f^T, Q) • [NOr5[CO]p5 v^mol / s] = Vol ■ f6{T, Q) ■ [NHj^oJ6 v^mol / s] = Vol • f / T, Q) • (NH3r7[O2f7 vjmol / s] = Vol • fg(T, Q) • [NH3rto2f8 vjmol / s] - Vol ’ f^T, Q) • [NHjW9 v3C[mol / s] = Vol • f 10(T, Q) • [NH^asf10 * aio et , / ij0 : des coefficients The internal temperature of the catalyst T and the exhaust gas flow rate Q through the catalyst are determined, i.e. either measured or estimated by an electronic control unit of the motor vehicle, and are subsequently considered as input data. In a theoretical approach such as presented above, it is necessary to calibrate as many two-dimensional functions, y, as there are reactions considered. In the case presented above, ten two-dimensional functions are to be calibrated for the reactions affecting nitrogen monoxide NO and ammonia only. It is also necessary to estimate, in addition, the concentrations of the rest of the reactants involved in each of the reactions identified above (here carbon monoxide CO, hydrocarbons CHr, cesium oxide Ce2O3, dihydrogen H2 and dioxygen O2) which will in turn be determined via new reactive schemes tionals. In addition, it is necessary to determine the parameters (i,, for each of these new reactions.

[0118] It thus appears that the determination and calibration of an exact model taking into account all of the reactions affecting the concentration of nitrogen monoxide NO and ammonia becomes very complex.

[0119] Indeed, there are many more functions to calibrate than observed phenomena (i.e. the production of nitrogen monoxide NO and ammonia NH3 at the outlet of the catalyst in the system considered here) and different solutions would be possible, all correctly adjusting the experimental results, but without the certainty that one of them correctly describes the physical and chemical phenomena involved.

[0120] Furthermore, 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.

[0121] In the method detailed below, a certain number of hypotheses will be made in order to resolve these two problems and to arrive at a solution which is both easy to calibrate and to embed in a computer.

[0122] 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 internal combustion engine and at least one first three-way catalyst, and for which it is sought to estimate the quantities emitted of nitrogen monoxide NO and ammonia NH3. Nevertheless, it will be understood that the teaching below can be applied to other chemical reactions.

[0123] The system is considered homogeneous in space, that is to say that the temperature and the concentrations are the same at all points of the system considered. In other words, the model is a 0D model. The molar fractions inside and at the exit of the system are identical and it is therefore possible to write:

[0124] [Eq. 8]

[0125] . Xn()^ _ , x^o _ _ V5 +

[0126] [Eq. 9] [0!27] . Xnh^ - Qou! ■ XNH} + v4 + v5 - v6 - v7 - v8 - v9 + v10

[0128] [Eq. 10]

[0129] _ dt -19'' 10

[0130] With XNO and XNH^ the molar fractions at the output of the system that we are seeking to determine.

[0131] 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

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139]

[0140] the one at the exit: [Eq.n]e,„«e,„=e Based on these assumptions, equations [Eq. 8] to [Eq. 10] are written: [Eq. 12] Q ■ XNOi„ - Q - XNO - h - v2 - V3 - v4 - v5 + v8 = 0 [Eq. 13] Q • Xnh^ -QXNh3 + v4 + v5 - v6 - v7 - v8 - v9 + vi 0 = 0 [Eq. 14] dnNH-,^ dt '" ~ ^9-^f0 The dynamics of the gas-phase species have been disrupted, which has the effect of changing their balance equations from differential equations to algebraic equations.

[0141] By definition, the concentration of species A is written:

[0142] [Eq. 15]

[0143] [41- 11A - xdn L^J “ flight “ Flight

[0144] With XA the molar fraction of species A in all the species present in the catalyst, and n the total quantity of species in the catalyst, in moles

[0145] For species in the gas phase, the ideal gas law is applied.

[0146] [Eq. 16]

[0147] P.Vol — nRT

[0148] We can then reformulate the equation [Eq. 15] as follows:

[0149] [Eq. 17]

[0150] [a\—xapI(rT)

[0151] By neglecting the effect of pressure variations in the reaction rates (i.e. by considering P substantially constant) in a new generic function gpT, Q), we can write the following equations:

[0152] [Eq. 18] [0!53] v[mol / s] = Vol-g(T,Q)-XA% /

[0154] with v: the reaction rate for a two-reactant reaction in gas form

[0155] [Eq. 19] [01561 v[mol / S] = Vol-g^Qj-X / f^ /

[0157] with v: the reaction rate for a reaction comprising a single reactant in gas form.

[0158] For each reaction rate, only the dependence on a single gaseous reactant is retained, the one considered to be limiting. The other reactant is not taken into account.

[0159]

[0160]

[0161]

[0162]

[0163]

[0164]

[0165]

[0166]

[0167]

[0168]

[0169]

[0170]

[0171]

[0172]

[0173]

[0174]

[0175]

[0176]

[0177] if it is also in the gaseous state or if it is considered in excess. We then reformulate equations [Eq. 18] and [Eq. 19] as follows: [Eq. 20] vfmol / s] = Vol • g(T, Q) • XA® with v: the reaction rate for a two-reactant reaction in gas form [Eq. 21] v[mol / s] = Vol with v: the reaction rate for a reaction involving a single reactant in gas form. Returning to the case of estimating the quantities of nitric oxide NO and ammonia NH3 produced, nitric oxide NO and ammonia NH3 will be considered limiting species. Carbon monoxide CO, hydrocarbons CH^, dihydrogen H2, dioxygen O2, cesium oxide Ce2O3 and adsorption sites as will be considered excess species. The reaction rates defined in relation to equations [Eq. 5] to [Eq. 7] are reformulated as follows: v{mol / s] - Vol • Q) • Xnok1 vjmol / s] = Vol • g^T, Q) • XNO“2 v(mol / s] = Vol • g3(T, Q) • v^niol / s] = Vol ■ g^T, Q) • XNO“5 v^mol / s] = Vol • g6(T, Q) - Vol-g^XQ^^f10 More precisely, carbon monoxide CO, hydrocarbons CHr, dihydrogen H2 and caesium oxide Ce2O3 are in excess if the richness of the fuel / air mixture is greater than 1. Conversely, dioxygen O2 will be considered in excess if the richness is less than 1. The assumptions made above will be valid or not depending on the richness value. However, for a spark ignition engine, generally regulated to richness equal to 1, the overestimations and underestimations of the model will be compensated through its calibration (for given regulation characteristics).

[0178] The powers a of the gaseous reactants in equations [Eq. 20] and [Eq. 21] are considered equal to unity in all reaction rates and the equations can be rewritten as follows:

[0179] [Eq. 22]

[0180] v[mol / s] = Vol ■ g(T, Q) • XA

[0181] with v: the reaction rate for a two-reactant reaction in gas form

[0182] [Eq. 23] 101831 ^nol / s] = Vol-g(TQ)

[0184] with v: the reaction rate for a reaction comprising a single reactant in gas form.

[0185] The combination of equations [Eq. 12] to [Eq. 23] makes it possible to write the balance equations in a linear form with regard to the mole fractions X, which can be obtained explicitly, and therefore without the need for an iterative calculation, making it possible to use a calculation step 100 to 1000 times larger in iterative simulations by exact model, with a negligible loss in precision.

[0186] Applied to the determination of the quantities of nitrogen monoxide NO and ammonia ïV773, we then obtain the following equations:

[0187] [Eq. 24]

[0188] 0 - Q ■ XNOin - Q - XNO- Vol • gc^ T,Q)- XNO + Vol ■ gp^o(T, Q) ■ X^

[0189] [Eq. 25]

[0190]

[0191] [Eq. 26]

[0192] ( . v —ü— — Vol ' g (T, Q) ■ - Vol • g, (T. Q ) ■ ( ) dt °a_NH-o 7 3 ad_NHg' ■ J \ yoi y

[0193] With:

[0194] a_d_NH3 ; Desorption power of ammonia NH3

[0195] [Eq. 27] Ur Q) = «V, g) + gp-, q) + gp-, q) + g4(r, q) + gpr, q)

[0196] Reactions consuming NO

[0197] [Eq. 28] 101981 e) = gV- e)

[0199] Reactions producing NO

[0200] [Eq. 29] 102011 &™,(re)= g6(.T,Q)+ gl(T,Q)+ gs(T,Q}+ g^Q)

[0202] Reactions consuming NH3

[0203] [Eq. 30] 102041 e) = 4T- e)+ e)

[0205] Reactions producing NH3

[0206] [Eq. 31] 102071

[0208] NH3 adsorption reaction

[0209] [Eq. 32] [ozæi «*,,(re)- sw(Te)

[0211] NH3 desorption reactions

[0212] The initial system contained ten two-dimensional functions to be calibrated (fi to f10). The new system includes only six, noted gc-NiT &p_NO' ^c_NH^ &p_NH£ ^a_NH^ ^d_NHy

[0213] Additionally, the mole fractions XNO and can be isolated from the first two equations and obtained explicitly.

[0214] Adsorption phenomena are considered immediate: any species A entering the system is stored instantly. Instead of calibrating an adsorption rate and a desorption rate, only the desorption rate is taken into account. account.

[0215] For the present case, ammoniaNH3 can be adsorbed:

[0216] [Eq. 33]

[0217] v9 = Q-Xnh,

[0218] [Eq. 34]

[0219] Q = Q.XNOin-Q-XNO-Vol-gc^(^

[0220] [Eq. 35]

[0221] 0 = .Q.+ Vol. j Q) .xNo_ Vof.g^T, e) • ÀW + Volgd_N^ Q) ■ )al°

[0222] [Eq. 36]

[0223] dnNfi . . / x «10 -^ = Q-XNHim-Vo^^

[0224] The system is thus reduced to five functions to be calibrated, noted gcJW' 8p_NCF Sp-NHJ Sd_NHr

[0225] The following assumptions apply to the specific case of nitrogen monoxide NO and ammonia NH3 emissions. The choice of these assumptions was made in response to purely empirical or simplification criteria.

[0226] The oxidation of ammonia NH3 to nitrogen monoxide NO is neglected. The reaction rate v8 is then considered zero. This makes it possible to make the balance equation nitric oxide NO independent of the molar fraction of ammonia NH3. Equations [Eq. 34] to [Eq. 36] are rewritten as follows.

[0227] [Eq. 37]

[0228] 0 = 2 • XNOht - Q • XNO-Vol • gcNO{ T, Q) • XNO

[0229] [Eq. 38]

[0230] 0= .Q.xNH}+Vol.gp^(T, Q).XNO-Vobgc^(T, Qj-X^Vol-g^T, Q) ■

[0231]

[0232] [Eq. 39] ^ = Q.XxH!_.Vol.gjjjHST,Q)

[0233] This implies that the molar fractions of nitric oxide NO and ammonia NH3 can be written as follows:

[0234]

[0235] [Eq. 40] Ano “ Q+Volgc^

[0236]

[0237] [Eq. 41] &-Volgc,^TQ)

[0238]

[0239] [Eq. 42] = Q ' - Vol ■ Sdm

[0240] In order to simplify the calibration, the coefficient can be considered equal to unity. The set of equations [Eq. 40] to [Eq. 42] can be rewritten as follows:

[0241]

[0242] [Eq. 43] y 6¾¾ NO

[0243]

[0244] [Eq. 44] _ V7^'%h ( T,Q)XNO+gJxH ( NH3~ Q+Vel-g^bQ)

[0245]

[0246] [Eq. 45] ~~ÏT = Q • Xnh -gd {T,Q)- hm! l* » Ut i\ Il ' MV

[0247]

[0248]

[0249] Empirically, we set: [Eq. 46] Q) ~ 8c_NO_t( T} ' Sc_^O_q{ Q)

[0250] This simplification is based on experience, in fact the function g? ( Q) acts by modulating the function g T( T).Thus, for low flow rates, we ag^ no ô) — t ruais its value decreases as the flow rate becomes . important.

[0251] This transforms a two-dimensional function into two one-dimensional functions, easier to calibrate and with less risk of extrapolation.

[0252] Empirically, we pose:

[0253] [Eq. 47] [°254i

[0255] Indeed, experimentally, at iso-temperature, we observe a variation of the function proportional to the flow rate which passes through the catalyst.

[0256] Equations [Eq. 43] and [Eq. 45] can then be rewritten as follows:

[0257] [Eq. 48]

[0258] y _________________

[0259] [Eq. 49]

[0260]

[0261] At this stage, we have the set of equations [Eq. 44], [Eq. 48] and [Eq. 49] in order to determine the production of nitrogen monoxide NO and ammonia NH^ at the outlet of a catalyst. However, depending on the placement of a catalyst, other simplifications can be made.

[0262] In a three-way catalyst downstream of the internal combustion engine, the adsorption / desorption phenomena of ammonia NH3 are not considered. Indeed, a catalyst thus arranged in the exhaust line, close to the engine, is subject to a fairly rapid rise in temperature.

[0263] The value nNH'ias is then zero and it is then possible to rewrite the equation [Eq. 44] as follows:

[0264] [Eq. 50]

[0265] _ ^spNH(t,q)-xno ' Q+Vol-gf. ^

[0266] Then, by combining equations [Eq. 50] and [Eq. 48], we obtain:

[0267] [Eq. 51]

[0268] _ q NH^ ' Ql-Volg^T'jg^Q) ' NO™

[0269] In such a catalyst any dependence on the flow rate Q in the previous expression can be neglected. We can then rewrite the equation [Eq. 51] as follows:

[0270] [Eq. 52]

[0271] XNHi_^gp„m(T)-XmK

[0272] The function Q iyA thus combines the formation function of ammonia NH3 and the (^cjvH,) function of oxidation of ammonia NH3 into a single function, simpler to calibrate. It can be seen as a "net" production rate of ammonia NH3.

[0273] At this stage, equation [Eq. 52] makes it possible to determine the production of ammonia at the outlet of the catalyst. The quantity of nitrogen monoxide at the outlet of this same catalyst is determined using equation [Eq. 48].

[0274] In many cases, a second catalyst is provided in the exhaust line, downstream of the internal combustion engine and a first catalyst, in order to increase the efficiency of treatment of the various pollutants of the engine.

[0275] In such a second catalyst, the formation and oxidation of ammonia NH3 are neglected. Indeed, either the first catalyst is already initiated and therefore the second will lack nitrogen monoxide NO to form ammonia NH3, or the first catalyst is still cold and the second catalyst will be even colder, which will prevent it from forming ammonia NH3,

[0276] Only the adsorption / desorption phenomena will be considered in this second catalyst:

[0277] [Eq. 53]

[0278] f tX ~ q — q — ' nNH3_as

[0279] 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 the few resources required, make this process an ideal candidate for application in the context of on-board OBM monitoring in a Euro 7 standardized vehicle.

[0280] The physical approach used in this invention is advantageous compared to other statistical or machine learning approaches due to its explainability and the need for fewer tests (generally quite expensive) for its calibration. Indeed, the contribution of theory to the model makes it possible to better predict the response of the system in areas where there would be less learning data. The field of use of the system is better covered.

[0281] Finally, the simplifications made to the model facilitate the calibration task with negligible loss of precision.

[0282] The steps of the estimation method are notably executed by a calculation means, included in the on-board electronic computer of the vehicle or in a specific computer. The computer comprises in all cases at least one processor, a memory and means of communication with the rest of the vehicle and notably the sensors and estimation means, via a wired network, notably of the CAN type or a wireless network.

[0283] The estimation method illustrated by the figure [Fig. 1] comprises four steps main ones.

[0284] A first step 1 of measurement and estimation.

[0285] A second step 2 of estimating the emissions at the output of the internal combustion engine.

[0286] A third step 3 of estimating the emissions at the outlet of at least one first catalyst.

[0287] A fourth step 4 of estimating the emissions at the outlet of a second catalyst.

[0288] Nitrogen oxides NOX are formed at very high temperatures in the combustion chamber, when the oxygen O2 in the ambient air is able to react with nitrogen N2. For a spark-ignition engine, this mainly involves the formation of nitrogen monoxide NO, but which can then be transformed into nitrogen dioxide NO2 with the ozone O3 in the ambient air.

[0289] Ammonia is not formed in the engine but in the catalyst, 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.

[0290] The concentration of nitrogen oxides NOX at the engine outlet (in ppm) is determined as a function of the torque estimated by the computer. This function can be given in the form of 1D maps.

[0291] Other variants are possible by also considering the dependence on the rotational speed of the internal combustion engine via 2D maps, which are then a function of the estimated torque and the rotational speed.

[0292] Alternatively, a 1D or 2D map may be provided for each combustion mode designated by MEA actuation information.

[0293] The MEA activation information is information indicating in which phase of catalyst heating the vehicle is located.

[0294] Indeed, a three-way type pollution control catalyst must be heated to reach a threshold temperature from which it has a predetermined minimum treatment efficiency. This temperature is generally reached by degrading the combustion efficiency of the engine, for example by delayed fuel injection.

[0295] Nevertheless, the increase in temperature thus generated being significant, and the degradation of the combustion efficiency being significant, this heating phase cannot be maintained indefinitely. There then appears a cycling between several operating phases of the internal combustion engine. The active phase is thus indicated by the MEA actuation information.

[0296] Taking into account other variables, such as the partial recirculation rate of EGR exhaust gas or richness 1, which are taken into account partly via the engine operating point (rotation speed / load), the combustion mode (for a given engine setting) or the characteristics of their regulation, is therefore not necessary.

[0297] In the application case described here, an Id mapping dependent on the estimated torque is preferred. Indeed, such a 1D mapping is simpler to calibrate, reduces the risk of extrapolation of the model and makes it possible to maintain sufficient cycle accuracy.

[0298] The nitrogen oxides NOX generated by the internal combustion engine are admitted into the first catalyst in order to reduce them.

[0299] The reduction achieved is not complete, and nitrogen oxides NOX are still present at the outlet of the first catalyst. The residual nitrogen oxides NOX and the ammonia NH3 generated in the latter are then possibly admitted into a second catalyst. This second catalyst then achieves a reduction of the residual nitrogen oxides NOX.

[0300] The method for estimating the quantities of nitrogen monoxide NO and ammonia NH3 in the polluting emissions of a vehicle equipped with a spark-ignition internal combustion engine and an exhaust line with at least one first three-way catalyst according to the invention comprises the steps presented further below.

[0301] In a particular case, the internal combustion engine may also have other particularities, in particular a partial recirculation circuit of the exhaust gases at the intake, called an EGR circuit (English acronym for “Exhaust Gas Recirculation”).

[0302] 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 three-way catalyst is illustrated by figure [Fig.l] and comprises the following steps:

[0303] During a first step 1, the temperature in the first catalyst, the flow rate in the first catalyst, and the torque of the internal combustion engine are measured or estimated.

[0304] During a second step 2, the molar fraction of nitrogen monoxide in the gases leaving the internal combustion engine is determined, by applying a map which is a function of the estimated torque of the engine forming a first map.

[0305] During a third step 3, the molar fraction of nitrogen monoxide in the gases leaving the first catalyst, arranged downstream of the internal combustion engine, is determined by applying the equation [Eq.48], depending on the molar fraction of nitrogen monoxide produced by the engine, the flow rate and the volume of the first catalyst, as well as a 1D map (fîc_NO_f) depending on the temperature in the first catalyst forming a second map, and a 1D map ( "c_no_q) depending on the flow rate in the first catalyst forming a third map. The molar fraction of ammonia in the gases leaving the first catalyst is also determined by applying equation [Eq. 51], a function of a 1D map (SPnNH^ depending on the temperature in the first catalyst and the molar fraction of nitrogen monoxide in the gases admitted, equal to the molar fraction of nitrogen monoxide in the gases emitted by the internal combustion engine. Said 1D map (SPnNH^) forms a fourth map.

[0306] When the motor vehicle is equipped with a second three-way catalyst upstream of the first three-way catalyst, the method continues with a fourth step 4.

[0307] During this fourth step 4, the molar fraction of ammonia in the gases leaving the second catalyst is determined by applying equation [Eq.53], a function of a 1D map (Sd_NHcf) depending on the temperature in the second catalyst and the number of moles of adsorbed ammonia, the value of which is obtained by integrating equation [Eq. 49]. Said 1D map (nh^t) forms a fifth map.

[0308] The molar fraction of nitrogen monoxide in the gases leaving the second catalyst is determined by applying the equation [Eq. 48], depending on the molar fraction of nitrogen monoxide in the gases leaving the first catalyst, the flow rate and the volume of the second catalyst, as well as a 1D map fîcjwj) dependent on the temperature in the second catalyst forming a sixth map and a 1D map ^c_no_q) dependent on the flow rate in the second catalyst forming a seventh map.

[0309] The model ([Eq.48], [Eq. 49], [Eq. 52] and [Eq. 53]) makes it possible to describe in a simplified but reliable manner the generation and catalysis of pollutant emissions in a motor vehicle equipped with a spark-ignition internal combustion engine and at least one first three-way catalyst, and where appropriate (frequently) equipped with a second three-way catalyst.

[0310] In order to use this model, the following functions must be calibrated:

[0311] - the 1D mapping as a function of the estimated engine torque or the 2D mapping function of engine rotation speed and estimated engine torque, giving the molar fraction of NOX at engine output, by combustion mode and by fuel type,

[0312] - the functions involved in determining the molar fraction of NOX in output of each catalyst ([Eq. 48]),

[0313] - the functions involved in determining the number of moles of adsorbed NH3 ([Eq. 49]),

[0314] - the functions involved in determining the mole fraction of the en output of the first catalyst ([Eq. 52]), and

[0315] - the functions involved in determining the molar fraction of NH3 in output of the second catalyst (if present) ([Eq. 53]).

[0316] In other words, a map (1D or 2D) is to be calibrated for the NOX emissions at the engine outlet in addition to the maps used to determine the NOX and NH3 emissions at the outlet of the catalysts gc NO gpnjjH and

[0317] To carry out this calibration, dynamic tests are carried out covering the combustion modes, the engine field (rotation speed / torque), the flow rates and the temperatures in the at least one catalyst, likely to be observed during road use by the end customer.

[0318] To carry out such a calibration, the following acquisitions are carried out, in particular at an acquisition frequency of 10 Hz:

[0319] Engine output emissions: NOX

[0320] Emissions downstream first catalyst: NOx

[0321] Exhaust emissions: NOX, NH3

[0322] Internal temperatures in each catalyst

[0323] Estimated torque

[0324] MEA action information

[0325] Flow rate through each catalyst.

[0326] The model is calibrated for a given technical definition, catalyst aging status, ECU calibration, and ambient conditions (temperature, pressure, humidity).

[0327] Based on the acquisitions made, the calibration is broken down into three stages:

[0328] Calibration of the quantity of nitrogen oxides NOx at the engine outlet,

[0329] Calibration of the quantity of nitrogen oxides NOX and the quantity of ammonia at the outlet of the first catalyst, and

[0330] Calibration of the quantity of nitrogen oxides NOx and the quantity of ammonia NH3 at the outlet of the second catalyst (if present).

[0331] As seen above, the quantity of nitrogen oxides NOX generated by the engine can be determined based on a one-dimensional map depending on the estimated torque, or based on a two-dimensional map depending on the estimated torque and the rotational speed of the engine.

[0332] According to the embodiments, a 1D or 2D mapping is provided for each combustion mode of the engine indicated by the MEA activation information.

[0333] 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 case of the example application, the indicated engine torque. The breakdown of this map is quite fine, in particular with a step of 10 Nm for 1D mapping based on engine torque.

[0334] 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 type model, for which a learning process is carried out on the mapping measurements.

[0335] This is a static model calibrated on dynamic cycles, consequently the measurement of nitrogen oxides NOX at the engine output must be well synchronized in advance with the engine events used.

[0336] The expression obtained ([Eq. 48]) to calculate the molar fraction of nitrogen monoxide NO at the outlet of the catalyst is applied indifferently to each catalyst present. Only the origin and the 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 catalyst.

[0337] When equation [Eq. 48] is applied to the first catalyst, the value X^o^ corresponds to the molar fraction of NOX in the gases leaving the engine and calculated in the first step of the process and XNO is the molar fraction of NOX in the gases leaving the first catalyst.

[0338] In the present case, Q denotes the flow rate passing through the first catalyst (including the low pressure EGR if necessary), T the internal temperature of the first catalyst (homogeneous if a 0D model has been considered) and Vol the volume of the first catalyst.

[0339] The functions gw T) and gc NO q(Q) 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.

[0340] The function gw (T) can be adjusted independently of the function g^ no for small flow rates, the function g^ Q) taking a value equal to 1 in such cases.

[0341] For large flow rates, the function g^ ( (7) takes values ​​lower than 1, in order to account for efficiency losses in the treatment of nitrogen oxides NOX.

[0342] The molar fraction of ammonia NH3 leaving the first catalyst is given by the equation [Eq. 52] in which Xwoin represents the molar fraction of nitrogen oxides NOX leaving the engine, calculated in the first step and Xnh^i represents the molar fraction of ammonia NH3 leaving the first catalyst.

[0343] The ^pn_NH. function is determined by bench measurements. This function presents an increase in value as the temperature increases up to a maximum and then a decrease in amplitude as the temperature continues to increase until it becomes zero. This accounts for the mechanisms of ammonia formation and then ammonia oxidation at high temperature.

[0344] The molar fraction of nitrogen monoxide NO at the outlet of the second catalyst is calculated with an expression similar to that used for the first catalyst ([Eq. 48]) modified to take into account the gases coming from the first catalyst:

[0345] [Eq. 54]

[0346] y =________________________ NO-2 Q_2^V0l_2-gcJ.OJ,_7(T_2).gc_NO_2_Q(Q_2)

[0347] The variables are:

[0348] : molar fraction of nitrogen oxides NOX leaving the first catalyst

[0349] Q_2: flow rate through the second catalyst

[0350] T_2: internal temperature of the second catalyst

[0351] Vol_2: volume of the second catalyst

[0352] XNO2: molar fraction of nitrogen oxides NOX at the outlet of the second catalyst

[0353] The method for calibrating the functions g T_2) and g 2 ( Q_2 ) for the second catalyst is identical to that used to calibrate the functions 8c_no_t( T) and %c_no_q( Ô) for the first catalyst.

[0354] The production of ammonia NH3 in the second catalyst only takes into account the adsorption and desorption phenomena. In the model, two equations ([Eq. 49] and [Eq. 53]) had been deduced to obtain the number of moles of ammonia NH3 stored and the fraction of ammonia NH3 at the outlet of the catalyst. These equations are adapted to take into account the admitted gases coming from the first catalyst:

[0355] [Eq. 55]

[0356] XA,7 / ;i_2 — gd T_2) ■ n^H^as

[0357] [Eq. 56]

[0358] ±^=Q_2.X^-Q_2-gd^

[0359] Where:

[0360] Xnh^: molar fraction of NH3 leaving the first catalyst and calculated in the previous step.

[0361] ^NH3_as ; number of moles of NH3 stored in the second catalyst.

[0362] : molar fraction of NH3 at the outlet of the second catalyst.

[0363] The function is determined from values ​​measured on the bench. It has a zero value until the temperature reaches a predetermined value. completed accounting for the storage by adsorption of ammonia, then an increase accounting for the release by desorption of the stored ammonia.

[0364] This function is very sensitive to temperature, its calibration is important in order to be precise during the first moments of driving when the catalyst is cold, while the NOXNH3 measurement sensor has not yet reached operating temperature and the adsorption / desorption phenomena are present.

[0365] 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

Claims

1. Method for estimating the quantity of polluting species in the exhaust gases of a motor vehicle equipped with an internal combustion engine and at least one first three-way catalyst, the estimation method making it possible to estimate the quantity of polluting species in the exhaust gases, in particular before a possible concentration sensor is sufficiently hot to carry out measurements, the method comprising the following steps: a. the chemical reactions involved in the first three-way catalyst having as reactant or product the polluting species whose quantity in the exhaust gases must be estimated are identified, b. the reaction rates of each identified chemical reaction are determined, c. a mass balance is carried out in the first 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 based on the mass balance.

2. An 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 catalyst, the flow rate in the first catalyst, and the torque of the internal combustion engine are determined, b. the molar fraction of nitrogen monoxide in the gases leaving the internal combustion engine is determined by applying an initial map based on the estimated engine torque, c. the molar fraction of nitrogen oxides in the gases leaving the first catalyst, located downstream of the internal combustion engine, is determined as a function of the molar fraction of nitrogen monoxide produced by the engine, the flow rate in the first catalyst and the volume of the first catalyst, as well as a second 1D map dependent on the temperature. temperature in the first catalyst and a third 1D map dependent on the flow rate in the first catalyst, d. the molar fraction of ammonia in the gases leaving the first catalyst is also determined, as a function of a fourth 1D map dependent on the temperature in the first catalyst and the molar fraction of nitrogen oxides in the gases emitted by the internal combustion engine.

3. Estimation method according to claim 2, wherein, when the motor vehicle is equipped with a second three-way catalyst upstream of the first three-way catalyst, the method comprises the following steps: a. determining the molar fraction of ammonia in the gases leaving a second catalyst, as a function of a fifth 1D map dependent on the temperature in the second catalyst and as a function of the value of the number of ammonia adsorption sites, b. determining the molar fraction of nitrogen monoxide in the gases leaving the second catalyst as a function of the molar fraction of nitrogen monoxide in the gases leaving the first catalyst, the flow rate in the second catalyst and the volume of the second catalyst, as well as a sixth 1D map dependent on the temperature in the second catalyst and a seventh 1D map dependent on the flow rate in the second catalyst.

4. Estimation method according to claim 2 or 3, in which the maps are calibrated according to measurements made during tests.

5. Estimation method according to claim 1, wherein the pollutant species are carbon dioxide CO2, carbon monoxide CO, hydrocarbons HC, ammonia, nitrogen monoxide NO, nitrogen dioxide NO2 or nitrous oxide N2O.

6. Motor vehicle equipped with an estimation system configured so as to carry out the estimation method according to any one of claims 1 to 5, in particular within an on-board diagnosis.

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