EP1815118B1 - Device and method for determination of the quantity of nox emitted by a diesel engine in a motor vehicle and diagnostic and engine management system comprising such a device - Google Patents

Abstract

The invention relates to a device for determination of the quantity of NOx emitted by a diesel engine ( 10 ) in a motor vehicle with common-rail fuel supply means ( 12 ) for the cylinders thereof, of the type comprising pressure recording means ( 32 ) in at least one cylinder of the engine and means ( 50 ), for determining the mass fraction of oxygen in the mixture admitted into the cylinder. Said device comprises means ( 58, 68 ), for determining a temperature of the flame front on combustion of the mixture, means ( 52 ), for determining the mass of fuel burnt in the cylinder and means ( 70 ), for calculating the quantity of NOx emitted by the combustion of the mixture in the cylinder as a function of the recorded pressure, the mass fraction of oxygen in the mixture, the temperature of the flame front and the mass of fuel burnt.

Description

The present invention relates to a device for determining the amount of NOx emitted by a motor vehicle diesel engine associated with common rail fuel supply means for the cylinders thereof, of the type comprising means for acquiring the fuel. pressure in at least one cylinder of the engine and means for determining the oxygen mass fraction of the mixture admitted into the cylinder.

The invention also relates to systems for diagnosing and monitoring the operation of the engine using such a device.

The amount of nitrogen oxides, or NOx, emitted by a diesel engine is an important factor in the operation thereof.

Indeed, the emission of NOx, which are polluting molecules, must be minimized. For this purpose, the amount of fuel and the air flow injected into the cylinders are determined to minimize the formation of NOx during the combustion of the mixture in the cylinders.

The engine is also generally associated with depollution means arranged in the exhaust line thereof, such as for example a NOx trap, and the operation of the engine is then controlled to optimize the operation of the pollution control means. The engine can thus be controlled according to several modes of operation by changing the quantities of fuel and air injected into the cylinders. For example, the engine can run in rich mode for regeneration of the NOx trap.

A bad adjustment of the engine, due for example to the aging of the injectors and / or the cylinders, has the effect of increasing the emission of NOx. Thus, the amount of NOx emitted by a diesel engine is representative of the state of operation of the engine.

Accurate knowledge of the amount of NOx emitted by the engine optimizes the operation of the engine, as well as the amount of pollutant released into the atmosphere by the vehicle.

Devices for determining the amount of NOx emitted by a motor vehicle diesel engine associated with common roll feed means thereof use the engine control values to determine the amount of NOx emitted, such as example of injection maps, and / or air flow EGR maps if the engine is associated with an exhaust gas recirculation loop (EGR).

However, such systems are not based on the actual characteristics of the engine operation but on predetermined setting values at the factory.

However, the characteristics of the engine evolve over time due to the aging of its organs, such as its injectors and cylinders. Thus, in case of significant drift of these characteristics, the amount of NOx determined can be highly erroneous.

Other systems for determining the amount of NOx emitted by a diesel engine determines the average temperature of the ignited mixture in the cylinders to deduce a quantity of NOx at steady state and consequently the mass of NOx emitted per cycle. engine by the engine.

However, under certain conditions, the results returned by such systems have a relatively low accuracy and such systems do not make it possible to calculate the amount of NOx at each instant of the combustion phase of the engine cylinders.

The object of the present invention is to solve the aforementioned problem by proposing a device for determining the amount of NOx emitted by a diesel engine which is precise, low in computation time and which determines in real time the amount of NOx emitted by engine.

• des moyens de détermination d'une température du front de flamme lors de la combustion du mélange admis dans le cylindre ;
• des moyens de détermination de la masse de carburant brûlée dans le cylindre ;
• des moyens de calcul de la quantité de NOx émise par la combustion du mélange dans le cylindre en fonction de la pression acquise, de la fraction massique en oxygène du mélange, de la température du front de flamme et de la masse de carburant brûlée déterminées.

For this purpose, the subject of the invention is a device for determining the amount of NOx emitted by a motor vehicle diesel engine associated with common rail fuel supply means for the cylinders thereof, of the type comprising means for acquiring the pressure in at least one cylinder of the engine and means for determining the oxygen mass fraction of the mixture admitted into the cylinder, characterized in that it comprises

• means for determining a temperature of the flame front during combustion of the mixture admitted into the cylinder;
• means for determining the mass of fuel burned in the cylinder;
• means for calculating the amount of NOx emitted by the combustion of the mixture in the cylinder as a function of the pressure acquired, the oxygen mass fraction of the mixture, the temperature of the flame front and the mass of burned fuel determined.

• les moyens de détermination de la masse de carburant brûlée dans le cylindre comprennent des moyens de détermination de la quantité instantanée de chaleur dégagée lors de la combustion du mélange admis dans le cylindre et des moyens de détermination de la masse instantanée de carburant brûlée dans le cylindres en fonction de cette dernière et du potentiel calorifique du carburant injecté dans le cylindre ;
• les moyens de détermination de la quantité instantanée de chaleur dégagée lors de la combustion du mélange sont adaptés pour déterminer celle-ci à partir du premier principe de la thermodynamique en fonction de l'angle vilebrequin du cylindre et de la pression dans celui-ci ;
• les moyens de détermination de la température du front de flamme comprennent des moyens de détermination de la température du mélange admis non brûlé pendant la combustion de celui-ci et des moyens de détermination de la température du front de flamme dans le cylindre en fonction de cette température du mélange admis non brûlé ;
• les moyens de détermination de la température du mélange admis non brûlé pendant la combustion de celui-ci sont adaptés pour déterminer celle-ci à partir d'un modèle thermodynamique de compression isentropique selon la relation : $${\mathrm{T}}_{\mathrm{nb}}\mathrm{=}{\mathrm{T}}_{\mathrm{nb}}^{\mathrm{0}}{\left(\frac{{\mathrm{P}}^{\mathrm{nb}}}{{\mathrm{P}}^{\mathrm{0}}}\right)}^{\frac{\mathrm{k}}{\mathrm{k}\mathrm{-}\mathrm{1}}}$$
  

où T_nb et P^nb sont respectivement la température du mélange admis non brûlé et la pression correspondante dans le cylindre pendant la combustion du mélange,

et P⁰ sont respectivement une température et une pression de référence du mélange admis dans le cylindre à un instant prédéterminé avant le début de la combustion du mélange admis, et k est un coefficient polytropique prédéterminé ;

• il comprend des moyens de détermination de la quantité instantanée de chaleur dégagée lors de la combustion du mélange admis dans le cylindre et des moyens de détermination de l'instant du début de la combustion du mélange admis propres à comparer la quantité instantanée de chaleur déterminée à une valeur seuil prédéterminée et à déterminer l'instant de début de la combustion lorsque la quantité instantanée de chaleur déterminée est supérieure à la valeur seuil ;
• les moyens de détermination de la température du mélange admis pendant la combustion de celui-ci comprennent :
  • des moyens de détermination du nombre de moles du mélange admis dans le cylindre ; et
  • des moyens de détermination de la température T⁰ _nb de référence à partir d'un modèle thermodynamique du mélange admis en fonction du nombre de moles du mélange admis et de la pression P⁰ dans les cylindres à l'instant prédéterminé avant le début de combustion ;
• les moyens de détermination de la température
  
  de référence sont adaptés pour déterminer celle-ci selon la relation : $${\mathrm{T}}_{\mathrm{nb}}^{\mathrm{0}}\mathrm{=}\frac{{\mathrm{P}}^{\mathrm{0}}\mathrm{\times }{\mathrm{V}}^{\mathrm{0}}}{\mathrm{n}\mathrm{\times }\mathrm{R}}$$
  
• les moyens de détermination de la température du front de flamme sont adaptés pour déterminer une température adiabatique théorique du front de flamme ;
• les moyens de détermination de la température adiabatique du front de flamme sont adaptés pour déterminer celle-ci à partir d'un modèle thermodynamique de conservation de l'enthalpie des réactifs et des produits de la combustion du mélange admis dans le cylindre en fonction de la température du mélange admis non brûlé pendant la combustion de celui-ci et de la fraction massique en oxygène de celui-ci ;
• le modèle thermodynamique de conservation de l'enthalpie est un modèle polynomial du premier ou du second ordre ;
• le modèle polynomial est un modèle selon la relation : $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{c}}_{\mathrm{1}}\mathrm{+}{\mathrm{c}}_{\mathrm{2}}\mathrm{\times }\mathrm{Tnb}\mathrm{+}{\mathrm{c}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}$$
  

où T_ad est la température adiabatique du front de flamme, XO₂ est la fraction massique en oxygène du mélange, et c₁, c₂ et c₃ sont des coefficients prédéterminés ;

• le modèle polynomial est un modèle selon la relation : $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{c}}_{\mathrm{1}}\mathrm{+}{\mathrm{c}}_{\mathrm{2}}\mathrm{\times }\mathrm{Tnb}\mathrm{+}{\mathrm{c}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}\mathrm{+}{\mathrm{c}}_{\mathrm{4}}\mathrm{\times }\mathrm{P}$$
  

où T_ad est la température adiabatique du front de flamme, XO₂ est la fraction massique en oxygène du mélange, P est la pression dans le cylindre, et c₁, c₂, c₃, c₄ sont des coefficients prédéterminés ;

• le modèle polynomial est un modèle selon la relation : $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{c}}_{\mathrm{1}}\mathrm{+}{\mathrm{c}}_{\mathrm{2}}\mathrm{\times }{\mathrm{T}}_{\mathrm{nb}}\mathrm{+}{\mathrm{c}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}\mathrm{+}{\mathrm{c}}_{\mathrm{4}}\mathrm{\times }\mathrm{P}\mathrm{+}{\mathrm{<figure-callout\; id="5"\; label="c"\; filenames="imgf0003.png"\; state="\{\{state\}\}">c</figure-callout>}}_{\mathrm{5}}\mathrm{\times }{{\mathrm{XO}}_{\mathrm{2}}}^{\mathrm{2}}$$
  

où T_ad est la température adiabatique du front de flamme, XO₂ est la fraction massique en oxygène du mélange, P est la pression dans le cylindre, et c₁, c₂, c₃, c₄ et c₅ sont des coefficients prédéterminés ;

• les moyens de détermination de la quantité de NOx émise par la combustion du mélange admis dans le cylindre sont adaptés pour déterminer celle-ci à partir d'un modèle chimique de production de NOx lors de la combustion du mélange dans le cylindre ; et
• le modèle chimique est un modèle selon la relation: $${\mathrm{Q}}_{\mathrm{NOx}}\mathrm{=}\frac{\ln \mathrm{\left(}\mathrm{P}\mathrm{\right)}\mathrm{+}\mathrm{1}}{\mathrm{b}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}}\mathrm{\times }\exp \mathrm{\left(}\frac{{\mathrm{T}}_{\mathrm{ad}}\mathrm{-}\mathrm{c}}{\mathrm{d}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}}\mathrm{\right)}\mathrm{\times }\frac{\mathrm{MCB}}{\mathrm{MCI}}$$
  

où Q_NOx est la quantité instantanée de NOx émise par le moteur, P est la pression dans le cylindre, T_ad est la température adiabatique du front de flamme dans le cylindre, XO₂ est la fraction massique en oxygène -du mélange admis dans le cylindre, MCB est la masse instantanée de carburant brûlé dans le cylindre, MCl est la masse de carburant injectée dans le cylindre, et b, c et d sont des paramètres prédéterminés.According to particular embodiments, the aforementioned device comprises at least one of the following features:

• the means for determining the mass of fuel burned in the cylinder comprise means for determining the instantaneous quantity of heat released during the combustion of the mixture admitted into the cylinder and means for determining the instantaneous mass of fuel burned in the cylinders depending on the latter and the heating potential of the fuel injected into the cylinder;
• the means for determining the instantaneous amount of heat released during the combustion of the mixture are adapted to determine it from the first principle of thermodynamics as a function of the crankshaft angle of the cylinder and the pressure therein;
• the means for determining the temperature of the flame front comprise means for determining the temperature of the admitted unburned mixture during the combustion thereof and means for determining the temperature of the flame front in the cylinder according to this permitted unburnt mixture temperature;
• the means for determining the temperature of the unburned admixed mixture during the combustion thereof are adapted to determine it from a thermodynamic model of isentropic compression according to the relation: $${\mathrm{T}}_{\mathrm{nb}}\mathrm{=}{\mathrm{T}}_{\mathrm{nb}}^{\mathrm{0}}{\left(\frac{{\mathrm{P}}^{\mathrm{nb}}}{{\mathrm{P}}^{\mathrm{0}}}\right)}^{\frac{\mathrm{k}}{\mathrm{k}\mathrm{-}\mathrm{1}}}$$
  

where T _nb and P ^nb are respectively the temperature of the unburned admitted mixture and the corresponding pressure in the cylinder during the combustion of the mixture,

and P ⁰ are respectively a temperature and a reference pressure of the mixture admitted into the cylinder at a predetermined time before the start of the combustion of the admitted mixture, and k is a predetermined polytropic coefficient;

• it comprises means for determining the instantaneous quantity of heat released during the combustion of the mixture admitted into the cylinder and means for determining the instant of the beginning of the combustion of the admitted mixture suitable for comparing the instantaneous quantity of heat determined at a predetermined threshold value and determining the start time of the combustion when the instantaneous amount of heat determined is greater than the threshold value;
• the means for determining the temperature of the mixture admitted during combustion thereof comprise:
  • means for determining the number of moles of the mixture admitted into the cylinder; and
  • means for determining the reference temperature T ⁰ _nb from a thermodynamic model of the admitted mixture as a function of the number of moles of the admitted mixture and the pressure P ⁰ in the cylinders at the predetermined time before the start of combustion ;
• the means for determining the temperature
  
  of reference are adapted to determine it according to the relation: $${\mathrm{T}}_{\mathrm{nb}}^{\mathrm{0}}\mathrm{=}\frac{{\mathrm{P}}^{\mathrm{0}}\mathrm{\times }{\mathrm{V}}^{\mathrm{0}}}{\mathrm{not}\mathrm{\times }\mathrm{R}}$$
  
• the means for determining the temperature of the flame front are adapted to determine a theoretical adiabatic temperature of the flame front;
• the means for determining the adiabatic temperature of the flame front are adapted to determine it from a thermodynamic model for the conservation of the enthalpy of the reagents and the products of the combustion of the admixture admitted into the cylinder as a function of the temperature of the admitted unburned mixture during the combustion thereof and the oxygen mass fraction thereof;
• the thermodynamic model of conservation of enthalpy is a polynomial model of the first or second order;
• the polynomial model is a model according to the relation: $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{vs}}_{\mathrm{1}}\mathrm{+}{\mathrm{vs}}_{\mathrm{2}}\mathrm{\times }\mathrm{Tnb}\mathrm{+}{\mathrm{vs}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}$$
  

where T _ad is the adiabatic temperature of the flame front, XO ₂ is the oxygen mass fraction of the mixture, and c ₁ , c ₂ and c ₃ are predetermined coefficients;

• the polynomial model is a model according to the relation: $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{vs}}_{\mathrm{1}}\mathrm{+}{\mathrm{vs}}_{\mathrm{2}}\mathrm{\times }\mathrm{Tnb}\mathrm{+}{\mathrm{vs}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}\mathrm{+}{\mathrm{vs}}_{\mathrm{4}}\mathrm{\times }\mathrm{P}$$
  

where T _ad is the adiabatic temperature of the flame front, XO ₂ is the oxygen mass fraction of the mixture, P is the pressure in the cylinder, and c ₁ , c ₂ , c ₃ , c ₄ are predetermined coefficients;

• the polynomial model is a model according to the relation: $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{vs}}_{\mathrm{1}}\mathrm{+}{\mathrm{vs}}_{\mathrm{2}}\mathrm{\times }{\mathrm{T}}_{\mathrm{nb}}\mathrm{+}{\mathrm{vs}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}\mathrm{+}{\mathrm{vs}}_{\mathrm{4}}\mathrm{\times }\mathrm{P}\mathrm{+}{\mathrm{vs}}_{\mathrm{5}}\mathrm{\times }{{\mathrm{XO}}_{\mathrm{2}}}^{\mathrm{2}}$$
  

where T _ad is the adiabatic temperature of the flame front, XO ₂ is the oxygen mass fraction of the mixture, P is the pressure in the cylinder, and c ₁ , c ₂ , c ₃ , c ₄ and c ₅ are predetermined coefficients ;

• the means for determining the amount of NOx emitted by the combustion of the mixture admitted into the cylinder are adapted to determine it from a chemical model of NOx production during the combustion of the mixture in the cylinder; and
• the chemical model is a model according to the relation: $${\mathrm{Q}}_{\mathrm{NOx}}\mathrm{=}\frac{\ln \mathrm{\left(}\mathrm{P}\mathrm{\right)}\mathrm{+}\mathrm{1}}{\mathrm{b}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}}\mathrm{\times }\exp \mathrm{\left(}\frac{{\mathrm{T}}_{\mathrm{ad}}\mathrm{-}\mathrm{vs}}{\mathrm{d}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}}\mathrm{\right)}\mathrm{\times }\frac{\mathrm{MCB}}{\mathrm{MCI}}$$
  

where Q _NOx is the instantaneous quantity of NOx emitted by the engine, P is the pressure in the cylinder, T _ad is the adiabatic temperature of the flame front in the cylinder, XO ₂ is the oxygen mass fraction of the mixture admitted into the cylinder. cylinder, MCB is the instant mass of fuel burned in the cylinder, MCl is the mass of fuel injected into the cylinder, and b, c and d are predetermined parameters.

• détermination de la température du front de flamme lors de la combustion du mélange admis dans le cylindre ;
• détermination de la masse de carburant brûlée dans le cylindre ; et
• de calcul de la quantité de NOx émise par la combustion du mélange dans le cylindre en fonction de la pression acquise, de la fraction massique en oxygène du mélange, de la température du front de flamme et de la masse de carburant brûlée déterminées.

The subject of the invention is also a method for determining the amount of NOx emitted by a motor vehicle diesel engine comprising common rail fuel supply means for the cylinders thereof, of the type comprising an acquisition step. the pressure in at least one cylinder of the engine, and a step of determining the oxygen mass fraction of the mixture admitted into the cylinder, characterized in that it comprises a step of:

• determination of the temperature of the flame front during combustion of the mixture admitted into the cylinder;
• determining the mass of fuel burned in the cylinder; and
• for calculating the amount of NOx emitted by the combustion of the mixture in the cylinder as a function of the pressure acquired, the oxygen mass fraction of the mixture, the temperature of the flame front and the mass of fuel burned determined.

The subject of the invention is also a system for diagnosing malfunction of a motor vehicle diesel engine, characterized in that it comprises a device of the aforementioned type, means for comparing the quantity of NOx emitted at a predetermined threshold and means for triggering an alarm when the amount of NOx is greater than this threshold.

The invention also relates to a system for controlling the operation of a motor vehicle diesel engine associated with NOx depollution means arranged in an exhaust line thereof, characterized in that it comprises a device of the aforementioned type, means for calculating the amount of NOx stored in the depollution means as a function of the amount of NOx determined by the device and control means, as a function of the amount of NOx stored, of the operation of the engine for pilot the operation of the means of depollution.

The invention also relates to a system for controlling the operation of a motor vehicle diesel engine, characterized in that it comprises a device of the aforementioned type and adjustment means adapted to adjust the operation of the supply means according to the quantity of NOx emitted determined to correct drifts of the operation thereof.

According to another characteristic, this system is characterized in that the engine is associated with means for recirculating part of the exhaust gas at the inlet thereof, and in that the adjustment means are furthermore adapted to adjust the operation of the recirculation means as a function of the quantity of NOx emitted determined, to correct drifts of the operation of the supply means and / or recirculation.

• la figure 1 est une vue schématique d'une unité de propulsion à moteur Diesel d'un véhicule automobile associé à un dispositif selon l'invention.
• la figure 2 est une vue schématique plus en détail du dispositif selon l'invention ;
• la figure 3 est un organigramme du fonctionnement du dispositif selon l'invention ; et
• la figure 4 est un graphique de résultats renvoyés par le dispositif selon l'invention lors d'une campagne de test.

The present invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the accompanying drawings, in which:

• the figure 1 is a schematic view of a diesel engine propulsion unit of a motor vehicle associated with a device according to the invention.
• the figure 2 is a schematic view in more detail of the device according to the invention;
• the figure 3 is a flowchart of the operation of the device according to the invention; and
• the figure 4 is a graph of results returned by the device according to the invention during a test campaign.

On the figure 1 a diesel engine 10 of a motor vehicle is associated with means 12 with common rail for supplying fuel to its cylinders, for example comprising a common supply rail delivering fuel under high pressure to controlled injectors suitable for injection into the engine 10 engine cylinders in the form of multiple injections for example.

The engine 10 is also associated with a loop 14 for recirculating part of the exhaust gas, or EGR, at the inlet thereof. The recirculation loop 14 comprises a bypass line 16 of an exhaust line 18 of the engine 10. This bypass line 16 is capable of taking exhaust gases at the outlet of the engine 10 and delivering them to means 20 for admitting air / exhaust gas mixture at the inlet of the Engine 10. These intake means 20 also receive air from an air inlet 22 and deliver to the engine 10 an air / exhaust gas mixture.

For the purpose of treatment of pollutant emissions from the engine 10, and in particular the emission of nitrogen oxides, or NOx, means 24 of pollution control are arranged in the exhaust line 18. The means 24 of depollution comprise by for example a NOx trap adapted to store NOx and destock them in a non-polluting form for their discharge into the atmosphere.

In a conventional manner, the operation of the motor and of the components which have just been described is controlled by a unit 30 for controlling the operation of the engine.

The unit 30 is connected to means 32 for acquiring (i) the pressure in each cylinder of the engine, comprising for example a piezoelectric deformation sensor arranged in the cylinder head adapted to measure the pressure of the combustion chamber of the (ii) the engine speed, comprising for example a speed sensor, (iii) the desired engine torque by the driver of the vehicle, comprising, for example, a sensor of the position of the accelerator pedal of the vehicle, and iv) the motor angle, comprising for example a hall effect sensor arranged on the motor shaft.

The unit 30 is also connected to means 34 for acquiring the air flow at the engine inlet, for example a flow meter arranged in the air inlet 22 of the intake means 20.

The unit 30 is adapted to determine injection instructions for the feed means 12, in particular a pilot injection set point and a main injection set point for each cylinder and for each engine cycle, as a function of the speed, the torque and the crankshaft angle of the cylinder, the latter being determined by the unit 30 as a function of the engine angle acquired.

The unit 30 also determines, for the engine cycle, an airflow EGR setpoint for the intake means 20 as a function of the speed, the torque and the crankshaft angle of the cylinder.

The unit 30 is also adapted to implement a strategy for controlling the operation of the means 24 of depollution in controlling the phasing and / or the quantity of fuel injected into the cylinders in order to control the storage / retrieval states of the depollution means 24.

The engine 10 is associated with a device according to the invention for determining the amount of NOx emitted by it. This device determines such an amount based on the amount of admixture burned into the combustion chamber of each cylinder during the propagation therein of a flame front, the admitted mixture in a cylinder being defined as the sum quantities of fresh air, exhaust gas and fuel admitted into the cylinder.

In the example shown on the figure 1 this device is implemented by a subunit 36 of the unit 30. In another variant, the device can also be implemented by a dedicated information processing unit.

It will now be described, in relation to the figures 2 and 3 , the arrangement and the operation of the device for determining the amount of NOx emitted by the engine 10.

The amount of NOx emitted by the engine is determined according to a chemical model of the production of NOx during the combustion of the mixture admitted into a cylinder of the engine. This model has the variable oxygen mass fraction XO ₂ of the mixture admitted into the cylinder, the instantaneous mass MCB of fuel burned in the cylinder, the pressure P in the cylinder and a theoretical temperature Tad of the flame front propagating in the chamber. the combustion of the cylinder, and preferably, a theoretical adiabatic temperature of the flame front, as will be explained in more detail later.

The device for determining the amount of NOx emitted by the engine 10 comprises means 50 for determining the oxygen mass fraction XO ₂ of the admitted mixture to be burned in the cylinder during a motor cycle. These means 50 receive as input the acquired airflow DA and the TEGR rate of recycled exhaust gas at the engine inlet.

The TEGR rate of the recycled exhaust gas is determined by the unit 30 as a function of the airflow DA acquired and the operating point of the motor, for example from a predetermined map stored in the unit 30.

The means 50 also receive the total amount MCI of fuel injected into the cylinder for the engine cycle and are adapted to determine the richness of the mixture admitted according to it, as is known per se. This MCI quantity is determined by the unit 30 as a function of the injection instructions delivered to the supply means 12, for example by summing up the quantities of fuel injected into the cylinder for the engine cycle.

The means 50 for determining the oxygen mass fraction XO ₂ of the mixture then determine it as a function of the richness of the admitted mixture and the TEGR rate determined on the basis of a combustion balance of the admitted mixture, the mass fraction of the mixture. oxygen XO ₂ admitted being classically directly proportional to the richness and the rate of EGR, as is known per se in the state of the art

The device according to the invention also comprises means 52 for determining the instantaneous quantity MCB of fuel burned in the cylinder during the engine cycle.

où dα est une variation prédéterminée de l'angle vilebrequin a du cylindre, dQ est la quantité de chaleur instantanée dégagée par la combustion du mélange pendant la variation dα de l'angle vilebrequin, V et P sont le volume de la chambre de combustion et la pression dans celle-ci à l'instant de début de la variation dα de l'angle vilebrequin respectivement, dV et dP sont les variations du volume de la chambre de combustion et de la pression dans celle-ci correspondant à la variation dα de l'angle vilebrequin respectivement, et k un coefficient polytropique prédéterminé.For this purpose, the means 52 comprise means 54 for determining the instantaneous amount of heat released by the combustion of the mixture in the cylinder during the combustion phase of the cycle thereof. This determination is made as a function of the acquired pressure P in the combustion chamber of the cylinder and the crankshaft angle α of the cylinder, from the first principle of thermodynamics, according to the relation: $$\frac{\mathrm{dQ}}{\mathrm{d\alpha }}\mathrm{=}\frac{\mathrm{1}}{\mathrm{k}\mathrm{-}\mathrm{1}}\mathrm{\times }\left(\mathrm{V}\mathrm{\times }\frac{\mathrm{dP}}{\mathrm{d\alpha }}\mathrm{-}\mathrm{k}\mathrm{\times }\mathrm{P}\mathrm{\times }\frac{\mathrm{dV}}{\mathrm{d\alpha }}\right)$$

where dα is a predetermined variation of the crankshaft angle α of the cylinder, dQ is the amount of instantaneous heat released by the combustion of the mixture during the variation dα of the crankshaft angle, V and P are the volume of the combustion chamber and the pressure in it at the moment of beginning of the variation dα of the crankshaft angle respectively, dV and dP are the variations of the volume of the combustion chamber and the pressure in the this one corresponding to the variation dα of the crank angle respectively, and k a predetermined polytropic coefficient.

This quantity of heat dQ determined is delivered to means 56 for determining the amount of fuel burned corresponding. The means 56 are able to determine this amount of fuel by dividing the amount of heat dQ by the value of the mass energy content of the fuel used in the engine, or PCI for lower heat potential (in J / kg). The value PCI is for example mapped in the means 56.

The device according to the invention also comprises means 58 for determining the temperature T _nb of the admitted _unburnt mixture at a moment after the start of the combustion of the mixture in the cylinder. This temperature T _nb of the admitted unburned mixture is calculated by making a hypothesis of isentropic compression of the admitted unburned mixture since a moment before the start of the combustion. This temperature T _nb of the admitted unburned mixture is then used for the determination of the theoretical adiabatic temperature T _ad of the flame front propagating inside the combustion chamber of the cylinder, as will be explained in more detail later. .

The means 58 for determining the temperature T _nb comprise means 60 for determining the number of moles n of the admitted mixture present in the combustion chamber of the cylinder before the start of the combustion as a function of the air flow DA acquired, the rate TEGR of recycled exhaust gas at the engine inlet and the total amount of fuel injected MCI into the cylinder.

du mélange admis à un instant prédéterminé avant le début de la combustion dans le cylindre, par exemple correspondant à un angle vilebrequin α⁰ compris dans la plage d'angles vilebrequin [-60° ; -20°] avant le point mort haut (PMH) du cycle du cylindre.The number n of moles is then delivered to means 62 for determining the temperature

admitted mixture at a predetermined time before the start of combustion in the cylinder, for example corresponding to a crankshaft angle α ⁰ included in the crankshaft angle range [-60 °; -20 °] before the top dead center (TDC) of the cylinder cycle.

The detection of the instant of the start of combustion of the mixture is carried out by means 64 for comparing the instantaneous quantity dQ of heat released by the combustion of the admitted mixture, determined by the means 54, at a predetermined threshold.

When the quantity of heat reaches this threshold value, the beginning of the combustion of the admitted mixture is detected and the calculation of the temperature T _nb of the admitted unburned mixture during the combustion is started.

en considérant le mélange admis comme un gaz parfait selon la relation : $${\mathrm{T}}_{\mathrm{nb}}^{\mathrm{0}}\mathrm{=}\frac{{\mathrm{P}}^{\mathrm{0}}\mathrm{\times }{\mathrm{V}}^{\mathrm{0}}}{\mathrm{n}\mathrm{\times }\mathrm{R}}$$

où V⁰ et P⁰ sont le volume de la chambre de combustion et la pression dans celle-ci à l'instant prédéterminé avant le début de combustion du mélange admis, et R est la constante des gaz parfaits.The means 62 then determine the temperature

considering the mixture admitted as a perfect gas according to the relation: $${\mathrm{T}}_{\mathrm{nb}}^{\mathrm{0}}\mathrm{=}\frac{{\mathrm{P}}^{\mathrm{0}}\mathrm{\times }{\mathrm{V}}^{\mathrm{0}}}{\mathrm{not}\mathrm{\times }\mathrm{R}}$$

where V ⁰ and P ⁰ are the volume of the combustion chamber and the pressure therein at the predetermined time before the start of combustion of the admitted mixture, and R is the ideal gas constant.

The values of V ⁰ and P ⁰ are for example stored in the means 62 following the last acquisition of the pressure P in the cylinder for the crankshaft angle α ⁰ included in the range of crankshaft angles [-60 ° ; - 20 °] before the top dead center of the cylinder cycle, the crankshaft angle α ⁰ corresponding to the volume V ⁰ of the combustion chamber of the cylinder.

et la pression P⁰ avant le début de combustion sont délivrées comme température et pression de référence à des moyens 66 de détermination de la température T_nb du mélange admis non brûlé pendant la combustion, c'est-à-dire lors de la propagation du front de flamme dans la chambre de combustion du cylindre. Les moyens 66 déterminent cette dernière à partir d'un modèle thermodynamique de compression isentropique de la phase de compression du cycle du cylindre selon la relation : $${\mathrm{T}}_{\mathrm{nb}}\mathrm{=}{\mathrm{T}}_{\mathrm{nb}}^{\mathrm{0}}{\left(\frac{{\mathrm{P}}^{\mathrm{nb}}}{{\mathrm{P}}^{\mathrm{0}}}\right)}^{\frac{\mathrm{k}}{\mathrm{k}\mathrm{-}\mathrm{1}}}$$

Temperature

and the pressure P ⁰ before the start of combustion are delivered as a temperature and a reference pressure to means 66 for determining the temperature T _nb of the admitted unburned mixture during the combustion, that is to say during the propagation of the flame front in the cylinder combustion chamber. The means 66 determine the latter from a thermodynamic model of isentropic compression of the compression phase of the cylinder cycle according to the relation: $${\mathrm{T}}_{\mathrm{nb}}\mathrm{=}{\mathrm{T}}_{\mathrm{nb}}^{\mathrm{0}}{\left(\frac{{\mathrm{P}}^{\mathrm{nb}}}{{\mathrm{P}}^{\mathrm{0}}}\right)}^{\frac{\mathrm{k}}{\mathrm{k}\mathrm{-}\mathrm{1}}}$$

The means 66 determine the temperature T _nb continuously for a period of time corresponding to the combustion of the mixture admitted into the cylinder. This period corresponds for example to the range of crank angle [0; 120 °] after TDC if the engine load is partial
or the range [-15; 120 °] with respect to the TDC if the engine load is substantially maximum.

The determined temperature T _nb is delivered to means 68 for determining the adiabatic temperature T _ad of the flame front during the combustion of the mixture admitted into the combustion chamber of the cylinder.

où H_initial est l'enthalpie du mélange admis avant l'instant de début de combustion de celui-ci et H_final est l'enthalpie admis des gaz brûlés issus de la combustion du mélange admis par le front de flamme.These determine the temperature T _ad from a thermodynamic model of conservation of the enthalpy of the reagents and products of the combustion of the mixture according to the relation: $${\mathrm{H}}_{\mathrm{initial}}\mathrm{(}\mathrm{P}\mathrm{,}{\mathrm{T}}_{\mathrm{nb}}\mathrm{,}{\mathrm{XO}}_{\mathrm{2}}\mathrm{)}\mathrm{=}{\mathrm{H}}_{\mathrm{final}}\left(\mathrm{P},,{\mathrm{T}}_{\mathrm{ad}},,{\mathrm{XO}}_{\mathrm{2}}\right)$$

where H _initial is the enthalpy of the admitted mixture before the combustion start time of the latter and _final H is the admitted enthalpy of the flue gases resulting from the combustion of the mixture admitted by the flame front.

où c₁, c₂ et c₃ sont des coefficients prédéterminés.Advantageously, this enthalpy conservation model is approximated by a polynomial model, the adiabatic temperature T _ad of the flame front being determined by the means 68 according to the relationship: $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{vs}}_{\mathrm{1}}\mathrm{+}{\mathrm{vs}}_{\mathrm{2}}\mathrm{\times }\mathrm{Tnb}\mathrm{+}{\mathrm{vs}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}$$

where c ₁ , c ₂ and c ₃ are predetermined coefficients.

The correlation between the adiabatic temperature determined according to equation (5) and an adiabatic temperature determined from a complex model thereof based on equation (4) has a correlation coefficient R ² substantially equal to 99.43. %.

où c₁, c₂, c₃, c₄ sont des coefficients prédéterminés.In another embodiment, the means 68 also receive as input the pressure P measured in the combustion chamber of the cylinder and determine the adiabatic temperature of the flame front according to the relation: $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{vs}}_{\mathrm{1}}\mathrm{+}{\mathrm{vs}}_{\mathrm{2}}\mathrm{\times }{\mathrm{T}}_{\mathrm{nb}}\mathrm{+}{\mathrm{vs}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}\mathrm{+}{\mathrm{vs}}_{\mathrm{4}}\mathrm{\times }\mathrm{P}$$

where c ₁ , c ₂ , c ₃ , c ₄ are predetermined coefficients.

The introduction of the pressure P into the cylinder in relation (6) makes it possible to obtain a coefficient R ² substantially equal to 99.5%.

où c₁, c₂, c₃, c₄ et c₅ sont des coefficients prédéterminés.In another embodiment, the means 68 also receive as input the pressure P measured in the combustion chamber of the cylinder and determine the adiabatic temperature of the flame front according to the relation: $${\mathit{T}}_{\mathit{ad}}\mathit{=}{\mathit{vs}}_1\mathit{+}{\mathit{vs}}_2\mathit{\times }{\mathit{T}}_{\mathit{nb}}\mathit{+}{\mathit{vs}}_3\mathit{\times }{\mathit{XO}}_2\mathit{+}{\mathit{vs}}_4\mathit{\times }\mathit{P}\mathit{+}{\mathit{vs}}_5\mathit{\times }{{\mathit{XO}}_2}^2$$

where c ₁ , c ₂ , c ₃ , c ₄ and c ₅ are predetermined coefficients.

The introduction of the square of the mass fraction XO ₂ in relation (7) makes it possible to obtain a coefficient R ² substantially equal to 99.97%.

Thus, the means 68 determine the _ad adabatic temperature of the flame front in a simple and inexpensive way in computing time, while determining it reliably.

où Q_NOx est la quantité instantanée de NOx émise par la combustion du mélange admis dans le cylindre en gramme par kilogramme de carburant injecté dans le cylindre par degré vilebrequin, et b, c et d sont des paramètres prédéterminés.Finally, the device according to the invention comprises means 70 for calculating the instantaneous quantity of NOx emitted by the combustion of the mixture admitted into the cylinder as a function of the pressure P in it, of the adiabatic temperature T _ad of the front of the cylinder. flame, .of the oxygen mass fraction XO ₂ of the mixture and the instantaneous mass MCB of burned fuel. This calculation is made from a chemical model of NOx production in the predetermined cylinder, for example according to the relation: $${\mathrm{Q}}_{\mathrm{NOx}}\mathrm{=}\frac{\ln \mathrm{\left(}\mathrm{P}\mathrm{\right)}\mathrm{+}\mathrm{1}}{\mathrm{b}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}}\mathrm{\times }\exp \mathrm{\left(}\frac{{\mathrm{T}}_{\mathrm{ad}}\mathrm{-}\mathrm{vs}}{\mathrm{d}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}}\mathrm{\right)}\mathrm{\times }\frac{\mathrm{MCB}}{\mathrm{MCI}}$$

where Q _NOx is the instantaneous amount of NOx emitted from the combustion of the admixture admitted into the cylinder in grams per kilogram of fuel injected into the cylinder per crankshaft degree, and b, c and d are predetermined parameters.

Due to the time difference between the combustion phases in the cylinders that never take place simultaneously, the instantaneous quantity _{NO x} of NOx produced during the combustion of the mixture in the cylinder is therefore substantially equal to that emitted by the engine 10.

The figure 3 is a flowchart of the operation of the device for determining the amount of NOx emitted by the motor just described.

Successively at the start of the vehicle, the operation consists of 50 to select the reference i of the cylinder in which the next combustion mixture takes place.

Then, at 52, the total fuel mass MCI, the air flow DA and the EGR rate injected TEGR in this cylinder i are determined.

A next step 54 then consists in determining, as a function of the values determined at 52, the richness of the admitted mixture and then the oxygen mass fraction XO ₂ of the mixture admitted into the cylinder i.

The operation of the device according to the invention then consists in determining the instantaneous quantity of heat released by the combustion of the mixture admitted into cylinder i according to equation (1) and comparing it, at 58, with the value detection threshold of the instant of start of combustion of the mixture.

As long as this instant is not detected, that is to say as long as the quantity dQ is below the detection threshold, process 58 loops on step 56.

du mélange à l'instant prédéterminé avant le début de combustion de celui-ci selon la relation-(2).If the combustion start time is detected at 58, a subsequent step 60 of the operation is a temperature determination step

mixing at the predetermined time before the start of combustion thereof according to the relation- (2).

Step 60 is then followed by a step 62 of determining the temperature T _nb of the admitted unburned mixture at a moment after the start of combustion according to equation (3). Step 62 is continued by determining the adiabatic temperature T _ad of the flame front according to relation (5) as a function of the temperature T _nb of the admitted unburned mixture, of the oxygen mass fraction XO ₂ of the mixture, and the pressure P of the cylinder i if the relation (6) or the relation (7) is used.

The instantaneous mass MCB of fuel burned in the cylinder i is then determined at 64 as a function of the amount of heat determined previously, as described above.

The operation then continues with a step 66 of determining the instantaneous quantity _{NO x} of NOx emitted by the combustion of the mixture in the cylinder i according to equation (8).

Following the determination of the quantity Q _NOx , a test is carried out at 68 to know if the combustion of the mixture in the cylinder i is complete, for example by testing whether the instantaneous quantity of heat dQ determined is less than a second predetermined threshold value.

If the result of this test is positive, step 68 then loops on step 50 for the choice of a new cylinder i.

If the result of this test is negative, a new instantaneous quantity of heat dQ is determined at 70.

Step 70 then loops on step 62 for the determination of a new instantaneous quantity _NOx of NOx emitted by the combustion of the mixture in the cylinder i at a moment following the combustion, by the implementation of the steps 62 , 64 and 66.

The device according to the invention implements a determination algorithm requiring a small sum of calculations, while allowing the determination of the amount of NOx emitted by the engine in real time and instantaneously, that is to say including at each moment of the combustion phase of the cylinder.

Other embodiments of the device according to the invention are possible.

For example, in a variant, the device comprises a chain for acquiring the pressure in a single cylinder of the engine and the device is able to determine the quantity of NOx emitted by the combustion of the mixture admitted into this cylinder and to multiply the amount of NOx determined by the number of cylinders of the engine to obtain the total amount of NOx emitted by the engine.

où N est le nombre de cylindres du moteur, afin d'obtenir la quantité de NOx totale émise par le moteur.Alternatively, the device comprises a pressure acquisition chain in any number of cylinders of the engine, and is able to determine the amount of NOx emitted by these systems and to multiply the latter by $\frac{\mathrm{NOT}}{\mathrm{not}},$

where N is the number of cylinders of the engine, in order to obtain the total amount of NOx emitted by the engine.

The figure 4 illustrates the accuracy of the determination of the amount of NOx emitted the engine implemented by the device according to the invention. On the abscissa, it is represented, for different operating points of a test diesel engine, the amount of NOx determined using a model. complex physical production of NOx, and the ordinate corresponding amounts obtained by the device according to the invention.

The device according to the invention thus makes it possible in a simple way to obtain an important precision for a large operating range of the engine.

Thus, it is possible to use such a device in more complex systems for diagnosing and / or controlling the operation of the diesel engine 10 using information on the amount of NOx emitted by the engine.

A first system is a system for diagnosing the malfunction of the engine 10. In fact, if the emission of NOx is abnormally high, a malfunction of the engine 10 can be diagnosed.

The diagnostic system comprises for this purpose a device according to the invention which delivers the instantaneous amount of NOx emitted by the engine to means for comparing it to a predetermined threshold. Means for triggering an alarm receive the results of this comparison and trigger an alarm, for example the activation of an indicator light arranged on the dashboard of the vehicle, when the amount of NOx determined is greater than this threshold.

It is also possible to envisage a system controlling the operation of the diesel engine 10 for controlling the storage and retrieval states of the pollution control means 24 based on the amount of NOx emitted by the engine.

Such a system comprises for example a device for determining the amount of NOx emitted by the engine according to the invention delivering this amount to means for calculating the amount of NOx stored in the means 24 of depollution according to it .

The quantity of stored NOx determined is then delivered to means for comparing it to first and second predetermined thresholds. Means for triggering the regeneration of the depollution means 24 receive the result of this comparison and trigger the operation of the engine 10 in the regeneration mode of the depollution means 24 when the amount of NOx stored therein is greater than first threshold, and disable such a mode of operation of the engine 10 when the amount of NOx stored is less than the second threshold.

The regeneration of the depollution means is then triggered according to information that remains relevant throughout the life of the vehicle. The operation of the engine associated with the control of the means 24 of depollution is then optimized.

It is also possible to envisage a system for controlling the operation of the motor 10 comprising the device according to the invention and means for adjusting the operation of the means 12 for supplying the motor 10. The adjustment means are adapted to adjust the operation of the power supply means 12 as a function of the amount of NOx emitted determined by the device in order to correct drifts in the operation thereof. For example, the means for adjusting the feed means 12 are adapted to adjust the phasing and / or the quantities of fuel injected into the cylinders to minimize the emission of NOx by the engine 10.

The adjustment means may also be adapted to regulate the operation of the recirculation loop 14 as a function of the amount of NOx emitted by the engine 10 to correct drifts in the operation of the supply means 12 and / or the recirculation loop 14 so as to also to minimize NOx emission.

Claims (21)

1. Device for determining the amount of NOx emitted by a motor vehicle diesel engine (10) associated with means (12) with a common manifold for supplying fuel to the cylinders thereof, of the type comprising means (32) of acquiring the pressure in at least one cylinder of the engine and means (50) of determining the oxygen mass fraction of the mixture admitted into the cylinder, characterised in that it comprises

   - means (58, 68) of determining a temperature of the flame front during combustion of the mixture admitted into the cylinder;

   - means (52) of determining the mass of fuel burned in the cylinder; and

   - means (70) of calculating the amount of NOx emitted by combustion of the mixture in the cylinder according to the acquired pressure, the oxygen mass fraction of the mixture, the temperature of the flame front and the mass of burnt fuel which have been determined.
2. Device according to Claim 1, characterised in that the means (52) of determining the mass of fuel burned in the cylinder comprise means (54) of determining the instantaneous amount of heat given off during combustion of the mixture admitted into the cylinder and means (56) of determining the instantaneous mass of fuel burned in the cylinder according to the latter and the calorific potential of the fuel injected into the cylinder.
3. Device according to Claim 2, characterised in that the means (54) of determining the instantaneous amount of heat given off during combustion of the mixture are adapted to determine it using the first law of thermodynamics according to the crankshaft angle of the cylinder and the pressure therein.
4. Device according to any one of the preceding claims, characterised in that the means (58, 68) of determining the temperature of the flame front comprise means (58) of determining the temperature of the admitted mixture not burned during combustion thereof and means (68) of determining the temperature of the flame front in the cylinder according to this temperature of the unburned admitted mixture.
5. Device according to Claim 4, characterised in that the means (58) of determining the temperature of the admitted mixture not burned during combustion thereof are adapted to determine it using a thermodynamic model of isentropic compression according to the equation: $${\mathrm{T}}_{\mathrm{nb}}\mathrm{=}{\mathrm{T}}_{\mathrm{n}}^{\mathrm{0}}{\left(\frac{{\mathrm{P}}^{\mathrm{nb}}}{{\mathrm{R}}^0}\right)}^{\frac{\mathrm{k}}{\mathrm{k}\mathrm{-}\mathrm{1}}}$$

   

   
   where T_nb and P^nb are respectively the temperature of the unburned admitted mixture and the corresponding pressure in the cylinder during combustion of the mixture,

   

   and P⁰ are respectively a reference temperature and pressure of the admitted mixture in the cylinder at a predetermined instant before the start of combustion of the admitted mixture, and k is a predetermined polytropic coefficient.
6. Device according to Claim 4 or 5, characterised in that it comprises means (54) of determining the instantaneous amount of heat given off during combustion of the mixture admitted into the cylinder and means (64) of determining the instant of the start of combustion of the admitted mixture suitable for comparing the determined instantaneous amount of heat with a predetermined threshold value and for determining the instant of start of combustion when the determined instantaneous amount of heat is greater than the threshold value.
7. Device according to Claim 5 or 6, characterised in that the means (58) of determining the temperature of the admitted mixture during combustion thereof comprise;

   - means (60) of determining the number of moles of the mixture admitted into the cylinder; and

   - means (62) of determining the reference temperature

   

   using a thermodynamic model of the admitted mixture according to the number of moles of the admitted mixture and the pressure P⁰ in the cylinders at the predetermined instant before the start of combustion.
8. Device according to Claim 7, characterised in that the means (62) of determining the reference temperature

   

   are adapted to determine it according to the equation: $${\mathrm{T}}_{\mathrm{nb}}^{\mathrm{0}}\mathrm{=}\frac{{\mathrm{P}}^{\mathrm{0}}\mathrm{\times }{\mathrm{V}}^{\mathrm{0}}}{\mathrm{n}\mathrm{\times }\mathrm{R}}$$

   
9. Device according to any one of the preceding claims, characterised in that the means (58, 68) of determining the temperature of the flame front are adapted to determine a theoretical adiabatic temperature of the flame front.
10. Device according to any one of Claims 4 to 8 and Claim 9 taken together, characterised in that the means (68) of determining the adiabatic temperature of the flame front are adapted to determine it using a thermodynamic model of conservation of the enthalpy of the reagents and products of the combustion of the mixture admitted into the cylinder according to the temperature of the admitted mixture not burned during the combustion thereof and the oxygen mass fraction thereof.
11. Device according to Claim 10, characterised in that the thermodynamic model of conservation of enthalpy is a polynomial model of the first or second order.
12. Device according to Claim 11, characterised in that the polynomial model is a model according to the equation: $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{c}}_{\mathrm{1}}\mathrm{+}{\mathrm{c}}_{\mathrm{2}}\mathrm{\times }\mathrm{Tnb}\mathrm{+}{\mathrm{c}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}$$

    

    
    where T_ad is the adiabatic temperature of the flame front, XO₂ is the oxygen mass fraction of the mixture, and c₁, c₂ and c₃ are predetermined coefficients.
13. Device according to Claim 11, characterised in that the polynomial model is a model according to the equation: $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{c}}_{\mathrm{1}}\mathrm{+}{\mathrm{c}}_{\mathrm{2}}\mathrm{\times }{\mathrm{T}}_{\mathrm{nb}}\mathrm{+}{\mathrm{c}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}\mathrm{+}{\mathrm{c}}_{\mathrm{4}}\mathrm{\times }\mathrm{P}$$

    

    
    where T_ad is the adiabatic temperature of the flame front, XO₂ is the oxygen mass fraction of the mixture, P is the pressure in the cylinder, and c₁, c₂, c₃, c₄ are predetermined coefficients.
14. Device according to Claim 11, characterised in that the polynomial model is a model according to the equation: $${\mathrm{T}}_{\mathrm{ad}}\mathrm{=}{\mathrm{c}}_{\mathrm{1}}\mathrm{+}{\mathrm{c}}_{\mathrm{2}}\mathrm{\times }{\mathrm{T}}_{\mathrm{nb}}\mathrm{+}{\mathrm{c}}_{\mathrm{3}}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}\mathrm{+}{\mathrm{c}}_{\mathrm{4}}\mathrm{\times }\mathrm{P}\mathrm{+}{\mathrm{c}}_{\mathrm{5}}\mathrm{\times }{{\mathrm{XO}}_{\mathrm{2}}}^{\mathrm{2}}$$

    

    
    where T_ad is the adiabatic temperature of the flame front, XO₂ is the oxygen mass fraction of the mixture, P is the pressure in the cylinder, and c₁, c₂, c₃, c₄ and c₅ are predetermined coefficients.
15. Device according to any one of the preceding claims, characterised in that the means (70) of determining the amount of NOx emitted by combustion of the mixture admitted into the cylinder are adapted to determine it using a chemical model of NOx production during combustion of the mixture in the cylinder.
16. Device according to Claim 15 and Claim 9 taken together, characterised in that the chemical model is a model according to the equation: $${\mathrm{Q}}_{\mathrm{NOx}}\mathrm{=}\frac{\ln \mathrm{\left(}\mathrm{P}\mathrm{\right)}\mathrm{+}\mathrm{1}}{\mathrm{b}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}}\mathrm{\times }\exp \mathrm{\left(}\frac{{\mathrm{T}}_{\mathrm{ad}}\mathrm{-}\mathrm{c}}{\mathrm{d}\mathrm{\times }{\mathrm{XO}}_{\mathrm{2}}}\mathrm{\right)}\mathrm{\times }\frac{\mathrm{MCB}}{\mathrm{MCI}}$$

    

    
    where Q_NOx is the instantaneous amount of NOx emitted by the engine, P is the pressure in the cylinder, T_ad is the adiabatic temperature of the flame front in the cylinder, XO₂ is the oxygen mass fraction of the mixture admitted into the cylinder, MCB is the instantaneous mass of fuel burned in the cylinder, MCl is the mass of fuel injected into the cylinder, and b, c and d are predetermined parameters.
17. System for diagnosing the malfunctioning of a motor vehicle diesel engine, characterised in that it comprises a device in accordance with any one of the preceding claims, means of comparing the emitted amount of NOx with a predetermined threshold and means of activating an alarm when the amount of NOx is greater than this threshold.
18. System for controlling the operation of a motor vehicle diesel engine associated with means of NOx pollution control arranged in an exhaust line thereof, characterised in that it comprises a device in accordance with any one of Claims 1 to 16, means of calculating the amount of NOx stored in the pollution control means according to the amount of NOx determined by the device and means of controlling, according to the stored amount of NOx, the operation of the engine in order to control the operation of the pollution control means.
19. System for controlling the operation of a motor vehicle diesel engine, characterised in that it comprises a device in accordance with any one of Claims 1 to 16 and adjustment means adapted to adjust the operation of the supply means according to the emitted amount of NOx determined, in order to correct deviations in the operation thereof.
20. System according to Claim 19, characterised in that the engine is associated with means of recirculating some of the exhaust gases to the input thereof, and in that the adjustment means are moreover adapted to adjust the operation of the recirculation means according to the emitted amount of NOx determined, in order to correct deviations in the operation of the supply and/or recirculation means.
21. Method of determining the amount of NOx emitted by a motor vehicle diesel engine (10) comprising means (12) with a common manifold for supplying fuel to the cylinders thereof, of the type comprising a step of acquiring the pressure in at least one cylinder of the engine, and a step (54) of determining the oxygen mass fraction of the mixture admitted into the cylinder, characterised in that it comprises a step of:

    - determining (at 62) the temperature of the flame front during combustion of the mixture admitted into the cylinder;

    - determining (at 64) the mass of fuel burned in the cylinder; and

    - calculating (at 66) the amount of NOx emitted by combustion of the mixture in the cylinder according to the acquired pressure, the oxygen mass fraction of the mixture, the temperature of the flame front and the mass of burnt fuel which have been determined.

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