U.S. patent application number 11/720303 was filed with the patent office on 2008-01-17 for 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.
This patent application is currently assigned to PEUGEOT CITROEN AUTOMOBILES SA. Invention is credited to David Gimbres.
Application Number | 20080010973 11/720303 |
Document ID | / |
Family ID | 34951987 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080010973 |
Kind Code |
A1 |
Gimbres; David |
January 17, 2008 |
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
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.
Inventors: |
Gimbres; David; (La Queue en
Brie, FR) |
Correspondence
Address: |
NICOLAS E. SECKEL;Patent Attorney
1250 Connecticut Avenue, NW Suite 700
WASHINGTON
DC
20036
US
|
Assignee: |
PEUGEOT CITROEN AUTOMOBILES
SA
Route de Gisy
Velizy-Villacoublay
FR
78140
|
Family ID: |
34951987 |
Appl. No.: |
11/720303 |
Filed: |
November 25, 2005 |
PCT Filed: |
November 25, 2005 |
PCT NO: |
PCT/FR05/02941 |
371 Date: |
June 4, 2007 |
Current U.S.
Class: |
60/276 ;
73/23.31 |
Current CPC
Class: |
F02D 41/1462 20130101;
F02D 35/026 20130101; F02D 35/023 20130101; F02D 41/0275
20130101 |
Class at
Publication: |
060/276 ;
073/023.31 |
International
Class: |
F01N 11/00 20060101
F01N011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 26, 2004 |
FR |
0412597 |
Claims
1. Device for determining the amount of NOx emitted by a motor
vehicle diesel engine associated with common rail means for
supplying the engine cylinders with fuel, of the type comprising
means for acquisition of data concerning pressure in at least one
cylinder of the engine and means for determining the mass fraction
of oxygen in the intake mixture in the cylinder, wherein said
device includes means for determining a flame front temperature
during combustion of the intake mixture in the cylinder; means for
determining the mass of fuel burned in the cylinder; and means for
calculating the amount of NOx emitted by combustion of the mixture
in the cylinder as a function of the detected pressure and the
values determined for the mass fraction of oxygen in the mixture,
the flame front temperature and the mass of fuel burned.
2. Device according to claim 1, wherein the means for determining
the mass of fuel burned in the cylinder include means for
determining the instantaneous amount of heat released during
combustion of the intake mixture in the cylinder and means for
determining the instantaneous mass of fuel burned in the cylinders
as a function of this latter and of the calorific potential of the
fuel injected into the cylinder.
3. Device according to claim 2, wherein the means for determining
the instantaneous amount of heat released during combustion of the
mixture are adapted to determine this amount as a function of the
crank angle of the cylinder and of the pressure within the
cylinder, using the first law of thermodynamics.
4. Device according to claim 1 wherein the means for determining
the flame front temperature include means for determining the
temperature of the unburned intake mixture during combustion of
that mixture and means for determining the flame front temperature
in the cylinder as a function of that temperature of the unburned
intake mixture.
5. Device according to claim 4, wherein the means for determining
the temperature of the unburned intake mixture during combustion of
that mixture are adapted to do so using a thermodynamic model of
isentropic compression according to the equation: T nb = T nb 0 ( P
nb P 0 ) k k - 1 ##EQU9## where T.sub.nb and P.sup.nb are
respectively the temperature of the unburned intake mixture and the
corresponding pressure in the cylinder during combustion of the
mixture, T.sub.nb.sup.0 and P.sup.0 are respectively a reference
temperature and reference pressure of the intake mixture in the
cylinder at a predetermined moment before the start of combustion
of the intake mixture, and k is a predetermined polytropic
coefficient.
6. Device according to claim 4, which includes means for
determining the instantaneous amount of heat released during
combustion of the intake mixture in the cylinder and means for
determining the moment when combustion of the intake mixture starts
capable of comparing the determined instantaneous amount of heat
with a predetermined threshold value and of determining the moment
when combustion starts when the determined instantaneous amount of
heat exceeds the threshold value.
7. Device according to claim 5 wherein the means for determining
the temperature of the intake mixture during combustion of the
latter include: means for determining the number of moles of the
intake mixture in the cylinder; and means for determining the
reference temperature T.sub.nb.sup.0 as a function of the number of
moles of the intake mixture and the pressure P.sup.0 in the
cylinders at the predetermined moment before combustion starts,
based on a thermodynamic model of the intake mixture.
8. Device according to wherein the means for determining the
reference temperature T.sub.nb are adapted to do so according to
the equation: T nb 0 = P 0 .times. V 0 n .times. R ##EQU10##
9. Device according to claim 1 wherein the means for determining
the flame front temperature are adapted to determine a theoretical
adiabatic temperature of the flame front.
10. Device according to claim 4, wherein the means for determining
the flame front temperature are adapted to determine a theoretical
adiabatic temperature of the flame front, and the means for
determining the adiabatic temperature of the flame front are
adapted to determine it as a function of the temperature of the
unburned intake mixture during combustion of that mixture and the
mass fraction of oxygen in the intake mixture, based on a
thermodynamic model of conservation of the enthalpy of the reagents
and of the products of combustion of the intake mixture in the
cylinder.
11. Device according to claim 10, wherein the thermodynamic model
of conservation of enthalpy is a polynomial model of the first or
second order.
12. Device according to claim 11, wherein the polynomial model is a
model according to the equation:
T.sub.ad=c.sub.1+c.sub.2.times.T.sub.nb+c.sub.3.times.XO.sub.2
where T.sub.ad is the adiabatic temperature of the flame front,
XO.sub.2 is the mass fraction of oxygen in the mixture, and
c.sub.1, c.sub.2 and c.sub.3 are predetermined coefficients.
13. Device according to claim 11, wherein the polynomial model is a
model according to the equation:
T.sub.ad=c.sub.1+c.sub.2.times.T.sub.nb+c.sub.3.times.XO.sub.2+c.sub.4.ti-
mes.P where T.sub.ad is the adiabatic temperature of the flame
front, XO.sub.2 is the mass fraction of oxygen in the mixture, P is
the pressure in the cylinder, and c.sub.1, c.sub.2, c.sub.3,
c.sub.4 are predetermined coefficients.
14. Device according to claim 11, wherein the polynomial model is a
model according to the equation:
T.sub.ad=c.sub.1+c.sub.2.times.T.sub.nb+c.sub.3.times.XO.sub.2+c.sub.4.ti-
mes.P+c.sub.5.times.XO.sub.2.sup.2 where T.sub.ad is the adiabatic
temperature of the flame front, XO.sub.2 is the mass fraction of
oxygen in the mixture, P is the pressure in the cylinder, and
c.sub.1, c.sub.2, c.sub.3, c.sub.4 and c.sub.5 are predetermined
coefficients.
15. Device according to claim 1, wherein the means for determining
the amount of NOx emitted by combustion of the intake mixture in
the cylinder are adapted to do so using a chemical model of the
production of NOx during combustion of the mixture in the
cylinder.
16. Device according to claim 15, wherein the means for determining
the flame front temperature are adapted to determine a theoretical
adiabatic temperature of the flame front, and the chemical model is
a model according to the equation: Q NOx = ln .function. ( P ) + 1
b .times. XO 2 .times. exp .function. ( T ad - c d .times. XO 2 )
.times. MCB MCI ##EQU11## where Q.sub.NOx is the instantaneous
amount of NOx emitted by the engine, P is the pressure in the
cylinder, T.sub.ad is the adiabatic temperature of the flame front
in the cylinder, XO.sub.2 is the mass fraction of oxygen in the
intake mixture in the cylinder, MCB is the instantaneous mass of
fuel burned in the cylinder, MCI is the mass of fuel injected into
the cylinder, and b, c and d are predetermined parameters.
17. System for diagnosing malfunctioning of a motor vehicle diesel
engine, which includes a device according to claim 1, means for
comparing the amount of NOx emitted with a predetermined threshold
and means for triggering an alarm when the amount of NOx exceeds
this threshold.
18. System for controlling the operation of a motor vehicle diesel
engine associated with means for depollution of NOx arranged in an
exhaust line of the engine, which includes a device according to
claim 1, 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 means for controlling the operation of the engine,
according to the amount of NOx stored, in order to manage the
operation of the depollution means.
19. System for controlling the operation of a motor vehicle diesel
engine, which includes a device according to claim 1 and adjustment
means adapted to adjust the operation of the supply means according
to the determined amount of NOx emitted, in order to correct drifts
in the operation of the supply means.
20. System according to claim 19, wherein the engine is associated
with means for recirculating a part of the exhaust gases into the
engine, and in that the adjustment means are also adapted to adjust
the operation of the recirculation means according to the
determined amount of NOx emitted, in order to correct drifts in the
operation of the supply means and/or the recirculation means.
21. Method for determining the amount of NOx emitted by a motor
vehicle diesel engine comprising common rail means for supplying
fuel to the engine cylinders, of the type comprising a step for
acquisition of data concerning pressure in at least one cylinder of
the engine and a step for determining the mass fraction of oxygen
in the intake mixture in the cylinder, characterised in that it
includes a step for: determining the temperature of the flame front
during combustion of the intake mixture in the cylinder;
determining the mass of fuel burned in the cylinder; and
calculating the amount of NOx emitted by combustion of the mixture
in the cylinder as a function of the detected pressure, and the
values determined for the mass fraction of oxygen in the mixture,
the flame front temperature and the mass of fuel burned.
Description
[0001] The present invention relates to a device for determining
the quantity of NOx emitted by a motor vehicle diesel engine
associated with common rail means for supplying the engine
cylinders with fuel, of the type comprising means for acquisition
of data concerning the pressure in at least one cylinder of the
engine and means for determining the mass fraction of oxygen in the
intake mixture in the cylinder.
[0002] The invention also relates to systems for diagnosing and
controlling the operation of the engine using such a device.
[0003] The amount of nitrous oxides, or NOx, emitted by a diesel
engine is a piece of data important to its operation.
[0004] Indeed, the emission of NOx, which are pollutant molecules,
must be minimised. To that end, the amount of fuel and the air flow
injected into the cylinders are determined so that the formation of
NOx during combustion of the mixture in the cylinders is
minimised.
[0005] The engine is also generally associated with depollution
means arranged in its exhaust line such as, for example, a NOx
trap, and the operation of the engine is then controlled in order
to optimise the operation of the depollution means. The engine may
thus be controlled according to several modes of operation by
modifying the amounts of fuel and air injected into the cylinders.
For example, the engine may operate in rich mode in order to
regenerate the NOx trap.
[0006] Poor adjustment of the engine, due, for example to aging of
the injectors and/or the cylinders, has the effect of increasing
the emission of NOx. Thus, the quantity of NOx emitted by a diesel
engine is representative of the operating state of the engine.
[0007] Accurate knowledge of the amount of NOx emitted by the
engine makes it possible to optimise both the operation of the
engine and the amount of pollutant expelled into the atmosphere by
the vehicle.
[0008] Devices for determining the amount of NOx emitted by a motor
vehicle diesel engine associated with common-rail means for
supplying the engine cylinders with fuel use engine adjustment
values to determine the amount of NOx emitted, such as, for
example, injection maps and/or EGR maps of air flow if the engine
is associated with an exhaust gas recirculation (EGR) loop.
[0009] However, such systems are not based on the actual features
of the operation of the engine but on adjustment values which are
predetermined at the factory.
[0010] Moreover, the features of the engine change over time
because of aging of its components such as, for example, the
injectors and the cylinders. Thus, where there are major drifts in
these features, the amount of NOx determined may be highly
erroneous.
[0011] Other systems for determining the amount of NOx emitted by a
diesel engine determine the mean temperature of the burning mixture
in the cylinders in order to deduce from it an amount of NOx at
equilibrium and thereafter the mass of NOx emitted by the engine
per engine cycle.
[0012] However, under certain conditions, the results returned by
such systems are of relatively low accuracy and such systems do not
allow the amount of NOx to be calculated at each moment of the
combustion phase of the engine cylinders.
[0013] The aim 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 accurate,
requires little calculation time and which determines in real time
the amount of NOx emitted by the engine.
[0014] To that end, the invention relates to a device for
determining the amount of NOx emitted by a motor vehicle diesel
engine associated with common rail means for supplying the engine
cylinders with fuel, of the type comprising means for acquisition
of data concerning the pressure in at least one cylinder of the
engine and means for determining the mass fraction of oxygen in the
intake mixture in the cylinder, characterised in that it includes
[0015] means for determining a flame front temperature during
combustion of the intake mixture in the cylinder; [0016] means for
determining the mass of fuel burned in the cylinder; [0017] means
for calculating the amount of NOx emitted by combustion of the
mixture in the cylinder as a function of the detected pressure and
the values determined for the mass fraction of oxygen in the
mixture, the flame front temperature and the mass of fuel
burned.
[0018] According to particular embodiments, the above-mentioned
device includes at least one of the following features: [0019] the
means for determining the mass of fuel burned in the cylinder
include means for determining the amount of instantaneous heat
released during combustion of the intake mixture in the cylinder
and means for determining the instantaneous mass of fuel burned in
the cylinders as a function of this latter and the calorific
potential of the fuel injected into the cylinder; [0020] the means
for determining the amount of instantaneous heat released during
combustion of the mixture are adapted to determine this amount as a
function of the crank angle of the cylinder and the pressure within
the cylinder, using the first law of thermodynamics; [0021] the
means for determining the flame front temperature include means for
determining the temperature of the unburned intake mixture during
combustion of that mixture and means for determining the flame
front temperature in the cylinder as a function of that temperature
of the unburned intake mixture; [0022] the means for determining
the temperature of the unburned intake mixture during combustion of
that mixture are adapted to do so using a thermodynamic model of
isentropic compression according to the equation: T nb = T nb 0
.function. ( P nb P 0 ) k k - 1 ##EQU1## where T.sub.nb and
P.sup.nb are respectively the temperature of the unburned intake
mixture and the corresponding pressure in the cylinder during
combustion of the mixture, T.sub.nb.sup.0 and P.sup.0 are
respectively a reference temperature and reference pressure of the
intake mixture in the cylinder at a predetermined moment before the
start of combustion of the intake mixture, and k is a predetermined
polytropic coefficient; [0023] it includes means for determining
the amount of instantaneous heat released during combustion of the
intake mixture in the cylinder and means for determining the moment
when combustion of the intake mixture starts capable of comparing
the determined instantaneous amount of heat with a predetermined
threshold value and of determining the moment when combustion
starts when the determined instantaneous amount of heat is greater
than the threshold value; [0024] the means for determining the
temperature of the intake mixture during combustion of that mixture
includes: [0025] means for determining the number of moles of the
intake mixture in the cylinder; and [0026] means for determining
the reference temperature T.sub.nb.sup.0 as a function of the
number of moles of the intake mixture and the pressure P.sup.0 in
the cylinders at the predetermined moment before combustion begins,
based on a thermodynamic model of the intake mixture; [0027] the
means for determining the reference temperature T.sub.nb.sup.0 is
adapted to do so according to the equation: T nb 0 = P 0 .times. V
0 n .times. R ##EQU2## [0028] the means for determining the flame
front temperature are adapted to determine a theoretical adiabatic
temperature of the flame front; [0029] the means for determining
the adiabatic temperature of the flame front are adapted to
determine that temperature as a function of the temperature of the
unburned intake mixture during combustion of the intake mixture and
of the mass fraction of oxygen in the intake mixture, using a
thermodynamic model of conservation of the enthalpy of the reagents
and the products of combustion of the intake mixture in the
cylinder; [0030] the thermodynamic model of conservation of
enthalpy is a polynomial model of the first or second order; [0031]
the polynomial model is a model according to the equation:
T.sub.ad=c.sub.1+c.sub.2.times.T.sub.nb+c.sub.3.times.XO.sub.2
where T.sub.ad is the adiabatic temperature of the flame front,
XO.sub.2 is the mass fraction of oxygen in the mixture, and
c.sub.1, c.sub.2 and c.sub.3 are predetermined coefficients; [0032]
the polynomial model is a model according to the equation:
T.sub.ad=c.sub.1+c.sub.2.times.T.sub.nb+c.sub.3.times.XO.sub.2+c.sub.4.ti-
mes.P where T.sub.ad is the adiabatic temperature of the flame
front, XO.sub.2 is the mass fraction of oxygen in the mixture, P is
the pressure in the cylinder, and c.sub.1, c.sub.2, c.sub.3,
c.sub.4 are predetermined coefficients; [0033] the polynomial model
is a model according to the equation:
T.sub.ad=c.sub.1+c.sub.2.times.T.sub.nb+c.sub.3.times.XO.sub.2+c.sub.4.ti-
mes.P+c.sub.5.times.XO.sub.2.sup.2 where T.sub.ad is the adiabatic
temperature of the flame front, XO.sub.2 is the mass fraction of
oxygen in the mixture, P is the pressure in the cylinder, and
c.sub.1, c.sub.2, c.sub.3, c.sub.4 and c.sub.5 are predetermined
coefficients; [0034] the means for determining the amount of NOx
emitted by the combustion of the intake mixture in the cylinder are
adapted to do so using a chemical model of production of NOx during
combustion of the mixture in the cylinder; and [0035] the chemical
model is a model according to the equation: Q NOx = ln .function. (
P ) + 1 b .times. X .times. .times. O 2 .times. exp .function. ( T
ad - c d .times. X .times. .times. O 2 ) .times. M .times. .times.
C .times. .times. B M .times. .times. C .times. .times. I ##EQU3##
where Q.sub.NOx is the instantaneous amount of NOx emitted by the
engine, P is the pressure in the cylinder, T.sub.ad is the
adiabatic temperature of the flame front in the cylinder, XO.sub.2
is the mass fraction of oxygen in the intake mixture in the
cylinder, MCB is the instantaneous mass of fuel burned in the
cylinder, MCI is the mass of fuel injected into the cylinder, and
b, c and d are predetermined parameters.
[0036] The object of the invention is also a method for determining
the amount of NOx emitted by a motor vehicle diesel engine
comprising common rail means for supplying the engine cylinders
with fuel, of the type comprising a step of acquisition of data
concerning pressure in at least one cylinder of the engine, and a
step of determination of the mass fraction of oxygen in the intake
mixture in the cylinder, characterised in that it includes a step
of: [0037] determination of the flame front temperature during
combustion of the intake mixture in the cylinder; [0038]
determination of the mass of fuel burned in the cylinder; and of
[0039] calculation of the amount of NOx emitted by combustion of
the mixture in the cylinder as a function of the acquired pressure
and of the values determined for the mass fraction of oxygen in the
mixture, the flame front temperature and the mass of fuel
burned.
[0040] The object of the invention is also a system for diagnosing
the malfunctioning of a motor vehicle diesel engine, characterised
in that it includes a device of the aforementioned type, means for
comparing the amount of NOx emitted with a predetermined threshold
and means for triggering an alarm when the amount of NOx exceeds
this threshold.
[0041] The object of the invention is also a system for controlling
the operation of a motor vehicle diesel engine associated with
means for depollution of NOx arranged in an exhaust line of the
engine, characterised in that it includes 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 means for controlling the operation of
the engine according to the amount of NOx stored, in order to
manage the operation of the depollution means.
[0042] The object of the invention is also a system for controlling
the operation of a motor vehicle diesel engine, characterised in
that it includes a device of the aforementioned type and adjustment
means adapted to adjust the operation of the supply means according
to the determined amount of NOx emitted, in order to correct drifts
in the operation thereof.
[0043] According to another feature, this system is characterised
in that the engine is associated with means for recirculating part
of the exhaust gases at the engine intake, and in that the
adjustment means are also adapted to adjust the operation of the
recirculation means according to the determined quantity of NOx
emitted, in order to correct drifts in the operation of the supply
means and/or the recirculation means.
[0044] A clear understanding of the present invention will be
facilitated by the following description, given solely by way of
example and described in reference to the appended drawings, in
which:
[0045] FIG. 1 is a schematic view of a diesel engine motor vehicle
propulsion unit associated with a device according to the
invention.
[0046] FIG. 2 is a more detailed schematic view of the device
according to the invention;
[0047] FIG. 3 is a flowchart of the operation of the device
according to the invention; and
[0048] FIG. 4 is a graph of the results returned by the device
according to the invention during a series of tests.
[0049] In FIG. 1, a motor vehicle diesel engine 10 is associated
with common rail means 12 for supplying the engine cylinders with
fuel, for example, comprising a common supply rail delivering fuel
at high pressure to controlled injectors capable of injecting fuel
into the cylinders of the engine 10 in the form of multiple
injections, for example.
[0050] The engine 10 is also associated with a loop 14 for
recirculation of part of the exhaust gases, or EGR, at the engine
intake. The recirculation loop 14 includes a bypass line 16 of an
exhaust line 18 of the engine 10. This bypass line 16 is capable of
taking exhaust gases leaving the engine 10 and delivering them to
means 20 taking in air/exhaust gas mixture at the intake of the
engine 10. These intake means 20 also receive air from an air inlet
22 and deliver an air/exhaust gas mixture to the engine 10.
[0051] For the purposes of processing the emissions of pollutants
from the engine 10, and in particular the emission of nitrous
oxides, or NOx, depollution means 24 are arranged in the exhaust
line 18. The depollution means 24 include for example a NOx trap
adapted to store NOx and release them in a non-polluting form for
expulsion into the atmosphere.
[0052] Normally, the operation of the engine and the components
which have just been described is controlled by a unit 30 for
controlling the operation of the engine.
[0053] The unit 30 is connected to means 32 for detecting (i) the
pressure in each cylinder of the engine, comprising, for example, a
piezoelectric deformation sensor arranged in the head of the
cylinder and adapted to measure the pressure in the combustion
chamber of the cylinder, (ii) the engine speed, comprising for
example a speed sensor, (iii) the engine torque desired by the
driver of the vehicle, comprising for example a sensor for sensing
the position of the accelerator pedal of the vehicle, and (iv) the
engine timing angle, comprising for example a Hall effect sensor
arranged on the engine drive shaft.
[0054] The unit 30 is also connected to means 34 for detecting the
flow rate of air entering the engine, for example a flowmeter
arranged in the air inlet 22 of the intake means 20.
[0055] The unit 30 is adapted to determine injection settings for
the supply means 12, in particular a pilot injection setting and a
main injection setting for each cylinder and for each engine cycle,
as a function of the engine speed, the torque and the crank angle
of the cylinder, this latter being determined by the unit 30
according to the engine timing angle detected.
[0056] The unit 30 also determines, for the engine cycle, an EGR
air flow rate setting for the intake means 20 according to the
engine speed, torque and crank angle of the cylinder.
[0057] The unit 30 is also adapted to implement a strategy of
managing the operation of the depollution means 24 by controlling
the phasing and/or the amount of fuel injected into the cylinders
in order to manage the storage/release states of the depollution
means 24.
[0058] The engine 10 is associated with a device according to the
invention for determining the amount of NOx emitted by the engine.
This device determines such an amount on the basis of the amount of
intake mixture burned in the combustion chamber of each cylinder
when a flame front propagates within it, the intake mixture in the
cylinder being defined as the sum of the amounts of fresh air,
exhaust gas and fuel taken into the cylinder.
[0059] In the example illustrated in FIG. 1, this device is
implemented by a sub-unit 36 of the unit 30. In another variant,
the device may also be implemented by a dedicated data processing
unit.
[0060] A description will now be given, with reference to FIGS. 2
and 3, of the arrangement and operation of the device for
determining the amount of NOx emitted by the engine 10.
[0061] The amount of NOx emitted by the engine is determined in
accordance with a chemical model of the production of NOx during
combustion of the intake mixture in an engine cylinder. This model
uses as a variable the mass fraction of oxygen XO.sub.2 in the
intake mixture in the cylinder, the instantaneous mass MCB of fuel
burned in the cylinder, the pressure P in the cylinder and a
theoretical temperature T.sub.ad of the flame front propagating in
the combustion chamber of the cylinder, and preferably, a
theoretical adiabatic temperature of the flame front, as will be
explained below in more detail.
[0062] The device for determining the amount of NOx emitted by the
engine 10 includes means 50 for determining the mass fraction of
oxygen XO.sub.2 in the intake mixture to be burned in the cylinder
during an engine cycle. These means 50 receive as input the
detected air flow rate DA and the rate TEGR of recycled exhaust gas
entering the engine.
[0063] The rate TEGR of recycled exhaust gas is determined by the
unit 30 as a function of the detected air flow rate DA and the
operating point of the engine, for example using a predetermined
map stored in memory in the unit 30.
[0064] 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 intake mixture according to that
amount, as is known in the art. This amount MCI is determined by
the unit 30 according to the injection settings delivered to the
supply means 12, for example by adding together the quantities of
fuel injected into the cylinder for the engine cycle.
[0065] The means 50 for determining the mass fraction of oxygen
XO.sub.2 in the mixture then determine this fraction as a function
of the richness of the intake mixture and the determined TEGR rate
using as its basis a combustion balance of the intake mixture, the
mass fraction of oxygen XO.sub.2 admitted being usually directly
proportional to the richness and the EGR rate, as is known in the
state of the art.
[0066] The device according to the invention also includes means 52
for determining the instantaneous amount MCB of fuel burned in the
cylinder during the engine cycle.
[0067] To that end, the means 52 include means 54 for determining
the instantaneous amount of heat released by combustion of the
mixture in the cylinder during the combustion phase of the cycle of
the cylinder. This determination is performed as a function of the
detected pressure P in the combustion chamber of the cylinder and
the crank angle .alpha. of the cylinder, using the first law of
thermodynamics, according to the equation: d Q d .alpha. = 1 k - 1
.times. ( V .times. d P d .alpha. - k .times. P .times. d V d
.alpha. ) ( 1 ) ##EQU4## where d.alpha. is a predetermined
variation of the crank angle .alpha. of the cylinder, dQ is the
instantaneous amount of heat released by combustion of the mixture
during the variation d.alpha. in the crank angle, V and P are
respectively the volume of the combustion chamber and the pressure
within it at the moment when the variation d.alpha. of the crank
angle begins, dV and dP are respectively the variation in the
volume of the combustion chamber and the variation in the pressure
within it corresponding to the variation d.alpha. in the crank
angle, and k is a predetermined polytropic coefficient.
[0068] This determined amount of heat dQ is delivered to means 56
for determining the corresponding amount of fuel burned. The means
56 are capable of determining 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 NCV for net calorific value (in J/kg).
The NCV value is for example mapped in the means 56.
[0069] The device according to the invention also include means 58
for determining the temperature T.sub.nb of the unburned intake
mixture at a moment after the start of combustion of the mixture in
the cylinder. This temperature T.sub.nb of the unburned intake
mixture is calculated by making a hypothesis of isentropic
compression of the unburned intake mixture from a moment which
precedes the start of combustion. This temperature T.sub.nb of the
unburned intake mixture is then used to determine the theoretical
adiabatic temperature T.sub.ad of the flame front propagating
inside the combustion chamber of the cylinder, as will be explained
in more detail below.
[0070] The means 58 for determining the temperature T.sub.nb
include means 60 for determining the number of moles n of the
intake mixture present in the combustion chamber of the cylinder
before the start of combustion as a function of the detected air
flow rate DA, the rate of recirculated exhaust gas TEGR entering
the engine and the total amount of fuel MCI injected into the
cylinder.
[0071] The number n of moles is then delivered to means 62 for
determining the temperature T.sub.nb.sup.0 of the intake mixture at
a predetermined moment before the start of combustion in the
cylinder, for example corresponding to a crank angle .alpha..sup.
included within the range of crank angles [-60.degree.;
-20.degree.] before top dead centre (TDC) of the cylinder
cycle.
[0072] Detection of the moment when combustion of the mixture
starts is performed by means 64 for comparing the instantaneous
amount of heat dQ released by combustion of the intake mixture,
determined by the means 54, at a predetermined threshold.
[0073] When the amount of heat dQ reaches this threshold value, the
start of combustion of the intake mixture is detected and
calculation of the temperature T.sub.nb of the unburned intake
mixture during combustion is triggered.
[0074] The means 62 then determines the temperature T.sub.nb by
considering the intake mixture to be a perfect gas according to the
equation: T nb 0 = P 0 .times. V 0 n .times. R ( 2 ) ##EQU5## where
V.sup.0 and P.sup.0 are the volume of the combustion chamber and
the pressure within it at the predetermined moment before the start
of combustion of the intake mixture, and R is the perfect gases
constant.
[0075] The values of V.sup.0 and of P.sup.0 are for example stored
in memory in the means 62 after the last acquisition of data
concerning the pressure P in the cylinder for the crank angle
.alpha..sup.0 included within the range of crank angles
[-60.degree.;-20.degree.] before top dead centre of the cylinder
cycle, the crank angle .alpha..sup.0 corresponding to the volume
V.sup.0 of the combustion chamber of the cylinder.
[0076] The temperature T.sub.nb.sup.0 and the pressure before the
start of combustion P.sup.0 are delivered as the reference
temperature and reference pressure to means 66 for determining the
temperature T.sub.nb of the unburned intake mixture during
combustion, that is, during propagation of the flame front in the
combustion chamber of the cylinder. The means 66 determine this
temperature using a thermodynamic model of isentropic compression
in the compression phase of the cylinder cycle according to the
equation: T nb = T nb 0 .function. ( P nb P 0 ) k k - 1 ( 3 )
##EQU6##
[0077] The means 66 determine the temperature T.sub.nb continuously
during a period of time corresponding to the combustion of the
intake mixture in the cylinder. This period corresponds for example
to the range of crank angles [0; 120.degree.] after top dead centre
if the engine load is partial or the range [-15 ; 120.degree.]
relative to TDC if the engine load is approximately at maximum.
[0078] The determined temperature T.sub.nb is delivered to means 68
for determining the adiabatic temperature T.sub.ad of the flame
front during combustion of the intake mixture in the combustion
chamber of the cylinder.
[0079] These means determine the temperature T.sub.ad using a
thermodynamic model of conservation of the enthalpy of the reagents
and of the products of combustion of the mixture according to the
equation:
H.sub.initial(P,T.sub.nbXO.sub.2)=H.sub.final(P,T.sub.ad,XO.sub.2)
(4) where H.sub.initial is the enthalpy of the intake mixture
before the moment when combustion of the latter starts and
H.sub.final is the intake enthalpy of the exhaust gases produced by
combustion of the intake mixture by the flame front.
[0080] Advantageously, this model of conservation of enthalpy is
approximated by a polynomial model, the adiabatic temperature
T.sub.ad of the flame front being determined by the means 68
according to the equation:
T.sub.ad=c.sub.1+c.sub.2.times.T.sub.nb+c.sub.3.times.XO.sub.2 (5)
where c.sub.1, c.sub.2 and c.sub.3 are predetermined
coefficients.
[0081] The correlation between the adiabatic temperature determined
according to equation (5) and an adiabatic temperature determined
using a complex model of the same based on equation (4) has a
correlation coefficient R.sup.2 approximately equal to 99.43%.
[0082] 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 equation:
T.sub.ad=c.sub.1+c.sub.2.times.T.sub.nb+c.sub.3.times.XO.sub.2+c.sub.4.ti-
mes.P (6) where c.sub.1, c.sub.2, c.sub.3, c.sub.4 are
predetermined coefficients.
[0083] The introduction of the pressure P in the cylinder into
equation (6) gives a coefficient R.sup.2 approximately equal to
99.5%.
[0084] In another embodiment, the means 68 also receive as input
the pressure P measured in the combustion chamber of the cylinder
and determines the adiabatic temperature of the flame front
according to the equation:
T.sub.ad=c.sub.1+c.sub.2.times.T.sub.nb+c.sub.3.times.XO.sub.2+c.sub.4.ti-
mes.P+c.sub.5.times.XO.sub.2.sup.2 (7) where c.sub.1, c.sub.2,
c.sub.3, c.sub.4 et c.sub.5 are predetermined coefficients.
[0085] The introduction of the square of the mass fraction XO.sub.2
into equation (7) gives a coefficient R.sup.2 approximately equal
to 99.97%.
[0086] Thus, the means 68 determine the adiabatic temperature
T.sub.ad of the flame front in a manner which is simple and
requires little calculation time, whilst determining that
temperature reliably.
[0087] Finally, the device according to the invention includes
means 70 for calculating the amount of instantaneous NOx emitted by
combustion of the intake mixture in the cylinder as a function of
the pressure P in the cylinder, the adiabatic temperature T.sub.ad
of the flame front, the mass fraction of oxygen XO.sub.2 in the
mixture and the instantaneous mass MCB of fuel burned. This
calculation is performed using a predetermined chemical model of
production of NOx in the cylinder, for example according to the
equation: Q NOx = ln .function. ( P ) + 1 b .times. X .times.
.times. O 2 .times. exp .function. ( T ad - c d .times. X .times.
.times. O 2 ) .times. M .times. .times. C .times. .times. B M
.times. .times. C .times. .times. I ( 8 ) ##EQU7## where Q.sub.NOx
is the instantaneous amount of NOx emitted by combustion of the
intake mixture in the cylinder in grams per kilogram of fuel
injected into the cylinder for each crank degree, and b, c and d
are predetermined parameters.
[0088] Because of the time lag between the combustion phases in the
cylinders, which never take place simultaneously, the instantaneous
amount Q.sub.NOx of NOx produced during combustion of the mixture
in the cylinder is thus approximately equal to that emitted by the
engine 10.
[0089] FIG. 3 is a flowchart of the operation of the device just
described for determining the amount of NOx emitted by the
engine.
[0090] After starting the vehicle, the operation consists at 50 of
selecting the reference i of the cylinder within which the next
combustion of mixture will take place.
[0091] Then, at 52, the total mass of fuel MCI, the air flow rate
DA and the rate of recirculated exhaust gas TEGR injected into this
cylinder i are determined.
[0092] A subsequent step 54 then consists of determining, as a
function of the values determined at 52, the richness of the intake
mixture and then the mass fraction of oxygen XO.sub.2 in the intake
mixture in the cylinder i.
[0093] The operation of the device according to the invention then
consists at 56 of determining the instantaneous amount of heat dQ
released by combustion of the intake mixture in the cylinder i
according to equation (1) and of comparing this, at 58, with the
threshold value for detecting the moment when combustion of the
mixture starts.
[0094] As long as this moment is not detected, that is, as long as
the amount dQ is lower than the detection threshold, the method 58
loops back to step 56. If the moment when combustion starts is
detected at 58, a subsequent step 60 of the operation is a step to
determine the temperature T.sub.nb.sup.0 of the mixture at the
predetermined moment before the start of combustion thereof
according to equation (2).
[0095] Step 60 is then followed by a step 62 to determine the
temperature T.sub.nb of the unburned intake mixture at a moment
after the start of combustion according to equation (3). Step 62
continues by determining the adiabatic temperature T.sub.ad of the
flame front according to equation (5) as a function of the
temperature T.sub.nb of the unburned intake mixture, the mass
fraction of oxygen XO.sub.2 in the mixture, and the pressure P of
the cylinder i if equation (6) or equation (7) is used.
[0096] 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 has been described above.
[0097] The operation then continues via a step 66 to determine the
instantaneous amount QNOx of NOx emitted by combustion of the
mixture in the cylinder i according to equation (8).
[0098] Following the determination of the amount Q.sub.NOx, a test
is performed at 68 to find out whether combustion of the mixture in
the cylinder i has finished, for example by testing whether the
determined instantaneous amount of heat dQ is below a second
predetermined threshold value.
[0099] If the result of this test is positive, step 68 then loops
back to step 50 to select a new cylinder i.
[0100] If the result of this test is negative, a new instantaneous
amount of heat dQ is determined at 70.
[0101] Step 70 then loops back to step 62 to determine a new
instantaneous amount Q.sub.NOx of NOx emitted by combustion of the
mixture in the cylinder i at a moment following combustion, by
implementing steps 62, 64 and 66.
[0102] The device according to the invention implements a
determination algorithm requiring a small number of calculations,
whilst allowing the amount of NOx emitted by the engine to be
determined in real time and instantaneously, that is, at each
moment in the combustion phase of the cylinder.
[0103] Other embodiments of the device according to the invention
are possible.
[0104] For example, as a variant, the device includes a data
acquisition chain for the pressure in a single cylinder of the
engine and the device is capable of determining the amount of NOx
emitted by combustion of the intake mixture in this cylinder and of
multiplying the determined amount of NOx by the number of cylinders
in the engine in order to obtain the total amount of NOx emitted by
the engine.
[0105] As a variant, the device includes a data acquisition chain
for the pressure in any number n of engine cylinders, and is
capable of determining the amount of NOx emitted by these systems
and of multiplying this latter by N n , ##EQU8## where N is the
number of engine cylinders, in order to obtain the total amount of
NOx emitted by the engine.
[0106] FIG. 4 shows the accuracy of the determination of the amount
of NOx emitted by the engine implemented by the device according to
the invention. The x-axis shows, for different points of operation
of a diesel test engine, the amount of NOx determined using a
complex physical model of NOx production and the y-axis shows the
corresponding amounts obtained by the device according to the
invention.
[0107] The device according to the invention thus enables a high
degree of accuracy to be obtained, in a simple manner, for a large
range of operation of the engine.
[0108] 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 data on the amount of NOx emitted by the
engine.
[0109] A first system is a system for diagnosing malfunctioning of
the engine 10. Indeed, if the emission of NOx is abnormally high, a
malfunction of the engine 10 may be diagnosed.
[0110] To that end, the diagnostic system includes a device
according to the invention which delivers the instantaneous amount
of NOx emitted by the engine to means for comparing this amount
with a predetermined threshold. Means for triggering an alarm
receive the result of this comparison and trigger an alarm, for
example, activation of an indicator light on the instrument panel
of the vehicle, when the determined amount of NOx exceeds this
threshold.
[0111] It is also possible to envisage a system controlling the
operation of the diesel engine 10 in order to manage of the states
of storage and release of the depollution means 24 on the basis of
the amount of NOx emitted by the engine.
[0112] Such a system includes, for example, a device according to
the invention for determining the amount of NOx emitted by the
engine and delivering that amount to means for calculating the
amount of NOx stored in the depollution means 24 as a function of
that amount.
[0113] The determined amount of stored NOx is then delivered to
means for comparing that amount with 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 mode for regeneration
of the depollution means 24 when the amount of NOx stored in the
latter is above the first threshold, and deactivate such a mode of
operation of the engine 10 when the amount of stored NOx is below
the second threshold.
[0114] The regeneration of the depollution means is thus triggered
according to an item of data which remains pertinent throughout the
life of the vehicle. The operation of the engine associated with
the management of the depollution means 24 is thus optimised.
[0115] It is also possible to envisage a system for controlling the
operation of the engine 10 comprising the device according to the
invention and means for adjusting the operation of the means 12 for
supplying the engine 10. The adjustment means are adapted to adjust
the operation of the supply means 12 according to the amount of NOx
emitted determined by the device in order to correct drifts in the
operation of the supply means. For example, the means of adjusting
the supply means 12 are capable of adjusting the phasing and/or the
quantities of fuel injected into the cylinders in order to minimise
the emission of NOx by the engine 10.
[0116] The adjustment means may also be adapted to adjust the
operation of the recirculation loop 14 according to the amount of
NOx emitted by the engine 10 in order to correct drifts in the
operation of the supply means 12 and/or the recirculation loop 14,
in order likewise to minimise the emission of NOx.
* * * * *