U.S. patent application number 10/487544 was filed with the patent office on 2005-01-06 for method for regenerating an exhaust gas filtering device for diesel engine and device therefor.
Invention is credited to Fayard, Jea-Claude.
Application Number | 20050000211 10/487544 |
Document ID | / |
Family ID | 8866779 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050000211 |
Kind Code |
A1 |
Fayard, Jea-Claude |
January 6, 2005 |
Method for regenerating an exhaust gas filtering device for diesel
engine and device therefor
Abstract
The invention concerns a method for regenerating a device
filtering exhaust gases produced by a diesel engine, said method
being of the type wherein particles, retained on a filtering means
(22) of the filtering device, are burnt by the action of a
combustion catalyst system. Said method consists essentially in
retaining the hot exhaust gases around the filtering means (22) so
as to feed to the particles, at least part of the heat energy
required for their combustion and in burning said particles to
regenerate the filtering device. The invention also concerns a
device for implementing the method, comprising a means for
producing a combustion catalyst (20), a filtering means (22) of
exhaust gases and a diesel oil injecting means, the means for
producing a combustion catalyst and filtering means being contained
in a reaction chamber (18).
Inventors: |
Fayard, Jea-Claude; (Lyon,
FR) |
Correspondence
Address: |
JAMES C. LYDON
100 DAINGERFIELD ROAD
SUITE 100
ALEXANDRIA
VA
22314
US
|
Family ID: |
8866779 |
Appl. No.: |
10/487544 |
Filed: |
April 22, 2004 |
PCT Filed: |
August 7, 2002 |
PCT NO: |
PCT/FR02/02819 |
Current U.S.
Class: |
60/295 ;
60/297 |
Current CPC
Class: |
F01N 13/017 20140601;
F01N 2330/02 20130101; F01N 2610/08 20130101; F01N 3/035 20130101;
F01N 3/0231 20130101; F01N 3/30 20130101; F01N 13/0097 20140603;
F01N 2610/03 20130101; F01N 3/0253 20130101 |
Class at
Publication: |
060/295 ;
060/297 |
International
Class: |
F01N 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2001 |
FR |
0111180 |
Claims
1-19. (Canceled)
20. A method for regeneration of a device for filtering the exhaust
gases produced by a diesel engine in which particles retained on a
filtration means of said filtration device are burnt through the
action of a combustion catalyst, comprising retaining the hot
exhaust gases around the filtration means in order to provide the
particles with at least some of the heat energy necessary for their
combustion, and burning said particles with at least some of the
heat energy necessary for their combustion, so as to regenerate the
filtration device.
21. The method of claim 20, further comprising: employing a
combustion catalyst production means in the filtration device,
measuring a temperature .theta..sub.m in the vicinity of the
combustion catalyst production means, comparing .theta..sub.m with
a temperature .theta..sub.r corresponding to the temperature at
which the combustion of diesel fuel in the presence of the
combustion catalyst is complete, if .theta..sub.m is greater than
or equal to .theta..sub.r, initiating post-injection of diesel fuel
through an injection means into the filtration device for a
determined period of time, so as to cause a temperature rise of the
particles in order to permit their combustion.
22. The method of claim 21, further comprising: measuring a
pressure P.sub.m in the vicinity of the combustion catalyst
production means, said pressure P.sub.m reflecting the degree of
obstruction of the filtration means by the particles, measuring the
temperature .theta..sub.m, comparing said pressure P.sub.m with a
reference pressure P.sub.r corresponding to the maximum acceptable
degree of obstruction, comparing .theta..sub.m with .theta..sub.r
if P.sub.m is greater than or equal to the pressure P.sub.r,
initiating the post-injection of diesel fuel if .theta..sub.m is
greater than or equal to .theta..sub.r.
23. A device for carrying out the regeneration method of claim 20,
comprising a combustion catalyst production means, a means for
filtration of said exhaust gases downstream of said combustion
catalyst production means, and a means for injection of diesel fuel
upstream of said combustion catalyst production means, said
combustion catalyst production means and filtration means being
contained in a reaction enclosure along the flow path of the
exhaust gases produced by an engine.
24. The device of claim 23, wherein said filtration means,
comprising a set of filtering units and is exposed in a chamber for
receiving the exhaust gases, with said exhaust gases heating said
filtering units.
25. The devise of claim 24, wherein said filtration means comprises
at least two particle filters having a body, formed by the
filtering units which are connected together by a joint, and a
metal casing.
26. The device of claim 23, wherein said means for injection of
diesel fuel communicates with a line for discharging the exhaust
gases.
27. The device of claim 23, wherein said means for injection
comprises a diesel fuel reservoir and a chamber for injecting the
diesel fuel contained in said reservoir into the discharge
line.
28. The device of claim 27, wherein said chamber is supplied, on
the one hand, with diesel fuel through a first line connecting it
to said reservoir and, on the other hand, with compressed air
through a second line connecting it to the engine, said chamber
having an orifice through which the diesel fuel is injected into
said filtration device.
29. The device of claim 23, further comprising an electroinc
control module.
30. The device of claim 23, further comprising at least one
temperature sensor, placed inside said enclosure and adapted to
measure the temperature .theta..sub.m in its interior.
31. The device of claim 23, further comprising at least one
pressure sensor, placed inside said enclosure and adapted to
measure the pressure P.sub.m in its interior.
32. The device of claim 30, wherein the electronic control module
is connected to a temperature sensor and to a pressure sensor, and
compares the respectively measured values of .theta..sub.m and
optionally P.sub.m with the reference values .theta..sub.r and
optionally P.sub.r, and initiates the injection of diesel fuel into
the discharge line through said injection system when the
measurements .theta..sub.m and optionally P.sub.m are greater than
or equal to the reference values .theta..sub.r and optionally
P.sub.r.
33. The device of claim 32, wherein the lines supplying the chamber
of the injection system with diesel fuel and compressed air each
have a solenoid valve controlled by the electronic control module,
opening of the solenoid valves leading to the intake of diesel fuel
and compressed air into the chamber and therefore to the injection
of diesel fuel into the exhaust gas discharge line.
34. The device of claim 28, wherein the chamber of the injection
system is provided with a nozzle in front of the orifice, making it
possible to inject the diesel fuel in a nebulized form into the gas
discharge line.
35. The device of claim 24, wherein the filtering units preferably
consist of silicon carbide or any other equivalent material whose
structure is of a honeycomb type.
36. The device of claim 23, wherein the combustion catalyst
production means comprises at least one cartridge based on platinum
or any equivalent material that catalyzes the conversion of the
nitrogen monoxide (NO) contained in the exhaust gases into nitrogen
dioxide (NO.sub.2), the NO.sub.2 which is produced catalyzing the
combustion reaction of the particle clogging the filter.
37. The device of claim 23, wherein the capacity of the second
reservoir is preferably equivalent to the maximum volume of diesel
fuel injected during the post-injection.
38. The device of claim 25, wherein the particle filters are placed
in parallel in the enclosure.
Description
[0001] The present invention relates in general to the field of
particle filters and, more particularly, to a method for
regeneration of an exhaust gas filtration device for a diesel
engine.
[0002] Furthermore, the present invention also relates to a
filtration device intended to retain the carbon-based and soot
particles produced by the engine, and to burn them regularly in
order to prevent them from accumulating, the latter phase
constituting the regeneration to which the method according to the
invention relates.
[0003] The development of the industrial age has led to serious
consequences for the environment. Specifically,
pollution-generating industries as well as automobiles are the
source of a significant discharge of pollutants into the
atmosphere, which is leading to its modification. This modification
is twofold. Firstly, a chemical modification is observed. This is
reflected especially by a continuing increase in the air
concentration of compounds derived from carbon. These compounds
are, in particular, carbon monoxide (CO) and certain unburnt
hydrocarbons due to incomplete combustion. The presence of these
compounds in the atmosphere constitutes a much more significant
direct health risk. For instance, CO is a very powerful respiratory
toxin. Polycyclic aromatic hydrocarbons (PAHs) such as benzopyrene,
benzanthracene as well as fluoranthrene, which are particularly
common in smoke, dust or engine exhaust gases, are known
carcinogens.
[0004] The atmosphere is also being modified by the release of
solid particles. These particles are classified according to their
size. The smallest particles, referred to as unsedimentable
particles because they cannot be deposited on the ground under the
effect of gravity, are the most dangerous for human health because
they are capable of entering the pulmonary alveoli. They
furthermore contaminate the uppermost layers of the atmosphere and
are therefore responsible for global pollution.
[0005] In view of this alarming fact, the public authorities at
both the national and international level are therefore attempting
to establish pollution control standards. These standards pertain
to the automobile industry in particular. Automobile companies
therefore regularly have to make modifications to their vehicles in
order to bring them into compliance with these standards.
[0006] Besides the development of new engines having a lower and
lower fuel consumption, more particular efforts have been made to
develop new exhaust systems intended to reduce the emission of
unburnt polluting gases and solid particles. Automobile
manufacturers have therefore developed catalytic converters or
catalyzers, generally consisting of a stainless steel casing, a
thermal insulator and a honeycomb support impregnated with precious
metals such as platinum or rhodium. These catalyzers make it
possible to reduce the emissions of polycyclic hydrocarbons and CO,
in particular, and to do so in a proportion of the order of 50%.
However, they have no effect on solid particle emissions. These
catalyzers do not therefore offer any significant improvement in
the air quality, particularly as regards diesel engines which
produce a great deal of solid particles.
[0007] Other techniques have been developed in order to limit the
emission of polluting particles by vehicles. One of these is the
particle filter. This filter makes it possible to reduce by 90% the
total mass of particles emitted by diesel engines. It is even more
effective for the retention of very fine particles, for which the
retention factor can be as much as 99%.
[0008] The particle filter, however, requires regeneration in order
to burn the particles that have been trapped. The particles are
generally trapped by a filtering cartridge which is a component of
the particle filter. In order to withstand the elevated
temperatures involved, this cartridge may consist of a porous body
of cordierite, quartz or silicon carbide, generally with a
honeycomb structure so as to provide a maximum surface area for
filtration.
[0009] One major drawback of such a particle filter consists in the
incomplete combustion of the particles retained by the filtering
cartridge. This is because, under the conditions of urban use, the
temperature reached by the exhaust gases is insufficient to cause
their combustion, significantly reduce the clogging of the filter
and therefore regenerate it. Without chemical assistance, the
carbon-based particles produced by the combustion of diesel fuel in
diesel engines will not begin to oxidize significantly until above
500.degree. C. These temperatures are almost never reached under
urban driving conditions.
[0010] It therefore seems necessary to employ a chemical method in
order to eliminate these particles. Various techniques are used in
order to permit their combustion.
[0011] A first technique consists in providing, upstream of the
filter, a catalyst for the oxidation of the nitrogen monoxide (NO)
contained in the exhaust gases into nitrogen dioxide (NO.sub.2),
the latter having the property of catalyzing the combustion of the
carbon-based particles beginning at 250.degree. C. This method,
however, necessitates the use of a diesel fuel in which the sulfur
content is less than 50 ppm (parts per million), in order to
maintain sufficient NO to NO.sub.2 conversion efficiency.
[0012] This technique, which is referred to as "Continuous
Regenerating Trap" (C.R.T.), combines the effects of the particle
filter and of the NO oxidation catalyst. In order to ensure
satisfactory operation of the filters, this system requires regular
regeneration which reduces the pressure drop across the filter
while eliminating the risk of uncontrolled and exothermic
regeneration.
[0013] Such operation is obtained only when the exhaust gases or
the combustion enclosure are at a temperature in excess of
300.degree. C. for at least 30% of the operating time of the
vehicle.
[0014] Otherwise, violent reactions connected with the excessive
concentration of carbon-based particles clogging the filter are
developed. These reactions consist in the unduly rapid combustion
of a large mass of particles, which generally leads to destruction
of the filter by thermal shock, since the temperatures reached are
locally very high.
[0015] Other techniques resort to the use of organometallic
additives put into the diesel fuel, such as cerium, iron,
strontium, calcium or the like. These techniques make it possible
to obtain an effect similar to that obtained with NO.sub.2, by
catalyzing the combustion of the carbon-based materials at
temperatures of around 300.degree. C.
[0016] A first drawback of these techniques is the prohibitive cost
of the additives which are used.
[0017] Another major drawback resides in the fact that it is
necessary to provide an extra additive delivery device.
[0018] Yet another drawback of these techniques is that they have
an even greater susceptibility to clogging of the filter, and
therefore to the reactions which result from this, if the
temperatures reached during operation are not high enough, since
the additives present in the carbon-based materials contribute even
more to rapid blocking of the filtering medium.
[0019] Other techniques have consisted in experimenting with
devices based on extra heating means such as burners, electrical
resistors or the like. These extra heating means are employed only
when the cartridge is beginning to clog up, which entails an
increase in the pressure drop. Such a regeneration device is
employed with the engine running, that is to say when there is a
significant flow rate of exhaust gas. Such a device therefore
requires a large heating power in order to heat the exhaust gases
and the mass of the filtering cartridge simultaneously to the
appropriate temperature.
[0020] In such a technical context, it is an object of the present
invention to provide a method for regeneration of a filtration
device which overcomes the drawbacks of the existing technical
difficulties, consisting in dealing with the carbon-based and soot
particles emitted by diesel engines.
[0021] It is another object of the invention to provide a
regeneration method which thus avoids any risk of particle
accumulation in the filtration device, and therefore any risk of
uncontrolled regeneration.
[0022] It is yet another object of the invention to provide a
regeneration device which does not lead to significant additional
fuel consumption and, more generally, does not lead to additional
financial cost for the user.
[0023] It is yet another object of the invention to provide a
regeneration device which does not degrade the performance of the
engine, in particular through pressure drops due to the
backpressure exerted by the exhaust gases on the engine when the
filtration device becomes clogged.
[0024] Lastly, it is a final object of the invention to provide a
filtration device for carrying out the regeneration method
according to the invention.
[0025] These objects, among others, are achieved by the present
invention which relates firstly to a method for regeneration of a
device for filtering the exhaust gases produced by a diesel engine,
this method being of the type in which particles retained on a
filtration means of said filtration device are burnt through the
action of a combustion catalyst. This method consists essentially
in retaining the hot exhaust gases around the filtration means in
order to provide the particles with at least some of the heat
energy necessary for their combustion, and in burning said
particles so as to regenerate the filtration device.
[0026] According to one variant, this method also consists in:
[0027] employing a combustion catalyst production means in the
filtration device,
[0028] measuring a temperature .theta..sub.m in the vicinity of the
combustion catalyst production means,
[0029] comparing .theta..sub.m with a temperature .theta..sub.r
corresponding to the temperature at which the combustion of diesel
fuel in the presence of the combustion catalyst is complete,
[0030] if .theta..sub.m is greater than or equal to .theta..sub.r,
initiating post-injection of diesel fuel through an injection means
into the filtration device for a determined period of time, so as
to cause a temperature rise of the particles in order to permit
their combustion.
[0031] According to yet another variant, this method also consists
in:
[0032] measuring a pressure P.sub.m in the vicinity of the
combustion catalyst production means, said pressure P.sub.m
reflecting the degree of obstruction of the filtration means by the
particles,
[0033] measuring the temperature .theta..sub.m,
[0034] comparing said pressure P.sub.m with a reference pressure
P.sub.r corresponding to the maximum acceptable degree of
obstruction,
[0035] comparing .theta..sub.m with .theta..sub.r if P.sub.m is
greater than or equal to the pressure P.sub.r,
[0036] initiating the post-injection of diesel fuel if
.theta..sub.m is greater than or equal to .theta..sub.r.
[0037] The invention also relates to a filtration device for
carrying out the regeneration method according to the invention.
This device has a combustion catalyst production means, a means for
filtration of said exhaust gases downstream of said combustion
catalyst production means, and a means for injecting diesel fuel
upstream of said combustion catalyst production means, said
combustion catalyst production means and filtration means being
contained in a reaction enclosure along the flow path of the
exhaust gases produced by an engine.
[0038] The filtration means, consisting of a set of filtering
units, is exposed in a chamber for receiving the exhaust gases,
with said exhaust gases heating the filtering units.
[0039] The filtration means preferably consists of at least two
particle filters having a body, formed by the filtering units which
are connected together by a joint, and a metal casing.
[0040] The means for injecting diesel fuel advantageously
communicates with a line for discharging the exhaust gases.
[0041] According to another preferred feature, this injection means
comprises a diesel fuel reservoir and a chamber for injecting the
diesel fuel contained in said reservoir into the discharge
line.
[0042] The chamber injection chamber is thus supplied, on the one
hand, with diesel fuel through a first line connecting it to said
reservoir and, on the other hand, with compressed air through a
second line connecting it to the engine, said chamber having an
orifice through which the diesel fuel is injected into the
filtration device.
[0043] The device advantageously has an electronic control
module.
[0044] The device also includes at least one temperature sensor,
placed inside said enclosure, used to measure the temperature
.theta..sub.m in its interior.
[0045] According to another noteworthy variant, it also includes at
least one pressure sensor, placed inside said enclosure, used to
measure the pressure P.sub.m in its interior.
[0046] It is noteworthy that the electronic control module is
connected to the temperature and pressure sensors, compares the
respectively measured values of .theta..sub.m and optionally
P.sub.m with the reference values .theta..sub.r and optionally
P.sub.r, and initiates the injection of diesel fuel into the
discharge line through said injection system when the measurements
.theta..sub.m and optionally P.sub.m are greater than or equal to
the reference values .theta..sub.r and optionally P.sub.r.
[0047] The lines supplying the chamber of the injection system with
diesel fuel and compressed air each advantageously have a solenoid
valve controlled by the electronic control module, opening of the
solenoid valves leading to the intake of diesel fuel and compressed
air into the chamber, and therefore to the injection of diesel fuel
into the exhaust gas discharge line.
[0048] The chamber of the injection system is advantageously
provided with a nozzle in front of the orifice, making it possible
to inject the diesel fuel in a nebulized form into the gas
discharge line.
[0049] The filtering units are advantageously made of silicon
carbide or any other equivalent material whose structure is of a
honeycomb type.
[0050] According to another noteworthy feature of the invention,
the combustion catalyst production means consists of at least one
cartridge based on platinum or any equivalent material that
catalyzes the conversion of the nitrogen monoxide (NO) contained in
the exhaust gases into nitrogen dioxide (NO.sub.2).
[0051] According to another noteworthy feature, the capacity of the
second reservoir is preferably equivalent to the maximum volume of
diesel fuel injected during the post-injection.
[0052] The particle filters are advantageously placed in parallel
in the filtration device.
[0053] The present invention will be understood more clearly on
reading the following description, given with reference to the
drawings which represent an exemplary embodiment of the filtration
device according to the invention without implying any limitation,
and in which:
[0054] FIG. 1 represents a schematic overall view of the system
which comprises the filtration device and makes it possible to
carry out the regeneration method.
[0055] FIG. 2 represents a view in longitudinal section of the
filtration device according to a first embodiment.
[0056] FIG. 3 represents a view in cross section, on the axis
II-II, of the filtration device represented in longitudinal section
in FIG. 3.
[0057] FIG. 4 represents a variant of the latter embodiment, seen
in a longitudinal section of the filtration device.
[0058] FIG. 5 represents a view in longitudinal section of the
filtration device according to a second embodiment.
[0059] The system for carrying out the regeneration method
according to the invention is schematically represented in FIG. 1,
according to a preferred embodiment. Various mechanical elements of
the vehicle, which may or may not be components of the filtration
device and which contribute to the regeneration of the device,
cooperate in this system.
[0060] A diesel engine 10, supplied with fuel from a main reservoir
12 via a supply system 14, produces exhaust gases during operation.
These gases are recovered using a manifold (not shown) at the
outlet of the engine, and are discharged through a discharge line
16. This line enters an enclosure 18 containing a combustion
catalyst production means 20 and a filtration means 22. A
temperature sensor 24 and a pressure sensor 26 are also placed in
the enclosure 18. The function of these sensors is to measure the
temperature and the pressure in the vicinity of the combustion
catalyst production means. The data relating to these measurements
are transmitted to an electronic control module 28, by which they
are analyzed.
[0061] The electronic control module is connected to two lines 30
and 32 and controls their opening. The line 30 connects a secondary
reservoir 34 to the injection chamber 36. The secondary reservoir
34 supplies the injection chamber 36 with diesel fuel. It is itself
supplied from the main reservoir 12 through a pipe system 38.
[0062] For its part, the line 32 connects the engine 10 to the
injection chamber 36. It allows the engine 10 to supply the
injection chamber 36 with compressed air.
[0063] The lines 30 and 32 are opened using two solenoid valves 31
and 33, which are electrically controlled by the electronic control
module.
[0064] A detailed view of the enclosure 18 in longitudinal section
is represented in FIG. 2.
[0065] The enclosure contains the combustion catalyst production
means 20 and the filtration means 22. The combustion catalyst
production means 20 consists of two cartridges 20a and 20b for
producing combustion catalysts.
[0066] These cartridges are preferably on a metal support so as to
obtain the least possible thermal inertia. According to a preferred
embodiment, these cartridges are preferably based on platinum and
the nitrogen monoxide (NO) contained in the exhaust gases is
converted inside them into nitrogen dioxide (NO.sub.2), which
constitutes the combustion catalyst. The NO.sub.2 which is produced
diffuses to the filtration means 22.
[0067] The filtration means 22 consists of a set of
three-dimensional filtering units. These filtering units are
advantageously of the silicon carbide honeycomb type.
[0068] According to a first embodiment, which is represented in
FIG. 2, these filtering units are assembled so as to form the body
of a particle filter. The filtration means accordingly consists of
three particle filters 22a, 22b and 22c. These particle filters,
arranged in this way, are represented as seen from above in FIG. 3.
The filters consist of a body 40 and a metal casing 42. The body 40
is formed by assembling a plurality of filtering units 44 which are
separated by a joint 46, the function of which is to compensate for
their expansion.
[0069] In its lower part, the enclosure 18 contains a retention
chamber making it possible to increase the residence time in the
enclosure for the exhaust gases purified by passing through the
filtration means (filtering units or particle filters).
[0070] This extension of the residence time of the exhaust gases
allows them to heat the filtering units or the particle filters,
and therefore the particles themselves. This noteworthy feature
allows the latter to be maintained at a temperature much higher
than the usual temperature. This temperature may reach the
temperature for their combustion in the presence of the combustion
catalyst. In this case, the regeneration takes place without diesel
fuel being injected.
[0071] A variant of this embodiment is represented in FIG. 4.
According to this variant, the particle filters 22a, 22b and 22c
are arranged the other way round. The device then has a particular
region for retention of the as yet unfiltered exhaust gases.
Specifically, the latter are contained between the catalyst
cartridges and the lower support 48 of the filters, which allows
the exhaust gases to have a longer dwell time before they enter the
particle filters, a fact which will, on the one hand, promote the
heat exchange between the gases and the filters and, on the other
hand, limit the loss of heat by exchange with the surroundings.
[0072] According to a second embodiment of the device according to
the invention, the filtering units 44 are independent of one
another. Accordingly, each filtering unit is separated from the
ones adjacent to it by a space sufficient to allow their expansion.
This arrangement is particularly advantageous because, on the one
hand, it makes it possible to reduce the thermal expansion stresses
very significantly, particularly in the event of vigorous
combustion of the particles which are retained, which greatly
limits the risk that the filtering units will be damaged; on the
other hand, the surface area available for the transmission of heat
by the gases is increased considerably, which commensurately
reinforces this transmission of heat.
[0073] A variant of the second embodiment, which is represented in
FIG. 5, consists in arranging the filtering units 44 the other way
round in the filtration device, with a support being positioned in
the lower part, similarly as in the variant of the first embodiment
which is represented in FIG. 4. The advantages of this arrangement
are the same as those mentioned above in the description of FIG.
4.
[0074] According to an exemplary embodiment, each filtering unit is
a square-based cylinder having a width and a depth of 35 mm, and a
length varying from 150 to 300 mm.
[0075] If the temperature is not sufficient to initiate combustion
of the particles, the regeneration is carried out by injecting
diesel fuel.
[0076] In order to do this, the temperature in the vicinity of the
catalyst production means is measured using the sensor 24. The
measured temperature value .theta..sub.m is received by the
electronic control module. The module compares this value
.theta..sub.m with a reference value .theta..sub.r, corresponding
to the temperature at which combustion of the diesel fuel takes
place completely in the presence of the catalyst.
[0077] If the measured temperature .theta..sub.m is greater than or
equal to the reference value .theta..sub.r, the electronic control
module initiates opening of the solenoid valves 31 and 33. This
opening leads to the intake of diesel fuel and compressed air into
the chamber 36. The diesel fuel mixes with the compressed air in
the chamber 36, and the mixture formed in this way is injected in a
nebulized form into the gas discharge line 16. This injection is
carried out through an orifice arranged in the wall of the chamber
36, in front of which there is a nozzle fixed to the chamber,
making it possible to obtain a nebulized jet under pressure.
According to an exemplary embodiment, the chamber 36 is of the
compressed-air paint spraygun type.
[0078] When the necessary quantity of diesel fuel, predetermined by
the electronic control module, has been injected, the diesel fuel
supply is interrupted by closing the solenoid valve 33. Only the
supply of compressed air continues, so that the latter instead of
the mixture is injected into the line 16. The purpose of this
extended supply of compressed air is to eliminate all the remaining
diesel fuel in the injection chamber 36 and the line 16.
[0079] The capacity of the secondary reservoir 34 is determined so
that it corresponds to the maximum volume of diesel fuel necessary
for the regeneration. In this way, excessive consumption of diesel
fuel cannot take place. By virtue of this embodiment, the frequency
of the regeneration cycles is furthermore limited by the time taken
to fill the second very reservoir 34, which also makes it possible
to avoid consequent extra fuel consumption.
[0080] The fuel injected into the discharge line 16 enters the
enclosure and undergoes complete combustion in the catalyst
production means. This combustion leads to a significant rise in
temperature, up to a temperature .theta..sub.c at which combustion
of the particles clogging the filtration means will take place. The
NO.sub.2 molecules which are produced will catalyze this combustion
reaction. This reaction therefore takes place at a temperature
lower than the normal temperature. During this combustion, the
solid particles are converted into gases, which are discharged.
[0081] The filtration means is therefore freed from deposits and
recovers its full filtration capacity.
[0082] According to a particular embodiment, the measurement of
.theta..sub.m may be processed by the electronic module in order to
evaluate the temperature of the particles in the filtration means.
Specifically, if .theta..sub.m is close to the temperature at which
the particle combustion can take place without post-injection of
diesel fuel, the computer may decide not to initiate this
post-injection, which allows a substantial fuel saving to be
made.
[0083] According to a variant of this embodiment, an additional
temperature sensor is arranged in proximity to the filtration
means, so as to obtain the exact temperature of the particles.
[0084] A third mode of operation consists in simultaneously
measuring the temperature and the pressure in the catalyst
production means, using the temperature sensor 24 and the pressure
sensor 26. The measured pressure value P.sub.m reflects the degree
of obstruction of the filtration means by the particles.
Specifically, if the filtration means is clogged, it is more
difficult for the exhaust gases to pass through, so that they exert
a backpressure. Measuring the pressure P.sub.m therefore
corresponds to the best way of monitoring the clogging of the
filtration means. The electronic control module compares the
measured value P.sub.m with a reference value P.sub.r,
corresponding to the maximum acceptable degree of obstruction of
the filtration means. The electronic control module then initiates
the post-injection of diesel fuel if P.sub.m is greater than or
equal to the pressure P.sub.r, which leads to regeneration of the
filtration means. The benefit of this mode of operation is that the
post-injection is initiated only when the filtration means has
reached a determined degree of clogging, which allows the extra
fuel consumption to be limited greatly.
EXAMPLE
[0085] A filtration device used with an industrial vehicle engine
is presented below as a nonlimiting example, namely the
supercharged Renault VI 620-45 engine with a 10 liter cylinder
capacity and a power of 190 kw. This engine is used in city
buses.
[0086] The filtration device is composed of:
[0087] Two platinum-based catalyst cartridges for converting NO
into NO.sub.2. These cartridges, which are 7.5 inches in diameter
and 3 inches long, were fitted in parallel on a metal support as
represented in FIG. 2. The volume of catalyst was determined so
that the NO to NO.sub.2 conversion ratio is more than 85%.
[0088] Three IBIDEN particle filters, of the silicon carbide
honeycomb type, fitted in parallel. These filters have a cross
section of 162 cm.sup.2 (diameter 143.8 mm) and a length of 254
mm.
[0089] A diesel fuel injection system having an injection chamber
as described above and a secondary reservoir with a capacity of 50
cm.sup.3. The injection system delivery rate is 50 cm.sup.3 per
minute. This delivery rate was determined so that the rise in
temperature of the exhaust gases due to the post-injection is
between 170 and 250.degree. C., depending on the conditions of
use.
[0090] An electronic module controlling the post-injection of
diesel fuel. A timer limits the duration of the post-injection to 1
minute, and specific programming of the module makes it possible to
obtain at most one post-injection every 5 minutes.
[0091] The trial was carried out on a rig and the conditions
corresponding to urban driving conditions.
[0092] The electronic module was set so that the post-injection is
initiated as soon as the backpressure reaches 120 mb and the
temperature of the gases is more than 300.degree. C.
[0093] It is known that, in order for the regeneration to take
place correctly, it is necessary that the time for which the
temperature of the exhaust gases is in excess of 300.degree. C.
should be more than 30% of the working time of the vehicle.
[0094] The device described in this example makes it possible to
obtain an exhaust gas temperature constantly in excess of
300.degree. C., regardless of the initial temperature of the
exhaust gases.
[0095] The value of the backpressure measured after each
regeneration process of the filtration device is thus 50 mb, which
corresponds to the backpressure value measured on a new filtration
device. The regeneration of the device is therefore complete.
[0096] The regeneration method according to the invention, and the
associated filtration device, are therefore particularly suitable
for processing the exhaust gases of municipal transport vehicles.
In fact, the gases produced by these vehicles are generally at a
temperature below that necessary in order to allow regeneration of
conventional filtration devices, which leads to clogging of these
devices and therefore their rapid deterioration owing to vigorous
combustion reactions. The results obtained with the present
technique, however, make it possible to envisage a minimum lifetime
of 100,000 km for the filtration device on vehicles of this
type.
[0097] Such a technique could also be used in automobiles. In fact,
because these operate at much higher engine speeds, the exhaust
gases which are produced are at much higher temperatures, possibly
in excess of 500.degree. C. The problem of filter regeneration is
therefore less crucial. Existing systems, however, generally use
organometallic additives in order to catalyze the particle
combustion, which leads to a significant operating cost. The device
according to the invention, associated with its regeneration
method, makes it possible to overcome this problem of cost.
[0098] Although the filtration device according to the invention
may not include new technical elements, the inventors have
succeeded in combining and adapting various existing techniques in
order to enhance their effects and obtain a device which has a very
high efficiency, in order to combat the emission of polluting
particles produced by diesel engines and, furthermore, in order to
obtain excellent results in terms of the regeneration of filters,
even in the case of vehicles whose engine speeds do not make it
possible to obtain exhaust gases which are at high temperature.
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