U.S. patent application number 09/929961 was filed with the patent office on 2002-06-27 for exhaust-gas cleaning unit with particle filter and nitrogen oxygen store, and operating method therefor.
Invention is credited to Duvinage, Frank, Kurze, Stefan, Liebscher, Thomas, Nolte, Arno, Paule, Markus, Ruzicka, Norbert, Schommers, Joachim.
Application Number | 20020081238 09/929961 |
Document ID | / |
Family ID | 7652967 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081238 |
Kind Code |
A1 |
Duvinage, Frank ; et
al. |
June 27, 2002 |
Exhaust-gas cleaning unit with particle filter and nitrogen oxygen
store, and operating method therefor
Abstract
An exhaust-gas cleaning unit includes a particle filter and a
nitrogen oxide store disposed upstream of the particle filter. A
method for operating the exhaust-gas cleaning unit includes a
nitrogen oxide regeneration phase and a sulphur regeneration phase
for the nitrogen oxide store and a soot regeneration phase for the
particle filter. A longer period is selected for the sulphur
regeneration phase than for the nitrogen oxide regeneration phase.
At least part of the sulphur regeneration phase and at least part
of the soot regeneration phase are performed as a combined
regeneration phase, in which the regeneration phases are performed
in immediate succession or one regeneration phase is performed
intermittently at a number of intervals during the other
regeneration phase.
Inventors: |
Duvinage, Frank;
(Kirchheim/Teck, DE) ; Kurze, Stefan;
(Markgroningen, DE) ; Liebscher, Thomas;
(Fellbach, DE) ; Nolte, Arno; (Stuttgart, DE)
; Paule, Markus; (Remshalden, DE) ; Ruzicka,
Norbert; (Steinenbronn, DE) ; Schommers, Joachim;
(Allmersbach i.T., DE) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
7652967 |
Appl. No.: |
09/929961 |
Filed: |
August 15, 2001 |
Current U.S.
Class: |
422/168 |
Current CPC
Class: |
F01N 3/0835 20130101;
F02D 41/1439 20130101; Y02A 50/2341 20180101; F01N 3/0857 20130101;
F02D 41/024 20130101; Y02T 10/26 20130101; B01D 2255/908 20130101;
F02D 41/1454 20130101; B01D 53/9481 20130101; F01N 3/0231 20130101;
F01N 3/085 20130101; F02D 41/029 20130101; B01D 53/944 20130101;
Y02A 50/20 20180101; F01N 3/0821 20130101; F02D 41/028 20130101;
B01D 53/9495 20130101; Y02C 20/10 20130101; F02D 41/1475 20130101;
Y02A 50/2344 20180101; F01N 2570/12 20130101; F02D 41/0275
20130101; Y02T 10/12 20130101; B01D 2255/912 20130101; F01N 2570/04
20130101; F01N 3/0842 20130101; F02D 41/0055 20130101; Y02A 50/2322
20180101; F01N 3/0885 20130101; B01D 2251/208 20130101; F01N
2570/16 20130101; F01N 13/009 20140601; F01N 2570/14 20130101; F01N
3/2033 20130101 |
Class at
Publication: |
422/168 |
International
Class: |
F01N 003/00; F23J
011/00; B32B 027/02; B01D 050/00; B01D 053/34 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 15, 2000 |
DE |
100 40 554.1 |
Claims
What is claimed is:
1. An exhaust-gas cleaning unit, comprising: a particle filter; and
a nitrogen oxide store, the nitrogen oxide store being disposed
upstream of the particle filter.
2. The exhaust-gas cleaning unit according to claim 1, wherein the
exhaust-gas cleaning unit is configured for a diesel engine of a
motor vehicle.
3. The exhaust-gas cleaning unit according to claim 1, further
comprising an oxidation catalytic converter, the oxidation
catalytic converter being disposed at least one of between the
nitrogen oxide store and the particle filter, upstream of the
nitrogen oxide store and downstream of the particle filter.
4. The exhaust-gas cleaning unit according to claim 1, wherein the
particle filter includes a coating configured to perform one of an
oxidation catalytic converter function, an HC/CO/O.sub.2 storage
function and a soot oxidation assisting function.
5. The exhaust-gas cleaning unit according to claim 1, further
comprising a lambda probe disposed downstream of the particle
filter.
6. A method for operating an exhaust-gas cleaning unit having a
particle filter and a nitrogen oxide store disposed upstream of the
particle filter, the method comprising the steps of: performing a
nitrogen oxide regeneration phase with, at least temporarily, a
rich exhaust-gas composition for the nitrogen oxide store;
performing a sulphur regeneration phase with an elevated
temperature and, at least temporarily, a rich exhaust-gas
composition for the nitrogen oxide store; and performing a soot
regeneration phase with, at least temporarily, a lean exhaust-gas
composition and an elevated exhaust-gas temperature for the
particle filter; wherein a longer period is provided for the
sulphur regeneration phase than for the nitrogen oxide regeneration
phase; and wherein at least part of the sulphur regeneration phase
and at least part of the soot regeneration phase are performed as a
combined sulphur and soot regeneration phase, the combined sulphur
and soot regeneration phase including one of: a plurality of
shorter intermittent sulphur regeneration phases during a longer
soot regeneration phase; a plurality of shorter intermittent soot
regeneration phases during a longer sulphur regeneration phase; a
soot regeneration phase and a sulphur regeneration phase in
immediate succession; and a sulphur regeneration phase and a soot
regeneration phase in immediate succession.
7. The method according to claim 6, wherein the exhaust-gas
cleaning unit includes a lambda probe disposed downstream of the
particle filter, the method further comprising the steps of:
monitoring the exhaust-gas composition with the lambda probe during
the nitrogen oxide regeneration phase for a breakthrough of
reducing agent, the breakthrough of reducing agent indicating an
end of the nitrogen oxide regeneration phase; and monitoring the
exhaust-gas composition with the lambda probe during the soot
regeneration phase for oxygen content, the oxygen content being
indicative of an end of a soot burn-off.
Description
FIELD OF THE INVENTION
[0001] The invention relates to an exhaust-gas cleaning unit having
a particle filter and a nitrogen oxide store and to a method for
operating a unit of this type. Exhaust-gas cleaning units of this
type are suitable in particular for cleaning the exhaust gases of
diesel engines from, for example, motor vehicles.
BACKGROUND INFORMATION
[0002] European Published Patent Application No. 0 758 713
describes an exhaust-gas cleaning unit in which an oxidation
catalytic converter is connected upstream of the particle filter,
as seen in the direction of flow of the exhaust gas, and the
nitrogen oxide store is connected downstream of the particle
filter. As an alternative to the nitrogen oxide store, a nitrogen
oxide reduction catalytic converter may be used. The oxidation
catalytic converter is used to convert nitrogen monoxide which is
contained in the exhaust gas in soot regeneration phases of the
particle filter into nitrogen dioxide, which promotes the soot
burn-off in the particle filter. The nitrogen oxide store or the
nitrogen oxide reduction catalytic converter is used to collect or
convert nitrogen monoxide which is formed by the reaction of the
nitrogen dioxide with the soot particles. The soot regeneration
operations occur, for example, every 60 minutes for about three
minutes with a lean exhaust-gas composition and temperatures of
between approximately 400.degree. C. and 500.degree.C. Conventional
nitrogen oxide regeneration phases for the nitrogen oxide store are
performed approximately every 10 seconds to every few minutes, in
each case for approximately 0.5 seconds, with a rich exhaust-gas
composition. When a nitrogen oxide regeneration phase of this type
falls in the period of a soot regeneration phase, it is performed,
by an additional increase in temperature, as a correspondingly
short sulphur regeneration phase, in order to prevent gradual
sulphur poisoning of the nitrogen oxide store.
[0003] Various methods for nitrogen oxide (NO.sub.x) regeneration
and sulphur regeneration of a nitrogen oxide store are
conventional. For example, German Published Patent Application No.
197 50 226 describes a method for NO.sub.x regeneration in which a
desired, rich exhaust-gas composition is generated substantially
only by engine measures, including suitable control of exhaust-gas
recycling.
[0004] It is an object of the present invention to provide a new
type of exhaust-gas cleaning unit and a corresponding operating
method for this unit.
SUMMARY
[0005] The above and other beneficial objects of the present
invention are achieved by providing an exhaust-gas cleaning unit
and method as described herein.
[0006] The exhaust-gas cleaning unit according to the present
invention includes a nitrogen oxide store connected upstream of the
particle filter. Connecting the nitrogen oxide store upstream of
the particle filter, as seen in the direction of flow of the
exhaust gas, has a number of particular advantages. For example,
nitrogen oxides, which have been temporarily stored in the nitrogen
oxide store, may be liberated at the elevated exhaust-gas
temperature which is required for soot regeneration of the particle
filter and may additionally assist the soot regeneration in the
form of nitrogen dioxide (NO.sub.2). Furthermore, sulphur
regeneration of the nitrogen oxide store, which requires relatively
high exhaust-gas temperatures of typically between 600.degree. C.
and 700.degree. C., may be combined with soot regeneration of the
particle filter, for which elevated exhaust-gas temperatures of
between approximately 400.degree. C. and approximately 600.degree.
C. are generally used, the fact that the nitrogen oxide store is
connected upstream of the particle filter resulting in a natural
temperature gradient along the exhaust-gas flow which matches these
temperature requirements.
[0007] A respective oxidation catalytic converter may be provided
upstream of the nitrogen oxide store, between the nitrogen oxide
store and the particle filter and/or downstream of the particle
filter. Depending on the particular arrangement, an oxidation
catalytic converter of this type assists with raising the
exhaust-gas temperature, soot regeneration by generating NO.sub.2
and/or avoiding hydrocarbon (HC) and/or carbon monoxide (CO)
emissions.
[0008] An HC/CO/O.sub.2 storage coating and/or an oxidation
catalyst coating and/or a coating which promotes the oxidation of
soot may be provided in the particle filter, preferably in each
case in an inlet-side part thereof. Thus, unburned hydrocarbons and
carbon monoxide may be trapped or oxidized and/or the soot burn-off
during the particle filter regeneration may be assisted.
[0009] An exhaust-gas according to the present invention may
include a lambda probe downstream of the particle filter. This
probe may be used to monitor the soot burn-off behavior during the
particle regeneration and to detect any breakthrough of reducing
agents during the NO.sub.x regeneration of the nitrogen oxide
store.
[0010] The operating method according to the present invention
includes firstly sulphur regeneration phases for the nitrogen oxide
store, which are performed for a longer period than the NO.sub.x
regeneration phases, in order to achieve complete sulphur
desorption. Moreover, combined sulphur and soot regeneration phases
are provided, during which the sulphur regeneration of the nitrogen
oxide store and the soot regeneration of the particle filter may be
linked in terms of time by the two regeneration operations being
performed immediately after one another or by one regeneration
operation being performed intermittently at intervals during the
other regeneration operation. In this manner, the thermal
exhaust-gas energy may be utilized for both regeneration
processes.
[0011] In the operating method according to the present invention,
a lambda probe downstream of the particle filter may be used
firstly to detect the progress of a soot regeneration phase and
secondly to detect a breakthrough of reducing agents during a
nitrogen oxide regeneration phase and therefore that the latter
phase has ended.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic block diagram of an exhaust-gas
cleaning unit for a diesel engine having a particle filter, an
upstream nitrogen oxide store and an optional downstream oxidation
catalytic converter.
[0013] FIG. 2 is a schematic block diagram of an exhaust-gas
cleaning unit having an oxidation catalytic converter disposed
upstream of the nitrogen oxide store.
[0014] FIG. 3 is a schematic block diagram of an exhaust-gas
cleaning unit having an oxidation catalytic converter disposed
between the nitrogen oxide store and the particle filter.
[0015] FIG. 4 is a schematic block diagram of an exhaust-gas
cleaning unit having a particle filter that includes a coating
configured to perform an exhaust-gas cleaning function.
DETAILED DESCRIPTION
[0016] The exhaust-gas cleaning unit, only the relevant components
of which are illustrated in FIG. 1, is suitable in particular for
cleaning the exhaust gas from a diesel engine, for example in a
motor vehicle. The exhaust-gas cleaning unit includes, as
components which are active in the exhaust-gas cleaning in an
exhaust system 1, a particle filter 2 and a nitrogen oxide store 3
which is connected upstream of the particle filter 2, as seen in
the direction R of flow of the exhaust gas, as well as, optionally,
an oxidation catalytic converter 4 connected downstream of the
particle filter 2.
[0017] A control unit, which may formed, for example, by an engine
control unit which controls the exhaust-emitting diesel engine, is
used to control the operation of the exhaust-gas cleaning unit. The
control unit determines the operating state of the exhaust-gas
cleaning unit using various sensors arranged in the exhaust system
1. These sensors include in particular a first sensor arrangement
S1. Upstream of the nitrogen oxide store 3, for detecting the
lambda value, the nitrogen oxide content and the temperature of the
exhaust gas, a second and third sensor arrangement S2, S3 between
the nitrogen oxide store 3 and the particle filter 2 and downstream
of the latter, respectively, in each case to determine pressure and
temperature, and, also downstream of the particle filter 2,
upstream or downstream of the optional oxidation catalytic
converter 4, a fourth sensor arrangement S4 for determining the
lambda value and oxygen and/or nitrogen oxide content. Depending on
the particular application, only some of the abovementioned sensors
may be provided.
[0018] FIGS. 2 to 4 illustrate variants of the unit illustrated in
FIG. 1. In the unit illustrated in FIG. 2, an oxidation catalytic
converter 5 is additionally provided upstream of the nitrogen oxide
store 3. In this case, the optional oxidation catalytic converter 4
downstream of the particle filter 2 may be smaller.
[0019] In the exhaust-gas cleaning unit illustrated in FIG. 3, an
oxidation catalytic converter 6 is connected between the nitrogen
oxide store 3 and the particle filter 2. Again, the optional
oxidation catalytic converter 4 downstream of the particle filter 2
may be smaller.
[0020] The exhaust-gas cleaning unit illustrated in FIG. 4 uses a
modified particle filter 2a which, in an inlet-side section 7, is
provided with a coating which is active in cleaning of the exhaust
gas. Depending on the particular application, this coating is
selected so that it fulfils an oxidation catalyst function or an
HC/CO/O.sub.2 storage function or a function of promoting soot
burn-off. Suitable materials for such coatings are conventional and
therefore require no further explanation. In the first case, the
coating acts as an oxidation catalyst, i.e., it catalyzes oxidation
of gaseous, oxidizable exhaust-gas constituents. In the second
case, the coating serves to store unburned hydrocarbons, carbon
monoxide or oxygen contained in the exhaust gas at the inlet side
of the particle filter 2a, depending on the operating state of the
diesel engine and of the exhaust-gas cleaning unit. In this manner,
it is possible, for example, to prevent a breakthrough of unburned
hydrocarbons and of carbon monoxide. In the third case, the coating
serves as an oxidation aid in the soot burn-off during the soot
regeneration of the particle filter, with the result that the soot
burn-off may occur even at relatively low temperatures.
[0021] Because the nitrogen oxide store 3 is arranged upstream of
the particle filter 2, each of the installations illustrated may be
operated so that the functions of these two exhaust-gas cleaning
components 2, 3 may be adapted to one another and assist one
another with optimum utilization of the thermal energy contained in
the exhaust gas. As is conventional, the nitrogen oxide store 3
fulfills the nitrogen oxide reduction function, by temporarily
storing nitrogen oxides, for example by adsorption in nitrate form,
during lean operation of the diesel engine and releasing them and
reducing them to form nitrogen during periodic regeneration or
desorption phases. These NO.sub.x regeneration phases are performed
at typical intervals of one to a few minutes, for a period of
typically slightly less than one second to a few seconds, during
which period a rich exhaust-gas composition is set. Any secondary
emissions of unburned hydrocarbons and carbon monoxide which arise
may be oxidized by the subsequent oxidation catalytic converter(s)
4, 6.
[0022] In the unit illustrated in FIG. 4, a breakthrough of
unburned hydrocarbons and/or carbon monoxide may also be prevented
as a result of the particle filter coating 7 containing a material
which has an HC/CO/O.sub.2 storage function and, depending on the
exhaust-gas atmosphere and exhaust-gas temperature, is able to
temporarily store hydrocarbons and carbon monoxide and/or to
oxidize them using temporarily stored oxygen.
[0023] The particle filter 2 collects particles contained in the
exhaust gas for a running distance of typically of the order of
magnitude of a few hundred kilometers or several operating hours of
the diesel engine, until its storage capacity is reached, after
which it is subjected to soot regeneration. For this soot
regeneration, the exhaust gas is raised to a suitably high
temperature of typically 400.degree. C. to 600.degree. C. by
corresponding engine measures, and a lean exhaust-gas composition
with an oxygen content of preferably greater than 5% is
established. This operation is typically performed for a few
minutes, after which period the soot has been completely burnt off
and the particle filter 2 has been regenerated.
[0024] The soot regeneration of the particle filter 2 may be
assisted by the upstream nitrogen oxide store 3 as a result of the
latter previously being laden with nitrogen oxides. Then, as soon
as the exhaust-gas temperature for starting a soot regeneration
operation is raised to over 400.degree. C., e.g., to over
450.degree. C., the nitrogen oxide store 3, under the lean
exhaust-gas atmosphere, releases additional NO.sub.2, which acts as
a soot burn-off agent and assists soot burn-off in the downstream
particle filter, which begins at particle filter temperatures of
below 400.degree. C., with the result that the regeneration speed
of the particle filter 2 is increased. If the diesel engine
includes an exhaust-gas recycling system, the soot regeneration of
the particle filter 2 may be enhanced further by deactivating the
exhaust-gas recycling during this period, leading to higher
NO.sub.x raw emissions. As a result, additional nitrogen dioxide
for accelerated soot burn-off is provided to the upstream oxidation
catalytic converter 5 directly and via the oxidation of nitrogen
monoxide to form NO.sub.2 in the NO.sub.x store 3.
[0025] If, in the unit illustrated in FIG. 4, the particle filter
coating 7 is formed by a material which assists with soot
oxidation, the soot burn-off is promoted by this coating 7, which
has the effect of causing the soot to be burnt off even at a
relatively low temperature.
[0026] When using sulphur-containing operating substances, in
particular fuel and oil, for the diesel engine, the nitrogen oxide
store 3 may gradually become covered with sulphur contained in the
exhaust gas and, as a result, loses its ability to store NO.sub.x.
In order for the sulphur which has been incorporated in the
nitrogen oxide store 3, generally in sulphate form, to be released
again, it is conventional to perform corresponding desulphating
phases from time to time. These phases are typically required in
each case after a few thousand operating kilometers and if possible
are maintained for a few minutes, typically up to about 15 minutes
for complete sulphur regeneration. The sulphur regeneration
requires the nitrogen oxide store 3 to be heated to a relatively
high temperature of, typically, above 600.degree. C., e.g. to
650.degree. C.
[0027] The times at which a sulphur regeneration of the nitrogen
oxide store 3 is performed may be linked to soot regeneration of
the particle filter 2, since both operations require elevated
exhaust-gas temperatures and therefore the elevated thermal
exhaust-gas energy may be utilized for both regeneration
operations. By way of example, sulphur regeneration may be
performed immediately before or immediately after a soot
regeneration. A further possibility is for both regeneration
processes to be performed quasi-simultaneously, as a result of the
process parameters for one regeneration operation being established
in principle for over and above a certain period, but during this
period the process parameters are intermittently switched over for
brief periods to those required for the other operation. By way of
example, it is possible, during soot regeneration of the particle
filter 2, during which in principle a lean exhaust-gas composition
is established, to intermittently, for example every 15 seconds to
60 seconds, switch over for a brief period of, for example, three
seconds to 10 seconds, to a rich exhaust-gas composition, and in
this manner to bring about sulphur regeneration of the nitrogen
oxide store 3.
[0028] This time-matching of soot regeneration of the particle
filter 2 and sulphur regeneration of the nitrogen oxide store 3 is
assisted by the specific arrangement of the nitrogen oxide store 3
upstream of the particle filter 2 and the standard temperature
gradient in the exhaust system 1, since this arrangement means
that, at a given, elevated exhaust-gas temperature, the nitrogen
oxide store 3 tends to be at a higher temperature than the particle
filter 2 which follows it downstream. In this manner, it is
possible, without further additional heating measures, to set the
temperature of, for example, 650.degree. C. which is required for
the sulphur regeneration in the nitrogen oxide store 3 and, at the
same time, to set the slightly lower temperature of approximately
400.degree. C. to 600.degree. C. required for soot regeneration in
the particle filter 2. Moreover, the relatively high thermal
inertia of the particle filter, which results from its mass, does
not cause any delay to the temperature control of the NO.sub.x
store 3. Furthermore, the increase in the exhaust-gas temperature
may be at least partially affected by oxidation, for example, of
additionally injected fuel.
[0029] Connecting the oxidation catalytic converter 5 upstream of
the nitrogen oxide store 3, in accordance with the unit illustrated
in FIG. 2, given its particularly high temperature stability, may
contribute to protecting the nitrogen oxide store 3 from very high
exothermic temperatures during this oxidation, in that it oxidizes
at least some of the oxidizable constituents contained in the
exhaust gas, and as a result, at least partially relieves the
nitrogen oxide store 3 of this oxidation function. In this manner,
the thermal aging of the nitrogen oxide store 3 may be
minimized.
[0030] As the above description of example embodiments illustrates,
the exhaust-gas cleaning unit according to the present invention
and the associated operating method according to the present
invention allow the thermal exhaust-gas energy to be utilized for
the regeneration operations of both the nitrogen oxide store 3 and
the particle filter 2. Moreover, the upstream nitrogen oxide store
3 is able to assist and accelerate the soot regeneration of the
particle filter 2 by additionally providing nitrogen oxide and by
increasing the exhaust-gas temperature by exothermic oxidation of,
for example, fuel which is introduced into the exhaust gas by
additional injection into the diesel engine.
[0031] The exhaust-gas sensor arrangements S1 to S4 of the
exhaust-gas cleaning unit, for measuring the temperature, the
pressure and the nitrogen oxide and oxygen content in the exhaust
gas at the various locations of the exhaust system, may be used to
control the sequence of the various regeneration operations
described above. For example, arranging the lambda probe S4
downstream of the particle filter 2 upstream or downstream of the
optional oxidation catalytic converter 4 allows the exhaust gas to
be monitored both with regard to a breakthrough of reducing agent
during nitrogen oxide regeneration phases, which indicates that the
nitrogen oxide desorption has been completed, and with regard to
the oxygen content during the soot regeneration of the particle
filter 2, with the result that the burn-off behavior of the soot
may be determined and complete conclusion of the soot burn-off may
be detected.
* * * * *