U.S. patent application number 15/034786 was filed with the patent office on 2016-12-08 for exhaust gas post treatment device.
The applicant listed for this patent is ROBERT BOSCH GMBH. Invention is credited to Carsten Becker, Harald Bressler, Christoph Osemann.
Application Number | 20160356200 15/034786 |
Document ID | / |
Family ID | 51871053 |
Filed Date | 2016-12-08 |
United States Patent
Application |
20160356200 |
Kind Code |
A1 |
Bressler; Harald ; et
al. |
December 8, 2016 |
EXHAUST GAS POST TREATMENT DEVICE
Abstract
An exhaust gas post-treatment system for purifying exhaust gas
from an internal combustion engine, and to a corresponding method.
The system includes a particle filter, a device having catalytic
oxidation function, and at least one mixing chamber which are
combined to form a constructive unit.
Inventors: |
Bressler; Harald; (Westheim,
DE) ; Osemann; Christoph; (Karlsruhe, DE) ;
Becker; Carsten; (Kernen I.R., DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROBERT BOSCH GMBH |
Stuttgart |
|
DE |
|
|
Family ID: |
51871053 |
Appl. No.: |
15/034786 |
Filed: |
November 11, 2014 |
PCT Filed: |
November 11, 2014 |
PCT NO: |
PCT/EP2014/074220 |
371 Date: |
August 5, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02T 10/24 20130101;
F01N 13/009 20140601; F01N 2610/02 20130101; F01N 3/2066 20130101;
F01N 2900/1411 20130101; F01N 3/2882 20130101; F01N 2570/14
20130101; F01N 13/0097 20140603; F01N 3/021 20130101; F01N 3/035
20130101; F01N 3/106 20130101; F01N 2240/20 20130101; F01N 3/103
20130101; F01N 3/2892 20130101; F01N 2610/01 20130101; F01N 13/1888
20130101; F01N 2900/0416 20130101; F01N 2900/1404 20130101; F01N
2900/1406 20130101; Y02T 10/12 20130101; F01N 2900/1402 20130101;
F01N 2250/02 20130101 |
International
Class: |
F01N 13/00 20060101
F01N013/00; F01N 3/20 20060101 F01N003/20; F01N 3/28 20060101
F01N003/28; F01N 3/035 20060101 F01N003/035; F01N 3/10 20060101
F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 15, 2013 |
DE |
10 2013 223 313.2 |
Claims
1-15. (canceled)
16. An exhaust gas post-treatment system for purifying an exhaust
gas of an internal combustion engine, comprising: a particle
filter, a device having catalytic oxidation function, and at least
one mixing chamber which are combined to form a constructive unit;
wherein (i) the particle filter, the device having the catalytic
oxidation function or (ii) the particle filter having the catalytic
oxidation function and the at least one mixing chamber, are
combined with one another to form the constructive unit, which is
situated in a cylindrical container or forms such a container.
17. The exhaust gas post-treatment system of claim 16, wherein the
particle filter and the device having catalytic oxidation function
are combined to form a particle filter having a catalytic oxidation
function.
18. The exhaust gas post-treatment system of claim 16, wherein the
cylindrical container has end parts that detachably connect the
cylindrical container to elements of the exhaust gas post-treatment
system.
19. The exhaust gas post-treatment system of claim 16, wherein the
at least one mixing chamber has structures and is configured to mix
a supplied exhaust gas stream with a reducing agent to form an
exhaust gas/reducing agent mixture that is injected by an injection
device or is produced by this device.
20. The exhaust gas post-treatment system of claim 19, wherein the
structures of the at least one mixing chamber include guide
surfaces that conduct the exhaust gas/reducing agent mixture in a
spiral flow pattern to an outlet of the mixing chamber.
21. The exhaust gas post-treatment system of claim 16, wherein
downstream from the at least one mixing chamber there is situated
at least one catalytic converter device including at least one SCR
catalytic converter, ammonia oxidation catalytic converter, and/or
diesel oxidation catalytic converter.
22. The exhaust gas post-treatment system of claim 21, wherein the
at least one catalytic converter device is accommodated with the
constructive unit in the cylindrical container or forms such a
container.
23. An exhaust gas post-treatment system for purifying an exhaust
gas from an internal combustion engine, comprising: an exhaust gas
post-treatment device including a particle filter having a
catalytic oxidation function, at least one mixing chamber, and an
SCR catalytic converter, which are situated in combined form in a
cylindrical container, the exhaust gas post-treatment device
converting nitrogen oxides of the exhaust gas resulting from the
internal combustion engine at least at times with an efficiency of
greater than 50%; wherein the particle filter having the catalytic
oxidation function, the at least one mixing chamber, and the SCR
catalytic converter are combined detachably with one another, and
wherein the cylindrical container has at least one removable end
part configured to afford access to the particle filter having the
catalytic oxidation function.
24. The exhaust gas post-treatment system of claim 23, further
comprising: an additional catalytic converter device for limiting
the ammonia content in the exhaust gas stream exiting from the
exhaust gas post-treatment system.
25. A method for purifying exhaust gas, the method comprising:
producing, by an internal combustion engine, an exhaust gas having
between 2 g NO.sub.x/kWh and 12 g NO.sub.x/kWh; conducting the
exhaust gas from the internal combustion engine to an exhaust gas
post-treatment system, including a particle filter having a
catalytic oxidation function and at least one mixing chamber;
providing catalytic oxidation of pollutants and deposition of
particles from the exhaust gas using the particle filter having a
catalytic oxidation function, and producing a first treated exhaust
gas; and mixing the first treated exhaust gas with a reducing agent
in the at least one mixing chamber to form an exhaust gas/reducing
agent mixture; wherein the exhaust gas post-treatment system for
purifying an exhaust gas of an internal combustion engine, includes
the particle filter having the catalytic oxidation function and the
at least one mixing chamber which are combined to form a
constructive unit, wherein (i) the particle filter, the device
having the catalytic oxidation function or (ii) the particle filter
having the catalytic oxidation function and the at least one mixing
chamber, are combined with one another to form the constructive
unit, which is situated in a cylindrical container or forms such a
container.
26. The method of claim 25, wherein the exhaust gas/reducing agent
mixture is further prepared in a catalytic converter device
situated downstream from the at least one mixing chamber, and
wherein the catalytic converter device produces a second treated
exhaust gas.
27. The method of claim 25, wherein the method is controlled by at
least one control unit as a function of a selection of ascertained
and evaluated parameters of the exhaust gas post-treatment system,
the parameters including at least one of a particle mass, a
particle number, an exhaust gas pressure, a temperature, an exhaust
gas flow quantity, a reducing agent quantity, an exhaust gas
composition, an exhaust gas concentration, a reducing potential,
and an oxidation potential.
28. The method of claim 27, wherein the at least one control unit
enables, by modifications of parameters of the internal combustion
engine and/or modifications of the parameters of the exhaust gas
post-treatment system, a timely adaptation efficiently purify the
exhaust gas.
29. The exhaust gas post-treatment system of claim 23, wherein the
efficiency is greater than 90%.
30. The exhaust gas post-treatment system of claim 23, wherein the
efficiency is greater than 95%.
31. The exhaust gas post-treatment system of claim 23, wherein the
efficiency is greater than 99%.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an exhaust gas including a
particle filter having a catalytic oxidation function and at least
one mixing chamber, combined to form a constructive unit, and to a
corresponding method for exhaust gas post-treatment.
BACKGROUND INFORMATION
[0002] Internal combustion engines, in particular diesel-operated
motor vehicles, emit a complex mixture of air pollutants including
particles, or fine materials, and gaseous compounds, inter alia
nitrogen oxides (NO.sub.x), carbon monoxide (CO), and uncombusted
hydrocarbons (HC). Due to stricter pollutant emission standards
that are now in effect, attempts are being made to regulate the
quantity of air pollutants emitted by an internal combustion
engine.
[0003] In exhaust gas post-treatment systems, in addition to an
oxidation catalytic converter and a soot particle filter, a
selective catalytic reduction (SCR) is used to meet the strict
exhaust gas regulations with regard to the NO.sub.x portion in the
exhaust gas. A reducing agent injected into the exhaust gas stream,
standardly urea or a water/urea solution, decomposes into ammonia,
which reacts with the nitrogen oxide contained in the exhaust gas,
forming water and nitrogen in the presence of a catalyst.
[0004] Coated particle filters having catalytic oxidation function
are already known, the catalytic material being contained in the
form of a coating or in some other way. Corresponding catalytic
converters are suitable for oxidizing uncombusted gaseous and
nonvolatile hydrocarbons and carbon monoxide to a large extent into
carbon dioxide and water. In addition, a portion of the nitrogen
oxides (NO.sub.x) that are present can be oxidized at the oxidation
catalytic converter into NO.sub.2. The hydrocarbon, deposited in
the particle filter in the form of soot particles, can be converted
to CO.sub.2 using the nitrogen dioxide. This process is known as
"passive regeneration." An increased portion of NO.sub.2 in the
exhaust gas promotes a subsequent reduction of the nitrogen oxides
(NO.sub.x), compared to a smaller portion.
[0005] Patent document WO 1999/039809 relates to a system for
selective catalytic reduction (SCR) for treating NO.sub.x and
combustion exhaust gas containing solid particles, there being
provided, in combination and in the following sequence, an
oxidation catalytic converter, a fine material filter, a source for
the reducing agent, an injection device with a reducing agent, and
an SCR catalytic converter. An oxidation catalytic converter that
is used, also called DOC (diesel oxidation catalyst), promotes the
conversion of HC and CO impurities of the exhaust gas, and at least
partly promotes oxidation of the fine material into water and
carbon dioxide. In addition, the oxidation catalytic converter
supports the oxidation of at least a part of the nitrogen monoxide
of the exhaust gas into nitrogen dioxide. A higher portion of
NO.sub.2 in the exhaust gas supports the conversion of NO.sub.x at
an SCR catalytic converter, and causes a passive regeneration of
the particle filter, deposited fine material particles being
oxidized. Disadvantageous are the large space requirement of the
components of the exhaust gas post-treatment system, and in
particular the situation of the individual components upstream from
the SCR catalytic converter. In addition, the voluminous and long
configuration of the installation results in a greater distance
from the internal combustion engine and, finally, a lower
temperature at the SCR catalytic converter. In particular given
dynamic operation, in this way premature dosing of reducing agent
is prevented, because the dosing can take place only starting from
a particular operating temperature at the SCR catalytic converter.
Accordingly, a configuration of oxidation catalytic converter, fine
material filter, and SCR catalytic converter represents a large
thermic mass that causes heat losses and, due to the large number
of components, a significant cost outlay.
[0006] Patent document DE 2012 015 840 A1 discusses a
post-treatment system for exhaust gas from an internal combustion
engine that, in a treatment device, combines a particle filter with
an SCR catalytic converter. Such a combination is abbreviated as,
inter alia, CDS, SDPF, SCRoF, or the like, an SCR catalytic
converter being situated on a particle filter substrate. The CDS
catalytic converter performs both a particle trap function and also
SCR functions. However, in such a combination a high loading of the
filter substrate with an SCR catalyst compound is required, which
can cause an unacceptably high pressure loss. In addition, high
thermic demands are placed on the catalyst compound in order to
withstand the high temperatures of a particle filter regeneration.
The described post-treatment system is further supplemented by a
second purification catalytic converter, for example realized as a
diesel oxidation catalytic converter and/or SCR catalytic
converter. In such a system, the required installation space, in
particular installation length, has turned out to be a problem. The
installation length is determined decisively by the length of a
mixing stretch that is necessary in order to mix the injected
reducing agent adequately with the exhaust gas. The associated heat
losses are high. In addition, such a system does not support the
passive regeneration of the filter substrate.
[0007] Patent document WO 2012/05672 A1 discusses an exhaust gas
train of an internal combustion engine having a decoupling element
between a hot exhaust gas line and a cold exhaust gas line for
compensating vibrations, and having a nitrogen oxide treatment
device. In addition, an injection device is provided for a
corresponding reducing agent, and a mixing device is provided for
mixing the exhaust gas with the reducing agent, which form a unit
that is connected to the coupling element.
SUMMARY OF THE INVENTION
[0008] According to the present invention, a post-treatment system
is provided for purifying an exhaust gas, containing at least
nitrogen oxides and soot particles, from an internal combustion
engine, which is characterized in that a particle filter, a device
having a catalytic oxidation function, and at least one mixing
chamber following the particle filter in the direction of flow of
the exhaust gas are combined to form a constructive unit. In
addition, a method for exhaust gas post-treatment is provided that
uses the post-treatment system.
[0009] The particle filter and the device having the catalytic
oxidation function can be separated spatially, for example being
provided on separate elements, or, in a specific embodiment, can be
provided as a particle filter having a catalytic oxidation
function.
[0010] A particle filter having an oxidation catalyst function is
configured to carry out particle trap functions and a conversion of
pollutants in the exhaust gas, as well as to enable a regeneration
of the particle filter. In general, particle filters have a
structure, or a barrier, for example in the form of a honeycomb
bearer having a multiplicity of mutually closed channels that are
realized such that exhaust gas containing particles flows through
porous walls of the bearer, and the particles are deposited in
pores.
[0011] As structures or bearers for catalytic layers, for example
honeycomb-shaped wall flow filters or honeycomb-shaped catalyst
bearers, for example made of ceramic, can be used. Metallic bearers
are also possible. The structure of the particle filter having
catalytic oxidation function must permit in particular, as an
essential property, the desired particle filter effect, and must
enable a catalytic activity that lends the filter the desired
oxidation function. As an essential property of this oxidation
function, non-oxidative or partly oxidative hydrocarbons and carbon
monoxide contained in the exhaust gas or arising during oxidation
of particles with oxygen in the exhaust gas train, for example
after a targeted temperature increase in the filter charged with
the particles, are oxidized at least partly to form CO.sub.2 and
water. As a further essential property, the oxidation function can,
in addition to the oxidation reactions named above, optionally also
oxidize nitrogen monoxide, at least in a limited temperature range,
in order to set a mass ratio that is favorable for subsequent
reactions for the nitrogen oxides contained in the exhaust gas.
[0012] The particle filter, the device for catalytic oxidation or
the particle filter having catalytic oxidation function, and the at
least one mixing chamber can be combined with one another by
detachable connecting elements to form a constructive unit. In a
specific embodiment, the constructive unit is situated in a
container, which may be in a cylindrical container, or forms such a
container.
[0013] In particular, the constructive unit is fashioned in such a
way that easy access to the particle filter is possible. Thus, the
cylindrical container that accommodates or forms the constructive
unit can have connecting parts in the form of end parts that
detachably connect the cylindrical container to elements of the
post-treatment system, the cylindrical container being accommodated
on the exhaust gas train. The end parts can be fastened by a
clamping device or by screws. Due to the detachable connection of
the cylindrical container to the exhaust gas train, the interior is
accessible, so that individual elements accommodated therein are
also accessible.
[0014] The at least one mixing chamber is fashioned to mix an
exhaust gas stream, supplied by the upstream elements of the
exhaust gas post-treatment system, with a reducing agent that is
injected by an injection device or produced thereby.
[0015] The at least one mixing chamber is in particular fashioned
to convert liquid reducing agent supplied by the injection device
to the gas phase, which agent is used in a subsequent reduction
catalytic converter, in particular an SCR catalytic converter. In
addition, the at least one mixing chamber is structured so as to
mix gas phases and/or gas-liquid phases along a mixing stretch.
[0016] In general, the flow path of the exhaust gas in an exhaust
gas post-treatment system is limited due to the installation
conditions and the low heat losses that are to be sought. According
to the present invention, through a structuring of the mixing
chamber the exhaust gas flow is given an overall path length that
is longer than the overall length of the at least one mixing
chamber. The mixing chamber can be an essentially tube-shaped
element that conducts the exhaust gas flow and promotes a mixing of
the exhaust gas flow and reducing agent. The mixing chamber can
have a cylindrical cross-sectional shape or some other suitable
cross-sectional shape, for example spherical. In addition, the at
least one mixing chamber can have internal mixing devices that are
fashioned to mix the exhaust gas flow and the injected reducing
agent while flow is taking place through the mixing chamber.
Corresponding mixing devices, also designated as structures, can be
used, in the form of mixing plates, mixing blades, screens, or
other known devices acting as static mixers. Dynamic mixing devices
are also conceivable, and here a plurality of mixing devices may be
used. In order to achieve a good distribution of the injected
reducing agent into the exhaust gas flow, in the interior of the at
least one mixing chamber corresponding structures are provided that
give the exhaust gas flow for example a rotational impulse, or a
swirl or turbulence, achieving a good swirl and thus a good
distribution of the reducing agent in the exhaust gas flow. The
structures can be fashioned in the form of guide surfaces that form
at least one helical path, so that the produced exhaust
gas/reducing agent mixture leaves the mixing chamber via an outlet
in a spiral flow pattern.
[0017] The reducing agent is injected into the exhaust gas flow
using an injection device. The reducing agent may be injected at a
position; the reducing agent injected for example by an injection
nozzle can be distributed uniformly and atomized in the exhaust gas
while it is conveyed along a flow path. In particular, for reasons
of space the distance between the injection device and a downstream
reducing catalytic converter should on the one hand be as small as
possible, while on the other hand however sufficient dwell time
must be available to ensure a satisfactory distribution and
atomization of the reducing agent in the exhaust gas flow. In the
case of a downstream reduction catalytic converter of the SCR type,
which reduces nitrogen oxides contained in the exhaust gas using
reducing agent, for example ammonia, the injection device can be
configured for example to inject an aqueous urea solution as a
precursor of the reducing agent. In this example, the injection
device can be charged with an aqueous urea solution with a
specified pressure from a supply tank via a dosing device that is
situated outside the mixing chamber. The mixing chamber is
fashioned to convert liquid injected reducing agent to the gas
phase. In addition, the mixing chamber is suitable for mixing gas
flows.
[0018] The injection device, for example in the form of injection
nozzles, can be situated on a cylindrical container that
accommodates the mixing chamber in such a way that the reducing
agent is injected into the mixing chamber by the injection device
in a radial pattern in the direction of the outer circumference.
The at least one injection nozzle can be oriented such that the
reducing agent is injected at an adjustable angle relative to a
fictive or real point of impingement on the wall of the mixing
chamber. Through the injection of the reducing agent into the hot
exhaust gas flow, the reducing agent is prepared by the heat of the
exhaust gas, which further improves its effectiveness.
[0019] A specific embodiment of the exhaust gas post-treatment
system according to the present invention includes, following the
elements combined to form the constructive unit--in particular a
particle filter having catalytic oxidation function and at least
one mixing chamber--at least one device, in particular at least one
catalytic converter, that is accommodated with the constructive
unit in the container or forms such a container. This may be a
reduction catalytic converter corresponding to the SCR type,
situated downstream from the at least one mixing chamber.
[0020] In an advantageous specific embodiment, in addition to or
instead of one or more SCR catalytic converters, one or more
purifying catalytic converters can be provided, such as a diesel
oxidation catalytic converter (DOC catalytic converter) and/or an
ammonia oxidation catalytic converter (AMO.sub.x catalytic
converters). Such oxidation catalytic converters can have a
suitable material coated with a catalyzing material or containing
in some other way a catalyzing material, whereby chemical reactions
can be catalytically excited that modify the composition of the
exhaust gas. Through the configuration of one or more catalytic
converters downstream from the at least one mixing chamber, an
NO.sub.x reduction can be further continued and/or completed,
achieving an increase in the conversion efficiency of the exhaust
gas post-treatment system. In particular, a limitation of the
ammonia portion in the treated, emitted exhaust gas can be
achieved. A catalytic converter can be present that has a first
catalytically active region and, situated downstream from the first
catalytically active region, a second catalytically active region
differing from the first catalytically active region. Thus, the
first catalytically active region can be suitable for an SCR
method, and the second catalytically active region, situated
downstream, can catalyze a further oxidation function.
[0021] In a specific embodiment of the system according to the
present invention for purifying exhaust gas, in addition to the
devices situated in the constructive unit in a cylindrical
container, i.e. a particle filter and a device having catalytic
oxidation function, or alternatively a particle filter having
catalytic oxidation function and at least one mixing chamber, at
least one catalytic converter is accommodated in the constructive
unit. In this way, there results an extremely compact exhaust gas
post-treatment system which may have only a single container in
which a plurality of devices having various functions are combined.
For example, the substrate of the at least one catalytic converter
can have an upstream region and a downstream region, an SCR
catalytic converter being situated at the upstream region and an
oxidation catalytic converter being situated at the downstream
region.
[0022] In a specific embodiment, the constructive unit situated in
a cylindrical container includes a particle filter having a
catalytic oxidation function, at least one mixing chamber, and an
SCR catalytic converter, the cylindrical container having at least
one removable end part that is fashioned to ensure access to the
interior of the cylindrical container, which may be to the particle
filter having the catalytic oxidation function. An exhaust gas
stream flowing into the constructive unit from an internal
combustion engine is treated in such a way that an NO conversion
efficiency is achieved that is at least at times more than 50%,
which may be more than 90%, particularly may be more than 95%, and
which may be more than 99%. In particular, correspondingly high
efficiency values are achieved at advantageous operating points of
the internal combustion engine.
[0023] In addition, a method is provided for treating an exhaust
gas stream that results from an internal combustion engine, the
still-untreated exhaust gas having between about 2 g NO.sub.x/kWh
and 12 g NO.sub.x/kWh. The exhaust gas stream is supplied to a
system for exhaust gas post-treatment that includes, in a
constructive unit, a particle filter having catalytic oxidation
function and at least one mixing chamber, pollutants in the exhaust
gas stream being catalytically oxidized and particles being
filtered out of the exhaust gas stream using the particle filter. A
first treated exhaust gas stream produced in this way is supplied
to the at least one mixing chamber, in which the first treated
exhaust gas stream is mixed with an injected reducing agent to form
an exhaust gas/reducing agent mixture.
[0024] In a development of the method, the exhaust gas/reducing
agent mixture is supplied to a catalytic converter device, a second
treated exhaust gas stream exiting from this catalytic converter
device being produced. This second treated exhaust gas stream can
be catalytically treated in a subsequent oxidation catalytic
converter, the ammonia contained in the second treated exhaust gas
stream in particular being catalytically converted.
[0025] In addition, the method according to the present invention
is set up to acquire relevant parameters of the exhaust gas
post-treatment system and to evaluate the ascertained data in at
least one control unit, sensors and various devices being included
in order for example to ascertain particle mass, number of
particles, exhaust gas pressure, temperature, exhaust gas flow
quantity, reducing agent quantity, exhaust gas composition, exhaust
gas concentration, and reduction and/or oxidation potential. In
addition, a method is provided for the at least one control unit in
order to enable adaptation through modification of a selection of
parameters of the internal combustion engine and/or modification of
the parameters of the exhaust gas post-treatment system, for
example the exhaust gas pressure, the temperature, the exhaust gas
flow quantity, the reducing agent quantity, the exhaust gas
composition, the exhaust gas concentration, and the reducing and/or
oxidation potential, in order to enable a maximally efficient
carrying out of the method.
Advantages of the Invention
[0026] The solution provided according to the present invention of
the exhaust gas post-treatment system creates a constructive unit
that achieves reduced installation space and a further reduced
overall mass, and thus also a reduced heat capacity of the system.
Due to the reduced constructive size of an integrated system
according to the present invention, the temperature-dependent
response behavior is improved in particular at low temperatures,
resulting in an earlier beginning of conversion. This is
advantageous in particular in those applications in which internal
combustion engines are frequently operated at low temperatures. In
addition, the costs of a corresponding exhaust gas post-treatment
system can be reduced compared to the previously known systems,
which have turned out to be disadvantageous due to the large number
of components and their configuration.
[0027] Through the design of the constructive unit, accommodated in
a cylindrical container, a large number of containers can be
omitted that have turned out to be problematic due to their
complexity, the overall size of the system, and costs. In addition,
additional supporting structures for the complex configuration of
the individual elements can be omitted. Due to the compactness
provided by the constructive unit, the exhaust gas post-treatment
system can be situated in the immediate vicinity of or directly on
an internal combustion engine, so that decoupling elements that
would otherwise have to be provided can be omitted, or can be more
favorably realized.
[0028] Through the possibility of placing the compact exhaust gas
post-treatment system close to the internal combustion engine, the
heat losses are kept low compared to the systems known from the
existing art. In particular high temperatures in the mixing chamber
integrated in the constructive unit enable an additional dosing of
reducing agent into the at least one mixing chamber in the case of
dynamic operation of the internal combustion engine, leading in
turn to a more effective conversion of the pollutants contained in
the exhaust gas stream. In addition, in this way the reducing agent
dosed into the hot exhaust gas is further prepared by the heat of
the exhaust gas, which further improves the functioning of the
exhaust gas post-treatment system according to the present
invention.
[0029] An advantageous effect is also achieved by the high
temperatures for the particle filter having catalytic oxidation
function that can be realized through the compactness according to
the present invention; thus, for example the reaction speed of the
oxygen and/or of the nitrogen dioxide with the deposited soot
particles and the pollutants present is greater. The introduction
and controlling of a possible thermal regeneration of the particle
filter having catalytic oxidation function also turns out to be
less demanding and thus able to be realized with lower outlay.
[0030] In addition, the integration of further catalytically active
elements can improve the conversion of components present in the
exhaust gas stream. In this way, for example greater throughputs
can be achieved in devices situated downstream through the
oxidation of nitrogen monoxide. In addition, an oxidizing effect of
the filter functionalized in this way relative to hydrocarbons,
upstream from another catalytic converter whose functioning is
negatively influenced by hydrocarbons, can protect this latter
catalytic converter.
[0031] An integration of an additional ammonia oxidation catalytic
converter in the configuration of the catalytic converters enables
an oxidation of excess ammonia not required as reducing agent,
reducing the environmental damage and risk of corrosion due to this
gas.
[0032] With the sensors provided according to the present
invention, for example a gas sensor and/or a temperature sensor,
there is the possibility of an improved controlling of the
conversion of the pollutants present in the exhaust gas. For
example in a controlling of the conversion of nitrogen oxides, the
quantity of reducing agents can be influenced in order to obtain an
optimal conversion, and on the other hand the temperature can be
regulated in order to remain in an optimal window for the course of
the catalytic activity.
[0033] Through one or more detachable connections at least of a
part of the cylindrical container, access to the individual
elements is ensured, which elements can be removed and cleaned or
exchanged.
[0034] Further advantages and specific embodiments of the subject
matter of the present invention are illustrated by the drawings and
are explained in more detail in the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 shows a schematic representation of an internal
combustion engine having an exhaust gas post-treatment system
according to the present invention.
[0036] FIG. 2 shows a perspective view of a mixing chamber.
[0037] FIG. 3 shows a top view of the mixing chamber according to
FIG. 2.
[0038] FIG. 4 shows a view of a constructive unit of the exhaust
gas post-treatment system according to the present invention.
[0039] FIG. 5 shows a cross-section through an exemplary embodiment
of an exhaust gas post-treatment system according to the present
invention.
DETAILED DESCRIPTION
[0040] In FIG. 1, reference character 10 designates an internal
combustion engine that is controlled by a (schematically shown)
control unit 12 via signal lines. Exhaust gas is conducted away via
an exhaust gas train 14 along a flow path 15 in which there is
situated an exhaust gas post-treatment system 16. Exhaust gas
post-treatment system 16 includes a particle filter 17 (shown only
schematically in FIG. 1) and a device having catalytic oxidation
function 19, which, combined, can form a particle filter having
catalytic oxidation function 18.
[0041] In addition, at least one mixing chamber 20 is shown,
combined with the particle filter having catalytic oxidation
function 18 to form a constructive unit 22. With the particle
filter having catalytic oxidation function 18, on the one hand
particles are filtered out from the exhaust gas flowing in exhaust
gas train 14, and a catalytic oxidation function is induced at the
catalytic converter integrated in the particle filter having
catalytic oxidation function 18.
[0042] The particle filters having catalytic oxidation function 18
have for example a honeycomb structure having a large number of
channels that are mutually sealed in such a way that the
particle-charged exhaust gas flows through porous walls of the
honeycomb body, the particles, formed essentially by carbon, being
deposited in pores of the walls. The particle filter having
catalytic oxidation function 18 can have a corresponding coating of
the channels of the honeycomb body, or can be made up of a
catalytically active mass. A regeneration of the particle filter
having catalytic oxidation function 18 can be realized in such a
way that a conversion, induced by the oxidation catalytic
converter, of nitrogen monoxide from the engine exhaust gas with
oxygen takes place in catalyzed fashion to form nitrogen dioxide,
and the carbon present as soot particles deposited in the particle
filter having catalytic function 18 is oxidized with the nitrogen
dioxide. Both nitrogen dioxide and nitrogen monoxide are carried
out from the particle filter having catalytic oxidation function
18, and are supplied to the further post-treatment. In the case of
oxidation of deposited soot particles with oxygen, particle filter
18, provided with the catalytic oxidation function, is capable of
oxidizing incompletely combusted intermediate products, for example
carbon monoxide.
[0043] In FIG. 1, further downstream from the particle filter
having catalytic oxidation function 18 a mixing chamber 20 is
indicated; these are combined to form a constructive unit 22.
Constructive unit 22 is made such that exhaust gas that flows
through constructive unit 22 comes into contact with the catalytic
centers of the particle filter having catalytic oxidation function
18 and is then conducted to mixing chamber 20. In particular,
constructive unit 22 is fashioned as a cylindrical container 44 in
which the particle filter having catalytic oxidation function 18
and mixing chamber 20 are combined.
[0044] An injection device 24 is situated on constructive unit 22
in such a way that a reducing agent is injected into the exhaust
gas stream and is mixed therewith to form an exhaust gas/reducing
agent mixture. For example, injection device 24 can include one or
more injection nozzles 36 that are fashioned to inject reducing
agent into the exhaust gas stream and in particular into mixing
chamber 20. For example, injection nozzles 36 can be situated
radially on the circumference of constructive unit 22. Injection
device 24 can include, in addition to injection nozzles 36, a fluid
source and a control unit, which are not shown in FIG. 1. The
reducing agent can for example be gaseous ammonia, ammonia in
aqueous solution, aqueous urea, or any other reducing agent known
in exhaust gas technology.
[0045] Mixing chamber 20 is fashioned to improve a mixture of the
injected reducing agent with the exhaust gas stream in mixing
chamber 20. Thus, mixing chamber 20 can have structures 26 that
form a rotational flow inside mixing chamber 20. FIG. 2 shows a
specific embodiment of a mixing chamber 20 in a perspective view.
Exhaust gas flowing along flow path 15 first moves into the
particle filter having catalytic oxidation function 18, and enters
downstream into mixing chamber 20. In mixing chamber 20, in FIG. 2
structures 26 are indicated that deflect flow path 15 of the
exhaust gas in such a way that this gas assumes a radial
orientation relative to a main direction of flow 28. For this
purpose, structures 26 can include guide surfaces 30 fashioned for
example in the form of a helical path. Optionally, guide surfaces
30 are fashioned on one or more linings 31 accommodated in mixing
chamber 20, a spiral flow pattern 32 being imparted to the exhaust
gas in the direction of outlet 34 from mixing chamber 20. Main
direction of flow 28 of the entering exhaust gas is blocked by
structures 26 accommodated in mixing chamber 20 in such a way that
the exhaust gas is guided along guide surfaces 30 in a spiral flow
pattern 32 (FIG. 3) and exits from mixing chamber 20 through outlet
34, the outlet direction being oriented essentially parallel to
main direction of flow 28. Through structures 26, the path length
of flow path 15 of the exhaust gas is increased relative to an
overall length of mixing chamber 20.
[0046] FIG. 3 shows a top view of mixing chamber 20, structures 26
being indicated fashioned as guide surfaces 30. The exhaust gas
entering into mixing chamber 20 is guided by guide surfaces 30 into
spiral flow 32, which guides the exhaust gas along a spiral path in
the direction of outlet 34 from mixing chamber 20. In addition,
injection device 24 for the reducing agent is shown schematically,
situated on the circumference of mixing chamber 20 in such a way
that reducing agent is injected into the interior of mixing chamber
20 and thus into spiral flow 32 of the exhaust gas stream.
Injection device 24 includes one or more injection nozzles 36 that
are oriented such that reducing agent is injected into mixing
chamber 20 with an adjustable injection angle 38, taking into
account the spiral flow 32 of the exhaust gas. Here, injection
angle 38 can have different angles relative to a tangent applied at
a point 40 of impingement on circumference 42 of mixing chamber
20.
[0047] Reducing agent injected by injection nozzle 36 in this way
via injection device 24 mixes with the exhaust gas, and is mixed
with the exhaust gas while flowing through mixing chamber 20 to
form an exhaust gas/reducing agent mixture. In addition, through
the heat and vapor of the exhaust gas, an aqueous urea solution
used as a reducing agent is hydrolyzed, so that ammonia is
formed.
[0048] FIG. 4 shows a view of constructive unit 22 in which
according to the present invention the particle filter having
catalytic oxidation function 18 and mixing chamber 20 are combined
to form a constructive unit 22. According to FIG. 4, constructive
unit 22 is fashioned as a cylindrical container 44, this container
being screwed or locked to exhaust gas train 14 by end parts 46,
47, fashioned for example having flange connections. Thus, the
interior of cylindrical container 44, or the elements accommodated
therein, i.e. the particle filter having catalytic oxidation
function 18 or the mixing chamber 20, are accessible for inspection
and/or in order to replace the various elements. Constructive unit
22 can also be connected to the exhaust gas train using coupling
elements, conceivably one or more clamps, clips, flexible tube
pieces, and/or similar devices, in order to enable a removable
connection between cylindrical container 44 and other components.
FIG. 4 further shows that one or more catalytic converter devices
48 of exhaust gas post-treatment system 16 can be accommodated in
constructive unit 22. Corresponding catalytic converter devices 48
are in particular one or more SCR catalytic converters 50 that are
situated downstream from mixing chamber 20 and that act as
purifying catalytic converters. The reducing agent mixed with the
exhaust gas in mixing chamber 20 is used to reduce nitrogen oxides
in SCR catalytic converter 50.
[0049] FIG. 5 shows a cross-section of an exemplary embodiment of
an exhaust gas post-treatment system 16 according to the present
invention. Reference character 15 indicates the flow path of the
exhaust gas in exhaust gas train 14, which enters into constructive
unit 22 as untreated exhaust gas and, along flow path 15, passes
through the particle filter having catalytic oxidation function 18,
mixing chamber 20, and downstream catalytic converter device 48,
which may be SCR catalytic converter 50. Injection device 24 is
situated in the region of mixing chamber 20. In further specific
embodiments (not shown) of exhaust gas post-treatment system 16,
catalytic converter device 48 can include a plurality of further
identical or different purifying catalytic converters, such as an
SCR catalytic converter 50, a diesel oxidation catalytic converter
(not shown), an ammonia oxidation catalytic converter (not shown).
In addition (also not shown), exhaust gas post-treatment system 16
can have one or more probes and/or sensors that are configured to
monitor operating characteristics and/or other parameters of
exhaust gas post-treatment system 16.
* * * * *