U.S. patent application number 10/527602 was filed with the patent office on 2006-09-07 for exhaust gas purification system of an internal combustion engine and method for purifying the exhaust gases thereof.
Invention is credited to Hartmut Lueders, Thorsten Mayer, Wolfgang Ripper, Johannes Schaller, Christian Walz.
Application Number | 20060196169 10/527602 |
Document ID | / |
Family ID | 31896145 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060196169 |
Kind Code |
A1 |
Ripper; Wolfgang ; et
al. |
September 7, 2006 |
Exhaust gas purification system of an internal combustion engine
and method for purifying the exhaust gases thereof
Abstract
An exhaust gas purification system for purifying the exhaust gas
of an internal combustion engine, especially an internal combustion
engine featuring auto-ignition and/or direct fuel injection, is
provided. The system includes at least one oxidation catalytic
converter disposed in an exhaust gas duct of the internal
combustion engine, at least one device for selective catalytic
reduction of the exhaust gases which is installed downstream of the
oxidation catalytic converter, and a feed device for feeding
reducing agent into the exhaust gas stream upstream of, or in, the
device for selective catalytic reduction. A switch-over device is
provided for selectively feeding reducing agent into the exhaust
gas stream upstream of, or inside, the at least one oxidation
catalytic converter. A corresponding method for purifying the
exhaust gas of an internal combustion engine is also provided.
Inventors: |
Ripper; Wolfgang;
(Stuttgart, DE) ; Schaller; Johannes; (Leonberg,
DE) ; Lueders; Hartmut; (Oberstenfeld, DE) ;
Walz; Christian; (Leonberg, DE) ; Mayer;
Thorsten; (Worms, DE) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
31896145 |
Appl. No.: |
10/527602 |
Filed: |
June 2, 2003 |
PCT Filed: |
June 2, 2003 |
PCT NO: |
PCT/DE03/01800 |
371 Date: |
April 3, 2006 |
Current U.S.
Class: |
60/286 ; 60/280;
60/295 |
Current CPC
Class: |
F01N 3/035 20130101;
F02B 37/00 20130101; F01N 2610/14 20130101; F01N 3/36 20130101;
F01N 2250/02 20130101; F01N 3/021 20130101; F01N 3/2066 20130101;
Y02T 10/12 20130101; F01N 13/009 20140601; Y02T 10/24 20130101 |
Class at
Publication: |
060/286 ;
060/280; 060/295 |
International
Class: |
F01N 5/04 20060101
F01N005/04; F01N 3/00 20060101 F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2002 |
DE |
102 43 270.8 |
Claims
1-16. (canceled)
17. An exhaust gas purification system for purifying an exhaust gas
stream of an internal combustion engine, comprising: at least one
oxidation catalytic converter provided in an exhaust gas duct of
the internal combustion engine; at least one device for selective
catalytic reduction of the exhaust gas stream, the at least one
device being provided downstream of the at least one oxidation
catalytic converter; and a feed device for feeding a reducing agent
into the exhaust gas stream one of upstream of the at least one
device for selective catalytic reduction and in the at least one
device for selective catalytic reduction; and a switch-over device
for selectively feeding the reducing agent into the exhaust gas
stream one of upstream of the at least one oxidation catalytic
converter and in the at least one oxidation catalytic
converter.
18. The exhaust gas purification system as recited in claim 17,
wherein the switch-over device is a valve.
19. The exhaust gas purification system as recited in claim 18,
wherein the switch-over device is a directional control valve.
20. The exhaust gas purification system as recited in claim 18,
wherein the switch-over device is a mixing valve.
21. The exhaust gas purification system as recited in claim 19,
wherein the switch-over device is temperature-controlled.
22. The exhaust gas purification system as recited in claim 20,
wherein the switch-over device is temperature-controlled.
23. The exhaust gas purification system as recited in claim 21,
wherein the feed device has a metering device and a nozzle for
distributing and atomizing the reducing agent in the exhaust gas
stream.
24. The exhaust gas purification system as recited in claim 22,
wherein the feed device has a metering device and a nozzle for
distributing and atomizing the reducing agent in the exhaust gas
stream.
25. The exhaust gas purification system as recited in claim 23,
wherein the at least one oxidation catalytic converter is disposed
in the immediate vicinity of an exhaust gas outlet of the internal
combustion engine.
26. The exhaust gas purification system as recited in claim 25,
wherein the at least one oxidation catalytic converter is a
catalytically coated particle filter.
27. The exhaust gas purification system as recited in claim 25,
further comprising: at least one particle filter provided between
the at least one oxidation catalytic converter and the at least one
device for selective catalytic reduction.
28. A method for purifying an exhaust gas stream of an internal
combustion engine, comprising: passing the exhaust gas stream
through at least one oxidation catalytic converter located in an
exhaust gas duct of the internal combustion engine, and through at
least one device for selective catalytic reduction located
downstream of the at least one oxidation catalytic converter; and
selectively performing at least one of: a) feeding a reducing agent
into the exhaust gas stream one of upstream of the at least one
device for selective catalytic reduction and in the at least one
device for selective catalytic reduction; and b) feeding the
reducing agent to the exhaust gas stream one of upstream of the at
least one oxidation catalytic converter and in the at least one
oxidation catalytic converter.
29. The method as recited in claim 28, wherein the reducing agent
is fed into one of the at least one oxidation catalytic converter
and the at least one device for selective catalytic reduction.
30. The method as recited in claim 28, wherein the reducing agent
is fed into the at least one oxidation catalytic converter and the
at least one device for selective catalytic reduction
simultaneously during a transition period.
31. The method as recited in claim 28, wherein the reducing agent
is fed by a nozzle.
32. The method as recited in claim 28, wherein the selective
feeding of the reducing agent is determined as a function of
temperature.
33. The method as recited in claim 30, wherein the reducing agent
is fed into the at least one oxidation catalytic converter at an
exhaust gas temperature of less than approximately 180.degree. C.
in the at least one oxidation catalytic converter.
34. The method as recited in claim 32, wherein the reducing agent
is fed into the at least one oxidation catalytic converter at an
exhaust gas temperature of less than approximately 180.degree. C.
in the at least one oxidation catalytic converter.
35. The method as recited in claim 33, wherein the reducing agent
is fed into the at least one device for selective catalytic
reduction at an exhaust gas temperature of more than approximately
180.degree. C. in the at least one device for selective catalytic
reduction.
36. The method as recited in claim 34, wherein the reducing agent
is fed into the at least one device for selective catalytic
reduction at an exhaust gas temperature of more than approximately
180.degree. C. in the at least one device for selective catalytic
reduction.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an exhaust gas purification
system of an internal combustion engine having a device for
selective catalytic reduction, and relates particularly to a method
for purifying exhaust gases of an internal combustion engine, in
which an exhaust gas stream is passed through a device for
selective catalytic reduction.
BACKGROUND INFORMATION
[0002] To lower the nitrogen oxide content of oxygen-rich exhaust
gas, such as that emitted by diesel internal combustion engines and
by internal combustion engines featuring direct gasoline injection,
it is known to introduce a reducing agent into an exhaust tract. A
suitable reducing agent is, for example, NH.sub.3, which may be
introduced as a gas into the exhaust gas stream. In such so-called
selective catalytic reduction (SCR), the ammonia is selectively
reacted with the nitrogen oxides present in the exhaust gas to form
molecular nitrogen and water.
[0003] The insufficient activity of the known SCR system at exhaust
gas temperatures below approximately 250.degree. C. is a problem.
Upstream installation of an oxidation catalytic converter provides,
on the one hand, a lowering of the content of deactivating
hydrocarbons and, on the other hand, oxidation of NO to NO.sub.2,
which leads overall to a marked increase in NO.sub.x conversion at
exhaust gas temperatures above approximately 200.degree. C.
Especially when used in passenger automobiles, however, phases
having such low exhaust gas temperatures occur relatively
frequently, as is illustrated by a mean catalytic converter
temperature of less than 180.degree. C. in the known MVEG test
cycle (MVEG: Motor Vehicles Emissions Expert Group; an expert group
of the European Commission).
[0004] To ensure good distribution of the reducing agent over the
SCR catalyst, a mixing section of approximately 40 cm may be
provided, with a mixing device, where appropriate. A mixing device
for an exhaust gas purification system is described in published
German Patent Application 101 31 803.0, which discloses that a
mixing body disposed in the exhaust pipe has a gas impingement
surface and a jet impingement surface, so that exhaust gas flowing
out of the internal combustion engine may impinge upon the gas
impingement surface, and reducing agent, which may be fed
transversely to the exhaust gas stream, may impinge upon the jet
impingement surface.
SUMMARY
[0005] An exhaust gas purification system in accordance with the
present invention includes at least one oxidation catalytic
converter disposed in an exhaust gas duct of an internal combustion
engine, and at least one device for selective catalytic reduction
of the exhaust gases, which device is installed downstream of the
oxidation catalytic converter. The exhaust gas purification system
further includes a feed device for feeding reducing agent into the
exhaust gas stream and admixing it therewith upstream of the
device, or in the device, for selective catalytic reduction (SCR
catalytic converter). According to the invention, the exhaust gas
purification system has a switch-over device and/or a further feed
device for selectively feeding reducing agent into the exhaust gas
stream upstream of, or inside, the at least one oxidation catalytic
converter. Using such a configuration of the oxidation catalytic
converter and the so-called SCR catalytic converter, it is possible
to obtain a reduction in the NO.sub.x emission to a level below
that which ensures compliance with the permissible exhaust gas
standards during the MVEG test cycle. Such a reduction in NO.sub.x
emissions may be achieved by additionally utilizing the
temperature-resistant oxidation catalytic converter, which is
already present and used for nitrogen oxide oxidation, for the
purpose of NO.sub.x reduction during a cold start phase. When
installed close to the engine, the oxidation catalytic converter
will reach a temperature of more than 100.degree. C. after about 50
seconds, which is sufficient for NO.sub.x reduction using NH.sub.3
or a reducing agent that splits off NH.sub.3.
[0006] Oxidation catalytic converters mainly have noble metals,
such as platinum, as the active component. Oxidation reactions of
hydrocarbons, carbon monoxide and nitrogen monoxide are thereby
promoted even at low temperatures. If NH.sub.3 is injected as the
reducing agent, these catalytic converters exhibit a relatively
strong NO.sub.x reduction activity even at temperatures below
100.degree. C.
[0007] If a configuration having a switch-over device instead of a
separate feed device for the oxidation catalytic converter is
chosen, this may reduce assembly costs. The present invention
provides, however, an example embodiment having separate and
separately controllable feed devices for reducing agent.
[0008] The switch-over device for selectively feeding the reducing
agent into the exhaust gas stream upstream of, or in, the oxidation
catalytic converter, or into the SCR catalytic converter, may be in
the form of a valve, especially a 3/2-way valve. In that manner,
the reducing agent may be fed selectively to the oxidation
catalytic converter or to the SCR catalytic converter, according to
the temperature level that these converters have reached in driving
operation.
[0009] One embodiment of the invention provides for the switch-over
device to be in the form of a mixing valve. In that manner, it is
possible for reducing agent to be admitted to the oxidation
catalytic converter and the SCR catalytic converter simultaneously
during a transition period. Using such a mixing valve, it is
possible to avoid an abrupt switch-over, so that, depending upon
the operating temperatures reached by the catalytic converters, an
optimum purifying effect may be obtained.
[0010] The switch-over device may be temperature-controlled, so
that, during a cold start phase with exhaust gas temperatures that
are still low, reducing agent may be admitted to the oxidation
catalytic converter and, after a warm-up phase, to the SCR
catalytic converter.
[0011] The feed device may include in each case a metering device
for quantity metering and nozzles for distributing and atomizing
the reducing agent in the exhaust gas stream.
[0012] At least one oxidation catalytic converter is disposed in
the immediate vicinity of an exhaust gas outlet of the internal
combustion engine, with the result that it reaches relatively high
temperatures and thus achieves a high purifying effect after only a
short time.
[0013] The reducing agent may be, for example, an
ammonia-containing or ammonia-releasing substance capable of
effecting NO.sub.x reduction. Examples of such a substance are urea
and ammonium carbamate.
[0014] In a method according to the present invention for purifying
exhaust gases of an internal combustion engine, an exhaust gas
stream is passed through at least one oxidation catalytic converter
disposed in the exhaust gas duct and through at least one device
for selective catalytic reduction (SCR catalytic converter)
installed downstream of the oxidation catalytic converter, and a
reducing agent is selectively fed to the exhaust gas stream
upstream of, or inside, the at least one oxidation catalytic
converter. The reducing agent may be selectively fed to both
catalytic converters simultaneously or to only one of the catalytic
converters. The reducing agent may be distributed and atomized by a
nozzle.
[0015] One embodiment of the method according to the present
invention provides for temperature-controlled feeding of the
reducing agent into the oxidation catalytic converter and/or into
the device for selective catalytic reduction.
[0016] If NH.sub.3 is admitted to the oxidation catalytic
converter, the latter exhibits a relatively pronounced NO.sub.x
reduction activity at temperatures below 100.degree. C. The useful
temperature window for NO.sub.x reduction is relatively narrow,
however, since above approximately from 250.degree. C. to
300.degree. C. nitrogen reduction no longer takes place but,
rather, additional nitrogen oxide production takes place as a
result of oxidation of NH.sub.3. In addition, relatively high
N.sub.2O selectivities may possibly be observed. It must,
therefore, be ensured that reducing agent is admitted to the
oxidation catalytic converter only in a starting phase (in the MVEG
test, only up to about 350 s). For example, the reducing agent is
fed into the oxidation catalytic converter at exhaust gas
temperatures of less than approximately from 150.degree. C. to
200.degree. C. in the oxidation catalytic converter.
[0017] After such a period of time, the SCR catalytic converter
will normally also have reached its operating temperature and
injection of reducing agent is switched to the SCR catalytic
converter. That may be done at temperatures of approximately from
150.degree. C. to 200.degree. C. in the SCR catalytic converter.
Metering of reducing agent onto the oxidation catalyst is possible
in principle at operating points with a low exhaust gas
temperature--that is to say, not only in the case of cold
starting--and provides a very effective NO.sub.x-lowering potential
in cases where only insufficient activity is achieved with the SCR
catalytic converter. With injection upstream of the oxidation
catalytic converter up to a time of about 600 s, therefore, a
marked increase in conversion by the exhaust gas purification
system may be achieved. A suitable, sensible switch-over point of
the temperature-controlled switch-over valve may lie at 100 to
200.degree. C., e.g., at 130 to 180.degree. C.
[0018] An example embodiment of the system according to the present
invention may, for example, provide a 3/2-way switch-over valve
which is operated in dependence upon the catalytic converter
temperatures and the operating point of the engine. Equipping an
existing system in that manner is relatively simple and may be done
with only little expenditure. The catalyst system, the temperature
sensors and the metering system are already present, and only the
switch-over valve and the reducing agent feed line upstream of the
oxidation catalytic converter need to be implemented. By a suitable
metering strategy, it is possible for effective reduction of the
nitrogen oxides to be achieved over an entire test cycle (MVEG
cycle). In the MVEG test, it is possible for an increase in
NO.sub.x conversion of approximately 40% to be achieved, with the
result that in the case of lowered untreated emissions it is even
possible to meet the relatively strict U.S. standards.
[0019] The oxidation catalytic converter may, in an example
embodiment, be in the form of a catalytically coated particle
filter. The catalytic coating of the particle filter acts in this
case similarly to the coating of an oxidation catalytic converter.
It is furthermore possible for a separate particle filter, which
effects filtering of the soot particles, to be provided between the
oxidation catalytic converter and the SCR catalytic converter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic illustration of an internal combustion
engine having an exhaust gas after-treatment unit in an exhaust gas
duct.
[0021] FIG. 2 is a schematic illustration of the internal
combustion engine according to FIG. 1 in a first operating
position.
[0022] FIG. 3 shows the internal combustion engine according to
FIG. 1 in a second operating position.
[0023] FIG. 4 is a chart showing typical temperature variations of
the components of the exhaust gas purification system during a test
cycle.
[0024] FIG. 5 is a chart showing typical NO.sub.x emission values
during a test cycle.
[0025] FIG. 6 is a chart illustrating the SCR activity of an
oxidation catalytic converter.
DETAILED DESCRIPTION
[0026] FIG. 1 shows an exhaust gas purification system according to
the present invention. In FIG. 1, an oxidation catalytic converter
4 and a device for selective catalytic reduction, referred to as
SCR catalytic converter 6, are disposed in an exhaust gas duct 28
of an internal combustion engine 2. Internal combustion engine 2
has an intake duct 21 for supplying fresh mixture 22, and outlet
ducts 26 which are combined in a manifold 27 to form exhaust gas
duct 28. Disposed in the exhaust gas duct is an exhaust gas turbine
24 of an exhaust gas turbocharger 23, which turbine 24 is coupled
via a shaft 25 to a compressor, not shown here. Exhaust gas
turbocharger 23 is optional and serves to improve the performance
and exhaust gas emission characteristics of internal combustion
engine 2.
[0027] Internal combustion engine 2 may be a diesel internal
combustion engine featuring auto-ignition or a gasoline engine
featuring direct fuel injection. Both types of engine emit a
relatively oxygen-rich exhaust gas. Exhaust gas stream 29 passes
successively through oxidation catalytic converter 4 and SCR
catalytic converter 6 and leaves the exhaust gas purification
system as purified exhaust gas 14 which is passed into the open air
via a muffler (not shown). The exhaust gas purification system
further includes a feed device 8 for feeding a reducing agent 81
into exhaust gas stream 29. Feed device 8 includes a switch-over
device 83 and also a first connection line 84, which is connected
to a first nozzle 85, and a second connection line 86, which is
connected to a second nozzle 87. First nozzle 85 is disposed
upstream of oxidation catalytic converter 4 in exhaust gas duct 28
and serves to finely distribute and atomize reducing agent 81
upstream of oxidation catalytic converter 4. Second nozzle 87 is
disposed upstream of SCR catalytic converter 6 and downstream of
oxidation catalytic converter 4 and serves to feed reducing agent
81 into exhaust gas stream 29 upstream of SCR catalytic converter
6.
[0028] First and second connection lines 84, 86 open into
switch-over device 83 which is able to provide for selective
distribution of the reducing agent to first and/or second
connection line 84, 86. Switch-over device 83 may be controlled
temperature-dependently, so that, in a cold running phase, reducing
agent 81 may be admitted to oxidation catalytic converter 4 and,
after a certain temperature has been reached, to SCR catalytic
converter 6.
[0029] FIG. 2 illustrates the cold running phase of the exhaust gas
purification system, in which reducing agent is admitted only to
first nozzle 85. This is illustrated by arrow 81 along first
connection line 84.
[0030] FIG. 3 illustrates the subsequent phase, in which the
catalytic converters have already reached a predetermined operating
temperature. In this case, reducing agent 81 is admitted to second
connection line 86 and second nozzle 87. This is illustrated by
arrow 81 along second connection line 86.
[0031] A typical transition temperature may lie at approximately
from 100.degree. C. to 200.degree. C., e.g., at about from 130 to
180.degree. C., above which a switch-over to admission of reducing
agent 81 to SCR catalytic converter 6 may take place. A switch-over
may also be made in an advantageous manner by a mixing valve, which
is able to provide for simultaneous admission to oxidation
catalytic converter 4 and SCR catalytic converter 6 in the
transition temperature range.
[0032] An alternative configuration according to the present
invention provides two separate feed devices for the oxidation
catalytic converter and the SCR catalytic converter.
[0033] In an alternative embodiment, oxidation catalytic converter
4 may be a catalytically coated particle filter which, by virtue of
its catalytic coating, has the same effect as an oxidation
catalytic converter. In addition to the configuration shown, a
separate particle filter may be disposed between oxidation
catalytic converter 4 and SCR catalytic converter 6. That particle
filter produces a further improvement in the purifying effect on
the exhaust gases.
[0034] FIG. 4 illustrates typical temperature variations of the
oxidation catalytic converter and the SCR catalytic converter
during a standardized test cycle. The so-called MVEG test will be
referred to hereinafter as an example of a test cycle. The time in
seconds is plotted on the horizontal axis and the temperature in
.degree. C. on the vertical axis. It will be apparent that the
oxidation catalytic converter (upper, jagged curve) is capable of
reaching temperatures of up to 200.degree. C. after a period of as
little as approximately 150 seconds. The temperature of the SCR
catalytic converter (lower, undulating curve) is still distinctly
below 150.degree. C. after 300 seconds. At those temperature ranges
in the SCR catalytic converter, feeding of reducing agent will not
yet produce satisfactory reduction results for NO.sub.x. Since the
oxidation catalytic converter reaches temperatures of more than
100.degree. C. after only a few seconds, it is possible for good
NO.sub.x reduction to be already achieved by feeding reducing agent
upstream of, or into, the oxidation catalytic converter. The dashed
vertical line at approximately 300 seconds represents the earliest
sensible time to commence NH.sub.3 injection upstream of the SCR
catalytic converter. The continuous vertical line at approximately
350 seconds represents the start of effective NO.sub.x reduction by
the SCR catalytic converter in the MVEG test cycle.
[0035] FIG. 5 illustrates the cumulative emission of NO.sub.x over
time in various systems for exhaust gas purification. The time in
seconds is shown on the horizontal axis and the cumulative amount
of emitted NO.sub.x is shown on the vertical axis. It will be
apparent that, by injecting reducing agent upstream of the
oxidation catalytic converter and in the SCR catalytic converter in
accordance with the present invention, it is possible for emissions
of NO.sub.x to be markedly reduced.
[0036] Lowermost curve 20 illustrates that only with the system
according to the present invention is it possible to comply with
the MVEG limit value of 0.9 g of NO.sub.x. Discontinuous curve 22
extending above the latter characterizes the curve for NO.sub.x
emissions in a conventional system composed of oxidation catalytic
converter and SCR catalytic converter arranged in series (so-called
conventional VR system without switch-over). Curve 24 illustrates
the emissions of a system that provides feeding of reducing agent
merely upstream of the oxidation catalytic converter. At first,
good reduction takes place, but the elevated temperatures at and
beyond approximately 800 seconds prevent effective NO.sub.x
reduction. From that point in time, the NO.sub.x emissions rise
steeply and even approach the values of untreated emissions (curve
26), since, at and above approximately from 300 to 350.degree. C.,
an additional quantity of NO.sub.x is produced.
[0037] FIG. 6 illustrates the NO.sub.x-reducing effect of the
oxidation catalytic converter as a function of temperature. It will
be apparent that, at and above a temperature of approximately
200.degree. C., NO.sub.x reduction falls markedly and that, at and
above temperatures of approximately 350.degree. C., NO.sub.x is
even additionally produced. The temperature is shown on the
horizontal axis and the conversion is shown on the vertical axis.
It will be apparent that the conversion of NO.sub.x declines
markedly at and above a certain temperature (approximately
200.degree. C.). That is the reason why, after the cold running
phase, the feeding of reducing agent upstream of the oxidation
catalytic converter should be discontinued and reducing agent may
continue to be fed only upstream of the SCR catalytic
converter.
* * * * *