U.S. patent application number 12/224611 was filed with the patent office on 2010-05-06 for exhaust system for an internal combustion engine.
Invention is credited to Holger Hulser, Martin Schussler.
Application Number | 20100107610 12/224611 |
Document ID | / |
Family ID | 38017024 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100107610 |
Kind Code |
A1 |
Schussler; Martin ; et
al. |
May 6, 2010 |
Exhaust System for an Internal Combustion Engine
Abstract
An exhaust system (1) for an internal combustion engine (2),
especially for a diesel engine, includes an exhaust manifold (3)
inside which at least one exhaust aftertreatment device is
disposed, and at least one DeNox unit that is arranged downstream
from a first oxidizing catalyst (4). In order to reduce the
NO.sub.x emissions a second oxidation catalyst (5) is disposed
upstream of the DeNOx unit.
Inventors: |
Schussler; Martin; (Graz,
AT) ; Hulser; Holger; (Graz, AT) |
Correspondence
Address: |
DYKEMA GOSSETT PLLC
FRANKLIN SQUARE, THIRD FLOOR WEST, 1300 I STREET, NW
WASHINGTON
DC
20005
US
|
Family ID: |
38017024 |
Appl. No.: |
12/224611 |
Filed: |
February 15, 2007 |
PCT Filed: |
February 15, 2007 |
PCT NO: |
PCT/AT2007/000084 |
371 Date: |
January 4, 2010 |
Current U.S.
Class: |
60/287 ; 60/299;
60/323 |
Current CPC
Class: |
F01N 13/0093 20140601;
F01N 3/2053 20130101; F01N 2560/026 20130101; F01N 13/009 20140601;
F01N 3/2066 20130101; F01N 2610/02 20130101; Y02T 10/12 20130101;
Y02T 10/24 20130101; F01N 9/005 20130101; F01N 3/106 20130101; F01N
13/011 20140603 |
Class at
Publication: |
60/287 ; 60/299;
60/323 |
International
Class: |
F01N 9/00 20060101
F01N009/00; F01N 3/10 20060101 F01N003/10; F01N 1/00 20060101
F01N001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2006 |
AT |
A 351/2006 |
May 9, 2006 |
AT |
A 799/2006 |
Claims
1. An exhaust system (1) for an internal combustion engine (2),
comprising an exhaust manifold (3) inside which at least one
exhaust aftertreatment device is disposed, at least one DeNox unit
arranged downstream from a first oxidizing catalyst (4), and a
second oxidation catalyst (5) is disposed upstream of the DeNOx
unit.
2. The exhaust system (1) according to claim 1, wherein the first
and second oxidation catalyst (4, 5) are configured for different
activities and/or for different temperature ranges.
3. The exhaust system (1) according to claim 1, wherein the first
and second oxidation catalyst (4, 5) comprise different masses of
noble metal, the second oxidation catalyst (5) having a larger mass
of noble metal than the first oxidation catalyst (4).
4. The exhaust system (1) according to claim 1, wherein the first
and second oxidation catalyst (4, 5) are arranged parallel with
respect to each other in the exhaust manifold (3) as regards flow,
with the flow through at least one oxidation catalyst (5) being
adjustable by means of an actuator (7).
5. The exhaust system (1) according to claim 1, wherein a first and
second oxidation catalyst (4, 5) are arranged in series in regard
to flow in the exhaust manifold (3), with at least one oxidation
catalyst (5) being capable of being bypassed via a bypass line (8),
with an actuator (7) being arranged in the bypass line (8).
6. The exhaust system (1) according to claim 1, wherein a first and
second oxidation catalyst (4, 5) are arranged in a single
housing.
7. The exhaust system (1) according to claim 1, including a
particulate filter (9) upstream of the DeNOx unit and downstream of
a dosing device (10) for reducing agents.
8. The exhaust system (1) according to claim 5, wherein the
actuator (7) is adjustable in a model-based way depending on the
NO.sub.x content in the exhaust gas, the temperature of the exhaust
gas, the pressure loss of the diesel particulate filter (9), the
air-mass flow, the fuel-mass flow, or the crankshaft speed.
9. The exhaust system (1) according to claim 8, including at least
one NO.sub.x sensor downstream of the DeNOx unit.
10. A method for operating an exhaust aftertreatment system for
reducing the nitrogen oxide emissions of an internal combustion
engine, preferably an SCR catalyst, with a sensor for determining
the NO.sub.x concentration being arranged in the exhaust manifold
downstream of the exhaust aftertreatment system, and with a
reducing agent or an aqueous urea solution being dosed to the
exhaust gas at a stoichiometric ratio to the NO.sub.x emissions
upstream of the exhaust aftertreatment system, and with the
NO.sub.x emissions of the internal combustion engine being
determined by means of a characteristic map of the engine or an
exhaust gas model, comprising measuring NO.sub.x emissions beneath
the minimum temperature of the exhaust gas and/or in operating
phases where no reducing agent is added with the sensor downstream
of the exhaust aftertreatment system and comparing obtained values
based on the characteristic map or model, and performing a
correction of the characteristic map or emission model in the case
of a deviation between the measured values and those based on the
characteristic map or model.
11. The method according to claim 10, wherein a correction of the
characteristic map or the model only occurs when an amount of the
gradient of the speed and/or torque of the internal combustion
engine lies beneath a predetermined threshold value.
12. The method according to claim 11, wherein exhaust gas conveying
time between the internal combustion engine and the sensor is taken
into account in the comparison of the measured values of the
NO.sub.x emissions with those based on the characteristic map or
model.
13. The method according to claim 12, wherein the correction
performed per correction step is smaller than a predefined
permissible maximum value.
Description
[0001] The invention relates to an exhaust system for an internal
combustion engine, especially for a diesel engine, comprising an
exhaust manifold inside which at least one exhaust aftertreatment
device is disposed, and at least one DeNox unit that is arranged
downstream from a first oxidizing catalyst. The invention further
relates to a method for operating an exhaust aftertreatment system
for reducing the nitrogen oxide emissions of an internal combustion
engine, preferably an SCR catalyst, with a sensor for determining
the NO.sub.x concentration in the exhaust manifold being arranged
downstream of the exhaust aftertreatment system, and with a
reducing agent, especially NH.sub.3 or an aqueous urea solution,
being dosed to the exhaust gas preferably at a stoichiometric ratio
to the NO.sub.x emissions upstream of the exhaust aftertreatment
system, and with the NO.sub.x emissions of the internal combustion
engine being determined by means of a characteristic map of the
engine or an exhaust gas model.
[0002] NO.sub.2 and NO are components of the raw exhaust gases of
diesel engines. NO is partly converted into NO.sub.2 in the
oxidation catalyst whose primary task is the combustion of CO and
HC residues. The thus obtained ratio of NO.sub.2 to NO is a
function of the noble metal concentration in the oxidation
catalyst, the space velocity, the partial pressure of NO.sub.x and
the temperature in the oxidation catalyst. NO.sub.2 is used in the
diesel particulate filter, which is typically flowed through after
the oxidation catalyst, as an oxidation agent for permanent
oxidation of the exhaust particulate stored thereon. As a further
component of a diesel exhaust system, a DeNOx unit can be used for
reducing the NO.sub.x emissions which is formed by an SCR catalyst
(Selective Catalytic Reduction) for example, in which NO.sub.x is
reduced with the help of dosed NH.sub.3. Both the NO and NO.sub.2
components of the exhaust gas should be reduced in this stage to
N.sub.2 to the highest possible extent.
[0003] For the following reasons, the highest possible activity of
the oxidation catalyst is desirable (corresponds to high mass of
noble metal): [0004] Light-off begins earlier; [0005] a complete
conversion of CO and HC, even when upstream additional HC is dosed
for combustion in the oxidation catalyst (for increasing the
temperature of the exhaust gas); [0006] complete conversion even in
case of ageing of the oxidation catalyst; [0007] high NO.sub.2
partial pressure after the oxidation catalyst in order to improve
the combustion of exhaust particulates in the diesel particle
filter;
[0008] This is counteracted in such a way however that for
catalytic activity or the complete conversion of NO.sub.x in the
DeNOx unit, a molar ratio of NO.sub.2/NO of 1 is advantageous.
Moreover, a ratio of NO.sub.2/NO>1 might lead to the formation
of laughing gas (N.sub.2O) in the DeNOx unit. In the case of a high
catalyst mass however, NO.sub.2/NO=1 is exceeded in relevant
operating points, which means that too much NO is converted into
NO.sub.2 in the oxidation catalyst.
[0009] JP 2005-002968 A discloses an internal combustion engine
with an exhaust manifold in which a powerful oxidation catalyst and
an SCR catalyst are arranged. The oxidation catalyst can be
bypassed via a bypass line. Once the exhaust temperature has
reached a value in which the inversion rate of the oxidation
catalyst is at least 50%, the exhaust gases are moved past the
oxidation catalyst in order to prevent excessive generation of
NO.sub.2 which would reduce the NO.sub.x conversion rate in the SCR
catalyst.
[0010] EP 1 357 267 A2 describes an exhaust system for a diesel
engine, comprising an SCR catalyst in the exhaust manifold,
upstream of which an oxidation catalyst and a hydrolysis catalyst
are arranged in parallel flow paths. Hydrolysis catalyst and
oxidation catalyst are flowed through simultaneously by separate
partial exhaust gas flows. This allows a compact arrangement and a
reduced exhaust backpressure.
[0011] An exhaust aftertreatment system of the mentioned kind is
known from U.S. Pat. No. 6,363,771 B1.
[0012] In the case of sufficient temperature of the SCR catalyst
(Selective Catalytic Reduction), the reducing agent must be dosed
to the exhaust gas in a suitable ratio, e.g. in a stoichiometric
one, to the NO.sub.x emissions of the internal combustion engine.
The NO.sub.x emissions of the internal combustion engine are
usually estimated through a characteristic map or an exhaust model.
Deviations in real engine operations from this characteristic map
or exhaust model lead to increased NO.sub.x or NH.sub.3 emissions
after the SCR catalyst. In particular, an NO.sub.x emission of the
internal combustion engine which is increased over the
characteristic map or model will lead to a control of the SCR
catalyst for dosing an insufficient quantity of reducing agent to
the exhaust gas and thus to increased NO.sub.x emissions after the
SCR catalyst. An NO.sub.x emission reduced over the characteristic
map or model on the other hand will lead in conventional methods to
the dosing of a large quantity of reducing agent, leading to
detrimental emissions of NH.sub.3 after the SCR catalyst. Although
precision could be improved by a further NO.sub.x sensor in the
exhaust manifold upstream of the SCR catalyst, these NO.sub.x
sensors are expensive.
[0013] It is the object of the invention to achieve a high
catalytic activity both in the oxidation catalyst as well as in the
SCR catalyst. It is a further object of the invention to improve
the catalytic reduction of the NO.sub.x emissions.
[0014] This is achieved in accordance with the invention in such a
way that a second oxidation catalyst is disposed upstream of the
DeNOx unit, with preferably the first and second oxidation catalyst
being configured for different catalytic activities and/or for
different temperature ranges. The oxidation catalysts preferably
comprise different quantities of noble metal.
[0015] It is provided in a first preferred embodiment that the
first and second oxidation catalyst are arranged in the exhaust
manifold as regards flow parallel with respect to each other, with
preferably the flow through at least one oxidation catalyst being
adjustable by means of an actuator. As an alternative to this, it
can also be provided that a first and a second oxidation catalyst
are arranged in regard to flow in series in the exhaust manifold,
with at least one oxidation catalyst being capable of being
bypassed via a bypass line. Preferably, an actuator is arranged in
the bypass line. The catalyst with the higher activity can be
activated or deactivated or be flowed through with a partial
quantity of exhaust gas.
[0016] The two oxidation catalysts can be housed in separate or in
a single common housing.
[0017] It can be provided in a further embodiment of the invention
that a particulate filter can be disposed upstream of the DeNOx
unit, preferably downstream of a dosing device for reducing agent.
The reducing agent can thus be sprayed into hotter exhaust gas and
a more complex mixing section can be realized.
[0018] An especially precise control of the catalytic activity can
be achieved when the actuator is adjusted in a model-based way
depending on the NO.sub.x content in the exhaust gas, the
temperature of the exhaust gas, the pressure loss of the diesel
particulate filter, the air-mass flow, the fuel-mass flow, the
crankshaft speed or the like, with at least one NO.sub.x sensor
preferably being disposed downstream of the DeNOx unit.
[0019] In order to improve the catalytic reduction of NO.sub.x
emissions, it is provided that beneath the minimum temperature of
the exhaust gas and/or in operating phases where no reducing agent
is added the NO.sub.x emissions are measured with the sensor
downstream of the exhaust aftertreatment system and are compared
with the values based on the characteristic map or model, and that
in the case of deviations between the measures values and those
based on the characteristic map or model a correction of the
characteristic map or emission model is performed, with preferably
the exhaust gas conveying time between the internal combustion
engine and the sensor being taken into account preferably in the
comparison of the measured values with those based on the
characteristic map or model.
[0020] The method utilizes the fact that at temperatures of the SCR
catalyst beneath approx. 200.degree. C. no reducing agent can be
added, because there is no hydrolysis and no reduction. At these
operating points, the NO.sub.x emissions after the SCR catalyst
correspond to the raw emissions when the duration of the transport
is taken into account. Specifically, the method uses a raw-emission
characteristic map of the internal combustion engine. It evaluates
whether the gradient in speed and torque is low, i.e. smaller than
a defined threshold value. If yes, the range of the characteristic
map in which the engine is located is determined and this value and
the raw emissions stored there are stored in a ring buffer. When no
reducing agent is injected by the exhaust aftertreatment system,
the currently measured emissions are compared with the stored
values by taking into account the transport period of the exhaust
gas. In the case of deviations, the respective range of the
characteristic map or the exhaust model is corrected, with only a
small change being permitted in each change step.
[0021] The invention is now explained in closer detail by reference
to the drawings, wherein:
[0022] FIG. 1 shows an exhaust system in accordance with the
invention in a first embodiment;
[0023] FIG. 2 shows an exhaust system in accordance with the
invention in a second embodiment;
[0024] FIG. 3 shows the nitrogen oxide conversion rate entered over
the temperature, and
[0025] FIG. 4 schematically shows an internal combustion engine for
performing the method.
[0026] FIG. 1 shows an exhaust system 1 of a diesel engine 2,
comprising an exhaust manifold 3 inside which a first oxidation
catalyst 4 and a second oxidation catalyst 5 are arranged.
Downstream of the two oxidation catalysts 4, 5, a DeNOx unit
arranged as an SCR catalyst 6 is arranged for selective catalytic
reduction of NO.sub.x with the help of a dosed reducing agent such
as urea or NH.sub.3. A particulate filter 9 can be arranged between
the dosing device 10 and the SCR catalyst 6. The first oxidation
catalyst 4 has a lower catalytic activity than the second oxidation
catalyst 5. The second oxidation catalyst 5 can be activated or
deactivated as required by means of an actuator 7.
[0027] The exhaust gas system 1 as shown in FIG. 2 differs from
this one in such a way that the first and second oxidation
catalysts 4, 5 are switched behind one another in respect of flow,
with the second oxidation catalyst 5 being capable of being
circumvented via a bypass line 8 in which the actuator 7 is
arranged.
[0028] The two oxidation catalysts 4, 5 can be separated from each
other or be arranged in a common housing.
[0029] When there is an increased demand for catalytic activity,
the second oxidation catalyst 5 is activated by means of the
actuator 7, by which exhaust gas is guided through the same.
Several actuators can optionally also be provided.
[0030] FIG. 3 shows a diagram in which the NO.sub.x conversion rate
CONV.sub.NOx in % is entered over the temperature T in .degree. C.
The ratio of NO.sub.2/NO is further shown. Line 20 designates the
NO.sub.x conversion rate in the case of an exhaust aftertreatment
system consisting of only one DeNOx unit. Line 30 shows the
NO.sub.x conversion rate for an aftertreatment system which
comprises a powerful oxidation catalyst and a downstream DeNOX
unit. Line 35 shows the ratio of NO.sub.2/NO for this case. Line 40
describes the NO.sub.x conversion rate for an exhaust
aftertreatment system which comprises an oxidation catalyst which
is optimized concerning the ratio NO.sub.2/NO=1 and a DeNOx unit.
Line 45 describes the ratio of NO.sub.2/NO for this case. The
dotted line 50 shows the optimal ratio of NO.sub.2/NO=1.
[0031] With the exhaust systems 1 as shown in FIGS. 1 and 2, all
NO.sub.2/NO ratios of the range A shown in FIG. 3 between curves 35
and 45 can be set by continuous setting of the actuator 7. The
setting of the actuator 7 which can be arranged as a flap for
example can occur in a controlled manner via an NO.sub.x sensor 10
disposed downstream of the DeNOx unit or can be set in a
model-based manner on the basis of measured variables such as the
temperatures of the exhaust manifold 3, pressure loss of the diesel
particulate filter, air-mass flow, fuel-mass flow, engine speed and
the like.
[0032] It is also possible to combine the systems shown in FIGS. 1
and 2.
[0033] The first oxidation catalyst 4 contains only so much noble
metal that in the temperature range of 200.degree. C. to
300.degree. C. there is no drop in the conversion in the SCR
catalyst 6. At temperatures beneath 200.degree. C., a large part of
the conversion in the SCR catalyst 6 would thus be avoided. It
would further not be possible to carry out all advantages gained
from high activity of the oxidation catalyst. High activity of the
oxidation catalyst has the following advantages: [0034] Light-off
commences earlier; [0035] a complete conversion of CO and HC, even
when upstream additional HC is dosed for combustion in the
oxidation catalyst (for increasing the temperature of the exhaust
gas); [0036] complete conversion even in case of ageing of the
oxidation catalyst; [0037] high NO.sub.2 partial pressure after the
storage catalyst in order to improve the combustion of exhaust
particulates in the diesel particle filter;
[0038] This is counteracted in such a way however that for
catalytic activity or the complete conversion of NO.sub.x in the
SCR reaction, a molar ratio of NO.sub.2/NO of 1 is advantageous.
Moreover, a ratio of NO.sub.2/NO>1 might lead to the formation
of laughing gas (N.sub.2O) in the SCR unit. In the case of a high
catalyst mass however, NO.sub.2/NO=1 is exceeded in relevant
operating points, which means that too much NO is converted into
NO.sub.2 in the catalyst.
[0039] Based on the described solution with two oxidation catalysts
4, 5, the use of catalytically coated diesel particulate filters
(in which NO.sub.2 would additionally be reproduced in a catalytic
way) can be avoided because in all operating ranges the gas flowing
in from the storage catalyst already has a sufficiently high
NO.sub.2 partial pressure.
[0040] In an uncoated diesel particulate filter 9, carbon is
incinerated more or less, but not NH.sub.3 (which would be the case
in a catalytic diesel particulate filter). That is why as an
addition an NH.sub.3 or urea dosing by means of a dosing device 10
can follow before the diesel particulate filter 9, although the SCR
catalyst 6 only follows after the diesel particulate filter 9. The
reducing agent can thus be sprayed into a hotter exhaust gas and a
longer and more complex mixing section can be realized, which thus
has an advantageous effect on the dimensions of the exhaust gas
system 1. The constructional combination of diesel particulate
filters 9 and SCR catalyst 6 is thus possible because no
intermediate section is required for dosing the reducing agent.
[0041] FIG. 4 schematically shows an internal combustion engine 101
with an exhaust manifold 102 in which an SCR catalyst 103 is
disposed. A dosing device 104 for a reducing agent such as NH.sub.3
or an aqueous urea solution opens into the exhaust manifold 102
upstream of the SCR catalyst 103. An NO.sub.x sensor 105 is
provided downstream of the SCR catalyst 103. NO.sub.x sensors 105
of this kind are used for example in onboard diagnostic
systems.
[0042] In the case of sufficient temperature of the SCR catalyst
103, reducing agent is dosed to the exhaust gas in a specific, e.g.
stoichiometric, ratio to the NO.sub.x emissions of the internal
combustion engine 101. The determination of the quantity of the
reducing agent to be dosed occurs on the basis of a characteristic
map or an exhaust model. Deviations from this characteristic map or
model in real engine operations lead to increased NO.sub.x or
NH.sub.3 emissions after the SCR catalyst 103. The characteristic
map preferably contains the NO.sub.x emissions of the internal
combustion engine as a function of speed and torque or a variable
proportional to torque such as the quantity of injected fuel.
[0043] In order to increase precision in the dosing of the reducing
agent, an NO.sub.x sensor 105 is used according to the method
proposed here, which sensor is already present downstream of the
SCR catalyst 103 within the scope of an onboard diagnostic system
for example. The method makes use of the fact that at temperatures
of the SCR catalyst 103 beneath approx. 200.degree. C. no reducing
agent can be added because no hydrolysis and no reduction occur. At
these operating points, the NO.sub.x emissions after the SCR
catalyst 103 correspond to the raw emissions when the duration of
the transport of the exhaust gas between the internal combustion
engine 101 and the NO.sub.x sensor 105 is also considered. In
addition to the NO.sub.x emissions via the NO.sub.x sensor 105,
speed and/or torque of the internal combustion engine 101 are also
detected in order to evaluate whether the amount of the gradient in
speed and/or torque lies beneath a predetermined maximum value. If
this is the case, the range of the exhaust characteristic map
(expressed for example as an interval over speed and torque) is
determined in which the internal combustion engine 101 is located,
and this value and the raw emissions saved there are stored in a
ring buffer. If no reducing agent is injected via the dosing device
104, the NO.sub.x emissions currently measured via the NO.sub.x
sensor 105 can be compared with the values stored in the ring
buffer by taking transport time into account. In the case of
deviations, the respective range of the characteristic map and/or
the exhaust model is corrected, with only minor changes being
permitted in each correction step. The correction performed per
correction step must not exceed a defined permissible maximum
value. In an especially simple embodiment of the method, the value
of the NO.sub.x emissions calculated from the characteristic map or
model is multiplied with a factor which corresponds to the
deviation between emissions calculated and those determined from
the characteristic map or model, by taking into account the dead
time. It is especially advantageous in this respect when the
correction factor(s) for the characteristic map or exhaust model
are stored in a non-volatile memory so that these corrections are
immediately available during the next start of the internal
combustion engine.
[0044] As a result of the described simple method, the raw NO.sub.x
emissions of the internal combustion engine 101 can be determined
without having to install an expensive second NO.sub.x sensor.
Deviations in the raw NO.sub.x emissions are independent of the
current temperature of the SCR catalyst 103.
* * * * *