Title of Invention

A METHOD FOR SELECTIVE CATALYTIC REDUCTION OF NITROGEN OXIDES IN THE EXHAUST GAS FROM AN INTERNAL COMBUSTION ENGINE AND AN EXHAUST GAS SYSTEM

Abstract The present invention relates to a method for the selective catalytic reduction of nitrogen oxides (NOx) in the exhaust gas from an internal combustion engine (2), a reagent addition point (5) for adding at least one of the following reagents: a) educing agent, and b) a reducing agent precursor being formed in the exhaust system (1) of the internal combustion engine (2) upstream of an SCR catalytic converter (3), and a structure (4) which the exhaust gas can at least flow around being formed immediately downstream of the reagent addition point (5), the method at least comprising the following steps: 1.1) determining a nitrogen oxide content of the exhaust gas; 1.2) determining a temperature of the structure (4); 1.3) determining a quantity of reagent required for reduction of the nitrogen oxide content determined in step 1.1); 1.4) determining a temperature of the structure (4) after addition of the quantity of reagent; 1.5) comparing the temperature of the structure (4) with a predeterminable target temperature; 1.6) calculating the temperature of the structure (4) using at least one of the following measures if the temperature is lower than the target temperature; 1.6a) adding a reduced quantity of reagent and 1.6b) increasing at least one of the following temperatures: 1.6b.1) the temperature of the structure (4) and 1.6b.2) an exhaust gas temperature; until the temperature of the structure (4), after addition of the quantity of reagent, is greater than or equal to the target temperature; and 1.7) adding the quantity of reagent through the reagent addition point and if appropriate increasing the temperature as described in step
Full Text Method for the selective catalytic reduction of
nitrogen oxides in the exhaust gas from an internal
combustion engine, and exhaust system
The present invention relates to a method for the
selective catalytic reduction of nitrogen oxides in the
exhaust gas from an internal combustion engine, in
particular in the exhaust system of motor vehicles, and
to a corresponding exhaust system. The invention deals
in particular with controlling the addition of a
reducing agent or a reducing agent precursor to the
exhaust gas.
Numerous countries throughout the world have
implemented statutory regulations which set an upper
limit for the level of certain substances in the
exhaust gas from internal combustion engines. These are
generally substances which it is undesirable to emit to
the environment. One of these substances is nitrogen
oxide (NOX) , the level of which in the exhaust gas must
not exceed statutory emission limits. On account of the
boundary conditions, for example the design of the
internal combustion engines with a view to achieving
favourable fuel consumption and the like, avoiding the
emission of nitrogen oxides within the engine so as to
lower the level of the nitrogen oxides in the exhaust
gas, is of only limited use, and consequently exhaust
gas aftertreatment is required in order to comply with
relatively low limits. In this context, it has emerged
that selective catalytic reduction (SCR) of the
nitrogen oxides is advantageous. This SCR method
requires a reducing agent which contains nitrogen. In
particular, the use of ammonia (NH3) as reducing agent
has proven to be one possible alternative. On account
of the chemical properties and statutory guidelines in
many countries, the ammonia is not usually held in the
form of pure ammonia, since this can lead to problems
in particular in the context of motor vehicles or other


mobile applications. Rather, instead of storing the reducing agents themselves, reducing
agent precursors are often stored and carried along in the vehicle. A reducing agent
precursor is to be understood in particular as meaning a substance which cleaves off the
reducing agent or can be chemically converted into the reducing agent. By way of
example, urea represents a reducing agent precursor for the reducing agent ammonia.
Other possible reducing agent precursors for ammonia as reducing agent include
ammonium carbamate, isocyanic acid or cyanuric acid.
The chemical conversion of the reducing agent precursor into the reducing agent, the
cleaving of the reducing agent from the reducing agent precursor and a possible change
in the state of the reducing agent precursor and/or the reducing agent are generally
based on endothermic processes, which require the input of energy. This input of
energy generally leads to a drop in the temperature of the exhaust gas and/or of
components in the exhaust system. However, it is known that a temperature change
during a chemical reaction also shifts the reaction equilibrium of this reaction. In
addition to the reaction products which are actually desired, undesirable by-products
may also form, depending on the current position of the reaction equilibrium.
Prior art document EP 1 469 173 Al discloses an exhaust gas system with a hydrolysis
catalyst, a SCR catalyst, an ammonia slip catalyst and a diesel particulate filter. It is
disclosed to adjust the temperature of an exhaust gas in view of the optimal
temperature of the components hydrolysis catalyst, SCR catalyst, ammonia slip catalyst
and DPF.
Consequently, the present invention is based on the object of proposing a method for
reducing nitrogen oxide in the exhaust gas from an internal combustion engine, in which
the formation of undesirable by- products when providing the reducing agent is
effectively avoided, and of proposing a corresponding exhaust system.


The method according to the invetion for the selective
catalytic reduction of nitrogen oxides in the exhaust
gas from an internal combustion engine, a reagent
addition point for adding at least one of the following
reagents:
a) a reducing agent, and
b) a reducing agent precursor
being formed in the exhaust system of the internal
combustion engine upstream of an SCR catalytic
converter, and a structure which the exhaust gas can at
least flow around being formed immediately downstream
of the reagent addition point, the method at least
comprises the following steps:
1.1) determining a nitrogen oxide content of the
exhaust gas;
1.2) determining a temperature of the structure;
1.3) determining a quantity of reagent required for
reduction of the nitrogen oxide content determined
in step 1.1);
1.4) determining a temperature of the structure after
addition of the quantity of reagent;
1.5) comparing the temperature of the structure with a
predeterminable target temperature;
1.6) calculating the temperature of the structure using
at least one of the following measures if the
temperature is lower than the target temperature;
1.6a)adding a reduced quantity of reagent and
1.6b)increasing at least one of the following
temperatures:
1.6b.l) the temperature of the
structure and
1.6b.2) an exhaust gas temperature;
until the temperature of the structure, after
addition of the quantity of reagent, is greater
than or equal to the target temperature; and
1.7) adding the quantity of reagent through the reagent
addition point and if appropriate increasing the
temperature as described in step 1.6b).


In the context of the present invention, directly
downstream is to be understood as meaning that the
structure represents the structure which is the next
exhaust system component downstream of the reagent
addition point, as seen in the direction of flow. The
SCR catalytic converter is in particular a structure
through which the exhaust gas can flow, such as for
example a honeycomb body which is provided with a
suitable coating. This may in particular be a titanium
dioxide (anatase)-supported vanadium/tungsten mixed
oxide and/or metal-exchanged zeolites, preferably iron
zeolites, in particular of the X, Y, ZSM-5 and/or ZSM-
11 type. The honeycomb bodies used may in particular be
standard ceramic and/or metallic honeycomb bodies which
have cavities, such as for example passages, which an
exhaust gas can at least flow through. It is preferable
for the honeycomb body to be formed from at least one
at least partially structured metallic layer. In this
case, the metallic layer may comprise sheet-metal foils
and/or porous metallic layers. The honeycomb body is
preferably produced by winding at least one at least
partially structured metallic layer and if appropriate
at least one substantially smooth metallic layer or by
stacking at least one at least partially structured
layer and if appropriate at least one substantially
smooth layer and intertwining at least one stack formed
in this way.
Preference is given to a method in which the reagent
added is ammonia as reducing agent and/or urea as
reducing agent precursor. In this context, the addition
of urea as a solid and/or in the form of an aqueous
urea solution is preferred.
In this case, depending on the temperature in the SCR
catalytic converter, the following primary reaction
takes place:


In this case, nitrogen monoxide (NO) is reacted with
nitrogen dioxide (NO2) and ammonia (NH3) to form
molecular nitrogen (N2) and water (H2O) . The provision
of the reducing agent ammonia from a reducing agent
precursor (urea) usually involves a multistage
reaction, in which thermolysis and/or hydrolysis is
often carried out. In the case of thermolysis, urea
((NH2)2CO) is thermally converted into ammonia and
isocyanic acid (HCNO). This is followed by hydrolysis,
in which the isocyanic acid is reacted with water to
form ammonia and carbon dioxide:

In particular, the hydrolysis and thermolysis are often
carried out at a hydrolysis catalytic converter, which
is usually applied in and/or on a coating of a
honeycomb body. Depending on the temperature of this
hydrolysis catalytic converter, in addition to the
desired primary reactions mentioned above, secondary
reactions also occur and in some cases result in
undesirable reaction products. In the preferred system
indicated above, in which ammonia is used as reducing
agent and urea is used as reducing agent precursor, in
addition to the formation of ammonia as indicated
above, it is also possible that, for example, biuret
( (NH2CO)2NH) may form. Biuret represents a viscous
product which can block the passages of the hydrolysis
catalytic converter when it is being formed on the
latter. In this way, firstly the yield of ammonia
achieved is reduced, and secondly the passages of the
honeycomb body start to clog up. Biuret can only be
removed from the honeycomb body with very considerable
difficulty, and consequently it is advantageous for the
temperature at which the thermolysis and/or hydrolysis
of the urea takes place to be selected in such a way
that no biuret is formed, since clogging of passages in


the hydrolysis catalytic converter can lead to failure
of this catalytic converter and therefore to inadequate
conversion of urea into ammonia.
In principle, step 1.3) of the invention is based on
stoichiometric reaction of the nitrogen oxide with the
reducing agent. When the reducing agent precursor
and/or the reducing agent is added in the exhaust gas,
the temperature of the exhaust gas is reduced, as
outlined above, and therefore the temperature of the
components through or around which the exhaust gas
flows is also reduced. This is not critical with regard
to undesirable by-products, such as for example biuret,
if the temperature of the exhaust gas is high enough.
However, if the exhaust gas temperature is in the
region of a critical temperature, the reaction
equilibrium may be shifted in the direction of the
generation of undesirable by-products. The target
temperature with which the temperature of the structure
is compared in step 1.5) should therefore be preset in
such a way that at the target temperature the formation
of the undesirable by-products, such as for example
biuret, does not exceed a predeterminable level. It is
preferable for the target temperature to be
predetermined in such a way that only small amounts of
undesirable by-products are formed.
The method according to the invention therefore takes
into account the drop in temperature of the exhaust gas
caused by the addition of the reducing agent precursor
and/or the reducing agent and initiates possible
measures to counteract this drop in temperature. In
accordance with step 1.6a), one of these measures may
consist in reducing the quantity of reducing agent to
be added. This means that although not all the nitrogen
oxides which are present in the exhaust gas are then
converted, depending on the operating state of the
internal combustion engine this may be acceptable.
Another possible step of a measure to counteract the


drop in temperature consists in increasing the
temperature of the system, specifically, on the one
hand, in increasing the temperature of the structure
located directly downstream of the reagent addition
point, and on the other hand the exhaust gas
temperature. Since this requires active measures, such
as for example electrical heating of the structure or
increasing the exhaust gas temperature by changing the
engine operating state or by injecting and oxidizing an
additional quantity of fuel, this gives rise to a
fundamentally undesirable secondary effect, for example
an increased fuel consumption. The method according to
the invention takes into account options 1.6a) and
1.6b) in such a way that the maximum possible
conversion of the nitrogen oxides present in the
exhaust gas takes place with the minimum possible
increase in fuel consumption but without the
temperature dropping below the target temperature.
In principle, the method according to the invention is
based, for example, on the fact that on account of the
engine management, the nitrogen oxide contents of the
exhaust gas on leaving the internal combustion engine
are always known. A certain time elapses before the
exhaust gas reaches the SCR catalytic converter from
downstream in the exhaust system, and this time can be
used accordingly to determine the quantity of reagent
that is to be added, and if appropriate also to take
the measures listed in step 1.6) . In particular, the
method according to the invention can also be combined
with an N0X adsorber, in which excess nitrogen oxide
levels can be reversibly stored. Subsequent
regeneration of the NOX adsorber can be planned in such
a way as to convert the stored nitrogen oxides as
completely as possible.
Step 1.6b.l) is to be understood as meaning that the
temperature of the structure is increased to a
sufficient extent for the temperature of the structure


to be reliably kept above the target temperature
despite the temperature dropping as a result of the
addition of the reagent.
According to an advantageous refinement of the method
according to the invention, the structure comprises a
honeycomb body.
This may in particular be a ceramic honeycomb body
and/or a metallic honeycomb body. In this context,
honeycomb bodies which form passages through which a
fluid, such as for example an exhaust gas, can flow are
likewise preferred in this context.
A refinement of the method in which the structure
comprises at least one of the following catalytic
converters:
3.1) a hydrolysis catalytic converter and
3.2) an SCR catalytic converter
is particularly preferred.
In particular when using an aqueous urea solution as
reducing agent precursor, the method according to the
invention is advantageous if the structure comprises a
hydrolysis catalytic converter in accordance with
variant 3.1), since in this case, in addition to the
energy required for the chemical reaction, it is also
necessary to apply the enthalpy of vaporization of the
water, which leads to a further reduced temperature
after addition of the reagent. If urea solution is used
as reducing agent precursor, therefore, there is an
increased probability of the formation of undesirable
by-products, such as for example biuret.
According to a further advantageous configuration of
the method according to the invention, step 1.1)
comprises at least one of the following measures:
4.1) measuring the nitrogen oxide content, and


4.2) determining the nitrogen oxide emission from the
engine characteristic data.
In particular if, in accordance with step 4.2), the
nitrogen oxide emission is at least partially obtained
from the engine characteristic data, it is
advantageously possible to use the time which it takes
for the exhaust gas to pass from the internal
combustion engine to the SCR catalytic converter to
carry out steps 1.1) to 1.6) of the invention. An
engine map or the engine characteristic data is to be
understood in particular as meaning the operational
engine map of the internal combustion engine. The
nitrogen oxide consumption can be calculated from the
available and measurable or predetermined
characteristic data of the engine, such as for example
the load, engine speed, etc. According to option 4.1),
the nitrogen oxide content may as an alternative or in
addition also be measured using a corresponding sensor.
It is possible to form a plurality of sensors, so that
different measured values are present at different
points of the exhaust system. These can be compared
with the nitrogen oxide emission from engine
characteristic data determined from option 4.2) . In
particular, it is also possible to design a computer-
aided model of the exhaust system, on the basis of
which, by means of measured supporting points with
respect to in particular the nitrogen oxide content,
the oxygen content and the temperature of the exhaust
gas at at least one point of the exhaust system, the
corresponding values can be determined in other regions
of the exhaust system.
According to a further advantageous configuration of
the method according to the invention, step 1.2)
comprises at least one of the following measures:
5.1) measuring the temperature of the structure, and
5.2) calculating the temperature.


In this case too, it is possible to calculate the
temperature of the structure, for example from the
engine characteristic data and the known specific
design of the exhaust system. Furthermore, it is
possible to determine the temperature of the structure,
the temperature of another component in the exhaust
system and/or the temperature of the exhaust gas itself
and to determine the temperature from this information.
According to a further advantageous configuration of
the method according to the invention, the target
temperature is at most 180°C, preferably between 120°C
and 170°C, in particular approximately 160°C.
These temperatures have proven particularly
advantageous to avoid the formation of biuret from
urea. These target temperatures in particular ensure in
a particularly advantageous way that clogging and
closing-up of the passages at least of the structure
can be effectively reduced to a significant extent or
even substantially prevented.
According to a further advantageous configuration of
the method according to the invention, step 1.6) is
carried out iteratively.
In particular if the nitrogen oxide content of the
exhaust gas is at least partially calculated from the
engine map, it is advantageously possible to opt for an
iterative approach when carrying out step 1.6), since
in this case, if the method is carried out with the aid
of a computer and a suitably fast processor, a
sufficient period of time is available to allow
iterative determination of measures 1.6a) and 1.6b) and
their effect on the temperature of the structure after
addition of the quantity of reagent.
Depending on the particular configuration of the
iterative process, it is in this way possible to


achieve a very accurate procedure with regard to step
1.6). In particular, with relatively large iteration
steps, it is possible, despite the iterative procedure,
to achieve a very rapid drop below the target
temperature after the addition of the quantity of
reagent.
According to a further advantageous configuration of
the method according to the invention, step 1.6) is
carried out continuously.
Carrying out step 1.6) continuously has the advantage
that the temperature can be made to drop below the
target temperature very quickly. In particular if
relatively large gradients are used in measures 1.6a)
and 1.6b), it is possible to ensure a rapid procedure.
According to a further advantageous configuration of
the method according to the invention, carrying out the
increase in temperature in accordance with step 1.6b.l)
comprises electrical heating of the structure.
In particular, the structure may comprise an
electrically heatable honeycomb body. The electrical
heating of the structure has the advantage that it is
possible to achieve a very rapid increase in the
temperature of the structure to above the target
temperature, and therefore the formation of undesirable
by-products, such as for example biuret, can be
effectively prevented. The electrical heating of the
structure allows a very dynamic adjustment and control
process.
According to a further advantageous configuration of
the method according to the invention, the execution of
the increase in temperature in accordance with step
1.6b.2) comprises at least one of the following
measures:


10.1)changing the operating point of the internal
combustion engine,-
10.2)electrically heating the exhaust gas upstream of
the structure, and
10.3)injecting and oxidizing hydrocarbons.
In accordance with step 10.1), a relatively minor
change in the operating point of the internal
combustion engine, which may involve a slightly
increased fuel consumption, can be used to effect an
increase in the exhaust gas temperature which can
compensate for the drop in temperature caused by the
addition of the reagent. In accordance with step 10.2),
electrical heating of the exhaust gas can be effected,
for example, by means of an electrically heatable
honeycomb body located upstream of the structure. In
accordance with step 10.3), it is possible to effect an
increase in the exhaust gas temperature and therefore
an increase in the temperature of the structure for
example by briefly operating the internal combustion
engine in rich-burn mode and by using a corresponding
oxidation catalytic converter in the exhaust section,
in particular upstream of the structure.
According to a further advantageous configuration of
the method according to the invention, at least one of
the following substances can be added as reagent:
11.1) ammonia and
11.2) urea.
It is in this way advantageously possible in particular
to prevent the formation of biuret on the structure.
According to another advantageous configuration of the
method according to the invention, the quantity of
reagent is reduced if a reducing agent content can be
detected in the exhaust gas stream downstream of the
SCR catalytic converter.


If it is possible to detect a reducing agent content
downstream of the SCR catalytic converter, a
superstoichiometric reducing agent content is present.
To prevent this, in accordance with the invention it is
possible to reduce the quantity of reducing agent or
reducing agent precursor to be added. In particular, an
oxidation catalytic converter, which can be used to
oxidize reducing agent which breaks through the SCR
catalytic converter, may be formed downstream of the
SCR catalytic converter.
A further aspect of the invention proposes an exhaust
system for an internal combustion engine, comprising an
SCR catalytic converter, a reagent addition point for
adding at least one of the following reagents:
a) a reducing agent and
b) a reducing agent precursor
and downstream of the reagent addition point a
structure which the exhaust gas can at least flow
around, control means for the addition of the reagent,
when controlling the quantity of reagent added as a
function of at least one of the following variables:
13.1) the exhaust gas temperature;
13.2) the temperature of the structure and
13.3) the nitrogen oxide content of the exhaust gas
taking into account the change in at least one of the
variables 13.1) and 13.2) caused by the addition of the
quantity of reagent.
The details and refinements which have been disclosed
in connection with the method according to the
invention can also be transferred and applied to the
exhaust system according to the invention. In
particular, the exhaust system according to the
invention can be used to carry out the method according
to the invention.
The following text describes the invention with
reference to the accompanying figure, without the


invention being restricted to the exemplary embodiments
shown therein and to the advantages disclosed.
The only appended figure, Fig. 1, shows an exhaust
system 1 according to the invention of an internal
combustion engine 2. The exhaust system 1 is shown
schematically. The exhaust system 1 comprises an SCR
catalytic converter 3. A hydrolysis catalytic converter
4 is formed upstream of the SCR catalytic converter 3.
A reagent addition point 5, which can be used to
introduce a reducing agent and/or a reducing agent
precursor into the exhaust system 1, is formed upstream
of the hydrolysis catalytic converter 4. In this
context, it is particularly preferable for the reagent
addition point 5 to be used to add urea as a solid
and/or in the form of an aqueous urea solution. The
hydrolysis catalytic converter 4 in this case forms the
structure which is formed directly downstream of the
reagent addition point 5 and which the exhaust gas can
at least flow around.
In operation, the nitrogen oxide content in the exhaust
gas from the internal combustion engine 2 is
determined. This can be done either using the
operational engine map of the internal combustion
engine 2 or by determination of the nitrogen oxide
content for example by means of a first measurement
sensor 7. On the basis of this nitrogen oxide content
determined in this way, the quantity of reagent
required for the reduction of the determined nitrogen
oxide content is determined in accordance with step
1.3). The reagent in this case comprises a reducing
agent and/or a reducing agent precursor. Furthermore,
the temperature of the hydrolysis catalytic converter 4
is determined, for example using a second measurement
sensor 8. As an alternative or in addition, it is
possible to determine the temperature of the structure
which a fluid can at least flow around, i.e. the
hydrolysis catalytic converter 4, from the operating


data of the internal combustion engine 2, taking
account of the known design of the exhaust system 1.
Based on the determined quantity of reagent, the
temperature of the structure after addition of this
quantity of reagent is determined. This temperature of
the structure after addition is compared with a
predeterminable target temperature. If the temperature
of the structure after addition of the quantity of
reagent is below the target temperature, the
temperature of the structure is calculated by at least
one of the following measures in accordance with step
1.6) :
1.6a) adding a reduced quantity of reagent, and
1.6b) increasing at least one of the following
temperatures:
1.6b.l) the temperature of the structure and
1.6b.2) an exhaust gas temperature.
In this case, the quantity in step 1.6a) can be reduced
continuously or iteratively or discontinuously, and the
same applies to the temperatures that are to be
increased. If the temperature of the structure after
addition of the quantity of reagents, taking into
account measure 1.6a), 1.6b), is above the target
temperature or corresponds to the target temperature,
the quantity of reagent is added and if appropriate the
temperature is increased accordingly. This can be done,
for example, by heating the hydrolysis catalytic
converter 4 or a honeycomb body 9 located upstream of
the hydrolysis catalytic converter 4. The electrical
heating can be done, for example, by electrical heating
means 10 to which the honeycomb body 9 and/or the
hydrolysis catalytic converter 4 is connected. An
oxidation catalytic converter 11 may be formed
downstream of the SCR catalytic converter 3, in order
to convert any reducing agent whieh breaks through the
SCR catalytic converter and therefore to prevent the
reducing agent from being released to the environment.
To monitor whether a breakthrough of reducing agent is


occurring, a third measurement sensor 12, which can be
used in particular to determine the concentration of
reducing agent in the exhaust gas, is formed downstream
of the SCR catalytic converter 3 . If the third
measurement sensor 12 indicates a significant
concentration of reducing agent, the quantity of
reagent added is reduced. Control means 13, which are
connected to the measurement sensors 7, 8, 12, the
electrical heating means 10, the internal combustion
engine 2 and the reagent addition point 5 via signal
lines 14, which are only indicated in the diagram, are
provided for the purpose of carrying out the method. In
the present exemplary embodiment, the signal lines 14
form a bus system with addressable databus. In
particular, the method according to the invention can
be carried out in the control means 13. The control
means 13 may, for example, be integrated in an engine
control unit for the internal combustion engine.
The method according to the invention and the exhaust
system 1 according to the invention advantageously
allow the selective catalytic reduction of nitrogen
oxides in the exhaust gas from an internal combustion
engine 2, during which the formation of undesirable by-
products, such as for example biuret if urea is used as
reducing agent precursor, is avoided as far as
possible. This advantageously lengthens the service
life of the exhaust system 1.

1 Exhaust system
2 Internal combustion engine
3 SCR catalytic converter
4 Hydrolysis catalytic converter
5 Reagent addition point

7 First measurement sensor
8 Second measurement sensor
9 Honeycomb body
10 Electrical heating means
11 Oxidation catalytic converter
12 Third measurement sensor
13 Control means
14 Signal line

WE CLAIM
3.1 A method for selective catalytic reduction of nitrogen oxides (NOx) in the
exhaust gas from an internal combustion engine (2), a reagent addition point
(5) for adding at least one of the following reagents:
(a) a reducing agent, and
(b) a reducing agent precursor being formed in the exhaust system (1) of the
internal combustion engine (2) upstream of an SCR catalytic converter
(3), and a structure (4) which the exhaust gas can at least flow around
being formed immediately downstream of the reagent addition point (5),
the method at least comprising the following steps:
1.1.determining a nitrogen oxide content of the exhaust gas;
1.2.determining a temperature of the structure (4);
1.3.determining a quantity of reagent required for reduction of the
nitrogen oxide content determined in step 1.1);
1.4. determining a temperature of the structure (4) after addition of
the quantity of reagent;
1.5.comparing the temperature of the structure (4) with a
predeterminable target temperature;
1.6.calculating the temperature of the structure (4) using at least one
of the following measures if the temperature is lower than the
target temperature;
1.6a) adding a reduced quantity of reagent and

1.6b) increasing at least one of the following temperatures:
1.6b.l) the temperature of the structure (4) and
1.6b.2) an exhaust gas temperature;
until the temperature of the structure (4) , after addition of the
quantity of reagent, is greater than or equal to the target
temperature; and
1.7. adding the quantity of reagent through the reagent addition point
and if appropriate increasing the temperature as described in step
1.6b).
3.1The method as claimed in claim 1, wherein the structure (4) comprises a
honeycomb body.
3.1The method as claimed in claim 1 or 2, wherein the structure (4) comprises
at least one of the following catalytic converters:
3.1) a hydrolysis catalytic converter (4) and
3.2) an SCR catalytic converter (3).
4. The method as claimed in one of the preceding claims, wherein step 1.1)
comprises at least one of the following steps:
4.1) measuring the nitrogen oxide content, and

4.2) determining the nitrogen oxide emissions from the engine
characteristic data.
5. The method as claimed in one of the preceding claims, wherein step 1.2)
comprises at least one of the following steps:
5.1) measuring the temperature of the structure (4), and
5.2) calculating the temperature.

6. The method as claimed in one of the preceding claims, wherein the target
temperature is at most 180°C, preferably 120 to 170°C, in particular 160°C.
7. The method as claimed in one of the preceding claims, wherein step 1.6) is
carried out iteratively.
8. The method as claimed in one of claims 1 to 6, wherein step 1.6) is carried
out continuously.
9. The method as claimed in one of the preceding claims, wherein the
execution of the increase in temperature in accordance with step 1.6b.l)
comprises electrical heating of the structure (4).
10. The method as claimed in one of the preceding claims, wherein the
execution of the increase in temperature in accordance with step 1.6b.2)
comprises at least one of the following steps:

10.1) changing the operating point of the internal combustion engine (2);
10.2) electrically heating the exhaust gas upstream of the structure (4),
and
10.3) injecting and oxidizing hydrocarbons.
11. The method as claimed in one of the preceding claims, wherein at least one
of the following substances can be added as reagent:
11.1) ammonia and
11.2) urea.

12. The method as claimed in one of the preceding claims, wherein the quantity
of reagent is reduced if a reducing agent content can be detected in the
exhaust gas stream downstream of the SCR catalytic converter (3).
13. An exhaust system (1) for an internal combustion engine, comprising an SCR
catalytic converter (3), a reagent addition point (5) for adding at least
one of the following reagents:

a) a reducing agent and
b) a reducing agent precursor and downstream of the reagent addition point (5)
a structure (4) which the exhaust gas can at least flow around, control means
(13) for the addition of the reagent, when controlling the quantity of reagent
added as a function of at least one of the following variables:

13.1) the exhaust gas temperature;
13.2) the temperature of the structure (4) and
13.3) the nitrogen oxide content of the exhaust gas
taking into account the change in at least one of the variables 13.1)
and 13.2) caused by the addition of the quantity of reagent.


The present invention relates to a method for the selective catalytic reduction of
nitrogen oxides (NOx) in the exhaust gas from an internal combustion engine
(2), a reagent addition point (5) for adding at least one of the following
reagents:
a) educing agent, and
b) a reducing agent precursor
being formed in the exhaust system (1) of the internal combustion engine (2)
upstream of an SCR catalytic converter (3), and a structure (4) which the
exhaust gas can at least flow around being formed immediately downstream of
the reagent addition point (5), the method at least comprising the following
steps:
1.1) determining a nitrogen oxide content of the exhaust gas;
1.2) determining a temperature of the structure (4);
1.3) determining a quantity of reagent required for reduction of the nitrogen
oxide content determined in step 1.1);
1.4) determining a temperature of the structure (4) after addition of the quantity
of reagent;
1.5) comparing the temperature of the structure (4) with a predeterminable
target temperature;
1.6) calculating the temperature of the structure (4) using at least one of the
following measures if the temperature is lower than the target temperature;
1.6a) adding a reduced quantity of reagent and
1.6b) increasing at least one of the following temperatures:
1.6b.1) the temperature of the structure (4) and

1.6b.2) an exhaust gas temperature;
until the temperature of the structure (4), after addition of the quantity of
reagent, is greater than or equal to the target temperature; and 1.7)
adding the quantity of reagent through the reagent addition point and if
appropriate increasing the temperature as described in step

Documents:

00224-kolnp-2008-abstract.pdf

00224-kolnp-2008-claims.pdf

00224-kolnp-2008-correspondence others.pdf

00224-kolnp-2008-description complete.pdf

00224-kolnp-2008-drawings.pdf

00224-kolnp-2008-form 1.pdf

00224-kolnp-2008-form 2.pdf

00224-kolnp-2008-form 3.pdf

00224-kolnp-2008-form 5.pdf

00224-kolnp-2008-gpa.pdf

00224-kolnp-2008-international publication.pdf

00224-kolnp-2008-international search report.pdf

00224-kolnp-2008-others pct form.pdf

00224-kolnp-2008-pct request form.pdf

224-KOLNP-2008-ABSTRACT 1.1.pdf

224-KOLNP-2008-AMANDED CLAIMS.pdf

224-KOLNP-2008-AMANDED PAGES OF SPECIFICATION.pdf

224-kolnp-2008-correspondence.pdf

224-KOLNP-2008-DESCRIPTION (COMPLETE) 1.1.pdf

224-KOLNP-2008-DRAWINGS 1.1.pdf

224-kolnp-2008-examination report.pdf

224-KOLNP-2008-FORM 1-1.1.pdf

224-kolnp-2008-form 18.1.pdf

224-kolnp-2008-form 18.pdf

224-KOLNP-2008-FORM 2-1.1.pdf

224-KOLNP-2008-FORM 3-1.1.pdf

224-kolnp-2008-form 3.pdf

224-kolnp-2008-form 5.pdf

224-KOLNP-2008-FORM-27.pdf

224-kolnp-2008-gpa.pdf

224-kolnp-2008-granted-abstract.pdf

224-KOLNP-2008-GRANTED-CLAIMS.pdf

224-kolnp-2008-granted-description (complete).pdf

224-kolnp-2008-granted-drawings.pdf

224-kolnp-2008-granted-form 1.pdf

224-kolnp-2008-granted-form 2.pdf

224-kolnp-2008-granted-specification.pdf

224-KOLNP-2008-OTHERS-1.1.pdf

224-kolnp-2008-others.pdf

224-KOLNP-2008-PETITION UNDER RULE 137.pdf

224-KOLNP-2008-REPLY TO EXAMINATION REPORT.pdf

224-kolnp-2008-reply to examination report1.1.pdf

224-kolnp-2008-translated copy of priority document.pdf

abstract-00224-kolnp-2008.jpg


Patent Number 249849
Indian Patent Application Number 224/KOLNP/2008
PG Journal Number 46/2011
Publication Date 18-Nov-2011
Grant Date 16-Nov-2011
Date of Filing 16-Jan-2008
Name of Patentee EMITEC GESELLSCHAFT FUR EMISSIONS-TECHNOLOGIE MBH
Applicant Address HAUPTSTRASSE 128, 53797 LOHMAR
Inventors:
# Inventor's Name Inventor's Address
1 BRUCK, ROLF FROBELSTRASSE 12, 51429 BERGISCH GLADBACH
PCT International Classification Number B01D 53/94,F01N 9/00
PCT International Application Number PCT/EP2006/007196
PCT International Filing date 2006-07-21
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10 2005 035 554.4 2005-07-29 Germany