U.S. patent application number 11/582913 was filed with the patent office on 2007-04-26 for method of avoiding undesired no2 emissions of internal combustion engines.
This patent application is currently assigned to MAN Nutzfahrzeuge AG. Invention is credited to Andreas Doring.
Application Number | 20070089406 11/582913 |
Document ID | / |
Family ID | 37441581 |
Filed Date | 2007-04-26 |
United States Patent
Application |
20070089406 |
Kind Code |
A1 |
Doring; Andreas |
April 26, 2007 |
Method of avoiding undesired NO2 emissions of internal combustion
engines
Abstract
A method of reducing undesired NO.sub.2 emissions of an internal
combustion engine that operates with excess air and has an exhaust
gas section, including providing the exhaust gas section with at
least one catalytic converter that operates with NO oxidation
activity, wherein the catalytic converter is adapted to increase
the NO.sub.2 content in the exhaust gas of the internal combustion
engine for exhaust gas post treatment processes. During operation
of the internal combustion engine, and adapted to a respective
operating level of the internal combustion engine and a state of
the catalytic converter, a content of materials that compete with
the NO oxidation is varied in such a way that downstream of the
catalytic converter only that theoretical NO.sub.2 content is
present in the exhaust gas that is required for a subsequent
exhaust gas post treatment.
Inventors: |
Doring; Andreas; (Munchen,
DE) |
Correspondence
Address: |
ROBERT W. BECKER & ASSOCIATES
Suite B
707 Highway 66 East
Tijeras
NM
87059
US
|
Assignee: |
MAN Nutzfahrzeuge AG
Munchen
DE
|
Family ID: |
37441581 |
Appl. No.: |
11/582913 |
Filed: |
October 18, 2006 |
Current U.S.
Class: |
60/295 ;
60/286 |
Current CPC
Class: |
F01N 2560/026 20130101;
F02D 41/0235 20130101; F01N 3/0231 20130101; Y02T 10/12 20130101;
F02D 2250/36 20130101; F01N 2430/06 20130101; F01N 3/106 20130101;
F01N 3/2066 20130101 |
Class at
Publication: |
060/295 ;
060/286 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 18, 2005 |
DE |
10 2005 049 655.5 |
Claims
1. A method of reducing undesired NO.sub.2 emissions of an internal
combustion engine that operates with excess air and has an exhaust
gas section, the method including the steps of: providing said
exhaust gas section with at least one catalytic converter that
operates with NO oxidation activity, wherein said catalytic
converter is adapted to increase the NO.sub.2 content in the
exhaust gas of the internal combustion engine for exhaust gas post
treatment processes that are adapted to follow; and during
operation of the internal combustion engine, and adapted to a
respective operating level of the internal combustion engine and a
state of said catalytic converter, varying a content of materials
that compete with the NO oxidation in such a way that downstream of
said catalytic converter only that theoretical NO.sub.2 content is
present in the exhaust gas that is required for a subsequent
exhaust gas post treatment.
2. A method according to claim 1, wherein said catalytic converter
that operates with NO oxidation activity contains platinum and/or
platinum oxide as an active component.
3. A method according to claim 1, wherein said step of varying a
content of materials is effected via the internal combustion
engine.
4. A method according to claim 1, wherein said step of varying a
content of materials is effected by adding the materials into the
exhaust gas of the internal combustion engine downstream of the
engine and upstream of said catalytic converter that operates with
NO oxidation activity.
5. A method according to claim 1, wherein the materials are
hydrocarbons.
6. A method according to claim 5, wherein said hydrocarbons are
non-combusted fuel.
7. A method according to claim 5, wherein the hydrocarbon
concentration in the exhaust gas of the internal combustion engine
is varied by means of a variation of engine parameters.
8. A method according to claim 7, wherein said engine parameters
are at least one of beginning of injection, injection pressure, AGR
rate, position of a butterfly valve on a suction side, and reduced
injections.
9. A method according to claim 1, which includes the further steps
of determining the theoretical NO.sub.2 content in an electronic
control unit with the aid of sensors and/or calculations and/or
characteristics, in conformity therewith controlling at least one
adjustment element of said electronic control unit, and by means of
said at least one adjustment element varying the proportion of the
material in the exhaust gas upstream of said catalytic converter
that operates with NO oxidation activity in such a way that the
theoretical NO.sub.2 value is adjusted downstream of said catalytic
converter.
10. A method according to claim 9, which includes, for a
determination of a theoretical NO.sub.2 content and for the control
of said at least one adjustment element, using at least one of the
following parameters and determination models: total quantity of
exhaust gas; hydrocarbon concentration in the exhaust gas upstream
of said catalytic converter that operates with NO oxidation
activity; the raw emission of NO and/or NO.sub.x; the raw emission
of the exhaust gas substituents that are to be reduced; the maximum
permissible residual emission of the exhaust gas substituents that
are to be reduced downstream of the exhaust gas post treatment; the
maximum permissible residual emission of NO.sub.2 downstream of the
exhaust gas post treatment; the maximum permissible residual
concentration of the added materials downstream of the catalytic
converter that operates with NO oxidation activity; the maximum
permissible residual emission of the added materials downstream of
the post treatment; the catalytic converter temperatures; the
exhaust gas temperatures; a catalytic converter model for
determination of NO.sub.2 conversions in the catalytic converter
that operates with NO oxidation activity; a catalytic converter
model for determination of conversion rates of the exhaust gas
substituents that are to be reduced in the exhaust gas post
treatment; the speed of the engine; the intake or supercharge
pressure; the quantity of fuel; the catalytic converter aging over
running time; the actual NO.sub.2 concentration and/or the actual
NO.sub.2 content downstream of the catalytic converter that
operates with NO oxidation activity; and the residual NO.sub.2
concentration and/or the residual NO.sub.2 content of the exhaust
gas downstream of the exhaust gas post treatment.
11. A method according to claim 10, which includes determining the
actual NO.sub.2 concentration and/or the actual NO.sub.2 content
and/or the residual NO.sub.2 concentration and/or the residual
NO.sub.2 content by means of one or more sensors.
12. A method according to claim 10, wherein determination of the
actual NO.sub.2 concentration and/or the actual NO.sub.2 content in
the exhaust gas is effected between said catalytic converter that
operates with NO oxidation activity and the following arrangement
for the exhaust gas post treatment.
13. A method according to claim 10, wherein determination of the
residual NO.sub.2 concentration and/or the residual NO.sub.2
content in the exhaust gas is effected downstream of the
arrangement for the exhaust gas post treatment.
14. A method according to claim 10, wherein the actual NO.sub.2
concentration and/or the actual NO.sub.2 content serves as an
actual value in a closed control loop, and wherein by continuously
comparing actual value and theoretical value and continuous setting
of the at least one adjustment element for variation of the
quantity of the materials to be added, said control loop adjusts
the theoretical NO.sub.2 value.
15. A method according to claim 10, wherein the residual NO.sub.2
concentration and/or the residual NO.sub.2 content serves as an
actual value in a closed control loop, and wherein by continuously
comparing actual value and theoretical value and continuous setting
of the at least one adjustment element for variation of the
quantity of the materials to be added, said control loop adjusts
the theoretical NO.sub.2 value.
16. A method according to claim 5, wherein a sensor is used to
determine the hydrocarbon concentration in the exhaust gas.
17. A method according to claim 10, wherein the hydrocarbon
concentration serves as an actual value in a closed control loop,
and wherein by continuously comparing actual value and theoretical
value and continuous setting of the at least one adjustment element
for variation of the quantity of the materials to be added, said
control loop adjusts the theoretical NO.sub.2 value.
18. A method according to claim 16, wherein for determination of
the hydrocarbon concentration, the sensor is disposed between said
catalytic converter that operates with NO oxidation activity and
the arrangement for the exhaust gas post treatment.
19. A method according to claim 16, wherein for determination of
the hydrocarbon concentration, the sensor is disposed downstream of
the arrangement for the exhaust gas post treatment.
Description
[0001] The instant application should be granted the priority date
of Oct. 18, 2005 the filing date of the corresponding German patent
application 10 2005 049 655.5.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a method of reducing
undesired NO.sub.2 emissions of internal combustion engines that
operate with excess air and have an exhaust gas section that is
provided with at least one catalyzer or catalytic converter that
operates with NO oxidation activity, whereby the catalytic
converter having NO oxidation activity is adapted to increase the
NO.sub.2 content in the exhaust gas of the internal combustion
engine for exhaust gas treatment processes that follow.
[0003] For a number of exhaust gas post treatment measures in
oxygen-rich exhaust gas of internal combustion engines, nitrogen
dioxide is a key molecule. For example, as described in EP 0341832
A1, nitrogen dioxide is used, for example, to oxidize soot or
carbon in particle filters. It also serves for the acceleration of
the selected catalytic reduction of nitrogen oxides with the aid of
urea, ammonia and hydrocarbons, as discussed in EP 1054722 A1,
JP200000225323 and US 2002 006 4956. For the NO.sub.x, retention
catalytic converter technology, it is necessary to be able to store
NO.sub.x, in lean phases as nitrate; such methods are described in
DE 196 36 041 A1 and JP 19990220418.
[0004] In this connection, the NO.sub.2 necessary for these
technologies is generated on platinum-containing catalytic
converters from the nitrogen monoxide emitted by the engine
according to the following equation:
2NO+O.sub.2.revreaction.2NO.sub.2 Equation 1
[0005] Depending upon the design of the catalytic converters, the
platinum content, and the application, the catalytic converters
have reaction start temperatures between 180 and 330.degree. C.
Reaction start temperature is here meant to designate that
temperature at which 50% of the nitrogen monoxide is oxidized to
nitrogen dioxide. However, the NO.sub.2 proportion of the overall
nitrogen oxides again drops as the temperature increases, since at
high temperatures the thermodynamic NO/NO.sub.2 equilibrium is on
the side of NO. For a better understanding, this interrelationship
is illustrated in FIG. 1.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a graph in which the NO.sub.2 proportion is
plotted against temperature.
[0007] As the velocity increases, i.e. as the retention time over
the catalytic converter decreases, a decline of the NO.sub.2
concentrations can also be observed.
[0008] Since the statutorily prescribed reduction cycles of
vehicles and engines generally provide low temperature regions in
which the threshold values are to be maintained, the catalytic
converters are designed such that they can already display high
NO.sub.2 contents at low temperatures. Otherwise, one could hardly
operate one of the previously addressed technologies for exhaust
gas post treatment at these temperatures. Thus, for example, at
200.degree. C. it is possible only with the aid of nitrogen dioxide
to produce acceptable conversions during the reduction of nitrogen
oxides with the aid of ammonia according to the equation:
NO+NO.sub.2+2NH.sub.3.fwdarw.2N.sub.2+3H.sub.2O Equation 2
[0009] Similarly, the oxidation of carbon-containing particles at
350.degree. C. at acceptable material quantity change velocities is
possible only with the aid of NO.sub.2 according to the equation:
NO.sub.2+C.fwdarw.NO+CO Equation 3
[0010] The high NO.sub.2 concentrations at low temperatures means,
however, that at higher temperatures generally more NO.sub.2 is
produced than is required. This leads to the main problem of the
NO.sub.2 based technologies, namely that unused NO.sub.2 can be
found in the emissions. NO.sub.2 is a toxic molecule that can lead
to chemical attack of the breathing passages. In addition, it
reacts in the atmosphere with oxygen to form ozone, and hence
increases the ozone concentration close to the ground. This is
particularly problematic in cities and urban areas since here the
ozone concentrations can increase significantly and thus also
contribute to damage to breathing passages and circulatory systems.
A further problem is that the emission thresholds are to be
maintained not only in the new state of the internal combustion
engine or vehicle, but also after a certain running time. Since the
effectiveness of catalytic converters customarily decreases over
time due to chemical deactivation, thermal loads, etc., the
catalytic converters are designed such that they still maintain the
threshold values even after a prescribed running time. However,
this means that they have to be over designed, which in the case of
catalytic converters that operate with NO.sub.2 oxidation activity,
in the new state they generate significantly more NO.sub.2 than
would be required. There is thus a conflict in goals between good
performance of the post treatment system at low temperatures and
over a long running time, and the undesired NO.sub.2 emissions at
high temperatures and a new catalytic converter.
[0011] It is therefore an object of the present invention to
provide a method that reliably prevents the NO.sub.2 emissions
without having a negative impact upon the effectiveness and
efficiency of the exhaust gas post treatment system that is
respectively used.
SUMMARY OF THE INVENTION
[0012] The inventive solution, for reducing undesired NO.sub.2
emissions with the arrangements of the aforementioned type,
provides a method wherein during operation of the internal
combustion engine, and adapted to the perspective operating level
of the internal combustion engine and the state of the catalytic
converter that operates with NO oxidation activity, the content is
varied of materials that compete with the NO oxidation in such a
way that downstream of the catalytic converter only that
theoretical NO.sub.2 content is present in the exhaust gas that is
required for the subsequent exhaust gas post treatment. As a
result, greater than required NO.sub.2 contents advantageously do
not even result.
[0013] The catalytic converter that operates with NO oxidation
activity that is used in this connection advantageously contains
platinum and/or platinum oxide as an active component.
[0014] An expedient possibility for introducing into the system the
materials that compete with the NO oxidation is realized via the
internal combustion engine, as a result of which a homogeneous
distribution is achieved in the exhaust gas without any additional
expenditure.
[0015] A further possibility is to effect the variation of the
content of the material that competes with the NO oxidation by
adding such material into the exhaust gas of the internal
combustion engine downstream of the engine and upstream of the
catalytic converter that operates with NO oxidation activity. The
advantage of proceeding in this manner is that the engine
procedures are not impacted.
[0016] The inventively added materials that compete with the NO
oxidation can be hydrocarbons. In this connection, it is
particularly advantageous to use the fuel that is used to operate
the internal combustion engine and is comprised of hydrocarbons.
This can be accomplished in that the hydrocarbon concentration in
the exhaust gas of the internal combustion engine is varied by
varying engine parameters, such as start of injection, and/or
injection pressure and/or AGR rate, and/or position of a butterfly
valve on an intake side, and/or reduced injections.
[0017] For the technical transformation of the inventive method, it
is advantageous to provide an electronic control unit that with the
aid of sensors connected thereto, and/or with the aid of
determination models stored in the control unit in the form of
computational steps and/or with the aid of characteristics stored
therein, determines the required theoretical NO.sub.2 content,
which is a function of the respective operating level of the
internal combustion engine. In conformity with the determined
theoretical NO.sub.2 contents, the electronic control unit controls
the adjustment element or adjustment elements that vary the content
of the material that competes with the NO oxidation in the exhaust
gas upstream of the catalytic converter that operates with NO
oxidation activity. In this connection, the control is effected in
such a way that the required theoretical NO.sub.2 content is
adjusted in the exhaust gas downstream of the catalytic converter
that operates with NO oxidation activity. Such electronic control
units, which are in a position to work out complex control
programs, are readily used for the control of internal combustion
engines and can be used to carry out the inventive method.
[0018] For the determination of the theoretical NO.sub.2 contents,
and for the control of the adjustment element or elements, a
plurality of parameters can be used that are already included by
the electronic control unit for controlling the internal combustion
engine, or can be included without great expense. Furthermore,
reference can be made to determination models that are already
implemented in the control unit in the form of programs or which
can be easily implemented therein. The aforementioned parameters
and determination models, ofwhich at least one is used for
determining the theoretical NO.sub.2 content and for controlling
the adjustment element, can include, for example, the total
quantity of exhaust gas, hydrocarbon concentration in the exhaust
gas upstream of the catyalytic converter having NO oxidation
activity, the raw emission of NO and/or NO.sub.x, the raw emission
of the exhaust gas substituents that are to be reduced, the maximum
permissible residual emission of the exhaust gas substituents that
are to be reduced downstream of the exhaust gas post treatment, the
maximum permissible residual emission of NO.sub.2 downstream of the
exhaust gas post treatment, the maximum permissible residual
concentration of the added materials downstream of the catalytic
converter having NO oxidation activity, the maximum permissible
residual emission of the added materials downstream of the post
treatment system, the catalytic converter temperatures, the exhaust
gas temperatures, the catalytic converter model for determining the
NO.sub.2 conversions in the catalytic converter having NO oxidation
activity, the catalytic converter model for determining the
conversion rates of the exhaust gas substituents that are to be
reduced in the exhaust gas post treatment, the speed of the engine,
the intake or supercharge pressure, the quantity of fuel, the
catalytic converter aging over the running time, the actual
NO.sub.2 concentration and/or the actual NO.sub.2 content
downstream of the catalytic converter having NO oxidation activity,
the NO.sub.2 residual concentration and/or the NO.sub.2 residual
content of the exhaust gas downstream of the exhaust gas post
treatment system.
[0019] The actual NO.sub.2 concentration and/or the actual NO.sub.2
content and/or the residual NO.sub.2 concentration and/or the
residual NO.sub.2 content that are advantageously usable for a
direct regulation of the theoretical NO.sub.2 content can be
determined by means of one or more sensors. In this connection, the
determination of the actual NO.sub.2 concentration and/or the
NO.sub.2 actual content in the exhaust gas stream is effected
between the catalytic converter having the NO oxidation activity
and the following arrangement for exhaust gas post treatment, while
the residual NO.sub.2 concentration and/or the residual NO.sub.2
content in the exhaust gas stream is determined downstream of the
arrangement for the exhaust gas post treatment.
[0020] With the actual NO.sub.2 concentration and/or the actual
NO.sub.2 content as an actual value, or the residual NO.sub.2
concentration and/or the residual NO.sub.2 content as an actual
value, a closed control loop can be realized in a straightforward
and hence advantageous manner that, by continuous actual
value/theoretical value comparison, and continuous setting of the
adjustment element or elements, which vary the quantity of the
added material, adjust the theoretical NO.sub.2 content.
[0021] A further advantageous possibility for realizing a direct
regulation of the theoretical NO.sub.2 contents is to use the
hydrocarbon concentration determined by one or more sensors in the
exhaust gas as an actual value in a closed control loop, and by
means of the control loop, by continuous actual value/theoretical
value comparison and continuous setting of the adjustment element
or elements, to convey the hydrocarbon concentration determined by
the sensor to the theoretical value thereof, and hence to adjust
the correct theoretical NO.sub.2 value. In this connection, the
hydrocarbon concentration can be detected not only between the
catalytic converter having NO oxidation activity in the arrangement
for the exhaust gas post treatment, but also downstream of the
arrangement for the exhaust gas post treatment. It is to be
understood that different theoretical values are prescribed in the
control loop as a function of the site of determination.
[0022] As described above, it is particularly advantageous, for
vehicles having the aforementioned type of internal combustion
engines, to use the hydrocarbons contained in the fuel for the
inventive method. In this connection, reference is made to the
known effect that non-combusted hydrocarbons in the exhaust gas,
significantly reduce the NO.sub.2 yields via catalytic converters
that operate with NO oxidation activity (chemical engineering
technology (72) 2000 pages 441-449, W. Weisweiler: "Removal of
Nitrogen Oxides from Automobile Exhaust Gases that contain
Oxygen"). Up to now, this effect has been viewed as being
undesirable, because as a result larger catalytic converters or
higher precious metal contents were necessary. The inventive method
intentionally utilizes this effect in order to control or regulate
the NO.sub.2 yields in such a way that always only that quantity of
NO.sub.2 results that is actually required for the subsequent
exhaust gas post treatment system. The NO.sub.2 emission can thus
be held to a minimum in all operating states of the internal
combustion engine, taking into consideration the state of the
catalytic converter that operates with NO oxidation activity.
[0023] As already mentioned, it is expedient in vehicles to recover
the hydrocarbons needed for lowering the NO.sub.2 contents from the
carry along fuel that contains hydrocarbons. This can, for example,
be produced by an adjustment of the fuel injection via an
electronic control unit (ECU). Thus, it is possible, by an
adjustment of the time point of injection and/or the injection
pressure to influence the emissions of non-combusted hydrocarbons.
A further possibility is to reduce the air/fuel ratio, for example
by throttling the intake air, which leads to an increase of the
hydrocarbon emissions. If an external exhaust gas return is
provided, the emission of hydrocarbons can similarly be varied by
varying the rate of return of the exhaust gas. It is also possible
to use reduced injections; in this connection, a second injection
is undertaken relatively late following the actual main injection.
Since due to the expansion of the combustion chamber the latter is
already greatly cooled off, no complete combustion of the fuel any
longer takes place, resulting in considerable emissions of
hydrocarbons.
[0024] The known methods that achieve the necessary content of
non-combusted hydrocarbon in the exhaust gas upstream of the
catalytic converter that operates with NO oxidation activity by
influencing the combustion process in the cylinder all have the
drawback that this can lead to fuel striking the cylinder walls.
This leads to dilution of oil and/or slaking of the cylinder liner.
It can therefore be very expedient not to produce the hydrocarbons
via the internal combustion engine, but rather to supply the
hydrocarbons by means of a separate metering device upstream of the
catalytic converter that operates with NO oxidation activity, it
after discharge from the cylinder chamber.
[0025] At this point it should be noted that of course technologies
for exhaust gas purification are known there based upon the supply
of hydrocarbons. For example, with NO.sub.x storage technology,
hydrocarbons and carbon monoxide are needed in the rich phases for
the regeneration of the NO.sub.x retention. The inventive method
differs from this technology on the one hand in that the catalytic
converter that operates with NO oxidation activity in contrast to
an NO.sub.x retention catalytic converter, operates with excess air
even where hydrocarbons are added, and on the other hand the
content of hydrocarbons that are not combusted are not relied upon
for the minimization of the NO.sub.2 emission.
[0026] A further exhaust gas purification technology that is used
with high hydrocarbon emissions, is the so-called HC-SCR process.
In this connection, nitrogen oxides are catalytically reduced with
the aid of hydrocarbon. The inventive method also fundamentally
differs from this process. On the one hand, with the HC-SCR
reaction on platinum-containing catalytic converters the NO.sub.x
conversion maximum is at low temperatures (<250.degree. C.) (MTZ
(57) 1996, pages 506-514, "NO.sub.x Reduction for Diesel Engines,
Part 1: Model Gas Test with Nitrogen-Free Reduction Means" T. Wahl,
U. Jacob, W. Weisweiler), so that the method can be expediently
utilized only at temperatures between 200 and 300.degree. C. In
contrast, the inventive method is typically used to reduce the
NO.sub.2 contents at higher temperatures of 280-400.degree. C. A
further difference is in the concentration of the hydrocarbons,
whereas for the HC-SCR method great excesses of hydrocarbons in
relation to the nitrogen oxides that are to be reduced are
necessary (typically 5-15 times the quantity), with the inventive
method the hydrocarbon concentrations are less than those for
NO.sub.x. In addition, for the HC-SCR method generally
short-chained hydrocarbons are used that are either separately
carried along or must be recovered from the fuel by cracking
(Chemical Engineering Technology (70) 1999 (10) pages 749-753
"Catalytic Cracking of m-dodecane and Diesel Fuel to Improve the
Selective Catalytic Reduction of NO.sub.x, in Automotive Exhaust
Containing Excess Oxygen" S. Kurze, W. Weisweiler).
[0027] Finally, in connection with particle filters, for the active
regeneration, to supply hydrocarbons in order to temporarily
greatly increase the exhaust gas temperature and thereby to realize
the oxidation of the deposited soot particles. Also with this
technology, the content of non-combusted hydrocarbons is not relied
upon for the minimization of the NO.sub.2 emission.
[0028] To add the correct quantity of hydrocarbons for the
adjustment of the theoretical NO.sub.2 contents, a determination or
calculation of the actual and theoretical NO.sub.2 contents are
needed for the catalytic converter that operates with NO oxidation
activity and/or for the complete post treatment system. In this
connection, the theoretical NO.sub.2 contents are to be selected
such that the desired conversion of the undesired exhaust gas
components, such as NO.sub.x, or soot, can be produced downstream
of the overall system with minimal NO.sub.2 emissions. For this
purpose, appropriate models are first produced at test stands and
are transferred into an electronic control unit (ECU). These models
then determine the optimum NO.sub.2 contents during the time that
the internal combustion engine is running. In this connection,
incorporated into the theoretical NO.sub.2 model is at least one of
the following parameters or determination models:
[0029] the total quantity of gas,
[0030] hydrocarbon concentration in the exhaust gas upstream of the
catalytic converter that operates with NO oxidation activity,
[0031] the raw emission of NO and/or NO.sub.x,
[0032] the raw emission of the exhaust gas substituents that are to
be reduced,
[0033] the maximum permissible residual emission of the exhaust gas
substituents that are to be reduced downstream of the exhaust gas
post treatment,
[0034] the maximum permissible residual emission of NO.sub.2
downstream of the exhaust gas post treatment,
[0035] the maximum permissible residual concentration of the
supplied materials downstream of the catalytic converter that
operates with NO oxidation activity,
[0036] the maximum permissible residual emission of the supplied
materials downstream of the post treatment system,
[0037] the catalytic converter temperatures,
[0038] the exhaust gas temperatures,
[0039] the catalytic converter model for the determination of the
NO.sub.2 conversions in the catalytic converter that operates with
NO oxidation activity,
[0040] the catalytic converter model for the determination of the
conversion rates of the exhaust gas contents that are to be reduced
in the exhaust gas post treatment (described in EP 0498598 A1, DE
4315278 A1, and EP 98114698 A1),
[0041] the speed of the engine,
[0042] the intake or supercharge pressure,
[0043] the quantity of fuel,
[0044] the catalytic converter aging over the running time,
[0045] the actual NO.sub.2 concentration and/or the actual NO.sub.2
content downstream of the catalytic converter that operates with NO
oxidation activity,
[0046] the residual NO.sub.2 concentration and/or the residual
NO.sub.2 content of the exhaust gas downstream of the exhaust gas
post treatment system.
[0047] Some of these parameters can be determined directly with the
aid of sensors, such as, for example, the quantity of exhaust gas
with the aid of a flow measuring device for the NO.sub.x raw
emissions of the aid of the NO.sub.x sensor. However, an indirect
determination via suitable models and easily accessible measurement
data is also possible, as is described in DE 4315278 A1. An example
for this would be the determination of the fuel mass from the speed
of the internal combustion engine, the number of cylinders and the
fuel injection quantity per stroke. However, a determination with
the aid of characteristics is also conceivable:
[0048] No.sub.x raw emissions from engine speed and engine
load,
[0049] NO raw emissions from engine speed and engine load,
[0050] NO.sub.2 conversion from exhaust gas quantity and catalytic
converter temperature, possibly additionally NO.sub.x raw
emission,
[0051] theoretical quantity of the exhaust gas components that are
to be reduced from engine speed and engine load, possibly exhaust
gas quantity.
[0052] With the aid of the thereby determined theoretical NO.sub.2
quantity, the quantity of hydrocarbons that is to be supplied can
be determined, and by means of the ECU, by varying engine
parameters such as beginning of injection, AGR rate, injection
pressure or butterfly valve position, can be adjusted or
hydrocarbons can be metered in upstream of the catalytic converter
that operates with NO oxidation activity, as a result of which the
NO.sub.2 contents can be varied.
[0053] If a suitable NO.sub.2 sensor mechanism, such as described,
for example, in EP 1384069 A1, JP 19980118026, JP 19970296435, and
US 2002/0064956, is available, then instead of a controlled
operation a closed control loop can be provided. In this
connection, the actual NO.sub.2 contents continuously readjusts the
theoretical NO.sub.2 contents with the aid of the variable
hydrocarbon concentrations. The NO.sub.2 sensor mechanism used for
this purpose can not only be disposed directly downstream of the
catalytic converter that operates with NO oxidation activity and
yet upstream of components for the exhaust gas post treatment, such
as SCR catalytic converter or particle filter, but also downstream
of the entire post treatment devices, yet still upstream of the
discharge into the atmosphere. Instead of NO.sub.2 sensors, it is
also possible to build in a sensor mechanism for the determination
of the hydrocarbon concentration, as described in DE 19991012102
A1.
[0054] It is to be understood that the previous aspects represent
examples only; one of skill in the art can embody the inventive
method in many ways.
[0055] The specification incorporates by reference the disclosure
of German priority document 10 2005 049 655.5 filed Oct. 18,
2005.
[0056] The present invention is, of course, in no way restricted to
the specific disclosure of the specification and drawings, but also
encompasses any modifications within the scope of the appended
claims.
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