Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-11-16
2003-02-18
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S295000, C060S297000
Reexamination Certificate
active
06519930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a configuration for monitoring a regeneratable NO
x
-storage device in an exhaust gas line through which an NO
x
-containing gas flows. The invention can be used in particular in relation to the monitoring of the exhaust gas of an internal combustion engine, especially Diesel and lean-burn engines.
Increasing environmental awareness and an ever increasingly strict exhaust gas legislation which that entails make it necessary for exhaust gas components that are classified as being harmful to be very substantially reduced. The three-way catalytic converter which is conventionally employed nowadays in motor vehicles is capable of converting carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO
x
). Monitoring and control of the catalytic converter is effected, for example, through the use of an oxygen probe. The probe detects a residual oxygen content in the exhaust gas, and the air-fuel ratio of the mixture to be fed to the engine is adjusted on the basis thereof. Suitable regulation of the residual oxygen content ensures that the catalytic converter adequately converts the exhaust gases. It is furthermore also known to ascertain the temperature profile at the catalytic converter and to use it as a warning or control parameter. A further development of that method makes it possible to ascertain the amount of heat which is liberated in the catalytic reaction and to draw conclusions about the exhaust gas characteristics of the engine by way of an entropy consideration, through the use of a lambda probe which is connected downstream of the catalytic converter. The three various possible ways of monitoring a three-way catalytic converter just described above are described in European Patent 0 298 240 B1.
An internal combustion engine in particular produces an increased level of pollutant emissions during a cold start phase. In order to reduce those pollutant emissions, heated catalytic converters are fitted in an exhaust gas line of the internal combustion engine. The mode of operation of a catalytic converter of that kind is to be found, for example, in International Publication No. WO 93/17228 or European Patent 0 628 134 B1 which is equivalent thereto. The use of adsorbers for the storage of unburnt hydrocarbons which are produced during the start phase, and the liberation thereof when the catalytic converter is in an operationally hot condition, are also part of the state of the art. Both are described, for example, in European Patent Application 0 485 179. It is precisely for the catalytic conversion of nitrogen oxides that zeolites and other materials which can also be used as a hydrocarbon storage device have proven to be suitable. Suitable catalysts are disclosed, for example, in European Patent Applications 0 459 396 and 0 286 967.
Therefore, as described above, the proper operability of a catalytic converter is monitored by checking its catalytic action during operation thereof. Various methods which are used for that purpose are described in International Publication No. WO 92/03643 or European Patent 0 545 976 B1 which is equivalent thereto, International Publication Nos. WO 94/21902 and WO 91/14855 or European Patent 0 521 052 B1 which is equivalent thereto, International Publication No. WO 92/03642 or European Patent EP 0 545 974 B1 which is equivalent thereto, and German Published, Non-Prosecuted Patent Application DE 26 43 739 A1. The latter discloses, for example, how the reaction which occurs at the catalytic converter is measured by way of temperature comparison measurement through the use of two temperature sensors. The temperature difference which is ascertained in that way gives an indication as to whether or not the catalytic converter is still operational. That mode of temperature monitoring can be employed not only in relation to a main catalytic converter but also in relation to a pre-catalytic converter.
For example, in the case of honeycomb bodies which are assembled from partially structured sheet layers, a temperature measurement sensor for monitoring purposes can be mounted between them. That is described in European Patent 0 603 221 B1.
The mode of operation of catalytic converters depends on the mode of operation of the internal combustion engine. In the case of stationary internal combustion engines, in Germany the TA-air is the regulation to be observed. Since the nitrogen oxide limitation depends on the fuel calorific efficiency of the internal combustion unit and on the kind of engine, the legislature introduced a so-called index-linking clause for compression ignition engines, which states that in accordance with the state of the art, engine-related and other measures are to be fully implemented for the reduction of emission levels. The background of the index-linking clause was the degree of development of nitrogen-removal installations, which was inadequate in 1985. Urea is used for nitrogen removal for stationarily operated internal combustion units.
In regard to internal combustion engines for motor vehicles, the planned use of urea fell through inter alia due to the requirement for a tank which had to be carried around for that purpose and the weight thereof. Based on the three nitrogen oxides which can be distinguished in terms of the formation thereof, more specifically fuel nitrogen oxide, prompt nitrogen oxide and thermal nitrogen oxide, other ways were sought for keeping down the formation of nitrogen oxide, in particular that of thermal nitrogen oxide. In relation to commercial vehicles, it is known to implement exhaust gas recycling with re-cooled exhaust gases. It is also known that the levels of NO
x
-emission can be reduced by water injection. However, that option involves the problem of anti-frosting and carrying an operating agent which is water. Another way of reducing the levels of nitrogen oxide emissions is to provide for intermediate storage thereof. That is possible, for example, through the use of a storage device which contains barium or platinum.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a configuration for monitoring an NO
x
storage device, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and configurations of this general type, with which an NO
x
-storage device can be checked at least in terms of its operability and which can be used in an exhaust gas line in a particularly compact manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for monitoring a regeneratable NO
x
-storage device in an exhaust gas line through which an NO
x
-containing gas flows, which comprises measuring a temperature in the exhaust gas line; inferring at least a storage capacity of the NO
x
-storage device from the measured temperature; computing NO
x
stored in the NO
x
-storage device in dependence on the NO
x
-containing gas flow; triggering a regeneration when a predeterminable limit value for the NO
x
is exceeded; and inferring at least one of operability, operating condition and storage capacity of the NO
x
-storage device from the measured temperature during regeneration, by comparison with at least one of a predeterminable temperature value and a predeterminable temperature band width.
The term “exhaust gas line” is used to denote all of those conduits which carry away the exhaust gas originating from an NO
x
-producing source, for example an internal combustion engine operability specifies whether or not the NO
x
-storage device is at all still capable of storing nitrogen oxides. Through the use of the procedure for monitoring operability, by presetting a limit value or a band width with respect to the measured temperature, it is possible to provide a is checking procedure which is directed to operability of the NO
x
-storage device, that complies with the exhaust gas requirements. The operating condition yields information which applies at least in regard to the moment in ti
Brück Rolf
Maus Wolfgang
Denion Thomas
Emitec Gesellschaft fuer Emissions Technologie mbH
Tran Binh
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