Power plants – Internal combustion engine with treatment or handling of... – By sorber or mechanical separator
Reexamination Certificate
2003-02-10
2004-11-30
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By sorber or mechanical separator
C060S274000, C060S295000, C060S297000
Reexamination Certificate
active
06823667
ABSTRACT:
This application claims the priority of German application 102 05 380.4, filed Feb. 9, 2002, the disclosure of which is expressly incorporated by reference herein.
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method and a device for removing particles, which have been deposited on a filter arranged in an exhaust system of a diesel internal combustion engine, by combustion.
To reduce the level of harmful exhaust gases from diesel internal combustion engines, and in particular to reduce the levels of soot particles, filters, in particular soot filters, are used in the exhaust system. These filters have the problem that they rapidly become blocked by the large quantities of soot which is produced and thereby become ineffective. For this reason, it is desirable for the soot on such filters to be eliminated by oxidation or combustion.
It is known from European publication EP 341 832 to form NO
2
in the exhaust gas from NO-containing exhaust gas by means of a platinum catalytic converter. This NO
2
makes it possible to burn soot at a temperature of less than 400° C. i.e. at the normal exhaust gas temperature. In this case, the problem exists that the diesel fuel has to have a very low sulphur content. Otherwise, the catalytic converter is poisoned and the soot in the filter can no longer be burnt as intended. However, sulphur-containing fuel is not available everywhere; this is a problem which, in particular, affects lorries used internationally.
It is known from U.S. Pat. No. 5,522,905 to add certain additives to the fuel of a diesel internal combustion engine. This reduces the ignition temperature of the soot in the filter to such an extent that combustion is possible at standard exhaust gas temperatures. These additives contain, inter alia, metal salts of an organic compound. In this context, the problem arises that the additives are expensive.
One object of the present invention is the object of providing a method and also a device which allow soot to be eliminated from a filter of a diesel internal combustion engine in an economically and ecologically appropriate way under a wide variety of conditions. In particular, the method and the device are also to be protected against incorrect intervention.
This object is achieved by passing NO-containing exhaust gas over a catalytic converter upstream of the filter in order to convert the NO in the exhaust gas into NO
2
, and then using NO
2
-containing exhaust gas to burn the particles which have been deposited on the filter when the sulphur content is lower than a predetermined sulphur content, the quantity of NO which has been converted into NO
2
being sufficient to enable the combustion of the particles to be carried out at a temperature of less than 400° C., and adding an additive which contains a metal salt of an organic compound to the fuel in order to reduce the ignition temperature of the particles which have been deposited on the filter to below the normal ignition temperature of the particles when the sulphur content is higher than the predetermined sulphur content. The object is also achieved by a device including an exhaust pipe having a filter and a catalytic converter, which is arranged upstream of the filter, for converting NO in the exhaust gas into NO
2
, additive-adding means for adding additive to the fuel, and sulphur content-measuring means for determining a sulphur content in the fuel. Advantageous and preferred configurations of the invention form the subject-matter of further claims and are explained in more detail below. The content of the claims is made part of the content of the application by express reference.
A method according to the invention has two possible method steps, a) or b). In a first method step a), NO-containing exhaust gas is passed over a catalytic converter, for example an oxidation catalytic converter, upstream of the filter. NO in the exhaust gas is converted into NO
2
, which is then used to burn .the particles which have been deposited on the filter. A quantity of NO
2
which is sufficient to carry out the combustion of the particles at a temperature of less than 400° C., in particular at standard exhaust gas temperature, is formed. For details in this connection, reference is expressly made to European publication EP 341 832, the content of which is hereby incorporated in the present description.
According to another method step b), adding an additive to the fuel is possible. This additive contains a metal salt of an organic compound, with the result that the ignition temperature of the particles which have been deposited on the filter is reduced to below the normal ignition temperature of the particles, in particular to the normal exhaust gas temperature.
Furthermore, according to the invention the sulphur content in the fuel is determined in order to carry out one method step or the other as a function of this measurement. If the sulphur content is lower than a predetermined sulphur content, method step a), i.e. the generation of NO
2
, is carried out. On the other hand, if the sulphur content is higher than a predetermined sulphur content, method step b), i.e. the addition of additive, is carried out. Although in principle NO
2
may be generated as well, because the catalytic converter has generally been deactivated by the high sulphur content, scarcely any NO
2
is actually generated.
This has the advantage that the poisoning of the catalytic converter has no adverse effect on the deposits of soot on the filter, but rather the soot or particles is/are still burnt. If the sulphur content, i.e. the content of the substance which poisons or deactivates the catalytic converter, is measured in order to make this decision, it is possible to obtain a precise indication of the ability of the catalytic converter to function and the possibility of carrying out method step a).
Advantageously, in each case only one of the two method steps is carried out. In principle, method step a), i.e. the generation of NO
2
, is particularly advantageously carried out. Method step b) is only carried out when the predetermined sulphur content has been exceeded.
It is possible and even, with a view to simplify the exhaust-gas management, advantageous for the exhaust-gas stream to be passed over the catalytic converter in accordance with method step a) even when method step b) is being carried out. However, since method step b) is only used if the sulphur content is too high, this sulphur content deactivates the catalytic converter and method step a) ceases to work.
There are various options for determining the sulphur content in the fuel. Firstly, it is possible to measure the exhaust gas back pressure upstream of the filter. If the sulphur content is too high, the catalytic converter is poisoned and its NO
2
formation function is reduced or eliminated. This leads to a rise in the exhaust gas back pressure, since the soot-burning operation effected by NO
2
is disrupted and the filter becomes clogged. For example, the fact that a certain exhaust gas back pressure has been exceeded can be deemed an indication of a predetermined sulphur content having been exceeded. The level of the sulphur content can be at least approximately determined from the extent to which the exhaust gas back pressure has been exceeded.
According to an alternative or additional option, it is possible to determine the sulphur content in the fuel, in particular in the fuel supply to the internal combustion engine. This can be achieved, for example, using a sulphur sensor. On the one hand, this may take place in a tank which holds the fuel. On the other hand, a determination of this type may also be performed in a fuel feed line to the internal combustion engine itself. A measurement of this type advantageously takes place independently of fuel mixing during a plurality of different refueling stops.
It is possible for the sulphur content to be determined in each case at predetermined time intervals. This makes it possible to reduce costs. The sulphur content should be predetermined at least each time th
Braun Tillmann
Ebelsheiser Oliver
Krutzsch Bernd
Marquardt Klaus-Juergen
Weibel Michel
Crowell & Moring LLP
Daimler-Chrysler AG
Denion Thomas
Tran Diem
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