Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
2003-03-07
2004-11-02
Nguyen, Tu M. (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S278000, C060S279000, C123S00100A, C123S003000, C123S568150
Reexamination Certificate
active
06810658
ABSTRACT:
This application claims the priority of German application 102 103 67.4, filed Mar. 8, 2002, the disclosure of which is expressly incorporated by reference herein.
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an exhaust-gas purification installation, for purifying an exhaust gas from an internal combustion engine, having an exhaust-gas catalytic converter which is arranged in an exhaust pipe of the internal combustion engine, and a catalytic fuel reformer adapted to generate a hydrogen-containing reformer gas which can be fed to the exhaust pipe on an entry side of the exhaust-gas catalytic converter. A hydrocarbon-containing fuel, which can be used to operate the internal combustion engine, may be fed to the fuel reformer in order to generate the reformer gas. The invention also relates to an exhaust-gas purification method for purifying exhaust gas from an internal combustion engine, using an exhaust-gas purification system having an exhaust pipe with an exhaust-gas catalytic converter arranged in the pipe and a catalytic fuel reformer, in which a fuel which is used to operate the internal combustion engine is fed to the fuel reformer in order to generate a hydrogen-containing reformer gas.
It is known from laid-open European specification EP 0 537 968 A1 to feed hydrogen-containing gas to exhaust gas from a lean-burn internal combustion engine in order to reduce nitrogen oxides. It is possible to achieve a relatively high reduction in the levels of nitrogen oxides using the supplied hydrogen at relatively low temperatures at special denox catalytic converters even when an excess of oxygen (lean exhaust-gas condition) is present. To generate the hydrogen-containing gas, in European specification EP 0 537 968 A1, it is proposed to use a catalytic reformer in which a fuel which is available on board the corresponding motor vehicle is reacted with the exhaust gas from the internal combustion engine, if appropriate with the addition of water, to form a hydrogen-containing reformer gas which is fed to the denox catalytic converter. Heating the reformer to its operating temperature and maintaining this operating temperature are achieved by the quantitative control of the flow of hot exhaust gas to the reformer. However, hot exhaust gas is not available immediately after the internal combustion engine has been started up, and consequently it takes a certain time to heat up the installation which has been described to its operating temperature, and the function of reducing the levels of nitrogen oxides is likewise only available after a certain time.
Furthermore, it is known from European Patent EP 0 621 400 B1 to feed reducing agent to the exhaust gas from an air-compressing internal combustion engine, i.e. an internal combustion engine which is usually operated with excess air, by late injection of fuel. Depending on the injection time, this fuel is used to heat the exhaust-gas after-treatment device by means of catalytic oxidation at an exhaust-gas catalytic converter or as a reaction partner for reducing the levels of nitrogen oxides at a denox catalytic converter. On account of the method by which it is provided, the reducing agent which is made available consists predominantly of hydrocarbons. However, these hydrocarbons are relatively slow to react compared to hydrogen and, consequently, neither the heating of the exhaust-gas after-treatment device nor the catalytic reduction in the levels of nitrogen oxides at low exhaust-gas temperatures is possible.
It is an object of the invention, using a fuel reformer, to provide an exhaust-gas purification installation and an exhaust-gas purification method with an improved exhaust-gas purification function in which improved operation of the fuel reformer is also possible. This object is achieved by way of an exhaust-gas purification installation having an exhaust-gas heater provided so as to heat an exhaust-gas part-stream which is fed to the fuel reformer. This object is also achieved by way of an exhaust-gas purification method including removing an exhaust-gas part-stream from the exhaust pipe, heating the exhaust-gas part-stream, and feeding the heated exhaust-gas part-stream to the fuel reformer.
An exhaust-gas purification installation according to the invention is distinguished by the fact that it has an exhaust-gas heater for heating an exhaust-gas part-stream fed to the fuel reformer. The reformer and the exhaust-gas heater are arranged as separate components in an additional branch outside the internal combustion engine exhaust pipe but on board a motor vehicle associated with the internal combustion engine. The reformer and the exhaust-gas heater can therefore be operated as far as possible independently of the operating state of the internal combustion engine. To generate a hydrogen-containing reformer gas, an exhaust-gas part-stream which is removed from the exhaust pipe of the internal combustion engine at any desired point flows through the reformer. The exhaust-gas part-stream is, at least from time to time and preferably when the reformer is starting up until it reaches its normal operating state, heated by the exhaust-gas heater before being fed to the reformer. As a result, the reformer catalytic converter is heated at the same time. The fuel which is also required to operate the reformer is taken from the normal fuel supply to the internal combustion engine and injected into the heated exhaust gas on the entry side of the reformer where it is, at least for the most part, vaporized. The heating of an exhaust-gas part-stream naturally takes place more quickly and effectively than the heating of the entire exhaust-gas stream, and consequently the reformer is soon ready for operation and able to supply hydrogen-containing reformer gas. At the same time, the outlay on energy is kept at a low level. Compared to the injection of the fuel into the main-gas stream, moreover, the arrangement according to the invention achieves significantly improved homogenization of the mixture fed to the reformer and therefore effective fuel reforming with a high yield of hydrogen.
In one configuration of the invention, the exhaust-gas heater is of electrically heatable design. The electrical energy required for the heating operation may, for example, be taken from the on-board power supply of the motor vehicle in question. The use of electric heating for the exhaust-gas heater allows the exhaust-gas part-stream to be heated very quickly and, moreover, a high degree of flexibility with regard to the shape of the exhaust-gas heater, since electrical heater elements for different outputs and operating voltages are commercially available at low cost in a very wide variety of forms.
In a further configuration of the invention, the exhaust-gas heater is of cylindrical configuration and, in its interior, has a coiled passage, which runs substantially in the axial direction, for guiding the exhaust-gas part-stream. This embodiment of the exhaust-gas heater creates a large heat-transfer surface area and achieves a correspondingly good heat transfer from the electrical heating to the exhaust-gas part-stream. For this purpose, the electrical heating may be provided in such a way that the inner or outer wall, as seen in the radial direction, or both walls of the coiled passage can be heated by one electrical heater element.
In a further configuration of the invention, a high-temperature heat exchanger, by means of which heat is transferred from the reformer gas emerging from the reformer to the exhaust-gas part-stream fed to the reformer, is also provided as part of the exhaust-gas purification installation. In this case, the high-temperature heat exchanger is connected downstream of the reformer in terms of flow and the reformer gas flows through it. Since the reforming process in the reformer preferably takes place at temperatures of above 500° C., the reformer gas which leaves the reformer has a relatively high heat content, a large proportion of which can therefore be fed to the charge gas. In this way, the energy bal
Kaupert Andreas
Strauhs Joerg
Wiesheu Norbert
Crowell & Moring LLP
DaimlerChrysler Ag
Nguyen Tu M.
LandOfFree
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