Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-04-09
2001-02-13
Hoang, Tu Ba (Department: 3742)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S285000
Reexamination Certificate
active
06185930
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims the priority of German Application Nos. 198 15 987.0 filed Apr. 9, 1998 and 198 26 831.9 filed Jun. 16, 1998, which are incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a method for reducing nitrogen oxide (NO) and particulates in the exhaust gas of an internal-combustion engine.
TECHNOLOGY REVIEW
One of the most important problems to be solved in the development of engines is the reduction of pollutant emissions in motor vehicle engines. Primarily, this concerns the reduction in nitrogen oxide emissions. Engine-related measures alone are not sufficient to meet the high requirements, for example using lean-mix fuels in direct-injection gasoline engines which, like diesel engines, contain a high proportion of O
2
in the exhaust gas. Additional measures for a secondary treatment of the exhaust gas are required to achieve the necessary reduction in pollutant emissions. Diesel engines also require a reduction in particulate exhaust gas components.
Apart from the carbamide-SCR-method, for which an additional reagent on a carbamide base is added to the exhaust gas to improve the subsequent catalytic exhaust gas treatment, the only option available at present is the use of a NO
x
storage or adsorption catalyst to reduce the nitrogen oxide emissions. With current NO
x
storage catalysts, the NO present in the engine exhaust gas is initially oxidized to higher valency NO
2
by means of a precious metal component in the catalyst. The advantage of NO
2
, as compared to NO, is that it is adsorbed more efficiently and at distinctly lower temperatures by the adsorbing agents in the storage or adsorption catalyst. For example, the adsorption of NO
2
on barium oxide (BaO) or barium carbonate (BaCO
3
) as adsorbing agents occurs at room temperature.
It is, however, a disadvantage of the above-outlined system that an extremely low-sulfur fuel, with less than 10 ppm weight, must be used. This is because the storage or adsorption catalyst will fail if a sulfur-containing fuel is used. As a result of platinum oxidation, SO
3
is formed from the SO
2
in the exhaust gas, so that stable barium sulfate is formed in the adsorption catalyst in place of the barium nitrate and the adsorption of NO
2
is either obstructed or cannot take place at all. Although the alkaline metals or alkaline earth metals used in the adsorption catalyst represent excellent NO
x
adsorbing agents, they also exhibit a high tendency to form stable sulfates. That is the reason why the adsorbing agents are “poisoned” by the sulfur contained in the fuel and their capacity to adsorb is reduced unless this is counteracted by corresponding desulfatizing measures. Desulfatizing, meaning a thermal decomposition of the sulfates, is in principle possible in a reducing atmosphere with simultaneous high temperature. With the presently available NO
x
storage catalysts, the storage of nitrogen oxides contained in oxygen-rich exhaust gases is also possible in principle and with a high degree of effectiveness for a large temperature range. However, there is a problem of fast aging of the catalyst as a result of the above-described sulfur poisoning of the NO
x
adsorption material.
The deposition of particulate exhaust-gas components on filtering material does not present a problem, per se. Most known filtering materials accept high degrees of deposit of such materials. This leads however, to the problem of filter regeneration, which has not yet been solved satisfactorily. Filter regeneration during engine operation can be achieved with the aid of metal containing fuel additives, e.g. cerium, iron, copper or manganese, or by burning off of particulates by ignition with a heating wire. The disadvantages of these solutions are the additional emissions of these additives which, over the long term, not only can result in clogging the filter, but also represent an additional environmental threat as secondary emission. There can also be potential problems associated with the use of special ignition devices for the heating wire.
Particle emission for diesel fuels essentially consists of carbon black, or amorphous carbon. Carbon black can be oxidized, as is known, by means of reactive fuel components such as nitrogen dioxide (NO
2
), elementary oxygen (O*), ozone (O
3
), as well as OH. Attempts have been made to partially oxidize the nitrogen oxide (NO), which is found in large amounts in the engine exhaust gas, to higher valency NO
2
by means of an oxidation catalyst with high platinum content, which is installed in front of the particle filter. This generally advantageous method, which does not require any secondary energy or any control/regulating unit, can be used successfully only if an extremely low-sulfur diesel fuel is used.
This system “fails” when using sulfur-containing fuels, such as are normally used nowadays, since the resulting SO
2
blocks the catalytically active areas of the catalyst, so that SO
3
is generated, but not the NO
2
necessary for the regeneration of the particle filter. This is because the selectivity of platinum catalysts is more than twice as high for SO
2
oxidation than for NO oxidation. Thus, a different method must be found for filter regeneration with the aid of NO
2
when using sulfur-containing fuels.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved method which is used for removing nitrogen from lean exhaust gases by means of a storage catalyst and for regenerating the particle filter and which remains continuously operational even in case of sulfur-containing fuels.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the method of reducing pollutants in an exhaust gas of an internal-combustion engine includes the following steps: producing, at a first location, a reactive gas component NO
2
from at least one part of the NO content of the exhaust gas by reaction with the oxygen, contained in the exhaust gas, under an energy effect; and reactively converting the NO
2
in a pollutant retaining system situated at a second location downstream of the first location as viewed in the flow direction.
The invention may be used with a piston-type internal-combustion engine which runs on hydrocarbon-based fuel.
According to a preferred embodiment of the invention, energy affects the NO in the exhaust gas via a non-thermal plasma, by means of which reactive gas components such as O*, O
3
and OH are formed simultaneously.
REFERENCES:
patent: 4473536 (1984-09-01), Carberg et al.
patent: 4916898 (1990-04-01), Gandhi et al.
patent: 5224346 (1993-07-01), Berriman et al.
patent: 5441401 (1995-08-01), Yamaguro et al.
patent: 6063348 (2000-05-01), Hinke et al.
Hentschel Kirsten
Lepperhoff Gerhard
Lüders Hartmut
Lüers Bernhard
FEV Motorentechnik GmbH
Hoang Tu Ba
Kelemen Gabor J.
Venable
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