Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Patent
1998-12-10
2000-12-19
Denion, Thomas
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
60285, 60295, 60303, 422177, F01N 300
Patent
active
061613789
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This application claims the priority of Japanese patent documents No. 8-146981, filed Jun. 10, 1996; No. 8-153718, filed Jun. 14, 1996; and No. 8-209587, filed Aug. 8, 1996, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to a purification apparatus for an exhaust gas which is discharged or emitted from an internal combustion engine such as an automobile, and particularly to an apparatus which includes a catalyst for purifying an exhaust gas from an internal combustion engine that is operated under a lean air-fuel ratio (a lean burn), and from an automobile which has such a lean burn internal combustion engine.
Exhaust gas discharged from an internal combustion engine such an automobile includes carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NO.sub.x) etc. which pollute the environment, adversely affect the human body, and disturb the growth and the development of plants.
Accordingly, up to now a great deal of effort has gone into reducing the amount of such pollutants by improving a combustion in the internal combustion engine, and developing a method for purifying the discharged or the emitted exhaust gas using a catalyst to obtain a steady result.
Gasoline engine vehicles frequently utilize a three component catalyst in which platinum (Pt) and rhodium (Rh) are main active components. The oxidation of HC and CO and the reduction of NO.sub.x are carried out at the same time to convert the above air pollution materials to harmless materials.
It is characteristic of a three component catalyst, that it operates effectively only for exhaust gases which are generated within a range ("window") in the vicinity of a stoichiometric air-fuel ratio.
In the conventional technique, the air-fuel ratio fluctuates in accordance with an operation condition of the automobile. A fluctuation region is principally controlled to the vicinity of the stoichiometric air-fuel ratio, which is a ratio between A (weight of air) and F (weight of fuel), being about 14.7 in case of the gasoline. Hereinafter, in the present specification, the stoichiometric air-fuel ratio is represented by A/F=14.7, but this value varies in accordance with kinds of the fuels.
However, when the engine is operated under a lean air-fuel ratio in comparison with the stoichiometric air-fuel ratio atmosphere, the fuel consumption can be improved. Therefore, the development of a lean burn combustion technique is promoted; and recently automobiles have been developed in which the engine is combusted under the lean area having the air-fuel ratio of more than 18.
However, when a conventional three component catalyst is adopted for purification of a lean burn exhaust gas, although the oxidation purification with respect to HC and CO is performed effectively, the reduction of NO.sub.x is not.
Accordingly, to promote the application of the lean burn system for large size vehicles and to enlarge the lean burn combustion time (that is, enlarge the operation area of the lean burn system), it is necessary to develop an exhaust gas purification technique which is suitable to the lean burn system. Thus, the development of a technique for purifying HC, CO and particularly NO.sub.x where a large quantity of oxygen (O.sub.2) is included in the exhaust gas, has been promoted vigorously.
Japanese patent laid-open publication No. 61,706/1988 discloses a technique in which HC is supplied upstream of a lean burn exhaust gas. The operation of a catalyst is facilitated by lowering the oxygen (O.sub.2) concentration in the exhaust gas to a concentration area for effective functioning of the catalyst.
Japanese patent laid-open publication No. 97,630/1987, Japanese patent laid-open publication No. 106,826/1987 and Japanese patent laid-open publication No. 117,620/1987, propose a technique in which N included in the exhaust gas (after the conversion of an easily absorbable NO.sub.2 by oxidizing NO) is absorbed and removed by contact with a catalyst having NO.sub.x absorbing ability. When the
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Azuhata Shigeru
Doi Ryouta
Hanaoka Hiroshi
Hiratsuka Toshifumi
Iizuka Hidehiro
Denion Thomas
Hitachi , Ltd.
Tran Binh
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