Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2000-06-30
2001-08-21
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S299000, C060S301000
Reexamination Certificate
active
06276132
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to improvements in an exhaust gas purifying system for purifying exhaust gas or burnt gas discharged from a combustion device such as an internal combustion engine, a burner, a furnace or the like, and particularly to the improvements in the exhaust gas purifying system using a catalyst for reducing nitrogen oxides (NOx) in exhaust gas discharged under a lean-burn operation in which an air-fuel mixture leaner than a stoichiometric level is supplied the combustion device.
It is well known that a three-way catalyst was used to oxidize carbon monoxide (CO) and hydrocarbons (HC) and to reduce nitrogen oxides (NOx) contained in exhaust gas discharged from an internal combustion engine of an automotive vehicle or the like. The three-way catalyst can effectively function in a stoichiometric atmosphere (exhaust gas having a stoichiometric air-fuel ratio). However, such three-way catalyst cannot function to reduce nitrogen oxides in a lean atmosphere (exhaust gas having a leaner air-fuel ratio than the stoichiometric level). In this regard, a technique for reducing nitrogen oxides in the lean atmosphere has been made in Japanese Patent No. 2600492, which a NOx trap agent can trap NOx in the lean atmosphere and can release NOx by enriching air-fuel ratio of exhaust gas flowing to the NOx trap agent so as to reduce the released NOx.
SUMMARY OF THE INVENTION
However, in such a technique disclosed in Japanese Patent No. 2600492, it is required to periodically lower the oxygen concentration in exhaust gas so as to enrich air-fuel ratio of exhaust gas flowing to the oxygen absorbing agent, even under the lean-burn operation. This makes insufficient a fuel economy effect due to the lean-burn operation. Additionally, the above technique requires to supply HC and CO as a reducing agent to accomplish reduction of NOx in the lean atmosphere in order to cause NOx to release from the NOx trap agent and to reduce NOx. Accordingly, HC and CO which has not been consumed in the NOx reduction reaction is required to be oxidized under oxidation reaction or oxidized by using a three-way catalyst disposed downstream of the NOx trap catalyst. Here, such a three-way catalyst for oxidizing HC and CO is disposed downstream of the NOx trap catalyst and considerably far from the engine, and therefore the temperature of exhaust gas in contact with the three-way catalyst is unavoidably lowered, thereby making it impossible to exhibit a sufficient oxidizing performance for HC and CO. Particularly immediately after engine starting, sufficient oxidation of HC and CO is difficult to be made.
It is an object of the present invention to provide an improved exhaust gas purifying system which can effectively overcome drawbacks encountered in conventional exhaust gas purifying techniques and systems.
Another object of the present invention is to provide an improved exhaust gas purifying system which can effectively oxidize HC and CO and reduce NOx even in a lean (exhaust gas) atmosphere in which air-fuel ratio is leaner than a stoichiometric level.
A further object of the present invention is to provide an improved exhaust gas purifying system which can effectively oxidize HC and CO and reduce NOx, exhibiting a sufficient fuel economy improvement effect due to a lean-burn operation of an internal combustion engine.
A still further object of the present invention is to provide an improved exhaust gas purifying system which can effectively oxidize HC and CO emitted from an internal combustion engine even immediately after engine starting.
An exhaust gas purifying system according to the present invention comprises an exhaust gas composition regulating device for producing a low HC concentration reducing agent in a lean exhaust gas atmosphere where air-fuel ratio is leaner than a stoichiometric value. The exhaust gas composition regulating device is disposed in an exhaust gas passageway of a combustion device The low HC concentration reducing agent is low in concentration of hydrocarbons to have an exhaust gas composition having a volume ratio of NOx/HC not less than 50 in the exhaust gas passageway immediately downstream of the exhaust gas composition regulating device. Additionally, a NOx treating catalyst is disposed in the exhaust gas passageway and located downstream of the exhaust gas composition regulating device. The NOx treating catalyst is arranged to reduce NOx in the presence of the low HC concentration reducing agent supplied from the exhaust gas composition regulating device. The exhaust gas composition of the low HC concentration reducing agent is obtained in the exhaust gas passageway immediately upstream of the NOx reducing catalyst.
REFERENCES:
patent: 4109461 (1978-08-01), Fujitani et al.
patent: 5272871 (1993-12-01), Oshima et al.
patent: 5357749 (1994-10-01), Oshuga et al.
patent: 5412946 (1995-05-01), Oshima et al.
patent: 5939037 (1999-08-01), Hepburn et al.
patent: 6122909 (2000-09-01), Murphy et al.
patent: 6138454 (2000-10-01), Fournier et al.
patent: 0510498 (1992-10-01), None
patent: 541 271 (1993-05-01), None
patent: 764 459 (1997-03-01), None
patent: 824 955 (1998-02-01), None
patent: 935 055 (1999-08-01), None
patent: 2600492 (1997-01-01), None
Toyoda et al., “The Quantitative Analysis of Multi-reactions on SCR Process,” Science and Technology in Catalysis, 1998, p. 363.
Ogura et al., “Selective Catalytic Reduction of Nitric Oxide with Methane on Pd/Co/H-ZSM-5 Catalysts,” Third Tokyo Conference on Advanced Catalytic Science and Technology, TOCAT3, Program and Abstracts, 1998, p. 49.
Matsumoto et al., “NOx storage-reduction catalyst (NSR) catalyst) for automotive lean burn engines,” International Symposium on Surface Nano-control of Environmental Catalysts and Related Materials (6thIketani Conference), Tokyo, 1996, pp. 74-75.
Kanesaka Hiroyuki
Onodera Hitoshi
Suga Katsuo
Denion Thomas
Foley & Lardner
Nissan Motor Co,. Ltd.
Tran Diem
LandOfFree
Exhaust gas purifying system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exhaust gas purifying system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exhaust gas purifying system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2496360