Internal combustion engine having lean NOx catalyst

Details Internal combustion engine having lean NOx catalyst Internal combustion engine having lean NOx catalyst

1999-12-16

2002-04-16

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...

C060S278000, C060S280000, C123S551000

Reexamination Certificate

active

06370871

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an internal combustion engine having a lean NOx catalyst and, more particularly, to an internal combustion engine having a lean NOx catalyst which is provided in an exhaust system of the internal combustion engine in which the atmospheric air in the exhaust system becomes especially an oxygen excessive state, for purging nitrogen oxide contained in an exhaust gas in this exhaust system by use of a reducing agent.
2. Description of the Prior Art
For example, an occlusive reduction type lean NOx catalyst may be exemplified as a catalyst used in an internal combustion engine such as a gasoline direct injection lean-burn engine, a diesel engine and the like exhibiting a high thermal efficiency in which the atmospheric air in an exhaust system is in an oxygen excessive state while quantities of hydrocarbon and carbon monoxide are small.
The occlusive reduction type lean NOx catalyst may be classified as an intermittent processing type lean NOx catalyst for temporarily occluding the nitrogen oxide to the catalyst in the lean atmospheric air, and promptly reducing and purging the nitrogen oxide occluded by supplying a proper amount of reducing agent to the catalyst in the reduction atmospheric air afterward.
Note that there is a selective reduction type lean NOx catalyst other than the occlusive reduction type lean NOx catalyst.
The selective reduction type lean NOx catalyst is categorized as a consecutive processing type lean NOx catalyst for consecutively selectively reducing and purging the nitrogen oxide by supplying the reducing agent to the catalyst. Further, the hydrocarbon may be exemplified as the reducing agent as disclosed in, e.g., Japanese Patent Application Laid-Open Publication No. 6-117225. Carbon monoxide in addition to the hydrocarbon is also known as the reducing agent.
When the hydrocarbon is used as the reducing agent, the hydrocarbon is partially oxidated to generate active species. Then, the active species react to the nitrogen oxide and reduce it, thereby generating nitrogen, water and carbon dioxide which are not harmful to the human body.
Then, according to the above-mentioned Publication, an engine fuel injection device normally used in the internal combustion engine, such as an injector, for the supply of fuel at a compression stroke, is also used for supplying the reducing agent by injection at expansion stroke through exhaust stroke. Of these injections, the former injection for driving the engine is termed a main injection, while the latter injection is called a sub-injection.
Further, activation of the lean NOx catalyst is needed for making the lean NOx catalyst function effectively. For activating the lean NOx catalyst, the lean NOx catalyst must be warmed up to above an activation temperature enough to function effectively. Then, according to the conventional technology, the catalyst temperature is raised to the activation temperature or higher by utilizing the heat of an exhaust gas emitted by the internal combustion engine.
The sub-injection is, as described above, conducted at the expansion stroke through exhaust stoke, and is therefore effected at a point of time when the piston moves more downward than a top dead center.
It is preferable in terms of performing the combustion that the fuel is injected when the piston is in the vicinity of the top dead center. Then, for attaining this, the fuel injection device is installed at a fixed injection angle. Therefore, the fuel is hard to vaporize in such a sub-injection that the fuel is injected when the piston is at a point lower than the top dead center of the stroke thereof. It might be therefore presumed that the as-liquefied fuel could be supplied as the reducing agent to the lean NOx catalyst.
It is more preferable for effectively utilizing the fuel as the reducing agent to vaporize the fuel than to liquefy the fuel. It is, however, difficult to well catch a timing for executing the sub-injection so as to vaporize the fuel in the fuel injection device such as the injector of which the original function is to inject the combustion-oriented fuel for driving the engine. Hence, there is desired a technology capable of supplying the as-vaporized reducing agent to the lean NOx catalyst without effecting the sub-injection.
According to the conventional technology, the lean NOx catalyst effectively functions after starting up the engine, at which time the Lean NOx catalyst can reach the activation temperature or higher. The lean NOx catalyst can not be warmed up to above the activation temperature in a stop state before starting up the engine.
Further, even after the start-up of the engine, it takes a considerable length of time till the lean NOx catalyst is activated, and during such period of time the lean NOx catalyst does not effectively function. Besides, in the internal combustion engine such as the direct injection engine and the diesel engine exhibiting the high thermal efficiency, when the internal combustion engine is in an operation state such as, e.g., in a light-load region, an exhaust temperature at that time is low, and hence the heat enough to activate the lean NOx catalyst is not transferred throughout the exhaust system due to the low exhaust temperature. Consequently, it might occur that the lean NOx catalyst is rather cooled by the low-temperature exhaust gas of the internal combustion engine, for example, during a deceleration after the acceleration.
Then, it becomes difficult to perform a recovery from so-called SOx-poisoning and a recovery from SOF(Soluble Organic Fraction)-poisoning of the lean NOx catalyst, and besides it is also difficult to remove particulate matters. Note that poisonings by sulfur without being limited to the SOx-poisoning are generically termed S-poisoning. Further, as known well, the SOF-poisoning is not defined as the poisoning caused by sulfur and does not therefore come under the category of the S-poisoning.
On the other hand, if an external load is applied to the internal combustion engine by executing intake/exhaust throttling operations in order to enrich the atmospheric air in the exhaust system with a rise in the exhaust temperature, this might in turn cause a deteriorated fuel consumption and lead to a production of particulate matters.
Further, though not disclosed in the above-mentioned Publication, the internal combustion engine is provided with a combustion heater of such a type as to effect the air suction from the atmospheric air in order to enhance a car room warming performance and an engine warp-up performance in some cases. The combustion gas emitted from the combustion heater is discharged to an exhaust passageway, and it can be considered that the lean NOx catalyst provided in the exhaust passageway is thereby activated. In that case, however, in a state where the internal combustion engine is driven, an exhaust pressure in the internal combustion engine is higher than an exhaust pressure in the combustion heater. Therefore, the combustion gas from the combustion heater can not be discharged to the exhaust passageway. Hence, it is impossible to effectively utilize the heat of the combustion gas from the combustion heater for warming up the lean NOx catalyst. Further, because of a differential pressure between the exhaust pressure in the internal combustion engine and the exhaust pressure in the combustion heater, it might occur that the engine exhaust gas flows back to the combustion heater via a combustion gas discharge passageway for discharging the combustion gas from the combustion heater to outside. Note that the combustion gas from the combustion heater and the exhaust gas emitted by the internal combustion engine are hereinafter simply called the combustion gas and the exhaust gas, respectively, unless otherwise specified.
SUMMARY OF THE INVENTION
It is a primary object of the present invention, which was devised under such circumstances to obviate the above problems, to provide an internal combustion engine having a lean NOx catalyst,

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