Internal combustion engine having lean NOx catalyst

Power plants – Internal combustion engine with treatment or handling of... – Material from exhaust structure fed to engine intake

Reexamination Certificate

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C060S280000, C060S281000, C060S599000, C123S551000

Reexamination Certificate

active

06253545

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 for purifying nitrogen oxide in an exhaust gas by use of a reducer when an exhaust system is especially in an oxygen excessive atmospheric air state, i.e., in a lean state, the lean NOx catalyst is used as a ternary catalyst in a catalyst converter provided in an exhaust system of the internal combustion engine and functioning as an exhaust gas purifying device.
2. Description of the Prior Art
What is known as a catalyst used in the internal combustion engine such as a gasoline direct injection lean-burn engine, a diesel engine and the like, in which the atmospheric air in the exhaust system is in the oxygen excessive state while quantities of hydro carbon and carbon monoxide are small, is a so-called lean NOx catalyst for purifying nitrogen oxide contained in the exhaust gas by using the hydro carbon and the carbon monoxide as reducing agents.
The lean NOx catalyst disclosed in, e.g., Japanese Patent Application Laid-Open Publication No. 6-117225 involves the use of the hydro carbon as the reducing agent. According to the technology disclosed in this Publication, the hydro carbon is partially oxidized to generate active species, and the nitrogen oxide is purified by reducing it by causing reaction between the thus generated active species and the nitrogen oxide.
The hydro carbon as the reducing agent is a main component of a gasoline and a light oil as fuels of the internal combustion engine. Accordingly, as for a supply of the hydro carbon to the lean NOx catalyst, an extra fuel may be supplied into the cylinders separately from other fuels such as the gasoline supplied into the cylinders when in a normal combustion in the internal combustion engine. The extra fuel might cause an incomplete combustion, and hence the exhaust gas is discharged to the exhaust system in a state where the exhaust gas contains a raw gas, i.e., the hydro carbon. Then, according to the above Publication, the extra fuel is supplied by effecting a fuel injection different from the fuel injection normally conducted at an intake-compression stroke. Then, the former normal fuel injection of these injections is called a main injection, and the latter different fuel injection is referred to as an auxiliary injection. The auxiliary injection is executed by changing an injection timing within the same intake-compression stroke other than the injection at the intake-compression stroke based on the main injection, or executed at an exhaust stroke in addition to the main injection. Further, a fuel injection device used for the main injection serves also as a fuel injection device used for the auxiliary injection.
According to this technology, however, since the same fuel injection device performs the main injection and the auxiliary injection as well, a large load must be put on the fuel injection device. Hence, there arises a problem in which a durability of the fuel injection device declines.
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, which is capable of supplying a reducing agent such as hydro carbon even by eliminating an auxiliary injection.
To accomplish the above object, an internal combustion engine having a lean NOx catalyst according to the present invention adopts the following constructions.
According to a first aspect of the present invention, in an internal combustion engine having in an exhaust system a lean NOx catalyst for purifying nitrogen oxide in an exhaust gas in an oxygen excessive state by using a reducing agent, the internal combustion engine having the lean NOx catalyst comprises a CO
2
concentration increasing means for increasing a concentration of carbon dioxide in intake air flowing through an intake system of the internal combustion engine.
Herein, “the internal combustion engine having in the exhaust system the lean NOx catalyst for purifying the nitrogen oxide in the exhaust gas in the oxygen excessive state by using the reducing agent” refers to, e.g., a gasoline direct injection lean-burn engine and a diesel engine. In these engines, a rate of the air is by far larger than a rate of the fuel with respect to a mixing rate of the air and the fuel in cylinders. Hence, in the internal combustion engine according to the present invention, the exhaust gas contains a greater quantity of oxygen than in other internal combustion engine exhibiting a comparatively high air/fuel ratio, whereas the hydro carbon and the carbon monoxide are small in their quantities in the present invention. Further, the lean NOx catalyst is classified into a selective reduction type and an occlusive reduction type. The selective reduction type refers to a consecutive processing method of consecutively performing selective reduction and purification of the nitrogen oxide by feeding the hydro carbon and the carbon monoxide as reduction agents. The occlusive reduction type refers to an intermittent processing method by which the nitrogen oxide is absorbed into the catalyst for the time being in the lean atmosphere, and after the catalyst has become saturated with the nitrogen oxide, appropriate quantities of the hydro carbon and/or carbon monoxide are supplied as the reduction agents, thereby the nitrogen oxide absorbed in the catalyst is reduced and purified at one time.
“The CO
2
concentration increasing means” may be means which is capable of increasing the concentration of the carbon dioxide in a relative comparison of the carbon dioxide to components other than this among the components of the intake air containing the carbon dioxide. Hence, the CO
2
concentration increasing means may be either means for adding the carbon dioxide to the intake system or means capable of increasing the concentration of the carbon dioxide in comparison to other components by decreasing other components in the intake gas.
However, a device, e.g., an exhaust gas recirculation (EGR) device for increasing the concentration of the carbon dioxide in the intake system by utilizing the carbon dioxide contained in a gas, a so-called outgoing gas immediately after flowing out of an exhaust port of the internal combustion engine body, is excluded. In other words, the CO
2
concentration increasing means is directed to means which is capable of adding, to the intake system, CO
2
of which the concentration is higher than the concentration of the carbo dioxide contained in the exhaust gas circulated to the intake system by the EGR device. The reason for such a restriction is that since the EGR device re-utilizes the combustion gas in the internal combustion engine, the concentration of the carbon dioxide contained in the exhaust and recirculation gas recirculated to the intake system by the EGR device becomes variable depending on a combustion state in the internal combustion engine, and hence the concentration of the carbon oxide is controlled with difficulty.
In the internal combustion engine having the lean NOx catalyst according to the present invention, the CO
2
concentration increasing means increases the concentration of the carbon dioxide contained in the intake air, in which case the reactions both from the hydro carbon to the carbon monoxide and from the carbon monoxide to the carbon dioxide are difficult to occur. To say it extremely, when the carbon dioxide is in a saturated state, the oxidation reaction between the hydro carbon and the carbon monoxide which are necessary to produce the carbon dioxide is difficult to progress, and, therefore, it follows that large quantities of the hydro carbon and the carbon monoxide are contained in the exhaust gas of the internal combustion engine in a free state.
Namely, in the internal combustion engine having the lean NOx catalyst of the present invention, there increase rates

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