Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
2001-05-21
2004-02-03
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S295000, C060S297000, C060S303000, C060S311000, C423S213200, C423S243070, C423S243080, C423S244060, C423S244070
Reexamination Certificate
active
06684627
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purifying method of internal combustion engine capable of suppressing degradation of exhaust purification efficiency of NOx-occluding reduction-type exhaust purifying catalysts due to SOx poisoning and thereby achieving higher purification efficiency of exhaust gas.
2. Related Background Art
The exhaust gas from an internal combustion engine is purified by an emission purifying catalyst such as a three way catalyst and then discharged to the atmosphere. The NOx-occluding reduction-type exhaust purifying catalysts have been also used as a kind of such exhaust purifying catalysts. The NOx-occluding reduction-type exhaust purifying catalysts are catalysts that occlude nitrogen oxides [NOx] under an excess condition of oxygen [O
2
] in exhaust gas but release the occluded NOx under a low-content condition of O
2
in exhaust gas to effect reduction thereof (whereupon carbon monoxide [CO] and hydrocarbons [HC] in the exhaust gas are oxidized).
The exhaust purification efficiency can be increased more when such NOx-occluding reduction-type exhaust purifying catalysts are used so as to occlude NOx in exhaust gas during lean operation but release and reduce the occluded NOx during stoichiometric or rich operation. These NOx-occluding reduction-type exhaust purifying catalysts are useful in increasing the exhaust purification efficiency of lean-burn engines, which are designed positively to employ the lean operation as against ordinary engines, and thus they are also contributing to improvement in fuel consumption.
SUMMARY OF THE INVENTION
These NOx-occluding reduction-type exhaust purifying catalysts have the nature of occluding sulfur oxides [SOx] more stably than NOx. The SOx in exhaust gas are produced by oxidation of sulfur component included in fuel or engine oil, during combustion in the internal combustion engine. Although the quantity of sulfur component is very small in fuel or engine oil, the amount of sulfur component occluded becomes gradually increasing as accumulated in the catalyst, because it is stably occluded in the NOx-occluding reduction-type exhaust purifying catalysts. Once the NOx-occluding reduction-type exhaust purifying catalysts occlude a lot of SOx, they will disable the proper occlusion and release-reduction of NOx. This is the so-called “SOx poisoning” in the NOx-occluding reduction-type exhaust purifying catalysts.
In the conventional NOx-occluding reduction-type exhaust purifying catalysts, most of occlusion capacity in mint condition is applied to the occlusion of NOx, whereas after the SOx poisoning only small part of occlusion capacity is applied to the occlusion of NOx. If this SOx poisoning is suppressed, it will become feasible to increase the occlusion capability and release capability of NOx and greatly enhance the exhaust purifying performance of the NOx-occluding reduction-type exhaust purifying catalysts. There are known techniques for suppressing the SOx poisoning of the NOx-occluding reduction catalysts, e.g., one described in Japanese Patent Application Laid-Open No. 2000-27712, but its effect is not satisfactory yet. The inventors conducted research toward further improvement in the exhaust purification performance and accomplished the present invention.
It is, therefore, an object of the present invention to provide an exhaust purifying method of internal combustion engine capable of suppressing the SOx poisoning of NOx-occluding reduction-type exhaust purifying catalysts, thereby further increasing the purification efficiency of exhaust gas.
The present invention is a method of purifying exhaust gas from an internal combustion engine, wherein by use of a sulfur solidifier comprising a metal element having a function of oxidizing sulfur component, and a basic metal element, the sulfur component being the cause of SOx poisoning is solidified before the exhaust gas flows into an NOx-occluding reduction-type exhaust purifying catalyst placed on an exhaust path.
According to the present invention, the sulfur solidifier solidifies the sulfur component (incl. sulfur oxides) before the exhaust gas flows into the NOx-occluding reduction-type exhaust purifying catalyst placed on the exhaust path, which can suppress the SOx poisoning of the NOx-occluding reduction-type exhaust purifying catalyst and further increase the purification efficiency of exhaust gas. A significant point here is that the aforementioned sulfur solidifier comprises the metal element having the function of oxidizing the sulfur component (incl. sulfur oxides), and the basic metal element. This permits the solidifier to effectively solidify the sulfur component (incl. sulfur oxides) being the cause of SOx poisoning of the exhaust purifying catalyst, which ensures the improvement in the purification performance.
It is preferable herein to preliminarily mix the sulfur solidifier in fuel. This premixing of the sulfur solidifier in fuel facilitates control of the ratio of the sulfur solidifier to fuel, thus contributing to increase in solidification efficiency of the sulfur component.
In another preferred embodiment, the sulfur solidifier can be added in an intake path, in a combustion chamber, or in the exhaust path, separately from the fuel. In this configuration, since the sulfur solidifier is added in the intake path, in the combustion chamber, or in the exhaust path separately from the fuel, it is feasible to select the position and timing of addition suitable for the solidification reaction and to adjust a loading amount according to the operational status of the internal combustion engine or the like (also including a situation where no load of the solidifier is desired), thus contributing to increase in the solidification efficiency of the sulfur component.
The metal element having the function of oxidizing the sulfur component (incl. sulfur oxides) in the sulfur solidifier, is preferably a transition element.
In another aspect, the basic metal element in the sulfur solidifier is preferably an alkali metal element or an alkaline earth metal element. The basic metal element being the alkali metal element or the alkaline earth metal element is prone to react with the sulfur component and form salts (solid matter), and is thus able to increase the solidification efficiency of the sulfur component.
Further, the basic metal element in the sulfur solidifier is preferably an alkali metal element having an atomic number equal to or higher than the atomic number of potassium. When the basic metal element is an alkali metal element having an atomic number equal to or higher than the atomic number of potassium, it is particularly easy to react with the sulfur component to form salts (solid matter), and thus is capable of further increasing the solidification efficiency of the sulfur component.
Further, it is preferable to make the solidified sulfur component held on the exhaust purifying catalyst and act as a catalytic component. When the solidified sulfur component is made to be held on the exhaust purifying catalyst and to act as a catalytic component in this way, the occlusion capability of the exhaust purifying catalyst can be maintained high. As a result, it is feasible to further enhance the exhaust purifying performance and suppress deterioration of the exhaust purifying catalyst.
When the sulfur solidifier is added to the intake air, air/fuel mixture, or recirculated exhaust gas before combustion in the cylinder of the internal combustion engine, it becomes feasible to adequately adjust the loading amount of the sulfur solidifier and adjust the loading timing. For example, when the sulfur solidifier is included in fuel, the loading amount and time of the sulfur solidifier are limited by injected fuel quantity and fuel injection timing. When the solidifier is added to the intake air, air/fuel mixture, or recirculated exhaust gas, it is feasible to effectively promote the solidification of the sulfur component (incl. sulfur oxide
Ito Taka-aki
Kato Kenji
Kawamura Tetsuo
Kimura Mareo
Mizuno Tatsuji
Nguyen Tu M.
Toyota Jidosha & Kabushiki Kaisha
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