초록 ▼

In the present invention, the No. 1 cylinder of an engine is connected to a first exhaust passage and the No. 2 to No. 4 cylinders are connected to a second exhaust passage. A three-way catalyst and a NO.sub.X absorbent are disposed in the first and second exhaust passage, respectively. A denitratin

In the present invention, the No. 1 cylinder of an engine is connected to a first exhaust passage and the No. 2 to No. 4 cylinders are connected to a second exhaust passage. A three-way catalyst and a NO.sub.X absorbent are disposed in the first and second exhaust passage, respectively. A denitrating catalyst is disposed in a common exhaust passage to which the first and second exhaust passage merge. The NO.sub.X absorbent absorbs NO.sub.X when the No. 2 to No. 4 cylinders are operated at a lean air-fuel ratio, and is regenerated, i.e., releases and reduces the absorbed NO.sub.X when the No. 2 to No. 4 cylinders are operated at a rich air-fuel ratio. However, NO.sub.X, without being reduced, is released from the NO.sub.X absorbent during a short period at the beginning of the regenerating operation. In the present invention, the No. 1 cylinder is operated at a rich air-fuel ratio during the short period at the beginning of the regenerating operation in order to produce NH.sub.3 at the three-way catalyst. Therefore, when NO.sub.X without being reduced is released from the NO.sub.X absorbent and flows into the denitrating catalyst on the common exhaust passage, NH.sub.3 produced at the three-way catalyst is also supplied to the denitrating catalyst. Thus, NO.sub.X released from the NO.sub.X absorbent at the beginning of the regenerating operation is reduced at the denitrating catalyst by NH.sub.3 produced at the three-way catalyst.

대표청구항 ▼

[ We claim:] [1.] A method for purifying combustion exhaust gas comprising:a step for contacting an exhaust gas having a lean air-fuel ratio with a NO.sub.X absorbent to cause the NO.sub.X absorbent to absorb NO.sub.X in the exhaust gas, wherein said NO.sub.X absorbent absorbs NO.sub.X in an exhaust

[ We claim:] [1.] A method for purifying combustion exhaust gas comprising:a step for contacting an exhaust gas having a lean air-fuel ratio with a NO.sub.X absorbent to cause the NO.sub.X absorbent to absorb NO.sub.X in the exhaust gas, wherein said NO.sub.X absorbent absorbs NO.sub.X in an exhaust gas when an air-fuel ratio of an exhaust gas is lean and releases the absorbed NO.sub.X when an air-fuel ratio of an exhaust gas becomes rich and wherein said NO.sub.X absorbent releases the absorbed NO.sub.X without reducing it during a short period after an air-fuel ratio of an exhaust gas is changed from a lean air-fuel ratio to a rich air-fuel ratio and releases the absorbed NO.sub.X after reducing it to N.sub.2 and H.sub.2 O after said short period has lapsed;a step for causing the air-fuel ratio of the exhaust gas contacting said NO.sub.X absorbent to be a rich air-fuel ratio in order to make the NO.sub.X absorbent release the absorbed NO.sub.X ;a step for supplying NH.sub.3 to the exhaust gas after it contacts said NO.sub.X absorbent during said short period in which the NO.sub.X absorbed in the NO.sub.X absorbent is released without being reduced; anda step for contacting the exhaust gas after NH.sub.3 is added with a NO.sub.X purifying means which reduces NO.sub.X in the exhaust gas by reacting the NO.sub.X with NH.sub.3 in the exhaust gas to, thereby, reduce the NO.sub.X released from the NO.sub.X absorbent in said short period by said NO.sub.X purifying means.