| 摘要 |
PROBLEM TO BE SOLVED: To reduce amount of contaminants accumulated in a trap by purging contaminants when temperature of the trap reaches a given temperature. SOLUTION: A three-way catalyst 26 acts at about 400 deg.C to 1000 deg.C in respect of efficiency and durability. A trap 32 acts in a window from about 300 deg.C to 400 deg.C in respect of efficiency. When fuel contains sulfur, the sulfur remains in the trap 32, and reduces a trapping efficiency of nitrogen oxide in the trap 32 and an efficiency at which the nitrogen oxides is finally converted to harmless nitrogen and oxygen in the trap. For purging the trapped sulfur, the trap 32 is heated up to about 650 deg.C. The purging operation takes about three to ten minutes at this temperature. In a lean mode, nitrogen oxides and sulfur oxides are accumulated in the trap for nitrogen oxide. After absorbing almost whole in the trap 32, the purging operation is performed. Via an operation for fuel injection amount, an exothermic reaction providing sufficient temperature rising occurs in the trap 32.
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