| 摘要 |
The invention is intended to provide good emission-cleaning performance by use of a three-way catalyst alone, without the need for a lean NOx catalyst, while ensuring a fuel economy improvement effect of lean burn operation, and to improve fuel economy up to high-load operating ranges while maintaining desired engine output performance by use of a supercharger. In a pair of preceding and following cylinders whose exhaust and intake strokes overlap each other, intake air supplied to the preceding cylinder ( 2 A, 2 D) is supercharged by a turbocharger ( 23 ) to produce combustion at a "lean" air-fuel ratio in the preceding cylinder ( 2 A, 2 D), and burned gas discharged from the preceding cylinder ( 2 A, 2 D) is introduced into the following cylinder ( 2 B, 2 C) through an intercylinder gas channel ( 22 ). Combustion in the following cylinder ( 2 B, 2 C) is made at an air-fuel ratio equal to or smaller than the stoichiometric air-fuel ratio by supplying fuel to the burned gas of a "lean" air-fuel ratio introduced from the preceding cylinder ( 2 A, 2 D), and gas discharged from the following cylinder ( 2 B, 2 C) is led to an exhaust passage ( 20 ) provided with a three-way catalyst ( 30 ).
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