To stably form appropriate air fuel mixture in proximity of an ignition plug regardless of conditions of engine speed or the like.

A cavity 12 is formed on an upper surface of a piston 4. A large diameter swirl flow flowing along a cylinder inner wall and a small diameter swirl flowing along an inner wall of the cavity 12 are formed by a swirl control valve provided in a suction air passage to generate cylindrical upward flow by pressure distribution difference between the two swirl flows. An injector 13 is provided at a lower part of the intake passage 7 of a combustion chamber 5 and injects fuel with penetration reaching inside of the upward flow. Injected spray is mixed with air in the upward flow to form air fuel mixture suitable for combustion and is transported to a proximity of the ignition plug 11 to be burned.

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