| 摘要 |
PROBLEM TO BE SOLVED: To improve combustion efficiency at low load operation. SOLUTION: Fresh air, sent from a scavenging port 5 formed on a cylinder head 2 to a combustion chamber 4, turns into a downward air flow bound for a top face 3a direction of a piston 3, then the air is guided to a curved recessing face 3b formed on the top face 3a of the piston for turning into an upward scavenging flow to generate a reverse tumble flow. Combustion gas is exhausted out of an exhaust port, 16 that opens/closes by the piston 3 being stratified by the scavenging flow. When the exhaust port 16 is closed, a strong tumble flow is generated inside the combustion chamber 4 to be intensified to the curved recessing face 3b, in a state of being converted into turbulence after the reverse tumble flow meets squish generated between the top face 3a of the piston and a lower face of the cylinder head 2 at an ignition position near top dead center. By injecting fuel thereon, combustion after ignition is accelerated, in combustion with the turbulence by the squish.
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