| 摘要 |
PROBLEM TO BE SOLVED: To enhance lean limit at the initial explosion of an engine by reinforcing a tumble flow. SOLUTION: A piston recessed part 21 generating an involute tumble flow in a piston top face 13a. Because the bumble flow rises to near the center part of a piston, in a state of being collected by the piston recessed part 21 so as to form a small tumble flow, the tumble flow becomes difficult to be collapsed and satisfactory ignitability can be obtained. Also because fuel-air mixture can face toward around the ignition part of an ignition plug at a high velocity, a combustion velocity can be increased, and lean limit at initial explosion can be improved relatively.
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