| 摘要 |
PROBLEM TO BE SOLVED: To prevent lowering of the concentration of HC and prevent knocking, by rapidly and surely burning a mixture around the top land of a piston. SOLUTION: An engine body is formed therein with a combustion chamber 17 having an annular bottom surface 18. A top land part 13t, extending from the outer periphery of the head surface 13h of a piston 13 to the upper edge of a first ring groove 151 of the piston, is exposed to the combustion chamber 17 through the annular bottom surface 18, when the piston comes up its top dead center. With this arrangement, an annular combustion chamber space 17a is defined around the top land part 13t.
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