| 摘要 |
PROBLEM TO BE SOLVED: To enhance burning rate by igniting a mixture around the center of a combustion chamber. SOLUTION: A boss part 21, through which an attaching hole 22 (thread hole) is pierced, is projected into a combustion chamber 14 in a cylinder head 13. A spark plug 13 is screwed into the attaching hole 22 in the boss part 21 and is tightened by a specified degree to locate an electrode 18a of the spark plug 18 around the center of the combustion chamber 14. With this arrangement, a mixture can be ignited around the center of the combustion chamber 14, and accordingly, the rate of burning can be enhanced while the distance of propagation of a flame can be shortened, thereby improving the combustion efficiency. Since the boss part 21 is projected into the combustion chamber 14, even by using a normal spark plug 18, the electrode 18a thereof can be located around the center of the combustion chamber 14, and accordingly, no expensive projected type ignition plug is required, and manufacturing cost of an engine can be reduced.
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