| 摘要 |
<P>PROBLEM TO BE SOLVED: To sufficiently enhance flame propagation characteristics while having a geometric compression ratio of 13 or greater, and to reduce fuel economy, in an spark ignition engine E having 0.3 liter or greater of a single chamber volume of a cylinder C. Ž<P>SOLUTION: Corresponding to an ignition plug 11 facing a ceiling 5a of a combustion chamber 5 in the cylinder C, a recessed part 32 is formed at the top of a piston 3. At least part of the inner face of the recessed part 32 is formed to have a spherical shape with which a virtual sphere IS having its center at the spark point CP of the ignition plug 11 is brought into contact when the piston 3 is at a top dead center (Steps S9, S10). The position, shape and volume of the recessed part 32 are set so that the volume V2 of a non-interfering portion of the virtual sphere IS brought into contact with the recessed part is regarded as the volume of the recessed part 32 and a volume ratio V2/V1 between the recessed part and the combustion chamber is set within a range of 0.31-0.37 (Steps S11, S12). Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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