Improvement in the thermal efficiency of automobile engines is being demanded as a means to reducing carbon dioxide emissions, which are considered to be the main cause of global warming. Improving thermal efficiency by means of higher compression ratios is known. But, in the case of gasoline engines, there is a limit for high compression ratios caused by knocking under high load conditions. Therefore, various variable compression ratio (VCR) mechanisms have been devised. However, in previous attempts, structural issues have arisen, whereby structural weight has increased, thereby necessitating excessive power at the time of operation. Previous attempts have also necessitated the makeup of an exclusive engine design, which therefore has not been practically utilized. In this study, a double piston method was devised. This mechanism enables the remodeling of a VCR engine through the replacement of only the piston system without changing the dimensions of the engine. In addition, this mechanism operates by piston inertial force. Therefore, it does not need excessive power and enables a lightweight, power-saving engine. In this paper, the basic characteristics of the prototype VCR engine are described based on the experimental results obtained in tests conducted with the engine.

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