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An increased cycle expansion ratio is beneficial from a thermodynamic viewpoint to increase the engine efficiency. In this study, the target compression ratio and corresponding thermodynamic cycle layout were investigated by means of a new ideal combustion cycle. To model the experimental pressure traces, the combustion was divided into three parts; constant volume combustion, early expansion combustion and late combustion. This study discussed optimal parameter values for compression ignition combustion under PFP constraints. These parameters included compression ratio, pressure ratios as well as cut-off ratios. Furthermore, this study experimentally investigated the limitation of thermal efficiency and the variation of energy losses under different geometric compression ratios, boosting pressure and degree of constant volume combustion. These experiments utilized a supercharged single-cylinder heavy duty diesel engine with PFP-capability of up to 30 MPa.