Experimental validation of a MW-scale sCO2 centrifugal compressor under subcritical inlet design conditions

Supercritical carbon dioxide (sCO2) power cycles offer high efficiency and compactness, making them promising for next-generation carbon-neutral power systems. However, compressor operation near the critical point remains a major challenge due to abrupt variations in thermophysical properties. Most megawatt-scale demonstrators have therefore adopted conservative supercritical inlet conditions (≥32 °C) to avoid the unstable near-critical regime. Although transient operation below the critical point has been reported in previous studies, experimental validation of a megawatt-scale compressor intentionally designed for sustained subcritical operation remains very limited, to the best of the authors’ knowledge. This study presents the experimental validation of a supercritical CO2 centrifugal compressor for a 2 MWe power system designed for a subcritical inlet temperature of 28 °C. The compressor, tested under full-pressure CO2 conditions, achieved a pressure ratio of 2.79 and a peak efficiency of 70% at 38,000 rpm. A customized start-up protocol incorporating controlled pressurization and temperature ramping, adapted from established industrial CO2 handling practices, enabled safe and stable operation through the two-phase region. An experimentally validated performance curve was obtained, providing key reference data for system-level modeling beyond ideal-gas assumptions. The results demonstrate the feasibility of stable and efficient compressor operation at a subcritical design point and contribute experimental evidence relevant to the commercialization of sCO2 power systems.