CO₂ is commercially available in various purity grades, typically containing impurities such as air components: nitrogen, oxygen, and water. This study examines how impurities affect the performance of a supercritical CO₂ (sCO₂) system. The analysis focuses on a sequential heating architecture under both supercritical and transcritical regimes. A multi-fluid mixture model was used to analyze the thermophysical properties of the investigated mixtures. The parametric analysis indicates that impurities strongly alter the thermodynamic properties of CO₂, such as specific heat, viscosity, and density, and significantly impact cycle performance. By analyzing twenty CO₂-based mixtures with varying purity levels and chemical compositions, the study reveals that impurities particularly affect the density of CO₂, leading to performance degradation. The results show that system performance is highly sensitive to CO₂ purity levels. Mixtures over 99.8% purity exhibited minimal performance losses, with net power reductions limited to 2%. Mixtures with 99% purity experienced losses ranging from 5% to 11%, while mixtures with 96% purity suffered reductions of up to 30%. These findings highlight the importance of analyzing impurity levels and compositions in CO₂ supply for sCO₂ systems, as they significantly influence efficiency and operational feasibility.
The results also highlight the need for impurity analysis tailored to specific system architectures and operating regimes.