Advances in direct-fired sCO₂ cycle and sCO₂ oxy-fuel combustion

The direct-fired supercritical CO₂ (DFSC) cycle is a novel, efficient, low-carbon emission power generation technology. This paper reviews various DFSC cycle layouts and their performance. Energy efficiencies for gas and solid fuel layouts are 49.32–65.7% and 18.25–53.19%, respectively. The supercritical CO₂ (sCO₂) combustor is a key hot end component for achieving high efficiency of the DFSC cycle system and green operation. This work traces the evolution of sCO₂ combustors and studies their design features, including geometry, cooling method, and nozzles. Given the two problems of CO emissions and combustion stability, a conceptual sCO₂ combustor is proposed from the aspects of nozzle structure, combustion organization method, and oxidizer composition, which provides ideas and references for the future development of sCO₂ combustors. Numerical combustion is significant for understanding sCO₂ oxy-fuel combustion characteristics, thus assisting the combustor design. Therefore, starting from the sCO₂ combustion kinetics, this paper summarizes the optimization methods of the kinetic models (chemical reactions, equation of state, thermodynamic and transport parameters, mixing rules) and compares the basic combustion characteristics with the kinetic models. On this basis, further summarizing the sCO₂ turbulent combustion characteristics. Limited by the high-precision numerical simulation’s computational efficiency and cost, an effective way to study sCO₂ oxy-fuel combustion and combustor design with machine learning assistance is proposed. Future research should focus on experiments and developing efficient, high-fidelity numerical simulation frameworks.