Performance analysis and design optimization of a supercritical CO2 Brayton cycle cooling and power generation system coupled with a scramjet

The supercritical CO₂ (SCO2) Brayton cycle is widely recognized for its potential applications in aerospace propulsion due to its performance and compactness. This study proposed a novel cycle layout based on a split-flow scheme that is suitable for conditions with a limited heat sink. Besides, a one-dimensional coupled model and solution strategy incorporating the dual-mode scramjet, regenerative cooling channels, and SCO₂ Brayton cycle were presented and validated against experimental data in literature. The coupling performance and impact factors of different Brayton cycle layouts under limited heat sink conditions were analyzed based on the proposed coupling model. Optimization methods were employed to determine the optimal designs for the three cycle layouts, and their performances were compared. The results indicated that the simple layout had superior regenerative cooling performance, with a SCO₂ regenerative cooling area ratio of up to 0.31 and a power output of 249 kW at Ma8. In contrast, the recuperated layout exhibited the best thermodynamic performance, with a maximum power output of 274 kW and an area ratio of only 0.23. An insufficient heat sink significantly limits the thermodynamic performance of the Brayton cycle, resulting in a maximum power output for all layouts as the SCO₂ mass flow rate increases. Furthermore, the new layout demonstrated a thermodynamic performance close to that of the recuperated layout but offered a regenerative cooling performance close to that of the simple layout, thus achieving the best overall performance. Under the Ma8 condition, the CO₂ regenerative cooling area ratio and maximum power output of the new layout reached 0.3 and 261 kW, respectively. The results of this study contribute to guiding the optimal design of the closed Brayton cycle in hypersonic vehicles.