Dynamic modeling and response characteristics of closed CO2 cycle with Li/SF6 fuel boiler to external disturbances

High-energy density power propulsion technology is of urgent demands for UUVs. In this paper, a novel closed transcritical CO2 cycle combining Li/SF6 fuel boiler is proposed, which has higher efficiency and energy density. To understand the dynamic response characteristics of this system in UUVs application environment, the dynamic simulation model was established and the dynamic response characteristics of the system to external parameter disturbances such as heat source heat load, cold source temperature, turbomachinery speed and their coupled disturbances were investigated. The results show that CO2 mass flow rate needs to be adjusted when the heat load disturbance of heat source exceeds 10 % to avoid overheat. The cycle pressure is not only affected by the turbomachinery speed disturbance, but also by CO2 density change caused by compressor inlet temperature disturbance. The response time of cycle pressure to turbomachinery speed disturbance is shorter than that to compressor inlet temperature. The transcritical CO2 cycle with the compression from gas phase is more resistant to clod source temperature disturbances than S-CO2 Brayton cycle. Inventory control is required to ensure the stability of compressor inlet status. This study provides insights into developing the novel high-energy density power systems for UUVs.