Coupling mechanism study of a free-piston Stirling engine–linear alternator–pulse tube cryocooler tri-system

A novel gas-coupled Free-Piston Stirling Engine–Linear Alternator–Pulse Tube Cryocooler (FPSE–LA–PTC) System is proposed to avoid the linear alternator high-temperature failure problem under extreme environments. Free-piston Stirling engine (FPSE)'s compression chamber is coupled to the linear alternator (LA) by the piston, and to the pulse tube cryocooler (PTC) by a tube. The pressure wave generated by the FPSE drives the LA for electricity and PTC to actively cool the LA. One-dimensional thermodynamic model was developed and validated by the prototype. The simulation result shows good agreement with experimental data, with the output power deviation less than 4 %, and the deviation of the indicated power distribution ratio between the LA and cooler was 13.2 %. The prototype system delivers 96.1 W of electric and 11 W of cooling power at 211 K with 500W heating, showing a drop in electric power from 114 W before coupling while providing additional cooling capacity. Intrinsic impedance analysis was conducted to explore the coupling mechanism and energy distribution among the Tri-System. Under the same heating power, the total indicated power of the FPSE remains constant, whereas the proportion consumed by the PTC decreases as cooling temperature increases. After coupling, the pressure amplitude in the FPSE's decreases from 3.01 to 2.54 bar, the hot-end temperature rises above 800 K, and the phase shift between the pistons increases from 62° to 70.7°. Energy transfer process in the coupled compression chamber is analysed. These results confirm the system's effective coupling and its potential for combined power and cooling generation in extreme environments.