Design of a free-piston Stirling engine-pump

A free-piston Stirling engine-pump (FPSEP) combines a Stirling cycle that provides power to an integral hydraulic pump. Stirling cycle engines offer potential advantages over internal combustion engines in fuel choice, quietness, and emissions. A Stirling-cycle, free-piston engine-pump has been investigated for use in human-scale, fractional horsepower applications and information.;A design has been developed that combines a free-piston Stirling engine with a single-piston pump, check-valves, and pressure relief valve. The Stirling engine prototype utilizes a pneumatic cylinder to actuate the displacer and thus control engine speed. Heat is supplied to the engine by an electric heater and cooling is provided by chilled water. The pump portion of the engine-pump consists of one single-acting piston with appropriate valve system for pumping fluid. The connecting linkage between the engine piston and the pump piston provides allowance for misalignment. In the proof-of-concept device, pressures, temperatures, positions and velocity are measured.;The performance and dynamic characteristics of the free-piston Stirling engine-pump have been simulated to determine its operating characteristics over a wide range of conditions. The simulation results indicate that a FPSEP operating at 550 psi (3.8 MPa) working pressure and with an engine displacement of 1.5 in3 (24.8 cm3) could produce 1.8 HP (1.3 kW) when operating at 4400 cycles per minute.;A free-piston Stirling engine-pump prototype has been built and tested. The ultimate gas working pressure of the prototype was 3.4 MPa (500 psi). The device was hydrostatically tested to this value. A beating phenomenon occurred during engine testing with forcing frequency of 5 Hz. For that reason, this prototype also has a speed limit for the displacer actuated by a pneumatic cylinder. The experimental results revealed that this engine without, insulation, using air and nitrogen as a working gas at a pressure of 0.69 MPa (100 psi) and 1.72 MPa (250 psi), provided significantly lower power than the simulation predicted. Because of hardware limitations desired operating temperature and pressure could not be achieved. Additionally, more friction and heat loss led to less power output than the simulation predicted.