The capabilities and unique features of the Stirling engines have made them suitable for a wide range of applications. Although these engines, compared to internal combustion engines, have less specific power, their structures are simpler and it makes them more reliable for long term missions. The structures of free piston Stirling engines are simpler and by use of non-contact seals, the friction between piston and cylinder will be minimized. The Longer life, high efficiency and possibility for use of any source of energy in free piston Stirling engines, make it possible to utilize them in solar energy convertors and today a number of NASA spacecrafts utilize them to produce electricity for spacecrafts. In the present work, using the linear dynamic analysis, a free piston Stirling engine is designed. After determination of principal dimensions of the engine, a finite element analysis is used to design the piston and displacer flexure bearings. After assembling the engine parts and initial tests, the actual operating frequency of the engine was measured. The operating frequency of the engine could be obtained by measuring the frequency of the output electrical current of alternator. The actual measured frequency of the engine is about 43Hz and it is possible to increase the operating frequency to 60Hz by changing the mass of piston and displacer. According to the assumptions of isothermal analysis, it is necessary to develop a numerical multi-dimensional analysis to get a better understanding of the engine operation. In this Thesis, using FLUENT code, a 2-D unsteady axis symmetric model is presented. The motion of piston and displacer boundaries is produced with the aid of user defined functions (UDF) in FLUENT and the grid is updating in each time step by layering method. To reduce the computational time, the initial temperatures of working fluid in various zones are set manually. These initial temperatures have great effect in achieving to quasi steady condition. The initial pressure is 1 MPa and initial velocities are considered zero. At the end of each time step, a user defined function is executed and calculates the average pressures and volumes of working spaces. The output cyclic power could be obtained from p-v diagram. The output power calculated by CFD analysis is about 10 watts but the isothermal analysis estimates an output power about 30 watts. It is obvious that the difference between calculated power outputs is related to poor operation of heat exchangers and we can increase the actual power output to about 40 watts by optimizing the heat exchangers and increasing the charge pressure. Key Words Stirling Engine, Free Piston Stirling Engine, Manufacturing, CFD analysis
