Study on Leakage Effect Factors of Two-Stroke Micro Free Piston Swing Engine.

The two-stroke micro free piston swing engine (MFPSE) is a portable power device. Its seal performance plays an important role in the dynamic properties and efficiency of microengines. The present work established the leakage model of the two-stroke micro free piston swing engine by utilizing the compressible flow Reynolds Navier-Stokes equation. The obtained nondimensional mass leakage was related to the seal gap height, seal inlet pressure, size factor and compression ratio. Simulation investigated how the different seal gap heights and size factors affected the pressure, temperature and mass leakage of micro engines. The results showed that when the seal gap height of the combustion chamber increased, the maximum pressure and cycle power declined, obviously. However, the maximum temperature was scarcely affected. The mass leakage was not greatly impacted when the compression ratio was less than 5. However, the mass leakage dramatically increased when the seal gap was more than 10 μm or the size factor was less than 0.4. The investigation revealed these mass leakage effect factors and provided a guide for the seal and structure design of the two-stroke micro free piston swing engine.