Research On Dynamic Characteristics And Leakage Problem Of Low-power Free Piston Stirling Engine

The free piston Stirling engine uses the helium as a working medium.This type of Stirling engine has some advantage: good adaptability of the heat source,high theoretical thermal efficiency,low-grade energy can be utilized and a simple structure,etc.so it has a bright application prospect of the efficient use of energy and waste heat recovery.In this paper,dynamic model of the free piston Stirling engine is established,computed and simulated.This model is analyzed and calculated by the rotation vector,and then the vector diagram is obtained.According to the design parameters of the engine,use the vector diagram to get the driving force of the pistons.Adams simulation software is used to establish the virtual prototype model of the power piston and displace piston.The pistons vibration curves are obtained through the simulation of the driving force of the piston,the stiffness coefficient and the damping coefficient of the vibration system.The piston displacement curve,velocity curve,acceleration curve are compared with the theoretical calculation to verify the correctness of the theoretical calculation results.The natural frequency of piston vibration system is studied.The vibration principle of piston vibration system is introduced.The piston vibration system is regarded as a single-degree-of-freedom damped vibration caused by simple harmonic excitation force.Using the principle of resonance,the natural frequencies of the piston vibration system are obtained through experiments.The vibration system of the piston is excited by the exciter,the strain gauge is pasted on the leaf spring,and the displacement signal is output by the signal amplifier through the Wheatstone bridge.The power piston vibration system and the displace piston vibration system are tested respectively by this test system,and the natural frequencies of the piston vibration systems are obtained.For the further of free piston Stirling engine performance test,the test platform is established and the engine test is carried out.The result of test is not good,for the engine does not start up.Through in-depth analysis of the test process and results find that the engine does not start up because the gap between the power piston and the cylinder is too big,resulting in excessive leakage of working fluid.And establish the engine starting excitation system,to ensure that the piston can establish sufficient pressure difference.Study of the clearance seals leakage character in power piston of free piston Stirling engine.A mathematical model of the clearance seal of the power piston is established based on the theoretical analysis.The influencing factors are analyzed,and the numerical calculation of the leakage is carried out.The influence of the size of the gap on the leakage is studied emphatically,and the leakage of the half-cycle is calculated by taking four group gaps.Set up a free piston Stirling engine piston leakage test platform and conduct the tests.The result shows that the smaller the gap,the smaller leakage,the better the sealing effect.Analyze the influence of leakage on engine start-up,and improve the heating method.