Simulation For Electromechanical Coupling System In Free Piston Linear Generator

Free Piston Linear Generator(FPLG)is a hot hybrid power device,which is thin and compact and has high efficiency and fuel flexibility compared with conventional engine.Since the beginning of the twentyfirst century,the researches on FPLG have gradually become a hot topic at home and abroad.Because of the complexity of operation of the FPLG and effects of cycle-to-cycle variation(CCV),the prototypes that can be stable running are still very few.Therefore,the studies on FPLG still have a big scientific value.Based on a conventional two-stroke engine,the 1-D and 3-D simulation models of a FPLG device were built,and this device is being developed.The FPLG in this thesis has a two piston structure and uses GDI(Gasoline Direct Injection)technology to supply fuel.The 1D model of electromechanical coupling system was built in MATLAB/Simulink and the gas exchange process was introduced in the model for the first time.Meanwhile,a control strategy for starting process was also designed and an explanation of mathematical theory of modeling and the coupling logic among sub-modules was clearly provided.The 1D simulation results show that the motion of the FPLG is very different from conventional engine.When the piston of the FPLG approaches to its top and bottom dead center(TDC?BDC),its speed will change suddenly.And the acceleration is much higher than that of conventional engine at TDC.Then,the key parameters of the proposed experimental device were optimized and the results show that appropriately increasing mass of mover ? intake pressure and ignition position can enlarge the output power of the device.Finally,the 3D simulation model was built in AVL-FIRE.And the initial and boundary conditions of 3D simulation model depend on the results of 1D simulation.During later period of exhaust process,especially at 180 ~ 240°CA,the 3D simulation results show that the exhaust gases near scavenging port flow back into scavenging pipe.And the scavenging efficiency of FPLG is lower than that of conventional two-stroke engine.Also,at 315°CA,the combustion reaction of FPLG is mainly concentrated in the center of combustion chamber.Then,the core flame gradually spread from the center to the surrounding area and the core flame move to the side of combustion chamber.When the piston continues to move up,reaching 345°CA,the in-cylinder combustion reaction rate in the combustion chamber become coincident.