Experiment And Simulation Reseach Of Free Piston Expander-Linear Generator Integrated Device

The free piston expander-linear generator integrated device was designed as a power outpout equipment based on the advantages of the free piston machine and linear generator, which could be used to recovery waste heat from vehicle internal combustion engine. This paper analysed and studied the working principle and the influences of intake pressure, working frequency and load resistance on the perfromance of the free piston expander-linear generator integrated devcie by the experiments in the air test rig. At the same time, the system model was built by MATLAB/Simulink software, and was experimentatlly validated by the test results. Moreover, the initial piston displacement, the piston-mover mass, the electromagnetic coefficient of the linear generator were studied by the performance evaluation index based on system model. Besides, for the asymmetry phenomenon of piston motion in the two cylinders happening in the test, the errors of the intake angle, exhaust angle and valve opening time, via the model, were analysed by the influences on the perfromance of the device.The results showed that after the stable running of the system during testing, the velocity, the acceleration, the load voltage and the load power would vary according to the periodic trends over time. Considing structural characteristics of the free piston device, BDC(bottom dead center) and TDC(top dead center) during the piston moving could vary when the working condition changes. In addtion, there are some problems of accuracy error when the device in the machining, assembly and debugging processes causing the asymmetry phenomenon of piston motion in the two cylinders during the test. When the exhaust angle is decreased, the exhaust valve would close before the piston reaching TDC, and there is a compression process between the exhaust valve closing and the piston reaching TDC, so a gap would exist between the piston and the head of the cylinder to protect the device. The accuracy error of the device parameter really could affect the preformance of the free piston expander-linear generator integrated devcie. The simulation results showed that the errors of the intake angle, exhaust angle and the valve pening time could cause the asymmetry phenomenon of piston motion in the two cylinders.