Free Piston linear Generator becomes a new solution and device for energy conversion highly integrated engine and linear machine due to its potential application on hybrid vehicles. This paper investigated the starting process of an opposed-piston free-piston linear generator (OPFPLG), and a prototype was built to carry out the experimental research of the startup process. The prototype adopts a piston synchronization mechanism and a pipeline connecting two bounce chambers to improve the self-balance performance of the system. The linear machine is used to start the engine because of its flexibility and controllability. The control strategies combining mechanical resonance and synchronization control methods were applied on the prototype for starting operation, and the test data collected for further analysis. When the linear motor’s thrust force was 240N, the maximum pressure in combustion cylinder achieved was beyond 11.8 bar with a compression ratio of 12:1, indicating that the mixture was ready for ignition. The system frequency was up to 14Hz, and the piston amplitude was about 56.5mm with a synchronization error of the opposed pistons less than 1.5mm. Especially, the piston synchronization error of the inner and outer dead center was nearly zero. Both the variation of synchronization error and the cyclic fluctuation of starting process were demonstrated with different synchronization control methods. The piston sync error of the dual current command control mode was found to be lower than that of the master-slave mode, and the cyclical fluctuation was smaller. The dual current command control method will be implemented to the prototype to start and maintain the piston motion synchronization during the starting process of the OPFPLG system.
Keywords opposed-piston, free-piston engine, starting process, cyclic fluctuation, synchronization control strategy