Research on starting process and control strategy of opposed-piston free-piston engine generator _ Simulation and test results

The operation process of free-piston engine generator (FPEG) can be divided into starting process and power generation process, and each of them faces severe challenges especially for the opposedpiston FPEG. As the first part of the investigation, this paper focuses the starting process of opposed piston FPEG. Two novel general methods to start the opposed-piston FPEG are investigated by the linear electric machine operating as linear motor. Both simulation and test results are presented, and the numerical model is successfully validated. The test results show that the maximum in-cylinder pressure of the engine cylinder is 11.85bar, indicating that the engine is ready for ignition, and the synchronization error of opposed-piston fluctuates within +/- 2 mm with the limitation of the synchronization mechanism Further investigations on the opposed-piston scheme performance with the displacement master-slave control strategy and current master-slave control strategy are carried out. The results demonstrate that both control strategies are feasible to start the opposed-piston FPEG. More importantly, the current master-slave control strategy has faster response to external interference and therefore the piston synchronization error is smaller. And the smaller motor force of the current master-slave control strategy makes the peak in-cylinder pressure reach the target value. Further research shows that the mass of moving parts, constant motor force and the synchronization mechanism are crucial factors for such schematic prototype during starting process. (C) 2021 The Authors. Published by Elsevier Ltd.