Optimization analysis of operational characteristics and power demand during opposed-piston free piston engine generator start-up process

During the start-up of opposed-piston free piston engine generator (FPEG), the linear motor operates in motor mode. The capacity of external power supply, along with the matching among motor force, initial rebound-cylinder pressure, and scavenging pressure, is critical for successful start-up of opposed-piston FPEG. In this study, a numerical model of the start-up process and a quadratic regression model based on response surface methodology were employed to predict the performance parameters of the opposed-piston FPEG during start-up, considering key controllable parameters. The applicability of the developed response surface model was evaluated using analysis of variance. Finality, based on the experimental test, the electric power demand during the start-up process was analyzed. The results indicate that, under conditions of sufficient electric power supply, motor force and initial rebound-cylinder pressure have significant effects on the start-up characteristics of opposed-piston FPEG. The start-up requirements can be satisfied when the motor force level is approximately 25% and the initial rebound-cylinder pressure is about 0.11 MPa, whereas scavenging pressure has no significant influence on the piston motion. The adjustment of scavenging pressure can focus on improving the combustion efficiency of the working medium in the cylinder, thereby reducing the number of commissioning variables during the start-up process. Furthermore, this study clarifies the electric power demand of the opposed-piston FPEG during start-up and provides guidance for the design of a matched energy storage system.