Abstract
The movement of piston in free-piston expander-linear generator (FPE-LG) mainly depends on the dynamic force balance among four kinds of forces (air impetus, air resistance, electromagnetic resistance and frictional resistance). In this paper, the Newton's Second Law and the first law of thermodynamics are used to analyze the single-piston FPE-LG, the change of four kinds of forces and work produced by the four kinds of forces are analyzed. Nominal work-electricity conversion loss coefficient is proposed for the firs time to represent the energy loss. The experiment results show that the work produced by four forces from top dead center (TDC) to bottom dead center (BDC) are higher than those from BDC to TDC. The minimum proportion of air resistance energy consumption is also more than 50%, the proportion of electromagnetic resistance energy consumption is less than 20%, and the proportion of frictional resistance energy consumption is more than 20%. Therefore, the total nominal work-electricity conversion loss can be effectively reduced by increasing intake time or intake pressure.
•Newton's Second Law is used to analyze the change of forces.•The first law of thermodynamics is used to analyze work produced by different forces.•Increasing intake time or intake pressure in a certain range can reduce energy loss.