Power Generation Characteristics and Parameter Sensitivity Analysis of Linear Generator Applied to Free Piston Engine Systems

The Free-piston engine system (FPES) is an innovative energy conversion system that directly couples the free piston engine and linear generator (LG). It is a promising alternative to traditional internal combustion engines due to its high efficiency, high power density, and potential for multi-fuel adaptability. This study presents a permanent magnet LG for application in FPES. The structure and test rig of the LG are introduced and established. A 2D finite element model (FEM) of the LG is developed and validated. The results show a relative error of less than 6% between the experimental and simulated results. The power generation characteristics of the LG are compared and analyzed under different motion profiles. When the LG moves at a constant speed, the three phase voltage curves exhibit regular and periodic changes. When the LG is integrated into FPES, the three phase voltage curves are different and display varying degrees of distortion, resulting in fluctuating output power around its maximum value. Moreover, an orthogonal experimental design is adopted to analyze the sensitivity and significance level of different factors on the output performance. The results show that the operating frequency has the greatest sensitivity and significant impact on the output power, whereas the center position exhibits the most minor sensitivity to output power. Besides, the external load significantly influences power generation efficiency, while the stroke length and center position display similar and relatively minor sensitivities to power generation efficiency.