Design and modeling of a free-piston engine generator

Abstract

Free-piston engine generators (FPEGs) can be applied as decarbonized range extenders for electric vehicles because of their high thermal efficiency, low friction loss, and ultimate fuel flexibility. In this paper, a parameter-decoupling approach is proposed to model the design of an FPEG. The parameter-decoupling approach first divides the FPEG into three parts: a two-stroke engine, an integrated scavenging pump, and a linear permanent magnet synchronous machine (LPMSM). Then, each of these is designed according to predefined specifications and performance targets. Using this decoupling approach, a numerical model of the FPEG, including the three aforementioned parts, was developed. Empirical equations were adopted to design the engine and scavenging pump, while special considerations were applied for the LPMSM. A finite element model with a multi-objective genetic algorithm was adopted for its design. The finite element model results were fed back to the numerical model to update the LPMSM with increased fidelity. The designed FPEG produced 10.2 kW of electric power with an overall system efficiency of 38.5% in a stable manner. The model provides a solid foundation for the manufacturing of related FPEG prototypes.

Graphical abstract

Keywords

free-piston engine generator / linear permanent magnet synchronous machine / system design / numerical model / finite element method

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Acknowledgments

This project was supported by the Shanghai Science and Technology Commission (No. 19511108500). We would also like to thank the sponsors of this study.

Competing interests

Zhen HUANG is the Editor-in-chief of Frontiers in Energy, who was escluded from the peer review process and all editorial decisions related to the acceptance and publication of this article peer review was handled independently by the other editors to minimise bias.

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