Generator Design Considering Mover Action to Improve Energy Conversion Efficiency in a Free-Piston Engine Generator

Abstract

In a free-piston engine generator (FPEG), the power of the engine can be directly regenerated by linear generators without a crank. The mover motion of this system is interrelated with engine and power generation efficiencies due to the direct connection between the mover of the generator and the piston of the engine. The generator should be designed to improve the overall energy conversion efficiency. The dimensions and mass of the mover limit its operating stroke and drive frequency. Herein, we propose a method for designing linear generators and constructing FPEG systems, considering the mover operation to improve engine efficiency. We evaluated the effect of mover operation on the engine and generation efficiencies using thermal and electromagnetic field analysis software. The proposed design method improves the overall energy conversion efficiency compared with a generator that considers only the maximization of generation efficiency. Setting the mover operation for higher engine efficiency and designing a linear generator to realize the operation can effectively improve the energy conversion efficiency of FPEGs.

Effect of Nonlinear Spring Characteristics on the Efficiency of Free-Piston Engine Generator

“…Improvement of the engine efficiency η en has a large impact on the energy conversion efficiency η o . Moving the piston at the appropriate piston drive frequency is important to improve the engine efficiency η en [19]. In addition, to improve the electrical efficiency η e , the linear machine should be operated only by power generation.…”

“…The engine efficiency and electrical efficiencies are about 40% and 90%, respectively. Therefore, the improvement of the energy conversion efficiency by improving the engine efficiency is remarkable [19]. To improve engine efficiency, the piston drive frequency must be set appropriately [13,19].…”

“…Therefore, the improvement of the energy conversion efficiency by improving the engine efficiency is remarkable [19]. To improve engine efficiency, the piston drive frequency must be set appropriately [13,19]. Piston motion, including piston drive frequency, is affected by piston mass, spring stiffness, and engine combustion force [20,21].…”