Assessment of fluid-structure interactions for free piston linear engine: the effect of cooling channel layout

The free-piston engine (FPE) is recognized as a promising power source for future hybrid electric vehicles, particularly as a linear range extender. However, increasing power output and operating frequency intensify thermal loads and challenge structural reliability, while cooling design guidelines for FPE remain limited. To address this issue, this study systematically investigates the influence of cooling channel layout on the thermal-fluid-structural characteristics of an FPE combustion chamber, which remains insufficiently explored in previous studies. A three-dimensional one-way thermo-fluid-structure coupling model was developed to evaluate four cooling channel layouts, including throughflow (top-bottom and bottom-top) and backflow (clockwise and anticlockwise) patterns under identical cooling capacity conditions. The results reveal a trade-off between thermal management and structural stability. Compared with the anticlockwise backflow pattern (Case A), the top-bottom throughflow pattern (Case D) achieved the best cooling performance, showing a 6.2% increase in heat dissipation efficiency and a 3.5% reduction in average temperature, while also exhibiting the lowest thermal stress. In contrast, the clockwise backflow pattern (Case B) showed the smallest deformation magnitude, with a radial offset deformation amplitude of 11.98 μm and a maximum second-order elliptical deformation amplitude of 6.45 μm. Overall, the throughflow structure demonstrates superior heat dissipation and thermal stress reduction, whereas the backflow structure is advantageous for deformation control. Among all configurations, the top-bottom throughflow pattern is recommended for high-load durability-critical operations, providing guidance for the thermal management and cooling system design of FPE.