Numerical optimization of a four-cylinder double-acting stirling engine based on non-ideal adiabatic thermodynamic model and SCGM method

The aim of this study is to optimize a four-cylinder, double-acting α-type Stirling engine with wobble-yoke mechanism using an optimization scheme incorporated with an efficient thermodynamic model. In this study, the non-ideal adiabatic thermodynamic model is improved by taking into account factors including pressure drops due to the sudden expansion or contraction of flow cross-sectional areas in the engine, multiple nodes in the regenerator adopted to accurately capture the temperature gradient in the regenerator, and the dependence of the transport properties (thermal conductivity and dynamic viscosity) of the working fluid on temperature and pressure. A parametric analysis is firstly performed to identify the designed parameters that need to be optimized. In this study, engine optimization is carried out by using the simplified conjugate-gradient method (SCGM). The effects of the weighting coefficients of the objective function are studied. For a particular case considered, the optimization successfully elevates the power output from 1062.56 to 1659.72 W, and thermal efficiency from 27.41% to 37.22%. Furthermore, the robustness of the optimization method is tested by giving different sets of initial guesses. It is found that the present approach can stably lead to the same optimal design and is independent of the initial guess.