Parametric study and design optimization of a kW-class beta-type Stirling engine

Abstract

• A theoretical model for predicting shaft power and engine speed is proposed. • Effect of geometric parameters on local maximum shaft power is studied. • A kW-class beta-type Stirling engine is tested and optimized. • The maximum shaft power was increased to 1503 W after optimization. A Stirling engine is an external combustion engine that can be operated using different types of heat sources. Stirling engines can be applied in many renewable energy fields. The purpose of this study was to optimize the design of a kW-class beta-type Stirling engine with a rhombic drive mechanism for a concentrated solar power system. In this study, an energy method and a modified non-ideal adiabatic model were used to predict the shaft power and operating speed of the proposed engine. The simulation results obtained using the model were validated by the experimental results. The experimental results revealed that the instantaneous maximum power of the proposed engine could reach 1312 W at 1390 rpm under a helium pressure of 6 bar and heating temperature of 650 °C. On the basis of the experimental results, the local maximum shaft power was obtained using the quadratic interpolation method. Therefore, the effect on shaft power of the engine speed could be ignored, thereby reducing the calculation time. The effects of the charged pressure and design parameters of the heat exchanger on local maximum shaft power were studied. Multivariable optimization of the prototype engine was conducted based on the results of the quadratic interpolation method. Both the simplified conjugate gradient method and the variable step size conjugate gradient method were adopted as optimization algorithms. The results indicated that the number of iterations required in the variable step size conjugate gradient method to approach the optimum point was approximately one-third that required in the simplified conjugate gradient method. The results demonstrate that the maximum shaft power of the prototype engine can be further increased from 1137 W to 1503 W. Thermal efficiency and mechanical efficiency can also be increased to 13.5 % and 94.3 %, respectively.