Thermodynamic, dynamic and flow friction analysis of a Stirling engine with Scotch yoke piston driving mechanism

Abstract

This study concerns with the thermodynamic and dynamic analysis of an alpha type Stirling engine with Scotch-yoke piston driving mechanism. The thermodynamic aspect of the analysis is treated with a polytrophic nodal approximation. The pressure of nodal volumes is calculated with modified Schmidt formula which takes into account the pressure differences between nodal volumes caused by flow friction. The flow friction is calculated with adapted Darcy formula. The variation of the gas temperature in nodal volumes are calculated via the first law of thermodynamics given for unsteady open systems. The dynamic behavior of the engine is modeled via the motion equations of pistons and crankshaft. For a 2 kW nominal shaft power and 1400 rpm nominal speed, dimensions and working conditions of the engine were investigated by using realistic inputs. It was estimated that an engine having about 1.44 L swept volume, 1000 K hot source temperature, 400 K cold source temperature, 9050 cm2 total inner heat transfer area, 6 bar charge pressure, 2000 W/m2K inner heat transfer coefficient may produce more than 2 kW shaft power. For 142 rad/s average crankshaft speed the optimum thermal efficiency and torque of the engine were determined as 31% and 15.63 Nm respectively.