The CFD methodology for simulating pumping loss from displacer and piston seals of free piston Stirling engine

Abstract

A new axisymmetric CFD model capable of describing pumping loss is proposed for free piston Stirling engine. Inclusion of clearance seals, bounce space, heater, cooler, and regenerator in a single model is the unique strength of this work. For transient simulation of engine, dynamic mesh was utilized for catering needs of moving boundaries. The model was validated with 12.5 kW component test power converter and successfully predicted indicated power, efficiency, pressure amplitude, pressure drop, and gas temperature in expansion and compression space at different piston amplitudes with 6% maximum deviation. The results showed that the heat exchange at heater and cooler was minimized at each flow reversal and was strongly influenced by oscillating gas-flow rate. The results also present optimum displacer and piston seal clearance at different charge pressure and operating frequencies. The displacer seal clearance could be increased up to 125 ?m without compromising power, however, engine output was severely affected with increasing piston seal gap.