Improving Power Density of Free-Piston Stirling Engines

Abstract

Analyses and experiments demonstrate the potential benefits of optimizing piston and displacer motion in a free-piston Stirling Engine. Isothermal analysis shows the theoretical limits of power density improvement due to ideal motion in ideal Stirling engines. More realistic models based on nodal analysis show that ideal piston and displacer waveforms are not optimal, often producing less power than engines that use sinusoidal piston and displacer motion. Constrained optimization using nodal analysis predicts that Stirling engine power density can be increased by as much as 58% using optimized higher harmonic piston and displacer motion. An experiment is conducted in which an engine designed for sinusoidal motion is forced to operate with both second and third harmonics, resulting in a piston power increase of as much as 14%. Analytical predictions are compared to experimental data and show close agreement with indirect thermodynamic power calculations, but poor agreement with direct electrical power measurements.

Heat Transfer Enhancement in Stirling Engines Using Fins with Different Configurations and Air Flow

“…The volume of working fluid rises quadratically as the radius of the Stirling engine rises, whereas the heat transfer space to the working fluid only grows linearly. The Stirling cycle is therefore reduced to the Otto cycle, often known as the adiabatic Stirling cycle [24].…”

Power-Optimal Control of a Stirling Engine’s Frictional Piston Motion

“…In this theoretical study we focus on how the piston motion influences the engine performance by applying methods similar to previous optimizations of Stirling engines' piston motions [7][8][9][10][11][12][13]. Experimental studies [14,15] have shown that power output improvements of Stirling engines are feasible through altering the piston motion.…”