Optimisation of a Quasi-Steady Model of a Free-Piston Stirling Engine

Ayodeji Sowale,Edward J Anthony,Athanasios John Kolios

doi:10.3390/en12010072

Abstract

Energy from waste heat recovery is receiving considerable attention due to the demand for power systems that are less polluting. This has led to the investigation of external combustion engines such as the free-piston Stirling engine (FPSE) due to its ability to generate power from any source of heat and, especially, waste heat. However, there are still some limitations in the modelling, design and practical utilisation of this type of engine. Modelling of the FPSE has proved to be a difficult task due to the lack of mechanical linkages in its configuration, which poses problems for achieving stability. Also, a number of studies have been reported that attempt to optimise the output performance considering the characteristics of the engine configuration. In this study the optimisation of the second-order quasi-steady model of the gamma-type FPSE is carried out using the genetic algorithm (GA) to maximise the performance in terms of power output, and considering the design parameters of components such as piston and displacer damper, geometry of heat exchangers, and regenerator porosity. This present study shows that the GA optimisation of the RE-1000 FPSE design parameters improved its performance from work done and output power of 33.2 J and 996 W, respectively, with thermal efficiency of 23%, to 44.2 J and 1326 W with thermal efficiency of 27%.

Highlights

The increasing demand for renewable forms of energy less harmful to the environment has led to increased interest and research into various applications that can harness such energy, especially from waste heat
An investigation was carried out on the recovery of exhaust waste from gasoline engine using Stirling engines, the results indicated a possibility of harnessing the waste heat recovered and converting into useful work with the aid of the Stirling engine integrated to the gasoline engine [23,24,25,26]
This shows that genetic algorithm (GA) application is a good precision tool for determining the optimal value of the free-piston Stirling engine (FPSE)’s design parameters; it is difficult to locate the exact point at which the maximum power could be achieved

Summary

Introduction

The increasing demand for renewable forms of energy less harmful to the environment has led to increased interest and research into various applications that can harness such energy, especially from waste heat. The free-piston Stirling engine (FPSE), which is an external combustion engine suitable for energy recovery application especially in combined heat and power systems, has many advantages such as a simple mechanical configuration and longevity, efficiency and thermal-to-electrical energy conversion. Different methods have been implemented to analyse the operational performance of the FPSE, such as the investigation using computational fluid dynamics (CFD) analysis [2,3]. These models could not describe the performance of the engine accurately due to the inability to define the spring stiffness and damping factors that determine the motions of the piston and displacer during engine operation. The second-order models are employed based on the ability to predict the relationship between the thermodynamics

Methods

Results

Conclusion