Development of a Stirling engine battery charger based on a low cost wobble mechanism.

Abstract

The benefits of the Stirling Cycle have been known for well over a century but several specific problems have prevented its common use in modern society. During 1989 this PhD project was undertaken to investigate various applications for the Stirling Engine and develop the one most likely to succeed commercially and be manufactured within New Zealand. The Stirling Engine Battery Charger For Yachts was selected and this thesis outlines the design development up to and including testing a pre-production prototype. Although the system is specifically designed to allow scaling to accommodate future designs of total energy system for yachts and for use in other applications, this thesis is restricted to the development of an air charged, 200 Watt (electric), LPG heated, hermetically sealed and ' pressurised unit suitable for charging 12 volt batteries. The chosen design utilised the four cylinder double acting configuration and incorporated a modified alternator to also act as a starter motor. Several of the key problems with the Stirling Engine which have prevented its commercialisation are identified early in the thesis and the succeeding Chapters present investigations and possible solutions to each. These investigations resulted in the development of a new kinematic mechanism design, further piston seal research, a combined starter alternator, alternative heat exchanger designs and another general system layout. To aid Stirling Engine design and optimisation a computer modelling package was developed. This system was based on a commercial Spreadsheet program and a customised published Quasi Steady Flow simulation routine. To verify the simulation an Alpha configuration engine was manufactured and tested prior to designing the prototype unit. The prototype engine/alternator successfully met its design power of 200 Watts. This thesis concludes with the detailed design of the prototype, its performance characteristics, a review of the system viability and recommendations for further development and other applications.