Modelling and development of an integrated electrical machine and linear engine

Abstract

A linear engine generator is a combustion engine which converts chemical energy into electrical energy directly, without requiring a crank to convert it to rotary motion. Instead, the linear engine uses a linear generator coupled directly to the oscillating piston, eliminating the need for mechanical transmissions like rack and pinion, belts and speed reducers, and gear system. As a result, it has the potential to dramatically reduce the volume, weight, friction, and complexity of a power generation system. Furthermore, physical integration of the combustion engine and the generator provides an alternative chemical-to-electrical energy converter to compete with fuel cell technology, with higher volumetric power density for electrification of automobiles, trains, and ships. In this thesis, the electromagnetic and mechanical aspects of a linear engine generator using the Joule cycle with a compact double-acting free piston mechanism is investigated. Two generator configurations are compared using a coupled dynamic model in LMS Imagine.Lab AMESim, namely long translator-short stator, and short translator-long stator linear machines. Alternative magnet configurations and translator lengths of linear permanent magnet synchronous machines are compared using the dynamic model. Finite Element Analysis is used to optimise, analyse, and compare the electromagnetic performance of the investigated machines. Attention is mainly focused on physically integrating the electrical machine within the engine compressor. The design of an integrated prototype of the linear electrical machine built within the compressor cylinder of an engine is proposed. By considering the complexity of manufacturing and number of components a prototype is manufactured and tested on a bespoke test rig to validate the design model. In general, a good agreement is shown between the predicted and measured results.