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In this study, a linear synchronous machine is compared with a linear transverse flux machine. Both machines have been designed and built with the intention of being used as the power take off in a free piston engine. As both topologies are cylindrical, it is not possible to construct either using just flat laminations and so alternative methods are described and demonstrated. Despite the difference in topology and specification, the machines are compared on a common base in terms of rated force and suitability for use as a generator. Experience gained during the manufacture of two prototypes is described.

Free-piston engines have the potential to offer a compact machine capable of delivering electrical power. In this work, the design and modelling of a linear tubular generator are presented and used to investigate the effect of the electrical machine design on engine performance. A cogging-force-reduction technique is presented and used as a case study to demonstrate the importance of the integrated design.

In a free piston engine, the translator of a linear generator is coupled directly to the moving cylinder of a thermodynamic engine. For a linear machine to have a constant active area, either the translator or the stator must be oversized. The length of the translator effects its mass, which in turn effects the engine performance. This paper investigates the effect of translator length on the overall power density of a free piston engine coupled to a cylindrical permanent magnet machine.