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One possibility for onboard electricity generation in a hybrid vehicle is a free piston engine incorporating an integrated linear generator. This paper presents the modelling and development of the linear engine generator concept, where a linear electrical machine is physically integrated within a free piston engine. Details and results of a multi-physics simulation of this concept are given, with a focus on the design of the electric machine. It is shown that a short translator design can result in the highest power density. This also gives the opportunity for integrating the electric machine physically within the compressor. Details of a prototype demonstrator of the resulting generator-compressor are given.

the aim of this paper is to investigate the integration of a tubular linear electrical machine with a linear free-piston combustion engine in order to create a single integrated free piston engine generator. The performance of the engine when coupled to a long and short translator electrical machine is discussed. To simulate the dynamic performance of the overall system, an integrated thermodynamic, mechanical and electromagnetic model is required. LMS Amesim software is used to model the thermodynamic engine and electromechanical finite element analysis is used for the electrical machine. The overall performance of an engine coupled to electrical machines with varying translator length is investigated. The performance of such a tubular generator is demonstrated by measurements on a 7-pole/6-slot prototype machine. The short translator generator design appears to perform better in terms of performance and capital cost, based on the dynamic simulation results of the system.

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.