Performance analysis of a flexi-fuel turbine-combined free-piston engine generator

The turbine-combined free-piston engine generator (TCFPEG) is a hybrid machine, generating both mechanical work from the gas turbine and electricity from the linear electric generator for battery charging. In the present study, the system performance of the designed TCFPEG system is predicted using a validated numerical model. A parametric analysis is undertaken based on the influence of the engine load, valve timing, the number of linear generators adopted, and different fuels on the system performance. It is found that when linear electric generators are connected with the free-piston gas turbine, the bottom dead centre, the peak piston velocity, and engine operation frequency are all reduced. Very minimal difference on the in-cylinder pressure and the compressor pressure is observed, while the peak pressure in the bounce chamber is reduced. When coupled with a linear electric generator, the system efficiency can be improved to nearly 50% by optimising engine load and the number of the linear generators adopted in the TCFPEG system. The system is able to be operated with different fuels as the piston is not limited by a mechanical system; the output power and system efficiency are highest when hydrogen is used as the fuel.