A new Ericsson free-liquid-piston engine (FLPEE) configuration was previously presented. This consists of a U-shaped tube filled with water in its lower part, and whose two branches are closed by cylinder heads fitted with valves. The space between the surface of the liquid and the cylinder head of one of the branches constitutes the compression space, while this same space constitutes the expansion space in the other branch. The configuration studied operates in an open cycle. This system is able to produce compressed air which can be expanded in an external device to produce mechanical energy. This FLPEE is thought to be suited for the conversion of thermal energy such as solar energy, biomass or flue gases. In this communication, the experimental bench is presented in detail. In particular, the valve control system of the compression and expansion spaces, the various sensors and the data acquisition system are described. Various experimental results are presented, notably in the form of (p, V) indicator diagrams of the compression and expansion cylinders. These results confirm what the theoretical modelling had predicted, namely that it is possible to obtain a set of values of the operational parameters of the system leading to a stable operation of the freepiston system.
A special configuration of Stirling liquid piston engine, known as Fluidyne, was invented fifty years ago and many works have been devoted to it since then. A variant of the Fluidyne is presented, in which the two ends of the U-tube containing the liquid piston are closed by valves, so that the system obtained belongs to the family of Ericsson engines rather than to the family of Stirling engines. This type of low-tech system is considered to be suitable for the production of low-power mechanical energy (up to 1… kW), for example for pumping or to drive an electric generator from renewable primary energy conversion (solar, biomass, hot gaseous effluents, ). In the system considered, the working fluid of the Ericsson engine is air in open cycle. Different configurations are proposed for the extraction of mechanical energy. The preliminary design of a first demonstrator is presented. Results of a dynamic “intracycle” model of this liquid piston Ericsson engine are presented in the case of the coupling with a linear generator. The model allows to determine the frequency of operation of the engine, the instantaneous liquid piston position and the instantaneous working gas properties, so that the global performance of the engine can be predicted.
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