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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.

The family of hot air engines with external heat input is divided in two subgroups: the Stirling engines, invented in 1816, have no valves whereas Ericsson engines, invented in 1833, have valves in order to isolate the cylinders. The valves give some advantages to the Ericsson engine. Amongst them, the most important one is that the heat exchangers are not to be considered as unswept dead volumes whereas the Stirling engine designer is faced to the difficult compromise between heat exchanger transfer area maximization and heat exchanger volume minimization. However, the distribution system of the Ericsson engine introduces some complexity and a non-negligible mechanical energy consumption in order to actuate them. An original and very simple system called "bash-valve" is proposed to provide answers to the difficulties related to the distribution system of the Ericsson engine. The "bash-valve" technology has been used in steam piston engines and pneumatic piston engines. In this system, the piston itself actuates the opening of the valves when being around the top dead center. When its moves to the bottom dead center, the piston loses contact with the valves and it closes under the effect of the return spring. Three different valves command laws of the expansion cylinder of the proposed hot air engine are studied. A comparison between energy performance of the engine with the expansion cylinder equipped with two kinds of bash valve technology and the energy performance of the expansion cylinder of an incomplete expansion Joule Ericsson cycle engine is presented as well as their influence on the design of the system.

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