**2. System modeling**

272 Thermodynamics – Interaction Studies – Solids, Liquids and Gases

Free-piston Energy Converter (FPEC) since 2002 aimed to develop an efficient new technology suitable for vehicle propulsion, auxiliary power unit and distributed power generation. The design and optimization of linear alternator and crankless engine, control strategy, numerical simulation and power management have been carried out systemically [6]. Dr. Peter Van Blarigan at Sandia National Laboratory presented the design of a dual piston free-piston engine generator with 40kW electric power output and the engine employed homogeneous charge compression ignition (HCCI) operating on a variety of hydrogen-containing fuels [7, 8]. Jakob Fredriksson and Ingemar Denbratt at Chalmers University of Technology investigated a two-stroke free-piston engine with different fuels using BOOST and SENKIN [9]. Czech Technical University had successfully developed a direct injection FPLA prototype recently, and steady operation had been realized based on precise motion control. When the prototype was running with frequency of 27Hz and compression of 9, the average power output was approximately 350W, but the efficiency had not been reported [10]. Mikalsen and Roskilly proposed a design of a single cylinder free-piston engine generator with gas-filled bounce chamber, simulated its working process and discussed the effects of parameters in a wide operating range to the engine's performance [11]. A novel approach of modeling the free-piston engines through the introduction of solution-dependent mesh motion in an engine CFD

Dimensionless analysis using Buckingham's theory was performed base on the parameters of a spark ignited FPLA prototype (as can be seen in Fig.1) in the following contents. The

To decrease the number of variables and still use the equations involved in the

To generalize the study of FPLA to a wide range of geometrical designs in order to find

 To establish a scale for the similitude concept so the experiments done on the existing prototype could be used to predict performances for FPLA with various sizes and

out the best geometric dimensions with most favorable performance.

toolkit OpenFOAM was also presented [12].

objectives of this work are:

modeling of FPLA.

dimensions.

Fig. 1. FPLA configuration
