Studio di fattibilità e ottimizzazione di un motore a pistoni liberi 'fuel flexible' ad elevata efficienza e ridotte emissioni = Feasibility study and optimization of a flex-fuel free-piston engine targeting high efficiency and low emissions

The automotive sector is increasingly focusing on improving the efficiency of propulsion systems to reduce pollutant and carbon dioxide emissions. Traditional internal combustion engines, however, do not always operate under optimal conditions, driving research toward alternative solutions that minimize system losses. In this context, free-piston engines offer the advantage of optimized combustion through a variable compression ratio, which enhances efficiency under partial load conditions and enables the use of different types of fuels. Furthermore, the absence of a crankshaft reduces frictional losses, further improving system performance. This thesis analyzes the behavior of a free-piston engine with an opposed configuration, examining the influence of operational parameters and conditions on its performance. Initially, a comprehensive overview of the characteristics of this engine type is provided, highlighting its differences compared to traditional thermal engines, with references to existing literature. The thesis then introduces the Gasdyn software, employed to simulate engine behavior using a one-dimensional model. Preliminary open-loop simulations, conducted without a PID controller, are described with the aim of understanding the engine dynamics and identifying the operational ranges of key input parameters. To optimize the number of simulations and ensure a homogeneous exploration of the parameter space, a Design of Experiment (DoE) approach based on Latin Hypercube Sampling (LHS) was adopted, allowing compliance with imposed variable constraints. A predictive model is also presented to establish a semi-empirical relationship between input conditions and performance parameters, enabling the anticipation of system behavior without conducting additional simulations. Finally, simulations conducted with PID control are presented. The objective of the PID controller was to regulate the compression ratio by adjusting the pressure in the engine's bounce chamber and the ignition position. In this phase, engine performance was analyzed by varying both the type of fuel and the compression ratio, highlighting differences based on the fuel used.