Exploring piston dynamics and combustion characteristics of free-piston engine linear generator with hydrogen-rich fuel

Free-piston engine linear generator (FPELG) is an innovative energy conversion device, offering multifuel adaptability and a simple structure. With the piston motion characteristics of FPELGs strongly correlated with the combustion process, the diverse combustion processes associated with various fuels lead to distinct piston dynamics and in-cylinder combustion characteristics. Therefore, this paper proposes a coupled simulation and iterative computation approach, integrating a zero-dimensional dynamic model with a multi-dimensional computational fluid dynamic model, then quantitatively analyses the piston dynamics and engine combustion characteristics of FPELGs using four typical hydrogen-rich fuels. The result reveals that hydrogen- and methane-fuelled FPELGs exhibit the highest and lowest operating frequencies, respectively. Furthermore, hydrogen-fuelled FPELGs showcase the highest peak pressure and temperature in-cylinder, the shortest combustion duration of the free-piston engine, the highest peak heat release rate, increased diffusion in the region of elevated temperature in-cylinder, and the lowest concentration of nitrogen oxide emissions.