Study on the Influence of Injection Timing from Fuel Injectors on In-Cylinder Gas Flow in Dual-fuel Free-piston Engines

Abstract

Injection duration is a key parameter affecting in-cylinder mixture formation and combustion in dual-fuel free-piston engines. This study utilizes a coupled numerical model to investigate its impact across a range of 0.05 to 0.25 ms. Simulation results indicate that a short injection duration (0.05 ms) significantly enhances in-cylinder swirl and turbulence, primarily by improving fuel atomization and the mixing rate. The peak turbulent kinetic energy (20 m²/s²) increases by 51% compared to the case with a 0.25 ms injection duration. This optimization promotes more complete combustion, which leads to optimal indicated thermal efficiency and heat release rate. However, it also increases the heat transfer coefficient and heat flux by 16.7% and 33.2%, respectively. Conversely, a longer injection duration enlarges the fuel-rich zone, leading to increased soot emissions. A comprehensive evaluation of performance and emissions identifies 0.05 ms as the optimal injection duration.