Research on the Influence of Scavenging Conditions and Port Geometry on Flow Characteristics and In-cylinder Swirl Dynamics of the Opposed Piston Two-stroke Diesel Engine

To investigate approaches for enhancing gas exchange performance in opposed-piston two-stroke (OP2S) engines, this study investigates the effects of intake conditions and port parameters on flow characteristics and in-cylinder swirl dynamics. This study employed a hybrid methodology integrating steady-flow scavenging experiments and computational fluid dynamics (CFD) simulations, and analyzed the governing mechanisms of four critical parameters: intake pressure, scavenging pressure differential, port lift, and port inclination angle—on the discharge coefficient and swirl ratio. The results indicate that increasing the scavenging pressure difference elevates gas flow velocity. By enhancing fluid inertia, this suppresses flow separation near the ports, thereby significantly improving both the discharge coefficient and swirl ratio. Increasing the port lift intensifies flow separation along the sidewalls of the ports, thereby reducing the discharge coefficient. Simultaneously, it alters the in-cylinder velocity distribution, causing the growth rate of the swirl ratio to gradually diminish. In a clockwise-swirl-oriented port configuration, the left ports feature a large inclination angle. Variations in the left inclination angle exert negligible influence on the discharge coefficient. However, increasing the right inclination angle expands the flow separation zone along the port walls, thereby reducing the discharge coefficient. Elevating the inclination angles on both sides enhances the tangential velocity component of the gas flow, leading to a significant increase in the swirl ratio.