Abstract: A three-dimensional computational fluid dynamics mode for a scavenging system is established to study the scavenging flow in opposed-piston two-stroke (OP2S) gasoline engine. The boundary and initial conditions are obtained from the simulated results of one-dimensional working process. As the opposed-piston relative dynamic characteristics of OP2S gasoline engine depend on different design and operating parameters, such as phase difference of opposed-piston motion and crank radius-connecting rod length ratio, a numerical simulation program is built using MATLAB/Simulink to define the opposed-piston motion profiles based on equivalent crank angle of opposed crank-connecting rod mechanism. The phase difference of opposed-piston motion only affects scavenging timing while crank radius-connecting rod length ratio affects scavenging timing and duration. Scavenging timing and duration are main factors which affect scavenging performance. The analysis results indicate that the optimal matching of phase difference of opposed piston motion and crank radius-connecting rod length ratio has the potential to achieve high scavenging and trapping efficiencies with a right flow in cylinder. Around the inner dead center, the phase difference of opposed-piston motion affects the relative velocity of opposed piston and minimum working volume, and the crank radius-connecting rod length ratio only affects the relative velocity of opposed-piston.

Key words: ordnance science and technology, opposed piston, crank-connecting rod mechanism, motion law, phase difference, crank radius-connecting rod length ratio