对置活塞二冲程汽油机活塞运动规律匹配分析

对置活塞二冲程汽油机活塞的相对运动规律,影响扫气过程的扫气正时和扫气持续期,而活塞相对运动规律主要取决于对置活塞运动相位差和曲柄连杆比。在采用MATLAB/Simulink进行对置曲柄连杆机构运动学分析的基础上,通过建立扫气系统的三维流体动力学仿真模型,并利用一维工作过程仿真提供的初始条件和边界条件,开展了对置活塞运动相位差和曲柄连杆比对扫气过程的影响规律研究,获得了较高的扫气效率和捕获率,实现了对置活塞相对运动规律的优化匹配。活塞运动相位差只影响扫气正时而不影响扫气持续期;曲柄连杆比同时影响扫气正时和扫气持续期。在内止点附近,不同的活塞运动相位差影响活塞相对运动速度和最小工作容积;不同的曲柄连杆比只影响活塞相对运动速度而不改变最小工作容积。

Matching Analysis of Piston Motion Law of Opposed-piston Two-stroke Gasoline Engine

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.