可变气门升程对4气门直喷汽油机缸内气流运动特性的影响

Experiment of VVL Influence on Airflow in a 4-Valve GDI Engine

在一台光学可视化4气门直喷汽油机上,利用粒子图像测速(PIV)测试系统对不同最大气门升程(Maximum Valve Lift,MVL)下缸内流场的变化规律进行试验研究,并通过循环分析法对不同的曲轴转角下涡流比以及高、低频湍动能等参数进行分析.结果表明,MVL为1.7,mm在距离上止点不同的测量面上,流动都以大尺度逆时针旋转的强涡流形式存在,并具有较长的保持期.较高的MVL下缸内流场以小尺度双涡结构存在.MVL为1.7,mm各测量平面的涡流比及高、低频湍动能在任一曲轴转角下均高于MVL为4.0,mm和6.8,mm,并且在压缩末期时,MVL为1.7,mm产生湍动能达到MVL为6.8,mm的2倍,有利于直喷汽油机的燃油雾化混合及火焰传播.

PIV system was used to study the change of in-cylinder airflow under different maximum valve lift（MVL）in a 4-valve optical GDI engine and cycle analysis method was used to analyze swirl ratio and fluctuating kinetic energy at different crank angles.Results show that on all the three planes under MVL1.7,mm,the flow is a counterclockwise large-scale swirl with long sustaining time,while the flow is a small-scale two-vortex structure flow under higher MVLs.Swirl ratio and both high and low frequency fluctuating kinetic energies on all planes with MVL,1.7,mm is larger than those under MVL 4.0,mm and MVL,6.8,mm at any crank angle.The frequency fluctuating kinetic energy with low MVL（1.7,mm） is 2 times larger than that with higher MVL（6.8,mm） at the end of compression stoke,and this is beneficial to fuel atomization,fuel-air mixing and flame propagation in GDI engine.