四气门发动机进气门相异升程下缸内气体运动稳态特性研究

Study on Steady-flow Characteristics of In-cylinder Air Motion of a 4-valve Engine with Inlet Variable Valve Dissimilitude Lift

利用CFD软件Fluent对某四气门发动机缸内气体流场进行稳态三维数值模拟计算,研究进气门相异升程对缸内气体流场及流通系数的影响。流通系数数值模拟结果和稳流气道试验结果吻合较好。研究结果表明:在不同相异角、相同凸轮轴转角下,发动机进气流通系数变化不大,涡流强度随着相异角的增大而增大;在同一相异角、同一凸轮轴转角、不同缸内横截面上,随着横截面与上止点距离的增大,涡流强度增大,涡心从多个逐渐减少为1个明显涡心,且涡心位置也逐渐发生转移,开始由接近缸壁处转移至汽缸中心附近。

Three - dimensional steady - flow numerical simulation of air flow field in the cylinder of a 4 - valve engine was made by using Fluent, a computational - fluid - dynamic （ CFD ） software, and the influences of inlet valve dissimilitude lift on in - cylinder air flow field and flow coefficient were studied. The flow coefficient simulation results agree well with steady - flow experiment results. The study concludes that the change of engine＇ s inlet flow coefficient is small and swirl intensity increases with the dissimilitude angle when dissimilitude angles are different and cam angles are same; at the same dissimilitude angle and same cam angle but on different in - cylinder cross section, the swirl intensity enhances when the distance between cross section and top dead center increases, and originally several vortex cores reduces to one obvious core, which gradually moves from near the cylinder wall to near the center of the cylinder.