可变气门升程与正时对直喷汽油机缸内流动特性的影响

利用CFD三维数值模拟软件模拟了1台缸内直喷汽油机的进气及压缩过程,分析比较了不同最大气门升程及进气正时下缸内流场的变化规律。结果表明:减小最大气门升程可以使进气行程中缸内气体的速度及湍动能显著增加,但在压缩末期的滚流比要略小;在小气门升程下,进气门早开或者晚开都会使得进气过程的湍动能显著增加,在距上止点5mm,10 mm,15 mm的3个横截面上,早开和晚开进气门会使最大平均湍动能分别增加28.29%和43.47%,20.7%和40.81%,23.07%和49.58%,但在压缩后期间,进气门早开或者晚开时对缸内的平均湍动能影响不大;在小气门升程下,进气门的开启时间对压缩末期湍动能的分布有较大的影响,早开或者晚开进气门会使缸内的湍动能趋于一致。

Effects of Variable Valve Lift and Timing on In-Cylinder Flow Characteristics of Gasoline Direct Injection Engine

The intake and compression process for a gasoline direct injection engine were simulated with CFD software and the change law of in-cylinder flow field under different maximum valve lifts and timings was analyzed.The results show that the gas velocity and turbulent kinetic energy significantly increase with the decrease of maximum valve lift in the intake stroke,but the tumble ratio is small at the end of the compression stroke.For a small valve lift,the early opening or late closing of intake valve will lead to the significant increase of turbulent kinetic energy in the intake stroke.Correspondingly,the maximum average turbulent kinetic energies at three cross sections of 5 mm,10 mm,and 15 mm away from TDC increase by 28.29％ and 43.47％,20.7％ and 40.81％,23.07％ and 49.58％ respectively.However,the early opening or late closing of intake valve has little effect on the average turbulent kinetic energy at the end of the compression stroke.In addition,the opening time of intake valve has a great influence on the distribution of turbulent kinetic energy at the end of compression,and the advance or delay of intake timing will promote the homogeneity of in-cylinder turbulent kinetic energy.