不同转速下汽油机缸内湍流特性仿真研究

Simulation Study on Turbulence Characteristics in Gasoline Engine with Different Engine Speeds

应用计算流体动力学理论,针对一款双气门单缸四冲程汽油机,对其在3500r.min-1和5500r.min-1两种工况下的进气、压缩及燃烧过程进行了数值仿真研究。研究结果表明:高转速时的滚流存在曲轴角度比低转速时长,但到达压缩后期滚流都已破碎,挤流成为湍流的主要表现形式;从进气中期到压缩冲程结束,低转速工况缸内湍流平均时间尺度大于高转速工况,在进气末期至压缩初期尤为突出;压缩中期缸内平均时间尺度变化较为剧烈;压缩上止点前20℃A左右缸内平均时间尺度达到谷值;点火时刻两种工况缸内长度尺度最大值均不超过0.46mm,小于火花塞击穿放电后瞬间的火核尺寸,且最大尺度均存在于气缸进气门侧。

The intake, compression and combustion strokes of a two-valve gasoline engine working individually at 3500 and 5500 rpm are diagnosed by using CFD method. The results show that tumble maintain longer with higher engine speed, but both of them have broken up before the late stage of compression, when squish control the flow field ; from the middle stage of intake to the end of compression stroke, mean time scale magnitude with lower engine speed is higher, especially from late intake stroke to early compression stroke; during the middle compression stroke, time scale change sharply; 20℃ A BTDC during the compression stroke, time scale reach the bottom; both the maximum of length scale at ignition time under the two work conditions are less than 0.46mm,which is less than flame kernel size during early development time, and they both exist near the intake valve side.