四气门柴油机缸内流场的LDA试验研究

Experiment Research of In-Cylinder Flow with LDAMeasurement in a Four-Valve Diesel Engine

在一台经过改装的单缸四气门柴油机上,由电机倒拖,使用LDA测量了缸内上部若干测点的速度信号,使用集总平均法对进气和压缩过程中缸内的流场分析计算了涡流的平均流速和湍流强度。结果表明在压缩过程中,从缸心到缸壁,切向湍流强度值大体相同。在压缩过程的初期和中期,缸内流场的切向速度曲线从缸心到缸壁变化较大,存在尖点;在压缩过程的后期、接近上止点位置时,由于挤流的作用,气缸中心的气体旋转角速度较外围明显增大,气缸中的气体分为燃烧室中心的高速圆柱区域和活塞顶上部的低速环形区域。在单进气道工作方式下,只影响进气和压缩初期的缸内流场。

On a reconstructive fourvalve diesel engine dragged by motor,the velocity of upper flowfield is measured with LDA.Mean tangent velocity and tangent turbulence intensity are calculated with the method of Ensemble Average.The result shows that tangent turbulence intensity is nearly the same from the outer to the center of the cylinder in the compression stroke.When the two inlet ports are opened,the tangent velocity varies greatly from the wall to the center in the beginning and midterm of the compression stroke.In the latter half of the compression stroke,the center flow revolves faster than the outer flow because of the squish flow.