内燃机瞬态缸内流场空间特性的研究

Study on Spatial Characteristics of the In Cylinder Flow Field in an I.C.Engine

本文应用空间滤波处理等数学方法分析了通过激光粒子图像测速技术实测的内燃机缸内瞬态流速场，结合通过流速场的数值微分而求得的瞬态缸内空间涡量场等实验结果，对瞬态内燃机缸内流场特性进行了探讨研究。结果表明，在压缩和膨胀过程中，缸内瞬态流场有相当大的随机性。一般地，瞬态低通滤波流速场基本上为一大涡流，但涡心多为一个区域，周边流速大小变化缓慢。而高通滤波后的流速场，呈现出很复杂的分布，流速场中存在许多空间随机分布而强度不等的局域涡，流速场的空间平均动能与曲轴转角很明显地存在一定的关系，随着曲轴转角的增加，动能衰减，但高通分量衰减得相对较慢。在活塞上有凹坑形燃烧室时，挤流和逆挤流作用显著地影响缸内流场。

In this paper,in cylinder flow fields in a four stoke engine were studied experimentally by instantaneous measurements of swirl flow velocity distribution with particle image velocimetry (PIV) and analytically by spatially high and low pass filtering techniques.Vorticity distributions were also calculated through the measured data.Vortex structure of the flow field was clearly visualized and the repeatability of the swirl flow velocity distribution at same conditions was found very poor,i.e.cycle variation was large.Spatially low pass filtered velocity field was found usually like a large scale vortex but with a quite large central area and with a quite averaged speed distribution far from the central area.Spatially high pass filtered velocity distribution showed many sub scaled local vortex randomly distributed in the flow field.In cylinder flow energy was found decaying at high rate but the sub scaled flow components at lower rate.Squish was found strongly affecting the swirl flow field.