四气门柴油机缸内流场LDA实验数据的分析研究

Analytical Method on In-Cylinder Flow LDA Data in a Four-Valve Diesel Engine

在一台经过改装的105单缸四气门柴油机上,由电机倒拖,使用激光多普勒测速仪(LDA)测量了缸内上部在进气和压缩过程的速度信号,分别使用小波分析法和集总平均法对进气和压缩过程中缸内的流场的平均速度和湍流强度进行了计算比较。小波分析结果中,对不同小波函数及小波分解层数分析结果进行了讨论。结果表明,在进气过程中,各尺度下的湍流强度值均较大,在压缩过程中,湍流强度值减小,使用集总平均法得到的湍流强度值大于小波分析法得到的结果。而且各不同尺度湍流强度变化曲线一致,说明各频段之间能量变化一致。

The in-cylinder flow evolvement process is investigated with the wavelet analytical method and ensemble average method. On a motoring modified four-valve diesel engine, the velocity of upper flowfield was measured with LDA. Mean tangential velocity and turbulent intensity were calculated and compared for the two methods. The analysis results with different wavelet functions are compared and wavelet analysis layers are discussed. The result shows that the turbulent intensity in different scales gives the higher value during the intake process than that during the compression process. The turbulent intensity curves with different scales vary coincidently, indicating the coincident energy transformation. During the compression process, the turbulent intensity with ensemble method is larger than that with the wavelet analysis method.