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柴油机喷雾本身有大量的波动,它们指的是喷雾中浓度和速度的波动。这些波动促进了空气的流动,也促进了形成燃烧混合物的波动的扩散过程。为了更好地了解柴油机喷雾,有必要研究波动特性。为了研究喷雾过程中初始波动对喷雾特性的影响,在此项研究中使用两级喷射的柴油机喷雾。改变两级喷射的喷油停顿时间能很容易地控制喷雾过程的初始波动范围。首先研究喷油停顿时间对内部流动和破裂长度的影响,其次通过在两级喷射时较短停顿时间的特殊情况来估算普通柴油机喷雾时的破裂长度。进而,用快速傅里叶变换算法(FFT)来分析由于两级喷射所形成的喷雾波动过程的自相关和互相关。混合过程的特征长度可通过将其作为喷雾过程中的相关长度来求得。最后,喷雾时的内部破裂长度要比由喷雾头部的贯穿度所求得的破裂长度长30％。最小相关长度总是与喷雾时的破裂长度一致的。最大相关长度大约80mm。这样由喷射控制所形成的喷雾过程的最大波动只能保持在距离油嘴头部80mm范围内。换句话说,喷雾涡流即便非常强,最多也只能持续3ms。
Diesel engine spray itself has a lot of fluctuations, they refer to the spray concentration and velocity fluctuations. These fluctuations promote the flow of air and also promote the process of dispersion that creates fluctuations in the combustion mixture. In order to better understand the diesel engine spray, it is necessary to study the fluctuation characteristics. In order to investigate the effect of initial fluctuations on spray characteristics during the spraying process, a two-stage injection diesel engine spray was used in this study. Changing the two-stage injection pause time can easily control the initial fluctuation range of the spray process. Firstly, the effect of injection pause time on internal flow and rupture length is studied. Secondly, the rupture length of common diesel engine spray is estimated by the special case of short pause time at two-stage injection. Further, the autocorrelation and cross-correlation of the spray fluctuation due to the two-stage injection are analyzed using a Fast Fourier Transform (FFT) algorithm. The characteristic length of the mixing process can be determined as the relevant length of the spraying process. Finally, the internal rupture length at spraying is 30% longer than the rupture length determined by the penetration of the spray head. The minimum correlation length is always the same as the rupture length of the spray. The maximum correlation length is about 80mm. The maximum fluctuation of the spray process thus formed by the injection control can only be maintained within 80 mm from the nipple head. In other words, even if the spray vortex is very strong, it can only last for 3ms.