Vortex flow and cavitation in diesel injector nozzles
Vortex flow and cavitation in diesel injector nozzles
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DOI：
10.1017/s0022112008002668
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发表时间：
2008-09-10
影响因子：
3.7
通讯作者：
Arcoumanis, C.
中科院分区：
文献类型：
--
作者：
Andriotis, A.;Gavaises, M.;Arcoumanis, C.
流动可视化以及三维空化流模拟已被用于表征在低速二冲程柴油机中使用的喷油器阀的透明复制品内的空化的形成。测试的设计已纳入五孔喷嘴与圆柱形以及锥形孔在不同的固定针升降位置操作。高速图像显示了喷嘴体积内喷射孔上游的不稳定蒸汽结构的形成，这被称为“弦状空化”。流量分布的计算以及喷嘴体积内弦线位置的三维重建表明，弦线位于再循环区的核心;它们源自喷嘴内部尖角处形成的预先存在的气穴部位，此处压力福尔斯低于流动液体的蒸汽压力，或者甚至源自孔出口下游的外部空气的抽吸。所获得的图像的处理已允许估计的平均位置和概率的出现在三维空间中的空化字符串作为针升力，空化和雷诺数的函数。出现的字符串的频率已与斯特劳哈尔数的旋涡内的囊体积的发展，后者已被发现是针升降机和孔的形状的函数。串的存在显著影响了喷嘴出口处的流动条件，从而影响喷射喷雾。喷射孔内形成的空化结构由于空化串的存在而显著改变，并且共同导致瞬时燃料喷射量的高达10%的变化。外推使用模型预测的实际尺寸的注射器在现实的注射压力下运行表明，空化字符串预计将出现在典型的注射事件的时间尺度内，这意味着显着的孔到孔和周期到周期的变化，在相应的喷雾发展。
Flow visualization as well as three-dimensional cavitating flow simulations have been employed for characterizing the formation of cavitation inside transparent replicas of fuel injector valves used in low-speed two-stroke diesel engines. The designs tested have incorporated five-hole nozzles with cylindrical as well as tapered holes operating at different fixed needle lift positions. High-speed images have revealed the formation of an unsteady vapour structure upstream of the injection holes inside the nozzle volume, which is referred to as '"string-cavitation'. Computation of the flow distribution and combination with three-dimensional reconstruction of the location of the strings inside the nozzle volume has revealed that strings are found at the core of recirculation zones; they originate either from pre-existing cavitation sites forming at sharp corners inside the nozzle where the pressure falls below the vapour pressure of the flowing liquid, or even from suction Of outside air downstream of the hole exit. Processing of the acquired images has allowed estimation of the mean location and probability of appearance of the cavitating strings in the three-dimensional space as a function of needle lift, cavitation and Reynolds number. The frequency of appearance of the strings has been correlated with the Strouhal number of the vortices developing inside the sac volume; the latter has been found to be a function of needle lift and hole shape. The presence of strings has significantly affected the flow conditions at the nozzle exit, influencing the injected spray. The cavitation structures formed inside the injection holes are significantly altered by the presence of cavitation strings and are jointly responsible for up to 10% variation in the instantaneous fuel injection quantity. Extrapolation using model predictions for real-size injectors operating at realistic injection pressures indicates that cavitation strings are expected to appear within the time scales of typical injection events, implying significant hole-to-hole and cycle-to-cycle variations during the corresponding spray development.