【作者】 刘芬；

【导师】 黄荣华；

【作者基本信息】 华中科技大学 ， 动力机械及工程， 2012， 硕士

【摘要】 喷雾结构决定了燃油分布及混合气的形成，对燃烧的好坏有直接影响，因此喷油器是GDI系统中非常关键的部件，而喷嘴内部的空化现象对雾化有着本质的影响。这主要表现在空化现象极大的影响了喷嘴出口处的速度、流量、和湍动能的分布，这些都与喷雾的初次破碎密切相关，因此喷嘴内部流动又是GDI发动机设计中必须要考虑的因素。理论和试验研究都表明：高压喷射的柴油喷嘴内部容易形成空化，而近年来有学者在研究中发现GDI多孔喷油器在喷射过程同样会产生空化现象，与柴油喷嘴相比目前对这GDI喷嘴内的空化现象的研究尚还不够深入。由于空化是一个不稳定的气液两相流动，而喷嘴的结构又决定了很难直接通过试验的方法观察喷嘴内部流动的情况，因此数值模拟成为喷嘴内部流动研究的重要手段。本文采用双流体法模拟了针阀位于最大升程和针阀运动时的喷嘴内部流动特性。计算预测了针阀在最大升程时喷孔内部是否会发生空化现象，并分析了喷孔内流动的不均匀性。同时，还研究了针阀运动对喷嘴内流的影响，以及喷孔内的空化发展规律。此外还输出了针阀运动时喷孔出口的流动信息，为后续的喷雾计算提供更准确地边界条件。课题组有两位师兄采用正交设计法研究了4种不同型号的喷油器在不同的喷射压力、喷射背压、定容室温度，以及不同碰壁角度和喷油脉宽等条件下的喷雾结构与粒径分布。本文将其中一种喷油器的试验数据作为数值计算的标定值，并采用离散液滴模型模拟了喷雾过程。计算中通过定义不同的初次破碎模型来导入喷嘴内流的计算结果，由此分析喷嘴内流对喷雾特性的影响。更多还原

【Abstract】 The spray structure determines the fuel distribution and mixture formation, andthen has a direct impact on the combustion, so GDI injector is a major component ofthe GDI combustion system. Furthermore the spray is essentially affected by thecavitation phenomenon inside the nozzle holes. The phenomenon of cavitation mainlyhas a great impact on the velocity, mass flow, and turbulent kinetic energy distributionat the nozzle exit. The cavitation is the one of dominant factors causing primarybreakup, so the internal nozzle flow must be considered in the design of GDI engine.Theoretical and experimental studies have both proved that: high-pressure dieselinjection nozzle is easy to form cavitation. In recent years, some scholars find that GDImulti-hole injector will also have cavitation in the injection process. Compared todiesel nozzle, the study of the cavitation inside the GDI nozzle is still not enoughcurrently. As the nozzle flow is an unstable gas-liquid two-phase flow, and the nozzlestructure also impedes the experiments to observe the nozzle flow directly, so thesimulation become an important research method of internal flow.This paper using two-fluid method simulate the internal flow of GDI multi-holeinjector at the maximum needle lift, besides the results predict whether or not thecavitation would occur and discuss the uneven flow between the six nozzle holes. Thestudy on cavitation distribution inside nozzle with needle valve lift movement is alsoput on. At the same time, the data of the internal flow calculation with needlemovement is gained and will be used as a boundary condition for the subsequent spraycalculation. The data contains the values of the liquid velocities, densities and theturbulence quantities at nozzle’s outlet. During the spray simulation, the data isintroduced by using different initial breakup model and the effects of internal flow onspray characteristics are also been analyzed qualitatively.更多还原