基于多种光学诊断的汽油直喷喷油器喷雾特性试验研究

Experimental Investigation of GDI Injector Spray Characteristics Based on Multiple Optical Diagnostic Methods

缸内直喷汽油机的喷雾特性在很大程度上决定了后续的混合气形成、燃烧及排放性能,利用光学诊断对汽油喷雾进行系统测试,可以获得喷雾一系列宏观和微观特征,对于优化燃烧、降低排放具有重要意义。对一款商用5孔GDI喷油器进行了系统的光学诊断,利用高速背光摄影、平面Mie散射高速摄影、相位多普勒干涉仪分别测量了喷雾形态、落点和粒径,并分析多种复杂的热力学边界条件(燃油喷射压力、环境背压和喷油脉宽)对喷雾特性的影响。研究表明:增加燃油喷射压力,喷雾落点分布更集中,更早发生喷雾干涉,喷雾贯穿距也随之增大,喷油锥角在喷雾初期增加较多,在喷雾后期几乎没有变化,粒径10μm以下的颗粒数量占比更大,雾化更好;增大背压,喷雾落点分布更分散,喷雾发生干涉的时刻更晚,喷雾粒径增大,粒径10μm以下的颗粒数量占比更小,雾化更差;喷油压力和背压的变化对粒径60μm以内的喷雾颗粒数量影响不大;增加喷油脉宽,喷雾落点分布更集中,更早发生喷雾干涉。

The spray characteristic of gasoline direct injection(GDI)injector strongly determines the subsequent fuel/air mixture formation,combustion and emissions.Systematic measurement of gasoline spray using the optical diagnostic method can obtain the macroscopic and microscopic characteristics of spray that are important to optimize combustion and reduce emissions.For a commercial 5-hole GDI injector,the high-speed diffused back-illumination photography,the planar high-speed Mie scattering photography and the phase Doppler interferometry(PDI)was respectively utilized to get the spray image,pattern and droplet size.Besides,the influences of thermodynamic boundary conditions including injection pressure,ambient back pressure,and injection duration on spray characteristics were analyzed.The results show that the increased fuel injection pressure would lead to a more concentrated spray pattern,earlier occurred spray plume interaction,longer penetration,larger spray angle in the early stage and more droplets with the size of smaller than 10μm,and hence better spray effect.Increased back pressure had a worse spray effect due to the completely opposite influencing law.The influence of injection pressure and back pressure on the number of particles smaller than 60μm is negligible.Increased injection duration would also lead to a more concentrated spray pattern and earlier plume interaction.