GDI喷油器超高压乙醇喷雾微观特性试验
Experimental on Microscopic Spray Characteristics of GDI Injector Fueled with Ethanol Under Ultra-High Injection Pressure

为系统研究超高喷射压力下缸内直喷(GDI)喷油器乙醇喷雾的微观特性, 采用相位多普勒粒子分析(PDPA)系统对10～50 MPa喷射压力下的喷雾进行了测试, 并结合纹影法所获取的喷雾图像分析了喷雾形态发展、液滴粒径粒速的空间分布及随时间的变化规律．研究结果表明：提高喷射压力, 枝状结构形成时刻提前, 喷雾破碎过程加快; 提高喷射压力, 喷雾头部粒速增加, 贯穿距变大; 喷雾锥角随喷射压力的提高小幅度上升; 提高喷射压力, 乙醇液滴的索特平均直径(SMD)、DV90和DV50明显下降, 但DV10下降幅度相对较小, 处于剧烈破碎区的液滴粒径减小; 超高压喷射有效抑制了25 μm以上大粒径液滴生成, 降低粒径分布的离散程度, 粒径为5 μm左右的液滴数量比例最大; 超高压喷射下, 在同一水平面不同测点位置, SMD的差异较小; 随着测点距喷孔距离的增大, 小液滴聚合现象会导致SMD变大．
To systematically study the microscopic spray characteristics of gasoline direct injection(GDI)injector fueled with ethanol under ultra-high injection pressure conditions，spray experiments were carried out using phase Doppler particle analyzer(PDPA)with injection pressure ranging from 10 MPa to 50 MPa. The change regulations of spray structure，droplet diameter and velocity in both space and time were analyzed with consideration of the spray images photographed by schlieren method. The results show that as injection pressure increases，branch-like structures’ occurring time decreases，and break-up and atomization processes are enhanced. Droplet velocity of spray head and penetration distance increase with the increase of injection pressure，and spray angle increases slightly. With increasing injection pressure，Sauter mean diameter(SMD)，DV90 and DV50 of ethanol droplets decrease obviously，but the decrease of DV10 is relatively small，and the droplet diameter of catastrophic break-up regime decreases. Under ultra-high injection pressure，the amount of large droplets whose diameter exceed 25 μm decreases obviously; the dispersion of the diameter reduces; the peak of diameter distribution appears around 5 μm; and the variation of SMD is relatively low at different transverse measurement points. Small droplet coalescence makes SMD larger with the increase of distance along the plume axis