外开环直喷喷油器在不同燃油过热度下的喷雾特性研究

Spray Characteristics of Outward-Opening Nozzle for DISI Engine in Different Fuel Superheat Degree Conditions

采用平面激光米氏散射和相位多普勒干涉(PDI)等激光测试技术,从宏观与微观两方面对不同燃油过热度下外开环直喷发动机喷嘴的喷雾特性进行了研究。测试燃料选用具有固定沸点和饱和蒸气压的正己烷。宏观特性通过喷雾贯穿距、喷雾角与喷雾宽度进行量化,微观特性主要关注索特平均直径(SMD)与粒径分布。采用环境压力与饱和蒸气压之比(pa/ps)作为衡量过热度的无量纲参数。研究表明:过热度由非闪沸区增大到完全闪沸区,喷雾结构由空锥的"伞"形变为实体的"钟"形。随着过热度的增大,喷雾贯穿距呈现先减小后增大的趋势,拐点发生在pa/ps为0.3附近。喷雾角在过热度较小(pa/ps>0.3)时基本上保持不变;过热度超过一定值(pa/ps<0.3)时喷雾角开始明显减小。SMD与粒径分布也表明:增大过热度,喷雾雾化变好,尤其在过热度由非闪沸过度到完全闪沸区(pa/ps由1.55降到0.11)时,SMD由16.03μm降到7.78μm,DV90由26.05μm降到12.89μm。

Outward-opening nozzle spray characteristics in direct injection spark ignition engine under various fuel superheat degree conditions were investigated using Laser Sheet Mie-Scattering and Phase Doppler Interferometer （PDI）. N-hexane possessing fixed boiling point and saturated vapor pressure was used as surrogate of gasoline. Macroscopic characteristics of the spray structure were measured with spray tip penetration, spray angle and spray width, and microscopic characteristics were indicated by Sauter Mean Diameter （SMD） and droplet size distributions. The ambient-saturation pressure ratio （Pa/Ps） was taken as indicator of superheat degree （SD）. Results show that the spray structure varies from hollow umbrella shape t to ＂solid bell＂ shape when SD increases from non-flash-boiling region to full-flash-boiling region. As pa/ps decreases （SD increases）, the spray penetration variation exhibits decrease-increase trend, and there exists a turning point at about pa/ps=0. 3. The spray angle keeps relatively steady when, and as p./ps〈0. 3 it significantly decreases. SMD and droplet size distribution interpret a fact that increasing superheat degree results in better spray atomization, especially SMD decreases from 16.03 μm to 7.78#m and Dv9o drops from 26.05 μm to 12.89/lm when SD increasing from non-flash-boiling region to full-flash-boiling region （corre- spondingly pa/ps decreases from 1.55 to 0.11）.