摘要
在可视化缸内直喷(GDI)汽油机台架上,通过进气道入口处翻板和进气道内挡板改变缸内滚流比,使用粒子图像测速技术(PIV)研究了可变滚流对低速条件下喷雾过程的影响,得到喷雾油束的速度场及其对应的剪切应变率和涡量场;进一步通过台架试验,研究可变滚流对燃烧和排放特性的影响.结果表明:翻板和挡板的组合可使缸内较早地形成高强度滚流,滚流比相对于原始状态提高近2倍;高滚流使剪切应变率最大值提高到2,400,s-1,增强了油束内部的剪切作用,涡量最大值也增加到6,000,s-1左右,油束卷吸作用增强,油滴与空气接触面积增大,动量交换加剧,使得喷雾角加大、贯穿距缩短,燃油液滴破碎加剧、蒸发加快,增强缸内油气混合,燃烧放热率增加,燃油消耗率得到改善;高滚流下的CO排放降低,相比低滚流下最大降低32.5%,;但HC和NOx排放增加,相对于低滚流比最大增加54%,和91%,.
In an optical GDI engine, the tumble ratio was controlled by a flap in the manifold and a baffle in the intake port. The effect of in-cylinder air motion on spray was studied by using particle image velocimetry (PIV) at variable tumble ratios. Spray was investigated from velocity field and its corresponding shear strain and vorticity field. Moreover, the influence of variable tumble ratio on combustion and emissions was studied under engine bench test. Results showed that high intensity tumble flow was formed through the combination of flap and baffle with that the tumble ratio is two times higher than the original one. High intensity tumble increases the maximum shear strain rate up to 2400 s-1, enhancing the oil shearing action. Meanwhile, the maximum vorticity increases to about 6000 s-1by rolling up of the airflow. The contact area between spray droplets and air becomes larger, and the momentum exchanges between them contribute to wider sprays cone angle and shorter penetration distance. It accelerates the breakup and evaporation of fuel droplets, promotes the air-fuel mixing process, and improves heat release rate and fuel consumption to some extent. Meanwhile, high tumble ratio can reduce CO emission up to 32.5%, compared with that at low tumble ratio. However, high tumble ratio increases HC and NOxemissions up to 54%, and 91%, respectively. © 2015, Chinese Society for Internal Combustion Engines. All right reserved.
出处
《内燃机学报》
EI
CAS
CSCD
北大核心
2015年第6期502-509,共8页
Transactions of Csice
基金
国家自然科学基金资助项目(51276127)
关键词
缸内直喷汽油机
可变滚流
低速
喷雾
燃烧
Combustion
Diesel engines
Direct injection
Drop breakup
Drops
Engines
Fuels
Shear flow
Shear strain
Spraying
Velocity
Velocity measurement
Vorticity
