可变滚流GDI发动机缸内气体流动特性模拟研究

Simulation Research on the In-Cylinder Flow Characteristics in a GDI Engine with Variable Tumble Ratio

在一台可变滚流比直喷汽油机(GDI)上对不同滚流强度下缸内冷态湍流流场进行了数值模拟研究,并通过PIV结果进行了实验验证。研究结果表明:进气翻板关闭将显著提高缸内滚流强度并产生较强的湍流,尤其在气门升程最大时刻,其滚流比约为翻板开启时的5倍,湍动能为后者的4倍左右;缸内流场在高滚流比工况时较早地形成单一大尺度涡,同时涡心更明显,流场更加规则,流速相对较高,在进气下止点时平均流速为20m/s;在压缩过程中,高滚流比工况湍流的黏性耗散较大,湍动能衰减较快;但在压缩末期缸内湍动能较低滚流比工况高,同时分布更加均匀。

The turbulent flow field was studied in a variable tumble ratio Gasoline Direct Injection（GDI） for different intensities of the cylinder tumble under cold state and verified by PIV results using numerical simulation.The results showed that：the intake flap closed cylinder will significantly increase the strength of the tumble and generate a strong turbulence.In particular the maximum valve lift time,the tumble ratio is approximately five times of the opening-plate condition,and turbulent kinetic energy about 4 times of the latter;cylinder flow field forms a single large-scale vortex at high tumble ratio condition earlier,while the vortex core is more obvious,flow field more regular,flow velocity more high up to 20 m /s.During compression,turbulent viscosity dissipates rapidly under tumble conditions,turbulent kinetic energy（TKE） decay faster,but at the end of the compression turbulent kinetic energy is more uniform and higher compared to low tumble ratio condition.