4气门直喷汽油发动机可变滚流进气系统的试验研究

Experimental Investigation on Flow Field of Variable Tumble Intake System for 4-Valve GDI Engine

针对可变滚流进气系统对直喷汽油机缸内气体流动特性的影响,建立了4气门可变滚流直喷汽油机光学可视化气道稳流试验台,采用粒子速度影像(PIV)技术研究了该进气系统缸内的流场分布。分析了气门开度、滚流阀位置、进出口压力差对缸内竖直平面和水平面速度流场分布的影响,并通过台架试验对可变滚流发动机的动力性和经济性进行研究。研究结果表明:缸内气流主要是绕垂直于气缸轴线的滚流运动;气门开度与整体流速成正比,与脉动速度呈非线性关系,并且在小开度时对流场分布影响较大;滚流阀关闭后,缸内滚流比明显增大,呈现出较强的顺时针方向气流运动趋势;进出口压差对流场分布影响不大,但增大压差能明显提高整体流速;在低速工况下,可变滚流进气系统更有利于提高发动机的动力性和经济性。

Aiming at influence of variable tumble intake system on in-cylinder flow characteristics, an visualized tumble intake port steady flow rig for 4-valve GDI engine was established to study the in-cylinder flow field distribution by using PIV technology. Influences of intake-valve lift, tumble valve position, pressure difference between inlet and exit on the flow velocity fields in vertical and horizontal planes were analyzed. Finally, engine power and fuel economy characteristics were also studied by bench tests. Results show that main movement of the in-cylinder gas is tumble flow around the cylinder axis intake valve opening is proportional to the entire flow velocity, shows nonlinear relation with the fluctuation velocity and influences greatly on the in-cylinder flow in small opening range. When the tumble control valve is closed, the tumble ratio in the cylinder increases significantly and exhibits a strong clockwise direction trend. Pressure difference between inlet and outlet has little effect on the distribution of the velocity field, but its increase can improve the overall flow rate. In low speed condition,the variable tumble intake system is more beneficial to enhance of engine power and fuel economy.