引射式EGR系统文丘里管内流动数值模拟分析

Numerical Simulation on Flow in Venturi Tube of EGR System for Turbocharged Diesel Engine

研究了采用文丘里管引射方式的增压柴油机EGR系统及结构,按照增压柴油机EGR系统工作原理,运用CFD-Fluent对文丘里管在不同EGR率引射情况下的内部流动进行了三维数值模拟,对文丘里管内空气与EGR废气形成的混合气的流场状态、速度场、压力场参数进行了分析。计算结果表明:EGR率对文丘里管压缩段前的初始压力恢复效果有较大影响,EGR率引射量越大,压力恢复效果越差,为了满足大EGR率的要求,应减小文丘里管扩压角,混合段喉口直径和EGR引射口直径可以适当增大,引射口的数量也可适当增加。

The method using Venturi tube as EGR system mixer of turbocharged diesel engine was studied. Based on EGR system operating principle, the three-dimensional flow in Venturi tube was simulated under guide-injection condition at different EGR rates using CFD-Fluent to analyze status, velocity and pres- sure in the flow field of EGR gas and air mixture. The numerical simulation results show that EGR rate has an obvious effect on initial pressure recovery before Venturi tube compression section. The more the EGR gas injected, the worse the pressure recovery effect. To meet the need of higher EGR rate, the diffusion angle of Venturi tube should be decreased appreciably, the throat diameter of mixing section, number and diameter of the EGR guide injection orifices should be increased properly.