高压喷射GDI喷孔几何结构对喷孔内流及喷雾特性的影响

采用大涡湍流模拟结合多相流耦合喷雾的方法对GDI喷孔内流和喷雾特性进行了数值研究,着重分析了喷射压力及喷孔结构形状对喷孔出流特性和液滴粒径的影响。结果表明:提高喷射压力有利于增加喷孔出口流速及湍动能,增强燃油破碎;当喷射压力提高到30MPa之后,进一步提高喷射压力时索特平均直径(SMD)变化不明显,但小粒径占比显著增加;对于变截面喷孔,变截面双曲线喷孔出口处速度和湍动能最大,其SMD最小,小粒径占比最多,有利于喷雾质量提高;与渐缩形喷孔相比,渐扩形喷孔出口处湍动能较大,有利于喷雾初次破碎,然而较多的空泡堵塞喷孔,喷孔出口处流速较低,不利于燃油二次破碎。

Effects of GDI Nozzle Geometry on Internal Flow and Spray Characteristics under High Injection Pressure Condition

The internal flow and spray characteristics for GDI nozzle were investigated by the large eddy simulation (LES) combined with multi-phase fluid and spray method.The effects of injection pressure and orifice geometry on the fluid characteristics and droplet size were mainly analyzed.The results show that the increase of injection pressure is beneficial to increase the flow velocity and turbulent kinetic energy at the nozzle outlet and enhance the fuel breakage.The SMD changes little,but the proportion of small droplet increases significantly when the injection pressure is beyond 30 MPa.The flow velocity and turbulent kinetic energy are the largest,the SMD is the smallest and the small droplet ratio is the most at the exit of hyperbolic orifice with the variable section,which is beneficial to improve the spray quality.Compared with the converging nozzle,the turbulent kinetic energy of expanding nozzle is larger at the outlet,which is beneficial to the initial breakup of spray.However,the more cavities block the orifice so as to the low flow velocity,which is not helpful to the fuel secondary breakup.