交叉孔喷油嘴内部流动特性的模拟

Numerical Simulation on Internal Flow Characteristics of Intersecting Hole Nozzles

为改善柴油机的喷雾特性,提出了交叉孔喷油嘴的结构,其特征是每个喷孔都由两个子喷孔交叉汇聚而形成.为探索交叉孔喷油嘴的内部流动特性,采用双流体模型,对一种圆孔喷油嘴和两种交叉孔喷油嘴在不同条件下的内部多相流动进行了三维CFD模拟.结果表明:交叉孔喷油嘴与常规圆孔喷油嘴内部流场结构有明显的差异,在圆孔喷油嘴中,压力在喷孔入口附近急剧下降,速度急剧上升;而在交叉孔喷油嘴中从喷孔入口到喷孔出口,压力逐渐下降,速度逐渐上升;圆孔喷嘴在空穴数较小的条件下会出现空穴,空穴区可从喷孔入口延伸到喷孔出口,而交叉孔喷油嘴内即使空穴数很小也不产生或只产生微量空穴,后者只在带盲孔扰动区的交叉孔喷油嘴发生;交叉孔喷油嘴的流量系数比圆孔喷嘴的高23%,~32%,.此外,交叉孔喷油嘴的特殊喷孔结构使其内部燃油产生冲击扰动,在喷孔出口产生了更大范围的高湍动能区,有利于促进射流雾化.

The configuration of intersecting hole nozzle, in which each orifice is formed by the converging of two child-holes, was proposed for the improvement of the atomization of diesel engines. To examine the internal flow characteristics of intersecting hole nozzle, the two-fluid model was applied in a 3D CFD package to simulate the internal multi-phase flow in a cylindrical hole nozzle and two types of intersecting hole nozzles. Numerical results show that the configurations of internal flow fields in intersecting hole nozzle are highly different with that in cylindrical hole nozzle. Firstly, for the cylindrical hole nozzle, the abrupt decrease in pressure and abrupt increase in velocity take place within a very short distance downstream the inlet of the hole. However, for the intersecting hole nozzles, the pressure gradually decreases and the velocity gradually increases from the inlet to the outlet of the hole. Secondly, for the cylindrical hole nozzle, cavitation emerges under condition of low cavitation number, and grows from the inlet to the outlet of the hole, while for the intersecting hole nozzles, cavitation hardly emerges or emerges with small amount, the latter case only appears in the intersecting hole nozzle with disturbing domain. Finally, the discharge coefficients of intersecting hole nozzle are 23%-32%, higher than that of cylindrical hole nozzle. Additionally, the internal impulsive disturbances, induced by the unique hole configuration of intersecting hole nozzles, leading to larger high turbulent kinetic energy domain at the cross section of the hole outlet, intensifing the atomization of the fuel jets. © 2015, Chinese Society for Internal Combustion Engines. All right reserved.