不同喷孔入口的柴油机喷嘴空化特性

Cavitation Characteristics of Diesel Engine Nozzle with Different Nozzle Entrances

柴油在柴油机喷嘴内部流动会直接影响其喷射和雾化,进而影响柴油机的性能和排放.线空化是柴油在喷嘴系统中脱离喷孔壁面后呈现线状形态的特殊空化现象.由于受到柴油机喷嘴真实尺寸的限制,使得燃油流动瞬间变化,同时线空化是随机性发生的,这两个现象使线空化试验的难度大大增加.本试验采用具有可视化记录功能的稳态实验装置,通过固定柴油机喷嘴内针阀升程并控制喷射压力使其全程处于稳定状态,研究不同喷孔入口的柴油机喷嘴在线空化现象中的形态分布特征.研究得出,喷射压力差对线空化影响较大,喷孔内部线空化分布长度与喷射压差呈正相关;此外,喷孔入口处的圆角结构会明显改变线空化在形成过程中的分布特征;几何诱导空化泡可以在涡旋运动的作用下聚集在漩涡中心从而促进线空化的发展;喷孔入口设置倒圆角结构可以明显抑制几何诱导空化和线空化的产生,从而提高柴油机的性能.

The flow of diesel fuel in the nozzle of diesel engines directly affects the fuel injection and atomization,thus affecting the performance and emission of the diesel engines.Linear cavitation is a special phenomenon in which diesel oil flow presents a linear shape after it breaks away from the nozzle wall in the nozzle system.Due to the size limitation of diesel engine nozzles,the fuel flow changes instantaneously and line cavitation is random.These two phenomena make the linear cavitation test more difficult.In this experiment,a steady-state experimental device with visual recording function was used.By fixing the needle valve lift in the diesel injector nozzle and controlling the injection pressure,the whole process was kept in a steady state.The morphological distribution characteristics of the injector nozzle with different nozzle entrances were studied to investigate their effect on linear cavitation.The results show that the injection pressure difference had a great influence on the linear cavitation,and the length of the linear cavitation distribution inside the nozzle hole was positively correlated with the injection pressure difference;furthermore,the fillet structure at the nozzle entrance obviously changed the distribution characteristics of linear cavitation in the development process,and geometrically induced cavitation bubbles gathered at the vortex center under the action of the vortex motion,thus promoting the development of linear cavitation.An inverted fillet structure was set at the nozzle entrance,which could significantly inhibit the initiation of geometrically induced cavitation and linear cavitation,thus improving the diesel engine performance.