针阀运动规律及其对喷嘴内流和喷雾特性影响

Needle motion and its influence on in-nozzle flow and spray jet characteristics

基于超快X射线成像技术研究了GDI喷油器针阀动力学特性和控制电流信号对针阀运动的影响规律。通过仿真计算分析了GDI喷嘴针阀抬升过程对内流空化现象和近场喷雾射流瞬态特性的影响,研究了针阀横向振动对于孔间不均匀性的影响。实验结果表明,针阀组件达到最大限位及落座时会与铁芯和阀座碰撞产生振荡,不利于喷油量的精确控制,减小控制电流能改善喷油控制精度。模拟结果表明,针阀抬升过程中,燃油在喷孔入口上表面产生空化,导致射流喷雾偏离喷孔轴线,最大偏转角可达到5°左右。喷射过程中喷雾油束的偏转会导致喷嘴沉孔出口位置积油,在燃烧的过程中产生积碳,影响发动机的颗粒物排放。在低针阀升程时,针阀横向振动会导致孔间流速不均匀,而随着针阀升程增加,孔间不均匀度显著降低。

Needle dynamic characteristics and the influence of control current on needle motion about gasoline direct injection(GDI)nozzle were researched based on ultrafast X-ray imaging technology.Transient characteristics of in-nozzle flow and near-field spray jets during needle lift process and effects of cavitation were simulated based on a standard 8-hole GDI nozzle.A real needle motion profile obtained by ultrafast X-ray imaging technology was applied to reflect the influence of needle lateral vibration on holeto-hole non-uniformity.The experimental results show that vibration occurs when needle module collides with iron core in the opening stage and with needle seat in the closing stage,which makes it difficult to control fuel injection precisely.Reduction of control current contributes to less vibration and more precise fuel injection.The simulation results show that cavitation at the upper face of nozzle leads to hydraulic flip phenomenon,so the fuel jet deviates from nozzle axis.Such kind of jet deflection is enhanced by intense entrainment between the jet and the ambient gas,and the maximum deflection angle is up to 5°.The jet deflection will cause nozzle tip wetting at the lower boundary of the contour-bore surface,which will deteriorate the engine particle emissions performance.The study also indicates that the lateral vibration of needle results in non-uniform flow characteristics between different holes,and such non-uniformity decreases as the needle lifts higher.