Research On Sealing Performance Of Needle Valve Assembled In High Pressure Common Rail Fuel Injector

Needle valve assembly is one of the precision pairs of high pressure common rail injector. When fuel pressure increases, the needle valve assembly pairing clearance gets deformed and easily brings the problem that fuel leakage increases or needle stucks, causing the abnormal operation of engine. The sealing performance of needle valve assembly has become an issue had to be taken into account, about improving the injection pressure of high pressure common rail injection system.This paper introduced high pressure common rail injectors’ working principle and important operating characteristics in detail. With the application of lubrication and tribology principle, an analysis of lubrication and sealing mechanism of needle couples was made, and two important sealing parts of needle couples pointed were the clearance oil film and sealing cone respectively. With simulation of the clearance oil film by Fluent software, this paper analyzed the influence of needle couples structural parameters and fuel injector’ key parameters to the needle couples’ sealing performance. With contact simulation of sealing cone by Mechanical APDL software, the contact stress distribution around sealing cone in collision and the influence of sealing band width to the sealing cone’ sealing performance was analyzed.FSI simulation of needle valve assembly was made by ANSYS Workbench and the results indicated that two-way FSI made a more accurate calculation of needle valve assembly deformation’ effect on the sealing performance of needle couples. It analyzed the clearance oil film thickness distribution and variation of the leakage rate under different fuel pressures. In order to improve the sealing characteristics of needle couples, six different structural schemes with annular groove machined on the needle oil film sealing surface was presented. Through analysis and comparison, it found that the annular groove could improve the sealing and lubrication properties of needle couples, and the sealing effect was closely related with the location and number of the annular groove.The testing program and equipment was designed to measure the sealing performance of needle valve assembly.The leakage rate law obtained by test, simulation and analytical method respectively were analyzed and compared. The results showed that leakage rate calculated by two-way FSI was most correspond with the test value. Needle valve assembly with annular grove structure was tested. The results showed that annular groove structure did improve the sealing characteristics of needle couples, and the relationship between annular groove’s position and the sealing effect was obtained. At the same time the impact of needle couples with annular groove on the fuel injector’s fuel supply performance was tested, and some suggestions about such needle couples’ application was introduced.Combining with the simulation and experiment, this thesis analyzed the influence of injection frequency, injection pulse width and nozzle tightening torque on the sealing performance of needle valve assembly. Through the study of these parameters which affect the sealing performance of needle valve assembly, it provided a theoretical basis of the needle valve assembly’s optimal design and fair use.