Effects of Structure and System Parameters on Fuel Leakage Characteristics of Precision Coupling Components in Fuel Injector for Modern Diesel Engine

Increasing rail pressure is the development trend of high-pressure common rail system. When the rail pressure reaches ultrahigh range, fuel leakage of precision coupling components could have a significant impact on system performance. In order to investigate the effects of system and structure parameters on the leakage characteristics of precision coupling components, guide the design of ultrahigh-pressure common rail system, simulations were carried out. Variation of fuel leakage were studied with different structure and system parameters. A three-dimensional model of oil film with eccentric was developed to simulate eccentric between two parts of coupling component. The leakage in control valve component increases with common rail pressure; however, there is no obvious change in leakage of control piston component with rail pressure. Leakage flow rates in both components increased for about 27 times with the coupling component clearance widths increase from 2 μm to 6 μm, due to the increase in flow area and velocity. When the eccentric ratio varies from 0% to 50%, the leakage in both components within single cycle increased by about 37%-38%. Derivation of equation confirms the correctness of analysis on the influence of clearance width and eccentricity on fuel leakage.