Design improvement of a high-pressure fuel pump for gasoline direct injection engines

Gasoline direct injection (GDI) engines, considered to be one of the leading candidates for the next-generation engines of passenger cars, are able to reduce exhaust emissions and fuel consumption radically. The GDI engine requires a high-pressure gasoline supply system that enables the direct injection of fuel into combustion chambers. The high-pressure fuel pump is considered to be one of the key technologies in the development of GDI engines. However, because of the low lubricating ability of gasoline, a wide clearance is needed between the plunger and barrel. This clearance should be wide enough to create hydrodynamic lubrication between the sliding elements. As such, it is difficult to generate the high pumping pressure required in the GDI fuel pump owing to the large amount of leakage flowing through this gap. In this study, an optimum plunger design is presented to maximize pumping pressure in the aspect of flow control. This paper analyses leakage flow characteristics in the clearance of the plunger and barrel in order to improve the pumping performance of GDI fuel pumps. Design parameters have been introduced to maximize pumping pressure in a limited space, and a geometrical optimization has been conducted. Evaluations of pumping performance are determined by the degree of pressure drop in the leakage path assuming a constant leakage flow. Both turbulence and incompressible models are introduced in computational fluid dynamics (CFD) analysis. On the basis of the results of CFD analysis in various geometrical cases, optimum groove depths have been found to generate maximum pumping pressure. This analysis demonstrates that an improvement in plunger design achieves superior pumping pressure over that of conventional pumps.