1-D SIMULATION OF THE CHARACTERISTICS OF FUEL PRESSURE PULSATIONS AND INJECTED FUEL MASS VARIATIONS CAUSED BY A HIGH-PRESSURE GDI PUMP OPERATION

In general, a GDI (gasoline direct injection) engine uses a single-piston type of high-pressure fuel pump (HPFP) driven by a camshaft. When the HPFP that pressurizes the fuel by a reciprocating piston operates, the pressure of the delivered fuel pulsates. If the fuel rail pressure (FRP) pulsation increases past a certain point, the fluctuation of the fuel injection rate also increases and the parts may be damaged. The FRP pulsation induced by a HPFP was computer simulated. The mitigation effect of the FRP pulsation with an orifice connecting the HPFP outlet and the fuel rail was investigated. Fuel pressure waves at both the HPFP outlet and the fuel rail were simulated according to changes of the opening and closing timing of a PCV (pressure control valve) in the HPFP. The signal-to-noise ratio from the simulated pressure wave was calculated. The fuel injection rate was also simulated. Three cases of fuel rail pressure conditions were used in the simulation: 50, 100, and 150 bar. In addition, four different engine speed conditions were used: 1500, 3000, 4500, and 6000 rpm. Three orifice diameters were also used: 0.75, 1.0, and 1.5 mm. When the PCV opening time came before the TDC and the engine speed was high, the pressure pulsation and injected fuel mass variation were appeared to belarge. When the PCV opening time was later than the TDC, there was no pressure pulsation and little variation in the injected fuel mass for all simulation condition.