INFLUENCE OF PRESSURE OSCILLATIONS IN COMMON RAIL INJECTOR ON FUEL INJECTION RATE

Fuel injection causes considerable oscillations of fuel pressure at the injector inlet. One of the reasons is hydraulic impact when the needle valve closes. For multiple injections, the previous injections affect the following. As both the fuel pressure in rail p(ac) and the injection rate grow, the oscillations increase. The pressure oscillation range at the common rail injector inlet at p(ac)=1500 bar is up to 350 bar, and at the rail pressure p(ac)=500 bar, the amplitude decreases to 80 bar. Physical properties of the fuel are also important. As the viscosity of the fuel increases, its hydraulic friction grows which results in a rapid damping of pressure oscillations. The data for an injector operating on sunflower oil is presented. As compared with diesel fuel, the oscillations range decreases from 400 to 250 bar at the same operating mode. The influence of the interval between the impulses of a double injection on the injection rate of the second fuel portion was investigated. Superposition of two waves during multiple injections may result in amplification and damping of the oscillations. Simulation was performed to estimate the influence of fuel type and time interval Delta tau between control impulses of a double injection on the injection quantity of the second portion at pressures of 2000-3000 bar. When the rail pressure p(ac) grows, the oscillations and their impact on the injection process increase. For diesel fuel at pressure of p(ac)=2000 bar, the variation in injection rates of the second portion is 2.36-4.62 mg, and at p(ac)=3000 bar - 1.58-6.63 mg.