Pressure characteristics of the fuel system for two-stroke diesel engines under different operational modes

Abstract

In this study, the pressure characteristics of the fuel system for two-stroke diesel engines were investigated experimentally. The driving pressure, fuel pressure, injection pressure, and pressure amplification piston (PAP) displacement under different working conditions and modes were tested. The results show that the fluctuation degree of injection pressure is higher than those of fuel pressure and driving pressure despite of the working conditions and modes. The more obvious the injection pressure fluctuation is, the more complex the variation of the PAP displacement. Before the fuel injection starts, the injection pressure peak under different pulse widths of pressure amplification control valve (PACV) for single-valve operational mode is about 83 MPa. The peaks of fuel pressure and driving pressure are relatively low. The variation of PAP displacement is stable. For double-valve operational mode, the injection pressure peak is about 88 MPa before the injection control valve (ICV) is energized when the dwell time is 10 ms. When the dwell time is not less than 20 ms, the injection pressure peak is about 160 MPa. The longer the dwell time is, the more obvious the PAP displacement fluctuates. For a certain working condition, the peaks of fuel pressure and driving pressure are relatively low. For the stable fuel injection stage, the ratio of fuel pressure to driving pressure is closed to the design value of 2.85. The PAP displacement increases almost linearly with time. The fuel pressure is almost 10 MPa higher than the injection pressure because of the frictional loss. After the fuel injection, for single-valve operational mode, the injection pressure and fuel pressure fluctuate very little. The fluctuation of driving pressure varies depending on whether the PAP has reached its maximum position. For double-valve operational mode, the surge of injection pressure after fuel injection could reach about 55.5 MPa. The fluctuation forms after fuel injection of fuel pressure and driving pressure are basically the same as injection pressure, but the fluctuation amplitude decreases gradually. Besides, the moment at which the system pressure and PAP displacement begin to decrease is delayed as the increase of the dwell time.