Vibration modelling of high-pressure fuel lines driven by pressure pulsation.

When the flow of fluid within a high-pressure line is abruptly halted, pressure pulsations are generated. This phenomenon is known as the water hammer effect. This may lead to significant stress and, in the worst-case scenario, result in various types of failures within the highly pressurized system. Similar issue is observed in diesel high pressure fuel line where pressure is well above 1600 bar. Due to multiple injection on off event, pressure pulsation gets created inside high pressure fuel lines (HPFL) which leads problems such as high strain on high pressure fuel lines, mechanical damage, uneven fuel injected quantity, vibration beyond specification limits for rail pressure sensor or in worst case extreme noise. Due to pressure pulsation, fluid will have its own natural frequency, and resonance occurs when it interacts with structural frequency. In this work, A comparative FEA analysis is conducted to evaluate strain in two distinct high-pressure fuel lines, with pressure pulsation serving as the forcing function. Pressure pulsation inside HPFL is obtained from hoop strain gauges. As high-pressure fuel lines are the thick-walled cylinders, pressure inside HPFL can be calculated using Lame’s equation of hoop stress in thick-walled cylinder. This obtained pressure pulsation signal is calibrated to account for variation due to autofrettage, temperature compensation, etc. The FFT of obtained pressure pulsation signal is used as forcing function for harmonic analysis and comparative assessment is done between two distinct lines. Also, the intensity and frequency of pressure pulsations can vary depending on engine speed, load conditions, and design of the fuel system. A sensitivity study is performed to check the impact of speed, load on pressure pulsation in HPFL.