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, results in various types of failures within the highly pressurized system. Similar issues are observed in diesel high pressure fuel line where pressure is well above 1600 bar. Due to multiple injections on-off events, pressure pulsation gets created inside high pressure fuel lines (HPFL) which leads to problems such as high strain on high pressure fuel lines, mechanical damage, uneven fuel injected quantity, vibration beyond specification limits for rail pressure sensors or in worst case extreme noise. This is due to high pressure pulsation which occurs when fluid/fuel natural frequency resonates with structural HPFL natural 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 Fast Fourier Transform (FFT) of obtained pressure pulsation signal is used as a 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 and load on pressure pulsation in HPFL.