2 The causes of high pressure pulses in the fuel supply and spill systems
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC/Circular.851 – Guidelines on Engine-Room Oil Fuel Systems – (Adopted on 1 June 1998) - Annex – Guidelines on Engine-Room Oil Fuel Systems - 2 The causes of high pressure pulses in the fuel supply and spill systems

2 The causes of high pressure pulses in the fuel supply and spill systems

  2.1 The most common fuel injection pumps (monobloc or "jerk" pumps) comprise a plunger moving up and down in a barrel which contains ports for fuel to enter and leave. The pump is designed to provide the variable fuel flow required for the engine to operate under fluctuating load or rpm, by adjustment of the plunger delivery stroke. At a point determined by the engine's fuel requirement, the plunger will uncover the ports and the internal pressures of between 800 bar and 1500 bar will be spilled back into the fuel supply and spill piping.

  2.2 Each injection pump action generates high magnitude spill pressures followed by periods of reduced pressure. As a result, maximum pressure differences exist between successive injection pumps in the engine firing order. The pressure differences accelerate columns of fuel within the piping system and when combined with the action of the circulating pump relief valve, can cause cavitation and reflected pressure waves. Cavitation implosions occur quickly, and can induce very short duration pressure pulses in excess of 100 bar.

  2.3 Tests have determined that the magnitude of pressure pulses in the fuel system of a typical medium speed engine installation is greatest at 40% to 60% engine load, and will reach 60 to 80 bar. The pulses are approximately 8 times the nominal pressure of the system. High-speed engines such as those installed on high-speed craft generate higher injection pressures and it is likely that the fuel system will experience correspondingly higher pressure pulses.

  2.4 High pressure pulses lead to vibration and fatigue and are responsible for many failures of equipment such as thermostats, pressostats and mechanical dampers. The failure of fuel lines and their components will invariably involve fatigue and the initiation of fractures due to tensile stress.


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