Metal Bellows Accumulators for Heavy Diesel Engines
In the fuel injection system of heavy diesel engines (e.g. marine engines and engines for power plants / two and four-stroke), pressure fluctuations are generated during the injection process by the high pressure pumps.
In most heavy diesel engines each cylinder has its own injection pump. During the phases of fuel extraction from the supply line, compression and injection as well as the release of unused fuel into the return line, cyclic pressure pulsations can result.
The supply line and the return line are at a lower pressure than that required for fuel injection and in such dual-pipe systems the above-mentioned pressure fluctuations can cause problems, depending on the size of the pressure variations. It is for this reason that superimposed pressure fluctuations from 0 to approx. 13 bar can occur in a 4.5 bar return line (see the graph, point 2). In other systems pressure peaks of over
50 bar have been measured.
This fluctuating pressure with its unacceptable pressure peaks not only creates an additional stress on the pipe system but also an additional load for all integrated fittings and equipment. Valves, filters, measurement and monitoring devices, e.g. viscosity meters, … can be
seriously impaired or damaged, sometimes even irreparably.
Until now a standard method for reducing or eliminating the pulsations has been to use hydraulic accumulators with nitrogen as the damping element and an elastomer diaphragm or bladder as the separating element between the gas and the fuel. The best damping results may be obtained by installing one damper in the supply line and one in the return line as close as possible to the engine. However,
such standard diaphragm and bladder accumulators have two main limitations: