MAN ES DF ME-GI M/E operation in VLSFO

Hello everybody,

What kind of measures should be taken for MAN ME-GI engines in case of prolonged operation in VLSFO?

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The option to run LNG fueled (DF) Main Engines on VLSFO (without gas injection) is widely considered nowadays due to the increasing LNG price.
MAN ES DF Main Engines can run continuously on VLFSO but operators must take precautions in order not to compromise the lifetime of the dual fuel components and the dual fuel piping of the Main Engines.
Of course, these precautions vary depending on the time that the Main Engine will operate on VLSFO mode only. According to a recent MAN ES recommendation, no actions are necessary for short term VLSFO operation up to two months.
For VLSFO operation from mid-term up to one year, the following actions are recommended:

  • Replace the gas injection nozzles with dummy nozzles without internal borings in order to protect the dual fuel injection valve against exposure to the fuel oil combustion process.
  • Inert the dual dual fuel system of the Main Engine with nitrogen once per week. By introducing nitrogen to a gas tight system the oxygen is removed and the risk of corrosion is eliminated.
    For long-term VLSFO operation, more than a year:
  • Replace the gas injection valves, the window valves, blow off valves, resume valve with dummies.
  • Purge the dual fual system with nitrogen (min.10 bar). Fill the outer pipe with 7 bar control air, to dry out any remaining humidity in the system. After releasing the control air pressure, close valve 831 and 832 to minimize the amount of atmospheric air returning into the system. Use the MOP to release the N2 pressure from the inner pipe and close valve 838 manually.

Before returning to gas injection mode, replace the dummy valves with originals, test their functionality and do leakage tests of inner and outer pipes.

The preservation of the Fuel Gas Supply System is another topic that has to be investigated with the corresponding Makers.

The above information is based on MAN ES SL 2022-722/PXN (publicly available in the MAN ES website) and private correspondence with MAN ES experts.

It is recommended to remain updated on the matter as these recommendations may change in accordance with the in-service experience gained.