MAN Diesel, which has been offering one of the most fuel flexible medium-speed power plant arrangements in the liquefied natural gas (LNG) transport sector, has announced it has added fuel sharing capability to its type 51/60DF marine engine for LNG carriers.

The new feature offers operators of LNG carriers the possibility to run the engine, not only in gas or diesel mode, but also on mixtures of gas and liquid fuel – hence the designation “Fuel Sharing mode”.
In other words, shortfalls or fluctuations in the availability of natural boil-off gas (NBOG) from the LNG cargo of a carrier powered by the 1,000 kW per cylinder MAN Diesel 51/60DF dual-fuel engine can be compensated by increasing liquid fuel injection beyond the quantity used by the dedicated pilot fuel injection system. Either heavy fuel oil (HFO) or distillate fuel can be used for this purpose, injected via the main fuel pumps.
MAN Diesel head of sales for LNG and cruise ship applications, Sokrates Tolgos, said the new fuel sharing capability of the 51/60DF engine gave the same level of fuel flexibility as in concepts based on steam turbine generators, but with the advantages of the much higher efficiency of dual-fuel diesel engines at both design point and part-load, much greater redundancy, much greater power flexibility, and lower installation space requirements, which translate into the potential for increased cargo capacity for given vessel dimensions.
The vast majority of today’s LNG projects require ships with cargo capacities in the range of 145,000 m3 – 215,000 m3 with a combined 35 – 45 MW of installed propulsion and onboard electrical power. MAN recommends four or five inline type 51/60DF dual-fuel engines of identical or similar cylinder count instead of an inhomogeneous mix of inline and vee engines to provide the required cylinder count and total power output. As a consequence, the MAN Diesel alternative minimises the drop in the vessel’s available power when an engine is out of service thus enabling the crew to carry out maintenance work on any engine at any time during the voyage.
At 1.5 g/kWh (IMO cycle E2) in gaseous fuel operating mode, the 51/60DF already complies with IMO Tier III limits for NOx by a considerable margin without the need for exhaust gas treatment or any other countermeasures.
The first production 51/60DF dual-fuel engines recently completed their factory acceptance testing at the MAN Diesel works in Augsburg, Germany.