LNG carriers are in principle large bulk carriers for liquid cargo, which differ from other such vessels by (1) having a cargo that needs a continuous boil off to keep it in the desired physical state, and by (2) operating at a somewhat higher speed.

Traditionally such vessels have been powered by steam turbines, for example by steam generated by burning the boil off gas, but which due to their inherent low efficiency have become extinct for all other kind of vessels.

For this reason of efficiency alternative solutions have now being developed, such as

  • Dual fual medium speed diesel electric

  • Dual fuel direct coupled low speed diesels

  • Heavy fuel direct coupled low speed diesels installed with reliquefaction.

This paper will discribe technically and discuss the proposed options 2 and 3 and show how these can be combined to give the owner and operator the possibility to use fuel and/or gas at random as dictated by the prevailing economical environment.

The particular advantage of the low speed duel fuel high pressure gas injection engine of being able to operate at any ratio of oil and gas will be highlighted.

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