main engine · propulsion system

Wärtsilä 46DF

The Wärtsilä 46DF is a dual-fuel, four-stroke, medium-speed marine engine, one of the best-known engines in the class of machinery that can run either on natural gas or on conventional liquid marine fuels. The DF in its name stands for dual fuel, and this flexibility is the engine's defining feature: it can operate in gas mode, burning natural gas as its main fuel with a small pilot injection of liquid fuel to ignite the charge, or switch to running entirely on marine diesel oil or heavy fuel oil, and it can transfer between the modes while running. In gas mode the engine works on the lean-burn Otto principle, mixing gas with a large excess of air and igniting it with the pilot fuel, which gives very low emissions of sulphur oxides, nitrogen oxides and particulates compared with a conventional oil-burning engine, helping ships meet the requirements of emission control areas and the global sulphur cap. This makes dual-fuel engines like the 46DF a leading choice for LNG carriers, which have gas available from cargo boil-off, and for cruise ships, ferries and other vessels adopting LNG as a cleaner fuel. As a medium-speed engine it runs faster than the low-speed two-stroke engines used for direct propulsion of large ships, and it is applied both as a main engine, often driving through a gearbox or as part of a diesel-electric power plant, and as a generating set. In a diesel-electric or dual-fuel-electric arrangement several such engines drive alternators feeding a common electrical system that powers propulsion motors and the ship's services, giving flexibility and redundancy. The 46DF represents the shift in marine propulsion toward cleaner-burning gas and dual-fuel machinery, and toward integrated electric power systems, as the industry works to reduce the environmental impact of ships while retaining the security of being able to fall back on liquid fuel.