The Wärtsilä 46F (and its dual-fuel sibling the Wärtsilä 50DF) is a large-bore medium-speed four-stroke trunk-piston marine and stationary diesel engine, with a 460 millimetre bore on the diesel-only variant and a 500 millimetre bore on the dual-fuel variant. The engine sits at the upper end of Wärtsilä’s medium-speed portfolio above the W32 and W34DF, and below the now-retired W64. Cylinder configurations range from L6 to V16 with rated outputs from approximately 7,200 kilowatts to 21,800 kilowatts, placing the W46F in direct competition with the MAN 48/60CR.
Cylinder data and outputs
The W46F in current rating produces 1,200 kilowatts per cylinder at 500 to 600 revolutions per minute. Configurations available include L6, L7, L8, L9, V12, V14, and V16, giving an output range of 7,200 to 19,200 kilowatts at 500 revolutions per minute. The 50DF dual-fuel variant produces approximately 950 to 1,000 kilowatts per cylinder in gas mode and slightly higher in diesel mode, with the same configuration range.
The 46F generation is the latest evolution of the 46-series engine family that traces to the original Wärtsilä 46 introduced in the early 1990s as the company’s response to growing cruise ship and FPSO demand. The 46F includes upgraded fuel injection, two-stage turbocharging on certain ratings, miller-cycle valve timing, and a redesigned cylinder head and piston ring pack to support brake mean effective pressures above 25 bar.
50DF dual-fuel and tri-fuel variant
The Wärtsilä 50DF is one of the most widely deployed dual-fuel marine engines in the world, with thousands of cylinder-units in service across LNG carriers, FPSOs, and large LNG-fuelled cruise vessels. The engine operates on:
- Heavy fuel oil, marine diesel oil, marine gas oil, low-sulphur fuel oil in conventional diesel cycle.
- Liquefied natural gas in lean-burn Otto cycle with a small diesel pilot.
- Boil-off gas from LNG cargo tanks, allowing LNG carriers to consume their natural cargo boil-off as fuel without venting.
In gas mode the engine meets IMO Tier III without aftertreatment. The 50DF has been a workhorse of the LNG carrier propulsion market since 2003 and a key enabler of the modern dual-fuel-electric LNG carrier configuration where four 50DF gensets feed a podded propulsion system.
Applications
The W46F and 50DF are concentrated in the largest power-density applications:
- LNG carrier main propulsion via dual-fuel-electric configurations (the 50DF is the dominant engine choice in the post-2003 LNG carrier fleet alongside MAN’s competing 51/60DF).
- Cruise ship integrated power plants for vessels above 100,000 gross tonnes, where four to six L9 or V12 units supply propulsion and hotel loads.
- FPSO main power generation in deep-water Brazilian, Gulf of Guinea, and North Sea fields.
- Naval auxiliary ships and amphibious vessels.
- Large stationary power plants in the 50 to 500 megawatt range, particularly in regions with stranded gas or LNG terminal availability.
Service network
The W46F and 50DF are supported globally by Wärtsilä Lifecycle services, with major service hubs in Singapore, Rotterdam, Houston, Pori, and Trieste. Engine condition monitoring through Wärtsilä Expert Insight is widely adopted on cruise and LNG fleets where unplanned downtime carries high commercial cost.