Wärtsilä 25 - the engine with true fuel flexibility

Wärtsilä 25 is a medium-speed, modular 4-stroke marine engine available in diesel, dual fuel LNG and - now - in dual fuel ammonia version. Learn more about the ammonia engine - visit the Wärtsilä Ammonia Lounge.

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Wärtsilä 25 - the engine with true fuel flexibility

The Wärtsilä 25 is a medium-speed 4-stroke marine engine with a future-proof, upgradeable modular structure that makes it easier than ever for you to target net-zero. Available in cylinder configurations from 6L to 9L and with a power output ranging from 1.7–3.4 MW, the Wärtsilä 25 provides reliable performance whether you are using it as a robust main propulsion engine or as a cost-efficient and flexible auxiliary engine. The engine is available in diesel and dual-fuel versions and now introducing ammonia.

The first 4-stroke ammonia engine

Ammonia will play a big role in the decarbonisation of shipping. One major piece in the puzzle – dual fuel engine technology – has been missing until now.  In 2020, Wärtsilä initiated the world’s first full-scale ammonia engine test, scaled it up and now an ammonia 4-stroke engine is ready to be introduced.

Key benefits of the Wärtsilä 25

  • High power output per cylinder, means fewer cylinders are needed, resulting in a more compact engine
  • Fewer overhauls through prolonged component lifetime - time between overhauls extended by a minimum of 30%
  • Outstanding fuel economy, low emissions, and smoke-free operation at all loads
  • Easily meets IMO Tier III requirements - the diesel engine complemented with an integrated Wärtsilä NOR® NOx reducer
  • Modular design for faster, easier upgrades and conversions to future fuels
  • Perfect for mechanical, diesel-electric and hybrid installations
  • 100% power output from both ends
  • Optimised to run both at both constant and variable speeds

Wärtsilä 25 product video

Expert Interview - Wärtsilä 25

One engine, three versions

The Wärtsilä 25 is perfect for use as a main engine onboard smaller merchant vessels, fishing boats, tugs, dredgers, and offshore support vessels. Whether you are looking for a diesel, biofuel, or dual-fuel engine for your main or auxiliary application, the Wärtsilä 25 is the answer. The Wärtsilä 25 Ammonia engine will help you immediately reduce greenhouse gas emissions by a minimum of 70% compared to a diesel engine.

All engine versions feature common rail, high-pressure fuel injection that enables cylinder-wise combustion control and fuel-injection settings for each operating point.

A future-proof investment

No matter what version of the engine you start with, the upgrade path is secured by the Wärtsilä 25’s outstanding modularity, which future-proofs your investment.

The modular, upgradable design allows you to reduce vessel fuel consumption and emissions from the first mile while providing the readiness to run on alternative fuels whenever viable – all without compromising performance. Whatever future fuel emerges as the most appropriate for your operations, the Wärtsilä 25 is ready for the challenge.

Wärtsilä 25, Wärtsilä 25DF and Wärtsilä 25 Ammonia Product guide and 3D models and drawings

Get technical data and system proposals for designing W25, W25DF and W25 Ammonia marine engine installations.

Customer stories

Discover the benefits others have already gained from Wärtsilä 25 engine.

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