The new Wärtsilä 31 engine

The Wärtsilä 31 is the first in a new generation of medium-speed engines, designed to raise the bar, in terms of efficiency and cost of ownership, fuel and operational flexibility, reliability and environmental footprint. With the launch of this new product, Wärtsilä is setting a new standard – leading the way with a 4-stroke engine that offers the best fuel economy in its class.


The marine sector continues to have challenging time with sluggish demand on the dry cargo sector, when again the off-shore sector is suffering from the low crude oil prices when at the same time there is a need to comply with increasingly stricter emission and fuel regulations.

In this challenging time period reduction of lifecycle cost of the investments as well as securing current and anticipated regulation fulfilment is of utmost importance. The marine business also experiences an increased interest in use of different fuels including gas or dual-fuel operation.

The new Wärtsilä 31 engine is developed taking all of these aspects into account to further enhance the business of its owner in regard of reduced lifecycle cost and increased uptime, reduced environmental impact in combination with increased fuel and operational flexibility and with guaranteed reliability and safe operation.

World record for most efficient engine

The Wärtsilä 31 engine has been awarded a Guinness World Records title as the world’s most efficient 4-stroke diesel engine. Guinness World Records is a universally recognised authority on record-breaking achievements, and the listing is based on the engine’s highest-recorded fuel efficiency levels. With the Wärtsilä 31, diesel fuel consumption can run as low as 165 g/kWh – putting it significantly ahead of any other 4-stroke diesel engine currently available on the market. Its exceptional fuel efficiency is made possible through use of new technologies, such as 2-stage turbocharging, a high-pressure fuel injection system and adjustable valve actuation, in combination with the next-generation engine control system.

By utilising the new technologies and optimising the engine parameters, efficiency is improved for all areas related to combustion, as well as thermal, mechanical (including friction and pump losses), and gas exchange efficiency.

Application areas

The Wärtsilä 31 can be used both as a main propulsion engine and in diesel electric configurations, or as an auxiliary engine, and it can be optimised for running either at constant speed, along a propeller curve or with constant torque. It is available in 8 to 16 cylinder configurattions and has a power output ranging from 4.2 to 9.8 MW, at 720 and 750 rpm.

Designed to serve a wide selection of vessel types, the Wärtsilä 31’s application areas include Offshore, Cruise & Ferry, and other marine segments. The engine comes in three alternative versions: diesel, dual-fuel (DF) and spark-ignited gas (SG). The multi-fuel capabilities that the Wärtsilä 31 brings to the market extend the possibilities for operators to utilise different qualities of fuels, from very light low sulphur fuel to very heavy diesel, and a range of different qualities of gas. Furthermore, the Wärtsilä 31 complies with the upcoming IMO Tier 3 regulations when operating on gas or, alternatively, on diesel coupled with a Selective Catalytic Converter (SCR), without resulting in any increase in fuel consumption.

This ground breaking new engine marks the first time that an engine platform has been developed concurrently for all its fuel variants. While previous engines were typically developed to run on diesel and subsequently adapted for gas, they were never fully optimised for the gas or dual-fuel modes. In contrast, the Wärtsilä 31 delivers maximum fuel efficiency and performance across all its fuel variants.

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  • W31_NOR3

New generation common rail fuel system

The unrivalled level of fuel efficiency and operating flexibility achieved by the Wärtsilä 31 is the result of a number of factors. The new-generation, common rail fuel injection system, developed specially for the Wärtsilä 31. The diesel and DF engines both use the exact same fuel injection system with multiple injection capability, thereby facilitating future conversion needs, as no separate pilot fuel needs to be added.

Aside from improved combustion and, therefore, higher efficiency, the benefits of the flexible common rail system include smokeless operation on all loads, as well as reduced particle emissions. The flexibility of the fuel injection result in improved performance – especially for low loads. This is key because many modern applications operate on far lower loads these days. The Wärtsilä 31 can operate on low sulphur fuels, marine diesel oil and HFO, without any restrictions on low load operation, while the DF engine can switch instantly between the different fuel modes independently of the fuel that is utilised.

Second-generation, two-stage turbocharging system

Another key technology is the two-stage turbocharging system. The Wärtsilä 31 utilises the second-generation, two-stage system with a pressure ratio capability above 10 bar and turbocharger efficiency of more than 75%. This improves upon the typical efficiency level of around 65-70% for a single-stage turbocharger. By enabling earlier inlet valve closing, resulting in a lower combustion temperature, the increased pressure ratio capability enables increased engine output, as well improving fuel economy.

The 2-stage concept also offers benefits in terms of operational flexibility, because the reduced inertia of the high-speed turbocharger improves loading performance and load acceptance from low loads. Furthermore, the second-generation, two-stage system has been optimised for minimum downtime through the incorporation of an extractable cartridge concept that facilitates turbocharger overhaul without touching any engine connections.

Adjustable valve actuation

In order to make optimal use of the common rail fuel system and 2-stage turbocharging system, adjustable valve actuation is required. Due to flexible valve actuation, the correct air-fuel ratio is ensured at all engine-operating conditions (in both steady state and transient operation). Meanwhile, control of the inlet valve closure can be set individually on each cylinder – a feature that also can be used to improve cylinder balancing.

In addition, the uptime and availability of the engine is enhanced further due to the fact that the new hydraulic valve actuation does not require periodic adjustment of inlet and exhaust valve clearance. On current engines, this has to be carried out at 1000-hour intervals, as the valve actuation is mechanically controlled.

Environmental footprint

The Wärtsilä 31 engine is optimised to comply with all current and anticipated IMO and EPA (United States Environmental Protection Agency) emission legislations. In gas operation, it complies with IMO Tier 3 and EPA Tier 3 without any need for after-treatment. While the diesel engine requires a SCR after the engine, it does not cause any losses in terms of fuel consumption.

This increased efficiency results in a reduced greenhouse effect, by lowering CO2 emissions, as well as the lower total hydrocarbon (THC) emissions of the gas engine, by up to 50%. The overall operational benefits also include smokeless operation and reduced particle emissions.

Fuel flexibility with modular design.

Operating flexibility

Regarding operational flexibility, the Wärtsilä 31 maintains outstanding performance across its complete operating range. This optimal operating performance is the result of the unique way in which the advanced UNIC engine control system has been combined with state-of-the-art technologies. A similar improvement in fuel consumption is achieved in both low-load running and high load operation. Meanwhile, fast starting and load transient response are improved as a result of the flexibility of the fuel injection and air-fuel ratio control, along with the benefits of the 2-stage turbocharging system.

Reliability & serviceability

With the Wärtsilä 31, maintenance operations and frequencies have been drastically reduced, resulting in significantly improved uptime. The first major overhaul is scheduled at 32,000 hours or 5 years of operations when operating on LFO or gas. While most engines of a similar output require their first maintenance interval after about 2000 operating hours, the Wärtsilä 31 has extended this by a factor of four – to 8000 hours.

When it comes to the all-important question of reliability, the Wärtsilä 31 has been verified and guaranteed through extensive calculations and simulations, utilizing Wärtsilä´s vast field experience of diesel, gas and dual-fuel engines. Rig testing was used for all newly introduced technologies and for the validation of the three laboratory engines and currently more than 30,000 hours have been accumulated altogether on rigs and laboratory engines.

Reliability has also been ensured through the minimisation of maintenance operations. For instance, valve clearance has been eliminated, and new service concepts using exchange units are introduced. One such example is the powerpack unit, which consists of a connecting rod, piston, cylinder liner and cylinder head with related pipes combined in one exchange unit, as opposed to the traditional single spare part concept. Maintenance intervals have also been extended. All this combines to ensure high reliability and fewer maintenance operations, resulting in significantly reduced service costs and increased uptime.

Modular design and future-proof engine

The key factor facilitating the increased uptime of the Wärtsilä 31 is its new modular design. The modular design also makes it possible to carry out fast, efficient engine conversions, as the diesel, DF and SG engine uses the same technologies and components. Furthermore, the standardised component interfaces allow engines to be converted to run on different fuels, without requiring any machining. Modular design does not only facilitate quick repairs, but it also supports future upgrades. Going forward, ship owners will be able to install the latest, state-of-the-art technologies simply by replacing the module containing the upgrade. This will be particularly useful when new emission standards are introduced, but it also may apply to future fuel types. In a world in which it is impossible to predict what new technologies and regulations the future might hold, this is an engine that can be relied on for many years to come – either in its current or upgraded form. This is why the Wärtsilä 31 has become known as the ‘future-proof’ engine.

Facts about Wärtsilä 31

• The most fuel-efficient engine on the market, delivering the lowest level of fuel consumption of any four-stroke engine worldwide
• Fuel flexibility through three different products in one engine platform: diesel, gas and dual-fuel
• Higher uptime, as well as reduced maintenance costs up to 20 per cent, due to longer component lifetime and reduced maintenance operations
• An engine automation system combined with flexibility of the technologies enabling easy adaptation for different operating profiles – leading to outstanding operational flexibility
• Modular design makes service and repairs easier, thus reducing downtime and making the engine “future proof”
• Reliability guaranteed through extensive validation and Wärtsilä’s vast field experience of diesel, gas and dual-fuel engines



STEPLESS VIC – a step towards greatness

As Vincent Van Gogh said, “Great things are done by a series of small things brought together,” and the Wärtsilä 31 is a perfect example of that. It took several new technologies in combination to achieve the engine’s record-breaking fuel efficiency. One of those key technologies, Stepless VIC (Variable Inlet valve Closing), received the Technology & Innovation Award 2015 for its important contribution to Wärtsilä 31’s greatness.

The team behind Stepless VIC, Sören Höstman, Saku Niinikangas, Johan Renvall and Magnus Sundsten, combined several small technical elements to create this technology. The long, iterative process began when Saku Niinikangas invented the basic idea for VIC, a new way of making variable valve timing. However, the team had to create and test many variations and add new innovations before all the technical issues were solved.

Over 50 different ideas were tested on a VIC rig in Vaskiluoto, Finland before VIC became an actual product. At the time, there were only two possible timings, on or off. The first engine equipped with VIC, a Wärtsilä 32, left the factory in 2008. Soon VIC became a standard solution on all Wärtsilä 32 engines.

From good to great

Despite their progress, the team did not quit there. In fast hydraulic systems, pressure pulses are a problem because it is essential to get the same hydraulic pressure in the system in order to get the same behavior, regardless of the engine speed or cylinder configuration. Therefore, the next step in developing the VIC technology further was to try to find a way to achieve consistent pressure.

The idea for Stepless VIC was born at a hydraulic fair in Tampere, where the team heard about the latest in solenoid technology. They learned that they could improve the current VIC product and make the inlet valve closing fully variable, if they put a solenoid valve in parallel with the current solution.

After this discovery, the team made prototypes using this concept, but many more thousands of hours of rig testing and many redesigns of the product still were required before the final product was born. Now Stepless VIC is a standard solution on all Wärtsilä 31 engines and is one of the seemingly small things that enables the Wärtsila 31 engine to achieve its great fuel efficiency.


Press release: first order

Wärtsilä 31

Wärtsilä 31DF 



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