Wärtsilä 31SG

The Wärtsilä 31SG is the first of a new generation of  pure gas medium speed engines, designed to set a new benchmark in efficiency and overall emissions performance in connection with Hybrid solutions.

The development of this engine is a direct result of Wärtsilä's on-going commitment to reduce the greenhouse gas emissions of its gas engines by 15%, by 2020 (from 2015 levels).

The Wärtsilä 31SG is available in 8 to 16 cylinder configurations and has a power output ranging from 4.2 to 8.8 MW, at 720 and 750 rpm. The launch of the Wärtsilä 31SG introduces a 4-stroke engine having the best fuel economy of any engine in its class. At the same time, it maintains outstanding performance across the complete operating range. Its modular design enables a significant reduction in maintenance time and costs, thereby improving power availability and reducing the need for spare parts.

    The Wärtsilä 31 retains its high efficiency and environmental values throughout the entire lifecycle of the vessel.
    • Available in Diesel, Dual Fuel (DF) and Pure Gas (SG) versions.
    • Lowest fuel consumption over a wide operating range.
    • Highest cylinder power in its segment, 610 kW/cylinder (Diesel).
    • Full output available for a broad range of gas qualities down to methane number 70 (DF & SG).
    • Meets the coming IMO Tier 3 regulations when operating on gas, and with an SCR when using diesel fuel. The SCR has a minimal effect on fuel consumption.
    • Reliability guaranteed through extensive validation and Wärtsilä’s vast manufacturing experience.
    • Supported by Wärtsilä’s extensive global service network.
    Technical data
    Wärtsilä 31SG IMO Tier III
    Cylinder bore 310 mm   Gas: Methane number ³ 70
    Piston stroke 430 mm   BSEC 7243 kJ/kWh
    Cylinder output 550 kW/cyl  
    Speed 750 rpm    
    Mean effective pressure 27.1 bar    
    Piston speed 10.75 m/s    
    Rated power 
    Engine type
    8V31SG 4400
    10V31SG 5500
    12V31SG 6600
    14V31SG 7700
    16V31SG 8800
    Engine platform A A* B C F Weight (tons)
    Wärtsilä 8V31SG 6080 6417 3251 3111 1496 57,5 t
    Wärtsilä 10V31SG 6720 7057 3251 3111 1496 65,2 t
    Wärtsilä 12V31SG 7682 7833 3144 3460 1546 76,5 t
    Wärtsilä 14V31SG 8321 8473 3144 3460 1646 85,5 t
    Wärtsilä 16V31SG 8962 9113 3144 3460 1646 93,2 t
    W31 technical data W
    Specific fuel energy consumption
    • At ISO standard reference conditions at 85% load
    • Lower calorific value of fuel 49 700 kJ/kg
    • Tolerance 5%
    • With engine driven pumps
    • Natural gas
    • Lower heating value min. 28 MJ/Nm3
    Download brochure

    The Wärtsilä UNIC is an embedded engine control system for Wärtsilä 4-stroke engines incorporating decades of experience, knowledge and expertise. It makes engines safe, environmentally energy efficient, reliable and flexible. Read more in the brochure. 

    Wärtsilä UNIC


    The Wärtsilä 31 is designed to be suitable for a broad range of ship types and applications, both as a main propulsion engine and in diesel electric configurations, or as an auxiliary engine. It can be optimised for running either at constant speed or along a propeller curve. In the Offshore sector, the Wärtsilä 31 is a perfect solution for OSV´s and drilling or semi-submersible vessels, where operational flexibility, high power density, long intervals between overhauls, and high levels of safety are of paramount importance.

    Methane Number

    Wärtsilä Methane Number Calculator

    We have developed this tool for ship owners and operators to calculate the Methane Number of the fuel gas.
    The calculation result indicates whether or not the given gas quality is suitable for use in Wärtsilä pure gas engines.

    Methane CH4
    Iso-butane (2-Methylpropane)i-C4H10
    Iso-pentane (2-Methylbutane)i-C5H12
    Neo-pentane (2,2-Dimethylpropane) neo-C5H12
    Mix-hexaneMix C6H14
    Mix-heptaneMix C7H16
    Carbondioxide C02
    Nitrogen N2
    Hydrogen sulfideH2S
    Total mol%
    Wärtsilä Methane number (WMN)
    Propane Knock Index (PKI)
    The calculation tool is owned by Wärtsilä and is made for customer use and is for guidance only. Changes in the tool is reserved at any time.


    • Why is Wärtsilä launching the pure gas engine for the marine market now?
    • How is the pure gas engine different from the dual fuel engine?
    • Is the pure gas engine replacing the dual fuel engine?
    • When should the pure gas (SG) engine be selected instead of the dual fuel (DF) engine?
    • What are the environmental benefits of the pure gas engine vs. the dual fuel engine?
    • Is the pure gas engine suitable for heavier gases with a lower methane number?
    • How does the single-fuel pure gas engine comply with the redundancy requirements of the marine sector?
    • What are the benefits of a pure gas-hybrid application?
    • When is the Wärtsilä 31SG ready for delivery for marine applications?
    • Does Wärtsilä have plans for other pure gas engines for the marine market?
    Business White Paper - Hybrid propulsion is part of the future for RoPax ferries

    Business White Paper: Hybrid propulsion is part of the future for RoPax ferries

    Green is undoubtedly the colour concept most dominating today’s shipping industry, and nowhere is this more true than in the ferry sector. Environmental considerations are, along with the need to optimize operational efficiency, high on the agenda of ferry operators around the world.

    Hybrid systems are being featured more and more on a variety of vessel types, but are particularly relevant to ferries since they are more likely to be operating within areas covered by strict environmental regulations.

    Download this white paper to get a better understanding of how to select the most appropriate power system configuration for your RoPax or RoRo ferry, not only for today, but for tomorrow as well.

    Shipping in the 2020 era – selection of fuel and propulsion machinery

    Environmental concerns have led to increasingly stringent emission legislation. What started as an onshore industry regulatory development is now impacting also the shipping industry. Shipping has lately faced multiple new regulations, and will soon be facing other major regulations. The global cap of an 0.5% maximum content of sulphur in fuel from 2020, and the IMO Tier III regulations (specifying that NOx emissions must be 80% lower than at the IMO Tier I level) within Emission Control Areas will force the shipping industry to consider alternatives beyond today´s standard solutions.

    Business White Paper - Hybrid propulsion is part of the future for RoPax ferries

    Find out what makes the Wärtsilä 31 tick

    Find out what makes the Wärtsilä 31...

    Next generation automation system enables Wärtsilä 31 performance. Download the brochure.

    Modularisation hand in hand with manufacturability

    The development of the new Wärtsilä 31 engine provided the perfect opportunity to exploit the benefits...
    29 May 2018
    • In Detail article

    Common rail fuel injection rules the...

    Very few marine engines are awarded a Guinness World Record. Thanks to Wärtsilä’s common rail injection...
    28 July 2017
    • Twentyfour7. article

    Press releases

    Product hologram


    Wärtsilä 31 - the most efficient engine in the world

    Welcome to a brand-new generation of engines. The Wärtsilä 31 is setting a new standard for energy efficiency, delivering the lowest level of fuel consumption of any four-stroke engine worldwide.
    20 October 2015
    • Twentyfour7. article

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