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.
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.
Get technical data and system proposals for designing W31SG marine engine installations.
Following Wärtsilä’s introduction of dual-fuel engine technology in the 1990s, LNG has become established as a viable and attractive marine fuel. This has led to the rapid expansion of the global LNG bunkering infrastructure, which now enables a larger-scale application of pure gas engines within the marine and offshore industries.
The SG engine ignites the gas fuel with the aid of a spark-plug instead of a liquid pilot fuel injection. The SG engine thus uses only gas as a fuel and does not need to be fitted with a separate back-up diesel fuel system.
The marine SG pure gas engine represents the lowest total cost of ownership with the lowest environmental footprint for operation in areas with a secured gas supply, for example on fixed short routes where gas bunkering infrastructure is available.
Compared to DF machinery configuration, the SG typically offers a 5% reduction in OPEX due to reduced maintenance and a lower fuel bill, a further 15% reduction in greenhouse gas emissions compared to the already low emission levels of the DF and a potential 5% reduction in total system investment cost.
With the SG lean-burn technology a reduction of approx. 15% in greenhouse gas emissions can be achieved compared to the already low emission levels of the DF engine. This reduction is achieved through a lower fuel consumption (C02 emissions) as well as a reduction in the unburnt methane emissions (CH4). In addition, the nitrous oxide emissions (NOx) are reduced a further 35% compared to the low Tier III levels of the DF engine.
The Wärtsilä 31SG engine is well-suited for gases with a low methane number. The gas-only focus with spark-ignition and the absence of a back-up diesel mode allows for a wide range of optimization possibilities.
Marine classification society rules dictate that a gas-powered single-fuel vessel must typically have redundant back-up power available corresponding to min. 40% of MCR. This requirement can be fulfilled with SG machinery using a redundant gas supply system (2 x C-tanks for example) and selecting a multi-engine configuration.
The Wärtsilä 31SG in a hybrid engine-battery configuration enables a significant reduction in engine running hours which can save up to 5-20% in maintenance cost. The redundancy and peak shaving capabilities of a hybrid system also allows for a higher average engine load. Together these factors translate into a lower fuel bill and corresponding reduction in greenhouse gases. The savings in fuel and emissions are typically 2-6% on top of the savings achieved with the switch to SG technology.