Wärtsilä 31SG

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 (NO_x) 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 without 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.