with a constant engine load after leaving the harbour. These applications typically use two-stroke slow- speed engines. In contrast, ferries or cruise ships mainly operate in coastal areas, may change engine load more frequently, and are typically equipped with four-stroke medium- speed engines. For smaller ships, such as support vessels and tugboats, the engine response with many engine load changes is crucial. Therefore, we cannot consider just one single ship engine as the operational parameter that will eventually affect the choice of engine technology. Two-stroke slow-speed engines burn more than 70% of the fuel used in global shipping. Because of their high efficiency and high power, these engines are mainly used in large ocean-going cargo ships. LNG is used in two forms of engine technologies that
4-stroke MS-Otto-SI 4-stroke MS-Diesel 4-stroke MS-Diesel 4-stroke MS-Otto-DF
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Figure 1 Two-stroke slow-speed engines: WtW - GHG IPCC - AR5 - Tier II (g CO 2 -eq/kWh engine output)
2-stroke SS-Otto-DF 2-stroke SS-Diesel-DF 2-stroke SS-Diesel-DF 2-stroke SS-Diesel-DF
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Figure 2 Four-stroke medium-speed engines: WtW - GHG IPCC - AR5 - Tier II (g CO 2 -eq/kWh engine output)
the different ship engines. It focuses on the latest marine engine models, engine generations where at least one engine has been built and delivered. The study confirms the first GHG study conclusion that LNG significantly improves air quality, particularly in ports and coastal areas. Beyond the benefits of reducing air pollutants, LNG reduces GHG emissions from international shipping and contributes to the IMO’s GHG reduction ambition. fuelled vessels cannot be summarised by one representative technology and propulsion and power provision system. Large container ships or bulk carriers, for instance, are used to transport goods from one continent to another, and hence mainly operate in deep-sea regions and mainly Results As mentioned, the GHG impact of LNG-
differ in their underlying combustion cycle and gas injection system: ➊ The WtW GHG emissions of the two-stroke slow-speed diesel dual-fuel engine (high- pressure gas injection) are 533g CO 2 -eq/kWh when using LNG. This is 23% less than the same engine operating on very low sulphur fuel oil (VLSFO) (688g CO 2 -eq/kWh), as shown in Figure 1 . ➋ The WtW GHG emissions of the two-stroke slow-speed Otto dual-fuel engine (low-pressure gas injection) are 594g CO 2 -eq/kWh when using LNG. This is a reduction of 14% compared with the VLSFO operation. For these LNG-fuelled engines, the GHG emissions of the supply chain contribute about 21-23% of the entire life cycle emissions (WtW). For oil-based fuels, the supply chain accounts for 15-16%.
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