Environmental and economic analysis of a cruise ship using LNG–MGO as alternative fuels

Abstract

As global rules to reduce greenhouse gas (GHG) emissions become stricter, the shipping industry, responsible for approximately 3% of global emissions, faces increasing regulatory pressure. The International Maritime Organization (IMO) aims to reduce CO₂ emissions by 40% by 2030 and achieve net-zero emissions by 2050, encouraging shipowners to consider alternative fuels such as LNG, hydrogen, ammonia, methanol, and biodiesel. Among these, LNG is currently the most widely used due to its technological maturity and lower (SO)x, (NO)x, and particulate emissions. This study examines the operational, environmental, and economic performance of a cruise vessel with dual-fuel engines operating on LNG and MGO over a typical 7-day itinerary. The average weekly consumption amounts to 150 tons of MGO and 570 tons of LNG. While LNG usage on the engine can reduce CO₂ emissions by up to 27% and (NO)x by 79% according to engine exhaust emission data, frequent shifts back to MGO significantly reduce overall benefits. A well-to-wake analysis shows that, including upstream emissions, LNG achieves only a 23.0% reduction in CO₂ emissions relative to MGO. When engine operating durations in MGO and LNG modes are included in the calculation, the CO₂ emission reduction decreases to 19,1%. The use of LNG reduces the CII index by 13,1%. Based on actual consumption data, (CO)2e emission reduction of 1,0% observed with the usage of LNG as an alternative fuel. Methane slip issue in LNG use increases the GFI value, narrowing the gap between LNG and MGO. To further improve LNG's decarbonization potential, additional mitigation pathways were explored. IMO emission measuring methods, including CII, GHG intensity, and GFI were calculated for this example vessel. Cost-benefit and SWOT analyses were conducted to assess LNG's effects on the vessel. Although LNG is an alternative fuel with a 20,1% advantage when consumption data and maintenance costs are included, it provides a 14,6% cost advantage. Operating the engines in LNG mode offers advantages in both fuel costs and carbon-emission reductions. Engines do not operate continuously in LNG mode. It was observed that the engines operate in MGO mode for 12,1% of the total operation time. Operational constraints and unexpected malfunctions lead to increased engine running hours in MGO mode. Operation in MGO mode diminishes the effectiveness of emission reductions, increases fuel expenditures due to higher fuel prices, and results in elevated vessel emission indices and associated carbon tax liabilities. Consequently, the payback period of the LNG system investment has been extended by more than 12.1%. In conclusion, LNG represents a practical short-term transition fuel for meeting IMO decarbonization goals, but long-term compliance will likely require engines capable of using zero-carbon fuels or integration of onboard carbon capture systems.