Investigation on marine LNG propulsion systems for LNG carriers through an enhanced hybrid decision making model

Since the use of LNG as an alternative fuel has drawn increasing attention from the marine industry, this paper aimed to evaluate three competitive LNG fuelled engine systems: ultra-steam turbine, four-stroke medium speed engine, and two-stroke low-speed engine systems. To achieve this goal, the paper developed an enhanced hybrid decision-making model which was applied to integrate the economic, environmental and technical performance of these systems. This model can be represented as a semi-quantitative multi-criteria decision making process in combination of several novel techniques, particularly ‘life cycle cost assessment’ for economic analysis, ‘life cycle assessments’ for environmental analysis, ‘fuzzy order preference by similarity to ideal solution’ for technical analysis and ‘fuzzy analytic hierarchy process’ for multi-criteria decision making. A case study with a 174K LNG carrier has revealed that the two-stroke low-speed engine system is the most effective overall and suggested that this type of engine system will hold the lead over the other candidates in the large LNG carrier market. It has also demonstrated the effectiveness of the proposed model to improve the inherent subjectivity in existing qualitative multi-criteria decision-making processes by guiding the overall process in a more objective direction. Finally, this paper has revealed an underlying novelty of the proposed model to enhance the level of confidence level in the decision by expanding our short-term perspective to the holistic one.