Emissions from vessels are a major environmental concern because of their impacts on the deterioration of the environment, especially global warming of the atmosphere. Therefore, the International Maritime Organization (IMO) concerns significant care to environmental protection through the reduction of exhaust emission and improvement of energy efficiency through technical and operational measures. Among the suggested measures from IMO, the alternative fuel such as natural gas has the priority to be used instead of fossil fuels. The present paper calculates the effect of using natural gas in a dual-fuel engine from environmental and energy efficiency perspectives. As a case study, a container ship has been investigated. The results of the analysis show that the percent of CO₂, NOx, and SOx emission reduction corresponding to using a dual-fuel engine operated by natural gas instead of a diesel engine operated by heavy fuel oil is about 30.4%, 85.3%, and 97%, respectively. Moreover, it found that NOx and SOx emission rates of the dual-fuel engine comply with the IMO 2016 and 2020 limits, respectively. Furthermore, the Energy Efficiency Design Index value in the case of using dual-fuel engine is lower than the value by using diesel engine by about 30%, and this value will be 77.18%, 86.84%, and 99.27% of the required value for the first, second, and third phases, respectively, as recommended by IMO.

船舶排放是一个主要的环境问题，因为它们会影响环境恶化，尤其是全球大气变暖。因此，国际海事组织 (IMO) 非常重视通过技术和操作措施减少废气排放和提高能源效率来保护环境。在 IMO 建议的措施中，优先使用天然气等替代燃料，而不是化石燃料。本文从环境和能源效率的角度计算了在双燃料发动机中使用天然气的效果。作为案例研究，对一艘集装箱船进行了调查。分析结果表明，CO ₂的百分比使用以天然气为动力的双燃料发动机代替以重油为动力的柴油发动机，对应的 NOx 和 SOx 排放量分别减少约 30.4%、85.3% 和 97%。此外，它发现双燃料发动机的 NOx 和 SOx 排放率分别符合 IMO 2016 和 2020 的限制。此外，使用双燃料发动机时的能效设计指标值比使用柴油机时的值低约 30%，该值将分别为所需值的 77.18%、86.84% 和 99.27%。分别按照 IMO 的建议进行第一、第二和第三阶段。