Worldwide concern regarding environmental pollution from the maritime sector is mainly reflected in the existing strict legislation for nitric oxides (NO_x) emissions and the forthcoming global 0.5% sulphur cap, in 2020. Attempts for compliance have motivated the introduction of alternative fuels. These fuels include Natural Gas (NG) and Liquefied Petroleum Gas (LPG), and are used in dual-fuel marine engines. Dual-fuel engines can utilize two independent operational modes; the liquid and the gas mode. The traditional liquid marine fuels, i.e., heavy fuel oil (HFO) and marine gas oil (MGO), are used in the liquid mode, while the gas mode utilizes the combustion of gaseous NG or LPG. All gas mode designs utilize a short pilot injection of liquid fuel as the ignition source. In this paper, we review the main design and operation principles of dual-fuel marine engines, their advantages and limitations, as well as the current dual-fuel engine portfolio of the main marine engine manufacturers.
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