Single-fuel mode

Single-fuel mode is operation of a dual-fuel engine on liquid fuel alone, with the gas or low-flashpoint fuel supply shut off. Every marine dual-fuel engine, MAN ME-GI and ME-LGIM, WinGD X-DF, and the four-stroke DF gensets, retains full liquid-fuel capability so the ship can run on marine diesel oil or fuel oil when gas is unavailable, during bunkering, or on a gas-system trip. In single-fuel mode a low-pressure Otto-cycle engine reverts to the diesel cycle and loses its Tier III NOx margin, so it needs EGR or SCR to stay compliant in an emission control area. The switch between gas and liquid is normally bumpless under load.