main engine · propulsion system

MAN B&W G90ME ME-GI-S

The MAN B&W G90ME-GI is a large low-speed, two-stroke crosshead marine engine that adds high-pressure gas injection to the electronically controlled ME platform, making it a dual-fuel main engine for the largest ships. Its designation is informative: the G marks the ultra-long-stroke Green series designed for efficiency at low propeller speeds, the 90 is the cylinder bore in centimetres, ME denotes electronic control, and GI stands for gas injection, the technology that allows the engine to run on natural gas as well as on conventional liquid fuel. Unlike the lean-burn Otto approach used by many medium-speed dual-fuel engines, the ME-GI engine injects gas at high pressure directly into the cylinder and burns it on the diesel principle, with a pilot injection of liquid fuel for ignition. This preserves the high efficiency and strong performance of the two-stroke diesel while allowing the ship to burn cleaner gas, and it largely avoids the methane slip associated with some gas engines. The engine can operate on gas or switch to liquid fuel such as heavy fuel oil or marine diesel oil, giving operators fuel flexibility and the ability to meet emission limits by running on gas in controlled areas. Engines of this size and type propel the largest merchant ships, including very large LNG-fuelled container vessels, and the GI variant is particularly suited to LNG carriers and other ships that can carry gas as fuel. As with all ME-series engines, electronic control of fuel injection and exhaust-valve timing optimises performance across the load range, improves manoeuvring and provides monitoring, while the crosshead construction allows separate cylinder and system lubrication for heavy-fuel operation. The G90ME-GI illustrates how the traditional low-speed diesel is being adapted to lower-carbon fuels, combining the efficiency and reliability of the two-stroke engine with the cleaner combustion of gas as the industry moves toward its emissions goals.