The height of a four-story building, the Wärtsilä RT-flex96C is a two-stroke turbocharged low-speed diesel engine designed by the Finnish manufacturer Wärtsilä.
It is designed for large container ships that run on heavy fuel oil. Its largest 14-cylinder version is 13.5 metres (44 ft) high, 26.59 m (87 ft) long, weighs over 2,300 tonnes, and produces 80,080 kilowatts (107,390 hp). The engine is the largest reciprocating engine in the world.
The 14-cylinder version was put into service in September 2006 aboard the Emma Mærsk.
The design is like the older RTA96C engine, with common rail technology instead of traditional camshaft, chain gear, fuel pumps and hydraulic actuators. All this provides the maximum performance at low revolutions per minute (rpm), lower fuel consumption and lower harmful emissions.
The engine has crosshead bearings so that the always-vertical piston rod allows a tight seal under the piston. Consequently, the lubrication of the engine is split: the cylinders and the crankcase use different lubricants, each being specialised for and dedicated to its role.
The cylinders are lubricated by continual, timed injection of consumable lubricant, formulated to protect the cylinders from wear and to neutralise the acids formed during combustion of the high-sulfur fuels commonly used. The crosshead design reduces sideways forces on the piston, keeping diametral cylinder liner wear in the order of only about 0.03 mm per 1000 hours.