The Wärtsilä RT-flex96C is a two-stroke turbocharged low-speed diesel engine designed by WinGD. It is designed for large container ships that run on heavy fuel oil. Its largest 14-cylinder version is 13.5 m high, 26.59 m long, weighs over 2300 t, and produces 80.08 MW. It is the largest reciprocating engine in the world.
The 14-cylinder version first entered commercial service in September 2006 aboard the Emma Mærsk. The design is similar to the older RTA96C engine, but with common rail technology (in place of traditional camshaft, chain gear, fuel pump and hydraulic actuator systems). This provides maximum performance at lower revolutions per minute (rpm), reduces fuel consumption and emits lower levels of harmful emissions.
The engine has crosshead bearings so the always-vertical piston rods create a tight seal under the pistons. Consequently, the lubrication of the engine is split: the cylinders and the crankcase use different lubricants, each being specialised for its designated role. The cylinders are lubricated by continuous 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 down to about 30 μm per 1,000 hours.