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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 kW. The engine is currently considered 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 based on the older RTA96C engine, but common rail technology has done away with the traditional camshaft, chain gear, fuel pumps and hydraulic actuators. The result is better 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. Consequencently, 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.
The descending piston is used to compress incoming combustion air for the adjacent cylinders which also serves to cushion the piston as it approaches bottom dead centre (BDC) to remove some load from the bearings. The engine is uniflow-scavenged by way of exhaust valves that are operated by electronically-controlled, common-rail hydraulics, thus eliminating the camshaft.
As of 2006, more than 300 RT-flex96C engines and older RTA96C engines were in service or on order.
Technical data (as of 2008)
|Configuration||Turbocharged two-stroke diesel straight engine, 6 to 14 cylinders|
|Displacement||1,820 litres per cylinder|
|Engine speed||22–102 RPM|
|Torque||7,603,850 newton metres (5,608,310 lbf·ft) @ 102 rpm|
|Mean effective pressure||1.96 MPa @ full load, 1.37 MPa @ maximum efficiency (85% load)|
|Mean piston speed||8.5 meters per second|
|Specific fuel consumption||171 g/(kW·h)|
|Power||up to 5,720 kW per cylinder, 34,320–80,080 kW (46,680–108,920 BHP) total|
|Power density||29.6 to 34.8 kW per tonne, 2300 tonnes for the 14 cylinder version|
|Mass of fuel injected per cylinder per cycle||~160 g (about 6.5 ounces) @ full load|
|Crankshaft weight||300 tons|