Wärtsilä-Sulzer RTA96-C

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The Wärtsilä RTA96-C turbocharged two-stroke diesel engine is currently considered the largest reciprocating engine in the world, designed for large container ships, running on cheap, heavy fuel oil. It is five stories high (13.5m), 27 m long and weight over 2300 tons in its largest 14 cylinders version producing more than 80 MW (109,000 hp). It was put into service in September 2006 aboard the Emma Mærsk.^[1]

1 Crosshead bearings
2 Technical data
3 Efficiency
4 References
5 External links

[edit] Crosshead bearings

The engine has crosshead bearings. One of the reasons that the large two stroke diesels use this design is so that the lubrication in the combustion area is separated from the crank case oil, which stays clean from combustion products. The upper portion is lubricated by continuous injection of consumable lubricant which is formulated to stand up to high temperatures and high sulfur.

Another reason is that the always vertical piston rod allows a tight seal under the piston. 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 center (BDC) to remove some load from the bearings.

[edit] Technical data

Configuration: turbocharged two-stroke diesel straight engine, 6 to 14 cylinders
Cylinder bore: 960 mm
Piston stroke: 2500 mm
Speed: 92–102 rpm
Mean effective pressure: 1.86 MPa @ full load, 1.30 MPa @ maximum efficiency (85% load)
Mean piston speed: 8.5 m/s
Specific fuel consumption: 171 g/(kW·h) (126 g/(bhp·h)) @ full load : 163 g/(kW·h) (120 g/(bhp·h)) @ maximum efficiency
Power: 5720 kW per cylinder, 34,320 to 80,080 kW (46,680 to 108,920 bhp)
Power density: 29.6 to 34.8 kW per tonne, 2301 tons for the 14 cylinder version
Amount of fuel injected in a single cycle of single piston: ~160 g @ full load

[edit] Efficiency

The Specific fuel consumption efficiency of the RTA96 is the best among piston engines. The minimum 163 g/kW·h translates to 3.6 MJ/kW·h / 0.163 kg/kW·h = 22.1 MJ/kg of work from chemical energy. With a 42.7 MJ/kg fuel, the efficiency is 22.1 MJ/kg / 42.7 MJ/kg = 51.7%. But this is not the best overall percentage, this title belongs to General Electric's GE Energy H-System with 60% efficiency in combined cycle, a combination of gas turbines and steam turbines. This system is in the 400–500 MW class, though, and comparable powered combined cycle turbines have comparable efficiencies.