If the Seven Wonders of the World was updated for the 21 st century, the Wartsila-Sulzer RTA96-C turbocharged two-stroke diesel engine could be a contender. If you are a student of the internal combustion engine in all its wonderous configurations, then feast your eyes on this set of numbers which outline the truly astounding engineering feat. It is the most powerful and most efficient engine in the world today.
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.
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.
At a length of 89 feet and a height of 44 feet, the total engine weight is 2300 tons - the crankshaft alone weighs 300 tons.
The RTA96C-14 can achieve a maximum power output of 108,920 hp at 102 rpm and astonishingly, at maximum economy the engine exceeds 50% thermal efficiency. That means, more than 50% of the energy in the fuel is converted to motion. Its Brake Specific Fuel Consumption (BSFC) at maximum power is 0.278 lbs/hp/hr.
Ship owners like a single engine/single propeller design and the new generation of larger container ships needed a bigger engine to propel them.While engine cylinder configurations for large-scale container liners have been discussed in the magnitude of 14, 16 and 18 cylinders, the 14-cylinder in-line low-speed engine is the first to be offered by any engine designer.
Ship owners prefer single engine/single propeller designs and the new generation of larger container ships (or post-Panamax) called for a bigger engine to propel them.
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|
|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|
|Torque||Up to 7,603,850 newton metres (5,608,310 lbf·ft) @ 102 rpm|
|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 (Whole motor uses up to 250 tons of fuel per day.)|
|Crankshaft weight||300 tons|
|Piston weight||5.5 tons|
|Piston Height||20 feet|
The RTA96C-14 turbocharged two-stroke diesel engine is produced by Swiss company Wartsila-Sulzer and is the largest and most powerful diesel engine in the world today.
The peak capabilities of the 14-cylinder RTA96C engine now exceed 80 MW, making it adequate for a single-screw Post-Panamax container liner, which is as large as container liners will get considering their greater cost-effectiveness.
Sulzer have also managed to increase cylinder output since they began first operation in 1997, due to the maintenance experience accumulated with the large number of RTA96C engines currently in service. The new kW rating of the new engine achieves a power output of 68,640 kW, a four percent increase on the initial RTA96C.
Despite the large amounts of power produced by these engines, surprisingly low wear rates have been achieved. Diametral cylinder liner wear is in the order of only about 0.03 mm/1000 hours.
This low cylinder wear is possibly attributed to a connecting rod that attaches to a "crosshead" which rides in guide channels, a fundamental difference to most automotive engines where the top of the connecting rod is attached directly to the piston. Instead, in this engine the top of the connecting rod attaches to a "crosshead" and a long piston rod then connects the crosshead to the piston. This lowers the sideways forces produced by the connecting rod and is absorbed by the crosshead and not by the piston. Sideways forces are what makes the cylinders in an auto engine become oval-shaped over time.
Fuel consumption at maximum economy is 0.260 lbs/hp/hour. Comparatively, most automotive and small aircraft engines can only achieve BSFC figures in the 0.40-0.60 lbs/hp/hr range and 25-30% thermal efficiency range.
The design and development of the RTA96C was close collaboration with the companies involved in the early stages of the first commercial project: the owner and operator P&O Nedlloyd BV, the ship designer and builder Ishikawajima Harima Heavy Industries Co Ltd (IHI), and the enginebuilder Diesel United Ltd.
The project began in March 1997 when the first engine, an 11-cylinder unit, was started on the test bed of Diesel United Ltd, Aioi.
Since then a total of 86 RT96C engines with eight, nine, ten, 11 and 12 cylinders in-line are in service or on order, 25 of these currently in service.