main engine · propulsion system

Wärtsilä RT-flex96C

The Wärtsilä RT-flex96C is a very large, low-speed, two-stroke crosshead marine diesel engine, one of the most powerful engines ever built and long associated with the propulsion of the largest container ships. Descended from the Sulzer RTA line of low-speed engines, it has a cylinder bore of 96 centimetres and is offered with a range of cylinder numbers, so that in its largest configurations it develops enormous power to drive the biggest ships at commercial speed on a single direct-drive propeller. The flex in its name refers to the common-rail electronic control system that distinguishes it from earlier camshaft-driven engines. In an RT-flex engine, fuel is supplied from a high-pressure common rail and injected under electronic control, and the exhaust valves are likewise electronically actuated, doing away with the traditional camshaft, fuel pumps and mechanical drives. This allows the timing and rate of fuel injection to be varied freely and optimised across the whole operating range, giving better fuel economy, cleaner combustion and low, smokeless running even at very low speeds, along with flexible manoeuvring and comprehensive monitoring. As a low-speed two-stroke crosshead engine it turns slowly enough to drive a large, efficient fixed-pitch propeller directly, without a reduction gearbox, and it is designed to burn heavy fuel oil economically on long deep-sea voyages, which is why engines of this class dominate the propulsion of large merchant ships. Its crosshead construction separates the combustion space from the crankcase, allowing separate cylinder and system lubrication suited to heavy fuel. Engines like the RT-flex96C, and their successors in the WinGD X-generation, represent the pinnacle of merchant-ship propulsion engineering: immense, efficient, electronically managed machines built to run reliably for years, and their performance and fuel consumption are decisive factors in the economics of operating the world's largest cargo ships. Because a single engine of this size can represent a large share of a ship's capital cost and almost all of its fuel bill, the care with which it is operated and maintained — clean treated fuel, correct cooling and cylinder lubrication, and the timely overhaul of its running gear and injection equipment, has a direct and lasting effect on the reliability and profitability of the vessel.