main engine · propulsion system

Wärtsilä X72

The Wärtsilä X72 is a low-speed, two-stroke crosshead marine diesel engine designed for the main propulsion of merchant ships such as tankers, bulk carriers and medium-sized container vessels. It belongs to the X-generation of low-speed engines, the electronically controlled successors to the earlier Sulzer RTA and RT-flex lines, and the 72 in its name is the cylinder bore in centimetres. Offered with a range of cylinder numbers, it provides the power needed to propel ships of these types at economical service speeds. The X-series engines use electronic common-rail control of fuel injection and exhaust-valve operation in place of the traditional camshaft, which allows injection timing and rate to be optimised across the whole load range. This delivers good fuel economy, clean and smokeless combustion even at low load, flexible slow-speed running for manoeuvring, and extensive monitoring and diagnostics. Designed with a long stroke relative to the bore, the engine turns slowly and develops high torque, so it can drive a large, efficient fixed-pitch propeller directly on the shaft without a reduction gearbox, which is the arrangement that gives large ships their propulsive efficiency. As a crosshead engine it separates the combustion space from the crankcase, allowing separate lubrication of the cylinders and the running gear, which suits operation on heavy fuel oil, and versions of such engines are increasingly offered with dual-fuel capability to burn gas as the industry moves toward lower-carbon fuels. Built to run continuously for long periods, the engine is maintained on a planned schedule covering its injection equipment, running gear, turbocharging and lubrication. The Wärtsilä X72 is representative of the modern low-speed main engine (efficient, electronically managed and reliable) that sits at the centre of a merchant ship's machinery and whose performance directly shapes the fuel consumption and operating economics of the vessel. Because the main engine dominates both the capital cost and the fuel consumption of a large ship, the reliability and efficiency of an engine such as the X72, and the discipline with which it is maintained over its long working life, are decisive for the safe operation and the commercial success of the vessel.