Wartsila NSD Declares 64 Ready For Market
A six-cylinder prototype of what is reportedly the world's largest medium-speed engine, the Wartsila 64, was started more than a year ago at the Wartsila NSD Vaasa research center in Finland. One thousand operating hours later, the Wartsila 64 is now in the endurance testing phase.
The manufacturer reports that test results have been encouraging in every respect, and — after minor adjustments — the engine's low fuel consumption can be demonstrated at NOx values clearly below the IMO curve.
The in-line and V-engine of the Wartsila 64 have different strokes 900 and 770, respectively. This indicates that the in-line engine is mainly prepared for geared propulsion systems, while the V-engine is slightly more optimized for dieselelectric installations in preparation for the day when singleengines and single-propellers cannot respond to the output needed by the largest container ships. A number of design solutions from Wartsila NSD are built into the engine. Early examples are the nodular cast iron piston skirt, and even more important, pressurized piston skirt lubrication, which together make it possible to elevate the maximum cylinder pressure to 160-170 bar.
The introduction of the antipolishing ring years ago has helped eliminate the problem with increasing oil consumption, while drastically reducing wear rates of piston rings, piston ring grooves and liners. The technology has been endurance tested for 1,000 hrs. at 220 bar cylinder pressure in a Wartsila 46 engine.
To accommodate the higher cylinder pressures Wartsila NSD, together with the piston suppliers, has developed a box-type piston, which offers an excellent structural rigidity.
The thick-pad bearing philosophy, which means that the bearings are designed for an ample oil film thickness, was also introduced together with the Wartsila 46 and has since been standard in all Wartsila engines. The crankshaft gives an impression of the ample bearing pins and journals The capacity to take high cylinder pressures was in fact a prerequisite for the development of the Low NOx Combustion process because one vital element in this process is increased compression pressure, which automatically leads to a higher combustion pressure. Thanks to a specially designed injection rate, the maximum cylinder temperature is lower than in a normal Seiliger process, which is an important element in the reduction of NOx.
