Wartsila Diesel Presents A New Auxiliary Engine, The Vasa 2 2 / 26
The recent introduction of Wartsila Diesel's Vasa 46 engine is now being followed by a new auxiliary engine, the Wartsila Vasa 22/26. According to the analysis made before the Vasa 46 project, a really reliable medium-speed engine is the optimum choice as the prime mover for virtually any ship type.
The output chart for the Vasa 22/ 26 shows that the four-, six- and eight-cylinder engines comply with the generally accepted output figures for auxiliary engines in general cargo vessels. The engine also meets with most specifications with respect to speed range.
Wartsila Diesel has carried out intensive studies on the stroke/bore ratio and found that the ratio 26/22 is optimum for thermal efficiency in engines of this size as well as for reaching a compression ratio high enough to cope with even the next generation of heavy fuels.
A compression ratio of 13:1 in combination with Wartsila Diesel's load dependent cooling system ensures high compression temperatures at all loads. Reliable combustion is the result.
The following are the main factors ensuring a reliable combustion in the Vasa 22/26: high compression temperatures at all loads, good atomization of the fuel oil and sufficient oxygen supply at all loads.
The engine block of the Vasa 22/ 26 is cast in one piece from nodular cast iron. Rigidity is the main design criterion. The fastening of the cylinder head screws and the main bearing screws into the engine block allows for optimum load distribu- tion. This results in negligible changes in the circularity of the main bearing bore and the cylilnder liner spacing, even at peak combustion pressures exceeding 200 bar.
The crankshaft of the Vasa 22/26 is forged in one piece with boled-on counterweights on each web. This ensures optimum balancing with superb features for an even and high oil film thickness in all bearings. The connecting rod is drop forged with an H-profile and hydraulically tensioned screws for fastening the bearing cup. Several thousand connection rods of this type are now in operation in Wartsila Diesel's engines and not a single one with ovalization of the big end bore or defects in the mating surface has been reported. The piston of the Vasa 22/26 consists of a steel crown and a nodular cast iron skirt. The use of two compression rings in combination with one oil scraper ring is possible thanks to the patented pressurized lubrication of the piston skirt and the piston design.
A centrifugal casting honed and treated to optimal surface finish and hardness makes for long life. An absolute prerequisite for good cylinder performance is an optimized cylinder wall temperature. This is a question of balancing the cooling water temperature, the water flow and the cylinder liner wall thickness in order to prevent the acid attacks which occur at wall temperatures or, the opposite, when excessive temperatures burn the lube oil off from the cylinder wall.
Here again, the load-dependent cooling system plays an important role. It allows optimum cylinder temperatures and operational reliability at all loads.
Nodular cast iron with high tensile strength in combination with a reliable design allows peak combustion pressures exceeding 200 bar without significant deformation of the flame plate. By minimizing deformation— both mechanical and thermal—the risk of deviation between the center line of the valve and seat is avoided. This results in reliable valve-seat function.
The designer of the Vasa 22/26, Wartsila Diesel, is one of the world's leading designers and manufacturers of diesel engines. Besides production plants located in Finland, Sweden, Norway, France, Spain and Singapore, the company also has several licensees and a worldwide network of sales and service facilities. For free literature giving complete information on Wartsila Diesel's new auxiliary engine Vasa 22/ 26,