The current oil market situation requires engine builders to concentrate their efforts on designs with both low fuel consumption and the capability of running on heavy fuel oil. Engines with a low fuel consumption and high heavy fuel oil compatibility demand a high firing pressure mean effective pressure ratio.
The engines included in the current M.A.N.—B&W production program have been designed with a view toward a high firing pressure ratio. In continuous service, the engines with bores from 32 cm to 52 cm operate at firing pressures of up to 145 bar. By means of precision changes not involving extensive redesign, high firing pressures can be attained with mechanical stresses remaining within controllable limits.
The engine program of M.A.N. (Maschinenfabrik Augsburg-Nurnberg AG) includes five four-stroke engines with bores from 200 to 520 mm, and five two-stroke engines with bores from 520 to 900 mm — three of which are long-stroke versions. The four-stroke engines cover an output range from 134 to 1,187 bhp per cylinder, and the two-stroke engines from 1,187 to 3,889 bhp per cylinder. The mean effective pressure of the four-stroke engines is 20 bar (25 bar with two-stage supercharging), and that of the two-stroke engines is 13 bar and 14.5 bar for the low-speed types and approximately 15 bar with the two-stage H engines. The maximum cylinder pressure of the medium-speed engines is up to 145 bar, and that of the two-stroke engines is 115 bar.
Today's engine production program at M.A.N. thus combines, on a high-power level, proven principles with present and future demands. The most important development targets for the updated program were:
Ability to burn heavy fuel oils up to 3,500 seconds Redwood 1 in the case of four-stroke engines, and up to 6,000 sR1 in the case of two-stroke engines; adherence to proven design concepts wherever expedient; variation in turbocharger arrangement and selection of optimum speed; type of construction fully developed in terms of production, engineering, and maintenance; and high quality standard.
By proven design principles M.A.N. understands that for as many components of different engine types as possible, the same design solutions are used, permitting the transfer of computed and measured results from trial data and practical experience.
The constant demand from the shipowners and shipyards for a smaller engine developing below 1,000 kW (1,341 bhp) and the rising interest in smaller stationary units for combined power/heat generation prompted M.A.N. to develop the 20/27 engine. This engine is available as an in-line unit with four to nine cylinders, and as a V engine with 12 to 18 cylinders.
The 20/27 engine is intended mainly for the following applications: as a propulsion engine for smaller vessels; as an auxiliary engine for power generation aboard ships; for stationary power-generating plants; and for plants combining power generation with waste heat recovery.
The 20/27 engine is offered in diesel, spark-ignited gas, and dual-fuel versions. The cylinder rating of the diesel engine is 100 kW (134 bhp) at 1,000 rpm according to the ISO definition. Its mean effective pressure and mean piston speed are 14.15 bar and 9 meters per second, respectively.