Sulzer Introduces A Longer-Stroke Medium-Speed Engine

Sulzer Brothers Limited of Winterthur, Switzerland, has introduced a longer-stroke version of their 400-mm bore medium-speed, four-stroke cycle engine. The new engine, called the ZA40S, is a longstroke version of their proven ZA40 engine. By increasing the engine stroke from 480 mm to 560 mm (stroke/bore ratio increase from 1.2 to 1.4), a significant improvement in fuel economy was achieved (4 g/bhp h), while increasing the maximum continuous rating from 870 hp to 900 hp, and lowering the engine speed from 580 rpm to 510 rpm.

The longer stroke and consequential slower rotation speed of the ZA40S have the advantages of: —Better combustion as the time available for combustion is increased; —Better mechanical efficiency due to lower friction losses in the engine bearings; —And improved combustion chamber geometry.

All of which contribute to the improvement in specific fuel consumption without increasing the maximum firing pressure above 155 bar as in the ZA40.

Sulzer achieved the characteristics of the ZA40S engine with a minimum number of design changes to the ZA40 engine components. The longer stroke is accomplished within the same frame dimensions as the shorter-stroke ZA40 by compensating for the increased crank throw with a shorter connecting rod. Three notable design features contained in the ZA40S which have demonstrated their importance for reliability and long component life on poorquality heavy fuel oils operation are: —Rotating piston—at maximum cylinder pressures above 150 bar, rotating pistons are an asset in guarding against scuffing and maintaining low wear rates while ensuring low lubricating oil consumption, generally less than 1.0 g/bhp h.

—Bore cooling—applied to all combustion space components (cylinder head, cylinder liner and piston crown) results in low stress levels, high rigidity and optimum metal temperatures, all prerequisites for satisfactory heavy-fuel performance.

—Exhaust valve technology—exhaust valve design incorporating water-cooled seat inserts, Nimonic valves and valve rotators, contributes to extended time between overhauls.

The ZA40S engine is available in an in-line configuration with six, eight or nine cylinders, and in a " V " configuration with 12, 14, 16 or 18 cylinders and ranging in power from 5,400 to 16,200 bhp at 510 rpm. At an economy rating of 750 bhp at 510 rpm, the " V " engines achieve a spec i f i c fuel consumption of 129 g/bhp h. By using an exhaust gas power turbine as an "efficiency booster," the specific fuel rate can be improved by 3 percent to 125 g / bhp h.

For further information and complete literature on the ZA40S engine from Sulzer Brothers, Circle 12 on Reader Service Card

Maritime Reporter Magazine, page 42,  Jan 1986

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