2000 1000 500

Speed 400 500 600 700 800 900 1000 rev/min

Figure 26.1 Power/speed ranges of Sulzer medium speed engine designs

The modern four-stroke Z-engines matured from a 400 mm bore family founded by the ZH40 two-stroke medium speed engine, designed in the early 1960s and installed in icebreakers, ferries and cruise ships. The uniflow-scavenged two-stroke design was succeeded in 1972 by a four-stroke version (the Z40) which was in turn completely redesigned and replaced in 1982 by the ZA40 engine. A longer stroke (560 mm instead of 480 mm) ZA40S engine was introduced in 1986 to succeed the Z40 and ZA40 designs. The performance development steps over the years are illustrated in Figure 26.2.


Figure 26.2 Development steps of successive Sulzer Z40, ZA40 and ZA40S designs illustrated by key performance parameters year

Figure 26.2 Development steps of successive Sulzer Z40, ZA40 and ZA40S designs illustrated by key performance parameters

In autumn 1988, three years after its announcement with a cylinder output of 660 kW, the ZA40S was uprated to 720 kW/cylinder following successful service experience and heavy fuel endurance tests. The new rating was associated with an increased maximum cylinder pressure of 165 bar and mean effective pressure of 24.1 bar, underwritten by thermodynamic and mechanical optimizations. Some design modifications were also introduced to improve product reliability and durability in general (Figure 26.3):

Exhaust wastegate

Exhaust wastegate

I I Introduced for all engine power steps 1-1 (600-720 kW/cyl)

Figure 26.3 Main modifications for uprated ZA40S engines

• An exhaust valve with a 45 degree seat angle, this refinement achieving: better cooling without reduction of mechanical and thermal safety at the higher engine load and maximum cylinder pressure; and more efficient seating due to a wider seat area.

• Sulzer's new combined 'jet-shaker' piston cooling principle in which the conventional shaker effect in the piston crown is supplemented by oil jets sprayed through nozzles. This offers advantages in lowering piston crown temperatures, thereby preventing carbon formation, and gaining an improved washing effect.

• A new version of the waste gate in the exhaust gas manifold before the turbine, securing a better match between the engine and turbocharger at the increased power rating.

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