Woodyard D. (ed.) Pounders Marine diesel engines and Gas Turbines

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660 Sulzer (Wärtsilä)

A VIT system was standard for ZA40S engines not equipped with a charge

air waste gate (see below). The helix of the pump plunger is shaped so as to

raise P

max

throughout the part-load range and thereby reduce part-load brake

speciﬁc fuel consumption.

The single-pipe exhaust system serving the ZA40S engine yields a reason-

able combination of the advantages of the pulse system (partially retaining the

kinetic energy of the exhaust gases) with the simplicity of a constant pressure

system. This had been recognized in the 1950s but could only be realized when

modern high-efﬁciency turbocharger types became available. Turbocharger

matching, however, can be demanding with the short valve overlap necessary

for low fuel consumption at full load; it may lead to surging at part loads and,

furthermore, a high-efﬁciency turbocharger shows a pronounced decrease in

charge air pressure at part load.

These difﬁculties were overcome in the ZA40S by using charge air bypasses

and charge air waste gates to create load-adaptable supercharging systems that

often enable the engines to surpass the performance of conventional super-

charging systems (Figure 26.15). The ZA40S system, Sulzer asserted, could be

tailored to give low fuel consumption through the normal engine load range but

Molykote-G

FIgure 26.13 ZA40S engine fuel injection valve

also adapted to yield the high torque required at part load in the propulsion of

icebreakers and short sea shuttle ferries. Progressively opened above about 85

per cent load, the optional waste gate valve allows higher boost pressures to be

used at part load for a substantial improvement of part-load brake speciﬁc fuel

consumption while avoiding excessive cylinder pressures at higher loads.

ZA40 and ZA40S engines 661

Shrink fitted

FIgure 26.14 ZA40S engine fuel injection nozzle

Exhaust

waste

gate

Turbine

Compressor

Charge air cooler

Air receiver

Engine

Exhaust gas receiver

Charge air waste gate

Charge air

bypass

FIgure 26.15 ZA40S engine turbocharging system with charge air bypass and

waste gate

662 Sulzer (Wärtsilä)

ZA50S engIne

Rising demand for compact, high-output medium-speed diesel propulsion

installations—particularly from cruise and ferry sectors—stimulated Sulzer to

introduce in 1995 a larger bore derivative to complement the successful ZA40S

engine. This 500 mm bore/660 mm stroke ZA50S design extended the power

range of the programme to 21 600 kW at 450 rev/min from six-, eight- and nine-

in-line and V12-, 14-, 16- and 18-cylinder models (Figures 26.16 and 26.17).

FIgure 26.16 Cross-section of ZA50S engine

The ZA50S engine was subsequently dropped from the programme, its output

range covered by the Wärtsilä 46 design.

A shorter and lighter engine than rivals in the same power class was sought

by the ZA50S designers, and attention was paid to reducing the engineroom

headroom requirement and the minimum distance necessary between engines

in multi-engine plants. The connecting rod design contributed to a particularly

low dismantling height.

The ZA50S engine inherited the main features of the ZA40S, notably the

rotating piston, fully bore-cooled combustion space, high stroke–bore ratio,

cylinder head without valve cages and load-adaptable turbocharging with sin-

gle-pipe exhaust system. The opportunity to innovate was taken, however, by

adopting hydraulic actuation for the gas exchange valves, standard for many

years in low speed two-stroke engine practice but introduced here for the ﬁrst

time to a medium-speed four-stroke design (Figure 26.18).

Hydraulic actuation—in conjunction with pneumatically controlled load-

dependent timing to provide variable inlet closing—yielded ﬂexibility in valve

timing, fostering lower exhaust gas emissions and improved fuel economy.

Variable inlet closing, together with optimized supercharging, delivered a very

ﬂat fuel consumption characteristic across the whole load range of the engine. A

considerable reduction in smoke levels in part-load operation was also secured.

A high stroke–bore ratio, similar to that of the ZA40S engine, underwrote

a compression ratio promoting clean and efﬁcient combustion over the whole

ZA50S engine 663

FIgure 26.17 eight-cylinder ZA50S engine

664 Sulzer (Wärtsilä)

engine load range. The combustion chamber is nevertheless sufﬁciently deep

for the clean combustion of heavy fuel, with low smoke emissions and low

thermal loadings of the surrounding components. The standard ZA50S engine

meets the nitrogen oxide emission limits set by the IMO; further reductions are

possible by engine tuning reﬁnements.

The designer reported that a robust engine block with underslung crank-

shaft combined maximum rigidity with low stresses. The spheroidal cast iron

block was designed for direct installation on resilient mountings. The main

and bottom end bearings follow experience with the ZA40S engine, featuring

bimetal aluminium/tin-alloy running surfaces on thin-walled shell bearings.

The bimetal-type bearings, which have demonstrated fatigue resistance and a

long life expectancy, also exhibit high resistance against wear and corrosion,

together with good embeddability and emergency running behaviour.

The symmetrical design of the rotating piston achieves even distributions

of thermal load and wear around the piston. The piston comprises a steel crown

and spheroidal graphite cast iron skirt. The crown is bore cooled with oil jet-

shaker cooling; and the skirt is provided with inner lubrication, whereby lube

oil is fed to the cylinder liner outwards from within the piston. Effective lubri-

cation of the liner, rings and pistons, with low lube oil consumption, is reported

from ZA40S installations. Full bore cooling of the combustion chamber—the

FIgure 26.18 Hydraulic exhaust and inlet valve drive for the Sulzer ZA50S engine.

the merits cited include: constant valve timing for the exhaust valves; variable valve

timing for the inlet valves (improving fuel economy, emissions and part-load opera-

tion); no valve clearance adjustment; and low noise operation

cylinder head, liner and piston crown—fosters optimum temperatures and tem-

perature distribution, low mechanical stresses and low thermal strains.

The ZA50S engine inherited the proven exhaust valve concept of ear-

lier Z-type engines, based on water-cooled seat inserts, Nimonic valves and

mechanical rotators but no valve cages. The inlet valves also feature mechani-

cal rotators. The times between valve overhauls are arranged to coincide with

those for the pistons.

A key contribution to economy and performance derives from another fea-

ture shared with the ZA40S engine: optimized supercharging incorporating a

simpliﬁed single-pipe exhaust system. Appropriate use is made of waste gates

and charge air bypasses to suit the individual application. The reported beneﬁts

are realized in low fuel consumption at both full and part loads, improved load

acceleration behaviour and reduced thermal loading of engine components.

Main parameters of ZA40S and ZA50S engines

ZA40S ZA50S

Bore, mm 400 500

Stroke, mm 560 660

Speed, rev/min 510 450

Mean eective pressure, bar 25.1 24.7

Mean piston speed, m/s 9.5 9.9

Cylinders 6, 8, 9L/12, 14, 16, 18V

output/cylinder, kW 720 1200

Power range, mcr, kW

4500–13 500 7200–21 600

Specic fuel consumption, g/kW h 183–185 181

S20 engIne

Introduced in 1988 for genset drives and small-ship propulsion, the Sulzer S20

engine was distinguished by a signiﬁcantly higher stroke/bore ratio (1.5:1) than

established contenders in its class (typically with ratios between 1 and 1.2).

The 200 mm bore/300 mm stroke design was available in four-, six-, eight- and

nine-cylinder in-line versions with a maximum rating of 160 kW/cylinder at

1000 rev/min on marine diesel oil or heavy fuel oil. A power band from 460 kW

to 1440 kW was covered over a speed range from 720 rev/min to 1000 rev/min.

Engines for genset duty (designated S20U) were offered with a higher rating to

cover power demands up to 1575 kW at 1000 rev/min (Figure 26.19). The S20

engine was displaced from the joint programme when Wärtsilä acquired New

Sulzer Diesel in favour of the Wärtsilä 20 series.

S20 engine 665

666 Sulzer (Wärtsilä)

The high stroke/bore ratio of the S20 engine allowed a greater compression

ratio while keeping the combustion space high enough to foster an undisturbed

fuel spray pattern for clean combustion. The height of the combustion space

also gave freedom in the choice of valve timing. A high compression ratio fur-

ther yields the high temperatures at the end of compression that are necessary

for quick ignition and clean combustion of heavy fuel oils, especially at low

loads. A pier-to-pier capability burning 700 cSt fuels is claimed, allowing aux-

iliary engines to operate in uni-fuel installations.

FIgure 26.19 Sulzer 6S20 engine

The S20 has almost the same overall dimensions as its predecessor, the

A20 engine, the height being uncompromised, thanks to a short connecting

rod design. The engine block combines crankcase and cylinder housing in one

rigid casting with an integral camshaft housing and charge air manifold. The

main bearing caps of the underslung crankshaft are secured by hydraulically

tightened studs both vertically and horizontally to increase the structural stiff-

ness of the block. Large crankcase doors on both sides of the engine offer good

access for maintenance. As far as possible, lubricating oil and cooling water

are distributed through drillings in the block to reduce pipework. A deep sump

provides a large oil capacity to reduce ageing of the lubricating oil and extend

intervals between oil changes.

The underslung crankshaft is a single-piece forging, machined all over,

with large-diameter crankpins and journals, and fully balanced with bolted-on

counterweights at each crank throw. Both main and big end bearings have thin-

walled aluminium/tin shells, a type which has demonstrated excellent running

and wear behaviour and has become standard for Sulzer’s four-stroke engines.

Provision is made at the free end of the crankshaft for a gear drive for pumps

and a shaft extension for power take-off drive.

High-tensile forged steel connecting rods have a diagonally split big end

with a serrated joint and hydraulically tightened studs. The rod is drilled longi-

tudinally to convey lubricating oil to the gudgeon pin bearing and piston.

A two-part piston—comprising bore-cooled steel crown and lightweight

nodular iron skirt—was speciﬁed for maximum reliability in heavy fuel serv-

ice. The corrosion-resistant steel crown addresses the high combustion pres-

sures and surface temperatures associated with heavy fuel operation; and the

cast iron skirt allows smaller running clearances at every load compared with

aluminium skirts. This enables the lateral thrust of the short connecting rod to

be distributed evenly over the full depth of the skirt. Better lubrication condi-

tions are also fostered over the entire power/speed range. Three piston rings

and a scraper ring are speciﬁed.

The cylinder liners are centrifugally cast from iron whose composition and

structure were specially developed to yield high mechanical and fatigue resist-

ance as well as good corrosion and wear resistance. The wall temperatures

obtained prevent low-temperature corrosion and minimize abrasive wear.

Individual cylinder heads, incorporating a thick bore-cooled ﬂame plate,

are held down by four hydraulically tightened studs. Each head accommodates

a central fuel injector, two inlet valves, two exhaust valves, a starting air valve

and an indicator cock. The exhaust valves and their housings were designed to

achieve high reliability and durability in heavy fuel operation, the speciﬁcation

calling for:

l Nimonic alloy valves with a high corrosion and heat resistance.

l Intensively cooled valve seat inserts in the cylinder head to allow

efficient cooling with even temperature distribution around the

valve seat.

S20 engine 667

668 Sulzer (Wärtsilä)

l Valve rotators.

l A cylinder head ﬂame plate which is particularly rigid and bore cooled

for minimum deformation under severe load conditions.

A helix-controlled fuel injection pump for each cylinder has a lubricating

oil barrier on the plunger to prevent fuel oil dilution of the system oil. The

regulating linkage for the pumps is inside the camshaft housing. The nozzles

of the fuel injection valves are cooled by lubricating oil.

Assembled from individual cylinder segments to facilitate overhaul, the

camshaft is driven from the crankshaft via a train of spur gear wheels.

A forced lubrication system for the engine is based on a deep sump. Before

the engine is started, oil is automatically delivered by a motor-driven pre-

lubrication pump.

Engine-driven pumps are arranged as standard for lubricating oil, jacket

cooling water and, in the case of marine diesel oil installations, fuel supply.

If required, a circulating pump can also be mounted for sea water or low-

temperature cooling water in a central cooling installation. The pumps are

driven from gearing at the free end of the engine.

Standardized ratings for engines operating on marine diesel oil or heavy

fuel oil, introduced in 1993, were accompanied by a uniﬁed turbocharging

match and a new cooling arrangement. The latter featured a compact, two-

stage charge air cooler and an oil cooler in series to create a cost-effective con-

ﬁguration with reduced cooling water ﬂow rates.

Turbocharging is based on a high-efﬁciency radial-type turbocharger in

conjunction with a single-pipe exhaust system. The pipe is assembled from

individual nodular cast iron segments for the cylinders, linked by bellows. As

an option, engines can be tuned for higher charge air pressures at part load to

give enhanced fuel economy in that operating range. Overpressure at full load

would then be avoided by ﬁtting a charge air waste gate to blow off excess air.

For gensets, such tuning has the added beneﬁt of achieving a quicker response

to changes in load. In propulsion engines, an automatically controlled bypass

is ﬁtted to connect the charge air manifold to the exhaust pipe at part load.

Maintenance is facilitated by hydraulic tightening devices for the cylinder

head holding-down studs, the main bearing studs and the connecting rod big

end studs.

669

C h a p t e r | t w e n t y s e v e n

Wärtsilä

The Wärtsilä Corporation grew from a modest Finnish base in the 1970s to

become a world force in four-stroke engine design and production through the

development of its own medium-speed programme and international acquisi-

tions. Enginebuilders absorbed into the group over the years include Nohab

Polar of Sweden, Stork-Werkspoor Diesel of The Netherlands, Wichmann of

Norway, the French companies Duvant-Crepelle and SACM, Echevarria of

Spain and Grandi Motori Trieste (GMT) of Italy.

In 1997 Wärtsilä Diesel’s Finnish parent group Metra took a dominant

holding in the newly formed Wärtsilä NSD Corporation, with Fincantieri of

Italy taking the remaining minority share. The new group embraced Wärtsilä

Diesel, New Sulzer Diesel and Diesel Ricerche (Fincantieri’s R&D arm) as

well as GMT, the enginebuilding division of Fincantieri, which became a fully

owned subsidiary in January 1999. The New Sulzer Diesel element brought

the signiﬁcant Swiss-designed low- and medium-speed engine portfolio under

the Wärtsilä umbrella. Wärtsilä Corporation’s medium-speed engine produc-

tion is now based in Finland and Italy, respectively focusing on small bore and

medium-to-large bore designs.

Wärtsilä Diesel laid the groundwork for its international growth in the early

1970s by deciding to develop a 320 mm bore medium-speed engine designed

from the outset for operation on heavy fuel. The resulting Vasa 32 engine was

tested at end-1976 and the ﬁrst production model delivered in 1978. The design

supplemented the company’s established smaller bore marine diesel oil-burn-

ing Vasa 22 series and helped to pioneer heavy fuel-burning medium-speed

engines for propulsion and auxiliary power.

Underwriting the Vasa 32 design’s pier-to-pier heavy fuel-burning capabil-

ity were a number of innovations which have since become standard medium-

speed engine practice: nodular cast iron pistons; forced exhaust valve seat

cooling to combat valve burning; an inverse cooling system to foster heavy

fuel operation in the low load range; a high injection pressure for improved

combustion; and a cylinder liner design with temperature control preventing

corrosion and deposit formation.