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

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680 Wärtsilä

Figure 27.10 Three Wärtsilä 6L20-powered gensets in the engineroom of a feeder container ship

air injection into the combustion chamber, contributing to optimized cylinder

head stiffness and valve performance.

An innovation in the W20 design was a multi-functional duct between the

cylinder head and the engine block (Figure 27.11). The multi-duct houses the

air duct from the air receiver to the cylinder head (the air duct creates the initial

swirl which helps to achieve optimum part-load combustion) and incorporates

the exhaust gas channel. The cooling water from the cylinder head is led to a

cast-in channel in the engine block through the multi-duct. The multi-duct is

also the support for the exhaust pipes, remaining in place when the cylinder

head is removed to ease maintenance.

A ‘distributed water ﬂow’ pattern is used to effect cooling of the exhaust

valves and cylinder head ﬂame deck. An even temperature distribution results

from increasing the ﬂow velocities on the exhaust side in general and around

the exhaust valve seat rings in particular.

The wear-resistant cast iron cylinder liner was designed for minimum

deformation thanks to its own stiffness and support from the engine block. It

was also important to tune the inner wall temperature to a level just above the

sulphuric acid dew point; this was addressed by creating an increased tangen-

tial cooling water ﬂow velocity just below the liner collar. The risk of bore pol-

ishing is eliminated by an anti-polishing ring at the upper part of the liner.

A traditional Wärtsilä concept was retained for the composite piston

(Figure 27.12) but reﬁned for a smaller bore engine operating on heavy fuel: a

nodular cast iron skirt, steel crown and pressurized skirt lubrication. Two com-

pression rings and a spring-loaded oil scraper ring are located in the crown,

Figure 27.11 The multi-duct of the Wärtsilä 20 engine facilitates maintenance of

the cylinder components

Wärtsilä 20 681

682 Wärtsilä

the efﬁciency of a three-ring concept having been proven in the Wärtsilä 46

engine. (Most of the frictional loss in a reciprocating combustion engine origi-

nates from the piston rings; a three-ring pack is considered optimal by Wärtsilä

with respect to function and efﬁciency.) Each ring is chromium plated and

dimensioned and proﬁled for its individual task. The top ring beneﬁts from a

special wear-resistant coating.

A connecting rod of forged and machined alloy steel with a stepped split

line lower end similar in design to that used in the Vasa 32 engines allows the

maximum pin diameter while still making it possible to pull the rod through

the cylinder liner (Figure 27.13). The advantage cited over the conventional

straight, oblique split line is an increase in pin diameter of at least 15 per cent,

a key factor in an engine designed for high combustion pressures. The fully

balanced crankshaft is forged in one piece and amply dimensioned for reliable

bearing performance. A small cylinder distance facilitates thin webs and large

bearing surfaces. A low bearing load and optimized balancing of the rotating

masses secure good oil ﬁlm thicknesses at all engine loads and speeds.

The low-pressure fuel system is an integrated part of the injection pump

achieved via a multi-functional housing which acts as a housing for the single-

cylinder pump, a fuel supply line along the whole engine, a fuel return line from

each pump, a housing for the pneumatic overspeed trip device and guidance

Figure 27.12 Wärtsilä 20 engine composite piston with nodular cast iron pressure-

lubricated skirt and steel crown

for the valve tappets. The high-pressure fuel line is also fully enclosed with

an alarm for possible leakages, and all fuel-carrying parts are housed in a

fully covered compartment (hot box). The high-pressure side is designed for a

2000 bar injection pressure although the pressure used is around 1500 bar. The

pump element itself features a solution to eliminate cavitation erosion. The fuel

injection valve is designed for uncooled nozzles which are heat treated for low

wear and high heat resistance.

A traditional two-circuit cooling water system incorporates a hot circuit for

jacket water and a cold circuit for air-cooling and oil cooling. The inverse cool-

ing principle introduced earlier by Wärtsilä on the cold circuit side has report-

edly proven valuable for engine operation on low-quality heavy fuels at part

load. A stepless electronically controlled version was developed for standard ﬁt-

ment to the W20 engine. The two pumps serving the cooling systems are engine

driven. The high-temperature (HT) cooling system is fully integrated into asso-

ciated engine components, virtually eliminating the use of pipes. Supply and

return channels are cast into the engine block while the pump cover and turbo-

charger support hold the connections between pump and engine block.

The system temperature is kept at a high level (about 95°C) for safe igni-

tion/combustion of low-quality heavy fuels at low loads. An engine-driven

pump of the cassette type is standard. The LT cooling system is also fully inte-

grated with the engine components (engine block, pump cover, air and lubricat-

ing oil cooler housings) and served by an engine-driven pump of the same type

as in the HT system. System temperature is electronically controlled as a func-

tion of engine load. The charge air temperature is optimized at every operating

point by heating the charge air with heat from the lubricating oil according to a

pre-set curve programmed into the electronic board.

The lubricating oil system is grouped compactly into two adjacent modules

at the ﬂywheel end: one contains the cooler thermostatic valves and ﬁlters, and

Figure 27.13 The connecting rod of the Wärtsilä 20 engine incorporates a stepped

split

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684 Wärtsilä

the other is a pump unit with a pre-lubricating pump and an engine-driven main

pump. The ﬁlter arrangement comprises three individual ﬁlter chambers which

can be switched off one by one when replacing the ﬁlter cartridge. A ‘safety mesh’

is also incorporated in each chamber. The paper-type ﬁlter cartridges are horizon-

tally positioned to facilitate proper cleaning of the chamber before a new cartridge

is installed. Centrifugal ﬁlters ﬁtted for further ﬁltration of the lubricating oil also

serve as the oil condition indicator.

A pulse turbocharging system was considered the best choice for an engine

designed for installations normally subject to frequent load variation and sud-

den load application. All cylinder conﬁgurations are served by an optimized

pulse system; no additional solutions are required for part-load operation.

The control and safety system is based on two cabling modules, one on each

side of the engine, and sensors of the ‘low mass’ type to avoid possible vibra-

tion damage. The sensors are prefabricated with the correct cable length and a

connector for connection to the cabling module. The modules in turn are con-

nected with multi-pin type connectors to the engine control unit (ECU) which is

resiliently mounted on the engine. Incorporated in the ECU is instrumentation

for local reading of engine and turbocharger speed, exhaust temperature after

each cylinder and after the turbocharger, an operating hour counter and elec-

tronic boards for speed measuring and charge air temperature control. Plug-in

connectors are provided for connecting the ECU to an external control system.

New W20 Layout

Seven years after Wärtsilä 20 engine production started, some design revi-

sions were made, mainly involving the ancillary equipment and with the aim

of improving environmental friendliness and adaptability to customer needs.

The main components, such as pistons, bearings and crankshaft, remained

untouched. The new layout was introduced at end-2000.

A drawback of the original layout was the paper cartridges used for lube

oil ﬁltration. The number of ﬁlter cartridges per engine varied between two and

four, depending on the cylinder conﬁguration. A typical genset installation of

three 9L20 engines running for 5000 h annually on heavy fuel oil would there-

fore generate hazardous waste in the shape of 100 used cartridges a year. The

main objective in revising the engine layout was to eliminate this waste and the

high cost of new ﬁlters for ship owners.

A completely new oil module was designed to enable the use of a fully auto-

matic back-ﬂushing lube oil ﬁlter incorporating elements of seamless sleeve fab-

ric with HT resistance. An overhaul interval of 1 year is recommended, and the

expected ﬁlter lifetime is 4 years. The channels directing the ﬂuids to the ther-

mostatic valves for the LT water and lubricating oil are integrated in the bracket

for the ﬁlter and the cooler. A horizontal position for the ﬁlter was chosen

because of space limitations and maintenance beneﬁts. The ﬁlter housing drains

automatically when the engine is stopped so that any overhaul inside the ﬁlter is

easier, and the risk of foreign particles entering the clean side is minimal.

The oil cooler design was also changed from a tube type to a brazed-plate

heat exchanger. The cooler needs no outer casing and its cooling capacity varies

with the number of plates (the height of the cooler); this makes it possible to use

one bracket for all engine cylinder conﬁgurations. The same basic oil module is

used on both LF (auxiliary) and LD (main) engines; it is simply rotated 180°.

The number and size of non-machined parts, after the oil ﬁlter, were reduced

signiﬁcantly to minimize the risk of foreign particles entering the system. Since

the Wärtsilä 20 cannot be equipped with running-in ﬁlters, to prevent damage to

the bearings or crankshaft during test runs, this redesign was necessary to allow

uninterrupted production. A dual drive, turbine-driven centrifugal oil ﬁlter is used

for removing particles from the ﬂush oil coming from the automatic ﬁlter. Both

dry and wet oil sumps are available. The main oil pump was moved to the front

of the engine to optimize the suction arrangement for every installation type.

The charge air cooling module was redesigned to ﬁt both versions of the

engine. A self-supporting ﬂange sealing was selected to eliminate the prob-

lems with sealing the cooler insert on the original design. The same cooler and

the outlet duct are used on both LD and LF engines. The compressor washing

arrangement is integrated in the water box for the cooler on the LD engine.

Also integrated in the design was the possibility to have a water mist catcher.

The water and fuel connections were moved to the sides of the engine to

improve the pipe layout and the support for the pipes. No piping disturbs the

overhaul space since all the pumps are arranged at the front of the engine.

Among the options are a direct-driven sea water pump, 100 per cent power

take-off at both ends, WECS digital control system, fully integrated standby

connections for water, fuel and lube oil, and fuel ﬂexibility (light and heavy)

possible for all engine types.

The old engine block design with loose feet (to make installation more

ﬂexible) had proved unnecessary in practice as it was useful in only a handful

of applications. The feet were thus integrated with the engine block casting to

reduce cost; the option to use loose feet was nevertheless retained and wider

feet were designed to create a more effective resilient mounting. The main oil

channel is machined in the engine block to reduce both labour and material

costs. The charge air receiver wall was provided with two openings since the

charge air duct can be placed at either end of the engine.

A major disadvantage of the Wärtsilä 20 engine for propulsion applications was

that the turbocharger could only be mounted at its free end. It was therefore decided

to make it possible for the turbocharger to be located at either end on the six- to

nine-cylinder models, the main contenders in the small-ship propulsion market.

WärTSiLä 26

The 260 mm bore/320 mm stroke Wärtsilä 26 engine (Figure 27.14) was

launched in 1995 as an eventual replacement for the SW28 model in the Stork-

Wärtsilä Diesel medium-speed programme. The design is characterized by a high

power density and the capability to run on heavy fuel up to 730 cSt viscosity. An

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686 Wärtsilä

advanced crankshaft design, signiﬁcantly reducing the distance between cylin-

ders, and a short connecting rod limiting the height of the engine contributed to a

short and low overall conﬁguration.

Propulsion and genset drive applications are now targeted by six, eight

and nine in-line and V12- and V16-cylinder models covering an output band

from around 1950 kW to 5440 kW at 900–1000 rev/min. Mean effective pres-

sures range from 24 bar to 25.5 bar, depending on heavy fuel or marine die-

sel oil operation, with power outputs up to 325 kW/cylinder (900 rev/min) and

340 kW/cylinder (1000 rev/min).

Most of the design work was executed at Stork-Wärtsilä Diesel in The

Netherlands. The designers deﬁned ﬁve key objectives: high reliability; low

fuel consumption and emissions; simple, space-saving installation; multiple

applications and fuel choices; and low operating cost per kilowatt. The goals

were addressed by combining technology developed speciﬁcally for the appli-

cation with design features of three earlier ‘new generation’ engines in the

Wärtsilä Diesel programme: the medium-speed W38 and W20 series and the

high-speed W200 series (Chapter 30).

High reliability was sought from the incorporation of structural and com-

ponent designs proven in these and other Wärtsilä engines, such as thick-pad

bearing technology and pressurized skirt lubrication. Extended times between

overhauls and enhanced lifetimes were also targeted.

Compact, more simple and accessible installations are addressed by inte-

grating ancillary support equipment (pumps, ﬁlters, coolers and thermostats) on

Figure 27.14 The W26 engine in V18-cylinder form; it is possible to change the lube

oil lter while the engine is running

the engine. Piping is eliminated from outside the engine; the channels for lubri-

cating oil and cooling water are all incorporated in the block and other castings;

and the inlet air receiver is also completely integrated in the engine block casting.

A multi-duct (Figure 27.15) combines several functions, providing a connection

between the inlet air receiver and the inlet port of the cylinder head, a ﬂow channel

for exhaust gases and a cooling water channel. It also supports the exhaust system

and facilitates dismantling of the cylinder head without disturbing that system.

The pursuit of integration reduced the overall number of Wärtsilä 26 engine

components by around 30 per cent compared with the SW28 design.

Engine length was saved by giving the crankshaft undercuts. The radii in

the transition from the crank web to the crankpin and from the crank web to the

journal are included in the web itself. As a result, it was possible to keep the

distance between the cylinders short and, at the same time, specify an optimum

bearing length. A beneﬁcial effect on the oil ﬁlm thickness of the bearings, and

hence their durability, was gained. The fully balanced crankshaft, suitable for

full power output to be taken off either end, was designed for maximum overall

rigidity and moderate bearing loads.

The highest possible rigidity was also sought from the cylinder head design

which features a conical intermediate deck and provides optimum support to

the ﬂame deck. The ﬂame deck has drilled coolant channels to inhibit large

thermal stresses. The exhaust valve seats are water-cooled and the valve tem-

peratures measured by sensors.

Flanged cylinder liners with tangential cooling water ﬂow are installed. The

liner is supported symmetrically at the top by the cylinder block and sized so

that the temperature on the inner wall remains high enough to prevent LT cor-

rosion yet low enough to ensure good lubrication. This design, proven on the

Wärtsilä 20 engine, makes drilled coolant holes unnecessary; as a result, a thin-

ner liner wall can be used. An anti-polishing ring at the top of the liner is spec-

iﬁed to prevent contact between the piston crown and the liner, thus avoiding

any bore polishing by combustion residues. High resistance to wear is further

fostered by elements in the alloy material of the liner. The anti-polishing ring

also contributes to a reported lubricating oil consumption of under 0.5 g/kW h.

Exhaust gas Cooling water Charge air

Figure 27.15 Schematic diagram of multi-duct connected to the cylinder head

(Wärtsilä 26 engine)

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688 Wärtsilä

The composite piston consists of an oil-cooled steel crown with three rings

(two ceramic chromium-plated compression rings and an oil distributor ring) and

a nodular cast iron skirt. Crown and skirt are fastened to each other by one cen-

tral bolt to foster an even, symmetrical load distribution (another feature whose

effectiveness had been demonstrated in the Wärtsilä 20 engine). Pressurized skirt

lubrication secures excellent tribological behaviour at high cylinder pressures.

A connecting rod with a horizontal split was developed for the Wärtsilä

26 engine, exploiting the ﬁnite element method to optimize the component

with regard to maximum stiffness and minimum mass. Key merits cited for the

resulting design are a short length, high rigidity, reliability and low mass (and

consequently a smaller load on the bearings). The rod is drilled with a single

hole without plugs for delivering lubricating oil to the piston.

An injection pressure of 2000 bar, necessary for ﬁne atomization of the fuel

and a short injection duration, is attained by closed barrel-type fuel pumps. Fuel

feed lines are integrated in the pump housing, and the fuel system is designed to

keep pressure pulses low. The high injection pressure dictated a very rigid cam-

shaft made of single-cylinder sections connected to each other by bearing journals.

Design details facilitate easier inspection and maintenance routines. The

stud bolts for the cylinder head, connecting rod and main bearing are hydrauli-

cally tensioned (Figure 27.16). When the head is removed, the multi-duct sup-

ports the exhaust gas piping and the insulation cover.

The seals of the cooling water pump can be replaced without dismantling the

pump itself. Replacement or inspection of the piston rings is possible without

disassembly of the liner: the piston can be partially removed from the liner for

this purpose.

The fuel pumps can be replaced quickly and simply without taking apart

the low-pressure piping and the tappets; the pump can be taken from the engine

Figure 27.16 The stud bolts for the cylinder head (shown here) as well as those for

the connecting rod and main bearing of the W26 engine are hydraulically tensioned

and overhauled under clean workshop conditions. Both air cooler and lubricat-

ing oil cooler are of the insert type, allowing convenient removal for cleaning,

and it is possible to change the oil ﬁlters while the engine is running.

A Wärtsilä-designed computer-based ECU protects the engine, warning

against possible problems before damage occurs. Signals from sensors are

transmitted to the unit via a CAN bus connection comprising a single cable

from one end of the engine to the other.

WärTSiLä 38

The 380 mm bore/475 mm stroke W38 design was developed by Wärtsilä

Diesel’s Dutch subsidiary Stork-Wärtsilä Diesel as a replacement for its age-

ing TM410 engine (see Chapter 28), ﬁlling a power gap in the group portfolio

between the Vasa 32 and W46 designs. The W38 series was introduced in 1993

with a speciﬁc rating of 660 kW/cylinder at 600 rev/min to cover a power band

from 3960 kW to 11 880 kW with six, eight and nine in-line and V12-, 16- and

18-cylinder models (Figure 27.17).

The design was distinguished by a new combustion philosophy applied to

achieve a high thermal efﬁciency and reduced NOx emissions (down by 50–70

per cent) without compromising fuel economy. The key parameters are a

stroke/bore ratio of 1.25:1, a maximum cylinder pressure of up to 210 bar and

a maximum fuel injection pressure of 1500 bar. Such parameters provide the

ﬂexibility to select a compression ratio, injection timing and injection rate that

allow the desired low NOx values to be attained.

A completely new fuel injection system was developed with the following

characteristics: suitable for continuous 1500 bar injection pressure; closed barrel;

Figure 27.17 V18-cylinder version of the Wärtsilä 38 engine

Wärtsilä 38 689