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

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670 Wärtsilä

Wärtsilä Diesel’s medium-speed engine programme was progressively

extended in the 1980s and 1990s with smaller and larger bore heavy fuel-burning

models to create the programme outlined in Table 27.1. The more recent designs

are the Wärtsilä 32 (a more modern longer stroke derivative of the Vasa 32), the

Wärtsilä 64 (the world’s most powerful medium-speed engine) and the Wärtsilä

50DF dual-fuel engine (derived from the Wärtsilä 46 design). Wärtsilä 20 and 32

engines are produced at the Vasa factory in Finland, while the Wärtsilä 26, 38,

46 and 64 engines are assigned to Wärtsilä Italia in Trieste. All the designs, apart

from the W64, are now available optionally with common rail (CR) fuel injection.

The various designs introduced features now widely used by other four-

stroke enginebuilders, Wärtsilä citing: side-mounted one-cylinder camshaft

sections; four cylinder head bolts for large engines; 1500 bar-plus fuel injec-

tion pressure; and a ‘hot box’ for fuel injection pumps and pipes. Advanced

machining systems allowed comprehensive integration of ﬂuid systems within

the engine block and the creation of multi-functional structural elements, sig-

niﬁcantly reducing the overall number of components.

Maximum cylinder pressure limits beyond 200 bar have been pursued by

the company (Figure 27.1), exploiting nodular cast iron piston skirts with

forced piston skirt lubrication: part of the oil for cooling the piston crown is

forced out through four nozzles leading to an annular oil distribution groove,

fostering well-controlled lubrication and hence increased reliability and

reduced liner wear. Thick-pad bearing technology has beneﬁted engines oper-

ating with high cylinder pressures.

A three-ring piston pack is standard for Wärtsilä engines as is an anti-pol-

ishing ring at the top of the cylinder liner (Figure 27.2). The function of the lat-

ter ring is to calibrate the carbon deposits on the piston top land to a thickness

Table 27.1 Wärtsilä medium-speed engines

Design Bore/Stroke

(mm)

Output

(kW/cyl)

Speed

(rev/min)

Cylinders

W20 200/280 200 720–1000 4, 6, 8, 9L

W26 260/320 340 900/1000 6, 8, 9L/12,

16V

W32 320/400 500 720/750 6, 7, 8, 9L/12,

16, 18V

W38B 380/475 725 600 6, 8, 9L/12,

16V

W46C 460/580 1000 500/514 6, 8, 9L/12,

16V

W46F 460/580 1200 600 6, 7, 8, 9L/12V

W64L 640/900 2150 333 6, 7, 8L

Anti-polishing ring

Bar

250

200

150

100

1960 1970 1980 1990 2000

Piston ring

technology

Pressure-lubricated

piston skirt

Piston ring

technology

Figure 27.1 Contributions to the development of the maximum cylinder pressure

limit in Wärtsilä engines

Figure 27.2 Anti-polishing rings have beneted all Wärtsilä engines (W32 engine

liner shown)

Wärtsilä 671

672 Wärtsilä

small enough to prevent contact between the liner inner wall and the deposits

in any position of the piston. Bore polishing is reportedly eliminated and liner

lifetimes can be doubled, accompanied by cleaner piston ring areas and signiﬁ-

cantly reduced lubricating oil consumption.

Low NOx combustion technology (whose principles are detailed in the sec-

tion Wärtsilä Vasa 32) can be applied to all current Wärtsilä models, reducing

noxious exhaust emissions without undermining fuel economy. The engines

can also be arranged for gas–diesel and dual-fuel burning installations (see

Chapter 2) and offered as part of group-supplied integrated Propac propulsion

packages embracing reduction gearing, propeller and control systems.

Wärtsilä has pioneered computer-based systems for engine control and

monitoring, condition monitoring and fault diagnosis, as well as multimedia

documentation and remote expert communication systems to support servicing

and maintenance (Figure 27.3).

WärTSiLä VASA 32

The 320 mm bore/350 mm stroke Vasa 32 engine (Figure 27.4) was designed

in the 1970s but beneﬁted from progressive reﬁnements yielding higher

power outputs, enhanced reliability and serviceability, and the acceptance

of fuels with higher CCAI numbers until the arrival in 1997 of the new gen-

eration Wärtsilä 32 (see section Wärtsilä 32). By that time, around 1900 Vasa

32 engines had been sold for marine service since the seagoing debut of the

design in 1978. Sustained demand nevertheless dictated continued production,

Figure 27.3 The engine computer is the ‘brain’ of the Wärtsilä engine Control

System (WeCS), shown here on a Wärtsilä 32

overlapping with the Wärtsilä 32 engine. The Vasa 32LN was produced in four, six,

eight and nine in-line and V12-, 16- and 18-cylinder models to cover propulsive

power demands from 1480 kW to 7380 kW at 720/750 rev/min. The D-rated ver-

sions offered 375 kW/cylinder while E-rated models yielded 410 kW/cylinder

with respective mean effective pressures of 21.9 bar and 24 bar.

The speciﬁcation comprises the following main elements:

Engine block: designed for maximum overall stiffness and cast in one piece

for all cylinder numbers; arranged for underslung crankshaft; and direct instal-

lation on resilient mountings possible.

Crankshaft: forged in one piece; fully balanced; and optional torsional

vibration dampers.

Connecting rod: forged in alloy steel and machined; and diagonally stepped

split in the big end.

Bearings: designed for maximum wear resistance.

Cylinder liner: special cast iron; and bore cooling for efﬁcient control of

liner temperature.

Piston/rings: composite piston with steel top and nodular cast iron skirt;

forced skirt lubrication; and ring set comprising three compression rings and

one oil scraper ring, all chromium plated.

Figure 27.4 The Wärtsilä Vasa 32 engine founded a family of heavy fuel-burning

designs

Wärtsilä Vasa 32 673

674 Wärtsilä

Cylinder head/valves: grey cast iron; absorbs the mechanical load with

a box section formed by an intermediate and an upper deck; mounted on the

engine block with hydraulically tensioned studs; twin inlet and twin exhaust

valves, all equipped with rotators; and water-cooled exhaust valve seats.

Camshaft: drop-forged one-cylinder shaft segments with integrated cams;

and bearing journals ﬁtted to the camshaft segments with ﬂange connections.

Fuel injection: one-cylinder pumps with built-in tappets; through-ﬂow type

pumps for heavy fuel operation; uncooled nozzles; and all fuel-carrying equip-

ment located in a drained and insulated space (the hot box) which keeps the

system at operating temperature and ensures safety in the event of leakage.

Exhaust pipes: nodular cast iron, the entire system enclosed in an insulat-

ing box for safety.

Low NOx Vasa 32

The Vasa 32 engine in 1994 became the ﬁrst in the Wärtsilä Diesel programme

to be released with low NOx combustion technology, a key measure calling for

the compression ratio to be increased from 12 to 14:1 to secure a sufﬁciently

high compression temperature. The smaller combustion space dictated reshap-

ing of the piston crown and the cylinder cover ﬂame plate to allow for the fuel

jets and good air/fuel mixing.

A new piston was developed for the higher maximum ﬁring pressure (raised

by 10 bar to 165 bar). Efﬁcient cooling of the alloyed steel crown of the compos-

ite piston was secured by applying the cocktail shaker principle. The piston pin

diameter was increased by 10 per cent to match the higher cylinder pressure. The

three-ring concept (as opposed to the original four-ring set) was also adopted

following good experience on the Wärtsilä 46 engine, the two compression rings

beneﬁting from a special wear-resistant chrome-ceramic coating (Figure 27.5).

The stiff bore-cooled cylinder liner was equipped with an anti-polishing

ring to keep carbon and ash build-up on the piston top land thin enough to pre-

vent contact between the liner inner wall and the deposits, regardless of the

piston’s position. The liner lifetime is reportedly doubled and the lubricating

oil consumption halved to 0.6 g/kW h or less.

The increased cylinder pressure also required the connecting rod to be

changed from the original diagonally stepped two-piece component to a fully

machined three-piece design with a horizontally split big end bearing. The change

yields greater safety at increased load and eliminates the need to interfere with

the big end bearing assembly when overhauling the piston; a disadvantage is the

increased number of parts. The load-carrying capability of the big end bearing

was raised by switching from an SnSb or SnAl to a BiAl material type.

Only a minor modiﬁcation to the cylinder head was necessary: a slight

reshaping of the ﬂame plate to provide more space for the fuel jets.

The fuel injection system was redesigned to handle demands for an increased

injection rate and improved atomization. As a result, the fuel cam is faster

and provides higher lift to compensate for the reduced plunger bore/stroke ratio.

The injection valve opening pressure was raised from 350 bar to 600 bar, mainly

to improve atomization at the start and stop of injection, and to maintain the

higher injection pressure needed for a shorter injection period and reduced igni-

tion delay. Improved part- and low-load performance was apparent, along with

reduced NOx formation and fuel consumption. Test results showed it was poss-

ible to reach an NOx level of 11 g/kW h, a 30 per cent reduction compared with

a standard Vasa 32 engine (IMO’s limit is 12 g/kW h NOx at 720/750 rev/min).

At the same time, the speciﬁc fuel consumption was lowered from 187 g/kW h

to 180 g/kW h while maintaining a reasonable combustion pressure of 165 bar,

only 10 bar higher than that of a standard Vasa 32 engine.

Wärtsilä Diesel also developed a planetary gear with controls to replace the

standard intermediate gear of the camshaft transmission. The arrangement allowed

a retarded fuel injection mode to be temporarily engaged while the engine was in

operation to meet modest local NOx emission limits (up to 30 per cent reduction

on normal emission levels at the expense of a rise in fuel consumption).

WärTSiLä 32

A new generation 320 mm bore model was introduced to the market in 1997,

the Wärtsilä 32 exploiting a longer stroke (400 mm) than its Vasa 32 predeces-

sor and incorporating design features established on the Wärtsilä 20, 26, 38 and

46 engines (detailed later in this chapter). A higher output than its predecessor

Figure 27.5 Composite piston of Vasa 32 low NOx engine designed for increased

combustion pressure and low friction

Wärtsilä 32 675

676 Wärtsilä

was offered (460 kW/cylinder at 750 rev/min on a mean effective pressure

of 22.9 bar) to give a power range up to 8280 kW from in-line six, eight and

nine and V12-, 16- and 18-cylinder versions. (The programme now includes a

seven-cylinder model.)

Scope for future speciﬁc power rises was demonstrated by the test engine

operating comfortably on an mep of 31 bar. A higher rating was subsequently

released (500 kW/cylinder at 750 rev/min on an mep of 24.9 bar) to extend

the power range to 9000 kW. A speciﬁc fuel consumption of 173–180 g/kW h

(without engine-driven pumps) is quoted, depending on nominal output or opti-

mal point operation.

Although slightly taller and heavier than the Vasa 32, the Wärtsilä 32 is more

compact and has a better power/weight ratio. Integration reduced the number of

components in the new engine by 40 per cent compared with its forerunner and

contributed to a neater look and lower production costs (Figure 27.6). Ducts for

water and oil are incorporated in the engine block, and low-pressure fuel pipes

were replaced by ducts integrated in the injection pump design.

A substantial reduction in the number of joints to be broken during engine

overhauls resulted. Further attention was paid to easing maintenance. The

multi-duct (Figure 27.7) containing the water system and the exhaust and air

piping, for example, stays in place when the cylinder head is lifted; the joints

for starting air, oil and return fuel are slide-in connections; and, as there is no

real jacket water, only a limited amount of water has to be drained when main-

taining the cylinder unit. Ergonomic reﬁnements were also pursued: the rocker

Figure 27.6 engine-driven pumps are standard for the Wärtsilä 32; note the clean

lines achieved by integrated duct systems which eliminate external piping

arm cover is suspended on hinges and stays in place when the rocker arms of

the injector are attended. Service pumps, including the pre-lubricating pump,

are arranged on the engine along with a lubricating oil module which incorpo-

rates an automatic back-ﬂushing ﬁlter (Figures 27.8 and 27.9).

Figure 27.7 The multi-duct remains in place when the cylinder head is lifted

(Wärtsilä 32 engine)

Figure 27.8 Lubricating oil module for mounting on the Wärtsilä 32 engine

Wärtsilä 32 677

678 Wärtsilä

The low-pressure fuel line comprises drilled channels in cast parts clamped

ﬁrmly on the engine block, these parts consisting of the pump housing, the tap-

pet housing, the fuel transfer housing and the multi-cover. For easy assembly/

disassembly, the parts are connected to each other with slide connections. Both

the whole low-pressure and high-pressure systems are housed in a fully cov-

ered compartment. The high-pressure system is designed and endurance tested

at 2000 bar, and the injection pressure is around 1800 bar. With a wear-resistant

low-friction coating on the fuel plunger, no lubricating oil is required for the

pump element. The proﬁled plunger geometry allows the clearance between

plunger and barrel to be kept small, thereby allowing only a minimum of oil to

pass down the plunger; this small leakage is collected and returned to the fuel

system. Any likelihood of fuel mixing with the lube oil is eliminated.

The turbocharging system is speciﬁed to suit the requirements of each

engine application from these standard options: pulse system, single pipe

exhaust (Spex) system and Spex system with exhaust waste gate and air bypass.

The systems are designed for minimum ﬂow losses on both exhaust and air

sides, the interface between engine and turbocharger streamlined to avoid all

the adaption pieces and piping often used in the past.

The Wärtsilä Engine Control System (WECS) serving the Wärtsilä 32 measures

a range of parameters and undertakes safety monitoring of the main bearing and

Figure 27.9 Lubricating oil module mounted on the side of a Wärtsilä 32 in-line

cylinder engine

cylinder liner temperatures, as well as individual exhaust valve monitoring. In the

case of the V18-cylinder model, for example, the computer-based system measures

97 temperatures, 10 pressures, four speeds, three positions and seven levels. It also

controls starting and stopping, the low-temperature (LT) thermostatic valve, waste

gate and bypass valves, and slow turning, and interfaces with external systems.

WärTSiLä 20

Introduced in 1992, the 200 mm bore/280 mm stroke Wärtsilä 20 engine

(Figure 27.10) was designed primarily as a genset drive to replace the long-

established Wärtsilä Vasa 22 but small-ship propulsion installations have also

been logged. An output per cylinder of 130 kW to 165 kW was initially offered,

depending on the nominal speed (720–1000 rev/min), but subsequent power

rises took the rating to 180 kW/cylinder (end-1998) and 200 kW/cylinder at

1000 rev/min (2003). The rating increases were underwritten by designing all

key components for a maximum cylinder pressure of 200 bar; engines are cur-

rently released with a P

max

of 170 bar.

The W20 series now embraces four-, six-, eight- and nine-cylinder models

covering a maximum continuous output range from 720 kW to 1800 kW. Up

to 24 000 h between overhauls have been achieved by engines running on light

fuel oils.

A ﬂat fuel consumption curve, with the lowest point preferably at part load, is

desirable for an auxiliary engine which seldom operates at full load and may often

run at a very low load. This was addressed in the Wärtsilä 20 design by optimiz-

ing the cylinder dimensions in conjunction with modern turbocharging technol-

ogy; adopting a pulse charging system; and exploiting a high cylinder pressure.

Physically, the Wärtsilä 20 was intended to be shorter and lower than any

existing engine in its performance class, with advantages in ease of installation

and maintenance. The nodular cast iron engine block was designed for maxi-

mum overall stiffness and local stiffness around the upper part of the cylinder

liner, and to incorporate a number of cast-in or machined water and oil chan-

nels in pursuit of component integration. The camshaft bearings are directly

housed in the block as is the camshaft gear train at the ﬂywheel end of the

engine. Provision is made for ﬁve engine-driven pumps (three are standard).

A four-point support conﬁguration underwritten by the overall stiffness of the

engine is especially attractive for resilient mounting, and the screwed-on feet

arrangement offers considerable freedom in foundation design.

The four-screw cylinder head and box-cone design is another Wärtsilä

tradition retained to achieve even sealing pressure and prevent liner deforma-

tion under high cylinder pressures. It also secures ample space for large inlet

and exhaust channels which are necessary for good gas exchange. The head

is mounted on the engine block with hydraulically tensioned studs, and is

arranged to house two inlet and two exhaust valves, all equipped with rotators;

the exhaust valve seats are water cooled. A starting air motor for all engine

cylinder conﬁgurations was speciﬁed in contrast to traditional direct starting by

Wärtsilä 20 679