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

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700 Wärtsilä

and consequently lower mechanical load; reduced delay in the pre-burning phase,

which lowers peak pressure and temperature and hence curbs NOx emission for-

mation; improved starting ability; and increased thermal efﬁciency.

The mono-element injection pump (Figure 27.26) was designed to serve the

twin injection system. A constant pressure relief valve eliminates the risk of

cavitation erosion by maintaining a residual pressure at a safe level over the full

operating ﬁeld. A drained and sealed-off compartment between the pump and

tappet prevents leakage fuel from mixing with lubricating oil. The pre-calibrated

pumps are interchangeable.

Figure 27.26 Wärtsilä 46 engine fuel pump designed to serve the original twin

injection system

Fuel system pipes and main components are located in a hot box to secure

safety at high preheating temperatures; fuel pipes outside the hot box are also

carefully shielded. The fuel feed pipes on the engine are equipped with pres-

sure pulsation dampers. Any fuel leakage from pipes, injection valves and

pumps is collected in a closed piping system which keeps the hot box and the

engine dry and clean.

The twin injection system was later replaced by a single injection conﬁgu-

ration as higher pressure traditional layouts became available (Figure 27.27).

Spex Turbocharging

Swirl-Ex turbocharging—a constant pressure system with an in-built diffuser—

was speciﬁed for early Wärtsilä 46 engines. It demonstrated high efﬁciency

but service experience showed up a disadvantage due to the large volume in

the exhaust pipe which made the load pickup slower than the standard in other

Wärtsilä engines. A faster turbocharging system based on a single pipe with a

much smaller volume was therefore developed, resulting in the Spex system.

This offers a swift load pickup and almost the same efﬁciency at high load as

the Swirl-Ex system.

The aim of an exhaust system is to transfer the energy released from the cylin-

der, after the exhaust valve has opened, to the turbine of the turbocharger in the most

effective way. This could easily be done by making the pipes as short as possible

Figure 27.27 Single injection system for later Wärtsilä 46 engines

Wärtsilä 46 701

702 Wärtsilä

and the areas wide without restrictions. There are, however, other parameters that

must be taken into account, such as uniform scavenging. Since all the cylinders

are connected to the common system there is an obvious risk that a pulse com-

ing from one cylinder at the beginning of the blow-down phase disturbs the scav-

enging of another cylinder. To avoid this, the design has to be suited to all the pos-

sible cylinder conﬁgurations and speed ranges that the engine type will cover.

Another parameter affecting scavenging is the pressure drop between inlet

and exhaust manifolds. The higher the pressure difference, the better resistance

the cylinder has against the disturbing pulses in the exhaust manifold; the pres-

sure difference is largely a function of the turbocharger efﬁciency. Thus there

are many parameters affecting the performance of the exhaust system, and the

ﬁnal design is a compromise between various factors.

Turbocharging of the W46 engine is now optimized for the given applica-

tion exploiting the Spex system as standard (original Swirl-Ex engine installa-

tions in service were reconﬁgured). For special applications, where low load

running accounts for a large proportion of the total operating time, a three-

pulse system is also offered for appropriate cylinder numbers. Pulse charging is

reportedly excellent at partial load operation and for fast load response, while

Spex charging is said to be excellent at high and steady loads, with the load

response remaining good. Spex is based on an exhaust gas system that com-

bines the advantages of both pulse and constant pressure charging. Compared

with a constant pressure system, the ejector effect of the gas pulses provides

better turbine efﬁciency at partial loads. Very small deviations in the scaveng-

ing between the cylinders result in an even exhaust gas temperature.

Modular-built exhaust gas systems on the W46 engine are designed to han-

dle high-pressure ratios and pulse levels while being elastic enough to cope

with thermal expansion in the system. Exhaust wastegate, air bypass and air

waste gate arrangements can be speciﬁed to satisfy speciﬁc operating require-

ments, such as load response or partial load performance.

A load-dependent cooling water system is used for the LT water circuit. At

low load the water temperature is elevated by transferring heat from the lubri-

cating oil to the charge air. This eliminates the risk of cold corrosion in the

combustion space and also improves the ability to burn fuels of low ignition

quality at low loads. The HT cooling water system operates constantly at a HT

to make the temperature ﬂuctuations in the cylinder components as small as

possible and to prevent corrosion due to undercooling. The charge air cooler is

split into HT and LT sections to maximize heat recovery. Engine-driven pumps

are available as an option.

A wet or dry sump lubricating oil system can be speciﬁed. On its way to the

engine the oil passes through a full ﬂow automatic ﬁlter unit and a safety ﬁlter

for ﬁnal protection. A small proportion of the ﬂow is diverted to a centrifugal

ﬁlter which acts as a lubricating oil condition indicator and warns the operator

of excessively dirty oil and wear. Both the safety ﬁlter and the indicator ﬁlter

are designed for cleaning while the engine is running. An engine-driven lubri-

cating oil pump can be provided optionally.

Wärtsilä 46F

Market drivers, particularly environmental regulations, dictated not just an

upgrade but the development of a new 46 engine design based on the origi-

nal cylinder dimensions but exploiting novel solutions for key components

and systems (Figure 27.28). The resulting 46F engine, launched in 2004, was

described as more powerful without compromising reliability, and offering

attractive power-to-weight and space ratios, competitive fuel and lube oil con-

sumptions, and low emissions regardless of fuel quality.

The original 46 engine series remained on offer alongside the 46F pro-

gramme, which covers a power band from 7200 kW to 14 400 kW with six-to-

nine in-line and V12-cylinder models. (A V20-cylinder version introduced in

2007 with an output of 23 000 kW was initially intended for land-based power

installations.) Installation, operational and maintenance beneﬁts ﬂowed from

the increased speciﬁc rating since an engine with fewer cylinders (say, seven

instead of nine) can be speciﬁed to deliver the same power. More compact

machinery spaces and easier installation procedures are further fostered by

built-on support system modules.

Figure 27.28 An in-line six-cylinder version of the 46F engine

Wärtsilä 46F 703

704 Wärtsilä

A higher speciﬁc output (1250 kW/cylinder) was achieved by increasing

engine speed (from 500/514 to 600 rev/min) instead of mean effective pressure

(25.9 bar) and applying the latest developments in turbocharging to make wider

use of the Miller valve timing concept. Under full load operation early closure

of the inlet valves fosters a low effective compression ratio and hence com-

paratively low temperatures at the end of the compression stroke. The charge

air, both somewhat expanded and cooled on its way through the receiver into

the cylinders, contributes to creating the initial conditions for environment-

friendly combustion: a low global temperature that is still high enough to guar-

antee reliable and stable ignition of the fuel–air mixture.

An optional variable inlet valve closure (VIC) facility—ﬁrst designed for

the Sulzer ZA40S medium-speed engine—controls the closing time of the inlet

valves. With VIC it is possible to arrange an early Miller cycle or remove it

completely, control being possible while the engine is operating.

Wärtsilä’s common rail fuel injection system, a standard ﬁtment on the 46F

engine, maximizes the scope for adjusting the injection process to the prevail-

ing operating conditions, fuel characteristics and emission limits (see Chapter

8). The engine is optionally offered with a conventional fuel injection system

based on twin-plunger injection pumps (see section Wärtsilä 64).

In the CR system updated for the W46F engine the high-pressure pumps

are mounted on a tappet housing module which is interconnected between

cylinders. The module carries all low-pressure fuel system supply and return,

including drains and sealing oil systems, fostering a low level of piping den-

sity. The pumps are driven by a camshaft incorporating two cam lobes, with

one pump assigned to every two cylinders of the engine; pump ﬁlling is suc-

tion controlled by linear solenoid valves. The suction control valve is built as a

module together with the solenoid.

Each pump primarily feeds into an accumulator, each of which in turn

serves two injectors. The accumulators are interlinked by small bore piping to

form a CR. The piping between the accumulators undertakes three functions:

equalization of the pressure; reduction of pressure pulsations; and system con-

nectivity during engine warm-up circulation with heavy fuel oil.

Fuel ﬂow to the two-stage injector’s nozzle is controlled by a shuttle valve

actuated by control oil which, in turn, is controlled by a solenoid valve. The con-

trol oil pump is engine driven for easy black start. Nozzle needle movement is

controlled by the fuel pressure in the nozzle gallery, and pressure acting on the

press-down piston which, under certain safety conditions, keeps the nozzle shut.

A Spex system is standard, with options of exhaust gas waste gate or air bypass

depending on the application. The turbocharger can be located at either the free or

the driving end of the engine, transversal alignment allowing the exhaust gas outlet

to be inclined in the longitudinal direction. The charge air receiver is integrated in

the engine block, and the two-stage self-supporting charge air cooler comprises

separate HT and LT water sections (an advantage for heat recovery applications).

A continuous bearing temperature monitoring system covers not only the

main bearings (as in some earlier engines) but for the ﬁrst time also the big

end bearings, the latter beneﬁting from a new installation system patented by

Wärtsilä. The bearing temperatures are recorded at a point roughly half-way

between the crank webs and a few millimetres beneath the crankpin surface. A

stationary antenna mounted on the intermediate wall in the crankcase records

the bearing pin temperature every time the crank throw passes the registration

unit (several times a second). The temperature pickup is passive and requires

no electrical supply. Kongsberg Maritime’s Sentry wireless temperature moni-

toring system, speciﬁed as standard for the big end bearings, can be linked to

Wärtsilä’s condition-based maintenance system.

Nodular cast iron was retained for the engine block but the new compo-

nent, with an attractive stiffness-to-weight ratio, is both lower and lighter than

that of the 46 engine. The rigid and self-supporting block is designed for resil-

ient mounting applications, hydraulically tightened main bearing screws and

side screws, and to provide easy internal access for service personnel.

WärTSiLä 64

The most powerful medium-speed design ever brought to the market—and

reportedly the ﬁrst to exceed the 50 per cent thermal efﬁciency barrier (Figure

27.29)—the Wärtsilä 64 engine was prototype-tested in six-cylinder form in

September 1996 (Figure 27.30). Production models became available from

autumn 1997 and have since logged propulsion applications in container ships,

multipurpose cargo vessels and chemical/product tankers. The engines are

assigned for manufacture by Wärtsilä Italia in Trieste.

nominal output of 2010 kW/cylinder at 333 rev/min was originally quoted

for the 640 mm bore/900 mm stroke in-line cylinder design on a mean effective

pressure of 25 bar and a maximum cylinder pressure of 190 bar (Figure 27.31).

The rating was later raised to 2150 kW/cylinder with meps up to 27.2 bar.

Power demands up to 17 200 kW can now be met by a programme of six-,

seven- and eight-cylinder in-line models, the 9L- and V12-cylinder versions in

1960 1970 1980 1990 2000

20 Bore

32 Bore

46 Bore

64 Bore

Figure 27.29 rise in thermal eciency of successive Wärtsilä medium-speed

engine designs

Wärtsilä 64 705

706 Wärtsilä

the original programme having been dropped. The V-engine had the same bore

but a shorter stroke (770 mm) and lower speciﬁc power rating (1940 kW/cyl-

inder at 400–428 rev/min on an mep of 22–23.5 bar) than the in-line design.

Performance was boosted by a high-efﬁciency TPL80E turbocharger, one of

ABB Turbo Systems’ latest TPL series (see Chapter 7).

Reliability is sought from traditional Wärtsilä solutions, notably a pressure-

lubricated piston skirt, large bearings with thick oil ﬁlms, thick collar cylinder

liners ﬁtted with an anti-polishing ring, high fuel injection pressures for opti-

mized combustion, and camshafts with high torque capacity and low Hertzian

pressures. Easier installation is addressed by built-on cooling water pumps and

lubricating oil system (including automatic ﬁlters). Simplicity of maintenance

is reﬂected in a maximum overhaul time of 3 h for the ‘strategic’ components

(main and big end bearings, pistons, cylinder heads and injection pumps)

thanks to design measures and special tools.

W64 engine Details

Engine block: Wärtsilä suggests that nodular cast iron is the natural choice

for modern engine blocks because of its strength and stiffness properties and

the freedom that casting offers. Optimum use was made of current foundry

Figure 27.30 The Wärtsilä 64 engine is the world’s largest and most powerful

medium-speed design

technology to integrate most oil and water channels, resulting in a virtually

pipe-free engine with a clean outer exterior. Resilient mounting, now common,

calls for a stiff engine frame; integrated channels designed with this in mind

thus serve a dual purpose.

Crankshaft and bearings: advances in combustion development require a

crank gear which can operate reliably at high cylinder pressures. The crank-

shaft must be robust and the speciﬁc bearing loads kept at an acceptable level;

this is achieved by optimizing the crank throw dimensions and ﬁllets. The spe-

ciﬁc bearing loads are conservative and the cylinder spacing (important for the

overall length of the engine) is minimized. Apart from low bearing loads, the

Figure 27.31 Cross-section of Wärtsilä 64 design

Wärtsilä 64 707

708 Wärtsilä

other crucial factor for safe bearing operation is oil ﬁlm thickness. Ample ﬁlm

thicknesses in the main bearings are ensured by optimized balancing of rota-

tional masses and in the big end bearing by ungrooved bearing surfaces in the

critical areas. All these features ensure a free choice of the most appropriate

bearing material. The other thick-pad bearing technology concepts proven on

the Wärtsilä 46 engine (see p. 698) are also applied.

Piston and rings: a rigid composite piston with a steel crown and nodu-

lar cast iron skirt has been adopted for highly rated diesel engines for years to

secure reliability in a high cylinder pressure and combustion temperature envi-

ronment. Wärtsilä’s patented skirt lubrication is applied to minimize frictional

losses and ensure appropriate lubrication of piston rings and skirt. Each ring of

the three-ring pack is dimensioned and proﬁled for a speciﬁc task. The pres-

sure balance above and below each ring is crucial in avoiding carbon depos-

its in the ring grooves of a heavy fuel engine. Experience has shown that this

effect is most likely achieved with a three-ring pack, Wärtsilä reports. Another

factor favouring a three-ring pack is that most frictional losses in a reciprocat-

ing combustion engine originate from the rings. An extended lifetime is sought

from the piston ring pack and ring grooves through wear-resistant coating and

groove treatment (Figure 27.32).

Cylinder liner and anti-polishing ring: the thick high-collar type liner is

designed with the stiffness necessary to withstand both pre-tension forces and

combustion pressures with virtually no deformation. Its temperature is controlled

by bore cooling of the upper part of the collar to achieve a low thermal load and

Induction

Cr-plated

Cr-ceramic

Hardened

Cr-ceramic

Figure 27.32 Three-ring pack for Wärtsilä 64 engine piston; note the anti-polishing

ring incorporated in the upper cylinder liner (top right)

avoid sulphuric acid corrosion. The cooling water is distributed around the liners

with simple water distribution rings at the lower end of the collar. At its upper

end the liner is ﬁtted with an anti-polishing ring to eliminate bore polishing and

reduce lube oil consumption. The ring’s function is to calibrate the carbon depos-

its formed on the piston top land to a thickness small enough to prevent any con-

tact between the liner wall and the deposits at any piston position. When there

is no contact between liner and piston top land deposits, no oil can be scraped

upwards by the piston; at the same time, liner wear is also signiﬁcantly reduced.

Connecting rod: a three-piece rod with all highly stressed surfaces machined

is the safest design for engines of this size intended for continuous operation at

high combustion pressures, according to Wärtsilä. For easy maintenance and

accessibility the upper joint face is placed right on top of the big end bearing

housing. A special hydraulic tool was developed for simultaneous tensioning of

all four screws. An intermediate plate with a special surface treatment is arranged

between the main parts to eliminate any risk of wear in the contact surfaces.

Cylinder head: high reliability and ease of maintenance were sought from

a stiff cone/box-like design able to cope with the high combustion pressure and

secure both cylinder liner roundness and even contact between the exhaust valves

and their seats. The head design is based on the four-screw concept developed by

Wärtsilä and applied for over 20 years. Such a design also provides the freedom

needed for designing inlet and exhaust ports with minimal ﬂow losses. The port

design was optimized using computational ﬂuid dynamics (CFD) analysis in

conjunction with full-scale ﬂow measurements. Wärtsilä’s extensive heavy fuel-

burning experience contributed to the exhaust valve design, the basic criterion

for which is correct temperature; this is achieved by carefully controlled cooling

and a separate seat cooling circuit to secure long lifetimes for valves and seats.

Fuel injection system: the split-pump technology ﬁrst introduced on the W64

engine offers advantages in terms of operating ﬂexibility, mechanical strength

and cost-effectiveness. Fuel injection timing can be freely adjusted independently

of the injected quantity, and tuning of the injection parameters according to the

engine’s operational conditions improves engine performance and reduces exhaust

emissions. Smaller closed-type pump elements—derived from high volume pro-

duction of smaller engines—reduce mechanical stresses and enhance reliability,

while lower loads on rollers, tappets and cams improve pump drive reliability.

This new solution was dictated when injection pump manufacturers sug-

gested that for such a large medium-speed engine it would be very difﬁcult to

produce pump plungers of the size and accuracy required to secure the reliabil-

ity associated with smaller engine designs. Since the output of the Wärtsilä 64

is approximately double that of the established Wärtsilä 46, it was decided to

use two plungers (each of roughly W46 size) per engine cylinder.

The two plungers have slightly different functions (Figure 27.33). Both pump

fuel at each stroke and are connected to the same line, from where fuel is led to

the nozzle via a single high-pressure line. Although both plungers pump the fuel

in a similar way, only one of them needs to be controlled to adjust the fuel quan-

tity. This made it possible to reserve the other plunger for another task: turning

Wärtsilä 64 709