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

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offer advice to the ship’s engineers on achieving optimized TBOs. The system

supports the operator with graphs, pictures, trends and text recommendations.

Communication is possible between ships, the operator’s headquarters and

Wärtsilä’s CBM centre in all directions.

Three different solutions are offered to suit the individual requirements of

owners and operators:

1. CBM Virtual Expert. The operator performs data collection and analy-

sis, and Wärtsilä’s expert knowledge is given as far as possible without

further involvement. The onboard engineers carry out data collection,

the expert system being used on the ship as well as at the operator’s

HQ. Such a solution typically suits the needs of owners and operators

who have their own technical experts.

2. CBM Report Agreement. The operator collects the data and Wärtsilä under-

takes the analysis. The owner or operator uses only the data collector, while

the data are analysed at Wärtsilä’s two-stroke CBM centre in Switzerland,

which sends the customer a regular report. This type of agreement typically

suits owners and operators without their own technical ofﬁce.

3. CBM Inspection Agreement. Wärtsilä carries out both data collection

and analysis. Wärtsilä service engineers visit the ship in port, collect

the data and send them to the CBM centre, from where the customer

receives a report. Such a solution suits owners and operators without a

technical ofﬁce and who want to outsource inspections.

rT-FLEX ELECTroniC EnginES

Wärtsilä’s RT-ﬂex system, offered as an option for most models in the RTA

programme, resulted from a project originated by Sulzer in the 1980s to

develop an electronically controlled low-speed engine without the constraints

imposed by mechanical drive of the fuel injection pumps and exhaust valve

actuation. Traditional jerk-type fuel injection systems combine pressure gen-

eration, timing and metering in the injection pump with only limited ﬂexibility

to inﬂuence the variables. In contrast, Wärtsilä’s common rail system separates

the functions and gives far more ﬂexibility for optimizing the combustion proc-

ess with injection and valve timing.

RT-ﬂex engines are essentially the same as their standard RTA equivalents

but dispense with the camshaft and its gear drive, jerk-type fuel injection pumps,

exhaust valve actuator pumps and reversing servomotors. Instead, they are

equipped with common rail systems for fuel injection and exhaust valve actua-

tion, and full electronic control of these functions (Figures 12.32 and 12.33).

The following beneﬁts for operators are cited for the RT-ﬂex system:

l Smokeless operation at all running speeds.

l Lower steady running speeds (in the range of 10–12 per cent nominal

engine speed) obtained smokelessly through sequential shut-off of injec-

tors while continuing to run on all cylinders. Very steady running at

7 rev/min has been demonstrated.

rT-ex electronic engines 431

432 Wärtsilä (Sulzer) Low-Speed Engines

l Reduced running costs through lower part-load fuel consumption and

longer TBOs.

l Reduced maintenance requirements, with simpler setting of the engine;

the ‘as new’ running settings are automatically maintained.

l Reduced maintenance costs through precise volumetric fuel injection

control, leading to extendable TBOs. The common rail fuel system and

Fuel pump

Camshaft

Servomotor

Camshaft drive

Common rail

WECS 9000

control

Supply

pumps

RT-flex

RTA Series

Sulzer

FigurE 12.32 The fuel pumps, valve actuator pumps, camshafts and drive train of

the standard rTA engine are replaced by a compact set of supply pumps and com-

mon rail fuel system on the rT-ex engine

Exhaust

valve

actuator

Fuel

injectors

Volumetric

fuel injection

control unit

1000 bar fuel HFO/MDO

200 bar servo oil

30 bar servo oil

Exhaust

valve

actuating

unit

WECS9500

control system

Crank

angle

senso

50 µ

6 µ

FigurE 12.33 rT-ex electronically controlled common rail systems

its volumetric control yields excellent balance in engine power devel-

oped between cylinders and between cycles, with precise injection tim-

ing and equalized thermal loads.

l Reliability underwritten by long-term testing of common rail system

hardware and the use of fuel supply pumps based on proven Sulzer four-

stroke engine fuel injection pumps.

l Higher availability resulting from integrated monitoring functions and

from built-in redundancy: full power can be developed with one fuel

pump and one servo oil pump out of action. High-pressure fuel and

servo oil delivery pipes, and electronic systems, are also duplicated.

l A reduced overall engine weight: approximately 2 tonnes per cylinder

lower in the case of a 580-mm-bore RT-ﬂex engine compared with its

conventional RTA counterpart.

The common rail for fuel injection is a manifold running the length of the

engine at just below the cylinder cover level; the rail and other related pipework

are arranged on the top engine platform with ready accessibility from above

(Figure 12.34). The common rail is fed with heated fuel oil at a high pressure

(nominally 1000 bar) ready for injection into the engine cylinders. The fuel sup-

ply unit embraces a number of high-pressure pumps mechanically driven from

the crankshaft and running on multi-lobe cams, which increase their supply

capacity and hence reduce the number needed. A four-pump set is sufﬁcient for

a six-cylinder RT-ﬂex 58T-B engine. The pump design, based on fuel injection

pumps used in Sulzer four-stroke engines, has suction control to regulate the

fuel delivery volume according to engine requirements (Figure 12.35).

Heated fuel oil is delivered from the common rail through a separate injec-

tion control unit for each engine cylinder to the standard fuel injection valves,

which are hydraulically operated in the usual way by the high-pressure fuel. The

control units, exploiting quick-acting solenoid rail valves, regulate the timing of

rT-ex electronic engines 433

WECS 9000

control

Volumetric

injection

control

6 5 4 3 2

Common rail

Cylinder

Fuel

High-efficiency

fuel pump

FigurE 12.34 Schematic layout of Wärtsilä rT-ex common rail fuel system

434 Wärtsilä (Sulzer) Low-Speed Engines

fuel injection, control the volume of fuel injected, and set the shape of the injec-

tion pattern. The three fuel injection valves in each cylinder cover are separately

controlled so that, although they normally act in unison, they can also be pro-

grammed to operate separately as necessary. The key features of the common

rail system are deﬁned as follows:

l Precise volumetric control of fuel injection, with integrated ﬂow-out

security

l Variable injection rate shaping and free selection of injection pressure

l Stable pressure levels in common rail and supply pipes

l Possibility for independent control and shutting-off of individual fuel

injection valves

l Ideally suited for heavy fuel (up to 730 cSt at 50°C) through clear sepa-

ration of the fuel oil from the hydraulic pilot valves

l Proven standard fuel injection valves

l Proven high-efﬁciency common rail fuel pumps.

The fuel injection pressure can be freely selected up to more than 1000 bar

over the whole load range. In combination with different injection patterns, this

provides the opportunity to optimize the engine in several ways: for example,

for low emission levels or improved fuel efﬁciency at non-optimum loads (see

Environmental performance section, p. 436).

The injection system can be adapted to different patterns such as pre-injection,

with a small part of the fuel charge injected before the main charge; triple

injection, with the fuel charge injected in three separate short sprays in suc-

cession; and sequential injection, with individual actuation of the fuel injec-

tion nozzles so that injection timing is different for each of the three nozzles

FigurE 12.35 Three of the six fuel oil pumps for a Wärtsilä 7rT-ex 60C engine

in a cylinder. Different shapes of cylinder pressure proﬁle during the engine

cycle can thus be created, which, with free selection of the rail pressure, allows

the optimum pattern to be selected in each case for the loads and performance

optimization target of the engine.

Selective shut-off of single injectors is valuable for low manoeuvring

speeds or ‘slow steaming’ as this facility fosters better injection and atomiza-

tion of the small quantities of fuel needed. In such modes, the common rail

system is controlled to use the three injection valves in sequence. Regulated by

an electronic governor, the RT-ﬂex engine demonstrated very steady running at

a lowest speed of 7 rev/min.

Exhaust valves are operated in much the same way as in conventional RTA

engines by a hydraulic ‘pushrod’, but with the actuating energy coming from a

servo oil rail at 200 bar pressure. The servo oil is supplied by hydraulic pumps

mechanically driven from the same gear train as the fuel supply pumps. An

electronically controlled actuator unit for each engine cylinder—operated by

hydraulic pressure from the servo oil rail—gives full ﬂexibility for valve open-

ing and closing timing. Two redundant sensors inform the WECS-9500 control

system (see below) of the current position of the exhaust valve.

Lube oil from the engine is used as servo oil to keep the system simple and

compatible. Before entering the servo oil circuit, the oil is directed through an

additional 6-m ﬁlter with an automatic self-cleaning device to ensure reliabil-

ity and a long lifetime of the actuator units and solenoid valves.

All functions of the RT-ﬂex system are controlled and monitored through

the integrated Wärtsilä WECS-9500 electronic control system. This modular

system has separate microprocessor control units for each cylinder, with over-

all control and supervision by duplicated microprocessor control units, which

provide the usual interface for the electronic governor and remote control and

alarm systems.

The full-load efﬁciency of RT-ﬂex engines is the same as their conven-

tional RTA engine equivalents, but improvements in part-load fuel economy

are gained. This results from the freedom allowed in selecting the optimum

fuel injection pressure and timing, and exhaust valve timing, at all engine loads

or speeds, while maintaining efﬁcient combustion at all times, even during

dead slow running. A similar freedom in exhaust valve timing allows the RT-

ﬂex system to keep the combustion air excess high by earlier closing as the

load/speed is reduced. Such a facility is not only beneﬁcial for fuel consump-

tion but also it limits component temperatures, which normally increase at low

load. Lower turbocharger efﬁciencies at part load normally result in low excess

combustion air with ﬁxed valve timing.

Another contribution of the RT-ﬂex system to fuel economy cited by

Wärtsilä is the capability to easily adapt the injection timing to various fuel

properties inﬂuencing poor combustion behaviour. VIT over load had been a

traditional feature of Sulzer low-speed engines for many years, using a mechan-

ical arrangement primarily to keep the cylinder pressure high for the upper load

range. This is much easier to arrange in an electronically controlled engine.

rT-ex electronic engines 435

436 Wärtsilä (Sulzer) Low-Speed Engines

Environmental performance: A very wide ﬂexibility in optimizing fuel

injection and exhaust valve processes enables RT-ﬂex engines to comfort-

ably meet IMO limits on NOx emissions. The most visible beneﬁt cited is

smokeless operation at all ship speeds, underwritten by superior combustion.

The common rail system allows the fuel injection pressure to be maintained

at an optimum level irrespective of the engine speed. In addition, at very low

speeds, individual fuel injectors are selectively shut off and the exhaust valve

timing adapted to help keep smoke emissions below the visible limit. In con-

trast, engines with traditional jerk-type injection pumps have increasing smoke

emissions as engine speed is reduced because the fuel injection pressure and

volume decrease with speed and power, and they have no means of cutting off

individual injection valves and changing exhaust valve timing (Figure 12.36).

As all settings and adjustments within the combustion and scaveng-

ing processes are made electronically, future adaptations are possible simply

through changes in software, which could be easily retroﬁtted to existing RT-

ﬂex engines. A possibility is to offer different modes for different emissions

regimes. In one mode, the engine would be optimized for minimum fuel con-

sumption while complying with the global NOx limit; then, to satisfy local

emissions regulations, the engine could be switched to an alternative mode for

even lower NOx emissions while the fuel consumption is allowed to rise.

rT-Flex Engines in Service

The RT-ﬂex system was ﬁrst applied to a full-size research engine in June 1998

at Wärtsilä’s facilities in Switzerland and represented the third generation of

electronically controlled Sulzer diesel engines. The ﬁrst RT-ﬂex engine, a six-

cylinder RT-ﬂex 58T-B model, was tested in January 2001 and later installed

as the propulsion plant of a 47 950 dwt bulk carrier, which was handed over in

September that year. The engine’s slow-running capability was demonstrated

by steady operation at speeds down to 12 rev/min. Subsequent orders called

0 25 50 75 100 Load [%]

MDO

HFO

Sulzer common rail

Smoke visibility limit

Conventional fuel injection system

RTX-3 engine test results with MDO and HFO (Provisional)

FSN

0.5

0.4

0.3

0.2

0.1

FigurE 12.36 Smoke emissions with conventional fuel injection and with rT-ex

common rail technology for engines burning heavy fuel and marine diesel oil

for seven-cylinder RT-ﬂex 60C models, the ﬁrst Wärtsilä low-speed engine

designed from the bedplate up with electronically controlled common rail sys-

tems (Figure 12.37).

The RT-ﬂex option was extended to all bore sizes in the RTA series, the

ﬁrst contract for a 12-cylinder RT-ﬂex 96C engine developing 68 640 kW at

102 rev/min being booked for container ship propulsion in early 2003. Tested

in May/June 2004, this debut 12RT-ﬂex96C engine demonstrated an ability

to run stably at speeds down to 7 rev/min, fostered by improved combustion

which also promotes smokeless operation across the speed range.

82-Bore Series

Introduced to the market at end-2005, the ‘82’ programme embraces four

engine types—the RT-ﬂex82C, RTA82C, RT-ﬂex82T and RTA82T—sharing a

common platform. The two C-versions target container ship propulsion while

the two T-versions address large tankers and bulk carriers. The ﬁrst two pro-

duction examples, both eight-cylinder RTA82C models, were tested in early

2008 by the Korean licensee Hyundai Heavy Industries, which collaborated

with Wärtsilä in developing the 820-mm bore designs.

Development was stimulated by a clear need to replace the long-established

840-mm bore RTA84C engine, which had served well in Panamax container

ship propulsion for many years but could not meet the power demands of later

tonnage of that class with capacities up to 5000 TEU. Studies led to the choice

of 4520 kW/cylinder at 102 rev/min as the maximum continuous output of the

RTA82C and RT-ﬂex82C engines, compared with the 4050 kW/cylinder rating

of the RTA84C series.

rT-ex electronic engines 437

FigurE 12.37 A 7rT-ex60C engine on test at Wärtsilä’s Trieste factory in italy

438 Wärtsilä (Sulzer) Low-Speed Engines

A broadly similar increased propulsion power scenario was also anticipated

for the next generation of VLCCs and ULCCs, with capacities larger than

200 000 dwt and 350 000 dwt, respectively. This demand could be addressed by

the new RT-ﬂex82T and RTA82T engines with a maximum continuous output

of 4520 kW/cylinder at 80 rev/min compared with the 4200 kW/cylinder offered

by the established RTA84T-D engine. Similar considerations apply to the pro-

pulsion of very large ore carriers of around 300 000 dwt for which the new ‘82’

engines are equally valid.

The possibility of meeting the requirements of two distinctly different

market segments—container ships and tankers/bulk carriers—with engines of

the same bore size and cylinder output (4520 kW/cylinder) opened the way to

developing new engine types based on the platform concept. Parameters were

thus standardized as far as possible so that many components could be the

same for both engine types. All four engines feature an 820-mm bore but two

different strokes appropriate for the ship type targeted. The C-versions have a

stroke of 2646 mm and the T-versions have a stroke of 3375 mm.

During the initial studies it became clear that, although the required power

could be readily identiﬁed, single running speeds could not be identiﬁed as the

optimum for the two main targeted propulsion markets for the engines. The

solution was found in widening the layout ﬁelds to provide a range of speeds at

the given maximum continuous rated power output.

The engine layout ﬁelds, usually deﬁned by the power/speed ratings R1,

R2, R3 and R4, are thus extended to higher speeds deﬁned by the additional

rating points R1 and R2 , respectively, but with 5 per cent greater shaft

speed (Figure 12.38). Any power and speed within this whole engine layout

ﬁeld may be selected as the contracted maximum continuous rating (CMCR)

point for an engine.

With the 5 per cent increase in shaft speed at the R1 point at the same

power as the R1 point, the engine is running at a 5 per cent lower mep. This

80 85 00 05 100 105

Speed [%]

Power [%]

R1+

R2+

100

105

FigurE 12.38 greater layout exibility is provided by the ‘82’ bore engines. The usual

power/speed layout eld for Wärtsilä low-speed engines, dened by the points r1,

r2, r3 and r4, is extended to the points r1 and r2

reduced bmep at the unchanged maximum combustion pressure (P

max

) gives

this R1 point the beneﬁt of a lower speciﬁc fuel consumption compared with

the R1 point. The higher running speed at the R1 point offers the possibil-

ity of freedom to select a smaller propeller diameter but with the ship sailing

at the same fuel consumption (tonnes/day) as at the R1 rating using a larger

diameter propeller. An extended layout ﬁeld also allows the appropriate pro-

peller diameter to be selected in the case of ships with reduced draught, such

as container tonnage in the broad size range from 3000 TEU to 5000 TEU.

35- and 40-Bore Series

A strategic alliance forged between Wärtsilä and Mitsubishi Heavy Industries

in September 2005 resulted in a new range of small two-stroke engines

launched on the market in 2008. The 350-mm and 400-mm bore designs, avail-

able in mechanically and electronically controlled variants, offer the most

appropriate power ratings and running speeds for propelling small-to-medium

size cargo tonnage. Tapping experience from earlier and current generations of

small bore engines, the designers sought compliance with IMO Tier II emis-

sion regulations, low fuel consumption and cylinder oil feed rate, high relia-

bility and long TBOs. Electrical power consumption, weight and dimensions

were other development factors as well as competitive manufacturing costs.

The Wärtsilä 350-mm bore engines—designated RT-ﬂex35 and RTA35

models—offer an MCR of 870 kW/cylinder at 167 rev/min. The 400-mm bore

RT-ﬂex40 and RTA40 engines deliver a maximum output of 1135 kW/cylinder

at 146 rev/min. All are available in ﬁve-to-eight-cylinder versions, the 350-mm

bore models thus covering a power range from 3475 kW to 6960 kW and the

400-mm bore models a band from 4550 kW to 9080 kW. The RT-ﬂex versions

beneﬁt from Wärtsilä’s latest common rail fuel injection technology and full

electronic control of injection and exhaust valve operation. Otherwise sharing

the same main characteristics and design features as the RT-ﬂex models, the

RTA engines exploit a traditional camshaft for mechanical actuation of the fuel

injection pumps and exhaust valve pumps.

RT-ex35/RTA35 RT-ex40/RTA40

Bore (mm) 350 400

Stroke (mm) 1550 1770

output/cyl (mcr, kW) 870 1135

Speed range (rev/min) 167–142 146–124

Mean eective pressure (bar) 21 21

Mean piston speed (m/s) 8.6 8.6

Cylinders 5–8 5–8

power range (kW) 3475–6960 4550–9080

rT-ex electronic engines 439

440 Wärtsilä (Sulzer) Low-Speed Engines

SuLzEr rL-TypE EnginES

Active in both four-stroke and two-stroke design sectors, Sulzer’s links with

the diesel engine dated back to 1879 when Rudolf Diesel, as a young engineer,

followed up his studies by working as an unpaid workshop trainee at Sulzer

Brothers in Winterthur, Switzerland. The ﬁrst Sulzer-built diesel engine was

started in June 1898. In 1905 the company built the ﬁrst directly reversible

two-stroke marine diesel engine and, 5 years later, introduced a valveless two-

stroke engine with an after-charging system and spray-cooled pistons. Airless

fuel injection was applied to production engines in 1932 and turbocharging

from 1954.

Low-speed crosshead engine designs from Sulzer after 1956 were of the

single-acting two-stroke turbocharged valveless type employing loop scaveng-

ing and manifested progressively in the RD, RND, RND-M, RLA and RLB

series. A break with that tradition came at the end of 1981 with the launch

of the uniﬂow-scavenged, constant pressure turbocharged RTA series with a

single poppet-type exhaust valve (Figures 12.1 and 12.2).The RTA engine’s

immediate predecessor in the programme was the loop-scavenged RL series of

which examples remain in service and merit attention here.

The RLA56, a small-bore two-stroke engine introduced in 1977, incorpo-

rated the basic design concept of the successful RND and RNDM series but

extended the power range at the lower end. This 560-mm bore engine, of com-

paratively long stroke design, was the ﬁrst model in the RLA series. It retained

many of the design features of the then most recent economical loop-scavenged

RLB type (Figures 12.39 and 12.40), both engines using many features of the

earlier RND-M series.

A number of RND-M engine features were retained for the RLA and RLB

type, namely:

l Constant pressure turbocharging and loop scavenging

l A bore-cooled cylinder liner and one-piece bore-cooled cylinder cover

and water-cooled piston crowns

l Double guided crossheads

l New cylinder liner lubrication system with accumulators for the upper

liner part and thin-walled aluminium–tin crosshead shell bearings.

Major new design features peculiar to the RL types were as follows:

l A new bedplate design with an integrated thrust block; a new box-type

column design

l A semi-built or monobloc-type crankshaft without a separate thrust shaft

l Location of the camshaft gear drive at one end for engines of four to

eight cylinders

l Multiple cylinder jackets

l A bore-cooled piston crown

l Modiﬁed crosshead

l A new design of air receiver.