WÄRTSILÄ RT82 ENGINE SERIES TECHNOLOGY REVIEW

2

WÄRTSILÄ RT82 ENGINE SERIES TECHNOLOGY REVIEW This is a brief guide to the technical features and benefits of Wärtsilä

RT-flex82T, RTA82T as well as the RT-flex82C and RTA82C low-speed

marine diesel engines.

INTRODUCTION ............................................................ 4

DEVELOPMENT BACKGROUND .................................... 7

EXTENDED LAYOUT FIELD ............................................ 7

RT-flex: CONCEPT AND BENEFITS ................................. 8

RT-flex COMMON-RAIL TECHNOLOGY DESCRIPTION ...... 8

RT-flex: REAL IN-SERVICE FUEL ECONOMY .................. 10

RT-flex: CLEANER FOR THE ENVIRONMENT ................. 10

RTA82C and RTA82T: TRADITIONAL FUEL INJECTION .. 11

ENGINE STRUCTURE .................................................. 12

RUNNING GEAR ......................................................... 12

COMBUSTION CHAMBER ............................................ 13

PISTON RUNNING FEATURES ...................................... 14

WÄRTSILÄ PULSE LUBRICATING SYSTEM .................... 14

TURBOCHARGING AND SCAVENGE AIR SYSTEM .......... 16

INSTALLATION ARRANGEMENTS ................................. 16

WASTE HEAT RECOVERY:

COST SAVINGS WITH REDUCED EMISSIONS ................ 17

SERVICE EXPERIENCE ................................................ 18

MAINTENANCE .......................................................... 21

REFERENCES ............................................................. 22

MAIN TECHNICAL DATA .............................................. 237RT-flex82T top of rail unit

3

The Wärtsilä RT-flex82C, RTA82C, RT-

flex82T and RTA82T are low-speed

marine diesel engines, with a power range

between 21,720 to 54,240 kW. The C-type

engine has a stroke of 2646 mm where

as the T-type is designed with 3375 mm

stroke. The engines are tailor-made for the

economic propulsion of the new generation

of Panamax container ships and for very

large and ultra large crude oil carriers as

well as ore carriers (VLCCs, ULCCs and

VLOCs respectively). In this role they offer

clear, substantial, benefits:

• Optimum fit to ship, with extended layout

flexibility

• Competitive first cost

• Low fuel consumption over the whole

operating range

• Low cylinder lubricating oil consumption

• High reliability and low maintenance costs

• Overhauls only after every three years of

operation

• Low exhaust gas emissions

• Full compliance with the IMO NOX emission

regulation of Annexe VI of the MARPOL

1973/78 convention.

The Wärtsilä RT-flex82T and RT-flex82C have

as additional benefits:

• Smokeless operation at all running speeds

• Low ancillary power requirements

• Extremely low stable running speeds

• Reduced maintenance requirements with

simpler engine setting and extendable time

between overhauls.

The possibility of meeting the requirements of

two distinctly different market segments with

engines of the same cylinder bore and cylinder

power opened the way for the development

according to the platform concept. The

Wärtsilä RT-flex82C, RTA82C, RT-flex82T

and RTA82T engines have been developed

on the basis of a common platform, sharing

as many components as possible to bring

benefits of rationalisation in the design and

manufacturing, lowering manufacturing costs

and rationalizing also spare parts stocks.

The latest generation of Panamax container ships delivered with capacities up to 5000 TEU uses service speeds of about 24 knots. Studies revealed that such ships can best be served with engines having around 4520 kW per cylinder. The ‘C’ series engines have been especially designed for this application. They are available with six to twelve cylinders to cover a power range of 21,720 kW to 54,240 kW, while at nominal speed running between 87 and 102 rpm.

With view to the new trend to design more economical vessels with a lower design speed, the ‘T’ series engine, RT-flex82T (long-stroke

INTRODUCTION

7 RT-flex82T

4

version) can be applied. They are available with six to nine cylinders to cover a power range of 21,720 kW to 40,680 kW.

New large crude oil tankers and ore carriers range in capacity between 200,000 tdw to more than 350,000 tdw. For this type of ship, the ‘T’ series engine version is available. Its nominal speed range lies between 68 and 80 rpm. The ‘T’ versions also perfectly suit for container vessel applications if a low shaft speed is required.

The shop tests of these newly developed engines started in 2008. By the end of August 2010, already 50 engines passed their shop tests successfully and the market has readily accepted these engines with 32 engines already in service. As of August 2010, orders booked amounted to 130 engines with an aggregate power of around 4.3 GW.

Output kW

80 000

60 000

50 000

40 000

30 000

20 000

10 000

8 000

6 000

4 000

Output bhp

100 000

80 000

60 000

40 000

20 000

10 000

8 000

6 000

60 70 80 90 100 120 140Engine speed, rev/min

160 180

3 000

RT-flex82CRTA82C

RT-flex58T-DRTA58T-D

RTA72U-B

RT-flex84T-DRTA84T-D

RT-flex68-DRTA68-D

RTA48T-D

RT-flex96CRTA96C

RT-flex60C-B

RT-flex50-DRTA50-D

RTA52U

RTA62U-B

RT-flex82TRTA82T

RT-flex40

RT-flex35

5

7 RT-flex82T

6

Wärtsilä has a policy of continuously updating its

engine portfolio and engine designs to adapt them

to the latest market requirements and to deliver

the benefits of technical improvements. Much in

the design of the new 82 series engines is based

on experience gained with the Wärtsilä RTA84T

engine type that was introduced in May 1991.

Continuous cost reduction in the shipping industry stresses the need for the lowest possible capital investment and operating expenditure. Maximum uniformity in design, common parts and excellent manufacturability can substantially reduce costs.

The platform concept is well practised in the automotive industry, where cars of completely

different brands are designed and built using a common platform with many common parts, even engines and body panels, to reduce costs. Wärtsilä successfully applied that principle with engine types of the same 820 mm cylinder bore and the same cylinder power of 4520 kW/cylinder but with a different stroke, while meeting the requirements of two distinctly different market segments. The engines share as many components as possible to bring benefits of rationalisation in the design and manufacturing, lowering manufacturing costs, and optimising spare parts stocks. Similarity in design facilitates a quick familiarisation of the ship’s crew with the on-board technology while maintenance can increasingly be carried out in a standardised way.

PRINCIPAL PARTICULARS

Engine type RT-flex82C RTA82C RT-flex82T RTA82T

Cylinder bore (mm) 820 820

Piston stroke (mm) 2646 3375

S/B ratio 3.2 4.1

Rating point R1 R1+ R1 R1+

Power/cylinder (kW) 4520 4520 4520 4520

Corresponding speed (rpm) 97 102 76 80

bmep (bar) 20.0 19.0 20.0 19.0

Mean piston speed (m/s) 8.55 9.0 8.55 9.0

Number of cylinders 6 to 12 6 to 9

Power range (kW) 21 720–54 240 21 720–40 680

Power Engine MCR

Engine layout field

Extendedlayoutfield

Conventionallayout field

R1 R1+

R3

R4R2 R2+

DEVELOPMENT BACKGROUND

EXTENDED LAYOUT FIELD

During the initial studies for the 820 mm-bore

family of engines it became clear that, although

the required power could be readily identified, a

single running speed range could not be identified

as optimum for the two principal markets for these

engines. The solution was found to widen 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 points R1+ and R2+ at the same powers as R1 and R2 respectively but with 5% greater shaft speed. 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% increase in shaft speed at the R1+ point at the same power as at the R1 point, the engine is running at five per cent lower brake mean effective pressure (BMEP). The reduced

BMEP at the unchanged maximum combustion pressure (pmax) gives this R1+ point the benefit of a reduced brake specific fuel consumption (BSFC) compared with the R1 point.

The extended field offers usefully widened flexibility to select the most efficient propeller speed for lowest daily fuel consumption, and the most economic propulsion equipment, namely the propeller, shafting, etc., together with the appropriate propeller diameter for the projected ship.

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The Wärtsilä RT-flex system is the result of a

long project since the 1980s to develop low-

speed marine engines with higher efficiency.

The system overcomes the constraints

imposed by mechanically driven fuel injection

pumps and exhaust valve actuation pumps and

offers far greater flexibility in engine settings to

reach maximum performance, independent of

the sailing conditions. Electronically controlled

fuel injection offers the possibility to adapt the

fuel injection timing and rate as well as the

exhaust valve timing for optimum combustion

under all circumstances. The objective is

to provide ship owners with a system that

renders minimum fuel costs while offering full

compliance with emission regulations.

The Wärtsilä RT-flex concept replaces the mechanical camshaft and its gear drive, fuel injection pumps, exhaust valve actuator pumps and reversing servomotors of a slow-speed two-stroke engine, by a common-rail system for fuel injection, exhaust valve actuation and air starting. These functions are fully electronically controlled. That offers also the possibility to switch off one or more fuel injectors per cylinder, resulting in better fuel

economy and also smokeless operation at low loads. Moreover, the common-rail system with its volumetric control excellently balances the load over the cylinders and avoids cycle-to-cycle fluctuations. The common-rail injection system can handle the same grades of heavy fuel oil as are already standard for Wärtsilä low-speed engines.

Summarising, the RT-flex system offers a number of interesting benefits to ship owners and operators:

• Lower fuel consumption

• Smokeless operation at all operating speeds

• Lower stable running speeds, in the range

of 10–15 per cent of nominal speed

• Longer running times between overhauls

• Reduced maintenance requirements and

costs

• Higher availability owing to the integrated

monitoring functions

• High reliability from the built-in redundancy,

provided by the ample capacity and

duplication in the supply pumps, main

delivery pipes, crank-angle sensors,

electronic control units and other key

elements.

The two common rail pipes are stretched over

the length of the engine and housed as a rail

unit in an enclosure at just below the cylinder

cover level. The common rails and other

related pipe work are neatly arranged in an

easy accessible rail unit box sitting on top of

the main platform and are readily accessible

from above.

Fuel injection and exhaust valve operation are controlled by individual Injection Control Units for each cylinder. The control units are directly mounted on the single-piece rail pipes and are controlled using servo oil through Wärtsilä electro-hydraulic rail valves.

The common rail for fuel injection is fed with heated fuel oil at the usual high pressure (nominally 1000 bar) ready for injection. The supply unit has a number of high-pressure fuel supply pumps running on single-lobe

RT-flex: CONCEPT AND BENEFITS

RT-flex COMMON-RAIL TECHNOLOGY DESCRIPTIONcams. Fuel oil and servo oil are supplied to the common-rail system by pumps mounted in a very compact arrangement at the after end of the engine. The aft location simplifies access and maintenance. The fuel supply pumps are of the reciprocating plunger type designed by Wärtsilä while the servo oil pumps are of proprietary make. The pumps are driven through gearing from the crankshaft. The number of pumps depends upon the number of engine cylinders and engine power output. The fuel supply pumps are grouped in one (six to eight cylinder engines) or two (nine to twelve cylinder engines) Fuel Pump Units and the servo oil pumps in one Servo Pump Unit. The fuel supply pumps make several strokes during each crankshaft revolution owing to the drive gear ratio. Fuel delivery volume and rail pressure are regulated through suction control

of the fuel supply pumps. The servo oil for operating the fuel control units and exhaust valves is drawn from the engine lubrication system through an automatic self-cleaning fine filter and delivered at pressures up to 200 bar.

Fuel is delivered from this common rail through a separate Injection Control Unit for each cylinder to the standard fuel injection valves which are hydraulically operated in the usual way, by the high-pressure fuel oil. The injection control units, using quick-acting Wärtsilä rail valves, regulate the timing of fuel injection, control the volume of fuel injected, and set the shape of the injection 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 programmed to operate separately as necessary.

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The key features of the Wärtsilä RT-flex

common-rail system are:

• Precise volumetric control of fuel injection,

with integrated flow-out security

• Variable injection rate shaping and free

selection of injection pressure

• Stable pressure levels in common rail

• Possibility for independent control and

shutting off of individual fuel injection valves

• Ideally suited for heavy fuel oil through clear

separation of the fuel oil from the hydraulic

pilot valves

• Well-proven standard fuel-injection valves

• Proven, high-efficiency common-rail fuel

pumps.

The RT-flex system also encompasses exhaust

valve actuation and starting air control. The

exhaust valves are operated in much the same

way as in RTA engines by a hydraulic pushrod

but with the actuating energy now coming from a

servo oil rail at about 200 bar pressure. The servo

oil is supplied by high-pressure hydraulic pumps

incorporated in the Servo Pump Unit with the

fuel supply pumps. The electronically controlled

actuating unit for each cylinder gives full flexibility

in timing for valve opening and closing.

All functions in the RT-flex system are controlled, monitored and executed through the integrated Wärtsilä WECS-9520 electronic control system which triggers the electro-hydraulic rail valves for the respective functions. This is a modular system with separate microprocessor control modules for each cylinder, which are all connected together by a CANbus. Devices such as rail valves are directly connected to and controlled from these modules. The crankshaft position is detected by a crank angle sensor and provided directly to each control module through a redundant SSI bus. Provision is also made in the control

system for access for machine health monitoring, maintenance, adjustments, and troubleshooting.

The control modules are housed in cabinets mounted on the side of the rail unit. All control functions are distributed between the control modules in such a way that if one module fails, the engine remains in operation. The WECS-9520 thus has benefits of a single module type, simple wiring, few control boxes of standardized design, good communication within the system, integration with the ship alarm systems, redundancy and easy troubleshooting.

The WECS-9520 offers unmatched flexibility for interconnectivity between the RT-flex engine control system and the ship’s integrated remote control and safety systems according to the DENIS-9520 interface specification.

Injection Control Unit (left) and Valve Control Unit (right)

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RT-flex: REAL IN-SERVICE FUEL ECONOMYWhereas Wärtsilä RTA-series engines have

excellent fuel consumption in general, the RT-

flex system enables further improvements to be

achieved in the part load range. This is because

of the freedom allowed by the RT-flex system

in selecting optimum injection pressure, fuel

injection timing and exhaust valve timing at all

engine loads or speeds, while ensuring efficient

combustion at all times, even during dead slow

running.

In addition the similar freedom in exhaust valve timing allows the RT-flex system to keep combustion air excess high by earlier valve closing as the load/speed is reduced. This is not only advantageous for fuel consumption but also limits component temperatures, which would normally increase at low load. With a fixed valve timing, lower turbocharger efficiencies at part load normally result in low excess combustion air.

Another important contribution to fuel economy of the RTA and RT-flex82C and T engines is the capability for easily adapting the injection timing to various fuel properties, especially for fuels having a poor combustion behaviour.

DELTA TUNING AND LOW-LOAD TUNING: A FUEL EFFICIENCY ALTERNATIVEThrough their flexibility in engine parameter

settings, RT-flex engines also have an alternative

fuel consumption curve as standard to give

lower BSFC (brake specific fuel consumption)

in what is for many ships the main operating

range. Through Delta Tuning and Low-Load

Tuning, the BSFC is lowered in the mid- and

low-load operating range at less than 90 per

cent engine power. The consequent increase in

NOX in that operating range is compensated by

reducing NOX emissions in the high load range.

With the three BSFC curves, the engines comply

with the NOX regulation of the MARPOL 73/78

convention.

The engines, which are compliant with IMO Tier II emission regulations, are available in so-called cost-optimized or efficiency-optimized executions. While the cost-optimized versions are equipped with the same turbochargers as used for the Tier I versions the efficiency-optimized versions benefit from the higher scavenge pressure of the latest turbocharger generation resulting in lower fuel consumption. Scavenge air coolers and auxiliary blowers have to be adapted to the higher pressure level whereas the scavenge air receiver is identical.

RT-flex: CLEANER FOR THE ENVIRONMENTExhaust gas emissions have become an

important aspect of marine diesel engines.

All Wärtsilä RT-flex and RTA engines comply

with the NOX emissions limit of Annex VI of

the MARPOL 73/78 convention as standard.

RT-flex engines, however, come comfortably

below this NOX limit by virtue of their

extremely wide flexibility in optimizing the

fuel injection and exhaust valve processes,

together with enabling the engines to use

Delta and Low-Load Tuning for improved part-

load fuel saving.

The most visible benefit of RT-flex engines is, naturally, their smokeless operation at all speeds. The superior combustion with the common-rail system is largely because the fuel injection pressure is maintained at the optimum level irrespective of engine speed. In addition, RT-flex engines are able to run stable at very low speeds, slower than

StandardDeltaLow load

BSFC

(g/k

Wh)

Load (%)100%90%80%70%60%50%40%

176

174

172

170

168

166

164

RT-flex82C R1+ Tier II Efficiency-optimized tuning

0

1

2

3

4

5

6

7

8

9

10

0% 25% 50% 75% 100%

7RT-flex82C 2 x MET71MA Tier I

7RT-flex82C 2 x MET71MB Tier II

Smoke visibility limitAuxiliary blower on/off

Smok

e Bo

sch

3 ltr

. (%

)

3 2 nozzle injection

Load (%)

Engine aft end with supply unit

Smoke curves measured during shop test when tuned for IMO Tier I and Tier II emissions limits. Both curves demonstrate smoke-free operation at all engine loads, even at minimum load.

10

camshaft-type engines. They can run without smoking at about 12% nominal speed. This is made possible by precise control of injection, optimized injection pressures and optimized valve timing.

The 820 mm-bore engines, both RT-flex and RTA types, were developed from the very beginning to comply with the forthcoming IMO Tier II and Tier III NOX emissions regulations. These amendments to the MARPOL 73/78 convention were agreed in March/April 2008 by the Marine Environment Protection Committee (MEPC) of IMO (International Maritime Organization). Tests have shown that the RT-flex engines are ready to being adapted to comply with the lower emissions standard.

A useful reduction in all exhaust emissions, including CO2, can be obtained with all 82-bore engines by combining the engine with a waste heat recovery plant (see page 17).

In connection with the investigations of the possibilities of the RT-flex system, Wärtsilä is carrying out a long-term research programme

to develop techniques for further reducing exhaust emissions, including NOX, SOX and CO2, in both RT-flex and RTA engines.

RTA82C and RTA82T: TRADITIONAL FUEL INJECTION

The Wärtsilä RTA82C and T retain a traditional,

mechanical camshaft arrangement for fuel

injection pumps and valve drives. One housing

combines the fuel injection pump and the

actuator pump for exhaust valve actuation for

one cylinder of the engine.

The camshaft driven fuel pumps are of the well-proven jerk-type (also called Bosch-type). This kind of fuel injection control by a helix in the plunger is applied on many two-stroke and four-stroke engines. The concave form of the cam profile of the fuel pump allows the use of a pneumatically activated swing arm for reversing. This concept is combined

with a dual injection timing (DIT) mechanism, which enables a certain shift of the injection timing. DIT can increase the firing pressure at part load for improved fuel consumption. The fuel pump cover contains suction and delivery valves and a cut out device for emergency stop. The distribution of the fuel to the three injectors is also integrated into the pump cover.

The camshaft is assembled from a number of segments, each segment for one of two cylinders of the engine. The segments are flange-mounted together and to the gear wheel.

The camshaft drive uses the well-proven arrangement of gear wheels housed in a double column located at the driving end or in the centre of the engine, depending upon the number of cylinders. There are four gear wheels in the camshaft drive. The main gear wheel on the crankshaft is in one piece and flange-mounted.

RTA fuel pump arrangement

RT-flex fuel pump arrangement

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ENGINE STRUCTURE

Wärtsilä RT-flex82C, RT-flex82T, RTA82C and

RTA82TT engines have a well-proven type

of structure, with a ‘gondola’-type bedplate

surmounted by very rigid, monobloc double-

walled columns and a cast-iron monobloc

cylinder block, all secured by pre-tensioned

vertical tie rods. The whole structure is very

sturdy with low stresses and high stiffness.

Both bedplate and columns are welded

fabrications which are also designed for

minimum machining.

A high structural rigidity is of major importance for today’s two-stroke engines with their long strokes. Accordingly, the design is based on extensive stress and deformation calculations carried out by using a full three dimensional finite-element computer model for different column designs to verify the optimum frame configuration. The double-walled column has thick crosshead guide rails for greater rigidity under crosshead guide shoe forces.

The dry cylinder jacket, typically of bolted execution, has a high rigidity. Access to the piston under-side in the cylinder jacket is

normally from the fuel side, but is also possible from the receiver side of the engine, to allow for maintenance of the piston rod gland and also for inspecting piston rings.

The tilting-pad thrust bearing is integrated into the bedplate in a very compact and thus stiff housing. Owing to the use of gear wheels for the supply unit drive in the RT-flex and RTA engines, the thrust bearing can be very short and very stiff.

RUNNING GEAR

The running gear comprises the crankshaft,

connecting rods, crosshead, piston rods and

pistons, together with their associated bearings

and piston rod glands. The crankshaft is semi-

built comprising combined crank pin/web

elements forged from a solid ingot and the

journal pins then shrunk into the crank web.

The main, bottom-end and crosshead bearings are all of white metal on steel shells. Each main bearing cap is held down by four hydraulically-tensioned elastic holding down studs. The main bearing saddle and cover are machined together. This results in an

optimal joint face transition zone for the upper and lower bearing shells. The main bearings have thin shells with thick white-metal layers, whereas the thin shells of the connecting rod bottom-end bearings have thin white-metal layers.

The crosshead bearing is designed to the same principles as for all other RT-flex and RTA engines. It also features a full-width lower half bearing with the crosshead pin being of uniform diameter. The crosshead bearings have a lower thin-shell lined with white metal for a high load-bearing capacity whilst the bearing covers themselves are lined with white metal. The two guide shoes are single steel castings with white metal-lined running surfaces.

Extensive development work has been put into the piston rod gland because of its importance in keeping crankcase oil consumption down to a reasonable level and maintaining the quality of the system oil. The piston rod glands are of a proven design with highly effective dirt scraping action in the top part and system oil scraping in the lower part. The glands are provided with large drain

Column with cylinder jacket and liners Bedplate with crankshaft

12

areas and channels. Losses of system oil are minimized as there is substantially a complete internal recirculation of scraped-off oil back to the crankcase. Hardened piston rods are standard to ensure long-term stability in gland behaviour.

In the RT-flex82C and RT-flex82T engines, the fuel supply pumps and servo oil pumps are arranged on the after side of the aftermost column. They are driven by gearing from the crankshaft in two or three separate groups. The crankshaft gearwheel is mounted on the thrust collar. Separating the gear drives splits the drive torque, and thereby reduces the sizes of the intermediate and crankshaft gearwheels and their inertias.

COMBUSTION CHAMBER

The well-proven bore-cooling principle is

employed in the cylinder cover, exhaust

valve seat, cylinder liner and piston crown to

control their temperatures, as well as thermal

strains and mechanical stresses. The surface

temperatures of the cylinder liner are optimized

for good piston-running behaviour.

The cylinder liners are seated in the cylinder block, and are sufficiently robust to carry the cylinder covers without requiring a support ring. A light sleeve is applied to the upper part of each liner to form a water jacket around the respective liner.

The solid forged steel, bore-cooled cylinder cover is secured by eight hydraulically-tensioned elastic studs. It is equipped with a single, central exhaust valve in Nimonic 80A alloy which is housed in a water-cooled, bolted-on valve cage of grey cast iron. The exhaust valve is hydraulically actuated and has an air spring. The cylinder cover also carries the electronically-controlled starting air valve.

Three fuel injection valves are symmetrically arranged in each cylinder cover. Each fuel injection valve is separately supplied and controlled from the common-rail system. Anti-corrosion cladding is applied to the cylinder covers downstream of the injection nozzles to protect the cylinder covers from hot corrosive or erosive attack.

The pistons comprise a forged steel crown with a short skirt. The pistons each have three piston rings, all of which are pre-profiled and

have a chrome-ceramic coating. The robust top ring has a gas-tight lock for improved sealing, less gas blow by and thus reduced ring groove temperatures. The gas-tight ring thus results in less carbonized deposits. The two lower rings act as oil distributors and emergency seals. Piston crown top-land height is increased and clearances optimized to improve the sealing properties and to reduce gas temperatures at the top ring level. The whole concept was validated before its introduction over three years’ operation on five units (9- and 12-cylinder RTA96C). All have safely passed more than 15,000 running hours (about three years’ operation) in sometimes a hard environment.

The short skirt is equipped with two bronze rubbing bands. The piston and its short skirt are secured to the piston rod from below by hydraulically-tightened bolts. The pistons continue with the well-proven combined jet-shaker oil cooling of the piston crown which provides optimum cooling performance. It gives very moderate temperatures on the piston crown with an even temperature distribution right across the crown surface.

Cylinder liner

13

PISTON RUNNING FEATURESThe time between overhauls (TBO) of low-

speed marine diesel engines is today largely

determined by the piston-running behaviour

and its effect on the wear of piston rings and

cylinder liners. For this reason, the 820 mm-

bore engines incorporate a package of proven

design measures that enable the TBO of the

cylinder components, including piston ring

renewal, to be extended to at least three years,

while allowing a low cylinder lubricating oil

feed rate.

The standard design measures applied to these engines for excellent piston-running behaviour include:

• Liner of the appropriate material

• Careful turning of the liner running surface

and deep, plateau honing of the liner over

the full length of the running surface

• Chromium-ceramic coated, pre-profiled

piston rings in all piston ring grooves

• Anti-Polishing Ring (APR) at the top of the

cylinder liner

• Ample thickness of chromium layer in the

piston-ring grooves

• Wärtsilä Pulse Lubricating System for

cylinder lubrication.

A key element is the deep-honed liner. Careful machining and deep, plateau honing gives the liner an ideal running surface for the piston rings, together with an optimum surface microstructure.

The Anti-Polishing Ring prevents the build up of deposits on the top land of the piston which would otherwise damage the oil film on the liner and cause bore polishing.

It is also important that the liner wall temperatures are optimized to keep the liner surface above the dew point temperature throughout the piston stroke to avoid cold corrosion. This ensures that the engines are insensitive to fuel sulphur levels. At the same time, the ‘under-slung’ scavenge air receiver and the highly-efficient vane-type water separators with effective water drainage arrangements ensure that as much water as possible is taken out of the scavenge air.

WÄRTSILÄ PULSE LUBRICATING SYSTEM

Cylinder lubrication is provided by the

Wärtsilä Pulse Lubricating System (PLS). The

system doses the right quantity of lubricating

oil for good piston-running behaviour. The

lubricating oil feed rate is electronically

controlled according to engine load and

can also be adjusted according to engine

condition. The guide feed rate with PLS is

0.7–0.8 g/kWh for engine loads of 50–100%

and all fuel sulphur contents greater than

1.5%. Inclined lubricating oil grooves on the

cylinder liner ensure optimum oil distribution

in the circumferential direction. PLS delivers

reduced cylinder oil consumption without

compromising piston-running reliability in

Piston

14

order to meet the demand from owners and

operators for lower cylinder oil feed rates.

Besides reducing operating costs, reduced

cylinder oil feed rates are also beneficial for

their significant influence on reducing air-

polluting emissions in terms of particulate

matter.

The cost savings achievable with PLS are significant. In case of a Wärtsilä 12RT-flex82C engine of 54,240kW maximum continuous output running at 85 per cent load for 7000 hours a year with cylinder lubrication oil costing US$ 2000/tonne, the reduction from a traditional feed rate of 1.1 g/kWh (0.8 g/bhph) with the existing accumulator system to the PLS guide feed rate of 0.7 g/kWh (0.5 g/bhph) can generate cost savings of some US$ 260,000 a year.

Such a reduction in cylinder oil feed rate is made possible through the improved distribution of cylinder lubricating oil to the cylinder liner, and the fully flexible, precise, timing of oil delivery. The key feature of the Pulse Lubricating System is that it delivers accurately metered, load-dependent quantities of lubricating oil to the cylinder liner running surface at the precise timing required. Electronic control ensures the accurate dosage and timing, with full flexibility in settings.

The 820 mm-bore engine types are equipped with eight lubricator quills in each cylinder. These deliver lubricating oil directly into the piston ring pack. Cylinder lubricating oil is supplied under pressure to the lubricators by a newly-developed dosage pump which is driven by pressurized servo oil, either from the RT-flex engine servo oil rail or, in RTA engines, a separate servo oil supply.

There is a single dosage pump unit for each cylinder. The feed rate and timing of the cylinder oil are electronically controlled through a solenoid valve at the dosage pump. There is full flexibility in the volumetric metering of the

cylinder oil delivery across the engine’s load range. The dosage is precisely regulated even for low feed rates.

Service experience with the Pulse Lubricating System has been very successful with excellent liner and piston ring conditions. Trials have been carried out both on the Wärtsilä RTX-4 research engine in Winterthur and on shipboard engines. The first production engine fully fitted with PLS successfully passed its shop test in May 2006, with other engines following. Since then, more than 250 PLS have been employed in newbuildings and retrofitted to existing engines.

Piston ring pack through scavenge ports

Arrangement of the Pulse Lubricating System for one cylinder of an RT-flex engine

15

TURBOCHARGING AND SCAVENGE AIR SYSTEMThe engines are uniflow scavenged with air

inlet ports in the lower part of each cylinder

and a single, central exhaust valve in each

cylinder cover. Scavenge air is delivered

by a constant-pressure turbocharging

system with two or three high-efficiency

exhaust gas turbochargers depending

on the numbers of cylinders. For starting

and during slow running, the scavenge air

delivery is boosted by electrically-driven

auxiliary blowers.

The scavenge air receiver is of an under-slung

design with integral non-return flaps, air cooler,

water separator and auxiliary blowers. The

turbochargers are mounted on the scavenge

air receiver which also carries the support

for the exhaust manifold. The turbochargers,

air coolers and air receiver are in a compact

arrangement that allows optimum gas flows

while minimizing engine width.

Special attention has been given to removing water condensate before the scavenge air enters the cylinders. Immediately

after the horizontal air cooler, the scavenge air is swung round 180 degrees to the engine cylinders, in the process passing through the vertically-arranged water separator. The highly efficient water separator comprises a row of vanes which divert the air flow and collect the water. This arrangement provides the effective separation of condensed water from the stream of scavenge air which is imperative for satisfactory piston-running behaviour.

7RT-flex82C

16

An environmentally-clean way to cut operating

costs is to employ waste heat recovery (WHR)

in a Rankine cycle to generate electricity. With

these 820 mm bore engines, the generated

electrical power can be sufficient to cover all

shipboard services while the ship is at sea.

It is the only technology commercially available today that reduces both fuel consumption and exhaust emissions (such as CO2, NOX, SOX, etc.) at the same time. It also avoids the running of auxiliary engines while at sea with the corresponding savings in maintenance and spare parts costs.

The waste heat recovery plant follows the well-established concept of passing the exhaust gases of the ship’s main engine through a exhaust gas economizer unit to generate steam for a turbine-driven generator. The quantity of energy recovered from the exhaust gases can be increased by adapting the engine to the lower air intake temperatures that are available by drawing intake air from outside the ship (ambient air) instead of from the ship’s engine room. The engine room ventilation system absorbs thus less power because the engine combustion air is coming from outside without aid of ventilators.

The overall result of this concept is that the quantity of energy recoverable from the exhaust gas is increased without affecting the air flow through the engine. Consequently, there is no increase in the thermal loading of the engine and there is no adverse effect on engine reliability.

Heat is also recovered from the engine’s scavenge air and jacket cooling water for feedwater heating. The scavenge air coolers are designed in such a way that the boiler feed water can be heated close to the evaporation temperature.

For example, a high-efficiency WHR plant associated with a 31,640 kW seven-cylinder Wärtsilä RT-flex82T engine in a VLCC could deliver around 1500 kWe at engine full load under ISO conditions with 7.5% exhaust gas bypass using a dual-pressure steam system. As such a vessel would need only 900-1100 kWe for ship services while at sea, the tanker could operate without running its auxiliary engines while at sea under a wide range of ship speeds. It would save more than 1400 tonnes of fuel a year, with corresponding savings in all types of air emissions, especially CO2.

Turbogenerator set for the high-efficiency waste heat recovery plant, with the exhaust-gas power turbine on the left, the generator on the right, and the steam turbine to the right of centre.

WASTE HEAT RECOVERY: COST SAVINGS WITH REDUCED EMISSIONS

INSTALLATION ARRANGEMENTSCareful attention has been given to facilitating

installation of the engine in the ship. The

seating involves a modest number of holding-

down bolts and side stoppers, and there are

no end stoppers, thrust brackets or fitted

bolts. Thrust transmission is by thrust sleeves

on a number of holding-down bolts. By this,

the engine fixation time and cost could be

reduced by about 40 to 45% compared to the

corresponding competitor’s engine.

The required specific area of the exhaust gas pipe (mm2/kW) is reduced by about 15% owing to less specific exhaust gas flow. In addition the temperature of the exhaust gas is significantly higher leading to a higher possible waste heat recovery rate.

All ancillaries and their arrangement are optimized to reduce installation time and operating costs, with electrical requirements reduced by about 20% owing to lower specific flow rates of cooling water and lubricating oil.

Cross section RT-flex82C

17

SERVICE EXPERIENCEEngine performanceBy the end of August 2010, 50 RTA and

RT-flex 82 engines had successfully passed

their shop tests. The 8RTA82C was the first

engine shop tested at Hyundai followed by

the 7RT-flex82C type in summer 2008. The

Type Approval Test of the C-type engine was

carried out in September 2008.

In spring 2009 the first 7RT-flex82T was successfully shop tested and the type approval test was carried out on the fourth engine of this type by the end of September 2009.

Performance measurements of the three engine types, RTA82C, RT-flex82C and RT-flex82T, fully confirmed the calculations made during engine lay-out regarding engine performance, engine vibrations and component stresses. The specific fuel consumption and the NOX values are well within the defined limits. Low smoke values at low load have been measured which confirms the superior common-rail technology of the RT-flex engines.

Injection pipe arrangement of an RT-flex engine

Piston crown with clean ring pack after 6300 running hours

18

Temperatures of the principal components

around the combustion chamber – the cylinder

cover, cylinder liner, piston crown and exhaust

valve – were measured on both ‘C’ and ‘T’

type engines. After the final optimization of

the fuel injection nozzles, these component

temperatures were measured to be well

below the target values in the design and

development process. It is notable that the

temperatures are very consistent with very

little circumferential variation around the

combustion chamber.

Static and dynamic stresses were measured in all principal components of the engine structure as well as in the running gear in both the ‘C’ version (8RTA82C and 7RT-flex82C) and the ‘T’ version (7RT-flex82T). The structural components measured were the bedplate, column, cylinder jacket, scavenge air receiver, cylinder liner and cylinder cover. The running gear components measured were the crankshaft, connecting rod, crosshead guide shoes, RT-flex supply unit and the supply unit drive.

When compared with calculations made during the engine lay-out, the measured values for all components are within the target stress limits. The cylinder cover bolts had to be slightly modified to meet the target values.

Torsional and engine vibration measurements were carried out. The torsional vibration calculations of the crankshaft were

very well confirmed by the measurements. The measured engine vibration values are well within the acceptable limits defined by the classification societies. Initially the vibrations of the upper platform in the outer fore corner of the RT-flex 82C were slightly above the limit and had to be reinforced.

Additional attention was paid in October 2009 to the first 10RT-flex82C with its two Fuel Pump Units at the rear end of the engine.

NOX emissions tests for IMO Tier II have been carried out on both the RT-flex82C and the RT-flex82T engine types during shop tests. The required NOX values of 14.4 g/kwh could be readily achieved by the special engine tuning. Specific fuel consumption figures (SFOC) were within the predicted values and the smoke values well below the visibility limits.

Piston runningThe pistons of these 820 mm-bore engines are

each equipped with three piston rings. All three

rings are pre-profiled and chromium ceramic

coated. The top ring is 24 mm high and gas tight.

The running behaviour of rings and liners during shop tests was without complaint. The first 8RTA82C engine entered service in November 2008 in the containership ‘SCI Chennai’ of Shipping Corporation of India. It has accumulated more than 7000 running hours by the end of January 2010. The ‘SCI

Chennai’ was chosen for following up in service through regular engine inspections. The piston-running behaviour of this engine is very satisfactory. The piston ring package is very clean and the liners are in good condition. Wear measurements were carried out at 6000 hours. Liner wear of 0.01 mm/1000 hours and radial top ring wear of 0.02 mm/1000 hours have been measured.

Cylinder lubricationAll the 820 mm-bore engines are equipped

with the Pulse Lubricating System (PLS).

The time-controlled dosage pumps fitted at

each cylinder are behaving well. The cylinder

oil feed rates in the engines in service are

adjusted between 0.8 and 0.9 g/kWh. It has

been clearly experienced that piston ring

packages and piston undersides are cleaner

when cylinder feed rates are kept according

to Wärtsilä’s recommended values. Over

lubrication leads to contamination of piston and

liner, and must be avoided.

Running gear and main bearingsThe running gears of all engines were

inspected after shop tests and later in service.

All components are in good condition. The

main bearing No.5 of the first 8RTA82C engine

was inspected after 5600 running hours.

The contact area on the white metal side

shows normal running marks and the back

Excellent condition of the cylinder liner with PLS after 6300 running hours

19

of the bearing shell is spotless without any

fretting marks. The crosshead and bottom-

end bearings are also showing good running

behaviour.

Common-rail supply systemThe RT-flex fuel supply pumps are running

well. One fuel pump was completely

dismantled for inspection of all components

after a shop test. All components were found to

be in spotless condition. The same inspection

is also planned after 3000 running hours in

service.

At the same inspection, the servo oil supply pumps and gear wheels of the supply system

were also found to be in good condition. The gear wheels showed normal tooth contact marks.

Common-rail unitInjection control units (ICUs) and valve control

units (VCUs) employed in the rail unit are

working according to expectations. A complete

inspection of ICUs and VCUs is also planned

after 3000 running hours.

High vibration amplitudes were measured in the servo oil rising pipes. The vibration had led to broken bolts in the pipe connecting pieces to the servo oil rail. This shortcoming was fully solved when reinforced pipe supports were introduced.

WECS control systemThe Wärtsilä WECS-9520 control system

is working well. The RT-flex82 engines are

equipped with the same hardware since

introduction of the WECS-9520 concept in

2004. Some software updates, however,

have been introduced as a result of further

component developments and when

malfunctions were reported from engines in

service.

The latest released software, build 082, incorporates low load and sequential injection operation functions, and an improved cylinder lubrication algorithm.

Good condition of the main bearing after 5500 running hours

Crosshead bearing after 3000 running hours Bottom end bearing after 8000 running hours

20

MAINTENANCEPrimary objectives in the design and

development of Wärtsilä low-speed engines

are high reliability and long times between

overhauls. Three years between overhauls are

now being achieved by engines based on the

latest design standards. At the same time, their

high reliability gives ship owners more freedom

to arrange maintenance work within ships’

sailing schedules. Yet, as maintenance work is

inevitable, particular attention is given to ease

of maintenance by including tooling and easy

access, and by providing easy-to-understand

instructions.

All major fastenings throughout the engine are hydraulically tightened. Access to the crankcase continues to be possible from both sides of the engine. The handling of components within the crankcase is facilitated by ample provision for hanging hoisting equipment.

The Wärtsilä RT-flex system is designed to be user friendly, without requiring ships’ engineers to have any special additional skills. The system incorporates its own diagnostic functions, and all the critical elements are made for straightforward replacement. In fact, the knowledge for operation and maintenance of RT-flex engines can be included in Wärtsilä’s usual one-week courses for RTA-series engines available for ships’ engineers. Training time usually given to the camshaft system, fuel pumps, valve actuating pumps, and reversing servomotors is simply given instead to the RT-flex system. Gear wheels of the supply unit drive

21

REFERENCES

7RT-flex82T

8RT-flex82C

22

MAIN TECHNICAL DATA

DEFINITIONS • Dimensions and weights: All dimensions are in millimetres and are

not binding. The engine weight is net in metric tonnes (t), without oil

and water, and is not binding.

• R1, R1+, R2, R2+, R3, R4 = power/speed ratings at the six corners

of the engine layout field (see diagram).

• R1 = engine Maximum Continuous Rating (MCR).

• Contract-MCR (CMCR) = selected rating point for particular

installation. Any CMCR point can be selected within the engine layout

field.

• BSFC = brake specific fuel consumptions (BSFC). All figures are

quoted for fuel of lower calorific value 42.7 MJ/kg, and for ISO

standard reference conditions (ISO 15550 and 3046). The BSFC

figures are given with a tolerance of +5%.

• Wärtsilä RT-flex82C and RT-flex82T engines have a lower part-load

fuel consumption than the corresponding Wärtsilä RTA82 engines.

• The values of power in kilowatts and fuel consumption in g/kWh

are the standard figures, and discrepancies occur between these

and the corresponding brake horsepower (bhp) values owing to the

rounding of numbers. For definitive values, please contact Wärtsilä

local offices.

• ISO standard reference conditions

Total barometric pressure at R1 1.0 bar

Suction air temperature 25 °C

Relative humidity 30%

Scavenge air cooling water temperature:

– with sea water 25 °C

– with fresh water 29 °C

Cylinder bore ................................................820 mmPiston stroke...............................................2646 mmSpeed ................................................... 87–102 rpmMean effective pressure at R1/R1+ ........................................... 20.0/19.0 barPiston speed at R1/R1+ .......................... 8.6/9.0 m/s

Fuel specification: Fuel oil .................................................700 cSt/50°C ISO-F 8217:2005,

category ISO-RMK700

Rated power, principal dimensions and weights

Cyl.

Output in kW atLength A

mmWeight tonnes97 / 102 rpm 87 rpm

R1 / R1+ R2 / R2+ R3 R4

6789

101112

27 12031 64036 16040 68045 20049 72054 240

21 72025 34028 96032 58036 20039 82043 440

24 30028 35032 40036 45040 50044 55048 600

21 72025 34028 96032 58036 20039 82043 440

11 04512 55014 05516 50018 00519 51021 015

745 840 9351 0051 1451 2301 335

Dimensions mm

B C D E F* G

4 570 1 600 10 930 5 400 12 700 2 310

Brake specific fuel consumption (BSFC) in g/kWhFull loadRating point R1/R1+ R2/R2+ R3 R4

BMEP, bar 20.0/19.0 16.0/15.2 20.0 17.9

IMO Tier IRTA 171/169 165 171 167

RT-flex Standard Tuning 171/169 165 171 167

IMO Tier IIRTA 177/175 171 177 174

RT-flex Standard Tuning** 173/171 167 173 170

Part load, % of R1/R1+ 85 70 85 70 60

RT-flex tuning variant Standard Standard Delta Delta Low-Load

IMO Tier I 168.1/166.1 168.1/166.1 167.1/165.1 166.0/165.0 164.5/162.5

IMO Tier II** 169.8/167.8 169.0/167.0 169.1/167.1 167.5/165.5 166.5/164.5

* Standard piston dismantling height, can be reduced with tilted piston withdrawal. ** These BSFC values are for engines equipped with the latest high-efficiency turbochargers. Application of the previous generation of turbochargers leads to BSFC values that are 2g/kWh higher.Delta Tuning and Low-Load Tuning are only available with the high-efficiency turbochargers.

WÄRTSILÄ RT-flex82C IMO Tier I and Tier IIMain data: Also available as traditional RTA type

Cylinder bore ................................................820 mmPiston stroke...............................................3375 mmSpeed ..................................................... 68–80 rpmMean effective pressure at R1/R1+ ........................................... 20.0/19.0 barPiston speed at R1/R1+ .......................... 8.6/9.0 m/s

Fuel specification: Fuel oil .................................................700 cSt/50°C ISO-F 8217:2005,

category ISO-RMK700

Rated power, principal dimensions and weights

Cyl.

Output in kW atLength A

mmWeight tonnes76 / 80 rpm 68 rpm

R1 / R1+ R2 / R2+ R3 R4

6789

27 12031 64036 16040 680

21 72025 34028 96032 580

24 30028 35032 40036 450

21 72025 34028 96032 580

11 04512 55014 05516 500

810 9151 0251 165

Dimensions mm

B C D E F* G

5 320 1 800 12 250 5 400 14 750 2 700

Brake specific fuel consumption (BSFC) in g/kWhFull loadRating point R1/R1+ R2/R2+ R3 R4

BMEP, bar 20.0/19.0 16.0/15.2 20.0 17.9

IMO Tier IRTA 167/165 162 167 164

RT-flex Standard Tuning 167/165 162 167 164

IMO Tier IIRTA 173/171 167 173 170

RT-flex Standard Tuning** 168/166 162 168 165

Part load, % of R1/R1+ 85 70 85 70 60

RT-flex tuning variant Standard Standard Delta Delta Low-Load

IMO Tier I 163.7/161.7 162.5/161.0 162.8/161.0 161.5/160.2 159.7/158.3

IMO Tier II** 164.8/162.8 164.0/162.0 164.1/162.1 162.5/160.5 161.5/159.5

* Standard piston dismantling height, can be reduced with tilted piston withdrawal. ** These BSFC values are for engines equipped with the latest high-efficiency turbochargers. Application of the previous generation of turbochargers leads to BSFC values that are 3g/kWh higher.Delta Tuning and Low-Load Tuning are only available with the high-efficiency turbochargers.

WÄRTSILÄ RT-flex82T IMO Tier I and Tier IIMain data: Also available as traditional RTA type

23

WÄRTSILÄ® is a registered trademark. Copyright © 2010 Wärtsilä Corporation.

Wärtsilä is a global leader in complete lifecycle power solutions for the

marine and energy markets. By emphasising technological innovation

and total efficiency, Wärtsilä maximises the environmental and economic

performance of the vessels and power plants of its customers. Wärtsilä

is listed on the NASDAQ OMX Helsinki, Finland.