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

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running surface of the piston ring is chamfered on approximately half of the

surface. MAN Diesel explains that a well-running ring has a ballistic shape,

starting at the top of the ring and ending at its bottom. The chamfering therefore

helps the ring to run-in swiftly and safely as well as securing good gas sealing.

Mark 9 large bore engines 351

FigurE 10.44 The oros P relief bore design (right) is specied for the updated K-type

engines, omitting the safety valve on the exhaust valve actuator

FigurE 10.45 A spray cooling insert secures a comfortably low piston temperature

for the Mark 9-rated large bore engines

352 MAN B&W Low-Speed Engines

PC rings are incorporated in the top of the liner to avoid the build-up of

carbon deposits on the topland, which would otherwise harm the cylinder con-

dition by scraping the lube oil off the walls. Overall, the combustion chamber

design is said to foster low wear rates at low cylinder oil feed rates, long TBOs

and good scufﬁng resistance.

With a view to omitting the safety valve on the exhaust valve actuator,

the Oros P version of the Oros design was chosen for the updated K-engines

(Figure 10.44). The reason was that the Oros piston leaves less room for ﬁtting

the exhaust valve spindle than with the traditional piston design. To prevent

contact between piston and spindle, therefore, a mechanical stop is built into

the exhaust valve air spring, thus limiting the maximum spindle lift.

The exhaust valve design previously used for engines without an Oros com-

bustion chamber featured relief bores in the exhaust valve oil cylinder, which

would be uncovered in the event of excessive spindle lift. With the mechani-

cal lifter, however, excessive lift and pressure relief using such bores were no

longer possible; for that reason, a safety valve was built into the exhaust valve

actuator.

Using the Oros P version, designed with a slightly lower piston dome, cre-

ates enough space to allow a slightly larger exhaust valve spindle lift. This

makes it possible to exploit the well proven relief bore design of the exhaust

valve oil cylinder, and the safety valve on the actuator is no longer necessary.

MAN Diesel asserts that such a solution represents a cost saving for engine

Alu-coat for running-In 0.1 mm

Grey cast iron base material

Cermet coating 0.3 mm

Grey cast iron base material

Chrome-plated bottom face

Grey cast iron base material

Alu-coating

Alu-coating for running-In 0.1 mm

Cermet coating 0.5 mm

1st ring

2nd ring

3rd ring

4th ring

Vermicular cast iron base material

Chrome-plated bottom face

FigurE 10.46 Hard-Coated/semi Alu-coat ring package

licensees and a simpliﬁcation for operators, yet with performance identical to

the original Oros design.

A spray cooling insert is now provided to obtain a comfortably low piston

temperature (Figure 10.45). Improved cooling is conﬁrmed by piston crown

temperature measurements taken on the testbed and on engines in service.

Comparative measurements with and without a spray cooling insert revealed a

temperature reduction at the central part of the crown, both on the combustion

chamber side and on the cooling side; the insert thus increases both of the mar-

gins against hot corrosion and underside coke formation.

An exhaust valve unit of a modiﬁed type uses a low-grade cast iron hous-

ing with water cooling around the spindle guide and bore-cooled twin stud

bosses. The upper part of the housing forms the bottom of the air spring and

the lower part forms part of the cooling chamber in the cylinder cover. Apart

from eliminating cold corrosion of the exhaust valve duct, the lower cooling

intensity slightly increases the exhaust gas energy, thus improving the potential

for waste heat recovery.

A W-seat of low height is used and a high spindle guide lubricated by the

controlled oil level system is being introduced. The system implies a minimum

oil level inside the air cylinder, secured by a high outlet (overﬂow) to the safety

valve. This ensures a level high enough to have oil on the top of the sealing

ring, the oil passing through three bores in the ﬂange. Furthermore, the safety

valve adjustment corresponds to this high oil level. No sealing air arrangement

or special type of sealing ring is required by this design, which means that the

old type ring can be used regardless of the type of valve spindle.

Modiﬁcations to the ME electronic control system reﬂected experience

gained from engines in service. Improvements have beneﬁted the hydraulic

servo oil supply, for which there are now two standards: engine driven and

electrically driven.

Engine-driven oil supply. The well proven design with a chain-driven

gearbox, which drives three to ﬁve high-pressure pumps, was selected for the

updated engines. A chain is particularly preferred on large bore engines because

of its reliability, easy installation and high tolerance against relative movements

of the crankshaft. Furthermore, the chain is used for driving the second-order

moment compensator on six-cylinder engines speciﬁed with such attachments.

Compared with the initial ME/ME-C large bore engine assembly, however,

the new design has been simpliﬁed. It comprises small accumulator blocks (one

for each pump) and a safety block positioned on the aftmost HCU. The large

double-walled supply pipe with forged connection pipes was replaced by stand-

ardized high-pressure pipes. Easing installation and avoiding vibrations from the

pumps, high-pressure hoses were installed between the pumps and HP pipes.

Electrically driven oil supply. If this arrangement is preferred, the complete

gearbox and chain drive are replaced by electrically powered HP pumps, which

are similar to the mechanical pumps. The chain drive section of the framebox

is omitted, thus making the engine structurally simpler than an engine with a

mechanical servo oil supply.

Mark 9 large bore engines 353

354 MAN B&W Low-Speed Engines

ME-B Engines

Electronically controlled fuel injection was extended to smaller bore MAN

B&W two-stroke engines in mid-2006 with the launch of the ME-B series,

initially comprising 350-mm and 400-mm-bore models but later extended to

embrace 460-mm, 500-mm and 600-mm-bore versions (Figures 10.48–10.50).

These S35, 40, 46, 50 and 60ME-B designs cover a power band from 4350 kW

to 19 040 kW and are marketed in parallel with their established mechanical

MC counterparts, which may be favoured by some shipyards and ship owners

in the targeted propulsion sectors.

Development was driven by a perceived market requirement for the low-

est possible propeller speed in relation to bore size, leading to a stroke–bore

ratio of over 4.4:1 for the S35, S40 and S50 designs (similar to that of MAN

Diesel’s 4T50ME-X research engine). The 46 and 60-bore models have slightly

lower ratios of 4.2 and 4:1, respectively. Type approval tests for the ﬁrst pro-

duction engine, a six-cylinder S40ME-B version, were completed in December

2007, since when models of all bore sizes have ﬂowed into service.

It was decided at an early stage of development to retain a slim camshaft

for controlling the exhaust valves, thereby also reducing the required capacity

of the electronic control system. While this small camshaft operates the valves

mechanically in the traditional manner, an electronically controlled fuel injection

FigurE 10.47 Trends in output per cylinder and specic weight for MAN B&W

90-bore engines from Mark 1 to Mark 9 status

system adapted from ME practice enables the ME-B engines to meet IMO Tier

II emission requirements.

Fuel injection is performed by one fuel booster per cylinder, similar to

the established system for larger bore ME engines. The pressure boosters are

mounted on HCU—two boosters per unit—with hydraulic oil supplied to the

HCUs via a single oil pipe enclosed in the camshaft housing. In addition to two

pressure boosters, the HCU is equipped with two ELFI valves and two Alpha

Lubricators. The accumulators used in the HCUs of the established ME engine

design are replaced by one buffer of hydraulic oil serving each HCU, which in

turn serves the injection needs of two cylinders.

ME-B engines 355

FigurE 10.48 Cross-section of S50ME-B engine

356 MAN B&W Low-Speed Engines

Compression of the oil with respect to its bulk modulus accounts for the

accumulator effect. The hydraulic system pressure is 300 bar (increased from

the 250 bar of the standard ME system). The higher pressure makes it possible

to omit the accumulators normally installed on the HCU; instead, a hydraulic

volume for each of the two cylinders is placed below the HCU inside the cam-

shaft housing. Two electrically driven pumps installed at the front end of the

engine provide hydraulic power for the injection system. In the event of failure

of one pump, more than 50 per cent engine power will remain available, ena-

bling 80 per cent ship speed to be maintained.

The ME-B fuel injection system offers the same possibility for rate shaping as

the established ME engines. Injection is controlled by a proportional valve allow-

ing continuous change of the injection pressure; typically, a gradual pressure

410 950 460 3710

3200

1405 2500

7376

1210 980 1270

2580

700

FigurE 10.49 Cross-sections of S40ME-B engine

increase during injection is desirable. Speciﬁc fuel consumption, as well as

emissions, is inﬂuenced by the injection proﬁle. One proﬁle is often favourable

for sfc but at the cost of high NOx emissions, while the opposite effects result

from another proﬁle. The freedom to choose the fuel injection proﬁle is thus a

valuable tool in minimizing sfc while keeping emissions within given limits.

Fuel valves similar to those of S35MC and S42MC engines are used for the

S35/40ME-B models, the fuel nozzles being of the proven slide type already

introduced as standard on all small bore engines.

The engine control system uses the same multi-purpose controllers (MPCs) as

the traditional ME control system. One MPC can control injection on two cylin-

ders, but one of the MPCs also controls the hydraulic pressure and therefore only

controls injection on one cylinder. A six-cylinder ME engine requires 13 MPCs,

while a corresponding small bore ME-B model may need only four MPCs.

ME-B engines 357

FigurE 10.50 ME-B engine combustion chamber

358 MAN B&W Low-Speed Engines

Most of the design concepts of the large bore Mark 9 engines are shared

by the ME-B series, including a piston with high topland, PC ring, twin stay

bolts, thin shell bearings, low friction guide shoes and thrust cams. The struc-

tural parts of the S35/40ME-B engines were designed to secure the rigid-

ity and strength required for the higher output. The bedplate is of welded

design, but the normal cast part for the main bearing girders is made from

rolled steel plates. The aim was to achieve homogeneity of the material used

for that bearing area with no risk of casting imperfections arising during ﬁnal

machining.

A new main bearing concept was under development at the launch of the

engines to decrease the production cost of the bedplate. In the new design,

the bedplate and bearing caps are ﬁnish machined as separate parts, with the

caps positioned by means of the bearing shell and kept in position with the

force from hydraulically tightened studs and high-friction coated shims placed

between bearing cap and bedplate. The proven main bearing design used on all

MAN B&W small bore engine designs, however, was to be retained until the

new development was completed.

A framebox of the proven triangular guide plane design with twin stay-

bolts—now standard on all updated MAN B&W engine types—was speciﬁed

to provide excellent support for the guide shoe forces.

Two possibilities are available for the cylinder frame—nodular cast iron

(KF) or a welded design with integrated scavenge air receiver—but it was

decided to use the cast solution because of the material’s high strength and

high E-modulus in countering the high ignition force. Furthermore, compared

with C3Cu material, the weight of a six-cylinder S35ME-B cylinder frame can

be reduced by 3 tonnes, corresponding to a 12 per cent cost reduction for the

frame.

A semi-built crankshaft, in one piece, is made of S34CrNi or S42Cr1 mate-

rial. Even though the stroke–bore ratio was raised for the new engines, the

cylinder distance is only slightly increased. Comprehensive FEM calculations

were performed to ensure that the geometry (including the journal diameters)

of the shaft was optimized for maintaining the rigidity, shrink-ﬁt and stresses at

the same level as for the MC-C engines.

Based on the design introduced for the MC-C engine, the thrust bearing

is very compact. Addressing the increased propeller thrust resulting from the

higher engine power, a ﬂexible thrust cam secures a more even force distribu-

tion on the pads. The overall dimension of the parts can thus be smaller than

that with the old design.

A connecting rod design based on that applied throughout the small bore

engine programme (initially introduced for the L35MC model) is used. To

reduce the production cost and oscillating forces, however, the new design is a

combination of those used in the MC-C and 35MC engines. The crosshead pin

design is taken from the S50MC-C engine, with the bearing dimensions based

on long experience with the S35MC engine (exploiting a hardened running sur-

face for the pin). The guide shoe is of the new low friction design.

Bearings are of the same thin-shell design as for the previous small bore

engine generation, the material on all large bearings being Sn40Al. The rela-

tive loads on the large bearings are in all cases below the design targets.

The increased power of the ME-B engines dictated careful investigation

of the combustion chamber to compensate for the higher ignition pressure and

thermal load, and also to raise the reliability of the components and further

extend the TBOs (Figure 10.50).

A slim cylinder liner used for other small bore MC-C/ME engines was also

applicable to the ME-B 35 and 40-bore types, but the material was upgraded

to Tarkalloy A to counteract the higher ignition pressure. A PC ring was also

introduced to prevent bore polish.

The bore-cooled piston has a semi-high topland and a crown shaped in

conjunction with the combustion chamber to cope with the increased power.

Extensive FEM calculations were carried out in evolving the crown geometry

to enable the high ﬁring pressure and mean pressure to be withstood. A piston

ring pack similar to those used for the established small bore engines features a

No. 1 ring with high CPR and Nos. 2 to 4 rings with angle cut. All of the rings

have an Al-coat on the running surface for safe running-in. If a prolonged TBO

is requested, a special ring pack with hard coating on the running surfaces of

No. 1 ring can be speciﬁed as an option.

As with the larger bore ME engines, an Alpha Lubricator is standard for

the ME-B models, bringing the beneﬁts of an ACC lubrication mode to smaller

bore designs: a low total cylinder lube oil consumption while maintaining an

excellent cylinder condition.

ME-B engines 359

FigurE 10.51 An ME-B engine showing the camshaft-activated exhaust valve

system and HCus serving two cylinders

360 MAN B&W Low-Speed Engines

Exhaust valves are actuated by a light camshaft (small diameter and small

exhaust cam) driven by a chain located at the aft end of the engine; the chain

size is smaller than the MC type chains ((Figure 10.51). Pursuing common. Pursuing common

spare parts for all four engines, the exhaust valves used for the S35ME-B and

S40ME-B models are the same as those for the S35MC and S42MC models,

respectively. The DuraSpindle design has a W-seat bottom piece.

Appropriate turbocharger models from MAN Diesel, ABB and Mitsubishi

can be speciﬁed for the ME-B engines. The turbocharger can be aft mounted,

as for the existing engines, or exhaust side mounted. The latest type of water

mist catcher and water drain arrangement were adopted. MAN Diesel’s TCA

turbochargers with variable nozzle ring technology (see Chapter 7) are option-

ally available, compensating (in terms of part-load fuel consumption) for the

absence of variable exhaust gas valve timing.

An auxiliary blower of the new integrated type, introduced on the Mark 8

version of the S50MC-C engine, yields a cost reduction of around 40 per cent

over the existing design. Maintenance is also lowered as the belt drive is omit-

ted for the integrated blowers.

See Chapter 9 for more details of MAN Diesel’s Intelligent Engine

development.