Woodyard D. (ed.) Pounders Marine diesel engines and Gas Turbines
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connects the fore and aft thrust bearing supports) in one piece, and shaping
it like a calliper, a significantly wider design margin is derived even though
engine outputs (and hence propeller thrust) have been increased. No cracks
have been reported on engines with this so-called Calliper design thrust bear-
ing (Figure 10.32). The bearing saddles have remained free of cracks, in com-
pliance with pre-calculated stress levels.
Exhaust Valves
Nimonic exhaust valve spindles are well accepted now that operators have
become acquainted with the long-lasting seat performance, despite dent marks.
Nimonic spindles are standard for 50MC and 60MC/MC-C engine models
upwards; and Stellite spindles are standard for smaller models.
Corrosion in the valve housing was effectively minimized by introducing
the optimized cooling water system; this raises the wall temperature in the
housing above the critical level for the formation of acid on the gas side of the
duct. The high temperature level dictates a cast iron spindle guide bushing.
Wear of the previously chrome-plated spindle stem has been effectively
reduced by the HVOF-based cermet coating introduced in 1997. Furthermore,
wear and corrosion problems at the spindle guide/spindle/seal area, caused by
combustion products, have been minimized over the years by design changes
to the sealing air system. Since the stem seal had difficulty in reaching life-
times similar to those of the valve seats, however, it was decided to replace the
sealing air system by a lubricating device tested with good results in long-term
service.
Reduced wear of the spindle stem (HVOF coating) and the long spindle
guide (grey cast iron) has been achieved, but the lifetime of the stem seal itself
is still sometimes too short. Tests with oil as the sealing medium instead of air
showed very low wear rates on the seals, along with a high cleanliness level
on the surfaces of the spindle stem and spindle guide. A system delivering the
necessary dosage of only approximately 1 kg/cylinder/day was developed for
Post-1997 service experience 331
B
A
Increased stiffness of thrust bearing support
B
A
CC
A-A
‘Calliper’ design
B-B
Indicated area
to be UT-tested
C-C
FigurE 10.32 Calliper-design thrust bearing
332 MAN B&W Low-Speed Engines
the medium and large bore engines. It is located in the top of the exhaust valve
and fed with oil from the valve’s hydraulic system; oil is fed to the spindle
guide via a small pipe. The sealing oil is taken from the circulating oil and is
therefore part of the necessary minimum oil consumption for keeping the sys-
tem oil viscosity and base number (BN) level at the prescribed equilibrium.
The latest design of exhaust valve on the small and medium bore engines
occasionally suffered from cooling water leaks at the lowermost O-ring
between the bottom piece and the cylinder cover. Investigations resulted in the
replacement of O-ring by a special Teflon seal with spring back-up (U-seal).
Tests showed that the best way of increasing valve seat lifetime was by
altering the seat geometry of the bottom piece to the patented W-seat configu-
ration, now standard on all MC/MC-C engines (Figure 10.33). Results are even
better when used with the new type of slide fuel valves.
Engines featuring the Oros combustion chamber (see p. 309) leave little dis-
tance between the piston top and the underside of the exhaust valve spindle. The
usual extended lift system for releasing high hydraulic pressure cannot therefore
be applied. A safety valve located in the actuator is used instead. Unfortunately,
a few cases of damaged exhaust valves and camshaft sections were experienced
due to different external factors including an insufficient release action of the
safety valve. The valve was subsequently redesigned so that, once activated, it
implements a special function to keep it open for around 20 s. In addition, a disc
spring was introduced in the exhaust valve on top of the spindle guide to avoid
damage to the air piston in the event of ‘over-shoot’/extended lift of the valve
spindle.
Fuel injection System
In general, the fuel pumps work well and without difficulties, although a few
incidents have been experienced and addressed:
l A combined puncture and suction valve used on the S60MC-C,
S70MC-C, S90MC-C and K98MC-C engines originally featured a bel-
low as a substitute for the conventional sealing rings in order to benefit
from a component needing little or no maintenance. The reliability of
the bellow was not satisfactory, however, and a new design eliminating
this element was introduced for the above engine models.
FigurE 10.33 W-seat conguration for exhaust valve
l Fuel pumps without shock absorbers were introduced on these same
engine types as a cost reduction measure, but this resulted in annoying
(although not damaging) pressure fluctuations in the fuel supply system.
Even though these measured fluctuations were within MAN Diesel’s and
the classification societies’ design limits, ship owners experienced prob-
lems with shipyard-installed equipment such as pumps, filters and pre-
heaters. The problems were avoided by re-introducing a shock absorber
on the fuel pumps of these engines.
l A new type of gasket between the fuel pump housing and the top cover
was introduced to cure leakage experienced on some K98MC/MC-C
and S90MC-C engines. The primary sealing is secured with a viton ring,
protected against corrosion attack by a steel bushing. A soft iron plate
of the same shape as the original seal forms the ‘groove’ for the square
viton ring.
l Fuel pump top cover fractures were experienced on small and medium
bore engines, initiated at the position where the inclined drillings for
the high-pressure pipes intersect with the central bore. The cause of the
failure in all cases was related to roundings that did not fulfil the MAN
Diesel specification. A design change has improved the safety margin
against failures, simplified manufacture and made the component less
sensitive to minor tolerance deviations (Figure 10.34).
Fractured fuel valve nozzles were found on large bore engines where slide-
type valves had been standard for some years. The main reason for the cracks
was residual stress from machining, but the high temperature of the valve nozzle
itself also contributed to fracturing because of the consequential high mean
stress. The problem was cured by optimizing the production parameters.
Pressure Testing Fuel Valves
MAN Diesel notes that in pressure testing conventional fuel valves, the test-
ing device is capable of supplying only 1–2 per cent of the normal fuel flow
rate on the engine, which is not sufficient to ensure proper atomization. If the
Post-1997 service experience 333
Previous New
Sharp edges to
be removed:
Radius: min.
0.5 mm
Crack initiation area
FigurE 10.34 Change to fuel pump top cover design
334 MAN B&W Low-Speed Engines
remaining test items in the procedure are fulfilled, the fuel valve nozzle will
work perfectly. As the atomization test can be omitted, it is not described in
new testing procedures, so verification of a humming sound is no longer pos-
sible nor necessary.
Pressure testing procedures for slide fuel valves are quite different from
those for conventional valves and—perhaps for that reason—have in some
cases been misinterpreted by operators. Slide fuel valves must be disassem-
bled and cleaned before pressure testing, and an atomization test must not be
performed on such valves. Cleaning is necessary because the cold and sticky
heavy fuel oil, in combination with the very small clearance between the cut-
off shaft and the fuel valve nozzle, would significantly restrict movement of
the spindle.
An atomization test is not acceptable because the very small needle lift
obtained during such a test would result in an unequal pressure distribution on
the cut-off shaft, resulting in a relatively hard contact in a small area. This,
together with the high-frequency oscillations during an atomization test, and
the low lubricity of the test oil, would significantly increase the risk of seizure.
The full lift of the needle, and the very good lubricity of heavy fuel oil, com-
pletely eliminates this risk during normal operation of the engine.
Wet spots have often been found under each slide fuel valve during sca-
venge port inspections. In a conventional valve the sac volume is emptied after
each injection; in the slide valve the fuel stays in the fuel nozzle until the next
injection. When turning the engine and after some hours of engine standstill,
however, the nozzle will empty and fuel will drip down on the relatively cold
piston crown, revealed as wet spots up to 300-mm diameter. After some hours
the drops will more or less evaporate, depending on the actual position of the
piston in relation to the scavenge ports, leaving only some ash on the piston
top. MAN Diesel advises that this is not normally an indication of malfunction.
Cylinder Cut-out System
A traditional problem with low load operation is engine fouling due to irregular
fuel injection and atomization leading to incomplete combustion. The irregular
injection may be caused by jiggling of the governor and/or play in the connec-
tions in the fuel pump rack control system. The effect in either case is that the
fuel pumps, when operating so close to the minimum injection amount, may
sometimes have just enough index to inject fuel; and at other times, just not
enough to do so.
By introducing a system whereby approximately half of the cylinders are
cut out, low-speed injection into the remaining working cylinders is consider-
ably improved, yielding more stable combustion and hence stable running and
minimizing particle emissions. To avoid excessive amounts of cylinder lube oil
collecting in the cylinders that are temporarily deactivated, the cutting out is
effected in turns between two groups of cylinders in order to burn surplus lube
oil and maintain the same thermal load on all cylinders.
Turns between the groups are made on a time basis, and group separation
is determined in order to halve the number of active cylinders and achieve the
smoothest possible firing order. To secure a safe start, the cut-out system is dis-
abled during the starting period and until the engine has been stabilized. Stable
operation down to 13 rev/min has been logged using the system.
oil Mist Detection
As well as applying an oil mist detector, MAN Diesel’s efforts to prevent
crankcase explosions have concentrated on designing an engine with ample
margins to prevent overheating of components. It was realized, however, that
when rare explosions occur, they originate from other causes such as factors
related to production, installation or incorrect maintenance of components or
lubricating systems. It is therefore recommended that:
l The oil mist detector is connected to the slowdown function.
l The oil mist detector has remote monitoring from the engine control
room.
l The relief valves are made with an approved flame arrester function.
Reliance was previously placed on specifying safety equipment that had
been type approved by the classification societies; type approval, however, is
not sufficient as it comprises checking only the opening pressure of the relief
valve.
In the event of a crankcase explosion, the pressure wave will send a large
amount of oil mist out of the crankcase and into the engineroom, where it will
be moved around by the ventilation. Its significant part could be sucked up into
the turbocharger air inlet. If the oil mist meets a hot spot it can be ignited;
it is therefore important to keep the insulation around the exhaust pipes in
good condition. The highest risk of igniting the mist, of course, is if the flame
arrester on the relief valve does not function properly. The relief valve speci-
fication has been updated, and only valves meeting this specification were
accepted on engines ordered after 1 May 1999.
oPErATiNg ADViCE
Service experience with MC engines of all of the bore sizes in diverse propul-
sion installations underwrites the following MAN Diesel assertions:
l There is still no substitute for careful monitoring or planned mainte-
nance by qualified personnel.
l Maintaining the turbocharging efficiency is essential: a drop of even a
few points can have adverse effects. Turbochargers and air coolers must
therefore be well maintained.
l Fuel valve condition and functioning are key factors in overall perfor-
mance. The spindle guide quality is the chief element, followed closely
by overhaul competence, valve nozzle condition and the correct installation
of the valve.
operating advice 335
336 MAN B&W Low-Speed Engines
l The differential pressure P
max
P
comp
should not be allowed to exceed
25–40 bar in service since this might lead to performance problems,
especially cylinder condition problems.
l Operating with excessive exhaust gas back pressure may lead to dif-
ficulties as the heat load increases. This is particularly relevant in boiler
types with closely spaced finned tubes, which use very low feedwater
temperature and/or low exhaust gas temperatures at the boiler outlet,
running an increased risk of soot deposits.
l Fuel quality-related difficulties are still encountered today, but crews
have become more conscious of the importance of good fuel treatment.
Ignition quality is of minor importance for low-speed engines.
ELECTroNiCALLY CoNTroLLED ME ENgiNES
In an MC engine the camshaft mechanically controls fuel injection and
exhaust valve operation, a linkage that delivers very limited timing flexibility.
Electronically controlled MAN B&W ME-series engines, introduced to the
market from 2001, dispense with the camshaft and exploit hydraulic–mechanical
systems supported by electronic hardware and software for activating fuel
injection and the exhaust valves. ME engines became available in bore sizes
from 500 mm to 1080 mm offering the same outputs as their MC engine coun-
terparts (Figure 10.35).
Electronically controlled fuel injection and exhaust valve actuation (Figure
10.36) allow individual and continuous adjustment of the timing for each cyl-
inder, securing the following key benefits.
0 10 000 20 000 30 000 40 000 50 000 60 000 70 000 80 000 90 000 100 000
kW
10 000 30 000 50 000 70 000 90 000 110 000 130 000 BHP
S50ME-C
L60ME-C
S60ME-C
L70ME-C
S70ME-C
K80ME-C
L80ME
S80ME-C
K90ME-C
K90ME
L90ME-C
S90ME-C
K98ME-C
K98ME
K108ME-C
95–127
105–123
79–105
91–108
68–91
89–104
70–93
57–76
89–104
71–94
62–83
61–76
94–104
84–94
90–94
r/min
(L4–L1)
FigurE 10.35 The original electronically controlled ME engine programme (the
K108ME-C was withdrawn in 2008 and a 650-mm bore S65ME-C model added in
2004)
Electronically controlled ME engines 337
Exhaust valve
Positional transducer
Fuel valves
Air spring
Hydraulic
pushrod
Oil supply to
hydraulic ‘pushrod’
for exhaust valve
Exhaust valve actuator
Activation piston
Fuel pump
Fuel pump plunger
Hydraulic piston
Umbrella sealing
Positional transducer
Distribution block
ELVA valve
To next
distribution
block
Low-pressure supply
Return oil to the bedplate
ELFI valve
Hydraulic piston
Fuel oil drain
Fuel oil outlet
Fuel oil inlet
X
F
AD
Hydraulic Cylinder Unit
High-pressure pipes
FigurE 10.36 Mechanical–hydraulic system for activating the fuel pump and exhaust valve of an ME engine cylinder
338 MAN B&W Low-Speed Engines
rEDuCED FuEL CoNSuMPTioN
l Fuel injection characteristics can be optimized at many different load
conditions, while a conventional engine is optimized for the guarantee
load, typically at 90–100 per cent mcr.
l Constant P
max
in the upper load range can be achieved by a combination
of fuel injection timing and variation of the compression ratio (the latter
by varying the closing of the exhaust valve). As a result, the maximum
pressure can be kept constant over a wider load range without overload-
ing the engine, leading to significant reductions in sfc at part load.
l On-line monitoring of the cylinder process ensures that the load distri-
bution among the cylinders and the individual cylinder’s firing pressure
can be maintained at ‘as new’ standard over the lifetime of the engine.
oPErATioNAL SAFETY AND FLExiBiLiTY
l The engine’s crash stop and reverse running performance is improved
because the timing of the exhaust valves and fuel injection can be opti-
mized for these manoeuvres as well.
l ‘Engine braking’ may be obtained, reducing the ship’s stopping distance.
l Swifter acceleration of the engine, since the scavenge air pressure can
be increased faster than normal by opening the exhaust valve earlier dur-
ing acceleration.
l Dead slow running is improved significantly: the minimum revolutions
per minute are substantially lower than those for a conventional engine;
dead slow running is much more regular, and combustion is improved
thanks to the electronic control of fuel injection.
l Electronic monitoring of the engine (based on MAN Diesel’s CoCoS-
EDS system) identifies running conditions that could lead to per-
formance problems. Damage due to poor ignition quality fuel can be
prevented by injection control (pre-injection).
l The engine control system incorporates MAN Diesel’s on-line overload
protection system (OPS) feature, which ensures the engine complies
with the load diagram and is not overloaded (often the case in shallow
waters and with ‘heavy propeller’ operation).
l Maintenance costs will be lower (and maintenance easier) as a result of
the protection against general overloading as well as overloading of indi-
vidual cylinders; and also because of the ‘as new’ running conditions
for the engine, further enhanced by the ability of the diagnosis system to
give early warning of faults and thus enable proper countermeasures to
be taken in good time.
ExHAuST gAS EMiSSioNS FLExiBiLiTY
l The engine can be changed over to various ‘low emission’ modes, its
NOx exhaust emissions reduced below the IMO limits if dictated by
local regulations.
l By appropriate selection of operating modes, ships may sail with lower
exhaust gas emissions in special areas, where this may be required
(or be more economical due to variable harbour fee schemes) without
having negative effects on the sfc outside those areas.
The following components of the conventional MC engine are eliminated
in the ME engine: chain drive for camshaft, camshaft with fuel cams, exhaust
cams and indicator cams, fuel pump actuating gear, including roller guides and
reversing mechanism, conventional fuel injection pumps, exhaust valve actu-
ating gear and roller guides, engine-driven starting air distributor, electronic
governor with actuator, regulating shaft, mechanical engine-driven cylinder
lubricators and engine side control console.
These elements are replaced on the ME engine by an electro-hydraulic
platform comprising a hydraulic power supply (HPS), a hydraulic cylinder
unit (HCU) with electronic fuel injection (ELFI) and electronic exhaust valve
actuation (ELVA), an electronic Alpha Cylinder Lubricator (see Chapter 4), an
electronically controlled starting valve, a local control panel, a control system
with governor and a condition monitoring system.
ME Engine Systems
Valuable experience was gained by MAN Diesel from its 4T50MX research
engine at Copenhagen, operated from 1993 to 1997 with a first-generation
intelligent engine (IE) system. Second-generation IE systems fitted to the
engine in 1997 aimed for simplified design, production and installation of
the key electronically controlled fuel injection and exhaust valve actuation
systems. Subsequent R&D focused on transforming the electronic elements
into a modular system, whereby some of the individual modules could also
be applied to conventional engines. This called for the development of a new
computer unit and large software packages, both of which had to comply with
the demands of classification societies for marine applications.
The second-generation IE system is based on an engine-driven high-pressure
servo oil system, which provides the power for the hydraulically operated fuel
injection and exhaust valve actuation units on each cylinder. Before the engine
is started, the hydraulic power system (or servo oil system) is pressurized by a
small electrically driven high-pressure pump. Fine-filtered main system lube
oil is used as the actuating medium supplied by engine-driven multi-piston
pumps at around 200 bar (Figure 10.37).
FuEL iNjECTioN SYSTEM
A common rail servo oil system applies the cool, clean and pressurized lube
oil to power the fuel injection pump of each cylinder. Each cylinder unit is pro-
vided with a servo oil accumulator to ensure sufficiently swift delivery of oil in
accordance with the requirements of the injection system, and to avoid heavy
pressure oscillations in the associated servo oil pipe system. The movement of
the pump plunger is controlled by a fast-acting proportional control valve (a so-
called NC valve), which, in turn, is controlled by an electric linear motor that
Electronically controlled ME engines 339
340 MAN B&W Low-Speed Engines
From main lube oil system
Bypass
valve
Main
filter
Redun-
dancy
filter
Tank return
Low pressure supply
Cylinder
arrangement
InVA
InFI
InVA
Cylinder
arrangement
Bypass
valve
Engine-
driven
pumps
High pressure
Accumulator
arrangement
Supply
Bypass
valve
Engine-
driven
pumps
Control
pump
Control
pump
Cylinder
arrangement
Cylinder
arrangement
InFI
InVA
InFI
InVA
InFI
Return
arr.
Return
arr.
Return
arr.
Return
arr.
Return
arr.
Return
arr.
Return
arr.
Return
arr.
FigurE 10.37 Servo oil system ow diagram for ME engine