Woodyard D. (ed.) Pounders Marine diesel engines and Gas Turbines
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VLCC project planners were given a wider choice with the introduction
of a longer stroke 900-mm bore model, the S90MC-T design, tailored to the
propulsion of large tankers. The layout flexibility enables operators to select
maximum continuous speeds between 64 rev/min and 75 rev/min in seeking
optimum propeller efficiency. The design parameters (Table 10.3) addressed
the key factors influencing the selection of VLCC propulsion plant, defined
by MAN B&W as the projected ship speed, the propeller diameter that can be
accommodated and engine compactness. An sfc of 159 g/kW h was quoted for
a derated S90MC-T engine served by high-efficiency turbocharger(s).
The dimensions of the S90MC-T engine were required not to exceed those
of the 800-mm bore S80MC series, which had established numerous references
in the ‘new generation’ VLCC market. MAN Diesel suggested that VLCCs with
Programme expansion 301
FigurE 10.8 S46MC-C engine cross-section
302 MAN B&W Low-Speed Engines
speed requirements of more than 15 knots could take advantage of the S90MC-
T engine, either as a full-powered six-cylinder model or as an economy-rated
seven-cylinder model. The S80MC engine, in seven-cylinder form, was consid-
ered an attractive solution for VLCCs required to operate with speeds of up to
15 knots.
Refinements also sought to maintain the competitiveness of the S80MC
design. Engine length, and hence engineroom length, represents dead vol-
ume and is normally to be minimized. The S80MC therefore benefited from a
remodelling of its bedplate and chain drive/thrust bearing to shorten the length
by 700 mm. The engine could then be pushed deeper aft into the hull, promoting
increased cargo capacity from a given overall ship length or reduced ship length
FigurE 10.9 L70MC Mk 5 engine cross-section
for the same capacity. The introduction of an optimized fuel system in conjunc-
tion with improved timing (already implemented on smaller bore MC engines)
raised thermal efficiency equivalent to a reduction in sfc approaching 3 g/kW h.
The sfc can be further improved at part load by specifying a high-efficiency tur-
bocharger and an adjustable exhaust gas bypass, an option which can be applied
in conjunction with a TCS power turbine system.
The S-MC-C series was expanded by a 900-mm bore design, the first
example of which entered service in mid-2000; the first units of another new
Programme expansion 303
Table 10.3 S90MC-T engine
Bore 900 mm
Stroke 3188 mm
Stroke–bore ratio 3.54:1
Nominal speed 75 rev/min
Mean piston speed
7.97 m/s
Mean eective pressure 18 bar
output/cylinder 4560 kW
Cylinders 5, 6, 7
Specic fuel consumption (mcr)
166 g/kW h
Table 10.4 MAN B&W 80- and 90-bore Mark 9 engines
S80ME-C K80ME-C K90ME K90ME-C
Bore (mm) 800 800 900 900
Stroke (mm) 3450 2600 2870 2600
Speed (rev/min) 78 104 94 104
Mean eective pressure (bar) 20 20 20 20
P
max
(bar) 160 160 160 160
Mean piston speed (m/s) 9 9 9 9
Cylinders 6–9 6–12 6–12 6–12
output/cylinder (kW) 4510 4530 5720 5730
Power range (MW) 27.1–40.6 27.2–54.4 34.3–68.6 34.4–68.8
304 MAN B&W Low-Speed Engines
type, the S80MC-C, were ordered in the same year. The 7S80MC-C and
6S90MC-C models have proved popular for VLCCs and ULCCs requiring
higher service speeds than before, their outputs, respectively, 7 per cent and
15 per cent higher than the 7S80MC Mark 6 engine (Figure 10.10).
Demands for slightly higher outputs from the L60MC and L70MC engines
were addressed by adopting S-MC-C design principles for these two types,
with a mean effective pressure of 19 bar and a mean piston speed of approxi-
mately 8.5 m/s. The output of the L60MC-C engine is 2230 kW/cylinder at
123 rev/min, while the L70MC-C engine delivers 3110 kW at 108 rev/min.
Among the targeted applications of the L-MC-C series were feeder container
ships.
980-mm-Bore MC/MC-C Engines
The propulsion demands of the largest and fastest long-haul container ships
were comfortably met until the mid-1990s by short-stroke K90MC and K90MC-
C engines (Figure 10.11) with an upper output limit of 54 840 kW. In 1994,
market interest in a new generation of 6000 TEU-plus ships with service speeds
of 25 knots or more stimulated the introduction of the K98MC-C series, which,
in 12-cylinder form, could deliver 68 520 kW (Figure 10.12). This 980-mm
bore/2400-mm stroke model shared key operating parameters with the 900-mm
bore MC/MC-C engines, notably a mean effective pressure of 18.2 bar and
8S80MC-C
42 240 BHP
M
S
PD
G
F
E
D
B
C
A
15%
Sea
margin
10%
Engine
margin
Ship
speed
(knots)
14.0 14.5 15.0 15.5 16.0 16.5 17.0
6S90MC-C
39 900 BHP
7S80MC-C
36 960 BHP
7S80MC Mk 6
34 650 BHP
Shaft power
BHP
40 000
35 000
30 000
25 000
20 000
Power estimation
300 000 dwt VLCC
M: Specified
engine MCR,
inclusive 10%
engine margin
S: Service rating
inclusive 15%
sea margin,
loaded ship in
service
PD: Propeller
design, loaded
ship at design
draught with
clean hull and
at calm
weather
conditions
FigurE 10.10 Engine selection for VLCC propulsion
a mean piston speed of 8.32 m/s. A propeller speed requirement of 104 rev/min
was selected as the design basis, resulting in a stroke–bore ratio of 2.45 and
an output per cylinder of 5710 kW. (A cylinder bore of 980 mm was not new
to the marine engine industry: in 1966 B&W introduced a K98 design, whose
12-cylinder version developed 33 530 kW; a number of these K98FF and
K98GF engines remain in service.)
A longer stroke K98MC version was introduced in 1997 to complement
the K98MC-C engine, with the same mcr but at a lower speed of 94 rev/min,
and the number of cylinder options for both series was expanded from 9–12
to 6–12. The first K98MC engine, a seven-cylinder model, was tested in mid-
1999 (Figure 10.13). The most powerful diesel engines ever commissioned at
the time—12-cylinder K98MC models with a maximum rating of 68 640 kW at
94 rev/min—entered service in 7500 TEU container ships in 2001/2002. The
programme was extended by a 14-cylinder K98MC/MC-C model taking the
output limit up to 80 080 kW.
Another route to higher powers for container ships was provided by MAN
Diesel in 2003 with the release of a 1080-mm bore version of the K-MC/MC-
C series developing 6950 kW/cylinder at 94 rev/min. The 14-cylinder model
of this K108 design, the world’s most powerful diesel engine, could thus
offer 97 300 kW. By then an electronically controlled ME engine, the K108
was dropped from the official programme in 2008, having been displaced by
uprated (Mark 7) K98ME and MC designs, which, in 14-cylinder form, can
deliver up to 87 220 kW. The first 14K98ME-C7 engine was due for completion
in 2009.
Programme expansion 305
Table 10.5 MAN B&W ME-B engine programme (see p. 354)
S35ME-B S40ME-B S46ME-B S50ME-B9
*
S60ME-B
Bore (mm) 350 400 460 500 600
Stroke (mm) 1550 1770 1932 2214 2400
Mean eective
pressure (bar)
21 21 20 21 20
Speed (rev/min) 167 146 129 117 105
Mean piston speed
(m/s)
8.6 8.6 8.3 8.6 8.4
output/cylinder (kW) 870 1135 1380 1780 2380
Cylinders 5–8 5–8 5–8 5–9 5-8
Power range (MW) 4.35–6.96 5.67–9.08 6.9–11 8.9–16 11.9-19
*
Engine is available in Mark 7, 8 and 9 variants with dierent ratings
306 MAN B&W Low-Speed Engines
LArgE BorE ENgiNES
The structural design of the K98MC, K98MC-C, S90MC-C and S80MC-C
engines is primarily based on that of the compact S-MC-C medium bore mod-
els. The main differences between the established K90MC/MC-C engines and
the new design are as follows.
Bedplate
All the new large bore engines are designed with thin-shell main bearings of white
metal. The rigidity of the bearing housing was increased substantially to reduce
stress levels and deformations. Furthermore, the change from the traditional stay
FigurE 10.11 K90MC-C engine cross-section
bolts to the twin stay bolt design, with bolts screwed into the top of the cast bear-
ing part, means that the geometry of the main bearing structure is simplified and
an improved casting quality is achieved. Finally, to improve the fatigue strength,
a material with upgraded mechanical properties was specified. The use of twin
stay bolts, fitted in threads in the top of the bedplate, has almost eliminated defor-
mation of the main bearing housing during bolt tightening. The match between
main bearing cap and saddle, secured in the final machining, is thus maintained
in the operational condition, yielding a highly beneficial effect on main bearing
performance.
A triangular plate design engine framebox was adopted for later K98MC/
MC-C engines when this was introduced on the S90MC-C and S80MC-C
Large bore engines 307
FigurE 10.12 K98MC-C engine cross-section
308 MAN B&W Low-Speed Engines
engines. The new design provides continuous support of the guide bar, thus
ensuring uniform deformation of the bar and a more even contact pattern
between guide shoe and guide bar that enhances guide shoe performance. In
addition, the continuous support contributes to a significant reduction of the
stress level in the areas in question. The holes in the supporting plate make
it possible to inspect all longitudinal welding seams from the back, and thus
ensure that the specified quality is secured.
Main Bearing
Tin–aluminium (Sn40Al) has proved very reliable as the bearing material for
the smaller engines, the alloy having a much higher fatigue strength at elevated
temperatures. The material may be applied to large bore engines to maintain
Engine RPM
MEP
P
max
P
comp
P
Scav
T/C inlet
T/C Outlet
SFOC
50% 75% 100% Load
27230 40845 54460 BHP
g/BHP h g/kW h
190
180
170
160
150
450
400
350
300
250
140
130
120
110
dg.C
P
scav.
T-exhaust gas
bar
(abs)
4.
3.
2.
1.
P
comp
P
max
bar (abs)
MEP
bar
20
18
16
14
12
r/min
95
85
75
65
140
130
120
110
100
90
80
FigurE 10.13 Performance curves for 7K98MC engine at iSo reference conditions
the reliability of the main bearings. Dry-barring on the testbed in some cases
caused light seizure of Sn40Al main bearing shells on S-MC-C engines, but
the problem was eliminated either by pre-lubrication with grease and high-
viscosity oil or by PTFE-coating the running surface of the shells.
Engine Alignment
Traditionally, bedplate alignment, especially on large tankers, has been per-
formed on the basis of a pre-calculated vertical position of the bearings, as
well as of the engine as such, and possibly also involving an inclination of the
entire main engine. On completing the pre-calculated alignment procedure, it
has been normal practice to check the alignment by measuring the crankshaft
deflections. Such checks are normally carried out either in drydock or with the
ship afloat alongside at the yard in a very light ballast condition.
Owing to repeated cases of bearing damage, presumably caused by the lack
of static loads in the normal operating conditions (ballast and design draught),
MAN Diesel introduced modified alignment procedures for bedplate and shaft-
ing (crankshaft and propulsion shafting) as well as modifying the vertical offset
of the main bearing saddles. In the modified bedplate alignment procedure, the
importance of the so-called sag of the bedplate is emphasized in order to counter-
act the hog caused by hull deflections as a result of the loading down of the ship,
and partly by deformations due to the heating up of the engine and certain tanks.
Combustion Chamber
A reconfigured combustion chamber (Figure 10.14) was developed for the new
large bore engines (800-mm bore and above), the key features being:
l Piston crown with high topland. In order to protect the piston rings from
the thermal load from combustion, the height of the piston topland was
increased (Figure 10.15). The resulting increased buffer volume between
the piston crown and the cylinder wall improves conditions for the rings
and allows longer times-between-overhauls (TBOs). The high topland
was first introduced in the mid-1990s, the positive service experience
leading to its use for all new engine types.
l Piston crown with Oros shape. With increasing engine ratings, the major
development challenge with respect to the combustion chamber com-
ponents is to control the heat load on them. The short-stroke large bore
engines have a rather flat combustion chamber because of the relatively
smaller compression volume; this makes it more difficult to distribute
the injected fuel oil without getting closer to the combustion chamber
components. Furthermore, the higher rating means an increased amount
of fuel injected per stroke. All this makes it more difficult to control
the heat load on the components in short-stroke engines compared with
long-stroke engines of the same bore size.
The heat load on the cylinder liner has been reduced by lowering the mat-
ing surface between cylinder liner and cylinder cover as much as possible (to
Large bore engines 309
310 MAN B&W Low-Speed Engines
New design
Previous MC design
FigurE 10.14 New and previous designs of MC engine combustion chamber
Piston
cleaning
ring
FigurE 10.15 Piston with high topland and PC ring in cylinder liner