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

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MAN B&W low-speed engines 291

Table 10.1 Milestones in evolving MAN Diesel’s MAN B&W MC programme

Year Development Mark Mean Eective

Pressure (bar)

Mean Piston

Speed (m/s)

max

(bar)

1981 L35MC introduced

1982 Full L-MC programme 1 15.0 7.2

1984 L-MC upgraded 2 16.2

1985 L42MC introduced 2 16.2 7.2

1986 K-MC introduced

S-MC introduced

L-MC upgraded

16.2

17.0

16.2

7.6

7.8

7.6

130

1987 S26MC introduced 16.8 8.2

1988 K-MC-C introduced 3 16.2 8.0 130

1991 MC programme updated 8.0

K and L-MC

S-MC

18.0

8.0 140

1992 S26MC and L35MC

updated

18.5 8.2

1993 S35MC and S90MC-T

introduced

K90MC/MC-C updated

6 18.0 8.0

1994 S42MC introduced

K98MC-C introduced

18.5

18.2

8.0

8.3

140

1995 K80MC-C upgraded 6 18.0 8.0

1996 L70MC upgraded

S70MC-C, S60MC-C,

S50MC-C introduced

S46MC-C introduced

18.0

19.0

8.2

8.5

8.3

150

1997 L80MC upgraded

K98MC introduced

18.0

18.2

8.0

8.3

140

1998 S80MC-C, S90MC-C,

L90MC-C introduced

S35MC upgraded

19.0

19.1

8.1

150

145

1999 S42MC upgraded 7 19.5

8.0

2001 L70MC-C introduced

L60MC-C introduced

19.0

8.5

8.3

150

292 MAN B&W Low-Speed Engines

rating (mcr). Based on the propulsion and the engine running points, the layout

diagram of a relevant main engine can be drawn in. The speciﬁed mcr point

(M) must be inside or on the limitation lines of the layout diagram; if not,

the propeller speed has to be changed or another main engine model must be

chosen. It is only in special cases that point M may be located to the right of

line L1–L2.

The speciﬁed mcr is the maximum rating required by the yard or owner for

continuous operation of the chosen engine. Point M can be any point within the

layout diagram. Once the speciﬁed mcr point has been selected, and provided

that the shaftline and auxiliary equipment are dimensioned accordingly, that

point is now the maximum rating at which an overload of 10 per cent is per-

missible for 1 h in 12 h. The continuous service rating (S) is the power at which

the engine is normally assumed to operate; point S is identical to the service

propulsion point (SP) unless a main engine-driven shaft generator is installed.

50% 75% 100% LOAD

1390 2085 2780 BHP/CYL

110

100

bar

MEP

Comp

Max

bar (abs)

140

130

120

110

100

bar

(abs)

Scav.

dg. C

450

400

350

300

250

g/BHPh g/kWh

140

130

120

110

190

180

170

160

150

Engine speed

Mean effective

pressure

Maximum combustion

pressure

Compression pressure

Scavenge air pressure

Exhaust gas temperature

inlet to turbocharger

Exhaust gas temperature

outlet from turbocharger

Specific fuel oil

consumption

T-Exhaust gas

FigurE 10.2 Performance curves for S60MC engine

All MC engines can be delivered to comply with the IMO speed-dependent

NOx emission limits for the exhaust gas, measured according to the ISO

8178 test cycles E2/E3 for heavy duty diesel engines. NOx emissions from a

given engine will vary according to the engine load and the optimizing power.

Speciﬁc fuel consumption (sfc) and NOx emission levels are interrelated

parameters, and an engine offered with both a guaranteed sfc and the IMO

NOx limitation will be subject to a tolerance of 5 per cent on the fuel con-

sumption (see also Chapter 3).

MC ENgiNE DESigN FEATurES

All MC series engine models are based on the same design principles and aim

for simplicity and reliability, the key elements comprising the following:

Bedplate. The rigid bedplate for the large bore engines is built up of longi-

tudinal side girders and welded crossgirders with cast steel bearing supports.

For the smaller bore engine types, the bedplate is of cast iron. It is designed for

long, elastic holding-down bolts arranged in a single row and tightened with

hydraulic tools. The main bearings are lined with white metal, and the thrust

bearing is incorporated in the aft end of the bedplate. The aft-most crossgirder

is therefore designed with ample stiffness to transmit the variable thrust from

the thrust collar to the engine seating.

MC engine design features 293

Engine margin

SP = 90% of MP

Sea margin

15% of PD

70% 75% 80% 85% 90% 95% 100% 105% 110%

Engine speed, % of L

= 0, 15

α = 0, 20

α = 0, 25 α = 0, 30

Power, % of L

110%

40%

50%

60%

70%

80%

90%

100%

Line 2 Propulsion curve, fouled hull and heavy weather (heavy running)

Line 6 Propulsion curve, clean hull and calm weather (light running)

MP Specified MCR for propulsion

SP Continuous service rating for propulsion

PD Propeller design point

HR Heavy running

LR Light running

FigurE 10.3 Ship propulsion running points and engine layout for S60MC model.

Line 2, propulsion curve, fouled hull and heavy weather (heavy running); Line 6,

propulsion curve, clean hull and calm weather (light running); MP, specied MCr for

propulsion; SP, continuous service rating for propulsion; PD, propeller design point;

Hr, heavy running; Lr, light running

294 MAN B&W Low-Speed Engines

Framebox. This is a single welded unit for the large bore models and a cast

iron unit for the smaller types, the design contributing to a very rigid engine

structure. The framebox is equipped on the exhaust side with a relief valve and

on the camshaft side with a large door for each cylinder providing access to the

crankcase components.

Cylinder frame. The cast iron cylinder frames on the top of the framebox

make another signiﬁcant contribution to the rigidity of the overall engine struc-

ture. The frames include the scavenge boxes, which are dimensioned to ensure

that scavenge air is admitted uniformly to the cylinders. Staybolts are tightened

hydraulically to connect the bedplate, the framebox and cylinder frames, and

form a very rigid unit.

Crankshaft. The conventional semi-built, shrink-ﬁtted type crankshaft is

provided with a thrust collar. The sprocket rim for the camshaft chain drive

is ﬁtted on the outer circumference of the thrust collar in order to reduce

the overall length of the engine—except for the high cylinder numbers of the

800-mm bore model and upwards in the programme for which the chain drive

is located between two cylinders. An axial vibration damper is integrated on

the free end of the crankshaft.

Connecting rod. In order to limit the height of the engines, a relatively

short connecting rod, comprising few principal parts, is speciﬁed. The large

area of the lower half of the crosshead bearing allows the use of white metal

or tin–aluminium on the small bore engine models. Floating guide shoes mean

that most of the alignment work formerly required with crosshead engine

pistons can be eliminated. The crankpin bearing for all engine models features

thin shells lined with white metal.

Cylinder liner. A simple symmetrical design fosters low lubricating oil

consumption and low wear rates. The liner is bore cooled on the larger engine

models and available in two different conﬁgurations—with or without insula-

tion of the cooling water jet pipes—so as to match the cooling intensity closely

to the different engine ratings. The joint between liner and cover is located

relatively low. This arrangement means that a larger part of the heat-exposed

combustion chamber is contained in the steel cylinder cover rather than in the

cast iron cylinder liner. Smaller bore engines feature a simple slim-type liner

without cooling bores. For both types of liner, adequate temperature control of

the liner surfaces safeguards against cold corrosion caused by the condensation

of sulphuric acid (originating from the sulphur content of heavy fuel) and, at

the same time, ensures stable lubrication conditions by preventing excessive

temperatures (Figure 10.4).

Cylinder cover. This is a solid steel component provided with bored pas-

sages for cooling water, a central bore for the exhaust valve and bores for fuel

valves, safety valve, starting valve and indicator valve.

Piston. An oil-cooled piston crown of heat-resistant chrome–molybdenum

steel is rigidly bolted to the piston rod to allow distortion-free transmission of

the ﬁring pressure. The piston has four ring grooves, which are hard chrome

plated on both upper and lower surfaces of the grooves. A cast iron piston skirt

(with bronze sliding bands on the large bore engines) is bolted to the underside

of the piston crown (Figures 10.5 and 10.6).

Piston rod. The rod is surface treated to minimize friction in the stufﬁng

box and to allow a higher sealing ring contact pressure. The piston rod stufﬁng

box, providing effective sealing between the clean crankcase and the ‘combus-

tion area’, has a proven record of very low amounts of drainage oil.

Camshaft. The fuel injection pumps and the hydraulic exhaust valve actua-

tors are driven by the camshaft. Cams are shrink-ﬁtted to the shaft and can be

individually adjusted by the high-pressure oil method. Like its predecessors,

the MC engine uses a chain drive to operate the camshaft and thus secures high

reliability since a chain is virtually immune to foreign particles. It also enables

the camshaft to be positioned higher, shortening the hydraulic connections to

the fuel valves and the exhaust valves and, in turn, minimizing timing errors

due to elasticity and pressure ﬂuctuations in the pipe system.

Exhaust valve. Hydraulic oil supplied from the actuator opens the exhaust

valve, and the closing force is delivered by a ‘pneumatic spring’, which leaves

the valve spindle free to rotate. The closing of the valve is damped by an oil

cushion on top of the spindle. The rotation force is provided by exhaust gas

acting on vanes ﬁtted to the valve stem. Extended service life from the valve

is underwritten by Nimonic valve spindles and hardened steel bottom pieces,

MC engine design features 295

Cast-in cooling pipes ‘Slim liner’

Bore-cooled

26–50MC

2nd generationMC

60–90MC

1st generationMC

60–90MC

60–70MCE

FigurE 10.4 Cylinder liner designs

296 MAN B&W Low-Speed Engines

S-MC-Mk 5 S50/60/70MC-C and L70MC Mk 6

with high topland

FigurE 10.5 Piston/ring pack assembly MC vs. MC-C engines

Inconel layer for TCS and K-MC-C plants

Relief groove

Hardened

New standard on 90–60MC

Piston skirt with lead–

bronze bands

Surface of O-ring

groove etc. N7 (smooth)

FigurE 10.6 Piston assembly

speciﬁed as standard on the large bore engines. The bottom piece features pat-

ented ‘chamber-in-seat’ geometry.

Fuel pump. Larger engine models incorporate pumps with variable

injection timing for optimizing fuel economy at part load; the start of fuel

injection is controlled by altering the pump barrel position via a toothed

rack and a servo unit. Individual adjustment can be made on each cylinder.

Additionally, collective adjustment of the maximum pressure level of the

engine can be carried out to compensate for varying fuel qualities, wear and

other factors. Both adjustments can be effected while the engine is running.

The pump is provided with a puncture valve, which prevents fuel injection dur-

ing normal stopping and shutdown.

Fuel oil system. The engine is served by a closed pressurized fuel oil

system, with the fuel preheated to a maximum of 150°C to ensure a suitable

injection viscosity. The fuel injection valves are uncooled. The fuel system is

kept warm by the circulation of heated fuel oil, thus allowing pier-to-pier oper-

ation on heavy fuel oil.

Reversing mechanism. The engine is reversed by a simple and reliable

mechanism, which incorporates an angularly displaceable roller in the fuel

pump drive of each cylinder. The link connecting the roller guide and the roller

is self-locking in the ahead and astern positions. The link is activated by com-

pressed air, which has proved to be a very reliable method, since each cylinder

is reversed individually. The engine remains manoeuvrable even if one cylinder

fails: in such a case the relevant fuel pump is set to the zero index position.

Shaft generators. All MC engines can be arranged to drive shaft genera-

tors. The power take-off/Renk constant frequency (PTO/RCF) system is MAN

Diesel’s standard conﬁguration for PTOs from 420-mm bore models and

upwards coupled to a ﬁxed pitch propeller. The system is mounted on brack-

ets along the bedplate on the exhaust side of the engine. The generator and its

drive are isolated from torsional and axial vibrations in the engine by an elas-

tic coupling and a tooth coupling mounted on a ﬂange on the free end of the

crankshaft. The drive comprises a three-wheel gear train. To ensure a constant

frequency, the planetary gear incorporates a hydraulic speed control arrange-

ment, which varies the gearing ratio. The frequency is kept constant down to

70 per cent of the main engine’s speciﬁed mcr speed, corresponding to 30 per

cent of the engine’s speciﬁed mcr power, making the system suitable for ﬁxed

pitch propeller installations.

The PTO/gear constant ratio (GCR) system is MAN Diesel’s standard

solution for PTO in plants featuring controllable pitch propellers. The system

comprises a compact unit with a step-up gear coupled directly to the generator,

which is located above the elastic coupling.

Power turbines. Larger MC engines (from 600-mm bore upwards) can be

speciﬁed with a turbo compound system (TCS), which exploits exhaust energy

surplus to the requirements of a high-efﬁciency turbocharger to drive a power

gas turbine (see Chapter 7). For engine loads above 50 per cent of the opti-

mized power, the gas turbine is mechanically or hydraulically connected to the

MC engine design features 297

298 MAN B&W Low-Speed Engines

crankshaft. Power is fed back to the main engine, thus reducing the total fuel

consumption. The standard system, designated TCS/power take-in (PTI)), is

delivered as a complete unit built on the engine. A combined PTO/PTI unit

embracing a PTO with associated generator and a TCS/PTI unit with a power

turbine coupled to the crankshaft gear is also offered.

ProgrAMME ExPANSioN

New models have entered the MC programme since its launch in response

to propulsion market trends at both ends of the power spectrum. A notable

addition in 1986—the S26MC series—took the low-speed engine deep into

small-ship propulsion territory, offering an output per cylinder of 365 kW at

250 rev/min. The nominal power of the 260-mm-bore/980-mm-stroke design

has since been raised to 400 kW at 250 rev/min and the 4- to 12-cylinder pro-

gramme covers an output range from 1100 kW to 4800 kW. With a stroke–bore

ratio of 3.77:1, this rating corresponds to a mean piston speed of 8.2 m/s and a

mean effective pressure of 18.5 bar. A ﬁring pressure of around 170 bar yields

an sfc of 179 g/kW h at the mcr. Reliable operation on poor quality heavy fuel

oil with a viscosity of up to 700 cSt/50°C is promised.

The key components of the S26MC engine (Figure 10.7) are based on those

well proven in the established larger bore models but with modiﬁcations to

suit the intended small-ship market. Design amendments since its introduction

include an improved axial vibration damper and reﬁnements to the crankshaft.

The cylinder cover and fuel injection system have also been upgraded, the auxi-

liary blower arrangement simpliﬁed and the exhaust valve provided with a new

closing system with built-in damping.

Similar reﬁnements have beneﬁted the L35MC engine, which pioneered

the MC programme. An upgrading in 1992 sought improved performance and

reduced maintenance costs, the new maximum power rating of 650 kW/cylin-

der at 210 rev/min, mean effective pressure of 18.4 bar and mean piston speed

of 7.35 m/s calling for increased diameters of the main and crankpin journals,

and reinforcement of the main bearing housing and bedplate. The crosshead

bearing, thrust bearing and piston and piston rod were also reinforced, and

the cylinder frame, camshaft arrangement and auxiliary blower arrangement

simpliﬁed.

A longer stroke S-version of the 350-mm bore design was introduced in

1993, this S35MC model delivering 700 kW/cylinder at 170 rev/min (since

increased to 740 kW/cylinder at 173 rev/min). A number of components were

modiﬁed in line with the longer stroke (1400 mm compared with 1050 mm),

but the main design features were unchanged.

The strong and rigid main structure of the S35MC is essentially the same as

the L35MC, but the bedplate and framebox are wider and higher due to the longer

stroke of the semi-built crankshaft. The connecting and piston rods are necessarily

longer, but the cylinder frame is identical. The main bearings are wider in order

to keep the bearing load inside the area ensuring good service results. Most of the

components in the S35MC combustion chamber are also similar to those of the

L-version. The exhaust valve design was unchanged but an improved sealing sys-

tem was introduced to further reduce the wear of the valve stem. The cylinder

cover is slightly higher to allow for the increased combustion space.

Multi-level cylinder lubrication was adopted to ensure sufﬁcient lubrication

of the liner. A modiﬁed piston pack comprises two high rings in grooves 1 and

2, and two rings of normal height in grooves 3 and 4. All of the rings are made

from an improved material. The fuel pump plunger diameter was increased

to satisfy the larger injection volume per stroke; and improved sealing was

introduced to prevent any fuel from leaking into the main lube oil, which is

Programme expansion 299

FigurE 10.7 S26MC engine cross-section

300 MAN B&W Low-Speed Engines

common to the crankcase and camshaft. The camshaft diameter was increased

to accept the larger torque from the fuel pumps.

The S35MC and the 1994-launched S42MC series were conceived to

improve the propulsive efﬁciency of plants for small-to-medium-sized ships

by lowering the engine speed, these 350-mm bore and 420-mm bore models,

respectively, distinguished by stroke–bore ratios of 4:1 and 4.2:1. The later

introduction of the S46MC-C model (also exploiting a 4.2:1 stroke–bore ratio,

then the highest of any production engine in the world) addressed the needs

of smaller tankers and bulk carriers, which can also be served by the S42MC

and L or S50MC engines. The 460-mm bore model extended the number of

ideal combinations of power, speed and number of cylinders for a given project

(Table 10.2 and Figure 10.8).

Choice in the mid-bore range (500 mm, 600 mm and 700 mm models) was

widened from 1996 by uprated versions supplementing the existing S50MC,

S60MC and S70MC engines. These new S50MC-C, S60MC-C and S70MC-C

models, which share the same design features as the S46MC-C, are more com-

pact (hence the C-designation) and offer higher outputs than their established

equivalents (an L70MC engine is shown in Figure 10.9). Stroke–bore ratios

were raised from 3.82 to 4:1, and the increased power ratings correspond to a

rise in the mean effective pressure to 19 bar.

Supporting the higher ratings are modiﬁed turbocharging and scavenge

air systems as well as modiﬁcations of the combustion chamber conﬁguration

and bearings. Installation space savings were achieved by reducing the overall

length of the C-engines (by around 1000 mm in the case of the six-cylinder

S50MC-C engine) and the overhauling height requirement compared with the

original designs. The masses are also lower (by 25 tonnes or 13 per cent for the

6S50MC-C), which yields beneﬁts in reduced vibration excitations. The MC-C

engines can be 100 per cent balanced.

Table 10.2 S46MC-C engine

Bore 460 mm

Stroke 1932 mm

Stroke–bore ratio 4.2:1

Speed 129 rev/min

Mean eective pressure

19 bar

output/cylinder 1310 kW

Mean piston speed 8.3 m/s

Cylinders 4–8

Specic fuel consumption (mcr)

174 g/kW h