106 Marine Engineering - WIT Press Marine Engineering Traction engines Engines for power generation...

MAN B&W medium-speed engines - the

right propulsion system for the merchant

ship types

J. Albers

This year saw the centennial of the Diesel engine's birthday. On 23 Febru-ary 1893, MAN and Rudolf Diesel signed a contract in Augsburg for thedevelopment and design of a thermal engine which bears the name of its

inventor to this day. This was the birth of the Diesel engine (Fig. 1).

After the development target, namely an efficiency superior to that ofall the engines which then were available, was reached in the year 1897,there was no stopping of the success of this engine any longer. In the year

1909 already, Diesel engines were being manufactured in almost all the Eu-

ropean countries.

At a ceremony held in Augsburg on 26.02.93, which was attended,among others, by notable professors, it was confirmed once again that tothis day, the Diesel engine still is the most economical thermal engine, andengines with a large swept volume reach efficiencies up to above 50% con-tribute to the protection of our environment. And this will not change - sobelieve the experts - during the foreseeable future.

MAN B&W was able at the beginning of May 1993 to present to thepublic the new L 32/40 engine, which is again a trend-setting development

for the future.

The fact that generally speaking this engine has similar combustionspace dimensions as the first Diesel engine, suggests to make a comparisonof the two four-stroke engines (Figs 2 + 3). This comparison presents 100years of development work. MAN then was, and MAN B&W nowadays stillis leading in the development and designing of four-stroke and two-stroke

Diesel engines for all fields of application.

Transactions on the Built Environment vol 1, © 1993 WIT Press, www.witpress.com, ISSN 1743-3509

106 Marine Engineering

Traction enginesEngines for power generationEngines for marine propulsion

This leading role in development is due to the fact that essential com-ponents of the engine are being developed and manufactured in the MANB&W/MAN factories. The vertical range of production for large medium-

speed four-stroke engines in Augsburg currently is high. This is to say thatvital engine components such as

the engine blockrunning gear componentscharge renewal componentscombustion space componentsinjection system components

components for the turbocharging system including the turbochargers properare being manufactured in our workshops. Moreover, MAN BfeW is in-tensely involved in the development of other essential components such aspistons, piston rings. No wonder, therefore, that the new engine conceptof the large medium-speed engines proved very successful, and the designtargets

high reliabilitylow lube oil and fuel oil consumption rateslong times between overhaul of vital engine componentsease of maintenance

were reached straight away.

The new engine family comprising the types L 32/40, L 40/54, L 48/60,L 58/64, V 48/60 (Fig. 4) was developed from the beginning of 1980 on-wards. The first engine was supplied in 1985, it was an engine of the L58/64 type which to this date has reached an operating time of more than50,000 hours and continues operating to the full satisfaction of the customer.

The output range extends from 2,640 kW to approximately 18,000 kWat speeds between 750 and 400 rpm. The rating diagram (Fig. 5) includesthe 32/40 engine which only slightly differs from the large medium-speedengines in design.

To mention some of the design features of modern MAN B&W four-stroke engines:


ENGINE CONSTRUCTION

One-piece engine block with individual cylinder jackets having through bolts

for the main bearings and longer cylinder cover bolts (Fig. 6). Suspended

crankshaftConstant pressure turbocharging

CYLINDER LINER WITH FIRE RING

The cylinder liners of MAN B&W Diesel engines are laser-hardened in theupper part, which lends them a useful life of 60,000 to 80,000 hours.

The cylinder liner is only cooled in the upper part, in way of the fire ring,

so as to reduce thermal stresses between the upper part of the cylinder linerand the lower part of the cylinder liner. Furthermore, this selective coolingof the liner provides for optimum temperatures also around the circumfer-ence, whereby corrosion is avoided and dimensional stability is achieved.

The fire ring has a slightly smaller diameter than the cylinder liner assuch. The piston crown is matched to this reduced diameter. This ensuresthat a contact between carbon deposits and the cylinder liner is avoided.The phenomenon called 'bore polishing' is thus avoided. All our large four-stroke engines feature separate cylinder lubrication (Fig. 7).

PISTON

The piston is of the composite type, consisting of a forged crown and anodular cast skirt (Fig. 8). The geometry of the cooling spaces ensures areliable, efficient 'shaker' effect with ideal temperatures at the piston crown.

CONNECTING ROD

As is the standard on such engines, the connecting rod is of the split typeand allows the piston with the connecting rod shank to be removed without

having to open the big-end bearing.

This solution of the joint being directly underneath the small end bear-ing allows for low headroom and hence for advantageous engine room di-

mensions (Fig. 9).

CYLINDER COVER

With due regard to the experience gained, MAN B&W has for the new en-gine types adopted cross-scavenged cylinder covers equipped with two ex-


haust valves and two inlet valves again. This provides for optimum chargerenewal. An essential point also is the simple exhaust gas and charge airpiping system which contributes to ease of maintenance.

It goes without saying that all these elements, which have proven veryefficient, are also used in the new 32/40 engine.

Four-stroke medium-speed engines are at present being built up to anoutput level of approximately 1,400 kW corresponding to approximately1,900 HP per cylinder, at speeds of 375-750 rpm. Two-stroke engines arenowadays being built with cylinder outputs up to 4,300 kW correspondingto 5,850 HP at 105 rpm.

However, this does by no means set limits to the use of four-stroke en-gines for marine propulsion, so that four-stroke engines can be appropriatelyused for practically all types of ship propulsion, because there is also thechoice of multiple-engine propulsion systems instead of single-engine propul-sions, means four-stroke engine plants - single or multi - offer a number ofadvantages, such as:

a) space savings, especially in respect of the overall height (Fig. 10)

b) free choice of propeller speed, with full engine power being available

c) uncomplicated, and hence cost-effective drive of shaft generators usingthe existing gearbox, up to the full rating of the Diesel engine andallowing for a free choice of the generator speed

d) advantageous part-load behaviour

e) PTO-PTI with the known advantage at low ship speeds and top speeds

f) high flexibility in case of multi-engine systems

g) redundancy - which means increased safety of multi-engine systems

h) resilient mounting

These advantages have meanwhile opened up practically all fields ofmarine application for four-stroke Diesel engines. Some examples:

REFRIGERATOR VESSELS (Fig. 11)

A series of ten refrigerator vessels with a capacity of 400,000 and 450,000cubic feet and a speed of 22 knots are equipped with the 9L 58/64 enginetype. This engine develops an output of 11,925 kW resp. 12,500 kW at 428rpm and drives a controllable pitch propeller via a flexible coupling and a


Marine Engineering 109

reduction gearbox. The propeller speed is 116 rpm. A shaft generator devel-oping 1,800 kW is driven via the gearbox and contributes to the shipboard

mains supply, together with the auxiliary gensets (3x 900 kW - 1,800 rpm).The auxiliary gensets alone would not be capable of cooling the cargo downto the necessary temperature. Particularly high temporary power input isrequired for this purpose and can be provided by the shaft generator.

CONTAINER VESSELS (Fig. 12)

Among others, four container ships of the Sietas type 148 were equippedwith one 6L 48/60 engine each. This engine develops an output of 5,310kW at 450 rpm but is operated at a reduced output of 4,750 kW - 447 rpm- with the benefit of a fuel oil consumption rate of 173 g/kWh. It drivesa controllable pitch propeller via flexible coupling/reduction gearbox at aspeed of 160 rpm. A shaft generator of 810 kW capacity at 150 rpm is

driven via the gearbox.

MULTI-PURPOSE (Fig. 13)

The motor vessel 'ANTJE' has been equipped with an MAN B&W four-stroke engine of the 7L 40/54 type developing 4,235 kW at 514 rpm. Theengine drives a controllable pitch propeller via flexible coupling and gear-box, at a speed of 160 rpm. A shaft generator developing 500 kW/1,500

rpm is driven via the gearbox.

TANKERS (Fig. 14)

The chemicals tanker M/T 'CONGER' has a capacity of 23,400 tdw. Thepropulsion engine is an MAN B&W 6L 58/64 main Diesel engine. Thepower developed by the engine, 7,440 kW at 400 rpm, is transmitted viaa reduction gearbox to a controllable pitch propeller running at a speed ofapproximately 130 rpm. With this rating, the tanker reached a speed of15.5 Kn during sea trials, which corresponds to a service speed of 14.5 Kn.

The on-board power supply is provided by a gear box-driven shaft gen-erator. The electrical output is 838 kW, the speed is 1,500 rpm. The tankerwill additionally have three generator sets each developing an electrical out-

put of 736 kW at 1,000 rpm.

It goes without saying that the propulsion system (except the auxiliaryengines) is operated on heavy fuel oil. The first one of these tankers wasdelivered to the shipowners on 09.03.91. Two further tankers of this type

have in the meantime also taken up service.



No wonder that the same engine concept has been chosen for all thesevarious types of vessels requiring various outputs.

CRUISING VESSELS

It is a fact that four-stroke engine propulsion systems are predominantlyused for modern cruise liners, but also for roll-on/roll-off vessels and ferries.These types of vessels can take full advantage of the above-mentioned ben-efits offered by four-stroke engines. Due to the high level of comfort whichis expected from present-day luxury cruising liners, measures of reducingvibrations and structure-borne noise enjoy top priority.

At a very early time already, MAN B&W was looking into the possibil-ity of resilient mounting of large-bore four-stroke engines, and as early as1968, the first ferry was equipped with four large-bore MAN B&W Dieselengines that were resiliency mounted. However, the engine concept whichwas then followed did not yet allow the engines to be resiliency mounteddirectly on the double bottom, without an intermediate frame.

One of the design objectives in the development of the four-stroke en-gine concept which MAN B&W commenced early in the 80s was the directresilient mounting of engines (Fig. 15). Vibration damping is known to de-pend, to a large extent, on the softness of the resilient mounting elements.The softer the mounting, the higher will the acceleration torques on the en-gines and their components be. Therefore, in order to provide for effectiveresilient mounting, a particularly rigid engine frame is indispensable. Thisfact necessarily points towards one-piece engine blocks. Nevertheless, thedesigning and attachment of components such as the turbocharger, charge-air cooler, Woodward governor, etc. has to be given particular attention.The technical layout of the engine mounting as such calls for particularcare and has to be adapted to requirements. As the structure-borne noisebecomes particularly disturbing at the frequency range from 35 to approx-imately 1,000 Hz, the mounting is engineered so that attenuation is partic-ularly effective in this frequency range (Fig. 16).

The graph very clearly shows the high damping effect over this range.Three distinct drive concepts have been developed for cruising liners - andpractically applied in numerous cases.

1. Diesel-electric

2. Diesel-mechanic with shaft generators

3. Diesel-mechanic with PTI/PTO.


A representative example of Diesel-electric drive doubtless is the cruis-

ing liner 'QE2', which you all know. What has been installed here is a

power station comprised of nine MAN B&W 9L 58/64 propulsion engines

developing an aggregate output of 95,600 kW at 400 rpm. The nine engineswere installed in two separate engine rooms. Each of the engines drivesa two-bearing generator with a power output of 10,500 kW. The voltageis 10,000 Volts, the frequency 60 Hz. The electric power so produced isused, inter alia, for the shipboard mains supply which takes approximately7,000 kW. The ship's propulsion is via two electric motors of a capacityof 44,000 kW each at 144 rpm. These synchro motors drive a controllablepitch propeller, at a speed that can be varied between 144 and 72 rpm. Thisbecomes possible by the use of two synchro converters of 11 MW capacityeach. Surely this is the Diesel-electric propulsion system best known in the

world at present (Fig. 17).

By the end of 1992/beginning of 1993 the French shipyard Chantiers de1'Atlantique delivered the two cruising liners 'Windward' and 'Dreamward'to the Klosters Cruise Line. The vessels are powered by a twin-screw father-and-son propulsion system, with one 6L 40/54 engine developing 3,960 kWat 510 rpm and one 8L 40/54 son engine developing 5,280 kW at 510 rpmeach driving one of the two controllable-pitch propeller screws via doublereduction gearbox and clutches. There is one primary generator for each ofthe son engines, developing 3,300 kW at 1,200 rpm. Moreover, the system

includes two auxiliary gensets of approximately 3,300 kW each (Fig. 18).

A type of propulsion system called hybrid drive has come more andmore into use lately. Hybrid drives are a combination of Diesel-electric andDiesel-mechanic propulsion. Similarly to a mechanical drive, the relativelylarge shaft generators are driven via the gearbox. These generators can alsobe used as propulsion motors powered by generator sets. The advantageof such systems is to be seen in the possibility of shutting down the largepropulsion engines and using the PTI motors for delivering the propulsivepower. For propulsion at relatively low ship speeds, both or either one ofthe two propulsion Diesels would have to be operated at low output, andhence with unfavourable efficiency, to deliver the necessary propulsion en-ergy. The more economical solution will then be the PTI propulsion motor

powered by the auxiliary generator sets.

To reach the ship's top speed, the PTI motor for each shaft can beadded to the two propulsion Diesels so as to upgrade the propulsion output,

and hence the ship's speed.

It goes without saying that in normal service the main Diesels are ca-pable of also driving the primary generator for the shipboard mains system.


The benefit of this hybrid propulsion is its high flexibility, and at the sametime economic efficiency over all operating and output ranges.

A typical example for the hybrid propulsion mode is the cruise liner'Oriana' which is being built at Meyer Shipyard, Papenburg. The mainpropulsion engines will be, per shaft, one 6L 58/64 engine and one 9L58/64 engine. The vessel will receive four auxiliary generator sets withthe engine type 6L 40/54 each developing 4,320 kW at 514 rpm. OnePTI/PTO/motor/generator developing 5,250 kW at 1,200 rpm per shaftwill be installed (Fig. 19).

It goes without saying that all these engines, the main propulsion aswell as the auxiliary engines, will be directly resiliency mounted.

The few examples I mentioned show that large-bore medium-speedDiesel engines are being installed in all kinds of ships. A more convincingproof of the reliability of large-bore MAN B&W four-stroke Diesel enginescan hardly be thought of. The reasons why so many shipowners decide tochoose large-bore MAN B&W four-stroke engines are:

- the definitely superior fuel economy

- the definitely low lube oil consumption

- the ease of maintenance which is reflected in short dismantling timesfor various components and low wear rates resulting in long timesbetween overhaul and long service lives.

As already mentioned at the beginning, environmental aspects are underdiscussion everywhere. This is not only true for the automobile traffic butalso for large-bore Diesel engine applications in power stations and ships.It is well known that SOx and NOx concentrations in the exhaust gas areproblematic and NOx concentrations, in particular have to be kept at a lowlevel. NOx reacts with the air-borne oxygen to form ammonium hydroxide.The ammonium hydroxide which forms is responsible for what we call acidicrain with its detrimental effects on the environment.

MAN B&W's present-day fuel-optimised engines reach NOx values of16-19 g/m3. Regulations must be expected to be amended by the year 2000to the effect that NOx concentrations of only 11 g/m3 are permissible. Toreach this goal, engine builders will have to make quite some effort. MANB&W is dealing with these problems quite some time already, and the firstresults have already been reached. It may be expected that measures suchas:

- derating



- ignition time variation

- addition of water to the fuel

will make it possible to reach the value of 11 g/m3 - although at the expenseof fuel oil consumption which will deteriorate by up to 10 g/kWh.

On the occasion of the Licensees Meeting in Augsburg, in his laudatoryspeech recalling Rudolf Diesel's merit and his idea, Prof. Dr. Ing. Dr. Ing.

Hans Dinger, Honorary Chairman of the Society for the Advancement ofScientific Research Combustion Engines called the Diesel:

'Good friend', 'Old boy', or 'Old fellow'.

This affection reflects the confidence we have in the Diesel. I think thisapplies, in particular, to the marine sector. MAN B&W has earned a bigshare in the merits of more than one century of Diesel engine development.



Figure 1



Figure 2



Comparison of Technical DataFirst Diesel Engine and ModernMS - Diesel Engine

Cylinder bore [mm]

Piston stroke [mm]

Cylinder output [kW]

Speed [Upm]

Mean piston speed[m/sec]

Mean eft. pressure [bar]

pe x cm

Firing pressure [bar]

Spec, output [kW/l]

SFOC [g/kWh]

1stDiesel Engine

250

400

14,7

172

2,29

5,2

11,9

35

0,75

326

L 32/40

320

400

440

750

10

21,9

219

180

13,7

182

Figure 3


Comparing the results from the strain gaugesmeasurements and the piezo sensors it is observedthat for short wave periods the piezo sensors givesslightly higher strain than the strain gauges. Forlonger waves the opposite result is found. The straingauge measurements should be regarded as a pointmeasurement of the strain due to the short length ofthe strain gauge (in the order of 1 cm). The measuredsignal may therefore to some extent be influenced bylocal stress concentrations The length of the piezocable is 15 cm in the measurement will thereforerepresent an average over this area. This differencein measuring area may be one reason for the observeddeviation between the two sensors. Another effect isthat the signal from the piezo cable to some extentis influenced by pressure forces acting on the cablefrom the surrounding material.

60-

50-

40-

20-

10-

DO

— —•;*—

FASTSEAModel TestsModel TeslsModel Tests

PiezoStrain Gauges Rsg.VcvesStrain Gauges Irp Waves

13*Gve per ice (s)

Figure 4: Vertical bending moment at midship,transfer function

A comparison between the measured time signal fromthe strain gauge sensor and the decoded fibreopticsensor results is shown in Fig. 5 in the case of animpulse wave. It is seen that both the magnitude andtime trace are very similar. The measuring length ofthe fiber is 15 cm. The good agreement between thesetwo measurements indicate that the point measurementof the strain gauges do not represent any significantsource of error compared to the strain averaged overa longer distance.


~ 50-

20-

10-

-10-

(_ -20-

-30-

-40-

-50-

Slrcin g.Fiber

65 70 75 80 90

Figure 5: Comparison between measured time historyfor vertical bending moment using strain gauges andfibreoptic sensors, impulse wave.

Effect of Hvdroelasticitv

The encounter frequency range covered by the testswas fg=0.1 - 0.65Hz (full scale values). This implythat we do not reach the natural frequency of the2-node mode of the model which is f j =1.80 Hz. Thisimply that steady state wave induced response at theelastic natural frequency (springing) will not beexcited for this model.

A typical result of measured response spectrum inregular waves is shown in Fig 6. The model scaleencounter frequency was 0.6 Hz corresponding to afull scale value of 0.13 Hz. (note that the result inthe figure represent model scale results and thegiven frequency is model scale encounter frequency).All wave energy is concentrated at one singlefrequency, but for the measured vertical bendingmoment at midships a pronounced response contributionis observed at the frequency of the first elasticmode.

In the case of impulse waves a much more pronouncedresponse was observed at the elastic frequency. Thetime history of the wave and the vertical bendingmoment at midships is shown in Fig 7. In the samefigure the resulting response spectra are shown. Itis observed that the impulse wave excited atransient, elastic response in the hull which gives asignificant contribution to the measured globalbending moment.



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GENERAL ARRANGEMENTS OF THEMAIN ENGINES

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Figure 17



Figure 18

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