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

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FigurE 12.39 Cross-section of 900-mm bore Sulzer rLB90 engine

FigurE 12.40 Longitudinal section of rLB90 engine

442 Wärtsilä (Sulzer) Low-Speed Engines

Bedplate with Thrust Block

For the RL-type engine bedplate, a new concept of great simplicity was

applied. Both the cross girders and the longitudinal structure are of single-wall

fabricated design giving very good accessibility for the welded joints. The cen-

tral bearing saddles are made of cast steel and only one row of mounting bolts

on each side is used to secure the bedplate to the ship’s structure.

The completely new design feature was the method of integrating the thrust

block into the bedplate (Figure 12.41) allowing an extremely compact design and

saving engine length. The ﬁrst crankshaft bearing on the driving end is a combined

radial–axial bearing. The bedplate is a one-piece structure for all engines from four

to eight cylinders, but, if required, it can be bolted together from two halves.

Thick-walled white-metal-lined bearing shells are used to support the

crankshaft and guarantee an optimum safety for the running of the crankshaft.

Crankshaft

In addition to the traditional semi-built-type crankshaft, a monobloc continu-

ous grain ﬂow forged type can be used. From four to eight cylinders, the crank-

shaft is a one-piece component with an integrated thrust collar section. Only

one journal and pin diameter was used for all engines up to eight cylinders. For

RLA engines larger than the RLA56, the crankshaft was semi-built, and the

thrust shaft separately bolted to the crankshaft.

Engine Frame

For the small RLA56 engine, a new method of frame construction was

used. Cast iron central pieces, on which the crosshead guides are bolted, are

Camshaft

driving gear

Thrust bearing

Lanchester

balancer

FigurE 12.41 integrated thrust bearing and camshaft drive for rL engine

sandwiched between two one-piece fabricated side-frame girders. This replaced

the traditional construction of ‘A’ frame bolted to the bedplate with side plates

attached with access doors forming the enclosure. Larger RL-type engines use

‘A’ shaped columns of fabricated double wall design, assembled with longitu-

dinal stiffening plates to constitute a rigid structure between the bedplate and

cylinder blocks (Figures 12.42 and 12.43).

Sulzer rL-type engines 443

FigurE 12.42 Structural arrangement of bedplate, columns and cylinder jackets for

12-cylinder Sulzer rL engine

FigurE 12.43 Arrangement of columns for rLA56 engine

444 Wärtsilä (Sulzer) Low-Speed Engines

Cylinder Jackets

The cylinder jackets are made of ﬁne lamellar cast iron produced as single

block units bolted together in the longitudinal plane to form a single rigid

unit, and held on top of the frame section by long tie bolts secured in the bed-

plate. For the small RLA56 engine, multi-cylinder blocks consisting of two or

three cylinders were standard and provide great rigidity of the structure. The

arrangement of the cooling water passages in the jackets ensures forced water

circulation and optimal water distribution around the exhaust canal.

Because of the steadily rising charge air pressures, the design of the

air receiver was modiﬁed to allow the use of automatic welding techniques.

Instead of a rib-stiffened plain side plate, a semi-circular pressure containment

was ﬁtted with an integral air inlet casing. The auxiliary blower is mounted on

the front end of the receiver, thus eliminating inclined ducts.

Combustion Chamber Components

The combustion chamber of RL-type engines is principally of the same shape

as that of the RND-M. The cylinder cover is basically a one-piece steel block

with cooling bores, while an identical arrangement of bore cooling is applied

to the upper collar of the cylinder liner, which is made from lamellar cast iron,

a material of good heat conductivity and wear resistance. Figure 12.44 shows

the arrangement with cover, cylinder liner and piston.

A new type of piston crown was introduced for the RL series engines. This

combustion chamber component similarly uses a bore cooling arrangement

(Figures 12.45 and 12.46) as previously only applied to the liner and cover.

Water cooling was retained but the piston bore cooling uses a somewhat differ-

ent mechanism to the force ﬂow system of the liner and cover.

The cooling space of the piston crown is approximately half ﬁlled with

cooling water, and, as a result of piston acceleration and deceleration, a ‘cock-

tail shaker’ effect is produced to provide excellent heat removal. This effect is

capable of ensuring efﬁcient heat transfer under all prevailing load conditions

in order to keep the vital temperatures on the piston crown and around the pis-

ton rings within suitable limits.

As a result of this new design, the crown temperatures were lowered com-

pared with the previous construction. Forged steel blocks were speciﬁed for

piston crown manufacture but cast steel versions were also used.

Cylinder Lubrication

Lubrication of the cylinder is through six quills mounted in the upper area of

the liner just above the cylinder jacket, as shown in Figure 12.47. The oil dis-

tribution grooves have a very small angle of inclination to avoid blow-by over

the piston rings and small but regular quantities of cylinder oil supplied by an

accumulator system. Two further lubrication points are provided below the

scavenge ports on the exhaust side with the necessary oil pumps positioned on

the front side of the engine above the camshaft drive.

FigurE 12.44 Combustion chamber components for rLA90 engine

Bore-cooled cylinder

cover with 8 studs

Fuel nozzle with

increased service life

Bore-cooled cylinder line

Bore-cooled piston head

Accumulator cylinder

lubrication, 8 lubricating

points

Four bronze bands

Exhaust ports

Inlet ports

Two lubricating points

below ports

Honed running surface

of lower liner parts

FigurE 12.45 detail view of rL engine piston with bore cooling

446 Wärtsilä (Sulzer) Low-Speed Engines

Crosshead design

The crosshead is similar to that used for RND engines and has double guided

slippers. The pin size was increased for safety and thin-walled half shells of the

FigurE 12.46 Arrangement of telescopic pipes for rL engine piston cooling

FigurE 12.47 Cylinder lubricator for rL engine

aluminium–tin type were used. The pin itself is of forged homogeneous steel of

symmetrical design and can therefore be turned around in case of damage. The

piston rod is connected to the pin by a single hydraulically tightened nut, while

the slippers, made of cast steel and lined with white metal, are bolted to the ends

of the pin. The cast iron double guide faces are ﬁtted to the engine columns.

The connecting rods of traditional marine type have a forged normalized

steel bottom end bearing, lined with white metal, held in place by four hydrau-

lically tensioned bolts. Compression shims are provided between the bottom

end bearing and the palm of the connecting rod.

piston Assembly

The piston (Figure 12.45) consists of a water-cooled cast steel crown, a cast

iron skirt with copper bandages and a forged steel piston rod, with the piston

rings ﬁtted in chromium-plated grooves.

The water-cooled piston has proved very reliable when running on heavy

fuels, and the use of water cooling has resulted in practically negligible sys-

tem oil consumption. (With oil cooling, oil is consumed usually as a result of

thermal ageing on hot piston walls. Oil leaks from oil-cooled pistons may also

occur on other engine types.) The two-part gland seals for the piston rod, and

telescopic piston cooling pipes can be inspected while the engine is running

and can be dismantled without removing the piston. The double-gland dia-

phragm around the piston rod completely separates the crankcase from the pis-

ton undersides, preventing contamination of the crankcase oil by combustion

residues or possible cooling water leakages. In addition, the freshwater piston

cooling water system is served by an automatic water drain-off when the circu-

lating pumps are stopped. This avoids leakages when the ship is in port.

Turbocharging Arrangement

All the Sulzer RL engines employ the constant pressure turbocharging system

and with the high-efﬁciency Brown Boveri series 4 turbochargers include pro-

vision for automatic cleaning. The layout of the turbocharging arrangement is

shown in Figure 12.48.

The use of the piston undersides to provide a scavenge air impulse elimi-

nates the need for large electrically driven auxiliary blowers. At higher loads a

simple ﬂap valve opens to cut out the piston underside pumping effect with a

consequent improvement in fuel consumption, whilst a small auxiliary fan incor-

porated in the scavenging system improves the smoke values at the lowest loads.

The piston underside scavenge pump facility allows the engine to start and

reverse even with total failure of all turbochargers. The auxiliary fan and engine

will even operate at up to 60 per cent load, thus giving a ‘take home’ facility.

The turbochargers are mounted on top of the large exhaust gas receiver with

the scavenge air receiver, which forms part of the engine structure beneath.

The charge air is passed down through sea water–cooled intercoolers, which

are mounted accessibly alongside the scavenge air receiver. Flap-type valves,

Sulzer rL-type engines 447

448 Wärtsilä (Sulzer) Low-Speed Engines

which operate according to the scavenge air pressure, direct the air inside the

three-compartment air receiver to the piston underside (at low scavenge air

pressure) or direct to the scavenge ports when the higher air pressure from the

turbochargers keeps the underside delivery ﬂap valves shut.

For RL-type engines equipped with only one turbocharger, a separate tur-

bocharger/air intercooler module is available as a standard option. This unit

can be located adjacent to the engine at either the forward or aft end, thus con-

siderably reducing the mounting height and width of the main engine. The tur-

bocharger module consists of a base frame onto which the turbocharger, charge

air cooler, air ducts and cooling water pipes are solidly mounted with ﬂexible

connections to the engine.

upgrading rLB Engines

Based on ﬁeld tests carried out between 1991 and 1995, a retroﬁt package

of modiﬁcations was introduced for Sulzer RLB90 engines in 1993 and for

RLB66 engines in 1995. The main element is the change to loop cooling in

the cylinder liners, an improved cooling technique that reduces the thermal and

mechanical stresses in the top collar of the liner (Figure 12.49). By optimizing

the running surface temperature, the system also reduces corrosive wear and

extends the TBOs up to 2 years.

The retroﬁt package comprises the loop-cooled cylinder liners as well as:

l A new fully gas-tight, vermicular top piston ring of increased thickness

l A modiﬁed top piston ring groove with increased height and increased

thickness of chromium layer

FigurE 12.48 Constant pressure turbocharging and operation of under-piston

supercharging (rL engine)

l Multi-level lubrication

l A new water guide jacket to suit the new liner

l A modiﬁed condensed water drain from the scavenge air receiver.

As RLB engines exploit loop scavenging with both scavenge and exhaust

ports in the lower part of the liner, the fully gas-tight top ring signiﬁcantly

reduces the lateral forces at the piston skirt in addition to reducing the blow-

by of hot combustion gases—both of which increase the piston skirt life. The

package can be applied to the engine either as a full package or step-by-step

(intermediate package) depending on service experience with the liners and

whether the general piston-running behaviour meets today’s expectations. It is

also possible to replace individual original liners with loop-cooled units when-

ever they need to be renewed; there is no problem in running loop-cooled and

original design liners together in the same engine.

(See Introduction for details of Sulzer’s early low-speed engines and

Chapter 9 for research engines).

Sulzer rL-type engines 449

FigurE 12.49 Loop cooling of the cylinder liner benets Sulzer rLB90 and rLB66

engines

451

C h a p t e r | t h i r t e e n

Burmeister & Wain

Low-Speed Engines

A pioneering Danish designer and builder of low-speed two-stroke crosshead

engines, Burmeister and Wain (B&W) focused in the post-War era on high-

pressure turbocharged single-acting uniﬂow-scavenged models with one cen-

trally located exhaust valve. The uniﬂow system fosters effective scavenging of

the exhaust gases from the cylinder in an even progressive upwards movement

with low ﬂow resistance through to the exhaust manifold via a large diameter

poppet-type exhaust valve (Figure 13.1).

Until 1978 all B&W engines operated on the impulse turbocharging system

(Figure 13.2), but the search for enhanced economy in the wake of contempor-

ary fuel crises dictated a change to the constant pressure system, yielding a

saving of around 5 per cent in speciﬁc fuel consumption (Figure 13.3). In the

years before its takeover by MAN of Germany in 1980, B&W introduced a

number of engine series—successively the K-GF, L-GF, L-GFCA and L-GB

programmes—before launching the MC design portfolio, which is still evolv-

ing under MAN Diesel’s MAN B&W brand (see Chapter 10).

All of these designs were improved variants of the K-GF series, which

itself introduced many notable design innovations such as box-frame con-

struction, intensively cooled cylinder components and hydraulically actuated

exhaust valves.

A major change to the structure of the company followed its purchase by

MAN, resulting in Copenhagen becoming the centre for two-stroke engine

development of all designs bearing the MAN B&W trademark.

K-GF typE EnGinES

B&W two-stroke engines based on the K-GF series featured many new design

features. Notable were the box-type construction of the crankcase and the use

of a hydraulically actuated exhaust valve instead of the conventional mechani-

cal rocker arm system used in the earlier K-EF types. A sectional sketch of

the K-GF is shown in Figure 13.4. As this model was rapidly superseded by

the L-GF and L-GB models, only brief details of the K-GF construction are

given here.