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

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462 Burmeister & Wain Low-Speed Engines

instead of to the turbochargers as in the impulse system. When the cylinders

exhaust into a large receiver, the outﬂow of gas is quicker because the large gas

impulse at the commencement of the exhaust period is levelled out in the gas

receiver, and the outﬂow of gas will not be retarded, as in the case of impulse

turbocharging where a pressure peak is built up in the narrow exhaust pipe

before the turbocharger.

The opening of the exhaust valve can be delayed about 15°, thereby length-

ening the expansion stroke and improving the efﬁciency and reducing the fuel

consumption. The energy before the turbine is less than that for impulse tur-

bocharging but as the pressure and temperature before the turbine is nearly

FiGurE 13.12 a 12-cylinder L90GFCa engine developing 34 800 kW at 97 rev/min

constant the turbine can be adapted to run at peak efﬁciency, and the blower

can supply sufﬁcient air above 50 per cent of engine load. The scavenging air

pressure is increased and the compression pressure somewhat decreased com-

pared with impulse turbocharging.

A small auxiliary blower is necessary for satisfactory combustion condi-

tions at loads of up to about 50 per cent. Two blowers of half capacity are used

for safety, and even with one of these out of action the other with half the over-

all capacity is satisfactory for starting and load increase. The engine will still

run at down to 25 per cent load but with a smoky exhaust.

The change from K-GF to L-GF resulted in a 2 per cent improvement in

the speciﬁc fuel consumption, and the lower speed accounts for a 5 per cent

improvement in propeller efﬁciency. Constant pressure turbocharging adds a

further 5 per cent to the improvement, resulting in a 12 per cent reduction in

speciﬁc fuel consumption between the L-GF and K-GF types. The next engine

model of the constant pressure turbocharged type was the L-GFCA ((Figures

13.12 and 13.13), shortly succeeded by the L-GB type., shortly succeeded by the L-GB type.

L-GB typE EnGinES

A further improvement in speciﬁc fuel consumption was yielded by the L-GB

and L-GBE series engines. By using the optimum combination of longer stroke,

increased output and higher maximum pressure and the newest high-efﬁciency

L-GB type engines 463

100%

80 85 90 95 100

(n(r/min))

0.20

0.25

0.30

(bar)

85 90 95 100% 105

110

100%

4500

4400

4300

4200

4100

4000

3900

3800

3700

3600

3500

3400

3300

3200

3100

3000

2900

2800

2700

2600

BHP/cyl.

3300

kW/cyl.

3200

3100

3000

2900

2800

2700

2600

2500

2400

2300

2200

2100

2000

1900

FiGurE 13.13 Load diagram for L90GFCa engine

464 Burmeister & Wain Low-Speed Engines

turbochargers, much lower fuel consumption rates were achieved. The L-GB

series had an mep of 15 bar at the same speed as that of the L-GFCA to give

an increase in power of 15 per cent and an increase in the ﬁring pressure from

89 bar to 105 bar. Accordingly, the important P

max

/mep ratio is almost the same,

but the speciﬁc fuel consumption is some 4 g/kW h lower than that of the

L-GFCA series. A further economy rating is obtained with engines of the L-GBE

type by holding the P

max

at reduced engine output (the so-called derating, as

outlined in Chapter 5: the practice of offering propulsion engines in both normal

and derated versions was adopted by many engine manufacturers, even for four-

stroke medium-speed engines) (Figure 13.14).

FiGurE 13.14 L-GB/GBE engine cross section

Bedplate and Main Bearing

The bedplate consists of high, welded longitudinal girders and welded cross

girders with cast steel bearing supports. For the four- and ﬁve-cylinder engines,

the chain drive is placed between the aftermost cylinder and the built-in thrust

bearing. For the six- to twelve-cylinder engines, the chain drive is placed at

the assembling between the fore and the aft part. For production reasons, the

bedplate can be made in convenient sections. The aft part contains the thrust

bearing. The bedplate is made for long, elastic holding-down bolts tightened

by hydraulic tool.

The oil pan is made of steel plate and welded to the bedplate parts. The oil

pan collects the return oil from the forced lubricating and cooling oil system.

For about every third cylinder, it is provided with a drain with grid.

The main bearings consist of steel shells lined with white metal. The bot-

tom shell can, by means of hydraulic tools for lifting the crankshaft and a

hook-spanner, be turned out and in. The shells are ﬁxed with a keep and the

long elastic studs tightened by hydraulic tool.

thrust Bearing

The thrust bearing is of the B&W–Michell type. Primarily, it consists of a steel

forged thrust shaft, a bearing support and segments of cast iron with white

metal. The thrust shaft is connected to the crankshaft and the intermediate shaft

with ﬁtted bolts.

The thrust shaft has a collar for transfer of the ‘thrust’ through the seg-

ments to the bedplate. The thrust bearing is closed against the crankcase and

provided with a relief valve.

Lubrication of the thrust bearing derives from the system oil of the engine.

At the bottom of the bearing, there is an oil sump with outlet to the oil pan.

Frame Section

The frame section for the four- and ﬁve-cylinder engines consists of one part

with the chain drive-located aft. The chain drive is closed by the end-frame

aft. For six- to twelve-cylinder engines the frame section consists of a fore and

an aft part assembled at the chain drive. Each part consists of an upper and a

lower frame box, mutually assembled with bolts.

The frame boxes are welded. The upper frame box is on the back of the

engine provided with an inspection cover for each cylinder. The lower frame box

is on the front of the engine provided with a large hinged door for each cylinder.

The guides are bolted onto the upper frame box and offer possibility for

adjustment. The upper frame box is provided on the backside with a relief valve

for each cylinder and on the front side with a hinged door per cylinder. A slotted

pipe for cooling oil outlet from the piston is suspended in the upper frame box.

The frame section is attached to the bedplate with bolts. The stay bolts con-

sist of two parts assembled with a nut. To prevent transversal oscillations the

assembly nut is supported. The stay bolts are tightened hydraulically.

L-GB type engines 465

466 Burmeister & Wain Low-Speed Engines

Cylinder Frame, Cylinder Liner and Stung Box

The cylinder frame unit is made of cast iron. Together with the cylinder liner

(Figure 13.15), it forms the scavenging air space and the cooling water space.

At the chain drive there is an intermediate piece. The stay bolt pipes and the

double bottom in the scavenging air space are water cooled. On the front the

cylinder frame units are provided with a cleaning cover and inspection cover for

scavenging ports. The cylinder frame units are mutually assembled with bolts.

Housings for roller guides, lubricators and gallery brackets are suspended

on the cylinder frame unit. Further, the outside part of a telescopic pipe is ﬁxed

for the supply of piston cooling oil and lubricating oil. A piston rod stufﬁng

box provided with sealing rings for scavenging air and oil scraper rings pre-

venting oil from coming up into the scavenging air space is at the bottom of

the cylinder frame unit.

A–A

B–B

FiGurE 13.15 Components of L-GB cylinder liner

The cylinder liner is made of alloyed cast iron and is suspended in the

frame section with a low located ﬂange. The uppermost part of the liner has

drillings for cooling water and is surrounded by a cast iron cooling jacket. The

cylinder liner has scavenging ports and drillings for cylinder lubrication.

Cylinder Cover

The cylinder cover is made in one piece of forged steel and has drillings for

cooling water. It has a central bore for the exhaust valve and bores for fuel

valves, safety valve, starting valve and indicator valve (Figure 13.16).

The cylinder cover is attached to the cylinder frame with studs tightened by

a hydraulic ring covering all studs.

L-GB type engines 467

G–G

H–H

A–A

FiGurE 13.16 Components of L-GB cylinder cover

468 Burmeister & Wain Low-Speed Engines

Exhaust Valve and Valve Gear

The exhaust valve consists of a valve housing and a valve spindle. The valve

housing is made of cast iron and arranged for water cooling, and is provided

with a bottom piece of steel with Stellite welded onto the seat. The spindle

is made of heat-resistant steel with Stellite welded onto the seat. The hous-

ing is provided with a spindle guide. The exhaust valve housing is connected

to the cylinder cover with studs and nuts tightened by hydraulic jacks. The

exhaust valve is opened hydraulically and closed by a set of helical springs.

The hydraulic system consists of a piston pump mounted on the roller guide

housing, a high-pressure pipe and a working cylinder on the exhaust valve. The

piston pump is activated by a cam on the camshaft.

Cover Mounted Valves

In the cylinder cover, there are three fuel valves: a starting valve, a safety valve,

and an indicator valve.

The fuel valve opening is controlled by the fuel oil pressure and is closed

by a spring. An automatic vent slide allows circulation of fuel oil through the

valve and high-pressure pipes and prevents the compression chamber from

being ﬁlled up with fuel oil in the event of a sticking spindle in a stopped

engine. Oil from venting and other drains is led away in a closed system.

The starting valve is opened by control air from the starting air distributor

and closed by a spring. The safety valve is spring loaded. The indicator valve

is placed near the indicator gear.

Crankshaft

The crankshaft for four- and ﬁve-cylinder engines is made in one part, and for

six- to twelve-cylinder engines in two parts assembled at the chain drive with

ﬁtted bolts. The crankshaft is semi-built with forged steel throws.

In the aft end the crankshaft features a ﬂange for assembling with the thrust

shaft. The crankshafts are balanced exclusively by borings in the crankpins,

although in some cases supplemented by balance weight in the turning wheel.

Connecting rod

The connecting rod is made of forged steel. It has a Tee-shaped base on which

the crank bearing is attached with hydraulically tightened bolts and nuts with

Penn-securing. The L90GBE engine has shims placed between the base and

the crank bearing, as this engine type needs a smaller compression chamber

because of a higher compression ratio. The top is square shaped on which the

crosshead bearings are attached with hydraulically tightened studs and nuts

with Penn-securing. The bearing parts are mutually assembled with bolts and

nuts tightened by hydraulic jacks.

The lubrication of the crank bearing takes place through a central drilling

in the connecting rod.

The crank bearing is made of steel cast in two parts and lined with white

metal. The bearing clearance is adjusted with shims. The crosshead bearings

are made of cast steel in two parts and provided with bearing shells.

piston–piston rod–Crosshead

The piston consists of a piston crown, piston skirt and cooling insert for oil

cooling (Figure 13.17). The crown is made of heat-resisting steel and is pro-

vided with ﬁve ring grooves, which are hard-chrome plated on both lands. The

skirt is made of cast iron. The piston rings are right- and left-angle cut and of

the same height.

The piston rod is made of forged steel and ﬁxed to the crosshead with a

hydraulic tightened stud. It features a central bore, which, in connection with

a cooling oil pipe and the cooling insert, forms the inlet and outlet for cooling oil.

L-GB type engines 469

FiGurE 13.17 Components of L-GB piston

470 Burmeister & Wain Low-Speed Engines

The crosshead is made of forged steel and is provided with steel cast guide

shoes with white metal on the running surfaces. A bracket for oil inlet from

the telescopic pipe and a bracket for oil outlet to slit pipe are mounted on the

crosshead ((Figure 13.18)..

Fuel pump and Fuel Oil High-pressure pipes

The fuel pump consists of a pump housing of nodular cast iron and a centrally

placed pump cylinder of steel with sleeve and plunger of nitrated steel. The

plunger has an oblique injection edge, which will automatically give an opti-

mum fuel injection timing. There is one pump for each cylinder. In order to

prevent fuel oil from being mixed into the separate lubricating system on the

camshaft, the pump is provided with a sealing device.

FiGurE 13.18 Components of L-GB connecting rod and crosshead

The pump gear is activated by the fuel cam, and the injected volume is

controlled by turning the plunger by a toothed bar connected to the regulation

mechanism. Adjustment of the pump lead is made with shims between top

cover and pump housing.

The fuel pump is provided with a pneumatic lifting device, which can, dur-

ing normal operation and turning, lift the roller guide roller free of the cam.

The fuel oil high-pressure pipes have protecting hoses. The fuel oil system

is provided with a device, which, through the pneumatic lifting tool, discon-

nects the pump in case of leakage from the high-pressure pipes.

Camshaft and Cams

The camshaft is divided into sections for each cylinder. The individual sections

consist of a shaft piece with an exhaust cam, a fuel cam, an indicator cam, and

coupling parts. The exhaust and fuel cams are made of steel with a hardened

roller race and are shrunk on the shaft. They can be adjusted and dismounted

hydraulically.

The indicator cams, which are made of cast iron, are bolted onto the shaft.

The coupling parts are shrunk on the shaft and can be adjusted and dismounted

hydraulically.

The camshaft is located in the housing for the roller guide. The camshaft

bearings consist of two mutually interchangeable bearing shells, which are

mounted in hydraulically tightened casings.

Chain drive and reversing

The camshaft is driven from the crankshaft by two 4

⁄2-in chains. The chain

drive is provided with a chain tightener, and guide bars support the long chain

strands. The camshaft is provided with a hydraulically actuated reversing gear

turning the camshaft to the position corresponding to the direction of rotation

of the crankshaft.

Starting air distributor, governor and cylinder lubricators are driven by sep-

arate chain from the intermediate wheel.

Moment Compensator

Four-, ﬁve- and six-cylinder engines are prepared for moment compensators,

which can be ﬁxed to the fore and aft ends of the frame section and are driven

by the camshaft through ﬂexible couplings. The moment compensator will

reduce the second-order external moments to a level between a quarter of the

original ﬁgure and zero.

Governor

The engine revolution per minute is controlled by a hydraulic governor. For

ampliﬁcation of the governor’s signal to the fuel pump, there is a hydraulic

ampliﬁer. The hydraulic pressure for the ampliﬁer is delivered by the camshaft

lubricating oil system.

L-GB type engines 471