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

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The bedplate of the TM410 engine is a U-shaped iron casting in which the

main bearing caps are ﬁtted with a serrated joint to form, with the bearing sad-

dles, a rigid housing for the thin-wall steel main bearing shells. For the TM620

engine what is in effect a single tooth serration is used for the main bearing cap

joint: the joint faces are inclined towards the abutment.

Bearing shells have copper–lead lining and lead–tin plating. Both upper and

lower shells can be removed easily by lifting the bearing cap. Large inspection

openings in the bedplate facilitate access to the crankcase, the covers being

provided with relief valves. Integrally cast columns in the in-line engine bed-

plate accommodate alloy steel tie-rods to connect bedplate and cylinder block

Stork-Werkspoor Diesel 741

FigurE 28.21 Cross-section of in-line SWD tM620 engine

742 Other Medium-Speed Engines

tightly together in a rigid construction preventing high-tensile stresses from

cylinder pressures being transmitted to these major cast iron elements. V-type

engines are ﬁtted with two rows of tie-rods. As the rods are in an oblique posi-

tion, a number of short bolts are additionally ﬁtted to prevent relative move-

ment of cylinder block and bedplate. A thick upper bridge between pairs of

cylinders on opposite V-banks also contributes to rigidity.

The crankshaft is a fully machined high-tensile continuous grain ﬂow forg-

ing in one piece. The large diameter journals and crankpins are provided with

obliquely drilled holes for the transmission of lubricating and piston cooling

oil. Counterweights ﬁtted on all crank webs are secured by two hydraulically

stressed studs and two keys.

A rigid iron casting cylinder block incorporates the cooling water jack-

ets and the camshaft space. Covers are arranged on the camshaft side of the

block to allow inspection of the cams and rollers. Three roller levers are ﬁt-

ted per TM410 engine cylinder: one each for the inlet and exhaust cams and

one for the fuel pump drive. Only two levers per cylinder—for the valves—are

arranged on the TM620 engine. The pushrod passages are equipped with seals

to prevent any oil leakage from entering the camshaft space.

The camshaft is ground to a single diameter over its entire length, with the

hardened steel cams hydraulically shrunk on with the aid of tapered bushes.

When necessary, the complete camshaft can be removed sideways; and cams

FigurE 28.22 An eight-cylinder Stork-Werkspoor Diesel tM620 engine installed to

power a container ship

can be exchanged without removing the camshaft from the engine since they

can be removed from the shaft at the forward end of the section. The cam-

shaft is driven from the crankshaft by nodular cast iron gearwheels and runs in

thin-wall bearings. The direct-reversible engine is provided with double cams

with oblique transition faces and a pneumatically controlled hydraulic revers-

ing gear to move the camshaft in an axial direction.

An extremely heavy big end is a feature of the connecting rod, forming a

rigid housing for the copper–lead lined lead–tin plated thin-wall steel bearing

shells. To allow the rod to be removed through the cylinder liner, the big end

is split by serrated joints in two planes. The design fosters a low headroom

and easy dismantling. The big end bolts are hydraulically stressed. The TM620

engine connecting rod is similar in principle to that of the TM410 component

but uses three pairs of studs, each set normal to the face of the joint it closes

rather than bolts at right angles to the axis of the rod.

Lower-rated TM410 engines were speciﬁed with a light alloy piston with a

cast-in top ring carrier and a cast-in cooling oil tube; the higher-rated models

and the TM620 engine exploited a two-piece piston. Both feature one chrome-

plated top ring, three compression rings with bronze insert and an oil control

ring above the gudgeon. The TM410 engine additionally uses a second oil con-

trol ring at the base of the skirt when the single-piece piston is ﬁtted.

The gudgeon pin is fully ﬂoating and the small end bearings have dif-

ferent widths in order to provide a greater area to withstand better the com-

bustion loads. The small end bearing material is of the same speciﬁcation as

the large end. The small end and piston cooling oil supply passes through

drillings in the connecting rod; the spent oil from the pistons and gudgeon

pins is expelled from the piston. In the case of the one-piece piston, however,

cooling oil passes through a separate drilling to the bottom of the big end.

Both engines deploy restrictors in the big end oil passages incorporating non-

return valves. Despite the three-part large end conﬁguration, both engines use

horizontally split two-part big end shells. The V-engine big ends run side-by-

side on the crankpin.

The special cast iron cylinder liner is provided with cooling water pas-

sages drilled to a hyperboloid pattern in its thick upper rim. This feature was

designed to secure intense cooling of the upper liner part and also to ensure, by

equalizing the temperatures of the connected liner rim and the cylinder block,

a perfectly circular liner when the engine is operating.

Two holes for cylinder lubrication are drilled in each liner from the bottom,

thus avoiding oil pipes through the cooling water spaces. Each hole feeds one

lubricating oil quill arranged halfway along the liner length. A normal Assa

cylinder lubricator is provided. There are four holes per cylinder in the case of

the TM620 engine.

Both engine types are equipped with four-valve cylinder heads with an

unusual two-bearing exhaust rocker design. In the case of the TM620 the inlet

valve is shorter than the exhaust valve and two fulcrum shafts are used with

different lengths of Y-shaped rockers to operate each pair of valves.

Stork-Werkspoor Diesel 743

744 Other Medium-Speed Engines

Cooling water is directed over the ﬂame plate of the head by the intermediate

deck which also serves the function of a strength member so that the ﬂame plate

itself can be thinner and thus better able to withstand thermal load. The exhaust

valves work in water-cooled cages and are Stellited on the seating face. Careful

cooling of the seat area, and hence of the sealing face, reportedly gave the valves

a lifetime between overhauls when burning heavy fuels not greatly inferior to

that experienced by valves in marine diesel-burning engines. The inlet valves are

seated on hardened cast iron inserts mounted directly in the cylinder head.

Cam proﬁles were designed to avoid rapid acceleration changes and thus to

minimize noise and dynamic stresses. The valve rockers are ﬁtted with needle

bearings that require no oil supply; all other contact faces within the cylinder

head covers are lubricated by separate impulse oiling equipment. The associ-

ated lubricator is driven, in parallel with the cylinder lubricator, from the cam-

shaft gear. The oil used for these purposes is drained separately to prevent

contamination of the crankcase oil should a fuel leak occur.

A dedicated fuel injection pump serves each cylinder. The injector is

equipped with an easily replaceable nozzle which is water cooled to prevent

carbon deposits forming when handling residual fuels. The TM410 fuel pump

is actuated by a spring-loaded pushrod which itself follows a lever-type cam

follower similar to those that actuate the valve pushrods. On the TM620 engine

the pump has an integral roller.

The mechanism for the starting air pilot valves is also used to stop the engine

at overspeed. In such an event, the mechanical overspeed trip actuates a pneu-

matic valve to allow air pressure into an auxiliary cylinder which then keeps

every fuel injection pump plunger lifted with the roller free of the cam (Figure

28.23). Safety devices for low lubricating oil pressure and for low cooling

FigurE 28.23 Fuel pump drive and cutout on SWD tM410 engine

water ﬂow are integrated in the engine systems and are thus independent of the

external electrical alarm system.

A more modern smaller bore design, the SW 280 engine, was introduced

by SWD in 1981 to ﬁll a gap between the TM410 and the SW 240 models and

remained in the Stork-Wärtsilä Diesel production programme until 1997 when

the Wärtsilä 26 series was launched (see Chapter 27). The 280 mm bore/300 mm

stroke design (Figure 28.24) developed 300 kW/cylinder at 720–1000 rev/min and

found favour as a genset drive in deep-sea tonnage as well as a propulsion unit

for smaller ships. It was available in six, eight and nine in-line and V12-, 16- and

18-cylinder versions to cover power demands up to 5400 kW.

Stork-Werkspoor Diesel 745

FigurE 28.24 Stork-Werkspoor Diesel SW 280 design

746 Other Medium-Speed Engines

A short and compact engine was sought by the Dutch designers, with power

available from both ends of the crankshaft. Engine-driven pumps could be

installed on a sideways-mounted gearcase. The design allowed for combustion

pressures up to 150 bar and associated high fuel injection pressures. Well-control-

led wall temperatures in the combustion space addressed heavy fuel operation.

A reduced number of overall components was achieved by replacing most

pipes for water and oil passage with drillings through the structure. This, and

other measures, lowered the risk of ﬂuid leakages and eased maintenance pro-

cedures. A rigid design was secured by incorporating the air duct, water and

lubricating oil galleries in the cylinder block casting.

The cylinder liner features a high collar and drilled cooling channels. The

piston comprises a pressed aluminium alloy body and a forged steel crown

which is cooled by lubricating oil and provided with hardened ring grooves.

The cylinder head is relatively high and very rigid, its stiffness largely achieved

by a special-shaped intermediate deck. The head incorporates four valves

whose seats are detachable; the exhaust valve seats are water-cooled.

A separate lubricating system serves the fuel pumps to prevent contamina-

tion of the main system oil. Pulse turbocharging was speciﬁed to secure the

maximum air supply over all loads. The scavenge air is heated for starting and

low load operations on heavy fuel.

yAnMAr

Like Daihatsu above, Yanmar Diesel is a proliﬁc Japanese producer of high-

speed and smaller medium-speed engines for genset and propulsion drives. Its

medium-speed propulsion engine programme has included the S185, M200,

M220, T240, T260, N260, Z280, N280 and N330 series, the designation

signifying the bore size in millimetres. Most are built in six-cylinder in-line

form, with the larger bore models also offering an eight-cylinder version. The

8N330-EN engine delivers 3310 kW at 620 rev/min.

Yanmar added to an extensive genset engine portfolio in 2006 with the six-

cylinder EY18 model, which covers power demands from 360 kWe to 750 kWe

with 720 rev/min and 900 rev/min variants. The compact 180 mm bore heavy

fuel-burning design features low-sac fuel valves, variable jacket water temper-

ature control and a valve stem seal with a back-pressure lip. Fuel economy is

enhanced and NOx emissions reduced by a staggered injection hole nozzle and

deep combustion chamber, and the latest generation turbocharger. The design-

er’s ASSIGN combustion technology and ECODiesel SAVETEN measures are

said to ensure a balance between fuel consumption and emissions of NOx and

smoke.

Development goals pursued by Yanmar to beneﬁt the designs have included

enhanced compatibility with heavy fuels and strengthened but lighter cylinder

blocks, bedplates and cylinder heads to lower overall engine weight. A com-

pact and lightweight reverse-reduction gear and compact arrangement of turbo-

charger and air cooler contribute to reduced overall engine length and height.

Measures to ease engine installation and servicing are also cited. Large

inspection windows on both sides of the cylinder block facilitate dismantling

and re-assembly of the main bearing and connecting rod. All pumps and ﬁl-

ters are arranged above engine installation level to simplify access. Full power

take-off is available from the front of the engines.

tWO-StrOKE MEDiuM-SpEED EnginES

The medium-speed engine market has long been dominated by four-stroke,

uniﬂow-scavenged designs but at one time a number of two-stroke designs

enjoyed popularity, notably the Polar loop-scavenged type—which ceased pro-

duction when Nohab introduced its four-stroke F20 range—and Sulzer’s uni-

ﬂow-scavenged ZH40.

Wichmann’s commitment to the two-stroke loop-scavenged trunk piston

concept was renewed in 1984 with the launch of its 295 kW/cylinder WX28

engine (Figure 28.25). The simple ‘valveless’ approach had been proven in

service by the Norwegian company’s earlier AX, AXG and AXAG designs.

The 280 mm bore/360 mm stroke WX28 covered an output band from 1180 kW

to 4735 kW at 600 rev/min with four, ﬁve and six in-line and V8-, 10-, 12- and

16-cylinder models.

Development focused on low fuel and maintenance costs with high reliabil-

ity. The engine was also claimed to be one of the lightest and most compact in

its power class. The ability to operate on heavy fuel (180 cSt) under all con-

ditions was another goal. A speciﬁc fuel consumption of 188 g/kW h resulted

from enhanced scavenging and fuel injection systems, and a maximum com-

bustion pressure of 140 bar is underwritten by rugged construction. The mean

effective pressure is 13.5 bar.

The valveless cylinder cover is of simple construction, the lack of ducts

for hot exhaust gas promoting uniform temperature distribution and low stress.

Fastened by eight hydraulically tightened nuts, the cover can be removed in a

few minutes and the piston withdrawn in 10 min. The connecting rod can be

disconnected while leaving the big end bearing on the crankshaft; this feature

reduces the necessary removal height.

Wichmann stressed the overall simplicity of the engine and the impact on

reliability and serviceability, citing fewer moving parts and hence fewer wear-

ing parts. Separate cylinder lubrication—a standard feature—permits matching

of the lubricating oil total base number to the fuel sulphur content. The oil is

distributed over the cylinder surface by a hydraulic lubricator via four bores

and quills.

Wichmann engines—including the earlier 300 mm bore/450 mm stroke

AXAG design—found particular favour in the Norwegian ﬁshing and offshore

vessel propulsion sectors. A/S Wichmann became part of the Finland-based

Wärtsilä Diesel group in 1986 and changed its name from Wärtsilä Wichmann

Diesel in January 1994 to Wärtsilä Propulsion A/S (now Wärtsilä Propulsion

Norway A/S).

two-stroke medium-speed engines 747

748 Other Medium-Speed Engines

The Wichmann 28 engine, which remained in production until 1997, was

released with the following speciﬁcation.

Cylinder block: cast iron monobloc design with integrated crankcase,

scavenging air receiver, water manifold and camshaft box; underslung type of

crankshaft support.

Crankshaft: fully forged and machined in Cr–Mo steel; dimensionally laid

out for 50 per cent power growth potential.

Cylinder liner (Figure 28.26): wear-resistant cast iron alloy; bore cooled

with strong-backed top section; balanced cooling water ﬂow for efﬁcient tem-

perature control; separate cylinder lubrication through four quills.

FigurE 28.25 Wichmann WX28l design

Cylinder head: cast iron, valveless, simple design; bore cooled with strong

backing to secure efﬁcient cooling and low stress level.

Piston (Figure 28.27): oil-cooled composite design with cast iron skirt and

steel crown; ring grooves hardened for low wear rate in heavy fuel operation;

integrated small end bearing in full gudgeon pin length.

Connecting rod: drop forged and fully machined; separate large end bear-

ing unit for easy piston withdrawal and low removal height.

Bearings: three-metal steel-backed type, interchangeable with main and

crank journal.

two-stroke medium-speed engines 749

FigurE 28.26 Bore-cooled cylinder liner and cover of Wichmann WX28 engine;

separate cylinder lubrication is standard

750 Other Medium-Speed Engines

Turbocharging: constant pressure system with auxiliary blower in series;

the moderate speed auxiliary blower boosts the turbocharger effort to ensure an

adequate air supply under all load conditions; the blower is engine driven via

low-pressure hydraulics using the engine lubricating oil and pump.

Fuel injection system: individual high-pressure monobloc pumps with

built-in roller tappet; short high-pressure pipes and temperature-controlled

nozzles for heavy fuel operation.

Auxiliary pumps: engine gear-driven units for lubricating oil, freshwater

and sea water.

FigurE 28.27 Composite piston (high alloy steel crown, cast iron skirt and light alloy

gudgeon pin support) and connecting rod of Wichmann WX28 engine