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

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Loyal to the two-stroke uniﬂow-scavenged principle for medium-speed

trunk piston engines—exploiting air inlet ports in the cylinder liner and exhaust

valves in the head—is the former General Motors’ Electro-Motive Division

(EMD), now the only exponent of the concept still serving the market. The US

designer argues better component wear life, reliability and serviceability over

four-stroke designs serving the same power range. Established in 1922, EMD

was fully incorporated into General Motors in 1941 and sold to a US-based

private equity partnership in 2005. The company claims to be the world’s larg-

est builder of diesel–electric locomotives, a rugged pedigree that has beneﬁted

marine and offshore propulsion and genset engine sectors.

EMD

’s current 710G series covers an output band from 1249 kW to

3730 kW at 720/750/800/900 rev/min from V8-, 12-, 16- and 20-cylinder mod-

els. The 230.2 mm bore  279.4 mm stroke design (Figures 28.28 and 28.29)

was launched in 1986 as a longer stroke derivative of the established 645FB

range. A more advanced turbocharger (yielding a 10 per cent increase in the

overall air–fuel ratio) and larger fuel pump plunger diameter contributed to the

higher power rating and lower fuel consumption. Increasing the stroke raised

the cylinder displacement by 10 per cent from 645 in.

to 710 in.

(hence the

model nomenclature).

A number of improvements beneﬁted the 710GB, GC and GC-T2 models

which offer outputs up to 187 kW/cylinder at 900 rev/min.

l An L-11 liner design for enhanced durability and performance, reduced

scufﬁng and higher wear resistance and better fuel economy.

l A Duracam camshaft, extending valve train component life and lower-

ing valve vibration.

l A Diamond 6-cylinder head with tangent ﬂow ﬁreface, yielding

improved cooling and better valve sealing, eliminating core plugs and

hence water leaks, and providing hardened valve guides for improved

valve and valve guide life.

l Improved unit fuel injector, with a new seal design, enhanced check

valve and stiffer follower spring.

l A four-pass aftercooler achieving improved thermal efﬁciency and

hence fuel economy, and exhaust emissions reduction.

l A new turbocharger incorporating an external clutch for easier

maintenance.

l Lower vibration levels from a new crankshaft and coupling disc-balanc-

ing technique.

With cylinders arranged in a V45° conﬁguration, the two-stroke uniﬂow-

scavenged 710G design features overhead camshafts actuating the four exhaust

valves per cylinder and the unit fuel injectors. A unitized cylinder power

assembly with jacketed liner and minimal bolted and gasketed water connec-

tions simpliﬁes maintenance and strengthens structural integrity.

A higher displacement than the 645FB series called for changes to the

crankcase, a larger diameter crankshaft, a new camshaft and larger diameter

two-stroke medium-speed engines 751

752 Other Medium-Speed Engines

plunger injectors. Longer piston rod assemblies and cylinder liners accommo-

dated the extended stroke, but overall the 710G engine was only fractionally

higher and longer than its predecessor. The 10 per cent increase in overall air–

fuel ratio was secured by the G turbocharger, signiﬁcantly reducing thermal

loading on critical components. A unit fuel injector with a larger (14.29 mm)

plunger diameter than the 645FB engine (12.7 mm) delivered a higher injection

rate and shorter injection period. In addition, a spray tip incorporating seven

oriﬁces yielded better combustion and higher thermal efﬁciency.

A piston crown design incorporating a toroidal-shaped combustion bowl

further fostered higher combustion efﬁciency when combined with the estab-

lished air swirl and well-atomized fuel spray. The larger cylinder displacement

Exhaust valve rocker arm

Exhaust valve bridge

Exhaust valve spring

Exhaust valve

Cylinder head

Piston

Thrust washer

Piston carrier

Piston pin

Crankcase

Cylinder liner

Blade connecting rod

Oil drain and vent

Air box handhole

cover

Piston cooling oil pipe

Piston cooling

oil manifold

Oil pan handhole cover

Oil pan

Oil level gauge

Strainer box

Lifting shackle base

Water discharge manifold

Exhaust elbow

Top deck cover

Camshaft

Injector rocker arm

Overspeed trip shaft

Fuel manifold

Injector adjusting link

Injector control shaft

Injector rack

Cylinder test valve

Fuel injector

Cylinder head crab bolt

Air inlet ports

Air box

Water inlet jumper

Water inlet manifold

Main lube oil manifold

Fork connecting rod

Connecting rod basket

Main bearing “A” frame

Main bearing cap

Crankshaft

Crankshaft counterweight

FigurE 28.28 general Motors EMD 710g two-stroke medium-speed engine with

overhead camshafts and unit injectors

enabled a 10 per cent larger combustion chamber, helping to minimize quench-

ing effects and promote lower emissions.

The capacity of the camshaft/valve train system was more than doubled

over the 645FB engine, allowing a reserve for future growth in injector size.

The camshaft base circle was increased from 2.5 in. to 3.25 in. diameter; the

cam roller follower diameter was increased by 0.375 in.; and the injector and

exhaust rocker arms were strengthened.

A larger and more efﬁcient turbocharger achieved a 15 per cent increase in

air ﬂow for reduced thermal loading. Transferring the over-running clutch from

the turbocharger housing to the engine gear train improved accessibility of the

clutch for inspection and replacement without disassembling the turbocharger.

An interesting feature of the 710G series is the single turbocharger with

externally mounted clutch which enables, in the lower load ranges, the turbo-

charger to be driven by the engine gear train in supercharger mode. Once the

engine load reaches around 65 per cent, the clutch disengages and allows the

exhaust gas to drive the turbocharger turbine. Full load can be accepted swiftly

and smoothly at any engine speed, says EMD, and a 10 per cent overload capa-

bility can be exploited for two out of every 24 h of running.

The electronically controlled engines are said to offer precise control and

facilitate tuning reﬁnements, with full feedback of operating parameters to cus-

tomer control and monitoring systems. Continuing efforts to extend the period

between overhauls has resulted in a current recommendation of 30 000 h for

two-stroke medium-speed engines 753

FigurE 28.29 An EMD 710g two-stroke medium-speed engine in V20-cylinder form

754 Other Medium-Speed Engines

engines with an average duty cycle. Ease of inspection and maintenance is also

claimed, a unit power assembly being exchangeable in 4 h. Emissions perform-

ance of 710G-T2 engines is reﬂected in IMO, US EPA Tier II and EU Stage

IIIA certiﬁcation.

Another medium-speed two-stroke design philosophy was pursued for many

years by Bolnes of The Netherlands until its acquisition by the Wärtsilä group

and the subsequent cessation of engine production. The company produced the

world’s smallest two-stroke crosshead engine, the last manifestation being the

190/600 series. The earlier 150/600 design is illustrated in Figure 28.30.

The 190 mm bore/350 mm stroke design delivered a maximum continu-

ous output of 140 kW/cylinder at 600 rev/min on a mean effective pressure of

14.1 bar. The range embraced 3–10 in-line models (excluding a four-cylinder

version) and V10–20 cylinder models covering an output band from 400 kW to

2800 kW. The crosshead took the form of a lower piston/scavenge pump, with

uniﬂow scavenging arranged via a single valve in the head. Air is drawn in by

the turbocharger, passes through a ﬁrst-stage air cooler to the scavenge pump and

then fed to the cylinder for the compression stroke via a second-stage air cooler.

Bolnes cited the following merits of the design:

l Very low lubricating oil consumption due to the complete separation of

combustion space and crankcase.

FigurE 28.30 Cross-section through Bolnes VDnl 150/600 two-stroke engine

l Unique air control due to the design of the 260 mm bore crosshead scav-

enge pump which was claimed to secure completely smokeless combus-

tion under all load conditions.

l High performance at low speed (for example, 110 per cent torque at 70

per cent rev/min).

l Separate lubrication systems promoting good heavy fuel-burning

operation.

l Simple maintenance.

Bolnes engines had a faithful following in ﬁshing, dredger, coaster and sur-

vey vessel propulsion sectors. The design was also valued as a test engine in

fuel and lubricating oil research laboratories.

gEnErAl ElECtriC

Four-stroke medium-speed trunk piston engines from US designer GE Marine

have found wider appeal in the international marine propulsion and genset

drive market in recent years, the current programme embracing V228 and L/

V250 designs. Both families have secured US EPA Tier II emissions compli-

ance certiﬁcation.

gE V228 Series

A power range from 1044 kW to 3355 kW at 900–1050 rev/min is covered by

V8-, 12- and 16-cylinder versions of the 228.6 mm bore V228 (formerly 7FDM)

design. High-strength nodular cast iron is used to create a rigid monobloc

main frame with a V45° cylinder conﬁguration and all water, fuel and exhaust

piping externally mounted to eliminate the potential for internal contamination.

Large access doors are provided to ease inspection and maintenance, while cas-

ing and ribbed cross-members dampen vibration.

Forged from high-quality steel and nitrided for long life, the one-piece

crankshaft features generous journals and crankpins to minimize surface loads;

large radii ﬁllet-welded counterweights also reduce stress to foster a longer

lifetime. The tri-metal main bearings are oversized to reduce pressure while

providing an oil-wedge formation for low wear, and a sacriﬁcial running-

in overlay promotes rapid conformity in start-up. Superior heat resistance is

sought from a nickel barrier, while a lead–tin overlay serves as a high-toler-

ance contaminant trap for particles and degraded oil.

Four-stud mounting of the unitized power assembly facilitates removal and

replacement of key components. Electron-beam welding of the steel cylinder

liner to the forged cylinder head prevents leakage, and stainless steel valve

seats, Inconel exhaust and chromed inlet valves and valve rotators are speciﬁed

to extend overhaul intervals and component lifetimes. High-strength composite

pistons incorporate forged steel crowns with oil splash cooling. A three-ring

arrangement distributing pressure more evenly and a cutback design contrib-

ute to lower lube oil consumption. The lightweight aluminium skirt offers

high heat resistance. The master and articulated rod share a common journal,

general Electric 755

756 Other Medium-Speed Engines

minimizing the engine length. Forged and hardened cams and journals on the

segmented camshaft foster reduced wear, and oversized end bearings decrease

loads for a longer camshaft life.

Precise fuel management and control are provided by GE’s electronic fuel

injection system, which helps to secure compliance with regulatory emissions

standards. GE group expertise in gas turbine technology was applied in design-

ing the turbocharger, a high compression ratio improving efﬁciency across

the load range. Dual modular pulse piping preserves exhaust pulse energy for

maximizing thermal efﬁciency, the dual pipe made of stainless steel for an

extended life.

A GE PowerStar controller houses the electronic governor unit, speed ref-

erence and load core, protecting the engine against overspeed, overload, low

oil and water pressures and positive crank pressure.

gE l/V250 Series

GE Transportation started developing its Evolution-series locomotive engines

in 1998, targeting a platform that would meet or exceed US EPA Tier II emis-

sions requirements without compromising fuel economy, reliability and dura-

bility. The resulting medium-speed design, well proven in locomotive duty,

was reﬁned in 2006 and launched as the V250 series for marine applications.

Compact and high power-to-weight installations are promised from the

250 mm bore/320 mm stroke design, which is released in V12- and V16-cyl-

inder versions to cover an output range from 2732 kW to 4661 kW at speeds

from 900 rev/min to 1050 rev/min. An electronic fuel injection system based

on an electronically controlled unit pump serving a standard conﬁguration side

entry injector fosters ﬂexible operation in a range of applications as well as

optimized combustion at different engine speeds and loads.

GE’s PowerStar II controller drives the fuel injection system, exploiting

advanced closing point detection to secure better fuel economy and emissions

control. The system features improved diagnostics and display of all engine

parameters and faults without the need for a laptop computer. Engine protec-

tion algorithms can predict problems early to avoid damage.

Turbochargers based on GE’s established design were developed in part-

nership with GE Aviation to boost the V250 engines, all aerodynamic features

being upgraded to satisfy combustion and engine-efﬁciency requirements

(Figure 28.31).

A new articulated piston with three rings meets weight requirements and

exceeds peak ﬁring pressure demands; the skirt and pin boss are supported by

the piston pin and are optimized to provide excellent lubrication and guidance.

A cylinder head with signiﬁcantly increased safety factors is achieved with a

wall supported by the head gasket, a thicker ﬂame deck, optimized placement,

larger exhaust seat ring cooling bores and smooth transition areas to avoid

stress concentrations.

The connecting rod beneﬁted from considerable design changes addressing

reliability. Requirements for oil ﬁlm thickness and pressure were met through

a combination of an increased bearing width and a smaller oil groove in the

bearing shell. The angle between the shank and big end split line maximizes

stiffness while allowing disassembly through the crankcase bore. Advanced

simulation tools developed by GE corporate R&D were used to verify the rod

design’s low-fretting risk.

High levels of reliability and durability were sought from the main bear-

ing, and the block, crankshaft and drive end were repackaged to offer sufﬁ-

cient room for bearing size increases. The same hardening process used on the

established FDM/FDS engines was applied for improved crankshaft fatigue

strength.

Easier maintenance is addressed by a segmented camshaft, sectional

exhaust manifold, unitized power assembly and other features to simplify

component removal and replacement. The cylinder head, water jacket, cylin-

der liner, piston and connecting rod can be withdrawn from the engine as one

assembly by removing a small number of connections and fasteners. Both inlet

and exhaust manifolds are compactly arranged between the V-cylinder banks

to contribute to a narrow overall engine width.

The V250 marine engine shares most components with its locomotive par-

ent, such as connecting rods, power assemblies, cams, pistons, high-pressure

fuel equipment, main frame, exhaust system and crankcase. A number of ele-

ments, however, had to be developed or reﬁned for marine applications: rigid

and isolation mounting systems; dual-impeller cooling water pump; mechanical

general Electric 757

FigurE 28.31 gE Marine’s V250 engine

758 Other Medium-Speed Engines

fuel transfer pumps; deep lube oil sump; class-certiﬁable integrated wire har-

ness; explosion-relief crankcase doors; heat shielding on the exhaust system;

ﬂywheel and air starting system; and seamless steel shielded fuel lines.

GE L/V250 data

Bore, mm 250

Stroke, mm 320

Cylinders

6/8l/12/16V

Compression ratio 16.8

Speed, rev/min 900–1050

power range, kW 1498–4661

An in-line cylinder derivative of the V250 family was introduced in 2008,

the L250 engine offered in six- and eight-cylinder models with respective max-

imum ratings of 1922 kW and 2564 kW and continuous ratings from 1498 kW

to 2330 kW. While based on the V-design, the engine featured a number of

reﬁnements and new components, including a main frame with optimized ribs

and an integrated air manifold, and a crankshaft with wide webs and tangent

ﬁllets. The air and oil ﬁlters, fuel pumps, low- and high-temperature thermo-

static valves and sea water pump were also new to the in-line engine.

In addition, the L250 was designed with engine-mounted ancillaries for

ease of installation and maintenance, and an integrated power take-off system.

The GE-designed and manufactured turbocharger can be ﬂexibly mounted at

either end of the engine, a facility (along with a narrower engine frame) that

eases retroﬁt projects.

759

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

Low-Speed

Four-Stroke Trunk

Piston Engines

The marine diesel propulsion market is dominated by direct-coupled low-speed

two-stroke crosshead engines and geared high-/medium-speed four-stroke trunk

piston engines but some Japanese and East Asian regional operators of coastal/

short sea, ﬁshing and small oceangoing vessels have long appreciated the mer-

its of a ‘hybrid’ alternative: the low-speed four-stroke trunk piston engine.

Low-speed four-stroke engine designs, a traditional Japanese speciality, are

characterized by simple and rugged construction and comparatively long strokes.

Nominal operating speeds, in some cases less than 200 rev/min, allow direct coup-

ling to the propeller. In contrast to the equivalent European/US engine sector,

served by high-/medium-speed machinery with a ﬁxed bore size and variable

number of cylinders, the Japanese designs are invariably based on a six-cylinder in-

line conﬁguration with a range of bore diameters to meet the desired power output.

As an example, Akasaka Diesels’ programme has over the years embraced

a dozen bore sizes from 220 mm to 510 mm, all offered in six-cylinder form

only. Other company ranges have extended up to 580 mm bore with outputs as

high as 735 kW per cylinder. Research and development efforts in the 1970s

addressed higher speciﬁc ratings, with some designers introducing two-stage

turbocharging systems to boost power. Enhanced operating economy, heavy

fuel-burning capability and reliability were pursued in the 1980s.

The drawbacks of the direct-coupled low-speed four-stroke engine concept

compared with medium-speed rivals are the ﬁxed propeller speed (though some

models are arranged for reduction gearing), higher weight and increased space

demands. But these are outweighed, according to proponents, by advantages:

improved reliability and reduced maintenance derived from a fewer number of

components; less noise and vibration; better fuel and lubricating oil consump-

tion ﬁgures; and a greater ability to handle low-grade fuels.

With few exceptions, however, the Japanese designs have made little impact

in Western markets where the geared medium-speed engine maintains its

760 Low-Speed Four-Stroke Trunk Piston Engines

supremacy in the small-ship propulsion arena. This failure to break through

decisively reﬂects the difference in traditional vessel designs and operating

philosophies between the Asian and European/US sectors. And not all the

Japanese enginebuilders have made special export efforts to the latter territo-

ries, acknowledging that a substantial spares and service support network is

required for credibility. The doorstep markets of Indonesia, South Korea, the

Philippines and Taiwan offer the best export potential. The domestic market

represents the baseload for production, the enginebuilders enjoying longstand-

ing relationships with small- to medium-sized yards.

Hanshin Diesel is perhaps the most well-known designer/builder of the

hybrids outside Japan, the Dutch shipping company Spliethoff having stand-

ardized on its engines for deep sea cargo ships in the 1970s/1980s. The EL

design (illustrated in Figure 29.1), evolved by Hanshin since the late 1970s,

typiﬁes the construction and performance characteristics of a contemporary

low-speed four-stroke design.

The EL programme was eventually reduced to 380 mm and 400 mm bore

models but past portfolios also included 300 mm, 320 mm, 350 mm and 440 mm

FigurE 29.1 Hanshin Diesel’s EL design