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

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Structurally, the Series 8000 is the ﬁrst MTU engine to feature modular

‘power units’, which can be quickly removed and replaced (Figure 30.19).

Each integrated module comprises:

l A cylinder head, including valve gear, fuel injector, exhaust T-piece and

coolant line segment.

l Cylinder liner.

l Piston and connecting rod.

l Spacer (for channelling coolant to the upper section of the liner and to

the coolant pipes).

Each power unit is attached to the crankcase by four hydraulically tight-

ened stud bolts which have to withstand the high ignition pressures but do not

perform a sealing function. A good seal is effected by securing the cylinder

liner directly to the cylinder head from below with 24 bolts. By separating the

functions of sealing and retention, MTU explains, wider design scope was cre-

ated for optimizing the channels, valve gear and cylinder head cooling.

High design rigidity and endurance strength were sought from the transverse-

ﬂow nodular grey cast iron cylinder head. Its exhaust ports and particularly

the inlet ports are said to yield excellent ﬂow coefﬁcients which establish the

fundamental conditions for fuel economy and low emission levels. Circularity

of the cylinder liner when the engine is running is sustained by the 24 evenly

spaced bolts around its perimeter and by which it is attached to the cylinder

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C-B2 C-B1

Exh.

flap

Exhaust

gas diffuser

C-A2 C-A1

Air flap

Carrier

housing

CAC

B1B2B3B4B5B6B7B8B9

B10

A1A2A3A4A5A6A7A8A9

A10

Air C: Compressor CAC: Charge-air cooler

Exhaust gas T: Turbine MDEC: MTU Diesel Engine Control

MDEC

FigurE 30.18 thermodynamic model of the mtu 20 v 8000 m70 engine and its

sequential turbocharging system

792 High-Speed Engines

head. That circularity underwrites highly efﬁcient sealing by the piston rings

and, combined with a special liner honing process developed by MTU, pro-

motes smooth running and durability. The high sealing efﬁciency of the rings

and liners is also the basis for the ‘exceptionally low blow-by levels’ dem-

onstrated by the Series 8000 engine, the designer reports. This signiﬁcantly

extends the life of the lubricating oil by reducing the amount of dirt escaping

past the rings.

FigurE 30.19 all the cylinder components of the mtu Series 8000 engine are

combined in a functional module termed a ‘power unit’ for ease of withdrawal and

replacement

A robust nodular cast iron crankcase extending well below the centreline

of the crankshaft is described as particularly rigid, the structure offering large

inspection ports to ease checking and maintenance. Integrated in the crank-

case are large lateral charge-air ducts to the cylinders, the central bore for the

camshaft operating the valve gear and a centrally located main oil gallery. The

cylinder liner is cooled only in its upper region and the crankcase is therefore

completely coolant free.

Wide, cross-bolted bearing caps retain the crankshaft with its bolt-on coun-

terweights. Both big end and crankshaft main bearings are of the micro-groove

type, and the latter can be replaced in-situ. Other key elements of the running

gear are fully machined connecting rods with diagonally split big ends, and

composite pistons comprising a forged steel skirt (for the ﬁrst time in an MTU

engine) bolted to a steel crown carrying two compression rings and an oil con-

trol ring. The pistons are cooled by nozzles spraying cooling oil.

Exceptional engine rigidity imparted by the power unit concept, and conse-

quently low-wear characteristics, were expected to help keep lube oil consump-

tion at a constantly low level throughout the period between major overhauls.

Conﬁdence in a promised overhaul interval of up to 24 000 running hours—

depending on the engine’s load proﬁle and power rating—was supported by trials

during which the test engines were subjected to an extremely severe alternating

load sequence as well as continuous operation at full and overload powers.

Minimizing the number and complexity of necessary interfaces, the pumps

for engine coolant, raw water, fuel (HP and LP) and lube oil, as well as the

associated ﬁlters and oil coolers, are mounted on the engine. The electronic

MDEC engine management unit is also arranged here. Locating all these

components together as a ‘service block’ on the free end of the engine fosters

accessibility and simpliﬁes integration of the engine with the ship’s systems.

Installation work is further reduced by an engine mounting concept proven

with the Series 1163 engine in many high-speed ferries, the torsionally resil-

ient, offset-accommodating shaft couplings and a special arrangement of the

air intake and exhaust connections.

Engine starting is effected by an air starter, the sequence incorporating an

initial slow-turn phase which allows engine functioning to be quickly checked

without having to open the decompression valves. This is followed immedi-

ately by the main starting sequence.

Contributing to trouble-free, low-maintenance operation are: an automatic oil

ﬁlter and two oil centrifuges in the secondary oil circuit (an indicator ﬁlter is ﬁtted

in the return line of the automatic ﬁlter for monitoring purposes); fuel ﬁlter car-

tridges with paper elements that can be replaced while the engine is running; and

an engine coolant ﬁlter. The circulation systems are also ﬁtted with running-in

ﬁlters which trap any dirt that has found its way into the engine ﬂuids during the

installation process.

Adopted from previous MTU engines is the TE cooling system. Raw water

never comes into contact with the engine components and the inlet temperature

of the coolant at the engine can be controlled to suit the operating conditions.

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794 High-Speed Engines

At low ambient temperatures and/or low engine loads, for example, the recooler

is bypassed so that the coolant remains at a high temperature and heats up the

combustion air. ‘White smoke’ emissions produced by cold engines can thus be

eliminated. At full power, however, the system provides highly efﬁcient cool-

ing and creates the optimum conditions for combustion, both in terms of fuel

economy and NOx emission levels, according to MTU.

MTU 20V 8000 M70 engine data

Bore

265 mm

Stroke 315 mm

Cylinders v20

output/cylinder 410 kW

power, max 9000 kW

power, continuous 8200 kW

rated speed 1150 rev/min

idle speed 380 rev/min

mean eective pressure 24.6 bar

mean piston speed 12.1 m/s

Weight/power ratio 5.3 kg/kW

Weight 43 tonnes

Specic fuel consumption

190–195 g/kW h

Dimensions (l  W  H) 7.4 m  1.9 m  3.3 m

uprated Series 8000 Design

The V20-cylinder Series 8000 engines have a continuous rating of 8200 kW

in M70 form and a peak power of 9000 kW in M90 form. Customer interest in

higher performance as well as anticipated stricter emission limits stimulated

the development of a 20V 8000 M71 variant of enhanced design with rated

outputs up to 9100 kW, which was unveiled in 2007. A challenge to the design-

ers was to raise the power while improving the engine’s characteristic qualities.

An 11 per cent power increase was achieved with the same bore and stroke

dimensions and rated speed by raising the brake mean effective pressure to

27.3 bar. To avoid increasing the thermal load on the engine, the charge-air

pressure was raised by developing the single-stage turbocharging system. At

rated power the charge-air pressure reaches an absolute value of 4.1 bar. The

high maximum permissible combustion pressure of 230 bar affords sufﬁcient

possibilities for a high compression ratio, thus ensuring that the engine’s start-

ing and idling characteristics with the increased power are as favourable as the

original design.

Classifying the M71 application called for the engine to be run at 10 per cent

overload, thereby achieving an output of 10 000 kW. The resulting 20V 8000

M71 engine was released in both consumption-optimized IMO and emissions-

optimized EPA Tier II variants.

A new combustion process was developed to achieve an improvement in

emissions performance meeting future requirements at all the power output

options without compromising fuel economy. The conﬁguration of the cylinder

crown recess in conjunction with the injection pattern and fuel injector design

was the most important variable in the combustion engineering. Computer-

aided 3D combustion modelling made it possible to reﬁne the design in fewer

steps. Development of the sequential turbocharging system, based on four

MTU ZR265 turbochargers, also contributed to the achievement of low fuel

consumption and minimal smoke levels at low engine speeds.

Continual feedback from 20V 8000 engines in diverse service contributed

to design reﬁnements seeking to maximize reliability and safety, MTU citing

these problems and solutions:

l Wear on the connecting rod axial bearing: coating of the bearing area

reduced the friction and signiﬁcantly reduced the wear.

l Vibrations on the HP fuel pump were reduced by a new screw design

and optimized piping arrangement.

l Leakages in exhaust pipe gaskets between cylinders and turbochargers:

a modiﬁed vee-clamp, improved gasket and E-ring were able to com-

pensate for the higher axial deformation.

l Leakages due to vibration of the coolant water connection pipes to the

turbocharger carrier housing: design changes reduced the vibration level

and eliminated the leakage.

mtu/DDC Designs

An alliance formed by MTU in 1994 with DDC resulted in the creation of two

advanced high-speed designs for joint marketing by the German/US partners,

the Series 2000 and Series 4000 engines, which were launched in 1996. MTU

was responsible for the basic design development of both engines and the vari-

ants for propulsion applications. Both series have proven highly successful in

propulsion and genset drive sectors, beneﬁting from progressive reﬁnements.

Series 2000

The Series 2000 design, with a 130 mm bore/150 mm stroke, is based on the

Mercedes-Benz 500 commercial vehicle engine (Figure 30.20). Models with

V90° 8, 10, 12 and 16 cylinders cover a propulsion band from 500 kW to

1790 kW, while genset drive applications start from 270 kW. The most powerful

version, intended for yachts, has a maximum speed of 2300 rev/min. A single-

stage turbocharging system is speciﬁed as standard but, when special require-

ments regarding power band width and acceleration characteristics are dictated,

Series 2000 engines can beneﬁt from MTU’s sequential turbocharging system.

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796 High-Speed Engines

Fuel injection, adapted from the commercial vehicle engine, was origi-

nally a solenoid valve-controlled pump/fuel line/injector system, each cylinder

having its own separate injection pump. MTU’s third-generation common rail

injection system was introduced from 2004 to create the more compact and

higher performance Series 2000CR engine, which reportedly set new standards

in power density in its class. The V16-cylinder version delivers 1790 kW from

a package weighing 3380 kg.

Marine versions are ﬁtted with MTU’s TE twin-circuit cooling system

(detailed earlier in the section Series 396 Engine) which fosters an optimum

temperature for all operating conditions: intake air can be heated at idling

speeds or at partial throttle and cooled at full throttle.

Series 4000

A number of notable design and performance features were highlighted by MTU

for the 165 mm bore/190 mm stroke Series 4000 engine whose designers focused

on high reliability and ease of maintenance without compromising compact-

ness (Figures 30.21 and 30.22). A propulsion power band from around 840 kW

to 2720 kW at 2100 rev/min is covered by the V90° 8-, 12- and 16-cylinder

versions.

Testing conﬁrmed fuel economy ﬁgures that reportedly set a new standard

for compact engines in the design’s performance class and speed range. A spe-

ciﬁc fuel consumption of 194 g/kW h was considered exceptional for an engine

with a power-to-weight ratio of between 2.7 kg/kW and 3.5 kg/kW.

FigurE 30.20 an mtu v16-cylinder Series 2000Cr engine

A key contribution, along with a high peak ﬁring pressure potential, is

made by the common rail fuel injection system—an innovation in this engine

category—whose development was carried out in conjunction with MTU’s

specialist subsidiary company, L’Orange (see Chapter 8).

The system, which allows inﬁnite adjustment of fuel injection timing, vol-

ume and pressure, embraces an HP pump, a pressure accumulator, injectors and

an electronic control unit. The tasks of pressure generation and fuel proportion-

ing are assigned to different components: pressure generation is the job of the

HP pump while metering of the fuel relative to time is the job of the injectors.

The ﬂexibility of the common rail system across the engine power band

enables it to deliver the same injection pressure (around 1200 bar) at all engine

speeds from full-rated speed down to idling (Figure 30.23). The HP fuel pump

and electronically controlled injectors are fully integrated in the ECS. Peak

pressures with the common rail system are around 20 per cent lower than with

conventional systems, reducing stress on the HP components. The pump is also

simpler and its plunger has no helices. Since the pressure-relief requirement

of conventional systems is eliminated, the mechanical effort is reduced, which

further enhances fuel economy.

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FigurE 30.21 mtu’s upgraded Series 4000 programme includes a v20-cylinder model

delivering up to 4300 kW

798 High-Speed Engines

One fuel rail is provided for the injectors and their respective solenoid

valves on each bank of cylinders. The fuel pressure is generated by the HP

pump driven via a gear train at the end of the crankcase. The electronic system

controls the amount of fuel delivered to the injectors by means of the solenoid

valves, while the injection pressure is optimized according to the engine power

demand. Separate fuel injection pumps for each cylinder are thus eliminated,

and hence the need for a complicated drive system for traditional pumps run-

ning off the camshafts. A reduced load on the camshaft and gearing system is

therefore realized, and the removal of the mounting holes for separate injection

pumps enhances the rigidity of the crankcase.

Maximum strength and optimized rigidity were sought from the crank-

case, with integration of the main lubrication and coolant circulation channels

reducing the number of separate components (Figure 30.24). The crankshaft,

machined all over and with bolted-on counterweights, is designed to withstand

FigurE 30.22 Cross-section of mtu Series 4000 engine

maximum combustion pressures of up to 200 bar. Wear-resistant sleeve bear-

ings contribute to longer service intervals. The cylinder head design, with inte-

grated coolant channels and stiffened base, also addresses a 200 bar pressure.

Provision is made for two inlet and two exhaust valves, and a fuel injector

located in the centre of the head (Figure 30.25).

A piston comprising an aluminium skirt and a bolted-on steel crown is

provided with chrome-ceramic coated rings which, in combination with the

plateau-honed cylinder liner, foster low lubricating oil consumption and an

extended service life. An optimized combustion chamber shape and the bowl of

the composite piston promote low fuel consumption and low emission levels.

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Idle speed

Injection pressure

Optimum injection pressure

with common rail system

Injection pressure with

conventional system

Nominal power

Engine speed

FigurE 30.23 performance of common rail fuel injection system of mtu’s Series

4000 engine

FigurE 30.24 the crankcases of mtu’s Series 2000 (right) and Series 4000 engines (left)

800 High-Speed Engines

Exhaust and turbocharging systems on the Series 4000 engine beneﬁt

from established MTU practice. A triple-walled exhaust system, with an outer

water-cooled aluminium casing, ensures that the surface temperatures do not

exceed permissible levels at any point while also securing gas tightness. Heat

dissipation via the cooling system is reduced. The exhaust pipework is posi-

tioned centrally between the V-cylinder banks. The turbochargers are mounted

in a water-cooled housing. A sequential turbocharging system is exploited

to deliver high torque at low engine speeds. A wide power band at high fuel

economy is also claimed, along with excellent acceleration capabilities without

black smoke emission.

A split-circuit cooling system for the engine and intake air complements

the sequential turbocharging system. It acts as an ‘intelligent’ cooling system

to maintain engine coolant, lubricating oil and intake air at an optimum tem-

perature for all operating conditions. When the engine is idling or running at

low load the temperature of the intake air is raised in order to ensure smooth

and complete combustion without generating white smoke emissions.

On the front end of the engine is an integral service block providing ease

of inspection and maintenance of the sea-water cooler, oil cooler, oil ﬁlter, oil

centrifuge and fuel ﬁlter. The turbochargers and charge-air coolers are located

at the ﬂywheel end.

Access openings in the crankcase are said to be large enough to allow all

running gear servicing to be performed without removing the engine, even

under restricted machinery space conditions. The application-tailored serv-

ice block integrated in the auxiliary power take-off end also simpliﬁes routine

maintenance tasks. A variety of ancillary mounting options enable the engine

to be matched to speciﬁc customer requirements.

FigurE 30.25 the four-valve cylinder heads of mtu’s Series 2000 engine (right) and

Series 4000 engine (left) with central fuel injector