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

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Early indication of necessary maintenance, based on the actual duty pro-

ﬁle, is provided by an electronic engine management system designed to foster

reduced downtime periods and lower servicing costs. A time-between-major-

overhauls of 18 000 h was anticipated by MTU.

uprated Series 4000 Engines

Four enhanced-power Series 4000 models developing 6 per cent to 10 per cent

more output than earlier versions were introduced in 2004 in response to the

demands of workboat and ferry operators. These V12- and V16-cylinder mod-

els beneﬁted from extensive service experience with the original design, which

remained in the programme. Two V16 M61R and M61 models with respective

ratings of 1520 kW and 2000 kW were added to the range for workboat propul-

sion, while V12 and V16 M71 models were uprated to 1850 kW and 2465 kW

respectively for the ferry propulsion market.

Even higher power rises along with improved shock resistance, electromag-

netic compatibility and acoustic signatures were offered for Series 4000 mod-

els launched in 2006 for naval applications. These engines fulﬁl the strictest

military requirements, such as the latest NATO standards, and comply with US

EPA Tier II emission regulations. Output per cylinder was increased by over

26 per cent (from 170 kW to 215 kW) at a rated speed of 2170 rev/min. A V12-

cylinder model can thus deliver 2580 kW and a V16 model 3440 kW. In addi-

tion, the upper power limit of the Series 4000 programme was signiﬁcantly

extended by the introduction, for the ﬁrst time, of a V20-cylinder version offer-

ing outputs up to 4300 kW.

Advances in fuel injection, turbocharging and electronic management sys-

tems (all MTU in-house specialties) contributed to the higher performance and

lower emissions. A new generation common rail fuel injection system exploits

an HP in-line pump and LEAD injectors with individual fuel accumulators to

secure a virtually constant pressure of 1800 bar across the entire engine operat-

ing range. MTU’s latest generation ADEC (Advanced Diesel Engine Control)

electronic management system facilitates triple injection modes (pilot, main

and after-injection) which promote optimum control of the injection process

for low pollution, high-efﬁciency combustion.

Progress in own-design turbocharger development was also tapped. The new

engines are ﬁtted with two turbochargers (V12- and 16-cylinder models) or four

turbochargers (for the V20-cylinder model) arranged in a single-stage sequen-

tial charging system, the turbochargers being switched-in or -out depending on

the engine speed.

niigata

The FX series from Niigata Engineering was completed in 1996 with a 205 mm

bore model to complement the established 165 mm and 260 mm high-speed

engines in a programme developed for fast commercial and military ves-

sel propulsion. The resulting 16FX, 20FX and 26FX models offer maximum

niigata 801

802 High-Speed Engines

continuous outputs from 1000 kW to 7200 kW in commercial service, with

slightly higher ratings available for naval propulsion. The 16FX engine is pro-

duced in in-line V8-, V12- and V16-cylinder versions running at 1950 rev/min,

the V20FX in V12 and V16 versions running at 1650 rev/min, and the V26FX

(Figure 30.26) in V12-, 16- and 18-cylinder versions running at 1300 rev/min.

Compact and highly rigid engines were sought by the Japanese designer

from a monobloc structure fabricated from nodular cast iron, with the exten-

sive use of light alloy elements contributing to a modest overall weight. Engine

width was minimized by adopting a V60° cylinder bank and overall length

reduced by minimizing the distance between cylinders while maintaining the

required bearing width.

A one-piece nodular cast iron piston was speciﬁed for the V16FX engine,

but the higher mechanical and thermal stresses imposed by the cylinder pres-

sure parameters of the V20FX ‘Blue Arrow’ engine inﬂuenced the selection

of a component with a steel crown and aluminium skirt for the larger design.

A bore cooling-type oil gallery structure on the crown reduces the temperature

of the piston at higher mean effective pressures. Higher cylinder pressures also

FigurE 30.26 Cross-section of niigata v26FX engine

foster increased piston blow-by, calling for a high sealing capability and wear

resistance from the piston rings. A chromium-ceramic coated top ring contrib-

utes to these properties, while an anti-polishing ring in the top of the cylinder

liner yields a lower lube oil consumption rate.

An output ceiling of 7200 kW at 1300 rev/min from the Niigata high-speed

engine portfolio is provided by the 18-cylinder version of the 260 mm bore

V26FX design. A monobloc frame of high-tensile strength ductile cast iron and

the use of light alloy parts where appropriate contribute to rigidity and light

weight from a compact envelope.

Niigata 16V20FX engine data

Bore

205 mm

Stroke 220 mm

Cylinders v16

output, mcr 4000 kW

Speed 1650 rev/min

mean piston speed 12.1 m/s

Specic fuel consumption 210 g/kW h

Weight 12 100 kg

Weight/power ratio 3.15 kg/kW

miller System for 32FX

The potential of the 32FX design was demonstrated by a development project

to create a lightweight, high-performance 320 mm bore medium-speed engine

series with a weight/power ratio of 4 kg/kW yielding outputs from around

8000 kW to 13 000 kW. Using the established 32CX engine as a basis, Niigata

reportedly achieved a rating of 769 kW/cylinder at 1030 rev/min from the 32FX

variant.

High output achieved by traditional development routes, Niigata explains,

is accompanied by an increase in mechanical load attributable to the higher

maximum pressure. Coping with the increased loading normally dictates the

speciﬁcation of thicker and hence heavier components. Thermal loads also rise,

resulting in elevated NOx emissions. Reducing the compression ratio to main-

tain P

max

at a normal level, however, lowers efﬁciency and undermines overall

performance and starting capability.

Given these constraints, Niigata opted for the Miller system to keep the

max

and temperatures in the combustion chamber at a normal level, and reduce

NOx emissions, while increasing the brake mean effective pressure. The sys-

tem is designed to reduce charge-air temperature and pressure before compres-

sion (thus lowering the combustion temperature) by subjecting the charge air

in the cylinder to adiabatic expansion.

niigata 803

804 High-Speed Engines

Miller systems come in two variants: an advanced closure timing, which

closes the intake valve before bottom dead centre; and a delayed closure tim-

ing, which closes the intake valve after BDC. Based on an engine performance

simulation analysis, Niigata selected the advanced closure timing route for the

6L32FX engine, adopting a closing timing of 10° before BDC in contrast to

the 35° after BDC applied in the 6L32CX engine (Figure 30.27).

In the Miller system, with the intake valve closed before BDC at the nor-

mal boost pressure, the exhaust temperature rises as the intake air volume is

reduced. This effect makes it necessary to increase the boost pressure to achieve

the targeted output, which lowers the exhaust temperature. Securing a higher

boost pressure than that obtainable with single-stage turbocharging called for

the adoption of a two-stage system in which the LP and HP turbochargers are

connected in series with two intervening air coolers (Figure 30.28).

Applying the Miller system in conjunction with two-stage turbocharg-

ing—LP and HP turbochargers connected in series with two intervening cool-

ers—secured the desired goal of a power rate of 38.2 (3.09 Mpa brake mean

effective pressure  12.4 m/s mean piston speed) at 110 per cent maximum

load—claimed to be the highest of any engine in the circa-320 mm bore class.

In addition, the NOx emission level with the Miller cam was 20 per cent lower

Conventional cam

Miller cam

Expansion

Exhaust

Volume V

Intake

Compression

Combustion

Pressuer P

FigurE 30.27 p–v diagram for miller system (niigata)

than with a conventional cam, equating to 5.8 g/kW h compared with the IMO

limit of 11.2 g/kWh at 1030 rev/min in E3 mode. Fuel consumption with a con-

ventional cam was lower than with the Miller cam at low loads (which could

anyway be improved by using a variable geometry cam) but it rose rapidly at

higher loads and exceeded the Miller cam at a load of around 75 per cent.

Supporting the performance boost, Niigata also investigated new materials

for key components to enhance engine reliability and reduce weight, notably:

a ceramic-sprayed bimetal cylinder liner; tri-alloy intake valves and pushrods;

and sodium-sealed and Waspaloy Inconel 718 exhaust valves. The ceramic-

sprayed coating was applied to the sliding part of the liner surface to improve

resistance to abrasion and seizure.

niigata 805

Intake

Exhaust

Low-stage

air cooler

Low-stage

turbocharger

Exhaust

bypass valve

High-stage

turbocharger

6L32FX test

engine

ExhaustIntake

High-stage

air cooler

Intake

bypass valve

FigurE 30.28 two-stage turbocharging system (niigata)

806 High-Speed Engines

paXman (man DiESEl)

Over 60 years experience in high-speed diesel design was exploited by Paxman

Diesels in creating the VP185 engine, launched in 1993 to join the UK-based

company’s established 160 mm bore Vega and 197 mm bore Valenta series

(Figure 30.29), which respectively offered speciﬁc outputs of 107 kW/cylinder

and 206 kW/cylinder. The new 185 mm bore design was introduced initially in

V12-cylinder form with outputs up to 2610 kW and complemented in 1998 by

a V18-cylinder version extending the power limit of the series to 4000 kW at

a maximum speed of 1950 rev/min. Paxman became a member of Germany’s

MAN B&W Diesel group (now MAN Diesel) in mid-2000, since when its pro-

gramme has ceased production.

In designing the 12VP185 engine (Figure 30.30), Paxman sought improve-

ments in compactness and lightness over its earlier models, goals dictating a

smaller swept volume, slightly higher ratings and a review of piston speeds.

The ﬁrst parameter to be ﬁxed was the stroke which was set at 196 mm; this,

linked to a crankshaft speed of 1800 rev/min, gave a mean piston speed of

11.8 m/s for continuous duty. An improved speed platform for marine appli-

cations was derived, the edge of which is bounded by a maximum speed of

1950 rev/min with a mean piston speed of 12.8 m/s.

The cylinder bore was ﬁxed at 185 mm which, coupled with a design

maximum mean effective pressure of 25.3 bar, delivered a maximum power of

FigurE 30.29 paxman v16-cylinder valenta engine

2610 kW at 1950 rev/min from the V12-cylinder conﬁguration: a rating prima-

rily targeting high-speed military and commercial marine markets, as well as

mega-yacht propulsion. An unrestricted rating of 2180 kW at 1800 rev/min was

quoted (at 45°C air and 32°C sea water conditions) for continuous marine duties

(for example, fast ferry propulsion) where the engine’s high torque capability

over a broad speed range was considered especially attractive for hydrofoil

service.

The

18-cylinder VP185 model offers a maximum output of 4000 kW at

1950 rev/min, a 3300 kW continuous power rating for fast ferries and patrol

craft, and 3000 kW at 1770 rev/min for unrestricted marine duty.

paxman (man Diesel) 807

FigurE 30.30 paxman 12vp185 engine; note the compact turbocharging arrange-

ment along the top

808 High-Speed Engines

A smaller bore and stroke than the Valenta design, combined with a switch

from a 60° cylinder bank angle to a 90° conﬁguration, achieved a layout which

was short and having a width under 1.5 m while providing an adequate plat-

form for the charge-air system mounted above the engine. The 90° bank angle

itself also lowered the proﬁle of the charge-air system to foster space efﬁciency

(Figure 30.31).

FigurE 30.31 Cross-section of paxman vp185 engine

A higher mean effective pressure normally leads to a lower compres-

sion ratio which in turn promotes poor starting characteristics, reduced ther-

mal efﬁciency and possible exposure to ignition delay damage. Some of these

problems can be addressed by the use of inter-cylinder charge-air transfer

arrangements but Paxman decided to adopt a compression ratio in excess of

13:1. The resulting VP185 engine was claimed to be simple and easy to start

under cold conditions, with good thermal efﬁciency and the potential to satisfy

low NOx emission limits. The combination of high boost levels and compres-

sion ratios demands a robust construction but Paxman sought to avoid a heavy

and cumbersome engine by securing robustness within a small and hence a stiff

envelope.

The reciprocating assembly of the engine was designed for high strength

and rigidity in handling a high maximum cylinder pressure and securing high

reliability with a long lifetime. The backbone is a compact crankcase cast in

high-strength spheroidal graphite iron to provide a stiff and solid support for

the underslung crankshaft. Crankcase doors along each side of the engine

give access to the connecting rod large ends for in-situ servicing and piston

removal.

The crankshaft is a machined steel forging, fully nitrided to yield strength

and durability. It is secured by main bearing caps which are drawn internally

against the deep-ﬁtting side faces of the crankcase by high-tensile set screws

and hydraulically tensioned main bearing studs. Such a conﬁguration, the

designer asserted, delivered good strength and stiffness characteristics to the

bottom end of the crankcase and provided solid support for the crankshaft.

A generous overlap between the crankpin and main bearing journals added

to stiffness and strength. Both main and big end bearings are of steel-backed

aluminium–tin type with thrust washers controlling axial location. The crank-

shaft is provided with a viscous torsional damper totally enclosed within

the gearcase.

Connecting rods of side-by-side design are forged in high-tensile steel,

fully machined and ferritic nitro-carburized. The large end is obliquely split

to allow the rod to pass through the cylinder liner and the joint faces are ser-

rated. The one-piece nodular cast iron pistons incorporate a large oil-cooling

galley above the ring belt, oil being supplied by accurately aligned standing

jets mounted in the crankcase. The pistons run in wet cylinder liners made of

centrifugally cast high-grade iron.

The cast-iron cylinder heads are designed to withstand the high ﬁring pres-

sures with an internal conﬁguration ensuring maximum ﬂame face stiffness and

high cooling efﬁciency. They incorporate two exhaust valves, two inlet valves

and a centrally mounted unit fuel injector (combined pump and injector) which

is ﬁxed with a single screw. The valves and injectors are actuated through a

pushrod arrangement from a single large diameter camshaft mounted cen-

trally in the vee of the engine. The stiffness of the actuating system reportedly

achieves valve control similar to that of an overhead camshaft, while the spe-

cially designed unit injectors yield very high rates of fuel injection with clean

paxman (man Diesel) 809

810 High-Speed Engines

cut-off, contributing to low NOx generation and good fuel efﬁciency. The fuel

cam design was based on an optimized width for long life and a large base cir-

cle, coupled with high rates of lift to secure the key injection characteristics.

A maximum injection pressure of 1400 bar promotes good combustion

characteristics with low emissions and fuel consumption. The unit injector

is rack controlled, the rack itself being controlled by a linkage operated from

twin shafts in the centre vee of the engine. The shafts in turn are coupled to

the governor via an overspeed protection assembly which closes the fuel racks

independently of the governor in the event of the engine overspeeding.

A safety merit of the unit injector (which combines fuel pump and injec-

tor in one unit) is that it eliminated the need for HP fuel pipes. The LP fuel oil

is delivered to the injectors by a gear-driven lift pump mounted on the main

gearcase. The fuel is fed to a sub-assembly—comprising cooler, ﬁlter (duplex

optional), reservoir and solenoid-operated shut-off valve—mounted high at the

free end of the engine for convenient access.

A single camshaft reﬂects the policy adopted by the designers of minimizing

the number of components. This, allied to the 90° cylinder bank angle, allowed

the camshaft gear to mesh directly with the crankshaft gear and so eliminate the

need for idlers in a critical area and reduce the component count even further.

Charge air is delivered by a ‘valve-less’ two-stage turbocharging system

designed for simplicity and ease of maintenance. Preliminary explorations of

single-stage HP ratio turbocharging showed poor low-speed torque characteris-

tics due to surge limitation, along with poor acceleration and load acceptance.

Sequential turbocharging was considered but the necessary valve gear and asso-

ciated control system conﬂicted with the primary aim of keeping the engine

as simple as possible, Paxman explains. Another factor was that few turbo-

charger designs in the smaller size range were capable of meeting the pressure

ratio required.

A two-stage turbocharging arrangement with intercooling and aftercooling

was ﬁnally adopted for the VP185 engine, based on six Schwitzer automotive-

type turbochargers with broad and stable operating characteristics: four turbo-

chargers provide low-pressure charge air and two provide the HP air.

Inlet air compressed in the LP turbochargers is fed through a raw water inter-

cooler to the compressors of the HP turbochargers; HP air is then passed through

the jacket water aftercooler into the air manifolds on either side of the engine.

The HP stage exploits a pulsed exhaust system to give good low-end per-

formance without recourse to complex valve systems associated with sequen-

tially turbocharged conﬁgurations. The turbocharging system’s high air/fuel

ratios, coupled with HP/high rate fuel injection, address low NOx emission

requirements. A highly responsive performance with good engine torque char-

acteristics is reported throughout the speed range (Figure 30.32).

All six turbochargers are mounted in the walls of a water-cooled gas-tight

casing, the turbine sides arranged on the inside and the compressors on the out-

side. The rotating assembly and compressor casing of each turbocharger form

a cartridge which can be replaced quickly without the need for lifting gear