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

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The camshaft-shifting facility is optional; a simpler design is speciﬁed for

engines whose projected operational proﬁles do not justify adjustable injection

timing. Retroﬁtting of the facility is possible at a later date, however, if service

conditions dictate.

The valve actuating camshaft is provided with different cams for full-

load and part-load engine operation, allowing valve timing to be tailored

optimally to the conditions. As with a reversible engine, the camshaft can

32/40 engine 587

Figure 22.18 L32/40 engine; note the separate camshafts for fuel injection and

valve actuation, respectively, on the left and right sides of this cross-section

588 Man Diesel

be shifted from one ﬁnal position to the other to engage the two different

cam conﬁgurations. Shifting is performed with the engine running. The load

point at which switchover from one cam contour to the other takes place can

be pre-set as required via the control system of the shifting mechanism (see

Chapter 16/Figure 16.3).

Load-dependent adaptation of valve timing promotes low pollutant com-

bustion in both high- and part-load operating modes. Clean combustion with

little emission of soot particles is reportedly secured over the full-load range.

The valve camshaft-shifting facility—like its fuel injection counterpart—is

an optional device: the standard engine version features just one cam contour.

The conversion to an adjustable system for the charge renewal side, however,

can be effected at a later date. Independent camshafts, along with the ability

to ﬁne-tune the timing and fuel pumps, reportedly underwrite almost constant

ﬁring pressures over the 85–100 per cent rating range, optimized performance

down to partial loads and the ability temporarily to handle fuels with poor igni-

tion qualities. Efﬁcient operation on low-grade fuels with viscosities of up to

700 cSt is also fostered. An optimized cam- and camshaft-shifting facility on

the fuel injection side allows IMO requirements on NOx emission levels to be

met; and changeover from open sea to coastal and harbour service (from fuel-

optimized to emissions-optimized/SOx-reduced operating mode) is relatively

simple.

The 32/40 design is based on a very stiff-cast monobloc single-part frame

which is suitable for direct resilient mounting or semi-resilient mounting of the

engine, with individual cylinder jackets as well as through bolts for the main

bearings and lengthened cylinder cover bolts: a principle applied ﬁrst in the

58/64 and subsequently in the 40/54 and 48/60 engines. The concept was mod-

iﬁed for the smaller bore engine (Figure 22.20).

Individual cylinder jackets allow the geometry of the cylinder liner to be

maintained under all load conditions, avoiding disturbing inﬂuences from

neighbouring cylinders. The main bearing through bolts and the cylinder cover

Figure 22.19 an L32/40 engine camshaft arranged for adjustment of fuel injection

timing

bolts extending to the middle frame range place the engine frame under com-

pressive pre-stress, promoting high component reliability despite the high ﬁr-

ing pressures.

The mounting arrangement of the cylinder liner in the jacket and engine

frame is shown (Figure 22.21). Cooling water is supplied to the cylinder

jackets only; none circulates in the engine frame structure, eliminating the

risk of corrosion and water penetration of the lubricating oil. Individual cyl-

inder jackets foster low distortion of the thick-walled laser-hardened liners. A

uniform temperature pattern over the entire liner surface is reportedly secured

through intensive cooling by a special water feed in its upper area.

A separate ﬁre ring (anti-polishing or carbon cutting ring) for the liner

in association with an appropriately stepped piston inhibits the formation of

combustion residue deposits on the liner; liner surface polishing is thereby pre-

vented and low lubricating oil consumption promoted. The ﬁre ring features jet

bore cooling like the previous one-piece liner design. Experience has shown

that removing the ring—necessary for piston withdrawal—can be carried out

quite easily with the simple tools provided.

A four-bolt cylinder cover was designed relatively deep to ensure an excel-

lent ﬂow of power from the nut contact faces of the cover bolts to the seal

between the cylinder head and the liner, as well as a very uniform distribution

of pressure at the circumference of this seat face (Figure 22.22). The charge

air and exhaust lines are arranged on opposite sides of the cover, the cylin-

der head depth allowing the ﬂow ducts to be conﬁgured to enhance the overall

32/40 engine 589

Figure 22.20 L32/40 engine frame

590 Man Diesel

Figure 22.21 L32/40 engine cylinder liner section; note the ame ring mounted on

the top

Figure 22.22 L32/40 cylinder head

efﬁciency of the turbocharging system. A bore-cooled ﬂame deck yields low

temperatures at the combustion chamber side and a high mechanical strength

permitting the high ﬁring pressures to be absorbed with a good safety margin.

Valve cages were omitted. Both exhaust and inlet valves are accommodated

in cooled seat rings, the exhaust valves featuring a rotator with a gas-driven

propeller vane at the valve stem. The cylinder head, rocker arm casing and a

section of the charge air manifold form a unit for maintenance purposes which

can be dismantled as a whole when a piston has to be withdrawn.

The composite piston, similar to 40/54 and 48/60 engine practice, consists

of a nodular cast iron skirt topped by a forged steel crown whose diameter is

reduced in way of the top land to match the ﬁre ring (Figure 22.23). The crown

is cooled by the cocktail shaker method (splash effect) in its inner and outer

areas, the latter also served by bore cooling. The conﬁguration of the cooling

chambers ensures a good shaking effect with the cooling oil supplied via the

connecting rod.

Chromium/ceramic coatings for the top piston ring and chromium-plated

second and third rings are speciﬁed to contribute to ring time-between-over-

hauls of 2 years or more. A nodular cast iron skirt allows a smaller clearance

with the rigid liner to be adopted compared with aluminium, this creating

favourable preconditions for piston ring running behaviour.

Smaller overall dimensions and more restricted space in the crankcase of

the 32/40 engine precluded the use of the connecting rod design used in the

larger members of the MAN medium-speed family which features a joint in

32/40 engine 591

Figure 22.23 L32/40 engine composite piston

592 Man Diesel

the upper part of the shank. The traditional marine head design was there-

fore adopted, with a joint arranged just above the big end bearing box (Figure

22.24). No drawback is suffered with respect to the required headroom for pis-

ton withdrawal since the distance between the four cylinder cover bolts is suf-

ﬁcient for the connecting rod shank to pass without difﬁculty.

Design and material speciﬁcations of other key wearing components target

extended lifetimes and maintenance intervals of at least 2 years for the liners

and exhaust valves. A very low wear rate of the valves is promised from the

Figure 22.24 The L32/40 engine connecting rod is a traditional marine head design

armoured seats and directly water-cooled seat rings. A clean gas-tight seat is

maintained by the exhaust valve rotator.

The designer asserts that constant pressure turbocharging is based on an

MAN uncooled turbocharger which, along with the charge air and exhaust gas

ducting arrangements, promotes a positive charge renewal performance and

hence fuel economy. MAN NR26 or NR34 radial-ﬂow turbochargers were

typically speciﬁed for all cylinder number versions of the engine. Streamlined

transitions from the cylinder heads to the exhaust gas line, as well as the double

diffuser arranged downstream of the compressor, help to keep pressure losses

in the exhaust gas system at a low level; and part of the kinetic energy of the

charge air leaving the compressor at high speed is transformed into pressure

on the air side. Both properties contribute to a substantial increase in overall

efﬁciency.

If an engine’s load proﬁle dictates, warm charge air can be withdrawn

directly after the compressor and supplied to the last section of the exhaust gas

line upstream of the turbine via a bypass. The section is provided with a spe-

cial belt to ensure perfect mixing of the bypassed air with the exhaust gas; a

relief valve can also be ﬁtted in the belt if required.

The charge air cooler can be of the single-stage or two-stage type. The lat-

ter is speciﬁed when the heat contained in the high temperature stage is to be

exploited or if, in the case of frequent part-load operation, the charge air is to

be preheated by the engine cooling water in the lower load range to ensure

favourable combustion conditions.

Ease of inspection and overhaul—a focus of medium-speed engine design-

ers in an era of low manning—is addressed by the four-bolt cylinder cover

with quick-acting seals and clamped and plug-in pipe connections. Only two

different types of hydraulic tools are required to handle all the main screwed

connections on the engine. The marine-type crankpin bearings allow the con-

necting rod to be withdrawn up the bore for piston and ring inspection without

disturbing the bearings. The exhaust gas line features quick-release couplings

that permit swift disconnection from the cylinder head.

MAN Diesel originally anticipated a 550 man-hour annual maintenance

workload for an eight-cylinder L32/40 engine running for 6000 h on heavy fuel.

The basic regular jobs are: replacing the fuel nozzles every 3000 h; overhauling

the exhaust valves (removing the cylinder cover) every 6000 h and overhaul-

ing the piston (including the replacement of rings and honing the liner) every

12 000 h. Service lives and maintenance intervals for the key components of

current 32/40 engines are indicated in Table 22.2.

32/40 engine renements

Continual development of the 32/40 engine has pursued reductions in smoke

emissions throughout the operating range without undermining fuel economy,

easier maintenance and improved ﬂexibility in setting the engine’s parameters

for speciﬁc projects. Many components were modiﬁed in meeting these goals,

32/40 engine 593

594 Man Diesel

such as the cylinder head, ﬁre ring, support ring, rocker arms, valve cones, pis-

tons, camshaft and gas exchange cams. Improved efﬁciency, particularly at loads

less than 50 per cent, was gained from a modiﬁed MAN NR-type turbocharger.

Measures to enhance emission values included a new injection nozzle

design with a smaller sac volume minimizing the amount of fuel sprayed into

the cylinder after the needle is closed. The beneﬁts are reduced dripping and

hence reduced smoke formation. A new cylinder head design incorporates an

improved combustion chamber geometry promoting unhindered atomization

of the fuel jets. The fuel injection pressure was also increased from its base of

1350 bar, and closing of the injection needle improved.

Efforts were also directed at reducing engine cost and weight, and facilitat-

ing maintenance. A redesigned rocker arm casing, for example, is lighter and

allows faster nozzle replacement. A new steel piston was released in 2001. The

lubricating oil and cooling water systems were combined into a single unit—

the frame auxiliary box—to create a compact, vibration-free package calling

for reduced piping.

48/60B engine

The 48/60 engine was originally introduced to series production in 1989 with

a rating of 885 kW/cylinder, which was progressively increased to 1050 kW/

cylinder. Further development of the 48/60 design was stimulated by the

higher propulsion power demands of cruise ships, ferries and large multi-pur-

pose cargo ships, as well as stricter environmental standards. The resulting

B-version was launched in 2002 with a 14 per cent rise in speciﬁc output to

1200 kW/cylinder at 500/514 rev/min from a lighter and more compact design.

The 48/60B programme spans a power band from 7200 kW to 21 600 kW with

six, seven, eight and nine in-line and V12, 14, 16 and 18-cylinder models. The

V-cylinder engines were released ﬁrst, with the in-line models planned to fol-

low in 2003 (Figure 22.25).

Table 22.2 Service lives and maintenance intervals for 32/40 engine

components

Component

Service Life (

1000 h) Maintenance interval (1000 h)

Cylinder liner 80–100 15–20

Piston crown 60–80 30–40

First piston ring 15–20 –

inlet valve cone 30–40 15–20

exhaust valve cone 30–40 15–20

Fuel injection nozzle 6–10 3

Retaining the original 480 mm bore/600 mm stroke dimensions, the design-

ers aimed to: reduce fuel consumption; optimize combustion with a view to

reducing NOx and soot emissions; boost the speciﬁc power output; reduce

engine width; lower engine weight; optimize a range of engine components

including the big end bearing; and reduce the overall number of engine com-

ponents. Easier maintenance, higher reliability and lower manufacturing costs

were also pursued. The goals were achieved by developing new sub-assemblies

and/or improving components.

Combustion beneﬁted from: a simpliﬁed exhaust gas system with only one

manifold and only one turbocharger on the V-cylinder engine; a redesigned

combustion space; a new fuel injection system with high injection intensity;

modiﬁed valve timings; and the new MAN TCA-series turbocharger (see

Chapter 7). The compression ratio was increased from 14.4 to 15.3, a rise

facilitated by a combustion space optimized by avoiding dead volumes, edges

and ribs in the combustion side of the cylinder cover. The fuel injection pres-

sure was increased from 1300 bar to 1600 bar, the higher intensity helping to

reduce visible ﬂue gas emissions, particularly in the part-load range. Higher

NOx emissions were neutralized by slightly delayed injection timing.

A signiﬁcant contribution to fuel economy came from the new MAN

TCA77 turbocharger through an increased ﬂow rate and an efﬁciency rise

of 8–10 per cent (Figure 22.26). The minimum speciﬁc fuel consumption of

173 g/kW h (for the V-engine at 85 per cent maximum continuous rating) is

48/60B engine 595

5 000 10 000 15 000 20 000 25 000

kW*available mid-2003

rev/min

1000

800–900

800

775

720–750

500–600

500–514

400–428

L21/31

L23/30A V23/30A

L27/38

L28/32A V28/32A

L32/40 V32/40

L40/54 V40/50

L48/60B* V48/60B

L58/64

Figure 22.25 Man medium-speed propulsion engine programme before the intro-

duction of common rail (Cr) fuel injection versions; the L40/54 and V40/50 series

have since been dropped

596 Man Diesel

7 g/kW h less than that of the original 48/60 design, while the emission values

on the IMO NOx test cycle are 8 per cent less at 12 g/kW h (Figure 22.27).

Accompanying the higher output, fuel economy and environmental friend-

liness is a lower speciﬁc engine weight (reduced by 16 per cent to 11.9 kg/kW).

The V12-cylinder 48/60B model, for example, develops 14 400 kW and weighs

181 tons, while its predecessor yields 12 600 kW from a weight of 193 tons.

For the V18-cylinder engines, the reduction in weight is approximately 15 tons

and the extra power around 2700 kW. The dimensions were also reduced: the

height remains the same but the B-engine is 800 mm (15 per cent) narrower,

thanks to a new exhaust system concept. A pair of 48/60B engines can thus be

mounted closer together than before, giving an installation width saving of 1 m.

The turbocharger and two charge air coolers were combined to form a single

module on the V-engine.

Internal reﬁnements included an improved piston, with steel crown and

nodular cast iron (or steel, if preferred) skirt. The cylinder head incorporates a

re-shaped combustion chamber, no valve cages, an innovative rocker arm con-

cept and a modiﬁed rocker arm cover. The connecting rod shank features opti-

mized bearing shells, an increased oil clearance, reduced rotating masses and a

strengthened bearing cover design.

Among the elements retained from the original design, with proven reli-

ability in heavy fuel operation, were the stepped piston with chrome-ceramic

ﬁrst ring; exhaust valve with propeller (to ensure a clean and gas-tight seat)

and MAN’s constant pressure charging system with exhaust gas wasting and

bypass control.

Invisible Smoke (IS) variants of the 48/60 became available in early

2001 incorporating measures to achieve low Bosch smoke ﬁgures throughout

the load range. The development was stimulated by requirements imposed

on cruise ships in environmentally sensitive regions such as Alaska. The

25 50 75 100

Load %

48/60

2 × NA 40

1 × TCA 77

Turbocharger comparison

µTC %

48/60 B

Figure 22.26 Comparison of turbocharger eciencies: the Man TCa77 on the

12V48/60B engine and the Man na40 on the original 12V48/60 engine