Woodyard D. (ed.) Pounders Marine diesel engines and Gas Turbines
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493
C h a p t e r | f i f t e e n
MAN Low-Speed
Engines
Low-speed marine diesel engines built by Maschinenfabrik Augsburg-
Nurnberg (MAN) were of single-acting two-stroke crosshead designs exploit-
ing loop scavenging. The programme was phased out after the German
company’s acquisition of Danish-based rival Burmeister & Wain (B&W) in
1980 and replaced by the MAN B&W MC series (Chapter 10). MAN’s KSZ
design (Figure 15.1) was introduced in the mid-1960s and followed progres-
sively by the KSZ-A, KSZ-B and KSZ-C types, each embodying refinements
to promote greater reliability and fuel economy. The KSZ-C and KSZ-CL
types represented the last examples of MAN loop-scavenged engine design
technology.
MAN engines had some notable features to promote simplicity of design,
ease of maintenance and low specific fuel consumption, not least the pioneer-
ing application—albeit only on the test bed—of electronic fuel injection to a
marine diesel engine.
MAN two-stroke engines employ constant pressure turbocharging (Figure
15.2) and are scavenged according to the loop scavenging system. The cylin-
der exhaust ports are located above the scavenging ports on the same side of
the liner, occupying approximately one-half of its circumference. The scaveng-
ing air is admitted through the scavenge ports, passing across the piston crown
and ascending along the opposite wall to the cylinder cover, where its flow is
reversed. The air then descends along the wall in which the ports are located,
expelling the exhaust gases into the exhaust manifold. The piston closes the
scavenging ports and then, on its further upward travel, also closes the exhaust
ports and compresses the charge of pure air in the cylinder.
When the KSZ series was introduced, it followed the traditional two-stroke
engine construction technique of cylinder blocks mounted on ‘A’ frames, which
sat on a cast bedplate, the three structural items held by a series of long tie-
rods. This method of erection was abandoned when MAN introduced the
KSZ-B type with the so-called box-type construction, which was retained for
the later KSZ-C and KEZ-B types. (This latter type was identical to the KSZ
494 MAN Low-Speed Engines
models, but featured electronic fuel injection—described from p. 504—instead
of the traditional mechanical fuel pump arrangement; it never entered produc-
tion, however.) In general design details, the KSZ-B and KSZ-C engines are
basically similar, but for the longer piston strokes of the latter series and other
refinements to achieve a considerable reduction in the specific fuel consump-
tion (Figures 15.3–15.5).
FigurE 15.1 Cross-section of KSZ 90/160 engine with older constant pressure paral-
lel injector supercharging system
DESigN pArtiCuLArS
MAN’s KSZ-B/BL and KSZ-C/CL ranges are of identical design, but with the
later model giving a 10 per cent reduction in the speed at the same power rat-
ing, this being achieved by raising the cylinder mean effective pressure. Minor
design changes were made only where the increase in piston stroke made them
necessary.
Design particulars 495
FigurE 15.2 Constant pressure turbocharging of KSZ-B and KSZ C/CL engines
FigurE 15.3 K8SZ 90/160 B/BL engine on the test bed
496 MAN Low-Speed Engines
Engine Structure
The significant constructional characteristic of the KSZ-B and KSZ-C type
engines is the box-shaped longitudinal girders comprising a deep-section single-
walled bedplate—a frame which is either in one piece or split (depending on
the number of cylinders) on cast, high cylinder jackets. In the largest (900-mm
bore) engine, the frame box is split horizontally (Figure 15.6) while in the
smaller engines of 700-mm and 520-mm bore, the frame is a single-piece steel
fabrication. For engines of seven to twelve cylinders the frames of engines
of the two largest bore sizes are vertically split, while smaller engines with
the camshaft gear drive located at the coupling end have no vertical split in
the frame structure. The cylinder jackets are cast in either two or three units
(Figure 15.7).
3200
Cylinder output
2800
2700
2400
2000
1600
1200
0
80 90 100 110 120 122
Speed (rev/min)
KSZ-B
KSZ-BL
Specific
fuel consumption
Firing pressure (bar)
Theoretical
propeller
characteristic
110
214
211
105
100
208
110
105
100
95
205
90
85
214
202
80
211
85
90
95
205
208
FigurE 15.4 performance curves for the K8SZ 90/160 engine
Design particulars 497
FigurE 15.5 Cutaway drawing of K8SZ 90/160 B/BL engine
FigurE 15.6 Construction method
498 MAN Low-Speed Engines
The box frame design allows a high degree of stiffness and contributes to a
gradual reduction in the deformations induced by the ship’s double bottom and
transmitted to the bedplate. These stiffness characteristics reduce the risk of
uncontrolled transverse loading on the crankshaft main bearings, and cylinder
liners at their clamping points are only slightly deformed by the outside struc-
ture. This contributes to keeping liner wear rates as low as possible.
running gear
The crankshafts of the larger engines are of built-up type with forged steel
crank throws pressed on to forged steel journals. Crankshafts for the small-
est (520-mm bore) engine have one-piece forged shafts of up to the highest
number of cylinders. The main bearings are of the so-called block bearing type
comprising three-metal shells, which can be replaced without subsequent fit-
ting. The crankpin bearing is also of three-metal type with a comparatively
thick white-metal layer.
The crosshead (Figure 15.8) features hydrostatic lubrication, a principle
that ensures an adequate oil film between the crosshead pin and the single
white-metal-lined bearing shell. The high oil pressure required for this purpose
is generated by double plunger high-pressure lubricators, which are directly
driven by linkages from the connecting rod to force oil under pressure into the
lower crosshead bearing shell.
Camshaft Drive
The box-shape construction of the frame forms a deformation-resistant casing
to accommodate the gear train of the camshaft drive. All engines have a gear
train with only one intermediate wheel. The wear pattern and backlash on the
intermediate wheel can be adjusted by draw-in and thrust bolts, which act upon
the frame at the bearing points of the intermediate wheel axle. The crankshaft
gear wheel is clamped directly to the shaft as a two-piece component.
Combustion Chamber Components
In order to control thermal stresses, thin-wall intensively cooled components
are used for the combustion chamber parts (Figure 15.9). The piston crown is
FigurE 15.7 Bedplate design
Design particulars 499
FigurE 15.8 Crosshead design
FigurE 15.9 Cross-section of combustion chamber
500 MAN Low-Speed Engines
of high-grade heat-resistant steel and incorporates the MAN jet-cooled honey-
comb system. An internal insert in the piston crown serves only to direct the
cooling water flow and, in particular, to generate water jets, which enter at the
edge of each honeycomb element, thereby intensifying the conventional ‘cock-
tail shaker’ effect (Figures 15.10 and 11).
The structural arrangement of the KSZ-C piston has the steel crown, insert,
piston rod and cast iron skirt all held together by a single row of waisted studs.
The freshwater for piston cooling (Figure 15.12) is fed into the piston rod with
return through the co-axial bores to telescopic pipes.
The cylinder cover comprises a stiff grey cast iron cap fitted with a thin-
walled forged heat-resistant steel bottom. The pre-tension between the cap and
the bottom, which is necessary to prevent micromotion, is achieved by an inner
row of studs. An outer row of larger studs secures the cover to the cylinder
block.
The cylinder liners are short single-piece units with intensive cooling of the
upper part achieved by bore cooling of the liner flange (Figure 15.14). The ver-
tical lands between the exhaust ports are also water cooled; the combined tech-
niques ensure that sufficient heat is removed from the piston rings, the upper
portion of the cylinder liner and the port lands to obtain a stable lubricating oil
film, to reduce the wear rate and not to interfere with ring performance in way
of the porting.
turbocharging
An important feature of MAN engines is the use of the space beneath some
of the pistons to supply charge air to assist the turbocharger at low loads and
Pump
Oil
outlet
Oil outlet to
crosshead
Connecting
rod
FigurE 15.10 Crosshead oil pump
Design particulars 501
FigurE 15.11 piston and piston rod
Piston
rod
Telescopic
pipes
Crosshead
Connecting
rod
Columns
FigurE 15.12 piston cooling arrangement
502 MAN Low-Speed Engines
Piston rod
Scraper
ring
Scraper
rings
Drain
holes
Drain from
scraper rings
Drain from top
scraper ring
Packing
rings
Garter
springs
Crankcase
Underpiston
scavenge space
Gas-tight
rings
FigurE 15.13 piston rod scraper box
FigurE 15.14 Cylinder liner and jacket