Man B&W L35MC6-TII Project Manual Download

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MAN B&W

6.04

Page 5 of 12

MAN Diesel

MAN B&W S50MC/MC-C-TII, S46MC-C-TII, S42MC-TII,

S40MC-C-TII, S35MC/MC-C-TII, L35MC-TII, S26MC-TII

198 71 42-2.0

Freshwater Generator

If a freshwater generator is installed and is utilis-
ing the heat in the jacket water cooling system,
it should be noted that the actual available heat
in the jacket cooling water system is

lower than

indicated by the heat dissipation figures valid for
nominal MCR (L

) given in the List of Capacities.

This is because the latter figures are used for
dimensioning the jacket water cooler and hence
incorporate a safety margin which can be needed
when the engine is operating under conditions
such as, e.g. overload. Normally, this margin is
10% at nominal MCR.

Calculation Method

For a derated diesel engine, i.e. an engine having
a specified MCR (M) equal to optimising point (O)
different from L

, the relative jacket water heat dis-

sipation for point M and O may be found, as previ-
ously described, by means of Fig. 6.04.02.

At part load operation, lower than optimising
power, the actual jacket water heat dissipation will
be reduced according to the curves for fixed pitch
propeller (FPP) or for constant speed, controllable
pitch propeller (CPP), respectively, in Fig. 6.04.04.

With reference to the above, the heat actually
available for a derated diesel engine may then be
found as follows:

Engine power equal to specified MCR
power M (equal to optimising point O).

For specified MCR (M) = optimising power
(O), the diagram Fig. 6.04.02 is to be used,
i.e. giving the percentage correction factor
‘Q

jw%

’ and hence for optimising power P

jw,O

= Q

jw,L1

jw%

___

100

x 0.9 (0.88)

[1]

Engine power lower than optimising power.

For powers lower than the optimising power,
the value Q

jw,O

found for point O by means of

the above equation [1] is to be multiplied by
the correction factor k

found in Fig. 6.04.04

and hence

= Q

jw,O

x k

15%/0%

[2]

where

Part load correction factor for jacket
cooling water heat dissipation

Engine load, % of optimising power (O)

FPP : Fixed pitch propeller

CPP : Controllable pitch propeller, constant speed

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

100%

FPP

CPP

178 59 45-7.0

Fig. 6.04.04: Correction factor ‘kp’ for jacket cooling
water heat dissipation at part load, relative to heat dis-
sipation at optimising power

FPP : k

= 0.742 x

+ 0.258

CPP : k

= 0.822 x

+ 0.178

= jacket water heat dissipation

jw,L1

= jacket water heat dissipation at nominal

MCR (L

)

jw%

= percentage correction factor from

Fig. 6.04.02

jw,O

= jacket water heat dissipation at optimising

power (O), found by means of equation [1]

= part load correction factor from Fig. 6.04.04

0.9 = factor for safety margin of cooler, tropical

ambient conditions

The heat dissipation is assumed to be more or less
independent of the ambient temperature conditions,
yet the safety margin/ambient condition factor of
about 0.88 instead of 0.90 will be more accurate for
ambient conditions corresponding to ISO tempera-
tures or lower. The heat dissipation tolerance from
15% to 0% stated above is based on experience.