Man B&W S50ME-B9.3-TII, Project Manual

Page: 146 / 337

MAN B&W 6.04
Page 5 of 12
MAN Diesel
MAN B&W MC//ME/ME-C/ME-B/-GI-TII engines 198 71 45-8.1
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
1
) 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) different from L
1
, the relative
jacket water heat dissipation for point M may be
found, as previously described, by means of Fig.
6.04.02.
At part load operation, the actual jacket water
heat dissipation will be reduced according to the
curves for fixed pitch propeller (FPP) or for con-
stant 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:
1. Engine power equal to specified power M.
For specified MCR (M) the diagram Fig.
6.04.02 is to be used, i.e. giving the percent-
age correction factor ‘Q
jw%
’ and hence for
specified MCR power P
M
:
Q
jw,M
= Q
jw,L1
x
Q
jw%
___
100
x 0.9 (0.88) [1]
2. Engine power lower than specified MCR
power.
For powers lower than the specified MCR
power, the value Q
jw,M
found for point M by
means of the above equation [1] is to be mul-
tiplied by the correction factor k
p
found in Fig.
6.04.04 and hence
Q
jw
= Q
jw,M
x k
p
15%/0% [2]
where
Part load correction factor for jacket
cooling water heat dissipation
Engine load, % of specified MCR (M)
FPP : Fixed pitch propeller
CPP : Controllable pitch propeller, constant speed
k
p
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 10 20 30 40 50 60 70 80 90 100%
FPP
CPP
178 06 643.3
Fig. 6.04.04: Correction factor ‘kp’ for jacket cooling
water heat dissipation at part load, relative to heat dis-
sipation at specified MCR power
FPP : k
p
= 0.742 x
P
S
__
P
M
+ 0.258
CPP : k
p
= 0.822 x
P
S
__
P
M
+ 0.178
Q
jw
= jacket water heat dissipation
Q
jw,L1
= jacket water heat dissipation at nominal
MCR (L
1
)
Q
jw%
= percentage correction factor from
Fig. 6.04.02
Q
jw,M
= jacket water heat dissipation at specified
MCR power (M), found by means of
equation [1]
k
p
= 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.