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MAN B&W 6.04
Freshwater Generator
If a freshwater generator <strong>is</strong> installed and <strong>is</strong> util<strong>is</strong>ing
the heat in the jacket water cooling system,
it should be noted that the actual <strong>available</strong> heat
in the jacket cooling water system <strong>is</strong> lower than
indicated by the heat d<strong>is</strong>sipation figures valid for
nominal MCR (L 1 ) given in the L<strong>is</strong>t of Capacities.
<strong>Th<strong>is</strong></strong> <strong>is</strong> 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 <strong>is</strong> operating under conditions
such as, e.g. overload. Normally, th<strong>is</strong> margin <strong>is</strong>
10% at nominal MCR.
Calculation Method
For a derated diesel engine, i.e. an engine having
a specified MCR (M) and/or a matching point (O)
different from L 1 , the relative jacket water heat d<strong>is</strong>sipation
for point M and O may be found, as previously
described, by means of Fig. 6.04.02.
Part load correction factor for jacket
cooling water heat d<strong>is</strong>sipation
kp 1.0
0.9
0.8
0.7
0.6
0.
0.4
0.3
0.2
0.1
0
FPP
CPP
0 10 20 30 40 0 60 70 80 90 100%
Engine load, % of matching power (O)
FPP : Fixed pitch propeller
FPP : k = 0.742 x p P __ S
PO CPP : k = 0.822 x p P __ S
PO CPP : Controllable pitch propeller, constant speed
+ 0.2 8
+ 0.178
178 06 64�3.2
Fig. 6.04.04: Correction factor ‘kp’ for jacket cooling
water heat d<strong>is</strong>sipation at part load, relative to heat d<strong>is</strong>sipation
at matching power
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At part load operation, lower than matching power,
the actual jacket water heat d<strong>is</strong>sipation 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
<strong>available</strong> for a derated diesel engine may then be
found as follows:
1. Engine power between matching and specified
power.
For powers between specified MCR (M) and
matching power (O), the diagram Fig. 6.04.02
<strong>is</strong> to be used, i.e. giving the percentage correction
factor ‘Q jw% ’ and hence for matching
power P O :
Q = Q x jw,O jw,L1 Q ___ jw%
100
x 0.9 (0.88) [1]
2. Engine power lower than matching power.
For powers lower than the matching power,
the value Q jw,O found for point O by means of
the above equation [1] <strong>is</strong> to be multiplied by
the correction factor k p found in Fig. 6.04.04
and hence
Q jw = Q jw,O x k p �1 %/0% [2]
where
Q = jacket water heat d<strong>is</strong>sipation
jw
Q = jacket water heat d<strong>is</strong>sipation at nominal
jw,L1
MCR (L ) 1
Q = percentage correction factor from
jw%
Fig. 6.04.02
Q = jacket water heat d<strong>is</strong>sipation at matching
jw,O
power (O), found by means of equation [1]
MAN B&W ME/ME�C/ME�GI engines 198 43 01�2.2
MAN Diesel
k p
= part load correction factor from Fig. 6.04.04
0.9 = factor for safety margin of cooler, tropical
ambient conditions
The heat d<strong>is</strong>sipation <strong>is</strong> 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 temperatures
or lower. The heat d<strong>is</strong>sipation tolerance from
�1 % to 0% stated above <strong>is</strong> based on experience.