Sfoc At Reference Conditions; Sfoc Guarantee - Man B&W S50MC-C8-TII Project Manual

MAN B&W
SFOC reference conditions and guarantee

SFOC at reference conditions

The SFOC is given in g/kWh based on
the reference ambient conditions stated in
ISO 3046-1:2002(E) and ISO 15550:2002(E):
1,000 mbar ambient air pressure
25 °C ambient air temperature
25 °C scavenge air coolant temperature
and is related to a fuel oil with a lower calorific
value of 42,700 kJ/kg (~10,200 kcal/kg).
Any discrepancies between g/kWh and g/BHPh
are due to the rounding of numbers for the latter.
For lower calorific values and for ambient condi-
tions that are different from the ISO reference
conditions, the SFOC will be adjusted according
to the conversion factors in the table below.
Condition
Parameter change
Scav. air coolant
per 10 °C rise
temperature
Blower inlet tem-
per 10 °C rise
perature
Blower inlet per 10 mbar
pressure rise
Fuel oil lower rise 1%
calorific value (42,700 kJ/kg)
With for instance 1 °C increase of the scavenge
air coolant temperature, a corresponding 1 °C in-
crease of the scavenge air temperature will occur
and involves an SFOC increase of 0.06% if p
adjusted to the same value.
MAN B&W MC/MC-C TII-engines
With Without
p p
max max
adjusted adjusted
SFOC SFOC
change change
+ 0.60% + 0.41%
+ 0.20% + 0.71%
 0.02%  0.05%
1.00%  1.00%
is
max
MAN Diesel

SFOC guarantee

The SFOC guarantee refers to the above ISO ref-
erence conditions and lower calorific value and is
valid for one running point only. The guaranteed
running point is equal to the powerspeed combi-
nation in the optimising point (O) = 100% SMCR
but, if requested, a running point between 85%
and 100% SMCR can be selected.
The SFOC guarantee is given with a tolerance
of 5%.
Recommended cooling water temperature
during normal operation
In general, it is recommended to operate the main
engine with the lowest possible cooling water
temperature to the air coolers, as this will reduce
the fuel consumption of the engine, i.e. the engine
performance will be improved.
However, shipyards often specify a constant
(maximum) central cooling water temperature
of 36 °C, not only for tropical ambient tempera-
ture conditions, but also for lower ambient tem-
perature conditions. The purpose is probably to
reduce the electric power consumption of the
cooling water pumps and/or to reduce water con-
densation in the air coolers.
Thus, when operating with 36 °C cooling water
instead of for example 10 °C (to the air coolers),
the specific fuel oil consumption will increase by
approx. 2 g/kWh.
2.08
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