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مهندسی کشتی - Engine Room Ventilation
یکشنبه 2 خرداد 1389

Engine Room Ventilation

   نوشته شده توسط: علی بنوتی    

 To providing suffi cient air for
combustion purposes in the main engine,
auxiliary diesel engines, fuel fi red boiler,
etc., the engine room ventilation system
should be designed to remove the
radiation and convection heat from the
main engine, auxiliary engines, boilers
and other components.
A suffi cient amount of ventilation air
should be supplied and exhausted
through suitably protected openings

arranged in such a way that these
openings can be used in all weather
conditions. Care should be taken to
ensure that no seawater can be drawn
into the ventilation air intakes.
Furthermore, the ventilation air inlet should
be placed at an appropriate distance
from the exhaust gas funnel in order to
avoid the suction of exhaust gas into
the engine room.
Major dust and dirt particles can foul air
coolers and increase the wear of combustion
chamber components.
Accordingly, the air supplied to the
engine must be cleaned by appropriate
fi lters. The size of particles passing
through the air intake fi lter should not
exceed 5μm.
Air temperature
Measurements show that the ambient
air intake temperature (from deck) at sea
will be within 1 to 3°C of the seawater
temperature, i.e. max. 35°C for 32°C
seawater, and max. 39°C for 36°C seawater.
Measurements also show that, in a normal
ventilation air intake system, where
combustion air is taken directly from
the engine room of a ship, the engine
room temperature is normally 1012°C
higher than the ambient outside air temperature.
This temperature difference
is even higher for winter ambient air
temperatures, see Fig. 5. In general, the
engine room temperature should never
be below 5°C, which is ensured by stopping
one or more of the air ventilation
fans, thus reducing the air supply to
and thereby the venting of the engine
room.
This means that the average air temperature
in a ventilated engine room will
not be lower than 5°C and not higher
than 39 + 12 = 51°C, say 55°C, as
often used as maximum temperature
for design of the engine room components.
Since the air ventilation ducts for a
normal air intake system are placed
near the turbochargers, the air inlet
temperature to the turbochargers will
be lower than the engine room temperature.
Under normal air temperature
conditions, the air inlet temperature to
the turbocharger is only 15°C higher than
the ambient outside air temperature.
This means that the turbocharger suction
air temperature will not be higher
than about 39 + 5 = 44°C (ref. 36°C
S.W.), say 45°C.

For arctic running conditions, a ducted
air intake system directly to the turbocharger
can be an advantage in order
to maintain suffi ciently high temperatures
for the crew in the engine room. With a
ducted air intake, the turbocharger’s
intake air temperature may be assumed
to be approximately equal to the ambient
outside air temperature.
Air supply
In the case of a low speed twostroke
diesel engine installed in a spacious engine
room, the capacity of the ventilation
system should be such that the ventilation
air to the engine room is at least 1.5
times the total air consumption of the
main engine, auxiliary engines, boiler,
etc., all at specifi ed maximum continuous
rating (SMCR).
As a rule of thumb, the minimum engine
room ventilation air amount corre-
sponds to about 1.75 times the air con
sumption of the main engine at SMCR.
Accordingly, 2.0 times the air consumption
of the main engine at SMCR may
be suffi cient.
On the other hand, for a compact engine
room with a small twostroke diesel
engine, the above factor of 1.5 is recommended
to be higher, at least 2.0,
because the radiation and convection
heat losses from the engine are relatively
greater than from large twostroke
engines, and because it may be diffi cult
to achieve an optimum air distribution in
a small engine room.
To obtain a correct supply of air for the
main engine’s combustion process,
about 50% of the ventilation air should
be blown in at the top of the main engine,
near the air intake to the turbochargers,


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