Under-cooling of the engine room should be avoided during all conditions (service conditions,
slow steaming and in port). Cold draft in the engine room should also be avoided, especially
in areas of frequent maintenance activities. For very cold conditions a pre-heater in the system
should be considered. Suitable media could be thermal oil or water/glycol to avoid the risk
for freezing. If steam is specified as heating medium for the ship, the pre-heater should be in
a secondary circuit.
10.2
Combustion air system design
Usually, the combustion air is taken from the engine room through a filter on the turbocharger.
This reduces the risk for too low temperatures and contamination of the combustion air. It is
important that the combustion air is free from sea water, dust, fumes, etc.
For the required amount of combustion air, see section Technical data.
The combustion air shall be supplied by separate combustion air fans, with a capacity slightly
higher than the maximum air consumption. The combustion air mass flow stated in technical
data is defined for an ambient air temperature of 25°C. Calculate with an air density
corresponding to 30°C or more when translating the mass flow into volume flow. The expression
below can be used to calculate the volume flow.
where:
combustion air volume flow [m³/s]
q
c
=
combustion air mass flow [kg/s]
m' =
air density 1.15 kg/m³
ρ
=
The fans should preferably have two-speed electric motors (or variable speed) for enhanced
flexibility. In addition to manual control, the fan speed can be controlled by engine load.
In multi-engine installations each main engine should preferably have its own combustion air
fan. Thus the air flow can be adapted to the number of engines in operation.
The combustion air should be delivered through a dedicated duct close to the turbocharger,
directed towards the turbocharger air intake. The outlet of the duct should be equipped with
a flap for controlling the direction and amount of air. Also other combustion air consumers,
for example other engines, gas turbines and boilers shall be served by dedicated combustion
air ducts.
If necessary, the combustion air duct can be connected directly to the turbocharger with a
flexible connection piece. With this arrangement an external filter must be installed in the duct
to protect the turbocharger and prevent fouling of the charge air cooler. The permissible total
pressure drop in the duct is max. 1.5 kPa. The duct should be provided with a step-less
change-over flap to take the air from the engine room or from outside depending on engine
load and air temperature.
For very cold conditions arctic setup is to be used. The combustion air fan is stopped during
start of the engine and the necessary combustion air is drawn from the engine room. After
start either the ventilation air supply, or the combustion air supply, or both in combination
must be able to maintain the minimum required combustion air temperature. The air supply
from the combustion air fan is to be directed away from the engine, when the intake air is cold,
so that the air is allowed to heat up in the engine room.
10-2
DBAD209883
Wärtsilä 46DF Product Guide
10. Combustion Air System
Summary of Contents for 46DF
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