10. Combustion Air System
10.1 Engine room ventilation
To maintain acceptable operating conditions for the engines and to ensure trouble free operation of all
equipment, attention to shall be paid to the engine room ventilation and the supply of combustion air.
The air intakes to the engine room must be located and designed so that water spray, rain water, dust and
exhaust gases cannot enter the ventilation ducts and the engine room. For the minimum requirements
concerning the engine room ventilation and more details, see the Dual Fuel Safety Concept and applicable
standards.
The amount of air required for ventilation is calculated from the total heat emission
Φ
to evacuate. To de-
termine
Φ
, all heat sources shall be considered, e.g.:
•
Main and auxiliary diesel engines
•
Exhaust gas piping
•
Generators
•
Electric appliances and lighting
•
Boilers
•
Steam and condensate piping
•
Tanks
It is recommended to consider an outside air temperature of no less than 35°C and a temperature rise of
11°C for the ventilation air.
The amount of air required for ventilation (note also that the earlier mentioned demand on 30 air ex-
changes/hour has to be fulfilled) is then calculated using the formula:
where:
air flow [m³/s]
qv =
total heat emission to be evacuated [kW]
Φ
=
air density 1.13 kg/m³
ρ
=
specific heat capacity of the ventilation air 1.01 kJ/kgK
c =
temperature rise in the engine room [°C]
Δ
T =
The heat emitted by the engine is listed in chapter Technical data.
The engine room ventilation air has to be provided by separate ventilation fans. These fans should preferably
have two-speed electric motors (or variable speed). The ventilation can then be reduced according to outside
air temperature and heat generation in the engine room, for example during overhaul of the main engine
when it is not preheated (and therefore not heating the room).
The ventilation air is to be equally distributed in the engine room considering air flows from points of delivery
towards the exits. This is usually done so that the funnel serves as exit for most of the air. To avoid stagnant
air, extractors can be used.
It is good practice to provide areas with significant heat sources, such as separator rooms with their own
air supply and extractors.
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.
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Product Guide Wärtsilä 34DF - 3/2012
Product Guide
10. Combustion Air System
