Wartsila ?31DF Series Product Manual page 153

Wärtsilä 31DF Product Guide
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:
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.
10.2.1 Charge air shut-off valve (optional)
In installations where it is possible that the combustion air includes combustible gas or vapour
the engines can be equipped with charge air shut-off valve. This is regulated mandatory where
ingestion of flammable gas or fume is possible.
10.2.2 Condensation in charge air coolers
Air humidity may condense in the charge air cooler, especially in tropical conditions. The
engine is equipped with an active dewpoint control to minimize condensation in the charge
air coolers and -receiver, by raising the LT-cooling water temperature based on ambient
humidity and charge air pressure. The engine is also equipped with a small drain pipe from
the charge air cooler and receiver for possible condensed water. Humidity sensor is mounted
in external system.
DBAE248994
q = combustion air volume flow [m³/s]
c
m' = combustion air mass flow [kg/s]
ρ = air density 1.15 kg/m³
10. Combustion Air System
10-3