10.1.1
Combustion air quality
The air temperature at turbocharger inlet should be kept, as far as possible, between 15...35°C. Temporarily
max. 45°C is allowed.
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.
During normal operating conditions the air temperature at turbocharger inlet should be kept between
15...35°C. Temporarily max. 45°C is allowed. 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 trans-
lating 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 heating of the supply air must be arranged. 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, "rigsaver" (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 equipped
with a small drain pipe from the charge air cooler for condensed water.
The amount of condensed water can be estimated with the diagram below.
Product Guide Wärtsilä 34DF - 3/2012
99
Product Guide
10. Combustion Air System
