Volvo D11 series, Installation Manual

Page: 172 / 212

Engine room, ventilation and sound proofing
70
Dimension of air intakes
and ducts
When installing is planned, the following basic facts
should be kept in mind:
All combustion engines, irrespective of make or type,
require a certain minimum amount of oxygen (or air)
for the combustion process. Diesel engines, however,
work with a somewhat larger air surplus than carbu-
retor engines.
All engines also emit a certain amount of radiant heat
to the environment, i. e. to the engine room.
The specific radiant heat is less for modern compact
engines than for older and less compact engines.
Modern, compact engines have a great advantage in
this respect.
Channels or ducts for inlet and outlet air
It is advantageous if the inlet and outlet air ducts can
be planned for at the construction stage, where they
can be placed in the hull or superstructure. This will
avoid the need for separate ducts.
For an installation, it is relatively simple to design a
system to provide the engine with enough air for the
combustion, but it is considerably more difficult to
lead the radiant heat away.
The engine itself sucks in air very effectively and,
naturally, will take in air from any direction. Should
the inlet or outlet air ducts be underdimensioned, the
engine will consequently suck air from both ducts
and no ventilation air will go out through the outlet
air ducts. This causes dangerously high engine room
temperatures.
Most of the radiant heat from the engine must be
transported out of the engine room. This is an
abso-
lute requirement to keep the engine room tempera-
ture below the permitted maximum limit.
Fans
To ventilate the engine room more effectively and
thus keep the engine room temperature at a low
level, a
suction fan must normally be installed in the
outlet air duct.
Fans must never be installed in the inlet air ducts, as
this could lead to overpressure in the engine room
with the risk of gas or air leaking out into other parts
of the boat.
For diesel engines, the fan can very well be ther-
mostat controlled and should start at approx. +60°C
(+40°F) engine room temperature, measured at the
engine room.
Engine room temperature
Remembering that the engine’s performance figures
apply at a test temperature of
+25°C (+77°F), it is
important that the inlet air temperature is kept as low
as possible. There is always a loss of power with in-
creased temperatures, and if the engine’s inlet air
is
constantly above +45°C (+113°F), the engine must
be
de-rated.
Engines without after cooler
< 25°C (77°F) > 25°C (77°F) > 45°C (113°F)
Full power Loss of power De-rating
output 3% per 5°C
Engines with after cooler
< 25°C (77°F)
> 25°C (77°F) > 45°C (113°F)
Full power Loss of power De-rating
output –2% per 0°C
The temperature of the inlet air at the air filters must
not be higher than +25 °C (+77 °F) for full power
output. During sea trial the air temperature in the air
filter should not exceed
20 °C (36 °F) above ambient
temperature.
The temperature of the engine itself is rather high in
some places. Certain separate electric components,
such as charging regulators and relays, should there-
fore be fitted on bulkheads or elsewhere where the
temperature is relatively low.
The
maximum temperature for areas where elec-
tric components are fitted is +70 °C (+158 °F). The
starter motor and alternator however, have their given
locations.
Engine room depression
Volvo Penta recommends that the depression in the
engine room does not exceed 0.5 kPa (0.07 psi) at
full speed. A small vacuum in the engine room is not
harmful but will prevent gases from being pushed out
from the engine room into the boat.