Engine Room Ventilation - Perkins 1106 Series Installation Manual

N40475 Chapter 5

Engine room ventilation

The engine room must be ventilated for two reasons:
1. To supply the engine with air for combustion.
2. To provide a flow of air through the engine room to
prevent an excessive temperature build up, which may
cause components such as the alternator to overheat.
Note: The air temperature entering the engine should not
exceed 52 C (126 F). The air temperature entering the
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engine room should not exceed 60 C (140 F).
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In most applications in temperate climates, the engine
will draw air from the engine room. If this is the case then,
as a rough guide, it can be taken that every horsepower
produced by the engines requires, as a minimum, 161 sq.
mm, (6.34 sq.ins.) of vent area. If the boat is likely to be
used in hot climates, and if engine room ventilation fans are
fitted, then a vent area of 322.58 sq.mm (12.7 sq.ins.) per
horsepower should be provided. Wherever possible a flow
of air through the engine room should be encouraged by
Figure 1
using forward facing intake vents to take advantage of ram
airflow, together with other vents to allow hot air to escape.
Noise absorbing chambers (1) with deflector baffles and
noise absorbent material (2) are positioned to direct
ventilation air flow over a large surface area of absorbent
material.
Cross sectional area of air flow path must not be too small.
With an effective ventilation system the engine air intake
temperature will be no more than 10 C higher than the
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outside air temperature.
Note: For the minimum cross section of air duct
per engine see 'Reference data' at the back of this
manual.
The air entry vents should be situated where spray is not
likely to enter them and some form of water trap is desirable
(see figure 1). Preferably the air ducts should reach the
engine compartment at the sides of the hull so that water
will fall into the bilge.
When the engines are shut down after a run at high output
in high ambient temperature conditions, it will be found
that very high air temperatures will build up in the engine
compartment. In boats with open cockpits this is usually of
no real consequence but if the engines are mounted below
a wheel house, then unpleasantly warm conditions may
result. In these circumstances engine room ventilation fans
are beneficial, preferably arranged to exhaust air from over
the engine.
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