Iveco Marine Diesel Engines, Installation Handbook

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MARCH 2004 ENGINE/BOAT CHOICE FACTORS
2.29
MARINE ENGINES INSTALLATION
Gliding boats
1.Torque limit curve/real average pressure/input, for the engine - 2. Absorption curve of a propeller
too big for the application - 3. Absorption curve of a propeller with the right size (pattern between
the cube and square one, except for the gliding phase when the square pattern is exceeded) -
4. Absorption curve of a propeller too small for the application - 5. Gap curve.
2.4 ENVIRONMENTAL CONDITIONS AND “DERATING”
Pressure, temperature and humidity of the air sucked by the engine, different from the reference val-
ues, play an important role in the supply of power when they vary substantially and persist in time.They
affect the density and therefore the weight of the air getting inside the engine and also the fuel quan-
tity regulated by the injection pump, in relation to the quantity of air inlet.
“Derating” consists in the adjustment of the injected fuel quantity according to the weight variation of
the air sucked by the engine, without affecting the optimum ratio, in the event of excessive air, that the
diesel engine needs and to prevent the growth of the combustion temperature and the exhaust smoke.
With the engine electronic control (EDC), the adjustment of the injection metering is a function imple-
mented by the managing software.
For the choice of an engine, it is necessary to consider the environmental factors to ensure that it has
a power suitable for the load in real operating conditions.
The engine behaviour in particular environmental conditions can be very different according to ist char-
acteristics and fittings:
■
Aspirated, supercharged, supercharged with aftercooler
■
Boosting with and without waste gate or controlled by VGT
■
Injection with mechanical pump or electronic control
Figure 3
M
rpm
1
2
3
4
5