Iveco Marine Diesel Engines, Installation Handbook

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The following section includes some considerations on the engine performance variations according
to the environmental conditions. However, IVECO reserves the right, when negotiating the contract,
to assess every single application to choose the most suitable engine setting and define the possible
“derating”.
Ambient temperature
A high temperature can lead to the engine power reduction, as a result of the air rarefaction, and there-
fore generate cooling, lubrication and onboard system operating problems. It can be due to the climate
conditions or an insufficient ventilation of the engine room.
The power reduction in aspirated engines amounts to 2% every y 5.5 °C increase above the reference
temperature of the test rule.
The reduction of power in supercharged engines depends on the work margin of the compressor and
the available supercharging pressure and, if present, on the efficiency of the air-water exchanger. It can
be null when there is more supercharging pressure and with an air-water exchanger having the right
size, or it can be equal to the percentage values mentioned for the aspirated engines.
When the temperature is below the reference value, there is no power reduction. Below certain val-
ues, it could be difficult to start the engine or some systems may be faulty.
Height
The engine operation at a high altitude, as a result of the lower atmospheric pressure, can lead to a
reduction of the quantity of air sucked and thus to a lower torque and power, compared to the typical
engine performance curves.
The lower performances depend on the characteristics of the turbocharger, where present, and of the
engine setting, i.e. of the air system capacity to compensate for the air rarefaction with a higher volume
of air inlet. On aspirated engines there might be, up to 2500 m in height, a power loss of 3.5 % every
300 m of difference in height, while on supercharged engines with turbine fitted with waste gate the
power reduction can be between zero and approx. 2.5% every 300 m of difference in height, accord-
ing to the size, type and matching of the turbocharger.
For a different adjustment of the quantity of injected fuel, the “derating” becomes necessary for those
applications where the critical height is exceeded for a long time and above which there is no com-
pensation for the quantity of air inlet. The derating becomes also necessary as a result of a lower
counter-pressure at the exhaust which leads to the turbocharger overspeed conditions and as a result
of the reduction of the water boiling temperature caused by a lower atmospheric pressure.
Humidity
The engine setting for its use in conditions of high air humidity does not happen frequently, save for the
operation in environments constantly above 60% of the relative humidity, as in Tropical forests.
In these cases it can be foreseen that every 10% increase of the relative humidity above 60% there can
be a derating of:
■
0,5% for ambient temperature of 30 °C
■
1% for ambient temperature of 40 °C
■
1.5% for ambient temperature of 50 °C
The “derating” is managed by IVECO during the contractual negotiations according to the operating
conditions of the boat supplied by the Customer.
MARCH 2004 ENGINE/BOAT CHOICE FACTORS
2.30
MARINE ENGINES INSTALLATION