Iveco Marine Diesel Engines, Installation Handbook

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The “specific consumption” represents the quantity of fuel used to obtain a unit of mechanical energy;
it is expressed in g/kWh and derives from the formula:
Where L is the volume in cm 3 of the fuel having specific gravity y (in g./ cm 3 ), consumed by the engine
in time t expressed in seconds, while power N (in kW) is supplied at given rpm.
The “hourly consumption” represents the quantity of total fuel used by the engine when supplying a
power with value N at constant rpm for 1 hour; it is expressed in kg/h and is derived as follows:
The corresponding value in litres is obtained by dividing the result by the fuel specific gravity; for the
diesel fuel y it amounts to 0.83 kg/dm
3 at ambient temperature.
As the consumption is related to the power supplied by the engine, the evaluations and the com-
parisons between hourly consumption rates must be made taking into consideration precise and
homogeneous engine operating conditions.
Load factor
It represents the average load in time of the power actually required to an engine, expressed as a per-
centage of the value of its maximum power.
As it represents the engine heavy duty index, it is a relevant indicator for the choice of the correct engine
in relation to its application and use. Analysing the engine “load factor” means evaluating which power
levels are required during the different work cycles in relation to its possible use at maximum power.
It is expressed by the following formula:
where :
• P
i
: power absorbed for time t
i
• P
max
: maximum power
• N : number of phases in which the work cycle can be split.
Example of calculation for an application having:
■
Max power 200 kW
■
Working cycle of 12 hours, out of which 3 hours at maximum power and 9 hours at half power
The resulting load factor is:
MARCH 2004 INTRODUCTION
1.14
MARINE ENGINES INSTALLATION