To calculate the SFOC of the main engine of the running ship, the procedure is as follows.
The experiment or the investigation time is set for one or one and half hour which time is sufficient to take the indicator cards of say all six units.
- An important condition is that the weather should be fine and engine RPM is fairly constant
- The engine is running at its service .
- The indicator and draw cards are taken for all the
- The following temperatures and pressures are recorded for purposes of record and investigation if needed
- Exhaust temperatures of all units.
- C/W outlet temperatures of all
- Temperature of C/W inlet.
- Piston cooling oil outlet temperatures of all units
- Piston cooling oil inlet
- Pressure drop across air cooler of T/C.
- Pressure drop across air filter of T/C.
- Temperature drop through
- Scavenge air
- Scavenge air
- Lub oil pressure and
- Engine load position
- Average RPM of engine calculated from counter readings taken at commencement of experiment and end of experiment, their difference divided by time in minutes
- Fuel consumption taken from clock readings taken at commencement of experiment and end of experiment given in litres
The SFOC can now be calculated as follows.
Total indicated power calculated from the cards using planimeter and engine constants for stroke length , cylinder area and average RPM found from experiment.
Indicated power produced per unit is given by
Where P is the mean effective pressure obtained from the card given in KN/M2.
A is the area of the cylinder given in M2.
L is the length of stroke given M ,and
N is the RPM
Hence power developed per unit is given by
P*L*A*N*2∏)/60 *KN/M2*M2*M = (P*L*A*N*2∏)/60 KNM/SEC
= (P*L*A*N*2∏)/60 KW
The total power developed will be
Sum of all units power as calculated above = total power developed.
The fuel consumed will be in litres obtained by difference in initial reading — final reading given in litres.
Assume the experiment time is 90 minutes which is 1.5 hours.
Therefore SFOC is given by
(Litres of fuel oil consumed *1000*ρ)/ (total power*1.5) and given as grams per KWhr.
Ρ is the specific gravity of the oil at the relevant temperature
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