Calculate SFOC the proper way!!
Calculationofthespecificfueloilconsumption(g/kWh)requiresthatenginepower,andtheconsumedfueloilamount(kg),areknownforacertainperiodoftime.
The first step requires the determination of engine’s power. The second step is to know the fuel amount consumed for a specific period of time. To achieve a reasonable measuring accuracy, it is recommended to measure over a suitablylongperiod-dependentuponthemethodemployedi.e.:
▪Ifadaytankisused,thetimefortheconsumptionofthewholetankcontentswillbesuitable.
▪Ifaflow-meterisused,aminimumof1hourisrecommended.
The most important of all is to perform our measurements while load is constant! And we have to be the strictest possible to that.
Sincebothoftheabove-mentionedquantitymeasurementswillbeinvolumeunits,itwill be necessarytoknowtheoildensity,inorder toconverttoweightunits.Thedensityistocorrespondtothetemperatureatthemeasuringpoint(i.e.inthedailytankorflow-meter). On the other hand we can find the density at measuring point by identifying the specific gravity. Specific gravity can be determined by usage of a hydrometer immersed in a sample taken at the measuring point. Density can also be calculated on the basis of fuel specs as a function of temperature. Normally,infuelspecifications,thespecificgravityisindicatedat15°C/60°F.
Next step is calculation of theconsumedoilquantityinkgwhich isobtainedbymultiplyingthemeasuredvolume(inlitres)by thedensity(inkg/litre).
Inordertobeabletocompareconsumptionmeasurementscarriedoutforvarioustypesoffuel oil, allowance must be made for the differencesin the lower calorific value (LCV) ofthefuelconcerned.
Normally, onthe testbed,gas oilwillhave beenused, havinga lowercalorific valueof approximately42,707kJ/kg.Ifnootherinstructionshavebeengivenbytheshipowner,itis recommendedtoconverttothisvalue.
Usually,thelowercalorificvalueofafueloilisnotspecifiedbytheoilcompanies.How-ever,bymeansofthegraph,Plate70611,theLCVcanbedeterminedwithsufficientaccuracy,onthebasisofthesulphurcontent,andthespecificgravity at 15°C. The corrected consumption can then be determined by multiplying the "measured consumption" as follows:
LCV/42,707 where LCV=thespecificlowercalorificvalue,inkJ/kg,ofthefueloilconcerned.
For more information and step by step examples please refer to your “Volume I” Operation Manuals.