DIESEL FUELS & DIESEL FUEL SYSTEMS

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Diesel Fuels & Diesel Fuel SystemsApplication and Installation GuideStep 5The last step calculates themaximum power capability of theengine at the resultant day tanktemperature for each time interval. Asummary table for each increment (t)is also prepared and shown in Table10:Note: The engines are power set atthe factory with 30 ±3°C (86±5°F) fuel to the engine transferpump. Higher fuel temperaturesreduce maximum power capability.The fuel stop power reduction is 1%for each 5.6°C (10° F) fuel supplytemperature increase above 30°C. Ifthe engine is operating below thefuel stop limit, the governor will addfuel as required to maintain therequired engine speed and power.(TDT - Tref ) 1Pcorr = Prated x[ 1 - X10°F 100 ]Where:Pcorr = Corrected Engine Power,bhpPrated = Rated bhpTref = 86° (Power setting)TDT = Actual day tank fueltemperature, °FExample:For t = 60, the corrected power ofthe engine is:(89.3°F - 86°F) 1Pcorr = 4640 bhp x [ 1 - X10°F100 ]Pcorr = 4625 bhpIncrementalTime (min)Day TankTemp. (°F)CorrectedEngine Power(bhp)0 85.0 -60 89.3 4625120 93.2 4607180 97.1 4588240 101.3 4569300 105.6 4549360 110.2 4528420 114.9 4506480 120.0 4482540 125.2 4458600 130.8 4432660 136.8 4405720 143.1 4375Refill 116.9 4497Table 10ConclusionThe previous calculations indicateday tank fuel temperatures can havean effect on the maximum powercapability of the engine. Theexample was based upon a fixedpitch propeller application. Typically,a fixed pitch propeller is selectedand sized to absorb 85-90% of theengine's name plate rating. In thisexample, this would equate to 3950-4175 bhp. The lowest calculatedcorrected power was determined tobe 4375 bhp. This would leave a 5-10% power margin and vesselperformance would not be affected.While vessel performance may notbe affected in this example, themaximum fuel temperature of143.1°F will put the fuel viscositynear or below the minimumallowable viscosity of 1.4 cSt at thePage 46©2005 Caterpillar®All rights reserved.
Application and Installation GuideDiesel Fuels & Diesel Fuel Systemsinjectors depending on the type ofdistillate fuel being used. In addition,the temperature of the fuel in thetank after refill is now 116.9°Finstead of 85°F as used at thebeginning of the iteration. Therefore,continued operation at full load onthis fuel tank would cause the fueltemperature to rise even higher thanthe maximum temperature shown inthis iteration. To protect the fuelinjectors a fuel cooler should beused in this application, despite thefact that available engine power isstill acceptable.Aside from the impact on engineperformance, maximum fuel tanktemperatures are also established byvarious marine classificationsocieties and regulatory bodies.Their interest is based upon theincreased risks of fire that resultsfrom elevated fuel temperatures.Useful Fuel Formulas and DataThe following information can be useful in sizing fuel coolers and heaters:Specific Gravity (SG) and DensityAPI Gravity = (141.5/SG) - 131.5SG = 141.5/(API Gravity + 131.5)SG =Density998 kg/m 3Density (kg/m 3 ) = SG x 998 kg/m 3 1 lbm/ft 3 1 ft 3Density (lbm/gal)= SG x 998 kg/m 3 x16.02 kg/m 3 x7.48 galMass Flow RateM (kg/sec) = Density (kg/m 3 ) x1m 31000 LxFlow Rate (L/min)60 (sec/min)M (lbm/min) = Density (lbm/gal) x Flow Rate (gal/min)©2005 Caterpillar®All rights reserved. Page 47
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DIESEL FUELS & DIESEL FUEL SYSTEMS

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