DIESEL FUELS & DIESEL FUEL SYSTEMS

Application and Installation GuideDiesel Fuels & Diesel Fuel SystemsAppendix 1Day Tank Sizing (WhenDay Tank Serves as a HeatSink)The fuel supply temperature mustbe within specified limits foroptimum injector life and maximumpower capability.Fuel systems without fuel coolersrely on the day tank to dissipate theheat of fuel returning from theengine. Day tank temperatures areaffected by the following conditions.• Day tank wetted surface area(including tank bottom)• Engine(s) fuel consumptionrate• Day tank replenishing level• Storage tank fuel temperature• Ambient temperature• Spaces contiguous to the daytank (void tanks, cofferdams,vessel shell plating, etc.)• Return fuel temperatureTank temperature calculation areperformed in five [5] steps. The firstdetermines the fuel mass in the tankat each time interval. The secondstep is based on a fuel mixtemperature resulting from theengine driven transfer pump flowrate to the engine and the returnflow rate to the day tank. The thirdstep determines the day tank fuelheight for each incremental timeelement. Typically, the calculationswill be based upon a 30-60 minuteiterative time function. The endpoint for the calculation is assumedto be when the day tank is refilled.The fourth step approximates theheat transfer from the tank to thesurrounding environment due to thetemperature difference between thefuel mix temperature and theambient temperature. Thisconvective heat transfer thendetermines the resultant tanktemperature. The fifth step evaluatesthe impact of the final fuel supplytemperature on the engine’smaximum power capability.The included example calculationsshould only be used to providegeneral guidance. If the day tanksize is marginal, use a fuel cooler.To simplify the followingcalculations, it is assumed the daytank walls are surrounded by freemoving air. If the tank walls arecontiguous to the shell plating, heattransfer from the day tank will beenhanced. Conversely, if the daytank is bounded by void spaces andcofferdams, heat rejection from theday tank will be retarded. Typically,most day tanks are located withvarious combinations of thepreceding boundary elements. Theindividual performing the evaluationmust be familiar with the installationas well as the fundamentalengineering concepts of the formulasused in the calculations.Day Tank CalculationsThe following information isrequired to perform the calculations:• Engine model• Engine developed power (MCRor CSR)• Engine speed©2005 Caterpillar®All rights reserved. Page 37