Medium/Heavy Duty Truck Engines Chapter 11

Medium/Heavy DutyTruck Engines, Fuel & Computerized Management Systems, 3EChapter 17Diesel Fuel CharacteristicsCopyright 2009 Delmar, Cengage LearningIntroductionDiesel engines will burn just about any fuel introduced into the engine cylindersTo maximize engine performance & service life, only fuels meeting the highest standards are usedDiesel fuel is a petroleum based productWhat is described as diesel fuel today will likely change a decade from nowAlthough in North America, diesel power is primarily confined to the commercial sector, 50% of the automobiles in Europe use diesel power There is some increase in the use of biodiesel but this is mainly confined to low percentages cuts into petroleum based diesel fuelCopyright 2009 Delmar, Cengage LearningFuel TerminologyAFR air-to-fuel ratio, actual ratio of air to fuel in a combustion reactionAsh suspended solids or soluble metallic compounds in diesel fuelsASTM American Society for Testing & Materials Organization, classifies fuels to a standardASTM #1D Fuel recommended for engines required to operate under variable loads & speedsASTM #2D Fuel recommended for engines required to operate under constant loads & speedsCopyright 2009 Delmar, Cengage LearningFuel TerminologyBoil Point temperature at which a liquid vaporizesCalorific Value potential heat energy measured in British Thermal Units (BTUs)Catalyst a substance that enables a chemical reaction without itself undergoing any changeCetane Number (CN) a measure of the ignition quality of a diesel fuelCloud Point temperature at which normal paraffins in fuel become less soluble & begin to precipitate as wax crystalsCopyright 2009 Delmar, Cengage LearningFuel TerminologyCrude Oil raw petroleumDiesel Fuel term to describe distillate petroleum compounds formulated for use in on-highway compression ignition (CI) enginesDistillate alternate name for diesel fuelFire Point temperature at which a liquid HC fuel evaporates sufficient flammable vapor to burn continuously in airFlame Front forward boundary of the reacting zone in-cylinder combustionCopyright 2009 Delmar, Cengage LearningFuel TerminologyFlame Propagation the way in which a fuel combusts inside the engine cylinder as determined by the manner the flame front spreadsFlash Point temperature at which a liquid HC fuel evaporates sufficient flammable vapor to momentarily ignite when a flame is brought to the surfaceFractions portion of a mixture separated by distillation or a cracking procedure

Copyright 2009 Delmar, Cengage LearningFuel TerminologyFuel-Air Ratio used to describe ratio of fuel to air in diesel combustionGasoline group of liquid petroleum fuels for use in spark ignited (SI) enginesKerosene widely used as heating oil & jet fuelMicroorganism Growth airborne bacteria & fungi entering vehicle & storage tanks through venting systemsCopyright 2009 Delmar, Cengage LearningFuel TerminologyNatural Gas (also liquefied natural gas: LPG & compressed natural gas: CNG) gaseous product of petroleum either suspended above liquid crude oil or dissolved in itOctane Rating measure of the antiknock quality of a fuel (usually gasoline)Oxidation Stability products of oxidizing stored diesel fuel can result in deposits, filter plugging & lacquering of fuel injection equipmentCopyright 2009 Delmar, Cengage LearningFuel TerminologyPhotochemical Smog reaction of HCs & NOxs with sunlight in the lower atmospherePour Point lowest temperature in which fuel can be pumpedSpecific Gravity the weight of volume of a liquid compared to the weight of the same volume of waterStoichiometric Ratio the exact ratio of reactants required for a chemical reaction to take place

Copyright 2009 Delmar, Cengage LearningFuel TerminologySulfur Content maximum sulfur amount in fuel as recommended by American Petroleum Institute (API) & Environmental Protection Agency (EPA)Viscosity measure of a liquids resistance to shear, a value that generally decreases as temperature increasesVolatility the tendency of a liquid to vaporizeCopyright 2009 Delmar, Cengage LearningPetroleumHC fossil fuels are found in the upper strata of the earths crust70% of energy consumed in North America & 40% worldwide is derived from petroleum productsAn unrenewable energy source with limited reserves

Copyright 2009 Delmar, Cengage LearningCrude OilThree types:Asphalt-basedParaffin-basedMixed-baseCrude petroleum must be refined to separate the fractions used to formulate fuels identified as diesel fuel, gasoline, kerosene & heavy furnace oilCopyright 2009 Delmar, Cengage LearningRefining Petroleum

Crude OilFractions separatedFractions graded & extracted by cut pointsGas taken off the top is natural gasIn descending order of boil:GasolineNapthaKeroseneLight gas oilHeavy gas oilLiquid remaining at bottom known as residuum

Copyright 2009 Delmar, Cengage LearningThermal & Catalytic CrackingCracking is a process by which heavier fuel oils may be chemically modified by dividing heavy molecules into smaller light moleculesThermal cracking subjects crude to high temperatures & pressures in a cylindrical towerCatalytic cracking is a more efficient method of accomplishing same objective

Crudes from various regions naturally yield various percentages of products from refining. Today, this natural extraction may not represent market demand.Cracking allows the crude to be refined more in accordance with the products required for the marketCopyright 2009 Delmar, Cengage LearningThermal & Catalytic CrackingHydrocracking is a catalytic cracking process undertaken in the presence of hydrogen, used to produce higher volatility, lighter fractions required in fuels

Copyright 2009 Delmar, Cengage LearningDiesel Fuel CharacteristicsCetane Number (CN) measure of the ignition qualityIncreasing CN reduces fuel density & therefore fuel mileageAs CN increases, ignition temperature decreasesIgnition Accelerators fuel additives that increase the CN valueCyclohexanol nitrate will raise CN by 7 points Ignition accelerators do not improve fuel; they merely lower ignition temperature & thereby reduce ignition lag.They should only be used after analysis of fuel by fuel supplier & then only as prescribed.Excessive quantities of ignition accelerator in fuel have the effect of advancing ignition timing which can cause engine damage.Copyright 2009 Delmar, Cengage LearningDiesel Fuel CharacteristicsHeating Value (Calorific Value)Heat energy released during combustionValue used to reckon the thermal efficiency of engines ability to produce power

Copyright 2009 Delmar, Cengage LearningDiesel Fuel CharacteristicsAPI Gravity is a measure of how the weight of a petroleum liquid compares with waterMeasured with a hydrometerUnderstanding API gravity helps troubleshoot persistent low-power & marginal emissions test failures

Copyright 2009 Delmar, Cengage LearningDiesel Fuel CharacteristicsUltra-Low Sulfur FuelsSulfur dioxide produced from combustion of diesel fuel is recognized as environmentally hazardousSulfur content of diesel fuels progressively legislated to lower levelsOff-Highway FuelsBunker fuels cut with glycol & other antigel compounds similar to jet fuelCopyright 2009 Delmar, Cengage LearningFuel Storage, Deterioration & PerformanceFuel chemistry is adjusted seasonally by the refiner/supplier due to temperature variablesStorage tanks may contain water, drain the water periodically, helping to prevent water buildupWater in fuel presents two main problems:If it collects in crossover pipe, becomes vulnerable to freeze-upIt promotes microorganism growth. Metabolic waste is acidic & has a corrosive effect on fuel system components. More common in systems that run only a couple of times a year

Add methyl hydrate (alcohol) to the tank to prevent freeze-up. Water & alcohol form a solution that can be absorbed by the fuel & pumped through the fuel systemIts good practice to keep fuel tanks full. This keeps moisture-laden air out of the tanks ad reduces water-in-fuel problems

A bulk fuel filtration set upCopyright 2009 Delmar, Cengage LearningFuel Storage, Deterioration & PerformanceClimate InfluenceWhen fuel is stored & exposed to high temperatures, its more volatile fractions are boiled off, lowering the CNFuel heaters sometimes used to help compensate for deficiencies in cloud point, pour point & viscosity ratings in colder climates

Copyright 2009 Delmar, Cengage LearningFuel ConditionersMost OEMs disapprove of their useVague mixture of cetane improvers, cleansing additives & pour point depressants in an alcohol baseGenerally create more problems than they solve, however there are occasions when they have to be usedUse only when no other option availableAlways follow manufacturers recommendationsCopyright 2009 Delmar, Cengage LearningFuel ConditionersFuel conditioners are not normally recommended by OEMsIf required to use them, the technician should understand their functionality

Always follow OEM & manufacturers recommendations when using aftermarket products!Copyright 2009 Delmar, Cengage LearningCosts of Operating a TruckFuel represents major expense in operating a truckThe diesel fuel of the future?

Copyright 2009 Delmar, Cengage Learning