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Copyright 2009 Delmar, Cengage Learning Medium/Heavy Duty Truck Engines, Fuel & Computerized Management Systems, 3E Chapter 17 Diesel Fuel Characteristics

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Copyright 2009 Delmar, Cengage Learning Introduction Diesel engines will burn just about any fuel introduced into the engine cylinders To maximize engine performance & service life, only fuels meeting the highest standards are used Diesel fuel is a petroleum based product What is described as diesel fuel today will likely change a decade from now Although 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 fuel

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Copyright 2009 Delmar, Cengage Learning Fuel Terminology AFR air-to-fuel ratio, actual ratio of air to fuel in a combustion reaction Ash suspended solids or soluble metallic compounds in diesel fuels ASTM American Society for Testing & Materials Organization, classifies fuels to a standard ASTM #1D Fuel recommended for engines required to operate under variable loads & speeds ASTM #2D Fuel recommended for engines required to operate under constant loads & speeds

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Copyright 2009 Delmar, Cengage Learning Fuel Terminology Boil Point temperature at which a liquid vaporizes Calorific Value potential heat energy measured in British Thermal Units (BTUs) Catalyst a substance that enables a chemical reaction without itself undergoing any change Cetane Number (CN) a measure of the ignition quality of a diesel fuel Cloud Point temperature at which normal paraffins in fuel become less soluble & begin to precipitate as wax crystals

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Copyright 2009 Delmar, Cengage Learning Fuel Terminology Crude Oil raw petroleum Diesel Fuel term to describe distillate petroleum compounds formulated for use in on-highway compression ignition (CI) engines Distillate alternate name for diesel fuel Fire Point temperature at which a liquid HC fuel evaporates sufficient flammable vapor to burn continuously in air Flame Front forward boundary of the reacting zone in-cylinder combustion

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Copyright 2009 Delmar, Cengage Learning Fuel Terminology Flame Propagation the way in which a fuel combusts inside the engine cylinder as determined by the manner the flame front spreads Flash Point temperature at which a liquid HC fuel evaporates sufficient flammable vapor to momentarily ignite when a flame is brought to the surface Fractions portion of a mixture separated by distillation or a cracking procedure

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Copyright 2009 Delmar, Cengage Learning Fuel Terminology Fuel-Air Ratio used to describe ratio of fuel to air in diesel combustion Gasoline group of liquid petroleum fuels for use in spark ignited (SI) engines Kerosene widely used as heating oil & jet fuel Microorganism Growth airborne bacteria & fungi entering vehicle & storage tanks through venting systems

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Copyright 2009 Delmar, Cengage Learning Fuel Terminology Natural Gas (also liquefied natural gas: LPG & compressed natural gas: CNG) gaseous product of petroleum either suspended above liquid crude oil or dissolved in it Octane 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 equipment

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Copyright 2009 Delmar, Cengage Learning Fuel Terminology Photochemical Smog reaction of HCs & NOxs with sunlight in the lower atmosphere Pour Point lowest temperature in which fuel can be pumped Specific Gravity the weight of volume of a liquid compared to the weight of the same volume of water Stoichiometric Ratio the exact ratio of reactants required for a chemical reaction to take place

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Copyright 2009 Delmar, Cengage Learning Fuel Terminology Sulfur 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 increases Volatility the tendency of a liquid to vaporize

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Copyright 2009 Delmar, Cengage Learning Petroleum HHC fossil fuels are found in the upper strata of the earths crust 770% of energy consumed in North America & 40% worldwide is derived from petroleum products AAn unrenewable energy source with limited reserves

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Copyright 2009 Delmar, Cengage Learning Crude Oil Three types: Asphalt-based Paraffin-based Mixed-base Crude petroleum must be refined to separate the fractions used to formulate fuels identified as diesel fuel, gasoline, kerosene & heavy furnace oil

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Copyright 2009 Delmar, Cengage Learning Refining Petroleum Crude Oil Fractions separated Fractions graded & extracted by cut points Gas taken off the top is natural gas In descending order of boil: Gasoline Naptha Kerosene Light gas oil Heavy gas oil Liquid remaining at bottom known as residuum

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Copyright 2009 Delmar, Cengage Learning Thermal & Catalytic Cracking Cracking is a process by which heavier fuel oils may be chemically modified by dividing heavy molecules into smaller light molecules Thermal cracking subjects crude to high temperatures & pressures in a cylindrical tower Catalytic 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 market

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Copyright 2009 Delmar, Cengage Learning Thermal & Catalytic Cracking Hydrocracking is a catalytic cracking process undertaken in the presence of hydrogen, used to produce higher volatility, lighter fractions required in fuels

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Copyright 2009 Delmar, Cengage Learning Diesel Fuel Characteristics Cetane Number (CN) measure of the ignition quality Increasing CN reduces fuel density & therefore fuel mileage As CN increases, ignition temperature decreases Ignition Accelerators fuel additives that increase the CN value Cyclohexanol 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.

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Copyright 2009 Delmar, Cengage Learning Diesel Fuel Characteristics Heating Value (Calorific Value) Heat energy released during combustion Value used to reckon the thermal efficiency of engines ability to produce power

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Copyright 2009 Delmar, Cengage Learning Diesel Fuel Characteristics API Gravity is a measure of how the weight of a petroleum liquid compares with water Measured with a hydrometer Understanding API gravity helps troubleshoot persistent low-power & marginal emissions test failures

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Copyright 2009 Delmar, Cengage Learning Diesel Fuel Characteristics Ultra-Low Sulfur Fuels Sulfur dioxide produced from combustion of diesel fuel is recognized as environmentally hazardous Sulfur content of diesel fuels progressively legislated to lower levels Off-Highway Fuels Bunker fuels cut with glycol & other antigel compounds similar to jet fuel

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Copyright 2009 Delmar, Cengage Learning Fuel Storage, Deterioration & Performance Fuel chemistry is adjusted seasonally by the refiner/supplier due to temperature variables Storage tanks may contain water, drain the water periodically, helping to prevent water buildup Water in fuel presents two main problems: If it collects in crossover pipe, becomes vulnerable to freeze-up It 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 system Its 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 up

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Copyright 2009 Delmar, Cengage Learning Fuel Storage, Deterioration & Performance Climate Influence When fuel is stored & exposed to high temperatures, its more volatile fractions are boiled off, lowering the CN Fuel heaters sometimes used to help compensate for deficiencies in cloud point, pour point & viscosity ratings in colder climates

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Copyright 2009 Delmar, Cengage Learning Fuel Conditioners Most OEMs disapprove of their use Vague mixture of cetane improvers, cleansing additives & pour point depressants in an alcohol base Generally create more problems than they solve, however there are occasions when they have to be used Use only when no other option available Always follow manufacturers recommendations

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Copyright 2009 Delmar, Cengage Learning Fuel Conditioners Fuel conditioners are not normally recommended by OEMs If required to use them, the technician should understand their functionality Always follow OEM & manufacturers recommendations when using aftermarket products!

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Copyright 2009 Delmar, Cengage Learning Costs of Operating a Truck Fuel represents major expense in operating a truck The diesel fuel of the future?