Medium/Heavy Duty Truck Engines, Fuel & Computerized Management Systems, 3E

1. Medium/Heavy DutyTruck Engines, Fuel & Computerized Management Systems, 3E Chapter 17 Diesel Fuel Characteristics

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Fuel Terminology • Sulfur Content … maximum sulfur amount in fuel as recommended by American Petroleum Institute (API) & Environmental Protection Agency (EPA) • Viscosity … measure of a liquid’s resistance to shear, a value that generally decreases as temperature increases • Volatility … the tendency of a liquid to vaporize

11. Petroleum • HC fossil fuels are found in the upper strata of the earth’s crust • 70% of energy consumed in North America & 40% worldwide is derived from petroleum products • An unrenewable energy source with limited reserves

12. 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

13. Refining Petroleum • 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 Crude Oil

14. 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

15. 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

16. Diesel Fuel Characteristics 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. • 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

17. Diesel Fuel Characteristics • Heating Value (Calorific Value) • Heat energy released during combustion • Value used to reckon the thermal efficiency of engine’s ability to produce power

18. 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

19. 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

20. 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 A bulk fuel filtration set up 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 It’s good practice to keep fuel tanks full. This keeps moisture-laden air out of the tanks ad reduces water-in-fuel problems

21. Fuel Storage, Deterioration & Performance • Climate Influence • When fuel is stored & exposed to high temperatures, it’s 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

22. 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 manufacturer’s recommendations

23. 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!

24. Costs of Operating a Truck • Fuel represents major expense in operating a truck • The diesel fuel of the future?