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Petroleum Fuels and Alternative Fuel Technologies

Petroleum Fuels and Alternative Fuel Technologies. Chapter 39. Objectives. Understand how petroleum is refined Describe the different characteristics of various blends of gasolines Know the effects of the different types of abnormal combustion

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Petroleum Fuels and Alternative Fuel Technologies

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  1. Petroleum Fuels and Alternative Fuel Technologies Chapter 39

  2. Objectives • Understand how petroleum is refined • Describe the different characteristics of various blends of gasolines • Know the effects of the different types of abnormal combustion • Decide on the best choice of gasoline or diesel fuel for a vehicle • Diagnose rich and lean fuel mixture problems • Describe the advantages and disadvantages of various types of alternative fuels

  3. Introduction • Motorists have questions about fuel used in their cars • Several kinds of fuels used in motor vehicles • This chapter deals with gasoline, diesel, and alternative fuels • This chapter also discusses rich and lean air-fuel mixtures and abnormal combustion • Conditions can result in engine damage, poor fuel economy, and poor performance

  4. Crude Oil • Raw petroleum (i.e., crude oil) • Used to make many products • Pumped from the ground • Heated by pumping it through pipes in hot furnaces into a fractionating column • Light hydrocarbon molecules are separated • Refining process breaks crude into fractions • Some fractions are blended into gasoline to correct octane, emissions, volatility, and storage life • Fractions may be used directly (e.g., kerosene and diesel)

  5. Diesel Engines and Diesel Fuel • Diesel engine • Compression ignition engine • Diesel • High-compression ratio • Low volatility: safe at room temperature • Automotive diesel fuel grades • 1-D: more volatile and thinner • Used in low temperatures • 2-D: lower volatility • Used in most driving conditions

  6. Diesel Engines and Diesel Fuel (cont'd.) • Cloud point: temperature at which paraffin separates from fuel • Cetane rating: describes how easily fuel ignites • The higher cetane rating, the easier it ignites • Diesel maintenance: water must not be allowed to accumulate • More frequent oil changes required • Biodiesel: renewable fuel • Diesel exhaust fluid: amount used is said to be about two percent of diesel fuel consumption

  7. Gasoline • Very flammable hydrocarbon • Incomplete combustion results in CO • Volatility • How easily a fuel evaporates • Vapor lock • Engine stalls because liquid fuel does not reach the carburetor • ASTM • Six volatility classes • Reid vapor pressure test measures volatility

  8. Air-Fuel Mixture • Desirable air-fuel mixture: 15:1 • Normal mixture is about 12:1 • Rich mixture: too much fuel • Poor fuel economy and increased emissions • Lean mixture: too much air • Poor drivability and higher idle speed • Gasoline engine run-on: engine continues to run after ignition key is off (i.e., dieseling) • Fuel ignites because of heat caused by pressure

  9. Spark Knocks, Carbon Noise, and Abnormal Combustion • Flame front travels across combustion chamber and pushes piston down • Travels 50-250 meters per second • Normal combustion • Air-fuel mixture burns in a controlled manner • Some abnormal combustion causes • Cylinder temperatures too high • Too lean an air-fuel mixture • Engine overheating or driver lugs an engine

  10. Abnormal Combustion • Abnormal combustion conditions • Cause spark knock and engine damage • Causes of preignition • Spark plugs of too high a heat range • Hot spots in combustion chamber • Loose spark plug • Detonation • Air-fuel mixture self-ignites due to pressure • Results in cylinder wall scuffing • Noise: cold knock or inaudible ping

  11. Excessive Carbon Buildup • May cause an increase in compression ratio • Oil-based carbon deposits • Traditional gummy black ones • Sometimes found on intake valves • Caused when oil and heat come together • Carbonaceous deposits • From fuel • Resemble cauliflower • Hard, dry, and tougher to remove • Cause drivability problems

  12. Regular Versus Premium Fuels • Octane: fuel’s ability to resist explosion • Using premium gasoline in a car designed for regular offers no advantage • Modern computer-controlled engines use a detonation sensor • Learns the best timing for the fuel • Changes in temperature, humidity, and pressure • Affect the octane number requirement

  13. Octane Standards • Antiknock index (AKI) • Measure of gasoline octane quality • Average of research octane number (RON) and motor octane number (MON) • RON gives higher reading • MON measures how much engine knock present under heavy loads • (R + M)/2: required by law to be listed on the octane decal on gasoline pump

  14. Gasoline Additives • Expensive • Added in minute quantities to fuel • Detergents and deposit control additives • Have a large effect on gasoline quality • Keep port fuel injectors from becoming fouled • Required by law since 1995 in all states

  15. Reformulated Gasolines • Gasoline refinement • Affects air pollution • Reformulated gasolines • Clean air by providing more complete combustion • Required by EPA in U.S. cities with worst air pollution • Cars can damage older rubber fuel lines • Less energy content, reducing fuel economy

  16. Oxygenated Fuels/Alcohols • Gasolines blended with ethers or alcohols • Ethyl alcohol at 10% concentration • MTBE at 15% concentration • Ethanol is about 35% oxygen • Gasoline with less than 10% alcohol requires no fuel system changes • Variables affecting fuel economy • Driving and engine condition • During the summer gasoline energy content higher

  17. Alternative Fuels • AFVs: any flexible fuel or dual-fuel vehicle • Ethanol vehicles must be designed to run on a blend of up to 85% denatured ethanol • P-series fuel is a liquid blend including ethanol, biomass cosolvent, and natural gas liquids • Methanol is methyl alcohol • Produces about half the energy of gasoline • Made from coal, natural gas, oil shale, wood, or garbage

  18. Alternative Fuels (cont'd.) • Characteristics of alcohol fuels • Invisible when burning • Methanol is very corrosive and poisonous • LP gas is a product of gasoline refining • Mostly propane with small amount of butane • Vapor above -40°F • Burns cleanly, fewer oil changes required, and has higher octane • Has less energy per volume than gasoline and must be stored under high pressure

  19. Alternative Fuels (cont'd.) • Compressed natural gas • Used in fleets, buses, and taxicabs • Full refill requires several hours • Stored under pressure in large cylinder • Gasoline engines can be retrofitted for CNG • Liquefied natural gas • Burns when mixed with air in ratio of 5 – 15% • Colorless, odorless, nontoxic, and noncorrosive

  20. Alternative Fuels (cont'd.) • Rebuilding concerns with alternative fuel engines • Besides gasoline, alternative fuel engines can run on E85, LPG, or CNG • Gasoline produces ash when it burns, which protects the valve seats from scuffing • LPG and CNG are cold, dry fuels that leave the valve seats unprotected • Hydrogen is a promising fuel for the future • No emissions • Produces about two-thirds of normal power

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