Transcript 1111128618_276723

Petroleum Fuels and
Alternative Fuel Technologies
Chapter 39
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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)
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
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From fuel
Resemble cauliflower
Hard, dry, and tougher to remove
Cause drivability problems
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning
Alternative Fuels (cont'd.)
• Compressed natural gas
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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
© 2012 Delmar, Cengage Learning
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
© 2012 Delmar, Cengage Learning