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Chapter 9. Automotive Engine Designs and Diagnosis. Introduction to Engines. All gas and diesel engines are internal combustion engines Largest part is the cylinder block The cylinder head sits on top of the block Engines are constructed from iron, aluminum, magnesium, and plastics. - PowerPoint PPT Presentation
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© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Chapter 9
Automotive Engine Designs and Diagnosis
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Introduction to Engines
• All gas and diesel engines are internal combustion engines
• Largest part is the cylinder block• The cylinder head sits on top of the block• Engines are constructed from iron, aluminum,
magnesium, and plastics
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Engine Classifications
• Operational cycles • Number of cylinders• Cylinder arrangement• Ignition type • Cooling system• Fuel type• Valve train type –
OHV, OHC, DOHC
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Overhead Valve
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OHC Valvetrain DOHC Valvetrain
Overhead Cam
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• Intake Stroke– The piston moves down and the intake valve
opens to draw air and fuel into the cylinder• Compression Stroke– The piston moves up with both valves closed to
compress the mixture
Four-Stroke Cycles
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• Power Stroke– With both valves still closed, the mixture is
ignited, and the expansion pushes the piston back down
• Exhaust Stroke– The piston moves up and pushes the spent gasses
out the open exhaust valve
Four-Stroke Cycles (Cont.)
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Firing Order
• The sequence in which the cylinders are ignited• Also indicates position of the pistons when a
cylinder is firing• For a four-cylinder firing order of 1342– #1 is at TDC compression– #3 is at BDC intake– #4 is at TDC exhaust– #2 is at BDC power
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Firing Order Examples
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Knowledge Check
• Explain what takes place during the four strokes of a gasoline engine.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Two-Stroke Gasoline Engines
• Produce power every two strokes instead of every four
• Not as fuel efficient as four-cycle• Emits more pollution than a four-cycle• Oil for lubrication is mixed with the fuel
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Engine Rotation
• Rotation standard set by SAE• Most engines rotate counterclockwise as seen
from the rear or flywheel side
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• Many factors affect combustion• Incomplete combustion causes the engine to
run poorly• Starts at the spark plug gap• Should move steadily across the air/fuel mixture• The rapidly expanding gases force the piston
down
Combustion
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Engine Configurations
• Inline • V-type • Slant• Boxer or opposed
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Engine Measurementand Performance
• Bore and stroke• Displacement• Compression ratio• Engine efficiency• Torque vs. Horsepower
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Bore and Stroke
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Displacement
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Compression Ratio
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Knowledge Check
• How does compression ratio affect an engine’s performance?
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Engine Volumetric Efficiency
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Engine Thermal Efficiency
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Engine Mechanical Efficiency
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Torque vs. Horsepower
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Hybrid Vehicle Engines
• Many hybrid electric vehicles (HEVs) use specially modified gasoline engines for improved fuel economy– Atkinson cycle engines – Miller cycle engine
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Atkinson Cycle
• Holds the intake valve open longer - during the time compression is taking place
• The open intake valve allows some of the mixture to escape back into the intake manifold
• This reduces the effective displacement and compression ratio
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Atkinson Cycle (Cont.)
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Miller Cycle
• An Atkinson cycle engine with forced induction (supercharger)
• The decrease in intake air and lower power is compensated for by the supercharger
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Diesel Engines
• Main power source for heavy-duty applications
• Operates similar to a gasoline engine
• Use high compression pressure to ignite fuel
• Larger than comparable gas engine
• Produce large amount of torque
• Run at low speeds
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
HCCI Engines
• Homogeneous charge compression ignition (HCCI) engines have the torque and efficiency of a diesel and the low emissions and power of a gas engine
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Other Powerplants
• Hybrid vehicles have at least two types of power or propulsion systems – usually an ICE and electric motors
• Hybrids do not require plugging in to charge
• EVs do require plugging in
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Toyota Prius MG2
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Other Powerplants (Cont.)
• Battery operated electric vehicles (EVs) – operate solely on battery powered electric motors
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Other Powerplants (Cont.)
• Fuel cell electric vehicles – use hydrogen to generate electricity to power electric motors
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Other Powerplants (Cont.)
• Rotary engines – another type of four-cycle ICE
• Rotary engines use a rotating triangular rotor, no reciprocating engine parts
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Other Powerplants (Cont.)
• Variable compression ratio engines can maximize power when needed and minimize fuel consumption when power is not needed
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Knowledge Check
• How do hybrid vehicle powertrains differ from non-hybrid vehicles?
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Engine Identification
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Engine Identification (Cont.)
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• Compression Test– Checks the compression of each cylinder
• Cylinder Leakage Test– Helps determine where compression is leaking
• Power Balance Test– Checks to see if all cylinders are producing the same
power• Vacuum Test– Helps to determine the engine’s efficiency by
measuring manifold vacuum
Engine Diagnostics
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Compression Testing
• Relative compression– Measures starter current flow when cranking
• Cranking compression– Dry and wet tests– Wet test checks for rings sealing
• Running compression– Used to determine valvetrain problems
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Relative Compression Test
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Cranking Compression Test
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Running Compression - Good
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Running Compression - Bad
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Knowledge Check
• A four-cylinder engine has the following compression readings, what could be the cause?1) 150 psi2) 150 psi3) 80 psi4) 80 psi
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Cylinder Leakage Test
• Pressurizes the cylinder
• Used to determine cause of leakage– Cracked head or
leaking head gasket– Leaking rings– Burnt valves
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Power Balance Testing
• Checks for each cylinder’s contribution
• Can be done manually• Typically a scan tool
test
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Knowledge Check
• While discussing power balance testing, Technician A says each cylinder should drop the same rpm. Technician B says a cylinder that does not drop rpm is a good cylinder. Who is correct?
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Engine Diagnostics (Cont.)
• Engine Oil Pressure Testing– Determines the wear on internal engine parts
• Fluid Leaks– Be sure to identify the correct fluid that is leaking
• Exhaust Smoke– Exhaust smoke diagnosis chart
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Engine Diagnostics (Cont.)
• Exhaust Smoke – Gasoline Engines– Grey/black smoke indicates excessive fuel– Blue smoke indicates burning oil– White smoke is coolant or ATF in combustion
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Common Engine Noises
• Abnormal Combustion Noises– Detonation or ping is most noticeable during
acceleration• Usually caused by advanced timing, overheating, or
lean mixtures
– Preignition or spark knock occurs when ignition occurs before the spark plug fires• Caused by carbon deposits, incorrect spark plug,
and cross firing
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Cleaning Carbon Deposits
• Excessive carbon buildup in the combustion chamber can cause several problems
• Chemical additives may remove or reduce deposits
• Carbon blasters force crushed walnut shells into combustion chamber to break up deposits
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• Ring Noise– A high-pitched rattling during acceleration
• Piston Slap– Normally heard when the engine is cold
• Piston Pin Knock– A sharp, metallic rap
• Ridge Noise– High-pitched rapping, louder on deceleration
Common Engine Noises (Cont.)
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• Rod-Bearing Noise– Usually heard at idle
• Main Bearing Noise– A dull, steady knock
• Tappet Noise– A light, regular, clicking sound
• Ping or Detonation– Rattling noise during acceleration
Common Engine Noises (Cont.)