Diagnose and repair light vehicle engines
Hsc
Chapter9_rev.pptxChapter 9
Automotive Engine
Designs and Diagnosis
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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
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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.
Cylinder Block Video
Click on image above to play video
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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.)
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The Four-Stroke Cycle Video
Click on image above to play video
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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
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Firing Order Examples
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Knowledge Check
Explain what takes place during the four strokes of a gasoline engine.
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Answers will vary.
During the intake stroke, the intake valve opens and the piston moves downward. This reduces the pressure in the cylinder and draws in the air/fuel charge. During the compression stroke, the intake and exhaust valves are closed and the piston moves upward. This compresses the air/fuel charge. During the combustion stroke, the spark plug ignites the air/fuel mixture, releasing a lot of heat and pressure. This forces the piston down, turning the crankshaft. As the piston moves upward, the exhaust valve opens to let the burnt exhaust gases out of the cylinder.
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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
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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
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Engine Measurement and Performance
Bore and stroke
Displacement
Compression ratio
Engine efficiency
Torque vs. Horsepower
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Bore and Stroke
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Displacement
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Compression Ratio
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Compression Ratio Video
Click on image above to play video
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Knowledge Check
How does compression ratio affect an engine’s performance?
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Increasing compression ratio can increase output by extracting more energy from combustion by generating more heat and pressure.
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Engine Volumetric Efficiency
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Engine Thermal Efficiency
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Engine Mechanical Efficiency
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Torque vs. Horsepower
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Hybrid Vehicle Engines
Many hybrid electric vehicles (HEVs) use specially modified gasoline engines for improved fuel economy
Atkinson cycle engines
Miller cycle engine
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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
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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
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Other Powerplants (Cont.)
Variable compression ratio engines can maximize power when needed and minimize fuel consumption when power is not needed
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Knowledge Check
How do hybrid vehicle powertrains differ from non-hybrid vehicles?
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Hybrid powertrains use electric motors to supplement the ICE and to drive the vehicle on battery power.
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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
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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 psi
2) 150 psi
3) 80 psi
4) 80 psi
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Blown head gasket or cracked head.
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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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Vacuum Testing Video
Tests ability of engine to draw in air
Can identify induction and cylinder sealing problems
Click on image above to play video
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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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Technician A
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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.)
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Diagnosing Engine Noises Video
Click on image above to play video
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