chapter 9

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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


Engine Classifications

• Operational cycles • Number of cylinders• Cylinder arrangement• Ignition type • Cooling system• Fuel type• Valve train type –

OHV, OHC, DOHC


Overhead Valve


OHC Valvetrain DOHC Valvetrain

Overhead Cam


• 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


• 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.)


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


Firing Order Examples


Knowledge Check

• Explain what takes place during the four strokes of a gasoline engine.


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


Engine Rotation

• Rotation standard set by SAE• Most engines rotate counterclockwise as seen

from the rear or flywheel side


• 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


Engine Configurations

• Inline • V-type • Slant• Boxer or opposed


Engine Measurementand Performance

• Bore and stroke• Displacement• Compression ratio• Engine efficiency• Torque vs. Horsepower


Bore and Stroke


Displacement


Compression Ratio


Knowledge Check

• How does compression ratio affect an engine’s performance?


Engine Volumetric Efficiency


Engine Thermal Efficiency


Engine Mechanical Efficiency


Torque vs. Horsepower


Hybrid Vehicle Engines

• Many hybrid electric vehicles (HEVs) use specially modified gasoline engines for improved fuel economy– Atkinson cycle engines – Miller cycle engine


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


Atkinson Cycle (Cont.)


Miller Cycle

• An Atkinson cycle engine with forced induction (supercharger)

• The decrease in intake air and lower power is compensated for by the supercharger


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


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


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


Toyota Prius MG2


Other Powerplants (Cont.)

• Battery operated electric vehicles (EVs) – operate solely on battery powered electric motors



• Fuel cell electric vehicles – use hydrogen to generate electricity to power electric motors



• Rotary engines – another type of four-cycle ICE

• Rotary engines use a rotating triangular rotor, no reciprocating engine parts



• Variable compression ratio engines can maximize power when needed and minimize fuel consumption when power is not needed


Knowledge Check

• How do hybrid vehicle powertrains differ from non-hybrid vehicles?


Engine Identification


Engine Identification (Cont.)


• 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


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


Relative Compression Test


Cranking Compression Test


Running Compression - Good


Running Compression - Bad


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


Cylinder Leakage Test

• Pressurizes the cylinder

• Used to determine cause of leakage– Cracked head or

leaking head gasket– Leaking rings– Burnt valves


Power Balance Testing

• Checks for each cylinder’s contribution

• Can be done manually• Typically a scan tool

test


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?


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


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


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


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


• 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.)


• 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.)

chapter 9

Documents

cengage learning

accessible website

intake valve

intake strokethe piston

bdc intake

cylinder firing order

stroke cycles

downexhaust strokethe