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PowerPoint for
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Chapter 12
Engine Design Classifications
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Contents

• Engine classifications
• Cylinder arrangement
• Alternative engines
• Typical automotive engines

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Engine Classifications

• Even though basic parts are the same, design
  differences can change the way engines operate
  and how they are repaired
• For this reason, you must be able to classify
  engines

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Common Engine Classifications

• Cylinder arrangement
• Number of cylinders
• Cooling system type
• Valve location
• Camshaft location

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Common Engine Classifications

• Combustion chamber design
• Type of fuel burned
• Type of ignition
• Number of strokes per cycle
• Number of valves per cylinder

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Cylinder Arrangement

• Refers to the position of the cylinders in
  relation to the crankshaft
• There are four basic cylinder arrangements
• inline
• V-type
• slant
• opposed

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Cylinder Arrangement
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Number of Cylinders

• Most car and truck engines have either 4, 6, or 8
  cylinders
• Some may have 3, 5, 10, 12, or 16 cylinders
• Engine power and smoothness are enhanced by using
  more cylinders

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Cylinder Numbering

• Engine manufacturers number each engine cylinder
  to help technicians make repairs
• Service manual illustrations are usually provided
  to show the number of each cylinder
• Cylinder numbers may be cast into the intake
  manifold

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Firing Order

• Refers to the sequence in which the cylinders
  fire
• Determined by the position of the crankshaft rod
  journals in relation to each other
• May be cast into the intake manifold
• Service manual illustrations are usually provided
  to show the firing order

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Cylinder Numbering and Firing Order
13
Cooling System Type

• There are two types of cooling systems
• Liquid cooling system
• surrounds the cylinder with coolant
• coolant carries combustion heat out of the
  cylinder head and engine block
• Air cooling system
• circulates air over cooling fins on the cylinders
• air removes heat from the cylinders

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Cooling System Type

• A. Air cooling
• B. Liquid cooling

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Fuel Type

• Engines are classified by the type of fuel used
• Gasoline engines burn gasoline
• Diesel engines burn diesel fuel
• Liquefied petroleum gas (LPG), alcohol (10
  alcohol, 90 gasoline), and pure alcohol can also
  be used to power an engine

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Ignition Type

• Two basic methods are used to ignite the fuel in
  an engine combustion chamber
• spark ignition (spark plug)
• compression ignition (compressed air)

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Spark Ignition Engine

• Uses an electric arc at the spark plug to ignite
  the fuel

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Compression Ignition Engine

• Squeezes the air in the combustion chamber until
  it is hot enough to ignite the fuel

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Valve Location

• Engines are classified by the location of the
  valves
• L-head engine
• also called a flat head engine
• I-head engine
• also called an overhead valve (OHV) engine

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L-head Engine

• Both the intake and exhaust valves are in the
  block

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I-head Engine

• Both valves are in the cylinder head

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Camshaft Location

• There are two basic locations for the engine
  camshaft
• Camshaft located in the block
• cam-in-block engine
• Camshaft located in the cylinder head
• overhead cam (OHC) engine

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Cam-in-block Engine

• Uses push rods to transfer motion to the rocker
  arms and valves
• Also called an overhead valve (OHV) engine

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Overhead Cam Engine

• Camshaft is located in the top of the cylinder
  head

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Overhead Cam Engine

• OHC engines may use one or two camshafts
• Single overhead cam (SOHC) engine
• uses only one camshaft per cylinder head
• Double overhead cam (DOHC) engine
• uses two camshafts per cylinder head
• one cam operates the intake valves, while the
  other cam operates the exhaust valves

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Combustion Chamber Shape

• Three basic combustion chamber shapes are used in
  most automotive engines
• pancake
• wedge
• hemispherical

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Pancake Combustion Chamber

• Valve heads are almost parallel to the top of the
  piston. Chamber forms a flat pocket over the
  piston head

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Wedge Combustion Chamber

• Valves are placed side-by-side
• Spark plug is located next to the valves
• When the piston reaches TDC, the squish area
  formed on the thin side of the chamber squirts
  the air-fuel mixture out into the main part of
  the chamber

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Wedge Combustion Chamber

• Provides good air-fuel mixing at low engine speeds

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Hemispherical Combustion Chamber

• Shaped like a dome
• Valves are canted on each side
• Spark plug is located near the center, producing
  a very short flame path for combustion
• Surface area is very small, reducing heat loss

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Hemispherical Combustion Chamber

• First used in high-horsepower racing engines.
  Excellent design for high-rpm use

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Combustion Chamber Types

• There are several less common combustion chamber
  classifications
• Each type is designed to increase combustion
  efficiency, gas mileage, and power while reducing
  exhaust emissions

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Swirl Combustion Chamber

• Causes the air-fuel mixture to swirl as it enters
  the chamber, improving combustion

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Four-valve Combustion Chamber

• Uses two exhaust valves and two intake valves to
  increase flow

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Three-valve Combustion Chamber

• Uses two intake valves and one exhaust valve
• Two intake valves allow ample airflow into the
  combustion chamber on the intake stroke
• Single exhaust valve provides enough surface area
  to handle exhaust flow

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Stratified Charge Combustion Chamber

• Uses a small combustion chamber flame to ignite
  and burn the fuel in the main, large chamber
• Lean mixture is admitted into the main chamber
• Richer mixture is admitted into the small chamber
  by an extra valve

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Stratified Charge Combustion Chamber

• When the mixture in the small chamber is ignited,
  flames blow into the main chamber and ignite the
  lean mixture
• Allows the engine to operate on a lean,
  high-efficiency air-fuel ratio
• fuel economy is increased

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Air Jet Combustion Chamber

• Has a single combustion chamber fitted with an
  extra air valve, called a jet valve
• Jet valve injects a stream of air into the
  combustion chamber at idle to improve fuel mixing
  and combustion
• At higher rpm, normal air-fuel mixing is adequate
  for efficient combustion

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Air Jet Combustion Chamber
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Precombustion Chamber

• Commonly used in automotive diesel engines
• Used to quiet engine operation and to allow the
  use of a glow plug to aid cold weather starting
• During combustion, fuel is injected into the
  prechamber, where ignition begins
• As it burns, the flame expands and moves into the
  main chamber

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Precombustion Chamber
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Alternative Engines

• Vehicles generally use internal combustion,
  4-stroke cycle, reciprocating piston engines
• Alternative engines include all other engine
  types that may be used to power a vehicle

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Rotary Engine

• Uses a triangular rotor instead of pistons
• Rotor orbits a mainshaft inside a specially
  shaped chamber
• This eliminates the reciprocating motion found in
  piston engines

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Rotary Engine
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Rotary Engine Operation

• Three complete power-producing cycles take place
  during every revolution of the rotor
• three rotor faces produce three intake,
  compression, power, and exhaust events per
  revolution

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Rotary Engine Operation

• Rotor movement produces a low-pressure area,
  pulling the air-fuel mixture into the engine
• As the rotor turns, the mixture is compressed and
  ignited
• As the fuel burns, it expands and pushes on the
  rotor
• Rotor continues to turn, and burned gases are
  pushed out of the engine

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Rotary Engine Operation
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Steam Engine

• Heats water to produce steam
• Steam pressure operates the engine pistons
• Known as an external combustion engine since its
  fuel is burned outside the engine

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Steam Engine

• Used on some of the first automobiles

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Gas Turbine

• Uses burning and expanding fuel vapor to spin
  fan-type blades
• Blades are connected to a shaft that can be used
  for power output
• Expensive to manufacture because of special
  metals, ceramics, and precision machining required

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Gas Turbine
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Two-stroke-cycle Engine

• Not used for automotive applications because of
  high emission levels and poor fuel efficiency
• Requires only one revolution of the crankshaft
  for a complete power-producing cycle
• Two piston strokes complete the intake,
  compression, power, and exhaust events

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Engine Operation

• Piston moves upward
• Air-fuel mixture is compressed
• Vacuum is created in the crankcase which draws
  fuel and oil into the crankcase
• Reed valve or rotary valve controls flow into the
  crankcase

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Engine Operation
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Engine Operation

• Piston reaches the top of the cylinder
• Ignition occurs
• Burning gases force the piston downward
• Reed valve or rotary valve closes, compressing
  and pressurizing the fuel mixture in the crankcase

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Engine Operation

• Piston moves down in the cylinder, uncovering the
  exhaust port
• Burned gases leave the cylinder
• Piston continues downward, uncovering the
  transfer port
• Pressure in the crankcase causes a fresh fuel
  charge to flow through the transfer port and into
  the cylinder

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Engine Operation
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Engine Lubrication

• Crankcase is used as a storage chamber for each
  successive fuel charge
• Lubricating oil is introduced into the crankcase
  along with the air-fuel charge to provide
  lubrication
• Oil mist lubricates and protects the moving parts
  inside the engine

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Miller-Cycle Engine

• Uses a modified four-stroke cycle
• Designed with a shorter compression stroke and a
  longer power stroke to increase efficiency
• Intake valve remains open longer to delay
  compression

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Miller-Cycle Engine
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Miller-Cycle Operation

• Piston slides down the bore with the intake valve
  open

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Miller-Cycle Operation

• Intake valve remains open as the piston starts up
  the bore. Supercharger pressurizes the intake to
  prevent back flow

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Miller-Cycle Operation

• Intake valve closes and compression occurs

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Miller-Cycle Operation

• Power stroke occurs

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Miller-Cycle Operation

• Exhaust stroke occurs

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Typical Automotive Engines
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Horizontally Opposed

• Provides the lowest center of gravity of any
  piston engine

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Overhead Cam V-8

• Features four chain-driven camshaftsand 32 valves

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Inline SOHC

• 16 valve, four cylinder engine with a belt driven
  camshaft and balance shaft

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Fuel-injected V-8

• This engine uses many aluminum parts

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Inline OHC

• This engine develops tremendous power for its
  small size

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DOHC V-8

• Starting motor is located in the center valley of
  the engine

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DOHC V-6

• Each cylinder head contains two camshafts

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V-8 Engine

• Note the reciprocating assemblyand the valve
  train

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Inline Diesel

• Six-cylinder engine with a rear drive belt for
  the injection pump

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Fuel-injected V-6

• This engine has a distributorlessignition system

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V-12 Engine

• Two roller chains drive theoverhead camshafts