CHAPTER 2.ppt

 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

Common Engine Classifications
 Cylinder arrangement
 Number of cylinders
 Cooling system type
 Valve location
 Camshaft location

Common Engine
Classifications
 Combustion chamber design
 Type of fuel burned
 Type of ignition
 Number of strokes per cycle
 Number of valves per cylinder
 Type of aspiration

 Refers to the position of the cylinders in
relation to the crankshaft
 There are five basic cylinder arrangements:
 inline
 V-type
 slant
 W-type
 opposed
Cylinder Arrangement

Cylinder Arrangement

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

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

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

Cylinder Numbering and Firing Order

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

Cooling System Type
A. Air cooling
B. Liquid cooling

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

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

Spark Ignition Engine
Uses an electric arc
at the spark plug to
ignite the fuel

Compression Ignition Engine
Squeezes the air in the
combustion chamber
until it is hot enough to
ignite the fuel

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

L-Head Engine
Both the intake and
exhaust valves are in
the block

I-Head Engine
Both valves are in the
cylinder head

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

Cam-in-Block Engine
 Uses push rods to transfer motion to the
rocker arms and valves
 Also called an overhead valve (OHV) engine

Overhead Cam Engine
Camshaft is located in the
top of the cylinder head

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

Combustion Chamber Shape
 Four basic combustion chamber shapes are
used in most automotive engines:
 pancake
 wedge
 hemispherical
 pent-roof

Pancake Combustion Chamber
 Chamber forms a flat pocket over the piston head
 Valve heads are almost parallel to the top of the
piston

Wedge Combustion Chamber
 The valves are placed side-by-side
 The 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 chamberthis improves air-fuel mixing at
low engine speeds

Wedge Combustion Chamber
Provides good air-fuel mixing at low engine speeds

Hemispherical Combustion Chamber
 Shaped like a dome
 The valves are canted on each side of the
combustion chamber
 The spark plug is located near the center
of the chamber, producing a very short
flame path for combustion
 The surface area is very small, reducing
heat loss

Hemispherical Combustion Chamber
First used in high-horsepower racing engines
Excellent design for high-rpm use

Pent-Roof Combustion Chamber
 Similar to a hemispherical chamber
 Has flat, angled surfaces rather than a
domed surface
 Improves volumetric efficiency and
reduces emissions

Pent-Roof Combustion Chamber

Other Combustion Chamber Types
 In addition to the four shapes just covered, there are
several less common combustion chamber
classifications
 Each type is designed to increase combustion
efficiency, gas mileage, and power while reducing
exhaust emissions

Swirl Combustion Chamber
Causes the air-fuel
mixture to swirl as it
enters the chamber,
improving combustion

Four-Valve Combustion Chamber
Uses two exhaust valves and two intake valves to
increase flow

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

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

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
 exhaust emissions are reduced

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

Air Jet Combustion Chamber

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 the fuel burns, the flame expands and moves
into the main chamber

Precombustion Chamber

 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

Rotary Engine
 Uses a triangular rotor instead of pistons
 The rotor orbits a mainshaft while turning inside a
specially shaped chamber
 This eliminates the reciprocating motion found in
piston engines

Rotary Engine

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

 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
 The rotor continues to turn, and burned gases are
pushed out of the engine

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

Steam Engine
Used on some of the first automobiles

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

Gas Turbine

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

Operation
 As the piston moves upward, the air-fuel mixture is
compressed
 Vacuum is created in the crankcase, which draws fuel
and oil into the crankcase
 A reed valve or rotary valve controls flow into the
crankcase

Operation

Operation
 When the piston reaches the top of the cylinder,
ignition occurs
 Burning gases force the piston downward
 The reed valve or rotary valve closes, compressing
and pressurizing the fuel mixture in the crankcase

Operation
 As the piston moves down in the cylinder, it
uncovers the exhaust port
 Burned gases leave the cylinder
 The 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

Lubrication
 The 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
 Inside the crankcase, some of the oil separates from the
fuel
 The oil mist lubricates and protects the moving parts
inside the engine

Miller-Cycle Engine
 Uses a modified four-stroke cycle
 Designed with a shorter compression stroke and a
longer power stroke to increase efficiency
 The intake valve remains open longer to delay
compression

Miller-Cycle Engine

Miller-Cycle Operation
The piston slides down
the bore with the intake
valve open

The intake valve remains open as
the piston starts up the bore
The supercharger pressurizes the
intake to prevent backflow

The intake valve closes and
compression occurs

The power stroke occurs

The exhaust stroke
occurs

Horizontally Opposed
Provides the lowest center of gravity of any piston
engine

Overhead Cam V-8
Features four chain-driven camshafts
and 32 valves

Inline SOHC
This 16-valve, four-cylinder engine has a belt-driven
camshaft and a balance shaft

Fuel-Injected V-8
This engine uses many aluminum parts

DOHC V-6
Each cylinder head contains two camshafts

V-8 Engine
Note the reciprocating assembly
and the valve train

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

V-12 Engine
Two roller chains drive
the overhead camshafts

CHAPTER 2.ppt

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CHAPTER 2.ppt