© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only
Engine classifications
Alternative engines
Typical automotive engines
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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
Type of aspiration
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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
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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
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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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A. Air cooling
B. Liquid cooling
Cooling System Type
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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),
gasohol (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 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
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Combustion Chamber Shape
Four basic combustion chamber
shapes are used in most automotive
engines:
pancake
wedge
hemispherical
pent-roof
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Pancake Combustion Chamber
Chamber forms a flat pocket over the piston head
Valve heads are almost parallel to the top of the piston
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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 chamber
this improves air-fuel mixing at low
engine speeds
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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
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
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Hemispherical Combustion Chamber
First used in high-horsepower racing engines
Excellent design for high-rpm use
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Pent-Roof Combustion Chamber
Similar to a hemispherical chamber
Has flat, angled surfaces rather than a
domed surface
Improves volumetric efficiency and
reduces emissions
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Pent-Roof Combustion Chamber
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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
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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
exhaust emissions are reduced
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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
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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 the fuel burns, the flame expands and moves into the main chamber
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Precombustion Chamber