© Goodheart-Willcox Co., Inc....© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Even though basic parts are the same, design differences can

Engine classifications

Alternative engines

Typical automotive engines

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

W-type

opposed

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

A. Air cooling

B. Liquid cooling

Cooling System Type

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

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 chamber

this 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

© Goodheart-Willcox Co., Inc....© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only Even though basic parts are the same, design differences can

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