Engine Fundamentals

Engine Classification

Lesson 9

March 2008

Engine Classification

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

Internal Combustion Engines

An engine, such as a gasoline or diesel engine, in which fuel is burned inside the engine

Designed to be run on any fuel that vaporizes easily or on any flammable gas

External Combustion Engines

An engine, such as a steam engine, in which fuel is burned outside the engine

Fuel is burned to produce heat to make steam

Fuel burning can take place within a few feet of the engine to several miles away

Diagram External Combustion

Engine Classification

Cylinder arrangement

Number of cylinders

Cooling system type

Valve location

Camshaft location

Engine Classification cont.

Combustion chamber design

Type of fuel burned

Type of ignition

Number of strokes per cycle

Number of valves per cylinder

Type of aspiration

# 1 Cylinder Arrangement

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

YouTube - engine configurations

Horizontally Opposed

Pancake Boxer

In - Line

V configuration

# 2 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

Numbering of Cylinders

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

# 3 Firing Orders

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

Numbering and Firing Order

# 4 Method of Cooling

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

# 5 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

Aspiration (how does air arrive)

Normal aspiration – atmospheric pressure

Forced induction (Turbo or Supercharger)

# 6 Method of Ignition

Two basic methods are used to ignite the fuel in an engine combustion chamber:

spark ignition (spark plug)

compression ignition (compressed air)

Spark Ignition

Compression Ignition

# 7 Valve Location

Engines are classified by the location of the valves:

L-head engine

also called a flat head engine

F-head engine

Compromise between I & L head engines

I-head engine

Both overhead valve (OHV) engines and overhead com (OHC) are I-head

‘I’ and ‘L’ Head

Both valves are in the cylinder head

Both the intake and exhaust valves are in the block

Flathead-Model T

F Head (1971 Jeep)

# 8 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 (OHV)

Uses push rods to transfer motion to the rocker arms and valves

Also called an overhead valve (OHV) engine

Diagram of OHV

Note the adjustment screw on the end of the rocker arm. Not all rocker arms have this adjustment. Check the shop manual for adjustment procedures.

Cam in Head

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

Diagram of OHC

Notice that the pushrod and rocker arm havebeen eliminated in this OHC engine. Less moving parts in the transmission of camshaft motion to open the valve.This not only reduces friction points and weight but also less points for wear and component breakage.

NOTE-not all OHC have eliminated the rocker arms.(See next slide)

Diagram of OHC with Rockers

Diagram of DOHC

# 9 Combustion Chamber Design

Four basic combustion chamber shapes are used in most automotive engines:

pancake

wedge

Hemispherical (hemi)

pent-roof

Pancake

Chamber forms a flat pocket over the piston head

Valve heads are almost parallel to the top of the piston

Wedge

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

Hemispherical (Hemi)

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

Pent Roof

Similar to a hemispherical chamber

Has flat, angled surfaces rather than a domed surface

Improves volumetric efficiency and reduces emissions

Pent Roof Combustion Chamber

Uses two exhaust valves and two intake valves to increase flow

Additional Combustion Chamber Designs

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

Swirl