Engine Ignition

1
Engine Ignition

• An Overview
• of the
• Ignition Systems Utilized
• in the
• Early Internal Combustion
• Engines

2
Types

• Hot Tube Ignition
• Igniter (low tension) Ignition
• Spark Plug (high tension) Ignition

3
Hot Tube Ignition

• Simplified Overview
• Hot tube ignition was used on the oldest of the
  internal combustion engines. Usually rather
  large engines. No electricity or spark is
  needed.

Air / Fuel Mixture
Piston
Closed end tube
Chimney
Figure 1
Heat source
As the air/fuel mixture is compressed, a portion
of the compressed mixture is forced into the
heated closed end tube. When the temperature and
pressure within the tube reach the required
point, the mixture ignites and ignites the
mixture in the cylinder. (Figure 1) Think of a
deisel engine with a glow plug
4
Igniters

• An igniter is simply a set of contacts or
  points. It consists of one moveable and one
  fixed contact. The two contacts bodies are
  separated and insulated from each other by a mica
  tube and washer. (Figure 2)

Figure 2

• Igniters are used in low tension ignition
  systems, which include
• Battery and coil
• Low tension magneto

5
Battery and Low Tension Coil

• The battery and low tension coil ignition system
  consists of a battery, a single field inductive
  coil, the igniter and a switch.
• When the engine is not running, the switch should
  be open to prevent the flow of current through
  the coil. The igniter contacts may or may not
  open base on the cycle of the engine. ( Figure
  3A)
• Current passing through the coil for an extended
  period of time will cause the coil to heat up and
  possibly burn out the coil.

Before starting the engine, rotate the flywheels
until the igniter is in the open position.
Close the switch and start the engine. (Figure
3B)
Igniter
-

Battery
Switch
Coil
Figure 3B
6
As the engine passes through the compression
cycle, the engine mechanism closes the igniter
contacts just prior to the point of firing. This
causes the electrical circuit to close and
current to flow through the coil. The current
flowing through the coil establishes an
electrical magnetic field (EMF). (Figure 3C)

-
Igniter
-

Battery
Switch
Coil
Figure 3C
When the engine reaches the ignition cycle, the
igniter is released, the contacts snap open.
With the contacts open, current ceases to flow
through the coil. The established EMF collapses
onto the core with the reverse voltage. This
reverse voltage seeks the ground potential
through the gap of the igniter contacts causing a
spark. (Figure 3D)
-

Igniter
-

Battery
Switch
Coil
Figure 3D
7
From Fairbanks-Morse - Principles Of Magnetos If
a piece of steel is bent into a "U", to make the
ordinary "magnet," the space between the ends
will be filled with invisible magnetic "lines of
force." The magnetism will be stronger at this
point than anywhere else about the magnet. If a
coil of wire is moved in and out of the space
between the poles, or is revolved in this space,
an electric current will be generated in the
wire, and if the ends of same are separated, a
spark will be produced between them.
Figure 4
8
The MAGNETO is simply a magnet, with a coil of
wire revolving between its poles (Armature), the
coil being provided with a suitable means whereby
the current generated is conducted off to the
engine igniter, the points of which are
alternately opened and closed at the proper
time.A peculiar thing about the Magneto is that
the current generated in the wire is strongest at
only two points in each revolution of the wire,
and to get the best spark the igniter points in
the engine must snap when the wire is at one of
these points.
Figure 5
9
The more lines of force crossed by the armature,
the greater the force or current is generated.
10
TYPES OF LOW TENSION MAGNETOS
- OSCILLATING - CONTINUOUS ROTATION
11
OSCILLATING MAGNETO
.

Figure 6A
The magneto is usually attached directly to the
Igniter. The trip mechanism closes the igniter
points and pre-sets the magneto armature to the
optimum position. (Figure 6B)

Figure 6B
As the trip mechanism releases, the armature
(under spring tension) rotates through the
optimum lines of force. At the same time the
points open. The resulting halt in current flow
collapses the field and reverse current flow
causes the spark. (Figure 6C)
Figure 6C
12
CONTINUOUS ROTATION MAGNETO (Low Tension)
The continuous rotating magneto works like the
oscillating magneto. The armature rotating
through the magnet field while the points are
closed and opened at the proper time. The
magneto is usually located near and attached to
the drive mechanism or timing gear. The igniter
trip mechanism is a separate system. This
requires that the armature rotation must be in
time with the Igniter. (Timing marks, crank
location, etc.)
Note Many continuous rotation magnetos require
a significant rotation speed to generate
sufficient current to create a spark. Therefore,
many models require starting the engine with a
battery coil and then switch over to the
magneto. The Fuller and Johnson early engines
had a two-way switch attached for just that
purpose.
13
High Tension Ignition (Spark Plug)
Buzz coil High Tension Magneto
14
These are the basic components of a buzz coil
ignition
Figure 7
15
As the trip contact closes, the circuit through
the primary coil is complete and the current
begins to flow. The current establishes an
electrical field around the iron core causing it
to become an electro-magnet. The electro-magnet
pulls on one of the buzzing contacts. (Figure 8A)
Figure 8A
As the buzzing contacts separate, the current
flow through the primary coil will cease and
causing the field to collapse around the
secondary coil and cause the current to spark
across the spark plug gap. (Figure 8B)
Figure 8B
As the field collapses, the iron core will loose
its magnetism. The buzzing contact will return
to its normally closed position and start the
process over again The buzz coil will continue
to oscillate between these two states as long as
the trip contacts remain closed.
16
High Tension Magneto

• Single Trip
• Continuous Rotation

17
WICO EK
Figure 9
Figure 10
18
The Wico EK magneto consists of the following
components. (Figure 10)
Figure 10
Electrically, the magneto looks like the
following. (Figure 11)
Figure 11
19
Theory of Operation
When the magneto is in the normal state
(un-tripped), the keeper (armature) channels the
EMF through the ferris cores and the magnets are
in equalibrium. (Figure 12A)
Figure 12A
During the first part of the mechanical trip, the
keeper (armature) is disconnected from the ferris
cores and the EMF field is generated around the
coils. (Figure 12B)
Figure 12B
During the second part of the mechanical trip,
the points are opened and the field collapses
around the secondary coil and causes a spark.
(Figure 12C) After the trip, the armature is
returned to the normal state and the process
repeats with the next mechanical trip.
20
Continuous Rotation Magneto (High Tension)

• International Harvester H1
• Wico H

The continuous rotation high tension magneto
operates the same way as the single trip magneto
only in a continuous manner. This requires
timing to match up to the engine mechanics,
just as with the continuous rotation low tension
magnetos.
For more information check out http//www.old-eng
ine.com/magneto.htm