1. Battery ignition systems and magneto ignition systems are the two main types of ignition systems used in spark ignition engines. Battery ignition systems use a battery to provide electrical power to the primary coil, while magneto ignition systems generate their own electrical current using a magneto. 2. Key components of both systems include an ignition coil, distributor, contact breaker, and spark plugs. The ignition coil increases the voltage sent to the spark plugs, while the distributor and contact breaker control spark timing. 3. Battery ignition systems are more commonly used in cars and light commercial vehicles due to their ability to produce spark at low engine speeds, while magneto ignition systems are better suited for applications where high

1. IGNITION SYSTEMS IN SI ENGINES
Sreenidhi Institute of Science and Technology
Yamnampet, Ghatkesar, Hyderabad, Telangana 501301

2. The compression ratio of petrol engine is maintained
at lower level to avoid self-ignition of petrol during
the compression process.
FYI: The uncontrolled explosions of petrol vapour is
known as knocking.
Hence an ignition system is necessary for the petrol
engine.
Ignition Systems in SI Engines

3. A smooth and reliable functioning of an ignition
system is essential for reliable working of an engine.
The requirements of such an ignition system are:
1. It should provide a good spark between the
electrodes of the plugs at the correct timing.
2. should function efficiently over the entire range of
engine speed.
3. It should be light, effective and reliable in service.
4.It should be compact and easy to maintain.
5.It should be cheap and convenient to handle.
6.The interference from the high voltage source
should not affect the functioning of the radio and
television receivers inside all automobile.

4. Battery Ignition System Magneto Ignition System

8. Battery Ignition System Components

11. Battery Ignition System Components
BATTERY provides power for system. i.e. electrical
energy for ignition
(Lead Acid for light duty & Alkaline for heavy-duty ).
IGNITION SWITCH allows driver to turn ignition on and off.
IGNITION COIL changes battery voltage to 30,000V during
normal operation and has a potential to produce up to 60,000V.
BALLAST RESISTOR is provided in series with the primary
windings to regulate the primary current.

12. Ignition Parts
SPARK PLUG uses high voltage from ignition coil to
produce an arc in the combustion chamber.
IGNITION SYSTEM WIRES connect components.
DISTRIBUTOR The function of the distributor is to
distribute the ignition surges to the individual spark plugs
in the correct sequence.
CONTACT BRAKER is a mechanical device for making & braking
the primary circuit of ignition coil.

13. Battery Ignition System:
• The battery ignition system is commonly
employed system in spark ignition engines.
• Battery is the source of current and it is
connected to the primary coil through a
starting switch.
• The other end of the primary coil is
connected to a condenser and a contact
breaker.
Ignition Systems in SI Engines

14. • The secondary coil is connected to a distributor in
the case of a multi-cylinder engine.
• The primary coil will have 100 – 200 turns
• The secondary coil will have usually 10,000 turns.
• Both the windings are mounted on a soft-iron core.
• The starting switch connects the primary coil to
the battery and current flows through it, setting up
a magnetic field.

15. • When the primary coil is switched off, the magnetic field
collapses and induces an emf in the secondary coil.
• The e.m.f. in the secondary coil will be greater if the collapse
of the magnetic field is rapid in the primary coil.
• A condenser connected in the primary ckt does this function
• The distributor and the contact breaker are connected to a
single cam shaft.
• The cam shaft rotates at half the crank shaft speed in the case
of four-stroke IC engines.

17. Distributor: This connects the secondary to each
cylinder at the time of ignition in a multi-cylinder engine.
Contact-breaker: This also works simultaneously with
the distributor to disconnect the primary circuit at the
time when ignition is required.
Spark Plug: When a very high voltage is applied across
the electrodes of the spark plug, a spark is produced,
which induces the combustion process.
Ignition Systems in SI Engines

22. An Electronic circuit breaker is used in place of the
mechanical circuit breaker.
The remaining components are the same as in
battery ignition system.
B. Magneto Ignition System:
The magneto coil ignition system is shown in
Fig. 3.23
The functioning of Magneto ignition system is
similar to Battery ignition system.
The only difference is that the magneto coil
replaces a battery to produce the initial voltage
required by the system.
C. Electronic Ignition system:

23. High Tension Magneto Ignition System

25. Comparison between
Battery Ignition and Magneto Ignition System
S.No Battery Ignition System Magneto Ignition System
1 Battery is necessary.
Difficult to start when
battery is discharged.
No battery is needed. No
problem of battery
discharge.
2 Maintenance problems
are more due to battery.
Maintenance problems are
less as there is no to
battery.
3 Current for the primary
circuit is obtained fro the
battery.
The required electric
current is generated by
the magneto.

26. Comparison between
Battery Ignition and Magneto Ignition System contd.
S.No. Battery Ignition System Magneto Ignition System
4. A good spark is available
at the spark plug even at
low speed.
During starting, quality
of spark is poor due to
low speed.
5. Efficiency of the system
decreases with the
reduction in spark
intensity as engine speed
rises.
Efficiency of the system
improves as engine
speed rises due to high
intensity spark.
6. Occupies more space. Occupies less space.
7. Commonly employed in
cars and light commercial
vehicles.
Mainly used in racing
cars and two wheelers.