This document summarizes the key components of an ignition system used in petrol cars, including a spark plug, ignition coil, distributor, and distributor cap. It explains that the ignition coil transforms the low voltage from the battery to the high voltage needed for the spark plug to ignite the fuel mixture. The distributor then routes this high voltage to the correct spark plug at the proper time. Ignition timing, or when the spark plug fires in relation to the piston position, is also discussed, noting that it can be advanced or retarded based on engine speed and load. Vacuum advance is mentioned as one method to control ignition timing.

1. Presented by:
DEEPAK KUMAR
+91-8950783197

2. Introduction
•This system is powered by a lead-acid
battery to provide a constant source of
electricity, magneto systems were
abandoned for systems which interrupted
current at battery voltage, used an ignition
coil and a distributor to route the ensuing
pulse to the correct spark plug at the
correct time to start a engine use in Petrol
cars.

3. Ignition Circuit Diagram -
Mechanically Timed Ignition

4. Spark plug
 A spark plug is a device for delivering electric
current from an ignition system to the
combustion chamber of a spark-ignition
engine to ignite the compressed fuel/air
mixture therein by means of an electric spark,
while containing combustion pressure within
the engine. A spark plug has a metal threaded
shell,
 electrically isolated from a central electrode by
a porcelain insulator. The central electrode,
which may contain a resistor, is connected by a
heavily insulated wire to the output terminal
of an ignition coil or magneto. The spark
plug's metal shell is screwed into the engine's
cylinder head and thus electrically grounded.

5. Ignition coil An ignition coil (also called a spark coil) is
an induction coil in an automobile's
ignition system which transforms the
battery's low voltage to the thousands of
volts needed to create an electric spark in
the spark plugs to ignite the fuel. Some
coils have an internal resistor while others
rely on a resistor wire or an external
resistor to limit the current flowing into
the coil from the car's 12 volt supply. The
wire which goes from the ignition coil to
the distributor and the wires which go
from the distributor to each of the spark
plugs are called spark plug wires or high
tension leads.

6. Distributor
 A distributor is a
device in the ignition
system of an internal
combustion engine
that routes high
voltage from the
ignition coil to the
spark plugs in the
correct firing order.

7. Distributor Cap
•Insulated plastic cap
•Transfers voltage from coil (wire) to Rotor.

8. Ignition Timing
How early or late the spark plug fires in relation to the position of the
engine piston.
Ignition timing must change with the changes in engine speed, load,
and temperature.

9. Ignition Timing
Timing Advance occurs when the plug fires sooner on compression
stroke (High engine speed)
Timing Retard occurs when plug fires later on compression stroke
(Lower engine speed)
BASE TIMING Timing without vacuum or computer control.

10. Methods of controlling Timing
Vacuum Advance
•Controlled by engine intake manifold vacuum and engine load.
•The vacuum diaphragm rotates the pickup coil against the direction
of distributor shaft rotation.

11. THANKS