This file contains Engine Ignition System.

1. BY
INDRANIL MANDAL
ASSISTANT PROFESSOR
DEPARTMENT-MECHANICAL ENGINEERING
IDEAL INSTITUTE OF ENGINEERING

2. INTRODUCTION
 In spark ignition engines, as compression ratio is lower, and the
self-ignition temperature of gasoline is higher, for igniting the
mixture for the initiation of combustion an ignition system is
must.
 The function of the ignition system is to initiate the flame
propagation process.
 It can be treated as a balance of energy between:
i. that provided by an external source
ii. that released by chemical reaction and
ii. that dissipated to the surroundings by means of thermal
conduction, convection and radiation.

3. IGNITION FUNCTION
Produces 30,000 volt spark across spark plug
Distributes high voltage spark to each spark plug
in correct sequence
Times the spark so it occurs as piston is nearing top
dead center
Varies spark timing with load, speed, and other
conditions

4. REQUIREMENTS OF AN IGNITION SYSTEM
 It should provide a good spark between electrodes of the
plugs at the correct timing.
 It should function efficiently over the entire range of
engine speed.
 It should be light, effective and reliable in service.
 It should be compact and easy to maintain.
 It should be cheap and convenient to handle.

5. BASIC IGNITION SYSTEM
Battery supplies power
to entire system
Ignition Switch
turns engine on or
off
Coil transforms volts
Switching device
triggers ignition coil
Spark Plug and
wires distribute
spark

6. IGNITION COIL
Transformer
2sets ofwindings
Primary windings
Secondary windings
Iron core
Produces magnetic
field

8. TYPES OF IGNITION SYSTEM
I. Battery ignition system
II. Magneto ignition system

9. BATTERY IGNITION SYSTEM
The function of this is to produce high voltage spark and
deliver it to the spark plugs at regular intervals and at the
correct time with respect to the crank position.

10. BATTERY IGNITION SYSTEM FOR MULTI CYLINDER ENGINES

11. MAIN COMPONENTS
 Battery of 6 to 12 volts
 Ignition switch
 Induction or ignition coil
 Contact breaker
 Condenser
 Distributor
 Spark-plugs

12.  To provide electrical energy for ignition, a storage battery is used.
 Two types of batteries are used for spark-ignition engines, the lead
acid battery and the alkaline battery. The former is used in light duty
commercial vehicles and the later on heavy duty commercial
vehicles.
 With the help of the ignition switch the ignition system can be
turned on or off.
 Ignition coil is the source of ignition energy in the conventional
ignition system. The coil stores the energy in its magnetic field and
delivers it at the appropriate time in the form of a ignition pulse
through the high tension ignition cables to the respective spark plug.
The purpose of this is to step up the 6 or 12 volts of the battery to a
high voltage, sufficient to induce an electric spark across the
electrodes of the spark plug.

13.  Contact breaker is a mechanical device for making and breaking
the primary circuit of the ignition coil. When the points are closed
the current flows and when they are open, the circuit is broken and
the flow of current stops.
 Condenser helps to collapse the magnetic field very rapidly by
absorbing part of the energy of the magnetic field which is thrown
back into the primary winding and produces a very high voltage in
the secondary.
 The function of the distributor is to distribute the ignition surges to
the individual spark plugs in the correct sequence and at the correct
instants in time.
 The spark plug provides the two electrodes with a proper gap across
which the high potential discharges to generate a spark and ignite the
combustible mixture within the combustion chamber.

14. DWELL ANGLE
 The dwell angle (or cam angle) is the angle moved by the
cam during the contact-closed period.

15.  Too small a dwell angle will result in lower secondary voltage and
hence poor sparks.
 Too large a dwell angle will lead to burning of condenser and the
contact points due to over-saturation of windings.
 I in milliseconds.
 The smaller the gap between the contact points when they are fully
open, the larger the dwell angle, and vice versa.

16. DRAWBACKS
 There are chances of discharging the battery.
 There are chances of misfiring at higher speed of the
engine.
 It requires complicated wiring.
 There are chances of failure.
 There are many mechanical complications in the operation
of the system.

17. MAGNETO IGNITION SYSTEM

19.  A magneto when rotated by the engine is capable of producing a very high
voltage and does not need a battery as a source of external energy. The high
tension magneto incorporates the windings to generate he primary voltage
as well as to step up the voltage and thus does not require a separate coil to
boost up the voltage required to operate the spark plug. Magnet revolves
and winding kept stationary.
 The variation of the breaker current with speed for the coil ignition system
and magneto ignition system in below fig. It can be seen that since the
cranking speed at start is low the current generated by the magneto is quite
small. As the engine speed increases the flow of current also increases.

20. ADVANTAGES OF MAGNETO IGNITION SYSTEM
 Since there is no battery or connecting table, the system is
more reliable.
 For medium and very high speed engines, the system is more
suitable.
 The space require is less, by using cobalt steel and nickel
aluminium magnet metals energy.
 This system in fairly reliable with resent development.

21.  At low speed and during cranking the voltage is very low.
Suitable modifications are necessary in the circuit to
overcome this.
 Adjustment of the spark timing has determined effect
upon the spark voltage or energy.
 The burning of the electrodes will result with powerful
sparks at high engine speeds.
 More costly.
 Starting is troublesome.
DISADVANTAGES OF MAGNETO IGNITION SYSTEM

22. COMPARISION

23. FIRING ORDER
 The order in which various cylinders of a multi-cylinder engine fire
is called as firing order.
 For four cylinder engines the possible firing orders are:
1-3-4-2 or 1-2-4-3
 For a six cylinder engine the firing orders can be :
1-5-3-6-2-4 or 1-5-4-6-2-3 or 1-2-4-6-5-3 or 1-2-3-6-5-4

24. IGNITION ADVANCE
 The angle of advance is the time in terms of crank angle provided to
burn the mixture inside the cylinder before starting the expansion.
This is the time required for the purpose of combustion as
combustion is not instant phenomenon. The combustion is a process
and the time taken for this process is independent of the speed of the
engine.
 It is always desirable that the maximum pressure of the mixture
should occur at TDC after combustion for the maximum power
developed by the engine.

25. ADVANCING MECHANISMS
 The point at which the rubbing block engages the cam has moved forward (spark occurs earlier).

26. VACUUM ADVANCE MECHANISM

27. IGNITION TIMING