Transcript Ignition system

Ignition system

An ignition system is a system for igniting
a fuel-air mixture. Ignition systems are
well known in the field of internal
combustion engines such as those used in
petrol (gasoline) engines used to power
the majority of motor vehicles.
Functions of ignition system
•Provides a method of turning a spark ignition engine
on & off.
•Operates on various supply voltages (Battery &
Alternator)
•Produces high voltage arcs at the spark plug
electrode.
•Distributes spark to each plug in correct sequence.
•Times the spark so that it occurs as the piston nears
the TDC on the
compression stroke.
•Varies the ignition timing as engine speed, load and
other conditions
change.
Requirements
•To make a spark inside the engines cylinders which is
strong enough to ignite the air/fuel mixture. In normal
atmospheric conditions only about 600 Volts are
needed to make a spark, however in the pressurised
environment of the engines cylinders, 8000 to 30,000
volts will be required.
•To ensure the spark happens at the right time for
each cylinder going through the 4 Stroke Cycle i.e. just
at the end of the compression stroke. The ignition
system also has to change the time at which the spark
occurs (the ignition timing) depending on engine
operating conditions e.g. how fast the engine is turning.
Factors consider for design
ignition system
Combustion chamber design
Air-fuel ratio
Engine speed range
Engine load
Engine combustion temperature
Emission regulation

Types of ignition system
 Mechanical
ignition system
 Electronic ignition system
 Distributor-less ignition system
Ignition Parts System
BATTERY provides power for system.
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.
SWITCHING DEVICE mechanical or electronic switch that operates
Ignition coil(Pick-up coil, Crank sensor, Cam sensor).
SPARK PLUG uses high voltage from ignition coil to produce an arc
in the combustion chamber.
IGNITION SYSTEM WIRES connect components.
Ignition Circuits
PRIMARY CIRCUIT
•Includes all the components
working on low voltage
(Battery, Alternator).
SECONDARY CIRCUIT
•Consists of wires and points
between coil out-put and the
spark plug ground.
Ignition Coil
Primary Windings are made up of several
hundred turns of heavy wire wrapped around
or near the secondary windings.
Secondary Windings consist of several thousand
turns of very fine wire, located inside or near
the secondary windings.
Distributor
•Actuates the on/off cycle of current flow through the ignition coil
primary windings.
•It distributes the coils high voltage to the plugs wires.
Distributor
•It causes the spark to occur at each plug earlier in the compression
stroke as engine speed increases, and vice versa.
•Changes spark timing.
•Some distributor shafts operate the oil pump.
Advantages of electronic ignition system
Moving parts are absent so no maintenance are required.
• Contact breaker point are absent so no arcing.
• Spark plug life increase by 50% & they can be use above
60000km without any problem.
• More power output.
• More fuel efficiency.
• Better combustion in combustion chamber about 90
to95% of air-fuel mixture. Is burn compared with 70-75%
with conventional
•
Types of Electronic Ignition System
 Capacitive
discharge ignition system
 Transistorized system
 Piezo –electric ignition system
 Texaco ignition system
Capacitive discharge ignition system
Capacitor discharge ignition (CDI) or thyristor
ignition is a type of automotive electronic ignition
system which is widely used in outboard motors,
motorcycles, lawn mowers, chainsaws, small engines,
turbine-powered aircraft, and some cars.
 It was originally developed to overcome the long
charging times associated with high inductance coils
used in inductive discharge ignition (IDI) systems,
making the ignition system more suitable for high
engine speeds (for small engines, racing engines and
rotary engines). The capacitive-discharge ignition uses
capacitor discharge current output to fire the spark
plugs.

Basic principle


Most ignition systems used in cars are inductive
discharge ignition (IDI) systems, which are solely relying
on the electric inductance at the coil to produce highvoltage electricity to the spark plugs as the magnetic
field collapses when the current to the primary coil
winding is disconnected (disruptive discharge).
In a CDI system, a charging circuit charges a high
voltage capacitor, and at the instant of ignition the
system stops charging the capacitor, allowing the
capacitor to discharge its output to the ignition coil
before reaching the spark plug.
Capacitive discharge ignition system
Advantage and disadvantage
•A CDI system has a short charging time, a fast voltage
rise (between 3 ~ 10 kV/μs) compared to typical
inductive systems (300 ~ 500 V/μs) and a short spark
duration limited to about 50-80 µs.
•The fast voltage rise makes CDI systems insensitive to
shunt resistance, but the limited spark duration can for
some applications be too short to provide reliable
ignition.
•The insensitivity to shunt resistance and the ability to
fire multiple sparks can provide improved cold starting
ability.
•
•
•
Since the CDI system only provides a short
spark, it's also possible to combine this
ignition system with ionization measurement.
This is done by connecting a low voltage
(about 80 V) to the spark plug, except when
fired.
The current flow over the spark plug can then
be used to calculate the temperature and
pressure inside the cylinder.
Piezo-electric ignition system
APPLICATION :
 Camping stoves
 Gas grills
 Lighters
 Potato guns
•It consist small spring loaded hammer when a
button is pressed , hit a quartz crystal
This sudden deformation produce a high voltage
& subsequence electrical discharge when ignite
the gas.
No external electric connection is required .
Sometimes wire are used to locate the sparking
location away from the crystal.
•Piezo-ignition system can be operated by lever
push button , only one electric spark generated
when pressed the button.
The development of synthetic piezo electric
material produce in above 22kW by mechanical
loading of a small crystal resulted in some
ignition system for single cylinder engine , but
due to difficulties of high mechanical loading
timely control & ability to produce sufficient
voltage.
Transistorized system
Emitter
Collector
Base
Block diagram
The electronic ignition system employed a
solid state electronic device made for semi
conductor transistor & thyristor are such
type of device that are
without opening & closing the contact . The
tiny size behaves as a relay and can operates
as a switch also at speed must higher than
those required.
 Transistor is a two junction construction &
thyristor is a three junction construction.

Both are made for N – type and P – type
semi conductor.
 In N-type the conductor take place through
electrons and P-type in hole which are the
vacuum size of the electron.
 They are basically made from silicon ,
germanium elements . After that doping with
aluminum , antimony , phosphorus , indium
etc.

The Texaco Ignition System
•The Texaco Ignition System (TTIS) is a high frequency system
with a bi-directional spark current, the duration of which is a
function of crankshaft rotation rather than time. The spark
current characteristics differ drastically from those of
conventional discharge systems and, as a result, current flow
through the plug gap can be maintained under extremely
turbulent conditions.
•Being essentially a constant current device, it prevents
excessive plug current flow during initial gap ionization,
providing a good plug life; yet it has high average current to
increase fuel ignition probability.
•TTIS is of solid state design, and both the spark timing and
spark duration are controlled by use of digital logic circuitry.