In spark-ignition engines, a device is required to ignite the compressed air-fuel mixture at the end of the compression stroke. Ignition system fulfills this requirement. It is a part of the electrical system which carries the electric current at the required voltage to the spark plug which generates spark at the correct time. It consists of a battery, switch, distributor ignition coil, spark plugs, and necessary wiring.
A compression ignition engine, i.e. a diesel engine does not require any ignition system. Because self-ignition of the fuel-air mixture takes place when diesel is injected in the compressed air at high temperature at the end of the compression stroke.
TYPES OF IGNITION SYSTEMS
There are three types of ignition systems which are used in petrol engines.
(a) Battery ignition system or coil ignition system.
(b) Magneto ignition system.
(c) Electronic ignition system.
In the battery ignition system, the current in the primary winding is supplied by a battery whereas it is supplied by a magneto in the magneto ignition system.
The battery ignition system is used in cars and light trucks. Magneto ignition system is used in some scooters. Both the systems work on the principle of mutual electromagnetic induction.
Electronic ignition systems use solid-state devices such as transistors and capacitors.
Magneto-ignition System Diagram
In this case magneto will produce and supply the required current to the primary winding. In this case as shown, we can have rotating magneto with fixed coil or rotating coil with fixed magneto for producing and supplying current to the primary, the remaining arrangement is the same as that of a battery ignition system. The figure given on the next page shows the line diagram of the magneto ignition system. In the magneto ignition system a magneto is used to generate electric current for producing the spark. A high tension magneto generates a very high voltage needed for spark plug
Main components of the magneto ignition system:
b) Permanent magnet
d) Soft iron field
f) Primary and secondary winding
g) Breaker points
The armature consists of an iron core on which there are two sets of windings 1) Primary 2) Secondary
Working of Magneto Ignition System :
The armature is driven by the engine. As the armature rotates, primary windings cut the lines of force of the magnetic field and induced current flows in the primary circuit. As the primary current reaches its maximum value in each direction, the primary circuit is suddenly opened by a contact breaker, and the current collapses. This action induces a very high voltage in the secondary winding which causes a momentary spark to jump at the spark plug gap. A distributor is provided which carries current to the spark plug through high tension wires. The condenser is used to eliminate the arching at the breaker points and intensifying the current in the secondary circuit. For multi-cylinder engines, a distributor and a rotor are required to distribute the current to different spark plugs.
(a) Better reliability due to the absence of battery and low maintenance.
(b) Better suited for medium and high-speed engines.
(c) Modern magneto systems are more compact, therefore require less space.
(a) Adjustment of spark timings adversely affects the voltage.
(b) Burning of electrodes is possible at high engine speeds due to high voltage.
(c) Cost is more than that of magneto ignition systems.
Advantages and Disadvantages of Magneto System Over Battery Ignition System :
1. It is more reliable as compared to the coil ignition system because there is no maintenance problem in the magneto ignition system.
2. As the speed increases, the voltage in the primary winding also increases rapidly and the Intensity of spark is also higher and provides better combustion, as compared to the battery ignition system. Thereforemagneto ignition is very popularly used in racing cars.
3. It is used for medium to high speeds.
4. Space required is less as compared to the coil ignition system.
5. By providing suitable shunts on magneto, the danger of burning of the spark plug is minimized.
6. Very light in weight and compact in size.
7. Automatic time adjusting of ignition can be affected.
1. The initial cost is very high as compared to the coil ignition system.
2. To start with, 75 RPM is necessary.
3. For high power engines, some other devices are necessary to start an ignition.
Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.