Ignition System
The spark ignition engines require some device to ignite the compressed air-fuel mixture inside the cylinder at the end of the compression stroke. The ignition system serves this purpose. It is a part of the electrical system that carries the electrical current to the spark plug which gives a spark to ignite the air-fuel mixture at the correct time.
This ignition system consists of a battery, switch, distributor, coil, spark plugs, and necessary wiring. Some system uses transistors to reduce the load on the distributor contact points. Other systems use a combination of transistors and a magnetic pick-up in the distributor.
Compression ignition engines do not have such ignition systems. In a compression ignition engine, only air is compressed in the cylinder, and at the end of the compression stroke, the fuel is injected which catches fire due to the high temperature and pressure of the compressed air.
Requirements of an Ignition System
The ignition system supplies high-voltage surges of current to the spark plug. These surges produce electrical sparks at the spark plug gap that ignite or set fire to the compressed air fuel in the combustion chamber. The sparking must take place at the correct time at the end of the compression stroke in every cycle of operation.
At high speed or during part throttle operation, the spark is advanced so that it occurs somewhere earlier in the cycle, the mixture thus has sufficient time to burn and deliver its power. The ignition system should function efficiently at the maximum and minimum speeds of the engine. It should be easy to maintain, light and compact. It should not cause any interference.
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To perform effectively, an ignition system must meet several key requirements:
1. Spark Generation
The primary function of an ignition system is to generate a high-energy spark through the wirings. This spark should be powerful enough to ignite the mixture reliably.
2. Timing Control
The ignition system must be capable of precisely controlling the timing of the spark plug's firing. Timing is critical for efficient engine operation, as it ensures that ignition occurs at the optimal moment in the engine's four-stroke cycle.
3. Voltage Regulation
The spark plug needs a perfect and continuous voltage to spark the fresh charge. Voltage regulation is necessary to prevent under- or over-firing of the spark plug.
4. Durability and Heat Resistance
Since the ignition system operates in a high-temperature environment within the engine bay, its components must be durable and heat-resistant to withstand these conditions over an extended period.
5. Compatibility with Fuel Types
The ignition system should be compatible with the type of fuel used in the engine, whether it's gasoline, diesel, natural gas, or another fuel source. Different fuels may require variations in spark plug design and ignition system components.
These are the requirements for a better ignition system.
Types of Ignition Systems
There are two types of ignition systems used in petrol engines-
- Battery Ignition System.
- Magneto Ignition System.
Both ignition systems are based on the principle of mutual electromagnetic induction. The battery ignition system is mostly used in passenger cars and light trucks. In the battery ignition system, the current in the primary winding is supplied by the battery, whereas in the magneto ignition system, the magneto produces and supplies the current in the primary winding. Let's discuss the both of these ignition systems-
Battery Ignition System
This is a battery ignition system diagram. It consists of a battery, armature, switch, ignition coil, condenser, contact breaker, distributor, and spark plug.
The primary ignition circuit starts at the battery and passes through the switch, ammeter primary winding, and contact breaker points to the ground. A condenser is also connected in parallel to the contact breaker points. One end of the condenser is connected to the contact breaker arm and the other end is grounded.
The secondary ignition circuit is not connected electrically to the primary ignition circuit. It starts from the ground and passes through the secondary winding, distributors, and spark plug to the ground.
How does the Battery Ignition System Work?
The ignition coil steps up 6 or 12 volts from the battery to the high tension voltage of about 20,000 to 30,000 volts required to jump at the spark plug gap, which ignites to combustible charge in the cylinder. The rotor of the distributor revolves and distributes the current to the four segments which in turn, send it to the spark plugs. The purpose of the condenser is to reduce arcing at the breaker points and thereby prolong their life. Because the ignition system is of four-cylinder engine, the cam of the contact breaker has four lobes. It makes and breaks the contact of the primary circuit four times in every revolution of the cam.
When the ignition switch is on, the current will flow from the battery through the primary winding. It produces a magnetic field in the coil. When the contact points open, the magnetic field collapses and the movement of the magnetic field induces current in the secondary winding coil. Because the secondary winding has many more turns of fine wire, the voltage increases up to 30,000 volts. The primary winding consists of 200-300 turns of thick wire. About 15,000 volts are necessary to make the spark jump at a 1 mm gap. The distributor then directs this high-voltage to the proper spark plug when it jumps the gap, producing a spark that ignites the combustible mixture in the cylinder.
Magneto Ignition System
This diagram shows the magneto ignition system of a four-cylinder engine. It consists of a magneto, instead of a battery, which produces and supplies current in the primary winding. The remaining arrangement in this system is the same as that in the battery ignition system. This Magneto consists of a fixed armature having primary and secondary windings and a rotating magnetic assembly that is driven by the engine. When the magnets rotate, current flows in the primary winding. The secondary winding gives high voltage current to the distributor, which distributes it to the respective spark plug.
In a Magento, the magnetic field is produced by means of permanent agents whereas in a conventional generator, the magnetic field is produced by passing some of the generated current through the field winding which produces the magnetic field.
The magneto may be either a rotating armature type or a rotating magnet type. In a rotating armature-type magneto, the armature carries the primary and secondary windings and the condenser rotates between the poles of a stationary horseshoe magnet.
| Sl. No. | Battery Ignition System. | Magneto Ignition System. |
|---|---|---|
| 1 | Current is obtained in the battery. | Current is generated by the Magento. |
| 2 | A spark plug is good even at low speed. | Poor sparking at low speed. |
| 3 | Starting of engine is easier. | Difficult starting. |
| 4 | If the battery is discharged, the engine can not be started. | Not much difficulty as a battery is not needed. |
| 5 | Occupies more space. | Occupies less space. |
| 6 | Complicated wiring. | Simple wiring, |
| 7 | Less costly. | More costly. |
| 8 | Spark intensity falls as the engine speed rises. | Spark intensity improves as the engine speed rises. |
| 9 | Used in cars, buses, and trucks. | Used in motorcycles, scooters, racing cars |
Conclusion
The ignition system is important to spark the fresh charge and start the engine. The SI engine ignition system is of two types and the battery ignition system is mostly used in many vehicles.
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