In this article, we discuss the coil ignition system in detail.
In this article:
What Is Coil Ignition System?
The coil ignition system is a method used in spark-ignition engines (typically petrol or gasoline engines) to generate a high voltage spark across the spark plug gap. This spark ignites the air-fuel mixture in the engine’s combustion chamber.
Main Components
Battery:
Provides low voltage (typically 12 volts) for the ignition system.
Ignition Coil:
Transforms low voltage into high voltage (up to 20,000–30,000 volts or even higher) needed to produce a spark.
Consists of two windings —
- Primary Coil: Few turns of thick wire.
- Secondary Coil: Large number of turns of fine wire.
Distributor:
Distributes high voltage to the correct spark plug in each cylinder in the proper firing order.
Usually includes rotor and distributor cap.
Contact Breaker (Breaker Points) or Transistor/Switch:
Controls when the current to the primary coil is interrupted — this “break” generates the high voltage pulse in the secondary side.
Condenser (Capacitor):
Absorbs excess current and prevents points from arcing.
Provides faster collapse of the magnetic field for a greater spark.
Spark Plugs:
Transforms high voltage into a spark to ignite the air-fuel mixture in the cylinder.
Working Principle:
- Primary Current Flow:
When the points are closed, current flows from the battery through the primary winding of the ignition coil.
This creates a strong magnetic field. - Opening of Contact Breaker:
When the points break (open), the current flow drops suddenly.
This collapses the magnetic field in the primary side of the coil. - Induced High Voltage:
This collapse induces a high voltage pulse in the secondary winding due to electromagnetic induction (Faradays’ Law).
This high voltage can range from 20,000 to 30,000 volts or more. - Distribution to Spark Plugs:
The high voltage pulse is routed through the distributor to the appropriate spark plug.
This generates a spark across its gap. - Ignition:
The spark ignites the air-fuel mixture in the cylinder, causing combustion.
Advantages
- Reliable and simple.
- Durable with proper maintenance.
- Easily adaptable to many engine designs.
- Less expensive than modern electronic systems.
Limitations
- Requires periodic maintenance (contact points, condenser, gap adjustment).
- Less accurate and less powerful at high rpm.
- Subject to wear over time — can cause weak sparks or misfiring.
- Less efficient than modern electronic ignition systems.
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