All modern petrol engines depend on ignition coils to generate the high voltage needed to ignite the air-fuel mixture inside the cylinders. Although many professionals know what ignition coils do, few truly understand the science behind their function. Let’s explore how electromagnetic principles power this essential part of the ignition system.
A Brief History of the Ignition Coil
The concept behind ignition coils has remained largely unchanged since its introduction over 100 years ago, even as vehicle electronics have advanced significantly.
The first coil-based ignition system was developed by Charles Kettering around 1910–1911. His design powered both the starter motor and the ignition system using one electrical setup, including a battery, a generator, and other electrical components. This setup delivered a stable power source to the ignition coil.
This system used a single ignition coil that sent high voltage through a distributor to each spark plug in the correct firing order. Known as the Kettering system, it was the industry standard until electronic ignition began replacing mechanical systems in the 1970s and 1980s.
How an Ignition Coil Produces High Voltage
The principle behind ignition coils is electromagnetic induction. When electric current flows through a coiled wire, it creates a magnetic field around it. This field stores energy and releases it as electricity when the current is interrupted.
- The amount of current flowing through the coil
- The number of wire windings
Using Magnetic Fields to Induce Voltage
When a magnetic field moves or changes near a coil, it induces an electric current—a process called inductance. This can be demonstrated by moving a magnet across a coil of wire.
- Faster movement or change in the magnetic field
- More coil windings
Collapsing Magnetic Fields and Voltage Generation
When the current that created a magnetic field is shut off, the field collapses rapidly and induces a voltage in the wire. The faster the collapse, the higher the voltage produced.
Mutual Inductance and Transformer Action
If two coils are positioned close to each other, a magnetic field from the primary coil will surround the secondary coil. When the field collapses, it induces voltage in both coils—this is known as mutual inductance.
In ignition coils, the secondary winding contains far more turns than the primary winding—typically 15,000 to 30,000 turns compared to 150–300 turns. This large ratio allows a 12-volt battery input to be transformed into 20,000 volts or more.
The Role of the Iron Core
Both the primary and secondary windings are wrapped around an iron core, which concentrates the magnetic field. This increases efficiency and ensures a strong, consistent spark is delivered when needed.
Conclusion
Ignition coils are essential to engine performance, using basic electromagnetic laws to produce the high voltage required for combustion. Understanding how they work not only helps with maintenance and troubleshooting but also reveals the brilliance of their design.