Ignition coil

An ignition coil is used in the ignition system of a spark-ignition engine to transform the battery voltage to the much higher voltages required to operate the spark plug(s). The spark plugs then use this burst of high-voltage electricity to ignite the air-fuel mixture. The ignition coil is constructed of two sets of coils wound around an iron core. Older engines often use a single ignition coil which has its output directed to each cylinder by a distributor, a design which is still used by various small engines (such as lawnmower engines). Modern car engines often use a distributorless system (such as coil-on-plug), whereby every cylinder has its own ignition coil. Diesel engines use compression ignition and therefore do not have ignition coils. An ignition coil consists of an iron core surrounded by two coils (windings) made from copper wire. The primary winding has relatively few turns of heavy wire, while the secondary winding consists of thousands of turns of smaller wire and is insulated from the high voltage by enamel on the wires and layers of oiled paper insulation. When the electrical circuit connected from the power source (e.g. the car's battery) to the primary winding is closed (by a contact breaker or transistor), current flows through the primary winding, which produces a magnetic field around the core. This current flow lasts for a period of time to build up energy in the coil. Once the coil is charged, the circuit is opened, and the resulting oscillation in the magnetic field induces a high voltage in the secondary winding. This high-voltage electricity travels through several components (such as a distributor and spark plug wires), before reaching the spark plug, where it is used to ignite the air/fuel mixture. The timing of the circuit opening must be coordinated with the rotation of the engine, so that the burst of high-voltage electricity is produced at the optimal time to ignite the air/fuel mixture.