Known for its incorporate electrical, mechanical and thermal isolation between the magnetic core, which is used for creating magnetic field, the pencil coil is one of the general categories of ignition coil. The engines generally use a mechanically times ignition system, and the key of this system is the distributor. Containing a rotating cam driven, a set of breaker points, a condenser and a distributor cap, the distributor is linked to the spark plugs and ignition coil with wires. And the pencil coil is inserted inside the spark plug insertion hole in the cylinder head.
Originally, every ignition coil system required mechanical contact breaker points, and a capacitor (condensor). More recent electronic ignition systems use a power transistor to provide pulses to the ignition coil. A modern passenger automobile may use one ignition coil for each engine cylinder (or pair of cylinders), eliminating a distributor to route the high voltage pulses.
Very early gasoline (petrol) internal combustion engines used a magneto ignition system, since no battery was fitted to the vehicle; magnetoes are still used in piston-engine aircraft. The voltage produced by a magneto is dependent on the speed of the engine, making starting difficult. A battery-operated coil can provide a high-voltage spark even at low speeds, making starting easier. When batteries became common in automobiles for cranking and lighting, the ignition coil system displaced magneto ignition.