The ignition system delivers voltage to ignite the fuel in the automotive vehicle. When the ignition switch is turned on, low-voltage electric current flows from the battery to the coil, which converts the current to high-voltage. The current then flows to the distributor, which delivers it to each of the spark plugs. The spark plugs send an igniting spark to the fuel/air mixture in the combustion chambers.
The ignition system supplies high-voltage current to spark plugs to ignite fuel vapor in the cylinders. There are many variations, but all gasoline-engine ignition systems draw electric current from the battery, significantly increase the currentís voltage, then deliver it to spark plugs that project into the combustion chambers. An electric arc between two electrodes at the bottom of the spark plug ignites the fuel vapor.
In older vehicles, a distributor, which is an electrical switching device, routes high-voltage current to the spark plugs. The distributorís housing contains a switch called the breaker points. A rotating shaft in the distributor causes the switch to open and close, interrupting the supply of low-voltage current to a transformer called a coil. The coil uses electromagnetic induction (see Electricity: Electromagnetism) to convert interruptions of the 12-volt current into surges of 20,000 volts or more. This high-voltage current passes back to the distributor, which mechanically routes it through wires to spark plugs, producing a spark that ignites the gas vapor in the cylinders. A condenser absorbs excess current and protects the breaker points from damage by the high-voltage surge. The distributor and other devices control the timing of the spark-plug discharges.
In modern ignition systems, the distributor, coil, points, and condenser have been replaced by solid-state electronics controlled by a computer. A computer controls the ignition system and adjusts it to provide maximum efficiency in a variety of driving conditions.