Capacitor discharge ignition Capacitor discharge ignition Capacitor discharge ignition (CDI) or thyristor ignition is a type of automotive electronic ignition system which is widely used in outboard motors, motorcycles, lawn mowers, chainsaws, small engines, turbine-powered aircraft, and some cars. It was originally developed to overcome the long charging times associated with high inductance coils used in inductive discharge ignition (IDI) systems, making the ignition system more suitable for high engine speeds (for small engines, racing engines and rotary engines). The capacitive-discharge ignition uses capacitor discharge current to the coil to fire the spark plugs. The history of the capacitor discharge ignition system can
Ignition 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. In older vehicles, a single coil would serve all the spark plugs via the ignition distributor. Notable exceptions are the Saab 92, some Volkswagens, and the Wartburg 353 which have one ignition coil per cylinder. The flat twin cylinder 1948 Citroën 2CV used one double ended coil without a distributor, and just contact breakers, in a wasted spark system. In modern systems, the distributor is omitted and ignition is instead electronically