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
Capacitor discharge ignition were vulnerable to vibration which drastically shortened their lifetime. In an automotive application, the thyratron CD ignition would fail in either weeks or months. The unreliability of those early thyratron CD ignitions made them unsuitable for mass production despite providing short term benefits. One company at least, Tung-Sol (a manufacturer of vacuum tubes) marketed a thyratron CD ignition, model Tung-Sol EI-4 in 1962, but it was expensive. Despite the failings of thyratron (tube type) CD ignitions, the improved ignition that they gave made them a worthwhile addition for some drivers. For the Wankel powered NSU Spider of 1964, Bosch resurrected