Capacitor discharge ignition
The capacitor discharge ignition (English: Capacitor Discharge Ignition CDI ) is a specialized form of ignition for gasoline engines. Here, a capacitor having up to 400 V DC voltage is charged and discharged with a thyristor via the primary winding of the ignition coil. By this sudden discharge caused on the secondary side 30 to 40 kV, which are then fed to the spark plug. The pulse at which the thyristor is turned on is determined by a control computer, or obtained from a characteristic curve. In contrast to the breaker ignition or transistor ignition, the ignition coil is used in the CDI not as energy storage, but only as a transformer. The energy for the spark comes from the capacitor, which is designed to high voltage and pulse resistant.
The CDI ignition produces stronger spark than a traditional coil ignition system, however, requires above all by the voltage converter from 12 to 400 V, a higher circuit complexity.
Legally, the English abbreviation of the capacitor discharge ignition lead to problems, since " CDI " is a registered trademark of Daimler AG.