Pre-ignition Pre-ignition Pre-ignition (or preignition) in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events. The phenomenon is also referred to as 'after-run', or 'run-on' or sometimes dieseling, when it causes the engine to carry on running after
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