ABSTRACT
For a spark to jump across an air gap of 0.6 mm under normal atmospheric conditions (1 bar), a voltage of 2-3 kV is required. For a spark to jump across a similar gap in an engine cylinder, having a compression ratio of 8 : 1, approximately 8 kV is required. For higher compression ratios and weaker mixtures, a voltage up to 20 kV may be necessary. The ignition system has to transform the normal battery voltage of 12 V to approximately 8-20 kV and, in addition, has to deliver this high voltage to the right cylinder, at the right time. Some ignition systems will supply up to 40 kV to the spark plugs.
