ABSTRACT
The fundamental purpose of the ignition system is to supply a spark inside the cylinder, near the end of the compression stroke, to ignite the compressed charge of air-fuel vapour.
For a spark to jump across an air gap of 1 mm under normal atmospheric conditions (1 bar), a voltage of 3-4 kV is required. For a spark to jump across a similar gap in an engine cylinder, having a compression ratio of 8 : 1, approximately 8-10 kV is required. For higher compression ratios and weaker mixtures, a voltage up to 30 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.
