TABLE OF CONTENTS The 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 0.6 mm under normal atmospheric conditions (1 bar) a voltage of 2 to 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 to 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.
Conventional ignition is the forerunner of the more advanced systems controlled by electronics. However, the fundamental operation of most ignition systems is very similar; one winding of a coil is switched on and off causing a high voltage to be induced in a second winding. A coil ignition system is composed of various components and sub-assemblies; the actual design and construction of these depend mainly on the engine with which the system is to be used.
For optimum efficiency the ignition advance angle should be such as to cause the maximum combustion pressure to occur about...
