The purpose of the ignition system is to ignite the air/fuel mixture in the combustion chamber at the proper time. In order to maximize engine output efficiency, the air-fuel mixture must be ignited so that maximum combustion pressure occurs at about 10' after top dead center (TDC).
However, the time from ignition of the air-fuel mixture to the development of maximum combustion pressure varies depending on the engine speed and the manifold pressure; ignition must occur earlier when the engine speed is higher and later when it is lower.
In early systems, the timing is advanced and retarded by a governor advancer in the distributor.
Furthermore, ignition must also be advanced when the manifold pressure is low (i.e. when there is a strong vacuum). However, optimal ignition timing is also affected by a number of other factors besides engine speed and intake air volume, such as the shape of the combustion chamber, the temperature inside the combustion chamber, etc. For these reasons, electronic control provides the ideal ignition timing for the engine.
Was this article helpful?