It should provide a good spark between the electrodes of the plugs at the correct timing.

The duration of the spark must be long enough with sufficient energy to ensure that ignition of the mixture has a high chance of occurring. The system must distribute this high voltage to each of the spark plugs at the exact time in every cycle, i.e., it must have in it a distributing device.

It should function efficiently over the entire range of engine speed. It should be light, effective and reliable in service. It should have source of electrical energy.

A method of producing high voltage from the source to produce a spark across the electrodes of the spark plug and yet limit the current flow to increase the life of spark plug. The usual voltage requirements are between 8000 V to 20000 V depending upon the compression ratio and operating conditions of the engine.

A system is necessary to supply high voltage to each spark plug at the correct timing on each cylinder of multi cylinder conditions of the engine. A distributor is used to this purpose.

An adjustment of spark advance with variation of load on the engine and its speed.

The intensity of spark supply should be sufficient to initiate combustion between the specified limits because too high intensity may burn the electrodes and too low intensity may not ignite the mixture properly to sustain a flame.