A follow-on circuit for extending the duration of the spark provided by a spark plug. The circuit is connected between the coil secondary and the spark gap, and has a capacitor that discharges to the point of connection through a resistor and inductor. The resistor may be made variable to control the amount and duration of the follow-on current, and hence the energy and duration of the spark event. The circuit may also be used with other ignitors and non-coil ignition circuits.
Terrence F. Alger II; Barrett W. Mangold