The most common method to produce an ignition spark is to charge up a DC current in an inductor (called and sold as an ignition coil) which is wired in parallel with the spark gap, and then use an electromechanical contactor to open the connection between the battery and coil.
Since the current through the inductor coil must continue to flow (this is a property of inductors) after the battery is disconnected, it will continue flow and it will pull charge from the surfaces of all of the metal connected to the positive side of the coil. This charge with no path to the other side of the coil causes a rapid and massive increase in voltage that quickly gets high enough to shred up O2 molecules in the air. The system must be designed such that the spark gap is the shortest (and preferably the only) air gap between the coil positive and the coil negative, and if it is, then the air will be broken down within that gap and a plasma arc will form and will last until the ignition coil current has drained away.
The inductance and internal resistance of the coil should be designed to maximize the energy stored in the current through the inductor (E=0.5*L*I^2) which can be built up in the coil between firing cycles.
