How does an ignition transformer provide high-voltage spark for an oil burner?

An ignition transformer steps up the burner’s line voltage to a very high secondary voltage, typically several kilovolts. The secondary is connected to two insulated high voltage leads that feed the ignition electrodes. When voltage rises high enough, it overcomes the air gap resistance and ionizes the air, creating a stable arc. That spark ignites the atomized oil spray. Reliability depends on correct electrode gap, clean ceramic insulators, good grounding, and intact high voltage cables so the spark jumps the intended gap instead of leaking to chassis.