How does a magneto generate the high voltage necessary to fire a spark plug?

A magneto generates the high voltage necessary to fire a spark plug primarily through the principle of electromagnetic induction. In the magneto system, the essential process involves the interruption of current flow in the primary circuit. When the current flows through the primary winding of the coil, it creates a magnetic field around the coil. As the magneto's rotor spins, it generates a change in magnetic flux, leading to the buildup of voltage.

When the current in the primary winding is interrupted—typically done by a points switch or a similar device—a rapid collapse of the magnetic field occurs. This collapsing magnetic field induces a much higher voltage in the secondary winding of the coil, which is connected to the spark plug. The induced high voltage can reach thousands of volts, allowing it to jump the gap of the spark plug and creating a spark necessary for ignition.

While options involving increasing fuel pressure, rotating a magnet, or using a high-voltage battery may also have their roles in an engine's overall operation, they do not directly pertain to the specific mechanism of how a magneto produces the high voltage required to ignite fuel-air mixtures in the combustion chamber. The essential action that leads to the generation of high voltage is the interruption of current flow in the primary circuit, making