What function do the porcelain coils/rings around a spark plug perform?

Question

does it have something to do with heat dispersion or what exactly?

Answer 1

Electrical insulation.The power going into the plug needs to jump the gap between the center electrode and the collector, and into the cylinder head to earth. Without the insulation, the current would just bypass the spark gap, and the fuel/air charge inside the cylinder would never get ignited. So the engine wouldn't run.

Answer 2

Insulation so the spark does not jump to the block instead of hitting the cylinder and to keep the heat from traveling up the wires and melting them.