Editing Spark plug (section)

==Operation==
[[File:Four stroke engine diagram.jpg|thumbnail|right|Components of a typical, [[four stroke cycle]], [[DOHC]] piston engine.{{unordered list

 | (E) Exhaust [[camshaft]]
 | (I) Intake camshaft
 | '''(S) Spark plug'''
 | (V) [[poppet valve|Valves]]
 | (P) [[Piston]]
 | (R) [[Connecting rod]]
 | (C) [[Crankshaft]]
 | (W) Water jacket for coolant flow
}}]]

The function of a spark plug is to produce a spark at the required time to ignite the combustible mixture. The plug is connected to the high voltage generated by an [[ignition coil]] or [[ignition magneto|magneto]]. As current flows from the coil, a voltage develops between the central and side electrodes. Initially no current can flow because the fuel and air in the gap is an insulator, but as the voltage rises further it begins to change the structure of the gases between the electrodes. Once the voltage exceeds the [[dielectric strength]] of the gases, the gases become [[ionized]]. The ionized gas becomes a conductor and allows current to flow across the gap. Spark plugs usually require voltage of 12,000–25,000&nbsp;volts or more to "fire" properly, although it can go up to 45,000&nbsp;volts. They supply higher current during the discharge process, resulting in a hotter and longer-duration spark.

As the current of electrons surges across the gap, it raises the temperature of the spark channel to 60,000&nbsp;[[Kelvin|K]]. The intense heat in the spark channel causes the ionized gas to expand very quickly, like a small explosion. This is the "click" heard when observing a spark, similar to [[lightning]] and [[thunder]].

The heat and pressure force the gases to react with each other, and at the end of the spark event there should be a small ball of fire in the [[spark gap]] as the gases burn on their own. The size of this fireball, or kernel, depends on the exact composition of the mixture between the electrodes and the level of combustion chamber turbulence at the time of the spark. A small kernel will make the engine run as though the [[ignition timing]] was delayed, and a large one as though the timing was advanced.{{citation needed|date=June 2022}}