These miniature lightning bolts are commonly called sparkplug firing by most mechanics. If the sparkplug doesn't fire, the engine doesn't start. When diagnosing a no start condition some mechanics will say the reason the engine won't start is because there is no fire.
It is the ignition system that produces the electrical energy that fires the plug. Spark also must be maintained long enough to allow complete combustion of the air fuel mixture in the cylinder. The ignition system then has to deliver this electrical energy to each sparkplug at the right time.
Ignition timing important as sparkplugs
In many engines the initial timing is specified at a point between five and 20° before top dead center. To get the most performance out of the engine the ignition timing must change as operating conditions also change. Most engine timing changes are required as engine rpm and load changes.
The higher the engine rpm the more often the sparkplug needs to be fired. The ignition system needs to keep up with the changing engine conditions. This means the ignition system must be able to monitor the rotation of the crankshaft and the relative position of each piston so that it can deliver a high voltage surge at the proper time during the compression stroke.
Coil provides the Spark
The ignition coil steps up the voltage by multiplying the battery voltage. The process that it uses to multiply battery voltage is also what gives the ignition part its name. An ignition coil is just that. Inside are coils of wire that use a magnetic field to increase voltage.
The construction of the coil and the magic of the magnetic field allows the coil to output pulses or bursts of high voltage that are sent to the sparkplug to ignite the air fuel mixture on the compression stroke.
This is just a simplified general overview of how the spark is created and used to start and run your engine. Although not everybody needs to know this information it can come in handy when you're trying to diagnose a no start condition.
You need three things for an engine to start. You need air, fuel and spark. If you are missing any of those three elements the result is a no start condition. If you find that it is the spark that is missing, all of your attention can focus on diagnosis and troubleshooting the no spark condition.
If you want to see what good and bad sparkplugs look like I have a video on my you fix cars website about replacing sparkplugs. For more of the latest auto repair posts on this site visit the blog auto repair page.