How it works: Spark Plugs

Early spark plug designs were developed in the late 1800s, while the basic design of spark plugs used in today’s vehicles dates back to about 1902—and has changed little during those 110 years.
The Basics - The spark plugs in your vehicle’s gasoline engine (diesel engines don’t have spark plugs) are essentially high-voltage conductors used to create tiny bolts of electricity— up to 40,000 volts or more—to ignite the air/fuel mixture inside each cylinder. When energized by an ignition coil, the electricity arcs across a gap at the bottom of the plug, much like lightning arcing to the ground.
Cool Facts - The basic construction of a spark plug is fairly simple—essentially an insulated electrode—but it withstands tremendous heat and pressure. With the engine turning at only 1000 rpm, each spark plug fires its jolt of electricity 250 times per minute. And if you’re on the highway, with the engine humming at 2500 rpm, each plug fires 625 times per minute! That’s 2,500 spark events per minute in a four-cylinder engine and 5,000 in a V-8. That’s a lot of little lightning bolts!
You need to know - All the heat and pressure spark plugs are subjected to take their toll, and they eventually lose some of the capability to generate the same hot bolt of electricity as when they were new. That can result in a loss of power and reduced fuel mileage. Other engine problems can affect the plugs’ performance, too. So, if your vehicle has higher mileage, have the spark plugs inspected and possibly replaced.